Improved teeming of steel for drill-pipe production

Abstract

The open-hearth shop at the Taganrog Metallurgical Plant is undertaking a comprehensive program to improve the technology employed for teeming steel from 150-ton ladles equipped with slide gates. The ladles were designed by the All-Union Scientific Research, Planning, and Design Institute of Metallurgical Machinery. The metal is bottom-poured into unlubricated through-type big-end-down ingot molds. Inserts made of kaolin wool are placed in the top part of the mold. The surface of the molten metal is protected by an ash-graphite mixture. A 140-160-ram-high region where the inserts are located is filled more slowly than the rest of the moldo Here, the stream is narrowed by partially closing the gate for I 1.5 rain. A specially designed gauge is used to objectively monitor the rate at which the mold is filled. Thermal insulation of the top part of the ingots with the inserts and the ash--graphite mixture has significantly improved the macrostructure of the metal. The ingots have a smooth surface free of ripples, and almost no ingots are rejected for cracks and scabs (steel 32G2). A distinguishing feature of drill-pipe production at the plant is the rolling regime. It is known that scab formation on tubes is reduced by reducing the deformation which occurs during piercing of the ingot. To reduce deformation during piercing, we use ingots of smaller diameter than normal. A redistribution of the strains between the piercing and Pilger mills (a reduction in the elongation factor during piercing from 1.74-2.07 to 1.58-1.62 and an increase in the elongation factor on the Pilger mill from 9.7-10.5 to 11-13.4) and a decrease in the diameter of Pilgermill rolls from 198 to 178 mm made it possible to reduce the proportion of tubes rejected for scabs and increase the output of 12-m drill pipe from 42.35-49.43 to 73.35-75.70%~