Improvement in the technology for the production of steel for tin plate

Abstract

In connection with the startup of the tin plate shop at the Karaganda combine, the combine has become the first facility in the sector to master the production of tin plate from steel 08kp. The steel is made in 300-ton converters and teemed into 16.3-ton ingots. The first stage of the technology provides for deoxidation of the steel in the ladle with ferromanganese ladle injection of the steel with argon, teeming from a 300-ton ladle through a slide gate with an 80-mm-diameter channel, and blocking of the ingots with cast-iron caps after the metal has rimmed in the ingot molds for 8-15 min. It was established that the optimum temperatures for the metal are 1540-1550~ before teeming and 1550-1560 before nitrogen injection. When the temperature of the steel is higher than 1560~ it is cooled with a slab before injection at a rate of 1.0-1.5 deg C/min. The optimum degree of oxidation of the steel in the mold is 0.03-0.04%, with the finishea steel having a manganese content of 0~ When the metal is insufficiently oxidized prior to teeming, a rimming intensifier is added to the mold in the amount 150o300 g/tono The intensifier is in the form of granules of ferric oxide from pickling solutions from hot-rolled sheet production and potash or soda. Several problems with the tin plate production practice were discovered during its introduction: a high incidence of inferior-quality metal at the slabbing mill due to surface defects, mainly seams and cracks; a large number of strip tears on the 1400 mill in the tin plate shop. To alleviate these problems, the combine conducted a study to improve the tin plate technology. The principal means of making the improvement were: a reduction in the linear teeming rate through the use of two slide gates with 60-mm-diameter channels; teeming into new ingot molds with more inclined sides; blocking the ingots with lump aluminum after the metal has rimmed in the mold long enough to form a solid skin 50-90 mm thick. While studying the teeming of heats through two slide gates with 60-mm orifices, we refined the duration of teeming and steel temperature and recorded the number of deviations and the instances of reclassification of the metal into other grades. The optimum teeming temperature was determined to be 1540-1550~ i.eo, the same as in the case of teeming through a single slide gate with an 80-mm orifice. Teeming time through two 60-mm slide gates was shortened by 3 min from the time taken in the case of one 80-mm gate (Table I). The time required to fill one ingot mold increased 1 min, while the frequency of deviations decreased from ii.i to 4.8%. This in turn led to a 2.0% reduction in the number of reclassified ingots. Useable output on the slabbing mill increased by 6.9%, while the amount of crop necessary was cut in half. Useable output increased partly as a result of a reduction in the amount of metal reject6 for seams and cracks from 3.0 to 0.7% and from 4ol to 0.3%, respectively. This result was achieved thanks to an increase in the minimum thickness of the dense ingot skin from 8 to 11-12 mm after the linear rate of filling of the mold was decreased and the teeming temperature was optimized. To reduce surface defects on the slabbing mill, we tested and introduced a new type of ingot mold, 16N, for 16.3-ton ingots. The conicity of the inside faces of the mold is 2% greater than on the previous molds. The new mold also has narrow wavy and broad curved faces. Model-17ST ingot molds were used earlier to teem ingots of the same size. These molds had inside faces with a 1.15-1.35% inclination and a smooth surface.