To investigate the weldability of A533-B steel plates, simulations of the coarse grained region of heat affected zone (with heat inputs of 10, 20 and 30 kJ cm(-1)) followed by inter-pass heating at 300 degrees C and post-weld heat treatments at 590 degrees C were carried out. The microstructural evolution, the hardness and the toughness of the simulated heat-affected zone were studied. With heat inputs of 10 and 20 kJ cm(-1), both of the simulated microstructures contain mixtures of lower bainite and auto-tempered martensite. With heat input of 30 kJ cm(-1), the simulated microstructure is composed mainly of lower bainite. The Charpy impact toughness has also been measured for the simulated heat input specimens, which were treated by inter-pass heating at 300 degrees C and post-weld treatment at 590 degrees C. (C) 2009 Elsevier B.V. All rights reserved.