Compressive residual stresses in LTT elongated bead welded in all positions for fatigue crack prevention of boxing fillet joints

Abstract

Authors previously proposed the LTT (Low Transformation Temperature) elongated bead method, through overlaying a welding bead on the conventional weld surface of boxing fillet welded joints for reduction of stress concentration at the weld toe and prevention of fatigue crack occurrence. Its feasibility was verified through limited experiments on a boxing fillet joint fabricated in flat welding position. In this study, the authors employed a newly developed flux cored 16Cr-8Ni LTT welding wire and proposed procedures for all welding positions, including arc-weaving procedure for flat position, paralleled continuous multi-pass procedure for horizontal position, arc on/off procedures for overhead position and vertical position, respectively, to prevent molten metal drop. Subsequently, adhering to the proposed welding procedures, large-size welding specimens were fabricated, and corresponding numerical models considering dilution between LTT welding material and base metal were developed to analyze the compressive residual stress distribution in the boxing fillet welded joint with LTT elongated bead. Finally, the analyzed residual stress was validated by experimentally measured results using both the section-cutting contour method and the X-ray diffraction method. The analyzed and measured results demonstrated that the proposed welding procedures can generate large compressive residual stresses with the range from −200 MPa to −800 MPa in the LTT elongated bead, which prevented the fatigue crack even the 6 times of conventional fatigue cracking cycles were set as the run-out cycle in the fatigue tests.