JPH0742528B2 - Method for producing high purity, high chromium content alloy - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a high-purity alloy having a high chromium content, which is used as an additive metal of an alloy.

[Prior Art] High-purity low-carbon ferrochrome (Cr 65% or more) is added as a main component chromium source in the superalloy field of nickel-based, iron-nickel-based, cobalt-based, etc., and is required for improving corrosion resistance or strength. It is indispensable. Further, in the fields of welding rods and powder metallurgy, they are used in large amounts by being mixed with iron and nickel powders as powdery additive materials.

The conventional methods for producing high-chromium low-carbon ferrochromes are roughly classified into (a) perane method, (b) sweden method, (c) multi-stage perane method, (d) and others.

Among them, the methods (a) and (b) are known as economical methods capable of mass production using an electric furnace. Also,
Method (c) is a method in which the primary slag of chromium ore is melted, deironed under weak reducing conditions, and finally strongly reduced to obtain low-carbon ferrochrome, which has a high Cr content of 85% to 90%. Be done. Further, as (d) other methods, an aluminum thermite method can be considered.

[Problems to be Solved by the Invention] However, in the above-mentioned (a) Perran method and (b) Sweden method, chromium ore that is economically available as a raw material is Fe.
As a result, the upper limit of the Cr content of the obtained low carbon ferrochrome is 72%. (C) The multi-stage perlan method has a problem in handling molten metal having a high melting point in the manufacturing process and requires treatment of low carbon ferrochrome having a low Cr content, which is generated in a large amount. The highest Cr content
It is about 91%, and there is a problem that there are many impurities such as Si, O, N in the product.

The present invention has been made in view of such circumstances, and an object of the present invention is to solve the above problems and provide a method for producing a high-purity, high-chromium-containing alloy having a chromium content of 95% or more.

[Means and Actions for Solving Problems] The method for producing an alloy of high purity and high chromium content according to the present invention comprises:
First step of nitriding low carbon ferrochrome by solid nitriding method to obtain ferrochrome nitride, and crushing ferrochrome nitride obtained in the first step, then nitriding by solid nitriding method to obtain high nitrogen content ferrochrome nitride The second step, the third step of mixing the particles obtained by crushing the high nitrogen-containing ferrochrome nitride to a particle size of -1 mm or less with an acid solution, stirring and deferring the iron, A method comprising a fourth step of denitrifying nitrogen-containing ferrochrome nitride by heating it in vacuum, wherein the third step comprises stirring and mixing the particles so that they are entirely suspended in the acid solution, or It is characterized in that a slurry comprising the particles and the acid solution is circulated by a circulation means and mixed and stirred.

Ferrochrome nitride obtained in the first step has a Cr content of 85 to 95.
% Nitride phase and a metallic phase containing Fe, Si, Co and 5 to 20% Cr. By the second step, the nitride in the ferrochrome nitride is changed from the Cr ₂ N form to the CrN form, the amount of solid solution Fe in this CrN is reduced, and the iron is efficiently deironed in the third process. It In the iron removal process, Si, P, S, Ni,
Impurities such as Co and Mn are removed together with iron. In the fourth step, the acid-treated ferrochrome nitride is heated in vacuum to be denitrified by the following reaction, and other impurity components such as C, 0 are removed.

CrN (s) → 2Cr (s) + 1 / 2N ₂ (g), Cr ₂ N (s) → 2Cr (s) + 1 / 2N ₂ (g), C (s) + O (s) → CO (g), In the above formula, (s) represents a solid and (g) represents a gas.

[Examples] In this example, the low carbon ferrochrome used as a raw material is Cr, 50% or more and C, 1% or less. Cr is
If it is less than 50%, the amount of Fe removed by the acid treatment is large and the efficiency is poor, and if C exceeds 1%, nitriding does not proceed smoothly. The low carbon ferrochrome is mechanically crushed into particles having a particle size of 5 mm or less, and this is nitrided by a solid nitriding method using a vacuum heating furnace. At this time, the vacuum furnace has a vacuum degree of 0.1T.
Nitrogen gas is introduced and nitriding is performed at a temperature of 1000 ° C to 1300 ° C below orr.

The ferrochrome nitride thus obtained contains about 7% of N, and when observed by a scanning electron microscope, it has a Cr content of 85% to 85%.
It consists of two phases, a 95% nitride phase and a Fe-based metal phase containing 10% to 20% of Cr and other Si and Co. Chromium nitride in this nitride is changed to the form of CrN by renitriding from the form of Cr ₂ N, and the amount of solid solution Fe in this CrN is reduced. As the iron is removed, impurities such as Si and Co are removed.

In the deferring step, the high nitrogen-containing ferrochrome nitride is crushed to 1 mm or less and treated with an acid, whereby most of the metal phase is removed and only the nitride phase is recovered. By vacuum heating the acid-treated nitride at a temperature of 1150 to 1500 ° C, low carbon ferrochrome having a Cr content of 95% or more can be obtained in a lump form. C, N, O are reduced in the steps of acid treatment and vacuum heating at this time, and a high-purity product can be obtained.

A preferred specific example of this embodiment will be described by using numerical values. Table 1 shows low carbon ferrochrome used as (1) raw material,
(2) Ferrochrome nitride nitrided in the first step,
(3) high nitrogen content ferrochrome nitride renitrided in the second step, (4) high nitrogen content chromium nitride after the acid treatment in the third step, and (5) high purity after denitrification in the fourth step. , The components of high chromium content alloys are shown.

With the composition shown in Table 1- (1), 30.0 kg of low-carbon ferrochrome having a grain size of 3 mm or less, 30.0 kg, was subjected to a nitriding treatment at 1150 ° C. for 24 hours in a vacuum heating furnace to obtain 32.4 kg of ferrochrome nitride in Table 1- (2). It was Grind this ferrochrome nitride to 0.30 mm or less, and weigh it 30.0 kg again in a vacuum heating furnace at 900 ° C for 24 hours
Nitrogen treatment of 900 Torr of nitrogen and nitrogen was performed, and ferrochrome nitride of Table 1- (3) having a high nitrogen content of 13.3% of nitrogen was used.
2.0 kg was recovered.

The high nitrogen content ferrochrome nitride was crushed to 0.30 mm or less and subjected to the following acid treatment. That is, using a stirrer with an upflow type blade in a reaction tank with a volume of 100, a blade diameter / tank diameter = 0.8, an output of 0.4 kw, and a rotation speed of 250 rpm,
Then, 12 kg of high nitrogen-containing ferrochrome nitride having a grain size of −0.30 mm as described above was added and stirred. Further in the reaction tank
The total amount of 62.5%, H ₂ SO ₄ was 8 at 10 Hr continuously added by a metering pump, and the reaction was carried out at 16 Hr from the start of addition.

The reaction slurry was filtered and washed with water, then collected as a cake (also referred to as a filtered product), mixed with water 40 and an aqueous solution of 25% NH ₃ , 0.5 in the reaction tank, filtered, washed with water and dried. The composition of the obtained dried product (8.0 kg) is shown in Table 1- (4). Further, 0.6 wt% of carbon black was added thereto and mixed, and subjected to vacuum treatment at 1350 ° C. for 24 hours for denitrification.
As shown in (5), 6.2 kg of a high-purity, high-chromium alloy with Cr 99.0% in which Si, P, S, Ni, Co, Mn, V, C, O, and N were all low was obtained.

This specific example will be further described. First, the particle size of low carbon ferrochrome, which is the first raw material, is-
It is preferable that Cr is 3 mm and the chemical composition is high in Cr and V and Mn are low. That is, if the particle size is coarser than this, it becomes difficult for nitrogen to enter in the nitriding step, and this makes it difficult to perform pulverization economically. Regarding the Cr component, if it is low, the amount of Fe to be removed by acid treatment tends to be large, and it is preferable that the Cr component is as high as possible even in the range that can be usually obtained (Cr 60 to 72%). Further, since Mn and V cannot be completely removed by acid treatment, it is preferable that the Mn and V be as low as possible. However, in this embodiment, commercially available low carbon ferrochrome may be used.

Next, the nitriding conditions are 1000 to 1300 ° C in the first step.
And the second step is lower than the first step
The temperature is preferably 800 to 1000 ° C. The nitrogen partial pressure is preferably as high as possible. In any case, operating conditions such as temperature, pressure and time can be determined within a range that can be economically implemented.

Furthermore, regarding the conditions in the acid treatment, the particle size is 1 mm or less, the reaction is carried out by a combination of stirring and a slurry circulation method so that the entire particles are suspended in the reaction tank, and sulfuric acid is continuously added. Is reduced and the chromium yield in the iron removal step can be improved, which is preferable.

The required amount of acid, concentration, reaction temperature, etc. can be slightly increased or decreased depending on the target Cr content in the product.

[Effects of the Invention] According to the present invention, the ferrochrome nitride obtained by nitriding low-carbon ferrochrome is pulverized, renitrided to obtain high-nitrogen ferrochrome, and then pulverized into fine particles in a reaction tank The acid solution is continuously added so that the whole particles are suspended to carry out a deironing reaction, and then vacuum denitrification is performed, so that the amount of impurities other than Fe from commercially available low-carbon ferrochrome is small,
It is possible to economically produce a high-purity, high-chromium alloy containing 95% or more of Cr.

Claims (1)

[Claims] 1. A first step of nitriding low carbon ferrochrome by a solid nitriding method to obtain ferrochrome nitride, and crushing the ferrochrome nitride obtained in the first step, followed by nitriding by a solid nitriding method to contain a high nitrogen content. A second step of obtaining ferrochrome nitride, a third step of mixing the particles obtained by crushing the high nitrogen content ferrochrome nitride to a particle size of -1 mm or less with an acid solution, stirring and deferring iron, A method comprising a fourth step of denitrifying the iron-containing high-nitrogen ferrochrome nitride by heating in vacuum, wherein the third step comprises stirring the particles so that they are entirely suspended in the acid solution. Mixing,
Alternatively, a method for producing a high-purity, high-chromium-containing alloy, characterized in that a slurry comprising the particles and the acid solution is circulated by a circulation means and mixed and stirred.