JPH02236238A - Manufacturing method of high purity, high chromium alloy - Google Patents

Abstract

PURPOSE:To economically produce a high-purity high chromium alloy by nitriding and crushing low carbon ferrochrome, adding acid solution while vigorously agitating the resulting grains in the acid solution and mixing the grains with the acid solution to perform iron removal, and then carrying out denitriding by means of vacuum heating. CONSTITUTION:Low carbon ferrochrome of >= about 50% Cr and <= about 1% C is crushed to <= about 5mm grain size and nitrided by a solid nitriding method. The resulting ferrochrome nitride is crushed to <=1mm grain size, and the grains obtained are subjected to acid treatment to undergo iron removal. The above acid treatment is carried out by agitating and mixing so that the ferrochrome nitride grains are suspended as a whole in the acid solution and also continuously adding the acid solution to perform reaction, by which impurities, such as Si, P, S, Ni, Co, and Mn, are removed simultaneously with the above iron removal. Subsequently, the ferrochrome nitride after iron removal is denitrided by means of vacuum heating, and simultaneously, C, N, O, etc., are removed. By this method, the high-purity high chromium alloy minimal in impurity content and having about 70-95% Cr content can be obtained by using relatively inexpensive material.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a method for producing a chromium alloy with high purity and high chromium content, which is used as an additive metal in an alloy. [Prior art] High-purity chromium-containing alloys (Cr 65% or more) are added as the main chromium source in the field of superalloys such as nickel-based, iron-nickel-based, and cobalt-based alloys, and are necessary to improve corrosion resistance or strength. It is indispensable.Also, in the field of welding rods and powder metallurgy, it is used in large quantities as a powdered additive mixed with iron and nickel powder.

Conventional methods for producing high-chromium, low-carbon ferrochrome can be roughly divided into (a) Perrin's process, (b) Suden's process, and (C
) Multi-stage Veran method, (d) Others. Among these, (a). Method (b) is known as an economical method that can be produced in large quantities using an electric furnace. Also, {C
) method involves melting the primary chromium ore slag and then deironating it under weak reducing conditions. By strongly reducing ferrochrome after ft, it is possible to obtain low carbon ferrochrome with a high Cr content of 85% to 90%. Furthermore, (d) the aluminum thermite method can be considered as another method. [Problem to be solved by the invention] However, in the above-mentioned (a) Veran method and <b> Sweden method, chromium ore, which is economically available as a raw material, is F.
Because it contains a large amount of e, the resulting low carbon ferrochrome C
The upper limit of the r component is 72%. (c) The multistage Perrin method is
Although a product with a high Cr content can be obtained, there are problems in handling molten metal with a high melting point during the manufacturing process, and it is necessary to process low-carbon ferrochrome with a low Cr content, which is generated in large quantities. It has drawbacks such as a large amount of impurities such as O and N. Furthermore, in the <d> aluminum thermite method, [A1]
There are problems such as the unavoidable contamination of chromium oxide and the high cost of the chromium oxide and reaction aids used as raw materials. The present invention has been made in view of the above circumstances, and aims to solve the above-mentioned difficulties and provide a method for producing a high-purity, high-chromium alloy with a chromium content of 70 to 95%. [Means and effects for solving the problems] The method for producing a high-purity, high-chromium alloy according to the present invention includes a first step of nitriding low-carbon ferrochrome by a solid-state nitriding method to obtain nitrided ferrochrome; A method comprising: a second step of deironating by acid treatment by reducing the particle size to 111 ml or less; and a third step of denitrifying the deironated ferrochrome nitride by vacuum heating. The acid treatment involves stirring and mixing the ferrochrome nitride particles, which have been crushed to a particle size of 1 ugliness or less, in an acid solution so that they are all suspended, and by continuously adding the acid solution. It involves making a reaction. The solid nitriding method in the first step is performed by placing low carbon ferrochrome in an airtight container and heating the container with a nitrogen atmosphere. The ferrochrome nitride obtained in the first step has a nitride phase containing 85 to 95% Cr, and Fe, S
It consists of two phases: t, Co, and a metallic phase containing 5 to 20% Cr. In the second step, Fe, SL, and P contained in the metal phase are removed by acid treatment. Impurities such as S, Ni, Co, and Mn are removed. In the second step, the particle size was increased to 11
1 or less, the iron removal time is shortened because iron removal is performed without stirring so that all particles are suspended in the acid solution, and the chromium yield is improved because sulfuric acid is added continuously. Can be done. In the third step, the acid-treated ferrochrome nitride is heated in vacuum to denitrify it by the reaction described below, and to remove other impurity components such as C and 0. Cr2N(s)-=2Cr(s)+1/2N2(g
), C (s) + O (s) → C O (g),
In the above formula, (S) represents solid and (κ) represents gas. [Example] In this example, low carbon ferrochrome as a raw material was Cr. 50% or more, C, 1% or less is used. If Cr is less than 50%, the amount of Fe removed by acid treatment increases, resulting in poor efficiency. <-If C exceeds 1%, nitriding becomes smooth. Not proceed. The low carbon ferrochrome is mechanically crushed to a particle size of 5 am or less, which is then nitrided by a solid state nitriding method using a vacuum heating furnace. At this time, the vacuum heating furnace has a vacuum degree of 0. ITorr or less, temperature from 1000℃
At 1300°C, nitrogen gas is introduced to perform nitriding. In the process of iron removal, this ferrochrome nitride is
By crushing the metal to a size smaller than m and treating it with acid, most of the metal phase is removed and only the nitride phase is recovered. The acid-treated nitride is denitrified by vacuum heating at a temperature of 1150 to 1350°C, and the Cr content is reduced to 70% to 95%.
A high chromium-containing alloy is obtained in bulk. In this acid treatment and denitrification process, C,N. O. Si, Co, etc. can be reduced and high purity can be obtained. Test 1: The results of examining the effects of the stirring method and the particle size of ferrochrome nitride on the above iron-coating process will be explained with reference to the attached drawings and Tables 1 to 3. Figures 1 and 2 are diagrams showing the stirring system of the acid treatment process corresponding to Examples 1 and 2, with Figure 1 showing the strong stirring system and Figure 2 showing the circulation system. Section 3 and Figure 4 are comparative example 1, respectively.
, 2. In Figures 1 to 4, ■ is a reaction vessel that holds the acid solution 2 and crushed ferrochrome nitride 3, 4 and 5 are rotary blades that stir the inside of the vessel, and 6 in Figure 2
, 7 are a pump and circulation pipe for circulating the acid solution, respectively. Example 1 in Figure 1 is an example in which a large rotary blade is used for strong stirring by increasing the number of rotations, Example 2 in Figure 2 is an example in which the acid solution and ferrochrome nitride slurry are circulated and stirred, and Figure 3 Comparative Example 1 in Figure 4 is an example in which stirring was performed by reducing the number of rotations of the rotary blade, and Comparative Example 2 in Figure 4 is an example in which stirring was not performed at all. Table 1 shows one preferred specific example of this embodiment which will be explained later, and (1) to (4) in the table respectively indicate (1) low carbon ferrochrome as a raw material, and (2) nitriding in the first step. This shows the components of the ferrochrome nitride, (3) chromium nitride after acid treatment in the second step, and (4) high purity, high chromium alloy after denitrification in the third step. In the second step, ferrochrome nitride with the ingredients shown in Table 1-(2) was used.The ferrochrome nitride with the ingredients shown in Table 1-(2) above was crushed, and the ingredients shown in Table 2 were crushed. Tests were conducted on the three types of particle size distributions shown below.These three types of distributions are hereinafter expressed as -3mm, -1mm, and -0.15+am as shown in Table 2.Table 2Table 3 Table 3 shows the results of acid treatment of ferrochrome nitride having the particle size distribution shown in Table 2, corresponding to Examples 1 and 2 and Comparative Examples 1 and 2.
+Fe) and impurities P and Si. As is clear from the results in Table 3, when the particle size is set to III1 or less, the Cr yield decreases somewhat, but the Cr content increases, and P. Si impurities decrease. Further, as for the stirring conditions, as in Examples 1 and 2, it is effective to use strong stirring or a combination of stirring and slurry circulation so that all the ferrochrome nitride particles are suspended in the acid solution. Test 2: In Test 1, preferred stirring conditions for acid treatment and particle size of ferrochrome nitride were clarified, so a preferred example of the present invention will be explained based on these conditions.
As the raw material for the first step, the ingredients shown in Table 1 (1), 3
Low-carbon ferrochrome with a particle size distribution of m or less was used. This was subjected to nitriding treatment at 1150°C for 24 hours in a vacuum heating furnace to obtain nitrided chrome. In the second step, this nitrided ferrochrome is crushed and treated with acid to make it a particle size of III1 or less. The components of ferrochrome nitride before acid treatment are shown in Table 1 (2). The reaction vessel for acid treatment was as shown in Example 1 of Test 1,
This is a strong stirring method. A reaction vessel with an internal volume of 100.11 mm has an upward flow type impeller, and the impeller diameter/tank diameter = 0.85
Using a stirrer with an output of 0.4 kW and a rotation speed of 250 rpm, 50 β of water was added, followed by 12 kg of the above-mentioned ferrochrome nitride with a particle size of -1.0 mm, and the mixture was stirred. Furthermore, 62.5% H 2 SO 4 was added to the reaction tank in a total amount of 8 Jl continuously at 108 r using a metering pump.
4. The reaction was carried out for 16 hours from the start of addition. This reaction slurry was filtered, washed with water, recovered as a cake, mixed in the reaction vessel in which 0.5β of 25% NHs water was added to 40 Jl of water, filtered, washed with water, and dried. The composition of the obtained 7.8 kg of dried material is shown in Table 1-(3)
It was shown to. Here, H2S04 was added continuously because, as shown in Comparative Examples 3 and 4 in Table 4, if the entire amount was initially added at once, the yield of chromium would decrease in the iron removal reaction. In order to improve the chromium yield, it is preferable to control the concentration of unreacted H2SO4 in the reaction vessel using a pH meter. Additionally, NH was added to the repulp water in order to reduce S in the product. Table 4 The components of the ferrochrome nitride deironated by the acid treatment as described above are shown in Table 1 (3), which is denitrified in the third step as follows. Carbon black 0.6wt% in ferrochrome nitride obtained in the second step
was added, mixed, and subjected to vacuum treatment at 1350°C for 24 hours to denitrify. In this way, as shown in Table 1-(4), St. P, S, Ni, Co, Mn, V
, C, 0, and N are all low, and a chromium alloy with a high purity of 93.4% Cr and a high chromium content can be obtained. We will further explain the second step of Test 2. First, regarding the particle size, the finer the particle size is -113 or less, the shorter the reaction time can be. As above −lm
In case (2), the acid treatment time was 16}1r, but for example, at -0.045um, it is possible to obtain the same purity with a reaction of 311r. However, in order to economically crush ferrochrome nitride, −II■ or less is appropriate. Particles larger than 1 size are undesirable because the reaction rate is slow and the resulting product contains many impurities. On the other hand, the reason why the stirring blade was an upward flow type blade is because the specific gravity of the ferrochrome nitride used in this example is as large as about 6,
This is because this format is preferable for efficiently stirring particles up to m with low power. However, even if there is strong agitation as a downward flow, a little more power is required, but there is no problem with operation.
[Effects of the Invention] According to the present invention, nitrided ferrochrome obtained by nitriding low-carbon ferrochrome is crushed, mixed with water, and while vigorously stirring, an acid solution is continuously added to remove iron. Since impurities are sufficiently removed and then vacuum denitrification is performed, St, P, S, Ni, Co.
Low amount of impurities such as Mn, C, N, O etc. <- Cr is 70
~95% high purity, high chromium-containing alloys can be produced economically.

[Brief explanation of drawings]

Figures 1 and 2 are examples of the present invention, showing different stirring methods in the acid treatment process, and Figures 3 and 4 are comparative examples of different stirring methods with respect to the above embodiments. This is a diagram showing. DESCRIPTION OF SYMBOLS 1... Reaction container, 2... Acid solution, 3... Ferrochrome nitride, 4, 5... Rotating vane, 6... Circulation pump, 7... Circulation pipe.

Claims (1)

[Claims] A first step of obtaining nitrided ferrochrome by nitriding low-carbon ferrochrome by a solid-state nitriding method, and a second step of reducing the particle size of the nitrided ferrochrome to 1 mm or less and removing iron by acid treatment.
and a third step of denitrifying the deironated ferrochrome nitride by vacuum heating, and the acid treatment in the second step involves placing the crushed ferrochrome nitride in an acid solution. A method for producing a high-purity, high-chromium alloy, which involves stirring and mixing the alloy so that the whole is suspended in water, and continuously adding and reacting an acid solution.