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Effect of low-temperature ausforming on bainitic transformation and mechanical properties in ultrahigh-strength bainitic steel

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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 ***-AF was applied to ultrahigh-strength bainitic steel before *** 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 *** 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 *** is observed that LT-AF not only retains more RA content but also facilitates improved RA *** 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

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 *** reveal △G^(β_1→α')>0 within the transformation tem- perature range 600—750 ***,the bainitic transformation cannot be initiated by the β_1→α' shearing *** 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 *** 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 *** peak decreased when bainite *** activation energy of the peak was the same as the apparent activation energy of bainitic transforma- *** 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

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 *** 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 *** 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 *** on the simulation data,DP780 steel was chosen as the research material,and Gleeble 3500 thermal simulation equipment was used for experimental *** thermal expansion curves were analyzed through regression to establish the dynamic model of DP780 steel phase transformation under ***,metallographic analysis was conducted to determine phase transformation type and grain size of DP780 *** results confirmed that the stress promotes the occurrence of semi-diffusion-type bainite ***,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

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 *** 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 *** 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 *** hardness of surface layers was about 3.5 times that of the bainite ***,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

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 *** steels are being considered as the material of choice for many advanced applications where yield strength above 500 MPa is required to reduce component *** Mo has been a key alloying element in producing such *** order to push the property envelope of ULCB steels it is interesting to combine Mo alloying with the microalloying elements Nb and *** effects between these elements bear synergies that cannot be achieved by single *** 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

Nucleation Mechanism for Bainite

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Journal of Materials Science & Technology 2002年第1期18卷 1-2页

作者： Xi ZHANG, Xuejun JIN and T.Y.Hsu(Xu Zuyao)School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200030, China [ Manuscript received October 8, 2001] Shanghai Jiao Tong Univ Sch Mat Sci & Engn Shanghai 200030 Peoples R China

Based on the experimental results that solute-depleted zone was observed in Cu-28Zn-4AI (mass fraction) at 523 K, AG is calculated as a positive according to the thermodynamic criteria for the spinodal decomposition of a ternary systems. So, the solute-depleted zone cannot be formed by spinodal decomposition. Dislocation density required by the formation of solute-depleted zone is estimated greater than 7.89×109 cm-2, according to the segregation of solute atoms around dislocations, which is not consistent with the practical situation for the alloy at 523 K. Associated with the internal friction experimental fact that internal friction peaks appear within the incubation for bainitic transformation in Cu-Zn-AI alloy, the equilibrium temperature, TO, is evaluated as 433 K for solute-depleted Cu-25Zn-3.4AI, which is lower than the experimental temperature 523 K. Thus, nucleation by shear mechanism is impossible in this circumstance. Therefore, it is concluded that, like bainite in steels and Ag-Cd, bainite in Cu-Zn-AI alloys nucleates by diffusional mechanism, just implied by the experimental existence of solute-depleted zone.

关键词： bainitic transformation Prebainitic phenomenon Solute-depleted zone Diffusion Nucleation