SUBSTANTIATION OF CORRECTIVE ACTIONS FOR COMPENSATION OF DESCENDING CARBON IN STEEL DURING MANUFACTURE THE COLD-ROLLED FLAT PRODUCTS FOR FORMING
The relevance of the work. There are situations in the practice of metallurgical production when steel melting with a chemical composition intended to complete the determined order is reassigned to the production of rolled metal from another steel grade. With the formal accordance of chemical composition of melted steel to the requirements for a different steel grade, crucial control parameters of process that are traditionally used for a new grade of steel, may turn out to be inappropriate for structural and phase transformations in steel with real chemical composition. To prevent the release of non-conforming products is necessary to develop and apply operational corrective actions. The purpose of the work is selection and rationale of operational corrective actions in the production of cold rolled sheet products of quality classes CQ, DQ and DDQ of mild quality steel to compensate for the reduced carbon content in meltings assigned to complete the respective orders. Microscopy methods were used to study the structure and phase composition of steel with a carbon content of 0,008 - 0,04 % in hot-rolled and cold-rolled states. Data on the mechanical properties of hot-rolled and cold-rolled steel were obtained by standardized tensile test methods. Based on the test results, reliable multiple approximations of influence of control characteristics of the technology on properties of cold-rolled steel were constructed, which were subsequently used in optimization of thickness of semi finished rolled product for cold rolling as a compensating effect at the fluctuations of carbon content within the above limits. The novelty of the work lies in the identification and rationale of corrective actions for a technological system in which cold rolling is carried out on a continuous four-stand mill with roll feed. The results of the work consist in determining the temperature of the end of rolling and the increment of the thickness of the semi finished rolled product as operational compensating effects at assigning steel meltings with a low carbon content for rolling into a technological system with a continuous four-stand mill with roll feed. The practical significance of the work is to prevent the yield of non-conforming products at using the proposed solution in the production of cold-rolled steel of quality classes CQ, DQ and DDQ 0,6-2,0 mm thick.