Effect of the diffused content of carbon on mechanical properties of multilayered composite steel

Introducing carbon diffusion is an effective method for fabricating composite steel with high strength and high ductility. Herein, three kinds of low-carbon martensite steels with different silicon contents were selected as high-strength layer materials. The effective mechanisms of the diffused content of carbon between the neighboring layers on the strength and ductility of martensite–austenite composite steel were researched. Results revealed that the martensite–austenite composite steel with different diffused contents of carbon was obtained by changing the silicon content in the martensite layer. Some carbon atoms diffused from the austenite layer into the neighboring martensite layers, resulting in an increased hardness of the martensite layer. With increasing the diffused content of carbon, the hardness of the martensite layer increased gradually. When the increment of carbon content within martensite layer was 0.16 wt%, 0.23 wt% and 0.25 wt%, respectively, the tensile strength increment of composite steel was 1, 23 and 110 MPa, respectively, as compared with the monolithic martensite steel. This indicated that the increased diffused content of carbon was beneficial for improving the tensile strength of composite steel. Accompanied with the decrement of carbon content inside the austenite layer, the elongation of composite steel was 13.6%, 17.3% and 17.9%, respectively. With decreasing the hardening ability of the austenite layer, the coordinated deformability between the neighboring layers was decreased. Consequently, the elongation of composite steel was reduced. This finding indicated that the slight diffusion of carbon atoms between neighboring layers was beneficial for improving the ductility of composite steel.