Research on the mechanism of Cu addition on the grain boundary characteristics and toughness in CGHAZ of low carbon low alloy steel

Abstract

In this study, the coarse grained heat affected zone (CGHAZ) of Cu-containing/free steels was simulated at various heat inputs by thermal simulator. A comparative study was conducted to reveal the role of Cu addition and heat input in toughness variation by microstructural observation and crystallographic analysis. The results showed that the toughness exhibited a plateau-like variation with heat input increasing, which was mainly determined by the distribution of high angle grain boundary (HAGB). Also, a considerably higher toughness was achieved in Cu-containing steel irrespective of heat input. This attributed to the grain boundary distribution and variation selection. Cu addition weakened the variation selection and promoted the formation of more Bain groups, which helped to increase the fraction of HAGB and improve the impact toughness. In addition, Cu addition resulted in a higher fraction of boundary length in V1/V2, V1/V3, V1/V5 variant pair, which was beneficial to accommodate the transformation strain and release the residual stress, leading to a higher toughness in Cu-containing steels.