US 2027994 A
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Jan. 14 1936. T. MISHIMA MAGNET STEEL CONTAINING NICKEL AND ALUMINIUM Filed Jan. 20, 1932 Y 2 Sheets-Sheet 2 YUV/$525774 Patented Jan. 14, 1936 UNITED STATES MAGNET STEEL CONTAININGNICKEL AND ALUMINIUM Tokushichi Mishima, Ochiai-machi,
Toyotama-gori, Tokyo, Japan Application January 20, 1932, Serial No. 587,822 In Japan March 9, 1931 4 Claims.
The invention relates to a strong permanentv magnet comprising to 40% nickel, 7 to 20% alummium and the remainder iron. It has for its object to economically obtain a permanent l 5 magnet which possesses an extremely high coercive force and a strong residual magnetism Without being quenched after casting and preserves these qualities without being influenced by thermal changes and mechanical shocks and has small specific gravity and non-corrosive property.
Heretofore many magnet steels, such as tungsten, chrome, and chrome manganese-steels have been known. However, in order to obtain the best magnetic property, they must necessarily be quenchedand consequently they often suier from deformation and quenching cracks.- Befsides, not only their coercive force and residual magnetism are low, but also during the use of 20 these magnets their coercive force and residual y magnetism decrease gradually.
The high-cobalt steel alone has a considerably high coercive force and strong residual magnetism. However, it has the disadvantages that it must be forged and heat-treated which is dimcult, and in addition its cost is very high so that its general uses are greatly hindered.
Nickel is a ferromagnetic substance while aluminium is a paramagnetic one, and it has been 30 known to all that these metals give no beneficial effects upon the coercive force and residual mag,- netism of steels when they are added to the latter individually.
Now nickel steels containing 5- 30% nickel are called irreversible steel by(which is meant that they become `transformed at-appreciably higher temperatures on heating than on cooling. That is, the Ac2 point (the temperature at which magnetism is lost on heating) is considerably higher than the Arz point (the temperature at which magnetism begins to obtain on cooling), and the difference amounts to over 400 C. For this reason, when cooling high-nickel steels from high temperature above the Acz point, the Arz transformation points are suppressed and the steels become non-magnetic at room temperature due to the retention of y-iron. This is the reason Why scientists insist upon, and metallurgists give asro sent, to the fact that the nickel steels can not be used for magnet steels.
According to the invention it is possible to ecoi preserve these qualities permanently Without being inuenced by thermal changes and mechanical shocks. For this purpose the invention provides for a permanent magnet containing iron as its. chief component, with the addition of 540% 5 nickel and 'l-20% aluminium.`
In the accompanying drawings. Figs. 1 to 6 explain the principle upon which the invention is based; Figs. 1 to 3 being curves showing the relation between the temperature and the intensity of magnetization; Figs. 4 to 6 show the relation between the thermal dilatation and the temperature corresponding to Figs. l to 3; and Fig. 7 shows the demagnetizing curves, that is the fourth quadrant of the hysteresis curves comparing the magnetic properties of the steel according to the invention and those of other known steels.
Now, the reason why according to the invention a permanent magnet having high coercive force and strong residual magnetism can be obtained without being quenched, is explained with reference to the accompanying drawings.
Take a nickel alloy or an irreversible nickel alloy having such relation between the intensity of magnetization and temperature as shown in Fig. l, and add to it a certain amount of aluminium. Then, as shown in Fig. 2 the point Arz at which magnetism begins to obtain on cooling comes near the point Acz at which magnetism commences to be lost on heating; by then increasing the amount of aluminium and attaining a proper amount, the point Ara, as shown in Fig. 3, coincides with the point Acz the irreversible steel thus changing into a reversible one. It will also be seen from Fig. 4, that the irreversible nickel steel" has the point Aca, where the steel changes from a state to y state on heating, considerably higher than the point Ara, where the steel changes from Iy state to a state on cooling. And the temperature-difference between Aca and Ara is in fact over 400 C.
According to the invention the phenomena are entirely different and proceeds as follows: with the gradually increased amount of aluminium, the point Ars comes, as shown in Fig. 5, nearer and nearer to the point Aca, and with such a definite addition as corresponds to Fig. 3, the point A3 disappears entirely as shown in Fig. 6. Thus the irreversible nickel steel" can be changed into a reversible one by the addition of aluminium, while the transformation point A3 entirely disappears. It can therefore easily be seen that according to the invention high coercive force and strong residual magnetism are obtained without 2 the steel being quenched after casting, or by annealing it at proper temperature after casting.
Several examples showing the compositions and magnetic properties of the alloy according to the invention are illustrated below:
Chemical composition Magnetic proporties (per cent Alloy No. C i Resduil oerc ve magno Iron Nickel Mfn force (Hc) ism (88u58) (Br) (gauss) I Rest. 18.0 l0. 120 9, 100 65. 3 24. 5 10. 0 240 9, 600 57. 0 30. 8 12. 0 9, 400
In Fig. 7, the curves I, 2 and 3 show the characteristic properties of the magnet steels corresponding to the above alloys I, II and III, while the curves 4, 5 and 6 show those of tungsten, chrome, and chrome manganese-steels respectively. As clearly seen in this figure, all the magnet steels previously known have poor coercive force, whereas the steel according to the invention has an extremely high coercive force Hc and a strong residual magnetism Br. Therefore the product of these two qualities (BrXHc) is obviously far greater than those of other known steels. It is noted that the presence of carbon of below 1.5% and/or a small amount of impurities does not materially affect the magnetic properties of the alloy according to the invention.
As described above, according to the invention the nickel steel, formerly entirely disregarded as a permanent magnet steel, can now be easily changed into a strong permanent magnet steel by an addition of a proper amount of aluminium, which is a cheap material. The steel Permanent magnets made of alloys which eml body additional elements such as vanadium, molybdenum, tungsten, manganese, copper, cobalt and chromium and which have similar properties necessary for permanent magnets form the subject-matter respectively of the following divisional applications: 673,796, May 31, 1933; 35,207, Aug. 7, 1935; 35,208, Aug. 7, 1935; 673,795, May 31, 1933; 35,209, Aug. 7, 1935; 9,685, March 6, 1935.
In this case also it is noted that the presence of carbon of below 1.5% and/or a small amount of impurities does not materially affect the magnetic properties of the alloy.
1. A permanent magnet comprising 5 to 40% nickel, 7 to 20% aluminium and the remainder iron.
2. A permanent magnet comprising 5 to 40% nickel, 7 to 20% aluminium and the remainder substantially iron.
3. A permanent magnet comprising 5 tc 40% nickel, 7 to 20% aluminium, from trace to 1.5% carbon and the remainder iron.
4. A permanent magnet comprising 5 to 40% nickel, 7 to 20% aluminium, from trace to 1.5% carbon and the remainder substantially iron.