US2138797A - Manufacture of iron - Google Patents

Description

Patented Nov. 29, 1938 UNITED STATES MANUFACTURE OF IRON Marvin J. Udy, Niagara Falls, N. Y., assignor to Monsanto Chemical Company, a corporation of Delaware No Drawing. Original application December 3,

1934, Serial No. 755,767.

Divided and this application August 7, 1937, Serial No. 157,840

3 Claims.

This application is a division of Serial No.

} 755,767 filed Dec. 3, 1934.

This invention relates to the manufacture of iron, steel and alloys thereof, and has for its principal object the provision of a process for the economic production thereof.

A further object of this invention is the provision of a process for the production of iron of a high degree of purity.

A still further object of this invention is the recovery of phosphatic values in the metallurgy of iron.

In previously known related processes it is the practice to treat a phosphatic pig iron, to which may have been added scrap iron, with lime and iron ore or mill scale until the impurities have been decreased to the desired degree. In a modification of the basic open-hearth process, known as the Hoesch Process (Bradley Stoughton Metallurgy of Iron and Steel-1913, page 149) wherein a highly phosphatic slag is recovered, this process results in the production of steel. This process utilizes a relatively low slag volume and results, during the first part thereof, in the removal of 55% of the carbon, 86% of the phosphorus, 64.6% of the manganese, and 38% of the sulfur, together with all of the silicon. From these results it is evident that sulfur is removed with great difllculty and that the removal of the remaining impurities, with the exception of silicon, is also attended with some degree of difficulty.

I have now discovered that themanufacture of iron and/or steel may be considerably simplified and a purer product obtained if, instead of selecting a raw material with a low content of impurities, I deliberately choose or prepare an alloy of high, or relatively high, impurity content and then remove the impurities 1n the alloy by means of the proper slag. My discovery is based upon the observation that when such alloys as ferrophosphorus, ferrosilicon or ferromanganese, which normally contain a relatively high proportion of the alloying constituents, are treated with a basic exodizing slag, not only are .those ele- 'ments whichare present in major proportions effectively removed but the ordinary impurities which are present in minor proportions, such as sulfur, tin, and others, are also removed and more effectively than has hitherto been observed.

' For the purpose of the present specification and claims I shall confine myself to ferrous alloys, such alloys having, in addition to the iron necessarily present, alloying elements such as phosphorus, silicon and manganese, which elements are present in major proportions, that is, in amount, say, about 10% by weight of the alloys. I am not necessarily confined to the use of a single alloying element combined with iron in the ferrous alloy, but may employ an alloy containing two or more alloying elements combined with iron. Examples of suitable alloys are ferrophosphorus-silicon, ferromanganese-phosphide, ferromanganese-silicon' In the case where two or more alloying elements combined with iron are employed, I prefer to have the sum of such alloying elements other than iron total at least 10 per cent of the weight of the alloy, although such requirement is subject to some degree of flexibility, as will later more fully appear.

In additionto the alloying constituents present in major proportion, most ferrous alloys contain varying amounts of elements which may be termed impurities. These elements may consist of sulfur, titanium, vanadium, chromium, tin, etc. Another source of the minor impurities entering my process will consist in the use of scrap iron, the application of which will presently more fully appear.

A further variation of my process is exemplified by the production of pure or ingot iron. As is well known in the production of pure iron, it has been customary to use pig iron or scrap with as low a content of impurities as possible, and then to treat the molten bath with suitable eliminating agents to combine with the impurities present. Such treatment was necessarily carried out in a high powdered open-hearth furnace and involved a long-time treatment at a high temperature. The production of pure or ingot iron by these prior processes involved the careful selection of the raw materials; for example, it was customary to select, as a starting material, a pig iron of the following analysis:

Phosphorusnot over 1.00 and as low as possible.

. Sulfurnot over 0.05 and as low as possible. Silicon-not over 2.00 and as low as possible. Instead of employing materials of a high degree of purity, that is a high iron content, I

make use of ferro-alloys having a comparatively low iron content and treat such alloys in the molten state with a basic oxidizing slag whereby the major alloying elements, together with the impurities present therein, and those added by the addition agents, are substantially eliminated.

By this means I may obtain a pure or ingot iron in which the ordinary impurities may be within the following ranges in percentages:

Such an ingot iron is quite comparable with and in some cases may exceed the purity of ingot iron produced by earlier known processes.

As in earlier known processes, the selection of the materials to be treated by my process is of some importance, though the purity of the raw tent of the major alloying element, it may be.

said, as a general principle, that I desire such element tobe as high as practical, the actual percentage being usually dictated by economic considerations. This upper limitation is suggested by my observation that the scavenging effeet on metalloids or minor impurities which are usually difficult'to remove will be amaximum.v It is also my observation that the amount of the major alloying element present in the metallic raw' material may be graduated to suit the amount of minor non-metallic raw materials to be removed during the refining operation. In general it may be said that the greater the amount of the major alloying element scavenged from the molten alloy, the greater will be the elimination of the associated minor impuritiv As a practical example of my process, I will describe its operation with respect to the treatment of ferrophosphorus, this being an alloy of iron and phosphorus of commercial importance at the present time.

For practical purposes I prefer to use, as starting material, a commercial grade ,of ferrophosphorus, such, for example, as may be prepared by smelting phosphatic and iron-bearing materials either in the blast or electric furnace. Such materials usually have a phosphorus content,

varying from 15% to 28% and, as such, are directly useable in my process. In many cases, however, I may add to such commercial ironphosphorus alloys an additional amount of iron either, as cast iron or scrap, being careful, however, that the total phosphorus content of the mixture is not, lowered appreciably below For the purpose of the present specification and claims, I shall designate such an alloy as an iron containing a relativelyhigh proportion'of phosphorus, since, as may be seen from the prior art, the phosphorus content is much greater than that hitherto considered practicable.

Accordingly, I produce first an iron-phosphorus alloy or ferrophosphorus either by smelting scrap iron and phosphatic material in an electric furnace according to the method taught by Carothers in U. S. Patent 1,410,550, or that described by Gray in U. S. Patent 831,427. The source of iron in'the former case may be any suitable scrap material or it may be a1. ore of iron. In the latter process ore is usually employed. The ferrophosphorus produced in the electric furnace will vary in content from 17% to 28% phosphorus, and from 0.1% to 3.0% silicon; while that produced in the blast furnace will average 16% to 21% phosphorus, 0.1% to 1.0% silicon, and 0.1% to 1.0% sulfur.

I 'next provide a basic lined furnace, either a' gas-fired, open-hearth or an electric type being suitable, and, if conveniently located to the ferro-.

-of lime to 20 pounds of iron ore containing, say

76% F8203, although these proportions may be varied to suit the requirements of the refining operation and of the slag produced. The molten ferrophosphorus is then runjnto the furnace at a controlled rate so that thereaction does not be come-too violent.

A rapid elimination of the phosphorus now takes place with considerable evolution of heat in the bath. When the phosphorus in the metal has decreased to from 1 to 3 per cent, the slagis removed and replaced with a fresh slag of the same. character as first used. The refiningoperation is continued at a high heat until the phosphorus in the metal has been reduced to between 0.10% and 0.001%. At this point the metal is withdrawn into a ladle, and degasifying or deoxidizing agents are added. These may consist of.

aluminum or ferrotitanium in relatively small amounts. The molten alloy is now cast into ingot molds.

In certain cases I may employ the ferrophosphorus in lump form, by adding such material directly to the basic oxidizing slag. By proper choice of lump size the'vigor of the reaction may be controlled. During the addition of the ferrophosphorus l tunps or before such addition, I may add additional quantities of iron as cast or scrap iron.

1 Because of the rapidity with which the charge can be heated in the electric furnace, some advantage will result from operating in this type of furnace. There will be a greater contamination with carbon when operating in such a furnace;

however, for certain purposes this may not be objectionable.

The amount of basic oxidizing slag used in the first refining is proportioned so that it will contain from 18 to 24% of phosphoric acid as P205 when finished, although this figure will vary somewhat.

In prior processes for and iron the amount of slag formed amounted to from 10% to 30% by weight of the amount of such iron or steel treated. My process, on the the production of steel,

The amount of basic oxidizing slag used in the second refining operation may be equal in amount to that firstused. Because of the lower phosphorus in the metal, however, such slag will contain less phosphoric, acid. The removal of the refined metal from below this second slag is conveniently done by pouring it from below, as is done in a tilting furnace. The second slag. will then remain in the furnace and,'being of low phosphorus content, may be used as a first refining slag in a subsequent operation. Additional quantities of slagging ingredients may be added, if desired.

The impurities present in the iron produced according to my process will be within the following ranges:

Phosphorus 0. 10 to 0.001 Silicon (ll. 10. to 0. 004 Carbon 0. 14 to 0. 01

Sulfur 0. 003 to 0. 001

The actual amount of impurity present in the iron produced by my process will be dependent upon the type of furnace used and the care taken in operating the same. In general, a slightly higher carbon content will be obtained in the electric furnace than in the open-hearth furnace.

The pure iron produced will analyze between 99.56 and 99.98% Fe, and is especially suited for uses where a high degree of corrosion resistance is desired. Because of its freedom from the usual impurities, it is also favored for the manufacture of special iron alloys or steel.

The intermediate product produced under the first refining slag may contain from 0.6 upto 2 or 3 per cent of phosphorus. If the phosphorous is to be further reduced by subsequent treatment, it is advantageous to stop the treatment with the first slag when the phosphorus in the metal is in the neighborhood of 2 or 3 per cent. If, however, a high phosphorus ingot iron is desired, it is best to carry the scavenging of the phosphorus down with the first slag until the content of this element isin the range of from 0.65 to about 1.07% phosphorus. When carried to this point, the minor impurities present, namely, the carbon, manganese, silicon and sulfur, will total in the aggregate less than 0.30% and usually somewhat more than 0.015% of the alloy.

The high phosphorous iron may becast into ingots, forged and rolled or otherwise fabricated. When hot rolled and annealed, a 22-gauge iron sheet prepared from an ingot iron containing between 0.65% and 1.07% phosphorus will have an ultimate tensile strength of from 80,000 to 85,500 pounds per square inch, a yield point of 70,000 to 73,000 pounds per square inch," and an elongation in 2 inches of from 15% to 20%.

While I am uncertain asto the exact reason for the almost complete elimination of the impurities in the metal produced by my process, I believe it to be connected with the elimination of the large amount of the major alloying element such, for example, as phosphorus present in proportion to the iron. Apparently the scavenging of the large quantities of phosphorus which I employ carries into the slag most of the impurities present in the iron and iron ore.

This scavenging action is particularly noticeable in the case of sulfur, which may be present in the original raw materials in rather large quantities. I have found, for example, in one case that where sulfur was present in the ferrophosphorus alloy to the extent ofv 0.65%, one

treatment with a basic oxidizing slag served to reduce the amount of this impurity to 0.03%. This corresponds to a sulfur elimination of 96%.

The scavenging action of the phosphorus present in the high phosphorus-iron alloy 'is, of

course, not confined to its effect on sulfur, but is also effective in removing silicon, manganese, tin, etc. sulting from my process is characterized by a As I have indicated above, the metal revery lowcontent of those impurities normally present in commercial iron or steels, and is thereby distinguished over the prior art products and process.

My process is eifective, as has already been stated, not only with ferrophosphorus but also with ferrosilicon, ferromanganese and mixtures of these alloys. For most practical results I prefer to limit the content of the majorallowing carbon steel or any .of the various alloy steels by the addition of the proper alloying constituents.

In the foregoing specification I have described. various specific means by which my process may be carried out. It will be apparent, however, to those skilled in the art that my invention is susceptible to various changes and modifications without departing from the spirit thereof; and I desire, therefore, that my invention be not limited to any specific modifications except as indicated by the prior art or as specifically set out in the appended claims.

What I claim is:

1. An ingot iron containing:

Per cent Phosphorus between 0.60 and 3.00

Silicon between 0.10 and 0.004 Carbon between 0.14 and 0.01 the remainder being iron.

2. An ingot iron containing;

Per cent. Phosphorous between 0.65 and 1.07 Silicon between 0.10 and 0.004 Carbon between 0.14 and 0.01 Sulfur between 0.003 and 0.001 the remainder being iron.

3. An ingot iron containing:

4 Per cent Phosphorous"--- between 0.65 and 1.07 Silicon" between 0.10 and 0.004 Carbon between 0.14 and 0.01 Sulfur between 0.003 and 0.001

the remainder being iron, said ingot iron having a tensile strength of more than 80,000 pounds per square inch.

- MARVIN J. UDY.