Effects of nickel on the critical cracking potential of 29Cr-4Mo ferritic stainless steels in a hot chloride solution

Abstract

Although much research has been performed on the effect of nickel on the chloride SCC of ferritic stainless steels, most is concerned with the influence of nickel content on the SCC susceptibility in views of time to failure. However, there is lack in data about the effect of nickel on the critical cracking potential (E[sub cc]) that is a potential above which SCC does occur. The time to failure places an emphasis on the reaction rate of SCC, whereas the E[sub cc] provides an electrochemical criterion whether or not SCC occurs for given alloy/environment systems. E[sub cc] for low interstitial ferritic stainless steels has been demonstrated to be a potential for crack initiation and is determined by the competing rates of generation of fresh surface by slip-induced film breakdown and repassivation. The objective of this research is to investigate the effects of nickel on the E[sub cc] of low interstitial ferritic stainless steels, placing emphasis on clarifying the reason that small amounts of nickel significantly increase the chloride SCC susceptibility of these materials.