Enhancement of the fatigue strength by application of a low transformation temperature (LTT) welding consumable

Abstract Low transformation temperature (LTT) welding consumables offer the possibility of enhancing fatigue strength in welded components without post-treatment. By lowering the martensite start temperature ( M S ), the volume expansion during transformation near ambient temperature is reduced, which decreases welding-related tensile residual stresses in fatigue-critical areas. To evaluate this effect, longitudinal stiffeners were used. To evaluate this effect, longitudinal stiffeners were used, a LTT and conventional filler serve as welding consumable; also, high frequency mechanical impact (HFMI) treatment was carried out. Three single-pass and six additional-pass sample series were investigated for residual stress and fatigue strength. The additional welds were applied in fatigue-cracked critical areas with different weld shapes, achieved by varying welding parameters. Mechanical tests on reference samples evaluated the properties of the diluted LTT welds. Although reduced toughness was observed, no fatigue cracks occurred in LTT single-pass weld roots. The fatigue strength at two million cycles increased from 81 to 121 MPa compared to conventional welds, while HFMI reached 146 MPa. With an additional LTT weld pass, the results varied from 138 to 196 MPa, depending on the shape and residual stress state. The results show that LTT fillers effectively enhance fatigue performance, and that weld geometry and parameter selection are as critical as the chemical composition for maximizing the LTT effect.