Corrosion Study of Base Material and Welds of a Ni–Cr–Mo–W Alloy

Abstract

Alloys containing chromium (Cr) and molybdenum (Mo), as the major alloying elements, are widely used in various industries where the material experiences corrosive environments. Chromium (Cr), when added in an optimum amount, forms a Cr2O3 passive film which protects the underlying metal in aggressive solutions. Molybdenum (Mo) forms its oxides in the low pH solutions, thus, enhances the uniform corrosion resistance of an alloy in reducing acids and assists in inhibition to localized corrosion. Minor alloying elements, like tungsten (W) and copper (Cu), also improve the overall corrosion resistance of an alloy in specific solutions. In the present study, corrosion resistance behavior of commercial iron-based alloys (316L SS, 254 SMO and 20Cb3) and nickel-based alloys (Monel 400, Alloy 625 and C-276) was studied in the acidic solutions. While the corrosion behavior of wrought alloys has been widely studied, there is little to no information on the corrosion performance of their welds, typically being the weak regions for corrosion initiation and propagation. Therefore, an attempt was undertaken to investigate the uniform and localized corrosion performance of base metal, simulated heat-affected zone and all-weld-metal samples of a Ni–Cr–Mo–W alloy, C-276. The study was conducted in aggressive acidic solutions. Various corrosion and surface analytical techniques were utilized to analyze the results.