The role of copper in microstructure and toughness of intercritically reheated coarse grained heat affected zone in a high strength low alloy steel

Abstract

This paper presents an investigation on the role of Cu addition in microstructure and toughness of intercritically reheated coarse grained heat affected zone (ICCGHAZ), aiming at elucidating the influencing mechanism of Cu addition on toughness in terms of reverted transformation, alloying element diffusion and variant selection. The element of Cu has a significant effect on reverted structure and Cu-rich precipitates by influencing the diffusion of alloying elements and variant selection. On the one hand, the addition of Cu changed the diffusion kinetics of Ni and Mn, decreasing the segregation of elements at grain boundaries. Accordingly, the reverted structure at grain boundary with an adverse effect on toughness was reduced. Moreover, Cu addition changed the feature of CP group during variant selection, and thus increased the high angle grain boundary density. On the other hand, Cu-rich precipitates were increased after Cu addition, which was easier to originate crack. But, the ductile character of the reverted structure would overwhelm the harmful effect of Cu-rich precipitates on the toughness. As a result, a higher low temperature toughness with impact energy of 72.8 J at −40 °C was achieved in 1.5Cu steel than that in 0Cu steel (36.3 J).