Effect of Ni content on rolling toughness of laser-parc hybrid welded martensitic stainless steel

Laser-arc hybrid welding of AISI 420 martensitic stainless steel (MSS) was studied by employing three types of commercial filling wires with different Ni content. Weld toughness is dependent on the contents of retained austenite (C-RA) and high-misorientation (> 15 degrees) martensite (C-HM) in the lower part of the weld (LaserZ). As the Ni content of filling wire increases from 13% to 20%, the C-RA and the C-HM increase to about 4% and 57%, respectively. It increases the weld toughness. The crack location of Erichsen sample changes from the fusion line to the BM, but the crack in the LaserZ is not suppressed thoroughly during the rolling with 45% reduction. As the Ni content increases to 66%, the C-RA and C-HM increase to about 12% and 60% respectively. It further increases the weld toughness, and the rolling crack in the LaserZ is suppressed. The general criterion, which only employs Erichsen result to predict whether the weld meets the rolling requirement or not, is not suitable for the MSS, both the C-RA and the C-HM must be taken into account. The toughness improvement was discussed according to crack propagation behavior.