US2502284A

US2502284A - Decarburization of steel

Info

Publication number: US2502284A
Application number: US787488A
Authority: US
Inventors: George V Slottman
Original assignee: Air Reduction Co Inc
Current assignee: Airco Inc
Priority date: 1947-11-22
Filing date: 1947-11-22
Publication date: 1950-03-28
Anticipated expiration: 1967-03-28

Description

March 28, 1950 G. v. SLOTTMAN ,5 ,284

DECARBURIZATION OF STEEL Filed Nov. 22, 1947 2 Sheets-Sheet 1 INVENTOR GEORGE v. SLOTTMAN ATTORNEYS March 28, 1950 G. v. SLOTTMAN DECARBURIZATION OF STEEL 2 Sheets-Sheet 2 Filed Nov. 22, 1947 M G- m gum ATTORN EYS Patented Mar. 28, 1950 UNITED STATES PATENT OFFICE DECARBURIZATION OF STEEL Application November 22, 1947, Serial No. 787,488

3 Claims. I

This invention relates to the manufacture of steel and particularly to the elimination of excess carbon from the steel during production thereof.

In an application Ser. No. 728,868, I have described a method of producing steel in an open hearth furnace in which, after the steel has reached the point of decarburization, oxygen is introduced through a pipe to burn and thus elimihate the excess carbon. The oxygen disseminates through the molten metal rapidly and is startlingly efficient as a decarburizer until the carbon content falls below 0.25%. Thereafter the effectiveness of the oxygen decreases rapidly until,

,in the region of .03% carbon, the emciency is only about 5%. This is readily understood because the molten metal consists of a shallow layer only about 25 inches deep in a surface area in the vicinity of 600 square feet. The oxygen must diffuse through distances of up to 20 feet and therefore much of it is lost during the latest stages of the reaction, by combination with iron and in the overlying slag layer. While no dimculty is experienced in the early stages of decarburization because the oxygen disseminates rapidly, as is evidenced by carbon monoxide flames over the entire surface of the metal, it is relatively diflicult to bring the carbon content below 0.25% by the method as heretofore practiced.

It is the object of the present invention to provide a method of applying oxygen more eiiectively in the decarburizing of steel, whereby the apparatus.

In accordance with the present invention, the production of steel may be carried out in an open hearth or other suitable furnace. In an open hearth furnace, selected scrap is first melted on the hearth and, when melting is completed, suitable additions are made in accordance with the usual practice. The heat is continued until analysis of the metal indicates that the composition is satisfactory except for the excess carbon conthe manner described and particularly in open hearth practice.

At this point, the furnace is tapped and the metal is withdrawn. Oxygen is introduced to the metal for the purpose of eliminating the excess carbon and bringing the carbon content down to the required percentage for the particular purpose for which the metal is intended. Introduction of oxygen may be accomplished in a variety of ways. In one embodiment of the invention, a holding receptacle is provided, through which the molten metal flows continuously while oxygen is introduced to the flowing metal. Instead of introducing the oxygen in a holding receptacle, it may be directed into the flowing stream of metal leaving the furnace. Or, the molten metal may be delivered to a relatively large receptacle of substantial depth compared with its crosssectional area, and oxygen may be introduced to the molten metal until a satisfactory composition is attained. Thereafter the completed metal heat may be delivered to a receptacle for transportation such as a ladle. In each of the cases mentioned, the molten metal is subjected to the action of sufficient oxygen to consume the excess carbon and bring the carboncontent to the required percentage. Since the metal is no longer in the form of a shallow layer as on the hearth of the open hearth furnace, there is no problem of dissemination of the oxygen. All of the metal is subjected uniformly to the action of oxygen which reacts actively with the carbon present, and the desired result is readily attained.

Although oxygen of commercial purity, that is 99.5% or better is most suitable for the purpose, it is not essential. Oxygen of purity range from to 99.5% or better may be utilized successfully for the purpose of the present invention. The reaction is slower with lower grades of oxygen, but nevertheless the carbon may be consumed effectively and more satisfactorily with respect to certainty of results than by the method as heretofore commonly practiced, in which iron ore is added as an oxidizing agent to eliminate carbon.

Referring to the drawing, 5 indicates an open hearth furnace. having a hearth 6, a charging opening I and a tapping hole 8. Scrap steel may be melted on the hearth 6 in the usual manner with suitable additions of lime to form a slag and of blast furnace iron to provide the molten steel 9 and its overlying layer of slag [0. Heat is supplied in the usual manner by burners (not shown) at the ends of the furnace. The details tent which is always present in steel produced in $5 of the furnace structure form no part of the present invention, and since such furnaces are in common use, further description is unnecessary.

When the heat is completed, except for the presence of excess carbon, the molten metal is tapped through the tapping hole, 8 and is delivered by a runner l l to a receptacle l2 of suitable heat resistant construction, affording a relatively deep space as compared with the cross-sectional area. The receptacle l2 has an outlet l3 through which the metal flows, by means of a runner it, into a ladle IS. The apparatus is proportioned so that the flow of molten metal is continuous, that is, the amount flowing into the receptacle I2 is continuously withdrawn through the outlet l3. While the molten metal is in the receptacle I2, it is subjected to the action of oxygen supplied through a tuyere it which is connected by a pipe 11 to a source of oxygen under suitable pressure. Thus the oxygen bubbles up through the molten metal, and the carbon content is rapidly oxidized and thus eliminated. The molten metal flowing into the ladle I will have a predetermined carbon content, the operation being regulated in view of the proportion of carbon present in the molten steel as it leaves the furnace 5. More or less oxygen may be supplied as required to accomplish the intended purpose.

Referring to Fig. 2 of the drawing, a furnace I8, for example of the open hearth type having a hearth l9, charging Openings 20 and a tapping hole 2|, is operated in the manner hcreinbefore described until the steel has the required composition except for excess carbon. The furnace is then tapped, and the molten metal is delivered through a runner 22 into a ladle 23. A pipe 24 is disposed so that it discharges oxygen into the flowing stream of molten metal in the runner 22. The pipe 24 may be connected to a source of oxygen under suitable pressure. Thus, all of the metal flowing from the furnace is subjected to the action of oxygen, which reacts with the carbon in the metal during transit through the runner 22 and in the ladle 23. The excess carbon is thus eliminated to the desired point to produce steel of the required carbon composition.

In Fig. 3, a furnace 25 has a tapping hole 26 and the molten metal 27 therein, after reaching a suitable composition except for excess carbon, is delivered through a runner 28 to a receptacle 29 which is relatively deep as compared with its cross-sectional area, and adapted to hold the entire heat or a part of the heat from the furnace 25. A pipe 30 extends into the receptacle 29 and encloses an inner pipe 3! through which oxygen is supplied from any suitable source. A coolant may be delivered to the pipe 30 from a source 32 and withdrawn through a pipe 33, so that the pipe 39 and the pipe M will not be consumed. The oxygen is'delivered to the molten metal which is held in considerable depth and the carbon is readily consumed so that a metal of the desired carbon composition is easily obtainable. In each of the cases described, the difficultyarising through the necessity for disseminating oxygen through a shallow layer of molten metal in the open hearth furnace is eliminated. Where there is a considerable depth of metal, the oxygen, having a tendency to rise to the surface, thoroughly impregnates all of the metal and comes into contact with the carbon which it oxidizes.

Various changes may be made in the procedure as described without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The method of decarburizing steel which comprises subjecting it in a molten state in an open hearth furnace to an initial refining operation with reduction of the carbon content thereof to about 0.25%, withdrawing the initially decarburized steel in a molten state from the furnace, maintaining the withdrawn steel in a molten state, and forming a flowing body of the initially decarburized and molten steel which is relatively deep with respect to its cross-sectional area, and thereafter introducing a gas containing more than 45% oxygen into the lower portion of said relatively deep body of molten steel until it has reacted with the carbon content of the molten steel sufiiciently to bring about a further substantial reduction of the carbon content thereof.

2. The method of decarburizing steel which comprises subjecting it in a molten state in an open hearth furnace to an initial refining operation with reduction of the carbon content thereof to about 0.25%, withdrawing the initially decarburized steel in a molten state from the furnace, maintaining the withdrawn steel in a molten state, flowing the withdrawn molten steel past a source of a gas containing more than 45% oxygen, and introducing gas lrom said source into the flowing stream and reacting the oxygen content thereof with the carbon of the flowing molten steel in amount sufficient to substantially further reduce the carbon content thereof.

3. The method of decarburizing steel which comprises subjecting it in a molten state in an open hearth furnace to an initial refining opera tion with reduction of the carbon content thereof to about 0.25%, withdrawing the initially decarburized steel in a molten state from the furnace, maintaining the withdrawn steel in a molten state, and forming a body of the initially decarburized and molten steel which is relatively deep with respect to its cross-sectional area, and thereafter introducing a gas containing more than 45% oxygen into the lower portion of said relatively deep body of molten steel until it has reacted with the carbon content of the molten steel sufiiciently to bring about a further substantial reduction of the carbon content of the molten steel.

GEORGE V. SLOTTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 16,690 Martien Feb. 24, 1857 465,672 Lindenthal Dec. 22, 1891 1,133,317 Rice Mar. 30, 1915 1,312,474 Fisk Aug. 5, 1919 1,394,103 McGlynn Oct. 18, 1921 1,484,465 Billings Feb. 19, 1924 1,756,054 Crum Apr. 29, 1930 2,074,164 Clair Mar. 16, 1937 FOREIGN PATENTS Number Country Date 12,356 Great Britain of 1886 20,245 Great Britain of 1902 156,548 Great Britain Apr. 5, 1922

Claims

1. THE METHOD OF DECARBURIZING STEEL WHICH COMPRISES SUBJECTING IT IN A MOLTEN STATE IN AN OPEN HEARTH FURNACE TO N INITIAL REFINING OPERATION WITH REDUCTION OF THE CARBON CONTENT THEREOF TO ABOUT 0.25%, WITHDRAWING THE INITIALLY DECARBURIZED STEEL IN A MOLTEN STATE FROM THE FURNACE, MAINTAINING THE WITHDRAWN STEEL IN A MOLTEN STATE, AND FORMING A FLOWING BODY OF THE INITIALLY DECARBURIZED AND MOLTEN STEEL WHICH IS RELATIVELY DEEP WITH RESPECT TO ITS CROSS-SECTIONAL AREA, AND THEREAFTER INTRODUCCING A GAS CONTAINING MORE THAN 45% OXYGEN INTO THE LOWER PORTION OF SAID RELATIVELY DEEP BODY OF MOLTEN STEEL UNTIL IT HAS REACTED WITH THE CARBON CONTENT OF THE MOLTEN STEEL SUFFICENTLY TO BRING ABOUT A FURTHER SUBSTANTIAL REDUCTION OF THE CARBON CONTENT THEREOF.