Fatigue properties of austempered ductile iron-to-steel dissimilar arc-welded joints

The structural design of mechanical systems increasingly leads to the adoption of different materials in order to improve the performance of a structure. A possible solution is the adoption of dissimilar arc-welded joints, which often must be able to withstand high cyclic loads under service conditions. Being a recently available joining technology, the design standards and recommendations do not report fatigue strength categories for dissimilar joints, therefore dedicated investigations are necessary. In the present contribution, the fatigue behavior of EN-JS-1050 austempered ductile iron-to- S355J2 steel dissimilar arc-welded joints has been experimentally investigated to determine the fatigue strength categories of some typical welded details and to compare them with the categories provided by standards and recommendations for homogeneous welded steel joints. First, dissimilar joints were evaluated by metallographic analysis, then micro-hardness profiles were measured. Experimental fatigue tests were performed on (i) partially-penetrated butt-joints and fully-penetrated ground butt joints under axial loading and (ii) fully-penetrated butt joints and cruciform non-load-carrying fillet-welded joints under four-point bending loading. All joints were in the as-welded conditions. The fracture surfaces of the joints were analyzed to identify fatigue crack initiation locations