Effect of grain boundary character distribution and grain boundary phosphorus segregation on the brittleness of an interstitial-free steel

Grain boundary character distribution and grain boundary P segregation in an interstitial-free steel annealed for up to 4 h at 700 degrees C after cold rolling are investigated using electron backscatter diffraction and Auger electron spectroscopy. During annealing, the recrystallized grain size and hardness of the steel do not change apparently, being similar to 10 mu m and 90HV, respectively, but the number percentage of random high-angle grain boundaries initially increases with increasing annealing time until reaching a maximum at 3 h and then decreases slightly after that. The random high-angle grain boundaries play an important role in the steel embrittlement. Both P grain boundary segregation and ductile-to-brittle transition temperature (DBTT) of the steel increase in the same trend with increasing number percentage of random high-angle grain boundaries. The relationship between DIM and P boundary concentration (C-P) is linear, being expressed as DBIT(degrees C)=3.12C(P)-118.87 (C-P, at%), showing that the annealing treatment of cold-rolled interstitial-free steel should be precisely designed to avoid embrittlement. (C) 2016 Elsevier B.V. All rights reserved.