Microstructure of high carbon and high boron ferroalloy made with hybrid powder/wire overlaying under nitrogen protection

In order to improve the low toughness and crack initiation of the overlayed high boron iron-based alloy (HBIA), HBIA was prepared by adding nitride ferrochrome and nitride-former under nitrogen protection. The effect of alloying element N on the microstructure and properties of prepared HBIA was investigated by the microstructure, micro zone composition and hardness tests. The results indicate that the microstructure of HBIA with N₂ protection consisted of primary crystal Fe₂B, α-Fe+Fe₂B eutectic structure and granular M(C, N) compound. N addition brought lots of M(C, N) compound precipitations and resulted in structure refinement of the primary Fe₂B, and cracking in the overlay was also restrained. The microhardness of HBIA rapidly increased to 67.8 HRC due to adding nitrogen. However, excessive N₂ would result in incomplete growth of Fe₂B phase and slight decrease of hardness.