Study Of Nodular Cast Iron's Laser Hardened Layer And Its Wear Resistance

Laser heat treatment on nodular cast iron different pearlitic content and distribution was performed, the hardened layer's microstructure and its friction and wear properties have been studied extensively in this paper.Pearlitic content in the matrix of nodular cast iron was changed by normalization. The laser operating parameter were; Laser power P=1000W, scaning speed V=16mm/s, beam diameter D=5.2mm. It has discovered that laser hardened layers of nodular cast iron with different pearlitic content and distribution are different, and they can be divided into three types according to their microstructural characters: (1)Pearlite transformation type; (2)Pearlite+ferrite transformation type; (3)Ferrite transformation type. The investigation concentrated on the following aspects: The influence of normalizing temperature on the hardened depth, the thickness of incomplete quenched zone and microhardness, phase structure of the area around the nodular graphites in hardened layer, the fracture and martensitic dimension of the hardened layer. Temper transformation process and the tempering resistance of the hardened layer.Wear tests bath under the conditions of lubrication and dry have demonstrated that the wear resistance of different kinds of nodular cast iron's laser hardened layer is much better than that of un-laser hardened nodular cast iron. The pearlitic content in the original matrix of nodular cast iron influences slightly on the wear resistance of its hardened layer and hardened layer keeps the lower friction character of nodular cast iron. Wear race surface, debris and wear surface microstructure have been analysed and found that the plastic flowing and nodular graphite shape changing in all types of hardened layers can be resisted in wearing process, this is the main reason that laser hardened layer's wear resistance is so excellent.