Microstructure and mechanical properties of plasma arc welding joint for laser melting-deposited AerMet100 ultrahigh-strength steel

The repair of laser melting-deposited AerMet100 ultrahigh strength steel(UHSS) heat-treated samples with groove machined was conducted by low-cost plasma arc welding(PAW). And the microstructure and mechanical properties of welding joint were examined by optical microscopy(OM), scanning electron microscopy(SEM), X-ray diffraction (XRD), micro-hardness test and the tensile mechanical test. The experimental results indicated that the welding zone with low hardness values mainly consisted of columnar grains with about 200μm width which epitaxial growth from substrate grains, and in which the cellular morphology character appearing at the bottom in comparison with dendrite with lateral branching appearing at the top. Three zones, i.e., sufficient quenched zone, insufficient quenched zone and high-temperature tempered zone, were divided by heating affected temperature and microstructure characteristic in heat affected zone (HAZ), and there was a lowest hardness value region distributed in high-temperature tempered zone. Compared to that of undamaged heat treated forged one, the tensile mechanical property of the repaired laser melting deposited sample got a few decrease but was still well, in which the tensile strength σ_b, yield strength σ_s, elongation δ₅ and reduction of area Ψ was 1627Mpa, 1285Mpa, 10.5% and 45% respectively. In addition, the isothermal thermal simulation test surveyed that the tensile fracture position locating in high-temperature tempered zone with the lowest hardness value could ascribe to the growth of alloy carbide and increase of reverted austenite in over-aged temperature.