Evaluation of the ductile-to-brittle transition temperature shift due to temper embrittlement and neutron irradiation by means of a small-punch test

Abstract

By means of a small-punch testing technique, the effects of heterogenous intergranular impurity segregation and neutron irradiation on the ductile-to-brittle transition temperature (DBTT) of impurity-doped and undoped alloy steels were investigated. It was found that antimony-doped steels and, in particular, non-homogenized steels with extremely heterogeneous intergranular dopant segragation frequently show initiation of microcracks as indicated by the appearance of serrations in the load-deflection curves. In this case the ductile to brittle transition is spread out over a wider temperature range than for tin- or phosphorus-doped steels as well as for undoped steel. The upper and lower bounds of the DBTT are uniquely correlated with the maximum and average values of the impurity segregation concentration distributed along grain boundaries. These relationships demonstrate the embrittling potency of the segregants, in agreement with results obtained from Charpy V-notch tests. Neutron irradiation of tin-doped steels caused the DBTT to shift to higher temperatures than that of undoped steels. The experimental results suggest a linear correlation between the DBTTs obtained from small-punch tests and those obtained from Charpy V-notch tests, as predicted by a recently developed kinetic model.