The significance of variant pairing in governing toughness of coarse-grained heat affected zone (CGHAZ) in Nb-bearing high strength structural steels

Abstract

We have addressed here a scientific gap of elucidating the significance of Nb on impact toughness of coarse-grained heat affected zone (CGHAZ) in a structural steel, from the perspective of crystallographic structure, particularly, digitization and visualization of variant pairing. At Nb content of 0.03 wt%, there was a dominance of V1/V8 pairing such that the density of low angle grain boundaries (LAGBs) was high. However, with the increase of Nb content to 0.06 wt%, the bainite transformation temperature was decreased in conjunction with the significant decrease in V1/V8 pair and increase in V1/V2 pair. This transition in variant pair from V1/V8 to V1/V2 with increase in Nb content was responsible for superior toughness in CGHAZ together with high density of high angle grain boundaries (HAGBs).