Investigation of compact tensile and fracture mechanical properties of a duplex stainless steel bimetal composite with the interfacial zone

Abstract

The interfacial zone formed in the manufacturing process of bimetal or laminated metal composites owes complicated microstructures and properties. This special feature greatly affects the fracture toughness and fatigue strength of metal composites. The crack growth behaviours, from a weak layer (AH36 carbon steel) to a strong layer (2205 duplex stainless steel), at the interfacial zone of a hot-rolled bimetal composite (2205/AH36 BC) were investigated. To clarify the potential factors altering the crack growth behaviour near the interface, the variations in fracture force under different loading speeds and directions were obtained from a well-designed micro tensile machine. The results indicate that the influence of crack propagation direction on the tensile fracture force when passing through the interfacial zone is greater than the force at the initial notch of crack. The tension loading speed determines the shielding or amplification effect on the crack tip, verified by the microstructural characteristics along the crack path. The crack tip displacement and yield situations were studied by the mechanism analysis, numerical simulation and microstructure observation. It is found that the influence of interface and strong steel layer on the crack tip opening displacement (CTOD) and yield zone size is great in the early stage of crack propagation. Loading speeds have a greater impact on the microstructure of 2205 steel adjacent to the interface, but a small influence on the CTOD and yield zone size of composite. These results could be used as a reference for guiding the design of new bimetal composite parts.