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Enhanced strength and toughness in 40CrNiMo steels by austempering below martensite start temperature

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Journal of Iron and Steel Research(International) 2022年第5期29卷 810-818页

作者： Xiao-xiao Liu Zheng Zhang Jie Zhang Ran Yang Cheng-shuang Yu Jun-wei Qiao Li-na Han College of Materials Science and Engineering Taiyuan University of TechnologyTaiyuan030024ShanxiChina Zhejiang Laifual Drive Co. Ltd.Shaoxing312462ZhejiangChina

The austempering above and below martensite transition temperature(M_(s))was employed in a medium-carbon low-alloy 40CrNiMo steel,and the bainite and martensite multiphase microstructures with different volume fractions were obtained.Here,the effect of pre-existing martensite on subsequent transformation of bainite microstructure and mechanical properties is focused and researched.The microstructure with a volume fraction of pre-existing martensite(V_(PM)),bainite(V_(B)),and martensite/austenite(V_(M/A))constituents of approximately 28%,46%,and 26%,respectively could be obtained by austenitizing below M_(s)(280℃)for 1 h,and an optimum combination of strength,ductility,and impact toughness(yield strength of 1420 MPa,ultimate tensile strength of 1795 MPa,total elongation of 7.9%,and V-notch impact value of 37 J)was achieved.The considerable enhancement of mechanical properties in the sample austenitized below M_(s)is mainly ascribed to the formation of the pre-existing martensite,resulting in an effective reduction in the size of the bainite plates and martensite/austenite constituents.

关键词： austempering Pre-existing martensite Bainite plate Multiphase microstructure Mechanical property

austempering of hot rolled transformation-induced plasticity steels

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Journal of University of Science and Technology Beijing 2008年第2期15卷 143-149页

作者： Zhuang Li Di Wu Department of Materials Engineering Institute of Shenyang Aeronautical Engineering Shenyang 110034 China State Key Lab of Rolling and Automation Northeastern University Shenyang 110004 China

Thermomechanical controlled processing （TMCP） was conducted by using a laboratory hot rolling mill. austempering in the salt bath after hot rolling was investigated. The effect of isothermal holding time on mechanical properties was studied through examining of the microstructure and mechanical properties of the specimens. The mechanism of transformation-induced plasticity （TRIP） was discussed. The results show that the microstructure of these steels consists of polygonal ferrite, granular bainite, and a significant amount of stable retained austenite. Strain-induced transformation to martensite of retained austenite and TRIP occur in the hot rolled Si-Mn TRIP steels. Excellent mechanical properties were obtained for various durations at 400℃. Prolonged holding led to cementite precipitation, which destabilized the austenite. The mechanical properties were optimal when the specimen was held for 25 min, and the tensile strength, total elongation, and strength ductility balance reached the maximum values of 776 MPa, 33%, and 25608 MPa.%, respectively.

关键词： austempering hot rolling transformation induced plasticity mechanical properties

austempering of Hot Rolled Si-Mn TRIP Steels

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Journal of Iron and Steel Research(International) 2006年第5期13卷 41-46页

作者： LI Zhuang WU Di HU Rong State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 Liaoning China Department of Material Engineering Institute of Aeronautical Engineering Shenyang 110034 Liaoning China College of Foreign Languages Jiangxi Normal University Nanchang 330027 Jiangxi China

The austempering after hot roiling in hot roiled Si-Mn TRIP （transformation-induced plasticity） steels was investigated. The mechanism of TRIP was discussed through examination of the microstructure and the mechanical properties of this kind of steel. The results showed that the strain induced transformation to martensite of retained austenite occurs in hot rolled Si-Mn TRIP steels. The sample exhibited a good combination of ultimate tensile strength and total elongation when it was held at the bainite transformation temperature after hot deformation. The stability of retained austenite increases with an increase in isothermal holding time, and a further increase in the hold- ing duration resulted in the decrease of stability. The mechanical properties were optimal when holding for 25 min, and tensile strength and total elongation reached the maximum values （774 MPa and 33 ;, respectively）.

关键词： austempering hot rolling TRIP mechanical property

Influence of Hot Deformation and Subsequent austempering on the Mechanical Properties of Hot Rolled Multiphase Steel

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Journal of Materials Science & Technology 2006年第6期22卷 763-768页

作者： Zhuang LI Di WU Shenyang Institute of Aeronautical Engineering Shenyang 110034 China State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 China

Influence of hot deformation and subsequent austempering on the mechanical properties of hot rolled multiphase steel was investigated. Thermo-mechanical control processing （TMCP） was conducted by using a laboratory hot rolling mill, where three different kinds of finishing rolling reduction, and austemperings with various isothermal holding duration were applied. The results have shown that a multiphase microstructure consisting of polygonal ferrite, granular bainite and larger amount of stabilized retained austenite can be obtained by controlled rolling processes. Mechanical properties increase with increasing the amount of deformation because of the stabilization of retained austenite. Ultimate tensile strength （σb）, total elongation （σ） and the product of ultimate tensile strength and total elongation （σb-σ） reach the maximum values （791 MPa, 36% and 28476 MPa%, respectively） at optimal processes.

关键词： Hot deformation austempering Hot rolled multiphase steels Mechanical properties

Influence of austempering process on microstructures and mechanical properties of V-containing alloyed ductile iron

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Journal of Iron and Steel Research(International) 2018年第1期25卷 81-89页

作者： Jun-jun Cui Li-qing Chen State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110819 Liaoning China College of Mechanical and Vehicle Engineering ShenyangInstitute of Technology Fushun 113122 Liaoning China

The influence of austempering time and vanadium addition on microstructure and mechanical properties of the alloyed ductile iron has been investigated. The 0.30 wt% V-containing and V-free alloyed ductile irons were firstly austenitized at 850 ℃ for 1 h and then austempered in a salt bath at 300 ℃ for 2, 3 and 4 h, respectively. For the 0.3 wt% V-containing alloyed ductile iron, the transformation product （ausferrite） was finer, and a small amount of martensite and a large amount of stable austenite were obtained after austempering for 2 h, while higher hardness and compressive strength of 62.8 HRC and 3000 MPa were achieved. For the V-free alloyed ductile iron, lower hardness and compressive strength were measured to be 56.8 HRC and 2320 MPa. As the austempering time increases, the amount of stable austenite decreases in the V-containing ductile iron, typically for the start of the second stage formation （retained austenite （γτ） →α ＋ carbide）. Based on this, it is assumed that the optimal processing window （OPW） was narrowed due to the addition of 0.30 wt% V as compared to the V-free ductile iron. When the hardness of 0.30 wt% V-alloyed ductile iron was higher than 59 HRC, the highest wear resist- ance was obtained. The mechanical cutting plays a dominant role in abrasive wear process.

关键词： Alloyed ductile iron Vanadium austempering Microstructure Property Wear resistance

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 investigated.Scanning electron microscopy(SEM)and X-ray diffraction were used to analyze the microstructure.The worn surfaces were observed via laser scanning confocal microscopy and SEM.Results indicated that,under low austempering temperatures,the mechanical properties differed,and the wear resistance remained basically unchanged.The 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 loads.The samples showed little difference in wear resistance at different isothermal temperatures,whereas the thickness of their deformed layers varied greatly.The results are related to the initial hardness of the sample and the stability of the retained austenite.Meanwhile,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

EFFECT OF austempering ON TRANSFORMATION INDUCED PLASTICITY OF HOT ROLLED MULTIPHASE STEELS

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Acta Metallurgica Sinica(English Letters) 2007年第1期20卷 1-8页

作者： Z. Li D. Wu The State Key Laboratory of Rolling and Automation Northeastern University Shenyang 110004 China Shenyang Institute of Aeronautical Engineering Shenyang 110034 China

Effect of austempering on the transformation induced plasticity （TRIP） of hot rolled multiphase steel was investigated. Polygonal ferrite, granular bainite, and a large amount of stabilized retained austenite could be obtained in the hot rolled multiphase steel. Strain induced martensite transformation （SIMT） of retained austenite and TRIP effectively occur under straining owing to austempering after hot rolling, and mechanical properties of the present steel remain at a relatively high constant value for austempering at 400℃. The mechanical properties of the steel exhibited a good combination of tensile strength （791MPa） and total elongation （36%） because the stability of retained austenite is optimal when the steel is held for 20min.

关键词： austempering hot rolled multiphase steel mechanical property strain-induced transformation transformation-induced plasticity （TRIP）

Effect of Cu content on microstructures and mechanical properties of ADI treated by twostep austempering process

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China Foundry 2019年第3期16卷 168-176页

作者： Peng-yue Yi Er-jun Guo Li-ping Wang Yi-cheng Feng Chang-liang Wang School of Material Science and Engineering Harbin University of Science and Technology

The effect of Cu content on the microstructures and mechanical properties (yield strength, ultimate tensile strength, impact energy, fracture toughness) of austempering ductile iron (ADI) treated by two-step austempering process were investigated. High Cu content in nodular cast irons leads to a significant volume fraction of retained austenite in the iron after austempering treatment, but the carbon content of austenite decreases with the increasing of Cu content. Moreover, austenitic stability reaches its maximum when the Cu content is 1.4% and then drops rapidly with further increase of Cu. The ultimate tensile strength and yield strength of the ADI firstly increases and then decreases with increasing the Cu content. The elongation keeps constant at 6.5% as the Cu content increases from 0.2% to 1.4%, and then increases rapidly to 10.0% with further increase Cu content to 2.0%. Impact toughness is enhanced with Cu increasing at first, and reaches a maximum 122.9 J at 1.4% Cu, then decreases with the further increase of Cu. The fracture toughness of ADI shows a constant increase with the increase of Cu content. The influencing mechanism of Cu on austempered ductile iron (ADI) can be classified into two aspects. On the one hand, Cu dissolves into the matrix and functions as solid solution strengthening. On the other hand, Cu reduces solubility of C in austenite and contributes more stable retained austenite.

关键词： Cu-alloyed ADI two-step austempering process mechanical properties austenite stability

Effects of Holding Temperature for austempering on Mechanical Properties of Si-Mn TRIP Steel

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Journal of Iron and Steel Research(International) 2004年第6期11卷 40-44页

作者： LI Zhuang WU Di Northeastern University Shenyang Institute of Aeronautical Engineering

A new type of high strength steel containing a significant amount of stable retained austenite was obtained by austempering immediately after intercritical annealing.This sort of low carbon steel only contains alloying elements of silicon and manganese rather than nickel and chromium.Its mechanical properties were enhanced considerably due to strain-induced martensite transformation and transformation-induced plasticity(TRIP)of retained austenite when it was strained at temperatures between Msand Md,because retained austenite was moderately stabilized due to carbon enrichment by austempering.austempering was carried out at different temperatures and 400 ℃ was found to be optimal.Tensile strength,total elongation and strength-ductility balance reached the maximum values and the product of tensile strength and total elongation exceeded 30 135 MPa % when the TRIP steel was held at 400 ℃ and strained at 350 ℃.

关键词： austempering intercritical annealing retained austenite strain-induced martensite transformation transformation-induced plasticity(TRIP) mechanical property