In recent years,in order to achieve the lightweight of automotive components,countries have continuously explored and developed low-cost high-strength metal materials.Q&P steel has gradually become the mainstream product of automotive high-strength steel with high strength,high ductility and easy weldability.In order to optimize the actual production process,the effect of the original microstructure on the phase transformation behavior of high-strength steel in the process of hot working was investigated.The austenitizing and grain growth of high-strength steel plates with different original microstructure and the phase transition during cooling were observed in situ by dynamic thermodynamic simulation tester,Confocal-Laser-Scanning-Microsco-py(CLSM)and Axia Chemi tungsten filament scanning electron microscope(SEM).The results show that when the final cool-ing temperature is 350 ℃,550 ℃ and 680 ℃,the original microstructure of the high-strength steel plate at the three final cool-ing temperatures is"martensite+ferrite"(M+F),"bainite+ferrite"(B+F)and"pearlite+ferrite"(P+F),respectively.It is found that the critical austenitic temperature(Ac1)of the high-strength steel plate with the original microstructure of"P+F"is 647.9 ℃,which is 417 ℃ different from the critical temperature of austenite grain abnormal growth.The growth mode of austenite grains is grain boundary migration and small grain merger,and the average austenite grain size is 0.66 μm.The mar-tensitic initial transition temperature(Ms)is 362 ℃,so there is a wide hot processing process window,which is conducive to the flexible control of Q&P heat treatment process in industrial production.
high-strength steeloriginal microstructurerule of phase transformationin-situ observationP+F microstructurelightweight
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