Low Transformation Temperaure Materials and Welding Residurl Stress-Application of the Laser Speckle Method to Strain Measurement in the Welding Process (Report 7)-

Abstract

Recently, materials with low transformation temperature have been investigated for improvement of reliability in welded joint. Due to the introduction of compressive residual stress by using the material, fatigue strength or resistance to cold cracking are improved. In this report the authors examined the effects of phase-transformational behavior on residual stress and their distribution using some basic models and some types of the behavior. Expansions and temperature range of phase-transformation detected in the previous report using the laser speckle strain measurement are also used in this report. Results show that reduction of residual stress from tensile to compressive occurs only with severe restraint condition and low transformation temperature, especially low Mf temperature. In the previous report, the authors suggested the possibility of superplasticity during phase-transformation. Experimental results of residual stress distribution indicated the necessity of consideration for superplasticity by using the low transformation temperature materials.

Analysis of martensite transformation behaviour in welded joint using low transformation temperature welding wire

“…The M s point was clearly lower than the fixed beam result using LTTW O and the result of the strain change by the laser speckle method using LTTW B,R by Muramatsu. [25][26][27][28] O,B and R are one of LTTW. The M s point using LTTW was clearly lower in the fixed beam result than Muramatsu's result of the strain change using LTTW B,R measured by the laser speckle method.…”

“…Furthermore, numerical calculations using the measurement results were carried out to estimate the residual stress. [25][26][27][28] However, a welded structure is different from a welded joint, and the shape of the welded joint or structural restraint influences the generation of residual stress, and so evaluation of welded structures is necessary. The boxing fillet welded joint was adopted as an example of a welded structure, and many papers have reported that the residual stress of the fillet corner region influences the fatigue strength.…”