The changes that appear in mechanical properties of steel sheets and the reasons of them and their effects on forming process

Steel sheets are formed into various shapes and have a wide usage in many industries. Thescrapping caused by the breaking or the localized necking of the sheet during the formingprocess affects the continuity, economy and quality of the production in a negative way.Therefore, the production losses must be controlled by selection of proper steel sheet withgood formability and also by using steel sheets that have uniform mechanical properties. Themechanical properties of the same quality steel sheets differ from company to company, fromcast to cast of the same company, from coil to coil of the same cast and in different regions ofthe coil. Formable steel sheets with tight range of mechanical properties are produced bycontrolling metallurgical factors and optimizing steelmaking, hot rolling, cold rolling andannealing processes.In this study, the production stages of steel sheets were studied first. The factors in eachsector that cause mechanical properties to change were mentioned. The steel sheet standardswere studied and they were classified in two groups as hot rolled and cold rolled steel sheets.Typical mechanical properties of steel sheets were explained and the methods to attain themwere mentioned. The ranges of mechanical properties typical of sheet produced by variousproduction stages in different qualities were investigated with the aim of the studies whichwere made beforhand. To understand the reasons of the changes of mechanical properties,some fundamental metallurgical concepts were mentioned. In addition to this, the act ofchemical composition of sheet metal in mechanical properties were described and processvariants of all production stages that cause mechanical properties to deviate from desiredvalues were summarized. Several sheet metal forming methods, some mechanical tests andforming limit curves were mentioned then. The affects of mechanical properties to steel sheetformability were explained.In order to determine the parameters indicating the formability of the material, by the help ofnew developed sampling method, it was searched if the material properties differ from cast tocast, in different regions of the coil and in orientations relative to the rolling direction. Thesteel sheet investigated by using a uniaxial tensile test was 1,2 mm in thickness and SCGA270 D in quality degrees as cold rolled low-carbon steel sheet. To find the grain size of thematerial, an electron microscope analysis was applied to only one sample. The other testswere hardness test and Erichsen test. It was observed that the mechanical properties differ inall defined situations.Keywords: Uniform, consistency, formability, hot rolled, cold rolled, microstructurevariables, forming limit curves.