Current Issue

• MICROSTRUCTURE AND PROPERTIES

  Variant selection of α phase in β-type Ti-15Mo alloy

  Ren Cheng, Min Xiaohua, Fei Qi

  2024, 49(9):  1-10.  doi:10.13251/j.issn.0254-6051.2024.09.001

  Abstract ( 97 )   PDF (5708KB) ( 114 )  

  SEM and EBSD were used to investigate the variant selection behaviour of the α phase in the β matrix and at the β grain boundaries in the Ti-15Mo alloy after solution treatment and aging. The results show that the solution treated specimen consists of single β grains without any preferred orientation. In the solution treated and aged specimen, the intragranular α phase does not undergo variant selection, instead, self-accommodation occurs among α variants, leading to a cross distribution of α phase variants at 60°. The variant selection of the film-like grain boundary α phase is influenced by the misorientation of adjacent β grains. A minor misorientation causes α phase to retain a Burgers orientation relationship with β grains on either side, whereas a major misorientation affects the precipitation of the α phase due to the interface orientation. The variant selection of the grain boundary Widmanstätten microstructure relies on the nucleation site. When the nucleation takes place at the film-like grain boundary α phase, it selects the same variants as the film-like grain boundary α phase. Nonetheless, when the nucleation occurs at the interface between the film-like grain boundary α phase and the β matrix, it is influenced by both.

  Difference of microstructure and properties between bulb and flat of Cu-bearing low-carbon bulb flat steel

  Liang Fengrui, Su Hang, Chai Feng, Sun Mingxuan

  2024, 49(9):  11-17.  doi:10.13251/j.issn.0254-6051.2024.09.002

  Abstract ( 38 )   PDF (4682KB) ( 28 )  

  Microstructure evolution of Cu-bearing low-carbon bulb flat steel during hot-rolling-induction heating-solid solution-tempering treatment was characterized using electron back-scattered diffraction (EBSD), field emission scanning electron microscopy (FE-SEM) and energy disperse spectroscopy (EDS). The difference between the bulb and flat was analyzed based on the strengthening mechanism. The results show that at different heat treatment stages, the grain size of flat is smaller than that of the bulb, while the precipitation of Cu-rich particles in the flat is improved. After aging at 680 ℃ for 2 h, compared with the bulb, the flat exhibit a higher strength and hardness and a relatively lower elongation. During hot-rolling-induction heating-solid solution-tempering process, the bulb flat steel undergoes thermal deformation, ferrite austenite transformation, martensitic transformation, and recovery stages in sequence. The strength difference of about 50 MPa between the flat and the blub is attributed to the major factor of the size difference of Cu-rich particles, the secondary factor of the difference in grain size and the weak factor of the difference in dislocation density.

  Effect of continuous annealing on microstructure and properties of 350 MPa cold-rolled high corrosion resistant weathering steel

  Wang Nai, Ma Degang, Li Jianying, Ma Guangzong, Sun Lu, Sun Hongliang, Ji Minglong

  2024, 49(9):  18-23.  doi:10.13251/j.issn.0254-6051.2024.09.003

  Abstract ( 44 )   PDF (3537KB) ( 45 )  

  Effect of continuous annealing process on microstructure and properties of 350 MPa cold-rolled high corrosion resistant weathering steel was studied by simulating continuous annealing process with Gleeble-3500 annealing machine. The results show that with the increase of annealing temperature, the strength of the tested steel decreases first and then increases, the annealing temperature is the key factor affecting the microstructure and properties of the tested steel, whereas, the effect of strip speed, slow cooling temperature and rapid cooling temperature on properties of the tested steel is limited. When the annealing temperature is lower than 800 ℃, only recovery and recrystallization in the tested steel occur, and the microstructure is composed of ferrite and carbide, the strength of the tested steel decreases with the increase of annealing temperature. When the annealing temperature is 800 ℃, the yield ratio reaches a minimum value of 0.53, exhibiting the characteristics of duplex steel, and is annealed at the critical austenitizing temperature Ac₁. When the annealing temperature is higher than 800 ℃, the tested steel occurs recovery, recrystallization and austenitization transformation, and the microstructure is composed of ferrite, bainite and carbide after cooling, and the strength of the tested steel increases with the increase of annealing temperature. Based on the comprehensive analysis, two process routes, low-temperature annealing and high-temperature annealing, can be used in industrial production to obtain the tested steel that meet the standard requirements.

  Isothermal phase transformation behavior and cooperative regulation of microstructure and properties and flat coil of hot rolling 65Mn steel strip

  Tian Yaqiang, Yao Zhiqiang, Nian Baoguo, Zhang Junfen, Zhang Xiaolei, Song Jinying, Zhang Mingshan, Chen Liansheng

  2024, 49(9):  24-30.  doi:10.13251/j.issn.0254-6051.2024.09.004

  Abstract ( 58 )   PDF (5095KB) ( 39 )  

  Isothermal transformation curve (TTT curve) of 65Mn steel was obtained by quenching phase change machine. Based on this curve, the evolution of microstructure and mechanical properties at different coiling temperatures was studied, and the possible causes and control methods of flat coil were discussed. The results show that the typical microstructure of the 65Mn steel, namely proeutectoid ferrite and pearlite, is obtained between 600-750 ℃. The TTT curve presents a typical "C" shape, with a "nose tip" temperature of 550 ℃. The incubation period is relatively short at this temperature, only 0.25 s. Within the typical microstructure formation temperature range of the 65Mn steel, the incubation period gradually increases with the increase of temperature, and the content of proeutectoid proeutectoid ferrite increases, while the content of pearlite decreases. According to the actual production, the selected coiling temperature of the 65Mn steel is between 650-750 ℃, and the microstructure is proeutectoid ferrite and pearlite. With the coiling temperature decreases from 750 ℃ to 650 ℃, the proeutectoid ferrite content decreases from 19.4% to 4.1%, and the distribution gradually transitions from block distribution to network distribution. The pearlite lamellar spacing decreases from 277.0 nm to 178.0 nm, resulting in an increase in the yield strength of the 65Mn steel from 534 MPa to 637 MPa, an increase in ultimate tensile strength from 776 MPa to 899 MPa, an increase in hardness from 18.8 HRC to 24.3 HRC, and a decrease in percentage total extension at fracture from 28.9% to 19.4%. In actual production, the coiling temperature and the holding time before coil discharging are adjusted based on TTT curve and the evolution of microstructure and mechanical properties under different coiling temperatures can achieve synergistic regulation of microstructure, mechanical properties and flat coil defects.

  Microstructure and properties of high hardenability high-carbon chromium bearing steel

  Wang Bingnan, Jia Yuxin, Wang Shanshan, Zhang Yahui

  2024, 49(9):  31-35.  doi:10.13251/j.issn.0254-6051.2024.09.005

  Abstract ( 56 )   PDF (2423KB) ( 35 )  

  Martempering and austempering treatments were conducted on three types of high-hardenability high-carbon chromium bearing steels, namely GCr18MnMo steel, GCr18MnMo1 steel and GCr19SiMnMo1 steel. The differences in their microstructure, maximum hardenability size, retained austenite and impact properties were compared. The results show that the hardenability is ranked from high to low as GCr19SiMnMo1 steel > GCr18MnMo1 steel > GCr18MnMo steel. If the hardenability standard is that the core hardness is greater than or equal to 55 HRC, the maximum hardenability size of GCr18MnMo steel is approximately 70 mm, the maximum hardenability size of GCr18MnMo1 steel is approximately 100 mm, and the maximum hardenability size of GCr19SiMnMo1 steel is approximately 130 mm. When these three tested steels undergo austempering, the retained austenite content can be guaranteed to be less than 1%. During martempering, the retained austenite content of GCr18MnMo and GCr18MnMo1 steels is less than 15%, and for GCr19SiMnMo1 steel, the retained austenite content can be reduced to less than 1% by additional tempering while ensuring high hardness. The impact properties of these three specimen steels are very close, and the impact property after austempering is approximately 70% higher than that after martempering. Only GCr19SiMnMo1 steel can be used for parts with wall thickness or diameter more than ϕ100 mm to ensure that the core troostite meets the requirements.

  Microstructure and mechanical properties of long-term high temperature serviced Inconel 783 superalloy bolts

  Zhou Hao, Wang Shuai, Zeng Yanping, Ma Zhibao, Zhou De, Guo Derui, Dong Shuqing

  2024, 49(9):  36-42.  doi:10.13251/j.issn.0254-6051.2024.09.006

  Abstract ( 31 )   PDF (4015KB) ( 27 )  

  Inconel 783 superalloy bolts after about 30 000 h service at 605 ℃ were studied, and the thermodynamic equilibrium process of the tested material was simulated using Thermo-calc software to study the trends of precipitated phase types and compositions with respect to temperature. The microstructure and precipitated phase characteristics of the specimens, sampled from the thread and polished rod parts of the bolts, were investigated by means of optical metallographic microscope(OM), scanning electron microscope(SEM) and transmission electron microscope(TEM), and the mechanical properties such as Brinell hardness, tensile and impact tests were tested. The results show that the grain size at the polished rod of the bolt is slightly larger than that at the thread, and the morphology, size and quantity of γ′ and β precipitates at the thread and polished rod are roughly the same. In addition, the γ′ phase is mainly nano-sized particles. The β phase is mainly characterized by two features, one is relatively large in size and distributed in the grain and grain boundary, and the other is relatively small in size and distributed in the grain boundary as a network. At the same time, the precipitation of γ′ phase and Heusler-Ni₂AlX phase is found in the β phase. The hardness value at the thread of the bolt is higher than that at the polished rod, and the yield strength at the thread is slightly higher than that at the polished rod, but the elongation and reduction of area at the polished rod tested at high temperature are slightly higher than those at the thread.

  Microstructure and properties of P91 steel pipe after long term high temperature service

  Zhang Yingwei, Bai Jianqiang, Bai Zhanqiao, Li Weili, Shen Kang, Dong Shuqing

  2024, 49(9):  43-46.  doi:10.13251/j.issn.0254-6051.2024.09.007

  Abstract ( 29 )   PDF (1776KB) ( 21 )  

  Rated operating temperature of the P91 steel pipe was 541 ℃, the operating pressure was 17.5 MPa, and the specification was ϕ194 mm×25 mm. After about 78 000 h of service, its hardness was below the lower limit of the standard. Microstructure and properties of the P91 steel pipes used in a subcritical boiler after long-term service was investigated by means of metallographic, transmission electron microscopy, chemical phase analysis, creep-rupture properties and other test methods, respectively. The results show that the widening of martensite laths and the coarsening of the M₂₃C₆ phase at the grain boundaries of the P91 steel pipes after long-term high-temperature service are the main reasons for the decrease in high-temperature strength. Specimens were taken from the P91 steel tubes for endurance testing, resulting in creep rupture strength value of 72 MPa for 100 000 h of extrapolation at 566 ℃. Data can be used as the reference for the assessment of the creep life of the P91 steel.

  Microstructure evolution of P92 steel at different isothermal temperatures

  Zhao Yongtao, Wu Yinhu, Lu Haitao, Wang Rui, Lei Bingwang

  2024, 49(9):  47-50.  doi:10.13251/j.issn.0254-6051.2024.09.008

  Abstract ( 37 )   PDF (3683KB) ( 27 )  

  Microstructure transition temperatures of the P92 steel were determined by expansion method. After austenitizing, the steel was isothermal treated at different temperatures for different time. Microstructure evolution of the P92 steel isothermal treated at different temperatures for different time was analyzed by OM and SEM. Microhardness of the P92 steel under different states was measured by Vickers hardness tester. The results show that martensite transformation occurs at isothermal temperature of 370 ℃ and below for 1 h, and microstructure of the P92 steel at room temperature is martensitic. Bainite transformation occurs at isothermal temperature of 400-430 ℃ for 1 h. When isothermal treated at 520-620 ℃ for 1 h, the supercooled austenite is relatively stable and doesn't change in a short time. When isothermal treated at 650 ℃ and above for a long time (25 h), eutectoid decomposition of supercooled austenite occur, forming pearlitic structure. When isothermal treated at 680-770 ℃ for 25 h, there is proeutectoid ferrite precipitation, and with the increase of temperature, the proeutectoid phase increases. With the increase of isothermal temperature(160-770 ℃), the hardness of the P92 steel shows an overall downward trend, and gradually decreases from 516 HV to 163 HV.

  MATERIALS RESEARCH

  Effect of LPSO phase on hot deformation behavior of ultra-light Mg-Li alloy

  Wu Huajie, Zhang Yuqing, Kuang Yafei, Wu Ruirui, Wang Dan, Liu Baosheng

  2024, 49(9):  51-57.  doi:10.13251/j.issn.0254-6051.2024.09.009

  Abstract ( 31 )   PDF (3658KB) ( 24 )  

  Effects of deformation temperature and strain rate on the high temperature flow stress and microstructure of the Mg-5Li-11Gd-1Zn-0.5Zr alloy were studied by using Gleeble-3500 thermal simulator at 250-400 ℃ and strain rate of 10^-3-1 s^-1. The results show that the steady-state flow stress of the alloy decreases with the increase of deformation temperature and increases with the increase of strain rate. With the increase of deformation temperature, the long period stacking ordered (LPSO) phase kinks or refines, and the degree of dynamic recrystallization of the alloy increases gradually. With the increase of strain rate, the LPSO phase distribution is more uniform and the grain size of the alloy increases gradually. The thermal deformation activation energy calculated according to the Arrhenius theory is 142.65 kJ/mol. The instability area and safe area are obtained from the hot processing map, the easy processing area of the alloy is in the range of the deformation temperature of 350-400 ℃ and strain rate of 0.011-0.45 s^-1, where the granular LPSO phase can promote dynamic recrystallization.

  Regulating microstructure and mechanical properties of 7075 aluminum alloy via microalloying

  Chen Zijian, Lin Yejia, Li Chuanqiang, Deng Renxuan, Dong Yong, Zhang Zhengrong

  2024, 49(9):  58-63.  doi:10.13251/j.issn.0254-6051.2024.09.010

  Abstract ( 43 )   PDF (4787KB) ( 28 )  

  Microstructure, phase composition, tensile properties and hardness of a series of modified 7075 aluminum alloys were comparatively studied by co-adding trace elements of Ni, RE (La and Ce) and Mg, so as to regulate the microstructure and mechanical properties of the 7075 aluminum alloy. The results show that after Ni-RE-Mg microalloying, the type of second phases in as-cast 7075 aluminum alloy does not change, but their content increases, and also the grain size is refined to some extent. In addition, the tensile property of as-cast 7075 alloy is improved via Ni-RE-Mg microalloying, and the maximum tensile strength of the as-cast alloy is 338 MPa when the mass fraction of Ni-RE-Mg is 0.2%. After solution treatment and aging, the precipitated phases in the alloy increase and the age-hardening phenomenon is more obvious with the increase of microalloying element content. When the Ni-RE-Mg mass fraction is 1.0%, the maximum hardness of the 7075 alloy after solution treatment and aging (6 h) reaches 155 HV0.5.

  Effect of Mo content on microstructure and wear resistance of high carbon steel

  Sun Taoan, Wu Zhengyi, Zhou Jishun, Xiao Bingzheng, Wang Haichuan, Fan Dingdong, Deng Aijun

  2024, 49(9):  64-71.  doi:10.13251/j.issn.0254-6051.2024.09.011

  Abstract ( 33 )   PDF (5990KB) ( 39 )  

  Based on JMatpro software, the variation curves of microstructure and phase content with temperature and the CCT curves of high carbon steels (0.95%C) with different Mo contents were calculated and analyzed, and the heat treatment process was determined. The effect of Mo content on the microstructure and wear resistance of the tested steels was studied by means of metallographic microscope, scanning electron microscope and dry sand wear machine. The results show that the heat treatment process of the Mo-bearing high carbon steel based on the JMatpro calculation and analysis is holding at 770 ℃ for 1 h followed by water quenching, and then tempering at 200 ℃ for 2 h followed by furnace cooling. The microstructure of the steel treated by this process is mainly cryptocrystalline martensite, twin martensite and carbide particles. The addition of Mo element improves the hardness and wear resistance of the steel. When the Mo content is 3%, the hardness and wear resistance of the steel are the best, which are 16% and 30.84% higher than that of non-Mo high carbon steel, respectively. When the Mo content is greater than 3%, more carbides that are difficult to decompose will precipitate on the grain boundary of the steel and accumulate seriously, resulting in uneven hardness. These carbides fall off during the wear test to form pits, thus reducing the wear resistance of the steel.

  Measurement of CCT curves and carbide intergranular precipitation temperature of 4Cr5Mo2V hot-working die steel

  Gao Xingcheng, Wu Boya, Wu Xiaochun

  2024, 49(9):  72-79.  doi:10.13251/j.issn.0254-6051.2024.09.012

  Abstract ( 196 )   PDF (5564KB) ( 32 )  

  Microstructure and hardness of 4Cr5Mo2V steel at different cooling rates were observed and measured by using thermal expansion meter, resistance meter and hardness tester, combined with scanning electron microscope and energy dispersive spectroscopy. CCT curves of the tested steel were plotted, and the temperature of carbide intergranular precipitation in the steel was determined. The results show that as the cooling rate decreases, the hardness decreases and the microstructure transforms into martensite, bainite and pearlite in sequence. The critical cooling rates for pearlite and bainite transformation are 0.015 ℃/s and 0.25 ℃/s, respectively. When the cooling rate is not greater than 0.25 ℃/s, carbides precipitate along the grain in the steel, and as the cooling rate decreases, the temperature of carbide precipitation along the grain increases. At a cooling rate of 0.01 ℃/s, the highest precipitation temperature is 1022 ℃.

  Continuous cooling transformation behavior and precipitation pattern of XGTC300L enamelled steel

  Yuan Jing, Chen Feida, Zhong Haiqing, Tang Xiaoyong, Zhu Yingyu, Leng Yemin, Xiao Hu, Tian Shiwei

  2024, 49(9):  80-85.  doi:10.13251/j.issn.0254-6051.2024.09.013

  Abstract ( 19 )   PDF (5159KB) ( 29 )  

  Temperature-expansion curves of the XGTC300L enamelled steel at different cooling rates were obtained by a Gleeble-3500 thermal simulation test machine. The dynamic CCT curve of the steel was drawn by studying the microstructure characteristics and hardness variation of the specimens at different cooling rates. The results show that the matrix of the XGTC300L enamelled steel after hot deformation consists of ferrite when cooled within the range of 0.2-50 ℃/s, and the ferrite grain size decreases with the increase of cooling rates. At the cooling rate of 0.2 ℃/s, the steel exhibits the lowest hardness value, about 96.6 HV0.1. In the range of 0.5-5 ℃/s, the hardness value changes little, about 110.0 HV0.1. In the range of 10-30 ℃/s, the hardness value is about 120.0 HV0.1. At the cooling rate of 50 ℃/s, the steel reaches its highest hardness value, about 137.9 HV0.1. At the fast-cooling rate of 30 ℃/s, boron-containing carbides are found in the ferrite matrix and grain boundary, while only strip cementite precipitates at the grain boundary at the slow cooling rate of 0.2 ℃/s. In the range of 0.2-50 ℃/s, with the increase of cooling rate, the start temperature of transformation is decreased from 850 ℃ to 810 ℃, the end temperature of transformation is decreased from 840 ℃ to 750 ℃, and the transformation time decreases gradually. In the dynamic CCT curve, only the ferrite phase region is found, and the phase region of bainite or martensite is not found. Therefore, the controlled cooling process after rolling of the XGTC300L enamelled steel should adopt a higher cooling rate of more than 30 ℃/s to obtain smaller ferrite grains and a certain number of boron-containing precipitates, so as to improve its comprehensive performance.

  Dynamic CCT curve of 18CrNiMo7-6 wind power gear steel

  Lu Feng, Li Qi, Sun Xuejiao, Qiu Guoxing

  2024, 49(9):  86-90.  doi:10.13251/j.issn.0254-6051.2024.09.014

  Abstract ( 28 )   PDF (2752KB) ( 41 )  

  Double-pass compression tests of 18CrNiMo7-6 wind power gear steel with 30% deformation at 1150 and 1050 ℃ were carried out by Gleeble-3800 thermal simulator. The thermal expansion curves of the steel at cooling rates of 0.1-30 ℃/s were measured, and the dynamic continuous cooling transformation curves of the steel were drawn by metallographic-hardness method. The microstructure transformation of the steel at different cooling rates was analyzed, and the influence of cooling rate on its microstructure evolution and hardness was explored. The results show that the phase transition temperature of the 18CrNiMo7-6 wind power gear steel is Ac₁=759 ℃, Ac₃=835 ℃. Under the experimental conditions of double-pass rolling at high temperature, when the cooling rate is less than 0.5 ℃/s, the microstructure of the tested steel is ferrite + pearlite and a small amount of bainite. When the cooling rate is 0.5-1 ℃/s, ferrite gradually disappears and lath bainite begins to appear in the steel. As the cooling rate continues to increase, the content of bainite in the steel increases first and then decreases. When the cooling rate is greater than 10 ℃/s, the microstructure of the tested steel is full martensite. With the increase of cooling rate, the hardness of the tested steel gradually increases from 295 HV to 449 HV.

  Static recrystallization behavior of 12%Cr ultra-supercritical rotor steel

  Zhang Xuezhong, Liu Jiansheng, Jiao Yongxing, Li Fei, Chen Fei

  2024, 49(9):  91-95.  doi:10.13251/j.issn.0254-6051.2024.09.015

  Abstract ( 20 )   PDF (2338KB) ( 21 )  

  Static recrystallization behavior of 12%Cr ultra-supercritical rotor steel at high temperature was studied by double-pass hot compression test using Gleeble-1500D thermomechanical simulator. Effects of strain rate and prestrain on the static recrystallization behavior of the tested material were discussed, and effects of deformation temperature and pass interval time were also elaborated. According to the test results, the kinetics model for static recrystallization and the static recrystallization grain size model of the material were established. The results show that the volume fraction of static recrystallization increases with the increase of temperature and prestrain. Moreover, the increase of strain rate and the extension of pass interval time are also conducive to the occurrence of static recrystallization. The static recrystallization activation energy of the material is calculated to be 3.155×10⁵ J/mol. Combined with the static recrystallization grain growth model, the grain refinement process conditions are established.

  PROCESS RESEARCH

  Evolution of LPSO phase and properties of Mg-Y-Gd-Zn-Zr alloy at different aging temperatures

  Ren Guangxiao, Wang Chao, Cao Xijuan, Wang Kai, Wang Hongxia, Cheng Weili, Niu Xiaofeng

  2024, 49(9):  96-102.  doi:10.13251/j.issn.0254-6051.2024.09.016

  Abstract ( 31 )   PDF (3431KB) ( 16 )  

  The microstructural evolution of the Mg-6Y-3Gd-3Zn-0.5Zr alloys in the as-cast, solid solution and aging states and its influence on the mechanical properties were investigated by using OM, SEM, XRD, TEM and property testing methods. The results show that the as-cast alloy consists of dendritic α-Mg matrix with a continuous network of 18R-LPSO and Mg₂₄(Gd, Y, Zn)₅ mixed phases at the grain boundaries. After solid solution treatment, the most of Mg₂₄(Gd, Y, Zn)₅ phase and part of the 18R-LPSO phase are dissolved back into the matrix. A large amount of lamellar 14H-LPSO and Mg₃(Y, Gd) and Mg₅(Y, Gd) phases are precipitated in the matrix after aging at 250 ℃ and 300 ℃. Only 14H-LPSO phase is precipitated in the crystals after aging at 400 ℃. The tensile strength and elongation of the as-cast alloy are 222.7 MPa and 4.1%, respectively. The strength of the alloy decreases and the elongation increases slightly after aging. The alloy peak aged at 400 ℃ shows the greatest decrease in strength due to the large number and size of 14H-LPSO precipitated in the crystals, and the tensile strength decreases by 39 MPa compared with that of the as-cast state.

  Effect of austempering on microstructure and mechanical properties of carbide-free bainitic steel with Al

  Ren Pengshuai, Qin Feng, Zhou Qian, Zhao Leijie, Cui Hu, Peng Ziao, Wu Changsheng

  2024, 49(9):  103-109.  doi:10.13251/j.issn.0254-6051.2024.09.017

  Abstract ( 24 )   PDF (4141KB) ( 32 )  

  Two carbide-free low alloy bainitic steels containing 0.60% and 1.17% Al were austempered with different processes and different microstructure and mechanical properties were obtained, and then the effect of austempering on the microstructure and properties of the tested steels was studied by using optical microscope, scanning electron microscope, transmission electron microscope, X-ray diffraction, as well as impact and tensile tests. The results show that when the bainitic transformation is incomplete, the microstructure of the carbide-free bainitic steels is composed of bainitic ferrite, retained austenite and a large amount of martensite, while the microstructure of the tested steels is composed of bainitic ferrite, retained austenite and a very small amount of martensite when the bainitic transformation is complete. And when the bainitic transformation is complete, the size distribution range and volume fraction of retained austenite in 0.60%Al steel are higher than those in 1.17%Al steel, while the bainitic ferrite lath of 1.17%Al steel is finer than that of 0.60%Al steel. The yield strength of 0.60%Al steel is slightly lower than that of 1.17%Al steel, but its impact property, tensile strength and total elongation after fracture are significantly higher than that of 1.17%Al steel, demonstrating much excellent comprehensive mechanical properties.

  Heat treatment optimization and carbon partitioning behavior of Cr-alloyed Q&P steel

  Zhang Yu, Li Shengyang, Wei Xiaolu, Chai Zhisong, Li Yong

  2024, 49(9):  110-116.  doi:10.13251/j.issn.0254-6051.2024.09.018

  Abstract ( 21 )   PDF (3585KB) ( 16 )  

  A new type of Cr-alloyed (>2%) Q&P steel was designed, and the effects of quenching and partitioning processes on the microstructure and properties of the tested steel were studied. The effect of Cr on the volume fraction of retained austenite and carbon partitioning of the Q&P steel was evaluated through thermodynamic calculations. The results show that when the quenching temperature is 230 ℃ and the partitioning temperature is 400 ℃, the Cr-alloyed Q&P steel obtains the best strength-plasticity matching (tensile strength of 1180 MPa, percentage total extension at fracture of 18.6%), and the strength-elongation product reaches 21 GPa·%. At the same time, in a wide quenching temperature range (210-270 ℃), the strength-elongation product exceeds 19.5 GPa·%. Thermodynamic calculation results show that compared with conventional composition Q&P steel, Cr-alloying increases the carbon content in austenite during the partitioning process, thereby increasing the volume fraction and stability of retained austenite.

  Effect of thermo-mechanical treatment on microstructure and mechanical properties of novel Ti-free maraging steel welding seam

  Zhang Qingke, Zhu Huitao, Chen Genbao, Chen Litian, Xia Yajin, Hu Fangqin, Song Zhenlun

  2024, 49(9):  117-124.  doi:10.13251/j.issn.0254-6051.2024.09.019

  Abstract ( 21 )   PDF (8313KB) ( 21 )  

  A newly developed 18Ni based maraging steel without Ti and Al was welded and then subjected to a thermo-mechanical treatment. Microstructure evolution and property change during the welding, high temperature annealing, rolling, recrystallization heat treatment and aging processes were characterized, and the effects of thermo-mechanical treatment on the microstructure, phase and mechanical properties of the welding seam were analyzed. The results show that the initial welding seam includes melting zone, transition zone and heat affected zone, which is significantly different from the matrix, but the phase is basically martensite. After high temperature annealing at 1050 ℃, 72.7% cold rolling and recrystallization annealing at 900 ℃, the difference in microstructure between the welding seam and the matrix gradually disappears. After recrystallization, the microstructure, phase, microhardness, tensile strength, elongation and other properties of the welding seam tend to be consistent with the matrix. There is no strain concentration or fracture at the welding seam under tensile loading. The strength of the welding seam after aging at 450 ℃ is close to 2 GPa, which indicates that the difference in microstructure between the welding seam and the matrix of the novel maraging steel can be eliminated by proper thermo-mechanical treatment.

  Solution treatment-air quenching-aging process for 6063 aluminum alloy

  Chen Yan, Pei Yuehan, Zhang Chuang, Song Hua, Lian Fabo, Guan Shixue, Wang Yang, Wang Xiaoxue

  2024, 49(9):  125-131.  doi:10.13251/j.issn.0254-6051.2024.09.020

  Abstract ( 28 )   PDF (2866KB) ( 26 )  

  The solution treatment-air quenching-aging processes for 6063 aluminium alloy were studied. The air quenching rates under different air pressures were obtained by finite element analysis, and the alloy properties under different solution treating temperatures (540, 550, 560 ℃), solution treating time (30, 60, 90 min) and air quenching rates (5, 6, 7 ℃/s) were investigated by orthogonal tests, and based on which, the properties under different aging processes (aging temperatures of 180, 200, 220 ℃, aging time of 2, 4, 6 h) were studied, and compared with that required by the national standard T6 and that of the initial annealed state. The results show that the influencing factors of the solution treatment and air quenching process on the strength of the 6063 aluminum alloy are ranked in descending order as the following: air quenching rate, solution treating temperature and solution treating time, and the influencing factors on the elongation are ranked in descending order as the following: solution treating temperature, air quenching rate and solution treating time. When the aging temperature is 180 ℃ and 200 ℃, as the aging time increases, the strength and hardness of the alloy increase, while the elongation decreases. The optimal solution treatment-air quenching-aging process for the 6063 aluminum alloy is 550 ℃×30 min solution treatment+7 ℃/s air quenching+180 ℃×6 h aging. After this process, the properties of the alloy are higher than the requirements of standard T6, and the strength is increased by more than once compared to the annealed state, and the hardness is also significantly increased, indicating a significant strengthening effect.

  Effect of heat treatment on microstructure and properties of laser deposited Ti-5321 metastable β titanium alloy

  Wei Wenyi

  2024, 49(9):  132-138.  doi:10.13251/j.issn.0254-6051.2024.09.021

  Abstract ( 22 )   PDF (5751KB) ( 40 )  

  Effect of solution treatment temperature on the microstructure and mechanical properties of the laser-deposited Ti-5321 near-β titanium alloy was investigated. The results show that the as-deposited Ti-5321 alloy specimens consist of lath-like primary α phase and β phase, with tensile strength above 1050 MPa and elongation after fracture about 4.5%, and the fracture mode is ductile-brittle mixed fracture. After solution treatment at 770 ℃ and aging, the primary α-phase content decreases, the tip dissolution effect is obvious, the microstructure is mainly composed of short rod-shaped α-phase and precipitates of fine needle-like secondary α-phase, meanwhile the tensile strength of the specimen is above 1180 MPa, the elongation after fracture is about 0.8%, and the fracture mode is changed to brittle fracture. When the solution treatment temperature is 820 ℃ and 870 ℃ respectively, the primary α-phase content is further reduced, the tip dissolution phenomenon is further enhanced, and the primary equiaxed α phase appears, the secondary α phase content increases, meanwhile the tensile strength of the specimen is above 1180 MPa, and there is almost no plasticity. This is because as the solution treatment temperature increases, the size of the secondary α phase decreases, the resistance to plastic deformation becomes stronger, and the strain difference between the secondary α phase and the β matrix increases under external loading, resulting in microcracking and leading to plasticity deterioration.

  Effect of aging temperature on microstructure and properties of 6101 aluminum alloy

  Huang Huiyi, Le Yongkang, Liao Bin, Qin Yiming, Li Feilong, Dai Xiaojie, Yang Chao

  2024, 49(9):  139-143.  doi:10.13251/j.issn.0254-6051.2024.09.022

  Abstract ( 27 )   PDF (3538KB) ( 26 )  

  6101 aluminum alloy extrusions with different front beam outlet temperatures were aged by different aging processes, and the 6101 aluminum alloy specimens after corresponding heat treatment were tested by OM, SEM, EDS, tensile test, conductivity test and other test methods. The results show that the comprehensive properties of the 6101 alloy are preferable when the front beam outlet temperature is 450 ℃ and the process is aging at 280 ℃ for 48 h, the tensile strength is 132 MPa and the conductivity is 59.8%IACS. When the front beam outlet temperature is 500 ℃ and the process is aging at 270 ℃ for 48 h, the 6101 alloy can obtain preferable comprehensive properties, its tensile strength is 141 MPa and conductivity is 59.7%IACS. Under the both process conditions, 6101 aluminum alloy extrusion can meet the product requirements of high strength and high conductivity characteristics.

  Effect of tempering treatment on properties and intergranular corrosion sensitivity of 05Cr17Ni4Cu4Nb steel

  Liu Yu, Gao Yuhao, Liu Xiaoyong, Luo Xianfu, Wang Jia, Sun Xulu, Wu Zepeng

  2024, 49(9):  144-151.  doi:10.13251/j.issn.0254-6051.2024.09.023

  Abstract ( 20 )   PDF (4839KB) ( 26 )  

  The microstructure and properties of 05Cr17Ni4Cu4Nb martensitic stainless steel were observed and tested by means of metallography microscope, scanning electron microscope, transmission electron microscope, hardness and impact tests, respectively. The effect of tempering on its intergranular corrosion sensitivity was studied by intergranular corrosion test. The results show that after tempering at 650 ℃ for 2 h, the density and size of the Cu dispersion-strengthened phase in the tempered tested steel decrease and increase, respectively. The inverting austenite phase forms and grows along the boundary of the original austenite phase and the original martensitic lath, the Cr-containing carbides decompose, and the Cr element is separated out to form a strip precipitated phase, but the distribution of Cr element is more uniform, resulting in a decrease in the strength of the steel, an increase in toughness, and the intergranular corrosion sensitivity of the material is reduced due to the supplementation of Cr element in the original Cr poor region.

  Effect of aging on mechanical properties and corrosion resistance of Al-Si-Cu-Mg cast alloy

  Xia Linyan, Shi Xiangqin, Liu Yiqing, Zhou Mohao, Deng Wei

  2024, 49(9):  152-157.  doi:10.13251/j.issn.0254-6051.2024.09.024

  Abstract ( 16 )   PDF (3001KB) ( 23 )  

  Effect of aging treatment (single aging and two-step aging) on the microstructure, mechanical properties and corrosion resistance of Al-Si-Cu-Mg cast alloy was studied. The results show that the microstructure of the Al-Si-Cu-Mg cast alloy after aging is composed of α-Al matrix and eutectic Si phase. After single aging at 170 ℃ for 10 h, the peak hardness of the alloy is 151.8 HV0.1, the tensile strength and yield strength are 287 MPa and 252 MPa, respectively, and the elongation is 10.6%. However, the corrosion resistance is poor, and the maximum intergranular corrosion depth reaches 113.3 μm. As compared with that after the single aging, after the optimized two-step aging at 90 ℃ for 3 h and 170 ℃ for 4 h, the mechanical properties and corrosion resistance of the tested alloy are greatly improved. The peak hardness is increased by 5.7%, and the tensile strength and yield strength are increased by 4.5% and 6%, respectively. Moreover, the elongation is increased more than twice. The corrosion resistance improves, and the maximum intergranular corrosion depth is reduced to 60.0 μm. The fine and uniform Si phase and relatively less gray-black acicular β phase and black block structure are responsible for the improvement of mechanical properties and corrosion resistance of the tested alloy.

  Effect of heat treatment process on microstructure and mechanical properties of 42CrMo-R steel tyre

  Wan Zhijian, An Tao, Yu Wentan, Liu Xuehua, Tong Le, Zhao Hai

  2024, 49(9):  158-164.  doi:10.13251/j.issn.0254-6051.2024.09.025

  Abstract ( 38 )   PDF (8002KB) ( 39 )  

  42CrMo-R test steel was designed and smelted and rolled into a tyre. Effect of heat treatment process on microstructure and mechanical properties of the 42CrMo-R steel tyre were studied by means of metallographic microscope, scanning electron microscope, tensile testing machine, hardness tester and other methods. The results show that after quenching in the range of 830-980 ℃, the matrix of the 42CrMo-R steel tyre is lath martensite, when the quenching temperature exceeds 890 ℃, the proportion of lath martensite increases significantly, and when quenched at 860 ℃, the original austenite grain size distribution is uniform and the strength is the highest, so it is the optimal quenching temperature. Tempered in the range of 520-600 ℃, the tyre matrix microstructure are all tempered martensite. With the increase of tempering temperature, the hardness, tensile strength and yield strength all show a downward trend, while the elongation and percentage reducation of area basically show an upward trend. After quenching at 860 ℃and tempering at 560-580 ℃, the 42CrMo-R steel tyre has a relatively high proportion of tempered martensite, a small amount of undissolved ferrite and there is a large margin of R_m, R_p0.2, hardness and elongation compared with customer requirements, and it has good microstructure and comprehensive mechanical properties.

  Effect of superconducting magnet heat treatment on mechanical properties of N50H stainless steel jacket

  Tu Zhengping, Wu Yifei, Yu Anhua, Chen Xiaowei, Wang Weijun

  2024, 49(9):  165-168.  doi:10.13251/j.issn.0254-6051.2024.09.026

  Abstract ( 21 )   PDF (2095KB) ( 19 )  

  At present, the most mature low-temperature superconductor (LTS) is the Nb₃Sn superconductor, and YBCO in high-temperature superconductor (HTS) has become a candidate material for superconducting coils in China Fusion Engineering Test Reactor (CFETR) because of its excellent properties and no need for heat treatment. However, the mechanical properties of 316L, 316LN, JK2LB and other jacket materials do not meet the requirements of future superconducting magnets at low temperatures. Therefore, taking N50H austenitic stainless steel as the research object, the mechanical properties of the cold-worked specimens after heat treatment were tested to explore the effect of heat treatment on the mechanical properties of the N50H stainless steel. The results show that before heat treatment, the tensile strength of the N50H stainless steel is about 1800 MPa and the yield strength is above 1500 MPa at 4.2 K. After the two Nb₃Sn heat treatments, the tensile strength of the N50H stainless steel increases to more than 1800 MPa, and the yield strength is slightly higher than that without heat treatment. At the same time, the elongation is higher than 25% after both heat treatments and the maximum change is 5% compared with that without heat treatment. These further verifie the feasibility of the N50H stainless steel as YBCO and Nb₃Sn CICC jacket material in the future.

  Effect of post weld heat treatment on microstructure and properties of hot wire TIG welded 10Cr9Mo1VNb boiler steel

  Lai Chunming, Li Qin, Zhou Jialin, Wu Xinghuan, Huang Yan

  2024, 49(9):  169-175.  doi:10.13251/j.issn.0254-6051.2024.09.027

  Abstract ( 17 )   PDF (4246KB) ( 27 )  

  Hot wire TIG multi-layer and multi pass welding tests were conducted on 10Cr9Mo1VNb boiler steel, and the welded joints were subjected to post weld heat treatment at different temperatures (740-790 ℃) and time (1-4 h). The effects of post weld heat treatment on the microstructure and properties of the joints were analyzed using hardness, metallography, room temperature tensile testing, Charpy impact testing, SEM and other experimental methods. The results show that the post weld heat treatment can transform the martensite formed in the welding process into tempered martensite, which can significantly improve the uniformity of the microstructure and properties of each zone of the joint. When subjected to heat treatment at 740 ℃, the strength slightly reduces with the increase of heat treatment time, while both the plasticity and toughness further improve. However, when subjected to heat treatment at 790 ℃, the strength, plasticity and ductility decrease with the increase of time, mainly due to the coarsening of carbides such as M₂₃C₆ in the joint.

  Pre-deformation on microstructure and properties of 7085 ultra strength aluminum alloy ring

  Liu Qiang, Sheng Zhiyong, Zhang Chao, Li Jie, Chen Ze, Chen Songyi, Chen Kanghua

  2024, 49(9):  176-184.  doi:10.13251/j.issn.0254-6051.2024.09.028

  Abstract ( 21 )   PDF (5711KB) ( 24 )  

  Mechanical properties and stress corrosion resistance of 7085 aluminum alloy ring after solution treatment-pre-deformation(1.5%, 3%, 5%)-aging treatment were studied by means of residual stress, tensile, impact and stress corrosion tests, and the change characteristics of microstructure were analyzed and observed by means of optical microscope(OM), scanning electron microscope(SEM), transmission electron microscope(TEM). The results show that the maximum residual stress of the 7085 aluminum alloy ring decreases by 87.2% when the pre-deformation is 3%. Tangential direction(TD) tensile strength, yield strength and elongation are significantly higher than that of radial(RD) and axial direction(AD). The anisotropy index of tensile strength and yield strength of the alloy change little after pre-deformation, but the anisotropy index of elongation increases significantly. In advance, the increase of the deformation is helpful to improve its stress corrosion resistance. TEM microstructure of the alloy shows that with the increase of deformation, the size of intragranular precipitates increases, as well as the density and the volume fraction of precipitates, the grain boundary precipitates (GBPs) coarsen, the particle spacing of GBPs increases, and the width of precipitation free zone (PFZ) increases gradually.

  Effect of decarburization annealing time on microstructure and texture of Cu-bearing grain oriented silicon steel

  Hua Xiaojie, Bai Lu, Zhang Chi, Shu Zeteng, Yan Chengliang, Yang Falin, Ye Qin, Dong Xiangyun

  2024, 49(9):  185-190.  doi:10.13251/j.issn.0254-6051.2024.09.029

  Abstract ( 20 )   PDF (5085KB) ( 20 )  

  Cold-rolled plate of Cu-bearing grain oriented silicon steel was subjected to decarburization annealing at 840 ℃ for different time (1-13 min). The effect of annealing time on the content of C and O elements, primary recrystallized grains, oxide layer and texture of the grain oriented silicon steel was investigated. The results show that with the increase of decarburization annealing time, the content of O increases gradually, while the content of C decreases first and then remains unchanged. Due to the uneven stress in the thickness direction during the one-stage cold rolling process, the recrystallized grain size of the steel plate is uneven. As the decarburization annealing time increases, the inhomogeneity becomes more obvious. With the increase of decarburization annealing time, the thickness of oxide layer increases, the proportion of rotating cube texture {001}<110> and cube texture {001}<100> decreases gradually, the content of {111}<112> texture increases first and then decreases, and the proportion of Goss texture {110}<001> is basically unchanged.

  Effect of aging treatment on mechanical properties at room temperature and low temperature of 15-5PH stainless steel

  Xu Feng, Sun Qiang, Jia Yunhao

  2024, 49(9):  191-197.  doi:10.13251/j.issn.0254-6051.2024.09.030

  Abstract ( 21 )   PDF (8392KB) ( 32 )  

  15-5PH precipitation-hardened stainless steel was solution treated at 1040 ℃ for 1 h, and then aged at 480 ℃ for different time (1, 2, 4 h). The microstructure, fracture morphology and properties were observed and tested to study the effect of aging time on its mechanical properties at room temperature and -50 ℃. The results show that the tensile and impact properties of the 15-5PH steel at room temperature don't change significantly with the aging time increasing. The tensile properties at -50 ℃ have no obvious change, but the impact absorbed energy is significantly improved, the impact absorbed energy is increased from 31.5 J to 77.5 J, due to the longer the aging holding time, the higher the reversed austenite content in the steel, resulting in better low-temperature impact property.

  Effect of quenching transfer time on microstructure and properties of tempered 16CrSiNi steel

  Ma Luyi, Dong Zhi, Yang Lixin, Li Shijian, Cui Jing, Kang Chong

  2024, 49(9):  198-203.  doi:10.13251/j.issn.0254-6051.2024.09.031

  Abstract ( 25 )   PDF (7047KB) ( 21 )  

  By adjusting the quenching transfer time, the mechanical properties and the microstructure changes of 16CrSiNi steel after tempering were studied by using the universal test machine, metallographic microscope and scanning electron microscope. The results show that as the quenching transfer time increases from 10 s to 100 s, the tensile strength of the 16CrSiNi steel after tempering decreases from 1154 MPa to 676 MPa, the elongation increases from 16% to 28%, and the percentage reduction of area decreases from 68% to 52% and then to 70%. The microstructure experiences transformation from lath martensite to equiaxed blocky ferrite, then to coexistence of ferrite and tempered martensite, and further to pearlite, finally the microstructure is mainly composed of ferrite, tempered martensite and pearlite. The quenching transfer time has a significant effect on the tensile macroscopic fracture of the 16CrSiNi steel. With the increase of quenching transfer time, the fibrous area of the fracture gradually decreases, the radiation area and shear lip area increase, the fracture morphology changes from brittle fracture to ductile fracture. The microscopic fractures are mainly characterized by dimples. When the quenching transfer time is less than 30 s, the dimples are small and dense, while when over 30 s, the dimple size increases significantly. For the 16CrSiNi steel rods with a diameter of ϕ10.5 mm, the quenching transfer time shall be controlled within 30 s to ensure that the microstructure and properties are basically not affected.

  Off-line heat treatment of 43 kg/m climbing switch rail

  Yang Han, Lan Chaofeng, Wang Xiong, Wan Jingbin

  2024, 49(9):  204-208.  doi:10.13251/j.issn.0254-6051.2024.09.032

  Abstract ( 16 )   PDF (2345KB) ( 15 )  

  In order to improve the overall performance of 43 kg/m climbing switch rail made of U71Mn steel after off-line heat treatment and avoid the spark defect at the small section step of switch rail during heat treatment, by changing the machining sequence and processing quantity, as well as using underspeed quenching heat treatment methods with different vehicle speeds and wind pressures for different section length ranges, the surface hardness, section hardness, morphology of hardened layer and microstructure of the heat-treated switch rail were tested and analyzed. The results show that after adopting the improved process of processing from the tip to the 35 mm section according to the 35 mm section size, processing from the 35 mm section to the heel end according to the finished product size, and then machining to the finished product size after heat treatment, the hardness of the small section significantly improves, reaching 32.0-34.5 HRC. Microstructure consisted of pearlite and a small amount of ferrite, without any abnormal structures such as martensite or bainite, and eliminated spark defects, fully meeting the relevant requirements.

  Ion nitriding process for small modulus subway couplings

  Chen Lin, Li Ziyan, Bai Xiaobo, Li Shuangxi

  2024, 49(9):  209-215.  doi:10.13251/j.issn.0254-6051.2024.09.033

  Abstract ( 15 )   PDF (3076KB) ( 21 )  

  Research on ion nitriding process was conducted with respect to subway coupling made of 31CrMoV9 structural alloy steel and with modulus of 4 mm. The surface hardness and the depth of the nitrided layer and microstructure were analyzed and the bending fatigue property test was conducted by means of optical microscope, microhardness tester and fatigue bending machine. The results show that when NH₃ flow unchanged, the uniformity of the nitrided layer depth from tooth crest to tooth root and the bending fatigue strength increase, and the thickness of the surface compound layer is more uniform with the increase of Ar flow. The nitriding process which meets the drawing's technical requirements is ultimately determined as follows: nitriding at 540 ℃ for 36 h and flow ratio of NH₃ to Ar is 10 to 7 to get 280 Pa furnace pressure. Finally,through the actual production verification, the nitriding process has good operability.

  Effect of aging on precipitated phases and mechanical properties of ADC12 aluminum alloy

  Yang Zhe, Chen Shuisheng

  2024, 49(9):  216-220.  doi:10.13251/j.issn.0254-6051.2024.09.034

  Abstract ( 35 )   PDF (1814KB) ( 17 )  

  Pre-aging, single-stage aging and double-stage aging treatments were carried out on ADC12 aluminum alloy, and the effects of different artificial aging treatments on the precipitated phases and mechanical properties of ADC12 alloy were investigated by means of microstructure characterization, EDS analysis and hardness, tensile and impact tests. The results show that different aging treatments lead to differences in the microstructure morphology and phase composition of the alloy. After pre-aging, dispersed precipitated phases are formed in the microstructure of the alloy, so that the impact absorbed energy reaches the highest value of 18.60 J. After single-stage aging, the precipitated phases in the alloy are rounded, and the tensile strength reaches the highest value of 202.56 MPa. After double-stage aging, fine needle-like precipitated phases are formed and the hardness reaches the highest value of 161.27 HBW. These results indicate that the double-stage aging has the best effect in improving hardness, the single-stage aging has the best performance in tensile strength, and the pre-aging is the most effective in improving impact properties.

  Effect of local post weld heat treatment zone arrangement on residual stress of thick-walled pipe girth weld

  Liu Zi, Kong Weimin

  2024, 49(9):  221-225.  doi:10.13251/j.issn.0254-6051.2024.09.035

  Abstract ( 19 )   PDF (2666KB) ( 21 )  

  Variation and distribution of welding residual equivalent stress, circumferential stress and axial stress in 16MND5 steel thick-walled cylinders under different heating conditions of local heat treatment standards (B31.1, B31.3, ASME section NB, BS2633 and AWS D10.10) were studied by using the viscoelastic plastic finite element method. A comprehensive analysis was conducted on the welding residual stress in the center and vicinity of the weld seam, as well as on the heat treatment stress attached to the edge of the heating zone. The influence of heated band width and insulation band width on the local post weld heat treatment effect was also discussed. The results show that after local heat treatment, uneven heating at the edge of the heating zone causes a certain increase in stress, and the presence of the insulation zone can alleviate the temperature gradient, thereby reducing the additional stress at the edge of the heating zone. For thick-walled cylinders, when subjected to local heat treatment according to AWS D10.10 standard, the center of the weld seam can achieve a similar effect as the overall heat treatment, and the residual stress relief effect of welding is the best.

  Effect of solution treatment on microstructure and mechanical properties of surfacing layer on inner wall of rolling stock axle box

  Li Zhe, Li Rui, Cai Lei, Jin Junjun

  2024, 49(9):  226-231.  doi:10.13251/j.issn.0254-6051.2024.09.036

  Abstract ( 14 )   PDF (4097KB) ( 15 )  

  Effects of solution treatment on the strength, toughness and residual stress of the repaired surfacing layer were analyzed by observing the microstructure, testing the mechanical properties and testing the residual stress of the specimens before and after solution treatment. The results show that before the solution treatment, the grains in the clad zone are large and uneven, the grains in the heat affected zone are thick, and the substrate zone consists of ferrite and pearlite. After solution treatment at 900 ℃ for 3.5 h, the proportion of ferrite in the substrate zone increases and the distribution is more uniform, the coarse grains in the heat affected zone and the clad zone disappear, the grains are refined, and the grain boundary characteristics and grain structure are significantly improved. Solution treatment significantly makes the tensile strength of the surfacing layer incrense from 810 MPa to 925 MPa, with an increase of about 14%. In addition, the solution treatment results in a general decrease in hardness, from 154 HV to 143 HV for the substrate, from 238 HV to 228 HV for the heat affected zone, from 243 HV to 226 HV for the clad layer, and at the same time, the peak residual compressive stress is reduced from 232 MPa to 182 MPa, with a reduction of 21.6%. These changes indicate that solution treatment improves the plastic deformation ability and overall performance of the material by reducing defects, improving grain uniformity and eliminating residual stress.

  Heat treatment with consistency of microstructure and serviceability for TC18 titanium alloy bar

  Yin Weidong, Yin Hui, Xiang Wei, Luo Hengjun, Lü Xiaogen, Zhai Ruizhi, Xu Zouyuan

  2024, 49(9):  232-235.  doi:10.13251/j.issn.0254-6051.2024.09.037

  Abstract ( 18 )   PDF (2942KB) ( 18 )  

  TC18 titanium alloy was subjected to single-phase zone heat treatment with different processes (temperature of T_β+(15-35) ℃, and time of 0.5, 1, 2, 4 h) to obtain the initial microstructure with different grain sizes. The effect of grain size on the properties of the duplex annealed TC18 titanium alloy bar was investigated, and the heat treatment process with consistent microstructure and serviceability was obtained. The results show that with the increase of average grain size, the tensile strength of the TC18 titanium alloy increases first and then decreases, while the elongation after fracture, percentage reduction of area and fracture toughness show the opposite trend. To ensure that the TC18 titanium alloy components have both high tensile strength and good plasticity and toughness, the grain size should be controlled within the range of 300-430 μm, with the corresponding single-phase zone temperature and holding time being T_β+(25-35)℃ and 2-4 h, respectively.

  Effect of homogenization on microstructure of 3003 aluminium alloy ingot

  Zhang Wei, Chen Zijian, Lin Yongcheng

  2024, 49(9):  236-241.  doi:10.13251/j.issn.0254-6051.2024.09.038

  Abstract ( 21 )   PDF (4929KB) ( 17 )  

  Homogenization treatment was carried out at 580-620 ℃ for 4-10 h to study the effect of different homogenization processes on the microstructure evolution of 3003 aluminium alloy ingot. The results show that the precipitates in the alloy ingot are mainly MnAl₆((FeMn)Al₆) and Al_0.41MnSi_0.74(Al₁₂(FeMn)₃Si), while the MnAl₆((FeMn)Al₆) phase is almost completely dissolved during the homogenization process. However, the Al_0.41MnSi_0.74(Al₁₂(FeMn)₃Si) phase is gradually subject to aggregation, coarsening and dissolution during the homogenization process. With the increase of homogenization temperature and prolongation of holding time, the evolution of precipitates is accelerated gradually. The optimum homogenization process of the 3003 aluminium alloy which can quickly obtain uniformly distributed, round and coarse precipitates is holding at 600 ℃ for 8 h.

  Effect of aging time on microstructure and mechanical properties of 7175 aluminum alloy

  Ji Qingtao, Sun Youzheng, Yang Hui, Zhao Zhongchao, Shi Xiaoming

  2024, 49(9):  242-246.  doi:10.13251/j.issn.0254-6051.2024.09.039

  Abstract ( 27 )   PDF (5155KB) ( 22 )  

  Microstructure and mechanical behavior of the 7175 aluminum alloy during aging process at 120 ℃ for different time were systematically studied by means of OM, SEM, TEM, Vickers hardness tester and universal tensile testing machine. The results show that after solution treatment and aging, the microstructure of 7175 aluminum alloy is typical fibrous structure, with no obvious recrystallization occurring, and there is no obvious difference in grain morphology and second phase during aging. As the aging time increases, the size of precipitated phase at the grain boundary gradually increases, the particle size of precipitated phase in the grain increases, with the average particle size changing from 5.87 nm to 8.38 nm. When aged at 120 ℃, the hardness of 7175 aluminum alloy reaches the peak at 16 h, and the peak hardness is 196.5 HV. When aged at 120 ℃ for 16 h, the precipitated phase in the grain is much quantity, small and evenly distributed, which effectively improves the hardness of the alloy. At the same time, the yield strength of the alloy increases rapidly from 471 MPa to 490 MPa, when the aging time is 10-16 h, and the change of yield strength tends to be flat when the aging time is greater than 16 h.

  Effect of intercritical annealing temperature on microstructure and mechanical properties of 0.2C-8Mn-2Al steel for auto

  Cao Zhongyu, Jia Huapo, Zhao Baowei

  2024, 49(9):  247-250.  doi:10.13251/j.issn.0254-6051.2024.09.040

  Abstract ( 18 )   PDF (1933KB) ( 15 )  

  Effects of intercritical annealing temperature on the microstructure and mechanical properties of hot rolled 0.2C-8Mn-2Al steel were studied by using scanning electron microscope (SEM) and tensile testing. The results show that microstructure of the annealed 0.2C-8Mn-2Al steel is mainly composed of austenite and ferrite. In the range of 780 ℃ to 900 ℃, with the increase of annealing temperature, the volume fraction of austenite transformation in the 0.2C-8Mn-2Al steel before and after stretching gradually increases. Meanwhile, the tensile strength, elongation and product of strength and elongation of the 0.2C-8Mn-2Al steel first increase and then decrease. The austenite transformation volume fraction of the 0.2C-8Mn-2Al steel annealed at 900 ℃ is the highest, reaching 43.4%. The tensile strength, elongation and product of strength and elongation of the 0.2C-8Mn-2Al steel annealed at 840 ℃ reach maximum values, which are 1208.6 MPa, 31.2% and 37.71 GPa·%, respectively. 840 ℃ is the optimal annealing temperature for the hot rolled 0.2C-8Mn-2Al steel.

  Effect of aging treatment on microstructure and properties of solution treated and cold-drawn TB9 titanium alloy

  Li Shijian, Hu Fuchang, Ma Luyi, Qu Feng, Yan Zhaopeng

  2024, 49(9):  251-254.  doi:10.13251/j.issn.0254-6051.2024.09.041

  Abstract ( 26 )   PDF (2944KB) ( 14 )  

  Effect of aging treatment at 450-600 ℃ for 8 h on the microstructure and mechanical properties of solution treated and cold drawn TB9 titanium alloy was investigated. The results show that the microstructure of the TB9 alloy changes significantly with aging temperature. When aged at 450-500 ℃, fine and uniformly distributed α-phase precipitates, which significantly enhances hardness and strength but results in poor plasticity. When aged at 550-600 ℃, the size and volume fraction of α-phase increase, leading to more uniform grain structures. Aging temperature has a significant impact on strength and plasticity. When aged at 450 ℃, strength reaches a peak of about 1700 MPa with nearly zero elongation. As the aging temperature increases, the strength decreases, while the elongation increases. When the aging time is 550 ℃, the strength is about 1400 MPa and the elongation is 14%. At 600 ℃, the strength is 1200 MPa and the elongation is 22%. The tensile fracture characteristics show brittle fracture at lower temperature (500 ℃) and ductile fracture at higher temperature (600 ℃). Therefore, to achieve an optimal balance of strength and plasticity for TB9 titanium alloy, the recommended aging temperature is 550-600 ℃.

  Effect of heat treatment on magnetic permeability of austenitic stainless steel

  Lan Xianhui, Ge Zhengfu, Ma Peng, Chen Chuan, Zhou Tao, Liu Wei, Li Chao

  2024, 49(9):  255-259.  doi:10.13251/j.issn.0254-6051.2024.09.042

  Abstract ( 19 )   PDF (1967KB) ( 16 )  

  Based on the concept of relative permeability μ, a heat treatment of 1050 ℃×2 h for 316L austenitic stainless steel under vacuum condition of <10 Pa was conducted. The relative permeability values of the original, heat-treated and processed after heat treatment specimens corresponding to the thickness direction and the outside diameter direction after machining by the water-cutting were measured and analyzed by means of the direct measurement of Stephens magnetic permeability meter Ferromaster Plus. The results show that compared with the original specimen, the average permeability in the thickness direction of the heat-treated specimen decreases by 14.0%, and the average permeability in the outside diameter direction after machining by the water-cutting decreases by 16.2%. Compared with the heat-treated specimen, the average value of magnetic permeability in the thickness direction of processed specimens after heat treatment is 1.04, and there is no change. Heat treatment can not only reduce the permeability of raw materials, but also improve the stability of permeability of the processed materials after heat treatment.

  Effect of solution treatment on microstructure and propertiesof 50Cr-50Ni alloy

  Xiong Wei, Dai Zhiyong

  2024, 49(9):  260-264.  doi:10.13251/j.issn.0254-6051.2024.09.043

  Abstract ( 27 )   PDF (3587KB) ( 14 )  

  In order to improve the properties of 50Cr-50Ni alloy and expand its application range, the solution treatment test at 1180 ℃ for different time was carried out, and its microstructure, mechanical properties and corrosion resistance were tested and analyzed. The results show that the 50Cr-50Ni alloy has better microstructure uniformity, elongation and corrosion resistance when solution treated at 1180 ℃ for 2 h. With the extension of solution treatment time, its elongation and corrosion resistance deteriorate, but the tensile strength and hardness increase significantly.

  Analysis of carbon black on surface of steel workpieces carburized and quenched in pit furnace

  Li Chaoqing, Zhang Wei, Li Yao

  2024, 49(9):  265-267.  doi:10.13251/j.issn.0254-6051.2024.09.044

  Abstract ( 17 )   PDF (1265KB) ( 17 )  

  Causes, corrective methods and preventive measures were described for carbon black appearing on the surface of 18CrNiMo7-6 steel shaft workpieces carburized and quenched in pit furnace by chemical composition analysis and physical and chemical detection. By shot blasting and re-quenching the workpieces with surface carbon black, it is confirmed that the carbon black originates from the quenching process. The results show that the problem of surface carbon black can be effectively solved by adjusting the staged increase of quenching carbon potential to 0.65% C_p for 2 h and then to 0.83% C_p for 5 h, increasing the temperature of enriched gas droplets to 830 ℃, and increasing the gap between workpieces to 30 mm. It is verified by tests that the carbon black on the surface of the steel is generated during the quenching and holding stage. By adjusting the carbon potential and the furnace gap of the workpiece, the generation of carbon black on the surface of the steel can be avoided.

  SURFACE ENGINEERING

  Effect of ultrasonic surface rolling process on corrosion resistance of 304 stainless steel

  Chen Xinjian, Sui Rongjuan, Wang Yanfei, Cheng Yanhai, Gao Linhao

  2024, 49(9):  268-274.  doi:10.13251/j.issn.0254-6051.2024.09.045

  Abstract ( 30 )   PDF (3440KB) ( 10 )  

  Effect of ultrasonic surface rolling process (USRP) on the corrosion resistance of 304 stainless steel surface was investigated. The surface morphology, microstructure, residual stress and surface roughness were analyzed by means of scanning electron microscopy, X-ray diffraction analysis, and metal surface roughness meter, respectively. The corrosion resistance and integrity of the oxide film was assessed using electrochemical tests and o-phenanthroline color development experiments. The results indicate that the value of R_a for the 304 stainless steel is reduced from 0.60 μm to 0.28 μm after USRP treatment. The surface grain size is reduced from 23.13 μm to 20.80 nm, and the surface residual stress is changed from 20 MPa to -329 MPa. Compared with the untreated specimen, the minimum corrosion current density I_corr of the USRP treated specimen is 0.94×10^-5 A/cm², which is reduced by 71%. The oxide film resistance R_p is 2.59×10⁶ Ω·cm², increased by 2 times. The range of color rendering value of phenanthroline is narrowed and the color rendering area is decreased, indicating that the surface defects are reduced and the quality of the surface oxide film is improved. For the 304 stainless steel, USRP treatment promotes the grain refinement near the surface layer, produces residual compressive stress, reduces surface defects, denseres oxide film, and then blocks the electrochemical reaction process, and improves the corrosion resistance.

  Effect of TiC content on microstructure and wear resistance of AlCoCrFeNi high-entropy alloy clad layer

  Zhang Hongliang, Wang Mingxin, Zhang Jingbing, Li Yutao, Jin Tounan

  2024, 49(9):  275-279.  doi:10.13251/j.issn.0254-6051.2024.09.046

  Abstract ( 23 )   PDF (4013KB) ( 10 )  

  AlCoCrFeNi-2xMo-xTiC (x=0, 0.1, 0.25, 0.4) high entropy alloy clad layer was prepared on 40CrNiMo steel surface by laser cladding method. The effect of TiC and Mo content on the microstructure and wear resistance of the AlCoCrFeNi-2xMo-xTiC alloy clad layer was studied through XRD, SEM, EBSD, TEM, and wear resistance tests. The results show that after in-situ formation of TiC, the microstructure of the clad layer consists of BCC and TiC phases. As the atom fraction of TiC increases, the size of carbide precipitates gradually increases, and the grain size of the clad layer is significantly refined, decreasing from 109 μm to 15 μm. The AlCoCrFeNi-0.8Mo-0.4TiC clad layer has the highest hardness of 750 HV0.3, which is 300 HV0.3 higher than the AlCoCrFeNi alloy clad layer. The hardness and wear resistance of the clad layer increase with the increase of atom fraction of TiC. The wear surface of the AlCoCrFeNi alloy clad layer has more debris, and the wear mechanism is adhesive wear. The wear mechanism of the AlCoCrFeNi-0.2Mo-0.1TiC, AlCoCrFeNi-0.5Mo-0.25TiC, and AlCoCrFeNi-0.8Mo-0.4TiC alloy clad layers are abrasive wear.

  Double-flare plasma aluminizing on 45 steel surface

  Liu Hailiang, Xu Zili, Liu Yang, Hu Jiabin

  2024, 49(9):  280-283.  doi:10.13251/j.issn.0254-6051.2024.09.047

  Abstract ( 15 )   PDF (1965KB) ( 14 )  

  Fe-Al-N and Fe-C-N alloy layes were prepared on the surface of 45 steel by double-glow plasma aluminizing technology and plasma carbonitriding technology, respectively. The surface microhardness and phase composition of the two alloy layers were analyzed, and the microstructure of the surface, element distribution were observed. The results show that the surface hardness of the Fe-Al-N alloy layer formed on the surface of the 45 steel is as high as 750.27 HV0.1, which is much higher than the surface hardness of the Fe-C-N alloy layer, and it is 3-4 times of that of the matrix. The cross-sectional hardness distribution curves of the two alloy layers are gradient; the surface of the Fe-Al-N alloy layer is more even and dense, and the compound aggregation phenomenon is formed, showing better wear resistance.

  NUMERICAL SIMULATION

  Failure analysis and laser surface composite treatment of piercing plug for seamless steel pipe based on FEM simulation

  Mu Jian, Wu Hebao, Zhang Xun, Li Xiaolong, He Yin, Li Jianjun

  2024, 49(9):  284-289.  doi:10.13251/j.issn.0254-6051.2024.09.048

  Abstract ( 24 )   PDF (2712KB) ( 14 )  

  Finite element method (FEM) was used to analyze the temperature field, stress field, and thermo-mechanical coupling field of the piercing plug, and the maximum thermo stress, maximum coupling stress, maximum surface temperature, stress concentration area, and fatigue crack type were determined. And laser cladding+high-temperature slow oxidation composite treatment was carried out on 20Cr2Ni4 steel to improve the mechanical properties and high-temperature resistance of the plug. The FEM simulation results show that the thermo-mechanical coupling stress of the plug is the vector sum of thermo tensile stress and mechanical compressive stress. The coupling stress is dropped by about 5.7% compared with the peak value of thermo stress. The value of thermo-mechanical coupling stress is mainly affected by thermo stress, and the changing trend and distribution are mainly affected by mechanical stress. the failure of the plug originates from the crack source on the inner surface under the combined action of thermo fatigue and mechanical fatigue, and propagates radially outward to form fatigue cracks on the surface. The results of laser surface composite treatment show that after laser cladding and high temperature slow oxidation treatment, the surface hardness of 20Cr2Ni4 steel can reach 494 HV0.025, the surface strengthening layer is firmly bonded to the matrix, and the content of oxygen element in the matrix is less and more evenly, which effectively improves the service life of the plug.

  Application of model-free adaptive control in heat treatment of large 12Cr2Mo1V steel

  Gao Xinbo, Qin Qingliang

  2024, 49(9):  290-296.  doi:10.13251/j.issn.0254-6051.2024.09.049

  Abstract ( 30 )   PDF (2685KB) ( 9 )  

  For the heating and post-welding heat treatment of large-diameter thick-walled 12Cr2Mo1V steel, the medium-frequency induction heating method was adopted and the model-free adaptive control (MFAC) algorithm replacing the traditional PID algorithm was selected for temperature control. Firstly, the physical parameters of the workpiece were analyzed, and parameters such as heating frequency, coil current, and power configuration were calculated. Then, the obtained parameters were input into COMSOL software to simulate on-site conditions and perform magnetic-thermal coupled simulation analysis, validating the feasibility of the calculated data. Next, the MFAC architecture was constructed in the SIMULINK simulation platform and compared to the traditional PID method, and the two algorithms were actually applied to observe the heating effect in the field. The results show that when large workpieces are heated to the target temperature of 700 ℃, the temperature fluctuation is smaller, the stability is higher, and the uniformity is better.

  OVERVIEW

  Research progress on mechanical properties and oxidation resistance of CrAlN-based coatings

  He Tao, Cao Hongshuai, Li Beibei, Qi Fugang, Zhao Nie, Liao Bin, Ouyang Xiaoping

  2024, 49(9):  297-307.  doi:10.13251/j.issn.0254-6051.2024.09.050

  Abstract ( 45 )   PDF (4170KB) ( 27 )  

  CrAlN coatings are extensively applied in the protection of the cutting tools and molds due to their higher hardness and abrasive resistance. Firstly, the structure of CrAlN coatings and its effect on the mechanical properties and thermal decomposition mechanism of the coatings is introduced in the present review, and then pointing out that the Al content and its existence mode are important factors affecting the structure and properties of CrAlN crystals. Secondly, research status of CrAlN-based multicomponent coating and multilayer coating about the mechanical properties and high temperature oxidation resistance properties is reviewed. Focused on the doping modification of elements and the designing of multilayer coating structure, the advantages and disadvantages of various modification methods are compared and analyzed, then the doping of Si, Y, V and their influence to the performance of coating are summarized, and pointing out that constructing nanoscale multilayer coating can significantly improve the performance. Finally, the high-temperature oxidation behavior and high-temperature failure mechanism of CrAlN-based coatings are discussed, providing a reference for the performance optimization of CrAlN-based hard coatings.