在扭转疲劳试验中，非调质钢FAS2340半轴零件性能比调质钢42CrMoH零件高出50％以上。为研究其原因，对上述两种半轴零件进行了研究。金相观察发现，在感应淬火过程中FAS2340钢中形成大量规则排列的微小质点，经TEM和相分析对比发现，质点主要由未熔解的渗碳体颗粒构成，并且占总数70％以上Fe3C质点尺寸分布在5~9nm范围内。大量的Fe3C质点促进零件表层晶粒细化，并在随后的淬火冷却过程中形成均匀细小的马氏体组织，零件使用性能得到显著提高。
Mechanical properties of Semi-axle of non-quenching and tempering steel (FAS2340) was improved and was 50% higher than quenched and tempered steel (42CrMoH) in torsion fatigue test. In order to clear the reason, two Semi-axles of FAS2340 and 42CrMoH were investigated. Microstructure shows that a large number of reticular small particles are formed in FAS2340 during induction hardening. According to results of TEM and Phase analysis, the small particle is constituted mainly by no-melting cementite particles, and the Fe3C particles (diameter: 5-9nm) are more than 70%. The austenite grain size of hardened layer is refined accordingly. Then, fine and uniform martensite laths are formed in following quenching process. Performance of parts significantly is increased due to refining microstructure.
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