Continuous cooling phase transformation behavior of extra large replacement ring steel HG80
The thermal expansion curve of HG80 steel during continuous cooling was measured using the Formator-FⅡ thermal expansion phase change instrument.The continuous cooling transformation curves(CCT curves)of the experimental steel were plotted based on the microstructure and Vickers hardness,and the effect of different cooling rates on its microstructure transformation was analyzed.The results show that during the continuous cooling,HG80 steel undergoes a phase transformation from austenite to ferrite,pearlite,bainite and martensite.When the cooling rate is less than 0.1 ℃/s,the microstructure of the HG80 steel is ferrite and pearlite,and the microhardness is relatively low,which is 214 HV2.When the cooling rate is 0.3-0.5 ℃/s,the microstructure consists of ferrite,pearlite and bainite,and the microhardness increases to 240 HV2.When the cooling rate increases to 3 ℃/s,the microstructure is ferrite and bainite,and the microhardness is 299 HV2.When the cooling rate is 5-20 ℃/s,the microstructure is bainite and martensite,and the microhardness increases rapidly.When the cooling rate is greater than 20 ℃/s,only martensitic transformation occurs,and the microhardness reaches its highest value of 571 HV2.
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