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.