The trend towards more material and energy efficiency through lightweight design requires the use of high strength steels. These steels tend to form brittle mi-crostructures during welding processes and therefore, they are particularly susceptible to cold cracks. Cold cracks are from the quality point of view problematic. They arise in the welded joints during cooling when the local combination of brittle microstructure, tensile stresses and diffusible hydrogen reaches a critical limit.
In this thesis, a cold crack assessment method is presented and validated. It is based on a multi-step approach. Critical combinations of the three cold crack influence parameters- brittle microstructure, tensile stresses and hydrogen concentration- are identified using an enhanced simulation and testing center Gleeble 3500. The experimental results form the basis of a material specific cold cracking criterion which are implemented in a new developed cold crack simulation tool. In addition to the cold crack criterion, the locally FE- calculated weld cold crack influence parameters are introduced to the cold crack simulation tool. The cold crack susceptibility of the local FE- calculated cold crack influence parameters is then quantitatively predicted by means of the cold crack criterion. The transferability of the identified cold crack criterion on complex welded components is proved.
The work includes:
1-Enhancement of the physical welding simulation for the testing of the cold crack susceptibility.
2-Determination of a material specific cold crack criterion for 100Cr6, HDT1200M and C45
3-Development of a cold crack simulation tool
4-Material characterization under Laser beam welding conditions
5-Implementing of the approach on Gleeble specimens and an industrial component.