ニオブ炭化物による鉄基合金の表面硬化処理

抄録

A modified coupled-diffusion method using iron intermediate layer has been investigated for the surface modification of steels. The process consists of two stage heat-treatments. On the first stage heat-treatment for the diffusion of carbide forming element, Nb, solute distribution profile showed bending points at the concentrations where intermetallic phases, FeNb and Fe₂Nb, were formed. The distribution of carbide volume fraction after carbon diffusion on the second stage heat-treatment was dependent upon the concentration profile of niobium on the first stage heat-treatment. The specimen subjected to the two-stage heat-treatment had a modified surface layer consisting of NbC layer about 15 μm thick on the surface and the carbide volume fraction decreased toward the steel substrate. It was demonstrated that the specimen having such a microstructure showed a promising effect to suppress a crack formation in the carbide layer.