Abstract
In this study, we attempted to evaluate the residual stress distribution in welds accompanied by phase transformation using X-ray stress measurement. First, relationship between the phase transformation behavior and the residual stress of welded specimens with different phase transformation was discussed. In the specimen with martensite in the weld, reduction in tensile stress due to martensite transformation shown in residual stress distribution followed conventional behavior. However, in the specimen with bainitic ferrite in the weld, the residual stress in the transverse direction was almost the same as the residual stress in the longitudinal direction, and the residual stress did not follow conventional behavior. Next, X-ray elastic constant in the weld was measured, and then the residual stress was reevaluated. In the specimen with bainitic ferrite in the weld, X-ray elastic constant had anisotropy, and the reevaluated residual stress followed conventional behavior. In conclusion, it was shown that depending on the phase transformation behavior, it is difficult to use X-ray elastic constant estimated by Kröner model; however, if we use the measured value, we are able to evaluate the residual stress more accurately.
Highlights
It is well known that the residual stress from the welding process affects the various fracture strengths of a welded structure [1]
In the specimen A, which had martensite in the weld metal, the calculated X-ray Young’s modulus (Ehkl) and X-ray Poisson’s ratio in the longitudinal and transverse directions were almost the same values, and the value was almost the same as the value estimated by the Kröner model
In the specimen B, which had bainitic ferrite, the X-ray Young’s modulus and the X-ray Poisson’s ratio in the longitudinal and transverse directions were not the same value and showed anisotropy, and the value in the longitudinal direction was larger than the value estimated by the Kröner model
Summary
It is well known that the residual stress from the welding process affects the various fracture strengths of a welded structure [1]. The analytical evaluation of weld residual stress accompanied by phase transformation has been attempted by relating these residual stress behaviors with the cooling rate and modeling them [7, 8], the phase transformation behavior is affected by various materials science factors. It is not always realistic to accurately evaluate the weld residual stress using only an analytical approach It would be significant if we were able to evaluate complex residual stress distributions in welds accompanied by phase transformation in detail through an experimental approach using the nondestructive technique represented by X-ray stress measurement. We used specimens with different phase transformation and evaluated in detail the residual stress distribution using X-ray stress measurement, focusing on the effect of phase transformation on the residual stress distribution. Welding current l (A) Welding speed v (mm/s) Shielding gas Shielding gas flow rate (e/s)
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