US1612570A - Making iron alloys - Google Patents

Description

The recess involves several sta esj b Patented Dec. 28, 1926.

UNITED STATES LEON CAMMEN, OF NEW YORK, N. Y.

MAKING IRON ALLOYS.

'No Drawing.

The present invention refers to a process for producing extremely low carbon steels, with special reference to so-called electric sheets, such as silicon steel sheets, and describes a process whereby an extremely lowcarbon material may be obtained commercially. I

T. D. Yensen ('lransactions, American Institute of Electrical Engineers, vol. 34, pp. 52001 if.) reports that by melting electrolytic iron alloyed with silicon in a vacuum furnace he has obtained a maximum permeability some 500 per cent higher than .is encountered in commercial silicon steel sheets. While this has been generally ascribed to the use of vacuum melting, my own work would indicate that the remarkable results obtained by Yensen were due primarily to the nearly total absence of carbon in his samples due to the use of electrolytic iron as a starting matcrial, and to the comparative freedom of the product from oxides and nitrides. In the present invention it is proposed to attain the same end by means that would permit to produce the desired material in commercial quantities, at a price not too much above that of similar steels as now made.

The first stage is carried on in a Bessemer converter which is overblown, i. e., blown until the iron beginsto burn. This happens whenboth the silicon and the carbon blow' are completed, and the blast still continued. At the end of such a blow the metal contains a fairly low amount of carbon, say 0.05, and is heavily oxidized. It is then ready for the second stage which is carried on in some kind of a furnace which must satisfy, two essential conditions: thsfuriiaceshould be capable to raise the temperature of the metal to 1550 de cent. or over and there must be no chance for the metal to be contaminated by carbon (either solid as from the electrodes, or gaseous, as from carbon monoxide in the furnace atmosphere). An electric inductionfurnace satisfies these conditions.

At a temperature of the order of 1550 deg. cent, the tendency is for the carbon to deoxidize iron. It is im ortant however to bear in mind that the desired end is to reduce the carbon to say 0.001 per cent, and this means that even at 0.002 per cent the reaction of deoxidation of the iron oxide by carbon, with consequent elimination-of the carbon as Application filed March 26. 1926. Serial No. 97.774.

carbon monoxide, must continue. But 0.002

per cent carbon means 2 parts of carbon to 100,000 parts of the mass, or an extremely tenuous dilution, and of course no carboniron oxide reaction can take place unless the carbon, or more precisely carbide of iron, come into direct contact with oxide of iron. Because of the extremely low content of carbon towards the end of the reaction, it is absolutely necessary that the oxide of iron, while not in such quantities as to make its reduction to iron prohibitively expensive, should be so thoroughly distributed through the mass of the metal as to ensure in a positive manner the ability of every tiny drop of carbide of iron to come into direct contact with a drop of oxide of iron.

It has been found that addition of iron ore to a metal bath does not insure such an intimate mixture of the oxide of iron and the bath as to produce the desired result. It is for this reason that an. overblown converter stage is used as the first stage, as it naturally results in an iron thoroughly and uniformly deoxidized, and such handling as is necessary to transfer the metal from the converter to the induction furnace provides a stirring of the metal and increases its uniformity.

The time period during which the metal has to be held in the induction furnace depends on several factors, such as the amount of decarbonization achieved in the Bessemer stage, and is a matter which any skilled metallurgist is capable of determining for himself with due regard to the conditions of operation in his plant.

The metal is next deoxidized in the usual manner, and the proper additions ofalloying elements, such as silicon, aluminum or the like are made. In this part of the process common practice may'be used. 1

This may be followed by the addition of such elements as zirconium, to eliminate sulphur, or titanium, to eliminate at least some of the nitrogen or nitrides formed thereby.

The metal may be delivered to the furnace from the converter with the slag formed in the latter, and held in the furnace with this slag until the desired degree of, carbon reduction has been obtained;

whereupon the converter slag is removed,

and a deoxidizing slag is substituted.

Where conditions permit, a material increase in efliciency of the process may be secured by operating the Bessemer stage in a somewhat unusual manner. In this case, the iron is supplied to the converter veryhot, 1550 deg. cent. or over. When iron is blown at this temperature, the carbon starts to burn before the silicon. At first the temperature is raised still more by the burning of the carbon, but as the amount of this latter decreases, the temperature falls off and finally goes below the critical point for this process. When this happens, the silicon begins to burn, and by the time this is burnt oilt, the metal is reheated again to the temperature where it is capable of burning carbon. The blowing should be however continued for a while even after the end of the second carbon-burning 'stage, so as to produce a very thorough distribution of oxides in the iron for the furnace stage.

Where manganese is used as deoxidizer, and the purpose .is toproduce a material of high magnetic permeability, the following variation of the process may be used. The

second stage is carried out in a furnacewith a neutral bottom, the .metal then being transferred,into another similar furnace (which need not be run at such a high temperature) with an acid bottom. The advantage of using in this case an acid bottom lies in the fact that silicon dioxide in the slag oxidizes the manganese in the metal, with the result that the silicon in the metal increases and manganese in the metal decreases, with simultaneous formation of MnO in the slag. Low manganese in electric steel has been found'to be an advantage. It isnot always advisable to use an acid bottom, however, which is the reason for using here 'two' electric furnaces: if the metal from the converter were delivered direct to an acid lined furnace and kept at the high temperaturerequired here, there would be an intensive ing is continued until and beyond the. end

of the period of carbon burning; second, the furnace stage wherein the metal is held under such conditions that it cannot be contaminated by carbon, and a temperature is maintained of the order of 1550 deg. cent. or

more.

. 2. A process as described in claim 1, wherein the metal is delivered to the furnace from the converter with the slag formed in the latter, and held in the furnace with this slag until the desired degree of carbon reduction has been attained, whereupon the converter slag is removed, and a deoxidizing slag is substituted.

3. A process as described in claim 1,

wherein after the desired degree of carbon reduction has been attained, manganese is one of the deoxidizing elements added to the bath, and wherein the carbon reduction is carried out in a furnace with a neutral lining, and the manganese deoxidation reaction substantially in a furnace with an acid linmg.

4. A process as described in claim 1, wherein the metal is delivered to the Bessemer converter at such a temperature that the carbon begins burn ahead of the sili- COIL Signed in New York, in the county and State -of New York, March 25, A. D. 1926.

LEON CAMMEN.