Fatigue improvement in high-strength steel welded joints with compressive residual stress

In order to improve fatigue properties of gusset fillet welded joints in high-strength steels, intensification of compressive residual stress around the weld toe was studied using computer simulations of welded joints with low transformation temperature (LTT) weld metal. A boxing fillet weld metal of elongated bead shape is most effective for the formation of compressive residual stress. An elongated bead is also preferable for the reduction of stress concentration at the weld toe. In the case of a 70-mm-long elongated bead formed using LTT weld metal with martensite start temperature (Ms) of 150 °C (indicated by Ms 150 °C), a residual compressive stress of about −450 MPa was formed at the weld toe position, whereas in the case of conventional boxing fillet welding using conventional weld metal (Ms 500 °C), a residual tensile stress of 450 MPa was formed at the weld toe. Fatigue measurements of gusset fillet welded joints with an elongated bead were conducted using 800-MPa grade steel plates. Results showed that the elongated bead welding method achieved a significant improvement in fatigue properties. It is equal to the fatigue lifetime of welded joints treated using high-frequency peening methods such as high-frequency impact treatment and ultrasonic impact treatment.