Combined hardening and non-hardening embrittlement of an interstitial free steel

The ductile-to-brittle transition temperature (DBTT) and hardness of an interstitial free steel solid-solution-strengthened by phosphorus are experimentally evaluated under different conditions. The results demonstrate a linear relationship between DBTT and hardness under constant phosphorus grain boundary concentration and grain size. The DBTT increases with increasing hardness, showing a hardening embrittlement effect. With reference to a previous study concerning the effect of phosphorus boundary segregation on the ductile-to-brittle transition for the same steel, which shows a non-hardening embrittlement effect, it is seen that the two embrittlement effects are independent of each other and that the combined embrittlement effect under an average grain size of ~ 70 μm can be expressed as DBTT (°C) = 0.24HV + 1.60CP − 34.8, where HV is the Vickers hardness value and CP is the phosphorus boundary concentration in at.%.