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Ultra-low-carbon steel spheroidization and torsion

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Journal of Iron and Steel Research International 2018年第9期25卷 968-974页

作者： Yan-jun Yin Ji-quan Sun ai-min zhao Jin Gou Institute of Engineering Technology University of Science and Technology Beijing Beijing 100083 China Collaborative Innovation Center of Steel Technology University of Science and Technology BeijingBeijing 100083 China

Spheroidizing annealing and torsion testing of 0.027 wt% carbon steel rod were conducted to evaluate spheroidization kinetic behavior at 943 K （670 ℃） under deformed and non-deformed states. Kinetic curves were also predicted using the Johnson-Mehl-Avrami-Kolmogorov equation, and the results agree well with the experimental ones. After spheroidization was performed twice, the spherical cementite and precipitated carbides became smaller and the distribution was more uniform. Comparison of materials subjected to single and double spheroidizing annealing indicated a difference in grain size. Torsion performance was considerably improved under double spheroidization, especially the maximum torque with slight variations.

关键词： Ultra-low-carbon steel Spheroidization Spheroidization kinetic Torsion property

Mechanical properties and characteristics of nanometer-sized precipitates in hot-rolled low-carbon ferritic steel

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International Journal of minerals,Metallurgy and Materials 2014年第3期21卷 266-272页

作者： Xiao-pei Wang ai-min zhao Zheng-zhi zhao Yao Huang Liang Li Qing He Engineering Research Institute University of Science and Technology Beijing

The microstructures and properties of hot-rolled low-carbon ferritic steel have been investigated by optical microscopy, field-emission scanning electron microscopy, transmission electron microscopy, and tensile tests after isothermal transformation from 600°C to 700°C for 60 min. It is found that the strength of the steel decreases with the increment of isothermal temperature, whereas the hole expansion ratio and the fraction of high-angle grain boundaries increase. A large amount of nanometer-sized carbides were homogeneously distributed throughout the material, and fine（Ti, Mo）C precipitates have a significant precipitation strengthening effect on the ferrite phase because of their high density. The nanometer-sized carbides have a lattice parameter of 0.411-0.431 nm. After isothermal transformation at 650°C for 60 min, the ferrite phase can be strengthened above 300 MPa by precipitation strengthening according to the Ashby-Orowan mechanism.

关键词： ferritic steel nanoparticles mechanical properties carbides precipitation strengthening

Mechanical properties and wear resistance of ultrafine bainitic steel under low austempering temperature

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International Journal of minerals,Metallurgy and Materials 2020年第4期27卷 483-493页

作者： Wei Liu You-hui Jiang Hui Guo Yue Zhang ai-min zhao Yao Huang Collaborative Innovation Center of Steel Technology University of Science and Technology BeijingBeijing 100083China School of Mechanical Engineering Weifang University of Science and TechnologyShouguang 262700China China Electric Power Research Institute Beijing 100192China

The mechanical properties and wear resistance of the ultrafine bainitic steel austempered at various temperatures were *** electron microscopy(SEM)and X-ray diffraction were used to analyze the *** worn surfaces were observed via laser scanning confocal microscopy and *** indicated that,under low austempering temperatures,the mechanical properties differed,and the wear resistance remained basically *** tensile strength of the samples was above 1800 MPa,but only one sample austempered at 230°C had an elongation of more than 10%.The weight loss of samples was approximately linear with the cycles of wear and nonlinear with the *** samples showed little difference in wear resistance at different isothermal temperatures,whereas the thickness of their deformed layers varied *** results are related to the initial hardness of the sample and the stability of the retained ***,the experimental results showed that the effect of austempering temperature on the wear resistance of ultrafine bainitic steel can be neglected under low applied loads and low austempering temperature.

关键词： bainitic steel mechanical properties wear resistance austempering temperature

Effects of Mn and Cr contents on microstructures and mechanical properties of low temperature bainitic steel

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Journal of Iron and Steel Research International 2017年第3期24卷 290-295页

作者： Hui Guo Peng Zhou ai-min zhao Chao Zhi Ran Ding Jia-xing Wang Collaborative Innovation Center of Steel Technology University of Science and Technology Beijing Beijing 100083 China Institute of Engineering Research University of Science and Technology Beijing Beijing 100083 China

The effects of Mn and Cr contents on bainitic transformation kinetics,microstructures and mechanical properties of high-carbon low alloy steels after austempered at 230,300 and 350 ℃ were determined by dilatometry,optical microscopy,scanning electron microscopy,X-ray diffraction and tensile tests. The results showed that Mn and Cr can extend bainitic incubation period and completion time,and with the increase of Mn and Cr content,the bainitic ferrite plate thickness decreased and the volume fraction of retained austenite increased. TRIP（ transformation induced plasticity） effect was observed during tensile testing which improved the overall mechanical property. The increase of Mn concentration can improve the strength to a certain extent,but reduce the ductility. The increase of Cr concentration can improve the ductility of bainitic steels which transformed at a low temperature. The low temperature bainitic steel austempered at 230 ℃ exhibited excellent mechanical properties with ultimate tensile strength of（ 2146 ± 11） MPa and total elongation of（ 12. 95 ± 0. 15） %.

关键词： Low temperature bainitic steel Kinetics Retained austenite TRIP effect

Effects of ausforming strain on bainite transformation in nanostructured bainite steel

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International Journal of minerals,Metallurgy and Materials 2017年第3期24卷 264-270页

作者： Hong-liang Fan ai-min zhao Qing-chun Li Hui Guo Jian-guo He Engineering Research Institute University of Science and Technology Beijing Beijing Institute of Technology Press Beijing Institute of Technology School of Materials Science and Engineering Liaoning University of Technology School of Materials Science and Engineering Tsinghua University

The effects of ausforming strain on bainite transformation in high-carbon low-alloy nanobainite steel were investigated using a Gleeble 3500 thermomechanical simulator machine. The bainite transformation speed at 300°C was found to be accelerated by ausforming at 300, 600, and 700°C under applied strains ranging from 10% to 50% followed by isothermal transformation at 300°C. The ausformed bainite volume fraction varied with the ausforming strain because of the mechanical stabilization of the deformed austenite. Ausforming at low temperatures not only enhanced the bainite ferrite volume fraction but also refined the microstructure substantially. Although the amount of bainite ferrite might have been reduced with increasing strain, the microstructures were refined by ausforming. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

关键词： Alloy steel Bainite Carbon Enzyme kinetics Ferrite Microstructure Nanostructured materials Phase transitions Strain Volume fraction

Microstructure and properties of 1100 MPa grade low-carbon hot-rolled steel by laser welding

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Journal of Iron and Steel Research International 2018年第2期25卷 228-234页

作者： Chen Dong ai-min zhao Xi-tao Wang Qi-hang Pang Hui-bin Wu Collaborative Innovation Center of Steel Technology University of Science and Technology BeijingBeijing 100083 China Engineering Research Institute University of Scienceand Technology Beijing Beijing 100083 China

The microstructure and mechanical properties of the butt joint of 1100 MPa grade hot-rolled low-carbon steel by laser welding were investigated by scanning electron microscopy, micro-hardness and tensile tests. The yield strength and tensile strength of the laser welded joint reached 100.2 and 99.5% of the base material （BM）, respectively. However, the elongation of the welded joint only reached about 60% of BM. The lowest and highest hardness areas both existed in the incomplete recrystallization zone. The width of the softened area of the welded joint is about 240-260 pro. The element distribution has no obvious change for C, Cr, Si, Mn, Ti, etc.

关键词： Hot-rolled steel Laser welding Microstructure Mechanical property Element distribution

Texture evolution of commercial pure Ti during cold rolling and recrystallization annealing

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International Journal of minerals,Metallurgy and Materials 2012年第6期19卷 530-535页

作者： Hai-tao Jiang Ji-xiong Liu Zhen-li Mi ai-min zhao Yan-jun Bi Metallurgical Engineering Research Institute University of Science and Technology Beijing Beijing 100083 China

X-ray diffraction （XRD） was employed to analyze the texture evolution of commercial pure （CP） Ti during cold rolling and re- crystallization annealing. The texture components were measured by electron backscattered diffraction （EBSD） after recrystallization an- nealing. The CP Ti tends to form a texture with the basal pole tilted 30°-40° away from the normal direction toward the transverse direction. The texture of the initial hot-rolled plate can be classified into three kinds, i.e., the pyramid texture （1013）[5230] and （2021）[1015], the basal plane texture （0001）[2110], and the stronger_prism_texture （1120）[0001]. After cold rolling and annealing （700℃,60 min）,_the main texture components are the cold-rolled texture （1125）[1123] and the recrystallized texture （1013）[5230]. The texture （2021）[1015] is in- herited from the texture of the initial hot-rolled plate with the decrease of orientation density gradually. The volume contents of the cold-rolled texture {2115}（0110） and the recrystallized texture {1013}（1210） are calculated by EBSD. After recrystallization annealing, the specimen is rich in the recrystallized texture and inherits some of texture components from the cold-rolled texture. When the annealing time is prolonged, the anisotropic value decreases.

关键词： titanium cold rolling recrystallization annealing textures

Precipitation Strengthening by Nanometer-sized Carbides in Hot-rolled Ferritic Steels

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Journal of Iron and Steel Research International 2014年第12期21卷 1140-1146页

作者： Xiao-pei WANG ai-min zhao Zheng-zhi zhao Yao HUANG Zhi-da GENG Yang YU Sheet Metal Research Institute Shougang Research Institute of Technology Metallurgical Engineering Research Institute University of Science and Technology Beijing

The mechanical properties of the hot-rolled plates of Ti steel and Ti-Mo steel after isothermal transformation in a temperature range of 600 700 ℃ for 60 min have been tested, and the microstructures of the matrix and the characteristics of precipitated nanometer-sized carbides have also been examined by scanning electron microscopy and transmission electron microscopy. The precipitation regularity of nanometer-sized carbides has been studied by thermodynamic method and the contributions of corresponding strengthening mechanisms to the total yield strength have been calculated. The tensile strength of hot-rolled Ti-Mo ferritie steel can achieve 780 MPa with an elongation of 20.0% after being isothermally treated at 600 ℃ for 60 rain, and the tensile strength of Ti steel is 605 MPa with an elongation of 22.7%, according to the results of tensile tests. The critical nucleation size of （Ti,Mo）C is smaller than that of TiC at a given isothermal temperature, but the nucleation rate of （Ti, Mo）C is larger than that of TiC. The grainrefinement strengthening and precipitation strengthening contribute the main amount of the total yield strength. The major increase in yield strength with the decrease of isothermal temperature results from the contribution of precipi tation strengthening. The contribution of precipitation strengthening to the yield strength of the steels has been esti mated. The ferrite phase can be strengthened by about 400 MPa through precipitation strengthening in Ti-Mo steel isothermally treated at 600 ℃ for 60 rain, which is about 200 MPa higher than that of Ti steel under the same conditions.

关键词： ferritie steel nanometer sized carbide thermodynamic method precipitation strengthening

Effect of Annealing Process on Microstructure and Mechanical Property of 1100 MPa Grade TRIP Steel

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Journal of Iron and Steel Research International 2015年第7期22卷 622-629页

作者： Hong-xiang YIN Zheng-zhi zhao ai-min zhao Xiao LI Han-jiang HU Jiang-tao LIANG Metallurgical Engineering Research Institute University of Science and Technology Beijing Beijing Laboratory of Metallic Materials and Processing for Modern Transportation

To develop super-high strength TRIP steel for automobile application with good combination of strength and plasticity, an ultra high-strength TRIP steel 0.2 %C-2.0% Si-1.8% Mn was investigated at different intercritical annealing temperatures and bainitic isothermal temperatures. Microstructures were observed by scanning electron mi- croscopy, transmission electron microscopy, electron backscatter diffraction, and X-ray diffraction, and mechanical properties were tested under a uniaxial tensile testing machine. It shows that the best comprehensive mechanical properties were obtained for the experimental steel particularly annealed at 820 ℃ and austempered at 410 ℃. Yield strength of the tested steel mainly depends on ferrite, while the high strength of the tested steel is related to mar- tensite which forms through blocky austenite transformation during cooling and subsequent tensile test attributed to the TRIP effect. Hence, it could be concluded that the grain size of the retained austenite and carbon content in re- tained austenite are the main reasons for high elongation of the tested steel.

关键词： TRIP steel retained austenite intercritical annealing bainitic isothermal temperature automobile steel