RU1770382C - Method of desulfurization and vacuum processing of bearing steel - Google Patents

Abstract

SUMMARY OF THE INVENTION: when treating metal with basic reducing slag (from solid slag-forming), the composition of the latter is known to be in the amount of (4-180 / хДЗ kg / t steel, where AS is the required amount of sulfur removed in mass fractions, and the amount evacuation cycles are calculated by the formula N / 30 + 4 / p /, where n is the amount of lime added in kg / t of steel being smelted.

Description

The invention relates to the field of ferrous metallurgy. Specifically, to the out-of-furnace treatment of steel, mainly bearing, using evacuation.

The aim of the invention is to improve the quality of the metal by globular, nitride nonmetallic inclusions and increase the resistance of the refractory lining of the vacuum cleaner.

An example of a specific embodiment of the method.

Bearing steel was smelted in a 100-tonne arc furnace.

After finishing the metal in the furnace by chemical composition and temperature, the metal in the ladle was treated with the main reducing slag, consisting of solid slag-forming: lime, fluorspar and lump aluminum. At the same time, the melt was purged with argon.

Silicon was doped with metal in a furnace, in a ladle, and in a vacuum.

Depending on the degree of desulfurization required, solid slag-forming substances were introduced (as a rule, instead of lime) in various amounts. The mass fraction of sulfur in the starting metal varied from 0.015% to 0.045%. In order for large sulfide inclusions to not form in the metal, it is necessary to have a sulfur content of less than 0.005% in bearing steel. Thus, sulfur from 0.010 to 0.040% must be removed during the slag treatment period. The more sulfur needs to be removed, the more intensively the slag processing of metal is organized, the more deoxidants settle. argon flow rate and purge duration are increased.

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In this case, more limestone was also deposited in the melt.

In the total amount of lime smelted, it ranged from 0.4 kg / t to 7.2 kg / t of smelted steel.

After the desulphurization of steel in the ladle was completed, the metal was subjected to batch vacuum. The number of required evacuation cycles was calculated by the claimed formula N 30 + + 4 gk. Based on the amount of lime added in kg / t, the number of evacuation cycles of bearing steel was varied from 32 to. 59.

A detailed effect of the claimed features on the object of the invention is presented in Table. 1. It should also be noted that in the experimental metal, the mass fraction of titanium is 2-3 times lower compared to the metal of the base technology, which led to a sharp decrease in the amount of nitrides.

Out-of-furnace treatment of known steel bearings has the following advantages.

During the decomposition of limestone, CaO is formed, and СОа, С02 - a mild oxidizing agent interacts with calcium dissolved in the metal, oxidizes it and, in the form of nonmetallic inclusions, it passes into slag. Thereby, the formation of large globular non-metallic inclusions in the metal is reduced even when the metal is treated with slag under pronounced reduction conditions.

The formation of large globular inclusions in the metal will be practically excluded if the amount of lime introduced into the melt is related to the amount of calcium coming from the slag into the metal during processing and the efficiency of the reduction slag treatment (phase contact surface, mass transfer rate), which in turn, it is dictated by the necessary degree of steel desulfurization.

Otherwise, if the amount of limestone deposited is more than 180 x A S or less than 40 x A S (A S is the required amount of sulfur removed in mass fractions), this will lead to a deterioration in the quality of the metal. In the first case, due to the reoxidation of the metal, associated with excessive processing of the melt with CO2 oxidizing gas, in the second, due to the excess of calcium in the metal, which further leads to the formation of large globular inclusions.

Moreover, if the mass fraction of sulfur in the metal by melting is high, i.e. significant removal required

sulfur, the coefficient before AS must be maintained at the upper level, closer to 180. At the other extreme, when a slight removal of sulfur is required, the coefficient is maintained at a level closer to 40.

Washing the metal with CO2, in addition to the positive effect of removing calcium, leads to a certain increase in oxygen in the system, which can negatively affect the removal of sulfur from the metal. However, due to an increase in the degree of melt mixing (due to the release of CO2), a noticeable

5, no improvement in sulfur removal occurs.

The increased oxidation of the metal before its evacuation allows one to organize the most effective type of deoxidation of bearing steel (without forming inclusions) —carbon deoxidation in vacuum.

However, in order to ensure that the mass fraction of oxygen in the finished metal (evacuated) is minimal, and with

5 at the lowest cost, it is necessary that the duration of the vacuum treatment (the number of evacuation cycles) is consistent with the oxygen level in the starting metal, i.e. with the amount

0 limestone for metal desulfurization.

The more limestone is introduced into the melt, the greater the mass fraction of oxygen in the parent metal, the more vacuum cycles the bearing steel must undergo. In this case, the metal will contain a minimum amount of oxygen, and hence the total contamination of the steel with oxygen-containing non-metallic inclusions will be

0 negligible.

The heat loss from the decomposition of limestone is compensated by the heat input from the oxidation reactions of aluminum and silicon, which are part of solid slag-forming materials.

The number of evacuation cycles of more than + 4p (where p is the amount of lime added in kg / t of smelted steel) leads to unnecessary heat losses, equipment wear, less than N 30 + 4p - to increase the mass fraction of oxygen in the finished metal and further to an increase in pollution, became oxygen-containing non-metallic

5 inclusions.

Claims (1)

SUMMARY OF THE INVENTION A method for desulfurization and evacuation of bearing steel, comprising treating the metal in a ladle with solid slag-forming and neutral gas portioned evacuation of the melt, which consists in the fact that in order to increase the quality of the metal according to globular, nitride nonmetallic inclusions and increase the resistance of the refractory lining of the vacuum cleaner, lime is introduced into the composition of solid slag-forming (40-180) x D5 kg / t of steel, where DZ is the required amount of sulfur removed in mass fractions, and the number of evacuation cycles is determined by the formula N (30 - 4п), where n is the amount of limestone introduced into kg / t of smelted steel. Prototype From the experimental data it also follows that an improvement in the quality of bearing steel is achieved with fewer batch evacuation cycles. chi