AN ALLOY FOR STEEL DEOXIDATION
ABSTRACT
An objective of the present invention is to provide a complex composition that could allow not only to perform its main function of removing oxygen from a liquid steel, but also to expand its functionality by adding titanium in certain ratios to the alloy, thereby supplementing it with additional properties due to modification and microalloying, as well as enhancing mechanical and usage properties of the treated steel such as wear resistance, toughness, weldability, fire resistance, cold resistance and plasticity, as well as to enhance assimilation of silica in the process of melting the metal, to reduce its loss and to reduce a cost price of a finished steel.
DESCRIPTION
The invention relates to a field of ferrous metallurgy, in particular, to processes for creating an alloy for deoxidation, modification and microalloying of steel.
The known method for steel deoxidation is deoxidation by metallic aluminum (1). Aluminum being a deoxidizer is the most widespread and inexpensive, the most affordable and easy-to-use deoxidizer, however, it has drawbacks. First of all, it is associated with the fact that in the process of ladle deoxidation using aluminum as the deoxidizer, the actual aluminum assimilation degree is not more than 30-40% (2), and after deoxidation, it converts into Al2O3 oxide and suspended in the melt steel in the form of very fine particles, while this takes very long time for it to rise to the surface and to convert into slag. The reason is that Al2O3 particles are very fine as compared to other deoxidation products. Common deoxidation products such as MnO and SiO2 have a large size of the particles, so they rise to the surface of the melt steel easily and withdrawn by means of a slag catcher. Al2O3 suspended in this way eventually remains in a solidified steel article in the form of non-metallic inclusions. The more non-metallic inclusions remain in the article, the worse mechanical properties of the cast steel become.
An alloy (being a prototype) for steel deoxidation is known (being an iron-aluminum-silica alloy), the alloy has the following composition, in wt.%: 10.0-30.0 of silica; 30.0-75.0 of aluminum; the remainder of iron and impurities within acceptable ranges (patent of Ukraine UA60931А, С22С35/00) (3).
A drawback of this alloy is that the steel treated with this alloy has a rather low wear resistance and other mechanical and usage properties.
An objective of the present invention is to achieve, due to additional deoxidation and modification by a titanium introduced into the prototype composition in certain ratios, a deeper and more stable deoxidation, to improve mechanical and usage properties of the treated steel such as wear resistance, toughness, weldability, fire resistance, cold resistance and plasticity, as well as to improve the assimilation of silica in the melting process of the metal, to reduce its loss and to reduce a cost price of a finished steel.
Titanium is a proper steel deoxidizer and modifier that surpasses aluminum in terms of its deoxidizing power. It binds nitrogen and sulfur to form rigid compounds by neutralizing their influence onto the steel. In combination with other elements, it increases viscosity, rigidity and wear resistance of the steel, corrosion resistance, while maintaining weldability (4).
Owing to strong and chemically active titanium introduced into the known prototype composition in the ratios of 6-15%, a complex metallurgic alloy is obtained, where each element of the complex (Al, Si, Ti) supplements each other and cumulatively allows to carry out a deeper and more stable steel deoxidation. This is achieved during combined deoxidation, modification and microalloying of the liquid steel with aluminum, silica and titanium.
The subject matter of the claimed invention is as follows:
An alloy for steel deoxidation comprising aluminum, silica and iron, wherein, in order to enhance mechanical and usage properties, it further comprises titanium and maximum allowable values of impurities at the following ratio of components, in wt.%:
| Alloy grade | Weight fraction of chemical components, % | |||||||||
| Al | Si | Ti | Cu | Pb | Mn | Zn | S | P | Fe | |
| Impurities, not more than | ||||||||||
| The claimed alloy | 20-28 | 8-15 | 6-15 | 0.5 | 0.1 | 0.5 | 0.05 | 0.03 | 0.03 | Remainder |
Table 1
The established limits of the ratio of components in the alloy are reasonable.
A reason for establishing the content limit of aluminum of from 20 to 28% according to the present invention is to aim at reduction of damaging the steel by non-metallic inclusions such as Al2O3 which are formed in the aluminum-containing deoxidizers as mentioned above. It is believed that this is the most suitable content in terms of deoxidation price and efficiency.
The composite deoxidizer of the present invention has 8-15% of silica embedded therein. Silica (Si) also possesses a proper deoxidizing power, and after a deoxidation reaction, it forms a cluster with SiO2, Al2O3, TiO2 etc., as well as converts into the slag easily.
The presence of 6.0-15.0 wt. % of titanium in the proposed alloy facilitates the deeper and more stable deoxidation of the steel. However, in this case, it is necessary to dose an amount of the introduced additives as well, since an excessive final amount of titanium (being greater than 0.03-0.04 wt. %) may reduce the level of plastic and viscous properties of the cast steel.
In particular, reduction of the titanium concentration below a certain limit in the alloy will not ensure the desired deoxidation, microalloying and modification effect of the remaining non-metallic inclusions during treatment of the steel. At the same time, an exceedance of acceptable limits of the concentration of these elements (Al, Si and Ti) is not reasonable, since the manufacturing cost of the claimed alloy will be increased, and positive properties during its use will not significantly differ from the claimed limits in terms of the composition.
In laboratory conditions, by loading iron, aluminum, titanium and ferrosilicium scrap in a certain sequence to an induction furnace, three compositions of the claimed steel deoxidation alloy as well as one known composition having an average vale of ingredients have been smelt (Table 2).
| Alloy | Weight fraction of chemical components, % | |||||||||
| Al | Si | Ti | Cu | Pb | Mn | Zn | S | P | Fe | |
| Impurities, not more than | ||||||||||
| I | 24 | 8.5 | 10 | 0.5 | 0.1 | 0.5 | 0.05 | 0.03 | 0.03 | Remainder |
| II | 24.2 | 8.4 | 10.2 | 0.4 | 0.1 | 0.4 | 0.05 | 0.02 | 0.02 | Remainder |
| III | 23.9 | 8.5 | 10.1 | 0.4 | 0.1 | 0.5 | 0.05 | 0.02 | 0.03 | Remainder |
| Prototype | 45 | 20 | 0 | 0.3 | 0.1 | 0.5 | 0.04 | 0.02 | 0.03 | Remainder |
Table 2
Hereinafter, a brief description of a process for smelting the claimed alloy deoxidizer will be provided.
A laboratory induction crucible mid-frequency furnace of an IST series having a yield of a final alloy of 10 kg was used as a furnace unit.
All portion of a steel scrap was successively loaded into a crucible of the furnace, and after its complete meltdown, titanium scrap, ferrosilicium and aluminum scrap were loaded into the furnace. The alloy was stirred thoroughly, adjusted to a letdown temperature and ladled out to special mold boxes.
In order to obtain a test sample of the claimed alloy, a furnace charge consisting of the following materials was used:
1) Steel scrap St3 having the following composition of chemical elements in %:
C – 0.19, Si – 0.21, Mn – 0.5, S – 0.03, P – 0.035, Cu – 0.3, Cr – 0.2, Fe – the remainder.
2) Aluminum scrap having Al content of at least 99%
3) Ferrosilicium FeSi65 according to the GOST1415-93
4) Titanium scrap having Ti content of 95%
The obtained alloys were used for deoxidizing the steel grade St35. The steel is treated with identical amounts of the known alloy and the claimed alloy (1.5 g/kg of steel) without any additional corrections.
During metallographic analysis, a grain-size number of the steel structure and contamination index with the non-metallic inclusions were evaluated. Results of the conducted test have shown that the deoxidation with the claimed novel “Alloy for steel deoxidation” facilitates formation of the fine-grained structure, thereby resulting in change of mechanical properties of the steel.
Based on the obtained data, it has been supposed that the developed composition of the complex alloy allows to increase strength properties (σ0.2 and σb) of the final product up to a level of 740-760 MPa and, at the same time, to increase deformability characteristics (a value of overall uniform elongation at a maximum load – δmax, and a ratio between a tensile strength and a flow stress (σв/σ0.2) due to formation of the fine-grained structure based on nanodispersed carbonitride phases and change of morphology of the non-metallic sulfur-based inclusions. Therewith, these products will have an increased seismic resistance (fatigue strength), cold resistance, fire resistance and fire durability, while maintaining weldability.
Due to increase of the flow stress up to 15-20 percent, low-carbon structural steel grades have a higher level of plasticity and a smaller tendency to formation of cracks in hot state which is important during continuous steel teeming.
Table 2 provides results of laboratory tests of the mechanical properties of the steel of the claimed alloys. Tensile strength tests were carried out on a versatile test machine of MIG series for 100 tons, and the toughness was determined on a Charpy impact machine.
| Variant | Mechanical properties of steel | |||
| σb | σt | δ, % | KCU+20
kJ/m2 |
|
| The claimed alloy for steel deoxidation | 750 | 315 | 23 | 75 |
| The known alloy (prototype) | 630 | 270 | 19 | 60 |
Table 3
Therefore, the claimed invention “An alloy for steel deoxidation” as compared to the prototype, due to additional content of titanium, allows to:
– carry out a deeper and a more stable steel deoxidation;
– reduce the content of the non-metallic inclusions significantly;
– modify the remaining non-metallic inclusions into advantageous complexes and to ensure their uniform distribution within the steel volume;
– enhance the mechanical and performance properties of the steel;
– increase the assimilation of silica by the steel and to reduce its loss.
In the course of subsequent experimental-industrial melting operations, it has been found that each kilogram of the claimed titanium-containing deoxidizer that also acted as a catalyst for silica assimilation reduces a consumption of ferrosilicium (FeSi) used in the melting process per 2-3 kilograms which may ensure a high economic benefit.
The conducted experimental-industrial melting operations and the achieved research and technical effect allows to state that the claimed composition of the steel deoxidizer is substantially novel.
Sources of technical information:
1. V.L. Trybushevsky, Ph.D., L.V. Trybushevsky, B.M. Nemenenok, D.Sc., G.A. Rumyantseva, Ph.D. (BNTU). Special aspects of deoxidation of steel with aluminum s.3-8 Metallurgy : Republican interagency collection of research papers. Vol. 35 / ed. team: V. I. Tymoshpolsky [et al.]. – Minsk : BNTU, 2014.
2. S.G. Melnyk, A.I. Trotsan, А.А. Onishchenko, B.Ph. Belov, PJSC “Donetskyy zavod ferrosplavov” regarding use of Al-containing ferroalloys for steel deoxidation s1-4. 204/CASTING AND METALLURGY 3(72).2013
3. Patent of Ukraine UA60931 A, С22С35/00
4. Ivchenko A.V. Reinforcement for construction operations in seismic areas. Manufacturing, usage and control aspects. Aspects, Min Miner Sci. 11(3). AMMS. 000762. 2023. s 1-5
CLAIMS
- An alloy for steel deoxidation comprising aluminum, silica and iron, wherein, in order to enhance mechanical and usage properties, it further comprises titanium at a following ratio of components, in wt.%:
– 20-28% of aluminum;
– 8-15% of silica;
– 6-15% of titanium;
impurities:
– 0.5% at most of copper;
– 0.1% at most of lead;
– 0.5% at most of manganese;
– 0.05% at most of zinc;
– 0.03% at most of sulfur;
– 0.03% at most of phosphorus;
– the remainder of iron.
Authors: Abbasov Маzаhir Аbbаs oglu; Кuпgurоv Yurii Yurievich