Application of laser peening without coating on steel welded joints

Purpose - Laser peening without coating (LPwC) is an innovative surface enhancement technology for introducing compressive residual stress in metallic materials. The purpose of this study is to examine the characteristic at the laser-peened welded zone and the fatigue lives of the welding joints. Design/methodology/approach - LPwC conditions for 490 MPa grades of structural steels were selected. By using the conditions, the characteristic at the laser-peened welded zone, residual stresses, hardness and roughness of welding toes were examined. Moreover, the fatigue lives of the toes of box-welded joints and butt welded joints pre-treated by LPwC were compared to the fatigue lives of those that were not pre-treated by LPwC. Findings - The main results are: LPwC conditions for 490 MPa grade steels were established; residual stresses, Vickers hardness and roughness at the laser-peened welded zone were revealed; and LPwC can dramatically extend the fatigue life of welded joint. Originality/value - The effects of LPwC on structural steels, which are widely used in bridge members, have not been well clarified; the effect of LPwC on welded zones in these structures is particularly unclear. If LPwC can be carried out such that compressive residual stress is imparted on structural steels and the welded zones in the bridge members, the fatigue lives of bridge members will be greatly increased. The paper fills some of these gaps.