JPH0245685B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for making a carburizing agent that has a high dissolution rate and therefore a high carbon yield, in which carbon powder is compacted with a binder. Recarburizers are used to increase the carbon content of molten steel and iron. The properties require high purity, ie low content of harmful entraining substances such as sulfur, hydrogen, nitrogen, etc., as well as high dissolution rates. The dissolution rate can be improved by four parameters: 1. Optimal particle size. 2. Low ash content. 3. Increased bulk density. 4. As high a degree of graphitization as possible or good graphitizability (A.
Mihajlvoic/B.Marincek: Auflo¨sungkinetik
von techni-schen graphite in
Eisenschmelgen, Arch.Eisenhu¨ttenwesen44,
No. 7 (see page 507 et seq.). It has been found that a particle size of 4 to 5 mm is advantageous. The high powder proportion had a particularly unfavorable effect on the dissolution rate (B.Marincek: Beurteilung
verschiedener Aufkohlingsmittel, Schweizer
Archiv, March 1968, pages 89 et seq.). The maximum dissolution rate of high purity graphite was obtained in an inert gas atmosphere with a carbon content of 99.9% and a particle size of 4-5 mm. The bulk density of graphite with this particle size is approximately 800
Kg/ ^m2 . For the same particle size configuration, bulk density is a measure of the depth of immersion and thus the amount of contact area between the molten iron and the recarburizer. An increase in bulk density therefore has the effect of increasing the dissolution rate of the recarburizer in molten steel or iron. It is therefore an object of the present invention to develop a process for the preparation of high bulk density recarburizers which have a higher dissolution rate in molten steel and iron than comparable known recarburizers. This object is solved according to the invention in a process for producing a carburizing agent in which carbon powder is compressed with a binder, by adding to the mixture a dense component with a particle size of less than 2 mm in order to increase the density of the compact. As alloying components and non-slag-forming additives commonly used in the production of dense iron and steel, the alloying components of the steel produced in each case, such as Fe, Cr,
Metal powders of Ni, W, Co, Mo, Mn, V or copper can be used individually or in mixtures. It is likewise possible to use metal chips, such as gray cast iron chips, or additives which do not form slags, such as ferromanganese and ferrosilicon powders. As carbon powders it is possible to use powders of all customary carburizers which contain a high carbon content and only small amounts of harmful entrained substances such as sulfur, hydrogen, nitrogen and ash. Particularly advantageous, however, are powders of carbon materials with a distinct stone structure, such as premium cokes or electrolytic graphite. Among the commonly used binders, in addition to oxyethylcellulose, starch, pitch and bitumen are suitable as binders. Compaction is carried out by extrusion, briquetting or pelletizing, and the shaped body must then be dried or calcined, depending on the type of binder, in order to reduce the volatile content or hydrogen content. The binder must not increase the proportion of harmful entrained elements in the recarburizer. According to a particularly advantageous embodiment of the method, particle size 2
1:10~ of graphite powder of less than mm and high density component
Add 1% oxyethylcellulose and dry mix in a 10:1 ratio, add water depending on the fineness of the solid components.
10-25% and alkali metal or alkaline earth metal base or aqueous ammonia are mixed at 1% to the dry mixture. This mixture is then compressed by known methods into compacts with a size of 3 to 15 mm, which are then
Dry at 80-180°C for 5-20 hours. The invention will now be explained by way of example. Example 1 129 parts by weight of gray cast iron chips with a particle size of <2 mm are dry mixed for 5 minutes with 69 parts by weight of graphite powder with a particle size of 0 to 2 mm (analytical values are shown in the table) and 2 parts by weight of oxyethyl cellulose. After adding 40 parts by weight of water, the mixture is homogenized for a further 5 minutes. Then 10% caustic soda
Add 0.06 parts by weight. After mixing for a further 2 minutes, the mixture obtained is processed into shaped bodies in an extruder with a die 35 mm thick with cylindrical holes 5 mm in diameter, which are then dried to a residual moisture content of <0.5%.
The bulk density of the dried compact was 1600 Kg/m ³ and the carbon content was 37% by weight. Example 2 A molded body is produced as in Example 1 from 69 parts by weight of gray cast iron chips and 129 parts by weight of graphite powder. The bulk density of the dried compact is 1100Kg/m ³ and the carbon content is 70
Weight%. The amount of carbon absorbed by the molten steel was measured as a measure of dissolution rate under similar conditions for the recarburizers shown in the table. The experiment was conducted in a 5-ton induction furnace. The same amount of carbon, 30 kg, was added each time. Samples were taken after 5, 10 and 15 minutes, respectively. The figure shows the amount of carbon absorbed (carbon yield) relative to the total amount of molten metal. + means Example 1, × means recarburizing agent of Example 2, 0 means graphite,
□ is a curve showing the relationship between reaction time (minutes) and carbon yield in the case of petroleum coke and △ is pitch coke. As is clear from the curves in the figure, the dissolution rate of the recarburizer prepared according to the invention, as well as its carbon yield after 15 minutes, is higher than that of the best known recarburizer, graphite. Table Analysis of fine graphite Carbon 99.2% by weight Hydrogen 0.013 Titanium 0.05 Sulfur 0.02 Volatile content 0.57% by weight Ash 0.15 Moisture 0.2 [Table]

[Brief explanation of the drawing]

The figure shows the carbon yield of various recarburizers.

Claims (1)

[Claims] 1. In a process for producing a carburizing agent with a high dissolution rate, in which carbon powder is compressed with a binder and subsequently dried or calcined, a density particle with a particle size of less than 2 mm is added to the mixture in order to increase the density of the compact. A process for producing a recarburizer with a high dissolution rate, characterized by the addition of alloying ingredients commonly used in iron and steel manufacturing and additives that do not form slag. 2. The manufacturing method according to claim 1, wherein pure metal powder of a steel alloy component is used as the high-density component. 3. The manufacturing method according to claim 1, wherein metal chips of gray cast iron, for example, are used as the dense component. 4. Process according to claim 1, in which non-slag-forming additives such as ferromanganese and ferrosilicon powders are used as the dense component. 5 Graphite powder with a maximum particle size of 2 mm is dry mixed with the dense component in a ratio of 1:10 to 10:1 with the addition of 1% oxyethyl cellulose, 10 to 25% water and an alkali metal or alkaline earth metal. Adding less than 1% of base or aqueous ammonia to the dry mixture, then compressing it into a molded body with a size of 3 to 15 mm, and drying it at 80 to 180°C for 5 to 20 hours. The manufacturing method according to any one of Items 1 to 4.