US2687954A - Alloy - Google Patents

Description

Patented Aug. 31, 1954 ALLOY James M. Lohr, Morristown, N. J., assignor to Driver-Harris Company, Harrison, N. J a corporation of New Jersey No Drawing. Original a ry 1, 1952. her 19, 1951, Serial No.

1949, Serial No.

2,581,420, dated Janua this application Octo 4 Claims. 1

This invention relates to alloys and more particularly to alloys for electric resistance units.

In the manufacture of electrical resistance units, an alloy having the property of resisting oxidation at high temperature is essential. The alloys forming the subject matter of this invention are characterized by ability to resist oxidation and by a prolonged life, exceeding that of other known alloys when used under high temperature conditions. Since the introduction of nickel-chromium-iron alloys as electric resistance units, many developments have occurred that have improved their resistance to oxidation. In a number of prior patents I have disclosed and claimed various alloying additions of calcium, zirconium and aluminum which greatly improve the life of heating elements. It has also been proposed to add rare earth metals, such as cerium, to nickel-chromium-iron alloys to improve the life of the heating elements.

I have found that when calcium and aluminum as well as rare earth metals are added to nickelchromium-iron alloys, better results are obtained than if the calcium, zirconium, aluminum group or the rare earths are used alone. The present invention is, therefore, directed to the addition of small quantities of the rare earths with calcium and aluminum to nickel-chromium-iron alloys. I have found that such combination of addition elements greatly increases the period of life of nickel-chromium-iron alloys when employed under conditions where they are subjected to high temperatures. The alloys forming the subject matter of the present invention may also contain small amounts of either silicon or manganese or both of these elements. The rare earth metals may be added as misch metal" having an approximate composition of 45 percent cerium, 30 percent lanthanum, 20 percent ytterbium and didymium. Although it is convenient to add the rare earth metals in the form of misch metal," I do not restrict myself to the use of this material as one or more of the rare earth metals may be added singly and its effect is of a similar nature. The additions may be used to advantage with the nickel-chromium-iron alloys of which the best known examples are the alloys of 30 to 70 percent nickel, to 25 percent chromium, balance iron.

This application is a division of my copending application Serial No. 117,510, filed September 23, 1949, now Patent No. 2,581,420. The claims of this application are directed to alloys containing 30 to 50 percent nickel and 10 to 25 percent chromium, and more specifically to alloys containing pplication September 23, ,510, now Patent No.

Divided and 2 substantially 35 percent nickel and substantially 20 percent chromium.

In the examples hereinafter described, the additions were made to the alloys consisting of substantially 35 percent nickel, 20 percent chromium and balance iron. Rare earth metals, such as misch metal, with calcium and aluminum may be added to such alloys with or without silicon. The proportions of nickel in such alloys may vary from 30 to 50 percent and the chromium from 10 to 25 percent with the balance iron. Employing nickel-chromium-iron alloys of these proportions, I have added calcium, aluminum and misch metal in the quantities or amounts hereinafter mentioned.

In preparing alloys containing the addition elements above mentioned, the quantities of such addition elements are subtracted from the iron content. For example, when additions are made to base alloys containing 30 to 50 percent nickel, 10 to 25 percent chromium, the final alloys will contain 30 to 50 percent nickel, 10 to 25 percent chromium, the addition elements calcium, aluminum and the rare earth metals in the percentages hereinafter stated, and the balance iron. While the proportions of calcium, aluminum and rare earth metals may vary within certain limits, I have found that the best results are obtained when these materials are present in the final alloys within the following limits:

Percent Calcium .001-20 Aluminum .01-1.0 Rare earth metals Trace-0.50

If the alloys contain manganese, silicon, or carbon, they may be present within the following limits:

Percent Manganese .02-4.0 Silicon .20-3.0 Carbon 0.25 max.

While alloys having the properties desired to a very high degree are obtained within the limits before mentioned, the preferred range of addition elements is as follows:

The alloys so prepared have been tested for resistance to oxidation at high temperature by a modification of the method approved by the American Society for Testing Materials Accelerated Life Test for Metallic Materials, B76-39. In conducting such test, :the silky is produced in the form or a wire, drawn to a diameter approximately .025" and tested at a temperature of 1950 F., instead of a temperature of 2050 R, which is the temperature of the standard ASTM method for testing the 60 nickel, 15 chromium alloys, The useful life" in hours for wire of substantially 35 percent nickel, fldparcentnchromium containing calcium, zirconium and aluminum as addition elements, balance iron, is of the order of 100 hours. The useful life" of the alloys of the present invention, according to the above described test, is of the order '0! 400 hours. Thus, the useful life is increased around 300 percent over that of the alloys containing the calcium, zirconium, aluminum group when the rare earth metals are added with calcium and aluminum in the proportions herein-stated.

The alloys are prepared in the usual manner by placing the ingredients in a bath, heating until the alloying elements become molten and then pouring. In adding rare earth metals to a molten bath, it is necessary to add considerably larger quantities than will be found in the cast metal because they vaporize readily and pass out of the bath. In many instances, with additions of the rare earth metals only a spectrographic trace of one or more of the rare earth metals is found in the cast material. The presence of such traces, however, in combination with calcium and aluminum, greatly increases the oxidation resistance of the alloys. added in amounts sufficient to leave a residue in the cast alloys up to .2 percent but in most instances the use of such amounts is not necessary.

In the test referred to above the increase or electrical resistance at temperature with time is The rare earth metals maybe 4 plotted and an increase of 10 percent in resistance is known as the useful life." The life of the tiejsted specimen to burn-out is known as total ilclaim:

l. A nickel-chromium-iron alloy consisting substantially of percent nickel, substantially 20 percent chromium, .001 to .20 percent calcium, .01 to 1.0 percent aluminum, a trace to .50 percent of a, rare earth metal, balance essentially iron.

2. A nickel-chromium-iron alloy consisting substantially of 35 ,percent nickel, substantially 20 percent chromium, .001 to .07 percent calcium,

-01 to .40 percent-aluminum, a trace to .20 percent of a rare'earth metal, balance essentially iron.

3. A nickelchromium-iron alloy consisting substantially of 35 percent nickel, substantially 20 percent chromium, .00il to .20 percent calcium, .01 to 1.0 percent aluminum, a trace to .50 percent cerium and lanthanum, balance essentially iron.

4. A nickel-chromiumiron alloy consisting substantially of 35 percent nickel, substantially 20 percent chromium, .00 to .07 percent calcium, .01 to .40 percent aluminum, a trace to .20 percent cerium and lanthanum, balance essentially iron.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,941,648 Armstrong Jan. 2, 1934 2,581,420 Lohr Jan. 8, 1952 FOREIGN PATENTS Number Country Date 488,926 Great Britain July 12, 1538

Claims (1)

1. A NICKEL-CHROMIUM-ION ALLOY CONSISTING SUBSTANTIALLY OF 35 PERCENT NICKEL, SUBSTANTIALLY 20 PERCENT CHROMIUM, .001 TO .20 PERCENT CALCIUM, .01 TO 1.0 PERCENT ALUMINUM, A TRACE TO .50 PERCENT OF A RARE EARTH METAL, BALANCE ESSENTIALLY IRON.