Effect of single pass welding heat input on microstructure and hardness of submerged arc welded high strength low carbon bainitic steel

The bead on plate test method was employed to investigate the effect of single pass welding heat input on microstructure and hardness of submerged arc welded high strength bainitic steel. The weld metal microstructure contains very high volume fraction of acicular ferrite regardless of heat input. By contrast, with the increase in heat input, the main microstructure in coarse grained heat affected zone (HAZ) changes from a mixture of lath martensite and ferrite sideplate to full ferrite sideplate. Microhardness measurement showed that maximum hardness values always present at the coarse grained HAZ under lower heat input condition, which indicates that the minimum heat input of experimental steel should be higher than 0.92 kJ mm(-1) to avoid the formation of welding cold crack. The size distributions of complex inclusions in the weld metal are very similar for all heat inputs mainly because the short residence time does not make the inclusion grow rapidly.