Heat Treatment of Metals

Effect of vacuum low pressure carburizing on microstructure and properties of austenitic stainless steels 304 and 316L

Cheng Ru, Tian Yong, Song Chaowei, Wang Haojie

2022, 47(9): 1-5. doi:10.13251/j.issn.0254-6051.2022.09.001

Abstract ( 221 )

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Surface strengthening of 304 and 316L austenitic stainless steels was processed by using vacuum low pressure carburizing process. The microstructure, phase composition and microhardness distribution of the carburized layers were analyzed by means of optical microscope, scanning electron microscope, Thermo-Calc software, X-ray diffractometer and microhardness tester. The offsets of different diffraction peaks in the carburized layers and the changes in lattice parameters before and after carburizing of the tested steels were calculated. Combined with the effects of molybdenum on carburizing process of the austenitic stainless steels, the differences in the carburized layer thickness, surface hardness and mechanism of carbides precipitation after carburizing of 304 and 316L austenitic stainless steels were compared and studied. The results show that the carburized layers produced by 750 ℃ carburizing for 2.6 h are composed of expanded austenite and Cr₂₃C₆ phases, the austenite lattice constant has increased by 1.33% and 1.14% respectively for 304 and 316L stainless steels, and Cr₂₃C₆ is mainly precipitated in strip shape on the expanded austenite grain boundaries. The surface hardness of the 304 and 316L stainless steels after carburizing at 750 ℃ for 2.6 h is over 2 times higher than that of substrate.

Effect of aging treatment on microstructure and mechanical properties of extruded 2195 Al-Li alloy

Wang Zhiwen, Yang Rongdong, Huang Yuanchun, Li Hui

2022, 47(9): 6-11. doi:10.13251/j.issn.0254-6051.2022.09.002

Abstract ( 112 )

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Effect of heat treatment on microstructure and mechanical properties of as-extruded 2195 Al-Li alloy was investigated. The results show that the mechanical properties of the as-extruded alloy can be significantly enhanced by solution treatment and artificial aging treatment, which is related to the type, size, number density and distribution of precipitated phases. The 2195 Al-Li alloy precipitation sequence during the aging process is SSSS(supersaturated solid solution)→GP zone+δ′/β′(Al₃(Li,Zr))→δ′+θ′(Al₂Cu)+T₁(Al₂CuLi)→θ′+T₁. The T₁ phase plays a leading role in precipitation strengthening. After solution treatment at 525 ℃ for 60 min and artificial aging at 170 ℃, the peak aging time of the 2195 Al-Li alloy is 36 h, under which the tensile strength, yield strength and elongation are 579 MPa, 537 MPa and 5.5%, respectively.

Effect of heat treatment time on microstructure and mechanical properties of TC4 titanium alloy fabricated by selective laser melting

Gao Xing, Zhang Ning, Ding Yan, Jiang Bo

2022, 47(9): 12-17. doi:10.13251/j.issn.0254-6051.2022.09.003

Abstract ( 99 )

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By using optical microscope, scanning electron microscope and electronic universal testing machine, effect of time of solution and aging treatment on microstructure and mechanical properties of TC4 (Ti6Al4V) alloy fabricated by selective laser melting (SLM) was investigated. The results show that the annealed SLM-fabricated TC4 alloy is mainly composed of continuous α_GB, basketweave α and transformed β phases. After solution and aging treatment, the microstructure of the specimens all presents as the morphology of basketweave. Under the condition of solution treatment at 920 ℃ and aging process of 550 ℃×3 h, air cooring, with the solution time increasing from 2 h to 6 h, the primary α phase(α_P) is significantly coarsened and the length of part α_P is up to 16 μm. The lamellar α phase is also coarsened and the length of lamellar α phase increases from 5-15 um to 20-30 um. The continuous α_GB phase becomes discontinuous and its width increases from 2.7 μm to 4.4 μm. Meanwhile, there is largersize α colony presented. The tensile strength increases from 1045.2 MPa to 1156.9 MPa, the elongation decreases from 13.6% to 6.7%. Under the condition of aging at 550 ℃ and the solution process of 920 ℃×2 h, WQ, with the aging time increasing from 3 h to 8 h, the fraction of transformed β phase increases. The length of α_P phase decreases from 40-60 μm to 30-40 μm. The α_GB phase is also continuous while its width increases from 2.7 μm to 4.5 μm. The lamellar α phase coarsens slightly. The tensile properties do not change remarkably. Therefore, it can be concluded that the duplex microstructure is difficult to obtain by changing time of solution and aging treatment at solution temperature of 920 ℃ and aging temperature of 550 ℃ for the SLM-fabricated TC4 alloy, and it has no beneficial effect on improving comprehensive mechanical properties.

Effect of microwave sintering process on microstructure and properties of Ti-Mg composites

Xia Pengzhao, Xu Ying, Cai Yanqing, Zhao Sitan, Lou Bingjie

2022, 47(9): 18-26. doi:10.13251/j.issn.0254-6051.2022.09.004

Abstract ( 84 )

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In order to determine the optimal microwave sintering process for preparing Ti-Mg composites, Ti-15Mg composites were prepared by microwave sintering. The effects of sintering temperature and holding time on microstructure, mechanical properties and corrosion resistance of the composites were systematically studied by means of scanning electron microscope, differential thermal analysis, X-ray diffraction, optical microscope, compression test and corrosion resistance test. The results show that when the sintering temperature is 540-600 ℃, with the increase of sintering temperature, the densification degree of the composites increases, the porosity decreases, the compressive strength and corrosion resistance increase. When the sintering temperature is 600 ℃, magnesium is uniformly distributed in the titanium matrix, and the performance of the composites is the best, meeting the performance requirements of medical materials. The continuous increase of sintering temperature leads to a large amount of volatilization of magnesium in the composites. The porosity increases and the strength of the composites decreases. Ti-15Mg composites prepared by microwave sintering have the characteristics of fast and stable sintering, so the effect of holding time on properties of composites is not obvious.

Effect of partitioning time on microstructure and properties of low carbon hot rolled F-Q&P steel

Su Zhangzhu, Wu Run, Li Zhao, Wu Teng, Qin Jinzhu

2022, 47(9): 27-30. doi:10.13251/j.issn.0254-6051.2022.09.005

Abstract ( 85 )

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Using a two-high reversing mill, effect of partitioning time of the relaxation-quenching partition (F-Q&P) process on microstructure and mechanical properties of tested steel was studied. The results show that under the relaxation-quenching partitioning (F-Q&P) process, the microstructure of the tested steel is mainly composed of polygonal ferrite, lath martensite and retained austenite. When the partitioning time is prolonged, the strength of the tested steel decreases, the yield ratio first decreases and then increases, the elongation increases, and the hardening index n value and the retained austenite content first increase and then decrease. After partitioning for 60 s, the tested steel has the lowest yield ratio and highest n value, 0.62 and 0.12, respectively, and the tensile strength and elongation are 1090 MPa and 19.0%, respectively, the mechanical properties are optimum.

Optimization of heat treatment process parameters of Fe-Mn-C-Al series TWIP steel

Wang Kai, Wang Rongji, Zhou Tong, Peng Song

2022, 47(9): 31-35. doi:10.13251/j.issn.0254-6051.2022.09.006

Abstract ( 89 )

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In order to improve the yield strength and mean while retain the better plasticity of TWIP steel, BP neural network and genetic algorithm were used to optimize heat treatment process parameters. Taking annealing temperature, holding time and cooling method as input, the product of yield strength and elongation as output, a 3-4-1 BP neural network model was established. Through the optimization of genetic algorithm, the heat treatment process parameters with the maximum product of yield strength and elongation were obtained. The results show that the optimized heat treatment process parameters are annealing temperature of 768 ℃, holding time of 35 min and furnace cooling method. And the accuracy of the prediction result is verified by experiments.

Effect of average pass reduction on microstructure of asynchronous rolled-solution treated 6016 aluminum alloy sheet

Lin Lingfeng, Yuan Gecheng, Yang Lian, Ding Canpei

2022, 47(9): 36-40. doi:10.13251/j.issn.0254-6051.2022.09.007

Abstract ( 70 )

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When the cumulative deformation amount was constant, the processes of rolling with 9, 5, 3, and 2 passes on the asynchronous rolling mill, and the average pass reduction ratios of 16%, 27%, 40% and 55%, respectively, were used for strong shear rollied 6016 aluminum alloy sheet, which was then solution treated at 540 ℃ for 30 min in a heating furnace. The microstructure characteristics and macroscopic texture were analyzed by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). The results show that with the increase of pass reduction, the number of the second phase increases, and the shear texture strength of E, F and r-cube shear texture increases. After solution treatment, the strength of shear texture slightly declines. After the solution treatment, the matrix grains and the second phase particles of the alloy sheet with a pass reduction of 55% are refined, the average grain size is 44.5 μm, and the size of second phase particle ranges from 0.3 μm to 0.5 μm, and which is dispersed in the matrix.

Effect of annealing process on microstructure and corrosion resistance of Ti-4Al-2V alloy

Wang Lu, Wang Feng, Zhang Mingwei, Liu Rui, Fu Zhengyuan, Liu Jingshun

2022, 47(9): 41-46. doi:10.13251/j.issn.0254-6051.2022.09.008

Abstract ( 77 )

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Extruded bars of Ti-4Al-2V alloy were treated by ordinary annealing, recrystallization annealing and double annealing, and the microstructure before and after heat treatment was characterized by X-ray diffractometer and scanning electron microscope. Meanwhile, the corrosion resistance of the titanium alloy in 3.5%NaCl solution was tested by electrochemical workstation, and the correlation between the heat treatment process and the corrosion tendency of the alloy was analyzed. The results show that there is no obvious macro and micro defect on the surface of the untreated alloy rod, and the microstructure of the titanium alloy is mainly α phase annealed at different temperatures. After double annealing at 960 ℃+570 ℃, the alloy is composed of coarse-grained α phase and fine needle-like α phase. The untreated alloy is accompanied with a basketweave microstructure, and a small amount of Widmannstatten structure and two-state structure are obtained after different heat treatment. By analyzing the polarization curves and electrochemical impedance spectroscopy of titanium alloy annealed at different temperatures, it can be seen that compared with the untreated alloy, the self-corrosion current density of the alloy annealed at 760 ℃ is smaller, the corresponding polarization resistance is larger, and the corrosion tendency is smaller. The Nyquist plot of the alloy after double annealing at 960 ℃+570 ℃ shows the largest capacitive arc resistance, indicating better corrosion resistance.

Effect of shot peening diameter on properties and damage evolution of GH4169 alloy

Li Lei, Zhu Xujun, Zhang Li, Tian Fuzheng

2022, 47(9): 47-53. doi:10.13251/j.issn.0254-6051.2022.09.009

Abstract ( 50 )

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Microstructure and mechanical properties of GH4169 alloy after shot peening with different projectile diameters were studied by semi-automatic optical microscope, laser scan confocal microscope and MTS-Landmark mechanical property test machine. The apparent damage evolution of the GH4169 alloy was analyzed during uniaxial tensile process by digital image correlation method (DIC). The results show that as the projectile diameter increases from ϕ0.6 mm to ϕ4.3 mm, the surface fine-grained layer thickness of GH4169 alloy increases from 420 μm to 530 μm and its surface roughness increases by a maximum of 80.8% compared to the original specimen. After shot peening, the yield strength and tensile strength of the material are increased and its elongation decreases. The damage evolution law of the GH4169 alloy is similar before and after shot peening with the increase of plastic deformation. The material appears uniform and slow deformation in the initial stage, and begins to be damaged rapidly when the damage factor reaches the critical value. The larger the shot peening diameter is, the smaller the critical plastic strain is, and the faster the material damage occurs. The damage evolution equation of GH4169 alloy is established, which has a great significance to the life assessment of shot peening reinforced materials.

Effect of gas atomization parameters on characteristics of 1720 MPa maraging steel powder used for selective laser melting process

Liu Zaixi, Lu Dehong, Wang Changjun, Liu Zhenbao, Liang Jianxiong

2022, 47(9): 54-59. doi:10.13251/j.issn.0254-6051.2022.09.010

Abstract ( 58 )

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1720 MPa maraging steel powders were manufactured by vacuum induction melting gas atomization (VIGA) process, and the effect of atomization pressure, superheat degree and gas heating temperature on powder characteristics was studied. The results show that when the atomization pressure, superheat degree and gas heating temperature are relatively higher, the yield of fine metal powder and the bulk density are higher, and the powder flowability is better. The optimal atomization parameters are the nozzle diameter of ϕ5 mm, the atomization pressure of 5.0 MPa, the superheat degree of 245 K, and the gas atomization temperature of 100 ℃. The aging steel powder under this process has good sphericity with powder flowability of 20.15 s/50 g and bulk density of 4.23 g/cm³.

Effect of pulsed magnetic field on microstructure and mechanical properties of 7A04 aluminum alloy under solution treatment

Cheng Qiao, Wang Jun, Xu Liang, Tian Jianming, Chen Zhongyi, Ma Yonglin

2022, 47(9): 60-64. doi:10.13251/j.issn.0254-6051.2022.09.011

Abstract ( 43 )

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Effect of pulsed magnetic field parameters on the microstructure and mechanical properties of 7A04 aluminum alloy under solution treatment was investigated by means of optical microscope, scanning electron microscope, Vickers hardness tester and universal testing machine. The results show that the pulsed magnetic field can promote the decomposition of S phase and accelerate the diffusion of its alloying elements, so as to obtain the solid solution structure with better saturation. After pulsed magnetic field solution treatment of 60 min, the tensile strength of the solution treated 7A04 aluminum alloy is increased by about 96 MPa, the microhardness is increased by about 20 HV50, and the elongation is decreased by about 0.9%. In the process of solution treatment of 7A04 aluminum alloy, the pulsed magnetic field is increasing the diffusion coefficient by reducing the diffusion activation energy of solute atoms, the solution process is accelerated, so that the solution treatment time is shortened.

Effect of cryogenic treatment on microstructure and mechanical properties of 15%SiC_p/2009 aluminum matrix composite

Pan Ran, Liu Baosheng, Zeng Yuansong, Qu Haitao, Wang Dong, Mu Yanhong

2022, 47(9): 65-70. doi:10.13251/j.issn.0254-6051.2022.09.012

Abstract ( 52 )

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Effect of long time cryogenic treatment on microstructure and mechanical properties of solution treated and aged SiC particles reinforced aluminum matrix composite was studied by means of hardness tests, X-ray diffraction analysis, mechanical tests and transmission electron microscope (TEM) observation. The mechanism of cryogenic treatment improving mechanical properties of the tested composite was analyzed in terms of microstructure. The results show that the hardness of the aged aluminum matrix composite with cryogenic treatment reaches the peak value (about 211.7 HV0.1) by 2 h earlier than that without cryogenic treatment. During the whole aging stages, the hardness of aged specimens with cryogenic treatment is higher than that without cryogenic treatment. During the under-aging stage, there are fine and uniformly distributed needle-like precipitates in microstructure of the specimens with cryogenic treatment, which is not apparent for that without cryogenic treatment. During the over-aging stage, large-size precipitates appear in both groups of the specimens with and without cryogenic treatment, the precipitate size and distribution are obviously uneven in that without cryogenic treatment, but the mechanical properties of both groups tend to be almost the same with the increase of aging time, as the effect of cryogenic treatment on mechanical properties of aluminum matrix composites is declined.

Effect of heat treatment on microstructure and mechanical properties of TC4 alloy plate directly rolled by EB ingot

Zhang Haoze, Wang Junsheng, Gong Penghui, Zhan Haiyi, Wang Kai

2022, 47(9): 71-78. doi:10.13251/j.issn.0254-6051.2022.09.013

Abstract ( 61 )

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TC4 titanium alloy ingot cast by electron beam cooling bed furnace were rolled for three times to obtain plates of different thicknesses. The effect of different annealing temperatures (750, 780, 810 and 850 ℃) on microstructure and mechanical properties of the plates was studied. The results show that the microstructure of single reheat rolled sheet is not sufficiently fragmented, and the morphology of primary α phase can't be significantly changed by increasing the annealing temperature. After double reheat rolling and triple reheat rolling, the original lamellar structure is gradually fragmented completely, and the ratio of the primary equiaxed α phase is correspondingly increased. With the increase of annealing temperature, the primary α phase of double reheat rolled plates spheroidizes gradually, and the primary α phase of triple reheat rolled plates begins to grow gradually at 780 ℃, and the secondary α phase shows a tendency of thickening and widening. The comprehensive analysis reveals that after the single reheat rolled plates annealed at 810 ℃, the double reheat rolled plates annealed at 840 ℃, and the triple reheat rolled plates annealed at 750 ℃, a good combination of strength and plasticity is obtained. By analyzing the fracture morphology of the corresponding alloy plates, both the room temperature fracture mechanism and the high temperature fracture mechanism are typical ductile fracture.

Effects of multi-axial forging and T852 heat treatment on microstructure and mechanical properties of Al-Cu-Li alloy

Zhong Liwei, Feng Zhaohui, Gao Wenli, Chen Junzhou, Lu Zheng

2022, 47(9): 79-86. doi:10.13251/j.issn.0254-6051.2022.09.014

Abstract ( 62 )

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Effect of multi-axial forging with different passes and T852 heat treatment on microstructure and mechanical properties of Al-Cu-Li alloy was studied by means of SEM, EBSD, TEM and tensile test. The results show that the grain structure of the Al-Cu-Li alloy is significantly refined after multi-pass multi-axial forging, and the grain size is reduced from 450 μm in as-homogenized state to 5 μm in as-forged state with six passes. The grain refinement mechanism is mainly continuous dynamic recrystallization, accompanied by discontinuous dynamic recrystallization. After T852 heat treatment, the precipitates on grain boundary of the as-forged alloy with six passes present discontinuous distribution, and a large number of lath-shaped T₁ phases and a small amount of θ′ phases are precipitated in the grains. Compared with the coarsened T₁ phase in as-homogenized state, the T₁ phase in as-aged state is obviously refined. After 6 passes forging and T852 heat treatment, the tensile strength, yield strength and elongation of the alloy are 544 MPa, 462 MPa and 8.6%, respectively, which are 2.0, 2.4 and 4.1 times of those in as-homogenized state, and the corresponding fracture mode changes from brittle fracture to ductile fracture.

Effect of solution treatment on austenite grain growth of low expansion GH2909 superalloy

Chen Qi, Zhou Yang, Fu Jianhui

2022, 47(9): 87-91. doi:10.13251/j.issn.0254-6051.2022.09.015

Abstract ( 92 )

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In order to analyze the effect of solution treatment temperature and time on austenite grain growth in GH2909 superalloy and obtain the grain growth law, the GH2909 superalloy was solution treated at different temperatures (1000-1080 ℃) for different time (1-4 h). The average grain size of austenite in GH2909 alloy after different solution treatment processes was measured, and the austenite grain growth model during solution treatment was established. The results show that the austenite grain size of GH2909 alloy increases gradually with the increase of solution treatment temperature and time, and the Laves phase in the structure gradually redissolves. When the solution treatment temperature is lower than 1020 ℃, the GH2909 alloy has good ability to resist austenite grain coarsening, which can effectively guide the grain size control in the forging process of GH2909 alloy.

Laser shock peening process with low pulse energy of 316L stainless steel

Qin Enwei, Liu Lixia, Liu Chengwei, Lu Haifeng, Wu Shuhui

2022, 47(9): 92-97. doi:10.13251/j.issn.0254-6051.2022.09.016

Abstract ( 82 )

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Using 316L stainless steel as the model material, the low-energy high-repetition rate laser shock peening process was systematically studied. A concept of laser spot coverage ratio was established. For the spot diameter d between 0.4-0.8 mm, the saturation coverage ratio is 6-7, under which the matching relationship between the manipulator movement rate v and the spot diameter d is v=70d. The maximum residual compressive stress increases with the decrease of the spot diameter. When the spot diameter d is 0.4 mm, the maximum residual compressive stress is 662 MPa, and the depth of the residual compressive stress affected layer is 565 μm. The surface roughness of the laser shock peened area does not increase significantly, but there is a step with certain height between the laser shocked and unshocked zones. At a laser power density of 1.59 GW/cm², the step height is 23 μm.

Low temperature normalizing process of nodular cast iron travel wheel

Xiao Jieliang, Sun Hao, Li Fei, Hu Ping, Chen Jinggang, Jiang Zhaofeng

2022, 47(9): 98-102. doi:10.13251/j.issn.0254-6051.2022.09.017

Abstract ( 58 )

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Low temperature normalizing process test of a kind of Cu microalloyed nodular cast iron travel wheel was carried out, and the microstructure and mechanical property data of the flange and spokes of the travel wheel normalized at 850 ℃ and 860 ℃ were obtained. The effect of alloying element Cu on microstructure and properties of nodular cast iron and the change of the temperature range of austenitization and pearlite transformation were analyzed. The results show that 95% pearlite of the nodular cast iron travel wheel can be obtained by normalizing at 850 ℃, reaching fully normalized state, and the mechanical properties meet the requirements of QT650-4 grade. Meanwhile, the microstructure and properties after normalizing at 850 ℃ and 860 ℃ are compared. Although the microstructure and properties after normalizing at 850 ℃ and 860 ℃ can meet the requirements, the surface hardness after normalizing at 860 ℃ is higher than that normalized at 850 ℃, and the mechanical cutting performance is relatively poor. It shows that the temperature window of this travel wheel normalizing process is very narrow. Therefore, it is better to choose the normalizing process at 850 ℃. The heat treatment process has been applied in engineering, and the produced travel wheels have been exported in batches.

Effect of isothermal time in spheroidizing annealing on microstructure and properties of high carbon H13 steel

Guo Zhikai, Lian Mingyang, Zhuo Xingjian, Ye Lei, Cao Peize, Wang Chaofeng, Shang Qiuyue

2022, 47(9): 103-107. doi:10.13251/j.issn.0254-6051.2022.09.018

Abstract ( 101 )

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High carbon H13 steel was spheroidizing annealed with different isothermal time and then quenched and tempered. The effect of isothermal time on microstructure and properties of the high carbon H13 steel was studied by means of scanning electron microscope, hardness test and impact property test. The results show that with the increase of isothermal time, the hardness of the high carbon H13 steel after quenching and tempering increases first and then decreases, the impact property decreases first and then increases, but the wear resistance increases first and then decreases. When the isothermal time is 2 h, there are more strip and granular carbides at grain boundary of the high carbon H13 steel after quenching and tempering, which reduces its impact property. When the isothermal time is 3 h, there are more granular carbides with larger size inside the grains of high carbon H13 steel after quenching and tempering, which improves its wear resistance significantly, and offers good comprehensive properties.

Optimization of quenching process of high strength and toughness Q690D steel for construction machines

Ji Dejing, Yang Weiyu, Bai Yaqiong

2022, 47(9): 108-112. doi:10.13251/j.issn.0254-6051.2022.09.019

Abstract ( 67 )

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Effect of quenching temperature from 880 ℃ to 1100 ℃ on microstructure, original austenite grain size and impact property at -20 ℃ of the Q690D steel with 30 mm thickness was investigated by means of full-automatic phase transition equipment, optical microscope, scanning electron microscope and transmission electron microscope. The results show that when the quenching temperature is below 950 ℃, the average austenite grain size of the tested steel is less than 10 μm, with the increase of quenching temperature, the Nb, V, Ti microalloyed carbides dissolve and the impact absorbed energy at -20 ℃ increases gradually. When the quenching temperature increases from 950 ℃ to 1100 ℃, the impact absorbed energy at -20 ℃ of the tested steel decreases from the maximum value 150 J to 19 J, with the rapid growth of austenite grains. The optimum quenching process of the Q690D steel is 950 ℃×20 min, and then water cooling.

Effect of heat treatment process on microstructure and mechanical properties of N06600 alloy hot rolled plate

Wen Fangming, Hao Xiaobo, Cao Heng, Zhang Qiang, Li Bobo, Liu Yinqi

2022, 47(9): 113-118. doi:10.13251/j.issn.0254-6051.2022.09.020

Abstract ( 74 )

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Effect of heat treatment process on microstructure and mechanical properties of N06600 alloy hot rolled plate was studied. The results indicate that the N06600 alloy plate is composed of austenite+carbides along the grain boundary+carbides in grain. The content of carbides and the strength decrease with the increasing of solution treatment temperature. Obvious recrystallization occurs and some grains grow up significantly after solution treatment at 980 ℃. When the solution treatment temperature rises to 1020 ℃, the recrystallization is finished and the average grain size increases up to 127 μm, and all the carbides are dissolved in matrix. At the same time, the strength decreases drastically and the elongation increases greatly, and a large amount of twins are found in the microstructure. For the low alloying and carbide content, the difference between the transverse and longitudinal directions on the microstructure and mechanical properties of the N06600 alloy plate produced by alternative rolling process is small and the anisotropy of mechanical properties is not significant, and even with a double solution treatment at 650 ℃+950 ℃ or 950 ℃+650 ℃, or water quenching for raising cooling rate, the microstructure and mechanical properties still remain stable.

Effect of soaking temperature on microstructure and properties of 980 MPa grade high strength steel with different chemical composition

Ai Bingquan, Kuang Shuang, Tian Xiugang, Yang Feng, Wang Yuhui, Lu Zhiqiang, Wang Zhao, Hao Lei

2022, 47(9): 119-124. doi:10.13251/j.issn.0254-6051.2022.09.021

Abstract ( 73 )

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Continuous-annealing process was simulated to treat 1.4 mm chilled steel strips with different chemical composition by Using Gleeble-3500 thermal simulation machine, and the mechanical properties and microstructure of the simulating annealed specimens were analyzed by means of universal tensile testing machine, optical microscope, scanning electron microscope and EDS. The results show that other annealing parameters are the same, under the premise of low C and high Mn composition, the C-Mn-Si(high)+Cr+Mo steel with alloying elements Cr, Mo and high Si content and the C-Mn-Si(low) steel without alloying elements Cr, Mo and with low Si content can obtain 980 MPa grade dual-phase steel with mechanical properties meeting requirements when annealed at soaking temperature of 760 ℃ and 780 ℃. The microstructure of the C-Mn-Si(high)+Cr+Mo steel is composed of ferrite, island-like martensite and a small amount of bainite at different soaking temperatures. The difference is that the ferrite at high soaking temperature has small grain size and a large amount, uneven morphology, and the martensite content is relatively less, and the bainite is needle-like or cluster-like. The microstructure of the C-Mn-Si(low) steel is composed of ferrite, martensite and a small amount of bainite and retained autensite. The difference lies in the refinement of ferrite grain at high soaking temperature, not obvious rolling characteristics, less martensite content, and less granular bainite. The retained autensite is bright white stripes, which is mainly caused by local enrichment of Mn. In essence, the difference of microstructure between the C-Mn-Si(high)+Cr+Mo steel and C-Mn-Si(low) steel is caused by the different content of alloying elements Cr, Mo and Si, which affects the stability of undercooled austenite.

Effect of quenching temperature on microstructure and properties of Cr5MoVNi steel

Wang Shikai, Wang Rui, Kang Yan, Yu Zhiqiang, Yan Zhijie

2022, 47(9): 125-129. doi:10.13251/j.issn.0254-6051.2022.09.022

Abstract ( 74 )

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To investigate the effect of quenching temperature on microstructure and properties of Cr5MoVNi steel, the tested steel was quenched at 1000, 1050, 1100 and 1150 ℃ respectively, and then tempered at 230 ℃. Optical microscope (OM), scanning electron microscope (SEM), transition electron microscope (TEM), X-ray diffraction (XRD) and compressive tests were employed to investigate the microstructure and mechanical properties of the tested steel. The results indicate that, with the increase of quenching temperature, the retained austenite content in the matrix of the steel increases significantly and even reaches to 100% retained austenite; the hardness decreases monotonously, and the impact absorbed energy increases to the peak value of 20.1 J when quenched at 1100 ℃, and then decreases with further increase of quenching temperature. TRIP effect occurs in the retained austenite during compressive deformation, that is the reason why the compressive strain exceeds 35%.

Effect of controlled cooling process on microstructure and mechanical properties of hot-rolled dual phase steel

Xiong Weiliang, Liang Wen, Wu Teng, Liang Liang, Wu Haohong

2022, 47(9): 130-133. doi:10.13251/j.issn.0254-6051.2022.09.023

Abstract ( 66 )

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Based on the principle of alloy reduction,a 600 MPa grade hot-rolled dual phase steel with better strength and toughness was obtained by using hot rolling and ultra fast cooling technology, and then the effect of controlled cooling process on microstructure and mechanical properties of the tested steel was studied. The results show that with the decrease of relaxation time and coiling temperature, the volume fraction and grain size of ferrite decrease gradually, the tensile strength increases from 602 MPa to 637 MPa, the elongation decreases from 31.0% to 24.0%, the yield ratio is 0.53-0.59, and the n value is 0.17-0.21. Considering the mill load and mechanical properties, the appropriate coiling temperature and relaxation time for the tested steel are 150 ℃ and 7 s, respectively.

Effect of solution treatment on microstructure and properties of Incoloy825 alloy pipe

Zhang Yucheng, Jia Haomei

2022, 47(9): 134-139. doi:10.13251/j.issn.0254-6051.2022.09.024

Abstract ( 75 )

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Effect of solution treatment on microstructure and properties of Incoloy825 alloy was studied by means of metallographic analysis, tensile test and intergranular corrosion test. The results show that the grain size of the Incoloy825 alloy tends to increase with the increase of solution treatment temperature, but the grain growth rate is different at different solution treatment temperatures. When the solution treatment temperature exceeds 1000 ℃, the grains grow rapidly, accompanied by annealed twins. When the solution holding time is less than 30 min at 950 ℃, the mixed-sized grain structure appears in the matrix. After holding for 60 min, the mixed-sized grain state is improved, basically equiaxed grains are obtained with an average grain size of grade 7. With the increase of solution treatment temperature and the extension of holding time, the tensile strength and yield strength of the Incoloy825 alloy decrease to varying degrees, and the elongation increases. The intergranular corrosion rate of the Incoloy825 alloy decreases firstly and then stabilizes with the increase of solution treatment temperature and holding time. After solution treatment at 950 ℃ for 60 min, the corrosion rate basically stabilizes at 0.12 mm/y, and there is no significant difference in the intergranular corrosion rate with the increase of solution treatment temperature. The comprehensive effect of mechanical properties and intergranular corrosion resistance of the Incoloy825 alloy are the best after solution treatment at 950 ℃ for 60 min.

Effect of laser heat input on microstructure and mechanical properties of 1Cr17Ni2 stainless steel repaired by laser additive

Fan Zhao, Cheng Zonghui, Zhang Zhiqiang

2022, 47(9): 140-145. doi:10.13251/j.issn.0254-6051.2022.09.025

Abstract ( 55 )

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Experiment of 1Cr17Ni2 stainless steel repaired by laser additive Ni-based high temperature alloy powder was carried out. The effect of different laser heat input on microstructure and mechanical properties of the repaired 1Cr17Ni2 steel joints was studied. The results show that the laser additive repair joints of the 1Cr17Ni2 steel are divided into cladded zone, heat-affected zone and stainless steel matrix. The upper region of the cladded zone is uniformly distributed dendrite structure, and the primary arm is fully developed and its growth direction is consistent, which is roughly parallel to the height of cladding. The dendrite size decreases with the decrease of heat input and the gap between the dendrite grains increases. The middle and lower regions of the cladded zone are short columnar dendritic structure, and its growth direction is consistent, which size decreases slightly as the laser heat input decreases. The cladded zone is mainly composed of matrix phase γ, irregular phase δ and MC precipitated along grain boundary. The heat affected zone of the stainless steel side is mainly composed of massive δ ferrite, austenite, martensite and spherical pearlite, and there is a clear boundary with the cladded zone. With the decrease of laser heat input, the average hardness of the cladded zone increases at first and then decreases. When the laser heat input is 80 J/mm, the maximum hardness is 330.64 HV0.2, which is increased by 9.78% than that of stainless steel matrix.

Effect of programmable ion permeation on high temperature wear resistance of a novel hot-working die steel

Li Wenming, Luo Defu, Liao Hongyi, Pan Hongji

2022, 47(9): 146-152. doi:10.13251/j.issn.0254-6051.2022.09.026

Abstract ( 52 )

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Effect of programmable ion permeation (PIP) on microstructure and high temperature wear resistance of a novel hot-working die steel was studied by means of high temperature wear testing machine, X-ray diffraction (XRD), scanning electron microscope (SEM) and micro-hardness testing machine. The results show that when the novel hot-working die steel is treated by PIP, a dense and complete compound layer reaching 40 μm is formed. The out layer is composed of Fe₃O₄ phase, which can reduce the surface friction coefficient. The subsurface layer is composed of Fe_2-3N and Fe₄N phases, which can improve the surface hardness. When the wear test temperature is lower than 600 ℃, Fe_2-3N and Fe₄N phases exist stably. When the wear test temperature is higher than 800 ℃, Fe_2-3N and Fe₄N phases transform into α-Fe phase to form a nitrogen-containing martensite structure, which improves the high temperature wear resistance of the material.

Continuous cooling transformation curve of R350HT rail steel

Wang Ruimin, Liu Man, Zhou Jianhua, Zhang Qi, Su Xue, Xu Guang

2022, 47(9): 153-157. doi:10.13251/j.issn.0254-6051.2022.09.027

Abstract ( 74 )

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Thermal simulation test of European standard R350HT rail steel with different cooling rates was carried out on the Gleeble-3500 thermal simulation testing machine. The microstructure was observed, the hardness was measured, and the continuous cooling transformation (CCT) curves of the tested steel was drawn. The results show that when the cooling rate is between 0.5-2.5 ℃/s, the microstructure consists of pearlite and a small amount of proeutectoid ferrite. When the cooling rate is 3 ℃/s, martensite appears in the structure. Since the pearlite rail steel should not contain martensite, the cooling rate of the tested steel should be less than 3 ℃/s. At the same time, with the increase of cooling rate until 10 ℃/s, the pearlite transformation start temperature decreases, which is because the residence time in the high temperature region is shortened with the increase of the cooling rate, and the pearlite transformation is too late to occur, and the pearlite transformation requires a large degree of undercooling. In addition, with the cooling rate increasing to 20 ℃/s, the microstructure is basically composed of martensite. When the cooling rate is greater than 20 ℃/s, the microstructure only contains martensite. Hence, the critical cooling rate of martensite transformation is 20 ℃/s.

Isothermal deformation embrittlement phenomenon and mechanism of high molybdenum non-magnetic steel

Jiang Yiming, Qu Huapeng, Lang Yuping, Feng Hanqiu, Chen Haitao, Li Xiangming

2022, 47(9): 158-163. doi:10.13251/j.issn.0254-6051.2022.09.028

Abstract ( 64 )

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Thermodynamic characteristics of carbide precipitation in high molybdenum non-magnetic steel were calculated by using Thermal-Calc thermodynamic calculation software. The effect of aging temperature, isothermal deformation+aging temperature on the precipitation behavior of the tested steel was discussed by means of optical microscope, scanning electron microscope and other equipment, and the impact test was carried out. The results show that the precipitation phase is mainly produced at the grain boundary, and the temperature sensitive to precipitation of the tested steel is 700-900 ℃. After aging at 800 ℃ for 1 h, the formation of precipitates can be clearly observed at the grain boundaries of the tested steel, which are granular. Compared with no deformation, the precipitates are formed in large quantities under deformation conditions, the shape is strip-like, and the grain boundaries are obviously thickened. Compared with the aged specimens, the deformation before aging significantly shortens the incubation time of the precipitates and promotes the growth of the precipitates. After isothermal deformation+aging, the impact performance is significantly reduced, and the fracture mode is ductile fracture.

Microstructure and properties of microalloyed Cu-Ni-Sn-P alloy

Xiong Shujun, Wan Jia, Chen Jinshui, Guo Chengjun, Xiao Xiangpeng

2022, 47(9): 164-170. doi:10.13251/j.issn.0254-6051.2022.09.029

Abstract ( 54 )

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Effect of different nickel-tin ratios on as-cast, solid-solution and aging microstructure and properties of Cu-Ni-Sn-P alloys was analyzed, so as to optimize the composition ratio of nickel and tin elements in Cu-Ni-Sn-P alloys by means of optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), micro Vickers hardness tester and eddy current conductivity meter. At the same time, effect of different deformation heat treatment processes on the microstructure and properties of Cu-0.87Ni-1.82Sn-0.07P alloy was studied. The results show that for the Cu-Ni-Sn-P alloys with different composition, the Cu-Ni-Sn-P alloy (Cu-0.87Ni-1.82Sn-0.07P alloy) has the best comprehensive properties when Ni∶Sn is 1∶2, the hardness after solution and aging treatment is up to 119.9 HV0.5, and the conductivity is 35.0%IACS. The peak aging hardness of the alloy can be increased up to 164 HV0.5 after 30% pre-cold rolling before aging at 450 ℃. The fracture structure is mostly dimples with good toughness and the anti-softening temperature is 480 ℃. There is a tangential relationship between the age-strengthened precipitated phase and dislocation, and the precipitated phase presents spherical Ni-P particles. The precipitated particles at grain boundary are larger, and the precipitated particles in grain are generally smaller with sizes ranging from tens to hundreds of nanometers.

Continuous cooling transformation behavior of high-strength Q690D heavy steel plate

Li Jing, Liu Chen, Yang Yuehui, Yuan Shaoqiang, Ai Chenguang

2022, 47(9): 171-174. doi:10.13251/j.issn.0254-6051.2022.09.030

Abstract ( 78 )

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By using Gleeble-1500 thermo-simulator along with microstructure and hardness analysis, the continuous cooling transformation (CCT) curves of Q690D heavy steel plate were measured at different cooling rates. The results demonstrate that the proeutectoid ferrite and pearlite zones are observed at slow cooled rates. When the cooling rates reaches 3 ℃/s,the lath bainite appears. At larger range cooling rates, the microstructure of granular bainite and granular+lath bainite can be obtained for the tested steel. Moreover, when the cooling rate reaches 15 ℃/s, the martensite can be observed which indicates that the hardenability of the tested steel is better and the hardness values have little change. The hardness values of different thickness sections keep almost unchanged of the quenched and tempered Q690D heavy steel plate, the microstructure are uniformity. The microstructure and harness values for simulated specimens show the highly consistent with the Q690D heavy steel plate actually produced.

Heat treatment process and mechanical properties of selective laser melted Ti-6Al-4V alloy

Li Ying, Peng Shuang, Zhang Ting, Chai Xianghai, Weng Yiliu

2022, 47(9): 175-181. doi:10.13251/j.issn.0254-6051.2022.09.031

Abstract ( 55 )

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Ti-6Al-4V alloy round bar specimens were prepared by the selective laser melting(SLM) technology, and the tensile properties of the material were improved by different heat treatment processes. The high cycle fatigue properties of the Ti-6Al-4V alloy were also tested. The relationship between microstructure and tensile properties, as well as the fatigue crack initiation source and crack propagation mechanism of the Ti-6Al-4V alloy were revealed by microstructure and fracture analysis. The results show that the heat treatment process has a significant effect on the mechanical properties of the Ti-6Al-4V alloy fabricated by SLM. The solution aging heat treatment process at 920 ℃×1 h, water-rolling and 800 ℃×2 h, furnace-cooling exhibit preferable comprehensive tensile properties at room temperature. The microstructure at room temperature is composed of α phase on the grain boundary and lamellar α+β microstructure inside the grain. The formation of grain boundary in the Ti-6Al-4V alloy microstructure is related to scanning path of additive manufacturing process. During the heat treatment, α phase precipitate preferentially at the overlap of scanning zone. Compared with the fatigue life curve of the forgings, the fatigue life of the SLMed specimens is lower at the same maximum stress level, and the decreasing trend increases with the decrease of the stress level. At 400 MPa stress level R=-1, the fatigue life of the forgings has reached 2×10⁷ level, and the fatigue life of the SLMed specimens is low, only 1% of that of the forgings. The low stress fatigue life is due to the existence of faulty fusion in the SLMed specimens. The faulty fusion is easy to appear at the overlap of scanning zone, and the fatigue crack will also propagate along these defects.

Performance stability of 1180 MPa complex phase steel in Cr-Mo-Nb-Ti-B series

Tian Xiugang, Liu Jingbao, Kuang Shuang

2022, 47(9): 182-187. doi:10.13251/j.issn.0254-6051.2022.09.032

Abstract ( 44 )

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A 1180 MPa high strength complex phase steel in Cr-Mo-Nb-Ti-B series was designed and developed. From the perspective of microstructure control, bainite was introduced to make up for the high strength difference between the soft and hard phases between ferrite and martensite, the effects of soaking temperature and overaging temperature on mechanical properties and microstructure of the complex phase steel during continuous annealing were studied by means of Gleeble-3500 thermal simulation test machine, tensile test machine and optical microscope. The results show that when the soaking temperature is from 720 ℃ to 840 ℃, the bainite and martensite contents gradually increase with the increase of temperature, and the tensile strength and yield strength increase continuously as a whole, but the tensile strength and yield strength decrease when the temperature exceeds 840 ℃. With the increase of overaging temperature, the tensile strength decreases monotonically, and the yield strength fluctuates at first and then decreases gradually. When the soaking temperature is 790 ℃ and the overaging temperature is 280 ℃, the microstructure of the continuous annealed plate is a complex phase structure of ferrite, bainite and martensite, which makes the steel have better formability, the bending property and hole-expanding property are also greatly improved compared with the same grade dual-phase steel products.

Static CCT curve measurement and microstructure analysis of HRB400E anti-seismic structural rebar

Luo Yanping, Wang Jiahan, Li Muze, Zhang Yunxiang, Zhou Jianxun, Zhao Zhiheng

2022, 47(9): 188-193. doi:10.13251/j.issn.0254-6051.2022.09.033

Abstract ( 57 )

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The static continuous cooling transformation (CCT)experiments for anti-seismic rebar steel HRB400E were conducted on Gleeble-3500 thermal simulation test machine by expansion method, The microstructure and hardness of the steel under different cooling rates were observed and measured by optical microscope (OM), scanning electron microscope (SEM) and micro-Vickers hardness tester, and the effect of cooling rate on the transformation structure and properties of the steel was analyzed. The results show that when the cooling rate is below 3 ℃/s, the microstructure of the tested steel is ferrite and pearlite. With the increase of cooling rate, the pearlite content in the tested steel increases gradually and the lamellar spacing decreases. Bainite appears in the tested steel when the cooling rate is 4-10 ℃/s. When the cooling rate is higher than 10 ℃/s, the tested steel begins to undergo martensitic transformation. With the increase of cooling rate, the hardness of the tested steel increases gradually. When the cooling rate is within the range of 2-3 ℃/s, the pearlite content, lamellar spacing and mechanical properties of the tested steel meet the technical requirements of the national standard GB/T 1499.2—2018. The experimental results are in good agreement with the mechanical properties of industrial products, in which, the pearlite content and lamellar spacing of the finished specimen of ϕ8 mm rebar at the cooling rate of 3 ℃/s are 47% and 0.184 μm respectively, and yield strength R_eL, tensile strength R_m, ratio of R_m/R_eL, ratio of R_eL/R^s_eL, fracture total elongation A and total elongation at maximum force A_gt are 440 MPa, 569 MPa, 1.29, 1.10, 27.2% and 17.8%, respectively.

Control of δ-ferrite content and austenite grain size in 0Cr16Ni5Mo martensite stainless steel

Tian Wei, Pan Wei, Zhong Qingyuan

2022, 47(9): 194-201. doi:10.13251/j.issn.0254-6051.2022.09.034

Abstract ( 54 )

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δ-ferrite content of 0Cr16Ni5Mo steel was found to exceed the value specified in the technical agreement. In order to reduce the content of δ-ferrite while control the austenite grain size to meet the service requirement, the causes of ferrite formation were analyzed through theoretical calculations and thermodynamic simulation, and the microstructure and change of δ-ferrite content of the 0Cr16Ni5Mo steel were investigated by means of quenching and high temperature diffusion treatment at different temperatures. In addition, two kinds of cyclic heat treatments were used to control the austenitic grain size. The test results show that with the increase of quenching temperature, the austenite grain size of the 0Cr16Ni5Mo steel increases continuously, but the reduction of δ-ferrite content is relatively limited. The high temperature diffusion can reduce the δ-ferrite content obviously, however, when the diffusion temperature is higher than the transformation temperature of austenite to δ-ferrite, the δ-ferrite dissolution is relatively delayed. After high temperature diffusion at 1130 ℃, a variable temperature cyclic phase transformation heat treatment at 850 ℃ and 830 ℃ can be used to eliminate the martensitic inheritance and uniformly refine the austenitic grains.

Continuous cooling transformation behavior of high strength bridge steel Q690q

Zhou Wenhao

2022, 47(9): 202-207. doi:10.13251/j.issn.0254-6051.2022.09.035

Abstract ( 85 )

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Continuous cooling transformation behaviors of high strength bridge steel Q690q were studied under three different primary austenite states of fine-grained austenite (grain size of grade 10), coarse-grained austenite (grain size of grade 6.5) and fine-grained deformed austenite (grain size of grade 10.5 and 30% compression deformation) by means of MMS-200 thermo simulator, Imager M2m optical microscope, JSM-6490LV scanning electron microscope and FV-ARS9000 automatic Vickers hardness tester. The results show that when the cooling rate is the same, fine-grained austenite increases phase transformation starting temperature, transformation rate peak temperature and phase transformation finishing temperature, while coarse-grained austenite contributes to the formation of medium and low temperature structures, such as lath bainite and lath martensite, and the lath becomes more elongated, but the prior austenite grain boundary becomes clearer, and its hardness obviously improves. Meanwhile, after the fine grain austenite deformation, the phase transformation starting temperature and transformation rate peak temperature are higher, so that the ferrite becomes bulky, but that can reduce the pearlite transformation and promote the formation of carbon-free bainite, and the hardness is greater than the condition of fine-grained austenite at lower cooling rate, and there is no difference when the cooling rate is higher.

Industrial trial manufacture of 55SiCrNb steel for ultra high strength suspension spring

Chen Huande, Ma Han, Sun Guocai, Zhang Yu

2022, 47(9): 208-213. doi:10.13251/j.issn.0254-6051.2022.09.036

Abstract ( 67 )

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Continuous cooling transformation behavior of the supercooled austenite test 55SiCrNb steel was studied, and the effect of cooling rate on microstructure was clarified, and wire with a diameter of 16 mm was hot rolled via industrial production line. A strong steel wire with a diameter of 14.8 mm was fabricated through drawing and on-line induction heat treatment. The microstructure of steel wire consists of tempered troostite, a few tempered martensite and retained austenite, and exhibits tensile strength higher than 2160 MPa, and reduction of area larger than 44%, which is qualified for making springs with a strength level of 2100 MPa.

Microstructure and texture of Inconel783 superalloy bolt

Huang Youqiao, Li Wang, Zhu Xinping, Huang Yijun, Zhang Ning, Meng Li

2022, 47(9): 214-219. doi:10.13251/j.issn.0254-6051.2022.09.037

Abstract ( 49 )

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Microstructure and texture of Inconel783 superalloy bolts were studied, and β phase precipitation characteristic was paid special attention, meanwhile the microstructure and texture changes after stress relaxation experiment at high temperature were investigated. The results show that the grain size of γ phase is homogeneous, and γ′ precipitates distribute dispersely. Large β-phase particles are shown to align regularly, with the longitudinal axis parallel to the axis direction of bolt. The distribution of β-phase particles does not depend on the γ phase grain orientations and sizes, while it is mainly determined by smelting and hot deformation processes; the small β-phase particles precipitate at γ phase grain boundaries and inside grains, continuously or separately. Regarding texture, neither the β nor γ phase texture is strong, showing the effect of changing multi-directional stress during hot deformation. Using the axis direction of bolt as the sample reference direction x, <111>//x texture with higher intensity and <100>//x texture are observed in γ phase. The γ phase microstructure, β phase distribution and the textures of both phases are stable during stress relaxation at high temperature. By analyzing the distribution of essential small β-phase particles in Inconel783 superalloy, it is found that the precipitation behavior is influenced by the orientation of γ phase matrix and grain boundary characteristic. More small-sized β-phase precipitation occurs in <111>//x oriented γ grains, while the precipitation quantity does not show advantage at twin boundaries. It can be deduced that the precipitation of small-sized β-phase particles could be modified by controlling the grain size and texture evolution of γ phase during hot deformation and solution treatment processes.

Microstructure evolution of 280VK cold-rolled high-strength steel and precipitation mechanism during annealing process

Qiao Degao, Luo Xiaoyang, Hu Shuangxi, Hou Yuanyuan, Zhang Zhijian, Tang Xingchang

2022, 47(9): 220-226. doi:10.13251/j.issn.0254-6051.2022.09.038

Abstract ( 66 )

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In order to reveal the effect of annealing process on microstructure, texture evolution and mechanical properties, the hot-rolled microalloyed high-strength steel 280VK was cold-rolled and then annealed at different temperatures, then the microstructure was observed by SEM, TEM and EBSD, meanwhile the content of precipitates and mechanical properties were measured and analyzed. The results show that after annealing, a large number of TiC precipitated particles are generated in the matrix of the tested steel. As the annealing temperature increases, the grain size increases, the average size of precipitated particles increases but the number decreases, the tensile strength and yield strength decrease, while the elongation increases. Thermodynamic calculation shows that the priority order of the precipitates in the tested steel is TiN>AlN>TiC, and TiC is the main one.

Effect of silicon content on microstructure and mechanical properties of heat-resistant nodular cast iron

Zhao Jing, Wang Liping, Feng Yicheng, Jiang Wenyong, Wang Lei, Guo Erjun

2022, 47(9): 227-233. doi:10.13251/j.issn.0254-6051.2022.09.039

Abstract ( 99 )

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The influence of silicon content on microstructure and mechanical properties of heat-resistant nodular cast iron at room temperature and high temperature was studied by means of optical microscope, scanning electron microscope and electronic universal tensile testing machine. The test results show that with the increase of silicon content, the roundness of graphite gradually decreases. When the silicon content(mass fraction, similarly hereinafter) reaches 3.8%, fragmented graphite begins to appear in the matrix, and the spheroidization grade is grade 3. As the silicon content increases from 2.8% to 4.8%, the pearlite content decreases from 51.06% to 8.65%. With the increase of silicon content, the room temperature tensile strength first increases and then decreases, and the elongation decreases gradually. When the silicon content is 3.8%, the tensile strength is 726 MPa and the elongation is 1.6%. With the increase of silicon content, the high temperature tensile strength gradually increases and the elongation decreases gradually. When the silicon content is 4.8%, the tensile strength is 532 MPa and the elongation is 6%. A large number of cleavage planes and river patterns appear in the tensile fracture at room temperature, and the form is brittle fracture. Dimples and tear edges appear in the high temperature tensile fracture, and the tensile fracture form is ductile-brittle mixed fracture.

Effect of vanadium on nitrided layer of Cr12Mo die steel and its tribological behavior

Mei Lang, Fang Changyang, Li Qiuping

2022, 47(9): 234-239. doi:10.13251/j.issn.0254-6051.2022.09.040

Abstract ( 72 )

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Cr12Mo and Cr12MoV die steels were gas nitrided, and then the effect of V on microstructure and tribological behavior of Cr12Mo die steel was compared and analyzed. The results show that after gas nitriding, a nitrided layer with a depth of about 120 μm is prepared on the surface of both the two die steels, and the nitriding layer, diffusion layer and matrix are successively from the surface to the inside. The V improves the wear resistance of die steel, and the Cr12MoV steel shows better anti-wear effect. Compared with that on the increase of the hardness of the die steel matrix and the diffusion layer, the effect of V on the increase of the hardness of the zone near the maximum hardness value of the nitriding layer is more obvious. The effect of V on wear resistance of the nitrided layer of the two die steels is not obvious, but the main contribution of V is to promote the effective infiltration of N during nitriding, greatly improve the interface bonding force between the nitrided layer and the diffusion layer, avoid the cracking between the nitriding layer and the diffusion layer, and promote the change of the wear mechanism from fatigue wear to adhesive wear, and the service life of the nitrided layer is further improved.

Effect of Nb on microstructure and intergranular corrosion sensitivity of 00Cr21Ni6Mn9N stainless steel

Yan Zhikun, Chen Haitao, Lang Yuping, Qu Huapeng, Feng Hanqiu, Liu Rongpei

2022, 47(9): 240-244. doi:10.13251/j.issn.0254-6051.2022.09.041

Abstract ( 56 )

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In order to study the effect of Nb on microstructure and intergranular corrosion resistance of 00Cr21Ni6Mn9N stainless steel after solution treatment, the 00Cr21Ni6Mn9N stainless steel with 0.057%Nb and without Nb were solution treated at 950, 1000, 1050, 1100, 1150 and 1200 ℃ for 1 h, respectively, and the microstructure was observed. The results show that when the solution temperature is 950-1200 ℃, the grain size of the 00Cr21Ni6Mn9N stainless steel increases with the increase of the solution temperature. The addition of Nb promotes the appearance of mixed crystal structure in the 00Cr21Ni6Mn9N stainless steel and increases its complete recrystallization temperature. The tested steel without Nb can obtain a uniform grain size after solid solution above 1000 ℃, while the tested steel with 0.057%Nb needs to be above 1100 ℃ to obtain a uniform structure, and its size is slightly larger than that of the steel without Nb at 1000 ℃ completely recrystallized grain. With the increase of solution temperature and the growth of grain size, the content of the precipitated Z phase decreases, and the grain interface energy decreases. After solution treatment at 1150 ℃ and 1200 ℃ for 1 h, the grain refinement effect of Nb and the degree of grain growth caused by the increase of temperature become no longer obvious. Both steels have lower intergranular corrosion susceptibility, while the reactivation rate R_a of the 00Cr21Ni6Mn9N stainless steel with 0.057%Nb is further lower than that of the steel without Nb.

Effect of Ni content on microstructure and mechanical properties of quenched and tempered 40CrNiMo steel

Guan Yunqi, Li Liang, Hu Wenxiang, Shi Zhengliang, Xu Jia

2022, 47(9): 245-249. doi:10.13251/j.issn.0254-6051.2022.09.042

Abstract ( 125 )

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Effect of Ni content on microstructure, volume fraction of retained austenite, hardness, tensile strength and impact property at room temperature of quenched and tempered 40CrNiMo steel was studied by means of OES, SEM, XRD and mechanical testing instruments. The results show that with the increase of Ni content from 1.346% to 1.618%, the microstructure and content of retained austenite have no obviously change, while the lattice distortion of α-Fe increases. The hardness of the tested steel tempered at different temperatures increases by 5-10 HV. The tensile strength of the high Ni content steel tempered at 450 ℃ is 78 MPa higher than that of the low Ni content steel, meanwhile the increase of tensile strength decreases with the increase of tempering temperature. However, under the condition that the retained austenite content is almost unchanged, the increase of Ni content reduces the impact absorbed energy of the steel tempered at 450 ℃ and 500 ℃ by about 50%.

First-principles study on mechanical properties of Ti_x(AlNbZr)_100-x series multi-principal element alloys

Zhang Qian, Li Zhiang, Liu Qianqian, Liu Hongwu, Wang Qingfeng

2022, 47(9): 250-256. doi:10.13251/j.issn.0254-6051.2022.09.043

Abstract ( 59 )

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By calculating the solid solution parameters and phase diagram of alloy, the formation law of the solid solution phase of the Ti_x(AlNbZr)_100-x series multi-principal element alloys was studied. The effect of Ti content on structural stability and mechanical properties of the Ti_x(AlNbZr)_100-x series multi-principal alloy was investigated by means of first principles method based on density functional theory. The results show that the Ti_x(AlNbZr)_100-x series multi-principal element alloys can form a stable solid solution phase, and the alloy is mainly composed of BCC phase and Al₃Zr₅ phase. With the increase of Ti content, the liquidus line of the alloy decreases, and the phase formation temperature of Al₃Zr₅ decreases, when the Ti content is 60%-70%, Al₃Zr₅ phase disappears and the alloy is composed of a single BCC phase. Increasing Ti content can improve the structural stability of the alloy. When the Ti content is 25%-70%, the alloy has good mechanical stability. The bulk modulus, shear modulus and Young's modulus of the alloy increase with the increase of Ti content. The ground state energy and heat of formation of Ti_x(AlNbZr)_100-x series multi-principle element alloys decrease with the increase of Ti content, indicating that increase of Ti content can increase thermodynamic stability of the alloy system and make the alloy easier to form a solid solution phase.

Finite element simulation of vacuum low pressure carburizing and quenching of 16Cr3NiWMoVNbE steel C-ring

Yuan Li, He Dupeng, He Xin, Qin Xiangge

2022, 47(9): 257-263. doi:10.13251/j.issn.0254-6051.2022.09.044

Abstract ( 63 )

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Temperature field, concentration field, microstructure field and stress field of vacuumlow pressure carburizing and quenching of 16Cr3NiWMoVNbE gear steel C-ring were studied by using the finite element model of martensitic transformation kinetics and carbon concentration diffusion coefficient. The results show that the carbon concentration distribution obtained after carburizing quenching can well explain the final martensite distribution in the surface layer. A reliable basis is provided for predicting the carbon concentration distribution and martensite distribution of the gear steel after carburization and quenching.

Thermodynamic calculation and analysis on equilibrium precipitates in Ce-S containing free-cutting steel

Wang Yinghu

2022, 47(9): 264-271. doi:10.13251/j.issn.0254-6051.2022.09.045

Abstract ( 37 )

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Equilibrium precipitates in a Ce-S containing free-cutting steel at temperature from 300 ℃ to 1500 ℃ were calculated based on thermodynamic software Thermo-Calc and a diagram of the phase-transformation path was obtained during equilibrium solidification. The effects of Ce and S content on Ce₂O₂S phase and effects of S and Mn content on MnS phase were discussed, respectively. The results show that the main equilibrium phases in the Ce-S containing free-cutting steel are Ferrite, Ce₂O₂S, Corundum, Austenite, M₂(C,N), Liquid, M₂₃C₆, MnS, Sigma, Spinel and M(C,N). With the increase of Ce content, the precipitation of Ce₂O₂S increases gradually, but the change of S content almost has no effect on the Ce₂O₂S. With the increase of S content, the precipitation amount and precipitation temperature of MnS gradually increase. The change of Mn content almost has no effect on the precipitation amount of MnS, but increasing Mn content increases the precipitation temperature of MnS. The sulfides in the Ce-S containing free-cutting stainless steel casting billet are of spherical, ellipsoidal, spindle shape or short-bar-like, and are distributed in clusters along the grain boundary, belonging to a type of II sulfide. By adding the rare earth Ce, the proportion of spherical rare earth composite inclusions in the Ce-S containing free-cutting steel is relatively high, and the proportion of sulfides with length-width ratio≤3 reaches 84.86%, and the sulfide morphology control achieves good results.

Research progress of medium manganese steels with high product of strength and elongation for automobile

Wang Mingming, Ma Fei, Pei Weichi, Li Dongdong, Long Haiyang, Ji Hongchao, Liu Shuai

2022, 47(9): 272-280. doi:10.13251/j.issn.0254-6051.2022.09.046

Abstract ( 76 )

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Taking high product of strength and elongation medium manganese steel as subject, the influence mechanism of alloying and hot working process on the structure regulation of high product of strength and elongation medium manganese steel was reviewed, as well as the influence of different structures on product of strength and elongation of medium manganese steel, providing reference for the research, development and preparation of medium manganese steel. In addition, further research on the structure regulation and performance enhancement of medium manganese steel also put forward relevant suggestions.

Application status and development trend of on-site PWHT technology for pressure vessels

Wang Zhigang, Luo Yongzhi, Qin Zuowei

2022, 47(9): 281-285. doi:10.13251/j.issn.0254-6051.2022.09.047

Abstract ( 78 )

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Research and development trends of pressure vessel on-site post-weld heat treatment technology at home and abroad are reviewed. The on-site post-weld heat treatment methods and some of research and application results obtained by domestic and foreign researchers are briefly described, and the research and application direction of post-weld heat treatment technology for super large diameter and super thick wall vessels are prospected.

Design, development and application of automatic coating equipment with anti-carburizing paint for input shaft

Xia Xiaoyu, Fan Xin, Wei Hanwei

2022, 47(9): 286-292. doi:10.13251/j.issn.0254-6051.2022.09.048

Abstract ( 63 )

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A special automatic equipment for input shaft coating with anti-carburizing paint was designed and developed with good reliability, controllability, reproducibility, repeatability, safety and repairability. And a complete coating process was developed. After repeated verification, it meets the technical requirements of the anti-carburizing range and has good performance for reproducibility.

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