New refractories for plant handling the vacuum treatment of steel outside the furnace

Abstract

In the past 15-20 years the role of the processes of outside-furnace vacuum t~eatment of steel has increased so much that this trend is being assessed by specialists as one of the maiii 5nes in the development of steel-melting applied to high-grade metal. With this technique the steel from the furnace is produced as a semifinished product --unkilied steel with a certain Conteiit of sulfur m~d phosphorus. Further treatment (gas removal, oxidation and alloying, refining the chemical composition, and also bending) is done outside the steel-melting plant on vacuum equipment for outside-furnace operations (UVVS). This technology reduces the melting time, standardizes the heats, cuts the consumption of deoxidizing agents and alloying additives, improves the grading and reduces the scrap metal, and finally excludes the antiflake treatment of the blanks and roliings. A reduction in the oxygen content due to self-deoxidation by the carbon dissolved in the molten metal ensures practically complete assimilation of such deoxidizers as silicon and aluminum, which cannot be done with other technologies [1,2]. The steel deoxidized in vacuum by silicon and aluminum is less contaminated by oxide inclusions, and so, e.g., such steels as bearing, tube, and those for very deep drawing, are produced only with the use of outside-furnace vacuum methods [3].The evening-out of the chemical composition and melt temperature obtained in vacuum processing, and the good assimilation by the metal of alloying additives provides greater accuracy in correcting the final steel composition, restricting its limits for carbon to • 0.01%, manganese, silicon, and chromium to 9 0.05% [4], which is especially important in the production of low-alloy steels modified with boron, zirconium, and niobium, nonaging steel, and autolytic steel deoxidized with aluminum and cast in continuous steel-casting plants [5].Decarbonizing in vacuum is widelyused for the production of low-carbon (0.005-0.01%), mainly electrical engineering steels: relay, transformer, and dynamo. A significant advance in the melting of high-chromium (stainless) grades is the application of oxidative vacuum processing. Carbon oxidation, by blowing the melt ~ I d l--3/0.5--31[--2 / <I