Tensile and fatigue properties of sub-microcrystalline ultra-low carbon steel produced by hpt-straining

Abstract

Abstract The tensile and fatigue properties of ultra-low carbon steel after HPT-straining at a rotation-speed of 0.2 rpm under a compression pressure of 5 GPa were investigated. Elongated grains with 300 nm thickness and 600 nm length with high dislocation density were formed by the HPT-straining. The obtained Vickers microhardness was around 3.6 GPa. The engineering tensile strength of the HPT-processed ultra-low carbon steel for 5 and 10 turns was 1.9 GPa, which is similar to the value of maraging high-alloy steels. The elongation increased with strain (at 5 to 10 turns). The increase in elongation is caused by the reduction of the stress concentration due to the existence of continuously recrystallized grains. The fatigue strengths of HPT-processed specimens were twice as high as those of the 90 % cold-rolled specimen in the low-cycle fatigue region, whereas in the high-cycle fatigue region the fatigue strengths were not so different due to the high notch sensitivity of the HPT-processed specimens.