HEAT INPUT AND DILUTION EFFECTS IN MICROALLOYED STEEL WELD METALS

The sensitivity of weld metal microstructure and mechanical properties to variations in both heat input (i.e., cooling rate) and weld diluti on in submerged arc (SA) welding of microalloyed steel was examined. W eldments were prepared with weld metal dilutions of approximately 40% and 70% at heat inputs of 2.0, 3.3, 4.6, and 5.3 kJ/mm, using two comm ercial welding wires and a basic commercial flux. The high dilution we lds, which were ordinary bead-on-plate welds, resulted in microstructu res that ranged from ferrite with aligned second phase at low heat inp uts to acicular ferrite at high heat inputs. Special over-welding tech niques were used to make the low dilution welds, allowing use of the s ame welding parameters as those for the high dilution welds. The techn ique involved remelting of weld metal to simulate the effect of multip ass welding. The microstructure of these welds was predominantly acicu lar ferrite, independent of heat input. As a consequence, the low dilu tion welds had superior toughness compared to the high dilution welds.