Heat Treatment of Metals

Creep property and microstructure evolution at 700 ℃ of a novel Fe-Ni based superalloy

Jiao Chunhui, Pan Yanjun, Li Shengzhi, Bai Du, Li Bei, Deng Ge, Jia Xiaoshuai

2025, 50(2): 1-7. doi:10.13251/j.issn.0254-6051.2025.02.001

Abstract ( 70 )

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A novel Fe-Ni-based superalloy, intended for ultra-supercritical thermal power generating units, was evaluated under constant load conditions at 700 ℃ with varying stress levels of 250 MPa and 200 MPa. The service limit and creep life of the alloy were predicted, and the microstructure evolution during creep was analyzed. The results indicate that the creep life of the alloy at 700 ℃/250 MPa and 700 ℃/200 MPa is 2378 h and 12 716 h, respectively. Based on the Larson-Miller equation, the alloy can withstand stresses of approximately 152 MPa after 100 000 h and 134 MPa after 260 000 h at 700 ℃, fully meeting the service requirements (stress of 35 MPa, creep life of 100 000 h). Microstructure analysis reveals that high-density dislocations are distributed in the 700 ℃/250 MPa specimen, whereas fewer dislocations are observed in the 700 ℃/200 MPa specimen. The MC carbides with larger size within the grains predominantly exhibit blocky or rod-like morphologies, with faster growth rates under higher stress conditions. The smaller M₂₃C₆ carbides at grain boundaries precipitate primarily in chain form, and their width increases with prolonged creep exposure. The γ′ phase within the grains remains spherical but undergoes coarsening during creep. Notably, some grain boundary γ′ phases exhibit abnormal growth, forming PFZs/DCZs, which adversely affect the alloy's high-temperature creep performance.

Hot deformation behavior of Inconel617 alloy

Ding Zuojun, Ren Wenhao, Zhang Guo, Zheng Yue, He Xikou

2025, 50(2): 8-14. doi:10.13251/j.issn.0254-6051.2025.02.002

Abstract ( 29 )

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Hot compression simulation tests of Inconel617 alloy were carried out using Gleeble-3800 thermal simulation test machine in the range of deformation temperature of 950-1200 ℃ and strain rate of 0.001-1 s^-1. The hot deformation behavior under different deformation conditions were analyzed. The results show that the Inconel617 alloy exhibits obvious work hardening characteristics at the initial stage of deformation. As the strain increases, the flow stress increases to the peak value and then gradually decreases, showing dynamic softening dominated by dynamic recrystallization. The hot deformation constitutive equation of the Inconel617 is constructed based on the Arrhenius model modified by the hyperbolic sine function. The hot deformation activation energy Q is 418.4 kJ/mol. The hot working map of the Inconel617 alloy is constructed, and the appropriate hot working range is determined: deformation temperature of 1080-1170 ℃, strain rate of 0.012-1 s^-1.

Creep rupture property at 550 ℃ and microstructure evolution of 316H stainless steel forging for generation IV reactor

Zhang Zhifeng, Zhao Jiqing, Wang Xiaofang, Wang Yunhai, Yang Gang

2025, 50(2): 15-22. doi:10.13251/j.issn.0254-6051.2025.02.003

Abstract ( 25 )

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Creep rupture strength of 316H stainless steel forging was tested by rupture test machines at 550 ℃, and the fracture morphology and microstructure of the fracture specimens were analyzed by optical electron microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The results indicate that the 316H stainless steel forging has high creep rupture strength at 550 ℃, the creep rupture stress after 10 000 h determined through the isothermal extrapolation method is 314 MPa, which significantly exceeds the ASME design criteria. The fracture morphology of the 316H stainless steel forging consists of both dimple and intergranular fracture patterns. As the fracture duration increases, the proportion of intergranular fracture progressively rises, and the origin of the fractures transitions from non-metallic inclusions into second-phase particles at the grain boundaries. The 316H steel forging displays good structural stability throughout the 550 ℃ rupture test. As the applied stress reduces and fracture duration extends, the grain size progressively increases, the grain boundary area diminishes, and only a small amount of M₂₃C₆ and σ phases are precipitated at the grain boundaries

Influence of Mn on high-temperature mechanical properties of low Ni duplex stainless steel

Yang Yuheng, He Jianguo, Song Zhigang, Feng Han, Lü Jiesheng, Wu Xiaohan, Gu Yang, Zhu Yuliang

2025, 50(2): 23-28. doi:10.13251/j.issn.0254-6051.2025.02.004

Abstract ( 16 )

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High-temperature tensile tests were conducted on 17Cr-2Ni-2Mo-0.2N-xMn (x=2, 3, 4) duplex stainless steel at 900-1300 ℃ and 1 s^-1, and thermal compression tests were conducted with 50%, 60%, and 70% deformation at 900-1300 ℃ and 1 s^-1, respectively, to investigate the effect of Mn content on its high-temperature mechanical properties. The results indicate that at a deformation temperature of 900 ℃, ferrite undergoes dynamic recrystallization, while austenite only undergoes partial dynamic recrystallization. At a deformation temperature of 1200 ℃, ferrite mainly undergoes dynamic recovery, while austenite undergoes dynamic recrystallization. All specimens exhibit varying degrees of dynamic recovery or dynamic recrystallization during high-temperature deformation, with secondary hardening occurring in the final stage of the thermal compression test. In the thermal compression test, when the Mn content increases from 2% to 4%, the dynamic recrystallization behavior of 17Cr duplex stainless steel first intensifies and then slows down in the temperature range of 900-1100 ℃. However, at deformation temperatures of 1200 ℃ and higher, the effect of Mn content on the dynamic recrystallization behavior is relatively small. At the temperature range of 1150-1200 ℃, the thermal tensile deformation resistance decreases initially and then increases with the rise of manganese content, with 3% manganese providing the best hot working performance.

Microstructure and hot deformation behavior of U-50%Zr alloy for nuclear fuel

Li Yanfeng, Guo Hong, Li Mingyang, Hu Bingkun, Liu Jiancheng

2025, 50(2): 29-35. doi:10.13251/j.issn.0254-6051.2025.02.005

Abstract ( 19 )

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U-50%Zr alloy for nuclear fuel was prepared by high-frequency induction melting, and its microstructure and phase constituent were analyzed using metallographic microscope and X-ray diffractometer. The Gleeble-3800 thermal simulation test machine was used to conduct hot compression tests at different deformation temperatures (500, 550 and 600 ℃) and strain rates (0.01 s, 0.1 and 1 s^-1) to investigate its hot deformation behavior. The results show that, except for a deformation temperature of 600 ℃ and a strain rate of 0.01 s^-1, the U-50%Zr alloy exhibits significant work hardening characteristics under other deformation conditions. At the same strain rate, the peak stress decreases with the increase of deformation temperature, especially at 600 ℃, where the peak stress decreases significantly compared to 500 ℃ and 550 ℃. At the same deformation temperature, the peak stress increases with the increase of strain rate. After hot deformation, no phase transformation occurs in the microstructure, all of which are δ-UZr₂ phase. As the hot deformation temperature increases, the grain size of the alloy initially remains basically unchanged and then increases. At 500 ℃ and 550 ℃, the grain size is around 250 μm, and at 600 ℃, the grain size significantly increases to 493 μm. Based on peak stress, the constitutive equation of U-50%Zr alloy is established using the hyperbolic sine function Arrhenius model and temperature compensation factor Z parameter, with a hot deformation activation energy Q=694.9 kJ/mol. A hot working map is constructed using DMM dynamic material model, and the appropriate processing range is determined as follows: deformation temperature above 540 ℃, strain rate between 0.01 s^-1 and 1 s^-1.

High-temperature fatigue property of 30Cr1Mo1V rotor steel at 540 ℃

Na Risu, Zhang Yuetao, Zhang Shuo, Meng Weiran, Wang Xiao

2025, 50(2): 36-42. doi:10.13251/j.issn.0254-6051.2025.02.006

Abstract ( 20 )

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High-temperature fatigue tests were conducted on 30Cr1Mo1V steel under different stresses (450$\rightleftharpoons$0, 400$\rightleftharpoons$0, 350$\rightleftharpoons$0, 350$\rightleftharpoons$233, 350$\rightleftharpoons$175 MPa) at 540 ℃. The results indicate that the fatigue life of the 30Cr1Mo1V steel decreases rapidly as the peak stress exceeds 350 MPa. Under a stress of 350 MPa, the ferrite does not change too much, which maintains the initial polygon-like shape, and the ultimate failure feature of the steel is fatigue cracking. Nevertheless, when the stress rises to 400 MPa, the ferrite deforms remarkably and shows a wrinkled river-like shape after fatigue failure, meanwhile, the pores also appears at the intersection location of the ferrite bands. In addition, subjecting the long-term high stress level like at 350$\rightleftharpoons$233 MPa and 350$\rightleftharpoons$175 MPa are harmful to the fatigue life of the 30Cr1Mo1V steel, as continuous stress can significantly increase the number of fatigue pores inside the material. In summary, the 30Cr1Mo1V steel is relatively safe under service conditions of 540 ℃/350 MPa, with a fatigue life of 12 887 cycles, and a one-time attrition rate of approximately 0.007 76% which is less than the requirement of 0.01%.

Influence of martensitic multi-level structure and TiN inclusions on fracture toughness of 20CrMnTi steel

Long Shaolei, Zhu Dandan, Luo Xianglan, Yi Yanliang, Yang Ming, Lu Yemao, Liang Yilong

2025, 50(2): 43-51. doi:10.13251/j.issn.0254-6051.2025.02.007

Abstract ( 13 )

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Fracture toughness (K_IC) of 20CrMnTi steel was tested by using three-point bending specimens, and it was found that the value of K_IC decreases with grain coarsening, which contradicts the relationship between the K_IC and the grain size of other low carbon lath martensitic steels. Based on this, the fracture behavior of the 20CrMnTi steel was analyzed by means of OM, EBSD, SEM and thermodynamic model, fracture mechanics model. The results show that the relationship between the multi-level microstructure of the 20CrMnTi steel and K_IC established based on the Hall-Petch equation reveals that the martensitic lath block is the effective grain for fracture toughness. Still, the fracture morphology analysis reveals that the effective grains in the coarse or fine grain states of the 20CrMnTi steel are different. Further analysis reveals the presence of a certain number of irregular TiN inclusions on the fracture, and thermodynamic calculations show that the TiN inclusions are formed in the liquid-phase region with coarse size, which can easily lead to crack initiation. The crack propagation is analyzed with the help of SEM and fracture mechanics calculations, revealing that the crack propagation in the fine grain state of the 20CrMnTi steel is zigzagging and cross-cutting the lath martensite packet, which leads to a better fracture toughness, whereas the crack path in the coarse grain state is straight and shows a poor toughness. Therefore, the formation of TiN inclusions is the key factor leading to the abrupt change in fracture toughness of the 20CrMnTi steel, and the results of this study are of great significance in guiding the preparation of the high-performance 20CrMnTi steel.

Microstructure refinement and properties of as-cast Ti-6Al-4V titanium alloy

Sun Hao, Meng Xun

2025, 50(2): 52-60. doi:10.13251/j.issn.0254-6051.2025.02.008

Abstract ( 20 )

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Microstructure of the as-cast Ti-6Al-4V titanium alloy was refined by deformation combined with heat treatment. Firstly, the as-cast Ti-6Al-4V titanium alloy was subjected to solution treatment at 1100 ℃ and water cooling to transform the microstructure into martensite. Then, the microstructure was refined by repeated rolling at 750 ℃. The results show that the principles of microstructure refinement are the deformation twinning, dislocation rearrangement, crystal rotation and discontinuous dynamic recrystallization.Through tensile test, it is found that compared to the as-cast Ti-6Al-4V titanium alloy, the alloy treated with microstructure refinement has a better strength-plasticity matching relationship. The improvement of alloy strength is the result of the combined effect of fine grain strengthening and dislocation strengthening. The improvement of plasticity is due to the formation of a plastic zone at the crack tip during crack initiation and propagation, which hinders crack propagation and enhances the plasticity of the material. In addition, dislocations can complete slip transmission between the α and β phases, which can better coordinate the deformation between the α and β phases and further enhance the plasticity of the material.

Effect of Zr element on microstructure and properties of Cu-6Ni-3Ti alloy

Jing Qingxiu, Yang Xueqing, Wei Dandan, Wei Miao, Huang Xiaodong

2025, 50(2): 61-68. doi:10.13251/j.issn.0254-6051.2025.02.009

Abstract ( 14 )

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Effect of Zr content on the microstructure, mechanical properties and electrical conductivity of Cu-6Ni-3Ti-xZr alloy was investigated. The results show that zirconium elements mainly segregate at grain boundaries during solidification, forming zirconium-rich atomic clusters, slowing down the grain growth and inhibiting dendritic segregation. During the aging process, zirconium accumulates around the precipitated phases of the alloy, inhibiting the growth of the precipitated phases, and improving the hardness and its resistance to softening. When the content of zirconium elements is increased, Cu₄Zr is formed in the Cu-6Ni-3Ti-0.5Zr alloy. After aging at 450 ℃ for 2 h, the Cu-6Ni-3Ti-0.3Zr alloy has best mechanical and electrical properties, with tensile strength of 807 MPa, hardness of 230 HV2, electrical conductivity of 50%IACS.

Analysis of continuous cooling transformation of 4Cr13 steel for plastic mold

Zhao Zhengrong, Zhang Yunfei, Zhao Yingli, Fan Mingqiang, Bai Lijuan, Liu Lijun

2025, 50(2): 69-73. doi:10.13251/j.issn.0254-6051.2025.02.010

Abstract ( 16 )

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4Cr13 steel for plastic mold was prepared by vacuum induction furnace, its phase transition points and continuous cooling transformation (CCT) curve were measured by using a DIL805A quenching thermal dilatometer, and its continuous transformation process was analyzed by combining microstructure observation and hardness test. The results show that the phase transition points of the tested 4Cr13 steel are Ac₁=857 ℃, Ac₃=937 ℃, and there are only pearlite transformation zone and martensite transformation zone on the CCT curve. The 4Cr13 steel has a good hardenability, and the martensitic transformation temperature range is 67-397 ℃.When the cooling rate is 0.01-0.05 ℃/s, the main product of phase transformation of the 4Cr13 steel is pearlite, and the hardness is low, which is 172-193 HV. When the cooling rate is 0.1-1 ℃/s, the microstructure is martensite and retained austenite, and the hardness is increased to 528-688 HV. When the cooling rate is ≥1 ℃/s, the martensitic transformation is completely finished.

CCT and TTT curves of a carbide-free bainitic steel

Yang Siyuan, Li Aiguo, Luo Ping, Zhang Wenliang, Li Xianjun, Zhang Minghao, An Weicheng, Wang Kaize

2025, 50(2): 74-80. doi:10.13251/j.issn.0254-6051.2025.02.011

Abstract ( 13 )

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Continuous cooling transformation and isothermal transformation tests of undercooled austenite were carried out on a carbide-free bainitic tested steel by using the DIL-805A phase transformation tester. The CCT and TTT curves of the tested steel were obtained. The results show that the starting and ending transformation temperatures of austenite of the tested steel are 760 ℃ and 860 ℃, respectively, and the starting transformation temperature of martensite is approximately 300 ℃. When the cooling rate is between 0.1-15 ℃/s, the undercooled austenite mainly transforms to bainite+martensite complex structure. When the cooling rate is between 15-50 ℃/s, the undercooled austenite transforms into martensite. The microhardness of the tested steel increases with the increase of cooling rate, up to 742 HV0.5. When the tested steel undergoes isothermal transformation, the bainite transformation temperature range is 300-400 ℃, and the "nose tip" temperature is about 360 ℃.

Differences and optimization practice of banded structure in gear steels

Zhang Zhixing, Guo Ziqiang, Wang Hailong, Qin Xuan

2025, 50(2): 81-85. doi:10.13251/j.issn.0254-6051.2025.02.012

Abstract ( 14 )

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A comprehensive study on the formation mechanisms and differences in the banded structure of commonly used automotive gear steels, namely SCr420H, 16MnCr5, 20CrMnTiH, SAE8620H and 22CrMoH, which possessed varying alloy element compositions but underwent similar smelting and rolling processes, was conducted. In addition, the process was optimized. The findings reveal that SCr420H, 16MnCr5 and 20CrMnTiH steels exhibit relatively less pronounced banded segregation, whereas 22CrMoH and SAE8620H steels display distinct banded structures. The alloying elements Mo and Ni in 22CrMoH and SAE8620H steels affect the microstructure transformation during rolling and cooling, resulting in the development of an abnormal microstructure, bainite, in the final rolled steel. By adjusting the continuous casting superheat to a range of 15-30 ℃, maintaining a consistent pulling speed, intensifying the crystallizer and secondary cooling, achieving a homogeneous rolling heating temperature of 1200-1240 ℃, ensuring a diffusion duration of at least 90 min, and maintaining a final rolling temperature of 910-960 ℃, the banded structure in SAE8620H round steel is effectively improved to a grade of ≤2.0.

Effect of segregation on surface microstructure and hardness of induction hardened inner gear ring

Chen Yongxiang, Lü Hesheng, Yang Gang, Li Yong, Wang Chunli, Zhong Boying

2025, 50(2): 86-89. doi:10.13251/j.issn.0254-6051.2025.02.013

Abstract ( 10 )

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Segregation phenomenon of 42CrMoA steel inner gear ring was characterized, and the microstructure and hardness gradient of the induction hardened layer of the inner gear ring were analyzed. The results show that the microstructure of the 42CrMo steel inner gear ring forging is uneven, with severe banded structure and compositional segregation, which leads to uneven induction hardened layer structure, and the distribution of banded structure still exists. The banded structure and compositional segregation of inner gear ring forgings have a significant impact on the hardness gradient of the induction hardened subsurface and transition zone. The hardness gradient of the induction hardened subsurface and transition zone of the inner gear ring fluctuates greatly and exhibits a steep rise and fall phenomenon.

Effect of partial austenite reverse transformation process on microstructure and mechanical properties of Fe-8Mn-0.2C-3Al medium Mn steel

Liu Mingzhu, Ding Hua, Zou Yuming

2025, 50(2): 90-95. doi:10.13251/j.issn.0254-6051.2025.02.014

Abstract ( 13 )

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Microstructure and mechanical properties of Fe-8Mn-0.2C-3Al medium Mn steel treated by partial austenite reverse transformation (PART) process with two-step annealing were studied by means of field emission scanning electron microscope, X-ray diffractometer and universal testing machine. The results show that for the tested steel treated by PART process with the increase of first step annealing temperature, the austenite content gradually decreases from 49.7% to 21.6%, and the microstructure is lath-like, the yield strength gradually increases, while the tensile strength and elongation gradually decrease. After treated at 755 ℃ for 15 min and 620 ℃ for 30 min, the tested steel obtains optimal mechanical properties, with the tensile strength of 1087 MPa, elongation of 43.4%, and the product of strength and elongation of 47.2 GPa·%, which is attributed to that the moderate austenite stability can fully utilize the TRIP effect during the tensile process and improve the comprehensive mechanical properties of the steel.

Influence of austenite reverse transformation annealing temperature on microstructure and properties of Cu-containing medium manganese steel

Zhang Shenghao, Wang Bao, Li Sijia, Xiao Meimei, Zhou Jian'an

2025, 50(2): 96-101. doi:10.13251/j.issn.0254-6051.2025.02.015

Abstract ( 14 )

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Influence of austenite reverse transformation annealing temperature on microstructure evolution, mechanical properties and deformation behavior of 0.30C-5.21Mn-0.34Cu medium manganese steel was studied by means of SEM, EBSD, XRD and TEM. The results show that the microstructure of the steel after annealing is mainly composed of ferrite, retained austenite and martensite. As the annealing temperature increases, the content of retained austenite first increases and then sharply decreases, reaching a maximum of 20.38% at 700 ℃. As the annealing temperature increases, the tensile strength and yield strength of the tested steel show opposite changes. While the elongation and product of strength and elongation first increase and then decrease, which is basically consistent with the variation law of retained austenite volume fraction. When annealed at 700 ℃ for 60 min, the comprehensive mechanical properties of the tested steel are the best, with tensile strength, elongation, and product of strength and elongation reaching 1004 MPa, 54.80%, and 55.02 GPa·%, respectively.

Effect of heat treatment temperature on microstructure and mechanical properties of salt bath quenched 65Mn steel

Yang Bin, Wang Lin, Shen Hangrui, Feng Songke, Li Guofei, Liu Fuqiang, Fang Liuxin, Yang Lin

2025, 50(2): 102-106. doi:10.13251/j.issn.0254-6051.2025.02.016

Abstract ( 19 )

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Focusing on the strict requirements for blade sharpness, hardness and wear resistance of chaff cutter blade, the balance between hardness and toughness of 65Mn steel was achieved through salt bath quenching with different heating temperatures and tempering. The microstructure, hardness, friction and wear resistance of the steel were studied systematically. The results show that when austenitizing at 840 ℃, the lath martensite of the 65Mn steel after quenching is smaller, together with clear acicular martensite. After tempering, the carbide in tempered martensite precipitates at the lath martensite interface, and its distribution is more uniform combined with smaller particle in the martensite matrix. The hardness of the steel after salt bath quenching at 840 ℃ and tempering is the highest, which is 58.04 and 53.50 HRC, respectively, combined with no excessively loss of the wear resistance for the 65Mn steel, meeting the application requirements of agricultural machinery materials. As a consequence, salt bath quenching at 840 ℃ and tempering is the optimal heat treatment process.

Effect of rapid annealing temperature on evolution mechanism of microstructure and properties of SPCC steel for dust hoods

Hu Jingjing, Yuan Qing, Ren Jie, Xiong Le, Bao Linlin

2025, 50(2): 107-113. doi:10.13251/j.issn.0254-6051.2025.02.017

Abstract ( 9 )

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Based on the previously proposed rapid annealing method for SPCC steel, the influence of rapid annealing temperature on the relationship among grain size, orientation distribution, and mechanical properties of the SPCC steel was investigated. The results indicate that the rapid annealing temperature is a crucial factor affecting the size of ferrite grains. When the rapid annealing process is conducted at 650 ℃ for 100 s, the tensile strength of the SPCC steel can reach 487.09 MPa, with the elongation after fracture of 26.84% and the product of strength and elongation (PSE) of 13.07 GPa·%. At higher rapid annealing temperature, the grains become coarse, and the favorable {111} texture is enhanced, leading to a significant reduction in strength but a relatively high elongation. Conversely, at lower rapid annealing temperature, due to insufficient ripening of second-phase particles and no significant coarsening of ferrite grains, the material exhibits higher strength but a noticeable decrease in elongation. Furthermore, after grain refinement, the work-hardening ability of the material is diminished, and the {111} texture is weakened. The combined effect of these two factors results in a significant decrease in elongation compared to the traditional annealing methods under rapid annealing. Additionally, within a rapid annealing holding time of 100 s, a higher rapid annealing temperature facilitates a more uniform growth behavior among most ferrite grains, thereby improving the mixed grain structure of ferrite grains.

Effect of peak temperature of thermal cycling on microstructure and properties of heat affected zone of G115 steel pipe

Chen Qian, Chen Zhengzong, Liu Zhengdong, Cai Wenhe, Jiang Haifeng, Bao Hansheng, He Xikou

2025, 50(2): 114-120. doi:10.13251/j.issn.0254-6051.2025.02.018

Abstract ( 14 )

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Heat affected zone (HAZ) of the G115 steel pipe was simulated by Gleeble-1500D thermal simulation machine, and the microstructure and hardness of the subregions of heat affected zone were analyzed by means of OM, SEM, EBSD, TEM and microhardness tester. The results indicate that the welded heat affected zone of G115 steel pipe is mainly divided into the coarse grain heat affected zone (CGHAZ) with coarse equiaxed grains, the fine grain heat affected zone (FGHAZ) with a fine mixed grain structure of large grains surrounded by crushed fine grains, and the intercritical heat affected zone (ICHAZ) with tempered martensite, which shows a little difference from the base metal. The geometric dislocation density of the fully phase-transformed microstructure (CGHAZ,FGHAZ) (24.1×10¹⁴, 24.5×10¹⁴ m^-2) is approximately twice that of the incompletely phase-transformed microstructure (ICHAZ) (13.6×10¹⁴, 11.8×10¹⁴ m^-2), meaning that there is a significant stress-strain gradient at the interface between ICHAZ and FGHAZ. Only a small number of M₂₃C₆and Laves phases are present within the FGHAZ, which can completely dissolve at higher temperatures. The complete dissolution temperature of the MX phase is higher, and it is still distributed in a small number in the CGHAZ. The Cu-rich phase only precipitates spherically within the grains at the ICHAZ. After the thermal simulation, the hardness and microstructure are positively correlated with the thermal cycling peak temperature. The microhardness of the CGHAZ, FGHAZ and ICHAZ near the base metal is 437.55, 421.85 and about 375 HV0.2, respectively.

Effect of solution treatment and aging on microstructure and properties of laser powder bed fused FeCoNi alloy

Ye Guochen, Xia Zhonghu

2025, 50(2): 121-127. doi:10.13251/j.issn.0254-6051.2025.02.019

Abstract ( 11 )

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Effects of solution treatment and solution treatment+aging on microstructure and mechanical properties of the FeCoNi medium entropy alloy prepared by laser powder bed fusion were investigated. The results show that the microstructure of solution treated alloy is BCC single-phase structure, and during the solution process, the strip-shaped molten pool dissolves and the grains undergo recrystallization and coarsening. Granular Ni₃Fe phase precipitates at the grain boundaries and within the grains of the solution treated and aged alloy, and its content decreases with the increase of solution temperature. Solution treatment at 900 ℃ and aging at 470 ℃ refine the grain size of the alloy from 4.16 μm(solution treated) to 2.43 μm. During the solution treatment process, the disappearance of cellular structure and the release of residual stress result in a decrease in the hardness of the 900 ℃ solution treated alloy to 314 HV0.2 and a tensile strength of 709 MPa. After solution treatment and aging, Ni₃Fe intermetallic compounds precipitate from the matrix, which enhances the strength of the FeCoNi alloy. The hardness of FeCoNi alloy after solution treatment at 900 ℃ and aging at 470 ℃ is 508 HV0.2, and the tensile strength is 1238 MPa. The alloy strength is mainly contributed by precipitation strengthening and grain refinement strengthening. However, the accumulation of dislocations near the grain boundary precipitates can cause stress concentration, leading to a decrease in the plasticity of the FeCoNi medium entropy alloy.

Effect of annealing temperature on mechanical properties of cold-rolled CoCrFeNi high entropy alloy

Jiang Mengyuan, Wu Zhennan, Wu Chengbo, Xu Wang, Li Ning, Dong Fuyuan

2025, 50(2): 128-132. doi:10.13251/j.issn.0254-6051.2025.02.020

Abstract ( 12 )

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A CoCrFeNi high entropy alloy was prepared by vacuum induction melting casting method, and the effect of different annealing temperatures on the mechanical properties of the CoCrFeNi high entropy alloy in -196 ℃ cryogenic rolling and room temperature rolling states was systematically studied. The results indicate that there is only FCC phase in the CoCrFeNi high entropy alloy in all the cold rolled and annealed states, and the percentage total extension at fracture and uniform elongation increase with the increase of annealing temperature, while the tensile strength decreases. Among them, the alloy in both the cold-rolled states has a good strength plasticity matching when annealed at 700 ℃. At the same annealing temperature, the strength of cryogenic rolled alloy is higher than that of alloy rolled at room temperature. There are numerous dimples distributed on the fracture of the as-cast CoCrFeNi high entropy alloy. The dimples on the fracture of the CoCrFeNi high entropy alloy in the two rolling states are few and shallow, and no dimple appears in some locations. As the annealing temperature increases, the size of the dimples increases and the number of pores increases.

Effect of Nb addition and heat treatment on microstructure and properties of heterogeneous high carbon steel

Zhao Weinan, Lu Chao, Wang Haoyun, Cao Jianchun, Zhang Yongqing, Zhou Xiaolong

2025, 50(2): 133-141. doi:10.13251/j.issn.0254-6051.2025.02.021

Abstract ( 12 )

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High carbon steel Fe-0.86%C-0.04%Nb(mass fraction) was quenched at 1150 ℃ and tempered at different temperatures. The microstructure of the high carbon steel specimens under different heat treatment conditions was characterized by means of OM, SEM and EPMA. The macro and micro hardness tests were carried out by using Vickers hardness tester and nanoindentation tester, respectively, and compared with high carbon steel with the same C content. The effect of Nb on the microstructure and properties of high carbon steel was studied. The results show that the addition of Nb in high carbon steel can slow down the dissipation of C at the surface of specimen during quenching, and change the distribution of C at the core. The microstructure at the surface is martensite and retained austenite, and the microstructure at the core is composed of pearlite, proeutectoid ferrite and a small amount of martensite, and the heterostructure is obtained from the surface to the core. During tempering, Nb promotes the precipitation of fine granular carbides. After tempering at 300 ℃, the microstructure at surface of the high carbon steel specimen containing Nb is tempered martensite, and the microstructure of core is pearlite+ferrite+a small amount of tempered martensite, the Vickers hardness is 506 HV0.2 and 240 HV0.2, respectively, and the nanoindentation hardness of surface martensite and core pearlite is 4.20 GPa and 2.42 GPa, respectively. The surface has higher hardness, and the core has stronger toughness, showing the characteristics of hard surface and tough core.

Interfacial structure evolution and mechanical properties of Mg/Al composite sheet by corrugated/flat-flat rolling

Zhu Jinsen, Bian Liping, Luo Baoquan, Li Teng, Wang Tao, Liang Wei

2025, 50(2): 142-147. doi:10.13251/j.issn.0254-6051.2025.02.022

Abstract ( 10 )

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Mg/Al composite sheet was prepared by corrugated/flat-flat rolling, and the composite sheet was subjected to final annealing treatment at 200 ℃ for 1 h. The microstructure evolution and mechanical behavior of the interface of the Mg/Al composite sheet were investigated by means of metallographic microscope, scanning electron microscope (SEM/EDS), electron backscatter diffractometer and universal electronic tensile machine. The results show that the metallurgical bonding is realized at the interface after the first pass of the both rolling methods and intermediate annealing at 400 ℃ for 15 min, and no intermetallic compound is formed at the interface. After the second pass of corrugated-flat rolling and 200 ℃×1 h annealing, the grain size of magnesium alloy matrix shows uneven distribution at the trough and peak, and the grains at the trough are significantly refined, but the grain size is larger than that of the flat-flat rolling, The “staggered occlusion” intermetallic compound particles are formed at the interface, and the compounds are dispersed along the corrugated interface, possessing better interface bonding characteristics. While a straight and continuous intermetallic compound layer is formed at flat-flat rolling interface. The corrugated-flat rolling process has the deformation characteristics of local strong pressure and strong shear. Compared to the flat-flat rolling, Mg/Al composite sheet has higher tensile strength and yield strength, and lower plasticity.

Effect of Y addition and heat treatment on microstructure and properties of Al-Mg-Si-Y alloy

Bi Xiaoqin, Zhang Sen, Zheng Zeyuan, Qi Yulei, Fu Ying, Xu Qin

2025, 50(2): 148-154. doi:10.13251/j.issn.0254-6051.2025.02.023

Abstract ( 8 )

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Al-0.6Mg-0.5Si-xY (x=0, 0.1, 0.2, 0.3, 0.4) alloys were prepared and T6 heat treatment was carried out. The evolution of microstructure, electrical conductivity, and mechanical properties of the alloys after heat treatment were investigated. The results show that AlSiY phases are formed at the grain boundaries of the alloy with Y addition after heat treatment, and granular and rod-like AlSiY phases are precipitated in intragranular mode. The white granular Mg₂Si phases are dispersed in the alloy matrix. After heat treatment, the average grain size of the alloys is increased compared to their as-cast state, but it decreases with the increase of Y addition. After heat treatment, electrical conductivity of the alloys initially increases and subsequently decreases with the increase of Y content. The electrical conductivity reaches the highest value of 55.2%IACS by addition of Y with 0.3%, which is 1.7% higher than that of the as-cast alloy. After heat treatment, an increase in grain size of the alloys results in a reduction of grain boundaries, and the precipitation of solved Si atoms reduces the solid solution distortion, thereby improving the conductivity of the alloys. The tensile strength and hardness of the alloys after heat treatment exceed those of the as-cast alloy, exhibiting an initial increase followed by a subsequent decrease with the addition of Y. The tensile strength and hardness of the alloys reach the highest values of 206.2 MPa and 91.3 HV0.1 respectively by addition of Y with 0.3%, which are 36.6% and 40.5% higher than those of the as-cast alloy. The heat-treated alloys exhibit a significantly reduced elongation compared to the as-cast alloys. The heat treatment promotes a large amount of second phase precipitation in the alloys, thereby improving the strength and hardness of the alloys. However, the reduction in grain boundaries and the augmented presence of precipitated phases contribute to a diminished elongation in the heat-treated alloy compared to the as-cast alloy.

Solution treatment and aging of 7055 aluminum alloy containing Ce

Fang Hongjie, Yang Yuzeng, Zhang Zhikai, Min Hong, Liu Zhendong, Shen Yuxin

2025, 50(2): 155-159. doi:10.13251/j.issn.0254-6051.2025.02.024

Abstract ( 11 )

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A 7055 aluminum alloy sheet containing 0.1%Ce was prepared in the laboratory, and different solid solution treatments (solution temperature of 465, 470, 475, and 480 ℃, holding time of 20, 40, and 60 min) and aging treatments (aging temperature of 120 ℃, holding time of 0-36 h) were carried out, and the microstructure and mechanical properties were observed and tested by using metallographic microscope, scanning electron microscope, transmission electron microscope, and electronic universal testing machine. The results indicate that there is a low melting point second phase at 470.83 ℃ in the cold-rolled alloy sheet. To avoid burning and reduce the mechanical properties of the sheet, the selection of the solid solution temperature should not exceed this temperature. The optimal solid solution and aging process for the alloy is 470 ℃×60 min+120 ℃×22 h. Under this process, the tensile strength is 577 MPa, the yield strength is 547 MPa, and the elongation is 9.47%.

Influence of pre-deformation on stress relaxation aging behavior of 2195 aluminum-lithium alloy

Zhang Liwen, Liu Qiang

2025, 50(2): 160-165. doi:10.13251/j.issn.0254-6051.2025.02.025

Abstract ( 8 )

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Different pre-deformations (0%-10%) were performed on the naturally aged 2195 aluminum-lithium alloy. The effect of pre-deformation on the microstructure and mechanical properties of the 2195 aluminum-lithium alloy after stress relaxation aging was studied by means of stress relaxation aging test at 180 ℃ under initial loading stress of 250 MPa, mechanical tensile test at room temperature and scanning electron microscope observation. The results show that as the pre-deformation increases, the residual stress after stress relaxation of the alloy generally decreases and then increases. The alloy with 4% pre-deformation has the lowest residual stress, which is more conducive to the accumulation of creep strain. The stress relaxation curve of the alloy without pre-deformation shows four-stage characteristics, while that of the alloy with pre-deformation show two-stage characteristics, which is attributed to the difference in evolution of microstructure of the alloy with or without pre-deformation. The yield strength and tensile strength of the stress relaxation aged alloy increase with the increase of pre-deformation. The elongation after fracture of the stress relaxation aged alloy without pre-deformation is the smallest, while that of the stress relaxation aged alloy with 4% pre-deformation is the largest. The intrinsic reason for the superior comprehensive mechanical properties exhibited by stress relaxation aged alloy with 4% pre-deformation is the uniform distribution of small-sized T₁ strengthening phases within the grains and the relatively narrow precipitation free zones at the grain boundaries. The fracture mechanism of stress relaxation aged alloy without pre-deformation treatment is intergranular fracture, while under 4% and 10% pre-deformation conditions, the fracture mechanism is transgranular ductile fracture and transgranular cleavage fracture, respectively.

Optimization of heat treatment process of 36CrNi3MoV steel forging for hot isostatic pressing machine

Shi Haopeng, Zhang Zhiyong, Shi Ruxing, Chen Ming, Dai Bojie, Kong Yuting

2025, 50(2): 166-171. doi:10.13251/j.issn.0254-6051.2025.02.026

Abstract ( 9 )

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Effects of quenching temperature, cooling method and tempering temperature on microstructure and mechanical properties of the 36CrNi3MoV steel forging for hot isostatic pressing machine were studied. The results show that when quenched between 770-860 ℃ and tempered at 600 ℃, the obtained microstructure is tempered martensite. With the increase of quenching temperature, the strength increases, while the impact property and plasticity decrease. When quenched with different cooling methods, the water quenched microstructure is the most uniform. The strength of water quenched steel is slightly higher than that of oil quenched. When tempered in the range of 580-620 ℃, with the increase of tempering temperature, the strength decreases, but the impact property and plasticity increase. The optimal heat treatment process consists of austenitizing in the range of 830-860 ℃, water quenching and then tempering at 600 ℃,which can achieve mechanical properties that meet the design requirements and NB/T 47008-2017.

Research progress of induction hardening technology for ball screw

Li Mingzhe, Chen Baofeng, Sun Lizhuang, Zhang Wenliang, Zhang Lun, Liu Junjie

2025, 50(2): 172-180. doi:10.13251/j.issn.0254-6051.2025.02.027

Abstract ( 12 )

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Induction hardening technology, as an advanced metal surface heat treatment strengthening method, can effectively improve the hardness and wear resistance of ball screws, thereby significantly extending their service life and performance stability. The key technical issues and challenges faced by induction hardening technology for ball screws were summarized, and its main research progress, covering basic principles, application of simulation technology, optimization of process parameters, specialized equipment, and other aspects, were systematically over viewed. Based on these, the prospects of induction hardening technology in the screw manufacturing industry were discussed.

Effect of annealing temperature on hot-rolled microstructure and texture of 1.45%Si non-oriented silicon steel

Xuan Dongpo, Guo Han, Xu Ning, Dong Linshuo, Zhang Jian, Li Zhijian, Liu Xuming

2025, 50(2): 181-186. doi:10.13251/j.issn.0254-6051.2025.02.028

Abstract ( 12 )

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Effect of different annealing temperatures on the hot-rolled plate of 1.45%Si non-oriented silicon steel was studied in order to guide the heat preservation process of the hot-rolled plate and provide a theoretical basis for its non-normalizing production. The results show that the microstructure of the hot-rolled plate has a large gradient along the thickness direction, and the surface layer, the subsurface layer and the center layer are equiaxed grains, deformed grains and fine equiaxed grains and deformed grains, respectively. With the increase of annealing temperature, the recrystallization ratio of hot-rolled plate gradually increases from 32.8% to 96.8%, and the microstructure of hot-rolled plate gradually uniform, the grain size of hot-rolled plate reaches 51.4 μm after annealing at 740 ℃ for 2 h, the γ texture and Goss texture in hot-rolled plate continue to decrease, and the λ texture gradually increases. Complete recrystallization can occur after annealing at a temperature higher than 740 ℃ for 2 h. In actual production, the hot-rolled coil crimp temperature (≥700 ℃) should be increased as much as possible, and the hot-rolled coil should be quickly stored in the slow cooling pit for insulation, so that complete recrystallization can occur as much as possible. Finally, after cold rolling and recrystallization annealing, the final product has excellent magnetic properties.

Effect of heat treatment process on mechanical properties at room temperature and high temperature of TC21 titanium alloy

Jiang Long, Zhao Wenpu, Zhang Chaoqun

2025, 50(2): 187-193. doi:10.13251/j.issn.0254-6051.2025.02.029

Abstract ( 9 )

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TC21 titanium alloy with different α phase lamella distributions was prepared by designing different heat treatment processes, and the precipitation of secondary α phase was controlled by aging. Combined with the results of mechanical property testing and analysis at room temperature and high temperatures, the effect of heat treatment on mechanical properties at room temperature and high temperatures of the TC21 titanium alloy was studied. The results show that after solution treatment at 980 ℃, following by annealing at 770 ℃, 810 ℃ and 850 ℃, respectively, the strength at room temperature of the alloy decreases with the increase of annealing temperature, while the plasticity increases. After annealing and aging at 550 ℃ for 4 h, the strength at room temperature of the alloy increases with the increase of annealing temperature, while the plasticity shows the opposite trend. With the increase of tensile test temperature, the plasticity of the TC21 titanium alloy treated by different processes is improved, and the strength retention rate is above 65% at 500 ℃, and the strength of TC21 titanium alloy annealed at 850 ℃ and aged at 550 ℃ is higher when used below 500 ℃.

Effect of annealing treatment on microstructure and mechanical properties of electron beam welding TC17 titanium alloy

Bian Hongyou, Liu Mingsong, Liu Weijun, Liu Yanshuo, Yu Xingfu

2025, 50(2): 194-199. doi:10.13251/j.issn.0254-6051.2025.02.030

Abstract ( 10 )

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Effect of annealing on the microstructure and mechanical properties of TC17 titanium alloy welded joint was studied by means of metallographic microscope, scanning electron microscope, hardness tester, and tensile testing machine. The results show that dynamic recrystallization occurs in the weld seam of the TC17 titanium alloy, and metastable β grains are formed, and there is no obvious second phase in the grains, which leads to softening of the weld zone. As the distance from the weld seam gets closer, the aspect ratio of the primary α phase in the heat affected zone decreases and the secondary α phase dissolves gradually, resulting in a gradual decrease in microhardness. After annealing at 600 ℃ for 4 h, the hardness of weld seam is increased by 41% compared with that of the welded state, and the hardness of heat affected zone is increased by 12.8% compared with that of the welded state. Due to the fine and dispersed secondary α phase precipitated in the metastable β phase in both the weld and heat affected zone, the microhardness of weld and heat affected zone is increased significantly compared with the welded state. The properties of the welded joint are mainly determined by the size and quantity of α phase. After annealing, the α phase has obvious strengthening effect, the tensile strength of the welded joint is increased by 14% compared with that of the welded state, and the tensile strength of joint is higher than that of the substrate, thus the fracture position of the joint is on the substrate.

Effect of finish rolling process on precipitation hardening of TiC in a titanium microalloyed steel

Wang Rui, Cui Yan, Peng Xiying, Feng Yunli, Sun Xinjun, Yong Qilong

2025, 50(2): 200-205. doi:10.13251/j.issn.0254-6051.2025.02.031

Abstract ( 11 )

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Nucleation parameters of TiC precipitation in austenite (γ) in a Ti microalloyed high-strength steel were calculated according to the solid solution precipitation theory and classical nucleation growth dynamics theory of binary precipitates. Then the TiC precipitation-time-temperature (PTT) curve and TiC nucleation rate-temperature (NrT) curve were drawn. The effects of finish rolling on the TiC nucleation rate, TiC precipitation rate, strength, and hardness were also studied. The results show that the temperature of the maximum nucleation rate of deformation-induced TiC precipitation is 740 ℃, the fastest precipitation temperature is 820 ℃, and the corresponding finish rolling temperature for the maximum hardness is 880 ℃. When the finish rolling temperature is 780-830 ℃, the rate of deformation-induced TiC precipitation is not significantly affected by temperature and has almost no effect on the hardness. As the finish rolling temperature increases from 830 ℃ to 880 ℃, the rate and precipitation amount of deformation-induced TiC precipitation decrease, promoting an increase in the amount of fine TiC precipitation during coiling, an increase in precipitation hardening effect, and an increase in hardness. When the finish rolling temperature is higher than 880 ℃, the hardness decreases due to the increase in grain size.

Effect of heat treatment parameters on surface contamination layer of Ti80 titanium alloy plate

Zhang Qiang, Liu Feng, Hao Xiaobo, Wang Fei, Yu Dongdong, Liu Xibo, Li Bobo

2025, 50(2): 206-211. doi:10.13251/j.issn.0254-6051.2025.02.032

Abstract ( 10 )

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Effects of heat treatment temperature and holding time on surface contamination layer of the Ti80 titanium alloy plate under atmospheric conditions and with/without surface anti-oxidation coating were studied by using metallographic method. The results show that when without surface anti-oxidation coating, as the heat treatment temperature increases and the insulation time prolongs, the thickness of the surface contamination layer on the Ti80 alloy plate continues to increase. When heat treated at 800-900 ℃, the surface contamination layer is relatively thin and easy to remove. However, when heat treated at 965-990 ℃, the removal of the surface contamination layer is difficult. When with surface anti-oxidation coating, the coating composition and coating thickness have a significant impact on the thickness of surface contamination layer on the Ti80 alloy plate. Choosing the appropriate type of coating and ensuring a certain coating thickness can significantly reduce the thickness of surface contamination layer on the Ti80 alloy plate after high temperature heat treatment, but it can not completely eliminate the surface contamination layer.

Nb element segregation behavior and homogenization law of GH2909 superalloy

Qi Huilin, Guo Xulong, Chen Qi, Zhou Yang

2025, 50(2): 212-217. doi:10.13251/j.issn.0254-6051.2025.02.033

Abstract ( 8 )

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Theoretical homogenization process of GH2909 alloy was calculated via JMatPro and homogenization experimental verification was conducted for the as-cast alloy at 1130 ℃ to 1190 ℃. Microstructure, element segregation and dissolution of Laves phase of the as-cast and homogenized GH2909 alloy were characterized by means of metallurgical microscope, scanning electron microscope and electronic probe. After heat treatment at 845 ℃ for 4 h and then air cooling for the homogenized GH2909 alloy, the distribution of needle-like η phase was observed, in order to evaluate homogenization effect of the GH2909 alloy. The results show that a mass of low melting point Laves phase exists in the as-cast GH2909 alloy and Nb element is the most important segregation element. Laves phase dissolves completely in the GH2909 alloy after 1150 ℃×7 h or 1130 ℃×10 h homogenization treatment. After complete Laves phase dissolution, 1190 ℃×35 h homogenization treatment decreases segregation coefficient to 1.046 and residual segregation coefficient to 0.059 of Nb element. After heat treatment at 845 ℃ for 4 h and air cooling for homogenized specimens, Nb-rich needle-like η phase precipitates along grain boundary and in grain with uniform diffusion of Nb element. Combining segregation coefficient with η phase precipitation behavior, 1150 ℃×7 h+1190 ℃×35 h homogenization treatment can realize complete homogenization of the GH2909 alloy.

Effect of cooling rate on microstructure of high reliability SAC-SBN alloy and its solder joints

Xia Ziqi, Cao Dali, Cao Lihua, Zhao Lingyan, Yang Jiaojiao

2025, 50(2): 218-224. doi:10.13251/j.issn.0254-6051.2025.02.034

Abstract ( 8 )

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In order to optimize the welding process of high reliability solder SAC-SBN alloy for automotive electronics, the influence of different cooling rates on microstructure of the SAC-SBN solder alloy and its solder joints was investigated. The test results indicate that the microstructure of the SAC-SBN alloy gradually coarsens with the decrease of cooling rate. Under the condition of a cooling rate of 48 ℃/s, the refinement degree of the alloy structure is optimal, while at a cooling rate of 0.13 ℃/s, the intermetallic compound (IMC) coarsens in the alloy and the Bi element exhibits grain boundary segregation. Compared with traditional SAC305 alloy, the SAC-SBN solder joints have a larger number and smaller size of IMC grains at the solder joint interface, which is attributed to the precipitation of Bi element at the interface grain boundary, which promotes the heterogeneous nucleation growth of (Cu, Ni)₆Sn₅. When the cooling rate is 48 ℃/s, the IMC layer at the SAC-SBN solder joint interface is the thinnest, as 1.96 μm. However, due to the difference in thermal expansion coefficients, the stress at the interface is relatively high, and voids appear in the IMC layer at the interface. When the cooling rate is 0.13 ℃/s, the IMC layer of the solder joint is the thickest, as 3.18 μm. And due to the interface reaction and maturation mechanism, there is stress between the Sn alloy matrix and IMC, resulting in voids in both the IMC layer at the interface and the (Cu,Ni)₆Sn₅ that has matured and grown inside the solder. When the cooling rate is 1.33 ℃/s, the solder joint structure is fine and there are no obvious defects.

Hot rolling process of non-tempered bainitic steel pipe for oil drilling

Ma Lina, Wang Xiaoyu, Nie Shunuo, He Jiaqi, Ouyang Siyi, Niu Sai, Wu Meng

2025, 50(2): 225-229. doi:10.13251/j.issn.0254-6051.2025.02.035

Abstract ( 10 )

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Effects of reheating temperature, cooling rate after rolling and tempering temperature on the microstructure and properties of hot-rolled non-tempered bainitic steel pipe for oil drilling were studied by laboratory heat treatment simulation. The results show that the reheating temperature decreases from 930 ℃ to 850 ℃, the sizes of bainite and lath martensite become smaller, and the impact absorbed energy of air-cooled tested steel increases from 19.48 J to 35.26 J. When reheated at 850 ℃, the microstructure is lath and packet martensite and granular bainite, the impact absorbed energy of air cooled tested steel is higher than that of furnace cooled. However, the impact property of the tested steel decreases after tempering at 300-400 ℃. In the actual production, the reheating temperature of the steel pipe during hot rolling should be properly reduced, and the cooling rate after rolling should be properly accelerated, so as to obtain the high toughness of the non-tempered bainitic steel pipe.

Changes in microstructure and properties of TP347HFG steel aged at 700 ℃

Song Tao, Xing Honggen, Wang Zhiwu, Zhang Yonglin

2025, 50(2): 230-234. doi:10.13251/j.issn.0254-6051.2025.02.036

Abstract ( 9 )

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By using SEM, EDS, TEM, universal testing machine and Brinell hardness tester, the changes in microstructure and properties of TP347HFG steel in as-received state and different aged states (aged at 700 ℃ for 500, 800, 1500, 2500, 3650 h) were analyzed. The results show that the relationship of total amount of precipitated phases vs aging time during the aging process of the TP347HFG steel at 700 ℃ is as follows: y=0.060-9.956×10^-5x+2.912×10^-7x²-2.707×10^-11x³-7.719×10^-15x⁴. The precipitated phase of the as-received TP347HFG steel is fine primary phase Nb(C, N). After aging for 500 h, M₂₃C₆ carbides precipitate and grow at the grain boundaries, and a small amount of σ phase appears after aging for 3650 h. After aging for 500 h, the fine second phase on the grain boundaries inhibits grain boundary slip, improves the hardness and strength, but reduces the material plasticity. After aging for 800 h, the precipitation of hard and brittle M₂₃C₆ carbides and the decrease in twinning quantity reduce the strength of the steel. After aging for 1500 h, the fine secondary Nb(C, N) plays a role in dispersion strengthening, increasing the strength and reducing the plasticity of the steel. When aged to 3650 h, with the coarsening of precipitated phases, the hardness value of the steel is decreased, the strength is slightly decreased, and the plasticity is slightly improved.

Pre-heat treatment process for large size NiCrMoV steel forgings

Li Guang, Qin Hongfu, Li Jie, Su Wenbo, Li Liangyu, Jin Ming

2025, 50(2): 235-240. doi:10.13251/j.issn.0254-6051.2025.02.037

Abstract ( 15 )

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In response to the problem of coarse grain and structural inheritance of high hardenability NiCrMoV steel forgings after forging, a process experiment using small-sized specimens was used to analyze the effect of heat treatment schemes such as pre-treatment before normalizing, multiple high-temperature normalizing treatments, two-phase region high-temperature side normalizing and annealing for cutting off the structural inheritance and for grain refinement. According to the size and shape characteristics of the rotor core shaft forgings, the optimal pre-heat treatment process scheme was developed, and control measures for austenitizing heating temperature and time and cooling process were proposed. The results show that after the optimal pre-heat treatment, the actual grain size of the actual produced large size forging body is sampled and tested as grade 6.5, and the ultrasonic testing of the forging meets the ø2 mm initial sensitivity requirement.

Influence of heat treatment process on microstructure and properties of SDP80C steel

Chen Shengnan, Peng Ruizhi, Wu Xiaochun

2025, 50(2): 241-246. doi:10.13251/j.issn.0254-6051.2025.02.038

Abstract ( 7 )

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Austenite continuous cooling transformation curve of pre-hardened die casting steel SDP80C was measured by using a thermal dilatometer, and the microstructure and mechanical properties under different aging processes were studied. The results show that the martensitic transformation starting temperature (Ms) of the SDP80C steel is 320 ℃, the austenite transformation starting temperature (Ac₁) is 695 ℃, and the austenite transformation ending temperature (Ac₃) is 841 ℃. Within the aging temperature range of 525-600 ℃, the increase of aging temperature promotes the formation and growth of NiAl phase and Cu-rich phase, and the martensite recovers. As a result, the hardness of the SDP80C steel gradually decreases while the impact property improves. After aging at 525 ℃ for 2 h, the SDP80C steel reaches the maximum hardness of 44.9 HRC and the impact absorbed energy is about 123 J, which is attribute to the precipitation strengthening of nano-scale NiAl phase and Cu-rich phase.

Effect of austenitizing temperature on microstructure and properties of 1500 MPa cold-rolled Q&P steel

Cai Shunda, Xin Lifeng, Song Liwei, Ruan Guoqing, Sun Rongsheng, Zhong Lili

2025, 50(2): 247-250. doi:10.13251/j.issn.0254-6051.2025.02.039

Abstract ( 10 )

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Effect of austenitizing temperature on microstructure, retained austenite content and mechanical properties of 1500 MPa grade Q&P steel was studied by means of optical microscope, scanning electron microscope, X-ray diffractometer and tensile testing machine. The results indicate that the tested steel is composed of ferrite, martensite and retained austenite austenitized at different temperatures, slow cooled, quenched and partitioned, but there are significant differences in the content of each phase and grain size. After the same slow cooling, quenching and partitioning process, the content of martensite and retained austenite significantly increases during intercritical austenitizing (750, 800 ℃), while there is no significant difference in the proportion of phases between high-temperature intercritical austenitizing at 800 ℃ and complete austenitizing at 850 ℃. The average grain size of the tested steel decreases with the increase of austenitizing temperature. The volume fraction of retained austenite in the tested steel austenitized at 750, 800 and 850 ℃ is 8.7%, 13.3% and 12.0%, respectively. The comprehensive mechanical properties of the tested steel are optimal when austenitized at 800 ℃, with a yield strength of 1169 MPa, tensile strength of 1503 MPa and elongation of 13.3%. The mechanical properties are mainly affected by the phase proportion, fine grain strengthening effect and retained austenite distribution.

Effect of diffusion time on microstructure and hardness of 20CrMnTi steel after vacuum low-pressure carburizing

Yu Penghan, Yan Haoming, Yang Shuai, Yu Xingfu, Liu Yongji, Dai Yougui

2025, 50(2): 251-255. doi:10.13251/j.issn.0254-6051.2025.02.040

Abstract ( 9 )

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20CrMnTi carburizing steel was subjected to vacuum carburizing treatment by using vacuum low-pressure pulse carburizing technology and quenching and tempering treatment, and the effect of diffusion time on the carbon concentration of the carburized layer, hardness, and microstructure was analyzed. The results show that after vacuum low-pressure pulse carburizing, when the diffusion time is short, e. g., 1125 min, due to the large surface carbon concentration gradient, significant internal stress is generated between the surface and subsurface layers, which can easily lead to internal cracks. When the diffusion time extends to 2125 min, the surface carbon content significantly decreases from 1.30% to 0.80%, the carbon content changes slowly from the surface to the core, and the surface hardness changes smoothly. When the diffusion time is short, after quenching, large-sized carbides and a large amount of retained austenite are observed in the surface layer. When the diffusion time prolongs, the carbide size and retained austenite content in the surface structure are significantly reduced. After 960 ℃ pulse vacuum low-pressure carburizing treatment for 52 min+diffusion for 2125 min, cooling to 840 ℃ for oil quenching, and then tempering at 180 ℃ for 2 h, the carbide in the carburized layer is grade 1, the core microstructure is grade 2, and the effective depth of carburized layer is about 3.12 mm, and the hardness changes smoothly from the surface to core, meeting the requirements of carburizing.

Effect of normalizing process on microstructure and properties of large nodular cast iron travel wheel containing Cu

Xiao Jieliang, Sun Hao, Li Fei, Hu Ping, Xie Yang, Chen Jinggang

2025, 50(2): 256-259. doi:10.13251/j.issn.0254-6051.2025.02.041

Abstract ( 9 )

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A normalizing process experiment was conducted on a large travel wheel made of nodular cast iron containing 0.460% Cu, and the effect of normalizing temperature (850 ℃ and 880 ℃) on the microstructure and mechanical properties of the travel wheel flange and spoke was studied. The results show that the large nodular cast iron travel wheel containing Cu can only obtain partial pearlite after low-temperature normalizing at 850 ℃, and there is still 25% to 30%(volume fraction) fragmented ferrite, resulting in the strength of the wheel flange not meeting the requirements. After normalizing at 880 ℃ (fan blown cooling) and tempering at 550 ℃, the mechanical properties of the flange and spoke can meet the requirements. More pearlite forms when normalized at 880 ℃ than that at 850 ℃. This is because as the normalizing temperature increases, the carbon content in austenite increases, the stability of undercooled austenite increases, and the C-curves shift to the right, making it easier to obtain pearlite during cooling. For the tested large nodular cast iron travel wheels, a higher normalizing temperature such as 880 ℃ is preferred.

Carburizing and quenching treatment of 18CrNiMo7-6 steel gear with small and medium modulus

Li Yao, Zhang Wei, Li Chaoqing

2025, 50(2): 260-263. doi:10.13251/j.issn.0254-6051.2025.02.042

Abstract ( 12 )

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Using orthogonal test, different processes of carburizing and quenching treatment were carried out on small and medium modulus gear made of 18CrNiMo7-6 steel, and the surface hardness, effective hardening layer depth, and microstructure after heat treatment were analyzed. The results show that the heat treatment processes with a strong carburizing potential of 1.10% and a diffusion carbon potential of 0.65%-0.85%, quenching time of 1.5 h and tempering time of 4 h, as well as quenching time of 1.0 or 1.5 h and tempering time of 6 h, can all achieve a surface hardness of over 59 HRC for the 18CrNiMo7-6 steel gear, and the effective hardening layer depth and microstructure meet the technical requirements. However, the microstructure observation finds that under the process of diffusion carbon potential of 0.85%, quenching time of 1.5 h, and tempering time of 4 h, both the carbides and retained austenite are at critical values, and there is a risk of exceeding the standard during mass production. After comprehensive consideration, the optimum carburizing and quenching process for the tested 18CrNiMo7-6 steel gear is determined as follows: strong carburizing potential of 1.10%, tempering time of 6 h, as well as diffusion carbon potential (0.65%-0.85%) matched with quenching time (1.0-1.5 h) by contour method.

Rapid and uniform temperature dropping method for heat treatment furnace

Liu Penghan, Zhou Chun, Li Zhengtao, Wen Changfei, Han Bing, Liu Yujia, Li Jiadong

2025, 50(2): 264-267. doi:10.13251/j.issn.0254-6051.2025.02.043

Abstract ( 12 )

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A novel rapid temperature adjusting method is proposed and experimentally validated to find a solution to the issues of low temperature dropping efficiency and uneven temperature distribution in traditional roller hearth open-flame heat-treatment furnace. Traditional methods rely on natural cooling or simple forced air cooling systems, resulting in slow cooling rates (66 h to cool from 600 ℃ to 200 ℃) and uneven temperature distribution. This leads to significant variations in the mechanical properties of the steel plates, impacting product quality and production efficiency. The novel cooling method integrates five measures: ① alternating pulse cooling of the burners to improve both cooling rate and temperature uniformity; ② increasing furnace negative pressure while raising the furnace door to enhance cold air intake; ③ increasing the exhaust fan frequency to control furnace pressure; ④ auxiliary cooling by steel plate, large-specification steel plates to absorb heat; and ⑤ accelerating hot gas turbulence by increasing the frequency of the top circulating fan to promote better heat mixing within the furnace. Comparative tests on a roller hearth annealing furnace demonstrate that the novel method reduces the cooling time from 600 ℃ to 200 ℃ to 26.9 h, representing at least a two-fold increase in cooling rate. Mechanical property tests show that the steel plates treated with the novel method exhibit significantly lower transverse variations in tensile strength and yield strength (less than 0.40% and 0.41%, respectively) compared to the traditional method. This novel method significantly improves the production efficiency, enhances product quality, and offers substantial economic and environmental benefits.

Prediction of critical temperature A₁ and A₃ of medium-Mn steel based on machine learning models

Zhang Zhiye, Wang Yan, Zhang Biao, Ji Ze, Liu Yaliang, Zhang Minghe, Feng Yunli

2025, 50(2): 268-277. doi:10.13251/j.issn.0254-6051.2025.02.044

Abstract ( 12 )

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In order to facilitate the design of heat treatment process of medium-Mn steel, a machine learning model for predicting the critical temperature A₁ and A₃ of medium-Mn steel was optimized. The critical temperature data of 496 groups of medium-Mn steels with different compositions were obtained by Thermal-Calc simulation software. Mn, Al and C compositions were taken as input characteristics, and phase transition temperatures A₁ and A₃ were taken as output targets. Three indexes of root mean square error (RMSE), mean absolute error (MAE) and determination coefficient (R²) were used to evaluate the prediction effect of the model. From seven machine learning models (LR, DT, SVM, GPR, Boosting, Bagging and ANN), the GPR model for predicting A₁ and the GPR and ANN model for predicting A₃ were screened. The results show that the GPR model for predicting A₁ has sufficient accuracy, that is the optimal model for A₁. The grid search method is used to adjust the hyperparameters of the preliminary model for predicting A₃, and the optimal model of A₃ (single-layer ANN model) is obtained. According to the chemical composition of medium-Mn steel in the applied literature, A₁ and A₃ are predicted by using the optimal model. The overall MAE of the predicted value and measured value of A₁ and A₃ is 9.95 ℃ and 13.57 ℃, respectively, and the minimum difference is 0.30 ℃ and 6.20 ℃, respectively, indicating that the model has high accuracy and can be used to predict the critical temperature of medium-Mn steel.

Simulation calculation of heating efficiency of heat treatment furnace based on ANSYS Fluent

Yu Liang, Zhang Fei, Tian Tong, Liu Yujia

2025, 50(2): 278-281. doi:10.13251/j.issn.0254-6051.2025.02.045

Abstract ( 12 )

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To improve the heating efficiency of the heat treatment furnace, a design scheme of adding nozzles on the top of furnace was proposed. The flow field distribution inside the furnace at different firing rates (0-120 m/s) of the furnace top nozzles was simulated by ANSYS Fluent software, and the temperature rise changes of the steel plates inside the furnace at different firing rates (30-210 m/s) were analyzed. The results show that after adding nozzles on the top of furnace, the flow field distribution inside the furnace is more uniform, and as the nozzle firing rate increases, the gas flow becomes more stable and uniform, and the temperature distribution inside the furnace becomes more uniform. At different nozzle firing rates, the heating rate of the steel plate in the furnace increases with the increase of firing rate, but beyond a certain threshold, the increase in heating rate of the steel plates is limited. It can be seen that adding nozzles on the top of furnace and optimizing the firing rate parameters can significantly improve the heating efficiency of the heat treatment furnace.

Influence of WC content on microstructure and wear resistance of AlCrFe₂Ni₂Mo_0.9 high-entropy alloy coatings

Wang Qingtian, Man Jiao, Wang Juncheng, Liu Genggen, Yang Bin

2025, 50(2): 282-291. doi:10.13251/j.issn.0254-6051.2025.02.046

Abstract ( 9 )

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By adding spherical WC particles with mass fraction of 10% to 30% to AlCrFe₂Ni₂Mo_0.9 high-entropy alloy powder, the coatings with various WC contents were prepared on 316L stainless steel by using high-velocity laser cladding technology. The effect of WC content on the phase composition, microstructure, element distribution, hardness, and wear resistance of the coatings was systematically evaluated by means of X-ray diffractometer, scanning electron microscope, energy dispersive spectrometer, microhardness tester, and friction wear tester. The results indicate that, without WC addition, the coating mainly consists of FCC phase, BCC phase and σ phase. As the WC content increases, the diffraction peak intensities of the BCC and σ phases gradually weaken, while that of the FCC phase strengthens. When the WC content reaches 30%, the phase composition is in a state where FCC phase and Fe₃W₃C phase coexist. With the increase of WC content, the microstructure of the coating transitions from dendritic to a more uniform equiaxed crystal morphology, significantly enhancing the fine grain strengthening effect. Simultaneously, partial dissolution of WC particles promotes the formation of an alloyed reaction layer and fishbone-like structures. As the WC content increases from 0% to 30%, the microhardness and wear resistance of the coating show a trend of first decrease and then increase, ultimately reaching the highest hardness of 567.22 HV at 30% WC content, along with the best wear resistance, reducing the wear rate to 0.68×10^-5 mm³·N^-1·m^-1, with a friction coefficient of 0.386.

Effects of activators and surface laser-quenching on low-temperature pack aluminizing of TC4 titanium alloy

Lu Jiacheng, Tian Xiaodong

2025, 50(2): 292-297. doi:10.13251/j.issn.0254-6051.2025.02.047

Abstract ( 9 )

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Effects of activators and surface laser-quenching pretreatment on low-temperature aluminizing of TC4 titanium alloy were studied. The solid powder pack cementation aluminizing of TC4 alloy was conducted between 550-700 ℃ for 4 h with three different activators of NH₄Cl, NH₄F and NaF, respectively, in the pack mixture, and the aluminizing of TC4 alloy substrate after surface laser-quenching was carried out. The cross-sectional morphology, element content and surface phase of the aluminized layers were analyzed by means of scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-Ray diffractometer (XRD). The results reveal that the three activators, NaF, NH₄F and NH₄Cl, can make Al content increase from 10.04% to 11.56%, 15.66% and 16.96%, respectively, of the surface layer of TC4 alloy after 700 ℃×4 h pack aluminizing. Compared with the Al content of the substrate, it is increased by 15.1%, 56.0% and 68.9%, respectively. The catalytic permeation effect of NH₄Cl is the best, followed by NH₄F, and the effect of NaF is the worst. The experiment results and the thermodynamic analysis are coincident. When the holding temperature drops to 600 ℃, there is almost no change in the surface Al content of the specimen after aluminizing. However, surface laser-quenching pretreatment of TC4 alloy substrate can refine the surface grain size and promote low-temperature aluminizing. After surface laser-quenching of TC4 alloy, the surface average grain size of α-Ti phase decreases continuously with the increase of laser power. When surface laser-quenched under 240 W, the average grain size of α-Ti phase is reduced by 47.9% compared with that without laser-quenching, and after four times laser-quenching at this power, the average grain size of α-Ti phase can be reduced by 68.6% than that without laser-quenching. The reduction of grain size of α-Ti phase on surface layer can promote the diffusion of aluminum in the surface layer, of which the content increases from 10.04% to 15.54% after 600 ℃×4 h aluminizing.

Influence of PIP/LQ composite process on properties of gun steel

Luo Yisong, Wang Fangzhou, Zhu Wei, Chen Shengyi, Luo Defu

2025, 50(2): 298-303. doi:10.13251/j.issn.0254-6051.2025.02.048

Abstract ( 8 )

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A composite treatment combining the advantages of two processes, PIP (Programable ion permeation) and laser quenching (LQ) for the gun steel material 25Cr3Mo3NiNbZr steel was performed to enhance its surface properties. After pretreatment of quenching and tempering, the tested steel was treated with PIP followed by laser quenching at different scanning speeds. Properties of the specimens were characterized by metallographic observation, XRD analysis, microhardness test, electrochemical corrosion and neutral salt spray test. The results show that scanned at the laser energy density of 2.31-3.00 J/mm², part of the compound layer decomposes, reducing the surface hardness, nitrogen-containing martensite generates in the diffusion layer, and the peak hardness of the subsurface layer is improved. Laser scanning speed of 39 mm/s (laser energy density of 2.31 J/mm²) is determined for the optimum process, when scanned at this speed, the microstructure is refined, more nitrogen-containing martensite transforms, less nitrides lose in the surface layer, and the eggshell effect is effectively alleviated. The corrosion resistance of the PIP/LQ composite process treated specimens is lower than that of the PIP treated specimens but still higher than that of the untreated specimens. It is concluded that the PIP/LQ composite process is feasible to improve the surface properties of gun steel.

Common failure problems and corresponding strategies for walking wheels of coal mining machines

He Xiao, Xu Hongxiang, Shi Lubing, Chen Shengchao, Li Ziyan, Rong Zeyu, Li Fuli

2025, 50(2): 304-311. doi:10.13251/j.issn.0254-6051.2025.02.049

Abstract ( 16 )

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Walking wheel, as the actuator of the walking device of the coal mining machine, often suffers from tooth breakage accidents due to the effect of strong impact loads. This seriously affects the working efficiency and poses a threat to the personal safety of the operators. Thus firstly, the failure modes of the walking wheel, such as wear, tooth breakage, spalling and plastic deformation of the tooth surface were expounded. Subsequently, for the tooth breakage failure, the coping strategies were summarized, including optimizing the product design, rationally selecting materials, increasing the gear modulus, installing protective devices and optimizing the heat treatment process. Finally, the suggestion of combining traditional carburizing and quenching processes with Q-P-T processes was proposed for heat treatment of walking wheel to improve its strength and toughness.

Fracture cause analysis of one tower bolt

Zhang Demei, Liang Xiaodong, Zhang Yan

2025, 50(2): 312-315. doi:10.13251/j.issn.0254-6051.2025.02.050

Abstract ( 20 )

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One tower bolt used in one wind-power station was fractured. The fracture cause of the failed bolt was analyzed by means of metallographic examination, SEM-EDS analysis, chemical composition testing and mechanical property testing. The results show that chemical composition and mechanical properties all meet the requirements of national standard. There is no abnormality for the microstructure. But the R value at the connection between the head of the fractured bolt and the screw is too small. The depth of Zn-Ni plating near the crack source is deeper than other edges, which indicates that during quenching and tempering treatment, cracks are generated at the intersection of the bolt head and the screw under the action of quenching stress. When in use, under the action of force, cracks continue to propagate, ultimately leading to fatigue fracture.

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