US2854329A - Rimming agents and method of producing rimmed steel - Google Patents

Description

United States Patent.

RIMlVIING AGENTS AND METHOD OF PRODUCING RHVIMED STEEL Walter N. Rossborough, Rocky River, Ohio, assignor to Rossborough Supply Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application July 18, 1957 Serial No. 672,586

8 Claims. (Cl. 75-53) This application, relating as indicated to rimming agents and the method of producing rimmed steels, is particularly directed to a specific composition of matter and to the use of this composition of matter to produce rimmed steel. This composition comprises generally globular ferric oxide, Cryolite and sodium nitrate.

In the field of fluoride addition agents to steel for producing rimmed steel, generally with a carbon content below .30 percent, useful for flat rolled products, such as sheets, wires or rods, it has been customary to use various fluoride-containing.materials, such as fluorite, i. e., fluorspar, sodium fluoride and Cryolite, as well-recognized slag fluidizing agents. In general, however, it has been found necessary to find an improved means of adding these to an ingot as well as improved ways of rimming the steel.

This invention particularly relates to a specific form of ferric oxide which, together with Cryolite, sodium nitrate and a small percentage of aluminum fines, produces.

an improved action in a rimming agent.

An object of this invention is to provide an improved.

composition of matter or rimming agent for rimming steel. A further object of this invention is to provide a flux to break down A1 0 inclusions in the steel which cause.

tears or imperfections in the finished rolled product.

Another object of this invention is to provide an improved method of rimming steel with the formation of fewer scabs, which will rim upon teeming of the steel in the ingot without a delayed rimming action, and rim inv a uniform manner without a concave or convex meniscus to the steel in the ingot.

Another object of this invention is to provide an improved composition of matter for rimming steels, which gives no initial surge or quick jump but rather rims with.

an even start.

For a further understanding of rimming agents, it is believed that certain material taken from the standard textbooks on steelmaking would indeed be helpful. One classification taken from one of the handbooks shows the relationship of rimmed steel to several of the other most common types of the finished steel ingots, and these are 2. Capped Steels 3. Semi-Killed Steels- 4. Killed Steels 0 0.10-0.25 0.03 Max.

Rimmed steel then is an incompletely deoxidized steel normally containing less than .25 percent carbon. However, in recent years they have extended this up to .30 percent carbon. Rimmed steels have the following characteristics: (A) during solidification the evolution of gases occurs suflicient to maintain a liquid ingot top (open seal) until a side and bottom rim of substantial thickness is formed (if the rimming action is intentionally stopped shortly after the mold is filled, the product is termed. capped steel); and (B) after complete solidification, the ingot consists of two distinct zones, a rim somewhat purer than when poured and a core containing scattered blowholes, a minimum of pipe and an average percentage of metaloids somewhat higher than when poured and markedly higher in the outer portion of the ingot.

The rimmed steels are permitted to continue in the molds until the evolution of gases which takes place causes a boiling action that interferes with the growth of the columnar crystals and promotes the formation of a tough, ductile skin, particularly useful in connection with the rolling of sheets, strips, plates, wires, rods and the like.

In making rimmed steel, the steelmaker attempts to obtain theproper rimming action in the mold because this surface determines to a large extent the solidity of the surface of the ingot. The rimming action is controlled by the iron oxide content of the slag, the slag viscosity, the temperature at which the metal is poured and the deoxidizers used. In rimmed steel the outer surface of the ingot is quite clean and low in carbon. This gives an excellent surface to the finishedproduct. These steels are also softer. The process called rimming is preferred when the steel is partially deoxidized with manganese used alone or with some other deoxidizer. When the metal begins to solidify, a brisk evolution of gases cleanses the surface of the growing crystals and this resultsin a skin of very clean metal, the thickness of the skin depending upon the skill of the steelmaker. When the metal is cooled to the point Where the solidification proceeds throughout the liquid, a great deal of gas is trapped and a porous interior results.

It is well known that steel which rims actively and occupies a minimum volume in the molds, indicative of relatively greater freedom from sub-surface blowholes.

Over-deoxidized heats of steel rim sluggishly, rise from 2' to 12 inches in the molds and invariably make thinskinned shadowed ingots. The so-called shadowed ingots result from the proximity of primary blowholes to the surface of the steel. Improperly rimmed steel tends toward increased carbon segregation. The method of cap: ping also exerts an important effect upon the segregation of carbon, phosphorus and sulphur.

For a complete understanding of rimmed steel, it is necessary to show its relationship to the other types of steels. There are three classes of plain carbon steel, killed, semi-killed and rimmed. In general all forging steels and generally all steels containing more than about .25 or .30 percent carbon are killed. Structural steels containing from .l5.25 percent carbon are generally semi-killed, and rimming steels fall in the range as indicated above. Killed steels are used in forgings and other high carbon steels, which indicates that they have been deoxidized sufficiently by proper amounts of ferrosilicon, aluminum and other strong deoxidizers for the metal to lie perfectly quiet when poured into an ingot mold. In killed steels there is no evolution of gases, and the top surface ingot solidifies almost immediately. In semikilled steels the heat is caught coming down at the desired carbon content, and the manganese is added, either in the furnace or in the ladle. If silicon is used, it is added in the ladle as 50 percent ferrosilicon. When aluminum is used, it is sometimes added in the molds, although in most plants additions of aluminum are made cept aluminum flouride;

both in the ladle and in the mold. In rimmed steels if the rimming action is intentionally stopped shortly after the molds are filled, the product is termed capped steel.

The above information is only submitted by way of introduction to the relationship of rimmed steels to killed and semikilled steels for a better understanding of the particular fluxing action of this invention.

To understand the problem of teeming steel ingots and of providing a proper rim activator, it is helpful to understand that it has been calculated in one instance that the oxidation of .01 percent carbon produced for each cubic foot of steel results in the formation of 9.2 cubic feet of CO at 2760 F. This amount of gas evolving from the ingot mold provides a vigorous boilingaction as observed in connection with the formation of the ingot. In connection with this, there is a relationship between the aluminum which is added in the rim activator and FeO. FeO, which is reduced by the aluminum, forms a nucleons for bubble formation. The bubble is a combination of gases, as, for example, carbon monoxide, and this oxides to carbon dioxide when it leaves the metal bath and goes into the air.

It is believed that the above explanation may be helpful in understanding the background in connection with this invention.

In general in connection with rimming agents, fluoride materials have been used. Examples of these materials will be given in order to provide a proper understanding of the developments in the art. It may be said that fluorides, such as iluorspar, have been used in connection with rimming agents and in briquetted form, as, for example in Pacz Patent No. 1,562,655, to promote fluidity in the slag-forming ingredient. Sometimes they were particular fluoride compounds, double salts, and they were also Cryolites. However, these used both the aluminum and the Cryolite together. Cape Patent No. 1,672,446 taught the addition of small amounts, 1 to 6 ounces, of fluorspar to a 3000 pound ingot in order to enhance the character of the rimmed steel. Williams Patent No. 1,727,088 taught fluorides plus aluminum (shot) to steel for low carbon steel for rimming agents, for example, 2 to 6 ounces of aluminum/ton of ingot and /z to 8 ounces of fluoride/ton of steel. This was particularly for 06-08 percent carbon and .28.35 percent manganese. Grossmann Patent No. 1,748,217 taught a small amount of ferrozirconium together with 8 ounces of calcium fluoride to a 3000 pound ingot. This patent particularly taught that any fluoride might be used, ex-

A morerecent patent, Kern Patent No. 2,620,267, taught fiuorspar, lime and Portland cement in a combination.

In addition to the above, there were found to be various materials for removing sulphur and phosphorus from the ladle, and one such patent is Harris Patent No.

1,920,465, which added the combination of an alkali fluoride, such as sodium fluoride, to calcium oxide or calcium carbonate. This was only an addition to the ladle for slag removal. As part of this invention Cryolite and sodium carbonate may be substituted for sodium fluoride, as, for example, they would use 1% parts of Cryolite and /2 part of sodium carbonate instead of 1 part of sodium fluoride.

Further in connection with desulphurizing agents, Frevert Patent No. 1,770,395 taught that fluorspar and soda ash were typical examples of materials used, but he also taught the combination of fluorspar and soda ash, as, for example, 75-96 percent soda ash and 4-25 percent fiuorspar. This was a ladle addition to cast iron in the amount of 10-15 pounds/ton.

This invention particularly relates to the addition of natural Cryolite, not synthetic Cryolite which may under certain conditions have a percentage of aluminum oxide as an impurity. Also, in. connection with this, the combination of Cryolite, aparticular kind of globular ferric oxide, sodium nitrate and a small amount of aluminum 4 fines are intended to be used. These would be used, as, for example, in the following manner:

Cryolite 17-50 precent (there must be at least 17 percent),

Sodium nitrate 10-15 percent.

Aluminum fines 7-2 percent.

Globular ferric oxide Balance up to about 65 percent.

To be specific about these materials, I would use:

Globular ferric oxide from 16 mesh down Cryolite (natural state):

On mesh, 1 percent max. Through 150 and on 200 mesh, 5 percent Through 200 and on 325 mesh, 20 percent Through 325 mesh, 74 percent Sodium nitrate, 10-15 precent (not over 15 percent) Aluminum fines, 16 mesh and finer These materials provide action in connection with the teeming of rimming steel, i. e., the pouring of the steel into the ingot, and after a small amount, perhaps 6 inches, was poured in the bottom of the ingot, the bag of this composition would be added to the teeming of the steel in the ingot. This would provide a rimming action on the way up, as the steel was being teemed into the ingot, whereas other rimming actions in the past have had delayed action. The rimming would be entirely across the ingot and not forming a concave or convex meniscus. It would be cumulative in its action, i. e., if additional material were added, it would promote additional rimming action. Other rimming agents reach a peak of activity and additional material would accomplish no further action, i. e., they would. be sluggish in their action. There is no initial surge or quick jump of the steel in the ingot, and there is an even start.

A specific example follows of a composition that I would use in connection with an 8000 pound ingot having .29 percent carbon and .50 percent manganese. In the past it was common practice to use 6 pounds of sodium fluoride and 6 pounds of mill scale. I have used 2 pounds of a composition consisting of 66 percent globular ferric oxide, 17 percent Cryolite, 15 percent sodium nitrate and 2 percent aluminum fines, in the mesh above indicated. It can be seen how much improved the material would be and the cost would also be much lower. Even assigning no cost to the mill scale, which is a by-product, 6 pounds of sodium fluoride would cost almost $1.50 in large quantities and 2 pounds of this material would cost less than $.30.

In connection with another composition, I would use 43 percent globular ferric oxide, 50 percent Cryolite, 7 percent of aluminum fines and no sodium nitrate.

To both of the above compositions, I may increase the activity by adding a limited amount of sodium carbonate from 1-10 percent. Sodium carbonate helps to dissolve the sodium aluminum fluoride, i. e., the Cryolite, and to break down the material into its reactive components.

Another example of this invention and its use is in connection with rim activators for resulphurized steel, such as SAE 1110, 1112 and 1114. On the 1114 grade in connection with an 8000 pound ingot, 1%. pounds/ton of this new and improved rim activator were used to get a rimming action with a good clean case A thick. This,

ranges but now in the extended range, up to .30 percent carbon, new and improved acting rim activators are necessary. This invention is particularly useful in this connection.

Varioustechnical explanations could be given on the action of this particular rimming agent, but rather than hypothesize this as to the action of the components, it seems best to let the composition and its success speak for itself.

Although the present invention has been described in connection with a few preferred embodiments thereof, variations and modifications may be resorted to by those skilled in the art without departing from the principles of the invention. All of these variations and modifications are considered to be within the true spirit and scope of the present invention as disclosed in the foregoing description and defined by the appended claims.

I claim:

1. A rimming agent comprising from 17 to 50 percent sodium aluminum fluoride, 2 to 7 percent aluminum fines, and the balance being globular ferric oxide.

2. The rimming agent of claim 1 in which from 10 to percent sodium nitrate is added to the mixture.

3. The rimming agent of claim 1 in which from 1 to 10 percent sodium carbonate is added to the rimming agent.

4. A rimming agent comprising from 17 to 50 percent natural sodium aluminum fluoride, which has a mesh of 1 percent on 150 mesh, 5 percent through 150 on 200 mesh, 20 percent through 200 on 325 mesh and 74 percent through 325 mesh, 10 to 15 percent sodium nitrate less than 16 mesh, 2 to 7 percent aluminum fines less than 16 mesh, and globular ferric oxide the balance less than 16 mesh.

5. A rimming agent comprising approximately 17 percent Cryolite, 15 percent sodium nitrate, 2 percent aluminum fines and the balance being 66 percent substantially globular ferric oxide.

6. A rimming agent comprising approximately percent Cryolite, 7 percent aluminum fines and 43 percent globular ferric oxide.

7. A method of producing rimmed steel which consists of adding to the steel while teeming in the ingot a composition comprising 17 to 50 percent natural sodium aluminum fluoride, 10 to 15 percent sodium nitrate, 2 to 7 percent aluminum fines, and the balance being substantially globular ferric oxide, said rimming agent causing the steel to rim on the way up to reduce the rimming time, to prevent initial surges or jumps in the rimming and to reduce resulphurization in the steel.

8. The method of claim 7 in which from 1 to 10 percent of sodium carbonate is added to the mixture to help dissolve the natural sodium aluminum fluoride.

References Cited in the file ofthis patent UNITED STATES PATENTS 1,562,655 Pacz Nov. 25, 1925 1,727,088 Williams Sept. 3, 1929 1,748,217 Grossman Feb. 25, 1930 1,770,395 Frevert July 15, 1930 1,920,465 Harris Aug. 1, 1933 FOREIGN PATENTS 513,473 Canada June 7, 1955

Claims (2)

1. 7. A METHOD OF PRODUCING RIMMED STEEL WHICH CONSISTS OF ADDING TO THE STEEL WHILE TEEMING IN THE INGOT A COMPOSITION COMPRISING 17 TO 50 PERCENT NATURAL SODIUM ALUMINUM FLUORIDE, 10 TO 15 PERCENT SODIUM NITRATE, 2 TO 7 PERCENT ALUMINUM FINES, AND THE BALANCE EING SUBSTANTIALLY GLOBULAR FERRIC OXIDE, SAID RIMMING AGENT CAUSING THE STEEL TO RIM ON THE WAY UP TO REDUCE THE RIMMING TIME, TO PREVENT INITIAL SURGES OR JUMPS IN THE RIMMING AND TO REDUCE RESULPHURIZATION IN THE STEEL.
2. 8. THE METHOD OF CLAIM 7 IN WHICH FROM 1 TO 10 PERCENT OF SODIUM CARBONATE IS ADDED TO THE MIXTURE TO HELP DISSOLVE THE NATURAL SODIUM ALUMINUM FLUORIDE.