US1826880A - Method of purifying ferrous metals - Google Patents

Description

Patented Oct. 13, 1931 UNITED STATES PATENT OFFICE Iq'o Drawing. Application filed August 22, 1928. Serial No. 301,434.

0 difficult to remove sulphur from the metal, in

the open hearth process, because the elimination of sulphur requires high heat and a reducing condition whereas an oxidizing condition obtains in the basic open hearth fur- In practicing the basic open hearth process the principal elements that are eliminated from the metal are silicon, manganese, carbon, phosphorus and some sulphur. The most important of these are phosphorus and 20 carbon and since phosphorus requiresv an oxidizing condition in the furnace, a condition which would eliminate sulphur would drive the phosphorus back from the slag into the metal. T

Because of the difliculty of eliminating sulphur, by the basic open hearth process, it has been customary for the steel plants to avoid a high sulphur content in the finished steel by using metals, in-the charges, that did not contain an excessive amount of sulphur.

Heretofore, when the steel has been high in sulphur, it has caused much difficulty in the.

rolling mills because ofthe tendency of the ingots and billets to crack and it is one of the objects of the present invention to overcome this difliculty in steels containing, What would ordinarily be considered, an excessive amount of sulphur. My invention, therefore, enables the use of metals, in the basic open hearth furnace, that have a higher sulphur content than would heretofore have been considered good practice and as such metals have a lower market value than low sulphur metals, my invention effects material economies in the manufacture of the steel.

The development of the automobile industry has resulted in a largedemand for deep-drawing steels and it is one of the objects of the invention to produce deep-drawing steels of a superior quality. It is a fur- 7 properties.

ther object of the invention to produce steel that will have an exceptionally good surface s and also be uniform and without hard spots. I have found that hard spots in steel are usually manganese and iron silicates and oxides and the elimination of these segregations of manganese and iron silicates and duce the strength of the Wire and are points at which the wire will break when bent.

In deep-drawing steels these hard spots also result in tearing of the metal and difficulty in shaping the metal in the dies.

In steel that is to be coated with zinc, lead, tin, nickel or other metals it is very important to have clean and uniform surfaces because, when the metal is pickled for the purpose of taking off scale, the acid will penetrate into the steel,if the surfaces are defective, and collect around the inclusions with the result that when the sheets are later heated in the coating process the hydrogenthat is liberated by the reaction of the acid on the steel is driven to the surface and raises the coating in the form of blisters, thereby producing a defective product.

My invention has for a further object the production of rim steel having a thicker and denser skin so that when this steel is rolled out into sheets it will have a clean and uniform surface. a In the manufacture of rim steel the metal is usually very active when poured into the molds and by the use of 'my invention the activity of the metal, in the molds, is kept under better control and the ingots have clean and dense surfaces which are not so sensitive to heating and burning in the soaking pits and heating furnaces.

This is very important because, with a less dense skin, blow-holes form close to the surface and the fire attacks the surface and makes spots which develop into seams in till rolling.

It is a further object of my invention to reduce the amount of deoxidizer, such as aluminum, silicon or manganese, that is required in the manufacture of killed steel. The term killed, as applied to steel, refers to a steel that has been practically degasified in the open hearth furnace but in pouring such steel into the molds it is customary to add a deoxidizer for the purpose of eliminating some of the iron and manganese oxide that is still in the steel and, by the use of my invention, the metal is so completely deoxidized, in the open hearth furnace, that very little, if any, deoxidizer is required in the molds.

In practicing my invention I utilize soda, in the form of commercial soda ash, as the means for reducing the iron and manganese oxides and silicates and otherwise purifying the metal. In my Patent 1.717 ,153. June 11, 1929, I disclosed a method of desulphurizing and purifying steel bv the use of soda ash and while that method has been found to produce beneficial results it has not been entirely satisfactory because the soda has a tendency to be more or less erratic in its action and the results sought for could not always be obtained with certainty. My present method is, therefore, an improvement on the method disclosed in my Patent 1.717,153 and this improvement eliminates all uncertaintv as to the results and permits a substantially uniform practice in the steel plant with practically uniform results.

Steels produced by my improved method, whether rim or killed steels, are practically free from dissolved iron oxides and the segregations of iron and manganese oxides and silicates that have given trouble heretofore in the manufacture of steel bv the standard basic open hearth method. When steels made by my improved method are rolled out into thin sheets these sheets have a smooth, clean surface with a high lustre. Such sheets are especially well adapted for being coated with tin,lead, zinc or nickel and because of the character of the surfaces the coating is uniform and so firmly united with the surface of the sheet that a thinner coating may be used. thereb a saving in th cost of coating is made possible.

In practicing my invention, in the basic open hearth process. I introduce into the molten metal. and preferablv into the molten iron before it is poured into the open hearth furnace. at purifying material which consists essentially of a mixture of soda ash and a controlling substance therefor, such as manganese dioxide, which will insure reliable results. The purifier may vary as to its composition but in addition to the materials specified, contains some lime to raise the melting. point of the soda ash, and I have found raaaeeo that the following composition is entirely satisfactory Commercial soda ash (NA COQ 90% Calcium oxide (CaO) as limestone 3 to 4% Manganese dioxide (MnC to 1% Chlorine, as calcium chloride (CaCIl about 'be melted at a temperature of from 2300 to 2600 F. and then run out ontoiron plates and broken up into pieces of from inch to 3 or 4 inches in size. From 2 to 4 pounds of the purifier, per ton of iron, treated, will give satisfactory results. Ihe purifier may be put into the transfer ladle, either before or during the pouring of the metal thereinto from the mixer or the blast furnace ladle, and the act-ion of the purifier is very pronounced. 'Ihe soda ash is broken up and the carbon dioxide'and other gases that are released produce a violent boiling of the metal. and this causes the purifier to be diffused throughout the body of the metal. 'I he soda ash takes the oxygen from the dissolved iron oxides and the manganese oxide and also reacts with the iron and manganese silicates forming sodium silicate and metallic iron and manganese. The sodium silicate rises to the surface of the metal and enters the slag and tends to make the slag more liquid.

Instead of melting the materials forming the purifier they may be mixed dry, in a will, through its action on the soda, produce heat and harden the materials when they are pressed into briquets.

When the purifier is introduced. into the open hearth furnace it enters the slag and makes it more liquid. This facilitates the boiling of the metaland causes it to be forced up through the slag, in the form of spouts or guysers, and as the metal passes through the slag it is washed by it and when above the slag the furnace gases are permitted to oxidize the impurities. The soda alone has a lower specific gravity than the usual open hearth furnace slag but the manganese oxide, which is present in the purifier, increases the gravity so that the lumps or briquets of the purifier will sink through the slag and float on the metal where they will melt and the purifier will h ve an opportunity to react with the impurities in the metal.

Having thus described my invention, I claim:

1. The hereindescribed method of purifying steel in the course of its manufacture by the basic open-hearth processwhich consists nsaaeeo in introducing into the molten metal a deoxidizing material in the form of an intimate mixture comprising commercial soda ash and manganese dloxide and wherein the soda ash is over three-fourths of the mixture and the manganese dioxide is an efiective amount, up to five per cent, for controlling the action of the soda ash as and for the purpose described.

2. The hereindescribed'method-of purifying steel in the course of its manufacture by the basic open-hearth process which consists in introducing into the molten metal a deoxidizing material in the form of an intimate mixture comprising commercial soda ash, a calcium compound and manganese dioxide and wherein the soda ash is over threefourths of the mixture, the calcium compound has a calcium oxide content that is an eifective amount, up to ten per cent, to substantially raise the melting point of the soda ash, and

the manganese dioxide is an efl'ective amount, up to five per cent, for controlling the action of the soda ash as and for the purpose described.

3. The hereindescribed method of purifying steel in the course of its manufacture by the basic open-hearth process which consists in introducing into the molten metal lumps of a deoxidizing material in the form of an intimate mixture comprising commercial soda ash, a calcium compound and manganese dioxide and wherein the soda ash is over three-fourths of the mixture, the calcium compound has a calcium oxide content that is an effective amount, up to ten per cent, to substantially raise the melting sodaash, and the man anese dioxide is an effective amount, up to ve per cent, for controlling the'action of the soda ash as and for the purpose described.

In testimony whereof, I

signature. v

CHARLES T. HENNIG;

point of the hereunto aflix my