球墨铸铁凸轮轴的激光表面熔凝处理

Laser Surface Melting Process for Camshaft Made of Ductile Iron

分析了激光表面熔凝处理后球墨铸铁凸轮轴硬化层的组织和性能特点 ,并与其它强化方法进行了比较。结果表明 ,采用适当的激光表面熔凝处理工艺参数 ,可以在表面获得搭接均匀、表面硬度大于 80HRA和厚度达1 0mm的硬化层 ;硬化层由熔凝层和淬硬层组成 ,其中熔凝层的基体组织主要为细小、均匀并且有一定方向性的亚共晶莱氏体 ,淬硬层主要由石墨球及其周围的硬质环、细马氏体和铁素体基体所组成。与其它铸铁凸轮轴强化方法相比 ,激光表面熔凝处理具有表面硬度高、组织细小均匀、零件畸变小和不影响心部性能等优点。

Microstructure and properties of the hardened layer on ductile iron camshaft strengthened by laser surface melting process were investigated, and also compared with these of the ones strengthened by other methods. The results show that a uniform hardened layer with the thickness of almost 1.0 mm and hardness of 80HRA is obtained on ductile iron camshaft surface strengthened with an appropriate laser surface melting process. The hardened layer can be divided into two zones including a melted layer and a quenched layer. The microstructure in the melted layer is a uniform, fine and orientational hypoeutectic ledeburite mainly, while the microstructure in the quenched layer is composed of some spheroidal graphite surrounded by hardened shell, fine martensite and ferrite. Compared with the other strengthening methods, the camshafts strengthened by laser surface melting process possess some advantages, such as much finer micro-structure, much higher hardness, less distortion and no changes in core's properties.