US2015690A - Manufacture of iron alloys - Google Patents

Description

Patented Qct l, 1935 MANUFACTURE OF IRONALLOYS Ren. Perrin, Paris, France, assignor to Socit dElectrochimie dElectrometallurgie et des Acieries Electriques dUgine, Paris, France, a

corporation of France i Q 1N0 Drawing. Application February 23, 1933,

- Serial No. 658,279. In France August 29, 1932 9 Claims. (01. 75-27) f This invention relates to improvements in the manufacture ofiron alloys of very low carbon content.

The presentpapplication is a continuation-inpart of my application, Serial No. 584,584, filed January 2, .1932, which describes the treatment of metals with slags by violently intermixing the metal, while'in a fluid molten state, witha fluid molten slag. v

The production ofiron-alloys and in particular alloyswith chromium and manganese, by the reducing action of carbon on the ore does not permit, even'ifthe'reducingagent is insufiicient in quantity, of obtaining verylow carbon contents. During the first phase of the refining of the metal with respect toits' carbon content by contact with the slag,'-which jat that stage of the operationis highly joxid-ized' because it is as yet insufficiently reduced,;-a considerable oxidation of the useful element such as, chromium or manganese for example takes; place and a corresponding reduction i'n =the;quality of; the alloy which, owing to this fact; ceases;to" ':om1 )ly with the required commerci'al'standards;

Reduction by metallic reducing agents such as silicon, which,maybe-a11Qyed with the basis element'of theiron alloy of; lowcarbon content to be produced, and in. all cases devoid of carbon or nearly so, permits 'of the-' working up of these low carbon alloys without introduction of carbon.

, It is necessaryhowever, inrthe course of this operation, to. eliminatealmost the whole of the metallic reducing a nt which tends to remain alloyed in part inth'e iron alloy to be produced, This operation'which isgenerally carried out by oxidation of the reducing agent at the expense of the oxygen of a slag charged with the oxides of the basis elem'ents of the iron alloy which it is desired to produce, presents great difficulties.

The further the operation of eliminating the metallic reducingagent- (the silicon for example) proceeds, the more the reducible oxides of the ore fused'in thepresence ofthe reducing agent are diluted byrthe oxides to which thismetallic reducing agent has given rise and by the bases intended to neutralize it so as to disturb the chemical equilibrium which tends to become established. The reaction becomes sluggish, and the exchanges between the bath of molten metal and the slag take place more and more slowly.

Slagging out becomes necessary in order to recharge a fresh quantity of ore rich in oxide and to fuse it in order to carry on the operation of elimination of the metallic reducing agent. slagging out operations followed by a fresh charge These clog the metallic bath which is the more re fractory'the nearer it comes to the refining desired.

Now it is known that the fusion of a metallic residuum in the electric furnace is difficult owing. 6

to the excessive conductivity of the metal. The consumption of kilowatts'increases greatly owing to this fact and all the items of the net cost involved in such additional consumption of energy are proportionately increased. Moreover 10 the contact of the electrode or electrodes with the products to be. fused is prolonged thus also producing a regular increase in the amount of carbon contained in proportion to the elimination of the metallic reducing agent by the reducible l5 oxides of the molten slag; Finally the prolonged heat at a very high temperature has a disastrous effect on the life of the linings and crowns of the furnaces.

To sum up: it may be observed that in the course of the operation of eliminating the metallic reducing agent, the fusion is rapid at the begin ning, facilitated as it is on the one hand by the high content of oxides in the ore to be fused (which disturbs the equilibrium in favour of a 25 rapid oxidation of the metallic reducing agent employed, accompanied by an evolution of heat brought-about by the reaction) and on the other hand by the fusible oxidized compounds formed in the course of the reaction. The reaction then' becomes very sluggish and it becomes necessary to slag out in order to breakup the equilibrium between the metal and the slag. The fusion of the'second charge and of the succeeding charges if there are any, thenproceeds very slowly because the .bath has lost much of its fluidity by the renewing of the slag and by the reduction of .the amount of the reducing metal (silicon for example) to about 5% or less. l I

If it is desired to obtain alloys containing a very small quantity of the reducing agent (0.50 or even O.l0%) ;sev,eral successive .slaggings' out will be necessary but they do not yield uniform results.

By means of the present invention these disadvantages may be avoided and in accordance therewith are obtained rapidly and with regularity iron alloys (such as ferrochromium and ferromanganese for example) with a. very, low carbon content and with the elimination as completely as possible of the metallic reducing agent.

This invention consists substantially in bring ing about in a continuous, rapid andintimate manner by the aid of violent intermixing, the contact of the molten metal with the oxidizing slag, the time taken to eliminate the reducing 55 tact.

In all cases, whether the slag passes through the metal or the metal is poured on to the slag, the operation lasts only about a minute and there is no need at all to supply any external heat.

The oxidizing slag which is to act on the metal may be either previously melted in a suitable furnace, and be used in minimum quantity and may be of a composition strictly determined in order that the equilibrium to be attained in the course of the violent intermixing shall correspond, in each case, to the practically total elimination of the metallic reducing agent associated with the molten alloy to be worked, or it may be run from the furnace itself where the alloy has been produced, into a suitable ladle, and thereupon the metal remaining in the furnace may be poured rapidly and in a thick jet upon the slag so as to produce a violent and turbulent intermixing of the slag and metal, as in the case of the second example described below.

It has been found in the case'of iron alloys of 0 low carbon content obtained according to this invention that:

(1) The elimination of the metallic reducing agent during the very short period of time that the operation lasts, can be pushed as far as is desired, that is to say until the residual content is comprised between 0.20 and 0.10 which permits of responding to all the requirements of steel manufacturers.

(2) By working always under similar conditions (composition and quantity of the metal and of the slag in the presence thereof and also the mode of bringing them violently into intimate which this violent. intermixing of the metal and.

the slag takes place has no influence on the desired reaction, the duration of the operation being too short.

Thetem-perature of the metal is without any great influence. It is sufiloient that the metal be quite fluid at the commencement of the operation, the heat evolved in this latter permitting of retaining its fluidity unafiected up to the end.

If it be attempted to obtain ferro chromium alloys for example by using silicon as the metallic reducing agent, it is possible by means of the present process either to obtain directly in a single operation and by the action of an oxidizing slag melted down separately, a ferrochromium alloy complying with current standards, that is 0.50 to 1% of Si, or to displace the state of equilibrium in the direction of a removal of the silicon to a greater extent by violently intermixing the slag and the metal of a charge composed of a mixture of silico-chromium, ore

desiliconized (Si comprised between 0.50 and 1%) by the first violent intermixing operation is again violently intermixed with a slag which has been melted down separately and is highly oxidized. The slag which has thus acted on Fe-Cr with 1% of silicon as the maximum is'used again for a first removal of silicon from a new heat of silicochromium by violent intermixing. Said slag is in the meanwhile kept liquid in the furnace for the preparation of oxidizing slag for desiliconizing.

The quantity of slag to be used will be merely a function of the amount of silicon contained in the ferro-silicon-chromium alloy from which the silicon is to be removed the amount of silicon contained therein being related to the amount of carbon aimed at for the ferro-chromium alloy which is to be produced.

The violent intermixing of the mass of molten metal and oxidizing slag may be effected mechanically by a gas for example. This intermixing must be violent so as to limit the duration thereof.

It is possible also to carry it out in a simple and economical manner by using a casting ladle which first receives the slag, either melted down separately, or run from the silico chromium alloy furnace or the like. The metal is then violently run in a thick jet on to the slag preferably from a considerable height and the slag finally comes to the surface which multiplies the surfaces of contact between the metal and the slag. It is then found that despite the very short duration of the operation the elimination of the metallic reducing agent (silicon for example) ,is practically terminated as soon as the slag has collected by decantation above the metal. The uniformity of the results obtained is perfect when attention is paid to the conditions of the respective weights of the metal and slag and the composition thereof. With ladles of the usual dimensions the result is easily obtained.

Any means other than the ladle may also be used for carrying out the violent intermixing operation. The ladle is however the most advantageous because it affords the simplest means of carrying out the operation in order to obtain a better result. There is every advantage in burning the silicon for example solely by reducing, if .necessary, the associated oxides of the basis elements ofthe alloy rather than favouring the elimination thereof by having recourse to the oxygen of the air.

I give below by way of examples which are not limitative some operations carried out in accordance with the present invention.

First example-The removal of the silicon from 600'kg. of metal containing Silicon 48.35% Iron 16.22% Chromium 35.20% Carbon 0.082%

was eifected by means of 3200 kgs. of ore (forming an oxidizing slag) melted down in a furnace constructed for this purpose, and of the following composition This oxidizing slag and the metal were run simultaneously and with violence into a ladle which, as soon as it had received the constituents of the reaction, was taken to the foundry above the ingot moulds.

About four minutes elapsed between the commencement of the run into the ladle and the commencement of the casting of the metal into the ingot moulds.

The metal of the first ingot mould had the following composition:

Silicon 0.89% Carbon 0.068%

980 kgs. of'metal of a marketable composition were obtained in a single operation, and a very short one compared withthat effected in a single furnace with the slag acting on the surface of the molten metal bath from which the silicon was to be removed.

Second example-300 kg. of silico-chromium of the following composition Chromium 37.20% Iron 12.30% Silicon 49.53%. Carbon 0.10%

were charged into a furnace together with 800 kg. of chromite mixed with 720 kg. of lime.

In this furnace a metal of the following composition was obtainedi Cr 69.80% Fe 29.05% Si 0.51% o 0.08%

The slagwas run into a ladle and when the slag had been run out of the furnace the metal remaining in the furnace was run rapidly and in a thick jet into the ladle. The metal mixed intimately with the slag with a vigorous and turbulent intermixing action.

The duration of the operation was one minute and the composition of the metal at the end-of the operation was:

Cr 70.50% c-.- -r 0.07% Si 0.08% Fe -r A 28.90%

In a few seconds therefore the removal of the silicon had been pushed very much further, owing to the intimate contact produced throughoutbetween the metal from which the silicon was to be removed andthe still oxidized slag, which was in contact in the furnace before evacuation into the ladle. This result could only have been obtained formerly with a complementary slagging out and a refining of about an hour without any certitude of obtaining the removal of the silicon to such a degree.

What I claim is: v v e 1. A process for manufacturing from an. iron alloy containing a substantial amount of a reducing agent and having a very low carbon content, an alloy practically free of reducing agent, which consists in violently intermixing said alloy in a molten condition with a very fluid previously molten slag capable of oxidizing the reducing agent present in the alloy, the violence being such as to form an intimate mixture in a short period of time of the slag and the alloy, and separating the slag from the alloy freed of reducing agent.

2. A process for manufacturing from an iron alloy containing a substantial amount of silicon and very little carbon, an alloy practically free of silicon, which consists in violently intermixing alloy in a molten state, which consists in violently intermixing with the said iron alloy a very fluid previously molten oxidizing slag, the violence being such that in the short period of time required to oxidize the said reducing agent an intimate mixture of slag and alloy is effected, and separating the slag containing the oxidized reducing agent from'the' iron alloy.

4. A process for collecting in a slag in an oxidized condition a high percentage of a reducing agent present in an iron alloy, which consists in violently intermixing with said iron alloy in a molten condition a slag capable of oxidizing the said reducing agent and of dissolving the reducing agent oxide so formed, and separating the ironalloy.

5. A-process for manufacturing an iron alloy practically freed of reducing agent and having a very low content of carbon which consists in imparting to a. mass of a molten iron alloy-containing a very low percentage of carbon and a high percentage of a reducing agent, a certain amount of kinetic energy and utilizing said energy for forcibly bringing together said iron alloy and a mass of very fluid molten oxidizing slag so as to atomize and violently intermix said slag with the iron alloyfor such a period of time as to oxidize nearly instantaneously substantially the whole of the said reducing agent, and then separating the slag from the metal. v

6. A process for manufacturing an iron alloy very poor in reducing agent and having a very' low content of carbon, which consists in causing a mass of very fluid previously molten oxidizing slag to be violently intermixed in a state of fine division and for a short period of time ,with a mass of molten iron alloy containing a reducing agent in substantial proportion, said finely divided slagito rise in and through the said iron alloy and to collect on the surface thereof.

7. A process for manufacturing an iron alloy very poor in reducing agent and having a very low content of carbon, which consists in treating in a furnace a raw iron alloy containing verylittle carbon and a high percentage of reducing agent by means of a very fluid oxidizing slag for such a period of time as to lower sensibly the content of reducing agent in the iron alloy and then violently intermixing the said slag and thesaid iron alloy for such a short period of time and with such a violence as to lower to a very small percentage the content of reducing agent of the iron alloy, and then separating the slag from the iron alloy.

8. A process for manufacturing an iron alloy having a very small content of reducing agent when starting from a massof raw iron alloy having a high content of reducing agent, which consists in placing at the bottom of a ladle a mass of previously molten very fluid ,oxidizing slag and rapidly pouring the said mass of raw iron alloy in thick jet onto the said mass of slag with such violence as to cause a rapid intermixing to take place between the mass of alloy and the mass of and allowing the tooxidize and to remove from the 'iron alloy into the slag the greater part of the reducing agent, and then separating the slag from the iron alloy.

9. A process for manufacturing an iron alloy having a very low content of reducing agent by starting from a mass of raw iron alloy having a high content of reducing agent, which consists in placing at the bottom of a. ladle a mass of a previously molten very fluid oxidizing slag and pouring the said mass of raw iron alloy in thick jet and from a considerable height onto the said mass of slag, and then separating the slag from the iron alloy.

RENE PERRIN.