US1814584A - Method for purifying steel - Google Patents

Description

1 July 14, 1931. H. A. BOST ET AL METHOD OF PURIFYING STEEL Filed Feb. 27, 1930 1 j n M 1 4 z T s E #6 M a 001K Patented July 14, 1931 UNITED STATES PATENT. OFFICE HENRY A. BOST, OF EUCLID) VILLAGE, AND EDGAR O. HUMMEL, OF SHAKER HEIGHTS,

, OHIO, ASSIGNORS TO THE OTIS STEEL COMPANY; OF CLEVELAND, OHIO, A. CORPORA- mnrnon non. PURIFYING STEEL\ Application filed February 27,1930. Serial No. 431,891.

This invention relates to a process of refining steel and steel alloys, particularly to the method of purifying and deoxidizing of nickel steel. One of the present methods used to purity and deoxidize steels contemplates killing and purifying the steel by the introduction of deoxidizing agents such as aluminum, titanium and silicon into the bath. A clean deoxidized steel is obtained in the bath by this method, but steel so treated becomes somewhat plastic andsemi-solid and flows sluggishly. As a result, it is not suitable for a relatively slow bottom pouring. If. top poured, it tends to harden too quickly and stick to the walls of the mold, forming scabs or rough surfaces on the ingot. These scabs do not weld to the ingot and may later fall oif, leaving cavities in the surface, or may be pressed into the sheets or strips as the ingot is rolled. Furthermore, since such steel does not flow readily, pits or cavities are apt to be formed on the surface of the i gots. a

filled 'more rapidly and thus before much of the heat is dissipated. As a result, a thin shell is formed quickly about the mass, due to the chilling effect of the mold, before the center has cooled appreciably. Subsequent contraction of the molten center relative to this shell is a phenomenon of cooling which results in folds, snakes or cracks on the surfaces. All of these surface irregularities must be removed by the expensive slabbing down, chipping and rerolling rocess before the ingot will produce satis actory 4 plates. If the steel is poured before any killing action, i. e., as open steel, the prob- 40 lems of s lashing and subsequent shrinking and crac g are somewhat, but only partially overcome and deoxidation and purification in the mold are difficult by the methods formerly used. The steel contains many impurities in the form of gases, occluded matters and oxides. The present methods of purifying unkilled steel in the molds consists o introducing deoxidizing agents, such as aluminum, silicon, titanium, etc, into the molten steel,

In top pouring of any steel, the molds are.

by throwing it into the mold as the metal is poured. .This use of such deoxidizers has one very material drawback. For instance, aluminum, the most powerful deoxidizer, when it combines with the oxygen in the steel forms aluminum oxide, which has an extremely high melting point. The temperature of the surrounding steel is lowered in melting the aluminum, and as a result, the aluminum oxide solidifies almost instantly and is entrapped in the surrounding mass of relatively cool steel. An ingot containing aluminum particles produces defective material, which when rolled is undesirable. 4

However, poured the flow of steel into the molds is sufiiciently slow so that a relatively heavy shell is formed by the time the mold is filled and the metal is somewhat chilled.

-This shell is capable of withstanding subsequent contraction of the partially cooled metal, without distortion or cracking.

Further; the unkilled steel flows smoothly along the mold walls and does not splash, with the resultthat a smooth surface is formed. Much of the heat is dissipated dur-' ing the filling and the excessive contraction causing cracks in the metal is eliminated. While these difficulties are encountered in the production of ordinary steels and all steel alloys, they are greatly increased when treating with nickel steel. These facts are Well recognized and it is well known that if nickel steel could be satisfactorily deoxidized and purified in the molds; ingots of uniform texture, free from cracks and surface irregularities, could be obta ned, and the ingot waste or crop would be limlted to a relatively small percent of the ingots.

With these controlling factors in mind, one of the objects of the method of our invention is to eliminate the difliculties here- I tofore encountered and'to effectively purify and deoxidize the steel in the molds.

Another object is to produce ingots of nickel steel free from cracks or cavities and if unkilled steel is bottom of uniform composition and structure, and

having smooth re ular surfaces.

More specifica y, our objects include elimination of expensive steps of slabbing shallow head and sink well is obtained.

Still another object of our invention is to accomplish these results by the use of relatively inexpensive and commonly used equipment.

Other objects and advantages will become apparent from the following s ecification, in which reference is made to t e drawing by numerals.

In the drawing The figure isa longitudinal sectional view of a number of molds and runners of the usual arrangement for bottom pouring.

Our method includes pouring the unkilled steel into molds and then introducing a molten deoxidizer, such as molten aluminum into the molds, preferably at the base of the metal. By this method none of the heat of the steel or alloy adjacent to the deoxidizer is lost in the melting of the deoxidizer. As

a result, the deoxidizing agent is effective immediately upon its introduction into the mold, and rises rapidly through the molten steel, thoroughly and uniformly acting upon the entire mass. Since none of the steel or alloy in the mold is chilled in melting the aluminum, the aluminum oxide is not entrapped and no traces of it are found in the treated ingots The ingot walls are smooth and the ingot free from voids, due to the steel having risen relatively slowly in the molds as unkilled steel and without splash- 1n 1 All occluded matter is carried near the upper surface of the ingot and remains in the upper ten percent thereof, which is cut off and before rolling as usual.

Our method is preferably used in connection with bottom pouring in which the molds l are filled to within the desired distance from the top, as indicated by the dotted lines 2. The deoxidizer, such as alumi num, is then introduced, for example, from a suitable chute, as indicated at 10, into the feeder 3 in solid or liquid state as the pouring continues. Due to the intense heat of the metal as it leaves the ladle and also the heat of the feeder, only melted aluminum is carried by the steel into the runner 4. It passes in liquid state into the base of the mold cavity through suitable openings 5, which should be located centrally of the molds and discharge vertically thereinto. About as soon as enough metal has been poured to carry the aluminum into the molds, pouring is stopped. That is, the

filled, so that after pouring enough metal to carry the aluminum into the molds, they will be filled the desired amount. Experience has proven that in the production of .nickel steel, about two-thirds of a pound of aluminum per ton of steel introduced into the feeder when a five or six foot tall ingot mold is filled to within 6 inches of the height of the ingot desired, effectively deoxidizes and cleanses the steel. All impurities which do not pass off as gas collect in the upper few inches of the ingot. The remaining portion is free fromimpurities, has a smooth surface, and is of very uniform composition throughout. No trace of aluminum or aluminum oxide remains in the ingot.

While we have described our invention particularly with reference to nickel steel, it may be applied to other steels or steel alloys, and will in many cases economically produce more satisfactory results than present methods.

Having thus described our invention, we claim:

1. A method of producing steel or steel alloys, which includes pouring the molten metal unkilled into a mold and at the time when the pouring is being completed introducing a previouslymolten deoxidizer'into the mold substantially at the base thereof, said deoxidizer being the only substantial amount of deoxidizer added to the metal after the beginning of the pouring operation.

2. A method of producing steel or steel alloys which includes introducing the molten metal unkilled into a mold from the base thereof and maintaining the condition of the steel substantially in the condition in which poured until the mold is filled to the required depth and introducing a molten deoxidizer within said mold through the gate and at the bottom of the .column of metal therein while suflicient pouring is still taking place to cause complete introduction of the deoxidizer into the metal within the mold, said deoxidizer being the only substantial quantity of deoxidizer added after the beginning of the pouring operation.

3. A method of deoxidizing and purifying steel or steel alloys in the bottom pouring process which consists of pouring the open molten metal substantially free from any deoxidizing agent into a central pouring tube and discharging the molten metal into runners forming passages into the bases of molds whereby the metal is introduced into a plurality of mold cavities at the bottom thereof and rises in the molds concurrently forming therein a column of substantially open steel, and introducing a deoxidizer into said central tube near the end of the pouring operation whereby the deoxldizer is I melted and carried into the molds in liquid state when the molds are substantially filled.

4. A method ofproducing nickel steel ingots, which includes pouring'open nickel steel of the desired chemical constituents,

into a mold until the mold is substantially filled with open metal, and then introducing a premolten deoxidizer into the metal at the base thereof at the end of the pouring operation. v

5. A method of producing nickel steel ingots, which includes pouring molten nickel steel of the desired chemical constituents into molds until the molds 'are substantially filled with metal and introducing premoltenaluminum in amounts of two-thirds to fourfifths of one pound per ton of nickel steel into the metal at the base thereof at the end of the pouring operation.

6. A method of producing nickel steel ingots, which includes introducing unkilled nickel steel relatively slowly into a-plurality of molds concurrently, then deoxidizing and purifying said nickel steel in said molds by the introduction of premolten aluminum into said mold cavities at the bottom surface of said molten metal when the molds are nearly filled, said molten aluminum being the only deoxidizer added after the beginning of the pouring operation,

7. The method of producing nickel steel or nickel steel alloys which includes pouring the molten metal in unkilled condition into a mold and upon the completion of the introduction of the metal into the mold introducing'a molten deoxidizer in liquid condition into the mold substantially at the base of the molten metal, said deoxidizer being the only substantial amount of deoxidizer added after thebeginning of the pouring operation.

8. The'method of deoxidizing and purifying steel or steel alloys which consists of pouring open steel substantially free from any deoxidizing agent into a mold and introducing a previously molten deoxidizer into the mold at the base of the molten metal at the completion of the pouring o eration, said deoxidizer being the only su stantial quantity of deoxidizer added after the beginning of the pouring operation. t

In testimony whereof, we hereunto afiix oursignatures.

' HENRY A. BOST. EDGAR C. HUMMEL.

Images