US2564844A - Copper-iron-chromium alloy - Google Patents

Description

Patented Aug. 21, 1951 UNITED STATES PATENT OFFICE COPPER-IRON-CHROMIUM ALLOY Allen W. Hodge,\Columbus, Ohio, assignor, by

mesne assignments, to Battelle Development Corporation, Columbus, Ohio, a corporation of a Delaware 7 Claims.

This invention relates to copper base alloys containing iron and small amounts of chromium, and its principal object is to provide an alloy which has exceptionally high strength after cold working combined with good resistance to corrosion, and which also has good enough electrical conductivity to permit its use in electrical equipment.

It has been found that the addition to copper of substantial amounts of iron along with small amounts of chromium produces copper base, ternary alloys which can be processed to have particularly good tensile strength and corrosion resistance. In the production of this alloy, pure copper is desirable but ordinary commercially pure copper is satisfactory. The addition of from 5 to per cent iron to the copper effects a very noticeable strengthening of the resulting alloy. More than 30 per cent iron, however, lowers the conductivity of the resulting alloy to a point beyond that which is normally found usable in electrical equipment, that is, below per cent I. A. C. S. (International Annealed Copper Standard). Below 5v per cent iron, the tensile strength of the resulting alloy drops ofl rapidly.

The chromium addition to the instant alloy not only increases the corrosion resistance, but has a strengthening effect out of proportion to the amount of chromium added. Since the effect of the chromium is dependent upon the iron content, all percentages of chromium are stated based upon the amount of iron present. When chromium is present in amounts equivalent to from 4 per cent to 7 per cent of the iron present in the alloys, very good corrosion resistance and high tensile strength are obtained in the resulting alloy. Good tensile strength may be obtained, however, when as little as 2 per cent chromium based on the iron content is employed, but these alloys have only fair resistance to corrosion. It is undesirable to have more than 7 per cent chromium based on the iron content present, because these alloys have proven to be very diflicult or impossible to fabricate.

As in most alloys, there is normally present small amounts of a deoxidizer, such as magnesium, aluminum or silicon. It is to be understood that these ingredients are not an essential part of the present alloy, but are more in the nature of adventitious elements which have no detrimental effect on the alloy.

There are a number of methods of making the copper base alloy containing iron and chromium which comprises the present invention which 2 will be readily apparent to those skilled in the art. One method which has been found to be very satisfactory for producing the instant alloy comprises melting the iron (preferably electrolytic scrap or other pure iron) and copper together in a magnesium oxide crucible, using a slag cover of lime, alumina and silica sand. Magnesium-copper in suificient quantity to deoxidize the melt is added shortly before pouring, and is completely stirred in with an iron rod. Immediately after the addition of the deoxidizer, chromium is added, either as ferrochrome or as chromium metal. The melt is poured into an ingot mold provided with a suitable refractory hot-top at a temperature of approximately 2,750 E: F. Immediately after pouring, the hottop may be covered with an exothermic compound to help reduce the amount of pipe formed in the ingot.

In order to enable one skilled in the art to more easily practice this present invention the following examples are set forth:

Example 1 In accordance with the melting procedure above set forth, 4.2 pounds of iron, 0.23 pound of chromium, 10 pounds of copper, and 0.60 pound magnesium copper (10% Mg) were melted to produce a heat having an analysis of 28.4 per cent iron, 0.92% chromium, and 0.24% magnesium with the balance copper. The ingot produced from this melt was scalped to clean the surface and then heated in a furnace at 1,550 F. for one-half hour. The ingot was next hot forged to a 4-inch square after which it was reheated to 1550 F. for one-half hour. The %-inch square was then further reduced by hot rolling to a /32 in. square in six passes and reheated to 1550 F. for one hour, followed by a water quench. The surface of the resulting square was cleaned by sand blasting and further reduced by cold rolling to 0.170 in. square in 7 passes. After again heating to 1550 F. for one hour in a natural gas atmosphere and water quenching the piece, the surface was then sand blasted and pickled in a conventional pickling bath. Employing conventional means for an nealing, quenching and cold drawing the metal, the piecewas then cold drawn through dies to produce wires sized to 27 gage, 28 gage and a 29 gage. These Wires were tested and results of these tests are shown in the following table wherein the tensile strength is set forth in p. s. i. and the conductivity in per cent of that of pure copper (international Annealed Copper Standard) The electrical conductivity is improved by aging the alloy for about 1 hour at 1050 F. and cooling slowly to room temperature. The wires in the example given were aged during drawing.

Example 2 The electrical conductivity may be further improved somewhat by a step-wise aging treatment, although at a cost of some loss in tensile strength. For example, 10-gage wire produced as in Example 1 was annealed for 1 hour at 1830 F.. quenched and aged 1 hour at 1200 F. This wire was drawn to IB-gage and again aged for 1 hour at 1020 F. and 2 hours at 840 F. This wire was drawn to 24-gage and aged 2 hours at 750 F., after which it was drawn to 2'7-gage and given a stress relieving treatment of A -hour at 570 F, After this treatment, the wire had the following A charge containing 1.46 pounds of iron, 0.13 pound of ferrochrome, 12.84 pounds of copper, and 0.60 pound of magnesium copper was melted in accordance with the procedure above described. This heat had an analysis of 11.8% iron, 0.17% chromium, 0.28% magnesium, 0.01% silicon, and the balance copper. The ingot thus produced was treated in accordance with the procedure set forth in Example 1 and-wires having a diameter of 27 gage, 28 gage, and 29 gage were produced as above set forth. Tensile strength tests and conductivity tests were made upon these wires and the following table sets forth the data thereby obtained.

Tensile Diameter, in. Strength, ,2 3 1 s l. '1 mos .0l30 (27 gage). 141, 000 50. 2 .0117 (28 gage) 158, 000 39. .0106 (29 gage) 1 159. 000 48. 4

It is apparent from the above table that less than 2% chromium based on iron content has only a minor effect upon the tensile strength and conductivity of the resulting alloys.

Example 4 period of several weeks, after which it still re tained its luster. A specimen of copper-iron alloy without chromium turned completely black in this time after similar exposure. Likewise a sample was placed outside in the atmosphere, accompanied by several commercial bronze and brass specimens. Although this specimen finally tarnished, it remained bright much longer than the other specimens, and did not tarnish as heavily at any time.

Proper processing of the alloy comprising the present invention results in a metal having approximately 400% of the tensile strength and about 35 per cent of the electrical conductivity of pure copper. Such a combination of mechanical strength and electrical conductivity can have important application in the electrical industry. The corrosion resistance of the copper-ironchromium alloy exceeds that of pure copper when the amount of chromium is between four and seven per cent of the weight of iron in the alloy. As previously pointed out, three per cent chrornium based on the iron content produces an alloy having a good tensile strength but low corrosion resistance.

It is apparent from the above-detailed description of the present invention, that the present alloy is advantageous in that it produces an alloy which combines exceptionally high tensile strength in the cold-worked condition with satisfactory conductivity properties. This alloy is furthermore of value in that it is highly resistant to corrosion. Because of this unique combination of properties, the instant alloy is remarkably suited for electrical contacts or other electrical uses wherein high resistance to corrosion and high tensile strength must be combined with good electrical conductivity. The instant alloy is, of course, adaptable to many uses other than electrical, such as springs, hinges, door knobs, and many other uses wherein it could replace bronze.

What is claimed is:

1. A copper-base alloy consisting of from 5 to 30% iron, chromium in an amount equivalent to 3 to 7% of the iron present, and the balance copper.

2. A copper-base alloy consisting of 28.4% iron, 0.92% chromium, and the balance copper.

3. A copper-base alloy consisting of from 5 to 30% iron, chromium in an amount equivalent to 4 to 7% of the iron present, and the balance copper.

4. A- heat-treated and worked, corrosionresistant, copper-base alloy comprising essentially from 5 to 30% iron, chromium in an amount equivalent to from 3 to 7% of the iron present, and the balance copper, said alloy having about 400% of the tensile strength and about 35% of the electrical conductivity of pure copper.

5. A heat-treated and worked copper-base alloy having a corrosion resistance exceeding that of pure copper and comprising essentially from 5 to 30% iron, chromium in an amount equivalent to from 4 to 7% of the iron present, and the balance copper, said alloy having about 400% of the tensile strength and about 35% of the electrical conductivity of pure copper.

6. A heat-treated and cold-worked corrosionresistant, copper-base alloy wire consisting of 28.4% iron, 0.92% chromium, 0.24% magnesium as deoxidizer, and the balance copper, and having an I. A. C. S. electrical conductivity not less than about 35% of that of copper, and a tensile strength of at least about 189,000 p. s. i.

ductivity not less than about 39% of that of 5 copper and a tensile strength of at least 141,000 p. s. i.

ALLEN W. HODGE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Hensel et a1. June 27, 1939 Schwarzkopf Oct. 15, 1940 FOREIGN PATENTS Country Date Great Britain May 12, 1927 France Mar. 31, 1927 France Feb. 11, 1931

Claims (1)

1. A COPPER-BASE ALLOY CONSISTING OF FROM 5 TO 30% IRON, CHROMIUM IN AN AMOUNT EQUIVALENT TO 3 TO 7% OF THE IRON PRESENT, AND THE BALANCE COPPER.