High strength weld metal design through nanoscale copper precipitation

Highlights: • Hardness map of all weld metal shows clearly the hardness variation. • Morphology and characterization of copper precipitation in welds is observed. • Mechanism of copper precipitation by welding thermal cycling is proposed. • Methodology for strengthening weld metal by copper precipitates is demonstrated. - Abstract: Deployment of advanced steels with superior yield and tensile strengths, as well as, toughness, ballistic and shock resistance is challenged by the lack of matching filler metals that can yield similar mechanical properties. In this research, strengthening of the weld metal through rapid formation of nanoscale copper precipitates, during reheating, within a ferrite matrix was proposed. A weld metal containing a nominal concentration of 2.49 wt.% Cu, without any precipitation reaction, was soft 300 HVN. On precipitation of nanoscale copper precipitates, with an average radius of 2.2 ± 0.45 nm and a high number density of 2.9 × 1023 m−3, the hardness increased by 50–100 HVN. The magnitude of this increase was inversely related to the peak temperature. The precipitation and extent of strengthening was rationalized based on thermodynamic calculations and Russell–Brown model, respectively