ANALYSIS OF ULTRA-LOW CARBON STEEL CASTING AT CURVILINEAR CCM

Abstract

Ultra-low carbon steel with a carbon content of no more than 0.006% is produced in the BOF shop of PJSC MMK. After the oxygen converter, a semi-product is subjected to a long ladle processing at the ladle-furnace unit (LFU), a circulation degasser and again at the LFU. Casting of such steel is carried out at all five slab casters operated in the shop. However, about three-quarters of the steel is cast at two curved-type combined casters operating in a two-strand mode. This fact is explained by the order for the width of continuously cast slabs of the same thickness, equaled to 250 mm. The organization of stable continuous casting of ultra-low carbon steel by the “re-smelting method” is a problematic issue. Analysis of the serial casting of this steel at curvilinear casters of the combined type was carried out in the frame of this work. The study was carried out by the method of statistical processing of production data of 69 smelting operations using correlation and regression analysis. Ultra-low carbon steel was represented by grades 006/IF, CR4, CR5, DX54D, DX57D, A365-A13, A365-A14. Slabs with a thickness of 250 mm had the following width: 1450 mm (24 smelting operations); 1560 mm (14 smelting operations); 1650 mm (9 smelting operations); 1750 mm (17 smelting operations); 1850 mm (5 smelting operations). The speed of drawing slabs from the mold varied from 0.60 to 0.82 m/min (0.70 m/min on average). Decreasing dependence of the duration of casting ulta-low carbon metal of one heat on the width of the cast slabs at combined casters of curvilinear type was established as a result of the study. The casting of metal is carried out in series of five smelting operations. The casting speed of slabs of the same width (1450 mm) varies in a wide range in 1.3 times. The main parameter influencing the speed of casting is the sequence of smelting in the series. With an increase in the serial number of the smelting operations, the average casting speed decreases connected with accumulation of organizational delays.