US1586591A - Manufacture of ferro-alloys, particularly ferrochromium alloys - Google Patents

Description

were -....-.---1;-126. 1 1,586,591 umrso STATES PATENT OFFICE.

RONALD WILD, OF HOLMESFIELD. ENGLAND, ASSIGNOR, BY MESNE ASSIGNMENTS, TO BUSTLESS IRON- CORPORATION OF AMERICA, A CORPORATION OF MARYLAND.

MANUFACTURE OF FERRO-ALLOYS, PARTICULARLY FERROCHROMIUM ALLOYS. No Drawing. Application filed February 5, 1923, Serial No. 617,172, and in Great Britain March 1, 1922.

The present invention is for improvements acterized by efiecting this reduction in presin and relating to the manufacture of ferroence of a substantial excess of the reducible alloys, and has particular reference to the a compound or compounds over the quantity manufacture of alloys of chromium and chemically equivalent to the reducing agent.

' 5 iron,-sucl1. for example, as ferro-chrome and I have found that, in 'contradistinction to metal of the type commonly known as stainoperating with substantially chemical equivless or unstainable iron and steel. alents of the reacting substances, the use in For convenience the invention will be desubstantial excess of a reducible metallic scribed exclusively in reference to the procompound or compounds has the effect of in- 10 duction of alloys of iron and chromium. hibiting the absorption of silicon by the re- In the manufacture of metal of the class duced metal and that the quantity of this known commercially as unstainable or stainclement thus absorbed may be so lowered as less iron and steel the alloy ferro-chrome is to give for all practical purposes an alloy employed. For the production of unstainoi' negligible silicon-content.

15 able steels this alloy may contain a substan- My experiments have shown that the adtial proportion of carbon, say 2 per cent or vantageous result associated with this inmore, but for making unstainable chromevention, namely, the production by silicon iron it is the practice to use the grade of reduction of a product containing but a low term-chrome known as carbon-free, i. e. proportion of absorbed silicon, is not to be 2 ferro-chrome of a carbon content not exceedobtained by the use of a slight'excess of ing 0.10 per cent. .As the carbon-free alloy the reducible body or of an excess in the as ordinarily obtainable is comparatively neighborhood of the quantity equivalent to costly the manufacture therefrom of stainthe reducer. My experiments have shown less iron is correspondingly expensive, and that the production of a low-silicon product 25 theuse of the latter is therefore practically by silicon reduction is not attainable by the 8 nrestricted to articles of high or relatively use of an excess of reducible oxide below high price. a minimum of 10 to 25 per cent, according to Ferro-chrome is usually prepared by re- Whether a low-chromium metal (such as unduction of chromite. By efi'ecting this re- Stainable metal, which may contain from 9 30 duction with an appropriate silicon reducer to 20 per cent of chromium) or a highit is possible to obtain directly a low carbon chromium metal (such as ferro-chrome, or carbon-free alloy, and silicon and silicides which may contain over 7 0 per cent of chrosuch asicalcium silicide have been proposed mium) is in course of preparat1on,'and acfor this purpose. The use of silicon-reduccordingas the temperature of the furnace 35 ers, however, results in the production of a is lower or higher, the production of a 'high u'ictal containing, according to circumchromium metal requiring, other conditions stances, a varying, but generally substantial, remaining the same, a greater excess than proportion of. silicon, and a process has been when a low-chromium metal is in question, described inwhich advantage is taken of this and likewise, other conditions remaining the 40 fact in order to produce a special alloy-steel same, a high temperature, with a more fluid containing a comparatively high minimum slag, demands the use. of av greater excess percentage of this'element. It is the purthan when the temperature is lower and the pose of the present invention to provide an slag less fluid. As will be understood, a improved and simple process for the manurule for allcases is not to be laid down,

facture of ferro-alloys as exemplified by and in a particular case the excess of re- 1170 'fcrro-chrome and stainless metal having a ducible bo y employed must be determined low content both in silicon and carbon. by a prelim nary run according to theoper- According to the present invention, the ative conditions to be employed in the manumanufacture of low-carbon or carbon-tree facture. By a substantial excess as referro-alloys, such, for example, as ferroferred to in this specification and in the chrome or stainless metal, by a process of the claims is meant an excess beyond the "limit type wherein a reducible compound or comof an equivalent quantity and not below pounds (such as the oxide or oxides) of a the minimum percentage above ment oned. metal or metals of the alloy is or are reduced To ensure satisfactory and regular results,

55 by exothermic reaction with silicon, is charunder operative conditions similar to those indicated in the specification, it is, however, recommended'to work with an excess well above the minimum stated, as I have shown in the specific examples hereinafter set forth.

he silicon-reducer may be ferro-silicon, preferably of high silicon-content, for instance -90 r cent.

The reduction may be carried out in presonce of a reagent having a special aflinity for oxidized silicon under furnace conditions, such, for example, as limestone or lime which combine with the silica and form a slag therewith.

Stainless chrome-iron or chrome-steel may be directly produced by effecting the reduction of a suitable oxidized com .und of chromium, such as chromite, Within a bath of molten iron or steel free from carbon, or of such content therein as shall provide for the desired proportion of carbon in the final alloy metal.

I prefer to utilize this direct process when manufacturin unstainable metal, because I have found that by effecting the reduction within a bath of steel in rcsence of a. substantial excess of the re ucible oxide, the absorption of silicon b the reduced metal appears to be still furt ier inhibited, and it is possible directly to obtain a low-silicon product with a considerably lower percentexcess. Reduction of'ore within a bath 0 steel has been previously proposed, but

according to my invention this reduction is carried out in a particular way, namely, in

presence of a substantial excess of the reucible oxide for the purpose and with the results aforesaid.

The reducing bath may consist essentially of a fused ferro-silicon of comparatively low silicon content, such a bath be' venicntly provided by a molten charge of iron or of mild steel containing the desired proportion of content, for instance, one of 80 to per cent. The carbon content of the form-silicon should be known so that allowance may be made therefor in preparing the bath accordingto the nature of For the direct production Proceeding in this way, fusing with a part of the 4 the bath is brought into condition for effective subsequent reduction and it has been found that by operating time aproduct of equivanamely, by first a ferro-silicon of high-silicon chromium although the total introduced in This second addireducible charge,

low content in silicon may be obtained the .subseq agent, with, of losses.

(6) The chromite and reducing agent are heated together to a temperature approaching that of reaction, and the requisite quantity of molten iron or steel is then added to the preheated mixture, heat being subsequently applied as required to ensure complction of the reaction or the production of a homogeneous melt.

(c) A fcrro-cln'ome is first prepared by reduction of chromite with a silicon-reclucer, the addition then made to the fused alloy of molten iron or steel, preferably containing dissolved oxygen or oxides (for example, recently blou-"n Bessemer metal), in requisite quantity to produce an alloy of the metallic composition of stainless metal and of low average content in both silicon and carbon through dilution, or dilution and oxidation, of the silicon present in the initial term-chrome. i

The excess of the chromite or the like. employed for the reduction necessarily depends upon circumstances, such as the nature of the reducible compound or the pnrticular composition of the bath, but a simple preliminary experiment suffices to determine the most advantageous proportions of the reacting substances in a given case. Ex-

amples of an appropriate excess both in the production of ferr0-chrome, and in the direct preparation of stainless chronic-iron. are given hereafter, but those acquainted with the art will readily appreciate that the excess specified in these examples can be only illustrative for the reason that with a chromite of a different composition, or with it differently constituted bath, the excess might be either greater or less than the figures given for obtaining a like result.

It will be appreciated that the content of the reducing agent in the bath determines the percentage in the final alloy of the charge added is not brought to the metallic According to circumstances, such as the furnace conditions, the yield of reduced metal varies, and as a rule will be found y to be considerably less than the quantity of the metallic element theoretically obtainable 150 from the reducible compound thereof, i. e. a process loss occurs for which allowance must be made, as will be understood by those skilled in the art. The operative details in any given case may, however, be readily determined by a simple preliminary trial.

Prior to the addition of the ferro-silicon or the like, an assay may be made of thc cai'bon content of the bath so that. by making allowance for the addition of the rcduc- 130 An electric furnace,

a smelting operation and may in any available furnace provided that the latter is capable of maintaining complete fusion of the materials throughout the op eration of the process and of permitting the finished product to beipoured or tapped into the moulds. External heating may be applied throughout or at any stage of the operations in order to maintain the requisite high temperature throughout the reduction. for instance, of the Heroult or Snyder type, may conveniently be employed.

At any convenient stage of the process, the material may be submitted to an oxidizing blow, and in such case it is preferred to ciicct this operation according to our concurrent specification, Serial No. 617,171, that is to say, in presence of an element, (for example, manganese) more readily oxidizable than chromium at the temperature of the blowing o eration. Said elementmay be introduced during the process of reduction as is described in concurrent specification.

The following examples will serve to indicate how the invention may be carried into effect, it being understood that these examples are given for illustrative purposes and not by way of limitation.

E mample I A 5 cwt. bath of a ferro-silicon alloy'was prepared by the addition to a bath of molten low-carbon steel of a high-silicon ferro-silicon (83 per cent silicon) of low carbon-content in such quantity as to give a melt containing approximately 9. per cent of silicon. A portion of the charge of reagent, namely, a mixture of lime and fluorspar, was added to the bath, and there were then introduced, in successive charges, 440 lbs. of chrome-iron ore, assaying 52.8 per cent of chromium sesquioxide, remainder of the charge of slag-forming reagent. as required to take up the oxidized silicon, to increase the fluidity of the slag and to assist-in obtaining a good yield of reduced metal. The total charge of the slagformiug mixture amounted to 40 lbs. of lime and 2.4 lbs. of fluorspar. On completion of the reduction, a small proportion of a deoxidizer such as manganese, ferrrnnangancse, or aluniiniun'i, was added according to, known practice in order to ensure a soun be carried out w the slag-forming Cr O and the p sion, and on -a-nalysis was ing agent, the carbon content may be known metal capable of casting into moulds of any not to be in excess of the quantity of this desired shape. There was obtained a stainelement desired in the finished metal. less alloy iron assaying as follows it is also advantageous, more particularly when nmnufacturing stainless iron, to fuse Chromium 12.95 in the bath, prior to addition of the silicon Carbon 0.09 reducer, a small proportion of a de-oxidiz- Silicon 0.36 ing reagent, such as ferro-man anese, silico- Manganese 0.20 manganese, or a little ferro-siTicon itself. Y Sulphur 0.032 The recess of this invention is primarily Phosphorus, 0.046

was 4 cwt. 3 qrs. 9 lbs.

It will be observed that the content of the ore in chromium sesquioxide, namely 232 lbs, was in excess of that reducible by the quantity of ferro-silicon employed, which was theoretically equivalent to about 180 lbs. of the oxide.

In like manner, ferro-alloys, such as those. commonly known as stainless steel, may prepared, the necessary higher proportion of carbon being supplied at an convenient stage of the process by the ad ition of suitable carbon-containing materials as are known in the art, for example, either by we of the metals employed for the initia hat or subsequently, say by the addition of the. requisite quantity of pig-iron for the furnace charge, or by coal or charcoal added to the metal in the ladle. l

Example II.

the moulds There were obtained 0 cwt.

of stainless-iron having the compos1t1on:---- i Per cent. Chromium 12.20 Carbon 0.03 Silicon 0.33 Man anese 0.30 Snip rm and phosphorus 0.04

E example III.

A. bath was made up of the following composition :--mild steel turnings 3 cwt., scrap lbs.,'l1me iron 1 cwt., chrome iron jore 100 40 lbs. Y

The mixture was 0.06 per cent carbonand 0.17 per cent iof chromium. There were then added v1 qr. 26 lbs. of a ferric-silicon,

j l' ghtto complete fufound to conta n assaying 83.3 per.- d cent of silicon and 0.28 per cent-of carbon.

kOllwas finished there were added 3 lbs. of terro manganese to bring the metal to the usual specification, and during tapping, the addition was made of 2 ozs. of aluminium in accordance with the known practice for pro ducing sound ingots.

The tapped product weighed 4 cut. 2 qrs. 20 lbs. and assayed as follows:-

Per cent. Chromium 12.54 Manganese 0.44 Silicon 0.44 Carbon 0.09 Sulphur 0.039 Phosphorus l 0.011 Theoretically, for the quantity of ferro- SlhCOn added and to give a silicon-remainder in accordance with the percentage composition indicated, about 155 lbs. of chromium oxide were necessary, whereas the total char-"e of chrome-iron ore corresponded to 211 lbs. of this oxide. It will be seen, however, that the quantity of ore added subsequently to the addition corresponding to 158 lbs. of chromium oxide, that is to say, the extra quantity was approximately that chemically equivalent to the reducing agent.

01 the total 400 lbs. of chrome-iron ore, equivalent to 144 lbs. of metallic chr0- mium 65.7 lbs. of metallic chromium were produced and absorbed by the bath, of metal in this instance being approximately 45.4 per cent of that contained in the whole of the chrome-iron ore used in the charge, and approximately 60 1' cent of that contained in the ore adderl subsequently to the reducing agent.

Example I V.

A bath was made up of the following composition:

Cwt. Qrs. Lbs. Mild steel tunings--- 3 l 0 File steel scrap l 1 0 Lime 0 2 O This mixture was brought to complete fusion and, on assay, was found to contain 0.07 per cent of carbon. There were added 1 qr. 24 lbs. of the same ferro-silicon as before, and then, in successive charges, 3 cwt. 2 qrs. 8 lbs. of chrome-iron ore, assayin 52.8 per cent chromium scsquioxide, the slag beingd tapped'ofl from time to time as reuire q The addition was then made of 1 qr. 8 lbs. of Swedish white iron and 4 lbs. of ferromanganese in order to bring the metal to the required specification, and, during tapping,

of the ferro-silicon 1 2 ozs. of metallic aluminium were added in accordance with known practice.

The tapped product weighed 4 cwt. 3 qrs.

9 lbs. and assayed as follows Per cent.

Chromium 9.86 anganese 0. 18 Silicon 0.14: Carbon 0.16 Sulphur 0.010 Phosphorus 0.009

It will be observed that the chrome-iron ore added to the reducing'bath was in considerable excess over the equivalent of the ferro-silico Theoretically, for the quantity of fcrro-silicon added and to give a silicon-remainder in accordance with the percentage composition indicated, about 153 lbs. of chromium oxide were necessary, whereas the total charge of the chrome-iron ore corresponded to 211 lbs. of this oxide,

lbs. of metallic chromium were produced and absorbed by the bath, a figure corresponding to a yield of approximately 37 per cent.

The stainless metal so produced possessed a high degree the physical attributes nec-' essary to enable it to be deformed or shaped y forging, rolling, drop-stamping, cold drawing or pressing, and like processes commonly employed in the manufacture of ob- 526138 for which metal of this type is suita' le.

Emamplc V.

An initial ferro-chrome was prepared by reducing a crushed and washed chromite with the calculated quantity of ferro-silicon whereby there was obtained an alloy containing 0.20 per cent of carbon and 12 per cent of silicon. To this alloy was added term-manganese, containing per cent of manganese and 7 per cent of carbon, in such Percent. Chromium 58. 50 anganese 8.00 Silicon 10.90 Carbon 0.86

gduced having the composition Per cent. Chromium 11.70 anganese 1. 60 ilicon 2. 18 Carbon 0. 18

The contents of the converter were then Chromium 12.00 Manganese 0.60 Silicon..." 0.18

Carbon Emample VI.

A charge of 56 lbs. of ferro-silicon, con taining 83 per cent of silicon, was fused in an electric furnace of the Snyder type and therewere added to the fused mass 500 lbs. of chrome-iron ore, assaying 52.8 per cent of chromium sesquioxide, Or O together with lbs. of limestone and 24-lbs. of fluorspar, and the whole contents of the furnace were brought to complete fusion. On tapping, 145 lbs. of ferro-chrome were obtained assaying Per cent. Chromium 60.70 Oarbon 0.12 Silicon 1.90

The content in chromium sesquioxide of the chrome-iron ore, namely 26 lbs. of-the oxide, was in considerable excess of that reducible by the ferro-silicon which was theoretically equivalent to about 167 lbs. of the chromium oxide.

While the invention has been described with special reference to the manufacture of iron-chromium alloys of the type of ferrochrome and stainless iron and steel, it is to be understood that I do not limit myself to this particular application and that the invention may be utilized for the production of other alloys in the manufacture of which difliculties of like nature to those presented by ferro-chrome and stainless metal are encountered. Other special metals may be present in the alloy in addition to the main special metallic component. For example, the stainless chrome metal may contain a proportion of other special metals such as nickel, tungsten, stance, up to 2 to 3 per cent, without detriment to the stainless properties.

The. excess of the reducible charge required for lowering the degrw of silicon absorption may be furnished by a single metallic compound or by different metallic compounds, and such excess may .be introduced at any convenient stage of the reduction process. For example, the process may be commenced by. heating together chromite a silicon reducer in chemically equivalent uantities and the required excess referre to provided by addition to the reaction mixture of a reducible compound of another metal (for instance, ferrous or ferric oxide) whose presence in the final alloy will either be undetrimental, or is desired to prothe manufacture of articles such as or the like, for invide a special metallic component. Or the chromite, or other reducible compound of a special metal, may be used in part excess and the' necessary balance for the total excess supplied by another appropriate reducible metallic compound.

Operating according to this invention it is possible readily and steels of an average silicon content of the order of 0.14 per cent to while working under the least advantageous conditions metals of this type have been ob tained containing about 1.0 per cent of silicon as the maximum content in this element. prepared by the process of this invention to be particularly free from the fault of segregation, this property manifesting itself in the divers finishing operations applied in spoons and the like, and my metal has shown itself of improved quality over like metal as usually produced by a purely melting operation. For cutlery and like uses, the steel made according to the pres ent invention may be hardened, tempered and polished in any desired manner as will be understood by those versed in the art.

As iron and steel of low and known carbon content are readily and cheaply obtainable, it will be seen that the invention provides a simple process for the direct production of special alloy to obtain stainless irons- 0.40 per cent I have found the unstainable metal knives,

steels and irons, as

well as for the manufacture of ferrochrome, in an expeditious and economical manner.

I claim:

1.-The process for the manufacture of ferro-chromium alloys which comprises bringing about an exothermic reaction between a silicon-reducer and a reducible metallic charge containing chromium, the amount of the total of said reducible metallic charge being ina substantial excess of the quantity chemically equivalent to the reducing agent.

'2. The process for the manufacture of ferro-chromium alloys which comprises bringing about an exothermic reaction between a silicon-reducer and a reducible metallic charge containing chromium, the amount of the tallic charge being in a substantial excess of the quantity chemically uivalent to the reducing agent, and subjecting the molten metallicqproduct to an oxidizing blow.

3. he process for the manufacture of ferro-chromium alloyswhich com rises reducing a ucible compound of c romium by exothermic reaction with a si1 e0nreducer in presence of iron and of.a substantial excess of said reducible chromium comound over the total of said reducible me- 4. The process for the manufacture of ferro-chromium alloys which comprises reducing chromite by exothermic reaction with a silicon-reducer in presence of excess of chromite over the quantity chemically equiv alent to the reducing agent.

5. The process for the manufacture of ferro-chromium alloys which comprises reducing chromite by exothermic reaction with ferro-silicon in presence of a substantial excess of chromite over the quantity chemically equivalent to the ferro-silicon.

6. The process for the manufacture of unstainable metal which comprises reducing a reducible compound of chromium by 'exothermic reaction with a silicon-reducer Within a molten ferrous bath of a content in carbon appropriate to the desired final metal and in presence of a substantial excess of said reducible chrominum compound over the quantity chemically equivalent to the reducing agent. a

7. The process for the manufacture of unstainable metal which comprises reducing a reducible compound of chromium by exothermic reaction with a silicon-reducer within a batch of low carbon steel in presence of a substantial excess of said reducible chr0- miiun compound over the quantity chemically equivalent to the reducing agent.

he process for the manufacture of unstainable metal which comprises the addition to a molten low silicon ferro-silicon of a reducible compound of chromium in a substantial excess of the quantity chemically equivalent to the reducing agent.

9. The process for the manufacture of unstainable metal which comprises the addition to a molten low silicon ferro-silicon of chromite in a substantial excess of the quantity chemically equivalent to the reducing a cut.

10. The process for the manufacture 0 unstainable metal which comprises fusing ferro-silicon with low carbon steel, and then making the addition to the resulting molten lcw silicon ferro-silicon of chromite in a substantial excess of the quantity chemically equivalent to the ferro-silicon.

11. The process for the manufacture of unstainable metal which comprises heating ferro-silicon with chromite in a substantial excess of the quantity chemically equivalent to the ferro-silicon to a temperature approaching that of reaction and incorporating in suitable proportion with the so heated mixture a molten ferrous bath of a carbon content appropriate to the desired final metal.

12. The process for the manufacture of unstainable metal which comprises reducing chromite by exothermic reaction with a silicon reducer within a molten ferrous bath with a content in carbon appropriate to the desired final metal and in presence of a substantial excess of chromite over the quantity chemically equivalent to the reducing agent.

13. The process for the manufacture of unstainahle metal which comprises reducing chromite by exothermic reaction with a silicon reducer within a bath of low-carbon steel in presence of a substantial excess of chromite over the quantity chemically equivalent to the reducing agent.

In testimony whereof I have signed my name to this specification.

"RONALD TVILD.

CERTIFICATE OF CORRECTION.

Patent No. 1,586,591.

Granted June 1, 1926, m

RONALD WILD.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page after the word "of" line 4, claim 4,

first occurrence insert the article and word "a substantial";

M. J. Moore, Acting Commissioner of Patents.