Patterns of the formation of the structure and properties of the X70 low-carbon steel after high-temperature helical rolling

Abstract

The results of studies of the effect of high-temperature helical rolling and subsequent interrupted high-rate cooling on the formation of the structure and mechanical properties of the X70 low-carbon steel were presented. In comparison with the ferrite-pearlite structure of the hot-rolled steel, the dispersed structure was formed after this processing. It included a mixture of quasi-equiaxial ferrite grains, acicular bainite, the martensite-austenite component along the boundaries of bainite laths and a small fraction of troostite regions. Besides that, microhardness HV0.05 values increased up to 2370 MPa, as well as yield strength and ultimate tensile strength enhanced by up to 35% and 20%, respectively, compared to those of the hot-rolled state. The strength properties of the steel with the ferrite-bainite structure increased significantly (1.55 times) with a decrease in the test temperature. At the same time, ductility improved by up to 20% when tested under liquid nitrogen conditions.