Influence of Post Welding Heat Treatments on Mechanical Properties of 300 Maraging Steel Welded by Plasma Arc Welding

Abstract

Maraging steels combine good weldability with superior mechanical properties compared to other ultra-high-strength steels, which makes them highly attractive for aerospace applications. However, the elevated temperatures reached during the welding process can influence their mechanical properties. This study analyzed the influence of post-welding heat treatments on the microstructural and mechanical behaviors of 300 maraging steel weld beads. To achieve this, joints produced by plasma arc welding were subjected to various heat treatments: solubilization at 820°C for 1 h, followed by artificial aging at 480°C for 3 h, or only aging at 480°C for 3 h. Morphological characterizations and mechanical tests were performed using optical and scanning electron microscopies, microhardness mapping test, and uniaxial tensile test. The results showed microstructural and mechanical modifications in the joints that were submitted to post-welding heat treatments. In the fusion zone, austenite islands were observed in both heat treatment conditions. It was calculated that the weld that underwent solubilization followed by aging heat treatment had a higher percentage of the phase (7.17%) than the weld that underwent only aging heat treatment (3.33%).  It was observed that the aging heat treatment on the weld beads promoted greater mechanical resistance compared to the solubilization followed by aging heat treatment. This behavior can be attributed to the reduced presence of austenite in this region. The use of an aging heat treatment in the joint promoted an average ultimate tensile strength of 1741 MPa, a value close to that required for welded components of motor envelopes (1765 MPa).