摘要：小四轮拖拉机中变速箱齿轮是关键件，齿轮材料的选用及热处理工艺参数的确定一直是我们探究的主题。原来采用20CrM
Ti材料，热处理工艺为气体渗碳，其渗碳温度高、时间长，易造成晶粒粗大、表面沉积碳黑等缺陷。由20Cr代替20CrM
Ti，热处理工艺采用中温气体碳氮共渗直接淬火的方法。设备为RJJ759T井式炉滴柱式可控气氛控制炉压，渗剂为煤油加液态稀土共渗剂。此工艺共渗温度降至880℃，共渗时间缩至3小时。节约能耗336，因缩孔造成的返修率降低到287，齿轮本身也得到了更好的耐磨性、表面硬度和心部综合机械性能。关键词：齿轮；气体碳氮共渗；工艺参数；耐磨性
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小四轮拖拉机变速箱齿轮工作时要承受强烈的摩擦磨损和高的交变弯曲应力和接触疲劳应力的作用，同时承受着强烈的冲击载荷作用。相应的这些齿轮常见的失效形式有过量磨损、表面剥落，甚至断齿等。因此，齿轮的技术要求是表面具有高硬度、高耐磨性、高接触疲劳强度，而心部应具有良好的综合力学性能。采用20CrM
Ti材料气体渗碳工艺（热处理工艺曲线图1）渗碳温度高930±10℃，渗碳时间长5小时。虽然按图纸技术要求：表面硬度、心部硬度、渗碳层厚度等都能达到。但齿轮内花键缩孔现象明显，返修率高，晶粒粗大，综
f合机械性能下降，材料本身经济性差，热处理生产周期长。本文齿轮以20Cr材料r