US1932306A

US1932306A - Electrical steels and method of making same

Info

Publication number: US1932306A
Application number: US593783A
Authority: US
Inventors: Edward M Freeland
Original assignee: Individual
Current assignee: Individual
Priority date: 1932-02-18
Filing date: 1932-02-18
Publication date: 1933-10-24
Anticipated expiration: 1950-10-24
Also published as: BE390446A; BE398905A; FR740867A; FR44079E

Description

Oct. 24, 1933.

E. M. FREELAND ELECTRICAL STEELS AND METHOD OF MAKING SAME Filed Feb. 18, 1932 0 0 0 0 0 W 0 o o m w 2 2 z Z M m 6 9 L Elo' INVENTOR W7 Patented Oct. 24, 1933 UNITED STATES ELECTRICAL STEELS AND METHOD OF 1 MAKING SAME Edward M. Freeland, Pittsburgh, Pa.

Application February 18,

, 15 Claims.

The present invention relates broadly to the art of metal working, and more especially to that branch of metal working having to do with the subjecting of a predetermined composition or alloy to a treatment of such nature that the electrical properties thereof are materially modified.

In an effort to improve the efficiency of different types of electrical apparatus, such for example as motors, dynamos, transformers and the like, it is customary to utilize a ferrous material, usually in the form of a series of sheets or laminae characterized by a high electrical efnciency from the standpoint for example of watt loss, magnetic permeability, low magnetic hysteresis and the like. In this connection it is known that sheets of iron-silicon, or iron-silicon-aluminum alloys constitute a superior material for this purpose. The present invention contemplates not only a variation in the constituent alloys utilized as to their relative proportions for obtaining certain predetermined results as required for example by the apparatus in which the finished product is to be used, but also a special mechanical and heat treatment whereby with a given material the desired electrical properties are imparted thereto.

It is customary in the art to divide so-called electrical steels into a number of different grades generally with reference to the particular use to which the steels are to be put. It is to be understood, therefore, that the term electrical steels as hereinafter utilized, unless specifically restricted to a specified grade by way of example, is to be considered as a generic term including all of the various grades without regard to the specific properties or uses contemplated.

For purposes of a better understanding of the invention, it will hereinafter be illustrated and described as applicable to a ferrous material, preferably containing silicon, having a low watt loss and produced initially from so-called strip material, the term strip being herein utilized in its commonly accepted sense in the metal roll ing art. 7

Experience in the production or electrical steels of the character herein contemplated has led to the conclusion that the desired electrical properties can be obtained only bya treatment which includes as one of the steps thereof a cold working operation, preferably in the form of cold rolling. It has heretofore been considered essen- 1932. Serial No. 593,783

tial to so effect the cold working or cold rolling operation as to definitely limit the maximum strain introduced into the material, it being understood that the reduction effected by the cold working operation necessarily determines the amount of strain introduced. The necessity of maintaining the strain so introduced below definite maximum limits has heretofore precluded the use of the cold working process for material in strip form for the reason that in cold rolling a hot rolled strip to gauge, the strain introduced has far exceeded the upper limits permissible at any. stage in the manufacture of electrical steels. The amount of reduction by cold work has heretofore been limited to a maximum of 540%, which is so small as to be of little consequence so far as concerns merely the step of cold rolling to reduce thickness.

The present invention is preferably characterized by the step of deliberately introducing a strain by cold rolling in excess of any limits heretofore considered permissible, and thereafter subjecting the material having such excessive strain therein to a controlled treatment such that the strain in excess of the maximum limit is effectively removed, and only the desired strain for imparting the required electrical properties is retained. In this manner I retain only that amount of strain which has heretofore been determined .as being decidedly beneficial, and make the process adaptable to the production in quantity of electrical steels. The adaptation to the strip process also enables the production of a product having materially greater lengths than has heretofore been possible, and thereby correspondingly reducing the fabricating costs in the manufacture of electrical apparatus. This will be readily apparent when it is considered that it is entirely possible to produce, in accordance with my invention, the desired grade of electrical steel in strip form having a length, for example, in the neighborhood of 1000 ft., and capable of being auto rnatically fed to a suitable punch or the like such as utilized in the fabrication. of the ma terial. Heretofore electrical steels could only be produced in lengths not to exceed approximately 15 ft. Such individual pieces required individual handling and feeding to the punches and the like, and therefore required the constant attend ance of an operator.

The present invention therefore has for one of its objects an improved method of producing electrical steel, as well as the production of a new article of manufacture comprising electrical steel in strip form having a length in excess of lengths heretofore obtainable from sheets as individually produced.

In the acompanying drawing I have shown more or less diagrammatically, by way of illustration only, certain preferred embodiments of the present invention. In the drawing:-

Figure 1 is a diagrammatic view, partly in side elevation, illustrating the various treatment steps to which strip material may be subjected in accordance with the present invention;

Figure 2 illustrates a modified method of heat treating material produced in accordance with the present invention;

Figure 3 is a chart illustrating one method of effecting partial strain removal prior to final heat treatment; 7

Figure 4 is a diagrammatic view, partly in side elevation, illustrating a slightly modified form of treatment from that shown in Figure 1; and

Figure 5 is a view similar to Figure 4, illustrating still another embodiment of my invention.

While it will be understood that Figures 1, 4 and 5, respectively, illustrate diiferent manipulative steps, processes or treatments to which the material is subjected in attaining the desired results, as the description proceeds, the relevancy of the different steps to the invention will become more clearly apparent.

Having reference more particularly to Figure 1 of the drawing, I have shown a slab 2 of desired composition suitable for use in accordance with the present invention. This slab is subjected to hot rolling, as commonly practiced in the art in a suitable series of hot rolling mills 3 of such nature as to form a hot rolled strip, herein illustrated in the form of a coil 4. It may be assumed, by way of example only, that the hot rolled strip thus pro-- duced and which is substantially free from any cold working strains, has a thickness of .0625 inches, and any desired width. I prefer to use a minimum finishing temperature of approximately 1300 F. This hot rolled strip, in accordance with the present invention, is subjected to a cold rolling operation in a continuous mill 5, herein illustrated as comprising four roll stands of the four-high type arranged in tandem.

By way of illustration only, it may be further assumed that the setting of the cold rolling mills is such as to reduce the thickness of the hot rolleTi strip to approximately .024 inches, this being a reduction of .0385 inches, equal to approximately 61%. It will be apparent to those skilled in the art that the figures herein given are representative of thicknesses frequently produced in the cold rolling of steel for purposes other than the production of electrical steels.

The cold rolling operation, while it is effective for reducing the hot rolled strip to the desired finished gauge, introduces in such material by reason of the reduction effected, a strain which is far in excess of the strain heretofore thought permissible in the production of steels to be used for electrical purposes. In accordance with the present invention, however, I take advantage of the strain introduction effected by such a cold rolling operation, and consider such strain as representing a desirable component and an undesirable component. In accordance with the present invention, the strip having these two strain components is subjected to a special heat treating operation of such nature as to retain the desirable component and eliminate the undesirable component.

It may be assumed that the strip leaving the cold rolling mill 5 is formed into a coil 6 for convenience in handling. This coil is then placed in a suitable coil b x '7 located in the de sired relationship to the charging end of a heat treating furnace 8 provided with suitable burners or resistors 9 effective for maintaining the desired temperature conditions therein. The coil 6 is progressively unwound from the coil box 7 and passed in single thickness through the furnace 8 at a speed which is determined not only upon the temperature conditions existing within the furnace, but also upon the composition of the material undergoing treatment, the thickness of such material and the amount of strain introduced therein by the cold rolling operation. Upon leaving the heat treating zone provided by the furnace 8, the strip material may again be formed into a coil 10, which will be characterized, as will be hereinafter more fully explained, by the elimination of the undesirable strain component and will have only the desirable strain component remaining therein. This coil may then be subjected to a final heat treating operation as by subjecting it to a box annealing operation in coil form in an annealing box 11. Upon removal from the annealing box, the strip material in coil form may be sold as an article of manufacture for use in the fabricating of electrical equipment, or may be cut into individual sheets and so sold for fabrication. When retained in coil form it is possible to obtain all of the advantages hereinbefore referred to with respect to use in automatic fabricating machines with a minimum of expense, attention and handling.

In other cases, the coil 10 as formed at the delivery end of the heat treating furnace 8 may be sheared into individual sheets 12, which sheets when placed in superimposed relationship as illustrated in Figure 2, may be subjected to a box annealing operation in a suitable annealing box 14. After the desired annealing operation, the sheets 12 as such may then be sold for use.

Reference has heretofore been made to a cold rolling operation effective for producing a reduction of approximately 61%. If this reduction is effected on strip having a relatively low silicon content, say for example approximately 1%, it will be found that the resulting strain in the strip is appreciably less than the strain which will result from exactly the same reduction on a steel having for example, approximately 2% silicon. It must therefore be borne in mind that the unde sirable strain component increases in amount as the silicon content of the material undergoing treatment increases, with the same percentage reduction by the cold mill.

With any given silicon content, the undesirable strain component will likewise vary with changes in the reduction effected by the cold rolling operation, the strain increasing with increased reductions and decreasing with decreased reductions. While the actual strain introduced under varying reductions is not a straight line function, it is a function which is readily deter minable.

In practicing my invention I have successfully employed a continuous heating furnace as indicated at 8 in Figure 1. The furnace had a length of 30 feet and was maintained at a temperature of approximately 1900 F. Silicon steel strip containing approximately 1% of silicon, which steel had been subjected to a 61% reduction by cold rolling and having a final thickness of .025 inches was passed through the furnace at a rate of 15 feet per minute, giving a total time in the furnace of two minutes. I have estimated that in the particular furnace employed the heat penetrated sufiiciently rapidly to bringthe strip up to the desired minimum temperature in approximately seconds. The additional 90 seconds of heating time was available for continued heating. Under the above conditions the heat treatment eliminated the undesirable strain component and left the desirable strain components therein.

In Figure 3 I have illustrated diagrammatically by the point A on the curve the particular heat treatment above described. The curve of Figure 3 is obtained by plotting the thickness of the material against the heating time in seconds. It is generally assumed that the rate of heat penetration varies directly with the thickness of the material; and hence if the strip being treated were only half as thick, that is to say, .0125 inches, then only 15 seconds would be required to bring it up to the desired minimum temperature. Adding to this the continued heating time of 90 seconds, the total time for treating such strip would be 105 seconds. This condition is indicated by the point B on the curve. As stated, if, as is generally assumed, the rate of heat penetration varies directly with the thickness of the material, the curve for determining the length of time for treating strips of different thicknesses will be a straight line connecting the points A and B. The points C, D, E and F have been marked on this line in Figure 3 to show the time required for heat treating strips having thicknesses, respectively, of .014, .016, .018 and .020 inches.

The above described curve is for steel having a silicon content of approximately 1% and which has been reduced approximately 61% by cold rolling. It sets forth the general principle of treatment to be followed in the continuous heat treatment of such strip for the elemination of the undesirable strain component, but it will be understood that the curve is by way of example only; that modifications in the heat treatment may be made; that the customary tolerances in mill practice are allowable, and that the percentage of reduction by cold rolling may be varied according to the particular circumstances encountered and the results desired.

In accordance with the' present invention, it is permissible to consider the heat treating operation by means of which the undesirable strain component is eliminated as involving two factors, these being respectively, time and temperature. If it is desired to decrease the time of treatment, it is necessary to eifect an increase in the temperature, while if it is desired to increase the time interval, this may be accomplished by effecting a reduction in the temperature conditions. The examples given therefore are by way of illustration of actual times required for a given temperature condition, it being possible in accordance with the invention to vary either the time or temperature by making a corresponding change as indicated in the other heat treating factor.

In like manner, since the undesirable strain component introduced into the material increase with higher silicon contents, and decrease as the silicon content is reduced, it is necessary to make a corresponding change in the time-temperature treatment to accommodate the treatment to the silicon content present in the material. In substantially the same way, it is also necessary where the percentage of reduction varies, either upwardly or downwardly, to effect a corresponding change upwardly or downwardly of the timetemperature treatment, it being remembered that in all cases the minimum. or desirable strain component is to be retained in the material and only the excess or undesirable strain component eliminated.

The present invention will thus be found to be applicable commercially to the cold rolling of silicon steel in strip form in direct accordance with the past commercial practices determined for cold rolling operations generally as applicable to products other than ferrous materials for elec- 'trical purposes, thus enabling commercial installations to be utilized for carrying out the present invention. Y

I have found that, depending upon the properties desired in the finished product, and effective uses to which such product is to be put, or, in other words, depending upon the grade of material to be produced, the silicon content may be varied through appreciable limits. As a general statement, it may be assumed that a silicon content of approximately 1% is desirable for example in the production of that grade of material known generally as electrical sheets; that a silicon content of approximately 2 5% is desirable for the production at that grade of material commonly referred to as special motor sheets; that a silicon content of approximately 3% is desirable for the production of that grade of material commonly referred to as special dynamo sheets, and that a silicon content of approximately 3 5% produces the desired properties for use in so-called transformer sheets. Inasmuch, however, as the determining factor in the different grades referred to is the actual watt loss per 1b., determined in accordance with lmown methods, and such watt losses are themselves subject to change, the figures and grades given must be considered as illustrative only. It will likewise be understood that the approximate percentages of silicon are not absolute, it being possible to utilize a silicon content varying for example, as much as 5% in one direction or the other and still obtain desirable results with the present invention. 1 have referred to 3%;% merely by way of example, as the upper limit of silicon. It is to be understood, however, that the actual amount of silicon present may be materially increased, as for example, up to approximately 6% if such a higher silicon content is desired, by reason of changes in the watt loss requirements or guarantees of the manufacturer.

All of the material produced in accordance with the present invention will be characterized by having a relatively low watt loss at a given flux density. As an example of guarantees which it is possible to meet, there is given below a table containing seven difierent grades of electrical steel, each with an identifying title together with the watt loss per lb. at frequencies of both and cycles at the assumed specific gravities indicated, the maximum watt losses in the case of some of the grades being shown for a plurality of different gauges, these ranges covering the gauges ordinarily manufactured. In all cases the watt loss is figured at a flux density of 10,000-B and determined in accordance with specification A-3428 of the American Society for Testing Materials. In each instance I have also indicated one permissible range of silicon variation for each grade:

Armature (Assumed sp. gr. 7.70)

8 Silicon .S-J-U. S. atandard gauge: 0

30 G. 29 Cl. 28 G. 27 G. 20 G 25 G. 24 G. 23 G. 22 G.

\Vntts per lb.--60 cycles 1. 85 l. 40 1. 46 1. 53 1. (l5 1. 85 2.15 2. 50 2. B0 \Vatts per kg.--60 cycles. 2. 97 3. 08 3. 20 3. 37 3. G3 4. 07 4. 73 5. 50 6. l5 \Vatls per lb.-5O cycles- 1.12 1. 17 1. 20 1. 30 1. 42 1. 53 1. 75 2. 00 2. 30 Watts per kg.-50 cycles... 2. 4.6 2. 57 2. 64 2. 86 3. 12 3. 37 3. 4. 40 5. ()5

Electrical (Assumed sp. gr. 7.70)

Silicon .75-1.6- U. 8. standard gauges Watts per lb.60 cycles.-- 1.15 l. 20 1. 28 l. 35 1. 40 1. 55 1. 80 2.10 2. 39 Watts per kg.60 cycles- 2. 53 2. 64 2. 82 2. 97 3. 08 3. 41 3. 9G 1. 02 5. 06 Watts per lb.50 cycles l. 00 l. 07 1.14 1.18 l. 30 1. 50 l. 70 l. 85 'atts per kg.-50 cycles. 2. 09 2. 20 2. 3 2. 51 2. 60 2. 86 3. 30 3. 7-1 1. 07 9 r a Special motor (Assumed sp. gr. 7.50)

Silicon B.03.0U. 5. standard gauges Watts per Ib.-(l0 cycles 1.00 I 1.03 1. 08 1. 15 I 1 20 1. 25 1.110 1011'} Watts per kg.-(i0 cycles. 2. 20 2. .27 2, 38 2. 5.5 2. 64 2. 75 2. ill; Watts pcr lb.5l) cycles... .81 .86 90 .9 1 .97 1.110 1.05 Watts per kg.50 cycles H 1.85 1 81') l 98 2 0T 2. l3 2. 2i) 2. 3]

Special dynamo (Assumed 51). 5:1. .50)

Silicon .-2..-5-s.5- U. s. slamlarrl /u Watts per lb.60 cycles Watts per kg.60 cycles Watts pcr ilL-SU cycllcs. 1 atts )er ,.50 c '0 es 1.98 l r s I I I 1M Regular transformer (Assumed m yr. 7.50)

Silicon 3 pZus-U. S. sirmdm u lmy m Watts per 1h. -c0 cycles 7n so l .99 .03 93 Vt'zltts per kgr-GO cycles 1. (i7 1. 76 1. 87 1. 96 2. 05 2. 16 Watts per lb.-50 cycles. 62 61 .158 71 75 78 Watts per kg.-5(l cycles 1.375 I l. 41 1.50 1. 56 1. 65 l. 72

Special transformer (Assumed sp. gr. 7.50)

Silicon 8% plus I Watts per lb.-60 cycles 70 Watts per kg.60 cycles. 1. 54 Watts per lb.-50 cycles.-- 56 Watts per kg.50 cycles 1. 24

Extra special transformer (Assumed sp. gr. 7.50)

Silicon 8% plus Watts per lb.-6O cycles. 61 Watts per kg.-60 cycles. 1. 42 Watts per lb.50 cycles. 52 Watts per kg.-50 cycles. l. 15

From the foregoing tables it will be noted that my improved electrical strip has 9. watt loss not exceeding 2.8 per pound in 22 gauge strip containing .3 to .'7% silicon and that the watt loss decreases progressively as the silicon content increases, within the range herein disclosed, and also decrease with a decrease in thickness of the strip.

With the embodiment of the invention illustrated more particularly in Figure 1 of the drawing, it will be understood that the coil material as delivered by the annealing box 11 for example, will have a coil set which will be reflected in the individual pieces formed therefrom. Inasmuch slight curvature reflected in the individual lamina may be objectionable. In accordance with the embodiment of Figure 2, the coil set may be eliminated, but in this case it is not possible to furnish to a customer a material in coil form .with its consequent advantages. In cases where the advantages of a coil without the objection as to coil set are required, I may practice a method as illustrated diagrammatically in Figure 4.

In this figure, I have shown a furnace 15 indicated as being a bell type electric furnace characterized by the ability to closely control temperature conditions. I may place within such furnace a coil produced in any desired manner, such for example as the product of the cold roll- .ing mill 5 of Figure 1 and subject the coil to such accurately controlled heat treating conditions as to efiect removal only of the undesirable strain component;

Thereafter tlriis coil may be placed in a suitable coil box 16 and passed through a heat treating furnace 17 corresponding to the furnace 8 of Figure l and effective for giving the final heat treatment to the material. Instead of coiling the material at a point closely adjacent the top of the furnace 1'7, I may carry it to a point ap-.

preciably removed therefrom before forming it into a coil 18. The location of the coil 18 relatively to the furnace 17 will be such that the material will have cooled to such an extent that it will not have a tendency even when coiled to take a coil set, but will always tend to return to its substantially fiat condition.

In Figure 5, I have also illustrated one method of practicing the invention means of which the desired results may be obtained. In this figure, I have shown an annealing box 19 having coils of material 20 therein. These coils may be the product either of a cold rolling mill as shown in Figure l, or of the usual hot mill. In the annealing box they are subjected to a suitable heat treating operation. Upon removal from the annealing box the coils may be placed in a suitable coil box 21 and fed therefrom between rolls 22 of a suitable mill effective for introducing a desired strain component into the material to the extent required to impart the desired electrical properties. Thereafter the material with this strain, representing only the desirable strain compo nent, may be passed through a furnace 23 corresponding to the furnaces 8 and 1'7, and then at a suitably remote point coiled into a coil 24. In this coil 24 the material will possess the same attributes as the material in coil 18 of Figure 4.

In accordance with the embodiments of the invention of Figures 4 and 5, it is possible to produce as an article of manufacture a coil of electrical strip wherein the strip itself is substantially free from any objectionable coil set of the character referred to.

It will be understood that when practicing the form of the invention shown in Figures 1 and 2, the annealing box temperatures will be such as to effect final removal of the strain. I have found that this temperature may vary within the range of from 1500 to 1700" F., although the lower temperature ranges of from 1550 to 1650 arepreferable. The same will of course be tru of the

heat treating furnaces

17 and 23.

The advantages of the present invention arise not only by reason of the new article of manufacture capable of production in accordance with my invention, but from the adaptability of a cold rolling process to the production of ferrous materials for electrical purposes.

This application claims my improved product generically and certain species thereof. My application, Serial No. 688,410, filed September 6, 1933, claims that range of silicon steels coming under my invention and having a silicon content of 2.75 to 3.5%, which range has herein been classified as special dynamo grade. My improved silicon steels which are classified herein as transformer grades, and comprehending a silicon range of 3% or more, are specifically covered by my copending application Serial No. 688,411, filed September 6, 1933.

While for purposes of a better understanding of the invention, I have indicated more or less diagrammatically different forms of apparatus and different steps which may be utilized in accordance with the invention, together with different silicon contents, reductions, thicknesses and time-temperature treatment conditions, it will be apparent to those skilled in the art that changes in all of these respects may be made in the manner indicated herein without departing either from the spirit of my invention or the scope of my broader claims.

I claim:

1. In the method of making silicon steel, the steps consisting in effecting a heavy reduction by cold work, heating the metal to remove at least a part of the strain, cooling it and then annealing it, the metal having some strain therein at the commencement of such annealing.

2. In the method of making silicon steel, the steps consisting in effecting a heavy reduction by cold work, heating the metal to remove part but not all of the strain thus imparted, cooling the metal, and then annealing it.

3. In the method of making silicon steel, the steps consisting in effecting a heavy reduction by cold work, heating the metal to remove part but not all of the strain thus imparted, cooling the metal, annealing it, allowing it to'cool after such annealing to a point where it will not acquire a coil set upon coiling, and then coiling it.

4. As a new article of manufacture, electrical steel in sheet-like form containing .3-6% silicon and having electrical properties characteristic of those obtained when a steel of substantially the same silicon content, within such range, is subjected to heavy reduction by cold work, followed by heating to remove part but not all of the strain thus imparted, cooling, and then annealing.

5. As a new article of manufacture, electrical steel in sheet-like form containing .3-6% silicon and having electrical properties characteristic of 'those obtained when a steel of substantially the same silicon content, within such range, is subjected to heavy reduction by cold work, followed by heating to remove part but not all of the strain thus imparted, cooling, and then annealing with in a temperature range of from 1500 to 1700 F.

6. As a new article of manufacture, electrical steel in sheet-like form containing .3-6% silicon and having electrical properties characteristic of those obtained when a steel of substantially the same silicon content, within such range, is hot rolled into a strip substantially free from cold working strains, then subjected to heavy reduction by cold work, then heated to remove part but not all of the strain thus imparted, then cooled, and then annealed.

7. As a new article of manufacture, electrical steel containing .3-6% silicon and having electrical properties characteristic of those obtained when a steel of substantially the same silicon content, within such range, is subjected to heavy reduction by cold work, followed by heating to remove part but not all of the strain thus imparted, cooling, and then annealing, the steel being in. the form of a strip as that term is used in the metal rolling art.

8. As a new article of manufacture, electrical steel in sheet-like form containing .36% silicon and having electrical properties characteristic of, those obtained when a steel of substantially the same silicon content, within such range, is subjected to heavy reduction by cold work, followed by heating to remove part but not all of the strain thus imparted, cooling, and then annealin the steel'being in the form of a strip and having a length in excess of that obtainable by pack rolling.

9. As a new article of manufacture, electrical steel in sheet-like form containing .36% silicon and having electrical properties characteristic of those obtained when a steel of substantially the same silicon content, within such range, is subjected to heavy reduction by cold work, followed by heatng to remove part but not all of the strain thus imparted, cooling, and then annealing, the steel being in the form of a coiled strip and further characterized by substantial freedom from coil set.

10. As a new article of manufacture, electrical steel in sheet-like form containing .3-6% silicon and having electrical properties characteristic of those obtained when a steel of substantially the same silicon content, within such range, is formed by hot roll'ng to strip form substantially free of cold working strains having a thickness of approximately .0625 inches, cold rolling to approximately .024 inches or 61%, passed through a furnace having a temperature of approximately 1900 F., the total heating time being such as to remove the undes?rable strain component in the steel, that is to say, about two minutes in the case of a steel whose silicon content is approximately l%, and increasing as the silicon content increases, then cooling and then annealing, the steel being in the form of a strip as that term is used in the metal rolling art.

11. As a new article of manufacture, electrical steel in sheet-like form containing .3-6% silicon and having electrical properties characteristic of those obtained when a steel of substantially the same silicon content, within such range, is formed by hot rolling to strip form substantially free of cold working strains having a thickness of approximately .0625 inches, cold rolling to approximately .024 inches or 61%, passed through a furnace having a temperature of approximately 1900 F., the total heating time being such as to remove the undesirable strain component in the steel, that is to say, about two minutes in a steel whose silicon content is approximately 1%, and increasing as the silicon content increases, then cooling, and then annealing by heating to a temperature of 1500-1700 F. and cooling, the steel being in the form of a strip as that term is used in the metal rolling art.

12. As a new article of manufacture, electrical steel in the form of strip, containing from .3% to silicon and having electrical properties characteristic of those obtained when a steel of substantially the same silicon content, within such range, is subjected to heavy reduction by cold work followed by heating to remove part but not all of the strain thus imparted, cooling, and then annealing, the watt loss property of such strip being not more than about 2.8 watts per pound in 22 gauge thickness and decreasing as the silicon content increases, and also decreasing as the thickness of the strip decreases.

13. As a new article of manufacture, electrical steel in the form of strip, containing from .3 to .7% silicon and having electrical properties characteristic of those obtained when a steel of substantially the same silicon content, within such range, is subjected to heavy reduction by cold work followed by heating to remove part but not all of the strain thus imparted, cooling, and then annealing, the watt loss property of such strip being not more than about 2.8 watts per pound in 22 gauge thickness, and decreasing as the thickness of the strip decreases.

14. As a new article of manufacture, electrical steel inthe form of strip, containing from 375% to 1.5% silicon and having electrical properties characteristic of those obtained when a steel of substantially the same silicon content, within such range, is subjected to heavy reduction by cold work followed by heating to remove part but not all of the strain thus imparted, cooling, and then annealing, the watt loss property of such strip being not more than about 2.3 watts per pound in 22 gauge thickness, and decreasing as the thickness of the strip decreases.

15. As a new article of manufacture, electrical steel in the form of strip, containing from 2% to 3% silicon and having electrical properties characteristic of those obta ned when a steel of substantially the same silicon content, within such range, is subjected to heavy reduction by cold work followed by heating to remove part but not all of the strain thus imparted, cooling, and then annealing, the watt loss property of such strip being not more than about 1.3 watts per pound in 24 gauge thickness, and decreasing as the thickness of the strip decreases.

EDWARD M. FREELAND.