Characterization and modeling of fracture behavior of spot welded joints in hot-stamped ultra-high strength steels

The development of ultra-high strength, hot-stamped manganese-boron steels (22MnB5) for the application in automotive production has established new potentials for lightweight construction, which combine thin sheet thicknesses and reduced weight with high strength and optimized passive safety performance. In this paper characterization and simulation methods for the failure behavior of spot welded components made of 22MnB5 are shown. Spot weld models are presented, which describe crack initiation in the softened heat affected zone (HAZ) around the spot weld, crack propagation into the components and thereby the influences of the softened HAZ on the component behavior. Therefore the deformation and fracture behavior of the different material zones of the spot welded joints have been characterized and modeled. The failure behavior of spot welded joints in hot-stamped 22MnB5 has been investigated and modeled under different loading types. To validate the simulation models, simulations have been carried out and compared to the results of a special component test with simple boundary conditions, which realizes crack initiation in the softened zone.