DE1022251B - Process for reducing the carbon content of high carbon ferrochrome - Google Patents

Description

GERMAN

The invention relates to a method for reducing the carbon content of high carbon Ferrochrome without significant contamination of the product with foreign matter in a simple and economical way Way using gases with the exclusion of lime or similar material.

The method consists in that a fluidized bed of the comminuted high-carbon ferrochrome is produced by a stream of oxidizing gas, the fluidized bed being kept at a temperature between 900 and 1400 ^° C. until a substantial part of the carbon and the metal of the ferrochrome is oxidized and the carbon is removed from the ferrochrome as carbon oxide and the partially oxidized ferrochrome is then treated at elevated temperature in the atmosphere of a reducing gas until a substantial part of the metal oxide component or content of the ferrochrome is reduced to metal.

The reduction stage of the process is also carried out in a fluidized bed, with a reducing Gas is used as the lifting gas.

Air is preferably used as the oxidizing gas, but pure oxygen or carbonic acid can also be used as well as other oxidizing gases or mixtures of these gases can be used.

Hydrogen is advantageous as a reducing gas. However, other reducing agents, e.g. B. Carbon monoxide, water gas, methane or mixtures of these substances can be used with advantage.

For example, the high-carbon ferrochrome should contain carbon in amounts between 4 to 8% in addition to its main components chromium and iron and its secondary components silicon, aluminum, calcium, magnesium and the like. Medium carbon ferrochrome contains 1 to 4% carbon and low carbon ferrochrome contains less than 1% carbon. A particularly desired and valuable ferrochromium low carbon content, less than 0.1 ° / ₀ carbon.

The ferrochromes mentioned in the preceding paragraphs are used as alloy materials in production used in steels with a low chromium content and in the manufacture of stainless steels. Since the Manufacture of these steels has lowered the carbon content to a certain low range and on this Must be kept in the range, it is possible to use the ferrochromes of higher carbon content for the production to be used only from steels that have a relatively low chromium content. When the chromium content of steel is high, e.g. B. in an 18/8 chrome / nickel stainless steel, ferrochrome must be the alloy metal can be used, which has a very low carbon content. The procedure is therefore used carbon content reduced by ferrochrome

the carbon content of

high carbon ferrochrome

Applicant:

Chromium Mining & Smelting Corporation, Limited, Sault Ste. Marie, Ontario (Canada)

Representative: Dr.-Ing. H. Ruschke, Berlin-Friedenau,

and Dipl.-Ing. K. Grentzenberg, Munich 27,

Pienzenauerstr. 2, patent attorneys

Claimed priority:
V. St. v. America January 27, 1953

Alan R. Millers, Sault Ste. Marie, Ontario (Canada),
has been named as the inventor

to produce, so that chromium steels can be produced which have a relatively high chromium content exhibit.

According to the invention, high-carbon ferrochrome, which contains, for example, a carbon content of 7.5%, is comminuted in a suitable mill in order to form a finely divided ferrochrome powder. The fineness of the divided high-carbon ferrochrome is so great that about 60% of the powder passes through, for example, a mesh sieve of 200 mesh. The finely ground ferrochrome is fed into a conventional fluid bed roaster which contains the usual heating and cooling devices and which is operated either continuously or intermittently, as is known in the art. Air or another oxidizing gas is blown up through this ferrochrome bed located in the roasting plant and the fluidized bed is brought to the desired temperature. According to the invention, the oxidizing reaction should be carried out at a temperature between 900 and 1400 ° C. The oxidizing conversion takes place until the carbon content is reduced to the selected value. The carbon content can be reduced to about 5 ° / ₀ ,

709 848/230

3 4

at the same time in a noticeable, but small table I

Amount of the metal components of the ferrochrome oxidized sieve distribution

will. If the oxidation is carried out so far that a _ | _ 35 mesh 1.75 ° /

Reduction of the carbon content to 2 ° / ₀ takes place, o_ 48 meshes 2 ^ 50 ° /

so a larger part of the metal of the ferrochrome 5 +65 meshes 6 25 ° /

oxidized. If a very low carbon content, _j_ 100 meshes 8 75 ° /

z. B. a carbon content of less than 1% carbon _j_ 150 mesh ll'oO ⁰ /

The material to be reached in the oxidation stage is _ | _ 2OO meshes 9.75 °,

the metal of ferrochrome largely becomes metallic. 2OO meshes 60.00 ° /

Converted to oxides. _ 10 10000 ""

After the oxidation stage, the partially oxidized ιυυ, υυ, "ferrochrome", which then contains the desired carbon The above number of meshes is the one that has been reduced with a gaseous reducing agent counting along an edge of a square sieve to reduce the metallic oxides in Metal umzu- with an edge length of 25.4 mm results, migrate. The reduction step is preferably also carried out in a fluidized bed. The reducing chromium is introduced into a roasting plant, which can be carried out in the same roasting plant with a transfer tube made of silicon carbide. Hydrogen is used as the carrier gas. It is equipped that has a perforated base to allow the fluidized bed to pass through at temperatures between 1000 of the carrier gas. Is the outside air to the Umsetzrohr through to 1400 ⁰ C or maintained somewhat higher, and the 20 the perforated bottom through with such a large GeReduktion to the metal velocity and quantity is carried out as long supplied that the Ferrochromoxyde are converted to metal. particles are kept in a fluidized bed. The temperature

The reduction step may be in any other suitable device temperature of the bed is carried out at a reaction temperature in which the increased 900-1400 ⁰ C. In the interstices partially oxidized ferrochromium of a reducing 25 are sampled and subjected to carbon under atmosphere at elevated temperature. seeks. Is the carbon content to the desired level

The invention is subsequently reduced in value in terms of production, the implementation requirements

a ferrochrome medium carbon content completed from direction and used for the reduction process

a high carbon ferrochrome described. prepared.

High carbon containing ferrochromium, the 50.9 ° / ₀ chromium 30 The following table shows the manner in which

and 7.3 ° / ₀ contains carbon, in a ball mill, the decarburization of the ferrochromium at temperatures

carried out dry to a powdery ferrochrome at between 700 and 1350 ° C for up to 5 ¹ Z ₄ hours

concluded that has the following sieve analysis. will.

Table II

Treatment of the roasted food Contents
7 "Cr according to the Beh
% c action
% Si 3.97 Flue gas analysis
· /, Co ₂ ; «/ ₀ O ₂ 20.3 (1) at 700 ° C for 0.66 hours 51.96 7.1 5.57 0.2 20.5 (2) at 700 ^° C. for 2.5 hours 51.84 6.9 5.59 0.5 21.0 (3) at 700 ^° C. for 3.5 hours 51.84 6.9 5.62 0.0 19.5 (1) at 1200 ^° C. for 0.66 hours 49.66 5.4 5.60 1.0 18.0 (2) at 1200 ° C for 1.66 hours 49.36 5.1 5.58 1.0 16.5 (3) at 1200 ^° C. for 3.16 hours 48.21 4.5 5.24 2.0 17.0 (4) at 1200 ^° C. for 4.66 hours 47.36 4.2 5.15 1.0 - (1) at 1350 ^° C. for 1.08 hours 45.40 3.7 '5.29 1.0 16.5 (2) at 1350 ^° C. for 2.5 hours 44.94 3.8 4.97 1.5 18.5 (3) at 1350 ^° C. for 4.5 hours 43.37 3.4 ^! 4.84 0.5 18.5 (4) at 1350 ^° C. for 5.25 hours 42.74 3.3 0.5

A test of Table II shows that at 700 ^° C. in 3 ¹ ₂ hours there is no noticeable carbon oxidation. At 1200 ^° C., the carbon is reduced to 5.4% in the first 0.66 hours of operation and then further to 4.2% after 4.66 hours. At 1350 ^° C., the carbon is reduced to 3.7% in the first 1.08 hours and then to 3.3% in 5.25 hours. 60

The partially oxidized material, which was produced at 1350 ^° C. in 5.25 hours and contains 42.74% Cr, 3.3% C and 3.97% Si, is heated in the roasting plant in the fluidized bed, with hydrogen as the carrier gas a temperature of 1300 ° C is fed 65 for 5 hours. The roasting plant is then closed and cooled and the reduced product removed. The reduced product showed the following chemical analysis: Cr = 49.04%; C = 3.79% and Si = 4.55%. It can be seen that the oxides have been substantially reduced. 70

The invention can thus be used in the treatment of ferrochrome with less than 7% carbon. The carbon content of ferrochrome with 1 to 4% or more carbon can be reduced significantly, if the teachings of the invention are followed. The expression "high carbon" as used in the claims Ferrochrome «is to be understood in the broadest sense and includes all ferrochrome metals, regardless of what they are to the carbon content, which can be reduced to the desired carbon content according to the invention target.

Claims (6)

Patent claims: 1. Process for lowering the carbon content of high carbon ferrochrome, thereby characterized that finely ground, high carbon Ferrochrome in a fluidized bed under The use of oxidizing gas as the lifting gas is kept at a temperature of 900 to 1400 ° C for a long time is until a substantial portion of the carbon and metal of ferrochrome and the carbon is oxidized of the ferrochrome is removed as carbon oxide, and that then the partially oxidized ferrochrome is treated at an elevated temperature in an atmosphere of reducing gas until a A significant part of the metal oxide content of the ferrochrome is reduced to metal. 2. The method according to claim 1, characterized in that the partially oxidized ferrochrome is ^{treated at a temperature between 1000 and 1400 0} C in this atmosphere of reducing gas. 3. The method according to claim 1, characterized in that that the reduction is carried out in a fluidized bed using reducing gas as the carrier gas will. 4. The method according to claim 3, characterized in that the fluidized bed is at a temperature from 1000 to 1400 ° C is held until a substantial part of the metal oxide content of the ferrochrome is reduced to metal. 5. The method according to claim 1 to 4, characterized in that the reducing gas consists of hydrogen consists. 6. The method according to claim 1, characterized in that the oxidizing gas consists of air.