US2232745A - Metallurgy of iron - Google Patents

Description

I Patented Feb. 25, 194i l i Q i 15 use in the production of relatively low-strength to effect dilution of ordinary soft iron to the ex- 15 UNITED STATES PATENT OFFICE METALLURGY or IRON Marvin I. Udy, Niagara Falls, N. Y.

No Drawing. Application January 28, 1939,

' Serial No 253. 40

15 Claims. (01.75-27) This invention relates to metallurgy and duced by means of simple operations of the ha for an object the provision of improved type of cupola operations. -metallurgical processes and materials. An im- The present invention permits the operaportant object of the invention isto provide an tions of foundries to be made more flexible by 5 improved method of altering the compositions enabling ordinary foundry operators to modify of metal products containing iron. Another imor alter, conveniently and accurately, the comportant object of the invention is to provide imposition of all or any part of the material proproved exothermic mixtures suitable for use in duced in any furnace heat without the, necesthe production of metallic iron. A more specific silly for employing. special equipment. The inobject of the invention is to provide a novel vention provides exothermic mixtures capable 10 method of producing metallic iron products suitof producing relatively pure metallic iron in defable for use in the production of high-strength I inite quantities per unit of weight, and, by castings from metal, of the type commonly promeans of simple calculations, a foundry operaduced in foundry cupolas, whichis suitable for tor may determine the proper quantity required castings, tent desired to form a product containing iron,

The invention will be described hereinafter carbon and silicon in desired proportions. Cumore particularly with respect to its use in the polas may be operated as usual to produce the production of metal suitable for use in the procustomary soft iron product, and dilution can duction of high-strength castings, but it is to be be eflectedl by addition of the exothermic mix- 20 understood that certain features are useful in tures to the ladies commonly employed for regeneral metallurgical procedures involving the ceiving molten metal from the cupolas.

production of metallic iron. The exothermic mixtures of the invention In the production of metallic iron products may consist essentially of iron oxide, lime (CaO) suitable for use in the production of high and a silicon-containing reducing agent, prefer- 25 strength castings, the invention employs the ably' low-carbon ferrosilicon. The iron oxide principle of dilution of relatively impure metalemployed may be in the, form of iron oxide ores .lic iron products with relatively pure metallic containing the usual im urities of such ores, or iron to form resulting products containing mea relatively pure iron oxide product such, for

' tallic iron in. increased proportions and, conexample, as mill scale or pyrites cinders may be 30 .sequently, containing other components in proemployed. In forming the exothermic mixtures, portions smaller than in the relatively impure I prefer to employ ferric oxide (FezOa) or a products subjected to treatment. In accordmaterial containing ferric oxide as the source of ance with the invention, dilution is effected by iron oxide, but an oxide containing iron in a reacting in contact with the impure metallic lower state of oxidation such, for example, as 35 products, while molten, exothermic mixtures magnetiteiFeaoi) may be employed. When an p ble f r in t0 Produce relatively P iron oxide product such as magnetite, containmolten iron. I ing iron in the lower state of oxidation, is em- -In many foundr es. pe at ons are confined ployed in an exothermic mixture, an additional for the most'part to the production f m substance containing readily available oxygen 40 6 n Products-sui l use in the producmust be incorporated in the reaction mixture tlon 01' Ordi ry 80 t iron, 0 low-Strength. castin order to provide for smooth and complete 1 8 P u 6093131111118 D about reaction. Magnetite-bearing material such as 3.15 percent carbon and about 2.25 percent silim scale may be d advantageously in form.

1- Iron products suitable for use in pr n ing exothermic mixtures also by treating it'45 relatively lushre g h n s (produc s preliminarily to oxidize the iron to the ferric containing, for example, about 2.9 percent carcondition with the production of ferric oxide. bon and about 2.0 percent silicon) require care- Oxidation may be accomplished readily by sinful control of the production processes or tering under oxidizing conditions. when high special equipment for their production. The temperatures are desired, the exothermic mix- 50 average small foundry is not provided with the tures in which the iron oxide is present entirely.-

special equipment or the necessary technical as ferric oxide may include one or mdfbl-jgv supervisory facilities to produce such products, dizing agents capable of reacting with silicon and consequently, the output of such a founto develop temperatures higher than those dedry is limited to products which can be ,proveloped by reaction of silicon with ferric oxide (FeaOa). Usually, I prefer to incorporate at least small amounts of one or more oxidizing agents of the type of sodium nitrate, sodium chlorate and manganese dioxide in the exothermic mixtures to insure the production of molten reaction products and to increase the temperature of the metal undergoing alteration, as higher temperatures promote the development of greater strength and uniformity in castings. The lime (CaO) may be present in the exothermic mixtures in free or uncombined condition, or it may be present in chemical combination with the iron oxide. The exothermic mixtu es preferably are formed of components in the form of particles minus loo-mesh in size, and the particles of the components preferably are thoroughly and intimately mixed. Mixing and grinding may be accomplished simultaneously by grinding the components together in suitable apparatus, as, for example, in a ball mill.

I have found that a mixture of lime, ferric oxide, and ferrosllicon when added to a ladle of molten soft iron reacts exothermically to produce pure iron and to dilute the soft ironto any desired carbon and silicon contents, depending upon the relative quantities of soft iron employed and pure iron produced. When fresh lime (CaO), ferric oxide and ferrosilicon are mixed intimately in the form of particles minus IOU-mesh in size and the mixtures formed into compact masses, they react readily on a ladle of molten iron. Due, however, to the radiation losses, it usually is advisable to increase the heat developed somewhat by the addition of excess silicon and an oxygen carrying agent like sodium nitrate or sodium chlorate or manganese dioxide to oxidize the excess silicon and produce additional heat. This is particularly desirable in the treatment of small batches of iron. Large batchesdo not need as much excess silicon, I have found that for the best results the iron oxide and lime should be chemically combined by heating the two materials in contact at elevated temperatures. The reaction between the iron oxide and the silicon is much more effective and rapid when the lime and iron oxide are chemically combined.

The lime (CaO) and ferric oxide may be combined chemically by heating a mixture of the two materials in finely divided form and under non-reducing conditions to a temperature of about 1200" C. or higher. The heating treatment may be so conducted as to result in the production of a fused product, or heating may be so controlled as to effect chemical combination without fusion resulting. When the heating treatment is carried out at a temperature sufficiently high to effect fusion, it is desirable to have present calcium oxide in amount sufilcient to combine with all ferric oxide present. Otherwise, some magnetite may be formed with consequent loss in heat developing capacity. When magnetite-bearing material is to be subjected to a sintering treatment under oxidizing conditions, lime may be admixed with the magnetite-bearing material to effect oxidation of the magnetite to ferric oxide and combination of calcium oxide with ferric oxide in a single operation. The lime and ferric oxide employed in forming the exothermic mixtures may be combined chemically in any suitably proportions. Good results may be obtained when the lime and iron oxide are chemically combined in the ratio, one molecule of calcium oxide (CaO) to one molecule of ferric oxide (F6203).

I may control the amount of silicon in the final metal product either by adjusting the amount of lime in the exothermic mixture employed, or by adjusting the amount of silicon relatively to the amount of iron oxide in the exothermic mixture. When silicon control is accomplished through control of the amount of lime employed, I employ an oxidizing agent with excess silicon, the silicon, lime and oxidizing agent being employed in proportions such as to effect oxidation of all silicon and reduction of substantially all iron with the production of a calcium silicate slag containing calcium oxide and silica in a molecular ratio of about 1.0 to 2CaO:1 SiO: and with the development of sufficient heat to make the slag thinly fluid. Higher ratios of lime to silica may be employed but ratios within the range set forth are quite satisfactory. When silicon control is accomplished by adjusting the amount of silicon relatively to the amount of iron oxide, the adiustment is such that silicon is employed in an amount insufficient to reduce all of the iron oxide present. In this case, a portion of the iron, in oxide form, enters the slag with calcium oxide and silica, forming a slag more readily fusible than a relatively pure calcium silicate slag.

In its preferred form, the invention contemplates the productlon and use of exothermic mixtures containing insufficient silicon to reduce all of the iron oxide, as considerable economy is effected owing to the saving in silicon through the production of readily fusible slags containing iron oxide, the iron oxide retained in the slag being usually no more expensive than lime as a slag-forming material. The proportions of iron oxide and silicon for incorporation in the exothermic mixture may be calculated according to the following equation:

Fe203+Si=FeO SiOz-i-Fe When lime (08.0) is present in the mixture in the ratio, one molecule of calcium oxide to one molecule of ferric oxide (Fezoa), the slag produced as a result of the reaction will contain calcium oxide, ferrous oxide and silicon dioxide in equi-molecular proportions, and the reaction may be represented roughly by the following equation:

CaO -FezOa+Si=FeO CaO SiOz-l-Fe While, as hereinbefore pointed out, I prefer to employ ferrosilicon as the reducing agent for reducing iron oxide to produce pure molten iron, my invention also contemplates the use of silicon-containing reducing agents in which the silicon is alloyed with such other metals as nickel, aluminum, magnesium and calcium. Also, those exothermic mixtures of my invention, in which ferric oxide chemically combined with lime is employed, may include such alloys of silicon as chrome silicon and ferrochrome silicon. Such exothermic mixtures are incapable of producing practically pure molten iron, as the molten iron produced will contain chromium; they may be employed for producing iron-chromium alloys directly, upon ignition in suitable containers, or

they may be caused to react in contact with molten metals to produce final products of altered compositions. Preferably, the exothermic mixtures of my invention contain no compounds of metals reducible to the metallic state, by exothermic reaction of the mixtures, other than iron oxide, or other thaniron oxide and manganese dioxide whenv the manganese dioxide is used primarily for the purpose of increasing exothermlcity.

The following example illustrates a process of my invention for diluting molten cupola metal with pure molten iron: T020 pounds of molten cupola iron (analyzing 3.15% C, 2.33% Si, 313% Mn) in a small ladle, I added 11.89 pounds of an intimate mixture consisting of 9.7 pounds of calcium ferrite (analyzing FezOa 69.0%, CaO 22.1%) .48 pounds of sodium nitrate and 1.71 pounds of ferrosilicon (analyzing 75% Si). The mixture ignited immediately and the reaction was complete in four and one-half (4 /2) minutes. The slag weighed 7.8 pounds and analyzed as follows: FeO 26.8%, CaO 25.4%, SiO: 32.60% (balance, sodium compounds from oxidizing agent and magnesium compounds from line). The metal analyzed as follows: C 2.72%, Si 2.08%, Mn .71%. The tensile strength of the altered iron product was 43,000 pounds per square inch as compared with 39,000 pounds per square inch before treatment.-

It will be appreciated that the treatment of the small quantity of metal employed in the above-noted example (20 pounds) involves some difficulties, particularly with respect to temperature control inview of large radiation losses. The results obtained serve to show, however, how the heat of reaction can be used to keep even small amounts of metal hot and at the same time reduce the carbon and silicon contents and produce metal suitable for use in the production of high-strength castings. Obviously, even better results canbe obtained in treating larger quantitles of metal.

Dilution or alteration of the compositions of metals to any suitable or desired degrees may be carried out. The degree of alteration or dilution to be practiced or achieved is a matter for determination on the basis of economic considerations.

2. The method of altering the composition ofa metal product containing iron which comprises igniting in contact with the metal product while molten an exothermic mixture consisting essentially of ferric oxide chemically combined with calcium oxide, and a low-carbon silicon-containing reducing agent.

3. The method of altering the composition of a metal product containing iron which comprises igniting in contact with the metal product while molten an exothermic mixture consisting essentially of ferric oxide chemically combined with calcium oxide, and low-carbon ferrosilicon.

4. The method of altering the composition of a metal product containing iron which comprises igniting in contact with the metal product while molten an exothermic mixture consisting essentially of ferric oxide chemically combined with calcium oxide, a silicon reducing agent and oxidizing material capable of developing by reaction with silicon a temperature higher than that resulting from reaction of the ferric oxide with calcium oxide, and a low-carbon silicon-contain- 7 ing reducing agent.

'1. An exothermic mixture suitable for use in the production of metallic iron consisting essentialiy of ferric oxide chemically combined with calcium oxide, and low-carbon ferrosilicon.

8. An exothermic mixture suitable for use in the production of metallic iron consisting essentially of ferric oxide chemically combined with calcium oxide, a silicon-containing reducing agent and oxidizing material capable of developing by reaction with silicon a temperature higher than that resulting from reaction of the ferric oxide with silicon.

9. An exothermic mixture suitable for .use in the production of metallic iron consisting essentially of ferric oxide chemically combined with calcium oxide and a silicon-containing reducing agent, the silicon being present in the mixture in an amount sufllcient to reduce only a portion of the iron of the ferric oxide to the metallic state, whereby control of silicon in the metal resulting from reaction and the production of a readily fusible iron oxide-bearing slag are provided for.

10. An exothermic mixture suitable for use in the production of metallic iron consisting essentially of ferric oxide chemically combined with calcium oxide and a low-carbon sillcon-containing reducing agent, the silicon being present in the mixture in an amount sufficient to reduce only a portion of the iron of the ferric oxide to the metallic state, whereby control of the silicon m the metal resulting from reaction and the production of a readily fusible iron oxide-bearing slag are provided for.

11. An exothermic mixture suitable for use in the production of metallic iron consisting essentially of ferric oxide chemically combined with calcium oxide and low-carbon ferrosilicon, the silicon being present in the mixture in an amount sufficient to reduce only a portion of the iron of the ferric oxide to the metallic state, whereby control of silicon in the metal resulting from reaction and the production of a readily fusible iron oxide-bearing slag are provided for.

12. An exothermic mixture suitable for use in the production of metallic iron consisting essentially of ferric oxide chemically combined with calcium oxide, a silicon-containing reducing agent and oxidizing material capable of developing by reaction with silicon a temperature higher than I that resulting from reaction of the ferric oxide with silicon, the silicon being present in the mixture in an amount sufficient to reduce only a portion of the iron of the ferric oxide to the metallic state, whereby control of silicon in the metal resulting from reaction and the production of a readily fusible iron oxide-bearing slag are provided for.

13. An exothermic mixture suitable for use in the production of a product containing metallic iron and'chromium, consisting essentially of ferric oxide chemically combined with calcium oxide, and an alloy containing chromium and silicon.

14; An exothermic mixture suitable for use in the production of a product containing metallic iron and chromium, consisting essentially of ferric oxide chemically combined with calcium oxide, and ferrochrome silicon.

15. An exothermic reaction mixture suitable for use in the treatment of molten metallic iron consisting essentially of ferric oxide chemically combined with calcium oxide, silicon-containing ent in an amount greater than that equivalent to one molecule of calcium oxide per atom of 8111- con present in the mixture, whereby control of silicon in the molten metal and the production of a. readily fusible, basic, iron oxide-bearing slag 5 are provided tor.

MARVIN J. UDY.