GB2091233A

GB2091233A - Process for preparing carburizing agents with an increased speed of dissolution

Info

Publication number: GB2091233A
Application number: GB8135181A
Authority: GB
Original assignee: VFT VERKAUFSGES TEER
Current assignee: VFT VERKAUFSGES TEER
Priority date: 1981-01-16
Filing date: 1981-11-23
Publication date: 1982-07-28
Also published as: DE3101168C2; SE8106735L; IT8149915A0; FR2498202B3; FR2498202A1; DE3101168A1; JPS57140635A; GB2091233B; NL8105217A; IT1172155B; BE891344A; SE451949B; JPH0245685B2

Abstract

The process is used for preparing carburizing agents with a high bulk density pressed into moulded articles, by adding alloy admixtures or admixing materials, which are usual in the production of steel or cast iron, in the form of powders or fine shavings to the carbon powders before compaction. Hydroxyethyl cellulose is preferably used as a binder with a gelling aid.

Description

SPECIFICATION Process for preparing carburizing agents with an increased speed of dissolution The invention relates to a process for preparing carburizing agents by compacting carbon powders with a binder, which have an increased speed of dissolution and therefore a higher carbon yield.

The carburizing agents are used for increasing the carbon content in steel and iron smelts.

Besides a high degree of purity, i.e. low contents of injurious impurities such as sulphur, hydrogen, nitrogen etc., the necessary properties include a high speed of dissolution.

The speed of dissolution may be improved by four parameters: 1. an optimization of the particle size, 2. a low ash value, 3. an increase in the bulk weight, 4. as high as possible a degree of graphitization or good graphitizability.

(A. Mihajlovic/B. Marincek: "Auflijsungskinetik von technischen Graphiten in Eisenschmelzen" (Dissolution kinetics of technical graphites in iron smelts) /Arch. Eisenhüttenwesen 44, No. 7, p. 507 ff.).

The most advantageous particle size has been found to be that of a grain diameter of 4 to 5 mm. A high proportion of powder had a particularly unfavourable effect upon the speed of dissolution (B. Marincek: "Beurteilung verschiedener Aufkohlungsmittel" (Evaluation of various carburizing agents) /Schweizer Archiv, March 1968, p 89 ff.).

The greatest speeds of dissolution on high-purity graphites were measured with a carbon content of 99.9% and a particle size of 4 to 5 mm in an inert gas atmosphere.

Graphite of this grain size has a bulk density of about 800 kg/m3. The bulk density with the same grain structure is a criterion for the depth of immersion and thus for the size of the contact surface between the iron smelt and the carburizing agent. An increase in the bulk density must therefore cause an increase in the speed of dissolution of the carburizing agent in the steel or iron smelt.

The object of the invention is thus to develop a process for preparing carburizing agents with a high bulk density which have a higher speed of dissolution in steel and iron smelts than comparable carburizing agents.

This object is attained according to the invention in a manufacturing process for carburizing agents by compacting carbon powders with binders in that, in order to increase the density of the moulded articles, a high-density component with a grain diameter of < 2 mm is added to the mixture.

Metal powders of the alloy components of the steel to be produced in each case, such as for example Fe, Cr, Ni, W, Co, Mo, Mn, V or Cu, may be used individually or mixed as the highdensity component. It is also possible to use metal shavings, such as cast-iron shavings or nonslag-forming admixtures such as ferromanganese or ferrosilicon.

The powders of all usual carburizing agents, which in addition to a high carbon content contain only small amounts of injurious impurities such as sulphur, hydrogen, nitrogen and ash, may be used as carbon powders. Particularly advantageous, however, are powders of carbon materials with a distinct graphite-like structure such as premium coke or electrographite.

Compaction may be carried out by extrusion, briquetting or pelletizing, which must be followed, according to the type of binder, by drying or calcination of the moulded articles in order to reduce the proportion of volatile components or hydrogen. The binder should not increase the proportion of injurious impurities in the carburizing agent.

In a particular embodiment of the process graphite powder with a grain diameter of 42 mm is mixed dry with the high-density component in a ratio of from 1 :1 O to 1 0 1 whiie adding 1% hydroxyethyl cellulose and mixed with from 10 to 25% of water according to the fineness of the solid components and less than 1% of a base of an alkali or alkaline-earth metal or ammonia solution relative to the dry mixture. This mass is then compacted in a manner known per se into pressed articles from 3 to 1 5 mm in size which are subsquently dried for 5 to 20 hours at from 80 to 1 80 C.

The invention is to be explained in greater detail in the following examples, without thereby being restricted.

EXAMPLE 1 129 parts by weight of cast-iron shavings with a grain size of < 2 mm are mixed dry with 69 parts by weight of graphite powder with a grain size of 0 to 2 mm (analysis in Table 1) and 2 parts by weight of hydroxyethyl cellulose for 5 minutes. After adding 40 parts by weight of water the mass is homogenized for a further 5 minutes. Then 0.06% by weight of 10% caustic soda solution are added. After a further 2 minutes of mixing time the finished mass is worked into pressed articles on an extrusion press with a die 35 mm thick which has cylindrical bores 5 mm in diameter; the pressed articles are subsequently dried to a residual moisture of < 0.5%.

The dried pressed articles have a bulk density of 1 600 kg/m3 and a carbon content of 37% by weight.

EXAMPLE 2 In accordance with Example 1, pressed articles are produced from 69 parts by weight of castiron shavings and 129 parts by weight of graphite powder. The dried pressed articles have a bulk density of 1100 kg/m3 and a carbon content of 70% by weight.

Of the carburizing agents listed in Table 2 the amount of carbon incorporated into the steel smelt was fixed under comparable conditions as a criterion for the speed of dissolution. The tests were carried out in a 5t induction furnace. The same amount of carbon of 30 kg was added in each case. Samples were taken after 5, 10 and 1 5 minutes in each case. The amount of carbon (carbon yield) incorporated by the smelt relative to the total amount is shown in the diagram.

As may be' seen from the diagram, the speed of dissolution of the carburizing agents produced according to the invention and their carbon yield are higher after 1 5 minutes than in the case of the best known carburizing agent - graphite.

Table I Analysis of fine-grained graphite Carbon content: 99.2% hydrogen content: 0.013% nitrogen content: 0.05% sulphur content: 0.02% volatile components: 0.57% ash 0.15% moisture 0.2% The % figures are to be taken as % by weight.

Table II grain size bulk density carbon content Carburizing agent (mm) (kg/m3) (% by weight) Al (acc. to Ex. 1) 5 1600 37 A 2 (acc. to Ex. 2) 5 1100 70 graphite 3-5 800 99 petroleum coke 3-5 600 97 pitch coke 3-5 450 98

Claims

1. A process for preparing a carburizing agent, which process comprises compacting a mixture of a carbon powder, a binder, and a high-density component with a grain diameter of less than 2 mm.

2. A process according to claim 1, wherein the high-density component comprises powder of a metal employed as an alloy component in a steel.

3. A process according to claim 1, wherein the high-density component comprises comminuted metal shavings.

4. A process according to claim 3, wherein the shavings are of cast iron.

5. A process according to claim 1, wherein the high-density component comprises powder of an alloy employed in iron or steel production.

6. A process according to claim 5, wherein the alloy is ferromanganese or ferrosilicon.

7. A process according to any preceding claim, wherein graphite powder with a maximum grain diameter of 2 mm is mixed dry with high-density component.

8. A process according to claim 7, wherein 1% hydroxyethyl cellulose is added during the dry mixing.

9. A process according to claim 7 or 8, wherein the dry mixture is mixed with from 10 to 25% of water and less than 1% of a base, relative to the dry mixture.

10. A process according to any preceding claim, wherein the carbon powder and highdensity component are employed in a ratio of from 1:10 to 10:1.

11. A process according to any preceding claim, wherein the mixture is moulded into particles from 3 to 1 5 mm in size and subsequently dried.

1 2. A process according to claim 11, wherein drying is effected at from 80 to 1 80 C for 5 to 20 hours.

13. A process for preparing a carburized agent, the process being substantially as described in examples 1 and 2.