US3105781A - Method for making cube-on-edge texture in high purity silicon-iron - Google Patents

Description

United States Patent 3,105,781 METHGD FOR MAKING CUBE-ON-EDGE TEX- TURE IN HIGH PURITY SILICGN-ERQN John L. Walter, Scotia, N.Y., assignor to General Electric tCompany, a corporation of New York No Drawing. Filed May 2, 1960, Ser. No. 25,840 4 Claims. c1. 148-111) This invention relates to grain-oriented magnetic alloys and more particularly to an improved method for producing bodies of iron-base magnetic alloys having a majority of the grains oriented in (110) [001] or cube-onedge crystalline orientation to provide at least one direction of easiest magnetization.

This application is a continuation-in-part of copending application Serial No. 859,847, filed December 16, 1959, now abandoned, and assigned to the same assignee as the present invention.

Various procedures and processes have been used in the past to produce sheet and strip materials from siliconiron, aluminum-iron, molybdenum-iron alloys and combinations of these alloys in which the bodies have a cubeon-edge orientation providing an easiest direction of magnetization. Generally, the basic concept behind the prior art processes has been to retain a small grain size during the hot rolling stages through the use of a dispersed second phase. The dispersed second phase prevents any appreciable grain growth from occurring during hot rolling and during annealing between cold rolling stages. It is not until the application of a final texture-developing anneal that the second phase is either removed or dissolved and grain growth is efiected.

Although the (110) [001] or cube-on-edge crystalline orientation is well known in the art in electrical sheet steels and is referred to in many standard texts, the following explanation of the orientation is included for the sake of clarity. The orientation may be described as one in which the unit cube lattices of the oriented grains have a plane containing diagonally-opposite 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. The (110) [001] designation is based upon the Miller Crystallographic Index System, a complete discussion of which may be found in Structure of Metals, C. S. Barrett, second edition, 1952, pages 1-25, published by the Macmillan Company. Material having this orientation is anisotropic and has optimum magnetic properties in the [001] direction parallel to the direction of rolling, the magnetic properties transverse to the direction of rolling being inferior to those of the rolling direction.

It is a principal object of this invention to provide a novel process for producing a (110) [001] grain orientation in iron-base magnetic alloys of high purity.

Another object of this invention is to provide a process for producing a cube-on-edge grain orientation in magnetic sheet material of up to about 15 mils thickness Without the use of a grain growth inhibiting second phase particle dispersion.

Another object of this invention is to provide a simpler and more economical process for the production of magnetic sheet materials having an easiest direction of magnetization.

Other objects and advantages of this invention will be in part obvious and in part explained by reference to the accompanying specification.

Generally, the present process comprises preparing an iron-base magnetic alloy, containing not less than about 92 percent iron, and not more than about 0.2 weight percent incidental impurities, rolling the body to a thickness of up to 15 mils, coating it with magnesia and then 3,105,781 Patented Oct. 1, 1963 subjecting the coated body to an anneal in a cleansing atmosphere for a length of time such that the coating will vaporize and the desired cube-on-edge orientation develop.

More specifically, the first step of the present process comprises preparing a suitable iron-base magnetic alloy which contains not more than about 0.2 weight percent total incidental impurities. Suitable alloys are those which contain from 2 to 6 percent silicon, up to 8 percent aluminum, and up to 5 percent molybdenum, or some combination of these metals and which contain not less than about 92 weight percent iron. While the silicon-iron alloys are those with which the present invention is concerned, the substitution of aluminum and/ or molybdenum in whole or in part for silicon can be effected according to well-recognized existing practices.

Having prepared an alloy as just outlined and cast it into ingot form, the ingot is then heated to a temperature within the range of from about 700 to 1200 C. and hot rolled, without any intermediate anneals between hot rolling stages to an intermediate or hot band thickness on the order of about mils (0.100 inch). At the hot band stage, the material is once again reheated to a temperature of from about 700 to 1200 C. and then cooled to room temperature or slightly above, for example, up to 200 to 300, then cold rolled to a thickness of up to about 15 mils (0.015 inch). Once the material has been reduced to this sheet-like form by rolling, it is coated with a layer of magnesia, which layer isolates the coated metal from the surrounding environment. The coated material is subjected to a final annealing in a cleansing atmosphere, specifically, either dry hydrogen having a dew point of no higher than-40 F. or vacuum containing no more than one micron of oxygen, for a period of time sufiicient to cause the magnesia layer to vaporize and to cause increased growth of those grains which are oriented in the [001] crystal orientation. Generally, the final annealing temperature will be on the order of from 1100 to 1300 C. and for periods of time of from 4 to 16 hours. Obviously, these temperature ranges may be extended somewhat in either direction by suitably varying the time periods, although the ranges stated represent those which will normally be most eflective to carry out the desired grain growth.

One of the important factors which is [felt to exert a controlling effect upon the orientation obtained is the amount of oxygen present in the thin strip material, that is, the material of up to 15 mils thickness. Generally speaking, the oxygen content in this material will be above six parts per million but should not exceed 0.005 weight percent (50 ppm.) if the cube-on-edge orientation is to be obtained. If the impurity content is too high or the oxygen content is excessively high, grain growth will be retarded due to the presence of dispersed second phases present in the material and optimum texture and magnetization properties cannot be obtained. If the oxygen is permitted to diffuse rapidly from the body to the surface of the material and is maintained at the surface, a (l00)[001] or cube texture would result. Thus, the apparent function of the magnesia coating is to retard growth until the oxygen content of the metal is too low (about 6 ppm. or less) to permit growth of cube oriented grains. The oxygen from the body apparently remains in the magnesia coating. Finally, when the magnesia coating vaporizes from the body, the cube-onedge orientation will result by growth of (110) [001] grains.

In view of the fact that the oxygen content at the surface of the body exerts a controlling effect on the orientation, it is apparent that the cleansing environment used must not contain excessive amounts of oxygen. Generally, the oxygen content of the cleansing environment, viz., hydrogen or vacuum, must be low enough to pre- 3 vent oxidation of silicon at the 1100 to 1300" C. annealing temperatures. If the oxygen is in excess of this amount, then the metal body is not lowered sufiiciently in oxygen content to develop the cube-onedge orientation. Dry hydrogen, that is, hydrogen having a dew point no higher than -40 F., is acceptable as a cleansing atmosphere. Also, vacuum containing no more than one micron of oxygen can be used efiec-tively. Obviously, atmospheres containing less oxygen, for example, a hydrogen atmosphere of 70 F. dew point, are completely acceptable, the former limits representing the boundaries.

As a specific example of a material produced according to the present process, a silicon iron alloy containing 3 percent silicon was vacuum melted and cast into ingot shape. This material contained a total impurity content on the order of 0.006 percent by weight. The ingot was then heated to 1000 C., was then hot rolled to a band thickness of 100 mils (0.100 inch) with no reheating between rolling stages. The band was then annealed at 700 C. for 5 hours in dry hydrogen ('-70 F.) and cold rolled in stages of reduction of 50 percent to 6 mils (0.006 inch). Between each cold reduction, the material was given an anneal at 900 C. for 30 minutes in dry hydrogen (-70 F.).

Following reduction of the band to 6 mil strip, the material was electropolished to 5 mils (0.005 inch) to produce a smooth surface. This electropolishing also had the effect of somewhat lowering the oxygen content on the surface of the material and removing oxide and other contaminating particles. In order to determine what the effect of the magnesia was, one sample was prepared and coated with a layer of milk of magnesia while the other sample was left entirely uncoated. Both of the samples were then placed on plates of high purity alumina, to prevent any contamination, and heated to 1230 C. at a heating rate of 100 C. per hour. The samples were held at this temperature for a period of 8 hours in dry hydrogen ('70 F.). While dry hydrogen was used in this instance, it is also possible to use a vacuum environment and obtain the same results, as already described.

The secondary crystals of the uncoated sample had a cube or (100) [001] grain orientation, whereas the coated sample, which also contained a large number of secondary crystals, had a majority of the grains oriented in the (110) [001] orientation. Approximately 70 percent of the grains in the coated sample were in the (110) [001] orientation. Further, X-ray examination of 12 of the secondary crystals of the coated sample showed that for all the crystals examined, a (110) plane lies within 5 of parallel to the plane of the sheet and a [001] direction lies within 5 of the rolling direction.

Thus, the present process makes possible the. production of a magnetic sheet material in which a majority of the grains have the cube-on-ed ge orientation and are oriented within about '5 of the rolling direction used to produce the strip material.

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

1. The method of producing an alloy body having a majority of the grains oriented in the (1?10)[001] crystal orientation comprising, providing an initial cold rolled body of up to 15 mils thickness and consisting of at least 92 weight percent iron, 2 to 6 weight percent silicon, up to about 8 weight percent aluminum, up to about 5 weight percent molybdenum and from not less than 6 to not more than 50 parts per million of oxygen and containing not more than about 0.2 Weight percent total incidental impurities, which impurities do not form a second phase dispersion effectively restricting grain growth, applying a coating of magnesia to the exposed surfaces of the body isolating the surfaces from the surrounding environment, and annealing the coated body in an environment selected front the group consisting of hydrogen having a dew point no higher than 40 F. and vacuum containing no more than one micron of oxygen at a temperature of from about 1100 to 1300 C. for a period of time suflicient to vaporize the coating from. the body and orient a majority of the grains in the (110) [001] orientation.

2. The method of producing an alloy body having a majority of the grains oriented in the (110) [001] crystal orientation comprising, providing an initial cold rolled body of up to 15 mils thickness consisting essentially of 2 to 6 weight percent silicon, remainder substantially all iron, and from not less than 6 to not more than 50 parts per million of oxygen and containing not more than about 0.2 weight percent total incidental impurities, which impurities do not form a second phase dispersion effect-ively restricting grain growth applying a coating of magnesia to the exposed surfaces of the body isolating the surfaces from the surrounding environment, and annealing the coated body in a dry hydrogen environment having a dew point no higher than 40 F. at a temperature of from about 1100 to 1300" C. for from about 4 to 16 hours to vaporize the magnesia coating from the body and orient a majority of the grains in the (110) [001] orientation.

3. The method of producing a sheet-like alloy body having a majority of the grains oriented in the (110) [001] crystal orientation comprising, providing a cast alloy body consisting essentially of not less than about 92 weight percent iron, from about 2 to 6 weight percent silicon, up to about 8 weight percent aluminum, up to about 5 weight percent molybdenum and from not less than 6- to not more than 50 parts per million of oxygen and containing not more than about 0.2 weight percent total incidental impurities, which impurities do not form a second phase dispersion efiectively restricting grain growth, hot rolling said cast body at a temperature of from 700 to 1200 C. to an intermediate thickness of about mils, annealing said intermediate at an elevated temperature, cold rolling said annealed intermediate to a reduction of about 40 to 99.5 percent in substantially the same direction, using intermediate anneals where required to produce a final cold rolled body of thickness not exceeding about 15 mils, applying a coating of magnesia to the exposed surfaces of the body isolating the surfaces from the surrounding environment, and annealing the coated body in an environment selected from the group consisting of hydrogen having a dew point no higher than 40 F. and vacuum containing no more than one micron of oxygen at a temperature from about 1100 to 1300 C. for a period of time sufficient to vaporize the coating from the body and orient a majority of the grains in the [001] crystal orientation.

4. The method of producing a sheet-like alloy body having a majority of the grains oriented in the (110) [001] crystal orientation comprising, providing a cast alloy body consisting essentially of not less than about92 weight percent iron, from about 2, to 6 weight percent silicon, up to about 8 weight percent aluminum, up to about 5 weight percent molybdenum and from .not less than 6 to not more than 50 parts per million of oxygen and containing not more than about 0.2 weight percent total incidental impurities, which impurities do not form a second phase dispersion effectively restricting grain growth, hot rolling said cast body at a temperature of from 700 to 1200 C. to an intermediate thickness of about 100 mils, annealing said intermediate at an elevated temperature of from about 700 to 1200 C., cold rolling said annealed intermediate to a reduction of about 40 to 99.5 percent in substantially the same direction, using intermediate anneals where required to produce a final body of thickness not exceeding about 15 mils, applying a coating of magnesia to the exposed surfaces References Cited in the file of this patent UNITED STATES PATENTS Yensen Aug. 11, 1936 Cole et a1. Jan. 5, 1943 Langworthy Oct. 29, 1946 Fiedler et a1. June 7, 1960 Hollomon June 14, 1960

Claims (1)

1. 4. THE METHOD OF PRODUCING A SHEET-LIKE ALLOY BODY HAVING A MAJORITY OF THE GRAINS ORIENTED IN THE (110) 001! CRYSTAL ORIENTATION COMPRISING, PROVIDING A CAST ALLOY BODY CONSISTING ESSENTIALLY OF NOT LESS THAN ABOUT 92 WEIGHT PERCENT IRON, FROM ABOUT 2 TO 6 WEIGHT PERCENT SILICON, UP TO ABOUT 8 WEIGHT PERCENT ALUMINUM, UP TO ABOUT 5 WEIGHT PERCENT MOLYBDENUM AND FROM NOT LESS THAN 6 TO NOT MORE THAN 50 PARTS PER MILLION OF OXYGEN AND CONTAINING NOT MORE THAN ABOUT 0.2 WEIGHT PERCENT TOTAL INCIDENTAL IMPURITIES, WHICH IMPURITIES DO NOT FORM A SECOND PHASE DISPERSIOON EFFECTIVELY RESTRICTING GRAIN GROWTH, HOT ROLLING SAID CAST BODY AT A TEMPERATURE OF FROM 700 TO 1200*C. TO AN INTERMEDIATE THICKNESS OF ABOUT 100 MILS, ANNEALING SAID INTERMEDIATE AT AN ELEVATED TEMPERATURE OFF FROM ABOUT 700 TO 1200*C., COLD ROLLING SAID ANNEALED INTERMEDIATE TO A REDUCTION OF ABOUT 40 TO 99.5 PERCENT IN SUBSTANTIALLY THE SAME DIRECTION, USING INTERMEDIATE ANNEALS WHERE REQUIRED TO PRODUCE A FINAL BODY OF THICKNESS NOT EXCEEDING ABOUT 15 MILS, APPLYING A COATING OF MAGNESIA TO THE EXPOSED SURFACE OF THE BODY ISOLATING THE SURFACES FROM THE SURROUNDING ENVIRONMENT, AND ANNEALING THE COATED BODY AT A TEMPERATURE FROM ABOUT 1100 TO 1300*C. IN A CLEANSING ENVIRONMENT NON-OXIDIZING TO SILICON FOR A PERIOD OF TIME SUFFICIENT TO VAPORIZE THE COATING FROM THE BODY AND ORIENT A MAJORITY OF THE GRAINS IN THE (110) 001! CRYSTAL ORIENTATION.