Mechanism of increased strength and ductility of martensite-austenite composite steel with different thickness ratios

In this study, the mechanism of increased strength and ductility of a martensite-austenite composite steel with different thickness ratios was analysed. Results revealed that with increasing the thickness ratio between the martensite and austenite layers, the strength and uniform ductility of the composite steel initially increased and then decreased gradually. The best combination was obtained in a 2:1 specimen, with the strength and the uniform ductility being increased by 9% and 190% respectively, as compared with the monolithic martensitic steel. The slight diffusion of carbon atoms from the austenite layer into the martensite layer strengthened the steel, which offset the weakening effect of introducing the austenite layer. Moreover, the diffusion of heavy elements between the neighbouring layers, such as manganese and silicon, formed a transition layer with varying concentration which effectively coordinated the deformation behaviour of the neighbouring martensite and austenite layers.