Hard laser cladding layers were formed using high speed tool steel powder: JIS SKH40. After cladding, specimens were tempered in order to improve mechanical properties. Cladding layers are composed of both solidified and heat affected structure. Network shaped eutectic carbides are formed in the solidified structure. In close vicinity to the solidified boundary, carbide shape of heat affected zone is transformed into spheroidal and hardness increase. Mean hardness of as deposited cladding layer is around 840HV. By tempering, hardness increases up to around 1000 HV. Though tempering increases bend fracture strength of cladding layer, the maximum strength is around 60% of HIPed specimen. By tempering at 520°C or 560°C, cladding layers have equivalent wear-resistance to that of HIPed specimen.

In order to clarify the effect of change in carbon concentration on the growth of the compound layer on nitrided steel, we researched on the temporal change of concentration of the alloy elements in the surface layer and phase structure of the compound layer on nitrided steels containing various carbon concentrations in the matrix. As the result, it came out that the phase structure in the compound layer was caused by varying through time of carbon concentration distribution in the compound layer. Furthermore, it found out that the temporal change in the carbon concentration distribution occurred because both concentration of carbon from the matrix to the compound layer and decarburization from the surface of the compound layer to the atmosphere were affected by the gradient change of carbon potential in the through-thickness direction of the compound layer.