Effects of Rolling Temperature on the Microstructure and Mechanical Properties in an Ultrafine‐Grained Low‐Carbon Steel

Abstract

Ultrafine grained low‐carbon steels are fabricated by cryorolling and cold‐rolling martensite starting microstructure at liquid nitrogen temperature and ambient temperature, respectively. The results indicate that cryorolling process at liquid nitrogen temperature present more potential in refining ferrite grains in low‐carbon steel (132 nm) than ambient temperature deformation (330 nm). The tensile strength increase from 867.0 to 970.2 MPa for the specimen cryorolled at liquid nitrogen temperature compared to the specimen rolled at ambient temperature. The decreased elongation in the specimen at liquid nitrogen temperature is attributed to the coarse Fe 3 C particles during the annealing. Moreover, Fe 3 C particles precipitate during the cold‐rolling and subsequent annealing processes in the cold‐rolled specimen, while Fe 3 C particles in the cryorolled specimen are mainly formed during the annealing process due to the suppression of diffusion of carbon atoms during the cryorolling process.