Effect of post-weld heat treatments on strength and toughness behavior of T-250 maraging steel welded by laser beam

This paper elucidates here the strength and toughness behavior of T-250 maraging steel welded by laser beam under different approaches of three post-weld heat treatments, i.e. aging (A), solutionizing+aging (SA) and homogenizing+solutionizing+aging (HSA). The microstructures of the weld metals with A and SA processes both comprised of finely dispersive Ni₃(Ti, Mo) precipitates, small martensite lath and reverted austenite along the grain boundary. However, in the weld metal with HSA process, it exhibited the same Ni₃(Ti, Mo) precipitate with the large martensite lath and the absence of reverted austenite. The ultimate tensile strength and static toughness of the welded joint with HSA process were 1350.6 MPa and 63.8 MJ m⁻³, respectively. The static toughness has been remarkably improved from 71% to 91% of the applied parent metal compared with that of the welded joint with A process. The present study underscores that the Ni₃(Ti, Mo) precipitate and martensite are significant to ensure the high strength of welded joints. Due to its inconsistent deformation with the matrix of martensite, the reverted austenite has a notable influence on the toughness of welded joints. It shows that the post-weld heat treatments of HSA process can influence the mechanical behavior of welded joints by eliminating the reverted austenite.