Mixed mode fatigue crack growth behavior of Ni-Cr-Mo-V high strength steel weldments

The extensive use of Ni-Cr-Mo-V high strength steels in modern marine environment poses increasing requirements for accurate characterization of the fatigue crack growth (FCG) behavior of their welded joints. The present work reported a study on a new generation Ni-Cr-Mo-V high strength steel concerning the mixed mode FCG behavior of its welded joint. Effects of microstructure and welding residual stresses (WRSs) were emphasized. It was found that the 4% compliance offset criterion in the conventional ASTM procedure and the 10% offset criterion in the normalized ASTM procedure were suitable for determination of the crack opening force of high strength steel weldments. A new effective stress intensity factor range parameter as the crack growth driving force was proposed, which yielded fairly good correlation for the mixed mode FCG data. Acicular ferrite with basket-weave microstructure in the weld metal exhibited favorable crack growth resistance relative to the base material and was preferred to the welded joints. The attained master or intrinsic FCG curves for the base material and the weld metal on the basis of the proposed parameter provided a basic database for the design of high strength steels employed in modern marine structures.