RU2798491C1 - Method for producing a composite alloy based on chromium nitrides - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: production of a composite alloy based on chromium nitrides. The method for producing a composite material based on chromium nitrides includes preparing a powder of a chromium-containing material, high-temperature sintering of the said powder of a chromium-containing material in a nitrogen-containing gas atmosphere at a pressure above 0.1 MPa. As a powder of a chromium-containing material, a powder of low-carbon ferrochrome and/or metallic chromium is used, high-temperature sintering of the mentioned powder of low-carbon ferrochrome and/or metallic chromium is carried out in the mode of self-propagating high-temperature synthesis (HTS). During sintering, gaseous nitrogen is blown through the powder of low-carbon ferrochrome and/or metallic chromium, the specific consumption of which is 0.02-8.0 l/s⋅ cm². As a result of high-temperature sintering, a composite material is formed, consisting of chromium nitrides (Cr,Fe)₂N, Cr₂N and/or CrN and an alloy based on iron and/or chromium.

EFFECT: material obtained using low-carbon ferrochromium and/or metallic chromium powders with different contents of ferrum and impurity elements as starting materials and with minimal power consumption.

10 cl, 3 tbl, 1 ex

Description

The invention relates to methods for producing a composite alloy based on chromium nitrides, in particular to methods for producing a composite alloy based on chromium nitrides using chemical processes, namely self-propagating high-temperature synthesis (SHS). Such compositions are intended for use in metallurgy for alloying chromium-containing steels and alloys with nitrogen, as well as in powder metallurgy.

There are various methods for the synthesis of chromium nitrides and compositions based on them (Samsonov G. V. Nitrides. Kyiv. Naukova Dumka. 1969. C. 196-198).

Japanese patent JPS6183605A and Chinese patent CN103318855A describe methods for producing various compositions based on chromium nitrides by long-term treatment of chromium powder in a stream of ammonia at a temperature above 800°C. The methods make it possible to synthesize pure oxygen fine powders of chromium nitrides. However, these methods are uneconomical and unsafe due to the use of electric furnaces and the use of ammonia, and the synthesized fine powders of chromium nitrides are untechnological when alloying steel and alloys with nitrogen.

Yoshihiro Shoji, Masaru Yoshinaka, Ken Hirota, and Osamu Yamaguchi obtained high-density Cr ₂ N-CrN compositions by hot pressing a synthesized powder consisting of these compounds (Fabrication of Bulk Chromium Nitrides Using Self-Propagating High-Temperature Synthesis and Hot Isostatic Pressing Journal of the Japan Society of Powder and Powder Metallurgy 2002 Vol 49 No 4 P 323-326). Chromium metal powder with a dispersion of 2 microns was nitrided in the mode of self-propagating high-temperature synthesis at a pressure of 0.2-2.0 MPa to obtain a mixture of Cr ₂ N and CrN phases with different ratios. The method allows to obtain a high-density two-phase composite material Cr ₂ N-CrN in a wide range of changes in the ratio of components. However, the described method is very expensive and does not allow to obtain compositions containing iron. The resulting high-density materials based on chromium nitrides can be effective for alloying steel, but their use for these purposes is not acceptable from an economic point of view.

A submicron composite Cr ₂ N-CrN powder was obtained by heat treatment at ~1100 of a mixture of Cr ₂ O ₃ and C powders in a nitrogen-containing atmosphere (Susumu Morita, Hideaki Shimizu, Yasumasa Sayama. Synthesis of Chromium Nitride Powder by Carbo-thermal Nitriding. 15" International Plansee Seminar , Eds G. Kneringer, P. Rodhammer and H. Wildner, Plansee Holding AG, Reutte, 2001, Vol. and synthesized Cr ₂ N-CrN compositions are expensive for use as master alloys in steelmaking.

JP 62112771 describes a vacuum thermal process for producing a chromium-based composite alloy for stainless steel smelting, which may contain 10-20% nitrogen. In particular, when nitriding an alloy with 99.0% Cr, a two-phase product was obtained containing up to 17.4% N; when nitriding an alloy with 62% Cr, the nitrogen content was 6.8-11.0%. Such a two-phase composition consisting of CrN and Cr ₂ N or CrN and (CrFe) ₂ N is recommended for alloying chromium steels.

Bulgarian Patent No. 24137 describes a process for producing a high nitrogen chromium-based alloy. Here, a two-phase alloy powder CrN - Cr ₂ N is obtained by heating the chromium powder with 0.5% Fe to 1000-1200°C at a pressure of over 1.0 MPa. The nitrogen content in the powder product is 10-16%.

Composite alloy powder based on Cr ₂ N with different content of CrN or Cr(N) phases can be obtained by heat treatment of the parent metal (98.5% Cr) in a vacuum rotary furnace at a temperature of 1200-1400°C for 0.5-1.0 hours. The nitrogen content in such a composition is 4.1-13.5% (Dimitar Krastev. Nitriding of ferroalloys. VI th International Metallurgical Congress. Ohrid 2014.).

The given examples of methods for nitriding chromium or ferrochromium powders in high-temperature vacuum furnaces in a nitrogen-containing atmosphere to obtain composite alloys based on chromium nitrides are distinguished by the consumption of a large amount of electricity and are very long.

As a prototype, a method for obtaining sprayed powders containing chromium nitride was chosen (Patent RU 2666199). Prototype method includes

preparation of a powder mixture containing at least one component selected from the group including chromium (Cr), CrN and Cr ₂ N, and another component containing at least one component selected from the group including nickel, cobalt, nickel alloy, cobalt alloy and iron alloy, and sintering the powder mixture at a partial pressure of nitrogen above 1 bar to obtain sintered agglomerates, and sintering is carried out in a gas atmosphere containing at least 90 vol.% nitrogen, at a temperature above 1000°C, for at least at least one hour.

The prototype method allows to obtain a composite material, which is based on chromium nitrides, mainly CrN mononitride. The selected process is characterized by a long duration (up to 48 hours) and the consumption of a significant amount of electricity to maintain a high temperature (up to 1500°C).

The present invention solves the problem of creating a new method for producing a composite alloy based on chromium nitrides, which, with minimal power consumption, would make it possible to obtain materials containing chromium nitrides and a metal phase - an alloy based on iron and / or chromium, which are intended for use in metallurgy for alloying chromium-containing steels and alloys with nitrogen.

The problem is solved by the fact that a method is proposed for obtaining a composite alloy based on chromium nitrides by preparing a powder containing a chromium-containing material and its high-temperature sintering in an atmosphere of nitrogen-containing gas at its increased pressure, which, according to the invention, includes:

use as a powder of chromium-containing material powder of low-carbon ferrochromium and/or metallic chromium;

sintering said powder of low-carbon ferrochromium and/or metallic chromium is carried out in the mode of self-propagating high-temperature synthesis (SHS);

while during sintering through the powder of low-carbon ferrochrome and/or metallic chromium purge nitrogen-containing gas;

as a result of sintering, a composite alloy is formed, consisting of chromium nitrides (Cr,Fe) ₂ N, Cr ₂ N and/or CrN and an alloy based on iron and/or chromium.

The present invention makes it possible to obtain a composite alloy based on chromium nitrides using low-carbon ferrochromium and/or metallic chromium powders with different contents of iron and impurity elements (C, Si, P, S, O, etc.) as starting materials. However, in order to maintain sufficient exothermicity of chromium-based alloys, the iron content in low-carbon ferrochrome should be limited to 35%, and in chromium - 1.5%. The preferred content of iron in the powder of the original low-carbon ferrochrome 17-27%, and in the powder of the original chromium is not more than 0.5% iron, optimally not more than 0.1% iron.

In the present invention, it is possible to use powders of low-carbon ferrochromium and/or metallic chromium containing carbon and other impurity elements (Si, P, S, O, etc.) as starting materials in a wide concentration range. However, in order to obtain better quality nitriding products in the SHS mode and in order to increase the thermal effect of the combustion reaction, it is advisable to use low-carbon ferrochrome powder containing no more than 0.5% carbon, preferably no more than 0.1%, optimally no more than 0.03%, and/or chromium containing not more than 0.1% carbon, preferably not more than 0.06% carbon, optimally not more than 0.02% carbon.

Carbon is an undesirable impurity in most grades of nitrogen-containing steels and alloys. In addition, carbon and other impurities form refractory compounds (carbides, silicides, etc.) in the original low-carbon ferrochrome and chromium, as a result of which the exothermicity of the initial alloys decreases. Therefore, in the most preferred variants of the proposed technical solution, the concentration of carbon in the initial powders of low-carbon ferrochromium and/or metallic chromium should be minimal.

The sintering of the chromium-containing material can be carried out in the mode of self-propagating high-temperature synthesis (SHS) by blowing it with nitrogen-containing gas using powders of low-carbon ferrochromium and/or chromium of various dispersions. However, to speed up the process and achieve higher nitrogen concentrations in the combustion products, it is advisable to use finer powders of the initial alloys. As a chromium-containing material, it is advisable to use powders of low-carbon ferrochromium and/or chromium with a particle size of less than 0.315 mm, preferably less than 0.20 mm, optimally less than 0.10 mm. The finer the powder, the larger its reaction surface and the higher the heat release rate upon interaction with nitrogen. The combustion of a finer powder of low-carbon ferrochromium and/or chromium in the mode of self-propagating high-temperature synthesis occurs at a higher rate, and a greater amount of nitrogen is fixed in the combustion products.

In accordance with the proposed technical solution, the sintering of powders of low-carbon ferrochrome and/or chromium in the mode of self-propagating high-temperature synthesis when blowing nitrogen-containing gas through the powder of low-carbon ferrochrome and/or metallic chromium during sintering can be carried out in a wide temperature range. However, to achieve an acceptable rate of chemical reactions (the interaction of chromium with nitrogen), it is advisable to carry out the process at a temperature of 1100-1700°C, preferably at 1350-1550°C. The higher the sintering temperature, the higher the nitriding rate. However, at temperatures above 1700°C, the processes of melting of both initial alloys and combustion products begin to actively develop. Melting is accompanied by particle coagulation, which prevents the initial alloy from reacting with nitrogen.

For sintering powders of low-carbon ferrochromium and/or metallic chromium in the mode of self-propagating high-temperature synthesis (SHS) in a stream of nitrogen-containing gas to obtain a composite alloy containing chromium nitrides (Cr,Fe) ₂ N, Cr ₂ N and/or CrN and a metal phase based on iron, it is possible to use a nitrogen-containing gas with a nitrogen content in a wide concentration range. However, to obtain a product contaminated with less oxygen, it is advisable to use a gas containing at least 90.0 vol% nitrogen, preferably at least 99.0 vol% nitrogen, optimally 99.9% vol% nitrogen.

The process of sintering powders of ferrochromium and/or chromium in the mode of self-propagating high-temperature synthesis (SHS) when blown with nitrogen-containing gas can be implemented at almost any pressure exceeding 0.1 MPa. However, for stable combustion of the mentioned alloys, it is advisable to purge with nitrogen-containing gas at a pressure of 0.12-12.0 MPa, optimally at 1.0-7.0 MPa.

The process of sintering powders of ferrochromium and/or chromium in the mode of self-propagating high-temperature synthesis (SHS) when blowing with nitrogen-containing gas can be implemented at almost any gas flow rate that can be created at a pressure of 0.1-20.0 MPa. However, for stable combustion of the mentioned powders of ferrochromium and/or chromium, it is advisable to purge with nitrogen-containing gas at its specific consumption in the range of 0.02-8.0 l/s⋅cm ² , preferably 0.05-3.0 l/s⋅cm ² , optimally 0.1-1.0 l/s⋅cm ² .

The interaction of chromium with nitrogen is accompanied by the release of a significant amount of heat, 129 and 125 kJ/mol, respectively, for the Cr ₂ N and CrN phases. On the basis of such a level of exothermicity of nitride formation reactions, it is possible to carry out their synthesis in the mode of self-sustaining combustion (see, for example, Braverman B.Sh., Ziatdinov M.Kh., Maksimov Yu.M. Combustion of chromium in nitrogen // Physics of combustion and explosion. 1999 35, No. 5, pp. 40-45). Such a synthesis is carried out with natural nitrogen filtration using finely dispersed chromium powders. Coarse chromium powders cannot be nitrogenated in this way. Powders of low-carbon ferrochromium do not burn in nitrogen even when using very fine powders.

To solve the problem of creating a new method for producing a composite alloy based on chromium nitrides, which, with minimal power consumption, would make it possible to obtain materials containing chromium nitrides and iron or chromium alloys, quite unexpectedly, it turned out to be possible by high-temperature sintering of low-carbon ferrochromium and/or chromium powder in the self-propagating high-temperature mode. synthesis - SHS (Merzhanov A.G., Mukasyan A.S. Solid-flame combustion. Moscow. TORUS PRESS. 2007. 336 p.). In this case, a nitrogen-containing gas must be blown through the powder of low-carbon ferrochrome and/or metallic chromium. This variant of the SHS process is usually used in systems with low exothermicity. There are various options for stimulating the SHS process. Additional energy can be introduced into the reacting system either in the form of physical heat (increasing the initial charge temperature) or in the form of chemical heat (exothermic additives). Here, additional energy is supplied to the reaction zone due to the heated gaseous reagent - nitrogen. Moreover, the heating of the gas occurs in the reacting system itself. Nitrogen, being filtered through the burnt part of the mixture, heats up. And the already heated gas reacts with ferrochromium and/or chromium powder.

Below is an example of the proposed invention.

Example. As a powder of the initial chromium-containing material, a powder of low-carbon ferrochrome was used, which was obtained by grinding an alloy of grade FKh003A according to GOST 4757-91 and contained, wt. %: Fe 22.1, Al 0.12, Si 0.79, C 0.03 the rest is chromium (76.1%) and impurities (S, P, O, etc.). The particle size of the powder thus obtained was less than 0.315 mm, with 82% of the powder having a particle size of less than 0.20 mm. Powder in the amount of 90 kg is poured into a cylindrical crucible made of heat-resistant material. The crucible is placed in a high pressure SHS flow reactor. The working space of the reactor is sealed and filled with nitrogen of 99.9% purity up to a pressure of 12.0 MPa. By applying an electric pulse to the ignition device, a sample of an exothermic ignition mixture is ignited, from which an exothermic reaction of the formation of nitrides (Cr, Fe) ₂ N, Cr ₂ N, CrN is initiated. The synthesis process is carried out in such a way that nitrogen is continuously filtered through a crucible with low-carbon ferrochrome powder with a specific flow rate of 0.09 l/s⋅cm ² . Further, the process of nitride formation occurs in the mode of layer-by-layer combustion with cocurrent filtration of nitrogen through a crucible with powder in the direction of propagation of the combustion wave. After the completion of the nitriding process and cooling of the combustion products, the pressure in the working space of the SHS reactor is balanced with the external pressure. Next, the crucible with the reaction products (nitrided ferrochrome) is removed from the reactor and weighed. The resulting product is analyzed. According to X-ray phase analysis, it consists of chromium nitrides (Cr, Fe) ₂ N, Cr ₂ N and CrN and an iron-based alloy, and according to chemical analysis, it has the following composition, wt. %: N 11.2, Fe 19.6, Al 0.11, Si 0.70, C 0.03 the rest is chromium (67.6%) and impurities (S, P, O, etc.).

Tables 1-3 below show other examples of the invention. Table 1 shows the compositions and dispersion of the initial powder of chromium-containing material.

Table 1 No. Chrome material Content, % Particle size, mm Cr Fe C 1 Ferrochrome 76.1 22.1 0.03 ≤0.315 2 Ferrochrome 63.9 35.0 0.5 ≤0.10 3 Ferrochrome 70.1 28.9 0.1 ≤0.20 4 Chromium 98.1 1.5 0.1 ≤0.20 5 Chromium 99.5 0.01 0.02 ≤0.05 6 Mixture of ferrochromium and chromium
50:50 63.9 35.0 0.5 ≤0.10 98.1 1.5 0.1 ≤0.20

Table 2 shows the conditions for high-temperature sintering of powders of low-carbon ferrochromium and/or metallic chromium in the mode of self-propagating high-temperature synthesis by blowing nitrogen-containing gas through the powder.

table 2 No. High temperature sintering in SHS mode nitrogen gas Sintering temperature, °C Pressure, MPa Purity, % 1 6.0±1.0 99.0 1400-1550 2 12.0±1.0 99.9 1100-1350 3 2.0±0.3 99.0 1200-1450 4 8.0±1.0 99.9 1450-1650 5 0.17±0.05 99.9 1500-1700 6 0.7±0.2 99.0 1300-1500

Table 3 shows the phase and chemical compositions of the composite alloy based on chromium nitrides formed as a result of high-temperature sintering.

Table 3 No. Composite alloy based on chromium nitrides Phase composition N Cr Fe C 1 Cr ₂ N, (Cr,Fe) ₂ N, Fe 11.2 67.6 19.6 0.03 2 (Cr,Fe) ₂ N, Cr ₂ N, Fe 8.0 59.2 32.0 0.46 3 (Cr,Fe) ₂ N, Cr ₂ N, Fe 9.4 63.5 26.2 0.1 4 Cr ₂ N, CrN, Cr(N) 13.1 85.2 1.3 0.1 5 CrN, _Cr2N 17.9 81.7 0.02 0.04 6 Cr ₂ N, CrN, (Cr,Fe) ₂ N 12.4 71.0 16.0 0.29

Claims (17)

1. A method for producing a composite material based on chromium nitrides, including: - preparation of a powder of chromium-containing material; - high-temperature sintering of said powder of chromium-containing material in a nitrogen-containing gas atmosphere at a pressure above 0.1 MPa, characterized in that as a powder of chromium-containing material, a powder of low-carbon ferrochromium and/or metallic chromium is used; high-temperature sintering of said powder of low-carbon ferrochromium and/or metallic chromium is carried out in the mode of self-propagating high-temperature synthesis (SHS); at the same time, during sintering, gaseous nitrogen is blown through the powder of low-carbon ferrochrome and/or metallic chromium, the specific consumption of which is 0.02-8.0 l/s⋅cm ² ; as a result of high-temperature sintering, a composite material is formed, consisting of chromium nitrides (Cr,Fe) ₂ N, Cr ₂ N and/or CrN and an alloy based on iron and/or chromium. 2. The method according to p. 1, characterized in that low-carbon ferrochrome containing no more than 35 wt.% iron, preferably 17-27 wt.% iron is used as a chromium-containing material. 3. The method according to p. 1 or 2, characterized in that low-carbon ferrochrome is used as a chromium-containing material, containing no more than 0.5 wt.% carbon, preferably no more than 0.1 wt.%, optimally no more than 0.03 wt. .%. 4. The method according to p. 1, characterized in that metal chromium is used as a chromium-containing material, containing no more than 1.5 wt.% iron, preferably no more than 0.5 wt.% iron, optimally no more than 0.1 wt. % iron. 5. The method according to p. 1, characterized in that metal chromium is used as a chromium-containing material, containing no more than 0.1 wt.% carbon, preferably no more than 0.06 wt.% carbon, optimally no more than 0.02 wt. % carbon. 6. The method according to any one of paragraphs. 1-5, characterized in that as a chromium-containing material, a powder of low-carbon ferrochrome or metallic chromium is used with a particle size of less than 0.315 mm, preferably less than 0.20 mm, optimally less than 0.10 mm. 7. The method according to any one of paragraphs. 1-6, characterized in that high-temperature sintering of powder of low-carbon ferrochrome or metallic chromium in the mode of self-propagating high-temperature synthesis when blowing it with nitrogen-containing gas is carried out at a temperature of 1100-1700°C, preferably at 1350-1650°C. 8. The method according to any one of paragraphs. 1-7, characterized in that gaseous nitrogen is used containing at least 99.0 vol.% nitrogen, preferably at least 99.9 vol.% nitrogen, optimally at least 99.99 vol.% nitrogen. 9. The method according to any one of paragraphs. 1-8, characterized in that high-temperature sintering of ferrochromium or metallic chromium powder in the mode of self-propagating high-temperature synthesis when blowing it with nitrogen-containing gas is carried out at a pressure of 0.12-12.0 MPa, optimally at 1.0-7.0 MPa, while the flow rate of nitrogen-containing gas is 0.05-3.0 l/s⋅cm ² , optimally 0.1-1.0 l/s⋅cm ² . 10. The method according to any one of paragraphs. 1-9, characterized in that as a result of high-temperature sintering of ferrochromium or metallic chromium powder in the mode of self-propagating high-temperature synthesis, when blowing it with nitrogen-containing gas, a composite alloy is formed, consisting of chromium nitrides (Cr,Fe) ₂ N, Cr ₂ N and / or CrN and an alloy based on iron and / or chromium and containing elements in the following ratio, wt.%: 8-18 nitrogen, 0.01-32.0 iron, the rest is chromium and unavoidable impurities, the total amount of which is not more than 5.5% .