The effect of warm rolling on structure and mechanical properties of low carbon pipe steel

This paper presents results of a research on the effect of warm rolling on structure and mechanical properties of the low- carbon pipe steel. The warm rolling results in formation of anisotropic ultra- fine grained (UFG) structure with average grain / subgrain size 0.5 mu m in transverse direction and 20-30 mu m along the rolling direction. The formation of ultra-fine grained (UFG) structure leads to 1.5 times increase in strength by comparison to fine-grained (FG) structure keeping the required level of ductility. It is shown that impact strength at - 196 degrees C in UFG steel is 15 times higher than that in initial FG condition. It was established that the total work of fracture at - 196 degrees C increases due to growth of crack propagation distance in comparison to initial (FG) condition. Fractographic analysis of the sample after the test at - 196 degrees C revealed that in the condition after rolling the mixed type of fracture surface is observed, and in the initial condition demonstrates completely brittle fracture. In both conditions of the materials at all temperatures tested appeared areas with the cleavage on the crack surface.