Effects of coarse particles,prior austenite grains,and microstructures on impact toughness in heat-affected zone of Mg deoxidation steel plates without or with Al addition

Abstract

The effects of coarse TiN particles, prior austenite grains, and intragranular microstructures on the impact toughness in heat-affected zone of Mg deoxidation steel plates without Al (0Al) or with 0.02 wt-% Al (200Al) were studied from the cleavage initiation and propagation. The coarse particles are mainly TiN. 0.02 wt-% Al addition increases coarse TiN particles (>0.5 μm) from 124 to 151 mm^–3, increases brittle microstructures from 25% to 78%, and increases dislocations between ferrite laths, which impairs the toughness, although the austenite grain size is reduced from 213 to 184 μm. Coarse TiN particles alone can’t govern the brittle fracture with the additional effect of microstructures in the case of intragranular acicular ferrites (IAFs). The importance of intragranular microstructures on preventing crack propagation is greater than that of austenite grain boundaries when the grain size is smaller than a critical size to suppress the IAF formation for ferritic steels.