Microstructural Evolution and Mechanical Properties of Simulated Heat-Affected Zones in an Iron-Copper Based Multicomponent Steel

Abstract

NUCu-140 is a recently developed steel that relies on nano-scale Cu-rich precipitates to achieve yield strength levels in excess of 825 MPa (120 ksi). In order for NUCu-140 to be utilized as a structural material, a comprehensive welding strategy must be developed. Since NUCu-140 is a precipitation-strengthened material, this strategy must include a detailed understanding of the precipitate evolution that occurs in the heat-affected zone (HAZ) as a result of welding thermal cycles. A combination of dilatometry, HAZ simulations, and mechanical testing are presented to determine the mechanical properties that develop in the HAZ of NUCu-140. MatCalc kinetic simulations and Russell-Brown strengthening calculations were conducted to model the observed precipitate and mechanical property trends. The microhardness and tensile testing results reveal that local softening is expected in the HAZ of NUCu-140 welds. MatCalc simulations show that a combination of partial dissolution, full dissolution, and re-precipitation of the Cu-rich precipitates is expected to occur in the various HAZ regions. The predicted precipitate parameters are used as input to the Russell-Brown strengthening model to estimate the changes in strength expected due to changes in precipitate features. The measured and predicted strength levels exhibit very good quantitative agreement for the low-heat-input simulations and reasonable qualitative agreement for the high-heat-input weld simulations.