الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
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Abstract
Ultrafine grained structures in plain carbon steels is of great interest as a mean of cutting the cost of steel production and opening up the window of high mechanical properties. Almost all researches in this field were done at laboratory scale. In the present work, online industrial trials to achieve fine grained ferrite using the hot strip mill (HSM) containing six stands at Al Ezz Dekheila (EZDK) Steel Company starting with a commercial steel composition ( ~0.05% C, 0.05% Si and 0.5% Mn). The effects of deformation temperature at the last rolling stand (750, 775, 800, 815, and 890°C) and the effect of variation of strain at the last two stands on the microstructure and mechanical properties were studied. The coiling temperature was kept at 400°C, except the first trial which represents the condition of classical low carbon production the coiling temperature was 580°C. The mechanical properties (tensile and impact) and microstructure were evaluated. The produced microstructure indicates the presence of polygonal ferrite structure with average grain size of ~ 11μm in the classical rolling. In the second group of trials; as the deformation temperature increases, microstructures change from bimodal grain size distribution with average grain size of ~ 10μm to be a relative homogeneous ferrite microstructure with average grain size of ~ 5.9μm. In the third group of trials, the amount of strain was increased in the last two stands with deformation temperature of 800°C. The resulted microstructures consisted of fine equiaxed ferrite grain with average grain size less than 5μm and fine pearlite colonies and/or carbide precipitates are observed to be confined at grain boundaries. Strain induced dynamic transformation above Ar3 is suggested to be responsible for refinement processes as well as a continuous dynamic recrystallization mechanism. IV Comparing the processed steel using a finishing temperature of 890˚C which resulted in a ferritic grain size of 11μm with the fine grained (~5μm) steel, the yield stress has increased by 23% and the tensile strength increased by 12% on the expense of only 5% decrease in the ductility. However, the impact energy has improved by 7.5 %.