Phase transformation and mechanical properties in laser continuous heat treatment welds

The transformation and mechanical properties of the laser continuously heat treated welds of 2205 duplex stainless steel were investigated. The results showed that the central region of the weld metal is characterized by a high amount of austenite, while nearly equal level of ferrite and austenite is presented in the heat affected zone. The microstructural examination indicated that the secondary austenite precipitate at the front of the phase boundaries between the ferrite and austenite, which are considered as its preferential nucleation sites. It was demonstrated that the laser continuous heat treatment can eliminate the problems such as excessive ferrite and intermetallic phases and the secondary austenite can also be formed during the laser continuous heat treatment. The refined grain and secondary austenite formation in continuously heat treated welds result from the longer transformation time and the faster cooling rate. The optimal mechanical properties and an acceptable ferrite/austenite ratio throughout the weld regions correspond to the power level. The continuous heat treatment can improve the toughness of the weld and cause a change in the failure mode from quasi-cleavage to dimple rupture.