胎圈钢丝用SWRH72A钢的连续冷却转变曲线OA

The continuous cooling transformation curves of SWRH72A steel at cooling rates of 1-40 ° C/s were determined using a thermal expansion phase change instrument.Optical microscopy and microhardness testing were employed to analyze the microstructure and Vickers hardness at different cooling rates.The results show that the critical phase transformation temperatures Ac1 and Ac3 of SWRH72A steel were 692.7 ℃ and 759 ℃,respectively.At cooling rates of 1-30 ℃/s,pearlite transformation predominates,resulting in a microstructure composed of sorbite,pearlite,and a small amount of ferrite.The content of ferrite and pearlite gradually decreased with increasing cooling rate,while the sorbite formation rate rised from 84.4％to 90.06％,and hardness increased from 306 HV to 376.8 HV.When the cooling rate exceeded 30 ℃/s,lamellar martensite was observed in the microstructure,with the overall composition consisted of sorbite and martensite,indicated simultaneous pearlite and martensite transformations.As the cooling rate accelerated,the martensite content increased progressively,and hardness rised from 409.8 HV to 426.4 HV.At the same initial cooling temperature,faster cooling rates led to lower phase transformation start and finish temperatures,as well as shorter time required to complete the microstructural transformation.