LAUSR

Abstract Laser-arc hybrid welding of AISI 420 martensitic stainless steel (MSS) was carried out, and the microstructure-toughness relationship was discussed and established. The coarse-grained heat affected zone (CGHAZ) is the weakest area of the weld. The CGHAZ microstructure and the toughness assessed by Erichsen cupping test had a good agreement with the increase of heat input, indicating that the toughness was not only dependent on the grain size but also the contents of inter- and intra- granular carbides within the CGHAZ. By introducing the effects of the carbides, an equivalent grain diameter (D e ) was proposed to establish a new Hall-petch relationship between the CGHAZ microstructure and the toughness, whose fitting degree was increased from 0.677 to 0.974. The weld toughness was acceptable to meet the rolling requirement when the D e was smaller than 11 μm, under which the weld fractured along the base metal rather than the CGHAZ.