Effect of Welding Process on Microstructure and Impact Toughness of Welds in High Nitrogen TiN Steel

Abstract

The effect of welding process on the microstructure and impact toughness of high-nitrogen TiN EH36-TM steels was evaluated. In the weld metals of SSAW and TSAW, GBF was created along PAGB, and AF and a small amount of PF were observed in the grain. In TSAW with low basicity and high heat input, GBF was remarkably developed, and intragranular AF was more coarse. In the EGW weld metal, GBF was hardly generated and composed of intragranular AF and PF. As the heat input increased, the size of PAGB was increased and PF was developed at the FL, and in FL+1, the grain size of AF and PF was coarsened. Meanwhile, the FL of EGW showed a similar size without grain size growth compared with FL+5. Among the three welding processes applied, weld metals of SSAW and EGW well met the values required by the classification for the EH36 steel, but the weld metal of TSAW was insufficient. HAZ of high-nitrogen TMCP steels satisfy the value required by the classifications without significant change even when welding at various input heat conditions, and in particular, the weld metal of the high heat-input EGW showed relatively stable values from FL to FL+5.