US3634075A

US3634075A - Introducing a grain refining or alloying agent into molten metals and alloys

Info

Publication number: US3634075A
Application number: US791453*A
Authority: US
Inventors: Jean C Hoff
Original assignee: Kawecki Berylco Industries Inc
Current assignee: KB Alloys Inc
Priority date: 1969-01-15
Filing date: 1969-01-15
Publication date: 1972-01-11
Anticipated expiration: 1989-01-11
Also published as: ES375409A1; AT316158B; JPS5212122B1

Abstract

A molten metal or alloy is inoculated with metallic treating agent by pouring the molten metal into a troughlike passageway and by introducing a rodlike supply of the metallic treating agent into the molten metal flowing in the passageway under conditions insuring a disturbed but nonturbulent flow of the molten metal and resulting uniform distribution of the treating agent therein.

Description

United States Patent Inventor Jean C. Hoff Stamford, Conn. Appl. No. 791,453 Filed Jan. 15, 1969 Patented Jan. 11, 1972 Assignee Kawecki Berylco Industries, Inc.

New York, N.Y.

INTRODUCING A GRAIN REFINING OR ALLOYING AGENT INTO MOLTEN METALS AND ALLOYS 2 Claims, 1 Drawing Fig.

US. Cl 75/135, 75/138 Int. Cl C22c 1/06 Field of Search 75/l 35, 53,

[56] References Cited UNITED STATES PATENTS 2,595,292 5/1952 Reece 75/122 3,331,680 7/1967 Leupold a 75/53 Primary Examiner L. Dewayne Rutledge Assistant Examiner-E. L. Weise AttarneyPennie, Edmonds, Morton, Taylor and Adams ABSTRACT: A molten metal or alloy is inoculated 'with metallic treating agent by pouring the molten metal into a troughlike passageway and by introducing a rodlike supply of the metallic treating agent into the molten metal flowing in the passageway under conditions insuring a disturbed but nonturbulent flow of the molten metal and resulting uniform distribution of the treating agent therein.

PATENTED JAN] 1 1972 m Jean C. No"

INTRODUCING A GRAIN REFINENG R ALLOYING AGENT INTO MOLTEN METALS AND ALLOYS This invention relates to the modification of a molten metal or alloy with a master alloy of that metal containing a grain refining or alloying agent, or both.

The presently preferred method of introducing a grain refining agent into a metal such as aluminum and its alloys comprises adding an aluminum base master alloy containing the grain-refining agent to the molten aluminum or aluminum alloy in a holding furnace or casting ladle. The grain refining agent is an aluminum-insoluble metal, alloy or intermetallic compound which, when uniformly distributed throughout the molten aluminum, remains solid (or solidifies before the aluminum) and causes the aluminum to crystallize in fine grain size when the latter solidifies. In order to achieve this result, however, the grain-refining agent, which is added in very small amounts compared to the molten host metal, must not only be well distributed initially throughout the molten metal but it must remain well distributed until the molten host metal solidifies.

In order to obtain good initial distribution of a grain refining or alloying agent, there has been used heretofore an aluminum master alloy containing the agent in uniform distribution throughout the aluminum base. When this master alloy in solid form is added to a mass of the molten aluminum prior to casting, the solid metallic aluminum component of the master alloy melts and liberates the grain refining or alloying agent. In order to effect more uniform initial distribution of the treating agent throughout the molten aluminum, the master alloy heretofore has been added as relatively small discrete masses, but the smaller these discrete particles the more they contain combined oxygen from atmospheric oxidation and the larger the particles the more they tend to segregate in the bottom of the mass of molten aluminum.

Proposals have been made heretofore for introducing one metal into a stream of another molten metal, but these proposals have either intentionally or inadvertently introduced the extraneous metal of such composition, or in such a manner, as to cause disruption of the stream. In many casting operations, such turbulence as is evidenced by disruption of the metal stream is considered intolerable or at least undesirable because it promotes dissolution of the ambient at mosphere, or of one of its components, in the molten metal.

I have now devised a method of inoculating molten metals and alloys with a metallic treating agent such as a grain refining or alloying agent which avoids the problems experienced heretofore yet assures uniform distribution of the treating agent or of one of its constituents throughout the metal to which it is added. The method of the invention comprises pouring the molten metal from a source thereof into a confined troughlike passageway to form a stream of the molten metal flowing through the passageway, and simultaneously feeding into the turbulent mass of molten metal flowing in the trough a flow-disturbing solid rodlike supply of the treating agent, the rodlike supply of the agent being introduced into the stream of molten metal in such manner as to effect a significant disturbance of the flow without impairing the integrity of the stream. The rod is supplied at a rate not in excess of that at which it is consumed in the flowing molten metal in the trough, and the resulting inoculated molten metal is discharged into a casting zone. By feeding the master alloy into the molten metal flowing in the trough at a predetermined rate, the molten metal discharged to the casting zone will contain a predetermined proportion of the treating agent uniformly distributed therethrough.

The molten metals which can be treated by the method of the present invention include substantially pure metals and their alloys such, for example, as aluminum, zinc, copper, iron, nickel, and the like, which are to be cast.

The useful master alloys in practicing this invention are those generally considered to be compatible with the molten metal to which they are added. The treating agent component of the master alloy can be any metal, alloy or intermetallic compound which, when added to the molten host metal or alloy, causes the molten metal to be modified as desired. The grain refining and alloying agents generally used heretofore for the aforementioned metals and alloys are useful in practicing the present invention. These agents include boron, titanium, zirconium, niobium, tantalum and titanium, and zirconium, niobium, and tantalum borides and are contained in a metal base in amounts generally not exceeding about 10 percent by weight. For example, representative aluminum-base master alloys of this type are 0.5 to 5 percent boron, balance aluminum; 2 to 10 percent titanium or zirconium, or total of both, balance aluminum; and 0.1 to 5 percent boron, 2 to l0 percent titanium or zirconium, or total of both, balance aluminum. Similar grain-refining agents, except for their base metal, can be used for grain refinement of metals other than aluminum, but additional agents such as master alloys containing manganese and iron can be used for copper, brass and bronze. All of these treating agents are applicable for steel and other nonferrous metals, not only for grain refinement but for general alloying purposes. The composition of the master alloy should, of course, be as uniform as possible in order to obtain the maximum benefit of the unifonn distribution of the grain-refining agent throughout the molten host metal obtained by practice of the method of the present invention.

The added agent is supplied in the form of a solid rodlike body, that is, either in the form of a rod, wire, bar or strip, formed by any conventional procedure such as direct chill and continuous casting, extrusion, rolling, or rolling and drawing operation. The cross section of the rodlike body can be circular, oval, square, oblong, etc., but should offer a substantial impediment to the flow of the molten metal stream so as to effect a significant disturbance in its flow. In general, these rodlike forms range advantageously from about one-eighth inch to about one-half inch in diameter or maximum cross section, but smaller and larger sizes can be used effectively. The actual size is determined by the rate at which the master alloy is to be supplied to the molten metal, a relatively small diameter rod or wire being preferred for any predetermined supply rate in order to offer a maximum surface area: mass ratio for most efiicient consumption of the master alloy in the flowing molten metal. The rods can be any convenient length such, for example, as SOO-foot sections wound on a reel. However, the individual sections can also be welded end to end to obtain a virtually endless rod which is particularly desirable for supplying the treating agent to a continuous casting operation.

Pursuant to the invention, the rodlike master alloy is fed directly into a confined path of the molten metal flowing from a source thereof to a casting zone.

A trough is commonly used for carrying the molten metal from a holding furnace to a casting zone, and in such a case the rodlike master alloy is fed to the molten metal flowing through this trough. In operations where the trough delivers the molten metal to a distributor box from which the molten metal is distributed to a number of casting molds, the rodlike master alloy is advantageously introduced into the molten metal in the distributor box. Because of the problem of potential settling and resulting segregation of the treating agent or of one of its components in the molten metal in a casting mold, it is common practice to maintain the temperature of the molten metal in the holding furnace or casting ladle as close as practicable to the freezing point of the metal and thus limit the amount of superheat in the metal as it is cast. Consequently, it is presently preferred to introduce the master alloy rod or wire into the hottest zone of the turbulent molten metal stream, this generally being the zone closest to the point of delivery of the molten metal from the holding furnace or supply ladle. In addition to the advantage of greater heat availability in this zone for melting the base metal component of the master alloy, it has been found that this zone frequently is the one characterized by the greatest degree of circulation and therefore the zone most conducive to consumption and thorough admixing of the master alloy in the molten metal. The circulation of the molten metal as it flows through the remainder of the trough, or through branch troughs from a distributor box, as described hereinbefore, further effects and maintains thorough and uniform distribution of the treating agent in the molten metal as it is discharged to the casting zone.

In order to promote disturbance of the flow of the molten metal so as to increase its circulation in the trough without disruptive turbulence, it has been found particularly advantageous to feed the rodlike treating agent obliquely upstream into the stream of molten metal. As shown in the single FIGURE of the accompanying drawing, the rod 1 is fed through the open top of the trough 2 and in a direction toward the source 3 of the stream 4. In this way, the relatively blunt cross section of the rod is presented to the flow of molten metal and causes a significant disturbance in its flow pattern. The portion of the rodlike mass of agent immersed in the mo]- ten metal immediately downstream of this leading end tends, by surface tension between the molten metal and the rod, to hold the flowing molten metal in contact with the rod for a substantial distance downstream from the disturbance caused by its leading end and thus counteracts any tendency for the disturbance to cause disruption of the integrity of the stream. The sidewalls of the trough confine the flow of the stream beyond the point of addition of the agent and help to perpetuate throughout the length of the trough the disturbed flow, and the resulting mixing, produced upstream pursuant to the invention. Where the nature of the molten metal permits greater flow disturbance, the rod of treating agent can be introduced at a right angle into the stream, but in this case the flow rate of the stream, the surface tension of the molten metal, and the size of the profile of the rod should be such that substantially non-disruptive flow of the molten metal is obtained. Disturbed flow is desirable pursuant to the invention because it promotes circulation within the confined stream and insures uniform distribution of the treating agent throughout the host metal, but disruptive flow wherein the integrity of the stream is significantly impaired, as by breaking it up into smaller streams, is to be avoided because it promotes dissolution of one or more components of the ambient atmosphere in the molten metal. The formation and maintenance of a single coherent stream of molten metal from the pouring stage through the additive stage to the casting zone is thus made possible pursuant to the practice of the invention. When the rod is fed obliquely into the stream but in the same general direction as the flow in the stream, the molten metal flows smoothly around the surface of the rod and the end of the rod that is eroded by melting resembles that of a melting icicle and fits smoothly into the flow of the metal. This latter arrangement will supply the agent to the molten metal with a lesser degree of flow disturbance than the other arrangements previously described but nevertheless do so with a sufficient degree of distribution and effectiveness particularly when the length of the trough downstream of the point of entry of the rod is sufficient to make use of the disturbance is flow created by the entering rod.

The rodlike master alloy can be readily fed to the molten host metal stream by the type of feed device used for supplying welding or brazing wire to a welding or brazing operation. The device advantageously is capable of a variable feed rate so that the supply of master alloy to the molten metal can be closely and accurately metered. If desired, the feed device can also include a preheating element, such as an electric induction coil surrounding the rodlike master alloy, close to its point of introduction into the flowing stream of molten metal.

The following example is illustrative but not limitative of the practice of the invention:

A %-inch diameter rod of the master alloy composed of 5 percent titanium and 1 percent boron, both by weight, and the balance aluminum, was fed at the rate of inches of length per minute into a downwardly sloping casting trough in the form of a single coherent stream of molten aluminum flowing at the rate of 420 pounds per minute. The rod was fed obliqueten metal was supplied from a furnace at a temperature of about 1,380 F., and the temperature of the molten aluminum at the point of introduction of the master alloy rod was about 1,300 F. The circulation of the molten metal at this temperature completely consumed the master alloy rod as fast as it was, fed to the trough, and the disturbed but nonturbulent flow of the thus-inoculated molten metal, reflected by the walls of the trough as it moved along the remainder of the trough to the casting zone, produced a cast metal containing 0.002 percent by weight of titanium, as a grain refining agent in the form of titanium diboride and titanium-aluminum (TiAl thoroughly and uniformly distributed throughout the resulting grain-refining aluminum casting.

It will be appreciated, accordingly, that the method of the present invention is particularly effective for inoculating molten metals and alloys with an alloying or grain refining agent in such manner that the agent is uniformly distributed throughout the molten metal by the time it reaches the casting zone and remains similarly uniformly distributed throughout the metal in the final casting. Although the method will find its maximum use in grain growth control and alloying operations, it can also be used to introduce the same or other metals and intermetallic compounds of various metals and elements into a molten metal so as to aid in cooling the metal in a direct chill casting operation and thus avoid cracking of the casting at high casting rates.

I claim:

1. The method of continuously introducing a metallic treating agent into a molten metal which comprises pouring the molten metal from a source thereof into a confined troughlike passageway to form a stream of the molten metal flowing through the passageway, simultaneously feeding into the stream of molten metal flowing in the passageway a solid rodlike supply of the agent, the rodlike supply of the agent being introduced obliquely into the upstream portion of the stream of metal molten with the end of the rod facing upstream into the flow of molten metal so as to effect a significant disturbance of the flow without impairing the integrity of the stream and to permit the sidewalls of the trough to perpetuate said disturbance during flow of the molten metal throughout the remainder of the length of the trough in order to insure complete melting and assimilation of the treating agent in the molten metal stream, the rod being supplied at a rate not in excess of that at which it is consumed in the flowing metal in the trough, and discharging the resulting molten metal into a casting zone.

2. The method of continuously introducing a metallic treating agent into a molten metal which comprises pouring the molten metal from a source thereof into a confined troughlike passageway to form a stream of the molten metal flowing through the passageway, simultaneously feeding into the stream of molten metal flowing in the passageway a solid rodlike supply of the agent, the rodlike supply of the agent being introduced obliquely into the upstream portion of the stream of molten metal with the end of the rod facing downstream into the flow of molten metal so as to effect a significant disturbance of the flow without impairing the integrity of the stream and to permit the sidewalls of the trough to perpetuate said disturbance during flow of the molten metal throughout the remainder of the length of the trough in order to insure complete melting and assimilation of the treating agent in the molten metal stream, the rod being supplied at a rate not in excess of that at which it is consumed in the flowing molten metal in the trough, and discharging the resulting molten metal into a casting zone.