The Effect of Martensite Phase Transformation on Weld Residual Stress Distribution in High-Strength Steels – A Computational Study

High tensile residual stresses in a weld region are detrimental to the integrity and performance of welded structures. They are one of the controlling factors for hydrogen embrittlement, stress corrosion cracking, weld fatigue, to name a few. Residual stresses form in a welded structure as a result of non-uniform thermal expansion and contraction during the welding operation. Phase transformations, in particular the formation of martensite in steels, can have a profound influence on the local distribution of residual stresses in the weld. Recently, there have been heightened interests and research on utilizing low temperature austenite to martensite phase transformation to reduce the weld residual tensile stress. In this work, an integrated thermal-mechanical-metallurgical weld model is applied to systematically quantify the effect of martensite phase transformation on the formation of weld residual stress. The effect of martensitic phase transformation temperature, thermal expansion, strength of martensite relative to the base metal, and weld parameters are systematically studied. Gleeble and in-situ neutron diffraction experiments are performed to develop the constitutive relation of the steels having the martensite phase transformation. Results are presented and discussed for a thick-section seam welded high-strength pipeline steel as showed in Figure 1. Compressive stress is observed in weld toe (Figure 1b) using filler metal with low temperature martensitic phase transformation compare to tensile stress using conventional filler metal (Figure 1a). Also, stress distribution for a lap-joint of thin-gage advanced high-strength steel for an automotive body structure application is discussed.

(a)

(b)

Fig 1. Comparison of longitudinal weld residual stress distributions in a seam weld of pipeline steel using (a) the conventional weld filler metal, and (b) a special filler metal with low-temperature martensite phase transformation.