Isothermal transformation behavior of super-cooled austenite of EH47 crack-arresting steel
The phase transformation behavior of super-cooled austenite of EH47 crack-arresting steel during isothermal transformation was studied using a high-resolution thermal expansion transformation instrument.The microstructure characteristics of the experimental steel under different phase transformation conditions were characterized using scanning electron microscopy(SEM).Based on the obtained expansion curve and microstructure characteristics,the evolution of super-cooled austenite in the experimental steel under different isothermal transformation conditions was discussed.The results show that at a cooling rate of 40 ℃/s,the starting temperature of phase transformation in the experimental steel is 628-636 ℃.When the isothermal transformation temperature is between 630-570 ℃,the super-cooled austenite in the experimental steel exhibits transformation stasis phenomenon during the isothermal transformation.When the isothermal temperatures are 600 and 570 ℃,the phase transformation products of the experimental steel are a multiphase structure composed of acicular ferrite(AF),bainite ferrite(BF),granular bainite(GB)and martensite(M).When the isothermal temperatures are 540 ℃,510 ℃ and 480 ℃,the phase transformation products of the experimental steel are a multiphase structure composed of AF,bainite(B)and GB,and M disappears.For the experimental EH47 crack-arresting steel,in order to obtain a multiphase structure composed of AF,BF and GB,it is necessary to ensure that the isothermal temperature is between 540-480 ℃ and the isothermal time is not less than 10 min to avoid the appearance of M and other structures in the phase transformation products.
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