RU2395611C2 - Nitrogen containing alloy for steel alloying and procedure for its production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention refers to metallurgy, particularly to nitrogen containing alloys on base of calcium, silicon and iron. alloy contains wt %: calcium 5-34, silicon 17-55, nitrogen 11-29, iron - the rest. Alloy is produced from source material crumbled into powder with dimension of particles less, than 2.5 mm and it is placed in atmosphere of nitrogen containing not less, than 95 volume % of nitrogen at pressure 0.1-15.0 MPa. Further, there is initiated an exothermic reaction of calcium and silicon nitrides by source powder local heating to temperature of reaction start under a layer-by-layer mode of combustion. The said temperature and pressure are maintained to reaction end under the layer-by-layer mode of volume combustion. After-nitriding is carried out under the mode of volume combustion during 0.1-2.0 hours.

EFFECT: production of nitrogen containing alloy of low-2,5-3,5 g/cm³ density, which can be used with higher efficiency, when blown into steel in form of powder or powder wire.

7 cl, 1 tbl

Description

The invention relates to ferrous metallurgy, in particular to alloys for alloying steel, and in particular relates to a nitrogen-containing material based on calcium, silicon and iron.

Calcium is widely used in steelmaking as a highly effective deoxidizer. In addition, calcium is a good modifier. Improving the operational properties of the metal is achieved by a favorable change in the shape and type of oxide and sulfide inclusions.

In both domestic and foreign steelmaking, the main material used to process the melt with calcium is silicocalcium, an alloy of calcium with silicon and iron. Less commonly used are calcium carbide (CaC ₂ ) and calcium cyanamide (CaCN ₂ + C). Calcium cyanamide is obtained by heating calcium carbide powder in a nitrogen atmosphere. The industrial product thus obtained is a mixture of carbon powder and calcium cyanamide itself, as well as a significant amount of calcium oxide. A known mixture for alloying steel, containing 20-80% calcium cyanamide, 10-60% fluorspar, 1-9% aluminum and titanium, the rest is cryolite (USSR Author's Certificate No. 1067073, C22C 35/00, publ. BI No. 2, 1984). The disadvantage of this mixture is that along with the introduction of nitrogen into the steel, the melt is saturated with the same amount of carbon.

A known method of producing calcium cyanamide with traditional ferroalloys, such as ferrotitanium, ferromanganese and others (German patent No. 1533257, C22C 35/00, publ. 22.06.72), in which a mixture of powders of 50-90% calcium carbide with 50-10% ferroalloys are heated in an electric furnace for a time sufficient to obtain calcium cyanamide. Along with the fact that the method allows to obtain alloying material with a high nitrogen content, it has a significant drawback due to the high energy consumption and the need for long exposure at high temperature. In addition, the product obtained in this way has a high carbon content.

According to the invention according to the copyright certificate of the USSR No. 1765234, C22C 35/00, publ. in BI No. 36, 1992, “Modifying mixture”. A mixture is proposed containing magnesium, graphite, titanium dioxide, vanadium pentoxide, calcium nitride and ferrosilicon. The proposed mixture provides improved quality cast iron castings, however, it cannot be used to introduce nitrogen into steel with a low carbon content. Despite the fact that nitrogen is represented in the mixture by carbon-free calcium nitride, it additionally contains a large amount of carbon (graphite). In addition, the presence of a mixture of poisonous vanadium pentoxide makes it extremely dangerous to use. The mixture is obtained by mixing powders of magnesium, ferrosilicon, vanadium pentoxide, titanium dioxide, calcium nitride and graphite, followed by packing the mixture. Closest to the achieved result to the claimed object is “Metal composition and method for its preparation” (German patent No. DE 3011962, CL. C22C 29/16, publ. 15.01.87, authors Ziatdinov M.Kh., Maksimov Yu.M. . and etc.). The prototype patent proposes highly nitrogen alloying alloys containing Al, Ti, Si, Zr, V, Nb, Cr, Mn and Fe. Nitrogen in the amount of 5-17% is presented in the form of metal nitrides of 3-7 groups of the periodic system. A method for producing such alloying compositions consists in nitriding the powders of the initial ferroalloys in the combustion mode under increased nitrogen pressure and is characterized by a low power consumption. The disadvantage of the prototype invention is that the metal composition does not simultaneously allow Ca and Si to be introduced with nitrogen without the introduction of metals of 3-7 groups, and the method does not provide a calcium-containing alloy with nitrogen.

The technical result of the invention is the creation of a new alloying material, the main components of which are calcium, silicon, nitrogen and iron, as well as a cheap and effective method for producing such an alloy.

The problem is solved in that a nitrogen-containing alloy is proposed for alloying steel, including calcium, silicon, nitrogen and iron, the components of which are taken in the following weight ratio:

calcium 5-34 silicon 17-55 nitrogen 11-29 iron rest

A method is also proposed for producing said nitrogen-containing alloy for alloying steel, comprising grinding the starting material in the form of an alloy into powder and nitriding it in a combustion mode, in which an alloy or a mixture of several alloys containing calcium, silicon and iron is used as an alloy of the starting material, in the following their weight ratio, wt.%:

calcium 10-40 silicon 40-65 iron rest,

the alloy is crushed into a powder with a particle size of less than 2.5 mm, the powder is placed in a high-pressure unit in a nitrogen atmosphere containing at least 95.0 vol.% nitrogen at a pressure of 0.1-15.0 MPa, an exothermic reaction is formed calcium and silicon nitrides by local heating of the powder to the temperature of the start of the reaction in a layered combustion mode and maintain this temperature and pressure until the end of the reaction in a layered combustion mode, followed by nitriding in volumetric combustion mode at a pressure of 0.10-2.0 hours. The initial Ca-Si-Fe alloy may contain up to 5% of impurities (C, S, P, Al, etc.) due to the production technology.

When calcium interacts with nitrogen, the only Ca ₃ N ₂ nitride is formed, and a large amount of heat is released - 709 cal / g. In the silicon - nitrogen system, a strongly exothermic reaction also occurs with the formation of a refractory silicon nitride Si ₃ N ₄ (the thermal effect of the reaction is 1280 cal / g). At the same time, iron nitrides (Fe ₂ N, Fe ₄ N) are formed without noticeable heat release: 20.6 and 3.8 cal / g, respectively. Thus, there are necessary conditions for organizing the process of nitrogen saturation of the Ca-Si-Fe system in a self-sustaining combustion process due to the heat of the exothermic reaction of the formation of calcium and silicon nitrides without the use of energy from external sources (electric furnaces of various types, plasmatrons, etc.). In this case, the amount of iron in the initial charge should be limited, not more than 40%.

The obvious advantage of using the Ca-Si-Fe system as a base for nitriding, in order to obtain alloying alloys for steel, is that the nitrides Ca ₃ N ₂ and Si ₃ N ₄ contain the maximum amount of nitrogen - 18.9 and 39.9% respectively. Nitriding of silicon powders in the combustion mode is a well-studied process (see, for example, A.S. Mukasyan, V.M. Martynenko, A.G. Merzhanov et al. "On the mechanism and laws of combustion of silicon in nitrogen." Combustion physics and explosion, No. 5, 1986, p. 43-49). It turned out that without using preliminary heating of the initial silicon with an external heat source (i.e., an electric furnace), the combustion process can be carried out only at a nitrogen pressure of more than 12.0 MPa using a powder with a fineness of 0.01 mm.

The process temperature was about 2000 ° C, and the degree of conversion of silicon to nitride did not exceed 40%.

Attempts to obtain calcium nitride by burning calcium in nitrogen have failed. The fact is that calcium metal is a chemically very active metal. The process of obtaining a powder or even granules of calcium, as well as all subsequent operations with it should be carried out with utmost care, excluding contact with oxygen. Therefore, the synthesis of calcium nitride is an extremely expensive and time-consuming process, which makes it economically disadvantageous to use it in steelmaking.

The nitriding of Ca-Si-Fe alloys in the combustion mode is very attractive. The "excess" activity of calcium in the alloys is neutralized by silicon by the formation of silicides CaSi ₂ and CaSi.

In addition, these silicides are very fragile, therefore, obtaining the required dispersion powder is a relatively simple and inexpensive technological operation.

However, the implementation of nitriding in the combustion mode in the system Ca-Si-Fe-nitrogen is not so obvious. First, calcium and silicon interact with nitrogen at various temperatures: the maximum rate of silicon nitride formation at 0.1 MPa of nitrogen occurs at 1350-1450 ° C, and the optimum temperature for the synthesis of calcium nitride is 450 ° C. Secondly, calcium and silicon in the alloy form relatively chemically inert silicides, the rate of interaction of which with nitrogen is much lower than the rate of interaction of metallic calcium and silicon with nitrogen. Thirdly, alloys based on calcium and silicon with a calcium content of up to 50% begin to melt already at 970–980 ° С; therefore, nitriding of the powder in the traditional way, when the entire volume is simultaneously heated, did not lead to success. Before the active saturation of the alloy with nitrogen begins, the processes of sintering and fusion of the powder mixture into a monolithic mass rapidly develop with a sharp slowdown in the absorption of nitrogen and its subsequent cessation.

The technical result of the invention is the creation of such a method for the production of a nitrogen-containing alloy for alloying steel, including calcium, silicon and iron, which would be distinguished by the absence of energy costs, minimum duration and would allow to obtain a material with a maximum nitrogen content, with complete absence of losses of raw materials during nitriding and exclusion harmful emissions into the environment. Another important result of the invention is the creation on the basis of a new method of such a cheap nitrogen-containing alloy, which, due to the high nitrogen content, would ensure the introduction of the right amount of nitrogen into the steel at its minimum consumption.

Usually, when nitriding metals and alloys by traditional methods, heat release during the formation of nitrides is considered an extremely undesirable phenomenon, leading to accelerated sintering of the powder mixture, melting of the pore space and, ultimately, premature termination of nitrogen absorption. Attempts to slow down the rate of heat release by reducing pressure, diluting the mixture with inert or refractory components, etc. ultimately led to an increase in the duration of the process, a decrease in the quality of the product and its cost.

The essence of the proposed technical solution can be summarized as follows: a nitrogen-containing alloy based on Ca-Si-Fe alloys with a maximum nitrogen content is proposed, which is obtained by burning the initial powder in nitrogen, and the combustion itself is realized due to the heat released during the formation of calcium and silicon nitrides. Thus, utilizing the seemingly harmful heat during nitriding, it is possible to obtain a new highly efficient alloying alloy that cannot be obtained by conventional methods.

It turned out to be a rather unexpected positive fact that by varying the parameters of the nitriding process (composition of the initial alloy, particle size of the powder, pressure and composition of the nitrogen-containing gas, ignition temperature and duration of the process), which proceeds in the layer-by-layer combustion mode, the associated adverse factors can be overcome (low the melting temperature of the initial alloy, a large difference in the temperatures of formation of calcium and silicon nitrides, the presence of chemically strong silicides in the initial alloy).

In the present invention, the starting material should contain a sufficient amount of calcium and silicon, responsible for heat during nitriding. Studies have shown that the minimum amount of calcium and silicon, at which a stable combustion process due to the exothermic reaction of nitride formation is possible, is 10% and 40%, respectively, while their total amount should be at least 60%. The use of powders containing more than 40% Ca and more than 65% Si, as well as powders containing the total amount of Ca and Si more than 99%, is impractical for economic reasons, as well as from the point of view of safety. Such powders are expensive, and during operation are easily flammable, despite the fact that they are easily nitrided in the combustion mode to obtain a product with a high nitrogen content. We also note that for the same reasons, a mixture of calcium, silicon, and iron powders is not used as the starting material.

The initial alloy of the selected optimal composition, in accordance with the proposed technical solution, should be crushed into a powder, the particle size of which should not exceed 2.5 mm, and this should be a polydisperse powder, in which, along with large particles, there should be a sufficient amount of fine fraction for ensure high heat dissipation rate. Moreover, in the process of studying the laws of combustion of the powder of the initial alloy in nitrogen, it was found that large powder is nitrided only at high nitrogen pressure and using a powder with the maximum amount of calcium. In order to realize nitrogen combustion in a wider range of component ratios in the initial charge, as well as to make the process possible at low nitrogen pressure, it is necessary to use a finer powder: less than 0.63 mm or even less than 0.20 mm. In cases where the initial alloy contains a minimal amount of calcium, or when the process is carried out at a low nitrogen pressure, it is necessary to use a particularly fine initial powder - less than 0.05 mm. In addition, the use of finer powder of the initial alloy becomes appropriate when it is mixed with a certain amount of less exothermic ferroalloy. Powder alloy Ca-Si-Fe burns in nitrogen in a very wide range of pressure changes. From a technical point of view, for the safe implementation of the process, combustion must be realized at a nitrogen pressure of 0.1 to 15.0 MPa. In this range, it is possible to carry out stable combustion of the powders of the initial alloy of all selected compositions and for any dispersion proposed in the application. At a lower nitrogen pressure, the combustion of most compounds does not occur, or becomes unstable. When using pressures above 15.0 MPa, difficulties arise associated with the operation of high-pressure equipment, while at the same time, a qualitative change in the properties of the resulting product does not occur. In addition, studies have shown that the optimal (for various compositions and for a wide range of dispersion of the initial alloy) nitrogen pressure is 0.5-10.0 MPa.

When studying the nitriding process under various conditions, it turned out that a product with the best combination of operational properties is obtained by burning a mixture of powders of the initial alloy of various compositions. So, when burning a mixture of powders with low and high calcium, the product had a higher density than the product formed from a powder of one grade of the appropriate composition.

The initial alloy based on Ca-Si-Fe with a selected ratio of components has a low density (approximately 2.5-3.5 g / cm ³ ), the resulting nitrides Ca ₃ N ₂ (2.6 g / cm ³ ) and Si ₃ N ₄ (3.2 g / cm ³ ) is also much lighter than liquid steel, so they are most effective when they are blown into steel in the form of powders, or when used in the form of flux-cored wire. However, it often becomes necessary to use a nitrided alloy in its traditional form - in the form of pieces of various sizes. In the present invention, the problem of increasing the density of the nitrogen-containing alloy was solved by introducing into the initial charge powders of traditional alloying materials, usually used in steelmaking and compatible with a particular grade of smelted steel. The best results were shown by Al, Ti, V, Nb, Cr, and Mn alloys introduced into the mixture in an amount of 10-50%. The resulting product may contain from 0.1 to 40% of these metals. The optimal amount is - 0.5-10%.

For a clearer picture of the essence of the proposed technical solution, we consider in detail the specific implementation of the invention by the example of nitriding of a Ca-Si-Fe alloy containing 14.4% Ca, 52.5% Si. The starting alloy additionally contains 8.8% Ti and impurities 0.06% C, 0.005% S, 0.02% P, the rest Fe. The lump alloy in the delivery state (20-200 mm) was ground into a powder with a particle size of less than 0.315 mm. The powder was poured into a cylindrical container and placed in a high-pressure installation in a nitrogen atmosphere, creating a gas pressure of 5.0 MPa. The purity of the nitrogen used is 99.0%. By briefly supplying an electric pulse to the igniter for 10-15 s, we heat a small surface of the powder (5-10 cm ² ) to 1200 ° C, initiating the onset of the formation of Ca and Si nitrides, the heat of exothermic reaction generated in this case heats the adjacent layer of the initial alloy, initiating nitride formation reaction, etc. Thus, layer by layer, the alloy is saturated with nitrogen until the entire powder is completely converted to a nitrogen-containing cake. Studies with quenching (early termination of the process, by means of rapid cooling by rapidly replacing nitrogen with inert argon) showed that in the layer-by-layer nitriding (i.e., layer-by-layer combustion) 60-70% of nitrogen is absorbed, the remaining 40-30% in the mode volume afterburning. In this particular case, the product contained 19.4% nitrogen. If the process is stopped immediately after the completion of the stage-by-stage combustion, the amount of nitrogen in the product will be only 13.0%, i.e. 67% of the nitrogen content in the final product. The exposure time for volumetric overreaction was 1.2 hours, the nitrogen pressure was in the range of 3.0-2.0 MPa.

Other examples are presented in the table.

Table №№ Raw material The composition of the initial alloys, wt.% Particle size less than mm Pressure and purity of nitrogen, MPa /% Ignition temperature
° C Pressure and continue
the duration of nitriding, MPa / h The composition of the product, wt.% Sa Si Metals II-VII groups Sa Si N Metals II-VII groups one 2 3 four 5 6 7 8 9 10 eleven 12 13 one Ca-Si-Ti-Fe 14,4 52,5 Ti 8.8 0.315 5.0 / 99.0 1200 3.0-2.0 / 1.2 11.6 42,4 19,4 Ti 7.1 2 Ca-Si-Al-Fe 18.5 40,0 Al 12.8 0.05 12.0 / 95.0 1400 10.0-8.0 / 1.0 14.0 30,2 24.4 Al 9.7 3 Ca-Si-Zr-Al-Fe 20.6 54.8 Zr 6.5 0.315 2.5 / 99.9 800 2.0-1.5 / 1.5 16.5 43.8 20.1 Zr 5.1 Al 3.6 Al 2.8 four Ca-Si-Al-Fe - 80% 40,0 55.1 Al 0.1 0.20 1.0 / 99.0 1250 8.0-5.0 / 0.8 26.0 38.5 18,4 V 2.0 Si-V-Fe - 20% - 15.4 V 12.2 2,50 Al 0.2 5 Ca-Si-Al-Fe - 50% 40,0 55.1 Al 10.1 0.20 6.0 / 95.0 1100 4.0-3.0 / 0.1 18.1 26.7 11.0 Mn 38.9 Mn-Fe - 50% - 4.1 Mn 86.2 0.40 Al 0.31 6 Ca-Si-Al-Fe - 50% 25.1 65.0 Al 0.51 0.10 15.0 / 95.0 1300 12.0-10.0 / 0.5 10.1 26.2 20,0 Cr 39.8 Cr - 50% - 0.1 Cr 99.5 0.05 Al 0.20 7 Ca-Si-Al-Fe 26,4 57.1 Al 0.35 0.20 8.0 / 99.0 1300 7.0-5.0 / 0.5 20,4 44,2 22.6 Al 0.27 8 Ca-Si-Al-Fe - 50% 40,0 55.1 Al 0.1 0.05 10.0 / 99.5 1400 8.0-6.0 / 2.0 18.7 36.0 25.1 Al 0.31 Ca-Si-Al-Fe - 50% 10.0 41.1 Al 0.5 0.63 9 Ca-Si-Mg-Fe 20,4 49.4 Mg 6.2 0.20 2.0 / 99.9 1400 1.5-1.3 / 0.8 17.0 41.3 16,4 Mg 5.2 10 Ca-Si-Al-Fe - 50% 26,4 57.1 Al 0.35 0.125 0.1 / 95.0 900 0,1 / 2,0 11.6 26.2 12.1 Ti 30.1 Ti-Si-Fe - 50% - 2,4 Ti 70.1 0.05 Al 0.2 eleven Ca-Si-Al-Fe 40,0 55.1 Al 0.1 0.20 15.0 / 99.0 1200 12.0-10.0 / 1.2 28,4 39.1 29.0 Al 0.1 12 Ca-Si-Al-Fe 25.1 65.0 Al 6.5 0.05 2.5 / 99.0 1100 2.0-1.6 / 0.8 21.1 55.0 15.4 Al 5.5 13 Ca-Si-Nb-Al-Fe 17.9 46.3 Nb 10.6 0.16 7.0 / 99.9 1350 5.0-4.0 / 1.1 14/5 37.5 18.9 Nb 8.6 Al 9.4 Al 7.6 fourteen Ca-Si-Al-Fe 40,0 55.1 Al 0.1 0.315 4.0 / 99.0 1250 3.0-2.0 / 0.2 34.0 46.8 15.0 Al 0.1 fifteen Ca-Si-Mg-Fe - 30% 20,4 49.4 Mg 6, Ti 40.1 0.20 9.0 / 97.5 950 8.0-6.0 / 1.0 5.0 17.0 18.3 Mg 1.5, Ti 22.9, Al 2.6 Ti-Si-Fe - 70% - 8.7 Al 4,5 0.05

Claims (7)

1. A method of producing a nitrogen-containing alloy for alloying steel, comprising grinding the starting material in the form of an alloy into powder and nitriding it in a combustion mode, characterized in that an alloy or a mixture of several alloys containing calcium, silicon and iron is used as the alloy of the starting material in the following ratio of components, wt.%:
calcium 10-40 silicon 40-65 iron rest,
wherein the alloy (s) is ground into a powder with a particle size of less than 2.5 mm, the powder is placed in a high-pressure unit in a nitrogen atmosphere containing at least 95 vol.% nitrogen, at a pressure of 0.1-15.0 MPa, exothermic is initiated the reaction of the formation of calcium and silicon nitrides by local heating of the powder to the temperature of the beginning of the reaction in a layered combustion mode and maintain this temperature and pressure until the end of the reaction in a layered combustion mode followed by nitriding in volumetric combustion for 0.1-2.0 hours 2. The method according to claim 1, characterized in that the alloy additionally contains 0.1-20 wt.% Metals selected from a number of magnesium, barium, aluminum, titanium, zirconium, vanadium, niobium, chromium and / or manganese. 3. The method according to claim 1, characterized in that the alloy powder is mixed with one or more metal powders selected from the range of aluminum, titanium, chromium and / or manganese, or their alloys with iron, selected from the range of ferroaluminium, ferrotitanium, ferrosilicon, ferrovanadium, ferroniobium, ferrochrome, ferromanganese, ferrosilicotitanium, ferrosilicon zirconium, ferrosilicon vanadium, ferrosilicon and / or ferrosilicon manganese in an amount of 10.0-50.0 wt.%. 4. Nitrogen-containing alloy for alloying steel, characterized in that it is obtained by the method according to any one of claims 1 to 3. 5. Nitrogen-containing alloy according to claim 4, characterized in that it contains components in the following ratio, wt.%:
calcium 5-34 silicon 17-55 nitrogen 11-29 iron rest 6. The nitrogen-containing alloy according to claim 4, characterized in that it further comprises one or more metals selected from the series magnesium, barium, aluminum, titanium, zirconium, vanadium, niobium, chromium and / or manganese in the following ratio of components, weight. %:
calcium 5-34 silicon 17-55 magnesium, barium, aluminum, titanium, zirconium, vanadium, niobium, chromium and / or manganese 0.1-40 nitrogen 11-29 iron rest 7. Nitrogen-containing alloy according to claim 6, characterized in that it contains components in the following ratio, wt.%:
calcium 10-25 silicon 30-50 magnesium, barium, aluminum, titanium, zirconium, vanadium, niobium, chromium and / or manganese 0.5-10 nitrogen 15-22 iron rest