RU2732027C1 - Refining flux for out of furnace finishing of steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to ferrous metallurgy and can be used in out-of-furnace steel finishing on aggregates of complex steel processing (ACSP), ladle-furnace and vacuum devices. Refining flux for out-of-furnace steel finishing consists of briquettes from slag-forming mix containing binder 1–4 wt. % and pressed components containing Al₂O₃, 30÷99 wt. %. Flux contains wastes of secondary aluminium containing CaO, Al₂O₃, MgO, SiO₂ and consists of, wt. %: alumina slag or aluminothermic slag with Al₂O₃ content of 70–80 % 35–45; screenings of line alumoslates with Al₂O₃ content of 40–50 % 40–50; screenings of high-basic steel-smelting slags 15–20, at that content of SiO₂ in form of refractory mineral components with melting point higher than 1690 °C in free form is limited to 14 %, content of low-melting compounds of alkali metals in form of NaCO₃, KCO₃, NaCl, KCl, NaF in terms of oxides (Na₂O + K₂O) is limited to 10 wt. %, components with Al₂O₃ content in excess of 70 % in form of 0–1 mm fraction in total amount up to 40 %.

EFFECT: invention makes it possible to exclude formation of refractory transition compounds in the initial stage of slag formation process, to reduce duration of melting under the arc at the ladle furnace and specific consumption of aluminium.

1 cl, 1 tbl

Description

The invention relates to ferrous metallurgy and can be used in the technology of out-of-furnace finishing of steel on the AKOS units, ladle furnace (AKP) and vacuum tanks.

Refining flux is used for the treatment of metallurgical melts (desulfurization) in the process of tapping and out-of-furnace processing of metals to provide protection against secondary gas saturation and carbonization, reduce the waste of deoxidizers and assimilate non-metallic inclusions.

Known slag-forming mixture (RF patent No. 2605410, C21C 7/076, 2016), containing a slag component, sodium bicarbonate, and as a flux waste from the production of secondary aluminum: dust from the production of secondary aluminum, subjected to briquetting on a hydraulic briquetting press. A slag-forming mixture of this composition provides a set of necessary technological properties of a steel-melting slag cover only during long-term melt processing on ACP (vacuum equipment) and creates conditions for the release of white smoke due to the increased content of metallic aluminum (exothermic component) with a very high content of volatile alkali metal compounds (NaCO3, K2CO3 , NaCl, KCl, NaF, KF, Na2O, K2O) in an amount of (5 ... 20)%. The MgO content in an amount of (5.0 ... 12.0)% with a high content of alkali metal salts leads to the formation of forsterite (2 MgO * SiO2), while impairing the kinetics of the formation of cover steel-making slags. Further formation of more low-melting calcium aluminates with a composition close to eutectic (CaO: Al2O3 ratio close to 55%: 45%; melting point 1345 C) slows down due to the formation of a heterogeneous slag "substrate" of increased viscosity.

Combustion of metallic aluminum in slag (reaction of interaction with Fe2O3, MnO) with an excess of chemically unbound alkali metal salts leads to the formation of "white smoke" and deterioration of the environmental situation in steel-making shops.

The briquetted slag-forming mixture (RF patent №2401869, С21С 7/00, 2010) is most fully related to modern technological requirements. The briquette from the slag-forming mixture contains a binder in a ratio in wt. % 1 ÷ 4 and compressed particles, including aluminum oxide Al ₂ O ₃ in wt. % 30 ÷ 99 or aluminum oxide Al ₂ O ₃ and aluminum in wt. % 30 ÷ 99 and 1 ÷ 20, respectively, while the components are selected, depending on the content of Al ₂ O ₃ , in the following ratios in wt. %: 5 ÷ 35 Al ₂ O ₃ >90; 30 ÷ 70 Al ₂ O ₃ from 55 to 90; the rest is Al ₂ O ₃ <55, and the particles forming the briquette have the following fractional composition, wt. %:> 60 with fraction 0 ÷ 1 mm; 60> 25 with fraction 1 ÷ 3 mm; the rest - with a fraction of 3 ÷ 5 mm, and the volume of the briquette is 40 ÷ 70 cm ³ , its bulk density is 7 ÷ 2.0 g / cm ³ , the moisture content of the briquette is within 1 ÷ 5%, and its volume is 40 ÷ 70 cm ³ .

This type of slag-forming briquette provides a more complete fulfillment of the technological properties of the steel-making slag in the process of out-of-furnace melting.

The disadvantages of these slag-forming briquettes are: excessive content of a fine fraction of Al2O3 ((0-1) mm - over 60%. At the initial stage of slag formation (1520-1550) C, when carrying out averaged blowing of smelting in a ladle at an ACP or AKOS, heterogeneous viscous slags with a large content of undigested lime.With low open porosity (GOST 2409-2014), the conditions for dissolution of such a briquette are difficult due to poor impregnation of it with low-melting phases containing (Fe2O3, MnO, (Na2O + K2O) * Al2O3; (Na2O + K2O) * SiO2) And only after heating the briquette to the slag temperature with overheating of at least 150 C above its melting point (1420 ... 1450) C does the eutectic interaction of calcium and aluminum oxides begin with a noticeable diluting effect.

The second drawback is the recommendation to use corundum production waste and high-alumina materials breakage in the charge of these briquettes. Such materials have a sufficiently high melting point and high slag resistance in relation to highly basic steel-making slags. This also slows down the conditions of slag formation in the ladle, especially when forced cooling of the cover slag during technological operations for the introduction of ferroalloys, ligatures and other operations associated with cooling the slag zone.

The objective of the invention is to create conditions for the accelerated formation of cover refining steelmaking slag during out-of-furnace steel processing on AKOS units, ladle furnace (ACP), vacuum pumps.

The technical result consists in the elimination of the formation of refractory transition joints in the initial stage of the slagging process, in reducing the duration of the melt "under the arc" (on the ACP), which indirectly creates the preconditions for reducing the specific consumption of ladle refractories (ladle slag belt).

The technical result is achieved by the fact that the refining flux for out-of-furnace finishing of steel is a briquette of a slag-forming mixture - which contains a binder in the ratio (1-4)% wt. and compressed particles of components containing aluminum oxide Al ₂ O ₃ in wt. % 30 ÷ 99, while the components are selected, depending on the content of Al ₂ O ₃ , in the following ratios in wt. %: 5 ÷ 35 Al ₂ O ₃ >90; 30 ÷ 70 Al ₂ O ₃ from 55 to 90; the rest is Al ₂ O ₃ <55, and the particles forming the briquette have the following fractional composition, wt. %:> 60 with fraction 0 ÷ 1 mm; 60> 25 with fraction 1 ÷ 3 mm; the rest - with a fraction of 3 ÷ 5 mm, according to the invention, contains waste of secondary aluminum and contains CaO, Al203, MgO, SiO2 and consists of masses. %:

- alumina slag or alumothermic slag with Al2O3 content (70-80)%) - 35-45

- screenings of ordinary aluminum slag with a reduced Al2O3 content (40-50); - 40-50

- screenings of highly basic steel-making slags - 15-20,

the content of SiO2 in the form of refractory mineral components with a melting point above 1690 C in free form is limited to 14%. (quartz, tridymite), which excludes the formation of refractory transition compounds at the initial stage of the slag formation process at a relatively cold slag-metal system, and the content of low-melting alkali compounds of alkali metals (NaCO3, K2CO3, NaCl, KCl, NaF) in terms of oxides ( Na2O + K2O) is limited to 10% wt., Components with Al2O3 content over 70% - in the form of a fraction (0 ... 1) mm in a total amount of up to 40%. The briquette has a volume of 25-80 cm3, the bulk density is 1.0-2.8 g / cm3, the moisture content of the finished briquettes is 0.2-3.0% abs., The open porosity is 10-22%.

The cycle of technological processing includes:

- crushing of lumpy materials to a fraction (2-5) mm;

- drying to moisture (105C) no more than 1.0%;

- separation (fractional screening) on a screen according to the required set of technological fractions;

- selection of technological samples for intermediate control of chemical analysis of prepared components;

- crushing of individual components to a dust-like fraction (-1 mm);

- intermediate storage of components with the formation of batches for subsequent mixing - depending on the "order portfolio";

- batch mixing of prepared components (including the introduction of binders), sampling of the finished powder composition for "intermediate control"; carrying out "intermediate control";

- briquetting of the prepared intermediate mixture4

- intermediate storage of uncured briquettes;

- drying of briquettes;

- intermediate storage of dried briquettes during their cooling, sampling for acceptance tests; acceptance tests.

- packing and packaging, labeling of products that have passed acceptance tests;

- storage of finished products in places of appropriate storage.

In the proposed invention, these disadvantages are solved as follows:

1. In the composition of the charge increased the proportion of "middle fraction" (1-3) mm of alumina components; and the share of "small" is limited - with Al2O3 content over 70% - in the form of a fraction (0 ... 1) mm in a total amount of up to 40%. Due to this, the open porosity increases (GOST 2409-2014) and the conditions for the impregnation of briquettes with viscous cold slag are improved - at the first stage of slag formation.

2. By reducing the SiO2 content in the "refractory mineral phases" (quartz, tridymite), the conditions for the formation of a number of refractory compounds in the slag are excluded; especially - dicalcium silicate (2CaO * SiO2; melting point 2170 C), which blocks the dissolution of lime in slags. This creates conditions for the effective formation of a homogeneous slag, the flow of desulfurization conditions, a decrease in the "secondary gas saturation" of the metal and its "secondary oxidation". This allows you to increase the assimilation of elements from deoxidizers and ligatures. In addition, the accelerated formation of liquid slag in the ladle allows to reduce the number of cases of forced heating of the slag by an arc when introducing ferroalloys or flux-cored wire and, accordingly, to reduce the total “time spent on the melt under current” when processing at the automatic transmission.

3. The limited content of impurities of alkali metals (Na2O + K2O) excludes the formation of "white smoke" and allows the inert gas to be purged at the ACP or AKOS with a higher intensity, somewhat reducing the duration of the final melting in the ladle.

4. The overall reduction in the duration of the “time spent on current melt” creates favorable conditions for reducing the erosion of refractories in the slag belt of the lining of steel-pouring ladles.

Tests of the proposed refining flux for out-of-furnace finishing of steel were carried out at the UPK KKTs PJSC "MK" Azovstal ".

4 variants of the technology and the flux proposed by IZOMETIKA LLC have been tested at the outlet in various combinations with standard slag-forming materials. Acceleration of the formation of liquid slag was visually noted.

According to the results of the conclusion, the use of a flux as an alternative to the currently used flux is technically possible, while the degree of desulfurization is 3.3% lower and the specific cost of desulfurization is 1.93 UAH / t higher.

In the course of the analysis, such indicators as processing time, aluminum consumption were taken into processing, and the heats were divided into groups of steel grades: carbon, low-alloy and strip.

Preliminary results have shown that:

- it is technologically possible to reduce the processing time using the tested flux by an average of 13.7 minutes at a specific consumption of this flux - (0.96 ... 1.5) kg / t, an average of 1.35 kg / t;

- the desulfurization rate is 0.29 10 ^-3 % / min versus 0.20 10 ^-3 % / min on comparative heats;

- the assimilation of aluminum in the experimental melts is higher: the aluminum content in the finished metal was 0.035% at a specific consumption of 0.302 kg / t versus 0.033% at a consumption of 0.312 kg / t in comparative heats;

- the amount of removed sulfur is on average 0.0179% for the experimental and 0.0149% for the comparative data set;

- the temperature of the metal at the beginning of the melting process in the ladle furnace is lower by an average of 3.4 degrees, incl. on low-alloy grades it is 3.3 degrees lower, on strip grades it is 5.7 degrees lower.

A tendency towards a decrease in the specific consumption of aluminum is revealed. Consumption was: for experimental - 140 kg / bucket, for comparative - 162.9 kg / bucket;

The aluminum content in the finished metal in the pilot and comparative melts is close. This can be explained by the better fluidity of the slag when using the proposed flux.

The results of heat treatment with the use of the tested flux on the UPC are presented in the Table.

1 Duration of processing on the UKP on experimental heats for 13.7 minutes. less than comparative ones.

2 The temperature of the metal at the beginning of processing at the UKP is on average 3.4 ° C lower, incl. on n / doped - by 3.3 ° С, on strip - by 5.7 ° С.

3 Desulfurization rate: - on experimental - (0.0268-0.009) / 60 = 0.29⋅10 ^-3 % / min;

- on comparative (0.0217-0.0068) / 73.7 = 0.20-10 ^-3 % / min.

4 Total consumption of aluminum: - for experimental: 0.015 + 0.140 + 0.147 = 0.302 t / pl. when the Al content in the finished metal is 0.035%;

- on comparative: 0.01 + 0.163 + 0.142 = 0.315 t / pl. with an Al content of 0.034% in the finished metal).

Claims (3)

Refining flux for out-of-furnace finishing of steel is a briquette from a slag-forming mixture containing a binder of 1-4 wt. % and compressed particles of components containing aluminum oxide Al ₂ O ₃ , 30 ÷ 99 wt. %, characterized in that as components containing aluminum oxide Al ₂ O ₃ , it contains waste secondary aluminum, contains CaO, Al ₂ O ₃ , MgO, SiO ₂ and consists of, wt. %: alumina slag or alumothermic slag with A1 ₂ O ₃ content 70-80% 35-45 screenings of ordinary alumina slag with Al ₂ O ₃ content 40-50% 40-50 screenings of highly basic steelmaking slag 15-20, while the content of SiO ₂ in the form of refractory mineral components with a melting point above 1690 ° C in free form is limited to 14%, the content of low-melting compounds of alkali metals in the form of NaCO ₃ , K ₂ CO ₃ , NaCl, KCl, NaF in terms of Na oxides ₂ O + K ₂ O limited to 10 wt. %, components with an Al ₂ O ₃ content over 70% in the form of a fraction of 0 ... 1 mm in a total amount of up to 40%, and the briquette has a volume of 25-80 cm ³ , the bulk density is 1.0-2.8 g / cm ³ , moisture content of finished briquettes 0.2-3.0 abs.%, open porosity 10-22%.