Combined APFIM–TEM study of Nb(CN) precipitation in HSLA steel

Abstract The strengthening of high strength low alloy (HSLA) steel has been attributed to the strain induced formation of small carbonitride precipitates during processing that inhibit recrystallisation of the austenite and produce a fine grained steel. The size and number density of the small Nb(CN) precipitates that formed in a HSLA steel containing 0·05 wt-% Nb have been measured after various stages of the thermomechanical process by atom probe field ion microscopy (APFIM) and transmission electron microscopy (TEM). The complementary results indicated that recrystallisation of the austenite during thermomechanical processing was inhibited by the precipitates, and that the mechanism was consistent with a subgrain boundary pinning model.MST/657