Microstructural and mechanical effects of nickel and manganese on high strength steel weld metals

摘要

Neural network modelling suggested that the impact strength of high-strength steel weld metals could be increased at moderate expense to yield strength once Ni additions are made in a controlled manner with respect to Mn. Based on these predictions, shielded metal arc welding was used to prepare weld metals with Ni at 7 and 9 wt.% while Mn was at 2.0 or 0.5 wt.%. Tensile testing showed that these new weld metals have yield strengths between 720 and 850 MPa. Charpy toughness levels up to 113 J at -40℃ were recorded. It was found that once Ni exceeds a critical point, which depends on Mn concentration, toughness decreases. LOM, SEM, TEM and APFIM was used to characterize the microstruc-ture that consisted of retained austenite, martensite and bainite. EDX and SIMS showed segregation of Mn and Ni to dendrite boundary regions. APFIM brought greater understanding of the microstructural composi- tion at a local level. Correlations were made between the microstructure and mechanical properties.