US2343481A

US2343481A - Permanent magnet steel

Info

Publication number: US2343481A
Application number: US440875A
Authority: US
Inventors: Kenneth L Scott
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1942-04-28
Filing date: 1942-04-28
Publication date: 1944-03-07
Anticipated expiration: 1961-03-07

Description

Patented Mar. 7, 1944 PERMANENT MAGNET STEEL Kenneth L. Scott, Western Springs, 111., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application April 28, 1942, Serial No. 440,875

7 Claims.

This invention relates to permanent magnet steel and a method of making such steel, and more particularly to permanent magnets of such steel and a method of making the same.

Carbon manganese steel is well known as a permanent magnet material, although other steels such as chromium, cobalt, or tungsten have been more commonly used in recent years. However, now because of restrictions on the quantity which may be used of certain critical'materials, many of the ordinary magnet steels are nolonger generally available and therefore resort must be had to combinations involving the use of smaller quantities of the restricted materialsv or to materials not restricted. Thus, carbon manganese steel is again being pro-posed as a permanent magnet material.

Some difliculties have been experienced with carbon manganese steel due to the necessity of water quenching and the consequent rapid cooling of the steel, which sometimes causes serious cracking and warping. It is generally understood that by rapid cooling through water quenching the precipitation of carbides is held at an incipient stage and that this produces the desired magnetic properties. However, rapid cooling tends to cause cracking and warping.

It is an object of the present invention to provide an improved permanent magnet steel and an improved method of making the same.

In accordance with one embodiment of this invention, a small percentage of chromium is added to the carbon manganese'steel melt and then the alloy is quenched in oil. An oil quench affords a substantially slower cooling rate than that afforded by a water quench, thus reducing warping or cracking of the steel.

The above described and other objects and advantages of this invention will be apparent from the following detailed description:

Carbon manganese steel as used for permanent magnets heretofore had in general the composition of .5% to 1% carbon. .5% to 1.25% man-' ganese and the rest iron. While this composition produced a permanent magnet steel having satisfactory magnetic properties, the steel had to be water quenched to prevent rapid precipitation of carbides and consequent loss of magnetic properties. Because of the physical properties of this composition, rapid cooling had the undesirable effect of causing cracking and warping of the steel. By adding .2% to .'75% chromium to a melt of carbon manganese steel of the composition just described, it appears that the former rate of precipitation of carbides is sufi'iciently reduced so that slower cooling in an oil quench is feasible. Slower cooling reduces greatly the warping and cracking of the steel heretofore encountered. It further appearsthat an alloy comprising .5% chromium, .6% carbon, .85% manganese and the rest iron, gives satisfactory magnetic and physical properties for many purposes.

The carbon, manganese, chromiumand iron may be first melted together and the .alloy thus produced cast into ingots and fabricated into the desired shapes. During casting and fabrication, the alloy cools slowly and carbides are precipitated in an excessive amount with a consequent loss of magnetic properties. The fabricated alloy is therefore reheated sufliciently to cause the carbon to reenter solution with the iron. With an alloy of the composition indicated above as satisfactory, a temperature of about 1450 F. appears to be slightly above the critical point and sufiicient to cause the carbon to reenter solution with the iron. It will be understood that with other alloys having different proportions, the

critical temperature may also be different. The I temperature is maintained long. enough to permit substantially all of the carbon to reenter solution with the iron. Then the alloy is quenched in an oil quench, thus providing a rate of cooling enough lower than tha afiorded by water to pre-' vent warping and cracking,while at the time 'mium, .5% to 1% carbon, .5% to 1.25% manganes and the rest iron together to form an alloy, heating the alloy to cause the carbon to enter solution with the iron and then cooling the alloy in an oil quench.

2. A method of making a permanent magnet comprising the steps of melting .5% chromium, .60% carbon, .85% manganese and the rest iron together to form an alloy, heating the alloy to cause the carbon to enter solution with the iron, and then cooling the alloy in an oil quench.

3. A method of making a permanent magnet comprising melting .2% to 375% chromium, .5% to 1% carbon, .5% to 1.25% manganese and the rest iron together to form an alloy, fabricating a magnet, reheating the alloy to cause the carbon to enter solution with the iron, and then cooling the alloy in an oil quench.

4. A method of making a permanent magnet which comprises heating an alloy of .2% to 175% chromium, .5% to 1% carbon, .5% to 1.25% manganese and the balance iron, to cause the carbon to enter solution with the iron and then quenching the alloy in oil.

5. A method of making a permanent magnet which comprises heating an alloy of .5% chromium, .60% carbon, 35% manganese and the balance iron, to cause the carbon to enter solution with the iron and then quenching the alloy in oil.

6. A permanent magnet comprising .2% to .75% chromium, .5% to 1% carbon, .5% to 1.25%

5 manganese and the rest iron, the alloy having 10 mium, .60% carbon, .85% manganese and the rest iron, the alloy having been heated to cause the carbon to enter solution with the iron, and cooled in an oil quench.

KENNETH L. SCO'I'I.