US2940882A

US2940882A - Magnetic material

Info

Publication number: US2940882A
Application number: US610906A
Authority: US
Inventors: Jr Walter R Hibbard; John L Walter
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1956-09-20
Filing date: 1956-09-20
Publication date: 1960-06-14
Anticipated expiration: 1977-06-14

Description

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MAGNETIC MATERIAL Walter R. Hibbard, Jr., Schenectady, and John L. Walter, Scotia, N.Y., assignors to General Electric Company, a corporation of New York No Drawing. Filed Sept. 20, 1956, Ser. No. 610,906

1 Claim. (Cl. 148-111) This invention relates to magnetically soft bodycentered cubic iron alloys and more particularly to a method for producing the (100) [001] crystallographic orientation with respect to the rolling plane and direction of rolling in cold-rolled and recrystallized sheet-like bodies of alloys consisting essentially of up to 5% silicon, balance substantially all iron, up to 8% aluminum, balance substantially all iron, and up to 5% molybdenum, balance substantially all iron.

As disclosed in a co-pending application for United States Letters Patent, Serial No. 610,909 filed concurrently herewith by the present inventors and assigned to the assignee of this application, sheet-liketjbodies composed of the previously mentioned materials have the body-centered cubic crystal lattice form and have optimum magnetic properties for certain uses when each crystal with this lattice form is oriented with respect to the rolling direction and the plane of the sheet such that the atoms which determine the planes corresponding to one pair of opposed parallel unit cube faces of the unit cube are substantially parallel to both the plane of the sheet and the rolling direction, another pair of opposed parallel unit cube faces are substantially parallelto the rolling direction and substantially perpendicular to the plane of the sheet, and the remaining pair of opposed parallel unit cube faces 'are sub stantially perpendicular to both the rolling direction and the plane of the sheet. This preferred orientation is customarily referred to as a 100) [001] orientation in the art. The niunerical notation used to describe .this orientation of crystal planes and directions and other crystallographic relationships which follow are according to theconventional Miller Crystallographic Index System, a more complete discussion of which may befound, for example, in Structure of Metals, by C. S. Barrett, McGraw-Hill Book Company, Inc, New York, 2nd Edition, 1952, pages 1-25.

As more particularly set forth in our co-pendingapplication previously referred to, polycrystalline sheet niaterial composed of the previously describedcompositions having a (100) [001] preferred orientation may be prepared by properly rolling and appropriately heat treating grain-oriented ingots or portions thereof. It will be appreciated by those skilled in the art that the term preferred orientation, as used hereinQdescribes arolled sheet metal body consisting of a plurality of grains having the body centered cubic lattice form, in which a majority of the grains, ie, 50% or more, each have a substantially identical crystal lattice orientation with respect to the rolling direction and the plane of the sheet. The grain oriented ingots or castings from which such sheet materials have been produced have consisted primarily of a plurality of elongated columnar as-cast grains, the longitudinal axes of which are substantially parallel to each other. As disclosed in the referenced copending application, the desired preferred orientation is attainable in the final sheet or strip-like material by rolling the grain-oriented ingots in one or the other of two alternative modes, accompanied by proper heat treatment.

We have found, however, that while the metal sheet. or strip produced in accordance with the aboveoutlined invention invariably has the desired (100) [001]. preferred orientation, otherwise known as cube texture, that ingots having substantially identical compositions which have been cast in the same apparatus and reduced by identical processing steps resulted in grain-oriented sheet material having dilfer'ent degrees of grain orientation, resulting, in the cases of those materials having a lower percentage of their grains so-oriented, in materials having somewhat less desirable magnetic properties. We have discovered that the degree of preferred orientation in such sheet material is directly related to the initial orientation of the grains in the starting casting,more specifically to the angular relationship of the cube faces or (100) planes of the crystal lattices of the starting material to the rolling direction and the rolling plane during the rolling operation, and therefore by controlling this relationship, polycrystalline sheet or strip like material having a very high degree of the desired cubeftex-- ture may be invariably produced by workingand. recrystallizing polycrystalline grain-oriented ingots or single crystal bodies of these compositions.

It is-therefore a principal object of our invention to provide a process whereby recrystallized sheet or strip like bodies composed of silicon-iron, molybdenum-iron and aluminum-iron alloys may be produced having a con sistent high degree of cube texture preferred orientation with respect to the plane of the sheets or strips and the direction in which the sheet or strip material was rolled.

Gther and specifically different objects of our invention will become apparent from the detailed disclosure and specific examples which follow.

Briefly statedand in accordance with one aspect of. our

' invention, we have invented a process for rolling and heat-treating body-centered cubic iron base alloysfto form polycrystalline sheet or strip-like materialwvhibh consistently has a higher degree of cube texture grain,

orientation than previously attainable, by rolling said alloys so that a unit cube face of substantially every grain of said starting material is initially substantially. parallel to the rolling plane and a unit cube edge of substantially every such grain is substantially parallel to the direction of rolling, and recrystallizing the so-rolled material by appropriate heat treatment.

Previous investigators have found that polycrystalline iron and body-centered cubic iron alloys such as,'.fo r example, commercial silicon-iron electrical grade alloys,

containing about 24% silicon, less than about 0.005%- carbon, balance substantially all iron, including minor amounts of impurities customarily present in such materials, tend to invariably assume certain well known preferred orientations or texture when subjected to substantial amounts of cold plastic deformation by unidirectional rolling. The cold-rolled texture of these materials is chiefly one in which the [110i directions of substantially all the grains lie along the direction of rolling, with a deviation of a few degrees, and (001) planes lie in the plane of the rolled sheet, with a deviation from'this position chiefly about therolling direction as an axis. These stable, cold-rolled crystal orientations have been identified as [011], (115) [1 10], (113) (112) [1101,(111) [1'10] and'(1l1) [112]. Thehigher the amount of unidirectional cold reduction given such materials, the greater is the'tendency of the grains to assume a (100) [011] orientation in the rolled sheet. This may best be described as an orientation in whicha pair of opposite unit cube faces of the body-centered cubic lattices of a majority of the grains in the sheet are? Patented June 14-, 19b9 substantially parallel to'the'plane of the sheet and the remaining four unit cube faces are substantially perpen dicular'to the plane of the sheet and inclined at about a 45 angle to the rolling direction, ,Upon recrystallization by annealing such cold-rolled sheets, the preferred orientation or textureofthe annealed sheet will change to an orientation which is different from the cold-rolled texture, the annealed preferred orientation of such materials has previously been found to consist of a majority of'the grains having a (110) [001] orientation. This orientation may be described as one in which the unit cube lattices of the oriented grains have a planecontaining diagonally oppositely cube edges substantially parallel to the plane of the sheet and a pair of opposite cube faces substantially perpendicular to the rolling direction and to'the plane of. the sheet. It would, therefore, reasonably be expected that when polycrystalline provided with a bottom consisting of a water-cooled copper block which was maintained at about room temperature during the pouring and the solidification of the molten metal. 11 During solidification, the major part of the superheat and the heat of fusion of the molten metal was extracted by means of a cooled mold bottom and the cast ingot so produced wasfound to be composed essentially of a plurality of elongated, columnar grains whose longitudinal axes were substantially parallel to each other and to the direction of heat extraction, as more fully discussed in our co-pending application. A slab was cut bodies of iron and the body-centered alloys of iron were severely cold rolled in one direction in a sheet material, the grains comprising .such' bodies would assume the (100) [011] stable texture or one of the previously mentioned variations thereof and when recrystallizedfby annealing, that the annealed texture] would be predomi ,nantly the (110) [001] orientation usually obtained.

As clearly .shown, however, in our previously refer It was found upon'investigation of such'columnar grain-oriented ingots that the individual columnar grains 7 all had their crystal structures oriented so that a'pair'of parallel unit cube faces ofthe body-centered cubic lat tice'form of the grains are substantially perpendicular to the'longitudinal grain axis. However, as between indi vidual'colurnnar grains, the other four unit'cuhe faces of the cubic lattice form in a particular grain-were only occasionally parallel to the corresponding-unit cube faces of any other grain. Since the longitudinal grain axes of the columnar grains of such an ingot are substantially parallel toeach other, the unit cube faces whichare substantially perpendicular to the longitudinal grain axes are substantially parallel to each other, while a similar degree of parallelism between corresponding unit cube faces which are substantially par'allel to the longitudinal grain axes is found only in a' few of the longitudinal grains.

We have discovered that the initial angular relation a a ship between the unitcube faces andedges of the cubic latticfforms'of such grains and the rolling direction and rolling plane; determines the kind of orientation'o .tained by rolling and heat treating these materials. If

thejproper initial angular relationship is established and maintained during rolling, the recrystallized sheet metal resulting therefrom will consistently have a higher degree 'In other initial angular relationships are established and maintained during rolling, a lower percentage of cube.

texture will be obtained or the less desirable conven- V tional (110) [001] preferred orientation or a variant thereof will be obtained inthe recrystallized sheet mate rial. J This may best be illustrated by the following examplesy" V A grain-oriented ingot was prepared by casting a molten alloy consisting essentially of about. 3 silicon, less than-about 0.01% carbon, balance substantially all iron,

'int tubular mold'of-fused alumina. which had been preheated to about 1300 to 1400 C.'and which was polycrystalline *sheetfor from the ingot having a pairof parallel faces extending across the width of the ingot; and substantially parallel to the longitudinal axes of the columnar grains. The faces of this slab were ground to provide a slab thickness of 0.040" and then etched by meansof an aqueous acid solution to a thickness of 0.032" to remove the cold worked surfaces. 7 V

The etching brought out'the macrostructure of the co. lurnnar grains on'the faces of theslab' and the crystal orientation of a number of these grains were determined by the conventional Laue back reflection X-ray diffraction technique. After the orientation of these grains was determined, the slab was cut into two pieces along a plane perpendicular to the face of the slab and substantially parallel to the longitudinal axes of the columnar grains.

One of the slab'portions containing six of the grains whose orientations hadbeen determined and which are hereinafter identified asgrains 1-6 inclusive, rolled to 0.005" thick'sheet m'aterial in a number of rolling passes, a cold reduction of about- 84%. During this cold rolling, the longitudinal axes of the elongated columnar grains were maintained substantially parallel to the rolling direction and the slabfaceswere maintained parallel to the rolling plane;

The other slab portion containing three of the grains;

whose orientation had been determined, and whichare hereinafter identified. as' g'r'ains 7f9 inclusive, was cold rolled to' 0.011" thick ,sheet imaterial in a number of rolling passes, a cold reduction of about 66%. During 1 this cold rolling, the longitudinal axes of the elongated columnar grains were jmaintaincdsubstantially perpendicular Io the rolling direction. .theslab .faces were maintained parallelto therQIlingplaneZ The rolling was terminated at the 6 6% reduction in thickness because the 1 crystals began to separate at the grain boundaries.

The nine'previously identified crystalswere .then removed from the'resultingstrip by cutting along the grain forv 16 hours to' efliect' complete: recrystallizationfof the' cold worked metal, It be apprciated'th'ati the com-' of cube texture or stated otherwise, a higher percentage V f its grains will have the (100) [001 orientation than may be otherwise obtainable. r

' initial, grain 'orientationrof grains 1'-9 maybest be de boundaries with a jeweler s s aw. These crystals were then etched by means of an aqueous acid 'solution to about 0.002" thickness and annealedatiabout 1000 C.

plete recrystallization of 'these' materials maybe accom; plished by heattreatmentjattemperatures varying from about 800* C. to l200 C. for periods of time as short as /2 hour or less depending upon the particular temperature selected. 7 b

After recrystallization the preferred orientation of the polycrystalline sheet'rnaterial'resulting from 9 annealed,

cold worked, single crystals or'grain's was determined by means of conventional X-ray diffraction techniques. The

crystallographic orientation of the as-cast grains comprising spccimensf1-9 weres'unilar in'tha't inall the grains,

a (100) plane or unit cube face] was substantially perpendicular to the longitudinal axis of each grain. The

scribedin terms of the angular relationship between the planar facesfof the grain, said faces corresponding to the original slab faces," and'constituting the 'face's upon which the deformation was accomplished, and a cube face'which 7 is parallel to the longitudinal axis of eachgrain and one ormoreedges thereofinfrelationship tothe rolling directionor the rolling plane. '-'I'hese original slab faces are was cold 7 gar ges parallel to the final surfaces of the sheet material and therefore parallel to the rolling plane and the plane of the resulting sheet.

Grain 1 had such a unit cube face or (100) plane tilted 27 from a parallel relationship with the grain face, said cube face having a cube edge substantially parallel to the rolling plane but inclined about 7 from the rolling direction.

Grain 2 had such a unit cube face tilted 12 from a parallel relationship with the grain face, with one of its cube edges substantially coincident with the rolling direction.

Grain 3 had such a unit cube face tilted 29 from a parallel relationship with the grain face with one of its cube edges substantially coincident with the rolling direction.

Grain 4 had such a unit cube face tilted 22 from a parallel relationship with the grain face, with one of its cube edges substantially coincident with the rolling direction.

Grain 5 had such a unit cube face tilted about 28 from a parallel relationship with the grain face, with one of its cube edges substantially coincident with the rolling direction.

Grain 6 had such a unit cube face tilted about 39 from a parallel relationship with the grain face and a cube edge substantially coincident with the rolling direction.

Grain 7 had a cube face tilted about 9 with respect to the rolling direction and one of its cube edges substantially perpendicular to the rolling direction and parallel to the rolling plane.

Grain 8 had a unit cube face tilted about 19 with respect to the rolling direction, and one of its cube edges substantially perpendicular to the rolling direction and parallel to the rolling plane.

Grain 9 had a unit cube face tilted about 40 with respect to the rolling direction and one of its cube edges substantially perpendicular to the rolling direction and parallel to the rolling plane.

After the rolled grains had been heat treated, as previously described, it was found that the polycrystalline material formed from grains 1 and 6 had assumed a (110) [001] cube on edge orientation, the material from grains 2, 3, 4, 5, 7 and 8 had assumed a substantially cubic texture, i.e., (100) [001], with only minor variations therefrom, and that the material from grain 9 had retained practically the same orientation as it had initially, i.e., nearly (221) [551].

From the foregoing it may be seen that single grains or crystals of these materials worked by rolling into sheet and heat treated to effect recrystallization, assume a cube texture grain orientation provided the initial material has a unit cube face substantially parallel to the rolling plane and a unit cube edge substantially parallel to the rolling direction. As seen from the behavior of these grains, in no case where the unit cube face was 30 or more from a parallel relationship to the rolling plane, was the recrystallized orientation a cube texture. In the case of grain 1, compared, for example, to grain 3, both materials had a unit cube face similarly tilted with respect to the rolling plane yet grain 1 recrystallized in the (110) [001] cube-on-edge texture and grain 3 in the (100) [001] cube texture. This may be accounted for by the fact that while both grains had a unit cube face tilted substantially equal amounts with respect to the rolling plane, the unit cube structure of grain 1 was misoriented with respect to the rolling direction, i.e., one of the unit cube edges of said unit cube face was inclined at an angle of 7 to the rolling direction, while a corresponding unit cube edge of grain 3 was substantially parallel to the rolling direction. Therefore, greater angular deviations than 7 may be tolerated in cases Where the degree of tilt of the unit cube face is small. When the angular relationship of the unit cube face approaches 30 to the rolling plane, the unit cube edge must be substantially parallel to the rolling direction in order for the sheet material to recrystallize in a cube texture grain orientation.

It is therefore apparent that if grain-oriented ingots are provided in which the crystal lattices of the several grains are substantially parallel to each other, and the ingots in which initially a high percentage of the grains have a unit cube face inclined at an angle of less than 30 to the rolling plane and a unit cube edge of said unit cube inclined about 10 or less to the rolling direction, are cold reduced at least 40% by unidirectional rolling, that upon recrystallization substantially all the grains will assume the cube texture grain orientation. Ingots having this high degree of grain orientation may be-prepared, for example, by casting molten metal on an oriented seed slab or crystal, as more particularly disclosed in the co-pending applications for United States Letters Patent Ser. No. 610,907, now abandoned, Walter and Fisher, and Ser. No. 610,908, now abandoned, Grenoble, both filed concurrently herewith and assigned to the assignee of this application. Additionally, single crystals made by any known procedure such as, for example, the procedure disclosed in detail in our previously referenced co-pending application Ser. No. 610,909, may be utilized as the initial material to be rolled according to our invention to produce the desired cube texture of polycrystalline sheet material.

While certain specific examples of our invention have been included for the purpose of completely and clearly disclosing our discoveries and invention, we do not intend our invention to be limited to such examples or limited in any way except as defined in the appended claim.

What we claim as new and desire to secure by Letters Patent of the United States is:

A method for improving the degree of preferred cube texture orientation in recrystallized rolled sheet material having body-centered cubic lattice form comprising the steps of providing an intermediate rolling blank consisting of a single crystal composed of a binary alloy selected from the about 5% silicon, balance substantially all iron, up to about 8% aluminum, balance substantially all iron, and up to about 5% molybdenum, balance substantially all iron, reducing the thickness of said single crystal by rolling to produce a worked sheet-like body having at least 40% cold reduction, said rolling being accomplished in a substantially unidirectional manner so that a unit cube face of the body-centered crystal lattice of a majority of the metal is maintained atan angle of not-more than 30 from a parallel relationship to the rolling plane and a unit cube edge of said unit cube face is maintained at an angle of not more than 10 from a parallel relationship to the rolling direction and causing said rolled sheetlike body to recrystallize in the cube texture preferred orientation by annealing said body at a temperature from 800 C. to 1200 C. for a time suflic-ient to cause the complete recrystallization of said metal body.

References Cited in the file of this patent UNITED STATES PATENTS 2,112,084 Frey et a1 Mar. 22, 1938 2,307,391 Cole et a1 Ian. 5, 1943 2,700,006 Dunn Jan. 18, 1955 group consisting essentially of up to