US2405455A - Permanent magnet - Google Patents

Description

Patented Aug. 6, 1946 PERMANENT MAGNET John D. Seaver, Marblehead, Mass, assignor to General Electric Company, a corporation of New York No Drawing. Application February 12, 1943, Serial No. 475,653

' Claims. (01. 175-421) The present invention is a permanent magnet. It is one of the objects of the invention to provide a machinable permanent magnet which has desirable properties and employs relatively small percentages of ingredients such as cobalt and molybdenum. Permanent magnets made of iron, cobalt and molybdenum usually have an alloy content of about 29%. According to the present invention the total content of cobalt and molybdenum is preferably about 20%. Moreover the present alloy is equal in magnetic properties and definitely superior in machinability to the prior iron, cobalt, molybdenum permanent magnets.

In carrying out the present invention, I employ an alloy which may contain about 2 to 8% cobalt, .5 to 3.5% copper, 10 to 20% molybdenum with the remainder iron except for impurities such as manganese, silicon and carbon. Generally the carbon content should not exceed about 25%, and silicon and manganese should not exceed respectively about .75% and 2%. Although the manganese and silicon are impurities an advantage may be obtained if the ratio of manganese and silicon is about 2 or slightly greater than 2:1. The presence of these ingredients in this ratio reduces the tendency of the alloy to crack during subsequent heat treating. While the present alloy is machinable the presence of carbon in the alloy is detrimental to that operation and should be eliminated as far as possible. A preferable composition consists of about 5% cobalt, about 2% copper, about molybdenum with the balance iron except for impurities such as manganese, silicon and carbon. In the preferred composition the maximum manganese content should not exceed about .60% and the silicon should not exceed about .30%.-

The alloy is prepared by melting the ingredients in a high frequency induction or other suitable furnace. A fluid slag forms on the surface of the melt and should not be permitted to run into the mold as the metal ispoured. This can be avoided by melting the alloy in an inert atmosphere, or in a vacuum, or by other well known means. The alloy may be cast in sand molds.

To obtain the most desirable permanent magnet properties the alloy is given a solution heat 2 treatment, for example by heating it for at least one hour to a temperature of 1300 0.1-15" C. in a suitable protective atmosphere, for example a reducing atmosphere such as hydrogen, carbon monoxide, converted city gas, or the like. The casting is quenched from the solution temperature preferably in boiling water. At this stage the alloy is soft and easily machinable. Thereafter it is age-hardened by heating for about one-half to sixteen hours at about 600 to- 700 C., preferably for two hours at a temperature of about 660 C.:l0 C.

An alloy containing 5% cobalt, 2% copper, 15% molybdenum with the remainder substantially all iron except for impurities such as carbon, silicon and manganese, has a coercive force about 225, a residual of about 10,150 and a maximum energy of about 1,130,000.

What I claim as new and desire to secure by Letters Patent of the United States, is: i

1. A permanent magnet containing 2 to 8% cobalt, .5 to 3.5% copper, 10 to 20% molybdenum with the remainder substantially all iron with the exception of impurities.

2. A permanent magnet containing 2 to 8% cobalt, .5 to 3.5% copper, 10 to 20% molybdenum, not more than 2%'manganese, not more than 35% silicon, and not more than ,25% carbon, the remainder iron.

3. A permanent magnet containing 2 to 8% cobalt, .5 to 3.5% copper, 10 to 20% molydenum, not more than 2% manganese, not more than .75% silicon and not more than 25% carbon, the remainder iron, the manganese and silicon being present in the alloy in the ratio of about 2:1.

4. A p rmanent magnet consisting of about 5% V JOHN D. SEAVER.