US2036576A - Process for making alloys - Google Patents

Description

priate temperature,

high recovery of Patented Apr. 7, 1936 I UNITED STATES 2,036,57 PROCESS FOR MAKING ALLOYS Charles Hardy, Pelham Manor, N. Y., assignor to Hardy Metallurgical Company, a corporation of Delaware No Drawing. Application August 25, 1933, Serial No. 686,777

' 1 Claim. (01. "25-433) This invention relates to the production of metal alloys and has for an object an improved method of combining an alloy metal with a molten mass of different metal. More particularly, the invention relates to a process for the production of alloys involving the reduction of metal oxides and the simultaneous incorporation of the resulting metals in molten masses of different metals. Another object of the invention is to provide a process in which the heat of reduction of alloy metal oxide is utilized for obtaining a high recovery of metal from the oxide undergoing reduction-and for more readily controlling the temperature of the molten mass of metal comprising the alloy metal and the base metal.

According to some heretofore customary methods for the production of alloys, the alloy metal is added to the base metal either in relatively pure form or in the form of a. relatively rich alloy of itself with the base metal. Other methods heretoforepracticed involve the addition of the alloy metal in the form of an oxide to a slag covered molten bath of the base metal, and subsequent reduction of the oxide by various means to incorporate the alloy metal in the base metal.

Various disadvantages attend the use of these heretofore practiced methods,

might be mentioned the extremely high cost of some alloy metals in the pure form, and the relatively high cost of others, the loss of heat accompanying the "reduction of the alloy metal at a place remote from that at which it is to be used,

and the difficulty with which certain alloy metal oxides are reduced from a slag and the relatively low recovery of metal therefrom.

I have discovered that if the powder of a metal having a strong aflinity for oxygen be intimately mixed with a comminuted alloy metal oxide, and the resulting mixture be heated to an approas, for example, by immersing it in a bath of molten metal, an almost instantaneous reduction of the alloy metal oxide to the metallic form occurs, and the alloy metal thus reduced is simultaneously incorporated in the base metal to form the alloy. I have further found that manifold advantages accrue to the use of such a process. The relatively low-priced oxide is used in place of the substantially pure alloy metal, the heat evolvedjn the reduction is con served in the molten mass of base metal, and a alloy metal is obtained.

I have found that a large number of the common alloy metals may thus be reduced from their oidrles, and a considerable number of reducing metals that possess the desired characteristics of high oxygen aflinity may be obtained upon the market in commercially pure form and at relatively low cost. For satisfactory results, the reducing metal must in general be used in a finely divided or powder form, or in other form presenting a large reactive surface. Reducing metals possessing the requisite affinity for oxygen are, generally speaking, of low atomic weight, are highly electropositive, and are usually members of the so-called alkali or alkaline earth groups, but other metals may be used in some cases. In any event, the reducing metal must possess a greater affinity for oxygen (or a higher heat of reduction) than the alloy metal used in conjunction therewith. Among the reducing metals which I have found to possess all the essential requisites and which I have successfully employed are:

Calcium, lithium, potassium, magnesium, ba-

rium, caesium, sodium, strontium. These metals may be employed in a relatively pure form, or they may be used as a mixture or alloy of two or more of them, or they may be mixed or alloyed with other metals.

Almost all of the common alloy metals may be reduced from the oxide by the use of a reducing metal such as described above. Oxides of the following alloy metals I have found to be effectively reduced by the use of the above mentioned reducing metals:

Titanium, manganese, berylium, cobalt, vanadium, zirconium, thorium, chromium, tungsten, phosphorous, nickel, silicon.

The oxide product used for reduction may be either a single metal oxide, or it may be a mixture of the oxides of two or more metals in any desired proportion, depending only upon the ,alloy, desired to be formed. For best results, the

oxide should be reasonably pure, that is, free from any undesirable contaminants. The presence of such contaminants, however, will not affect the operativeness of the process, but will.

is desirable for two reasons. In the first place, the reducing metal is thus introduced into the molten metal bath in close contact with the oxide to be reduced, and the reduction is enabled to take place before vaporization of the reducin metal, mechanical agitation, or other disturbance will separate the reagents. In the second place, both the reducing metal and. the oxide are frequently of lower specific gravity than the molten metal comprising the bath into which they are to be introduced. In carrying out the method of the invention, the mixture of reducing metal and oxide is preferably totally immersed in the molten bath of base metal in order to more thoroughly incorporate the reduced alloy metal in the molten bath and to bring about more complete recovery of the alloy metal from the oxide. Suitable immersion may be accomplishedby vigorously propelling a compressed adherent body of mixed reducing metal and alloy into the molten bath. My United States Patent No. 1,915,824

describes a suitable means for accomplishing this type of immersion.

The base metal-for the alloy may be of any of the common metals, or alloys thereof. Among the many which may be used iron, copper, tin, lead, zinc, aluminum, steel, brass, bronze, etc. might be mentioned. The molten bath of any of such metals may be held in any appropriate container such as furnace ladle, refining furnace, or the like.

In practicing the invention, I prepare the oxide of an appropriate alloy metal, and intimately mix therewith an amount of finely divided reducing metal (preferably calcium). This mixture is then placed in a mold and compressed into the form of a briquette or agglomerate by means of a hydraulic press, a. hand operated screw press,

or any such suitable device at such a pressure that the mixed powders are caused to adhere together, forming a compact mass having a shape determined by the shape of the mold used. The shape of the mold will generally be determined by the manner in which the briquette is to be introduced into the molten mass of base metal. If the propelling orshooting device described in my aforementioned United States Patent No. 1,915,824 is used, the shape may be cylindrical.

The compressed mass is then propelled below the surface of the molten base metal, held in a suitable container; Upon immersion, the compressed mass is quickly heated to the temperature of the molten mass, and, when the temperature has reached the point at which thereduction will commence, the reducing reaction is initiated. The reducing reaction is generally accompanied by a vigorous evolution of heat. The oxide is quickly reduced to the metallic state, and the metal promptly alloys itself with the base metal.

The reducing metal, by the same reaction which frees the alloy metal from the oxide, is itself oxidized and rises to the surface of the base metal, either as substantially pure oxide or after fluxing with other agents which may be present, forming a floating scum which may be removed or allowed to remain to help protect the surface of the metal from oxidation. If the turbulence of the molten bath, induced by convection currents set up by the evolution of heat during the reaction or by vaporized reducing metal bubbling through the molten bath, or by both, is insuffle cient to thoroughly distribute the alloy metal through the molten mass, it may be augmented by the operation of a suitable stirring device,

such, for example, as a stirring rod of some substancethat will not contaminate the alloy. The resulting alloy may be poured into molds, or it may be further treated in any desired manner.

All of the reduction reactions practicable in 5 the process of this invention liberate heat, and this heat is retained by the molten metal bath by virtue of the fact that it is liberated within the bath. In'some cases the amount of heat liberated is enormous, and may raise the temperature of the bath several hundred degrees. Such evolution of heat has several advantages. I have found, for example, that it tends to increase the amountof alloy metal recovered from the oxide over the amount that would be otherl5 wise recovered if the temperature were held at a lower value. It also reduces the amount of metal in the skull, and it tends to place the pouring temperature of the metal-under more accurate control. The metal is also rendered more fluid, and the higher temperature favors the elimination of non-metallic inclusions. Non- .metallic impurities are further eliminated if, as

frequently happens, they flux with the oxide of the reducing metal, as mentioned above.

In preparing alloys by means of this invention, I have found that purification of the alloy may be simultaneously accomplished, particularly when an amount of reducing metal in excess of the amount theoretically required to react with the alloy metal oxide is used. This purification may take the form of reduction of an oxide of the'base' metal which may be present, or it may take the form of elimination .of any other impurities more electronegative than the reducing metal. If the reducing metal will alloy with either the base metal or the alloy metal and such a result is not desired, the excess ofreducing metal employed, if any, should not be greater than the amount required to eliminate impuri-' ties more electronegative than either the alloy metal or the base metal.

In carrying out a method of the invention, a reducing agent which does not form objectionable alloys may be selected. In'such cases, great care in controlling the amount of reducing a ent to be added is not required, and anyreasonable amount in excess of the amount required to effect reduction of the alloy metal compound and the impurities may be employed. Thus, for example, calcium does not react with iron, chromium, or manganese, and, when alloying either or both of the latter two in steel, calcium may be used in reasonable excess. When calcium is employed in such a process, a portion functions to reduce the chromium or manganese oxides, or both, if present, and a portionds vaporized because of the high temperature of the bath. The calcium vapor passes upwardly through the metal, combining with impurities such as oxygen, phosphorous, sulphur, silicates, and some carbon, and removing them from the metal in the form of slag. The extreme reducing conditions resulting from the use of calcium are conducive even to the removal of such impurities as nitrogen.

It will be understood that in the foregoing specification and in the appended claim I use the phrase base metal to describe that metal which forms the base ofthe alloy; thus in bronze containing 10% tin, the balance being copper,-

By alloy metal, I mean that metal which is added 4 a large ratio to the base metal in relatively small amount, and which imparts to the alloy its special characteristics. Thus, in the foregoing examples tin and rhodium respectively would be the alloy metals.

It will be further understood that the terms powder and finely divided, as used in the foregoing specification and the appended claim refer to any physical form of the substance to which the terms are applied w ch will present of surface to volume, irrespective of the manner in which such surface-volume ratio is produced.

I claim: I

A process for incorporating a metallic alloy constituent which is substantially unalloyable with calcium into a molten bathoi iron or steel with which calcium is also substantially unalloyable and simultaneously removing non-metallic impurities from the bath or iron or steel, which comprises briquetting an oxide of a metallic alloy constituent selected from the group consisting of chromium and manganese with metallic calcium, the amount of the calcium briquetted being sumcient to reduce the oxide of the metallic alloy constituent and to combine with the non-metallic impurities to be removed from the bath of base metal, introducing the resultingbriquette into the molten bath, maintaining contact between the molten bath and the briquette until the calcium has reacted with the oxide of the metallic alloy constituent and with the non-metallic impurity to be removed from the bath, and separating the resulting calcium compounds from the bath, whereby an alloy substantially free from calcium is produced.

CHARLES HARDY.