The role of residuals and alloying elements in temper embrittlement

Abstract

A brief review of the general metallurgical properties of temper brittleness in low alloy steels emphasizes that this intergranular embrittlement is sensitive to essentially two categories of independent variables: the chemical composition of the grain boundaries (segregation of the solutes on an atomic scale), as well as the ‘mechanical-microstructural’ parameters of the alloy (microstructure and strength of the matrix, morphology of the carbides and grain boundaries, etc.). This paper, essentially devoted to the former, reviews and discusses the available segregation data in the light of recently proposed models. The segregation potencies and embrittling powers of the various impurities are compared, and their dependence on the alloy’s metallic components through chemical interaction between both types of solutes is particularly emphasized. The link between segregation and solubility in multicomponent systems and its use as a predictive means for impurity segregations is outlined. The discussion aims at showing that temper embrittlement is in no way a unique phenomenon, specific to low alloy steels, as was formerly considered, but rather a strikingly illustrative case of multicomponent segregation induced embrittlement, where some metallic alloying elements, although not embrittling per se , can drastically enhance the segregation of residual impurities, while some others can be used as scavengers to alleviate it.