US2112084A - Magnetic material and method of producing the same - Google Patents

Description

A, mmf ET AL 293%@84 TIC MATERIAL AND METHOD OF YHODUCING THE SAME 2 Sheeisheet l Filed Nov.

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and

March y22, 1938.

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A. A. FREY ET AL 2,1%,984-

MAGNETIC MATERIAL AND METHOD OF' PRODUCING THE SAME Filed Nov. l, 1954 2 Sheets-Sheet 2 Hg. i0,

\ Prepared by Process of zhis [nvenian-jlffg: 6400 \`Priar Ari Processed fi/(: 230

o [o z'a o 4a sa Frey and Bitty of Rolling Patented Mar. 22, 1938 UNITED vfs'rifrEs PATENT` @OFFICE MAGNETIC MATERIAL AND METHOD 0F PRoDUclNG THE SAME Application November l, M934, Semi No, iiii) (ill MSH-322i A et high Veg-f low hysteie .A owes ius 'the not ente@ met the one@ through the @sin erystois coincides section oi' magnetization of the m This invention speoieaiy contemplates tn me@ duction oi an espeeiaiy advantageous foz'ni grain oient tion in sheetsof ferro-magnetic inateiieiY which orientation is attained by subjecting the sheet its final stages of thickness reduction to of more specially predetermined cycies oi strm .ntrodiiction and annealing which combine to p Atime a WeH-bereci material il: ioige o due Feeystalizetion. Whiie pi y toese stiains are he t n type pi'oduce by e piensas o.

steriel they may Le titans@ ooi proper mechanical stressing', es a eomtiseci compressing stretch eotioi, of the metei'ioi'duiing the enneai. Those of lits" a @ed vai'iety may comfeiriientig-VA be ntextiel by e, conventional A on at a, tenjoeratue 'oeizetion for the given mote oai-silicon eli' is miiy e mos effective. p e"- ieo' ti'iiolmess oi from about factoiy performed the named oieei' om Y:fossn f disclosed application, Serial 193., by EF. 2i i AL, mbe?? directions of tolling. .E ered metenei in the :ih-estiman the oiigina orientation may be largely pzfesetved during, the iinoi high tempeature'heot treatment which is necessary to develop permeability and reduce hysteresis losses.

When manufactured by ordinary sheet-mill practice, the permeability of laminated silicon steels of the grades commonly utilized in the building of electrical apparatus decreases to relatively low values at the higher densities at which it is found advantageous to operate such equipment, it being ci the order of 250 at a flux density of 16,000 gausses. Such4 material, which may be characterized by large or small grain size depending upon the particular process adopted by the manufacturer, has been made with a guaranteed Q30-cycle watt loss of 0.55 to 0.60 watt per pound at 10,000 gausses for 14 mil sheets. When commercial steel comparable to that above mentioned is produced in accordance with the irnproved process of the present invention, a permeability of as 'high as 6,400 is observed at a flux density of 16,000 gausses. The 60-cycle watt loss at 10,000 gausses maximum flux density is as low as 33 watt per pound for 14 mil sheets of the same material. Since this material may be produced through the application of easily carrled out rolling and annealing operations, and since the enhanced characteristics are best in the direction ci' rolling, it will be appreciated that the process of this invention is one of an ceedingly practical and otherwise vvaluable nature.

The invention, itself, together with additional objects and advantages thereof, will best be derstood through the following description. ci a specific embodiment when taken in conjunction with the accompanying drawings, in which:

Figure l is a representation of the manner in which the atoms are arranged in a single crystal of magnetic material of the class typified by iron;

Fig, 2 is a diagram of curves illustrating certain magnetic characteristics of the crystal of Fig. 1;

Figs. 3 and 4 are representations of magnetic materials respectively having a random and a .preferred orientation of the axes of their grain or crystal structures;

Fig. 5 is a simplified representation of the conventional manner in which a sheet of' magnetic material is passed between two pressure rolls for the purpose of reducing its thickness;

Fig. 6 is a plan view of the sheet of Fig. 5 upon which is indicated two different manners in which the individual crystals in the material appear to orient themselves during the treating cycle of the present invention;

Fig. '7 is a perspective view of an enlarged portion of the sheet of Fig. 6, in which the two types of crystal orientation are further illustrated;

Fig. 8 is a diagram of curves showing the man-A ner in which the degree of the two types of orientation appears to progressively change when the material is subjected to a plurality of cycles of strain annealing;

high preference to the direction of rolling which the magnetic characterist cs of material produced by the process of this invention exhibit;

Fig. 12 is a simplified representation of one form of magnetic testing apparatus which may be utilized to indicate the degree of iibering and type of crystal orientation in sheet magnetic material;

Fig. i3 is a diagram showing how the position .of a circular specimen of the material is varied during test by the equipment of Fig. 12; and

Fig. 14 is a diagram of curves depicting the comparative results of tests made by the apparatus of Fig. 12 upon magnetic steel before and after the annealing operation in one of the treating cycles of the process ci this invention.

Referring to the drawings, 'the relative positoning of the atoms in a single crystal oi magnetic material oi the class typiiied by iron is the 'ffillustrated in Fig. l. In such material, as as in that which is typified 'by nickel, `the al is in the form of a cube having an atom allioys of iron, Lach crystal, termed body-cen tred cubic .tion at the geometric cenner atom indicated in Fig. l at of materials typifiedV by nickel ci :i: kel and another metal, auch as iror., to certain given or critical percentages, eac "tal, which is commoniy termed a face-centered cubic structure, has an additional atom at the center of each of the six faces thereof.

It is known that such cubic crystals possess different magnetic characteristics along different of their axes, which diifeiences are for the structure of Fig. l when in an unstrained condition represented by the magnetization curves of FigV 2. ructure, the direction of easiest to which the curve {B00} of Fig. 2 applies, is along any one of' the lthree tetragonal axes, one oi' which is indicated in Fig. 1 at [|00] and each of which defines a direction perpendicular to a face of the structure. Ranking next in ease of magnetization is any one of the directions from one corner of a face to a diagonally opposite corner of the same fece. The diagonal axis oi' one such direction is indicated in Fig. 1 at llll, which symbol also designates in Fig. 2 the applicable magnetization curve. Ranking last in order of magnetizability as typified by curve [lll] of Fig. 2 is any one of the directions diagonally through the cube determined by' any one of the trigonal axes, one of which is indicated in Fig. l at [I l Il, drawn from one corner of the structure to the diagonally opposite corner.

The characteristics of Fig. 2 are exhibited not only by pure iron, but also by alloys of iron with small amounts of any element that will go into solution therewith. Examples of such elements which is com: structure, in a ter thereof a 20. In the c and combina i are silicon, which, as already indicated, at the,

Such a reversed relation exists.

. lay the showing of I'Eie. e t ci stantially coincide. Increase in the percentage of iron above 20% in a nickel base alloy causes the crystal characteristics to start to approach those depicted in Fig. 2 for the body centered structure.

Magnetic materials known to the prior art have been of the non-bered or randomly oriented grain variety, and when subjected to examination as by an X-ray, elastic deformation, magnetic or optical testing apparatus in manners to be further explained; reveal the condition which is represented in Fig. 3. In that figure, each of the cross-hatched areas 2l represents an individual grain of the metal and the parallel lines drawn through each of these areas are assumed to indicate the direction of easiest magnetization through the grain. Each of these grains is made up of a large number of the cubic crystal structures previously described which are arranged side by side in a regular or parallel manner eifect, therefore, each grain assemblag magnetic characteristics comparable te the individual crystal structures of made up. Consequently, each grain 251 is possessed of the three different types ci a s [liti and [lill in the respective ations ci which the magnetizing characteristics body centered crystal material as depicted the curves of Fig. 2.

For the mentioned random orientation o crystai grains, distribution of the gr" a; substantially the same in all directions and no particular direction can, therefore, be preferred. Consequently, the highest obtainable magnetic property of material of the icri-:bered or randomly oriented grain variety may be expected to ice of some ave" suela as is indicated by the dotted. c Fig. which, in effect, represen. the three full-line curves. a random orientation, or a substant thereto, has been characteristic ci Y netic materials explains the ii characteristics of suoli materials e Wit those prepared in accord teachings ci' the present invention.

substantially the direct,

tion spoken et to pr t tion, t.- ncfg orientation the me einted out, airected by c er more speciali is in which lateral ecignu crystai structures appear to cci direction oi' sheet rolling while iaces cubes which these ed pear to be randomly oriented about this rolling erection The rolling operations may the present invention be performed in ner represented Fig. Si in wllicie materia 2S shown as being aeree a pair ci suitably driven compress which, in greatly magnified form, is represented at 21 in Fig. 6, in a direction parallel to the direction of rolling. As a consequence, certain of the axes of the crystals tend to line themselves up. as is also indicated in Fig. 6, in a direction displaced by 45 from the direction of rolling, and it is thus observed that in a sheet of ferro-magnetic material rolled in a single direction the direction of easiest magnetization is similarly displaced. In the case of silicon steel of the new commercially utilized grades a reduction in sheet thickness of from about, 30% to 60% ley auch rolling has 4been found to be the most eective in introducing the character of strains which are of the greatest advantage in achieving the objects oi the present invention. lin all cases reductions substan tially greater than the small values, of one or two percent, for example, sufficient to eect re crystallization nrcrely are found essential.A

'in effecting this reduction the strip may loe passed through rolling mill a number of times t amount lay which the thickness is reduced L, each be varied as is most it out that when :ma-

.eviieat different result enen. {iti} aires allinea ,For thi. c

allel to the direction materials,

cuestan .a ed by tite ici-oc 7'el-center crystal class` ess of the present invention exhibit their best magnetic characteristics in the direction of rolling and show considerably inferior properties in all other directions. The magnitude of this directional preference is generally indicated by the curves of Fig. 11 to be further discussed.

A proper choice of the initial and final thickness of the sheet to be treated and the conditions under which the rolling and subsequent anneal ing operations are administered is found to effect very favorable enhancements when only onecycle of rolling and annealing is appiied to the material. In many cases, however, it is observed that the greatest improvement may be effected when more than one cycle is applied, and in Fig. 8 there is iilustrated the changes in the two types of crystal orientation which appear to result when three cycles of the treatment of the present invention are applied to a material. in Fig. 9 the corresponding changes in magnetic characteristics in a sheet of 3.25% silicon steel reduced during these three cycles from an initial thickness of 0.075" to 0.010 are likewise shown.

During the first rolling operation of the treat'- ment program of Fig. 8, the type of orientation typified by the crystal 27 of Figs. 6 and 7 is ntroduced into the sheet and practicaly none of the second type typified by crystal 28 appears to result. When subsequently annealed, however, as the strains in the material disappear, most of the iirst type of orientation is found to disappear and a considerable preponderance of the second type is evidenced. Further reduction of the sheet by a second rolling then tends to restore the first type of orientation, which restoration is destroyed or converted into the second type of orientation by a second annealing process, at the endof which the preponderance of this second variety of crystal positioning is considerably greater than at the end of the first annealing period. A third rolling operation in turn likewise tends to restore theorientation to the first type, while a third or final annealing again increases the preponderance of the second type of orientation, bringing it to a. final point 30 which represents a greater degree of completeness than at the end of the first or second anneals, as the curves of Fig. 8 generally indicate.

Considering the application of the treating program of Fig. 8 to the 3.25% silicon steel whose characteristics are depicted in Fig. 9, in the original preparation of this material stock of a commercial grade of 3.25% silicon iron alloy was first melted in a suitable furnace and then allowed to solidify into an ingot. 'I'his ingot was reduced by standard and previously known processes of forging and rough rolling at temperatures of the general order of 1000 C. into a platelike sheet bar. This bar was next hot rolled at a temperature of between 800 C. and 1000 C. into match plates. By hot rolling, these plates were further reduced into strips 0.075" in thickness to which strips the program of strain-annealing referred to was applied.

The first step in this application consistedin rolling at room temperature these 0.075 sheets i to a thickness of 0.050. It may here be pointed out that the critical or most effective percentage of reduction depends upon the amount of alloying constituent, the nature thereof, and the degree of impurity in the alloy.

The 0.050 sheet thus rolled, was then annealed, at a temperature of the general order of 1200" C. for a period of time sufficient to recrystallize the small grains into considerably larger ones. At the end of this first anneal, the B-H or magnetization curve was as depicted at 32 in Fig. 9, While the corresponding permeability curve was asdepicted at 34 in the same figure. The curve last named was derived from the one first named by applying the equa-tion:

Induction (B) in gausses Magnetizing force H in oersteds At a representative density of 16,000 gausses, the material thus treated exhibited a permeability of i068.

To further improve its characteristics, this 0.050" sheet was then subjected to a second cold rolling operation, which reduced its thickness to 0,322, a. reduction cf slightly more than 50%. A second annealing was then effected at a temperature slightly lower than that of the first or of the general order of 1000 C., such reduction being found advisable to prevent excessive grain At the end of this second annealing, the rial exhibited the magnetization character'- depicted by the curve 36 of Fig. 9 and corresponding permeability characteristics depicted by the curve 38. At the previously chosen rep- `tatve fiux density of 16,000 gausses, the @ability was, by the second cycle of rollingannealing, raised to 2285.

A ythird cycie of rolling and annealing was then Permeability (p)== applied during which the material was reduced from a thickness of 0.022" to 0.010, and at the end of' this cycle, the material exhibited the magnetization and permeability characteristics depicted by curves 40' and 42, respectively. As a result of this third cycle of treatment, the permeability at the representative density of 16,000 gausses was raised to 3175. In the pictorial rep resentation of the three cycles of treatment of Fig. 8, this corresponds to the final condition indicated by point 30. The final 0.010 sheet thus prepared was found to exhibit relatively low power loss characteristics, the magnitude of which was considerably less than the same material when processed by prior-art methods.

In a multi-cycle program of treatment of the character just detailed, the temperature and duration of the intermediate annealing operations are preferably so selected as to produce a material of relatively fine grained nature. The

final annealing treatment, however, is found to f be most effective in enhancing magnetic characteristics when carried on at a relatively high temperature, of the general order of 1200 C. for a relatively long period, of the general order of several hours.

When 3.25% silicon steel is reduced to a final thickness of 0.014 and treated under optimum conditions in accordance with the teachings of the present invention, magnetization characteristics depicted by curve 44 of Fig. 10 have been observed. As compared with curve 46, which applies to the same material when processed by prior art methods, the substantial improvement made possible by this invention is at once evident. Whereas such prior art processed material exhibits at 16,000 lines per square centimeter a permeability of about 230, and has a watt loss at a oO-cycle fiux of maximum density of 10,000 gausses of about 0.45 Watt perpound,the same material when properly prepared in accordance with the present invention has, as reference to the permeability curve 48 which applies thereto will show, a permeability at 16,000 gausses of approximately 6400. Although not shown by curve 48, at zero fiux this improved material exu assumed that the materai was permeability of approximately 60,000. At a 60- cycle flux having a maximum intensity of 10,000 gausses the watt loss is only0.33 Wattper pound. In preparing the material whose characterisl tics are depicted by curves M and 48 in Fig. 10, the procedure was as follows: An ingot was prepared by melting stock of 3.25% silicon steel in hydrogen, the presence of which prevented excessive oxidation and removed appreciable quantities of carbon and sulphur. This ingot was forged into `billets which were hot roiled in a commercial strip mill to a thickness of 0.3.25. temperature during the inai ci maintained between 6 e30 L'.

ist/.ip was then pickled by 1min rs iiiiirie a for a time si' 'l te e temperat s en 350 000 15 minutes, and the wine.;

ydrogen a nat-elyA i0 hours was ,Us prepared exhibited risers@ jus'i; pre e., 1 improvement in the iiigii density p meabiiity and power less characteristics wie: le ferro-magnetic material sheets prepared in comience with the present invention exhibit is at f electrical `uses, as aireadv Within D s 01 particular 'precticai advantage. Furthermore. a

caiiy nient oneri,

When d to ether compara-ibis 'proportions of s ctersties have s to 'fie ianner is the treatment which it is desired e in the description thus far given isotropic at the beginning of application of the strain-annealing process which process thus directiy produced the advantageous final form of grain orientation. In addition, however, the treating program of this invention may be utilized to stabilize bering originally in the material as a result of other treatment. Considering as an example of such earlier treatment the before ren ferred to cross-rolling process which produces the best magnetic properties in a direction clis-` 3.0

prf-cassini; in one ci'oss-ieiiin,g, the

250 to in excess or" M0 at the named density.

Larger reductions in 'thickness are observed eiect beneficial results of correspondingly magnitude. Hence, by choosing a proper cyc crcssroiied material eut in a 45 direction,

pcs. f-:f'oieteiy stabiiize e cri Action during i 'ierature "lef tr^"'"^"i' ere are a nuniie denses of the ear" or second type ci orienta 'ii lentsin magi by suitable exciting means (not shown).

material, are as before indicated found to very closely check each other in establishing the presence of the type of orientation under course of discussion. Description of only one of these methods, the magnetic testing one, will therefore here suffice. An equipment for the making and representative results of this magnetic type of test are illustrated by Figs. 12 to 14, inclusive.

The preferred form of equipment shown in Fig. l2 requires that the specimen of material to be tested be in the form of a circular disc indicated at 50. Tins equipment comprises a magnetic circuit which includes a pair of separated pole pieces 52 and 53, between which a very high intensity of uni-directional magnetic flux is caused to flow Supported from a pair of stationary supports, the front one of which is shown at 54, by cooperating knife edges 55, is a yoke structure 51, which carries a member 58 into a suitably formed depression in which the circular specimen 50 of the material to be tested may be fitted and secured by means of screw 60. In the secured position, the sample lies within a Vertical plane which coincides with the direction of iiux passage between the two pole pieces.

By means of an adjusting screw 62, the sample carrying member 58 may be rotated relative to the supporting yoke 51, the amount of such rotation being indicated in degrees by the scale carried by member 5B and a reference line 63 carried by the yoke structure. To this structure is attached a pointer which a rocking or rotation of the structure causes to move along a stationary scale 66.

slidably mounted weight 68 nizay be moved in either direction from the centrai position in which the weight is illustrated.

In preparing the equipment for operation, the sample 50 is so attached to the supporting member 58 that the reference direction of rolling indicated by the dotted arrow l0 of the sheet material from which the sample is stamped is aligned with the' 90 point on the named scale. When this member is set, as illustrated, with the 0 point on its scale coinciding with the supporting yoke structure reference mark 63, the magnetic field will, in passing from one pole piece of the testing apparatus to the other, flow through the sample in a direction which coincides with that in which the sample material was rolled; A shifting of the sample carrying member in the yoke structure then displaces the sample rolling direction from that of the ux flow by an angle represented by e in Fig. i3, which angle is directly indicated by the carrying-member scale. 'Ihe intensity of the magnetic iield produced by the testing apparatus l is sufficiently high to assure that the flux will always iiow through the sample in the same direct path, which, in the illustrated equipment, is horizontal.

For .a material of the completely non-bered or randomly oriented grain variety in which the magnetic characteristics are the same in all directions, there will be substantially no torque set up in the circular test specimen by the passage of ux therethrough, regardless of its rotational position in the apparatus, and the pointer 65 will remain in the indicated mid position as long as the balancing weight 68 is at the center of the graduated arm 61. However, when the sample 50 is of the highly flbered or preferentially oriented grain variety, which possesses preferred directions Also afllxed to the structure is a graduated balancing arm or bar 6T, along which ab of easy magnetization, there will be certain rotational ranges where appreciable values of torque are set up by the flow of magnetic flux therethrough.

The apparatus of Fig. l2 measures for as many rotational settings as it is desiredv to observe this torque in terms of the position along the scale larm 61, to which the weight 68 must be moved,

The torque which results from the action of these forces is the rate of change of magnetic energy with the angle of displacement of these axes from the actual direction of flux flow. l

In Fig. 14 there is illustrated the results of tests made upon samples taken .from a sheet of 3.25% silicon steel prepared by the strain-annealing process of the present invention. Curve 12 applies to the material after subjection to one of the cold rolling operations, while curve 'Il applies to the same material after receiving a subsequent annealing treatment. In` both cases the zero point on the horizontal scale of the curves indicates the direction of rolling o! the particular material from which the specimen 50 was taken.

It will be noted that before the material is annealed, displacement oi the magnetization from the direction of rolling in a given direction causes positive values oi' torque to be set up in the specimen, the maximum of which in thev first half cycle of the curve 12 is indicated by Tml. However, after the material is annealed, comparable displacements between the magnetization and rolling directions set up in the specimen negative values of torque, the maximum of which during the rst half cycle of the curve 14 is indicated at Tmc. It has been observed that in the case of silicon steel of the character under discussion, such a reversal of torque is an indication oi' a. change in the preponderance of grain orientation from the iirst type discussed in connection with Figs. 6 to 8, inclusive, to the second type.

Consequently, if for each of a plurality of tests made on the material at difIerent points in the program of treatment the values of the maximum positive torques Tm observed are plotted above a horizontal reference line and those of the observed negative torques Tmz are plotted below this line there will result a curve of the general shape depicted in Fig. 8, the significance of which curve has already been discussed.

It will be seen that the described process of the' present invention affords means for producing ferro-magnetic material in sheet-like form having characteristics far superior to those attainable through theuse of any process previously known. Furthermore, the basic idea of producing highly preferred crystal orientation in magnetic materials to enhance their permeabllities at high i'lux densities, is capable of broad application and may be extended to materials of the face-centered cubic crystal variety typified by nickel with comparably benecial results. In such application, however, the diierent magnetic characteristics of the individual crystals and their different behaviour when subjected to annealing must, oi' course, be properly taken into account. By the term steel as used throughout the specincation.

.i 2,113,084 applicants have referred to iron-base mixtures containingr carbon in any desired relatively small amount without regard to whether that quantity is\ or is not s ufiiclent to produce pearlite on slow cooling. The term as here used thus includes ma' terials in which the carbon'content may be of the low order of .0.005% oreven less..

Since certain changes may be made in carrying out the above process without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

It is claimed as this invention:

1. In 'the method of making ferro-magnetic sheet material containing silicon and having improved electrical properties, the steps consisting of casting a steel ingot of the desired silicon content, reducing by hot rolling to a thickness appreciably in excess of the iinished size, reducing to the finished size by a plurality of cold rolling operations each of which effects a reduction in ,thickness of between 30% and 60% and thereby introduces substantial strains into the material that establish a preferred orientation of the material grains in which the crystallographic axes of easiest magnetization of the sheet materiel grains is aligned in a direction at an angle to the direc tion of rolling, in annealing after each of said rolling operations prior to the last at a temperature between 800 C. and 1000 C. to relieve these strains and to establish a preferential orientation of the crystallographic axes of the sheet material grains which oier the least resistance to m99- netization in a direction substantially coincident to that in which the sheet was rolled, in. cooiing the sheet after each anneal prior to the next rolling operation, and in a final anneal after the last rolling operation' for a period 'of severalhours at a temperature between 1100 C. and 1300" C.

2. In the methbd of making ferro-magnetic sheet material containing silicon having improved electrical properties-the steps consisting of reducing the material from considerably in excess of its iinal thickness to its nal thickness by a plurality of rolling operations each oi which effects a reduction inrthickness of between 30% and 60% thereby introducing substantial strains into the material and following each of said rolling operations by a heat treatment, each heat treatment except the last being at a temperature of between 700 C. and 1100o C. which relieves these strains and orients the crystallographic axes of the sheet material grains which cer the least resistance to magnetization in a direction substantially coincident with that in which the sheet was rolled, the iinal heat treatment being at a temperature of between 1100 C. and 1300 C. for a period of several hours.

3. In a method of making magnetic iron alloy Y in sheet-like form containing up to 6% silicon and characterized by relatively high permeability and relatively low watt loss, the steps which comprise reducing the sheet to its finished size by a plurality of cold rblling operations each of which eil'ects a reduction in thickness of between 30% and 60% and thereby introduces substantial strains that align the crystallographic axes of the sheet material grains which offer the least resistance to magnetization in a direction at an angle to the direction of rolling, following each of said rolling operations except the last by an anneal at a temperature between 700 C. and 900 C. to relieve the strains and orient the crystallographic axes of the sheet material grains which oil'er the least resistance to magnetization .in a

direction substantially -coincident with that in which the sheetwas rolled. in cooling the material substantially to room temperature after each anneal prior to the nextrolling operation, and'in followingl the "iinal rolling operation by an anneal at a temperature between 1100 C. and 1300 C. for several hours.

4. In the method of making ferro-magnetic sheet material containing silicon having improved electrical properties, the steps" consisting of reducing to the iinished size by a plurality of rollingoperations each beginning substantially at room temperature and each of which effects a reduction in thickness of between 30% and 60% thereby to align the crystallographic axes of easiest magnetization of the sheet material grains in a direction displaced by 45 from the direction of rolling, and heat treating after each of said rolling operations except the last at a temperature between 700 C. and 1000u C. to shift the orientation of the grain axes to a desired position which is substantially coincident with that in winch the sheet was rolled, in cooling the mate rial substantially to room temperature after each anneal prior to the next rolling operation, and in following the ilnal rolling operationby an anneal. ai. a temperature between 1100 C. and 1300 C. for from 'l to 12 hours.

5. Magnetic material comprising silicon-iron alloy' sheet reduced to its ilnal size by a plurality Y o f cold rolling operations, each of which introduces a reduction in thickness of between 30% and 60% and which introduces high intensity strains that align the crystallographic axes of easiest magnetization of the sheet material grains in a direction at an angle to the direction of rolling and subjected to an annealing treatment following each rolling operation at a temperature of the order of 900 C. .which relieves the strains and aligns the crystallographic axes of easiest magnetization of the sheet material grains in the dlrection of sheet rollingV and produces a material having relatively low watt losses and high-density permeability characteristics of the high order typified by a permeability of 6400 at a flux density of 16,000 gausses.

6. Magnetic material comprising silicon-iron alloy sheet reduced to its nal size by a plurality of cold rolling operations, each of which effects a reduction in thickness of between 30% and 60% and which introduces high intensity strains and so orients the alloy material grains as to align the crystallographic axes of easiest magnetization thereof at an angle of substantially 45 from the direction of rolling and subjected to an annealing treatment following each rolling operation at a temperature of the order of 900 C. which relieves these strains and so orients the alloy material grains as to align the .said axes of easiest magnetization in the direction of sheet rolling and produces amaterial having high density permeability characteristics of the order'typied by a permeability of 6400 at afflux density of 16,000 gausses and watt lossesof the order typified by 0.33 watt per pound in a sheet 14 mills thick when.

` subjected to a 60 cycle flux of 10,000 gausses maximum density.

7. Magnetic material of 'silicon iron alloy sheet reduced to its final size by a plurality of rolling operations carried on at substantially room temperature to. effect a reduction in thickness of between 30% and 60% and which introduces high intensity strains that align the crystallographic axes of easiest magnetization of the sheet material grains in a direction at an angle to the direction of rolling and subjected to an annealing operation following each rolling operation carried on at a temperature of between 800 C. and 1000 C. to relieve the strains and align the crystallographic axes of easiest magnetization of the sheet material grains in the direction of rolling and subjected to a nnal anneal of from 7 to 12 hours at a temperature of between 1100 C, and 1300 C. producing a. material having relatively low watt losses and high density permeability chacteristics of the high order typified by a permeability of 6400 lines at a flux density of 16,000 5 gauSSeS.

' ALBERT A. FREY.

FRANCIS BII'I'ER.

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