US2001015A - Production of iron-chromium alloys - Google Patents

Description

Patented May 14, 1935 UNITED STATES PATE T- OFFICE A PRODUCTION liglggu-cimomon Alexander L. Feild, Baltimore. Ma, uslguor, aw

mesne assignments, to Rustler: liron llorporatl'on of America, Baltimore, Md, a corporation oi Maryland No Drawing,

This invention relates to the production of ferrous alloys, especially iron-chromium alloys and more particularly to iron I One of the obiects of my invention. is the production in a simple, direct and highly e m- ,cient manner of successive-heats oi low-carbon iron-chromium alloys to difierent specifications oi chromium and carbon employing available the production of rustless iron of the lower chromium grades (6% to 12%) employing a. maximum of a variety of inexpensive raw materials at minimum expense depending upon the availability of these raw materials and fluctuations in their current markt prices.

Other objects in part will be obvious and in "part pointed out hereinafter.

The invention accordingly consists in the, com-- bination of elements, mixture of materials, composition of ingredientsand in the several steps and the relation of each .of the same to one or more 01 the others as described herein and the scope of the application of which is indicated in the following claims.

As conducive to a clearer understanding oi,

certain features of my invention it may be noted at this point that in the mining, oil relining and chemical industries and in structural and building trades, an inexpensive iron having corrosion-resisting and heat-resisting properties is coming into popular usage, as in mine ventilating equipment, furnace tubing, condenser tubing, oil transfer lines, heat exchangers,

plates, fluid valves, bolts, studs, flanges and like articles or parts, members and sections of equipment. The widespread use of rustless iron of this anaylsis is limited, however," by the ex-j pense of this metal as compared with heretofore known and/or used irons and steels wlthor without alloying metals.

Likewise, it may be further noted that-in the production of rustless iron in accordance with heretofore known and/caused methods, wherein the inexpensive chromium-bearing ingredients,-

rustless iron scrap, high carbon ierrochroma.

the production or rustless Application June 2d,, 19%, denial No @532 and chrome ore are employed, the large volumes of slag encountered greatly limit the amount of clean, high-grade metal which may be reliably produced in a single charging and melting operation. g

Accordingly, one of the objects of my invention is the production oi clean, high-grade ironchromiurn alloys of low-carbon contents, and

especially the rustless irons of low-chromium grades, in quantities greatly in excess of the l0 quantities produced in accordance with present 'methods, utilizing inexpensive and available raw materials including one or more of a number of chromium-bearing materials depending upon the comparative'low costs of these materials'and the cost at recovering their available chromium contents, employing known and/or used furnacing and operating equipment and maintaining satisfactory furnace operating conditions.

Referring now more particularly to the prac- 20 tice oi my invention, a. suitable furnace, such as a six-ton three-phase Heroult electric arc furnace employing carbon or graphite electrodes I and rated cycles, 2500 kva. at 126) to 180 volts and having a chromite brick lining car- 25 ried up to a height above the slag-line with the usual silica brick top side-walls and root, is prepared tor the reception of a charge of raw ma-. terials in any suitable manner. Conveniently, the furnace is thoroughly heated either by means of an oil torch temporarily placed within the i'urnace for this purpose or by applying power to the furnace and establishing electric arcs fromthe furnace electrodes to odd pieces of electrode butts placed on the furnace bottom.

After the furnace has been adequately preheated and the preheating means withdrawn, the initial charge of ingredients comprisir'igthe raw materials for a double heat of metal of desired analyses of chromium and carbon is g charged into the furnace. In the practice of my invention iron scrap, either low-carbon steel scrap, commonly known as base scrap, or iron-chromium scrap, such as readily available rustless iron orsteel scrap metal, and preferably both low-carbon steel scrap and rustless iron or steel scrap in suitable proportlons, are charged onto the bottom of the furnace. While the relative proportions of base scrap and rustless iron scrap, which are initially charged into the furnace may vary, between wide limits, it is ordinarily desirable to employ as much rustless iron or steel scrap as is available at a-low price. 'Ihisscrap, in the form of ingot butts, crop ends, scrap sheet,

punchings, clippings and the like, usually available'in and around the melt shop and various customer plants, amounts to from 25% to of the metal tapped, as more particularly pointed out in the copending application of William Bell Arness, Serial Number 719,810, filed April ,9, 1934 and entitled Production of rustless iron, and affords an inexpensive source of iron and chromium. Preferably, then. rustless iron or steel scrap in an amount representing 25% to 70% of the total chromium content of the double heat of metal to be tapp d. is charged into the i e, base scrap being added as necessary to complete the charge. Where, however, 'the market price of iron and steel scrap becomes excessive or where an acute shortage" of such scrap is encountered, there'is only available in and around the melt shop rustless iron or steel scrap amountinwto about 25% of the metal tapped. Under these conditions base scrapforms the principal part of the scrap charged. Of course, it will be understood that, where desired, rustless iron or steel scrap may be entirely omitted from the charge of ingredients.

Along with the initial charge of iron scrap (base scrap and/or rustless'ironor steel scrap).

there is preferably charged anadditional chromium-containing ingredient, such as the inexpensive chrome ore or the inexpensive high carbon ferrochrome. Since chrome ore is somewhat less expensivethan high carbon ferrochrome as muchofthismaterialisusedasmaybecon veniently. handled in the human. This is a figure which depends upon the tonnage'of the heat of metal being produced, the -dimensions of the furnace, the furnace operating voltage and the like, and is ordinarily determined empirically.

where the shortage of rustless iron scrap is rather acute or where rustless iron. or steel scrap. may be hadonly at apremium, the reduction in the amount of chromium introduced by the inexpensive rustless iron scrap (necessarily employed in a reduced amount) is preferably compensated for by chrome ore, in such quantities as is consistent. with good furnace operating conditions, andthe inexpensive chromium-containing ingredient, high carbon ferrochrcme. tion of chromium is preferably made in the form of chrome ore, because of the somewhat favorable price margin of this ingredient over high carbon i'err'ochrome, it will be understood that as a matter of convenience in furnacing the charge of ingredients the amount of chrome ore ordinarily used may bejpartially or com-. pletely replaced by an equivalent amount of high carbon ferrochrome. Excellent furnace operating conditions are obtained, however, where a balanced charge of both base scrap and rustless iron or steel scrap and chrome ore and high carbon ferrochrome is melted down in the furnace.

An oxide of iron, preferably roll scaled: added along with the ingredient charged into the furnace to oxidize carbon from the charge of ingredients as well as to remove and/or exclude carbon coming from the furnace electrodes. The amount of iron oxide charged into the furnace along with the iron scrap and chromiumcontaining ingredients is largely determined by the tendency of the ingredients topick up carbon from the furnace electrodes during the meltdown stage of the process, as more particularly ture normally present.

While this supplementary addipointed out hereinafter, and to a lesser extent upon the amount'of carbon directly introduced with the iron scrap and high carbon ferrochrome. The particular amount of iron oxide introduced with the charge in orderto achieve tapped metal of a low-carbon content is ordinarily determined empirically.

To assure the production of sound metal free from blowholes, gas-pockets, pits and the like, the large quantities of chrome ore utilized are preferably thoroughly dried at a high temperature prior to charging into the furnace. The pre-drying of the ore is carried out in any suit- -able manner, as by a long heating ina rbtary gas-fired kiln at such temperatures as to rid the ore of substantially all free and combined mois- The use of pre-dried materials, as opposed to the use of materials which contain substantial quantities of moisture as a result of the long exposure to atmospheric conditions during transportation and storage periods, eflectively minimizes the amount of moisture introduced into the furnace with the raw materials. The limitation thus imposed upon the amount of available moisture limits the amount of hydrogen evolved as a result of the decomposition of this moisture by the action of the electric furnace arcs and which is available to contaminate the metal during the prolonged melt-down period and subsequently come out of the metal during solidification in the molds to cause blow-holes, pitted sections and like defects, all as more particularly referred to in Patent No. 1,925,916 granted to William Bell Arness onSeptember 5, 1933 and entitled Process of producing alloys.

As illustrative of the practice of my invention in the production of a double heat of rustless-iron to desired specifications of chromium 8% to 10%, carbon .08% maximum and the balance substantially iron with the usual per-,

centagesof silicon and manganese and sulphur and phosphorus for the one specification, and chromium 16% to 18%, carbon .07% maximum and the balance substantially iron with the approximately 70% chromium, 6% carbon and the balance substantially iron), 2,000 pounds of chrome ore (analyzing approximately, 48% chromium oxide, CraO: 15% iron oxide, R101. and the balance unreducible oxides of aluminum,

magnesium, silicon and calcium) and 2,500

pounds of roll scale (substantially a pure iron oxide) are' char ed onto the chromite bottom of the electric arc furnace previously prepared for the reception of the charge, as more particularly described above.

Alternating current electrical energy is supplied the furnace-and the charge of ingredients begins to melt down forming individual pools of metal immediately beneath the furnace elec- I trodes. Under the continuing action of the intense heat of the electric furnace arcs the individual pools of metal soon merge into a single bath of ferrous metal containing considerable ing blanket of slag rich in the oxides of iron and chromium. The strongly oxidizing character of the slag blanket is effective throughout the melting down period in oxidizing carbon supplied the bath of metal by the low-carbon steel scrap, the rustless iron or steel scrap and the high carbon ferrochrome.

The slag overlying the bath of metaliacts. furthermore, as an eifective barrier between the metal and thecarbon or graphite furnace electrodes to prevent the pick-up of carbon from the electrodes in spite of the great avidity of the chromiumontaining ferrous metal bath for this elemen Incident to the removal and/or exclusion ofcarbon from "the metal bath by the oxidizing action of the slag blanket, there is a great tendency for chromium to be oxidized from the bath. To minimize the loss of chromium through oxidation the, melting operation is pref erably conducted at a high temperature. The use of this high operating temperature, which for convenience I designate as a temperature of superheat, promotes a preferential oxidation of carbon and permits the removal, and/or exclusion of carbon from the metal with a minimum oxidation of chromium from the bath.

The use of this high operating temperature furthermore'assures very thoroughoxidation of carbon from the bath and the realization of an extremely low carbon product in a minimum of ,time and with the consumption of aminimum ture 'of the furnace lining employed of power. 1

While no reliable method is know to me'for precisely determining the temperatures of metal and slag during the melt-down of the charge of ingredients, it is estimated that these temperatures are from about 3,l00 F. to 3,250 F.,-

temperatures which aresome 150 F. to 300 F.

higher than these ordinarily encountered in between the moltenchromium oxide contained in the slag and the chromium oxides dissolved in the metal bath limits the oxidation of chro mium from the bath and further contributions of chromium oxide)! to the slag. This action" greatly contributes tothe realization of a high chromium content of the ferrous metal bath.

When the charge of ingredients is completely melted down and samples taken from the bath for purposes of analysis indicate that the carbon content is at or below the desired low maximum value permissible, and the chromium content falls within the desired specified limits, the meltdown period is at an end. .At this stage of the process the furnace contains a bath of ferrous metal of desired specified analyses of carbon and chromium and an overlying blanket of slag. There are available in the slag great quantities of iron and chromium in the. form of oxides of these metals, although much of the iron oxide initially present has been lost during the'meltdown oxidation periodin removing and/or ex-- cluding carbon from the melting metal and in the oxidation of chromium from the melting metal incidental to the oxidation of carbon, all as more particularly described above.

The application of power to the furnace is discontinued, the furnace electrodes are raised and the first heat of metal is tapped from beneath the overlying blanket of slag into a suitable ladle for teeming or for transfer to a second furnace for refining. While fairly effective deoxidation of the tapped metal is achieved in the ladle by adding one or more of the deoxidizing agents, manganese, silicon, titanium, zirconium or the like, the metal is preferably transferred to a second furnace, conveniently a six-ton Heroultelectric arc furnace rated three-phase, 25 cycles, 2500 kva. at 120 to 180'volts; carrying a magnesite linin preferably pre-heated in any convenient manner, as indicated above. a

Power is applied to this furnace and the bath of metal is maintained at a desired refining temperature beneath a basic finishing slag of burnt lime and fine ferrosilicon. During the refining period the slag ingredients, burnt lime and fine ferrosilicon, preferably of the 75% silicon grade, are scattered over the surface of the metal bath from time totime. For the illustrative embodiment described above about 500 pounds of burnt lime and pounds of fine ferrosilicon of the 75% grade are effective in achieving a desired refining of the metal.

During the refining period the silicon and manganese contents of the heat of metal are age of silicon and manganese are achieved by the addition of 60 pounds of silico-manganese toward the end of the refining period.

After a suitable refining of the heat of metal is achieved, the application of power to the refining furnace is discontinued, the electrodes raised and the heat of metal tapped into a ladle for teeming. The metal is poured into suitable ingot molds and produces 15,400 pounds of ingots analyzing .05 carbon, 9.1% chromium, .40% manganese, silicon withthe usual low percentages of sulphur and phosphorus, and the balance substantially iron. The metal is clean, sound and, comparatively free from objectionable oxide inclusions.

It may be noted at this point that the tapped rustless iron is of lower carbon content than that produced in accordance with heretofore known and/or used processes. This highly desirable result is achieved by virtue of the reduction to a minimum of the-length of time for furnacing V ferrous metal of considerable chromium content (having a great thirst for carbon) By tapping the first of the double heats of metal almost immediately after the melt-down of the raw materials is completed a minimum carbon content is assured at this stage of the process. During the oxides of chromium, as more particularly indicated above. Great quantities of iron scrap, either low-carbon steel scrap or rustless iron scrap, or both low-carbon steel scrap and rust- I less iron scrap in desired proportions, are charged upon the slag present in the furnace.

In the production of rustless iron in the second of the double heats of iron-chromium al loys, rustless iron scrap is ordinarily omitted from the addition of iron scrap to the furnace since sufilcient chromium is usually present in the slag as oxides of chromium to achieve the desired chromium analysis. Although there is usually an adequate amount of iron oxide in the slag to maintain desired oxidizing conditions during further practice of the process, it will be understood that additional quantities of iron oxide may be added to the slag as required. Ordinarily, then, low-carbon steel scrap or base scrap is the principal ingredient charged upon the large quantity of slag retained in the furnace after the first of the double heats of metal has been tapped; illustratively 8,000 pounds are employed.

Alternating current electrical energy is again supplied the furnace and the base scrap melts down, the melting metal trickling through'the large quantity of slag present and forming a second bath of ferrous metal beneath the slag. As theapplication of power is continued more and more of the scrap is melted and contributes to the bath of ferrous metal underlying the blanket of slag.

It may be noted at this point that inasmuch as there is. very little chromium present in the second bath of ferrous metal (chromium amounting to about "1% is dissolved in the metal as it melts down-this small amount coming out of the slag retained in the furnace as well as the furnace bottom), the tendency toward carbon pick-up from the furnace electrodes is reduced to a minimum. This is a feature which is particularly important in the production of ferrous alloys of extremely low carbon contents (of the order of .03% to 06%).

When the iron scrap is completely melted slag as oxides at this .stage of the process-are recovered in a, reducing period, where a noncarbonaceous reducing agent, such as ferrosilicon, preferably employed in an amount chemically in excess of the oxides of iron and chromium present, is charged onto the slag overlying the bath of metal. To further increase the amount of chromium available and to take advantage of ,the heat expended during the reducing period, considerable quantities of chrome ore are conveniently charged onto the slag during the reducing period from time to time as furnace conditions permit. In the embodiment illustratively described the chrome ore added in this manner amounts to about 1,400 pounds a portion of which is added immediately prior to the addition of the reducing agent.

silicon of the reducing agent during this stage of the process is effectively prevented, in spite of the use of excess quantities of silicon necessary to achieve a high recovery of the metal values from the slag, byconducting the reduction under strongly basic slag conditions. The desired basic conditions are preferably achieved by employing burnt lime in an amount of about three to five times the total silicon content of the ferrosilicon employed.

To preclude hydrogen contamination of'the metal and assure the production of metal, sound and free from blow-holes, gas-pockets and the like burnt'lime is preferably pre-dried to eliminate substantially all free and combined moisture normally present in a manner more particularly described in Patent No. 1,925,916 of Willi Bell Arness referred to above.

In order to assure the maintenance of desired basic slag conditions during the reduction of the oxides of iron and chromium present, the burnt lime and reducing agent are preferably charged onto the slag as a mixture. Conveniently, the lime and the silicon reducing agent are mixed together on the floor of the melt shop and charged onto the slag overlying the bath of metal from time to time as furnace conditions permit.

By carrying out the reduction of the oxides contained in the slag under strongly basic conditions the acid silicates resulting from the reduction of the reducible oxides by the silicon reducing agentemployed react with the basic lime added to the slag and form a series of calcium silicates which are among the most stable components of the slag, all as more particularly described in Patent No. 1,932,252 of William Bell Arness, granted October 24, 1933 and entitled Process of producing alloys.

After all of the reducing agent and burnt lime have been added and have fused and completed their reactions with the ingredients present in the slag and metal anda substantially complete recovery of the oxides of iron and chromium present in the slag is accomplished, as evidenced by a change in color of successive samples taken from the furnace from a black to a light green or gray, the reduction stage of the process is at an end. 4 j

The second of the dual heats of'metal is then tapped into a ladle'for transfer to the refining furnace. The refining of this heat of metal is carried out in'a manner more particularly indicated above, employing about 500 pounds of burnt lime and 50 pounds of crushed grade of silicon in the preparation of a basic finishing slag. After the heat of metal is adjusted for silicon and manganese contents, as by the addition of about 75 pounds of silico-manganese toward the end of the refining period, the heat of refined metal is tapped into a ladle for teeming'.

The metal is poured into suitable ingot molds where it is allowed to cool and produces, for the illustrative example given, 11,500 pounds or rustless iron ingots analyzing approximately, .06% carbon, 16.8% chromium, .45% silicon, 50% manganese, and the balance substantially iron, with the usual low percentages of sulphur and phosphorus.

Where desired in the production of the first and/or second of the double heats of metal, supplementary additions of nickel, copper, cobalt, tungsten, molybdenum, vanadium, aluminum, ti-

on the example a given 5,000 pounds of burnt lime are used.)

thoroughly practical advantages are successfully achieved, It will be seen that the process lends itself to the rapid, eflicient and economical production, utilizing known furnace and operating equipment and employing a maximum of available and inexpensive raw materials, of iron-chromium alloys of carbon contents lower than those of iron-chromium alloys produced in accordance with heretofore known and/or used It will be further seen that the process is particularly favorable to maintaining a desired economic balance between the raw materials employed as sources of chromium by relatively adjusting the proportions of ingredients, rustless iron scrap, high carbon ferrochrome and chrome ore, in accordance with variations in the availability of rustless iron scrap and the fluctuations in its market price as compared with high carbon ferrochrome and Y chrome ore to such an extent as is consistent with the maintenance of good furnace operating conditions.

While as illustrative of :the practice of my invention the second of the double ,heats produced is rustless iron, it will be understood that where desired the charging of iron scrap upon the slag retained in the furnace after tapping the first of the double heats of metal may be varied between wide limits givinga rustless iron of low, intermediate or high chromium content, or, the addition of iron scrap may be entirely omitted and the reduction stage of the process immediately'carried out, in a manner more particularly indicated above, thereby achieving an ironchromium alloy of-very high chromium content and exceptionally low in carbon in the nature of a low-carbon ferrochrome. (To achieve a lowcarbon ferrochrome of maximum chromium con tent silicon metal or a very high grade ferrosilicon reducing agent is preferably employed as a substitute for-the 75% ferrosilicon reducing agent referred to above inorder to minimize the amount of iron added in the reducing agent.)

Likewise, it-will be understood that both the first and the second of the double heats of metal may be made to the same specificationof chromium by properly proportioning the amount of base scrap melted down on the slag retained in the furnace after ,tapping the first of the heated metal. Or, as desired, the first of the double heats of metal may be held in the refining furnace ,while the second of these" heats is being made and the two then refined and finished together obtaining metal of a single analysis of chromium and exceptionally ,lowin carbon (because of the unusually low carbon contents of the individual heats'combined) While in the illustrative embodiment of my invention the slag retained in the furnace after the tapping of the first of the dual heats, of metal contains suflicientchromium, as chromium oxide, to efficiently achieve metal of de-' sired chromium analysis in the second of the dual heats of metal, it may be noted at this point that in the production of rustless irons of very high chromium contents, advantage may be taken of the heat available during the second of high chromium contents advantage-may be taken .of the heat available during the reduction period of the process to melt a further quantity of chrome ore and have this ore react with the reducing agent employed to achieve a further enrichment of the metal in chromium, in a manner more particularly indicated above. I As many possible'embodiments may be made of my invention and as many changes may be made in the embodiment hereinbefore set forth, it will be understood that all matter described herein is to be interpreted as illustrative, and not in. a limiting sense.

I claim:

1 In the production of a double heat of ferrous alloys in an electric arc furnace, the art which comprises, melting down a charge of ingredients including iron scrap, a material rich in chromium, and an oxide of iron thereby forming a low-carbon bath of ferrous metal containing chromium and an overlying blanket of slag containing oxides of iro'n and chromium, withdrawing the bath of metal from the furnace leaving the slag therein, and reducing the oxides of iron andchromium contained in said slag thereby forming a ferrous product rich in chromium.

.2. In the production of a double heat of ferrous alloys in an electric arc furnace, the art which comprises, melting down a charge of base scrap, chromium-iron scrape,'high carbon ferrochrome, chrome-ore and iron oxide thereby forming .a low-carbon bath of ferrous metalcontaining chromium covered by an overlying. blanket'of slag rich in the oxides of iron and chromium, withdrawing the bath of metal from the furnace leaving the slag therein, and reduc- 'ing the oxides of iron and chromium of said slag thereby forming a ferrous product rich in chromium.

3. In the production of a double heat of ferrous alloys in an electric arc furnace, the art down a further quantity of iron scrap, the melt--.

ingfscrap trickling through said slag and forming a second bath beneath the slag, and reducing the oxides of iron and chromium contained in said slag thereby forming a ferrous product rich in chromium.

4. In the-production of 'a double heat of rustless iron in an electric arc furnace, the art which comprises, melting down a charge of base scrap, chromium-iron scrap and chrome ore thereby forming a low-carbon bath of ferrous metal containing chromium covered by an overlying blanket of slag rich in the oxides of iron and chromium, withdrawinglthe bath of metal from the furnace leaving the slag therein, melting down a further quantity of iron scrap on said slag said melting scrap trickling through said slag and forming a second bath of ferrous metal, and reducing the oxides of iron and chromium containedin said slag with a silicon reducing agent under strongly basic conditions forming a ferrous product rich in chromium and low in silicon. s Y

5. In the production of a double heat of ferrous alloys in an electric arc furnace, the art which comprises, melting down a charge of ingredients including base scrap, high carbon ferrochrome and roll scale, thereby forming a lowcarbon bath of ferrous metal containing chromium covered by an overlying blanket of slag rich in the oxides of iron and chromium, tapping the bath of metal from the furnace and leaving the slag therein, and reducing the iron and chromium oxides contained in said slag thereby forming a ferrous product rich in chromium.

6.- In the production of a double heat of rustless iron in an electric arc furnace, the art which comprises, melting down a charge of ingredients including rustless iron scrap and chrome ore thereby forming a low-carbon bath of ferrous metal containing chromium covered by a slag rich in the oxides of iron and chromium, withdrawing the bath of metal from the furnace and leaving the slag therein, melting down a quantity of iron scrap on said'slag, the melting metal trickling through the slag and forming a second bath of ferrous metal beneath the slag, and reducing the oxides of iron and chromium contained in said slag thereby enriching said metal in chromium.

7. In the production of a double heat of rustless iron in an electric arc furnace, the art which comprises, melting down a charge of ingredients including base scrap, high carbon ferrochrome, chrome ore and an iron oxide, thereby forming a low-carbon bath of ferrous metal containing chromium covered by a slag containing the oxides of iron-and chromium, withdrawing the bath of metal from the furnace leaving the slag therein, melting down a further quantity of base scrap on said slag, the melting metal trickling through the slag and forming a second bath of metal therebeneath, and reducing the oxides of iron and chromium contained in the slag with a silicon reducing agent in the presence of an excess of burnt lime thereby enriching said second bath of ferrous metal in chromium with a minimum of silicon contamination.

8. In the production of a double heat of rustless iron in an electric arc furnace, the art which comprises melting down a charge of ingredients including rustless iron ,scrap, high carbon ferrochrome, and roll scale thereby forming a low-carbon bath of ferrous metal containing chromium covered by-a slag rich in the oxides of iron and chromium, withdrawing the bath of metal from the furnace leaving the slag therein, refining the bath of metal withdrawing in a second furnace, melting down iron scrap on the slag retained in said first-mentioned furnace, the melting metal forming,a second bath beneath the slag, and reducing the oxides of iron and chromium contained in the slag thereby enriching said second bath in chro- 9. In the production of a double heat of rustless iron in an electric arc furnace having a chromite bottom, the art which comprises melting down a charge of ingredients including base scrap, rustless iron scrap, high carbon ferrochroine andan oxide of iron thereby forming a bath of ferrous metal containing chromium covered by a slag rich in the oxides of iron and chromium, withdrawing the bath of metal from the furnace leaving the slag therein, refining the withdrawn metal in a second electric arc furnace having a magnesite lining, melting down base scrap on the slag retained in said firstmentionedelectric arc furnace, the melting metal forming a bath of ferrousmetal beneath the slag, and reducing the oxides of iron and chromium in said slag thereby enriching said second bath in chromium.

10. In the production of rustless iron in an electric arc furnace, the art which comprises, melting down a charge of ingredients including iron scrap, a material rich in chromium and an oxide of iron, thereby forming a low-carbon bath of ferrous metal containing chromium and an overlying blanket of slag containing oxides of iron and chromium, withdrawing the bath of metal from the furnace leaving the slag therein, holding the withdrawn metal in a second furnace, reducing the oxides of iron and chromium present in the slag retained in said firstmentioned furnace thereby forming a ferrous product rich in chromium, withdrawing said ferrous product from said first-mentioned furnace and adding the products so withdrawn to the bath of metal held in said second-mentioned furnace, and refining and finishing the combined heats of metal achieving metal of a very low carbon content and a desired high chromium content.

11. In the production of rustless iron in an electric arc furnace, the art which comprises, melting down a charge of ingredients including base scrap, rustiess iron scrap, high-carbon ferrochrome, chrome ore and an oxide of iron, thereby forming a low-carbon bath of ferrous metal containing chromium covered by'a slag containing the oxides of iron and chromium, withdrawing the bath of metal from the furnace leaving the slag therein, holding the withdrawn metal in a second furnace, melting down a quan-- tlty of base scrap on the slag retained in said first-mentioned furnace, the melting metal trickling through the slag and forming a second bath of metal therebeneath, reducing the oxides of iron and chromium contained inthe slag thereby enriching said second bath in chro- ALEXANDER L.