利用金相显微镜、扫描电镜等试验手段，研究了经不同工艺预备热处理的9 Cr2 Mo钢的显微组织和碳化物形态、分布及大小，并测定了表面硬度。结果表明，9 Cr2 Mo钢淬火或正火态组织均为马氏体和下贝氏体，还有少量的未溶碳化物及残留奥氏体。钢的淬火组织中马氏体量要比正火组织中的多。经淬火＋高温回火或正火＋球化退火的9 Cr2 Mo钢，其组织均为铁素体基体和不同尺寸的碳化物颗粒，硬度基本能满足切削加工的要求。而经890℃×30 min油淬＋690℃×10 h回火的钢，其组织中碳化物颗粒较均匀细小，是一种良好的预备热处理组织。%Microstructure,morphology and distribution as well as size of carbides in 9Cr2Mo steel preliminary heat treated by different procedures were investigated by means of metallographic microscope and SEM , and its surface hardness was measured too .The results show that the microstructure of 9Cr2Mo steel after quenching or normalizing consists of martensite , lower bainite and small amount of undissolved carbide and retained austenite , and that amount of martensite in the as-quenched steel is more than that in the as-normalized steel .Furthermore , the microstructure of 9Cr2Mo steel hardened and high-temperature tempered or normalized and spheroidized is ferritic matrix with carbide particles different in size , and the resulting hardness is so low that the steel may be smoothly machined .After heating at 890 ℃for 30 min and oil quenching followed by tempering at 690 ℃for 10 h the steel offers fine and uniform carbides which is a proper microstructure developed by preliminary heat treating .
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