Role of minor addition of B in submerged arc weld metal for 500 MPa grade seismic steel plates

Abstract

In this study, we investigated the effects of boron content on the toughness of a 500 MPa-class structural steel weld. Submerged arc welding was performed using welding consumables with boron contents of 0, 0.001, and 0.003 wt% for heat input conditions of 34, 42, and 56 kJ/cm, respectively. The addition of boron reduced the grain boundary ferrite (GBF) and ductile–brittle transition temperature, resulting in improved impact toughness. Moreover, the addition of 0.001 wt% boron further increased the toughness of the weld metal. This was because the presence of boron at the austenite grain boundaries reduced its surface energy, thus delaying ferrite nucleation. In addition, the minor boron element prevented the formation of grain boundary ferrite (GBF) structures during solidification, and an acicular ferrite structure was created in the alloy during sufficiently slow cooling rates (higher heat input condition).