Influence of carbon, manganese and nickel on microstructure and properties of strong steel weld metals Part 3 -: Increased strength resulting from carbon additions

Neural network predictions suggested that the strength of a high strength steel weld metal with 7 wt-% nickel and 0(.)5 wt-% manganese could be increased significantly at moderate expense to impact toughness by additions of carbon. Based on this, three experimental weld metals were produced with carbon contents between 0(.)03 and 0(.)11 wt-%. Mechanical test results were in agreement with predictions. At low carbon content the microstructure was largely bainitic in dendrite core regions whereas martensite was found at interdendritic regions. From microstructural studies and dilatometry experiments it was found that carbon stabilised austenite to lower transformation temperatures and that the microstructure became more martensitic in nature. Effects on strength and impact toughness were explainable in terms of a refinement of the microstructure and tempering behaviour.