Abstract
In this study, nuclear grade 2.25Cr–1Mo steel was surface strengthened by quench–polish–quench (QPQ) at two salt bath nitriding temperatures (550 °C and 590 °C). At 250 °C and 450 °C liquid sodium, the fretting wear test was carried out, and the possible effects of salt bath temperature on friction performance and microstructure of different samples were investigated. The results show that the surface of 2.25Cr-1Mo steel after QPQ treatment forms a multilayer structure with a hardness 3.7–5.8 times higher than that of the substrate, while the excessively high nitriding temperature also causes premature failure of the nitride layer of QPQ 590. Compared to the substrate, QPQ 550 and QPQ 590 experienced 40% and 16% reductions in the material loss at 450 °C, and 86% and 57% at 250 °C, respectively. The substrate showed different wear mechanisms in liquid sodium at varying temperatures. At 250 °C, the abrasive wear is dominant, while at 450 °C, the adhesive wear is dominant, accompanied by abrasive wear. The nitrided samples are dominated by abrasive wear in liquid sodium at varying temperatures, accompanied by the corrosion effect of the liquid sodium.
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