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Journal of Iron and Steel Research(International) 2023年第9期30卷 1843-1853页

作者： Tian-yu Zhang Ling-yu Wang Yu Wang Jun Hu Hong-shuang Di Wei Xu State Key Laboratory of Rolling and Automation Northeastern UniversityShenyang 110819LiaoningChina

Low-temperature ausforming(LT-AF)prior to bainitic transformation leads to a noticeable acceleration of bainitic transformation kinetics;however,the effect of LT-AF on the retained austenite(RA)features and the resulting mechanical properties is still unclear.LT-AF was applied to ultrahigh-strength bainitic steel before austempering.The deformation behavior and the resulting dislocation substructures were investigated by thermomechanical simulator and transmission electron microscopy(TEM).The planar dislocation structures produced during deformation at 350℃ accelerate the bainitic transformation kinetics during isothermal holding.The effect of LT-AF on the bainitic transformation kinetics and the features of RA was elucidated via dilatometer measurement,TEM,scanning electron microscopy,and X-ray diffraction.It is observed that LT-AF not only retains more RA content but also facilitates improved RA stability.This trend is mainly due to the large amounts of planar dislocations in RA and bainitic laths inherited from undercooled austenite caused by LT-AF,the decrease in bainitic sheaves size,and the increase in filmy RA content compared to the sample without ausforming.A large fraction of filmy RA with high stability and the refinement of bainitic sheaves obtained by LT-AF remarkably enhance the strain hardening capacity and achieve significantly better ductility compared to the directly austempered sample.

关键词： Ultrahigh-strength bainitic steel bainitic transformation Low-temperature ausforming Retained austenite Strain hardening rate

Effect of post rolling stress on phase transformation behavior of microalloyed dual phase steel

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Journal of Iron and Steel Research(International) 2024年第3期31卷 688-699页

作者： Wen-quan Sun Sheng-yi Yong Tie-heng Yuan Ting-song Yang An-rui He Chao Liu Rui-chun Guo National Engineering Research Center for Advanced Rolling and Intelligent Manufacturing University of Science and Technology BeijingBeijing 100083China

The slow phase transformation of microalloyed dual phase steel makes the nonuniform stress and temperature fields during the post rolling cooling process have a significant impact on the phase transformation process.Given the relatively slow phase transformation of DP780 steel within the microalloyed dual phase steel series,the influence of stress on the phase transformation behavior of DP780 steel was investigated.To quantify the nonuniform thermal and stress conditions in the steel coil,a thermo-mechanical coupled finite element model of the hot-rolled strip cooling process was established.Based on the simulation data,DP780 steel was chosen as the research material,and Gleeble 3500 thermal simulation equipment was used for experimental validation.The thermal expansion curves were analyzed through regression to establish the dynamic model of DP780 steel phase transformation under stress.Subsequently,metallographic analysis was conducted to determine phase transformation type and grain size of DP780 steel.The results confirmed that the stress promotes the occurrence of semi-diffusion-type bainite transformation.Furthermore,an appropriate level of stress facilitates the growth of bainitic grains,while the increased stress inhibits the growth of ferritic grains.

关键词： Microalloyed dual phase steel Stress bainitic transformation Grain Finite element method

Influence of Vanadium Content on bainitic transformation of a Low-Carbon Boron Steel During Continuous Cooling

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Acta Metallurgica Sinica(English Letters) 2015年第6期28卷 692-698页

作者： Kwang-Su Kim Lin-Xiu Du Cai-Ru Gao State Key Laboratory of Rolling and Automation Northeastern University Department of Materials Kim Chaek University of Technology

The phase transformation behaviors during continuous cooling of low-carbon boron steels with different vanadium contents were studied by means of dilatometric measurement and microstructure observation. The bainite transformation behavior is not noticeably altered when the vanadium content is 0.042 and 0.086 wt%, and these steels exhibit full bainitic microstructure even at a cooling rate of 5 ℃/s. When vanadium content is increased to 0.18 wt%, ferrite is still present in the microstructure even at a cooling rate of 40 ℃/s. Vickers hardness of the steels with 0.042 and 0.086 wt% V is remarkably higher than that of the steel with 0.18 wt% V at a cooling rate higher than 10 ℃/s, and the difference is increased with the increase in cooling rate. Moreover, the amount of coarse vanadium precipitates formed in austenite is increased with the increase in vanadium content. The optimum content of vanadium to obtain bainitic microstructure is 0.086 wt% in this experimental low-carbon boron steels.

关键词： Microalloyed steel Vanadium bainitic transformation Boron Microstructure

THERMODYNAMICS OF bainitic transformation IN Cu-24 at.-% Al ALLOY

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Acta Metallurgica Sinica(English Letters) 1992年第6期5卷 465-467页

作者： XU Zuyao (T.Y.Hsu) ZHOU Xiaowang Shanghai Jiaotong University,China Professor,Department of Materials Science,Shanghai Jiaotong University,Shanghai 200030,China Shanghai Jiaotong Univ Shanghai China

Two driving forces △G^((β_1)+α')and △G^(β_1→β_2+α)for the bainitic transformation have been calcu- lated for Cu-24 at.-% Al alloy.Results reveal △G^(β_1→α')>0 within the transformation tem- perature range 600—750 K.Therefore,the bainitic transformation cannot be initiated by the β_1→α' shearing mechanism.On the other hand,the driving force △G^(β_1→β_2+α)to produce 5% of the α becomes negative only when the composition of the α satisfies x_(Al)~α≤0.204 at 700 K or x_(Al)~α=0.209 at 750 K.So the bainitic transformation can only proceed by β_1→β_2+α diffusional reaction with different diffusion amount at different temperatures.

关键词： Cu-Al alloy bainitic transformation thermodynamics

Combined Reconstructive and Displacive Mechanisms Involved in bainitic transformation

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Journal of Beijing Institute of Technology 2005年第4期14卷 416-419页

作者：苏铁健李树奎王富耻 School of Material Science and Engineering Beijing Institute of Technology Beijing100081 China

TEM observation and analysis have been conducted on bainitie transformation with and without the influence of externally applied tensile sress for alloyed steel 35MV7. Recrystallizafion was found to occur within the bainitic structures transformed at 450 ℃ in cases of both with and without the application of external stress, and coupling between the reconstructive and displacive mechanisms is expected, due to the relatively high holding temperature and high dislocation density yielded with the displacive mechanism. RecrystaUization was not observed within the bainitic structures transformed at lower temperature of 350 ℃, both with and without the application of stress; However, for the stressed specimen, the structure with very fine subgrains was found to be preserved and not reconstructed thermically, due to the low temperature and short holding time.

关键词： bainitic transformation stress reconstructive displacive

Relationship between Relaxation Internal Friction Peak at about 200℃(f≈1Hz)and bainitic transformation In a CuZnAl Alloy

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Journal of Materials Science & Technology 1992年第4期8卷 289-293页

作者：赵增祺陈(弓非)(弓段) 杨大智包耳 Physical Laboratory Baotou Research Institute of Rare EarthBaotou014010China Dept.of Materials Engineering Dalian University of TechnologyDalian116024China Dept.of Materials Engineering Yanshan UniversityQinhuangdao066004 China

The present investigation showed that the re- laxation peak at about 200℃ (f≈1Hz) was related to bainitic transformation in a CuZnAl alloy.The peak decreased when bainite precipitated.The activation energy of the peak was the same as the apparent activation energy of bainitic transforma- tion.According to the relations between the peak and the bainitic transformation,the mechanism of the peak has been discussed.

关键词： internal friction CuZnAl alloy shape memory alloy bainitic transformation

Chro-austempering treatment of a medium-carbon high-strength bainitic steel

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Journal of Iron and Steel Research(International) 2023年第2期30卷 317-327页

作者： Man Liu Jun-yu Tian Feng Cai Cheng-gang Pan Guang Xu The State Key Laboratory of Refractories and Metallurgy The Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of EducationThe Collaborative Innovation Center for Advanced Steels of Ministry of EducationWuhan University of Science and TechnologyWuhan430081HubeiChina Hubei Provincial Key Laboratory for New Processes of Ironmaking and Steelmaking Wuhan University of Science and TechnologyWuhan430081HubeiChina

The integrated processing of chromizing and austempering(termed chro-austempering)treatments was proposed.The microstructure and properties of a medium-carbon high-strength bainitic steel treated by chro-austempering treatments were investigated by metallography,scanning vibrating electrode technique,electrochemical workstation,and microhardness test.The results show that the high-strength bainitic steel with carbide-free bainite as matrix and the chromized layers on surfaces was successfully fabricated by chro-austempering treatment.The hardness of surface layers was about 3.5 times that of the bainite matrix.Meanwhile,the corrosion started from exposed bainitic matrix and proceeded along the depth direction,testifying that the surface corrosion resistance was significantly improved by chro-austempering treatment due to the formation of Cr_(7)C_(3)and(Cr,Fe)7_(7)C_(3)on the surface.

关键词： Chro-austempering Chromizing Austempering bainitic transformation Corrosion resistance Hardness High-strength bainitic steel

Isothermal Aging Kinetics in CuZnAl Shape Memory Alloy

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Journal of Materials Science & Technology 1993年第3期9卷 172-176页

作者： Zengqi ZHAO Lab.of Physics,Baotou Research Institute of Rare Earth,Baotou,014010,ChinaFeixia CHEN Dazhi YANG Dept.of Mater.Eng.,Dalian University of Technology,Dalian,116024,ChinaEr BAO Dept.of Mater.Eng.,Yanshan University,Qinhuangdao,066004,China Baotou Research Inst of Rare earth Baotou China

Isothermal aging behaviours of a CuZnAl shape memory alloy have been investigated by means of dilatometry.The length of the specimens during isothermal aging from 190 to 280℃ increases with the aging time at each temperature.The isothermal aging kinetics fits in Avrami equation and the time exponent n decreases with the increase in aging temperature.The apparent activation energy for the isothermal aging process was measured to be 109.0kJ/mol,which is about equal to that of a relaxation internal friction peak at about 200℃ (f≈1 Hz) in the alloy.

关键词： isothermal aging kinetics CuZnAl alloy shape memory bainitic transformation activation energy

MECHANICAL STABILIZATION OF DEFORMED AUSTENITEDURING CONTINUOUS COOLING transformation IN AC-Mn-Cr-Ni-Mo PLASTIC DIE STEEL

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Acta Metallurgica Sinica(English Letters) 1998年第2期11卷 93-99页

作者： D.S.Liu G.D.Wang X.H.Liu G.Z.Cui Northeastern Univ Shenyang China

The influence of prior austenite deformed at different temperature on the subsequent continuous cooling bainitic transformation has been investigated in an C-Ma-Cr-Ni-Mo plastic die steel. The results show that the prior deformation in low temperature region of austenite retards significantly the bainitic transformation. For the same continuous cooling schedule, as austenite deformed at lower temperature, the quantity of the classical sheaf-like bainite becomes less. The present results show that severe deformation leads to mechanical stabilization of austenite and causes the difficulty of bainitic ferrite propagation into the austenite.

关键词： plastic die steel deformed austenite continuous cooling bainitic transformation mechanical stabilization of austenite

Combined Effects of Nb and B MicroAlloying in Molybdenum Based Ultra Low Carbon bainitic (ULCB) Steels

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Journal of Iron and Steel Research(International) 2011年第S1期18卷 785-791页

作者： Hardy Mohrbacher NiobelCon bvba 2970 SchildeBelgium

ULCB steels have a great potential for structural as well as automotive applications due to the lean alloying concept and the favorable combination of strength and ductility.These steels are being considered as the material of choice for many advanced applications where yield strength above 500 MPa is required to reduce component weight.Traditionally Mo has been a key alloying element in producing such steels.In order to push the property envelope of ULCB steels it is interesting to combine Mo alloying with the microalloying elements Nb and B.Cross effects between these elements bear synergies that cannot be achieved by single alloying.The paper demonstrates how these synergies can be beneficially used in combination with appropriate processing.

关键词： grain refinement bainitic transformation precipitation hardening accelerated cooling tempering