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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8 h,使钢表面的碳的质量分数达到0.85%,渗层深度为2 mm。将经过渗碳热处理的试样加热到930℃保温20 min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、10 h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80~120 nm的贝氏体铁素体层片和分布于片间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 process and microstructure of ultrafine bainite in 38CrMoAl steel were studied. First of all, a drip-type controlled atmosphere automatic carburizing furnace was designed and carburized at 930 ℃ for 8 h to make the mass fraction of carbon on the steel surface reach 0.85% and the depth of the infiltration layer was 2 mm. The sample after carburizing heat treatment was heated to 930 ℃ for 20 min for austenitizing treatment. Then quenched directly into salt baths at 230, 255 and 280 ° C, respectively, and incubated in air for 0.5, 1, 2, 4 and 10 h, respectively. The microstructure and properties of the carburized layer of 38CrMoAl steel after heat treatment were analyzed by optical microscope, transmission electron microscope, X-ray diffraction and microhardness tester. The results show that the steel obtained better microstructure after holding at 230 and 255 ℃ for a certain period of time. The microstructure of the steel is characterized by superfine bainite microstructure consisting of bainitic ferrite with an average size of 80-120 nm Tensile and distribution in the sheet between the average thickness of a few nanometers to tens of nanometers of residual austenite film; transition layer is a mixture of superfine bainite and martensite; the heart is martensite. This super-fine bainite rolling contact fatigue performance significantly better than the conventional quenched and tempered gear material.