Surface-crack formation in the two-phase region when rolling thick microalloyed-steel sheet

Resumo

The formation of a surface defect (a lobed scab) in the final stage of large-diameter pipe production is analyzed. Surface microcracks are assumed to form in the rolling of thick sheet on account of problems in the two-phase region on rolling, with localization of the plastic strain, as well as the action of tensile stress in the surface layer and the attainment of limiting stress values. Physical modeling in the Gleeble system permits determination of the limiting stress (rupture strength) in rolling in the two-phase region, which depends on the temperature and is structure-sensitive. The limiting stress is determined by ferritic and bainitic transformation in the steel.