Effect Of Cold Rolling Reduction On Mechanical Properties Of Low Carbon Al-Killed Steel Sheet

Low carbon Al-killed steel, as the representative of the second generation of deep drawing steel, is a sort of high quality carbon structural steel. Low carbon Al-killed steel can be deoxidized quite completely and thoroughly by using Al as deoxidizer. All kinds of complex thin parts can be made of low carbon Al-killed cold-rolled steel sheets, which has good deep drawing performance. Because of its simple process, low cost, stable performance after the formation, low carbon Al-killed steel is being widely applied in the automotive, construction, household appliances industry and has a certain foundation status in the deep stamping sheet market. Investigating the effect of cold rolling reduction on properties of deep stamping sheet and finding the optimum reduction ratio to optimize the production process are significant for improving productivity and quality.At the beginning of the period, reasonable chemical composition and cold-rolled reduction ratios were determined. According to the experimental requirements, we got five different reduction ratios sheets by H-C single stand reversing cold rolling mill. In this experiment, the parameter values of the mechanical properties were obtained by the tensile test. To explain the macro performance of its mechanical properties, the micro structure of the low carbon Al-killed steel sheets were observed by the optical microscope(OM). The film samples, prepared by Ion thinning experiment, were studied by scanning electron microscopy(SEM) and energy spectrum analyzer(EDS) to survey the morphology and composition of the non-metallic inclusions.The experimental results indicate that for non-annealed steel sheets the increasing trend of hardness values slow down when the cold-rolled reduction ratio reaches about 65%, at which percentage the hardness values begin to decrease and secondary recrystallization occurs for annealed steel sheets. The effect of cold rolling reduction on properties of deep stamping sheets is small and the optimum reduction ratio is around 74% for the reached steel. Because of the large pressure and friction force at the edge of the steel sheet during the cold rolling, most non-metallic inclusions at the edge of the steel sheet are zonal, while the middle section are spherical or granular. The main features of the non-metallic inclusions in LCAK steel are that the number is a little more and the size is small. This suggests that the stirring process of the molten steel or the Bottom blowing process has some problems during the Secondary refining process.