Henry Granjon Prize Competition 2005 Winner, Category B “Materials behaviour and weldability” Microstructure and Properties of Novel High Strength Steel Weld Metals

Abstract

The relationship between alloying content, microstructure and properties has been studied for high strength steel weld metals with 7 wt. % nickel. Following neural network predictions, shielded metal arc welding was used to produce experimental welds with manganese at 0.5 or 2 wt. %, while carbon was varied between 0.03 and 0.11 wt. %. High manganese was positive for strength but very negative for impact toughness while manganese reductions lead to large impact toughness increases. Carbon additions up to 0.11 wt. % were found to increase yield strength to over 900 MPa while impact toughness was maintained and over 60 J was recorded at −100 °C. High resolution microscopy was used to characterise the microstructure. In dendrite core regions a mixture developed of predominantly upper bainite and a coarse grained, previously not documented constituent, characterised to be coalesced bainite. In interdendritic regions mainly martensite formed for high manganese weld metals. Manganese reductions were found to promote upper bainite while carbon additions were found to promote martensite. A constitutional diagram was constructed that summarises microstructure as a function of manganese and nickel contents. Mechanical properties of the weld metals were rationalised in terms of the relative amounts of the different microstructural constituents.