US3218202A - Method of using a critical cold rolling stage to produce silicon-iron sheets - Google Patents

Method of using a critical cold rolling stage to produce silicon-iron sheets Download PDF

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US3218202A
US3218202A US371881A US37188164A US3218202A US 3218202 A US3218202 A US 3218202A US 371881 A US371881 A US 371881A US 37188164 A US37188164 A US 37188164A US 3218202 A US3218202 A US 3218202A
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Ganz Dietrich
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Vacuumschmelze GmbH and Co KG
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
    • H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
    • H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
    • H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
    • H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
    • H01F1/147—Alloys characterised by their composition
    • H01F1/14766—Fe-Si based alloys
    • H01F1/14775—Fe-Si based alloys in the form of sheets
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1216—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the working step(s) being of interest
    • C21D8/1233—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
    • C21D8/1255—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest with diffusion of elements, e.g. decarburising, nitriding
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
    • C21D8/1272—Final recrystallisation annealing

Definitions

  • This invention relates to a process for producing silicon-iron sheets having a grain structure in which the cube faces are essentially parallel to the surface of the sheet while the edges are oriented in at least four directions.
  • Magnetic materials for various electrical engineering applications have been produced with preferred crystallographic orientation wherein the magnetic properties are anisotropic, that is, in at least one direction, and quite often in two directions in the plane of the sheet, the optimum magnetic properties are exhibited Whereas in other directions the magnetic properties are inferior.
  • .many magnetic materials such for example, as silicon-iron and nickel-iron alloys which crystallographic in the cubic system, are characterized by the direction of easiest magnetization being along the cube edge.
  • the permeability of these magnetic materials is higher in the direction parallel to the cube edge than in any other direction.
  • the ease of magnetization and permeability is poorer along a face diagonal of the cube and the poorest magnetic properties are exhibited along the long diagonal from opposite vertices of the cube.
  • the surface condition enables the secondary recrystallization of cube-on-face grain nuclei in preference to cube-on-edge and other orientations of grain nuclei which may be present at the end of the primary recrystallization phase of the final anneal.
  • This product comprises cube-on-face grains in which the preferred directions of magnetization are in the direction of rolling and in a direction perpendicular thereto.
  • Such products are of considerable value for producing transformers and other electrical devices in which magnetic flux is caused to travel in directions at angles to each other.
  • the magnetic sheets consist of grains whose crystal lattice structures comprise cube faces parallel to the surface of the sheet but whose edges are oriented in more than two directions. It would be desirable to have products in which the cube edges of such grains are oriented either randomly or in a plurality of directions, preferably four or more, whereby these applications could employ the material to better advantage.
  • One particular application for such silicon-iron sheets is in circular punchings which are required for small motors and generators, in both stators and rotors, as well as in other applications requiring complex magnetic paths deviating from each other at angles other than 90.
  • cube texture and face texture are defined for the purposes of this invention as follows:
  • Cube texture denotes a grain texture in a sheet of metal wherein there is over 50%, and preferably over 70%, of the crystal volume of grains having a cubic crystal lattice structure in which two cube faces are parallel, within 10, to the sheet surface, and the cube edges are so oriented that four edges are parallel within 15, to one direction in the plane of the sheet, usually the rolling direction, and four other cube edges are parallel, within 15, to another direction in the plane of the sheet perpendicular to the said one direction.
  • Face texture denotes a grain texture in a sheet of metal wherein there is over 50%, and preferably over and up to 95% or more, of the crystal volume of grains having a crystal lattice structure in which two cube faces are parallel, Within 10, to the sheet surface, and four of the twelve cube edges of such grains are (1) either randomly oriented or (2) are oriented parallel to at least four different directions, all of which deviate from the rolling direction, or (3) comprise a mixture of which the edges of at least 20% of the grains are so randomly oriented and/or oriented in at least four different directions with respect to the direction of rolling while the balance comprises cube texture grains in which the edges are parallel to the direction of rolling.
  • Randomly oriented cube edges as employed herein applies to a sheet of metal having a plurality of grains having a cubic crystal lattice structure wherein the cube faces are substantially parallel to the sheet surface, and denotes that the tube edges of said cube faces show no significant concentration in any particular direction but are scattered in all directions.
  • FIG. 5 of the drawing there is illustrated the difference between the orientation of the edges of cube grains in cube texture and face texture sheets.
  • a sheet of the magnetic material is analyzed to determine the percentage of cube grains, that is grains whose faces are parallel to or within 10 to the sheet surface. Then the adges of these cube grains are measured to determine the angle between the rolling direction and the four edges of each grain most closely parallel to the direction of rolling. The rolling direction is set as 0. These measurements are made up to S5 with respect to the rolling direction. The percentage, or number, of cube grains within each degree is plotted on coordinate paper and a curve is drawn.
  • curve B of FlG. 5 For a sheet with face texture grain orientation, as is apparent from curve B of FlG. 5, there are two distinct grain edge concentrations at the 25 and 65 angles in a probability type curve distribution. There are twice as many peaks in the curve B as compared to curve A, though each cube edge distribution peak in curve is half as high as the peaks of curve A. it should be understood that curve B is only illustrative, since there may be more cube edge distribution peaks, for exampl 6 or 8 within +90 and -99 of the rolling direction.
  • the object of the present invention is to provide a process for cold rolling in a predetermined manner sheets of silicon iron alloy and then subjecting the sheets to a final anneal which will cause nuceli having faces parallel to the sheet to grow preferentially whereby to produce a face texture in the sheet.
  • Another object of the invention is to provide a process with sheets of silicon-iron alloy comprising from 2% to silicon, up to 1% of manganese, molybdenum or chromium or any combination thereof, and the balance being iron to effect at least two stages of cold rolling wherein at least one of the last three stages of cold rolling effects a reduction in thickness of at least 93% and preferably 95% or higher while the other stages effect a reduction in thickness of at least 30%, and then subjecting the cold rolled sheet ,to a final anneal under conditions that will enable. grain nuclei having faces parallel to the surface of the sheet to grow in preference to other nuclei during the secondary recrystallization growth during the final anneal.
  • FIGURE 1 is a schematic showing of the orientation of the cube grains in a cube texture sheet
  • FIG. 2 is a schematic illustration of the arrangement of the crystal lattice cubes in a face texture sheet
  • FIG. 3 shows schematically the comparative magnetic flux in different portions of a ring punching of a sheet of magnetic material having a cube texture
  • FIG. 4 is a schematic showing of the relative amount of magnetic flux for different portions of a ring punching from a sheet having face texture, the magnetizing field being the same in all directions in both FIGS. 3 and 4;
  • FIG. 5 is a curve plotting the percentage of grains having a given angular deviation of the edges from the rolling direction for both cube texture and face texture sheets.
  • a sheet of silicon-iron produced in accordance with the invention in US. Patent 2,992,952 previously identified, comprises grains whose cube faces are parallel to the surface of the sheet, which in this case is parallel to the sheet of paper, while the cube edges are oriented parallel to the rolling direction a and in a direction transverse to the rolling direction namely direction [2.
  • FIG. 2 illustrates the orientation of the crystal lattices of grains in a sheet having face texture. It will be noted that the rolling direction a which extends in a direction vertically of the sheet of the paper is not necessarily parallel to any of the cube edges of the grains illustrated.
  • each of the four grains are parallel to the surface of the sheet but the cube edges, it will be noted are: parallel to four diffenent directions 0, d, e and f.
  • the direction (1 represents the rolling direction and accordingly the directions c, (I, e and f extend at an angle :25 and i65", respectively with respect to the rolling direc-- tion. It will be understood, of course, that there may additional directions of orientation of the cub edges in addition to those shown.
  • cube edges may also be parallel to directions forming angles of :37" and :53" with respect to the direction of rolling as well as the directions at 125 and :65.
  • the orientation of the cube races and the cube edges is not absolutely precise. Normally the cube faces will be Within 10 of parallelism to the surface of the sheet, usually within 5 of parallelism. Eimilarly, the cube edges even for cube texture material will not be oriented entirely as illustrated in FIG. 1. Usually the majority of the grains will have their edges parallel within 15 of the rolling direction. In some instances sharper texture alignment is obtained than in other instances. in a similar manner the directions 0, d, e and f in FIG. 2 do not represent the absolute direction of all the grains of the face texture sheet.
  • FIG. 3 of the drawing there is illustrated a circular punching in ring form which may be employed for electrical apparatus by providing therein teeth for the insertion of windings.
  • This punching has been prepared from cube texture material having grains oriented as illustrated in FIG. 1. It will be noted that for a given magnetizing force there will be a much greater magnetic flux in the rolling direction and in a direction transverse to the rolling direction as indicated by the four magnetic flux arrows at these points. In a direction slightly divergent from these directions the magnetic flux is much less and is represented by three arrows. At an angle of 45 from the rolling direction the magnetic flux in the sheet is reduced. It will be appreciated that in electrical apparatus it is desirable that the magnetic flux be substantially constant at every point in the punching in order to obtain uniformity of operation of a motor or other electrical equipment.
  • the total magnetic resistance at any given point in a punching having face texture is much less than that in any other material known heretofore including the cube texture material of FIG. 3. It has been found that sheets having a face texture when subjected to alternating current magnetization exhibit lower eddy current losses than sheets with the cubic texture. It is believed that this is due to the fact that with a face texture the spaces of the Blochs Walls separating the magnetic domains from each other are smaller than in sheets having cube texture.
  • An additional advantage lying with sheets having face texture is in the fact that they can be produced more simply and more reliably with a higher percentage of desirable grain orientation than sheets having the cube tex ture.
  • the process of the present invention which results in the production of sheets having face texture may be applied to silicon-iron alloys containing from 2% to 5% silicon, up to 1% of one element from the group consisting of manganese, molybdenum and chromium, with the balance being iron except for additives and impurities. It will be understood that sulfur, and other additives, may be present in the sheets in proportions to enable cube grain growth.
  • the iron-silicon alloy may be prepared by the usual practice either in open hearth or in an electric furnace or in a vacuum furnace for highest purity materials, cast into an ingot which ingot is then hot rolled or forged into a heavy plate.
  • the heavy plate may be of a thickness of as much as 0.5 inch or as thin as 0.080 to 0.10 inch in thickness.
  • the hot rolled plate will usually be pickled to remove any hot roll scale or other surface defects. Hot rolling normally will have been carried out at a temperature of as high as 1200 C. Thereafter the hot rolled plate is cold rolled once or twice and even three times, depending on the final gauge of the desired silicon-iron sheet. Between successive cold rolling steps the sheet is annealed at temperatures of from 800 C. to 1100 C., in a reducing atmosphere comprising either dry hydrogen, or wet hydrogen for one anneal in order to decarburize the alloy. A final anneal, described in detail in Patent No. 2,992,952, is employed to cause secondary cube grain growth.
  • the final stage of cold working preceding the final anneal reaches 93% whereas the immediately preceding stages do not exceed 80% of cold reduction there is normally obtained upon a suitable final anneal a secondary recrystallization texture with an orientation of (100) [012] wherein the cube edges have orientation of +25 25, +65 and -65 with respect to the rolling directions.
  • the cold reduction effecting at least about 93% reduction is the penultimate stage of cold rolling while the final stage effects less than 80% cold reduction there is obtained a face texture in the sheet following final anneal in which there may be as many as seven different orientations of the edges between zero degrees and with respect to the rolling direction.
  • stage in which the sheets have been cold rolled about 93% or more is the third stage prior to the final anneal, that is, it is followed by two additional stages in which the reduction during cold rolling is less than 80%, then the face texture will have completely random cube edge orientation.
  • a single cold rolling from the hot band to the final gauge must be in excess of 95% in order to be effective for the purpose of the present invention.
  • the sheet When so cold rolled the sheet will normally exhibit the [012] texture for a high crystal volume of the sheet after a secondary recrystallization anneal.
  • Particularly good results are obtained when the less drastic cold rolling stages comprise between 40% and 70% reduction whereas the most drastic step of cold rolling comprise 93% and higher. Not only is a greater proportion of the volume converted to grains whose faces are parallel to the face of the sheet but also the distribution of the direction of the cube edges is more widely split in at least four directions.
  • the sheets at final gauge will be of a thickness of 0.015 inch and less to as thin a sheet as about 0.005 inch.
  • the cold rolled sheet should have no thick adherent continuous oxide films on the surface when subjected to the final anneal. It will be understood that there may be a thin gray film or layer on the surface of the sheet at the time it enters the final anneal but extremely thick films are undesirable for reasons to be set forth thereinafter.
  • the final annealing temperature is preferably carried out at a temperature from 1100 C. to 1400 C. and preferably between 1200" C. and 1350 C. for a sutficient period of time to produce substantially complete secondary recrystallization.
  • grain nuclei have been found to be extremely sensitive to the surface energy and surface conditions of the sheet with respect to the growth thereof as compared to the growth of other nuclei such for example as cube-on-edge or [100] grain nuclei. It is absolutely necessary to remove all continuous films of oxides, silicates and the like from the surfaces of the sheets during the early stages of the final anneal and preferably before any substantial amount of secondary recrystallization grain growth occurs. The surfaces of the sheet usually will be bright if these oxide films are properly removed as will be set forth. Suitable annealing times for complete secondary recrystallization may be four hours at 1225 C. and as little as /2 hour at 1400 C. for sheets disposed in coils or stacks. A single sheet of a gauge of l or 2 mils may be completely secondarily recrystallized in a matter of a few minutes at 1400 C.
  • a refractory sheet separator between the adjacent turns or layers of the stack sheets to prevent them from Welding to each other and to permit a reducing atmos phere to enter and affect the surfaces of the sheet.
  • the separator refractory will be preferably a coating of fine refractory powder applied as a relatively porous layer to the surfaces of the sheet.
  • a finely divided powder such as aluminum oxide, zirconium oxide, or the like may be employed with good results.
  • the refractory should be so treated that it has no moisture and does not comprise any oxygen or oxides which will react with the surfaces of the sheet during the final anneal. Good results have been obtained by employing 200 to 350 mesh alumina that has been calcined or fired at temperatures of up to 1000 C. to 1400 C. and then stored in a sealed container to prevent moisture from entering therein until ready for use.
  • the stack or coil of cold reduced sheets with refractory coating applied, or a single sheet, is placed in the annealing furnace and an atmosphere that is non-carbonizing and non-oxidizing at annealin temperatures is introduced into the furnace.
  • the atmosphere may comprise a gas such as hydrogen which is substantially free from moisture, oxygen or other oxidizing components so that the sheet will not be oxidized during annealing but rather oxides will be reduced or caused to disappear rapidly.
  • a vacuum may be employed in the annealing furnace since under high vacuum conditions at annealing temperatures the silicon dioxide film on the surface of the sheets appears to react with the silicon in the sheet to form silicon monoxide which will rapidly evaporate from the surfaces.
  • the atmosphere should be such that at the surfaces of the sheet, rather than in some remote portion of the furnace, it has a dryness a nd freedom from oxygen so that continuous films will be caused to disappear. Excessively thick oxide layers on the sheets will take so long to be reduced that secondary recrystallization will have occurred before they are gone.
  • the hydrogen have a low dew point of the order of -50 C. when annealing at 1100 C. and below 40 C. when annealing at 1300 C.
  • Additions of helium, nitrogen or argon may be introduced into the hydrogen.
  • a high vacuum of at least l mm. of mercury at 1l00 C. and at least from l0 to l0 mm. at l300 C. and higher will give good results, during the final anneal. At these pressures silicon dioxide films will disappear promptly during the early part of the final anneal.
  • the prime requirement is that the atmosphere should be such that it will cause silica to be removed rapidly from the surfaces of the sheets at the annealing temperatures.
  • any coatings on or near the surface of the silicon sheet and the atmosphere that continuous films will be substantially completely removed from the surface of the sheet during the early part of the anneal prior to any substantial amount of secondary recrystallization occurring.
  • nuclei whose faces are parellel to the surface of the sheet will grow in preference to other grain nuclei and as a result a very high volumetric proportion of the sheet will be converted to face texture grains.
  • Example I An iron-silicon alloy comprising 2.8% silicon and 0.14% manganese, balance iron, was melted under vacuum and cast into an ingot. The ingot was heated to 1200 C. and hot rolled to a thickness of 2.6 mm. The hot rolled plate was then pickled and then cold rolled to a thickness of 1.8 mm. Following this the cold rolled sheet was annealed for five hours at 800 C. in hydrogen having a dew point of 70 F. Following the intermediate anneal the sheet was cold rolled to a thickness of 0.8 mm. a reduction of approximately 56%, and again subjected to an intermediate anneal for five hours at 800 C. in hydrogen having the dew point of 70 1 This annea G? if: decarburized the silicon-iron.
  • the sheet was then given a final cold working to effect a reduction from 0.8 to 0.04 mm, a reduction of thickness of 95%.
  • the sheet at final gauge was subjected to a final anneal for five hours at ll00 In hydrogen of a dew point of less than -50 C. These sheets were wrapped with chromium nickel plates in order to assist in the desired recrystallization. The sheets were bright by reaction of the hydrogen with the surfaces of the sheet. At the end of the anneal a substantially complete secondary recrystallization texture was obtained with an orientation almost completely of (100) [012]. More than of the secondary crystals exhibited a deviation of the cube edges of less than 10 from this orientaiton. In other words, there was obtained a face texture in which the cube-edges were oriented at angles of +25, -25, +65, and 65 with respect to the rolling direction in which nearly all of the grains had their edges aligned in these directions within 10".
  • Example H A vacuum melted alloy was prepared containing 2.7% silicon and 0.4% of manganese which after casting into ingots was heated to 1200 C. and hot rolled to a plate of a thickness of 2.6 mm. After pickling the plate. is cold rolled to a sheet of thickness of 0.l7 mm., a reduction in thickness of 93%. The sheet was then annealed for five hours at ll00 C. in dry hydrogen of a dew point of -50 C. The sheet had a high volumetric proportion of face tex'turc in which the cube edges were concentrated at directions of plus or minus 25 and plus or minus 65 with respect to the rolling direction.
  • Example 11 A portion of the band of Example II with a thickness of 0.17 mm. was subjected to an intermediate anneal for five hours at 900 C. in dry hydrogen of a dew point of -50 C. and was then cold rolled to a thickness of 0.08 mm., 53% reduction. This last sheet was then subjected to a final anneal as in Example I. Substantially all of the crystal texture comprised a face texture wherein the cube edges were concentrated at the following directions 0, +12", +78, -l2, 78, and 90 with respect to the rolling direction.
  • Example I V A portion of the band of Example Ill of a thickness of 0.08 mm. was detached prior to the final anneal and subjected to an additional intermediate anneal for five hours at 900 C. in dry hydrogen and then cold rolled to a thickness of 0.04 mm. to effect a reduction of 50%. The sheet was then subjected for five hours to a final anneal at ll00 C. in hydrogen of a dew point of 50 C. The sheets annealed .brigh. After the final anneal there is obtained a substantially complete secondary recrystallization of the entire volume of the sheet. A test of the orientation of the edges indicated that it was a face texture with a completely random cube edge orien tation.
  • Example V A portion of the ingot of Example If after being hot rolled to a plate of a thickness of 2.6 mm. was cold rolled in a single stage to effect a reduction of 97%. When subjected to a final anneal as in Example II it exhibited a face texture with an orientation of (100) [012]. When a portion of the sheet prior to the final anneal was annealed 5 hours at 900 C. and subjected to a further cold rolling to effect a reduction of 50% and then the resulting thin gauge sheet was subjected to at least similar final anneal there was obtained a face texture material wherein the cube edges were oriented randomly. This indicates the effect of following a high reduction cold rolling step by a cold rolling step in which a reduction of less than 70% is applied so as to produce random edge orientation in a face texture.
  • Example VI An alloy comprising 2.2% silicon, the remainder being iron, was vacuum melted and the resulting ingot was heated to 1200 C. and hot rolled to a plate of a thickness of millimeters. After pickling it was cold rolled to a sheet of a thickness of 0.2 mm., 96% reduction in thickness. Thereafter the sheet was annealed in one pass for ten minutes at 1000 C. in dry hydrogen, 50 C. The sheet was then cold worked again to reduce its thickness to 0.12 millimeters, 40% reduction in thickness. From the sheet so obtained, rings were punched and annealed in a vacuum of less than mm. at 1200 C. Examination of the rings indicated that they comprised grains having a face texture but with completely random edge orientation.
  • Example VII The ingot of Example VI after hot rolling to a plate of 5 mm. thickness had a portion separated and separately cold rolled to a thickness of 0.12 mm. in four steps, in each of which the reduction in thickness was in the range of from 55 to 70% with intermediate anneals at temperatures of from 800 C. to 1100 C. in dry hydrogen. The final anneal was similar to that as in Example VI.
  • the sheet showed cube texture wherein four of the cube edges did not deviate from the rolling direction more than 10%.
  • the cold rolling comprises at least one stage wherein the reduction is 93% and higher, is the fact that the face texture is easier to obtain in sheets having considerable thickness than cube texture can be obtained. Furthermore a higher proportion of the grains will have face texture than has been obtained for sheets with a cube texture exclusively.
  • the sheets of this invention will comprise a very high proportion of over 70% and usually over 90% of the volume of face texture grains.
  • the surface of the sheet at the time of initiation of the final anneal being free from any thick, adherent, continuous oxide surface layers and any sheet separator coating of a refractory material present on the surface being porous and substantially non-oxidizing to the sheet surface during the final anneal
  • the final annealing atmosphere being a reducing atmosphere substantially free from moisture and other oxidizing components which would react with the surface of the sheet, so correlating the final annealing temperature, the final annealing atmosphere and any materials present on or near the surface of the sheet that during the initial stages of the final anneal prior to the occurrence of any appreciable recrystallization any continuous surface oxides 10 on the sheet surface will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of the primary recrystallization will grow preferentially to other
  • the method of producing sheets of iron-silicon alloy having face texture comprising from 2% to 5% silicon, up to 1% of at least one element of the group consisting of manganese, molybdenum and chromium, and the balance being iron except for small amounts of impurities and additives, the steps comprising hot rol'ling an ingot to produce a sheet of a thickness of from about 0.5 to 0.08 inch of the silicon-iron alloy, cold rolling in at least two final stages the hot rolled sheet to final gauge to efiect a reduction of at least 93% in at least one of the stages, the reduction in the other stage being at least 30%, subjecting the cold rolled sheet to an intermediate anneal between the cold rolling steps at a temperature of from 800 C to 1100 C., and finally annealing the sheet at final gauge at a temperature of above 1100 C.
  • the surface of the sheet being free from thick adherent oxide surface layers and any sheet separator refractory coatings present on the surface of the sheet being substantially non-reactive during the final anneal
  • the final annealing atmosphere being a reducing atmosphere substantially completely free from oxygen, moisture and other oxidizing components which will react with the surface of the sheet, the atmosphere, the annealing temperature and any materials present on or near the surface of the sheet being so correlated that during the initial stages of the final anneal prior to the occurrence of any appreciable secondary recrystallization, any continuous surface oxides on the sheet will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of primary recrystallization will grow preferentially to produce a face texture in the sheet.
  • the method of producing sheets of iron-silicon alloy having face texture comprising from 2% to 5% silicon, up to 1% of at least one element of the group consisting of manganese, molybdenum and chromium, and the balance being iron except for small amounts of impurities and additives, the steps comprising hot rolling an ingot to produce a hot rolled sheet of a thickness of from about 0.5 to 0.08 inch of silicon-iron alloy, cold rolling in at least two final stages the hot rolled sheet to final gauge to effect a reduction of from 30% to in the penultimate cold rolling stage and a final reduction of at least 93% in the last stage, subjecting the cold rolled sheet to an intermediate anneal between the cold rolling steps at a temperature of from 800 C.
  • the sheet being free from thick adherent oxide surface layers and any sheet separator refractory coatings present on the surface of the sheet being substantially non-reactive during the final anneal, the final annealing atmosphere being a reducing atmosphere substantially completely free from oxygen, moisture and other oxidizing components which will react with the surface of the sheet, the atmosphere, the annealing temperature and any materials present on or near the surface of the sheet being so correlated that during the initial stages of the final anneal prior to the occurrence of any appreciable secondary recrystallization, any continuous surface oxides on the sheet will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of primary recrystallization will grow preferentially to produce a face texture in the sheet.
  • the steps comprising hot rolling an ingot of the alloy to produce a hot rolled sheet of a thickness of from about to 0.08 inch, cold rolling in at least two final stages of the hot rolled sheet to final gauge to effect a reduction of at least 93% in the penultimate cold rolling stage and a final reduction of from 30% to 80%, subjecting the cold rolled sheet to an intermediate anneal between the cold rolling steps at a temperature of from 800 C. to 1100 C., and finally annealing the sheet at final gauge at a temperature of above llOO C.
  • the surface of the sheet being free from thick adherent oxide surface layers and any sheet separator refractory coatings present on the surface of the sheet beingsubstantially non-reactive during the final anneal, the final annealing atmosphere being a reducing atmosphere substantially completely free from oxygen, moisture and other oxidizing components which will react with the surface of the sheet, the atmosphere, the annealing temperature and any materials present on or near the surface of the sheet being so correlated that during the initial stages of the final anneal prior to the occurrence of any appreciable secondary recrystallization, any continuous surface oxides on the sheet will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of primary recrystallization will grow preferentially to produce a face texture in the sheet wherein the cube edges are randomly oriented.
  • steps comprising cold rolling only once without any intermediate annealing a sheet having random grain texture of the iron-silicon alloy to final gauge to effect a reduction of at least and finally annealing the sheet at final gauge thickness at a temperature of above 1100 C. for a period of time sufiicient to effect substantially complete recrystallization thereof, the surface of the sheet at the time of initiation of the final anneal being free from any thick, adherent, continuous oxide surface layers and any sheet separator coating of a refractory material present on the surface being porous and substantially non-oxidizing to the sheet surface during the final anneal, the final annealing atmosphere being a reducing atmos phere substantiallyfree from moisture and other oxidizing components which, would react with the surface of the sheet, so correlating the final annealing temperature,
  • any continuous surface oxides on the sheet surface will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of the primary recrystallization Will grow preferentially to other grain nuclei to produce a face texture iii the sheet.

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Description

Nov. 16, 1965 ANZ ,218,202
0.6 3 METHOD OF USING A CRITICAL COLD RDLLING STAGE T0 PRODUCE SILICON-IRON SHEETS Flled May 28, 1964 2 Sheets-Sheet 1 Fig. I Fig. 2 CI CI ROLLING ROLLING DIRECTION DIRECTION MAGNETIC I MAGNETIC FLUX WITNESSES INVENTOR i n? Diet h G0 BY rlc nz Warm? D. GANZ 3,218,202
2 SheetsSheet 2 Nov. 16, 1965 METHOD OF USING A CRITICAL COLD ROLLING STA T0 PRODUCE SILICON-IRON SHEETS Filed May 28, 1964 wmDhxmk mmDO SNIVBQ :JO HSVLNBOHEId 3,218,202 METHUD F USENG A CRITICAL COLD ROLLlNG STAGE T0 PRGDUCE SILICGN-IRON SHEETS Dietrich Ganz, Hanan, Germany, assignor to Vacuumschmelze Aktiengeselischaft, Hanan, Germany, a corporation of Germany Filed May 28, 1964, Ser. No. 371,881 Claims priority, application Germany, Dec. 24, 1959, V 17,795 5 Claims. (Ci. 148112) This application is a continuation-in-part of my application Serial No. 77,757, filed December 22, 1960, and now abandoned.
This invention relates to a process for producing silicon-iron sheets having a grain structure in which the cube faces are essentially parallel to the surface of the sheet while the edges are oriented in at least four directions.
Magnetic materials for various electrical engineering applications have been produced with preferred crystallographic orientation wherein the magnetic properties are anisotropic, that is, in at least one direction, and quite often in two directions in the plane of the sheet, the optimum magnetic properties are exhibited Whereas in other directions the magnetic properties are inferior.
It is known that .many magnetic materials, such for example, as silicon-iron and nickel-iron alloys which crystallographic in the cubic system, are characterized by the direction of easiest magnetization being along the cube edge. The permeability of these magnetic materials is higher in the direction parallel to the cube edge than in any other direction. The ease of magnetization and permeability is poorer along a face diagonal of the cube and the poorest magnetic properties are exhibited along the long diagonal from opposite vertices of the cube.
Accordingly, efforts have been made to produce siliconiron alloys so that a majority of the grains have their lattice structures such that the crystallographic cubes are oriented with the cube edges of the various grains;being parallel to each other, usually parallel to the rolling direction for four of the cube edges, while four other cube edges are perpendicular to the rolling direction, with the cube faces being parallel to the surface of the sheet. This is known as the cube-on-face texture. Processes for producing magnetic sheets of silicon-iron alloy having the cube-on-face texture have been recently developed. Earlier a process had been developed for producing the socalled Goss texture wherein a cold rolled sheet is produced which after a final anneal has a grain texture wherein the lattices of the crystal structure correspond to cubes standing on edge so that four cube edges of each elementary cube lie in the rolling direction while the surface diagonals of two faces of the cube lie in the plane of the surface of the sheet but in a direction transverse to the rolling direction. This Goss texture or, as it is often designated, singly oriented, sheet has the preferred direction of magnetization in a direction of rolling but exhibits poor magnetic properties in a direction perpendicular to the rolling direction.
As disclosed in US. Patent 2,992,952, techniques for producing cube-on-face grain texture have been developed for processing silicon-iron sheets. Briefly these processes comprise repeatedly cold rolling silicon-iron alloy, with or Without certain additions of manganese and other alloying components, to effect reductions of 50 to 75% with intermediate anneals between successive cold rolling operations and finally subjecting the silicon-iron sheet to a final anneal at a temperature of from 950 C. to 1425" C. for a period of time to effect substantially complete secondary recrystallization. During this final anneal it is critical that the atmosphere be so free from oxidizing atent C 3,218,202 Patented Nov. 16, 1965 components that any silicon oxide films on the surface of the sheets will disappear and the sheet becomes mirror bright. The surface condition enables the secondary recrystallization of cube-on-face grain nuclei in preference to cube-on-edge and other orientations of grain nuclei which may be present at the end of the primary recrystallization phase of the final anneal. This product comprises cube-on-face grains in which the preferred directions of magnetization are in the direction of rolling and in a direction perpendicular thereto. Such products are of considerable value for producing transformers and other electrical devices in which magnetic flux is caused to travel in directions at angles to each other.
It has been found that for some applications in the electrical industry improved results may be obtained if the magnetic sheets consist of grains whose crystal lattice structures comprise cube faces parallel to the surface of the sheet but whose edges are oriented in more than two directions. It would be desirable to have products in which the cube edges of such grains are oriented either randomly or in a plurality of directions, preferably four or more, whereby these applications could employ the material to better advantage. One particular application for such silicon-iron sheets is in circular punchings which are required for small motors and generators, in both stators and rotors, as well as in other applications requiring complex magnetic paths deviating from each other at angles other than 90.
The terms cube texture and face texture are defined for the purposes of this invention as follows:
Cube texture denotes a grain texture in a sheet of metal wherein there is over 50%, and preferably over 70%, of the crystal volume of grains having a cubic crystal lattice structure in which two cube faces are parallel, within 10, to the sheet surface, and the cube edges are so oriented that four edges are parallel within 15, to one direction in the plane of the sheet, usually the rolling direction, and four other cube edges are parallel, within 15, to another direction in the plane of the sheet perpendicular to the said one direction.
Face texture denotes a grain texture in a sheet of metal wherein there is over 50%, and preferably over and up to 95% or more, of the crystal volume of grains having a crystal lattice structure in which two cube faces are parallel, Within 10, to the sheet surface, and four of the twelve cube edges of such grains are (1) either randomly oriented or (2) are oriented parallel to at least four different directions, all of which deviate from the rolling direction, or (3) comprise a mixture of which the edges of at least 20% of the grains are so randomly oriented and/or oriented in at least four different directions with respect to the direction of rolling while the balance comprises cube texture grains in which the edges are parallel to the direction of rolling.
Randomly oriented cube edges as employed herein applies to a sheet of metal having a plurality of grains having a cubic crystal lattice structure wherein the cube faces are substantially parallel to the sheet surface, and denotes that the tube edges of said cube faces show no significant concentration in any particular direction but are scattered in all directions.
Referring to FIG. 5 of the drawing there is illustrated the difference between the orientation of the edges of cube grains in cube texture and face texture sheets. In producing the curves a sheet of the magnetic material is analyzed to determine the percentage of cube grains, that is grains whose faces are parallel to or within 10 to the sheet surface. Then the adges of these cube grains are measured to determine the angle between the rolling direction and the four edges of each grain most closely parallel to the direction of rolling. The rolling direction is set as 0. These measurements are made up to S5 with respect to the rolling direction. The percentage, or number, of cube grains within each degree is plotted on coordinate paper and a curve is drawn.
As is evident from curve A in PEG. 5, in a cube texture sheet there is a high concentration of grains at and close to the and 90 angles, with the number of grains at angles departing therefrom diminishing along a typical, rapid probability curve drop ofi to practically zero grains in the 3Q to 60 angle ranges.
For a sheet with face texture grain orientation, as is apparent from curve B of FlG. 5, there are two distinct grain edge concentrations at the 25 and 65 angles in a probability type curve distribution. There are twice as many peaks in the curve B as compared to curve A, though each cube edge distribution peak in curve is half as high as the peaks of curve A. it should be understood that curve B is only illustrative, since there may be more cube edge distribution peaks, for exampl 6 or 8 within +90 and -99 of the rolling direction.
Fully random oriented cube grain texture is shown in curve C.
The object of the present invention is to provide a process for cold rolling in a predetermined manner sheets of silicon iron alloy and then subjecting the sheets to a final anneal which will cause nuceli having faces parallel to the sheet to grow preferentially whereby to produce a face texture in the sheet.
Another object of the invention is to provide a process with sheets of silicon-iron alloy comprising from 2% to silicon, up to 1% of manganese, molybdenum or chromium or any combination thereof, and the balance being iron to effect at least two stages of cold rolling wherein at least one of the last three stages of cold rolling effects a reduction in thickness of at least 93% and preferably 95% or higher while the other stages effect a reduction in thickness of at least 30%, and then subjecting the cold rolled sheet ,to a final anneal under conditions that will enable. grain nuclei having faces parallel to the surface of the sheet to grow in preference to other nuclei during the secondary recrystallization growth during the final anneal.
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 eference should be had to the following detailed description and drawing in which:
FIGURE 1 is a schematic showing of the orientation of the cube grains in a cube texture sheet;
FIG. 2 is a schematic illustration of the arrangement of the crystal lattice cubes in a face texture sheet;
FIG. 3 shows schematically the comparative magnetic flux in different portions of a ring punching of a sheet of magnetic material having a cube texture;
FIG. 4 is a schematic showing of the relative amount of magnetic flux for different portions of a ring punching from a sheet having face texture, the magnetizing field being the same in all directions in both FIGS. 3 and 4; and
FIG. 5 is a curve plotting the percentage of grains having a given angular deviation of the edges from the rolling direction for both cube texture and face texture sheets.
As illustrated in PEG. 1, a sheet of silicon-iron produced in accordance with the invention in US. Patent 2,992,952, previously identified, comprises grains whose cube faces are parallel to the surface of the sheet, which in this case is parallel to the sheet of paper, while the cube edges are oriented parallel to the rolling direction a and in a direction transverse to the rolling direction namely direction [2.
FIG. 2 illustrates the orientation of the crystal lattices of grains in a sheet having face texture. It will be noted that the rolling direction a which extends in a direction vertically of the sheet of the paper is not necessarily parallel to any of the cube edges of the grains illustrated.
The faces of each of the four grains are parallel to the surface of the sheet but the cube edges, it will be noted are: parallel to four diffenent directions 0, d, e and f. The direction (1 represents the rolling direction and accordingly the directions c, (I, e and f extend at an angle :25 and i65", respectively with respect to the rolling direc-- tion. It will be understood, of course, that there may additional directions of orientation of the cub edges in addition to those shown. Thus cube edges may also be parallel to directions forming angles of :37" and :53" with respect to the direction of rolling as well as the directions at 125 and :65.
it wili be understood, of course, that the orientation of the cube races and the cube edges is not absolutely precise. Normally the cube faces will be Within 10 of parallelism to the surface of the sheet, usually within 5 of parallelism. Eimilarly, the cube edges even for cube texture material will not be oriented entirely as illustrated in FIG. 1. Usually the majority of the grains will have their edges parallel within 15 of the rolling direction. In some instances sharper texture alignment is obtained than in other instances. in a similar manner the directions 0, d, e and f in FIG. 2 do not represent the absolute direction of all the grains of the face texture sheet. Within an angle of 5 there may be a substantial number of the grains whose edges correspond to the given directions, however, there will be a sub stantial proportion of grains whose edges will depart from any of these four directions by an angle of 10 or 15 In addition there are occasionally some grains Whose edges depart even more from these directions; This distribution is typified by the curves of FIG. 5. Asa rule, the cube faces of the grains are ordinarily much closer in parallelism to the face of the sheet than the cube edges with respect to any particular direction. of the benefits of the present invention are enhanced by the fact that not too great a proportion of the grains have their cube edges precisely parallel to the four directions 0, d, e and 7. As a consequence, there is a more uniform magnetic permeability in all directions as the sheet of material represented by FIG. 2 is subjected to a magnetic field whose direction varies from O to with respect to a given point.
Referring to FIG. 3 of the drawing there is illustrated a circular punching in ring form which may be employed for electrical apparatus by providing therein teeth for the insertion of windings. This punching has been prepared from cube texture material having grains oriented as illustrated in FIG. 1. It will be noted that for a given magnetizing force there will be a much greater magnetic flux in the rolling direction and in a direction transverse to the rolling direction as indicated by the four magnetic flux arrows at these points. In a direction slightly divergent from these directions the magnetic flux is much less and is represented by three arrows. At an angle of 45 from the rolling direction the magnetic flux in the sheet is reduced. It will be appreciated that in electrical apparatus it is desirable that the magnetic flux be substantially constant at every point in the punching in order to obtain uniformity of operation of a motor or other electrical equipment.
As illustrated in FIG. 4 of the drawing, in a punching having face texture, as a given magnetizing force is ap plied circumferentially with respect to the center of the punching the magnetic flux generated is constant in substantially all directions as represented by the three magnetic flux arrows throughout. For electrical motors and generators a punching having the magnetic properties as shown in FIG. 4 is greatly to be preferred to one having the properties shown in FIG. 3.
It will be understood, of course, that the magnetic flux; properties as shown in FIG. 4 are distinct from those ob. tained with a conventional isotropic hot rolled silicon sheet which has no orientation of grains of any type. The magnetic flux in the plane of the sheet of HG. is ex.
Some
tremely high for a given magnetizing force whereas for ordinary hot rolled silicon steel in which the grains are randomly distributed the magnetic flux would be much poorer through uniform in the plane of the sheet.
In particular the total magnetic resistance at any given point in a punching having face texture is much less than that in any other material known heretofore including the cube texture material of FIG. 3. It has been found that sheets having a face texture when subjected to alternating current magnetization exhibit lower eddy current losses than sheets with the cubic texture. It is believed that this is due to the fact that with a face texture the spaces of the Blochs Walls separating the magnetic domains from each other are smaller than in sheets having cube texture. An additional advantage lying with sheets having face texture is in the fact that they can be produced more simply and more reliably with a higher percentage of desirable grain orientation than sheets having the cube tex ture.
The process of the present invention which results in the production of sheets having face texture may be applied to silicon-iron alloys containing from 2% to 5% silicon, up to 1% of one element from the group consisting of manganese, molybdenum and chromium, with the balance being iron except for additives and impurities. It will be understood that sulfur, and other additives, may be present in the sheets in proportions to enable cube grain growth. The iron-silicon alloy may be prepared by the usual practice either in open hearth or in an electric furnace or in a vacuum furnace for highest purity materials, cast into an ingot which ingot is then hot rolled or forged into a heavy plate. The heavy plate may be of a thickness of as much as 0.5 inch or as thin as 0.080 to 0.10 inch in thickness. The hot rolled plate will usually be pickled to remove any hot roll scale or other surface defects. Hot rolling normally will have been carried out at a temperature of as high as 1200 C. Thereafter the hot rolled plate is cold rolled once or twice and even three times, depending on the final gauge of the desired silicon-iron sheet. Between successive cold rolling steps the sheet is annealed at temperatures of from 800 C. to 1100 C., in a reducing atmosphere comprising either dry hydrogen, or wet hydrogen for one anneal in order to decarburize the alloy. A final anneal, described in detail in Patent No. 2,992,952, is employed to cause secondary cube grain growth.
It has been found to be critical in the preparation of face texture silicon sheet that at least one of the last three stages of cold rolling effect a reduction of 93% and preferably 95% and higher. The other stages of cold rolling may effect a reduction of from 30 to 80%. Heretofore a final reduction in excess of 75% was not common and it was extremely rare to reach a cold reduction of 90%. All previous experience indicates that cold reductions up to 75%, or even 85% and up to 90%, result in a cube texture with cube edges aligned with the direction of roll- It is completely unexpected that different types of face texture i.e., random or concentrated in four or more directions, or different proportions of face texture with some cube texture orientation, or even different orientations of the cube edges of the grains are obtained as a result of different combinations of at least one extremely high reduction of 93% or higher combined with a lower cold working reduction for a stage preceding or following the high reduction step. Thus if the final stage of cold working preceding the final anneal reaches 93% whereas the immediately preceding stages do not exceed 80% of cold reduction there is normally obtained upon a suitable final anneal a secondary recrystallization texture with an orientation of (100) [012] wherein the cube edges have orientation of +25 25, +65 and -65 with respect to the rolling directions. If the cold reduction effecting at least about 93% reduction is the penultimate stage of cold rolling while the final stage effects less than 80% cold reduction there is obtained a face texture in the sheet following final anneal in which there may be as many as seven different orientations of the edges between zero degrees and with respect to the rolling direction. If the stage in which the sheets have been cold rolled about 93% or more is the third stage prior to the final anneal, that is, it is followed by two additional stages in which the reduction during cold rolling is less than 80%, then the face texture will have completely random cube edge orientation. A single cold rolling from the hot band to the final gauge must be in excess of 95% in order to be effective for the purpose of the present invention. When so cold rolled the sheet will normally exhibit the [012] texture for a high crystal volume of the sheet after a secondary recrystallization anneal. Particularly good results are obtained when the less drastic cold rolling stages comprise between 40% and 70% reduction whereas the most drastic step of cold rolling comprise 93% and higher. Not only is a greater proportion of the volume converted to grains whose faces are parallel to the face of the sheet but also the distribution of the direction of the cube edges is more widely split in at least four directions.
Following the cold rolling of the silicon-iron alloy sheet to final gauge it is then subjected to a critical anneal which effects secondary recrystallization and enables preferential grain growth of grains whose faces are parallel or essentially parallel to the surface of the sheet. The sheets at final gauge will be of a thickness of 0.015 inch and less to as thin a sheet as about 0.005 inch. The cold rolled sheet should have no thick adherent continuous oxide films on the surface when subjected to the final anneal. It will be understood that there may be a thin gray film or layer on the surface of the sheet at the time it enters the final anneal but extremely thick films are undesirable for reasons to be set forth thereinafter. The final annealing temperature is preferably carried out at a temperature from 1100 C. to 1400 C. and preferably between 1200" C. and 1350 C. for a sutficient period of time to produce substantially complete secondary recrystallization.
As is well known, primary recrystallization takes place first and occurs rapidly, depending on the amount of previous cold working and the temperature, so that it will be effected in a short period of time. Secondary recrystallization follows thereafter but requires a far longer time and higher temperature than that at which primary recrystallization occurs. The crystallographic orientation of the grain lattice is different as a rule in secondary recrystallization than the orientation of the primary grains. As primary recrystallation occurs there will be produced a considerable variety of grain nuclei which include a substantial number of nuclei whose crystallographic cube faces are essentially parallel to the surface of the sheet. These latter grain nuclei have been found to be extremely sensitive to the surface energy and surface conditions of the sheet with respect to the growth thereof as compared to the growth of other nuclei such for example as cube-on-edge or [100] grain nuclei. It is absolutely necessary to remove all continuous films of oxides, silicates and the like from the surfaces of the sheets during the early stages of the final anneal and preferably before any substantial amount of secondary recrystallization grain growth occurs. The surfaces of the sheet usually will be bright if these oxide films are properly removed as will be set forth. Suitable annealing times for complete secondary recrystallization may be four hours at 1225 C. and as little as /2 hour at 1400 C. for sheets disposed in coils or stacks. A single sheet of a gauge of l or 2 mils may be completely secondarily recrystallized in a matter of a few minutes at 1400 C.
If the sheets are annealed in coils or stacks as normal commercial practice will dictate, there is ordinarily applied a refractory sheet separator between the adjacent turns or layers of the stack sheets to prevent them from Welding to each other and to permit a reducing atmos phere to enter and affect the surfaces of the sheet. The separator refractory will be preferably a coating of fine refractory powder applied as a relatively porous layer to the surfaces of the sheet. A finely divided powder such as aluminum oxide, zirconium oxide, or the like may be employed with good results. The refractory should be so treated that it has no moisture and does not comprise any oxygen or oxides which will react with the surfaces of the sheet during the final anneal. Good results have been obtained by employing 200 to 350 mesh alumina that has been calcined or fired at temperatures of up to 1000 C. to 1400 C. and then stored in a sealed container to prevent moisture from entering therein until ready for use.
The stack or coil of cold reduced sheets with refractory coating applied, or a single sheet, is placed in the annealing furnace and an atmosphere that is non-carbonizing and non-oxidizing at annealin temperatures is introduced into the furnace. The atmosphere may comprise a gas such as hydrogen which is substantially free from moisture, oxygen or other oxidizing components so that the sheet will not be oxidized during annealing but rather oxides will be reduced or caused to disappear rapidly. A vacuum may be employed in the annealing furnace since under high vacuum conditions at annealing temperatures the silicon dioxide film on the surface of the sheets appears to react with the silicon in the sheet to form silicon monoxide which will rapidly evaporate from the surfaces. The atmosphere should be such that at the surfaces of the sheet, rather than in some remote portion of the furnace, it has a dryness a nd freedom from oxygen so that continuous films will be caused to disappear. Excessively thick oxide layers on the sheets will take so long to be reduced that secondary recrystallization will have occurred before they are gone.
it has been found to be critical that the hydrogen have a low dew point of the order of -50 C. when annealing at 1100 C. and below 40 C. when annealing at 1300 C. Additions of helium, nitrogen or argon may be introduced into the hydrogen. A high vacuum of at least l mm. of mercury at 1l00 C. and at least from l0 to l0 mm. at l300 C. and higher will give good results, during the final anneal. At these pressures silicon dioxide films will disappear promptly during the early part of the final anneal. The prime requirement is that the atmosphere should be such that it will cause silica to be removed rapidly from the surfaces of the sheets at the annealing temperatures. To accomplish this it is necessary to so correlate the annealing temperature, any coatings on or near the surface of the silicon sheet and the atmosphere that continuous films will be substantially completely removed from the surface of the sheet during the early part of the anneal prior to any substantial amount of secondary recrystallization occurring. Under these conditions nuclei whose faces are parellel to the surface of the sheet will grow in preference to other grain nuclei and as a result a very high volumetric proportion of the sheet will be converted to face texture grains. The following examples are illustrative of the practice of the invention.
Example I An iron-silicon alloy comprising 2.8% silicon and 0.14% manganese, balance iron, was melted under vacuum and cast into an ingot. The ingot was heated to 1200 C. and hot rolled to a thickness of 2.6 mm. The hot rolled plate was then pickled and then cold rolled to a thickness of 1.8 mm. Following this the cold rolled sheet was annealed for five hours at 800 C. in hydrogen having a dew point of 70 F. Following the intermediate anneal the sheet was cold rolled to a thickness of 0.8 mm. a reduction of approximately 56%, and again subjected to an intermediate anneal for five hours at 800 C. in hydrogen having the dew point of 70 1 This annea G? if: decarburized the silicon-iron. The sheet was then given a final cold working to effect a reduction from 0.8 to 0.04 mm, a reduction of thickness of 95%. The sheet at final gauge was subjected to a final anneal for five hours at ll00 In hydrogen of a dew point of less than -50 C. These sheets were wrapped with chromium nickel plates in order to assist in the desired recrystallization. The sheets were bright by reaction of the hydrogen with the surfaces of the sheet. At the end of the anneal a substantially complete secondary recrystallization texture was obtained with an orientation almost completely of (100) [012]. More than of the secondary crystals exhibited a deviation of the cube edges of less than 10 from this orientaiton. In other words, there was obtained a face texture in which the cube-edges were oriented at angles of +25, -25, +65, and 65 with respect to the rolling direction in which nearly all of the grains had their edges aligned in these directions within 10".
Example H A vacuum melted alloy was prepared containing 2.7% silicon and 0.4% of manganese which after casting into ingots was heated to 1200 C. and hot rolled to a plate of a thickness of 2.6 mm. After pickling the plate. is cold rolled to a sheet of thickness of 0.l7 mm., a reduction in thickness of 93%. The sheet was then annealed for five hours at ll00 C. in dry hydrogen of a dew point of -50 C. The sheet had a high volumetric proportion of face tex'turc in which the cube edges were concentrated at directions of plus or minus 25 and plus or minus 65 with respect to the rolling direction.
Example 11] A portion of the band of Example II with a thickness of 0.17 mm. was subjected to an intermediate anneal for five hours at 900 C. in dry hydrogen of a dew point of -50 C. and was then cold rolled to a thickness of 0.08 mm., 53% reduction. This last sheet was then subjected to a final anneal as in Example I. Substantially all of the crystal texture comprised a face texture wherein the cube edges were concentrated at the following directions 0, +12", +78, -l2, 78, and 90 with respect to the rolling direction.
Example I V A portion of the band of Example Ill of a thickness of 0.08 mm. was detached prior to the final anneal and subiected to an additional intermediate anneal for five hours at 900 C. in dry hydrogen and then cold rolled to a thickness of 0.04 mm. to effect a reduction of 50%. The sheet was then subjected for five hours to a final anneal at ll00 C. in hydrogen of a dew point of 50 C. The sheets annealed .brigh. After the final anneal there is obtained a substantially complete secondary recrystallization of the entire volume of the sheet. A test of the orientation of the edges indicated that it was a face texture with a completely random cube edge orien tation.
Example V A portion of the ingot of Example If after being hot rolled to a plate of a thickness of 2.6 mm. was cold rolled in a single stage to effect a reduction of 97%. When subjected to a final anneal as in Example II it exhibited a face texture with an orientation of (100) [012]. When a portion of the sheet prior to the final anneal was annealed 5 hours at 900 C. and subjected to a further cold rolling to effect a reduction of 50% and then the resulting thin gauge sheet was subjected to at least similar final anneal there was obtained a face texture material wherein the cube edges were oriented randomly. This indicates the effect of following a high reduction cold rolling step by a cold rolling step in which a reduction of less than 70% is applied so as to produce random edge orientation in a face texture.
9 Example VI An alloy comprising 2.2% silicon, the remainder being iron, was vacuum melted and the resulting ingot was heated to 1200 C. and hot rolled to a plate of a thickness of millimeters. After pickling it was cold rolled to a sheet of a thickness of 0.2 mm., 96% reduction in thickness. Thereafter the sheet was annealed in one pass for ten minutes at 1000 C. in dry hydrogen, 50 C. The sheet was then cold worked again to reduce its thickness to 0.12 millimeters, 40% reduction in thickness. From the sheet so obtained, rings were punched and annealed in a vacuum of less than mm. at 1200 C. Examination of the rings indicated that they comprised grains having a face texture but with completely random edge orientation.
Example VII The ingot of Example VI after hot rolling to a plate of 5 mm. thickness had a portion separated and separately cold rolled to a thickness of 0.12 mm. in four steps, in each of which the reduction in thickness was in the range of from 55 to 70% with intermediate anneals at temperatures of from 800 C. to 1100 C. in dry hydrogen. The final anneal was similar to that as in Example VI. The sheet showed cube texture wherein four of the cube edges did not deviate from the rolling direction more than 10%.
One of the advantages of the present process wherein the cold rolling comprises at least one stage wherein the reduction is 93% and higher, is the fact that the face texture is easier to obtain in sheets having considerable thickness than cube texture can be obtained. Furthermore a higher proportion of the grains will have face texture than has been obtained for sheets with a cube texture exclusively. The sheets of this invention will comprise a very high proportion of over 70% and usually over 90% of the volume of face texture grains.
It will be understood that the above description and drawing are illustrative and not limiting of the practice of the invention.
I claim as my invention:
1. The process of producing sheets of iron-silicon alloy having a face texture, the alloy consisting essentially of from 2% to 5% silicon, up to 1% of at least one element from the group consisting of manganese, molybdenum and chromium, and the balance being iron except for small amounts of additives and impurities, the steps comprising, cold rolling in at least two stages hot rolled sheet of the iron-Silicon alloy having a random grain texture to a final gauge to effect a reduction in thickness of the sheet of at least 93% in at least one of the last two stages or in at least one of the last three stages of cold rolling when more than two stages of cold rolling are applied thereto, the reduction in the thickness in the other stages being at least 30%, subjecting the cold rolled sheet to an intermediate anneal at a temperature of from 800 C. to 1100 C. between each two successive cold rolling stages, and finally annealing the sheet at final gauge thickness at a temperature of above 1100 C. for a period of time sutficient to effect substantially complete secondary recrystallization thereof, the surface of the sheet at the time of initiation of the final anneal being free from any thick, adherent, continuous oxide surface layers and any sheet separator coating of a refractory material present on the surface being porous and substantially non-oxidizing to the sheet surface during the final anneal, the final annealing atmosphere being a reducing atmosphere substantially free from moisture and other oxidizing components which would react with the surface of the sheet, so correlating the final annealing temperature, the final annealing atmosphere and any materials present on or near the surface of the sheet that during the initial stages of the final anneal prior to the occurrence of any appreciable recrystallization any continuous surface oxides 10 on the sheet surface will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of the primary recrystallization will grow preferentially to other grain nuclei to produce a face texture in the sheet.
2. The method of producing sheets of iron-silicon alloy having face texture, the alloy comprising from 2% to 5% silicon, up to 1% of at least one element of the group consisting of manganese, molybdenum and chromium, and the balance being iron except for small amounts of impurities and additives, the steps comprising hot rol'ling an ingot to produce a sheet of a thickness of from about 0.5 to 0.08 inch of the silicon-iron alloy, cold rolling in at least two final stages the hot rolled sheet to final gauge to efiect a reduction of at least 93% in at least one of the stages, the reduction in the other stage being at least 30%, subjecting the cold rolled sheet to an intermediate anneal between the cold rolling steps at a temperature of from 800 C to 1100 C., and finally annealing the sheet at final gauge at a temperature of above 1100 C. for a period of time to effect substantially complete secondary recrystallization thereof, the surface of the sheet being free from thick adherent oxide surface layers and any sheet separator refractory coatings present on the surface of the sheet being substantially non-reactive during the final anneal, the final annealing atmosphere being a reducing atmosphere substantially completely free from oxygen, moisture and other oxidizing components which will react with the surface of the sheet, the atmosphere, the annealing temperature and any materials present on or near the surface of the sheet being so correlated that during the initial stages of the final anneal prior to the occurrence of any appreciable secondary recrystallization, any continuous surface oxides on the sheet will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of primary recrystallization will grow preferentially to produce a face texture in the sheet.
3. The method of producing sheets of iron-silicon alloy having face texture, the alloy comprising from 2% to 5% silicon, up to 1% of at least one element of the group consisting of manganese, molybdenum and chromium, and the balance being iron except for small amounts of impurities and additives, the steps comprising hot rolling an ingot to produce a hot rolled sheet of a thickness of from about 0.5 to 0.08 inch of silicon-iron alloy, cold rolling in at least two final stages the hot rolled sheet to final gauge to effect a reduction of from 30% to in the penultimate cold rolling stage and a final reduction of at least 93% in the last stage, subjecting the cold rolled sheet to an intermediate anneal between the cold rolling steps at a temperature of from 800 C. to 1100 C., and finally annealing the sheet at final gauge at a temperature of above 1100 C. for a period of time to effect substantially complete secondary recrystallization thereof, the surface of the sheet being free from thick adherent oxide surface layers and any sheet separator refractory coatings present on the surface of the sheet being substantially non-reactive during the final anneal, the final annealing atmosphere being a reducing atmosphere substantially completely free from oxygen, moisture and other oxidizing components which will react with the surface of the sheet, the atmosphere, the annealing temperature and any materials present on or near the surface of the sheet being so correlated that during the initial stages of the final anneal prior to the occurrence of any appreciable secondary recrystallization, any continuous surface oxides on the sheet will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of primary recrystallization will grow preferentially to produce a face texture in the sheet.
4. The method of producing sheets of iron-silicon alloy having face texture, the alloy comprising from 2% to 5% silicon, up to 1% of at least one element of the group consisting of manganese, molybdenum and chromium, and
the balance being iron except for small amounts of impurities and additives, the steps comprising hot rolling an ingot of the alloy to produce a hot rolled sheet of a thickness of from about to 0.08 inch, cold rolling in at least two final stages of the hot rolled sheet to final gauge to effect a reduction of at least 93% in the penultimate cold rolling stage and a final reduction of from 30% to 80%, subjecting the cold rolled sheet to an intermediate anneal between the cold rolling steps at a temperature of from 800 C. to 1100 C., and finally annealing the sheet at final gauge at a temperature of above llOO C. for a period of time to effect substantially complete secondary recrystallization thereof, the surface of the sheet being free from thick adherent oxide surface layers and any sheet separator refractory coatings present on the surface of the sheet beingsubstantially non-reactive during the final anneal, the final annealing atmosphere being a reducing atmosphere substantially completely free from oxygen, moisture and other oxidizing components which will react with the surface of the sheet, the atmosphere, the annealing temperature and any materials present on or near the surface of the sheet being so correlated that during the initial stages of the final anneal prior to the occurrence of any appreciable secondary recrystallization, any continuous surface oxides on the sheet will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of primary recrystallization will grow preferentially to produce a face texture in the sheet wherein the cube edges are randomly oriented.
5. The process of producing sheets of iron-silicon alloy having a face texture, the alloy consisting essentially of from 2% to 5% silicon, up to 1% of at least one element from the group consisting of manganese, molybdenum and chromium; and the balance being iron except for small amounts of additives and impurities, the
steps comprising cold rolling only once without any intermediate annealing a sheet having random grain texture of the iron-silicon alloy to final gauge to effect a reduction of at least and finally annealing the sheet at final gauge thickness at a temperature of above 1100 C. for a period of time sufiicient to effect substantially complete recrystallization thereof, the surface of the sheet at the time of initiation of the final anneal being free from any thick, adherent, continuous oxide surface layers and any sheet separator coating of a refractory material present on the surface being porous and substantially non-oxidizing to the sheet surface during the final anneal, the final annealing atmosphere being a reducing atmos phere substantiallyfree from moisture and other oxidizing components which, would react with the surface of the sheet, so correlating the final annealing temperature,
the final annealing atmosphere and any materials present on or near the surface of the sheet that during the initial stages of the final anneal prior to the occurrence of any appreciable recrystallization any continuous surface oxides on the sheet surface will disappear whereby grain nuclei having faces parallel to the sheet surface present at the end of the primary recrystallization Will grow preferentially to other grain nuclei to produce a face texture iii the sheet.
ifieferenees Cited by the Examiner UNITED STATES PATENTS 2,940,882 6/1960 Hibbard et al l481l1 3,061,486 10/1962 Jackson 148-111 3,078,198 2/1963 Wiener 148-111 3,105,781 10/1963 Walter 148-111 DAVID L BECK, Primary Examinerl

Claims (1)

1. THE PROCESS OF PRODUCING SHEETS OF IRON-SILICON ALLOY HAVING A FACE TEXTURE, THE ALLOY CONSISTING ESSENTIALLY OF FROM 2% TO 5% SILICON, UP TO 1% OF AT LEAST ONE ELEMENT FROM THE GROUP CONSISTING OF MANGANESE, MOLYBDENIUM AND CHROMIUM, AND THE BALANCE BEING IRON EXCEPT FOR SMALL AMOUNTS OF ADDITIVES AND IMPURITIES, THE STEPS COMPRISING, COLD ROLLING IN AT LEAST TWO STAGES HOT ROLLED SHEET OF THE IRON-SILICON ALLOY HAVING A RANDOM GRAIN TEXTURE TO A FINAL GAUGE TO EFFECT A REDUCTION IN THICKNESS OF THE SHEET OF AT LEAST 93% IN AT LEAST ONE OF THE LAST TWO STAGES OR IN AT LEAST ONE OF THE LAST THREE STAGES OF COLD ROLLING WHEN MORE THAN TWO STAGES OF COLD ROLLING ARE APPLIED THERETO, THE REDUCTION IN THE THICKNESS IN THE OTHER STAGES BEING AT LEAST 30%, SUBJECTING THE COLD ROLLED SHEET TO AN INTERMEDIATE ANNEAL AT A TEMPERATURE OF FROM 800*C. TO 1100*C. BETWEEN EACH TWO SUCCESSIVE COLD ROLLING STAGES, AND FINALLY ANNEALING THE SHEET AT FINAL GAUGE THICKNESS AT A TEMPERATURE OF ABOVE 1100*C. FOR A PERIOD OF TIME SUFFICIENT TO EFFECT SUBSTANTIALLY COMPLETE SECONDARY RECRYSTALLIZATION THEREOF, THE SURFACE OF THE SHEET AT THE TIME OF INITIATION OF THE FINAL ANNEAL BEING FREE FROM ANY THICK, ADHERENT, CONTINUOUS OXIDE SURFACE LAYERS AND ANY SHEET SEPARATOR COATING OF A REFRACTORY MATERIAL PRESENT ON THE SURFACE BEING POROUS AND SUBSTANTIALLY NON-OXIDIZING TO THE SHEET SURFACE DURING THE FINAL ANNEALS, THE FINAL ANNEALING ATMOSPHERE BEING A REDUCE ATMOSPHERE SUBSTANTIALLY FREE FROM MOISTURE AND OTHER OXIDIZING COMPONENTS WHICH WOULD REACT WITH THE SURFACE OF THE SHEET, SO CORRELATING THE FINAL ANNEALING TEMPERATURE, THE FINAL ANNEALING ATMOSPHERE AND ANY MATERIAL PRESENT ON OR NEAR THE SURFACE OF THE SHEET THAT DURING THE INITIAL STAGES OF THE FINAL ANNEAL PRIOR TO THE OCCURENCE OF ANY APPRECIABLE RECRYSTALLIZATION ANY CONTINUOUS SURFACE OXIDES ON THE SHEET SURFACE WILL DISAPPEAR WHEREBY GRAIN NUCLEI HAVING FACES PARALLEL TO THE SHEET SURFACE PRESENT AT THE END OF THE PRIMARY RECRYSTALLIZATION WILL GROW PREFERENTIALLY TO OTHER GRAIN NUCLEI TO PRODUCE A FACE TEXTURE IN THE SHEET.
US371881A 1959-12-24 1964-05-28 Method of using a critical cold rolling stage to produce silicon-iron sheets Expired - Lifetime US3218202A (en)

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US3351501A (en) * 1964-06-04 1967-11-07 Westinghouse Electric Corp Process for producing magnetic sheets with cube-on-face grain texture
US4251295A (en) * 1979-05-11 1981-02-17 Westinghouse Electric Corp. Method of preparing an oriented low alloy iron from an ingot alloy having a high initial sulfur content
US4251296A (en) * 1979-05-11 1981-02-17 Westinghouse Electric Corp. Method of preparing an oriented-low-alloy iron from an ingot of controlled sulfur, manganese and oxygen contents
US4280856A (en) * 1980-01-04 1981-07-28 Kawasaki Steel Corporation Method for producing grain-oriented silicon steel sheets having a very high magnetic induction and a low iron loss
US4692193A (en) * 1984-10-31 1987-09-08 Nippon Steel Corporation Process for producing a grain-oriented electrical steel sheet having a low watt loss
CN112231368A (en) * 2020-09-18 2021-01-15 邯郸钢铁集团有限责任公司 Unary linear regression analysis method based on steel production big data

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DE4337605C2 (en) * 1993-11-01 1996-02-08 Eko Stahl Gmbh Method for producing grain-oriented electrical steel and magnetic cores made therefrom

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US2940882A (en) * 1956-09-20 1960-06-14 Gen Electric Magnetic material
US3061486A (en) * 1957-12-30 1962-10-30 Armco Steel Corp Non-directional oriented silicon-iron
US3078198A (en) * 1961-06-07 1963-02-19 Westinghouse Electric Corp Process for producing oriented silicon steel
US3105781A (en) * 1960-05-02 1963-10-01 Gen Electric Method for making cube-on-edge texture in high purity silicon-iron

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US2940882A (en) * 1956-09-20 1960-06-14 Gen Electric Magnetic material
US3061486A (en) * 1957-12-30 1962-10-30 Armco Steel Corp Non-directional oriented silicon-iron
US3105781A (en) * 1960-05-02 1963-10-01 Gen Electric Method for making cube-on-edge texture in high purity silicon-iron
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Publication number Priority date Publication date Assignee Title
US3351501A (en) * 1964-06-04 1967-11-07 Westinghouse Electric Corp Process for producing magnetic sheets with cube-on-face grain texture
US4251295A (en) * 1979-05-11 1981-02-17 Westinghouse Electric Corp. Method of preparing an oriented low alloy iron from an ingot alloy having a high initial sulfur content
US4251296A (en) * 1979-05-11 1981-02-17 Westinghouse Electric Corp. Method of preparing an oriented-low-alloy iron from an ingot of controlled sulfur, manganese and oxygen contents
US4280856A (en) * 1980-01-04 1981-07-28 Kawasaki Steel Corporation Method for producing grain-oriented silicon steel sheets having a very high magnetic induction and a low iron loss
US4692193A (en) * 1984-10-31 1987-09-08 Nippon Steel Corporation Process for producing a grain-oriented electrical steel sheet having a low watt loss
CN112231368A (en) * 2020-09-18 2021-01-15 邯郸钢铁集团有限责任公司 Unary linear regression analysis method based on steel production big data

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