Abstract: The effects of asymmetric hot rolling on the microstructure and mechanical properties of low alloy steel were investigated when the symmetric hot rolling and asymmetric hot rolling with roll velocity ratio of 1.2 were applied to the steel. The results show that asymmetric hot rolling can promote the austenite/ferrite transformation significantly and improve the microstructure uniformity along thickness direction of the steel strip. After the symmetric hot rolling process， the microstructure at the surface of the steel strip was fine ferrite layer and was coarse bainite at the thickness of 1/4 or 1/2. However， the microstructure through the thickness of the steel was the uniform ferrite after asymmetric hot rolling process. The tensile strength and elongation of the steel after these two rolling processes respectively， were very close， which were about 710~718MPa and 20%. After replacing the symmetric hot rolling process by the asymmetric one， the yield strength of the steel increased from 526MPa to 561MPa. The main reason is that the transformation strengthening is dominant in a symmetric hot-rolled steel， but grain refinement is more prominent for asymmetric hot-rolled steel.

Key words: asymmetric hot rolling, symmetric hot rolling, low alloy steel, microstructure uniformity, mechanical property, strengthening mechanism