In-situ measurement of stress and solid state phase transformation in low temperature phase transformation weld metal by synchrotron X-ray during welding process

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Reduction of welding residual stresses due to introduction of volume expansion via martensitic low temperature phase transformation has received more attention. In order to predict and control the mechanical performance and microstructure of welded structures, it is necessary to clarify the formation mechanism of stress and microstructure during the welding process. Therefore, we developed an in-situ measurement system using synchrotron X-rays, which allows simultaneous measurement of the phase transformation and stress during the welding process. We succeeded in measuring the time variation of the stress distribution and microstructure between the weld metal, heat affected zone, and base material, with the fastest time resolution (0.1 seconds) in the world. By using the in-situ measurement system to observe the entire specimen, we found that stress formation was largely responsible for the solid phase transformation and thermal contraction in the welding continuous cooling process.