Welding using low transformation temperature (LTT) filler materials is an innovative approach to mitigate detrimental welding residual stresses without cost-intensive post weld-treatments [1, 2]. Due to the local generation of compressive residual stresses in the weld line by means of a delayed martensite transformation a significant enhancement of the cold cracking resistance of highly stressed welded components can be expected. For the effective usage of these materials a deeper understanding of the microstructural evolution inside the weld material is necessary to determine the complex processes that cause the residual stress formation during welding. Solid-state phase transformation kinetics and the evolution of strain in LTT weld filler materials are monitored in-situ at the instrument ID15A@ESRF in Grenoble. The transferability to real components is implemented by using a realistic MAG welding process under consideration of structural restraint. During welding of multilayer joints, the phase transformation and phase specific strain evolution of each individual layer is investigated in transmission geometry by means of energy-dispersive X-ray diffraction EDXRD using high energy synchrotron radiation with a counting rate of 2.5 Hz. The measurement results of a 10% Cr / 10% Ni LTT weld filler are compared to data monitored for the conventional weld filler material G89. The in-situ data clearly indicate a strong effect on the local strain evolution and the formation of compressive strain. This results from the restraint volume expansion during the postponed austenite to martensite transformation of the LTT weld filler, which counteracts the thermal shrinkage. In contrast, for the conventional weld filler material the thermal contraction strains lead to tensile residual strain during welding. Furthermore, the results of in-situ observation during welding show that the transformation kinetic is dependent on the welding sequence.
In-situ analysis of the strain evolution during welding using low transformation temperature filler materials Short Title: In-situ analysis of the strain evolution during welding using low transformation temperature filler materials Article Type: Research Article
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