研究了38CrMoAl钢表面获得超细贝氏体组织的热处理工艺及其组织结构特征。首先利用自行设计的滴注式可控气氛全自动渗碳炉，在930℃对该钢渗碳8h，使钢表面的碳的质量分数达到0．85％，渗层深度为2mm。将经过渗碳热处理的试样加热到930℃保温20min进行奥氏体化处理。然后直接淬入温度分别为230、255和280℃的盐浴中，并分别保温0．5、1、2、4、10h后空冷。利用光学显微镜、透射电镜、X射线衍射仪及显微硬度计对热处理后38CrMoAl钢渗碳层的组织和性能进行分析研究。结果表明，该钢经过230和255℃保温一定时间后均获得较佳的组织结构，其组织特征是，表层是超细贝氏体组织，由平均尺寸为80～120nm的贝氏体铁素体层片和分布于片问平均厚度为几纳米到几十纳米的残余奥氏体膜组成；过渡层是超细贝氏体和马氏体的混合组织；心部是马氏体组织。这种超细贝氏体的滚动接触疲劳性能明显优于常规淬火回火状态下的齿轮材料。
The heat treatment to obtain ultrafine bainite in the surface layer of 38CrMoAI steel and the microstruc- ture characteristics of ultrafine bainite were investigated. The samples carbonized at 930 ℃ for 8 h were heated at 930℃for austenitization and then isothermal quenched at different temperatures in salt bath. The microstructures were investigated in the carburized layer by optical microscopy and transmission electron microscopy （TEM）, and the hardness was tested by HV-sclerometer. The results show that the samples which were isothermal quenched at 230 ℃ for 10 h and 255℃ for 4 h have obtained ultrafine bainite in the surface layer. The plate of ultrafine bainitic ferrite was as thin as 80 nm and film of retained austenite can reach a thickness of several nanometers; the mix- structures of the ultrafine bainite and low carbon martensite were formed in the transition layer, the low carbon martensite was formed in the center. The ultrafine bainite exhibits high rolling contact fatigue performance com- pared to the martensite under conventional quenching and tempering.
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