Effect of Cu and B addition on tempering behavior in the weld CGHAZ of high strength low alloy plate steel

To understand the effect of Cu and B on mechanical properties of the weld coarse-grained heat-affected zone (CGHAZ) of high strength low alloy plate steels, six alloys including different Cu and B content were prepared. The CGHAZ and tempered conditions were simulated by a Gleeble simulator and mechanical properties were measured by Vickers hardness test and charpy impact test. Toughness of as-welded specimens was deteriorated with comparing to base steels and decreased with increasing Cu + B content. Meanwhile, Vickers hardness showed an opposite tendency, which is due to formation of martensite in the weld CGHAZ. For as-tempered conditions, Vickers hardness at first decreased with increasing tempering temperature and then was reinforced at around 550 °C with an unexpected decrease of toughness, which was mainly due to the precipitation of Cu particles and carbides, such as (Ti, Nb)C and (Mo, Mn)₂C.