亚临界热处理对复合管高铬铸铁层组织及性能的影响

Effect of subcritical heat treatment on microstructure and properties of high chromium cast iron layer of composite pipe

针对铸态304不锈钢-过共晶高铬铸铁复合管高铬铸铁层硬度不足的问题,采用亚临界热处理来改变复合管过共晶高铬铸铁内层组织及性能。结果表明:亚临界热处理可以有效提升复合管高铬铸铁层硬度,复合管高铬铸铁层的宏观硬度随亚临界热处理温度的升高及保温时间的延长先增加后降低;其中530℃×5 h保温空冷的亚临界热处理使得复合管高铬铸铁层硬度提高最显著,提高了3 HRC左右。复合管高铬铸铁层的室温铸态组织为马氏体、奥氏体、M3C型和M7C3型碳化物;经过亚临界热处理后,析出弥散的M23C6型二次碳化物,降低了奥氏体中含碳量,提高了Ms点,促使奥氏体向马氏体转变。

To solve the problem of insufficient hardness of high chromium cast iron layer of as-cast 304 stainless steel-hypereutectic high chromium cast iron composite pipe,subcritical heat treatment was used to change the microstructure and properties of the high chromium cast iron layer.The results show that the subcritical heat treatment can effectively improve the hardness of the high chromium cast iron layer.The macrohardness of the high chromium cast iron layer increases first and then decreases with the increase of subcritical temperature and holding time.When treated at 530℃for 5 h,the hardness of the high chromium cast iron layer reaches the maximum value,which increased about 3 HRC.The as-cast microstructure of the high chromium cast iron layer is martensite,austenite,M3C and M7C3 carbide.After subcritical heat treatment,the dispersed M23C6 secondary carbide is precipitated,which reduces the carbon content in austenite,increases the Ms point and promotes the transformation of austenite to martensite.