Heat Treatment of Metals

Effects of austenitizing temperature and cooling rate on microstructure and properties of Nb-containing high carbon steel

Da Guangjie, Yang Zhongmin, Wang Kai, Chen Ying, Wang Huimin, Li Shaohua

2020, 45(6): 1-6. doi:10.13251/j.issn.0254-6051.2020.06.001

Abstract ( 77 )

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Heat treatment of a Nb-containing high carbon steel at different austenitizing temperatures and cooling rates was carried out by Gleeble 1500 thermal simulation test machine. The microstructure, hardness and pearlite lamellar spacing of the tested steel were observed and measured by means of metallographic microscope, scanning electron microscope and hardness tester. The results show that when the austenitizing temperature is 950 ℃, the grain size of the tested steel after quenching is 34 μm, the hardness is 813 HV5, and the microstructure cooled to room temperature with cooling rate of 0.1-5 ℃/s is pearlite+ferrite. When the austenitizing temperature is 1200 ℃, the grain size after quenching is 134 μm, the hardness is 827 HV5, and the microstructure cooled to room temperature with cooling rate of 0.1-1 ℃/s is pearlite + ferrite, while that with 5 ℃/s cooling rate is acicular martensite+a small amount of ferrite. Above 1220 ℃, all Nb is completely dissolved in austenite, and too high austenitizing temperature will result in too much grain growth. The pearlite lamellar spacing becomes smaller as the austenitizing temperature increases and the cooling rate increases, and the decrease in the lamellar spacing can increase the hardness value.

Influence of heat treatment on impact wear resistance of TC4 titanium alloy

Yu Wenchao, Li Yunkun, Xue Yanjun, Sun Ting, Shi Jie

2020, 45(6): 7-11. doi:10.13251/j.issn.0254-6051.2020.06.002

Abstract ( 89 )

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Hot rolled TC4 titanium alloy was annealed and solution treated+aged, respectively, the influence of different heat treatment processes on the mechanical properties and microstructure, as well as the impact wear resistance was studied. The results show that transformed β phase increases, and all of the strength, elongation and toughness are improved after annealing. As for the solution treated+aged specimen, the grain becomes finer and more homogeneous due to recrystallization, its strength is the highest but its elongation and toughness are lower than that of the hot rolled one. The annealed specimen has the lowest wear rate while the solution treated+aged specimen has the highest after 10 h impact wear experiment. Viewing from the fractography, the microcutting length on the annealed specimen is shorter, plastic stacking is observed at the end of microcutting, and the microstructure near wear surface is stretched plasticly. The better impact wear resistance of the annealed specimen can be attributed to its higher plasticity and toughness, which can absorb higher impact energy.

Finishing rolling process of 00Cr22Ni13Mn5Mo2N austenitic stainless steel

Li Bingbing, Zhuang Biao, Chen Haitao, Lang Yuping, Qu Huapeng, Feng Hanqiu, Chen Qingming

2020, 45(6): 12-16. doi:10.13251/j.issn.0254-6051.2020.06.003

Abstract ( 64 )

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In order to study the finishing rolling process of 00Cr22Ni13Mn5Mo2N austenitic stainless steel, the hot compression deformation behavior of 00Cr22Ni13Mn5Mo2N austenitic stainless steel was simulated by a Gleeble-3800 thermal simulator, with the deformation temperatures 800, 850, 900 and 950 ℃, the deformation 40%, 50%, 60%, and the strain rate 50 s^-1. Then the structural morphology before and after the solid solution heat treatment at 1080, 1120 and 1160 ℃ was observed. The results show that the recrystallization is more complete and the average recrystallization grain size is smaller with the increase of deformation at 800-950 ℃. After solution treatment for 1 h, the static recrystallization becomes more sufficient. With the increase of thermal deformation temperature under the deformation of 40%-60%, the more complete the recrystallization is, the larger the average recrystallization grain size is. The average recrystallization grain size of the steel increases with the increase of solution treatment temperature. The optimum processing of 00Cr22Ni13Mn5Mo2N austenitic stainless steel is the finishing rolling temperature 800 ℃, the compression deformation 60%, and the solution treatment temperature 1080 ℃.

Effect of warm rolling temperature on microstructure and properties of medium carbon Cr-Mo steel

Cao Kuo, Feng Yunli, Zhang Xinyue, Li Jie

2020, 45(6): 17-21. doi:10.13251/j.issn.0254-6051.2020.06.004

Abstract ( 59 )

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Effect of warm rolling temperature on microstructure evolution and mechanical properties of medium carbon Cr-Mo steel was investigated by means of scanning electron microscope(SEM), electron backscattered diffraction(EBSD) and tensile tests. The results show that the increase of rolling temperature has a favorable effect on the uniform distribution of the microstructure. When the rolling temperature increases from 500 ℃ to 600 ℃, the grain size of ferrite increases from 0.424 μm to 0.490 μm, the grain size difference decreases, and the yield strength decreases from 1380 MPa to 1062 MPa. The experimental steel rolled at 550 ℃ has the best plasticity and the highest plastic product reaches 5816 MPa·%.

Effect of tempering temperature on mechanical properties and fracture morphology of 3Cr3Mo2NiW steel

Li Pu, Wei Shizhong, Zhang Cheng, Wang Xiaodong, Luo Cheng

2020, 45(6): 22-27. doi:10.13251/j.issn.0254-6051.2020.06.005

Abstract ( 64 )

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The changes of mechanical properties and fracture morphology of 3Cr3Mo2NiW steel with tempering temperature were studied. The results show that with the increase of tempering temperature, the hardness of the experimental steel decreases, the toughness increases, and the secondary hardening occurs when tempered at 550 ℃. When the tempering temperature being above 600 ℃, the hardness decreases significantly, and the toughness increases greatly. The impact tested specimen tempered at 700 ℃ is not broken completely. After water quenching, the matrix structure gradually transforms into tempered martensite, tempered troostite and tempered sorbite as the tempering temperature increases. The fracture mode of tempered specimens in the temperature range of 300 ℃ to 600 ℃ is quasi-cleavage fracture, and the fracture mode of high temperature tempered specimen is ductile fracture. The microstructure and carbides obtained by tempering at different temperatures have a great influence on the impact toughness.

Interfacial heat exchange analysis of metal materials during spray quenching process

Xu Rong, Li Luoxing

2020, 45(6): 28-33. doi:10.13251/j.issn.0254-6051.2020.06.006

Abstract ( 59 )

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The interfacial heat exchange of aluminum alloy during spray quenching process was studied by end quenching test. The interfacial heat flux (q) and interfacial heat transfer coefficient (h) of all the tests were solved by inverse heat conduction method. The influence of spray pressure, nozzle diameter and surface roughness on the interfacial heat exchange was analyzed. The results show that the spray pressure has an effect on the whole quenching interface heat transfer process, but it has a greater effect on the transition boiling stage. The larger the spray pressure, the larger the q and its peak q_max, and the shorter the time to enter the nucleation boiling stage. The larger the nozzle diameter is, the larger q and q_max are, and the earlier the nozzle enters the nucleation boiling stage. However, there is an upper limit on the effect of increasing the nozzle diameter on the interfacial heat transfer. With the increase of surface roughness, q and q_max decrease first and then increase. Under the experimental conditions, the effects of spray pressure, nozzle diameter and surface roughness on the interfacial heat exchange are not affected by the other two parameters. Under the experimental conditions, the influence of any of the above three parameters, i.e. spray pressure, nozzle diameter and surface roughness, on the interfacial heat exchange is not affected by the other two parameters. In addition, the second increase of q curve during the nucleation boiling stage is resulted in some experiments due to intense nucleation boiling caused by the sprayed droplets with very small diameter uniformly covering the whole thermal surface.

Annealing process of Cu-Te alloys

Zhu Mingbiao, Li Mingmao, Li Zhaoxin, Tang Yingying

2020, 45(6): 34-38. doi:10.13251/j.issn.0254-6051.2020.06.007

Abstract ( 63 )

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The effects of annealing process on the mechanical and electrical conductivity properties and microstructure of Cu-Te alloys with 0.02%, 0.07%, 0.10%Te respectively were investigated. The mechanical properties and electrical conductivity of the alloys were tested under different annealing temperatures and annealing time, and the tensile fracture morphology changes at different temperatures were studied by scanning electron microscopy (SEM). The results show that the fracture of the Cu-Te alloys is of ductile type, and the fracture dimples become larger, deeper and more round with the inerease of annealing temperature. With the increase of annealing temperature and annealing time, the conductivity of the alloys continues to increase, while the tensile strength changes little when annealed at 350-390 ℃ for 1 h, the alloys are in the recovery stage. After annealing at 400 ℃ for 1 h, the tensile strength decreases greatly and the alloys are in the recrystallization stage. After cold deformation of 96.5% and annealing at 400 ℃ for 1 h, the Cu-Te alloys obtain the best overall performance.

Effect of self-tempering temperature on microstructure and properties of high strength fire-resistant and weathering construction steel with low yield ratio

Lin Tianzi, Hou Huaxing, Yang Ying, Zhang Tao, Zhang Zhe, Ji Wenbo

2020, 45(6): 39-42. doi:10.13251/j.issn.0254-6051.2020.06.008

Abstract ( 75 )

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Microstructure and properties of high strength fire-resistant and weathering construction steel with low yield ratio at different self-tempering temperatures were studied by OM, SEM and TEM. The results show that when the self-tempering temperature of the steel plate after water cooling is decreased from 550 ℃ to 350 ℃, the microstructure of the tested steel gradually changes from ferrite and a small amount of bainite to multiphase structure consisting of lath bainite and dispersed fine M-A islands. The size of bainite lath is further refined, the yield strength and yield ratio of the steel plate increase obviously, the tensile strength does not change much, and the percentage elongation after fracture decreases. When the self-tempering temperature is within the range of 450-500 ℃, the tested steel has lower yield ratio and better strength-toughness matching.

Effect of quenching temperature on microstructure and properties of ZG25MnCrNiMo steel

Peng Erbao, Chen Changduo

2020, 45(6): 43-45. doi:10.13251/j.issn.0254-6051.2020.06.009

Abstract ( 73 )

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Effect of quenching temperature on microstructure and properties of ZG25MnCrNiMo steel was studied by means of optical microscopy (OM), tensile test machine and impact test machine. The results show that the microstructure of quenched ZG25MnCrNiMo steel is lath martensite. In the temperature range from 840 ℃ to 930 ℃, with the increase of quenching temperature, the lath martensite in the microstructure gradually becomes finer and reaches the finest at 930 ℃. The tensile strength of the ZG25MnCrNiMo steel quenched at 840-930 ℃ and tempered at 600 ℃ first increases and then decreases, and the elongation and low temperature impact absorbed energy first decreases and then increases. The tensile strength of the steel quenched at 930 ℃is the highest, which is 992 MPa. The elongation and －40 ℃ low temperature impact absorbed energy of the steel quenched at 840 ℃ are the largest, which are 17.1% and 78 J, respectively.

Influence of solution treatment on hardness and wear resistance of TiB₂/6061 composites

Yang Hairui, Sun Yuejun, Liu Sizhe, Zhuang Weibin

2020, 45(6): 46-50. doi:10.13251/j.issn.0254-6051.2020.06.010

Abstract ( 69 )

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TiB₂/6061 composites with 3% TiB₂ was prepared by means of fluoride salt method. The effects of solution temperature and solution time on hardness and wear resistance of the composites were studied. The experimental results show that TiB₂ particles are dispersed in the 6061 Al alloy matrix, and the 6061 Al alloy matrix grains are significantly refined. As the solution temperature is constant, the hardness and wear resistance of the composites increase obviously with the increase of the solution time. However, as the solution time is 6-10 h, the properties of the composites do not change significantly. As the solution time is constant, the hardness and wear resistance of composites increase first and then decrease with the increase of solution temperature. Compared with as cast 3wt% TiB₂/6061 composite, the in-situ synthesized 3wt% TiB₂/6061 composite has the best hardness and wear resistance after solution treatment at 530 ℃ for 10 h, and the hardness of the composite is increased by 79.5% and the wear loss is decreased by 59.1%. After solution treatment, the plough grooves on the worn surface of the composites become finer and shallower, and the material shedding phenomenon decreases.

Effect of solution temperature on microstructure and hardness of GH3600 superalloy

Li Xiaobing, Li Wei

2020, 45(6): 51-54. doi:10.13251/j.issn.0254-6051.2020.06.011

Abstract ( 65 )

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Effect of solution treatment temperature on the microstructure and hardness of Ni-based superalloy GH3600 were investigated by optical microscopy, scanning electron microscopy, X-ray diffractometer and hardness tester. The results show that with the solution treatment temperature increasing, the secondary phase in the alloy dissolves gradually, the grain size of the matrix phase grows rapidly, and the hardness of the alloy decreases. When the solution treatment temperature is 1010 ℃, the uniform grain structure is obtained, the twin structure is formed, and the hardness value reaches 152.6 HV10.

Effect of normalizing cooling rate on creep rupture property of 2.25Cr1Mo steel

Wu Zhiguang, Gong Xueting, Li Xin, Zhao Jiqing, Han Shaoqiang, Gong Zhihua

2020, 45(6): 55-59. doi:10.13251/j.issn.0254-6051.2020.06.012

Abstract ( 60 )

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Effect of different normalizing cooling rate on the creep rupture property of 2.25Cr-1Mo steel was studied by means of SEM and creep testing machine. The results show that the extrapolated creep strength σ₁₀⁴ under 530 ℃ of the 2.25Cr-1Mo steel normalized with air, 30 ℃/min and 5 ℃/min cooling rate are all about 120 MPa. The creep rupture strength decreases conspicuously when the cooling rate drops to 1 ℃/min, the main reason is a large number of big size particles precipitated on the interface of ferrite and bainite, which results in the occurrence of creep holes. Meanwhile, a large number of proeutectoid ferrite appears, which leads to the strength of the matrix decrease and can not effectively hinder cracks to propogate, thus the creep rupture property decreases.

Effect of pre-aging on bake hardening properties of 6016 aluminum alloy for car body

Li Peng, Zhao Luyan

2020, 45(6): 60-62. doi:10.13251/j.issn.0254-6051.2020.06.013

Abstract ( 67 )

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Effects of different pre-aging treatments on microstructure and mechanical properties of 6016 aluminum alloy before and after baking were studied by means of hardness test, tensile test and transmission electron microscope. The results show that 6016 aluminum alloy has a strong ability of hardening by natural aging. The hardness of 6016 aluminum alloy after 24 h of natural aging is 45.6% higher than that of solid solution alloy. But after prolonged natural aging for more than 24 h, the hardness of the alloy has little change. The bake hardening effect of 6016 aluminum alloy can be improved by pre-aging treatment. After the pre aging with the process of heating at 550 ℃for 30 min solution and aging at 160 ℃ for 10 min, the yield strength and elongation of 6016 aluminum alloy are 131.4 MPa and 24.7%, respectively, then baking at 175 ℃ for 30 min, the yield strength of the alloy reaches 199.5 MPa, and the bake hardening value (BH) is 68.1 MPa, which is an ideal heat treatment process for 6016 aluminum alloy panel.

Effects of solution and aging temperature on microstructure and properties of QAL10-4-4 aluminum bronze after forging

Guo Heran, Feng Zaixin, Yin Ao, Zuo Sen

2020, 45(6): 63-66. doi:10.13251/j.issn.0254-6051.2020.06.014

Abstract ( 86 )

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Metallographic microanalysis, room temperature mechanical properties and hardness tests were carried out on as-hot-forged aluminum-bronze QAl10-4-4 after different solid solution and aging temperatures. The results show that the optimized solid solution temperature of the aluminum-bronze is 850 ℃, thus, a small amount of β′ phase is precipitated on the basis of α-phase and k-phase which result in the alloy obtain higher strength and hardness. On the solution treatment basis, after aging at 650 ℃ for 2 h, the tensile strength of the alloy is 726 MPa, the yield strength is 491 MPa, the hardness is 209 HBW, and the elongation is 22.7% due to the interaction between the tiny granule k phase precipitated from β′ martensite decompose and the finer α phase. Compared with the original untreated brone, the microstructure and properties of the aluminum brone are obviously improved and the alloy achieves good combination of strength and toughness.

Effect of annealing temperature on texture and magnetic properties of 6.5%Si ultra-thin strip

Liu Baozhi, Liu Pengcheng, Zhang Siyu, Zhang Hao, Zhang Lei, Xing Shuqing

2020, 45(6): 67-71. doi:10.13251/j.issn.0254-6051.2020.06.015

Abstract ( 61 )

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A 6.5%Si ultra-thin strip with thickness of 0.03 mm was fabricated by using of melt-spinning method, and subsequently annealed at 880 ℃ and 920 ℃ in vacuum furnace, respectively. The evolution of macro and micro texture under different annealing temperatures was investigated by means of X-ray diffraction and EBSD test. The results show that the 6.5%Si ultra-thin strip can be characterized by {001}<100> Cube, {110}<001> Goss and {112}<111> texture. The λ-fiber remains the dominant and the grain size increases gradually with the increase of annealing temperature. Especially, when annealed at 920 ℃, the size dominance of {001}<120> and {001}<100> grains increases gradually, and the unfavorable texture {111}<110> and {111}<112> decrease. Meanwhile, preeminent magnetic inductions of 1.644 T(B₅₀) and iron losses of 5.896 W/kg(P_10/400) are achieved.

Local surface laser quenching process of 12CrNi3 steel outside locking sleeve

Li Ling, Meng Xuan, Zhao Zhipeng, Yue Jiahong, Qi Ting

2020, 45(6): 72-76. doi:10.13251/j.issn.0254-6051.2020.06.016

Abstract ( 62 )

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The surface quenching test was operated on the 12CrNi3 outside locking sleeve by using semiconductor laser broadband, the microstructure, hardness and wear resistance of parts after treatment were detected and analyzed. The results show that the surface flatness is best after single pass scanning by the method of fixed spot, with the distance from the laser head to the center of the scanning area of workpiece 375 mm, the workpiece tilt 22°, the laser head tilt 18°, temperature 1350 ℃ and scanning speed 9 mm/s. The laser surface hardening with 750-1000 μm, but the shallowest is 443.1 μm. The structure of the hardening zone is fine martensite, hardness is up to 600-700 HV0.2, which is the 2 times of the matrix and about 1.3 times of the specimens after carburizing and quenching, and the wear resistance of the laser transformation hardening zone is obviously enhanced.

Application of subzero and cryogenic treatment in carburized gear parts

Zhu Ruifang, Liu Yonggang

2020, 45(6): 77-79. doi:10.13251/j.issn.0254-6051.2020.06.017

Abstract ( 68 )

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Through analyzing the subzero and cryogenic treatment process of 18Cr2Ni4WA and 20Cr2Ni4A steel, the reasonable process parameters were determined by test and applied to the actual production of carburized gear parts. The results show that the subzero and cryogenic treatments can improve the hardness of the carburized gears of 3-5 HRC, and can effectively increase the depth of hardened layer.

Effect of stress relief annealing on hydrogen absorption of TC18 and TC21 titanium alloy

Zheng Chao, Hu Shengshuang, Li Binbo, Ouyang Chenglong, Ouyang Delai

2020, 45(6): 80-83. doi:10.13251/j.issn.0254-6051.2020.06.018

Abstract ( 62 )

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Stress relief annealing of TC18 and TC21 titanium alloys was carried out in a pit-type air furnace according to GJB3763A-2004 standard with the highest temperature and longest holding time, respectively. The effect of stress relief annealing on hydrogen absorption of TC18 and TC21 titanium alloys was studied. The results show that the hydrogen content of TC18 titanium alloy increases after stress relief annealing in air furnace compared with that before stress relief heat treatment, while that of TC21 titanium alloy decreases. The hydrogen content of TC18 and TC21 is 0.0029% and 0.0025% respectively, that is much lower than that of required by material specifications(<0.015%) after stress relief in the air furnace. After stress relief annealing, the hydrogen content of TC18 and TC21 titanium alloys change regularly with the change from surface to center (depth), and there is little difference between the hydrogen content of inner layer and that of surface layer. Considering the amount of hydrogen absorption, stress relief annealing can be conducted for the two titanium alloys by air furnace.

Continuous cooling transformation of high aluminum TRIP steel and effect of hot deformation on its phase transformation

Huang Huiqiang, Di Hongshuang, Gong Dianyao

2020, 45(6): 84-88. doi:10.13251/j.issn.0254-6051.2020.06.019

Abstract ( 61 )

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Continuous cooling transformation curves, transformation law and the effect of hot deformation on transformation of a high aluminum TRIP steel were studied by means of thermal dilation test and hot-compressing thermal simulation test. In addition, the driving force of transformation was qualitatively analyzed. The results show that the CCT curves can be divided into three regions. With the cooling rate increasing, the volume fractions of ferrite and pearlite decrease, the volume fractions of bainite and martensite increase, respectively. The shape of bainite transforms from granular to feather-like or lath-like. As a result of dynamic recrystallization caused by hot deformation, the original austenite grain of the samples is refined and acicular ferrite is observed at high cooling rates. Hot deformation can provide more nucleation sites and higher driving force of γ→α transformation, thus resulting in a shorter bainite transformation incubation period and a finer the room temperature microstructure.

Coarsening behavior of secondary phase particles in Zr-Sn-Nb-Fe alloy

Wu Zongpei, Yang Zhongbo, Yi Wei

2020, 45(6): 89-92. doi:10.13251/j.issn.0254-6051.2020.06.020

Abstract ( 65 )

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The microstructure of Zr-0.3Sn-1.2Nb-0.2Fe alloy and Zr-0.5Sn-0.2Nb-0.8Fe alloy fuel cladding tubes annealed at different temperatures (450-550 ℃) were studied by means of SEM-SE and quantitative metallography analysis technique. The results show that increasing the temperature can promote the distribution uniformity and size coarsening process of the secondary phase particles. According to the second-order kinetics of Kahlweit theory, the secondary phase particle coarsening activation energy of the Zr-0.3Sn-1.2Nb-0.2Fe alloy and the Zr-0.5Sn-0.2Nb-0.8Fe alloy tubes are proven to be 209 kJ/mol and 179 kJ/mol respectively. The addition of Nb is considered to play an important role in increasing the coarsening activation energy of secondary phase particle.

Determination and analysis of SH-CCT curve of X80 pipeline steel with OD1422 mm

Yu Chenyang, Chi Qiang, Zhang Weiwei, Hu Meijuan, Chen Qinglong, Ge Jialin

2020, 45(6): 93-97. doi:10.13251/j.issn.0254-6051.2020.06.021

Abstract ( 65 )

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The Gleeble3500 thermo-mechanical simulation tester was used to simulate the thermal cycling process of the X80 pipeline steel with OD1422 mm at different cooling rates. The thermal expansion method was used to simulate the continuous cooling transformation curve of simulated heat affected zone (SH-CCT). Combined with microstructure analysis and hardness test, the microstructure change of welding heat affected zone (HAZ) of the X80 pipeline steel at different cooling rate conditions was studied. The test results show that the cooling rate has a significant effect on the phase transformation behavior of the steel. When the cooling rate is 1 ℃/s, the microstructure is transformed into bainite. When the cooling rate is 7 ℃/s, the martensitic transformation begins. When the cooling rate is 20 ℃/s, more lath bainite with higher dislocation density is obtained and the grain size is smaller. When the cooling rate is between 7 ℃/s and 20 ℃/s, the microhardness and impact property are greater than the base metal.

Precipitation behavior of χ phase and M₂₃C₆ carbide in low-activation duplex multi-principal element alloy Fe₅₁Mn₃₀Cr₁₉ during tempering at 475 ℃

Cao Weitao, Zheng Mingjie, Ding Wenyi, Wang Chao, Xin Jingping

2020, 45(6): 98-103. doi:10.13251/j.issn.0254-6051.2020.06.022

Abstract ( 54 )

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The precipitation behavior of χ phase and M₂₃C₆ carbide in low-activation duplex phase multi-principal element alloy Fe₅₁Mn₃₀Cr₁₉after tempering at 475 ℃ were studied by means of XRD, SEM, EBSD and TEM. The result shows that, after tempering, the precipitation behavior of χ phase and M₂₃C₆ carbide in the test materials exists similarities as well as differences. The similarities of the two precipitates are both exhibited the same cubic-cubic orientation relationship with its matrix, and the ratio of lattice constant of the precipitates and matrix is very close to 3∶1. However, the differences of the two precipitates are that χ phase is first precipitated inside the ferrite in the form of a dot-like, and there is no element segregation in the precipitation process, but the M₂₃C₆ phase always begins to precipitate at the interface of ferrite/austenite, and then gradually to expand into the ferrite region, which has a significant segregation of chromium. Based on the lattice structure of the two precipitations and their relationship with their parent phase, the formation mechanism of the two precipitations is also analyzed. Through the analysis of these characteristics of low-activation duplex phase multi-principal element alloy, it can provide an important reference for the control of the precipitated phase and the design of material properties.

CCT curves and properties of low yield rario high strength weathering steel

Yao Jitan, Sun Li, An Huilong, Xin Ruishan, Pan Jin, Zhao Yanqing

2020, 45(6): 104-107. doi:10.13251/j.issn.0254-6051.2020.06.023

Abstract ( 95 )

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Continuous cooling transformation (CCT) curves of a low yield ratio high strength weathering steel were plotted by means of expansion method combined with metallographical and hardness methods, and the mechanical properties and corrosion resistance of this steel were studied. The results indicate that the tensile strength of the tested steel reaches 575 MPa with 0.75 yield ratio, the impact property is excellent, and the corrosion resistance is obviously better than Q345B steel. When the tested steel after austenitizing is cooled to room temperature at a cooling rate of 0.1-100 ℃/s, its microhardness value increases from 131 HV0.5 to 218 HV0.5 with the increase of cooling rate. When the cooling rate is below 1 ℃/s, the microstructure of the steel is composed of ferrite and pearlite. When the cooling rate is in the range from 1 ℃/s to 20 ℃/s, the microstructure is composed of ferrite, pearlite and bainite. When the cooling rate is in the range from 20 ℃/s to 100 ℃/s, the pearlite disappears and the microstructure is mainly composed of ferrite and bainite.

Microstructure evolution of GH4096 alloy during long-term thermal exposure

Bai Yunrui, Hu Yuhao, Zhong Yan, Guo Huiming, Li Fulin, Fu Rui

2020, 45(6): 108-113. doi:10.13251/j.issn.0254-6051.2020.06.024

Abstract ( 65 )

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Based on the composition of powder metallurgy René88DT alloy, GH4096 alloy was prepared by using a new deformation process. The coarsening of the γ′ phase and the precipitation behavior of the grain boundary precipitated phase in the solution treated and aged GH4096 alloy during long-term thermal exposure between 700-900 ℃ were studied. The results show that the GH4096 alloy has good microstructure stability during thermal exposure at 700 ℃. The size of the intragranular γ′ particles is stable at about 70 nm, and no precipitated phase is observed at the grain boundaries. The secondary γ′ phases begin to grow by a coalescence process, and the discontinuous phases begin to precipitate on the grain boundaries after exposure at 750 ℃ for 500 h, however, the growth rate of γ′ phase and the precipitation rate of grain boundary precipitates are relatively low. When the exposure temperature is above 800 ℃, The coarsening rate of γ′ phase and the precipitation and growth rate of grain boundary precipitates are obviously accelerated. After long-term thermal exposure, the relationship between the size of the secondary γ′ phase and Larsen Miller parameter is approximately linear, and the main precipitates are M₃B₂ and μ phase.

Hot deformation behavior and hot processing map of DH780 steel

Wang Junfeng, He Yutian

2020, 45(6): 114-118. doi:10.13251/j.issn.0254-6051.2020.06.025

Abstract ( 79 )

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Hot deformation behavior of the experimental steel was investigated with a compression test on Thermecmastor-Z simulator at 800-1150 ℃ and strain rate range between 0.01-10 s^-1. The hot deformed microstructure was also observed. Based on the experimental data analysis, the hot deformation equation of the steel in austenite region and the processing map under 0.8 strain were established. The results show that the flow stress and the peak strain decrease with the increase of the deformation temperature. The activation energy in the austenite region is 385.91 kJ/mol. The optimal processing parameters determined by the power dissipation coefficient and the rheological instability are 1050-1150 ℃ and 0.01-0.1 s^-1. In this range, the full dynamic recrystallization occurs in the experimental steel, and the power dissipation coefficient is 17%-32%.

Anisotropy of microstructure and properties of Al-Cu-Mg-Sc alloy

Li Wangzhen, Sun Youping, He Jiangmei, Hu Yijie, Wan Siyu

2020, 45(6): 119-123. doi:10.13251/j.issn.0254-6051.2020.06.026

Abstract ( 55 )

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Microstructure and tensile properties of Al-Cu-Mg-Sc alloy sheet with different states at different orientations were investigated by means of microstructure analysis, tensile test and XRD analysis. The results show that the strengths of both the final rolled and the final aged alloy sheet in the direction of 0° with the rolling direction are higher than those of in the direction of 30°, 45°, 60° and 90°, as well as the elongation is higher. The anisotropic index value I_PA of the final aged alloy sheet is smaller than that of the final rolled one, and the performance is relatively uniform. R_m, R_p0.2and A along RD direction (0°) are 622.85 MPa, 529.38 MPa and 13.33%, respectively, and the comprehensive performance is excellent. The difference in the precipitation of the second phase in the two states affects the planar anisotropy of the alloy sheet. Schmid factor analysis show that the final rolled sheets contain (110)[111] and (001)[310] texture components, while the final aged sheets contain (110)[111], (001)[310] and (011)[100] texture component.

Tensile properties anisotropy of L485M pipeline steel

Kong Xianglei, Huang Guojian, Zhou Jing, Wang Yang

2020, 45(6): 124-128. doi:10.13251/j.issn.0254-6051.2020.06.027

Abstract ( 55 )

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Yield strength and tensile strength of L485M pipeline steel hot-rolled coil in four different directions (longitudinal, 30°, 45°, transverse) were tested by a Z1200 material tensile testing machine. Then the texture at different positions and in different directions of the coil thickness was detected and analyzed by an X' Pert Pro MRD X-ray diffractometer. The results show that the anisotropy of strength index of the steel is obvious, and the order of the strength is that transverse > longitudinal > 45°> 30°, and the transverse strength is obviously higher than that of the other three directions. The texture detection results of the steel show obvious consistency with the tensile properties, the main texture of longitudinal, 30° and 45° is {112}<111>, {001} <110>. Theoretically, the transverse and longitudinal crystallographic planes are the same, the difference of crystallographic directions is 90°, that is to say, the transverse texture is mainly {112} <110>, {001} <112>, so its properties are obviously different from that of other directions.

Microstructure and creep properties of Mg-3Al-1Si-xSr alloy

Chen Xinhao, Liu Xinyi, Li Yongxiang, Wang Wangbing, Zhang Zhichao, Wang Xu

2020, 45(6): 129-135. doi:10.13251/j.issn.0254-6051.2020.06.028

Abstract ( 54 )

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Microstructure of Mg-3Al-1Si alloy was adjusted by Sr microalloying and heat treatment processes (solid solution treatment and aging) to improve the creep properties of the alloy. The results show that the Sr element and solution treatment + aging treatment have a strong refining effect on the as-cast microstructure of the alloy. When the Sr content is 0.4% and the aging time is 24 h, the refining effect is the best. With the increase of Sr content and aging time, the creep life of the alloy increases. But the over-aging occurs when aging for 36 h which results in the decrease of creep life. After 420 ℃×10 h solid solution treatment + 180 ℃×24 h aging, the creep properties of the alloy is the best, with the creep life reaching 62.32 h, the steady-state creep rate reaching 5.545×10^-6 mm/s, and the creep fracture morphology gradually changes from cleavage fracture to ductile fracture.

Martensitic transformation and properties of in-situ NiTi-W composite

Jiang Jiang, Jiang Daqiang, Hao Shijie, Jiang Xiaohua, Guo Fangmin, Cui Lishan

2020, 45(6): 136-140. doi:10.13251/j.issn.0254-6051.2020.06.029

Abstract ( 86 )

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In order to obtain high performance NiTi based composite, an in-situ NiTi-W composite was prepared by means of vacuum arc melting, hot forging and wire drawing. Microstructure of the composite was observed by means of SEM. Reversible martensitic transformation behavior was measured by DSC, and tensile tests were conducted on WDT II-20 testing machine. SEM results show that the W fibers are refined to a few microns or even submicron scale and are elongated along the drawing direction. DSC test results show that the material shows complex reversible martensitic transformation behavior after annealing at different temperatures, and many heat absorption and desorption peaks are observed on heating and cooling thermal cycles curves. Tensile tests reveal that the yield strength of 600 ℃ annealed specimen increases greatly from about 200 MPa to about 800 MPa after pre-stretching deformation, the fracture stress is more than 1 GPa, and the fracture strain is as high as 40%. Furthermore, the specimen shows excellent linear hyperelasticity. Therefore, the composite should be a high-performance material with high strength, high plasticity and high linear hyperelasticity.

High temperature rheological behavior and microstructure evolution of GH3128 alloy

Liu Tingyao, Lai Yu, Fu Jianhui, Wei Yujun, He Yunhua, Pei Binghong

2020, 45(6): 141-148. doi:10.13251/j.issn.0254-6051.2020.06.030

Abstract ( 59 )

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Rheological characteristics of the GH3128 alloy at deformation temperature of 950-1150 ℃, strain rate of 0.01-10 s^-1 and strain rate of 30%-70% were studied by means of thermal simulation compression test. The constitutive equation of the GH3128 alloy was established based on the flow stress curves of the alloy and the Arrhenius model, and the hot processing map with deformation of 30%-65% was obtained. The relationship between the microstructure evolution and the plastic deformation parameters of the alloy during high temperature deformation was determined by combining the complete recrystallization condition diagram. Through the metallographic analysis, the evolution of carbides during hot deformation was investigated. The results show that the activation energy for hot working of the alloy is about 305 kJ/mol, and the reasonable processing zone is: deformation temperature 1050-1100 ℃, strain rate about 0.1 s^-1, in which the carbide in the alloy is substantially dissolved back, the microstructure is recrystallized sufficiently, and the grain size can be controlled to be less than 10 μm.

Lamellar structure thermal stability of inmedium-entropy eutectic CrCoNiNb_0.4 alloy

Wang Chengjie, Huang Chunhua, Li Jianwen

2020, 45(6): 149-152. doi:10.13251/j.issn.0254-6051.2020.06.031

Abstract ( 55 )

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Thermal stability of lamellar structure in CrCoNiNb_0.4medium-entropy eutectic alloy was characterized and examined. The results show that the lamellar structures in CrCoNiNb_0.4 medium-entropy alloy are stable when the heat treatment temperature is blower than 1023 K. While the heat treatment time increase from 24 h to 168 h, the lamellar spacing of lamellar structures in CrCoNiNb_0.4 eutectic alloy increases from about 0.19 μm to about 0.39 μm, and more and more precipitation phases are detected in the lamellar spacing, meanwhile, boundary splitting and edge spheroidization can be found in CrCoNiNb_0.4 eutectic alloy. The hardness of CrCoNiNb0.4 eutectic alloy shows a tendency of increase first and decrease later with the increase of heat treatment time under the synergy effect of precipitation strength and lamellar structure failure.

Thermal aging behavior of 14Cr-ODS steel

Zhang Zheping, Shi Qingzhi, Zhao Qian, Ren Qianqian

2020, 45(6): 153-156. doi:10.13251/j.issn.0254-6051.2020.06.032

Abstract ( 57 )

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In order to investigate the thermal stability of oxide dispersion strengthened (ODS) steel, 14Cr-ODS steel with Fe-14Cr-2W-0.3Ti-0.2V-0.07Ta-0.3Y₂O₃ (wt%) was prepared by means of mechanical alloying and hot isostatic pressing (HIP) sintering, and the long time thermal aging was carried out at 700 ℃ for 1000 h, 2000 h and 3000 h, respectively. The evolution of microstructure and secondary phases during the thermal aging was characterized. In addition, the Vickers microhardness values of the ODS samples were analyzed. The results indicate that no obvious change of microstructure can be found during the thermal aging process. The M₂₃C₆ particles partially dissolve into the matrix, thus promoting the precipitation of TiC and Y₂Ti₂O₇ nanoparticles during aging. The spherical Y₂Ti₂O₇ particles in the as-sintered ODS specimen turn into cuboidal without changing of size after long time aging. Both the matrix microstructure and secondary phases keep stable when the aging time increases to 2000 h and 3000 h, to which the microhardness results correspond.

Effect of initial microstructure on austenite transformation and grain growth behavior of 20CrMnTi steel during pseudo-carburizing process

Li Jun, Huang Jian, Jia Tao

2020, 45(6): 157-162. doi:10.13251/j.issn.0254-6051.2020.06.033

Abstract ( 58 )

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The cementite precipitation behavior of 20CrMnTi steel during spheroidizing annealing and its interaction with ferrite recovery and recrystallization were studied, and the effects of initial microstructure as-in hot-rolled state, quenched state and spheroidizing annealed state on austenite transformation and grain growth behavior during pseudo-carburizing were emphatically analyzed. The results show that coarse ferrite + pearlite microstructure and uniform fine lath martensite microstructure can be found in the hot-rolled and quenched specimens, respectively. However, the matrix and the carbide microstructures in the spheroidized specimens are nonuniform in micro-scale due to the interaction of carbide precipitating with recovery, recrystallization of martensite matrix. During pseudo-carburizing, the average grain size of austenite decreases in the order of hot rolled state, quenched state and spheroidizing annealed state, but the non-uniformity factor increases in the same order. The nucleation density and homogeneity of austenite related to the initial microstructure are one of the key factors controlling the austenite grain growth behavior during carburizing.

Comparison of microstructure and properties of low-nickel austenitic stainless steels

Zeng Yao, Yang Jianhong, Wang Bi, Qian Xuehai, Chen Xiaolong, Tian Yuhang

2020, 45(6): 163-166. doi:10.13251/j.issn.0254-6051.2020.06.034

Abstract ( 67 )

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For the cold-rolled drawability differences between grade J5A and grade J5 low-nickel austenitic stainless steels of Series 200 products, the composition design, metallographic structure, mechanical properties and martensitic content were analyzed and compared, and the mechanisms of cold working performance difference were studied. The results show that the unreasonable composition design of J5A steel results in lower nickel equivalent, poorer austenite stability and higher martensite transition point M_d_(30/50), large quantity of cold deformation induced martensite are generated during rolling, leading to severe work-hardening degree and poor drawability performance.

Comparison of materials for high-end shaft parts of rail transit

Su Liwu, Chen Ling

2020, 45(6): 167-172. doi:10.13251/j.issn.0254-6051.2020.06.035

Abstract ( 154 )

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Through the comparison of microstructure and properties of the high-end axle parts materials (35CrMoA, EA4T, EA1N, DZ2, 30CrNiMoV12, etc.), and the high-end shaft parts materials (35CrMo, 40CrNi2MoA, 34CrNiMo6, 30CrNiMo8, etc.) for rail transit after heat treatment, the materials for shaft parts were optimized. The comparison test results of axle parts show that, the strength and toughness of 30CrNiMoV12 steel after heat treatment is much higher than other materials, and its impact toughness, notch sensitivity and fatigue strength are the best in axle parts materials. It is the best choice for the axle parts with high-strength and structural size limitations, or under the conditions of frigid zone. The DZ2 material can be the secondary choice. The EA4T steel performance is close to DZ2 steel, but its low temperature impact toughness is not as stable as DZ2 steel. The overall strength of EA1N steel is only half of the 30CrNiMoV12 steel. The comparison test results of shaft parts show that, after heat treatment, 40CrNi2MoA, 34CrNiMo6, 30CrNiMo8 steels have good toughness, good low temperature impact toughness and stability, 30CrNiMo8 steel has better fatigue strength and lower notch sensitivity, suitable for high strength shaft and application under the conditions of frigid zone. In contrast, the strength of 35CrMo steel is slightly lower, its low temperature impact toughness is better, slightly lower than other materials and its stability needs to be improved.

Effect of B₄C on microstructure and properties of high-entropy alloy

Zhang Jie, Cheng Xiaonong, Luo Rui, Liu Ming

2020, 45(6): 173-177. doi:10.13251/j.issn.0254-6051.2020.06.036

Abstract ( 232 )

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High entropy alloy matrix composites B₄C/FeCoNiCrAl and B₄C/FeCoNiCrCu were prepared by microwave sintering process. The effects of different contents of B₄C on the microstructure and properties of high-entropy alloy were investigated. The results show that the addition of B₄C increases the lattice distortion of matrix alloy to a certain extent. The microstructure of the alloy consists of a high-entropy alloy basement region, a boride region formed by decomposition of boron carbide, and a carbide region. The boride of the body-centered cubic FeCoNiCrAl high-entropy alloy is needle-like, and the high-entropy alloy boride structure of the face-centered cubic structure FeCoNiCrCu is block-shaped, which is related to the atomic size difference in the alloy system. B₄C can significantly improve the strength and hardness of the alloy, and the plasticity decreases slightly. The 4% B₄C/FeCoNiCrAl alloy composite presents the highest hardness and compressive strength values of 627.1 HV0.5 and 1836 MPa, respectively, but the plasticity is poor, and the compression ratio is only 11%. The hardness and strength of the 4% B₄C/FeCoNiCrCu alloy composite are only 249.3 HV0.5 and 1413 MPa, which are lower than that of 4% B₄C/FeCoNiCrAl alloy composite, but the plasticity is good and the compression ratio can reach 35%.

Effect of Nb on cold rolled microstructure and texture of grain-oriented silicon steel

Meng Ranran, Duan Yanghui, Feng Yunli, Li Jie

2020, 45(6): 178-184. doi:10.13251/j.issn.0254-6051.2020.06.037

Abstract ( 53 )

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Effect of Nb on microstructure and texture of grain-oriented silicon steel during cold rolling was studied by means of OM and EBSD. The results show that both the Nb containing and the niobium free normalized plate have strip microstructure after cold rolling, but the Nb containing cold rolled plate is narrower in its width direction. The existence of Nb has an optimum effect on texture. After intermediate annealing, the secondary cold rolled texture of Nb containing cold rolled plate is obviously improved, compared with the second cold rolled plate without Nb, which has a lower strength rotating cubic texture and higher strength {111}<112> texture, with a maximum orientation density of 12.460.

Diffusion phenomena of Cu in binary alloys with equal atomic ratio

Wang Zi, Zhang Weiqiang, Fu Huameng

2020, 45(6): 185-188. doi:10.13251/j.issn.0254-6051.2020.06.038

Abstract ( 60 )

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Microstructure and composition distribution of diffusion layer of four binary equal atomic alloys, Cu₅₀Ni₅₀, Cu₅₀Co₅₀, Fe₅₀Ni₅₀ and Fe₅₀Cr₅₀, after copper plating and diffusion at 850 ℃ for 10 h, were studied. The results show that after diffusion treatment at 850 ℃ for 10 h, there is obvious mutual diffusion between Ni atom and Cu atom due to the existence of suitable vacancies in Cu₅₀Ni₅₀ alloy, and the mutual diffusion between Cu atom and Fe atom often occurs at grain boundary. In the diffusion couple of Cu-Fe₅₀Ni₅₀, there is mutual diffusion between Cu atom and Fe atom. In Cu-Fe₅₀Cr₅₀ and Cu-Cu₅₀Co₅₀ diffusion couple, no atoms diffuse.

Effect of La-Ce mixed rare earth on mechanical properties and corrosion resistance of Mg-Al-Mn alloy

Huang Ming, Chen Lichao, Chu Qian, Zhao Liping, Qin Chen, Tian Zhihua, Zhang Huimin

2020, 45(6): 189-193. doi:10.13251/j.issn.0254-6051.2020.06.039

Abstract ( 59 )

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Effect of La-Ce mixed rare earths on the microstructure, mechanical properties and corrosion resistance of Mg-Al-Mn alloys were investigated. The Mg-Al-Mn alloys with rare earth content (mass fraction) of 4.63%, 5.81% and 6.18% respectively were smelted in a T-1200CB crucible furnace. The specimens were solution treated at 430 ℃ for 24 h in a box-type resistance furnace, and then aged at 200 ℃ for 24 h. The microstructure of the specimens in different heat treatment states were observed, the tensile, hardness and salt spray corrosion tests were carried out on the specimens after solution treatment and aging. The effects of mixed rare earth on the microstructure, mechanical properties and corrosion resistance of the alloys were analyzed. The results show that with the increase of La-Ce mixed rare earth content in the alloy, the Mg₁₇Al₁₂ phase is gradually replaced by the Al₄(La, Ce) phase; the hardness, tensile strength and elongation are gradually reduced, and the mechanical properties are decreased; the corrosion rate of the alloy is gradually decreased and the corrosion resistance is improved.

Effect of eutectic silicon on crack formation and propagation of Al-20%Si alloy by in-situ observation

He Shaofu, Li Qingchun, Zhao Shuai, Chen Shuying, Chang Guowei

2020, 45(6): 194-196. doi:10.13251/j.issn.0254-6051.2020.06.040

Abstract ( 57 )

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Crack formation and propagation of Al-20%Si alloy were observed in-situ by using confocal laser scanning microscope, the effect of eutectic silicon on crack formation location and crack propagation mode of Al-20%Si alloy were studied. The results show that with the increase of solution temperature, the eutectic silicon phase in the Al-20%Si alloy changes into particles. During the tensile process, cracks easily occur at the needle-shaped eutectic silicon of the as-cast Al-20%Si alloy, and the cracks mainly propagate between the eutectic silicon. After solution at 560 ℃ for 6 h and aging at 190 ℃ for 10 h, the acicular eutectic silicon in the microstructure of the alloy transforms completely into granular silicon, the propagation rate is decreased, and the tensile strength and plasticity of the alloy are improved obviously.

Effect of Nb on microstructure and mechanical properties of hot-rolled low-carbon bainitic steel

Dong Changfu, Yuan Qing, Xu Guang, Hu Da

2020, 45(6): 197-200. doi:10.13251/j.issn.0254-6051.2020.06.041

Abstract ( 51 )

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Two kinds of steels based on C-Si-Mn system were designed in order to develop the 600 MPa grade hot-rolled bainitic steel, one was Nb-added, and another as the base steel without Nb addition. Microstructure observation, precipitation analysis and tensile test were conducted to investigate the effect of Nb on microstructure and mechanical properties of the hot-rolled low-carbon bainitic steel after melting and rolling. The results reveal that the bainitic lath is refined by the 0.025wt% Nb addition, and the strength and ductility of the steel are apparently increased. In addition, the dispersed carbonitride particles containing Nb provide the precipitation strengthening effect on the steel. It is concluded that the Nb addition improves the comprehensive performance of the low-carbon high-strength bainitic steel.

Effects of Si, Mn content on microstructure and properties of steel for 1000 MPa grade construction machinery

Li Youxin , Lou Zhenyang , Li Xiaohui

2020, 45(6): 201-205. doi:10.13251/j.issn.0254-6051.2020.06.042

Abstract ( 68 )

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Effects of Si and Mn content on microstructure and properties of steel for construction machinery were studied by means of optical microscope, scanning electron microscope and tensile testing machine. The results show that although the increase of Mn content promoted the grain growth, but the grain size is still low because the structure genetic effect is significantly higher than that caused by the change of Mn content, while the increase of Si content has little effect on the primary austenite grains. The increase of Mn content has no obvious effect on the precipitation of carbides in the quenched and tempered steel for construction machinery. Although the carbides in the specimens with increased Si content are still mainly granular, and has also a small amount of short rod carbides, the number of carbides is obviously less and the size is smaller. With the increase of Mn content, the tensile strength, yield strength and Brinell hardness of steel for construction machinery are improved, while the elongation, section shrinkage and impact absorbed energy at -40 ℃ are reduced to varying degrees. After adding Si content, the tensile strength, yield strength and Brinell hardness of steel for construction machinery are decreased, while the elongation, section shrinkage and impact absorbed energy at -40 ℃ are increased significantly, but the strength and Brinell hardness do not meet the standard requirements of steel for construction machinery; the appropriate Si and Mn content of steel for 1000 MPa grade construction machinery steel for test are 0.35 wt% and 1.12 wt%, respectively.

Crack sensitivity and formation mechanism of laser clad H13 steel

Yang Wei, Zeng Daxin, Liu Jianyong, Li Fengguang

2020, 45(6): 206-211. doi:10.13251/j.issn.0254-6051.2020.06.043

Abstract ( 78 )

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A multitrack overlapping clad layer was fabricated on H13 steel substrate by laser cladding with coaxial powder feeding, the microstructure characteristics were studied by means of optical microscope (OM), SEM and XRD. The clad layer cracks were detected by penetrant inspection method, and the crack density was quantitatively characterized by image processing. The effects of the laser cladding process parameters on crack sensitivity were studied, and the mechanism of crack formation was analyzed. The results show that the microstructure of H13 steel clad layer is mainly composed of martensite and residual austenite transformed from dendrite-like austenite. The crack sensitivity of the clad layer is high, most of them are thermal cracks, which initiates and propagates between austenite columnar dendrites. The laser power has a significant impact on the crack sensitivity of the clad layer, the higher the power, the lower the crack sensitivity, and the clad layer without cracks can be obtained by optimizing process parameters.

Effect of TiC content on microstructure and properties of laser clad layer on TC4 alloy

Xia Sihai, Wu Meiping, Ma Yiqing, Cui Chen

2020, 45(6): 212-215. doi:10.13251/j.issn.0254-6051.2020.06.044

Abstract ( 59 )

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Ni60A and (2%, 4%, 6%)TiC+Ni60A composite coatings were prepared on the surface of TC4 titanium alloy by laser cladding process. The influence of different TiC mass fractions on the microstructure and properties of the clad layer were analyzed by metallographic microscope, microhardness tester, X-ray diffractometer, and friction-wear machine. The results show that the microstructure of the clad layer without TiC is dominated by dendrites, and the TiC addition leads to the appearance of petal phase. The XRD analysis shows that hard reinforcing phases AlCCr₂, Al_0.24B_0.01Ni_0.75 appear in the clad layer, which can significantly increase the hardness of the clad layer. The results of microhardness and friction and wear tests show that the average hardness of the clad layer with TiC is significantly higher than that of the matrix, and the friction coefficient is significantly reduced. With the increase of TiC content, the hardness of the clad layer increases first and then decreases, while the friction coefficient decreases first and then increases. The hardness of the clad layer with 4% TiC is the highest, which is 213.3% higher than that of the matrix, and the friction coefficient is the lowest, which is 0.309 774.

Effect of water jet surface modification on oxide film morphology of homemade Zirlo alloy clad tube treated by accelerate corrosion

Li Gaosheng, Wang Wanlin, Ma Xue, Kong Shuyan, Li Huailin

2020, 45(6): 216-219. doi:10.13251/j.issn.0254-6051.2020.06.045

Abstract ( 61 )

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To improve the properties of homemade zircalloy clad tube and safety of reactor, the homemade Zirlo ally was impacted by water jet and investigated after high temperature and high pressure corrosion with dynamic water. The specimens were tested by SEM and AES to research the effect of the impact pressure of water jet on the oxide film. The results reveal that the water jet may cause good and harmful effect on corrosion of the zircalloy. The oxide film decreases by 4.3% when the impact pressure is up to 40 MPa, comparing with the specimen that is not impacted. However, the corrosion of specimens jetted with pressure of 10 and 20 MPa are worse than that of untreated specimens.

Ni-based laser alloyed layer on ductile iron roller surface and its wear properties

Wang Shuoyu, Zhang Lin, Xie Mingxiang, Ye Wenhu

2020, 45(6): 220-225. doi:10.13251/j.issn.0254-6051.2020.06.046

Abstract ( 71 )

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Ni-based alloyed layer was prepared on the surface of ductile iron QT600-3 by laser alloying. The phase composition, microstructure, mechanical properties, tribological properties at room temperature and high temperature of the alloyed layer were investigated by means of XRD, SEM, tribological tests and Raman spectrometer. The test results show that Ni-based alloyed layer exhibits good metallurgical bonding to the substrate, high microhardness (up to 720 HV0.1). At high temperature, its friction coefficient is less than 0.305 and wear rate is less than 7.55×10^-6 g·N^-1·m^-1. With the increase of laser scanning speeds, the microstructure becomes more denser, the microhardness increases first and then decreases, and the wear resistance at 700 ℃ increases, but the crack rate of the alloyed layer increases. During high temperature friction and wear experiment, the wear mechanism of the alloyed layer is mainly abrasive wear, fatigue wear and oxidation wear. Also, the increase of scanning speed improves the grain refinement and increases the microhardness. The wear products and carbides produced on the surface of the alloyed layer during high temperature wear play a positive role in improving wear resistance.

Effect of CO₂ on corrosion behavior of Q235 steel and X70 steel in oilfield groundwater environment

Wang Yue, Wang Dan, Xie Fei, Wang Xingfa, Guo Ziwei, Zhu Xinkun

2020, 45(6): 226-231. doi:10.13251/j.issn.0254-6051.2020.06.047

Abstract ( 54 )

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In order to find out the corrosion law of CO₂ on Q235 steel and X70 pipeline steel in the groundwater environment of Liaohe Oilfield, the effects of different CO₂ concentrations on corrosion behaviors of the two steels were investigated by using of potentiodynamic polarization technique and AC impedance technique. The corrosion interface of the specimens was characterized by means of metallographic microscope. The results show that with the increase of CO₂concentration, the radius of the AC impedance spectrum of the two steels decreases, the corrosion current density increases; the number, depth and area of corrosion pits increase, and the corrosion sensitivity increases. In low concentration CO₂environment (such as 10% CO₂), Q235 steel has higher corrosion sensitivity than that of X70 steel. And in high concentration CO₂ environment (such as 20%, 40%, 60%), the corrosion rate of Q235 steel is smaller and the corrosion resistance is better.

Cause analysis on spalling of working roll during cold rolling

Chen Wei, Wang Yong, Han Jian

2020, 45(6): 232-235. doi:10.13251/j.issn.0254-6051.2020.06.048

Abstract ( 70 )

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The spalling causes of working roll of tandem cold rolling mill housing F2 during rolling process were analyzed by ZEISS-AXIO microscope, Keyence VE9800 scanning electron microscope and Edax energy spectrometer. The results show that the spalling of the working roll is caused by the internal defects of the roll body. The macro-morphology of the spalling appearance is obviously different from the spalling appearance caused by the roll body surface cracks. The crack growth is formed at trajectory of concentric circle, which is center on the internal defect, and then the remaining parts are separated to form a spalling appearance when the cracks are extended to a certain position. The spalling occur from the inside in a concentric circle mode, and the crack source at the center of the roll often accompanied by metallurgical inclusion defects. The presence of inclusions will cut off the continuity of the roll materials and decrease its mechanical properties. Meanwhile, the local stress concentration in the roll will provide favorable conditions for the initiation and propagate of cracks. In order to avoid this problem, the purity of molten steel should be further improved, therefore, the probability of inclusion formation can be reduced.

Formation mechanism and preventive measures of pitting defects on surface of cold rolled continuous annealing strip steel

Zhao Haiqiang, Chen Hongye

2020, 45(6): 236-238. doi:10.13251/j.issn.0254-6051.2020.06.049

Abstract ( 57 )

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In view of the pitting defects on the surface of cold rolling continuous annealing strip, the causes of the pitting defects were found out through on-site open furnace inspection, the formation mechanism of the furnace roller nodules was found out by detection the chemical composition of the nodules, and reasonable and effective measures to prevent the furnace roller nodules were put forward based on the equipment and process characteristics of the continuous annealing unit. The results show that the serious roller nodules in the slow cooling section of the annealing furnace are the main cause of the pitting defects on the surface of the strip steel. In the actual production, the occurrence of furnace roller nodules can be effectively controlled by strengthening the cleaning effect of strip steel, optimizing the tension in the annealing furnace, controlling the O₂ content and dew point temperature in the annealing furnace, reducing the roughness of the furnace roller and arranging the production plan reasonably.

Numerical simulation and experimental verification of air-jet cooling control structure for steel sheet

Dong Chengzhi, Liang Xiao, Li Xianjun, Yang Tao, Hou Junqing, Luo Ping

2020, 45(6): 239-243. doi:10.13251/j.issn.0254-6051.2020.06.050

Abstract ( 78 )

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Three kinds of air-jet cooling control structure used for thin steel sheet cooling were simulated and analyzed. By comparing the velocity field and steel sheet temperature field in the air-jet cooling structure, it is determined and experimentally verified that the air-jet cooling control structure with single perforated plate can meet the requirements of steel sheet quenching and can obtain good cooling uniformity. The results show that the uniformity of velocity field and temperature field near the workpiece surface is improved when one or two perforated plates are set up compared with that without perforated plate. When the air-jet cooling control structure with single perforated plate is used to cooling the steel sheet, the maximum temperature difference on the workpiece is about 63.8 ℃ in 20 s. In 20 s, the average temperature of steel sheet is cooled from 920 ℃ to below Ms point (412 ℃), and the lowest cooling rate is about 27.2 ℃/s, which is greater than the critical cooling rate of martensitic transformation (27 ℃/s), that is, the air-jet cooling control structure with single perforated plate can be used for air-jet quenching of steel sheet.

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