Modification of the Structure of Low-Carbon Pipe Steel by Helical Rolling, and the Increase in Its Strength and Cold Resistance

Abstract

The paper reports the investigation results on the microstructure and mechanical properties of low-carbon pipe steel after helical rolling. The processing of the steel leads to the refinement of ferritic grains from 12 (for the coarse-grained state) to 5 μm, to the strengthening of ferrite by carbide particles, a decrease in the total fraction of perlite grains, a more uniform alternation of ferrite and perlite, and the formation of regions with bainitic structure. The mechanical properties of the steel have been determined in the conditions of static and dynamic loading in the range of test temperatures from +20 to–70°С. As a result of processing, the ultimate tensile strength increases (from 650 to 770 MPa at a rolling temperature from 920°С) and the viscoplastic properties at negative temperatures are improved significantly. The ductile–brittle transition temperature of the rolled steel decreases from–32 to–55°С and the impact toughness at the test temperature–40°С increases eight times compared to the initial state of the steel.