Effect of High-Strength Filler Metals on Fatigue

Fatigue life of welded joints is in general independent from the material strength. High-strength materials are only beneficial in the low-cycle-fatigue region due to their increased yield limit. This property leads to their application, for instance, in welded mobile crane structures. The high-cycle fatigue limit, however, depends mostly on the geometry and the metallurgy of the notch. Therefore, an optimized weld process is required to achieve a certain fatigue strength. This paper contributes to the obtainable fatigue limits for thin-walled, high-strength joints regarding an optimization of the gas metal arc weld process for fillet welds without additional post-treatment. A methodology is designed to manufacture welded specimens with minimized production scatter. The specimens were carefully analysed by metallographic studies, hardness, distortion and geometric weld toe measurements. The detailed analysis enables a profound link between experimental fatigue life and weld process settings. For the assessment of the fatigue life of thin-walled specimens, the nominal stress approach and the notch stress method are used. The thin wall thickness is considered in the nominal approach by a thickness correction factor. The experimental results showed that the highest fatigue strength for the specific specimen design in ‘as-welded’ condition can be obtained when using a high-strength metal-cored wire filler in combination with a three-component mixed gas.