US2280833A - Treatment of cast metals - Google Patents

Description

April 28, 1942.

A. B. KINZEL TREATMENT OF CAST METALS Filed Aug. 30, 1939 INVENTOR AUGUSTUS B. KINZEL ATTORNEY Patented; Apr. 28, 1942 TREATMENT OF CAST METALS Augustus 13.. Kinzel, Douglaston, Long Island,

N. Y., assignor to Electro Metallurgical Company, a corporation of West Virginia Application August 30, 1939, Serial No. 292,548

' (Cl. za -21c) 6 Claims.

This invention relates to cast metals and has for its principal object the provision of sound cast bodies of metals which shrink on solidifying and cooling, such as ingots and sand castings, substantially free from shrinkage cavities and pipes. Another object is the provision of castings in which the amount of metal required in the risers is considerably lessthan is normally necessary.

' Metal ingots which have been cast' in the usual manner, by pouring the molten metal into suitable molds and permitting it to remain undisturbed therein until solid, ordinarily contain cavities and pipes in the top portion of the ingot,

' which is the last to solidify. Moreover, impurities in the metal tend to segregate in the portion of the metal last to solidify. Consequently, the

ftop portion of the ingot is not ordinarily useful for the production of sound products of good quality and must be removed, generally by cropping, during fabrication of the ingot. Cropping, while heretofore considered necessary to insure sound metal products, is undesirable in that it entails a considerable loss of ingot metal.

Similarly, in sand castings, it is customary to the weight of metal required in the riser is as much as 50 percent of the total casting weight. Hence, it is evident that the value of metal lost in the riser may amount to a considerable sum.

It has been proposed to prevent the abovedescribed defects by 'adding suflicient heat to the top of a casting to maintain a pool of molten metal in the upper or normally unsound portion thereof for a longer time than is possible in ordinary casting practice. For example, U. S. Patent No. 937,163 to Mesta discloses the application of compressed air to the top of a steel ingot, which, it is said, is thereby heated by the exothermic oxidation of constituents of the steel. Also; U. S. Patent No. 933,751 to Hadfield discloses the burning of a layer of solid fuel on an ingot top by blowing compressed air jets against the fuel layer. Similarly, U. S. Patent No. 1,865,041 to Parsons discloses the combustion in oxygen jets of a layer of solid fuel on an ingot top. Thev treatment of.steel ingots by the previously proposed methods has been found to result frequent ly in the liberationoi large quantities of gases from the molten metal which may cause metal to boil over the top of the mold. Gas bubbles resulting from this reaction also may be trapped in the solidifying metal forming blowholes, thus partly defeating the purpose of the treatment.

In accordance with the present invention, blowholes, cavities, pipes, and segregated impurities in cast metal ingots and casting risers are either entirely or in large part eliminated, and an ingot or riser having a dense, clean, homogeneous structure throughout at least most of its mass is provided. Furthermore, the method of the present invention is carried out without the detrimental evolution of gases encountered in the aforementioned proposed methods. In ingots, this results in less loss of metal in the cropping operation. In risers thi s permits the use of less metal in theriser.

In performing the method of the invention, as applied to ingots of iron or steel, a thin layer of material comprising a highly reactive deoxidizing agent, such as ferrosilicon, is placed on the top of a solidifying ingot while the substantially undiluted pure oxygen gas is admitted into con-- tact with the top of the ingot. Heat evolved by the resulting exothermic oxidation reactions maintains the desired pool of molten metal in the top of the ingot, yet there is no detrimental evolution of gases from the metal during the course of treatment. The molten pool of metal then is cooled and solidified to produce" an ingot substantially free from blowholes, shrinkage cavities, segregated impurities, and other imperfections'throughout the upper portion of th ingot. Preferably the deoxidizing agent is added to the top of the ingot in a quantity insuflicient to change appreciably the composition of the molten metal.

. Treatment by the method of the invention may be commenced before or during solidification of the metal in the upper portion of the ingot.

Preferably, however, treatment is begun just Y the center, thereby restricting the initial formation of cavities and other shrinkage defects.

In the accompanying drawing, which illustrates the method of the invention:

Fig.1 is a diagrammatic vertical sectional view,

and apparatus of Fig. 3.

In the form of the invention illustrated in Figs. 1 and 2, the metal to be cast, for example molten steel, is poured into an ingot mold M through a centrally arranged opening in a cover or dome C, of steel, refractory brick, or other suitable material which rests on and closely fits the top of the ingot mold M. A plurality of oxygen discharge nozzles l2 in the cover C, arranged to deliver oxygen vertically downward to the periphery of the top of the ingot I, are

supplied with substantially pure oxygen by the header passage l3 which is in communication with the main oxygen supply conduit l4. As shown in Figs. 1 and 2, for example, the nozzles I! are arranged as the four corners of a square and the .cover C is so arranged that each nozzle is positioned immedately above the ingot top surface, adjacent to the periphery thereof, and preferably adjacent to a corner of the ingot. After the mold is filled with molten metal to the desired level, and either just before or just after pouring ceases, oxygen is discharged from the nozzles l2 against the top surface of the ingot I. The iron and other constituents of the steel, which are at or above their temperatures of ignition in oxygen, then begin to oxidize and liberate a large amount of high temperature heat.

Immediately after or before the oxygen jets are started. a coating D comprising a small quantity of a finely divided intimate mixture of a deoxidizing agent, such as ferrosilicon, and an inert or slowly oxidizable material, such as white silica sand or graphite, may be introduced through the opening 0 and is distributed more or less evenly over the top surface of the ingot.

This coating may be maintained on the top surface of the ingot for the whole duration of the oxygen treatment, additional mixture being added from time to time to replace any of the coating lost by oxidation.

, the continuous feeding of molten steel to the solidifying portion of the ingot to prevent the formation of shrinkage cavities.

When solidification has proceeded to within a short distance of the top surface of the ingot,-the application of oxygen is discontinued altogether and the ingot is allowed to solidify completely in the mold without further addition of heat. The length of time necessary to continue the oxidizing operation, and the best conditions of oxygen pressure and volume, depend largely on the size of the ingot and the temperature necessary to maintain the metal in the molten condition and to cause it to solidify at such a rate as to be substantially homogeneous in composition and structure.

In the described method of treating castings, the exothermic oxidation of any oxidizable constituents of the metal is carried out in the presence of a highly reactive deoxidizing agent, such as finely divided silicon, to inhibit oxygen absorption and to prevent the undesirable formation of gases in the molten metal. Silicon in the form of ferrosilicon has been found most advantageous, although other deoxidizing agents, such as aluminum, zirconium, vanadium, manganese, or mixtures of two or more such agents, may be substituted for a part or all of the silicon. Preferably the ferrosilicon or other deoxidizer is added in finely divided intimate mixture with an inert or relatively inert material, such as graphite; or white silica sand. Such a mixture permits a more uniform distribution of silicon over the top surface of the casting. The inert material also decreases heat losses from the top of the casting and slows down the rate of oxidation of the silicon somewhat to permit a uniform protracted heating effect.

I As one example of how the present invention has been carried out, the following is submitted: v

, A 500 pound ingot of 0.46 percent carbon steel was cast into an 8 inch by 8 inch by 30 inch mold and the flow of oxygen was started shortly before the mold was full.

Immediately after the oxygen treatment was started, several ounces of a 50:50 mix of white silica sand and ferrosilicon powder (75 percent silicon) were poured onto the metal and distributed uniformly over the surface.

The oxygen flow was continued for sixteen minutes during which period several additions of silica-ferrosilicon mix were made to the surface of the ingot, bringing the total quantity of added mix to fourteen ounces.

Treatment was carried out without excessive gas formation in the metal. The resulting ingot was free of gas bubble porosity, and had a shrinkage cavity in the top end which was very much smaller and shorter than those obtained under the same conditions without treatment by the method of the present invention.

An alternative form of the invention comprises .treating a casting, in the presence of a dexodizing agent, with a blanket of oxygen which is introduced in such a way as to avoid direct impingement of oxygen jets against the casting and deoxidizing agent. Thus, the oxygen is distributed substantially uniformly over the top surface, as contrasted to the localized jet treatment previously described.

As shown in Figs. 3 and 4, a dome C, having a pouring hole 0' in the center of its top, is supported on the top of an ingot mold M. The dome C is provided with side inlets I5 and I8 communicating with a common oxygen supply oxygen also is advantageous when the area of the casting top surface is sufficiently small that the intense heating effect of oxygen jets is unnecessary to keep the .top of the casting molten. Although the invention has been described principally as applied to the casting of steel ingots, it is evident that the principles also may be utilized in the treatment of risers and other types of castings.

What is claimed is: 1. The method of treating a solidifying cast body of iron or steel which comprises maintaining on the top of said body a coating comprising a finely divided intimate mixture of silicon in a substantial proportion, and an inert material; applying oxygen to oxidize said silicon; and at least partially by the heat of such oxidation, maintaining a pool of molten metal in the top of said body.

2. The method of treating a solidifying cast body of iron or steel which comprises maintaining on the top of said body a coating comprising a finely divided intimate mixture of fer rosilicon in a substantial proportion, and a less oxidizable material; pplying oxygen to oxidize said ferrosilicon: and at least .partially by the heat of such oxidation maintaining a pool of" molten metal-in the top of said body.

3. In a method of treating a cast body of iron or steel having a molten pool of metal in at least a portion of said body, the steps which comprise coating the top surface of said pool with a finely divided intimate mixture of silicon in a substantial proportion, and an inert material, retarding the cooling and solidifying of such pool by impinging one or more Jets of substantially undiluted pure oxygen on the mixture of silicon and an inert material, and cooling and solidifying such pool.

4. In a method of treating a cast body of iron or steel having a molten pool of metal in at least deoxidizing agent in a substantial proportion,.

a portion of said body, the steps which comprise retarding the cooling and solidifying of such pool by impinging a plurality of streams of oxygen on the surface thereof adjacent to the periphery thereof in the presence of finely divided silicon, and cooling and solidifying such pool.

5. In a method of treating a cast body of iron or steel having a molten pool of metal in at least a portion of said body, the steps which comprise maintaining a coating of a finely divided intimate mixture of silicon in a substantial proportion and a relatively inert material on the surface of said pool, and retarding the cooling and solidifying of such pool by introducing substantially undiluted pure oxygen over the surface of said pool in such a way as to avoid direct impingement of oxygen lets against said coatin and said surface, thereby maintaining a substantially uniformly distributed atmosphere of oxygen over said surface.

6. The method of treating a solidifying cast body of metal of the type which shrinks during solidification, which method comprises maintaining on the top of said body, while the latter is solidifying from a molten condition, a coating comprising an unbonded finely divided intimate mixture of an active exothermically oxidizable and a relatively inert material; applying oxygen to said mixture to oxidize said deoxidizing agent, thereby producing heat and supplying such heat to the top portion of said cast body; and at least partially by the heat of such oxidation, maintaining a pool of molten metal in the top of said body as solidification of the metal proceeds from the bottom of the cast body toward the top, thereby feeding molten metal down into said cast body to compensate for shrinkage of the metal and substantially prevent the formation of shrinkage cavities.

AUGUSTUS B. KIN ZEL.

Images