US3078198A - Process for producing oriented silicon steel - Google Patents

Description

Feb. 19, 1963 G. w. WIENER 3,078,198

PROCESS FOR PRODUCING ORIENTED SILICON STEEL Filed June 7, 1961 Rolling DirectV Good Magnetic Proportion M W @222 A Poorer Maqnetia Magnetic [90g PFOPOFNQS Proparti'as A-Cube on Edge or Single Orientation B-Cube on Face or Double Orientation WITNESSES |NVENTOR George W. Wiener United States Patent M 3,078,198 PROCESS FOR PRODUCING ORIENTED SILICON STEEL George W. Wiener, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed June 7, 1961, Ser. No. 115,548

14 Claims. (Cl. 148-111) This invention relates to a process for producing magnetic sheets of iron silicon alloy having a high proportion of double grain texture.

This application is a continuation in part of my application Serial No. 788,596, filed January 23, 1959, now abandoned.

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 or length of the sheet. This grain texture is of the (110) [001] or cube-on-edge 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 of the grains since this is the direction of easiest magnetization thereof. The direction of easiest magnetization of a cube grain is along the cube edges, more difiicult along any face diagonal and the most diflicult along the long cube diagonals. Therefore, in any other direction other than along the rolling direction, as, for example, the transverse direction of the sheet, the magnetic properties of the singly oriented sheets are greatly inferior because the magnetization is not parallel to the edge of the cube grain texture.

It has long been desirable to be able to produce silicon iron sheets in which the grains have a cube-on-face or double orientation, namely the (100) [001] type, in which the cube edges of the grains are parallel both to the sheet edge or direction of rolling and to a transverse direction in the plane of the sheet.

If sheets of a cube-on-face or double oriented grain texture were available so that a high proportion of the grains had two of their cube faces in or close to the plane of the sheets with their cube edges closely parallel both to the rolling direction and to the crosswise direction of the sheet, and the corresponding edges of the cubes being substantially parallel to each other, the magnetic properties of such sheets 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 combined procedure for annealing and chemical surface treatment of silicon iron alloy sheets for producing silicon alloy magnetic sheets having a high proportion of double oriented or cube-on-face grains.

Another object of the invention is to provide a process for effecting secondary recrystallization of a higher proportion of the volume of silicon iron .alloy sheets into l00) [001] grain texture under given annealing conditrons by chemically etching the sheets before annealing.

A further object of the invention is to provide a process for producing secondarily recrystallized cube-on-face or double oriented magnetic sheets from cold reduced sheets of silicon iron by subjecting the cold reduced sheets to an annealing process in a vacuum or in dry hydrogen wherein the sheets are annealed several times with an intervening chemical surface treatment which etches the surface of the sheets.

A still further object of the invention is to provide a process for producing magnetic sheets having an extremely high proportion of secondary cube-on-face grains which comprises cold reducing silicon iron alloys to de- 3,978,198 Patented Feb. 19, 1963 sired gage and then annealing the sheet in at least two successive anneals at elevated temperatures in atmospheres that will reduce silica, the sheets being chemically etched between successive anneals to condition the surfaces so that a high proportion of the grain texture is converted to cube-on-face grains.

Still another object of the invention is to chemically treat the surface of a cold rolled sheet of silicon iron alloy before annealing it at elevated temperatures while in an atmosphere capable of reducing silica so that secondary recrystallization cube-on-face grain growth will occur.

Still another object of the invention is to chemically treat the surface of a cold rolled sheet of silicon iron alloy before annealing it at elevated temperatures while in an atmosphere capable of reducing silica so that secondary recrystallization cubeon-face grain growth will occur and repeating at least once the chemical surface treatment and the high temperature annealing to develop a high proportionof cube-on-face grains in the sheet. 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:

The single FIGURE is a schematic view in perspective illustrating orientation of grains in siicon steel.

Referring to the drawing, there is illustrated a sheet of metal in which are schematically depicted a cube A which comprises a cube-on-edge or single oriented grain and a cube B which comprises 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 which is also the sheet edge direction. The direction of easiest magnetization of the alloy 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 cubc-on-edge 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 a direction parallel to the direction of rolling and four cube edges oriented in the crosswise direction, and best magnetic properties are obtained in both of these directions.

It has been discovered that cube-on-face or double oriented l to 8% silicon iron magnetic sheets having a high proportion of (100) [001] grain texture may be readily produced from cold rolled silicon iron alloy sheets, either (1) sheets cold rolled one or more times with intermediate stress relief anneals between successive cold rolling stages which impart a final reduction of at least 40%, or (2) singly grain oriented sheets given a single cold reduction of from about 60 to by applying to any of such sheets a combination of a chemical etching treatment of the sheet surfaces and to remove a significant amount of the material but in general less than 1%, a critical anneal of the cold reduced material under conditions which eflect complete secondary recrystallization provided that the annealing is carried out in an atmosphere such that silica is reducible at the annealing temperature. The chemical surface treatment is preferably applied to the sheets before the anneal, or the chemical etching treatment may be interposed at least once during the annealing process, or applied both before and at least once during the annealing.

For a more detailed teaching of the process for producing the silicon iron alloys, and their composition reference 3 should be had to corresponding application Ser. No. 85,432, filed January 27, 1961, now abandoned.

The critical process steps of the present invention cornprise subjecting the cold reduced silicon iron alloy sheets to a surface chemical etching treatment in combination with an annealing heat treatment at a temperature of from 1100 C. to 1425 C. in atmospheres capable of reducing silica, either extremely dry hydrogen or a high vacuum, for a period of time to cause secondary recrystallization. Growth of cube-on-face grains to an unusual extent will occur under these conditions. Such cube-on-face grains will grow when the surface of the silicon iron sheet is relatively free from any continuous oxides or other films and providing that the surface energies favor such crystal growth. In commercial silicon steel, in particular, there are present small amounts of components or impurities on the surfaces of the sheets which appear to inhibit cube-on-face grain growth, especially in sheets above 5 mils in thickness. The process of the present invention is highly effective in producing a high proportion of cubeon-face grains in thick gauge sheets, that is, above 5 mils in thickness, and particularly in sheets from 0 to 15 mils in thickness, and thicker. Also, in some cases when the secondary recrystallization process is either slow or fails to proceed to a substantial extent, the etching treatment will expedite the rate of recrystallization as Well as cause a high volume of secondary (100) [001] grains to be obtained.

If, after a period of time in the annealing furnace, the partially annealed sheet shows only a small volume of (100) [001] grain texture, it is again chemically treated so that it is lightly etched or polished and then again subjected to annealing in the same atmospheres and in the same temperature range as previously. Many more cubeon-face grains will be formed and they will absorb more grains of other primary crystalline textures than will occur without the interposed chemical treatment. The etching and annealing cycle may be repeated several times. This cyclic surface treatment and annealing under the conditions indicated, usually two or three cycles being adequate, will convert a very high proportion of the grain texture of the sheet to the cube-on-face grain orientation. Thus at least 70% of the texture of 10 to 14 mil thick siliconiron sheets comprising 2.50% to 3.25% silicon iron alloy may be converted to the cube-on-face grain orientation. In most instances, in excess of 90% of the sheet grain exture was converted to cube-on-face grain structure. it will be appreciated that such high conversions of the grain texture to double oriented grains are highly desirable for magnetic sheets to be employed in transformers, motors, generators, and other electrical apparatus.

The light etching or polishing to which the sheets of silicon steel are subjected either prior to or between successive anneals will remove at most a fraction of 1% of the sheet. Any chemical etching agent, such as hydrochloric acid, phosphoric acid, acidified ferrous ammonium sulfate, or the like, is effective. The acid may be in aqueone solution or in gas form. The sheets may be electroetched by applying thereto an electrical current while the sheet is immersed in an electrolyte, either acid or basic. Thus phosphoric acid, hydrochloric acid, sulfuric acid, disodium phosphate and potassium carbonate aqueous solution may be employed as electrolytes. The sheets may be passed into a dilute acid solution, and if desired, the solution being agitated and the sheets Withdrawn at the end of an immersion of a few seconds or up to a few minutes. The sheets can be etched in hydrogen gas containing 10% gaseous hydrogen chloride at 1100 C. for one minute. In any case a significant amount of. the sheet up to 1% is removed. The etching or polishing treatment so applied appears to condition the surface so that the surface energy favors the development of the nuclei and growth of cubeon-face grains.

The process of the present invention may be applied to sheets of silicon iron alloys containing from 1 to 8%, and preferably 2. to 6% by weight of silicon, less than 0.01%

carbon and the balance being iron except for small amounts of the order of from 0.01 to 0.5% of manganese, sulfur and other additives, and incidental impurities. While high purity silicon-iron alloy sheets may be employed, commercial open-hearth silicon steel has given excellent results when processed as disclosed herein.

The invention may be carried out by hot rolling the iron-silicon alloy ingots to desired thickness of from about 0.10 to 0.50 inch in one or more stages, then cold rolling the ingots to desired gage in one or more stages with intermediate anneals at from 750 C. to 1000" C. in wet or dry hydrogen. The final annealing also can be carried out on single oriented cold rolled sheets that may be prepared in any suitable manner. The cold reduction, which may be effected at room temperature, in practice may cause the sheets to heat up to temperatures of as high as 200 C. to 400 C. It is necessary that the cold reduced sheets be substantially free from any adherent surface films or coatings. However, small amounts of oxides may be present as discontinuous inclusions or particles.

The process of the present invention may be employed to produce double oriented silicon iron magnetic sheets of a thickness from 0.1 to 30 mils. Its outstanding results are obtained when applied to sheets of a thickness of from 5 to 25 mils.

The cold reduced sheets may be annealed either as a single continuous strip or sheet, though normal commercial annealing practice will dictate that an assembly be made either in coil form or as a stack comprising a number of 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 the surfaces or to allow evacuation to degas the metal surfaces. The inert inorganic refractory may comprise a coating of a fine. ceramic 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 pretreated, as for example, by calcining at a high temperature so that during annealing it will not evolve any moisture, oxygen or other oxidizing 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 from 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. A vacuum annealing furnace operating at a high vacuum of at least 10* mm. of mercury and preferably of at least 10 mm. of mercury, has given outstanding results. Gas filled annealing furnaces 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 -40 C. A relatively non-reactive gas such as helium, or argon similarly free from moisture and oxygen also may be employed. Mixtures of the gases, such as hydrogen and nitrogen, may be employed. The inert gases or very dry hydrogen may be at a low pressure, for example, 1 mm. of mercury pressure. The prime requirement is that the atmosphere should be such that it will be capable of reducing silica to silicon at the annealing temperatures. Under these conditions the sheets will come out of the anneal with a bright metallic surface.

Each of the annealing stages during the final anneal should be carried out at a temperature of from 1100 C. to 1425 C. and preferably from 1200 C. to 1350 C. The annealing should be carried out for sutlicient period of time at temperature to cause at least a partial growth of cube-on-face grains as a secondary recrystallization phenomena. At the higher temperatures of above 1200 C., primary or strain relief crystallization takes place in a minute or so, but the secondary recrystallization of a single sheet may take a fraction of an hour, for example, minutes. At 1100 C., the anneal of a single sheet may require as much as from /2 to 2 hours to cause complete secondary recrystallization. For stacked or coiled sheets the annealing time will be prolonged to as much as 24 to 48 hours at 1200 C.

It will be found that, in the absence of an initial chemical etching treatment of the sheet, cube-on-face grain growth on some sheets will soon reach a maximum of far below 50 volume percent, during the final anneal such that no matter how long the annealing is carried out thereafter no substantial increase in the size or number of grains appears to take place. An initial chemical etching treatment will enable a higher volume of secondary grains to be formed. Also, by removing the sheets from the annealing furnace and subjecting them to chemical surface treatment, there is effected a change in the surface energy characteristics such that when the sheets are again subjected to annealing, more cube-on-face nuclei will be formed and will grow while the first nuclei will grow at the expense of adjacent grains. Also the rate of growth of secondary cube grains is greatly increased by the etching treatment.

The following examples are illustrative of the practice of the invention:

EXAMPLE I A 3 /2 silicon-iron alloy was hot rolled to bands of 80 mils thickness, and the hot rolled bands were cold rolled to sheets of mils which were then stress relief annealed at 1200 C. in dry hydrogen. The annealed sheet was then cold rolled to 11 mil thickness. Half of this sheet was chemically etched for 1 minute in an etchant composed of 50 volume percent of 85% phosphoric acid and 50 volume percent of 30% hydrogen peroxide. After washing and drying, the etched sheet was cut into strips and stacked. The other, untreated half of the sheet was similarly cut into strips and stacked. Both stacks were placed in the same furnace and annealed at 1200 C. for 16 hours with an atmosphere of hydrogen gas of a 45 C. dew point. The average volume of secondary (100) [001] grains in the etched strips was 80%, while the average volume of secondary (100) [001] grains in the unetched strips was not in excess of 10%.

EXAMPLE II A heat of a nominal 3% silicon iron all-0y was prepared in an open hearth and hot rolled to a thickness of 0.150 inch. The resulting hot rolled band was chemically analyzed and had the following composition:

Carbon percent 0.041 Manganese do 0.10 Silicon do 3.19 Sulfur do 0.019 Nitrogen do 0.0028

ImpuritiesSrnall amounts not exceeding 0.2% total.

This hot rolled band was cold rolled to a thickness of 0.050 inch with intermediate anneals at a temperature of 700 C. to relieve strains. The cold rolled sheet was subjected to an anneal to 1100 C. in hydrogen for a period of from 2 to 8 hours. Crystallographic analysis of the texture of the sheet indicated it had a (110) [001] texture. Though many grains had their cube edges aligned in the rolling direction their cube faces were at angles varying from 20 to 75 from the sheet surface. This is the Well-known single oriented grain structure.

The annealed, cold rolled sheet of a thickness of 0.050 inch was then cold reduced by rolling to a thickness of 0.012 inch. The texture contained a large pro-portion of grains having (111) [112] orientation. The sheet was then annealed in a vacuum of below 1 micron absolute pressure at a temperature of 1200 C. for one hour. The

vacuum was capable of reducing silica at the annealing temperatures. Nickel-chromium alloy heating elements were disposed in the evacuated chamber and vapors of the metals were present. After the one hour anneal, the sheet, whose surface was bright, was removed from the furnace, cooled to room temperature, and then subjected to an etch treatment in an aqueous solution of ammonium sulfate acidified with 5% of its volume of sulfuric acid at a temperature of C. for a period of two minutes. A substantial amount of cube-cn-face nuclei were evident on the face of the sheet. The etched sheet was then subjected to an additional 1 hour anneal at 1200 C. in the vacuum furnace. The sheet was again removed from the furnace, cooled at room temperature, etched for a few minutes in the acidified ferrous ammonium sulfate solution and then the annealing was completed by heat treating it a third period of an hour at 1200 C. in the vacuum furnace.

An examination of the finally annealed sheet indicated at least 75% by volume of the sheet comprised a cubeon-face grain structure in which 32% of the cube grains had a [001] direction within the plus or minus 10 to the rolling direction. Over 90% of the cube-on-face grains had their cube faces within plus or minus 5 of the plane of the surface of the sheet.

Tests on magnetic properties gave the following significant results:

Table I Magnetic properties at the end of the second anneal period.

It will be noted that there was an outstanding improvement in the magnetic properties after the third anneal as compared to the second anneal.

EXAMPLE III The cold rolled 12 mil sheets of Example II were initially dipped for 30 seconds in an aqueous solution of ammonium sulfate acidified with 5% by volume of sul furic acid (concentrated) at 80 C. The chemically etched sheets were annealed in vacuum as set forth in Example 11 for one hour, cooled, etched in the same etchant, and then again annealed for one hour, again cooled, etched in the etchant and annealed for a third period of one hour. Over 90% of the grains in the tinal sheet had cube-on-face orientation. This Example III illustrates the benefits to be had when the cold rolled sheets of silicon steel are chemically etched before being annealed.

In other tests, the following etchants have given good results when applied to the iron-silicon sheets before and between anneals:

(1) Two minutes in 80 C. ferric ammonium sulfate acidified with 3% of its volume of concentrated sulfuric acid, followed by a 30 second electropolish in an electrolyte composed of orthophosphoric acid with from 1% to 20% by weight of chromic acid added thereto, the electropolishing being applied to the sheet at a current density of from 5 to 25 amperes per square inch.

(2) A 30 second etch in ferric ammonium sulfate con- 7 taining of its volume of sulfuric acid (concentrated) at 80 C.

(3) Thirty second clip in a solution comprising a mixture of 50% by volume of H PO (85%) and 50% by volume of 30% hydrogen peroxide, at room temperature.

(4) Thirty second dip in a solution comprising a mixture of 50% by volume of H PO (85%), by volume nitric acid (65%), 10% by volume hydrogen fluoride (4 and water at room temperature.

it will be understood that while the initial surface etching of the cold reduced silicon-iron sheets before the high temperature anneal is highly desirable, it is not indispensably necessary. Though as evident from Example I, the cube grain growth is enhanced by applying only an initial etch to the sheets. However, for a high degree of cube grain growth, chemical surface treatment by etching is necessary after the high temperature anneal has been initiated. The highest degree of cube-on-face grain texture has been obtained when the chemical treatment of the surface of the sheets has been applied both before the high temperature anneal and at least once during the high temperature anneal.

In some cases, due to processing and the composition, the secondary cube grains will comprise 70% to 95% or even higher of the sheet volume, said grains having two of their crystal lattice faces substantially parallel, within approximately 5%, to the sheet surface, but the corresponding cube edges may not be parallel to each other or to the edge of the sheet or the rolling direction. Thus, randomly edge oriented grains having cube faces substantially parallel to the sheet surface will predominate. The etching treatment of the invention will enable such cube grain growth to occur as effectively as with sheets in which the grain growth is predominantly (100) [001].

It will be understood that the above description and drawing are only exemplary.

I claim as my invention:

1. In the process of producing a sheet of double oriented magnetic sheet comprising an alloy from 1 to 8% 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 sheet being cold reduced to a ti ickness of less than 30 mils, the surface of the cold reduced sheet being substantially free of any adherent continuous film of oxides and other impurities, the steps comprising subjecting the cold reduced sheet to an annealing treatment wherein the sheet is initially partially annealed at a temperature of from 1100 C. to 14-25 C. for a period of time sufficient to initiate growth of cube-on-face grains by secondary recrystallization, the annealing atmosphere being non-carburizing and so free from oxygen, water vapor and oxidizing agents that silica on the surface of the sheets will be reduced during annealing, and thereafter subjecting the sheet to at least one cyclic treatment wherein the surface of the sheet is lightly etched to remove a significant amount but less than 1%, and the sheet is again annealed in the temperature range and conditions applied during the initial anneal to develop more cube-on-face grain nuclei and to convert by secondary recrystallization a predominant proportion of the sheet texture to cube-on-face grains with two faces sub stantially parallel to the surface of the sheet, and the corresponding edges of the cubes being substantially parallel.

2. The process of claim 1 wherein the annealing atmosphere comprises a high vacuum of a pressure less than 10 mm. Hg.

3. The process of claim 1 wherein the-annealing atmosphere comprises hydrogen of a dew point of below 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 sur- 8.. faces are separated by a relatively inert, inorganic refractory substantially free from evolvable moisture, oxygen and carbon dioxide.

5; The process of claim 1, wherein the cold reduced sheets are subjected to the chemical etching treatment before being annealed.

6. The process of claim 1 wherein the annealing atmosphere disposed about the sheet contains vapors of nickel.

7. 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 being iron except for small amounts of up to 0.5% of manganese and other additions and incidental impurities, the said thicker sheet being at least 2.5 times the thickness of the final desired sheet and having essentially a [001] grain texture, the steps comprising cold rolling the said thicker shoe to a thinner sheet having the desired final thickness, the thinner sheet having essentially a (111) [112] grain texture, producing an assembly in the form of a coil or stack from the cold rolled sheet, the assembly includingan inert inorganic refractory sheet separator substantially completely free from evolvable moisture, oxygen and oxidizing materials, and annealing the assembly at a and oxidizing materials that silica on the surface of the sheets is capable of being reduced during annealing, and thereafter subjecting the partially annealed sheets to at least one cyclic treatment wherein the surfaces of the sheets are etched to remove a significant amount but less than 1% of the material thereof and the sheets are again annealed in the temperature range and under the atmosphere conditions applied during the initial anneal to develop more cube-on-face grains and to convert by secondary crystallization a predominant proportion of the sheet texture to cube-on-face grains with two faces substantially parallel to the surface of the sheet and the cplrrlesponding edges of the cubes being substantially pera e.

I 8. The process of claim 7 wherein the atmosphere durmg annealing comprises a vacuum of an absolute pressure not in excess of 10- millimeters of mercury.

9. In the process of producing a sheet of double oriented magnetic material from a sheet comprising an alloy of 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 sheet being cold reduced to a final thickness of not in excess of about 30 mils, etching the surface of the cold reduced sheet for a period of time sufficient to remove a small amount of material from the surface of the sheet not exceeding about 1% of its weight, thereafter annealing the etched sheet at a temperature of from 1l00 C. to 1425 C. for a period of time sufficient to cause growth of cube-on-face grains by secondary recrystallization, the annealing atmosphere being non-carburizing and so free from oxygen, water vapor and oxidizing agents that silica on the surface of the sheets can be reduced during annealing, whereby to convert a predominant proportion of the sheet volume to secondary cubc-on-face grains with two faces substantially parallel to the surface of the sheet, and the corresponding edges of the cubes being substantially parallel.

10. 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 being iron except for small amounts of up to 0.5 of manganese and other additions. and incidental impurities, the said thicker sheet being at least 2.5 times the thickness of the final desired sheet and having essentially a (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 essentially a (111) [112] grain texture, etching the surface of the sheet for a period of time sufiicient to remove a significant amount but less than 1% of the sheet material, then producing an assembly 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 1425 C. for at least /2 hour at the highest temperature for a period of time suflicient to develop substantial numbers of cube-on-face grain nuclei in the surface of the sheet by secondary recrystallization, the annealing being effected in a non-carburizing atmosphere so free from oxygen, Water vapor and oxidizing materials that silica on the surface of the sheets is capable of being reduced during annealing, and thereafter subjecting the partially annealed sheets to at least one cyclic treatment wherein the surfaces of the sheets are etched to remove a significant amount but less than 1% of the material thereof and the sheets are again annealed in the temperature range and under the atmosphere conditions applied during the initial anneal to develop more cube-on-face grains and to convert by secondary recrystallization a predominant proportion of the sheet texture to cube-on-face grains with two faces substantially parallel to the surface of the sheet and the corresponding edges of the cubes being substantially parallel.

11. 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 being iron except for small amounts of up to 0.5 of manganese and other additions and incidental impurities, the said thicker sheet being at least 2.5 times the thickness of the final desired sheet and having essentially (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 essentially a (111) [112] grain texture, etching the surface of the sheet for a period of time sufiicient to remove a significant amount but less than 1% of the sheet material, then producing an assembly in the form of a coil or stack from the cold roller 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 1425 C. for at least /2 hour at the highest temperature for a period of time suflicient to develop substantial numbers of cube-on-face grain nuclei in the surface of the sheet, the annealing being carried out under a vacuum at an absolute pressure not exceeding 10- millimeters of mercury so that silica is capable of being reduced during annealing, and thereafter subjecting the partially annealed sheets to at least one cyclic treatment wherein the surfaces of the sheets are etched to remove a significant amount but less than 1% of the material thereof and the sheets are again annealed in the temperature range and under the atmosphere conditions applied during the initial anneal to develop more cube-on-face grains and to convert by secondary recrystallization a predominant proportion of the sheet texture to cube-on-face grains with faces substantially parallel to the surface of the sheet and the corresponding edges of the cubes being substantially parallel.

12. In the process of producing a sheet of double oriented grain texture magnetic material of an alloy of from 1 to 8% silicon, carbon less than 0.01% and the balance iron except for small amounts of up to 0.5% of manganese and other additive and incidental impurities, the steps comprising etching the surface of a cold rolled sheet of the material for a period of time to remove a significant amount but less than 1% of the weight of the sheet, and annealing the sheet at a temperature of from 1100 C. to 1425 C. for a period of time sufiicient to cause substantially complete secondary recrystallization of the sheet, the annealing of the sheet being efiected in a non-carburizing atmosphere so free from oxygen moisture, and oxidizing substances that silica may be reduced to silicon at the annealing temperatures, whereby a high proportion of the secondary grains have a [001] orientation.

13. The process of claim 12, wherein the annealing atmosphere comprises hydrogen of a dew point of not in excess of 40 C.

14. The process of claim 12 wherein the annealing is interrupted at least once and the surface of the sheet is again etched to remove a substantial proportion of the material but less than 1% by weight thereof, and then the annealing is again applied to effect a progressively increasing amount of secondary recrystallization to the place.

No references cited.

Claims (1)

1. IN THE PROCESS OF PRODUCING A SHEET OF DOUBLE ORIENTED MAGNETIC SHEET COMPRISING AN ALLOY FROM 1 TO 8% 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 IMPURITIEES, THE SHEET BEING COLD REDUCED TO A THICKNESS OF LESS THAN 30 MILS, THE SURFACE OF COLD REDUCED SHEET BEING SUBSTANTIALLY FREE OF ANY ADHERENT CONTINUOUS FILM OF OXIDES AND OOTHER IMPURITIES, THE STEPS COMPRISING SUBJECTION THE COLD REDUCED SHEET TO AN ANNEALING TREATMENT WHEREIN THE SHEET IS INTIALLY PARTIALLY ANNEALED AT A TEMPERATURE OF FROM 1100* C TO 1425* C. FOR A PERIOD OF RIME SUFFICIENT TO INITATE GROWTH OF CUBE-ON-FACE GRAINS BY SECONDARY RECRYSTALLIZATION, THE ANNEALING ATMOSPHERE BEING NON-CARBURIZING AND SO FREE FROM OXYGEN, WATER

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