Tensile and impact behavior of laminated composites based on ultrahigh carbon steel

The goal of this dissertation is to develop metal laminated composites for high strength and high toughness. The experimental part of this dissertation centers on three major objectives. The first one is to develop a laminated composite, based on ultrahigh carbon steel (UHCS), which can be selectively heat treated to achieve alternating hard UHCS and soft interleaf layers. The second objective is to maintain sharp and discrete interlayer boundaries in the UHCS laminated composite after selective heat treatment with no interdiffusion of carbon. The third objective is to achieve high notch-impact toughness in the selectively heat-treated laminated composite. Five laminated composites were investigated. They are UHCS/Fe-3%Si, UHCS/Hadfield manganese steel (HMS), UHCS/9%Ni-2%Si steel, UHCS/brass and UHCS/304 stainless steel (304ss) All five laminated composites were selectively heat treated to achieve the desired objective of alternating hard and soft layers. Charpy V-notch impact tests were performed on the first four laminates. Each laminate showed a lower ductile to brittle transition temperature (DBTT) than those obtained in the monolithic UHCS and the monolithic interleaf material making up the laminate. This improvement in DBTT is because the notch is blunted in the laminate by delamination at the discrete interlayer boundary or by the presence of the ductile and tough interleaf layer. Interlayer delamination is due to the non-perfect bond strength between the UHCS and interleaf layer.; HMS and 304ss are austenitic steels which have quite different thermal expansion properties with respect to the UHCS which is a ferritic steel. Thus, residual stresses build up in the selectively heat treated UHCS/HMS and the UHCS/304ss laminated composites. In some cases, fracture occurred in these laminates due to residual stress. A Timoshenko beam model is used to estimate the magnitude of this residual stress. The analytical results are compared with the numerical results obtained by the finite element method.