RU2462525C1 - Method for producing nitrided ferrovanadium - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: source alloy of ferrovanadium with the dispersion of less than 0.1 mm is pre-granulated to the size of 0.2-2.0 mm, the combustion process is carried out in a stream of nitrogen or a mixture of nitrogen with an inert gas in the direction of the reaction zone extension. Gaseous nitrogen or a mixture of nitrogen with an inert gas is fed at a rate of 99.6-700.0 mm/s. To increase the nitrogen content in the product it is advisable to enter into the original alloy of 10-20 wt % of the final product. The invention is aimed at reducing the operating pressure in the reactor, which increases the safety of the work to obtain nitrided ferrovanadium.

EFFECT: low strength of obtained briquettes of nitrided ferrovanadium facilitates dosing when entering of ligatures into the steel.

5 cl, 4 ex, 1 tbl

Description

The invention relates to the metallurgy of ferroalloys and can be used in the production of nitrided vanadium-containing alloys used in the smelting of various steel grades (structural, tool, steel with special properties).

A known method of producing nitrided vanadium, including pressing cylindrical tablets with a diameter of 20 mm from a powder of vanadium with a particle size of 140 mm, which are then placed in a sealed installation of constant pressure and ignited in an atmosphere of pure (99.9%) nitrogen at a pressure of 0.2-15 MPa (Yu.M Maksimov, M.Kh. Ziatdinov, A.G. Raskolenko, OK, Lepakova, Interaction of Vanadium with Nitrogen in Combustion Mode, Combustion and Explosion Physics, 1979, vol. 15, No. 3, pp. 161-164). The method allows to obtain a product containing up to 16% nitrogen.

The disadvantage of this method is the impossibility of burning ferrovanadium in nitrogen at pressures close to atmospheric, due to its lower heat release during the reaction of ferrovanadium with nitrogen and a lower melting point of ferrovanadium, as well as the high cost of the feedstock (vanadium powder).

Theoretical and experimental studies on the laws of combustion of metal powders in a stream of nitrogen-containing gas are known, in which it is shown that conducting self-propagating synthesis in a satellite stream of active gas (that is, when the direction of movement of the reaction zone coincides with the direction of the nitrogen stream) can increase the temperature of the reaction zone (super-adiabatic effect) and, thereby, increase the reaction rate at low pressures (Aldushin A.P., Seplyarsky B.S. Propagation of an exothermic wave stocks in a porous medium during gas blowing, Dokl. AN SSSR, 1978, v.241, No. 1, pp. 72-75. Yu.M. Maximov and B.Sh. Braverman. Concentration of Thermal Energy in Filtration Combustion of Metal Powders In. Book "Progress in combustion and detonation". Ed by AABorisov, SMFrolov, ALKuhl. - Moskow: Torus Press Ltd., 2004, p. 214, 215).

The disadvantage of these works is the lack of accounting for changes in gas permeability during heating of ferrovanadium in the reaction zone, which does not allow using the results obtained in them to obtain ferrovanadium without lengthy experimental studies.

It is known to use charge granulation during self-propagating synthesis in the process of burning granules of a mixture of Ti with C under the conditions of impurity gas filtration (A.P. Amosov, AG Makarenko, ARSamboruk, B. S. Seplyarskii, AASamboruk, I.O. Gerasimov, AV Orlov, and VVYatsenko. Effect of Batch Pelletizing on a Course of SHS Reactions: An Overview. International Journal of Self Propagating High Temperature Synthesis, 2010, vol. 19, No. 1, pp. 70-77).

It was found that granulation allows to increase gas permeability and reduce the sintering ability of the product.

There are no works on the effect of granulation on the combustion of alloy powders in the flow of a reacting gas, which does not allow creating the foundations of a technology for producing nitrided ferrovanadium at atmospheric pressures.

The closest in technical essence and the achieved result to the invention is a method for producing nitrided ferrovanadium, in which an iron-vanadium alloy powder containing 45-54 wt.% Vanadium, with a particle size of less than 0.08 mm, is burned in a nitrogen atmosphere at a pressure of 3-12 MPa ( A.S. USSR No. 1474178, 1989). Ferrovanadium with a sigma phase structure is used as a starting material for nitriding. The method allows to obtain nitrated ferrovanadium in self-propagating mode.

The disadvantage of this method is the need to use high (not less than 3 MPa) pressure, since due to the insufficiently high thermal effect of the reaction of the vanadium-iron alloy with nitrogen, the reaction rate (and, accordingly, the heat release rate) at lower pressures is insufficient to maintain a self-propagating reaction mode. The use of high pressures necessitates an increase in strength and, accordingly, an increase in wall thickness, of the reactor, and an increase in safety requirements.

To maintain a self-propagating reaction mode, it is necessary to supply a gaseous reagent (nitrogen) to the reaction zone, which can be achieved only with sufficient gas permeability of the mixture. The gas permeability of the mixture depends on the dispersion of the original powder. With a decrease in particle size, gas permeability decreases, and with an increase in particle size of the powder, the specific surface area decreases, which slows down the reaction. Another factor affecting the gas permeability of the charge is sintering and melting of the initial powder when it is heated in the reaction zone, which leads to a decrease in gas permeability and termination of the reaction. The change in gas permeability during the reaction is determined by the following factors: the maximum temperature in the reaction zone, the rate of temperature change, the melting temperature of the mixture, the sintering rate of the mixture and the product, and a number of other parameters determined by the individual properties of the mixture and the specific reaction, therefore, it is necessary to conduct the nitriding reaction in a self-propagating mode for each specific composition of the starting material to select empirically the specific conditions for the implementation of the method obtaining the target product (The concept of development of self-propagating high-temperature synthesis as a field of scientific and technological progress. Chernogolovka, 2003. S.233-236).

The objective of the present invention is to increase the safety of work on obtaining nitrided ferrovanadium by lowering the operating pressure in the reactor.

The problem is solved by the method of producing nitrided ferrovanadium by means of combustion in the combustion mode of preliminarily granulated to granule sizes of 0.2-2.0 mm ferrovanadium powder with a fineness of less than 0.1 mm in a stream of nitrogen or a mixture of nitrogen with an inert gas in the direction of the stream coinciding with the direction of propagation of the reaction zone.

After local ignition of the pre-granulated ferrovanadium, it interacts with nitrogen in the gas stream, which is supplied at a rate of 99.6-700.0 mm / s in the direction of propagation of the reaction zone. High maximum temperatures provide high rates of final product formation.

The boundary values for the gas flow rate were determined empirically. At flow rates of less than 99.6 mm / s, a self-propagating reaction mode cannot be achieved due to insufficient nitrogen supply. With an increase in the gas flow rate, the rate of nitrogen supply to the reaction zone increases, as well as the amount of heat transferred from the hot products to the reaction zone, and the rate and temperature of combustion increase. At flow rates of more than 700 mm / s, the amount of assimilated nitrogen decreases, and the pressure at the inlet to the reactor also increases significantly.

The dispersion of ferrovanadium powder determines the reaction rate and the amount of assimilated nitrogen. With a dispersion greater than 0.1 mm, it is not possible to realize a self-propagating propagation mode of the reaction zone, which determines the boundary condition for dispersion. The process can be carried out even with arbitrarily small particle sizes, however, long-term grinding to obtain such sizes is impractical due to the high energy costs.

Dilution of the reacting nitrogen gas with an inert gas leads to a slight increase in the burning rate and the conversion depth, which is due to an increase in the contribution of convective heat transfer.

When nitriding an alloy of iron with vanadium in a flow of a reacting gas in a self-propagating regime without granulation, temperatures close to its melting point develop in the reaction zone, which can lead to a sharp decrease in gas permeability and disruption of the reaction.

The interval of change in the size of the granules was determined empirically. When the granule size is less than 0.2 mm in the reaction zone, sintering of the charge occurs rapidly, which leads to the cessation of the propagation of the reaction zone. With granule sizes greater than 2.0 mm, due to a decrease in the reaction surface, the reaction rate and the heat release rate decrease, which also leads to the cessation of the reaction zone propagation.

When granulating, rosin is used as a binder, since it has a relatively low temperature and enthalpy of evaporation. During combustion of ferrovanadium in nitrogen, rosin evaporates when heated in front of the reaction zone and is carried away by a gas stream, condensing at the outlet. At the same time, nitrated ferrovanadium is not contaminated with rosin decomposition products. The maximum rosin contents were determined empirically and are due to the fact that at concentrations of less than 0.5% the granules were not strong enough and after drying a lot of fine dust fraction is formed, and at rosin concentrations of more than 2%, the granules stick together and are poorly separated from each other.

It is advisable to additionally introduce 10-20 wt.% Nitrided ferrovanadium into the initial alloy to increase the nitrogen content in the product. The introduction of the final product into the initial alloy reduces the sintering speed of the mixture, contributing to an increase in the conversion depth, however, the temperature in the reaction zone decreases, which leads to a slowdown of the reaction. It has been experimentally established the amount of additive at which the nitriding of ferrovanadium in the self-propagating mode is possible. When more than 20% of the final product is added to the initial charge, the process of nitriding ferrovanadium during combustion is not possible.

Ferrovanadium with a vanadium content of 45-55% is preferably used as a starting alloy.

The set of essential features of the invention allows to achieve a technical result, namely, reducing the working pressure in the reactor to close to atmospheric, which increases the safety of work on obtaining nitrated ferrovanadium.

Examples of the method.

Example 1. A solution of 5 g of rosin in 50 ml of acetone is prepared, this solution is mixed with 245 g of ferrovanadium powder with a fineness of less than 0.1 mm. The resulting mixture is rubbed through a sieve with a mesh size of 2.5 mm The granules formed are dried in an oven at a temperature of 100 ° C for one hour. The dried granules are sieved to separate granules from 0.63 mm to 1.0 mm in size, which are placed in a flow reactor consisting of a cylindrical reaction chamber with gas inlet and outlet devices and a device for setting the ignition coil. An ignition coil is brought to the backfill from the granules, a nitrogen flow is established at a speed of 184 mm / s, and a current pulse is applied to the ignition coil installed on the gas inlet side to initiate the reaction of ferrovanadium with nitrogen. After ignition, the reaction zone propagates in layers throughout the reactor, while maintaining a constant flow of nitrogen in the direction of propagation of the reaction zone. The flow is maintained until the product cools. The excess pressure at the inlet to the reactor is measured with an exemplary pressure gauge with a division value of 0.004 MPa. Overpressure does not exceed 0.004 MPa. The reaction product is briquettes from sintered granules with sizes close to the size of the original granules. The low strength of the briquettes of the product facilitates dosing when introducing the ligature into steel.

Example 2. A solution of 5 g of rosin in 50 ml of acetone is prepared, this solution is mixed with 245 g of ferrovanadium powder with a fineness of less than 0.1 mm. The resulting mixture is rubbed through a sieve with a mesh size of 2.5 mm The granules formed are dried in an oven at a temperature of 100 ° C for one hour. The dried granules are sieved to separate granules from 1.0 mm to 2.0 mm in size, which are placed in a flow reactor consisting of a cylindrical reaction chamber with gas inlet and outlet devices and a device for setting the ignition coil. An ignition coil is brought to the backfill from the granules, a nitrogen flow is established at a speed of 184 mm / s, and a current pulse is supplied to the ignition coil to initiate the reaction of ferrovanadium with nitrogen. After ignition, the reaction zone propagates in layers throughout the reactor, while maintaining a constant flow of nitrogen in the direction of propagation of the reaction zone. The flow is maintained until the product cools. The excess pressure at the inlet to the reactor is measured with a standard pressure gauge with a division value of 0.004 MPa. Overpressure does not exceed 0.004 MPa. The reaction product is briquettes from sintered granules with sizes close to the size of the original granules. The low strength of the briquettes of the product facilitates dosing when introducing the ligature into steel. The nitrogen content in the product is 7.46%.

Example 3. A solution of 5 g of rosin in 50 ml of acetone is prepared, this solution is mixed with 245 g of ferrovanadium powder with a fineness of less than 0.1 mm. The resulting mixture is rubbed through a sieve with a mesh size of 2.5 mm The granules formed are dried in an oven at a temperature of 100 ° C for one hour. The dried granules are sieved to separate granules from 0.315 mm to 0.630 mm in size, which are placed in a flow reactor consisting of a cylindrical reaction chamber with gas inlet and outlet devices and an ignition coil installation device. An ignition coil is brought to the backfill from the granules, a nitrogen flow is established at a rate of 99.6 mm / s, and a current pulse is applied to the ignition coil to initiate the reaction of ferrovanadium with nitrogen. After ignition, the reaction zone propagates in layers throughout the reactor, while maintaining a constant flow of nitrogen in the direction of propagation of the reaction zone. The flow is maintained until the product cools. The excess pressure at the inlet to the reactor is measured with a standard pressure gauge with a division value of 0.004 MPa. Overpressure does not exceed 0.004 MPa. The reaction product is briquettes from sintered granules with sizes close to the size of the original granules. The low strength of the briquettes of the product facilitates dosing when introducing the ligature into steel. The nitrogen content in the product is 4.24%.

Example 4. A solution of 1.25 g of rosin in 50 ml of acetone is prepared. This solution is mixed with 199.0 g of ferrovanadium powder with a fineness of less than 0.1 mm and 49.75 g of a product of combustion of ferrovanadium in nitrogen, crushed to a fineness of less than 0.1 mm, containing 7.46% nitrogen. The resulting mixture is rubbed through a sieve with a mesh size of 2.5 mm The granules formed are dried in an oven at a temperature of 100 ° C for one hour. The dried granules are sieved to separate granules from 0.315 mm to 0.630 mm in size, which are placed in a flow reactor consisting of a cylindrical reaction chamber with gas inlet and outlet devices and an ignition coil installation device. An ignition coil is brought to the backfill from the granules, a nitrogen flow is established at a speed of 184 mm / s, and a current pulse is supplied to the ignition coil to initiate the reaction of ferrovanadium with nitrogen. After ignition, the reaction zone propagates in layers throughout the reactor, while maintaining a constant flow of nitrogen in the direction of propagation of the reaction zone. The flow is maintained until the product cools. The excess pressure at the inlet to the reactor is measured with a standard pressure gauge with a division value of 0.004 MPa. Overpressure does not exceed 0.004 MPa. The reaction product is briquettes from sintered granules with sizes close to the size of the original granules. The low strength of the briquettes of the product facilitates dosing when introducing the ligature into steel. The nitrogen content in the product is 8.9%.

The described and other examples are given in the table.

Thus, the proposed method allows to obtain nitrided ferrovanadium at an overpressure of less than 0.004 MPa in the form of briquettes from weakly sintered granules with a high specific surface, which are easily absorbed by steel or crushed to the required dispersion. The low strength of the briquettes of the product facilitates dosing when introducing the ligature into steel.

Table But
measures at
measure Structure Powder dispersion Granule size mm Gas feed rate, m / s The nitrogen content in the purged gas, vol.% Spread rate
reaction zone, mm / s The nitrogen content in the product, wt.% one FeV (55% V) less than 0.1 mm
(-one hundred) 0.630 ÷ 1.0 184 one hundred 0.46 5.8 2 FeV (55% V) less than 0.1 mm
(-one hundred) 1.0 ÷ 2.0 184 one hundred 0.31 7.46 3 FeV (55% V) less than 0.1 mm
(-one hundred) 0.315 ÷ 0.630 99.6 one hundred 0.25 4.24 four 80% FeV (55% V) + 20% product less than 0.1 mm
(-one hundred) 0.315 ÷ 0.630 184 one hundred 0.30 8.9 5 FeV (55% V) less than 0.1 mm
(-one hundred) 0.315 ÷ 0.630 123 one hundred 0.44 7.36 6 FeV (55% V) less than 0.1 mm
(-one hundred) 0.10 ÷ 1.6 184 one hundred 0.38 6.6 7 FeV (55% V) less than 0.1 mm
(-one hundred) 0.315 ÷ 0.630 226.3 fifty 0.34 7.6 8 FeV (55% V) less than 0.1 mm
(-one hundred) 0.315 ÷ 0.630 700 one hundred 0.40 5.6 9 FeV (55% V) less than 0.1 mm
(-one hundred) 0.2 ÷ 0.315 one hundred 1.4 6.1

Claims (5)

1. A method of producing nitrided ferrovanadium, including the interaction of the initial alloy of ferrovanadium with gaseous nitrogen in the combustion mode, characterized in that the initial alloy of ferrovanadium with a fineness of less than 0.1 mm is pre-granulated to a size of 0.2-2.0 mm, and the combustion process is carried out a stream of nitrogen or a mixture of nitrogen with an inert gas in the direction of propagation of the reaction zone. 2. The method according to claim 1, characterized in that the feed rate of gaseous nitrogen or a mixture of nitrogen with an inert gas is 99.6-700.0 mm / s. 3. The method according to claim 1, characterized in that the combustion process is carried out at a pressure close to atmospheric. 4. The method according to claim 1, characterized in that 10-20 wt.% Of the final product is additionally introduced into the starting alloy. 5. The method according to claim 1, characterized in that the granulation of the starting alloy is carried out in a solution of rosin in acetone.