Microstructure and Fracture Behavior of Special Multilayered Steel

In this research, multilayered steel (MLS), which is composed of middle-carbon martensite steel, high-carbon martensite steel, and a pure Ni thin layer was obtained by the accumulative roll-bonding method. The microstructure and mechanical properties of the MLS were investigated by scanning electron microscopy (SEM), Vickers microhardness, tensile, and bending tests. In-situ SEM tensile tests were used to observe the crack initiation and propagation processes during the tensile loading. The results show that the ultimate tensile strength and bending strength of the MLS can reach 946 MPa and 3153 MPa, and the maximum elongation can reach 18%, which is related to the better combined quality of the interface. The middle and larger martensite layer (ML) becomes the weakest link of tensile fracture and interfacial delamination of the MLS during the tensile processes, because there are lots of large hard blocks Cr₂₃C₆ phases distributed in the middle thicker ML layer. Besides, the MLS can withstand larger bending deformation. When the MLS was bent to 180 degrees, neither macro-cracks in the outer side of the bending parts nor interfacial delamination can be found.