Manufacturing and predicted fatigue behaviour of welds using the low-transformation-temperature (LTT) effect

Fatigue strength often governs the design of welded steel. Conventional methods to improve fatigue performance, such as post-weld grinding or hammer peening, require additional manufacturing steps and are rarely applied in practice. An alternative approach is the Low-Transformation-Temperature (LTT) effect, which introduces compressive residual stresses via controlled martensitic phase transformations during welding. In this work, the submerged arc welding process was adapted to implement LTT welding using in situ alloying with commercially available high-alloy filler wires, enabling reproducible stress modification without additional post-treatment. Macroscopic weld inspection confirmed consistent geometry and defect-free seams, while EDS analysis revealed uniform chromium and nickel distribution. Hardness mapping showed a significant increase up to approximately 450 HV10, indicating successful martensitic transformation. Evaluation of an extended European fatigue database including LTT welds demonstrated fatigue strength improvements of 11 to 60 % for butt-welded joints and longitudinal stiffeners. Planned fatigue tests with precisely controlled cyclic loading and strain measurements will further quantify fatigue performance and scatter. These initial results confirm that LTT welding is a promising and cost-effective method to enhance fatigue strength in welded steel structures.