A new low carbon steel microstructure: Ultrafine ferrite grains with homogeneously distributed fine cementite particles

Low carbon steels containing carbon less than 0.2 wt.% are the most widely used ferrous alloys in structural application. These steels consist of ferrite of large volume fraction with pearlite as the remainder and exhibit a strength of similar to400 MPa. To date, considerable effort has been devoted to enhancing the strength of these steels. However, existing methods of improving their strength are limited by the counter effect of loss of ductility and toughness. To overcome this deficiency, a new low carbon steel microstructure and its processing route are reported in this study. The steel with the new microstructure-submicrometer scale equiaxed ferrite grains with fine cementite particles distributed uniformly - was manufactured by imposing severe plastic deformation to introduce ultrafine ferrite grains and subsequent static annealing for uniform precipitation of nanosized cementite particles. The strength of the steel with the new microstructure increased nearly 100%, over 800 MPa, without significant loss of ductility.