不同冷却速度对M390粉末冶金高速钢组织与硬度的影响

Effect of different cooling rates on microstructure and hardness of M390 powder metallurgy high-speed steel

利用热模拟试验、扫描电镜、X射线衍射、维氏硬度计等研究了M390粉末冶金高速钢的连续冷却相变规律及不同冷却速度对其组织和硬度的影响。结果表明:冷却速度主要影响M390粉末冶金高速钢的基体组织类型;随着冷却速度的增加,基体组织依次为铁素体、铁素体+马氏体以及马氏体。与基体组织的转变不同,冷却速度不改变碳化物的类型,碳化物均为3种类型,即MC型、M_(7)C_(3)型和M_(23)C_(6)型,但是对其尺寸和形态有影响。随着冷却速度的增大,M390粉末冶金高速钢的硬度整体上呈增加的趋势,冷却速度为1℃/s时,硬度出现明显升高,硬度增加的原因主要与基体组织中马氏体的含量和碳化物的弥散强化有关。

The continuous cooling transformation law of M390 powder metallurgy high-speed steel and the effects of different cooling rates on its microstructure and hardness were investigated by thermal simulation test,scanning electron microscopy,X-ray diffraction and Vickers hardness tester.The results show that the cooling rate mainly affects the matrix microstructure of the M390 powder metallurgy high-speed steel.With the increase of the cooling rate,the matrix microstructure is changed from ferrite,ferrite+martensite to martensite.Different from the change of matrix microstructure,the cooling rate does not change the types of carbides.Three types of carbides including MC,M7C3 and M23C6 are distributed in the steel.However,the cooling rate has an effect on carbides’size and morphology.With the increase of cooling rate,the hardness of the M390 powder metallurgy high-speed steel increases as a whole,and when the cooling rate is 1℃/s,the hardness increases obviously.The reason for the increase of hardness is mainly related to the content of martensite in the matrix and the dispersion strengthening of carbides.