US2192032A - Method for improving the magnetic properties of ferrous alloys - Google Patents

Description

Feb. 27, 1940. DAHL AL 2,192,032 METHOD FOR IMPROVING THE MAGNETIC PROPERTIES OF FERROUS ALLOYS Original Filed Feb. 15, 1956 2 Sheets-Sheet 1 Fig. l.

0 I Inventors: Otto Dahl, Franz Pawle by 6) 4 Then Att orne y.

Feb. 27, 1940. O. DAHL El AL. 2,192,032 METHOD FOR IMPRQVING THE MAGNETIC PROPERTIES OF FERROUS ALLOYS Original Filed Feb. 15, 1936 2 Sheets-Sheet 2 Inventors: Otto Dahl, Franz Pawlek y Their Attorney.

Patented Feb. 27,

METHOD FOR IMPROVING THE MAGNETIC PROPERTIES OF FERROUS ALLOYS Otto Dahl, Berlin-Friedman, and Franz Pawlek, Bcrlin-Niederschoneweide, Germany, assignors to General Electric Company, a corporation of New York Original application February 15, 1936, Serial No.

s PATENT OFFICE 64,138. 26, 1938, Serial March 11, 1935 Divided and this application October No. 237,156. In Germany 3 Claims. (01. 148-4) This application is a division of our copending application, Serial No. 64,138, filed February 15, 1936, now Patent 2,145,712, January 31, 1939, and entitled Method for improving the magnetic properties of ferrous alloys.

In order to obtain a uniform rise of magnetization throughout a wide field-strength range, as

well as a nearly complete saturation at low field strengths, it has been proposed to produce in magnetic materials, an ordered grain texture such as can be obtained by certain rolling and annealing processes. For instance, magnetic iron-nickel alloys can be cold-rolled, prior to the final annealing, with a reduction of thickness amounting to more than 90%, preferably more.

than 95%, after which the material is annealed at temperatures above the recrystallization limit. As a result of this treatment, an ordered position of the crystallites is obtained in the plates after the annealing, and this ordered position has an extraordinary favorable influence on the magnetic properties. 1

The present invention is an improvement of these methods and consists in subjecting the alloys during cooling, after the final annealing, to the influence of a magnetic field, in such a way that, depending upon whether the magnetization curves, as a function of the field strength, are to have a steeper or fiattershape, the-alloys are subjected either to the influence of a longiudinal' or transverse magnetic field. The terms, longitudinal and transverse, here, imply respectively the direction of rolling or the direction at right angles to the direction of rolling. While the influence of a magnetic field applied during mens which, for thepurpose, of an ordered grain structure, have been subjected, prior to the final annealing, to a cold rolling resulting in a decrease in thickness exceeding 90%. On the other harid. the curves denoted by b represent the results obtained with specimens that had been subjected to a lesser amount of cold rolling such as had been resorted to formerly. The indexes l to 3 indicate whether the alloy specimens were subjected to a magnetic field during the cooling and, if so, to what magnetic field. Specimens with index I were cooled without the application of a magnetic field; the specimens with index 2 were cooled with the simultaneous application of a longitudinal magnetic field, while specimens with index 3 were cooled with the simultaneous application of a transverse magnetic field.

Fig. 1 refers to a binary iron-nickel alloy with 40% nickel and iron; Fig. 2 refers to a binary iron-nickel alloy having equal parts of iron and nickel, while Fig. 3 refers to an iron-nickelcobalt alloy with 45% nickel, 30% iron and 25% cobalt. The alloy specimens were produced together and in exactly the same manner. All were obtained from a casting produced in a high frequency furnace from technically pure materials;

they were then reduced to a thickness of 0.3 mm. by way of florging or hot or cold rolling with intermediate annealing above the recrystallization temperature. The specimens of group b were subjected, during the last cold rolling to a decrease in thickness amounting to that is, a decrease in thickness which is close to the limit of the conventional rolling process used in connection with such alloys. In contrast to this, the specimens of group a were, in order to attain a good grain structure, subjected to a last cold wider induction range. On the other hand, the

simultaneous application of a high degree of cold I rolling and of a transverse magnetic field during cooling, results always in a magnetizing curve which is rectilinear through an unusually wide field-strength range. In particular,-the magnetization characteristic of the alloy represented in Fig. 2, which consists of equal parts of iron and nickel, is steeper than that of the magnetization curve of the alloy according to Fig. 1, which alloy has 40% of nickel and 60% of iron. Thus, if for certain reasons, a linear magnetization characteristic is desired through a field-strength range which is as wide as possible. the alloy. ac-

cording to Fig. 1, should be given preference to the alloy according to Fig. 2. This condition will always obtain whenever the field strength cannot be reduced at will by the selection of a small number of turns in a coil. However, if this reduction is possible, so that when dimensioning a coil, only the induction need be considered, the alloy, according to Fig. 2, should be given preference over the alloy of Fig. 1, for with the alloy, according to Fig. 2, the same eiTect can be obtained with a smaller amount of material.

Fig. 3 shows that the application of the method, according to the invention, is not limited to binary iron-nickel alloys, but that it can be also successfully applied to the iron-nickel-cobalt alloys. The improvement of the steep rise of the characteristic by the simultaneous application of a high degree of cold rolling and a longitudinal 'magnetic field during the cooling is, here, not so marked as was the case with the application of the longitudinal magnetic field in connection with the binary iron-nickel alloys, for the application of a magnetic field alone, permits obtaining a very steep curve. On the other hand, the improvement of the linear rise through a wide field-strength range, by applying simultaneously a high degree of stretching and a transversal magnetic field, is here quite considerable; Fig. 3 shows that the uniform rise begins practically at the point of origin and that it continues until saturation sets in. The hysteresis loop returns with the low remanence of a thousand gauss, nearly as linearly as it rises. Such an alloy is of major importance for communication engineering, for instance for Krarup lines, and also for transmitters, for a magnetic body consisting of that particular alloy, operates practically without harmonics. For this reason, an alloy oi' that composition and treatment must be primarily applied in all those cases which deal with circuits in which the harmonics have a disturbing eflfect, even at a slight amplitude. Such fields of application exist always in those cases mitting range .of the other channel and maythilissentail a mutual interference of both channe 4 The application or the object or the invention is not limited to the alloys which have been chosen by way of example. The entirely diiierent composition of the alloys in Figs. 1 and 2 on the one hand, and in Fig. 3 onthe other hand, indicates plainly that the method according to the invention will permit a considerable influencing of the magnetic properties in nearly all ferromagnetic substances. Which one of the known alloys must be chosen for any particular purpose, can be determined from case to case by a simple test. The method is particularly advantageous in connection with all those alloys in which the application of the conventional an- What we claim as new and desire to secure by Letters Patent of the United States, is:

1. A method for improving the magnetic properties of alloys consisting of nickel and iron which comprises cold working the alloy to effect a reduction in thickness of more than 90%, annealing the alloy and during cooling subjecting it to the influence of a transverse magnetic field.

2. A method for improving the magnetic properties of alloys consisting of iron and metal from the group nickel and cobalt which comprises cold working the alloy to efiect a reduction in thickness of more than 90%, annealing said alloy and during cooling" subjecting it to the influence of a transverse magnetic field.

3. A method for improving the magnetic properties of alloys consisting of iron and metal from the group nickel and cobalt which comprises cold rolling the alloy toefiect a reduction in thickness of more than 90%, annealing the rolled metal and during cooling subjecting it Y to the influence of a magnetic field which is applied in a direction transverse to the direction in which the metal was cold rolled.

OTTO DAI IL. FRANZ PAWLEK.

Images