Effect of warm-rolling on the strength and ductility of multilayered composite steel

Making composite steel is an effective method to improve the strength and ductility of steel, but it often follows the mixture rule. Further increasing the strength and ductility simultaneously of composite steel is challenging. In this study, warm-rolling was introduced into a multilayered martensite/austenite composite steel after the compositing process. Results revealed that some C atoms diffused from the martensite layer into the neighbouring austenite layer, resulting in a reduced hardness in the martensite layer of common composite steel. Introducing warm-rolling deformation not only hardened each layer effectively, but also clearly improved the ductility of the austenite layer. This facilitated the coordination deformability of the austenite layer and resulted in simultaneous improvements in strength and ductility for warm-rolled composite samples. Better mechanical properties (tensile strength of 1546 MPa and a uniform elongation of 14.9%) were obtained for a sample with a lower degree of reduction (10%). The mechanism leading to improved mechanical properties is analysed in detail in this paper.