Determination of Critical Strain Rate for Solidification Cracking by Numerical Simulation

Hot crack prevention during welding processing of metallic materials is an essential prerequisite of component safety. The causes of solidification cracking can be attributed to the occurrence of metallurgical and thermomechanical effects. Even though numerous hot cracking test procedures have been developed until now, unexpected solidification cracking during component welding cannot be avoided, since specifically in the hot cracking test the thermomechanical conditions and the local crack-critical strain rates around the weld pool may be very different from those in the component. In the presented numerical analyses, contrary to the well-known energy distribution models (according to Goldak for example), the experimentally determined weld pool geometry has directly been implemented as a 3D-function into the numerical simulations and thus conduced to high computational accuracy. The investigations were carried out using nickel-base Alloy 602 CA, since its solidification resistance exhibits a significant dependence on the shielding gas, which enabled studies of hot crack-critical as well as hot crack-uncritical material behaviour. Validation was carried out with the help of the MVT-test which allowed additional variation of the specimen loading rate. Numerical calculation of the solidification crack-critical limiting temperature versus various welding parameters and the investigated shielding gases could be performed. In order to provide a transferability of hot cracking tests to components, critical specimen loading rates were determined and the local crack-critical strain rates in close vicinity of a weld pool were calculated. It is demonstrated that the local critical strains and strain rates represent a crack criterion for a transferability.