Abstract: The wire cutting and corrosion of the three-pins shaft part were carried out， and the microstructure observation results showed that there was severe mixed crystal phenomenon in the area with the highest cold deformation rate of the three-pins shaft head. Through in-depth exploration of this phenomenon， it was analyzed that the reason for mixed crystals in this area is due to the significant deformation experienced on both sides of the shaft head during the cold extrusion process of the three-pins shaft. During the high-temperature carburizing process， small grains fused with each other， ultimately forming coarse grains. In order to eliminate coarse grains on both sides of the shaft head of the three pin shaft component， different normalizing and annealing pretreatment processes were adopted to cause a large amount of AlN compounds in the material to precipitate again and form segregation at the grain boundaries， forming new AlN precipitates that play a strong role in pinning the grain boundaries. The normalizing and annealing pretreatment processes with different process parameters can improve the austenite grain size of the three-pins shaft parts to varying degrees. The best pretreatment scheme for improving the effect is the pre normalizing process above 900 ℃. The adoption of this scheme can improve the grain size of the three-pins shaft parts that were originally severely mixed， and the grain size of the three-pins shaft parts can reach 7.0 or above.

Key words: Three-pins Shaft, Grain, Normalizing, Annealing

摘要： 对三销轴零件进行线切割与腐蚀，显微组织观测结果表明，三销轴轴头冷变形率最大的区域存在严重的混晶现象。对此现象进行深入探究，分析该区域混晶的原因为三销轴冷挤压过程轴头两侧区域经历了极大的形变，高温渗碳过程细小的晶粒相互融合，最终形成粗大的晶粒。为消除三销轴零件轴头两侧区域的粗大晶粒，采用不同的正火与退火预处理工艺，使材料内的AlN化合物再次大量析出，并在晶界处形成偏聚，形成新的AlN析出相起到了强力钉扎晶界的作用。不同正火与退火预处理工艺，均可不同程度改善三销轴零件的奥氏体晶粒度，改善效果最佳的预处理方案为900 ℃以上预正火工艺。采用该方案可使原本混晶严重的三销轴零件的晶粒得到改善，三销轴零件晶粒达到7.0级以上。

关键词: 三销轴, 晶粒, 正火, 退火