Abstract
In order to develop materials having corrosion resistance and wear resistance, NbC dispersed overlay weld alloys were formed on mild steel by a plasma powder welding process using mixed powders of NbC and Ni-50 mass%Cr alloy. The microstructure and hardness of these overlay weld alloys were studied by using SEM, TEM, EPMA and the hardness tester.
The matrix was contaminated by a large amount of Fe from mild steel and became the γ-phase, Fe(Ni, Cr) solid solution. Most of NbC was dispersed nearly uniformly as unmelted particles in the matrix alloy. A part of NbC was melted in the molten pool, and during solidification primary NbC, eutectic (γ+NbC) and eutectic (γ+NbC+M23C6) appeared.
With increasing mixing ratio of NbC, the hardness of the overlay weld alloys increased and reached HV370 at 60 mass%NbC.
The solidification process of the matrix alloy and the effects of the solidification structure on hardness were discussed by observation of the morphology and distribution of carbides.
