Effect of heat treatment on crack growth resistance of 420NiMo hard-faced coating applied on DIN 21CrMoV5-11 steel substrate using submerged arc welding (SAW)

In this study, the effect of heat treatment on the crack growth of 420NiMo martensitic stainless steel coating, applied using the submerged arc welding (SAW) process on a DIN 21CrMoV5-11 steel substrate, is investigated. Samples were heat-treated under different thermal cycles: stress relieving, annealing, and solution annealing. Subsequently, fracture toughness of the specimens was evaluated using the J-integral method and the Crack Tip Opening Displacement (CTOD) method. Microstructural characterization of the specimens revealed that the delta ferrite phase was approximately 11.2, 7.5, and less than 1 % for the stress-relieved, annealed, and solution-annealed specimens, respectively. Moreover, fracture mechanics evaluations showed that the 420NiMo martensitic stainless steel clad, solution annealed at 1050 °C, exhibited a higher fracture toughness. This increase in toughness is primarily attributed to the elimination of the delta ferrite phase from the grain boundaries and the dissolution of carbides within the microstructure during this thermal cycle.