US2992951A - Iron-silicon magnetic sheets - Google Patents

Description

July 18, 1961 R. G. ASPDEN 2,992,951

- IRON-SILICON MAGNETIC SHEETS Filed April 21, 1960 2 Sheets-Sheet 1 Fig. I.

Rolling DirecV WGood Magnetic Properties l B m A Poorer 4 Mflgfletic Magnetic p 1 p es Properties A-Cube on Edge or Single Orientation B-Cube on Face or Double Orientation Fig. 4.

Q L 42 L-Punching Fig.5.

E-Punching Rolling Direction Fig. 3. YWF-I'NESSES mvsm OR Robert G. Aspden MQ RGQ M Y July 18, 1961 R. e. ASPDEN 2,992,951

mowsrucon MAGNETIC SHEETS Filed April 21, 1960 2 Sheets-Sheet 2 United States Patent C 2,992,951 IRON-SILICON MAGNETIC SHEETS Robert G. Aspden, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 21, 1960, 'Ser. No. 19,440 9 Claims. (Cl. 148-111) This invention relates to a process for producing double oriented magnetic sheets of iron silicon alloy.

This application is a continuation-in-part of application Serial No. 681,333, filed August 30, 1957, now abandoned, and assigned to the assignee of the present invention.

Magnetic sheets of iron silicon alloy have been produced heretofore wherein the texture is such that the grains are oriented in only one direction, usually the direction of rolling. This grain texture is of the (110) [001] type. As is well known to those skilled in the art, the permeability and other magnetic properties are outstanding in the rolling direction or the [100] direction which is parallel to the cube edges, and this is the direction of easiest magnetization of the grains of iron and iron alloys. However, in any other direction as, for example, the transverse direction of the sheet, the magnetic properties are greatly inferior because the magnetization is not parallel to the cube edges of the crystal. 1

It has long been desirable to be able to produce silicon iron sheets in which the grains have a cube on face orientation, namely, the (100) [001] type. If sheets of a cube on face or double oriented grain texture were available so that a high proportion of the volume of the sheet, or the surface area, comprised grains having their cube faces in the plane of the sheets with cube edges parallel to the rolling direction and to the crosswise direction of thesheet and the corresponding edges of the cubes were substantially parallel, the magnetic properties of the sheet would be outstanding both in the rolling direction of the sheet and in the transverse direction of the sheet.

The object of the present invention is to provide a process for producing silicon iron alloy magnetic sheets having a high volume proportion of cube on face or double orientation grain texture from available silicon iron alloy sheets having single orientation. r

A further object of the invention is to provide a process for producing predominantly cube on face or double oriented grain texture magnetic sheets from cold reduced sheets having near (111) [112] grain texture by a suitable annealing process in a highly reducing atmosphere to produce complete secondary recrystallization.

A still further object of the invention is to provide a process for cold rolling silicon iron alloy having predominantly the (110) [001] texture and then annealing the coldreduced sheets under conditions whereby the surface was free of oxides so that cube on face grain growth would take place, at a temperature of from 1100 C. to 1400 Cjfor a period of time to effect substantially complete secondary recrystallization.

Other objects of the invention will in part be obvious and will in part, appear hereinafter.

For a better understanding of the nature and objects of the invention reference should be had to the following detailed description and drawing, in which:

FIG. 1 is a schematic view in perspective illustrating the several grain orientations involved herein;

FIG. 2 is a plan view of a ring magnetic lamination; FIG. 3 is a plan view of laminated punchings made from a sheet;

FIG. 4 is a plan view of an L-punching; FIG. 5 is a plan view 'of an E-punching; and FIG. 6 is a (100) polefigure of the orientation of the grains from a sample of silicon. steel produced in ac cordance with the present invention.

Referring to FIG. 1 of the drawing, there is illustrated a sheet of ferrous metal in which are schematically depicted a cube A which represents a cube on edge or single oriented grain and a cube B which represents a cube on face or double oriented grain. The cube A, it will be noted, stands on one edge with respect to the plane of the rolled surface of the sheet. Four edges of the cube A are aligned parallel to the rolling direction. The direction of easiest magnetization of the grain is along the cube edge or [001] direction. Therefore, the direction of easiest magnetization of the sheet is essentially in the direction of rolling when it comprises predominantly grains oriented such as is cube A. It will be noted, however, that the magnetization in the crosswise or transverse direction of the sheet proceeds along a face diagonal or [110] direction of cube A. As is well known, this [110] direction is much inferior magnetically. Cube B, on the other hand, has four cube edges oriented in the direction of rolling and four cube edges oriented in the crosswise direction, and best magnetic properties are obtained in both directions because the easiest direction of magnetization of the grains is in a direction parallel to these edges. Consequently, a sheet comprising all cube on face grains B will exhibit highest magnetic properties in both the direction of rolling and in a direction transverse thereto.

It has been discovered that cube on face or double oriented silicon iron magnetic sheets having a predominantly (100) [001] grain texture may be readily produced from certain available silicon alloy sheet material, and especially single or (110) [001] grain oriented sheets, by a single cold reduction of from about 60 to 95% applied to the sheet material followed by a critical anneal of the cold reduced material under conditions which effect complete secondary recrystallization provided that the annealing is applied to sheets having no continuous surface oxide films whereby cube on face grain nuclei will grow in preference to other crystal textures.

In particular, it has been found that a sheet of single oriented grain texture silicon iron alloy when cold reduced so that it consists predominantly of the (111) [112] grain texture will respond to the secondary recrystallization anneal of the present invention to produce a cube on face material in which a very high proportion or substantially all of the secondary recrystalized grains have cube faces parallel to the surface of the sheet, the cube edges thereof being parallel to the direction of rolling and the transverse direction and the corresponding edges of the cubes are closely parallel to each other.

It will be appreciated that after the cold rolling there may be observed small amounts of grains of a great variety of grain orientation textures, but a very high proportion of the surface area, for example, and higher, will be composed of grains of the 111) [112] texture or orientations quite close thereto. This is due to the fact that the original sheet before cold rolling will usually have only to of its area of grains with [001] texture or orientations near thereto.

The process of the present invention is applied to sheets of silicon iron alloys containing from 2% to 6% by the cube on edge or single grain orientation in accordance with well known practices in the art. Such starting magnetic sheets are sometimes described as having a Goss texture or, more precisely, the (110) [001] type of grain texture wherein a high volume of the sheet comprises grains with four edges parallel to the direction of rolling, while the remaining eight edges are at angles of roughly 45 to the plane of the sheet surface. These sheets may have a thickness of from about 5 to 50 mils.

The magnetic sheets having the cube on edge or single orientation are cold reduced, preferably by rolling, to effect a reduction in thickness of from about 60% to 95%. The cold reduction, effected at room temperature, though the sheets may heat up during the cold working operation to a temperature as high as 400 C., has been found to result in sheets in which the grain texture is predominantly of the (111) [112] type or near thereto.

The cold reduced sheets having predominantly (111) [112] grain texture, produced by this or any other suitable process from single oriented or other texture sheets, are then subjected to a critical annealing procedure. It is necessary that the cold reduced sheets before annealing be free from any-surface films or coatings of the adherent type. Heavy or thick oxide films should not be present on the sheets. However, small amounts of oxides of silicon may be present as discontinuous inclusions or particles.

While a single sheet may be annealed, normal commercial practice will dictate that'an assembly be made either in coil form or of a plurality of stacked sheets. There should be interposed between the surfaces of the sheets in such assembly, a layer of an inert inorganic refractory material to prevent Welding of the sheets and to allow escape of gases from the metal and to allow the selected annealing atmosphere gases to penetrate to all thesurfaces. The inert inorganic refractory may comprise a coating of fine powder sifted or otherwise applied to the surface of each sheet in the assembly. A finely divided powder such for example as aluminum oxide, zirconium oxide or high purity anhydrous magnesia will give good results. The refractory should be treated, as for example; by calcining at a high temperature so that during annealing it will not evolve any moisture, oxygen or other deleterious materials such as carbon dioxide or the like. Good results have been obtained by using as a sheet separator- 200 to 350 mesh alumina that has been calcined or fired at 1000 C. to 1400 C. and then stored in a sealed container until ready for use.

The assembly or stack of cold reduced sheets is' placed in the annealing furnace and a non-carburizing atmosphere is 'provided which is substantially completely free from'water, oxygen or other oxidizing components such that the sheet will not be oxidized during annealing,but rather will cause any oxides to be rapidly removed. Silicon'dioxide will be the main oxide on the sheet surfaces and at annealing temperatures of from 1100 C. to 1400 C. dry hydrogen or a high vacuum should be applied which will favor the reaction of the silicon dioxide with silicon in the sheet to form silicon' monoxide which will evaporate from the surfaces. Cube on face grains will grow by secondary recrystallization in preference to other grain textures only if the surface is free from any substantial continuous films. In practice, the furnace may be flushed continually by passing a stream of very dry, high purity hydrogen therethrough. It has been found to be critical that the hydrogen have a dew point of below 50 C. at 1100 C. and below 40 C. at 1300 C. Good results have also been obtained with helium, nitrogen or argon gases similarly free from moisture and oxygen. A still further highly successful annealing atmosphere is a high vacuum which vacuum should be of at least mm. of mercury at 1100 C., at least from 10- to 10 mm. at 1200 C., and at least from 10 to 10* at 1300 C. and higher. Obviously higher vacuums maybe employed. Mixtures .of

the gases, such as hydrogen and nitrogen, may be employed. The prime requirement is that the atmosphere should be such that it will cause silica to be rapidly removed from the surfaces of the sheets at the annealing temperatures. Under these necessary conditions the sheets will soon attain a bright metallic surface free of continuous films.

Annealing should be carried out at a temperature of from 1100 C. to 1400 C. and preferably from 1200 C. to 1350 C. for a sufiicient period of time at a temperature to produce substantially complete secondary recrystallization. As is well known, primary recrystallization takes place rapidly, depending on the amount of previous cold working and the temperature, such that it may be effected in most cases, at 600 C. to 1000 .C., but secondary recrystallization requires a far longer time and higher temperatures. No continuous films should .be present on the sheets at the time secondary recrystallization occurs. Suitable annealing times for complete secondary recrystallization are four hours at 1225 C. and as little as /2 hour at 1400 C. Below 1200" C. the annealing times are quite lengthy for complete secondary recrystallization. It will be understood that the temperature during annealing need not be constant but may be varied to some extent.

Following the indicated critical annealing process cold reduced sheets having predominantly the (111) [112] grain texture will be found to recrystallize first'to a fine grain primary texture and then substantially completely to a much coarser cube on face or double orientation texture wherein the grains have (100) [001] type of grain texture. It has been found that the secondary recrystallized grains will be almost completely oriented in the manner of cube B in FIG. 1 of the drawing wherein two faces of the cube are closely parallel to the rolling plane of the sheet and the corresponding cube edges of the several grains are very closely parallel to one another, with certain cube edges being closely parallel to the direction of rolling and others will be transverse to the rolling direction.

It should be understood that the secondary recrystallized grains when grown under the annealing conditions specified will be almost entirely of the cube on face texture. Most unconverted primary grains will not have this (100) [001] orientation. Consequently, all efforts should be directed to ensuring not only proper annealing conditions so that surface films are not present on the sheet surface, but secondary recrystallization should be caused to occur by employing a high enough annealing temperature applied for a long enough period. T On occa sion, a sheet that will not form secondary crystals at, for example, 1150 C., Will so so at 1250 C. or 1300 C.

The following examples illustrate the practice of the invention.

Example I Sheets of a 3% silicon iron alloy of a thickness of 14 mils were prepared with a predominantly (110) i001] bright reflecting surface. In a typical area one inch wide by seven inches long, there were a total of 19 secondary recrystallizedgrains extending through the thickness of the sheet. Examination of the sheet indicated all of the grains had their 100) planes parallel to 'thesurface of the sheet and 16 of-the 19 grains-had their; [.0011] .directions.within.-10 of the rolling'direction while theothers were only silghtly more out of line. The orientation of all of the cube edges are shown in FIG. 6 of the drawing which is a (100) pole figure plot thereof.

The magnetic material of this Example I was slit into a narrow tape and a core was wound from the tape. The direct current magnetic properties of the cores, measured in the rolling direction, were as follows: The tip induction was 17,900 gausses at a magnetizing force of 10 oersteds; for a tip induction of 15,000 gausses the coercive force was 0.19 oersted and the residual induction was equal to 12,600 gausses.

The three mil thick cold reduced sheets of this Example I were annealed in an atmosphere comprising hydrogen having a dew point of 60 C. After annealing, the surface was found to be bright and the surface area comprised secondary recrystallized grains predominantly cube on face with a very high percentage of the cube edges being parallel to one another.

In another experiment, 14 mil thick sheets of single oriented magnetic steel were rolled to approximately mils, a reduction of about 65%, and on vacuum annealing as in Example I, secondary recrystallized grain texture double oriented magnetic sheets were obtained.

Example 11 A sheet of a single oriented (110) [001] texture 3.25% silicon iron alloy of a thickness of 25 mils was cold rolled to a thickness of 8 mils, a reduction of 68%. The texture was predominantly (111) [112] texture. The 8 mil thick cold rolled sheets were annealed for four hours at 1225 C. in vacuum of mm. of mercury, as set forth in Example 1. After the annealing, a high proportion of the surface area comprised secondary recrystallized grains having cube on face orientation. All of the cube on face grains had their edges within 20 and the cube faces were within a few degrees of the plane of the sheet.

Example III Hot rolled plates of a thickness of 0.150 inch were prepared from an open hearth melt having the following composition:

Percent Carbon 0.019 Manganese 0.10 Silicon 3.19 Sulfur 0.019 Phosphorus 0.008 Iron Balance After being annealed for 7 minutes at 950 C. in hydrogen of a dew point of -50 to 70 C., the plate was cold rolled to a thickness of 0.050 inch, a 66% reduction. The cold rolled plate was decarburized for 20 minutes at 840 C. in wet hydrogen (25 C. dew point), and then annealed for 16 hours in -50 C. dew point hydrogen. This annealed 0.050 inch thick sheet had over 80% of its area comprised of cube on edge or (110) [001] grain texture.

The 0.050 inch sheet was then cold rolled to a thickness of 0.007 inch, an 86% reduction in thickness, and the resulting strip was annealed for 2 hours at 1100 C. in a vacuum of 10- mm. of mercury without making any effort to remove the continuous oxide film from its surface and no significant secondary recrystallization occurred. The annealed strip comprised over 80% of its area of cube on edge or (110) [001] primary grain texture. A torque magnetometer confirmed the fact that a high degree of single orientation texture was present.

The 0.007 mil annealed strip was then cold rolled to a thickness of 0.0025 inch, a reduction of 71%. The 0.025 strip was predominantly of the (111) [112] texturei Six separate strips were cut from this last strip. Three sets of .two strips were then annealed as follows: with the indicated results:

.(1) .16 hours at 1300 C. in a vacuum of 10" mm.

The surface was bright afterthe annealing. One strip etched in ferrous ammoniumsulfate showed that the entire strip area comprised grains of (100) [001] texture.

(2) One hour at 1300" C. in --70 C. dew point hydrogen. Substantially complete secondary recrystallization occurred. The surfaces were bright after the am nealin-g. One strip was etched with ferrous ammonium sulfate and revealed that of the area comprised (100) [001] grain texture.

(3) 16 hours at 1300 C. in hydrogen of a -25 to -30 C. dew point. Substantially complete: secondary recrystallization. The surface showed a gray oxide film after the annealing. Upon etching one strip with ferrous ammonium sulfate, only from 5% to 10% of the strip area comprised grains having (100) [001] grain texture, the remainder being various other orientations.

In other tests of 3.25% silicon iron sheets which were of the cube on edge texture, and cold rolled as indicated here to produce a predominantly (111) [112] grain texture final annealing at various temperatures and vacuum indicated that at 1100 C. a vacuum of an absolute pressure not greater than 10'- mm. of Hg and preferably lower was required to remove silicon oxides so as to enable cube on face secondary grains to grow, and a vacuum appreciably poorer than 10-* mm. was not satisfactory. When annealing at 1200 C., the vacuum had to be at an absolute pressure range of not greater than 10' to 10- mm. of Hg, while at 1300 C. to 1400 C. a vacuum of an absolute pressure not greater than from 10* and 10- mm. of Hg was suitable to enable silicon oxides to be removed and secondary recrystallization of cube on face grains to proceed rapidly. The degree of stacking and access of the vacuum to the interior was a factor in determining how low a vacuum was required, the wider sheets and heavier stacks required the lower absolute pressure at any temperature.

The present invention may be employed to produce double oriented silicon iron magnetic sheet from a thickness of 0.1 to 30 mils. The sheets will have above of the secondary recrystallized grains with their cube planes within a few degrees of the surface of the sheets, and nearly all the cube edges within 20 of the rolling direction. An important feature of the invention is the fact that highly purified or vacuum melted silicon steel need not be employed in practicing the invention. Commerioal silicon iron alloy magnetic sheets when processed in accordance with the present invention were converted to the cube on face secondary recrystallized grain texture orientation.

The double oriented silicon iron magnetic sheets of this invention can be employed to great advantage in electrical apparatus, such as motors, generators and transformers. As illustrated in FIG. 2 of the drawing, a stator lamination 10 for a motor or generator may be punched from a sheet or strip of the double oriented sheet. The lamination 10 comprises slots 12 into which a winding may be applied, and teeth 14 which carry a high magnetic flux. The back or peripheral portion 16 of the lamination carries magnetic flux in service. The arrows 18 indicate the two easiest directions of magnetization of the magnetic sheet. Therefore, the teeth 14 directly above arrows 18 will be readily magnetized to high flux densities while the periphery will also carry flux readily.

As illustrated in FIG. 3, magnetic steel sectors 26 for large generators and motors may be punched out of a large strip 20 so that the teeth 28 defining coil slots 30 wiH be essentially parallel to the direction of rolling of the sheet and therefore nearly parallel to one of the directions 22 of easiest magnetization, while the back 32 i is generally in the other direction 24 of easiest magnetiza- Completesecondary recrystallization;tookplace. 16 sheet so that one leg 42 is parallel to ope easiest direct.

tion 46 of magnetization while the other leg 44 is parallel to the other easiest direction 48 of magnetization. Consequently, the L punching will possess outstanding rnagne'tic properties.

An E-punching 50, as shown in FIG. 5, is so cut-from a double oriented sheet that the back 52 is parallel to the one easiest direction 60 of magnetization, while the legs 54, 56 and 58 are parallel to the other easiest direction 62 of magnetization.

It will be appreciated that lamination configurations and core structures other than those illustrated in FIGS. 2 to 5, may be prepared to obtain maximum benefit from the double oriented magnetic sheets of this invention.

It will be understood that the above description and drawing are illustrative and not limiting of the invention.

I claim as my invention:

1. In the process of producing a sheet of double oriented magnetic material from thicker sheet comprising an alloy from 2 to 6% by weight of silicon, carbon less than 0.01%, and the balance being iron except for small amounts of up to 0.5% of manganese and other additions, and incidental impurities, the said thicker sheet comprising predominantly grains having the (110) [001] orientation, the steps comprising cold reducing said thicker sheet from about 60 to 95% to the desired thickness whereby the grains are predominantly of (111) [112] orientation, the cold reduced sheet being substantially free from any adherent films, and annealing the cold reduced sheet at a temperature of from 1100 C. to 1400 C. for a period of time sufficient to produce a substantially complete secondary recrystallization of the metal, the annealing being effected in a non-carburizing atmosphere substantially free from oxygen, moisture and oxidizing agents such that silica is rapidly removed at the annealing temperature and no continuous oxide films are present on the sheet surface by the time secondary recrystallization occurs, whereby there results a sheet with a bright metallic surface and having a (100) [001] texture and characterized by a high percentage of its area comprising cube on face grains in the plane of the sheet with the corresponding edges of the cubes being substantially parallel.

2. In the process of producing a sheet of double oriented magnetic material from thicker sheet comprising an alloy from 2 to 6% by weight of silicon, carbon less than 0.01%, and the balance being iron except for small amounts of up to 0.5% of manganese and other additions, and incidental impurities, the said thicker sheet comprising predominantly grains having the (110) [001] orientation, the steps comprising cold reducing said thicker sheet from about 60 to 95 to the desired thickness whereby the grains are predominantly of (111) [112] orientation, the cold reduced sheet being substantially free from any adherent films, and annealing the cold reduced sheet at a temperature of from 1100 C. to 1400" C. for a period of time sufficient to produce a substantially complete secondary recrystallization of the metal, the annealing being effected in a vacuum at an absolute pressure of not greater than 10- mm. at 1100 C., not greater than from 10 to 10 mm. at 1200 C., and not greater than from to '10- at 1300" C. to 1400 C., so that any continuous oxide films are rapidly removed during the annealing while at temperature and are not present by the time secondary recrystallization occurs whereby there results a sheet with a bright metallic surface and having a (100) [001] texture and characterized by a high percentage of its area comprising cube on face grains in the plane of the sheet with the corresponding edges of the cubes being substantially parallel.

3. The process of claim 1 wherein the annealing atmosphere comprises hydrogen with a dew point of less than 50? .C. at 1100 C. to less than 40 C. at 1300 C.

.4. The process of claim 1 wherein the annealing is applied to the sheet disposed in an assembly where surfaces are disposed closely to other surfaces, and the sheet surfaces are separated by a relatively inert, inorganic refractory substantially free from evolvable moisture,- oxygen and carbon'dioxide.

5, In the process for producing a sheet of double oriented silicon ironof a thickness of from 0.1 to 30 mils from a thicker sheet of an alloy of from =2 -to 6% silicon, less than 0:01% carbon and the balancebeing iron except for small amounts'of' up to 0.5% of manganese and other additions, andiincidental impurities, the said thicker sheet being at least 225 times the-thickness of the final desired sheet and having a predominantly (110) [001] grain texture, the steps comprising cold rolling -the said thicker sheet to a thinner sheet having the desired final thickness, the thinner sheet having predominantly a (111) [112] grain texture and the surfaces being free from any substantial amounts of adherent films, producing an as sembly in the form of a coil or stack from the cold rolled sheet, the assembly including an inert inorganic refractory sheet separator substantially completely free from evolvable moisture, oxygen and oxidizing materials, and annealingthe assembly at a temperature of from 1100 C. to 1400 C. for at least /2 hour at the highest temperature for a period of time sufficient to effect a substantially complete secondary recrystallization of the metal, the annealing being effected in a non-carburizing atmosphere substantially completely free from oxygen, moisture and oxidizing agents such that silica will be rapidly removed at the annealing temperatures so that no continuous oxide films are present on the sheet surfaces by the time'secondary recrystallization occurs and the sheet has a bright metallic surface, thereby producing a sheet having a major proportion of its area comprising [001] grain texture.

6. In the process for producing a sheet of double oriented silicon iron of a thickness of from 0.1 to 30 mils from a thicker sheet of an alloy of from 2 to 6% silicon, less than 0.01% carbon and the balance beingiron except for small amounts of up to 0.5 of manganese and other additions, andincidental impurities, the said thicker sheet being at least 2.5 times the thickness of the final desired sheet and having a predominantly [001] grain texture, the steps comprising cold rolling thesaid thicker sheet'to a thinner sheet having the desired final thick.- ness, the thinner sheet having predominantly a (111') [112] grain texture and the surfaces being free from any substantial amounts of adherent films, producing an a'ssembly in the form of a coil or stack from the cold rolled sheet, the assembly including'an'inert inorganic refractory sheet separator substantially completely free from evolvable moisture, oxygen and oxidizing materials, and annealing, the assembly at a temperature of from 1100 C. to 1400 C. for at least /2 hour at the highest temperature for a period of time sufiicient to effect a substantially complete secondary recrystallization of the metal, the annealing being in a vacuum at an absolute pressureof not greater than l0 mm. at 1100 .C., not greater than from 1 0- to 10 mm. at 1200 C., and not greater than from 10- to 10* mm. at 1300 C. to 1400 C., so that continuous oxide films will be rapidly removed from'the sheet surfaces at the annealing temperatures and areno-t present by the time secondary recrystallization occurs and the sheet will have abright metallic surface, whereby a sheet having a high proportion of its area comprising (100) [001] grain texture.

7. The process of claim 5 wherein the atmosphere comprises a vacuum of less than '10- mm. of mercury.

8. In the process of producing a sheet of doubleoriented magnetic silicon steel comprising from 2 to 6% silicon, less than 0.01% carbon and the balance being iron except for small amounts of up to 0.5% of manga-. nese and other additives andincidental impurities, -the step comprising annealing a cold reduced sheet havinga surfacesubstantially free from any. adherent continuous coatings and having a predominantly (111) [112] grain texture at a temperature of from 1100 C. to 1400 0 for-a .periodoftime to effect substantially complete sec ondary recrystallization of the steel, the annealing of the sheet being carried out in a non-carburizing atmosphere substantially free from moisture, oxygen and reactive materials so that silica is rapidly removed at the annealing temperatures and is not present by the time secondary recrystallization occurs and the sheet has a bright metallic surface, thereby producing a sheet having a predominantly (100) [001] grain texture.

9. In the process of producing a sheet of double oriented magnetic material from thicker sheet comprising an alloy from 2 to 6% by weight of silicon, carbon less than 0.01%, and the balance being iron except for small amounts of up to 0.5% of manganese and other additions, and incidental impurities, the said thicker sheet comprising predominantly grains having the (110) [001] ori- 15 entation, the steps comprising cold reducing said thicker sheet from about 60 to 95% to the desired thickness whereby the grains are predominantly of 111) [112] orientation, the cold reduced sheet being substantially free from any adherent films, and annealing the cold reduced sheet at a temperature of from 1100" C. to 1400 C. for a period of time suflicient to produce a substantially complete secondary recrystallization of the metal, the annealing being carried out in an atmosphere which at the annealing temperature will enable surface oxides to be reduced and removed such that during the annealing the surface will rapidly approach a bright condition in which it is free from continuous films before secondary recrystallization occurs, whereby there results a sheet having a high proportion of secondary recrystallized (1100) [001] grains.

References Cited in the file of this patent UNITED STATES PATENTS Littmann June 14, 1949 May Jan. 6, 1959 FOREIGN PATENTS Germany May 29, 1957

Claims (1)

1. 8. IN THE PROCESS OF PRODUCING A SHEET OF DOUBLE ORIENTED MAGNETIC SILICON STEEL COMPRISING FROM 2 TO 6% SILICON, LESS THAN 0.01% CARBON AND THE BALANCE BEING IRON EXCEPT FOR SMALL AMOUNTS OF UP TO 0.5% OF MANGANESE AND OTHER ADDITIVES AND INCIDENTAL IMPURITIES, THE STEP COMPRISING ANNEALING A COLD REDUCED SHEET HAVING A SURFACE SUBSTANTIALLY FREE FROM ANY ADHERENT CONTINUOUS COATINGS AND HAVING A PREDOMINANTLY (111) (112) GRAIN TEXTURE AT A TEMPERATURE OF FROM 1100* C. TO 1400* C. FOR A PERIOD OF TIME TO EFFECT SUBSTANTIALLY COMPLETE SECONDARY RECRYSTALLIZATION OF THE STEEL, THE ANNEALING OF THE SHEET BEING CARRIED OUT IN A NON-CARBURIZING ATMOSPHERE SUBSTANTIALLY FREE FROM MOISTURE, OXYGEN AND REACTIVE

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