Toughness improvement by Cu addition in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels

The effect of microstructure and Cu addition in a simulated coarse-grained heat-affected zone (CGHAZ) of a high-strength low-alloy (HSLA) steel subjected to 100 kJ cm −1 heat input welding was studied. It has been observed that the primary microstructure in Cu-free HSLA steels is dominated by bainite, whereas, in Cu-bearing HSLA steels, the predominant microstructure is acicular ferrite. The acicular ferrite nucleated at intragranular complex inclusions consisting of Al and Ti oxides, covered with layer of MnS and CuS. The presence of high intensity of acicular ferrite and hard impingements between acicular ferrite laths or plates has contributed to the fine-grained and interlocked microstructure. The enhanced toughness in CGHAZ of Cu-bearing HSLA steel is attributed to the fine-grained interlocked microstructure of acicular ferrite.