The effect of boron on the wear behavior of iron-based hardfacing alloys for nuclear power plants valves

The effect of boron of Fe–Cr–C–Si alloys, replacing Stellite 6 traditionally used in nuclear power industry, on the high temperature wear resistance was characterized. Sliding wear tests of Fe–Cr–C–Si–xB (x = 0.3, 0.6, 1.0 and 2.0 wt%) alloys were performed in air at temperatures ranging from 300 to 725 K under a contact stress of 103 MPa. Low-boron alloys containing less than 0.6 wt% boron showed the excellent wear resistance than any other tested alloys in an elevated temperature. The improvement was associated with the matrix hardening by promotion of the γ → α′ strain-induced martensitic transformation occurred during wear. In addition, protective oxide layers formed on the contacting surface reduced the wear loss by minimizing the direct metal-to-metal contact. However, high-boron alloys containing more than 1 wt% boron showed somewhat larger amount of wear loss than low-boron alloys due to the absence of the strain-induced martensitic transformation and the presence of the brittle FeB particles connected with easy crack initiation.