The Relation between Ni Content and Temper Embrittlement Behavior in Low Alloy Steels

Abstract

The effect of alloying element, Ni, on the reversible temper embrittlement susceptibility of Ni-Cr low alloy steels was investigated by giving embrittling (step cooling)-reannealing (recovery of embrittlement) treatment cycles with the aid of Charpy impact test and electrical resistivity measurement. The reversible change of resistivity during heat treatment cycle was observed, which amount was directly related to Ni content and reversible change of fracture appearance transition temperature, that is, the amount of reversible change of resistivity became larger as the Ni content or the ΔFATT was higher. The resistivity change during heat treatment cycles involved both irreversible and reversible portions, in which the former came out of tempering process such as dislocation anihilation, carbide precipitation and growth. Thus, reversible portion of resistivity could be separated by tempering the specimen at 600°C for long time prior to the heat treatment cycle.
Fracture mode of Charpy specimens also changed reversively from transcrystalline to intercrystalline along prior-austenite grain boundaries for the first heat treatment cycle, while some smaller interface fracture than prior-austenite grain occurred after the second embrittling treatment.