Relaxation of Welding Residual Stresses by Reversed and Repeated Loadings

Abstract

The relaxation behavior of welding residual stresses by both reversed and repeated loadings was experimentally investigated using austenitic stainless steel JIS SUS316 and weldable high strength steel of JIS SM490A. The weld bead was deposited by electron beam welding on the plates of both materials along their longitudinal center lines. After welding, small size longitudinal welded joint specimens of SUS316 and medium size ones of SM490A with the center hole notch were cut out from the welded plates.
Eighteen small size welded joint specimens of SUS316 were subjected to reversed loading and 16 medium size ones of SM490A were subjected to repeated loading with the parameter of maximum stressand number of cycles imposed. Then the residual stress distributions of the plates were measured by the cut-release method. The result showed that welding residual stresses at the notch root were considerably relieved by the first one cycle of both repeated and reversed loadings and then gradually relieved with the following loading cycles. Also found was that welding residual stress in as-welded condition was more effectively relieved by repeated loading than reversed one.
In addition to the relaxation test, comparative fatigue tests were carried out of center hole-notched longitudinal welded joint and base metal specimens. The fatigue test result led to the conclusion that the fatigue strength of the longitudinal welded joint of SM490A by repeated loading decreased approximately 15 MPa than that of the base metal in the life regime up to 8×10⁶ cycles. On the contrary, the fatigue strength of longitudinal welded joint of SUS316 by reversed loading only decreased in the high cycle regime over than 10⁵ cycles.