Fracture toughness of martensitic stainless steel resistance spot welds

摘要

The paper is focused on the strength and fracture toughness of AISI420 martensitic stainless steel resistance spot welds under the tensile-shear loading. The failure behavior of AISI420 spot welds was featured by quasi-cleavage interfacial failure with low load bearing capacity and weak energy absorption capability which was a function of the weld fusion microstructure, predominately carbon and chromium rich martensite plus 8-ferrite. Fracture toughness of the fusion zone proved to be the most important factor controlling the peak load of the spot welds made on AISI420 failed in interfacial mode. A geometry-independent fracture toughness of the weld nugget Cc.a. 23 MPam~(0.5)) was determined using fracture mechanics concept. Through modeling it was found that there is a critical fracture toughness which beyond that the pullout failure mode can be obtained which is a function of sheet thickness and tensile strength of the base metal.