An appraisal of certain factors which influence toughness restoration (de-embrittlement) in some temper embrittled low alloy steels

Abstract

This paper describes and assesses the various factors which affect the degree of de-embrittlement, ΔFATT, of a selection of embrittled low alloy steels after a simple tempering heat treatment. It has been shown that the degree of de-embrittlement was variable and could be divided into two separate sets of data depending upon the embrittled fracture mode characteristics. The steels which failed in a wholly intergranular manner, predominantly the nickel-containing steels, exhibited large ΔFATT values of between 150 and 250°C. However, the non-nickel-containing steels, viz. the Cr-Mo and Cr-Mo-V steels, fractured in a mixed mode fashion, which comprised intergranular failure and transgranular cleavage, and exhibited much lower levels of toughness rejuvenation. When the raw data were corrected for grain size effects it was clear that the bulk phosphorus content of the steels significantly influenced the extent of de-embrittlement. Also when the de-embrittlement data were portrayed in terms of the embrittled condition toughness, FATT EMB, and corrected to a constant composition and grain size, it was observed that the degree of toughness restoration, ΔFATT, was insensitive to FATT EMB.