RU2626110C1 - Method of smelting low-alloy vanadium containing steel - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: in the charge, naturally-alloyed vanadium-containing cast iron of batch production is used, and after the melting slag has been loaded, the carbon oxidation is carried out with non-fluxed vanadium-containing pellets serially produced from titanomagnetite raw materials, after which the vanadium is reduced from slags of oxidation periods and "pure" boiling by introducing ferrosilicon in the period of preliminary deoxidation of metal from the calculation of 2-3 kg of silicon per ton of the spent pellets.

EFFECT: invention allows to reduce the cost of alloying vanadium steel, to improve the processability of melting and the quality of the metal due to the low sulfur content of vanadium-containing cast iron and vanadium-containing pellets, which practically excludes additional techniques for desulfurizing the metal, while a much lower content of coloured impurities provides additional increasing the quality characteristics of vanadium-containing steels for castings.

4 cl, 3 ex

Description

The invention relates to the field of metallurgy, in particular to the smelting of vanadium-containing steels for castings produced in the main open-hearth furnaces by the scrap process, and is aimed at reducing the cost of alloying vanadium steel and improving the quality of the metal.

The classic way of smelting vanadium-containing steels in the main open-hearth furnace is the introduction of vanadium-containing ferroalloys into the ladle. However, due to the high affinity of vanadium for oxygen and the increased oxidation of furnace open-hearth slag before the release of vanadium fumes from the ferroalloy is 20-30% and higher [1]. Known methods for the production of vanadium-containing steel in steelmaking units, including in an open-hearth furnace, by introducing into the ladle oxide vanadium-containing materials together with reducing agents [2]. In this case, as the oxide of vanadium-containing material using technical vanadium pentoxide, containing 83.0 wt. % V ₂ O ₅ . The disadvantage of this method is the regulated introduction in the composition of a single mixture of a large amount of oxide manganese-containing material. The low melting point of vanadium pentoxide (about 650 ° C) in combination with high-temperature oxide manganese-containing material does not provide stable assimilation of vanadium from pentoxide.

The closest in technical essence and the achieved result is the technology of introducing vanadium into the main open-hearth steel when using the “Mixture for alloying steel” [3], which contains, by weight. %: pig iron 6.0-17.0; ferrosilicon 0.1-1.0; Naturally alloyed with vanadium and titanium cast iron - the rest. The liquid mixture is poured into an open-hearth furnace during the preliminary deoxidation of the melt-intermediate. The disadvantage of this method is the need for the preparation of the “Mixture” melt in a separate container of liquid cast irons: redistributable and vanadium-containing. Such conditions cannot be ensured in the conditions of workshops smelting steel for castings, where only the scrap process is realized.

The objective of the invention is to reduce the cost of alloying with vanadium, increasing the manufacturability of the smelting and obtaining high-quality low-alloy vanadium-containing steel in the main open-hearth furnace operating by the scrap process for castings for critical purposes used in car building and other industries.

This goal is achieved by the fact that in the open-hearth furnace charge, working with a scrap process, including filling cast iron, scrap steel, fluxing into the furnace, melting the mixture, downloading slag, oxidizing period, “clean” boiling, preliminary deoxidation, alloying to steel grade in ladle, in the proposed method, pig iron vanadium-containing cast iron is used as the pig-iron component, and after downloading the melting slag, the carbon is oxidized by vanadium-containing iron ore pellets, after which dovosstanovlenie vanadium slag oxidation periods and "pure" boiling due to input ferrosilicon metal preliminary deoxidation period the rate of 2-3 kg of silicon from ferrosilicon consumed per tonne pellets. In this case, alloying to a predetermined grade of vanadium is carried out in the ladle by introducing vanadium-containing ferroalloys.

Pig vanadium-containing cast iron is a naturally-alloyed vanadium-containing cast iron of serial production, smelted in blast furnaces from iron ore titanomagnetite raw materials, for example, Kachkanarsky deposit, composition, wt. %: 0.4-0.5 V; 0.35-0.5 Mn; 0.05-0.1 Si; 0.15-0.18 Ti; 0.02-0.028 S; 0.06-0.07 P; 4.2-4.8 C; Fe - ost.

From the scientific and technical literature it is known the use of such cast iron in filling for producing vanadium-containing steels in acid open-hearth furnaces [4]. The disadvantage of this technology is that in an acidic process, due to the weak oxidation of vanadium, the consumption of vanadium iron in the filling is regulated by the grade content of vanadium in the finished steel, in particular, when the content in the steel is 0.05-0.09 wt. % vanadium, cast iron consumption in the filling is 11-19 wt. % This amount is much less than the consumption rates of cast iron in the charge of the main open-hearth scrap-process. In addition, the smelting is carried out without downloading the melting slag, i.e. does not involve the removal of phosphorus from the charge.

In a standard batch for steelmaking for castings in the main open-hearth furnaces by the scrap-process, the amount of pig iron and scrap iron is usually 40 wt. % of metal filling. With a complete replacement in the charge of pig iron for blast-furnace vanadium-containing pig iron, about 0.17 wt. % vanadium (calculated on the entire metal filling). In vanadium-containing grades of low alloy steels for castings, the content of vanadium is usually 0.03-0.12 wt. %

But with the standard melting technology in the main open-hearth furnaces, the scrap process at the necessary stages of dephosphorization and desulfurization removes the melting slag and the oxidized period slag. During these periods, most of the vanadium is oxidized, falls into these slags and is removed from the furnace. However, such a loss of vanadium in this case does not affect the economic indicators of the process, since the cost of pig iron and vanadium-containing cast iron has now become almost the same.

At the same time, it should be noted that the substitution of vanadium-containing pig iron in the open-hearth smelting furnace charge for the presence of residual vanadium in steel and the production of a metal that is cleaner in terms of harmful impurities (the content of non-ferrous metals — copper, zinc, lead, tin, and others. less than in pig iron), which positively affects the properties of steel for castings. In addition, the sulfur content in naturally-alloyed vanadium-containing cast iron is also lower than in pig iron, which reduces the time for metal desulfurization in open-hearth smelting, and, most importantly, eliminates the forced loading of slag during oxidation and “clean” boiling.

Thus, the introduction of vanadium cast iron into the filling in the main open-hearth scrap process (at its standard flow rate) for the smelting of low-alloy vanadium-containing steels for castings provides the solution to three problems:

- the introduction of part of the necessary vanadium in steel;

- improving the manufacturability of the main open-hearth scrap-process;

- an additional increase in the properties of the finished vanadium-containing steel due to the greater purity of the metal by color impurities.

As vanadium-containing pellets, commercially produced non-fluxed pellets are used from a concentrate of titanomagnetite ores, for example, Kachkanarsky deposit, composition, wt. %: 60-63 Fe total (in oxides), including 1.5-2.8 FeO; 0.5-0.6 V ₂ O ₅ ; 2.5-3.0 TiO ₂ ; 1.3-1.8 CaO; 4.0-4.5 SiO ₂ .

From scientific, technical and patent information, it is known to use such pellets for producing vanadium-containing steels [5].

However, all such technologies involve the use of only vanadium-containing pellets, pre-metallized, and are focused on obtaining vanadium-containing steels in electric arc furnaces.

According to the proposed solution, in the main open-hearth scrap process, the original (oxidized) vanadium-containing pellets used play a dual role: as a carbon oxidizer in the oxidation period and the period of “clean” boiling (there is no information on this technique in scientific, technical and patent sources), as well as An additional source of vanadium in the mixture.

Of the slag formed with the participation of vanadium-containing pellets, vanadium is re-reduced by silicon ferrosilicon together or after giving all regular deoxidizers during the preliminary deoxidation. The amount of silicon in the ferrosilicon necessary for the reduction of vanadium from furnace slag amounts to 2-3 kg per ton of spent vanadium-containing pellets and is determined based on the stoichiometric ratio of the reduction of vanadium oxides by silicon at an adopted silicon fume of 20-30%. A decrease in this flow rate below 2 kg of silicon from ferrosilicon will reduce the degree of additional reduction of vanadium, and an increase in excess of 3 kg of silicon from ferrosilicon will lead to an undesirable transition of excess silicon to metal. Vanadium recovered from furnace slag will provide an increase in the vanadium content in the metal before release, which will reduce the consumption of vanadium-containing ferroalloys specified in the ladle to achieve the vanadium grade in the finished steel.

The estimated balance sheet of vanadium with the proposed method of smelting is given below. In the calculation, we used the actual data on open-hearth melting obtained with the complete replacement of the pig iron in the charge for vanadium-containing, as well as the known data on the reducibility of vanadium from slag melts with silicon (taking into account the use of vanadium-containing pellets).

The average content of vanadium in the naturally doped series-produced vanadium cast iron, smelted from Kachkanar raw materials, wt. % - 0.435 The proportion of vanadium-containing cast iron in the mixture,% - 40 Vanadium is introduced into the mixture by cast iron, wt. % - 0.174 The average content in the pellets of vanadium, wt. % - 0.315 Consumption of unfluxed vanadium-containing pellets from Kachkanar raw materials (pellet consumption rate), kg / ton of liquid metal - 25 Vanadium is introduced into the mixture by pellets, wt. % - 0.008 The average share of vanadium from cast iron in finished steel,% - 7 The average degree of additional vanadium silicon from slags,% - 60 Vanadium is retained on average in cast iron steel, wt. % - 0.012 Vanadium from pellets is recovered, wt. % in steel - 0.005 The average vanadium content in steel before release, wt. % - 0.017

The calculation shows that in the proposed method it is possible to provide an average vanadium content in steel before the release of 0.017 wt. %, i.e. introduce about 25% of vanadium from its average brand amount (0.065 wt.%).

Examples of specific implementation.

Example 1. Steel grade 20GL for cast parts of wagon carriages was smelted in a 60-ton open-hearth main furnace using a scrap-process, in which pig iron vanadium-containing iron smelted from iron ore titanium-magnetite raw material (vanadium content - 0.442 wt.%) In amount was used 40 wt. % of the metal volume of the charge (instead of pig iron), steel scrap and fluxing materials. After the charge was melted and the melting slag was downloaded, carbon was oxidized during the oxidation period by non-fluxed vanadium-containing pellets of serial production (content of vanadium pentoxide 0.56 wt.%) In the amount of 25 kg per ton of metal, i.e. 1.5 tons of vanadium-containing pellets were introduced into the furnace. Forced download of slags of the oxidation period and the period of "clean" boiling was not performed. Additional slag guidance for the desulfurization of the metal was not required due to the low sulfur content in vanadium cast iron.

During the preliminary deoxidation, after giving the necessary deoxidants, 45% ferrosilicon in the amount of 7 kg was introduced onto the surface of the slag melt - based on 2.1 kg of silicon per ton of spent pellets. The vanadium content in the steel before release and in the finished steel was 0.016 wt. % The content of regulated elements in 20GL steel was within the norms of the technological instruction of the enterprise.

According to this technology, a series of 20 melts was conducted at a flow rate of vanadium-containing pig iron and vanadium-containing pellets in accordance with the above-mentioned flow rates when changing the flow rate of silicon from ferrosilicon to re-establish vanadium in the range of 2-3.5 kg per ton of spent vanadium-containing pellets.

Sulfur by melting - not more than 0.034% versus 0.045 wt. % during serial melting of steel 20GL on pig iron, as a result of which additional guidance of slags for metal desulfurization was not required. The average copper content was 0.09 wt. % against 0.15 wt. % in serial melts of steel 20GL on pig iron. The vanadium content in the finished steel was in the range of 0.014-0.020 wt. %

When the consumption of silicon from ferrosilicon in the amount of 3.5 kg per ton of spent vanadium-containing pellets (two melts), the silicon content in the finished steel was at the upper limit of the grade.

The main acceptance indicator, providing increased operational reliability and the elimination of emergency failures in the winter period of operation of cast parts, is the impact strength KCV ^-60 . Statistical analysis of a serial data array of 20GL steel showed that impurity copper has the most significant effect (like increased sulfur) on the reduction in toughness at low temperatures within the grade composition. At the same time, it is known that the positive effect of vanadium on the properties of steel, including toughness, begins already with a vanadium content of 0.01 wt. % [6].

The average impact strength in the specified series of 20 heats was KCV ^-60 = 24 J / cm ² . The average index of an array of serial melts of steel 20GL on pig iron is KCV ^-60 = 20 J / cm ² . Thus, the presence in the steel of 0.014-0.020 wt. % vanadium in combination with a smaller amount of colored impurities received from vanadium-containing cast iron, in particular copper (according to the inventive technology) provides an increase in the cold resistance of steel by KCV ^-60 by 20%.

Example 2. Vanadium-containing steel grade 20FTL was smelted in a 60-ton open-hearth main furnace using a scrap-process, in which pigment vanadium-containing cast iron smelted from iron ore titanium-magnetite raw material (vanadium content - 0.44 wt.%) In an amount of 40 wt. % of the metal volume of the charge (instead of pig iron), steel scrap and fluxing materials. After the charge was melted and the melting slag was downloaded, carbon was oxidized during the oxidation period by non-fluxed vanadium-containing pellets of serial production (content of vanadium pentoxide 0.56 wt.%) In the amount of 25 kg per ton of metal, i.e. 1.5 tons of vanadium-containing pellets were introduced into the furnace. Forced download of slags of the oxidation period and the period of "clean" boiling was not performed. In the period of preliminary deoxidation after giving deoxidizers in accordance with the technological instructions, 45% ferrosilicon in the amount of 7 kg was introduced onto the surface of the slag melt - based on 2.1 kg of silicon per ton of spent pellets. The vanadium content in the steel before release was 0.018 wt. % To adjust the vanadium content, 50% ferrovanadium was introduced in both 30-ton casting ladles in the amount of 39 kg (based on 20% vanadium fume). The vanadium content in the steel of both buckets was 0.07 wt. % (corresponding to the brand), sulfur content - 0.017 wt. %, phosphorus - 0.019 wt. %; the content of the remaining elements was within the brand composition. Thus, the proportion of the introduction of vanadium from vanadium-containing cast iron and vanadium-containing pellets to the obtained vintage content was 25.7%. All regulated mechanical properties of 20FTL steel corresponded to the norms of the Technological instruction of the enterprise.

Example 3. Vanadium-containing steel grade 32X06FL was smelted in a 60-ton open-hearth main furnace using the scrap process, in which pig iron vanadium-containing cast iron with a vanadium content of 0.43 wt. % (instead of conversion) in an amount of 40 wt. % of metal charge, steel scrap and fluxing materials. After melting and downloading the melting slag, the oxidation period was carried out by introducing vanadium-containing pellets in an amount of 1.5 tons. Forced download of slags of the oxidation period and "clean" boiling was not performed. During the preliminary deoxidation, along with regular deoxidizers, 8.5 kg of 45% ferrosilicon was added to the surface of the slag melt at the rate of 2.6 kg of silicon per ton of spent pellets. The vanadium content in the steel before release was 0.019 wt. % To adjust the vanadium content, 50% ferrovanadium in an amount of 40 kg was introduced into both 30-ton buckets in each bucket. The vanadium content in the finished steel was 0.08 wt. % (corresponding to the brand), sulfur content - 0.017%, phosphorus - 0.020%; the content of the remaining elements was within the brand composition. In this case, the proportion of vanadium introduced into the steel from vanadium-containing cast iron and vanadium-containing pellets in relation to the obtained vintage amount was 23.7%. All regulated mechanical properties of steel 32X06FL met the standards of the technological instructions of the enterprise.

Thus, the proposed method allows, under the conditions of the main open-hearth furnace operating by the scrap process, to smelter vanadium-containing steels for high quality castings while reducing the consumption of expensive vanadium-containing ferroalloys due to the use of naturally alloyed vanadium-containing cast iron and vanadium-containing pellets in the charge.

The effectiveness of the proposed technical solution lies in the fact that the cost of alloying steel with vanadium is reduced due to a part of the practically “free” vanadium introduced into the charge by vanadium-containing naturally-alloyed cast iron and non-fluxed vanadium-containing pellets, since their cost is almost the same with similar raw materials that do not contain vanadium. In quantitative terms, the reduction in the cost of steel from a decrease in the consumption of vanadium-containing ferroalloys (at their current market price) is about 200 rubles. 100 thousand tons - about 20 million rubles per ton or with annual production.

In addition, when vanadium-containing cast iron is used in the main open-hearth smelting mixture, instead of the usual conversion, the efficiency is manifested in an increase in the main open-hearth smelting processability, namely, a reduction in the consumption of fluxing materials for metal desulfurization and labor costs for multiple slag downloading after the oxidation period and the period of “clean” boiling. We also note that the economic advantage of the proposed technical solution is an additional increase in the quality characteristics of vanadium-containing steels smelted in the main open-hearth furnaces, due to the lower content of color impurities in the used vanadium-containing naturally-alloyed cast iron and vanadium-containing pellets.

Information sources

1. G.N. Oyx. “Steel production” (foundations of theory and technology). M .: Metallurgy, 1974, p. 385, 411, 414.

2. RF patent No. 2228372, 12.24.2002.

3. Copyright certificate. USSR No. 1395686, 01/15/1988.

4. E.I. Arzamastsev, V.I. Dovgopol. The article "The use of vanadium cast iron for alloying steel", in coll. “Complex processing of iron ores”, Proceedings of the Ural Scientific Research Institute of Ferrous Metals, Sverdlovsk, 1976, p. 95-100.

5. V.A. Rovnushkin, B.A. Bokovikov, S.G. Brothers, A.M. Amdur, E.I. Arzamastsev et al. Book “Cox-free processing of titanomagnetite ores”. M .: Metallurgy, 1988, p. 21-41, 136-205.

6. I.N. Golikov, M.I. Goldstein, I.I. Murzin. Monograph "Vanadium in Steel." M .: Metallurgy, 1968, 291 p.

Claims (4)

1. A method of smelting low-alloy vanadium-containing steel for castings in the main open-hearth furnace by a scrap-process, including filling the furnace with a cast iron component, scrap steel, fluxing materials, melting the mixture, downloading melting slag, oxidizing period, “clean” boiling, preliminary deoxidation metal, characterized in that pig iron vanadium-containing cast iron is used as the pig-iron component of the charge, and after downloading the melting slag, the carbon is oxidized by vanadium-containing and the iron ore pellets, followed by dovosstanovlenie vanadium slag oxidation periods and "pure" input through boil ferrosilicon metal preliminary deoxidation period the rate of 2-3 kg per tonne of silicon consumed pellets. 2. The method according to p. 1, characterized in that the pig iron vanadium-containing cast iron is used in the form of naturally-alloyed vanadium-containing cast iron of serial production, smelted from titanomagnetite iron ore raw materials of the composition, wt. %: 0.4-0.5 V; 0.3-0.5 Μn; 0.05-0.1 Si; 0.15-0.18 Ti; 0.02-0.028 S; 0.06-0.07 P; 4.2-4.8 C; Fe the rest. 3. The method according to p. 1, characterized in that as the vanadium-containing iron ore pellets are used commercially produced non-fluxed pellets from a concentrate of titanomagnetite ores of the composition, wt. %: 60-63 Fe total (in oxides), including 1.5-2.8 FeO; 0.5-0.6 V ₂ O ₅ ; 2.5-3.0 TiO ₂ ; 1.3-1.8 CaO; 4.0-4.5 SiO ₂ . 4. The method according to p. 1, characterized in that it is doped with vanadium to the grade composition by introducing vanadium-containing ferroalloys into the ladle.