Cruciform fillet welded joint fatigue strength improvements by weld metal phase transformations

Abstract

A B S T R A C T Arc welding typically generates residual tensile stresses in welded joints, leading to deteriorated fatigue performance of these joints. Volume expansion of the weld metal at high temperatures followed by contraction during cooling induces a local tensile residual stress state. A new type of welding wire capable of inducing a local compressive residual stress state by means of controlled martensitic transformation at relatively low temperatures has been studied, and the effects of the transformation temperature and residual stresses on fatigue strength are discussed. In this study, several LTTW (Low Transformation-Temperature Welding) wires have been developed and investigated to better characterize the effect of phase transformation on residual stress management in welded joints. Non-load-carrying cruciform fillet welded joints were prepared for measurement of residual stresses and fatigue testing. The measurement of the residual stresses of the three designed wires reveals a compressive residual stress near the weld toe. The fatigue properties of the new wires are enhanced compared to a commercially available wire.Keywords fatigue; residual stress; welded joints; weld metal phase transformations. N O M E N C L A T U R Eb 0 = width of the residual stress in tension or in compression e α = thermal expansion coefficient of ferrite e γ = thermal expansion coefficient of austenite h = leg length along the principal member h p = leg length along the transverse member t 1 = thickness of the principal member t 2 = thickness of the transverse member K t = stress concentration factor N = number of cycles to failure R = stress ratio S = stress level T 0 = thermodynamic equilibrium temperature T Ff = ferrite transformation finish temperature T Fs = ferrite transformation start temperature T Mf = martensite transformation finish temperature T Ms = austenite-to-martensite transformation start temperature x = distance from the weld toe T m = undercooling austenite-to-martensite transformation range temperature Correspondence: Ph. P. Darcis.

Development of 16Cr8Ni low transformation temperature welding material for optimal characteristics under various dilutions due to all repair welding positions

“…Ohta et al [8] adopted 10Cr10Ni LTT welding wire and doubled the fatigue strength of corner boxing fillet joint of high-strength steel HT780. Darcis et al [12] reported their results on the fatigue strength of cruciform fillet welded joints using three types of LTT welding wires with Ms temperature in the range 270–360°C. It was found that the fatigue life of LTT welded joints was at least three times longer than that of specimens using conventional welding wire.…”

Effect of Low Transformation Temperature Welding Consumable on Microstructure, Mechanical Properties and Residual Stress in Welded Joint of A516 Carbon Steel

“…Alberry and Jones reported that a reduction in processing temperature can drive the suppression of residual stresses [12]. Low-transformation-temperature (hereinafter LTT) welding consumables that exploit this phenomenon have been developed in recent years [13][14][15][16][17]. Conventional consumables have a transformation temperature of about 500 o C, but in an LTT welding material with Fe-10Ni-10Cr (wt.%) developed by Ohta et al, phase transformation occurred at 180 o C [14].…”

Effects of High Toughness and Welding Residual Stress for Unstable Fracture Prevention

“…Therefore, to prevent unstable fractures, welding residual stress distribution needs to be controlled. To date, some studies have investigated the possibility of using low transformation temperature (LTT) welding to decrease the tensile stress in weld joints, strengthening their mechanical properties and reducing their stress regarding distortion, cracking, and fatigue to improve relevant performance [13][14][15][16][17][18][19][20][21].…”