Strengthening a Medium-Carbon Low-Alloy Steel by Nanosized Grains: The Role of Asymmetrical Rolling

A medium-carbon low-alloy steel was prepared via the asymmetric rolling process with different ratios of upper and down roll velocities. Subsequently, the microstructure and mechanical properties were explored by using SEM, EBSD, TEM, tensile tests and nanoindentation. The results show that asymmetrical rolling (ASR) can significantly improve strength while retaining good ductility compared with conventional symmetrical rolling. The yield strength and tensile strength of the ASR-steel are 1292 +/- 10 MPa and 1357 +/- 10 MPa, respectively, which are higher than the values of 1113 +/- 10 MPa and 1185 +/- 10 MPa for the SR-steel. The ASR-steel retains good ductility of 16.5 +/- 0.5%. The significant increase in strength is related to the joint actions of the ultrafine grains, dense dislocations and a large number of nanosized precipitates. This is mainly because of the introduction of extra shear stress on the edge under asymmetric rolling, which induces gradient structural changes hence increasing the density of geometrically necessary dislocations.

Automated summary

A medium-carbon low-alloy steel was prepared using asymmetric rolling process and its microstructure and mechanical properties were investigated. The results showed that compared to conventional symmetrical rolling, asymmetrical rolling significantly improved the strength without sacrificing ductility. The ASR-steel displayed higher yield strength and tensile strength compared to SR-steel, along with good ductility. The increased strength was attributed to the presence of ultrafine grains, dense dislocations, and nanosized precipitates as a result of the asymmetric rolling process.