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1 Machine Dynamics Problems

1 2002

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Numerical Investigations of Residual Stresses During Wet Underwater Welding Considering Phase Transformations

Mahrenholtz O., Gross A.

Machine Dynamics Problems

2002

Vol. 26, No. 4

53-68

The aim of this work is to adapt the finite element method to the special problems of underwater wet welding. Besides the description of the heat transfer to the water the change of the microstructure is an important problem which has to be taken into account simulating the wet welding process. A phenomenological model describing the transformation kinetics is integrated in the finite element simulation. The necessary material parameters for the description of the transformation kinetics can be inserted from CCT and CHT diagrams, which are available for most of the weldable steels. A butt weld is investigated to simulate the temperature field, the evolution of the microscructure and the residual stresses. The calculated phase transformations are compared via the hardness. The residual strains inside the workpiece were measured with the neutron diffractometrie method. The results of the numerical simulation show that the material behaviour plays an important role in the analysis of the residual stresses. Young's modulus, yield strength, hardening and dilatation coefficient are measured depending on the microstructure. Simulations with the determined material behaviour lead to better agreement with the measured residual strains. In further investigations different solutions for reducing the residual stresses and the fraction of brittle phases in the weld and the HAZ are developed and tested with the adapted finite element procedure. The temperature field and the phase transformation in the weld and the heat-affected zone of a butt weld were calculated varying the welding parameters and using further heat sources. The comparison with the results of a simple wet weld shows that one proposed method leads to a reduced fraction of martensite.