Effect of nickel and tin additions on formation of liquid phase in copper bearing steels during high temperature oxidation

Abstract

It is well known that nickel is a beneficial alloying element in copper bearing steels as it prevents hot shortness. On the other hand, the addition of tin promotes hot shortness. Though some mechanisms for promoting these phenomena have been suggested, a quantitative discussion has still failed to establish the cause. In the present study, changes in the composition in the vicinity of the scale/metal interface owing to high temperature oxidation were experimentally determined using pure irons with copper, nickel, and tin additions. The experimental findings, such as the fraction of liquid phase and the change in composition in the progress of scale formation, were then explained by thermodynamic considerations using the Fe–Cu–Ni and Fe–Cu–Sn phase diagrams calculated from a computerised thermodynamic database. The thermodynamic considerations were also applied to a quantitative discussion on hot shortness and some measures for preventing hot shortness of copper bearing steels were suggested.