高温轴承钢M50连续冷却转变曲线的测定与分析

Determination and Analysis on Continuous Cooling Transformation Curve of High Temperature Bearing Steel M50

利用膨胀法在DIL805A型淬火膨胀仪对高温轴承钢M50(/%:0.82C,4.25Cr,4.17Mo,1.03V)开展了临界点测定及冷却速度0.02~40℃/s的连续冷却转变试验,并绘制了静态CCT曲线,结合室温下的显微组织以及维氏硬度分析,系统研究了冷却速率及奥氏体化温度(1 000℃和1 120℃)对高温轴承钢M50组织转变以及静态CCT曲线的变化影响。结果表明:高温轴承钢M50的临界点不受奥氏体化温度影响,Ac_(1)与Accm温度分别为808℃和852℃;珠光体转变的临界冷速为0.05℃/s,奥氏体化温度的提高促进了马氏体转变起始温度的降低以及贝氏体转变区间在静态CCT曲线上的右移,并且显著提升了高温轴承钢M50在较低冷却速率条件下的室温硬度。

The critical point measurement and continuous cooling transformation test with cooling rate 0.02~40 ℃/s of high temperature bearing steel M50(/%:0.82 C,4.25 Cr,4.17 Mo,1.03 V) are carried out by expansion method in DIL805 A quenching dilatometer,and the static CCT curve is drawn.Combined with the microstructure and Vickers hardness analysis at room temperature,the effects of cooling rate and austenitizing temperature(1 000 ℃and 1 120℃) on the microstructure transformation as well as the static CCT curve of high temperature bearing steel M50 are systematically studied.The results show that the critical point of high temperature bearing steel M50 is not influenced by austenitizing temperature.The temperatures of Ac;and Accm are 808 ℃ and 852 ℃ respectively;the critical cooling rate of pearlite transformation is 0.05 ℃/s.The increase of austenitizing temperature promotes the decrease of the initial temperature of martensite transformation and the right shift of bainite transformation interval on the static CCT curve,and significantly improves the room temperature hardness of high temperature bearing steel M50 at lower cooling rate.