US2839396A - Alloy - Google Patents

Description

ALLOY Peter R. Marsh, Montclair,

N. J., assignor to Driver- Harris Company, Harrison, N. .L, a corporation of New Jersey No Drawing. Application February 10, 1956 Serial No. 564,614

4 Claims. (Cl. 75-171) This invention relates to alloys, and more particularly to an alloy of nickel and chromium, containing appreciable amounts of aluminum and appreciable amounts of silicon, and a method of making the alloy.

One object of the invention is to produce an alloy which has a higher specific resistance than the standard nickel'chromium and nickel-chromium-iron alloys, and a higher resistance than the standard low temperature coefiicient of resistance alloys for use in low temperature resistors. Another object is to produce a heating element alloy having an improved life at standard testing temperatures and a life above these standard temperatures equivalent to the 80 nickel-20 chromium alloy at the standard temperatures.

A number of alloy systems, while having the property of potentially high resistivities, are found to involve extreme difliculties in their working and processing due to low ductility and non-malleability characteristics, and also are known to have the undesirable property of considerable growth when used at high temperature.

J. M. Lohr, in his U. S. Patent No. 2,533,735, has shown that when three percent of aluminum was added at the expense of an equivalent amount of nickel in the ductile and non-grown 80-nickel-20 chromium alloy, the resulting specific resistance, after a rapid 1700 to 2000 F. anneal and air quench, is increased from 640 ohms/c. m. f. for the basic 80 nickel-20 chromium alloy to 740 ohms/c. m. f. for the 77 nickel-20 chromium-3 aluminum alloy. By following the heat treatment as disclosed by Lohr, but in a temperature range of 900 to 1200 F. for 1 to 20 hours the latter resistance was increased to approximately 800 ohms/c. m. f. Although such an alloy is applicable for low temperature resistors with the property of a negligible temperature coeflicient of resistance, the alloy is not suitable as a high temperature heating element. In order to go to higher resistivities and to maintain heating element qualities, higher aluminum and silicon additions were tried to accomplish the objective of this invention. Although the melting point is lowered by such additions, the alloy can be operated nearer to its melting point without early failure due to the formation of selective but complex oxides of aluminum, silicon, and chromium forming an adherent and protective oxide film for enhancing the life at temperature. However, when attempts are made to produce such an alloy, the same undesirable properties common to the other high resistivity alloy systems, namely, relative non-forgeability and non-malleability, were encountered.

Melts containing a minimum of 4% aluminum and 1.3% silicon produced wire having a resistivity of about 840 ohms/c. m. f. which, upon response to heat treatment as disclosed by Lohr, rose to around 950 ohms/c. m. f. Attention then was focused on additions of 5% aluminum and /z% silicon, as it was determined that further additions of these elements results in an alloy having at least 1000 ohms/c. m. f. These experiences, however, made it obvious that there is a critical limit of total aluminum andsilicon additions after which nonmalleability occurs and which acts as a barrier to obtain desirable yields of t the higher resistivity material, unless "satisfactory mel-ting and forging processes were found to produce sound alloy ingots and bars.

' In order to eliminate non-rnalleability and increase the yield, the melt was fully deoxidized and degassified before the addition of-aluminum and silicon so as to minimize the formation of alumina and silica. In this manner :sound ingots were produced which, on forging, have a workingrange of 2000 to 2300 F. The only defects found were, in some cases, the formation of edge checks which were subsequently eliminated by the addition of small amounts of rare earth metals to the ladle, the addition being approximately 0.1%.

The details for the successful melting and forging of alloys consisting of 4 to 6% aluminum, 1 to 2% silicon, 20% chromium, 0.03 to 0.25% carbon, 1% maximum of manganese, residual amounts of magnesium and rare earths, and balance essentially nickel, are as follows:

All of the nickel and chromium are melted down under a ground glass lime slag. When all of the metal is melted, a dry dross forms which is skimmed oif with the slag. Carbon is then added in small amounts at a time until the bath is quiet and a porosity test shows no signs of gas. The temperature of the bath is then adjusted to allow for the exothermic reaction caused by the next addition so that the bath does not overheat. At this point the mag nesium is added, which effectively deoxidizes the bath. Immediately prior to tapping the furnace the aluminum and silicon are added and just before the melt is poured from the ladle the rare earth addition is made. The forging is carried out starting at 2300" F. and continuing to 2000 F., light blows being employed. at all times. The rolling to rod or strip is accomplished in the conventional manner.

Examples of life tests and analyses of the alloy as compared to the conventional nickel-20 chromium alloy type are as follows:

An alloy containing 0.04% carbon, 0.30% manganese, 1.08% silicon, 19.52% chromium, 4.92% aluminum, balance essentially nickel, had a useful life of 404 hours when tested at 2150 F., the temperature employed in testing the 80-20 nickel-chromium alloy.

Alloys containing 1.30% silicon, 4.27% and 5.2% aluminum and the other elements substantially in the same percentages as stated above showed a useful life of 325 hours and 315 hours, respectively. As compared to these results the useful life of an 80-20 alloy, when tested at 2150 F. is of the order of 200 hours.

By means of the above disclosed procedure, a workable electrical heating and resistance alloy is produced, having a higher specific resistance, higher life at standard heating temperatures, and higher operating temperature than can be accomplished by using the conventional 80 nickel-2O chromium alloy and without encountering undesirable growth characteristics.

While I have described the alloy as consisting essentially of the enumerated elements with the balance essentially nickel, the presence of small amounts of other elements, originally added to the melt as deoxidizers or present as impurities in one of the elements of the alloy, in amounts which have no appreciable effect on the properties and characteristics of the resulting alloy is to be considered to be within the scope of the invention.

1 claim 1. A ductile, low-growth, high electrical resistance and negligible temperature coefficient of resistance alloy consisting essentially of 15% to 25% chromium, 4% to 6% aluminum, 1% to 2% silicon, 0.03% to 0.25%

nickel.

2. A ductile, low-growth, high electrical resistance and negligible temperature coeflicient of resistance alloy consisting essentially of substantially 20% chromium, 4% to 6% aluminum, 1% to 2% silicon, 0.03% to 0.25% maximum carbon, 1% maximum manganese, balance essentially nickel.

3. A ductile, low-growth, high electrical resistance and negligible temperature coefficient of resistance element consisting essentially of 15% to 25% chromium, 4% to 6% aluminum, 1% to 2% silicon, 0.03% to 0.25% carbon, 1% maximum manganese, balance essentially nickel.

4. A ductile, low-growth, high electrical resistance and negligible temperature coefficient of resistance element 15 H consisting essentially of substantially 20% chromium, 4% to 6% aluminum, 1% to 2% silicon, 0.03% to 0.25 maximum carbon, 1% maximum manganese, bal' ance essentially nickel.

References Cited in'the file of this patent UNITED STATES PATENTS 2,174,919 Kay Oct. 3, 1939 10 2,304,353 Grifiiths Dec. 8, 1942 2,460,590 Lohr Feb. 1,1949

2,533,735 Lohr Dec. 12, 1950 FOREIGN PATENTS Australia Nov. 13, 1941

Claims (1)

1. A DUCTILE, LOW-GROWTH, HIGH ELECTRICAL RESISTANCE AND NEGLIGIBLE TEMPERATURE COEFFICIENT OF RESISTANCE ALLOY CONSISTING ESSENTIALLY OF 15% TO 25% CHROMIUM, 4% TO 6% ALUMINUM, 1% TO 2% SILICON, 0.03% TO 0.25% CARBON, 1% MAXIMUM MANGANESE, BALANCE ESSENTIALLY NICKEL.