2014 Volume 100 Issue 5 Pages 632-638
Displacement and strain during welding are important parameters for evaluation of weld joint. But in-situ measurement of these values needs non-conductive method because weld joint reaches to high temperature. So we applied electronic speckle pattern interferrometry (ESPI) system to measurement of displacement and strain during gas-tungsten-arc (GTA) welding of 9%Ni steel. This system detects interference of reflected laser illumination from weld joint surface. The change of interference depends on displacement of weld joint surface. ESPI measure-ment starts simultaneously with GTA heating, and continues during cooling after heating finished.
ESPI system reveals behavior of two dimensional displacement distribution during welding and martensitic transformation in weld joint. Quantitated displacement record of certain point in GTA heating area shows detail of martensitic transformation. Martensite start temperature (Ms) analyzed by ESPI result shows higher value than conventional value measured by uniform heating and cooling process. This result shows stress-assisted martensitic transformation occurred in this area, because tensile stress is forced after solidification of weld metal at GTA heating area. Quantitated value of Ms raising corresponds to additional chemical driving force for martensitic transformation. This driving force is estimated using free energy calculation. In the case of this study, this driving force is added as tensile stress at GTA heating area and ESPI result is useful to estimate the value of stress.
