JPH03188229A - Manufacture of high purity high chromium alloy - Google Patents

Abstract

PURPOSE:To manufacture the high chromium-contg. alloy by powdering high silicon-low carbon ferrochrome, thereafter subjecting it to nitriding treatment, furthermore to pulverizing, to acid treatment, removing iron and silicon therefrom and successively executing denitriding by vacuum heating. CONSTITUTION:At the time of manufacturing low carbon ferrochrome, the content of Si is increased to 2 to 4%, is embrittlea and is powdered into <=0.3 mm. It is charged to a vacuum heating furnace, is heated, e.g. to 1150 deg.C for many hours while an N2 gas is fed thereto and is transformed into ferrochrome nitride contg. about 13% N. The ferrochrome nitride is pulverized into the shape of grains of <=1 mm and is thereafter mixed with an acid soln. The mixture is stirred into the shape of slurry, and the contents such as Fe, Si, P, Ni, Co and Mn in the ferrochrome nitride are melted away. Next, the ferrochrome nitride is admixed with a small amt. of carbon black and is subjected to denitriding treatment by vacuum heating at a high temp., by which the high purity Cr alloy of high quality having about 99% Cr can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present 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 (65% or more Cr) 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 essential. In addition, in the fields 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 broadly classified into (a) the Perrin process, (b) the Swedish process, (c) the multi-stage Perrin process, and (d) others.

Among these methods, methods (a) and (b) are known as economical methods that can be produced in large quantities using an electric furnace. Also, (c
) method is a method in which the primary slag of chromium ore is melted, iron is removed under weak reducing conditions, and finally strong reduction is performed to obtain low carbon ferrochrome, and a product with a high Cr content of 85% to 90% can be obtained.

Furthermore, (d) an aluminum thermite method can be considered as another method.

[Problems to be Solved by the Invention] However, in the (a) Perrin process and (b) Swedish process, the chromium ore that is economically available as a raw material contains a large amount of Fe, so the Cr component of the resulting low carbon ferrochrome is The upper limit is 72%. (C) Although the multi-stage Perrin process can produce products with a high Cr content, 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. Furthermore, there are other drawbacks such as a large amount of impurities such as Si, O, and N.

Furthermore, in the (d) aluminum thermite method, contamination with [AI] is unavoidable, and chromium oxide and reaction aids used as raw materials are expensive.

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 high chromium content.

[Means and effects for solving the problems] The method for producing a high purity, high chromium alloy according to the present invention uses low carbon ferrochrome containing 2 to 4% silicon as a starting material, and reduces the starting material to a thickness of 0.3 mm or less. a first step of crushing, a second step of obtaining nitrided ferrochrome by nitriding the low carbon ferrochrome crushed to 0.3-1 or less in the first step by a solid nitriding method; In the third step, the ferrochrome nitride that has been deironated and desiliconized is heated under vacuum. and a fourth step of denitrifying.

The silicon content of low carbon ferrochrome specified by the Japanese Industrial Standards (JIS) is 1% or less, and it is difficult to crush it industrially into 3 parts or less.

If you use as a starting material a material that has been melted in an electric furnace to contain 2-4% silicon,
It can be easily crushed into pieces of 0.3 mm or less. By using low carbon ferrochrome with a small particle size, the second to fourth steps can be carried out efficiently.

Ferrochrome nitride obtained by heating in a nitrogen atmosphere in the second step has a nitride phase containing 98 to 99.5 wt% Cr and Fe.
, St, Co, etc.

In the third step, impurities such as Fe, Sj, P, Ni, Co, and Mn contained in the metal phase are removed by acid treatment. Since most of the 2-4 wt % silicon contained in the raw material is metallic silicon, it is removed by the acid treatment. In addition, the crushing in the third step is
During nitriding, the sintered lumps are crushed, so the operation is not particularly difficult.

In the fourth step, the acid-treated ferrochrome nitride is heated in vacuum to be denitrified by the reaction described below, and impurity components such as C1O are removed.

Cr2N(s) −+ 2Cr(s)+
1/2Nz(g), C(s)+0(s)−=
Co(g) [Example] In the first step, Table 1-(
The low carbon ferrochrome of the components shown in 1) was used as a starting material and was crushed to a particle size of 0.3 mm or less. All components in Table 1 are expressed in wt%.

After crushing the low carbon ferrochrome in the first step, in the second step, the crushed low carbon ferrochrome is charged into a vacuum heating furnace, nitrogen is introduced, and 760 To
[N]
-13.4 wt%, 34.0 kg of ferrochrome nitride shown in Table 1-(2) was obtained.

Subsequently, in the third step, acid treatment was performed as follows using the stirring apparatus shown in FIG. FIG. 2 shows a stirring device used in a comparative example. In FIG. 1, 1 is a reaction vessel, 2 is a slurry containing a mixture of ferrochrome nitride and an acid solution, and 4 is a stirring blade.

12 kg of the ferrochrome nitride crushed to 0.3 nm or less with 501 water were placed in a reaction vessel 1 having a volume of 1, and mixed using a stirrer. The agitator has upward flow type blades, blade diameter/tank diameter = 0.8, and rotation speed;
It was operated at 25 rpm.

In the stirring method using the stirrer, the entire amount of ferrochrome nitride particles is suspended in the acid solution, and the acid treatment is efficiently performed. 62.5% to the reaction vessel.

A total of 1 liter of H2SO4 was added continuously using a metering pump for 10
The mixture was added over 168 hours and stirring was continued for 168 hours from the start of the addition. Thereafter, the slurry in which the acid solution and ferrochrome nitride were mixed was filtered, washed with water, and dried to collect 8.0 magazines. Its components are shown in Table 1-(3).

FIG. 2 shows a stirring device used as a comparative example.

In FIG. 2, 3 is the ferrochrome nitride deposited on the bottom of the container, 5 is the stirring blade used in the comparative example, and the rest is the same as in FIG. 1. In the comparative example, the blade diameter/tank diameter = 0.6,
It was operated at a rotational speed of 150 rpm. Other conditions for acid treatment and recovery after acid treatment are the same as in the above examples. In this stirring method, the stirring force is weak, and some of the ferrochrome nitride particles are deposited at the bottom of the reaction vessel. The components of the ferrochrome nitride recovered in the comparative example are shown in Table 1-(5).

Comparing the components in Table 1-(5) and Table 1-(3>), it is found that the Cr content is higher in the Examples than in the Comparative Examples, and Si, P
impurities are decreasing.

In the fourth step, the recovered material obtained in the third step is
Add 0.3 wt% of carbon black and mix, 125
Denitrification was performed by vacuum heating at 0° C. for 24 hours. Through the fourth step, Cr is produced as shown in Table 1-(4).

88.5wt%, Si, 0.02wt%, other P,
S, Ni.

6.2 kg of a high-purity, high-chromium alloy containing low amounts of Co, Mn, V, C, O, and N was obtained.

In the fourth step, the acid-treated ferrochrome nitride is denitrified by the following reaction by heating in vacuum, and impurity components such as C and O are removed.

Cr2N(s>=2Cr(s)+1/2N2(
g), C(s) + 0(s) → Co(g)
, Carbon Bra Tsuku is added to the recovered material obtained in the third step.
Add 0.6 wt%, mix, and heat at 1250°C for 24 Hr.
Denitrification was performed by vacuum heating. Through the fourth step, Table 1
- Cr as shown in (4), 99. Ovt%, other S
i.

P, S, Ni, Co, Mn, V, C
A high-purity, high-chromium alloy with low levels of , O, and N is 6.2
g was obtained.

After crushing it by nitriding and crushing it, it is mixed with an acid solution and stirred to sufficiently remove iron and impurities, and then vacuum denitrification is performed, so that St, P, S, Ni.

High-purity, high-chromium alloys with low amounts of impurities such as Co, Mn, C, N, and O can be produced economically.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the stirring device of this example, and FIG. 2 is a diagram showing the stirring device of Comparative Example (1). DESCRIPTION OF SYMBOLS 1... Reaction container, 2... Slurry in which ferrochrome nitride and acid solution were mixed, 3... Ferrochrome nitride, 4
... Stirring blade of Example, 5... Stirring blade of Comparative Example.

Claims (2)

[Claims] (1) A first step in which low-carbon ferrochrome containing 2 to 4% silicon is used as a starting material, and the starting material is crushed into pieces of 0.3 mm or less, and the low-carbon particles are crushed into pieces of 0.3 mm or less in the first step. a second step of nitriding ferrochrome by a solid-state nitriding method to obtain nitrided ferrochrome; and crushing the nitrided ferrochrome to a particle size of 1 mm or less and mixing it with an acid solution.
A third step of deironating and desiliconizing by stirring acid treatment, and a fourth step of vacuum heating the ferrochrome nitride that has been deironated and desiliconized in the third step to denitrify it. A manufacturing method for high-purity, high-chromium alloys. (2) The acid treatment in the third step includes stirring and mixing the crushed ferrochrome nitride so that it is entirely suspended in the acid solution, and continuously adding the acid solution to cause a reaction. A method for producing a high purity, high chromium alloy according to claim 1.