JPH0660368B2 - Method for producing low carbon ferrochrome having high chromium content - Google Patents

Description

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

[Prior Art] High-purity low-carbon ferrochromium (Cr 65% or more) is added as a chromium source as an auxiliary component in the superalloy field of nickel-based, iron-nickel-based, cobalt-based, etc., and is necessary 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.

Conventional methods for producing high-chromium low-carbon ferrochrome are roughly classified into (a) perane method, (b) sweden method, and (c).
Multi-stage Perran method, (d) and others. this house,
The methods (a) and (b) are known as economical methods that can be mass-produced using an electric furnace. Further, the method (c) is a method of dissolving the primary slag of chromium ore, deferring iron under weak reducing conditions, and finally performing strong reduction to obtain low-carbon ferrochrome, which is 85% to 90%.
A high Cr content of Cr can be obtained. Furthermore, (d) the aluminum thermit method can be considered as another method.

[Problems to be Solved by the Invention] However, since the chromium ore that is economically available as a raw material contains a large amount of Fe, the (a) perane method and (b) sweden method described above have a Cr component of the low carbon ferrochrome obtained. Is 70
% Is the upper limit. (c) In the multi-stage perane method, although a high Cr content can be obtained, it is difficult to handle a high melting point molten metal in the manufacturing process, and it is necessary to treat a low carbon content low ferrochrome having a large Cr content. Further in the product
There are difficulties such as a large amount of impurities such as Si, O and N.

The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the above problems and provide a method for producing high-purity low-carbon ferrochrome having a high chromium content of 70% to 95%.

[Means and Actions for Solving Problems] A method for producing low carbon ferrochrome having a high chromium content according to the present invention comprises a first step of nitriding low carbon ferrochrome by a solid nitriding method to obtain ferrochrome nitride, The method is characterized by comprising a second step of deferring the ferrochrome nitride by acid treatment and a third step of denitrifying by heating the deferred ferrochrome nitride in vacuum.

The ferrochrome nitride obtained in the first step has a Cr content of 85 to
It consists of two phases: a 95% nitride phase and a metallic phase containing Fe, Si, Co and 5 to 20% Cr. The metallic phase of the ferrochrome nitride is efficiently removed in the acid treatment step of the second step, and ferrochrome nitride having a high Cr content can be obtained. In the third step, the acid-treated ferrochrome nitride is heated in vacuum to be denitrified by the following reaction, and other impurity components such as C and O are removed.

Cr ₂ N (S) → 2Cr (s) + 1 / 2N ₂ (g), C (s) + O (s) → CO (g) In the above table, (s) is solid, (g) is gas Represents

The low-carbon ferrochrome thus obtained is a high-purity, low-carbon ferrochrome having a high chromium content.

[Examples] In this example, the low carbon ferrochrome used as a raw material is Cr, 50%, C, 1% or less. Cr
Is less than 50%, the amount of Fe removed by the acid treatment is large and the efficiency is poor, and when C exceeds 1%, nitriding does not proceed smoothly. The low carbon ferrochrome is mechanically crushed to
The grain size is made to be less than mm and is nitrided by a solid nitriding method using a vacuum heating furnace. At this time, the vacuum furnace has a vacuum degree of 0.1 Torr and a temperature of 1000 ° C. to 1300 ° C.
Nitrogen gas is introduced and nitriding is performed.

The ferrochrome nitride thus obtained contains about 7% N, and when observed by a scanning electron microscope, it contains 85% Cr.
~ 95% nitride phase and Cr 10% ~ 20%
It consists of two phases, a metallic phase mainly composed of Fe containing Si and Co.
By crushing this ferrochrome nitride to 3 mm or less and treating it with an acid, 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 1350 ° C., a low carbon ferrochrome having a Cr content of 70% to 95% is obtained in a lump form. In the steps of acid treatment and vacuum heating at this time, C, N, O, Si, and Co are reduced and a high purity can be obtained.

A preferred specific example of the present invention will be described with reference to numerical values. Table 1
Low carbon ferrochrome with a composition of 3 mm or less, 3
0.0kg was subjected to a nitriding treatment at 1150 ° C. for 24 hours in a vacuum heating furnace to obtain 32.3 kg of ferrochrome nitride. This ferrochrome nitride was crushed to a size of 3 mm or less.
0 kg, while stirring with 60 3N, H ₂ SO ₄ aqueous solution,
48 Hr acid treatment was performed. Then, the components of 10.5 kg of ferrochrome nitride obtained by washing with water and drying are shown in Table 1.
Further, 0.4 wt% of carbon black was added to this and pulverized. This pulverized ferrochromium nitride (10.0 kg) was subjected to a vacuum treatment at 1250 ° C. for 24 hours for denitrification, and low-carbon ferrochrome having a high chromium content shown in Table 1 was obtained in a lump form. The specific example described here will be referred to as specific example 1 below. FCr in Table 1 is an abbreviation for ferrochrome, and the same applies to Tables 2 and 6.

Next, a specific numerical example will be described.

Test 1: Low carbon ferrochromium (Cr content, 60% -70%) easily obtained for industrial use has high toughness and high strength, so it is difficult to crush it to obtain a powder, and it is usually mechanical The particle size obtained by crushing is at least 1 mm. Ferrochrome nitride obtained by nitriding this has a nitrogen content of 8% or less, and the form of chromium nitride can be ground with Cr ₂ N. This ferrochrome nitride is crushed to a particle size of 0.3 mm or less, and this is again heated to 800 ° C to 1200 ° C.
When the nitriding treatment is performed at a temperature of ° C, the nitrogen content is 10% to 1
It increases up to 3% and the morphology of this nitride phase is CrN. Comparing this CrN with the above-mentioned Cr ₂ N, the amount of solid solution Fe in the nitride phase is smaller in CrN. Therefore, when the morphology of the nitride phase is CrN, Fe can be easily removed by acid treatment, and a low carbon ferrochrome having a high Cr content can be obtained.

A preferred specific example of Test 1 is as follows.

The ferrochrome nitride obtained in the first step of Concrete Example 1 was crushed to 0.3 mm or less and subjected to nitriding treatment at 1000 ° C. for 24 hours. The components of the nitride obtained here are shown in Table 2. This nitride was crushed to -0.3 mm and
The reaction was carried out for 24 hours. The composition of the obtained nitride after the acid treatment is shown in Table 2. Table 2 also shows the components of a mixture of 0.7 wt% of carbon and denitrification by vacuum treatment at 1250 ° C. for 24 hours.

In this manner, the ferrochrome nitride obtained by nitriding the low carbon ferrochrome as the raw material is pulverized and renitrided, and the low carbon ferrochrome obtained through the second and third steps in the same manner as in Example 1 is up to about 93%. It is shown in Table 2 that the chromium content is improved.

Test 2: If the particle size of the low carbon ferrochrome exceeds 3 mm in the first step, the nitriding time is extended and the nitriding rate is significantly reduced. When the particle size of ferrochrome nitride is 3 mm or less in the second step, the efficiency of removing the metal phase by acid treatment is improved, and when the particle size is less than 0.3 mm, a part of the nitride phase is eluted by the acid treatment and the Cr component is dissolved. Yield is reduced. In the case of hydrochloric acid, for example, the amount of acid required in the acid treatment is the following reaction formula: Fe (s) + 2HCl (l) → FeCl ₂ (l) + H ₂ (g) Cr (s) + 3HCl (l) → CrCl ₃ Calculated quantitatively by (l) +3/2 · H ₂ (g). That is, 10-30% excess acid of the HCl consumed in the previous equation is required. Regarding the concentration of the acid aqueous solution in the acid treatment, 1N
If it is less than 1, the amount of the acid aqueous solution becomes large, which affects the production cost. On the other hand, if it exceeds 3N, the yield of Cr is lowered, and salts of the eluted metal phase, such as FeCl ₂ and FeSO ₄ , are precipitated and fixed to the particles of the nitride phase to be recovered by the acid treatment. There is a risk that it may interfere with the cleaning and recovery operations.

As for the weight ratio of the acid aqueous solution and the ferrochrome nitride, when the ferrochrome nitride is large, the above-mentioned salt is produced and precipitated at a level higher than the solubility in the aqueous solution. On the other hand, if the amount is too small, the amount of the acid aqueous solution will be unduly large.
As is clear from the above description, the Cr content can be adjusted by adjusting the acid concentration of the acid treatment and the amount of ferrochrome nitride.

The test which examined the conditions of acid treatment is demonstrated.
The results are summarized in Table 3. Test in this table
No. 1 to No. 5 were carried out with HCl solution using the renitrided ferrochrome nitride powder shown in Table 2. Comparing the results of tests No. 1 and No. 3, when the acid concentration is increased, the chromium yield decreases, and when it is too low, the reaction takes a long time and the amount of acid used in the reaction increases, which is economical. It turns out that it is not suitable for. From this viewpoint, the range of acid concentration was determined to be 1 to 3N. Test No.2, No.4, No.5
About the amount of acid (ml) and the weight of the ferrochrome sample
It was studied by changing the ratio with (g). When the amount of acid is large, the Cr yield decreases, and conversely, when the amount of acid is small, deironing becomes insufficient.
In Table 3, the weight of all the samples other than the tests No. 4 and No. 5 is 100 g. Thus, the acid treatment condition is 1
In the case of treating with N to 3N, the outer ratio of ferrochromium nitride is preferably 8 to 25% by weight with respect to 100% by weight of the acid aqueous solution, and if it exceeds 25%, deironing is insufficient, and if it is less than 8%, the amount of the acid aqueous solution is unreasonable. Is not economically preferable.

Next, the results of studying the preferable range of the particle size of ferrochrome nitride before acid treatment will be described. Table 3 tests
No. 6 to No. 10 correspond to this examination.

Nitrogen the low carbon ferrochrome of 5mm or less, nitrogen 6.
4% ferrochrome nitride, crushed and tested No. 6
To the particle size range shown in the column of 10 samples (in mm, for example
(5/3 is a particle size of 5 mm to 3 mm, − indicates the following, the same applies hereinafter)
Acid treatment was performed with 3N sulfuric acid aqueous solution. Regarding the Cr yield after the acid treatment, 90% or more is observed at 0.074 mm or more, and the Cr yield is significantly reduced at less than 0.074 mm. If it is 3 mm or more, the reaction takes a long time, which is not economically preferable.

Test 3: There are various kinds of acids used industrially, but as economically used, two kinds, HCl and H ₂ SO ₄ , are considered. In this, case of HCl, washed with water after acid treatment, chlorine is easily removed on drying, less expensive H ₂
The present invention relates to a method for reducing S in a product when SO ₄ is performed, and it has been found that S can be easily removed by washing with ammonia water.

After the acid treatment performed according to Example 1, the acid was removed by decantation, 20 water was added, and the mixture was stirred and decanted again, and this operation was performed twice. After that, 20 kinds of 1N ammonia water, 1N hydrochloric acid aqueous solution, and 3 kinds of water solutions were respectively added and stirred,
It was decanted and filtered. As a result of drying this, the S component of the obtained oxide is shown in Table 4. As shown in this table, washing with ammonia water facilitates the elution of So ₄ ^2- ions adhering to particles etc. into the aqueous solution, and as a result it is possible to prevent the S component from being mixed into the dried product. .

Test 4: In the third step, carbon addition was C (s) + O
→ This is because O is removed by the reaction of CO (g). The range of particle size and temperature is to reduce C, O, N in the product. If the particle size exceeds 0.3 mm and the temperature is less than 1100 ° C,
If the C, O, and N are not sufficiently reduced and the temperature is 1400 ° C., there is a risk that the yield may decrease due to the volatilization of Cr and the heat resistance of the vacuum heating apparatus may be problematic.

The results of examining the effect of the addition of carbon are shown in Table 5. Test No.1 and No.2 are the acid-treated nitrides, which were vacuum-treated as they were without adding carbonaceous material, but even if the nitrogen content could be reduced, the oxygen mixed during the acid-treatment could not be removed. I understand. Tests No. 3 to No. 7 are denitrification by adding carbon necessary for the next reaction to oxygen existing before denitrification.

In Test Nos. 3 to 5, the grain size was examined. If the grain size is coarse, both C and O remain, and it is preferable that the grain size be 0.3 mm or less. In addition, tests No. 5 to No. 9 were conducted to examine changes with the denitrification temperature. As shown in Table 5, the denitrification temperature was 11
50 ° C to 1350 ° C is preferable, and Cr is 1400 ° C or higher.
The yield deteriorates, and C, N, and O tend to remain at low temperatures.

Test 5: The low-carbon ferrochrome having a high chromium content obtained by the method of Example 1 of the present invention is easier to crush and pulverize than the low-carbon ferrochrome produced by the conventional method. It is provided as an additive in the field of welding rods or powder metallurgy. The results of the above pulverization test are shown in Table 6. Two kinds of samples, that is, a low carbon ferrochrome having a high chromium content obtained by the method of Example 1, and a low carbon ferrochrome which is also a starting material in Example 1, were sampled, and all were ground under the same conditions to obtain a particle size distribution. Are compared. Grinding conditions were as follows: 7 vibrating mill with SUS pot and 35 kg of iron 20φ rod inserted as medium in it, 5 kg of each sample of 3/1 grain size was enclosed, and argon atmosphere was used. 30 minutes. The oxygen content of the sample (No. 1) obtained by crushing the present invention is 0.15 wt%, which is compared with the commercially available powder (oxygen content is 0.3 wt% or more),
It has the feature of keeping the oxygen content low.

As described above, the high chromium content low carbon ferrochrome obtained in the present example is economically pulverized, its particle size and composition are sufficient, and it can be used as an additive for welding rods or powder metallurgy.

[Effects of the Invention] According to the present invention, nitriding is performed to form two phases, a nitride phase and a metal phase, and the metal phase is removed by acid treatment and then denitrification is performed. Carbon ferrochrome can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yutaka Yano 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Susumu Ogawa Examiner, Nihon Kokan Co., Ltd.

Claims (7)

[Claims] 1. A first step of nitriding low carbon ferrochrome by a fixed nitriding method to obtain ferrochrome nitride, a second step of acid-treating the ferrochrome nitride to deiron, and deferred ferrochrome nitride. And a third step of denitrifying by heating in vacuum, a method for producing low-carbon ferrochrome having a high chromium content. 2. The production of low carbon ferrochromium having a high chromium content according to claim 1, wherein the ferrochrome nitride nitrided once is crushed and crushed in the first step and then nitrided a second time. Method. 3. In the first step, low carbon ferrochrome having a grain size of 3 mm or less is nitrided to obtain ferrochrome nitride,
The method for producing low-carbon ferrochrome having a high chromium content according to claim 1, wherein the ferrochrome nitride is treated at an external ratio of 8 to 25% by weight with respect to 100% by weight of a 1N to 3N acid aqueous solution. 4. The particle size of ferrochrome nitride before acid treatment is set to 0.
The method for producing low carbon ferrochrome having a high chromium content according to claim 3, wherein the thickness is 3 to 3 mm. 5. The production of low carbon ferrochromium having a high chromium content according to claim 1, wherein in the second step, the acid treatment is performed by using an aqueous solution of H ₂ SO ₄ and washing with aqueous ammonia. Method. 6. In the third step, carbonaceous material is added to ferrochrome nitride, pulverized and mixed to denitrify at a grain size of 0.3 mm or less and a temperature of 1150 ° C. to 1300 ° C. 1. The method for producing low carbon ferrochrome having a high chromium content according to 1. 7. A first step of nitriding low carbon ferrochrome by a solid nitriding method to obtain ferrochrome nitride, a second step of acid-treating the ferrochrome nitride to deiron, and the deferred ferrochrome nitride. A method for producing low-carbon ferrochrome having a high chromium content, comprising a third step of denitrifying by heating in vacuum and a fourth step of pulverizing the denitrified ferrochrome in an inert atmosphere.