US2307512A - Process of making copper base alloys - Google Patents

Description

Patented Jan. 5, 1943 2.307.512 I raoorss or MAKING corrannasn armors James M. Kelly, Traflord, Pa., assignor to Westinghouse Electric &

East Pittsburgh, Pa.

sylvania Manufacturing Company, a corporation of Penn- No Drawing. Application November 5, 1941,

Serial No. 417,876

1. Claim. 75-153)- This invention relates to copper base precipitation hardening alloys and particularly to the process of making them.

In the making of copper base precipitation hardening alloys, predetermined quantities of a1- loying elements, such as chromium, cobalt, silver, iron or other suitable elements are added to a copper melt. If oxygen is present in the copper melt, and in commercial practice such is invariably the case, the oxygen combines with the added alloying elements to form oxides. In many cases, the oxides thus formed are soluble and remain in the resulting alloy. In other cases, the

oxides formed float to the surface of the melt and the resulting alloy does not have the required composition.

Heretofore many attempts have been made to completely deoxidize a copper melt prior to adding the alloying elements to the melt. Certain deoxidizing elements have been accepted by the trade but all of the known deoxidizers have certain limitations. For example, silicon, vanadium, lithium, aluminum and titanium have been employed as deoxidizers, and while satisfactory for removing oxygen from the melt, they are unsatisfactory in that each combines with the oxygen to form complex oxide films which tend to produce cold-shuts in the finished casting of the resulting alloy.

Other known deoxidizers have one or more disadvantages in that they do not always removeall traces of oxygen, have too high a solubility in the solid state, are not sufliciently dense to remain in the copper melt but instead float thereon, give a violent reaction when added to the melt, or, whencombined with oxygen the result ing oxides remain within the melt instead of floating on the surface thereof where they can be removed. These disadvantages or faults, while tolerated by the trade for lack of something better, are objectionable and make it diflicult to commerciallyproduce and duplicate the copper base precipitation hardening alloys.

It is an object of this invention to provide for completely deoxidizing a melt of copper in the mliaking of copper base precipitation hardening a oys.

Another object of this invention is to utilize tungsten as a deoxidizer in the making of copper base precipitation hardening alloys;

Other objects of this invention will become apparent from the following description when taken in conjunction with the appended claim.

In the making of copper base precipitation hardening alloys, such as those known to the industry under the trade name of Cupaloy, and which comprise copper, chromium and silver, as disclosed and claimed in Patent No. 2,033,709, issued to F. R. Hensel et a1., or Cuferco, having copper, cobalt and iron as essential elements thereof, as disclosed and claimed in my Patents Nos. 2,147,844, 2,169,187, 2,169,190 and 2,210,670, all of which are assigned to the assignee of this invention, the copper base is first melted independently of the alloying elements. Thi procedure is followed in the making of all of the known copper base precipitation hardening alloys, whether the precipitation hardening agent be one or more of the elements chromium, cobalt, iron, silver, zirconium, thorium or the like.

In melting the copper, the furnace atmosphere is usually adjusted to I provide slightly oxidizing conditions. This may be accomplished by adjusting the gas-air ratio of the furnace atmosphere or by any other suitable means. After the copper is heated to a temperature between 1250 C. and 1300" C., about 1% of cupric oxide is preferably added to the molten copper to insure the presence of oxygen therein and to eliminate any hydrogen that may be absorbed by the melt. Thus the gases within the molten alloy are essentially oxygen.

In accordance with this invention, the copper melt is then completely deoxidized prior to the adding of the alloying elements thereto. The deoxidizer utilized is tungsten andmay be in the form of a tungsten alloy, or as pure tungsten metal. If the deoxidizer is in the form of an alloy, then care must be taken that the presence of the element other than tungsten is not objectionable in the resulting alloy. Preferably, the tungsten is in the form of a tungsten metal powder not coarser than mesh to facilitate the distribution thereof in the coppermelt for obtaining the combination thereof with the oxygen in the melt. Because of its high density ranging between 18.6

and 19.1, the tungsten is readilysubmerged inthe melt without any accompanying violent reaction. Instead it is found that the reaction occurring between the tungsten and oxygen is a serene, spontaneous reaction.

After the tungsten is added to the copper melt, the melt is agitated to effect the distribution of the tungsten throughout the melt with the resulting formation of the oxides. The oxide formed is tungstic oxide (W03) which has a density of 7.16 and floats to the surface of the melt in the form of a flufly typeof finely divided oxide distinguished by its bright yellow color. By agitating the melt, it is thought that. in' addition to combining with the oxygen in the melt, that any excess amount of the deoxidizer in the melt reacts with the oxygen of the atmosphere at the surface of the melt, the turbulenceof the melt exposing fresh surfaces of the copper bearing tungsten to the surface atmosphere to remove the residual tungsten therefrom.

The fine state of subdivision of the oxide, in addition to its low density, facilitates removal of the oxide from the melt, for it is found that upon holding the melt for about five minutes that the fluffy yellow oxide disappears, leaving the surface of the melt clean. This is because the tungstic oxide sublimes at approximately 700 C. whereby the surface of the melt is completely freed of the oxide, leaving a clean gas-free molten charge of copper.

The alloying elements are then added to the completely deoxidized melt of copper in the proportions and compositions required to form a particular alloy. Where the melt has been completely deoxidized, as described hereinbefore, an excellent recovery of the alloying elements added to the deoxidized melt is effected. For example, in the making of a precipitation hardening copper base alloy having copper, cobalt and iron as essential alloying elements thereof, where the copper melt has ben deoxidized by the addition of 1% of ferrotungsten alloy, the ferrotungsten alloy containing 82% of tungsten and 18% of iron, and alloying elements consisting of 1% of cobalt and 375% of iron are added to the deoxidized copper melt, an alloy having a composition of 98.15% copper, .95% cobalt, .92% iron and .005% tungsten is obtained. Here it is seen that only small but effective amount up to 1% of tungsten as the deoxidizer. Excellent results have been obtained where only 30% of tungsten metal pow der having a mesh size of about 200 is utilized for eliminating the oxygen from the melt.

That tungsten does not have the disadvantages through for effectively eliminating the oxygen present in the melt. The fact that the tungsten may be added to the copper melt without encountering a violent reaction is also of benefit, since it reduces the hazards in the foundry. Further,

no special provisions are necessary for removing .05% of cobalt is lost in the making of the alloy,

while only .01% of iron is unrecovered. The residual tungsten remaining in the alloy is so slight that it is doubtful if it has any beneficial effect. In other cases, where the melt is agitated while being held for a longer time it is impossible to obtain any determination of residual tungsten-in the resulting alloy. Similar results are obtained in making the copper-chromiumsilver alloys known to the trade as Cupaloy referred to hereinbefore. Castings of the alloys made by employing tungsten as the deoxidizing material show a sound internal structure free from porosity when cut open.

In making the copper base precipitation hardening alloys, it is preferred to employ from a the oxides formed when the tungsten combines with the oxygen within the melt with the exception of holding the melt for a short period of time sufficiently long to permit the sublimation of the oxides.

Although this invention has been described with reference to the making of certain copper base precipitation hardening alloys known to the trade, it is, of course, not to be limited thereto, as it is of value in the production of all copper base precipitation hardening alloys.

I claim as my invention:

In the process of making copper base-alloys, thesteps of, adding from a small'but efiective amount up to 1% of tungsten metal powders having a mesh size not coarserthan 100 mesh to the copper melt prior to the introduction of the alloying components, agitating the melt to distribute the tungsten throughout the melt and efiect the combining of the tungsten with the oxygen of the melt to form tungstic oxide (W03), the tungstic oxide formed floating to the surface of the melt, and holding the melt for a period of time sumcient to effect the sublimation of the tungstic oxide to leave the copper melt oxygenfree.

JAMES M. KELLY.