SU835610A1 - Slag forming mixture for casting rimmed steel - Google Patents

Description

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The invention relates to ferrous metallurgy, in particular, to the casting of boiling steel into molds or molds of continuous casting machines.

Low carbon boiling steel for the manufacture of products by the methods of deep and complex drawing and upsetting must have high plastic properties. In order to increase the level of plastic characteristics of boiling steel, in the process of casting into molds or into molds of continuous casting machines, it is treated with refining slags, which leads to the purification of metal from impurities and non-metallic inclusions and an increase in its quality.

Known slag for metal casting, containing, by weight. %:

Nepheline concentrate 65-95 Fluorine-containing material 5-35 1

The lack of slag is the absence of boron-containing materials in it, as a result of which boiling steel treated with this mixture has an increased tendency to aging.

As a prototype, a slag-forming mixture can be taken, consisting of a boroderloyl substance (borax) and a fluoride compound (cryolite), the ratio of which in the mixture is from

1: 1 to 3: 1, that is, the mixture has a composition, weight. %:

Boron-containing substance 50-75 Fluoride compound 25-50 2

The addition of such a mixture to a metal mirror during intensive boiling allows the steel to be cleaned of non-metallic inclusions, mainly alumina inclusions ().

The disadvantage of the mixture is its weak refining action with respect to harmful impurities of steel (sulfur and phosphorus), as well as an increased level of toxic fluoride emissions into the atmosphere of the pouring span due to the high content of cryolite (25-50%).

The aim of the invention is to improve the refining capacity of the mixture, reducing the content of non-metallic inclusions in the steel sheet, reducing the content and reducing the segregation of sulfur.

The goal is achieved by additionally adding nepheline to the mixture with a ratio of components, wt. %: Fluoride compounds of metals from the group: cryolite, fluorspar, fluorite concentrate 5-15 Nepheline 30-50 3 Boron compounds from the group; borax, datolite, borax, ulexite Else Nefelin is a natural mineral containing about 50% SiO2, about 30% ABO3, 5 to 22% of alkali metal oxides (Na2O and K2O), improves the refining capacity of the mixture and, accordingly, the slag foam. This is due to an increase in the content of alkali metal oxides (NaaO and K2O) in the slag and the associated increase in the distribution coefficient of sulfur and phosphorus between the slag and the metal. In addition, the oxides of sodium and potassium that pass into the composition of the slag lene form a strong, volatile reaction with sulfur during the reaction, and at the crystallization temperatures of the steel of the compound are sodium and potassium sulfides, as a result of which part of the sulfur is removed into the gas phase. The addition of nephe-20 lin to the mixture also provides an improvement in the assimilating ability of slag lena with respect to non-metallic inclusions in liquid steel by increasing the interfacial tension and 25 reducing the adhesion work between the metal and slag. Thus, the introduction of a mixture of nepheline provides a higher refining ability of the slag foam and, accordingly, a higher30 degree of steel purification from harmful impurities (sulfur and phosphorus) and non-metallic inclusions. Boron-containing compounds are good smooth, lagging behind in this respect35 only fluoride compounds, but, unlike the latter, do not produce harmful secretions. In addition, under the conditions of casting and crystallization of boiling steel, accompanied by the release of a large amount of reducing gas CO and intensive mixing of the metal and slag in the mold, boron is reduced from the compounds and transferred into the metal. In this case, microalloying45 of boiling steel with boron occurs and its tendency to aging decreases. Alkali or alkaline earth metal fluoride compounds provide viscosity reduction and increase in liquid-50 viscosity of the slag fiber. The mixture is prepared by mechanically mixing the initial components of the mixture that are crushed to a fraction of not more than 2 mm. Mix consumption - 0.3-1.0 kg / t steel. The mixture in the packaged form (in plastic or paper bags) was introduced into the mold to prevent the onset of steel casting. When casting steel on a continuous casting machine, the mixture is introduced onto the metal mirror in the crystallizer in equal portions, or continuously, in the course of casting. When casting steel into molds, the mixture should be used in pelletized form (pellets, briquettes, etc.). 65 4 The choice of Lredel content of the mixture components is determined as follows. When casting boiling steel with a high carbon content (such as StZkp), as well as chromium alloyed the crystallization of which is accompanied by insufficiently intense boiling and the formation of a relatively large amount of slag fiber, a mixture with the content of metal fluoride compounds, for example, cryolite at the upper limit (14–15%), is used, and nepheline is not It limits (30-32%), the rest - boron compound. An increase in the mixture of fluoride compounds of more than 15% leads to an increase in the amount of toxic emissions into the atmosphere and the deterioration of sanitary and hygienic working conditions in various spans of steel-smelting plants. When casting low-carbon blunt steel (type 08kp), which is intensively boiling in the mold with the formation of a relatively small amount of slag lena, it is sufficient to have the fluoride content in the mixture at the lower limit (5-6%); the nepheline content in this case should be at the upper limit (47-50%), the rest - boron compounds. When casting steel, whose crystallization conditions (boiling intensity, amount and consistency of slag foam) differ from the specified extreme cases, mixtures with intermediate content of fluoride and nepheline. The use of a mixture with a fluoride content of 5–15% ensures a decrease in viscosity and an increase in fluid mobility, and, as a result of the refining ability, the formation of a thick and viscous slag foam. Example 1. When pouring sfon boiling steel of the Stzkp brand into ingots weighing 9 tons into the molds before casting, they were placed in plastic bags of 9 kg of slag-forming mixture of the following composition, wt. %: cryolite-15, nepheline-30, borax - the rest (mixture No. 1, tab.). Time to fill the molds with metal - 8 min. The ingots were covered with yellow cast iron caps after 10 minutes. after the end of the mold filling. Example 2. When casting on top of steel grade Ozkp with a linear speed of 0.60, 8 m / min (a glass of a pouring ladle with a hole diameter of 35 mm) on ingots weighing 12 tons in molds before casting were placed 4 kg of slag-forming mixture of the following composition weight. %: cryolite - 5, nepheline - 50, datolite concentrate - the rest (mixture No. 2). Mold filling time 2.5-3 min. The ingots were sealed with aluminum 5 minutes after they were cast.

Example 3. When casting on top of steel 08kp, smelted in a two-bath furnace (peroxidized metal) with a linear speed of 0.1 - 1.5 m / min (a glass of a pouring ladle with a hole diameter of 60 mm) on sheet ingots weighing 14 tons into molds before casting, 7 kg of slag-forming mixture of the following composition were placed, weight. %: cryolite -and nepheline - 32, borax - the rest. Mold filling time 1.7-2.2 min. Ingots were covered with yellow cast-iron covers in 10-

12 minn or plugged with ferroaluminium after 5–8 min to cast elasse.

When casting from above boiling steel grades 08kp, St1kp, St2kp, StZkp to sheet ingots weighing 14-14.5 tons (through a glass with a channel diameter of 60 mm), slag-forming mixtures 1-5 and a mixture of prototype (6), mixture , not containing fluoride compounds (7), and a mixture with

increased content of fluoride compounds (8). The compositions of the mixtures, the content of sulfur and non-metallic inclusions in the ingot billet are given in the table.

Claims (1)

Claim A slag-forming mixture for pouring boiling steel, containing boron compounds and metal fluoride compounds, characterized in that, in order to improve the refining ability of the mixture, reduce the content of non-metallic inclusions in sheet steel, reduce the content and reduce segregation of sulfur, it additionally contains nepheline at 25 next ratio of components in weight. %: Fluoride compounds of metals 5-15 Nepheline 30-50 30 Boron Compound Else