Microstructural evolution of simulated heat affected zone in ASTM A533 type B steel plates

In order to investigate the weldability of ASTM A533 type B steel plates, simulated heat affected zone (HAZ) experiments with heat inputs of 20, 50, and 80 kJ cm⁻¹ were carried out. The thermal cycles used corresponded to the actual thermal cycles that occur in the coarse grained region of the real HAZ. The microstructural development and the toughness of the simulated HAZ were studied. It was found that with a heat input of 20 kJ cm⁻¹ the simulated HAZ microstructure gives larger amounts of lower bainite with significant amounts of auto tempered martensite. In the cases of heat inputs of 50 and 80 kJ cm⁻¹ both the simulated HAZ microstructures were composed chiefly of upper bainite. The specimen obtained from the simulation of a heat input of 20 kJ cm⁻¹ possesses higher toughness than those obtained from the simulations of heat inputs of 50 and 80 kJ cm⁻¹ Furthermore, the results also indicate that the tempering response is more sensitive in autotempered martensite than in bainite.