US2867557A - Method of producing silicon steel strip - Google Patents

Description

METHOD OF PRODUCING SILICON STEEL STRIP John H. Crede, Tarentum, Robert H. Henke, Fox Chapel, Edward L. Pulaski, Tarenturn, and Carl P. Stroble, Brackenridge, Pa., assignors to Allegheny Luzllum Steel Corporation, Brackenridge, Pa., a corporation of Pennsylvania I No Drawing. Application August 2, 1956 Serial No. 601,659

12 Claims. (31. 148-111 This invention relates to the production of silicon steel having a high degree of preferred orientation and highly directional magnetic properties. In particular this invention relates to the production of silicon steel strip having a high degree of [100] (110) or cube-nedge crystal orientation in the rolling direction.

Hereto-fore many difierent refinements have been made in the processing of silicon steel into cold rolled grain oriented strip and sheet form in a continuous efiort to improve the magnetic characteristics thereof. The state of the art and knowledge in the industry have now made it possible to produce silicon steel strip and sheet material having excellent magnetic characteristics with the result that any improvement in the processing which will provide an improvement of as little as 2 or 3% in the watt 'lossof the resulting magnetic material is now corisidered as a major contribution to the industry. In the past there have been two distinct processes utilized commercially to produce hot rolled strip or bands of siliconsteel which were then subjected to cold rolling reduction followed by a high temperature final anneal for developing the ultimate magnetic characteristics.

These two processes are known to the industry as the direct hot working process and the slab reheating process. In the direct hot working process, the steel ingot is heated and Worked directly without any intermediate reheating into the form of hot rolled strip material. In the slab reheating process, the heated ingot is worked into the form of slab which is then reheated 'to a high temperature in .the neighborhood of 2300 to 2550 F. and thereafter worked into the form of hot rolled strip, as described in Patent 2,084,337 issued June 22, 1937, to Goss and Patent 2,599,340, issued June '3, 1952, toLittmann et al.

As recognized in the Littmann et al. patent, attention has heretofore been focused primarily upon the amounts of cold reduction in the several stages and the "temperatures of the intermediate and final anneals in developing the magnetic characteristics. Further, it has heretofore been thought as .stated by Littmann et al. that the actual temperature of hot rolling, including the rate of cooling during and subsequent to hot rolling and specific temperatures at'the conclusion of the hot reduction, while of some importance, were relatively minor in effect when the hot rolled strip was subjected to cold rolling 'reduction followed by a high temperature final anneal. The only change in the hot processing of silicon steel in recent years has been that suggested .in the .Littmann et al. patent and such change .is applicable only to the slab reheating process.

-An object of this invention is the-provision, inthe processing of grain oriented silicon steel, for direct hot working the silicon steel ingot intohot rolled stripfor enhancing the magnetic characteristics of the steel when subjected to cold rolling reduction and. afinal high temperature anneal.

Another object of this invention is to provide a series 2,867,557 Patented Jan. 6, 1959 of steps which, when applied prior to the steps comprising any of the known cold rolling and annealing processes of making highly grain oriented silicon steel, will produce an improvement in the magnetic characteristics of the grain oriented steel strip. 7

A further object of this invention is to provide for the direct hot working of a heated silicon steel ingot into the form of a hot rolled strip having a thickness of 0.060 to 0.10 inch and a temperature of at least 1600 F. Without any intermediate reheating of the steel whereby,

when the. --hot rolled silicon steel strip, is thereafter subjected to cold rolling reduction and a final high temperature anneal, the steel will have enhanced magnetic characteristics.

Other objects of this invention will become apparent .from the following description.

The material to which this invention relates is silicon steel having a silicon content in general of about 2.5%

to 4.0% and preferably in the range of about 2.9% to 3.4%. A typical preferred range and a typical specific analysis for such a steel is as given in the following table.

Table I i g Percent by weight General Typical. range Silicon -2r90 3.40 3.15 CMbJn I .020- .035 .;028 Manganese. .035- .10 .0615 S ilf 1r. .=005 $025 .020 Phosphorus 005- .02 0 .008 Al vninum 05 max .01 C-vpp Br. 0 50 30 .080 NickeL 030--.- .050 .Tln 005 I020 010 ifhe silicon steel .is usually produced by the open hearth practice although other suitable melting techniques may be utilized, such steelbeing cast'into the form of large ingots having cross-sectional areas ranging from .19" x 35" to 26" x 36" orlarg'e'r. -In the'known direct hot zworking processes the ingot is heated in a suitable soaking zpit to a temperature in 'theneighborhood of '2200 to 2 300 and then hot worked directly -as by rolling on a -blooming mill to-produce a slab and hot rolling into the form of hot rolledstrip having a thickness 'of 0:060 to 0.10 inch-without regard as to' the temperature of :the metal so longas-itcan be processed into the form of hot rolled strip Without edgecracking and other defects.

In following the prior practice of direct hot working i to produce the hot rolled strip, the ingot is usually heated to a temperature of -from'2200 to 2300 F. after which itis Worked into a slab from '5 to 8 inches thick and then subjected to a series ofhot reductions on a reversing mill, usually in five passes, to reduce'the ,slab to a thickness of from Arto 1 A inchesatwhich time the "slab has a temperature of less than 1975 F., at.which temperature the slab is then rolledon a tandem mill to a thickness of- .060 to 0.10 inch. .Such hot rolled strip material'is then subjected to cold rolling reduction, preferably, intwo orgmore steps with an intermediate'. open rannealsat a temperature .of 1,600"F. to 1850 F. and

a high temperature annealofy2100 F. 102200" in dry-hydrogen. .In some cases a. heat treatment in the nature of a box anneal or a continuous heat treatment at a temperature of 1400 F. to ZOQOfF. is applied to the hot rolled. strip prior to the cold rolling." .Llsu ally. the rotrolled strip .is descalefd. jPreferably ,thecold rolled ,stripis subjected to a decar-burizingxheat treatment at a temperature of 1450 F. to 1500 F. in a degames? carburizing atmosphere for a brief final high temperature anneal.

In referring to the cold rolling reduction and heat treatments applied thereto it is recognized bythe industry that the correlation of the specific reductions accomplished in each pass and the temperatures of the intermediate open anneal, the decarburizing treatment and the final high temperature anneal has a controlling effect on the degree time prior to the ture of 2230 F. to 2275 F. The hot slab is thereupon of orientation produced. The correlation of these steps as such forms no part of this invention, as it has been found that the new direct rolling process to be hereinafter described when followed by any of the cold rolling reduction and heat treatments referred to will effect a beneficial and measurable improvement in the magnetic characteristics as opposed to the magnetic characteristics of grain oriented silicon steel strip of the same nominal composition produced by the prior direct hot working process and to which the same cold rolling reduction and heat treatment is applied.

In practicing this invention an extremely close control in maintained on all phases of thehot working of the metal starting with the temperature of soaking of the ingot and until the hot rolled strip is produced. It has been found that the temperatures maintained throughout the hot .working of the metal are critical for insuring consistently good results and effecting a definite and measurable improvement over results obtained by the prior art practice.

Preferably the ingot of silicon steel is thoroughly heated inja suitable soaking pit to a temperature above 2300 F. and up to 2475 F., the time and temperature varying in accordance with the size of the ingot. Thus, for an ingot having a cross-section of 19" x a heating cycle involving a minimum of 5. hours at a temperature. over 2300" F., including 3 hours at over2400 F., has been found to be satisfactory whereas for an ingot having a cross-section of 26" x 36", it is necessary to heat the ingot for a minimum of 7 hours at a temperature over 2300 F., including 3 hours at over 2400 F. Longer times at the higher temperature of over 2400 F. are not practical as the surface of the ingot tends to melt and drip to the bottom of the soaking pit and thereby destroy the bottom lining of the pit.

While all the reasons are not known as to why the thorough soaking of the ingot at the elevated temperature of 2300 'F. and higheris beneficial'to the process to be described, it has been found that the thorough soaking at such high temperature eliminates the austenite phase which may be present in the silicon steel as a minor component at lower temperatures. This is possible, for manganese, which. is an austenite former, is usually present as an impurity and other elements are also present asv impurities which tend tostabilize any such austenite phase. Where the manganese is present in excess of 0.10%, inferior final magnetic characteristics are usually obtained. Further, it is believedfthat certain of the impurities normally present wherescrap is utilized in making the steel tendto be preferentially dissolved, and thus segregated, in austenite. By heating the ingot to 2300" F. and higher, the unfavorable segregation of impurities within the ingot is prevented with the result that the impurities are uniformly dispersed in the steel as the steel is hot worked to the form of hot rolled strip. Such a distribution is essential to the occurrence of the secondary recrystallization mechanism through which a high degree of preferred orientation is ultimately developed in the final high temperature anneal referred to hereinbefore. The high temperature soaking of the silicon steel ingot is 'also'essential to permit the high speed hot working, as will be hereinafter described, to effect the required reduction to size of the hot rolled strip before the strip has cooled extensively and to enhance the magnetic properties of the resulting steel.

When the ingot is soaked as described, it is immediately rolled on a blooming mill sufficiently fast to produce a slab having a thickness of 5 to 8 inChes and a e pe aimmediately reduced on a single stand reversing mill in three passes to a thickness of /1 to 1 /2 inches at such a speed that the reduced slab has a temperature of not less than 2000 F. and preferably between 2000 F. and 2150 F. Such reduction on a 5-inch slab can be effected eificiently by three passes from the 5-inch slab in steps of 3 /2 inches to 2 inches to 1 inch.

The temperature of the reduced slab having a thickness of A inch to 1 inches as described has been found to be critical in the processing of the silicon steel and for effecting an improvement in the magnetic characteristics of the finished grain oriented steel strip. The high temperature of the reduced slab makes it possible to effectively hot roll the material in a tandem mill having six nonreversing finishing stands into the form of hot rolled strip having a thickness between 0.060 and 0.10 inch and a temperature of not less than 1600 F. and preferably not less than 1625 F. nor more than 1750 F. The temperature of the reduced slab, preferably not less than 2000 F., makes it possible to reduce the temperature differences between the front end and the back end of the hot rolled strip whereby a more uniform and consistent end to end quality is obtained in the finished strip. The

reductionin the temperature differences will be appreciated when it is considered that the reduced slab having a temperature of not less than 2000 F. is re duced, on the tandem mill at a speed such that the hot rolled strip thus produced is run off 'the last of the finishing mills at the rate of 1500 to 1700 feet per minute.

,As a typical processing of grain oriented silicon steel strip including the principles of this invention reference may be had to the following outline:

(1 Heat ingot for a minimum of 5 hours at a temperatureover2300 F., including 3 hours at not less than (2) Roll on blooming mill to produce slab having a thickness of 5 to 8 inches and a temperature not less than (3) Reduce slab to a thickness of A to 1% inches and a temperature not less than 2000 F. Such reduction (6) Where desired, box or open anneal the hot rolled strip at a temperature between 1400 F. and 2000 F. followed by a descale treatment.

(7) Cold roll the annealed strip to a thickness 1.3 to 2.5 times the final thickness.

(8) Open anneal the cold rolled strip at a temperature between 1600 F. and 1850 F.

(9) Cold roll to final thickness. (10) Open anneal cold rolled strip preferably in decarburizing atmosphere as in a wet reducing gas at a temperature substantially between 1400 F. and 1550 F. (11) Coat with an inorganic material to provide separation during step 12 and to provide an insulating film and to assist in chemical purification.

(12) Box anneal in dry hydrogen at a temperature substantially between 2100". F. and 2200 F.

In the process outlined, the control of the temperature of the direct hot working from the heated ingot to the hot rolled strip having a thickness of 0.060 to 0.10 inch, steps 5 through 12 being constant, will produce an effective and measurable improvement in the Watt loss and high density permeability of the resulting cold rolled grain oriented material as compared to the results obtained in processing identical material treated by the prior art direct hot working processing and the same cold rolling processing to strip of the same thickness. In all cases it has been found necessary to so control the speed or the 1m man-gem 'the'heate'd ingot a. the .redu'ced .slab having a thickness of to 1 /2 inches that the temperature of suchslab as it enters the No. 1

finishing stand of the six stand tandem mill is not less than.2000 F. if the improvement in magnetic characteristics is to be obtained. Likewise it has been found that the temperature of the 'hot rolled str'ipas it 'leaves the tandem .mill must benot less than 1600 F. and preferably not less than 1'625.F. and that such temperature is indicative of the :results which will be obtained.

In order to clearly illustrate theimprovement in magnetic characteristics imparted by the treatment of this invention, reference :may behad to the following comparison of treatments applied to 8 heats .in commercial production having a representative average analysis of 3.15% Si, 0.027% C, 0.078% Mn, 0.008% P, 0.019% S, 0.011% Cr, 0.071% Ni, 0.01% Al, 0.065% .Cu, 0.010% Sn and the balance iron and which were made by the open hearth procedure. 'Each heat was processed to 0.012 inch cold rolled strip coils in identical fashion except that the temperature-of the hot working to reduce the slabs to strip having-a thickness of-0.060 to 0.10 inch was varied so that certain of the coils ;were'produced from material which entered the No. 1 finishing stand at step '4 of the typicalgprocessing outlined hereinbefore at less than 2000 -F. and'others entered at a temperature of not less than 2000 F. as taught herein. The following table lists-the results obtained on 47 coils'produced from the 8 heats referred to.

From Table Kit is evident that substantial improvements are obtained in the watt loss and in the high density permeability of the resulting cold rolled grain oriented strip material, the reduction in the watt loss being phenomenal.

As is well known, silicon steel is somewhat arbitrarily classified in dillerent grades for different uses depending upon the guaranteed Watt loss of the material. Thus from any given heat some of the coils may meet one guaranteed specification, whereas others, because of higher watt loss, are classified in a lower class and sell at a reduced price. For commercial reasons, a premium grade of .012 inch thick of oriented silicon is one classified as having a Watt loss per pound of not over .580. As can be seen from Table II, material processed in accordance with this invention has exceptionally good magnetic characteristics, andfrom experience about 70% of such material will fall within the premium class. Where the grainoriented silicon steel strip produced has a gauge of .014 inch, even better results are obtained in that about 75% of the coils so produced will meet a watt loss per pound specification of .660 for the premium grade material.

In one of the prior art direct hot working processes the hot slab having a thickness of to 8 inches was reduced to a slab having a thickness of to 1 /2 inches on a reversing mill by subjecting it to five passes to reduce it from, say 5 inches to 4 inches, to 3.1 inches, to 2.25 inches, to 1.6 inches, to 1.0 inch in thickness. An examination of past records of strip produced utilizing such a five pass reduction reveals that such reduced slab had a temperature less than 2000 F. so that the metal entering the No. 1 finishing stand of. the tandem hot mill necessarily'had a temperature of less than 2000 F. The

[grain oriented strip thus produced did not have consistent'm'a'gnetic characteristics, but instead would have onlya minor .portion thatwouldfrneet premium specifications. The improvement obtained by'practicing this invention is clear whenthe results obtained on strip produced by the present method are compared with strip produced utilizing the five 'pas's reduction at starting temperatures of less than 2000F. of the ,prior'art process for .012 inch thick grain oriented silicon strip material.

Thus with the ste'e'l having an average la'dle analysis of 3.15%Si, 0.026% C, 0.061% Mn, 0.019% S, 0.052% Ni, 0;06 8% Cu andthe'balance iron processed as described in three passes on a reversing mill and admitted to the tandem mill at a tempear'ture over 2000 -F. in the production of 450 coils of .012 inch cold rolled and annealed 'silicon steel strip. it was found that the resulting steel had the following outstanding magnetic characteristics asobtained on Epstein'samples cut therefrom just prior to the final anneal and given the final anneal in a laboratory annealing furnace. I

Avg. coreloss, W':/# i -,u10H

.In Out Avg. In Out Avg.

Where substantially the same steel having an average "ladleanalysis of 3.18% Si, 026% C, .061 .Mn, .019% S,

.057-% Ni, .065 Cu and the balance iron was processed by theprior art practice of five passes on areversing mill and admitted to the tandem mill at a temperature of less than 2000 F. in the-production of 942 coils of .012 inch cold rolled and annealedsilicon steel strip, it Was found that the'resulting steel-had the following poorer magnetic characteristics as measured on Epstein samples cut and treated .as in the foregoing example.

Avg'core'loss, W.'/# ilOH In Out Avg. f In Out Avg.

foregoing two examples.

Avg. core loss, W,/# 1011 In Out Avg. In Out Avg.

In the last three examples given the results obtained are based on commercial production, each of the coils so produced having an average weight of 6,000 pounds with the core loss and permeabilities recorded being measured on samples taken from each of the inner and outer ends of the wound coils. It is thus evident that Where the temperature of the reduced slab is controlled so as to have a temperature above.2000 F. as it isadmitted to the No. 1 stand of the tandem mill and the steel is reduced to a thicknesszof 0.060 to 0.10 inch at a speed sufiicient that the hot rolled strip retains a tem-.

perature of not less than 1600 F. and is then processed to a given thickness of grain oriented silicon steel strip by standard practice, consistent improved core loss and high density permeability are obtained in contrast to the results obtained with the prior art direct rolling process in which the temperature of the reduced slab is less than 2000 F. as it is admitted to the No. 1 stand of the tandem finishing mill. The improvement of the core loss from .579 watt per pound to .569 watt per pound and the permeability at ulOH of from 1762 to 1787 and 1794 are remarkable and outstanding.

All of the results recorded hereinbefore and the classification with respect to core loss for the premiumvgrades were obtained by following a mill practice for measuring the quality of the silicon steel which is produced in coil strip form but shipped to the customer without having been subjected to the final high temperature anneal. The customer thereafter forms the strip into an article of manufacture, such as a wound core, and subjects such core to the final high temperature anneal. In such cases the mill personnel take an Epstein sample prior to shipping the coil to the customer and the Epstein sample is given the high temperature anneal in a laboratory furnace prior to measuring the core loss and high density permeability.

While such a test is indicative of the final results which will be obtained, such premium results are not obtained if the coil is given the final high temperature anneal in the mill prior to shipping the completely finished coil. However the same degree of improvement in core loss and high density permeability is obtained on the full finish coil where such coil is produced in accordance with this invention. As evidence of such improvement as measured on full finish coils of grain oriented silicon steel produced in accordance with this invention in comparison with the results obtained on full finish coils of grain oriented silicon steel produced in accordance with prior art practice, reference may be had to the results given in the following table. Such results are based on the commercial production of over 2000 coils averaging about 6000 pounds each in weight of .014 inch cold rolled grain oriented silicon steel strip having a typical average ladle analysis of 3.16% silicon, 026%, .067% manganese, .0l89% sulfur, 062% nickel, .067% copper and the balance iron. Each coil was directly hot worked from ingot to hot rolled strip and thereafter cold rolled and annealed in substantially the same manner except that some of them were given five passes on the reversing mill and were admitted to the tandem mill at a temperature of not Number of Number Temp. of admission Average Average passes a of coils to tandem mill corel ss, [110E versing mill watts/lb.

493 Not less than 2,000 E. 684 1, 770 5 1, 072 Bel w 2,000 F .708 1,757 5 425 Bel w 1 950 729 1, 741 3 278 N: t less than 2 000 It. .686 1,756 3; 127 Bel w 2,000 F 704 1, 744 3 54 Below 1,950" F 729 1,727

The results recorded" in the foregoing table are actual results measured on Epstein samples taken from the high 'loss end of full finish coils after a suitable stress relief anneal to relieve the stresses incurred by cutting the samples, that is, coils which have been subjected to the high temperature final anneal during the mill processing. As

is evident from the results given for the full finish commercial coils, whether the slab is reduced in three passes or in five passes, outstanding results are obtained where the reduced slab is admitted to the No. 1 stand of the tandem mill at a temperature of not less than 2000 F. In all of the test results recorded in all of the foregoing tables, the core loss values were those obtained as measured at an induction of 15,000 gausses.

While reference has been made hereinbefore to admitting the reduced slab to the finishing mill at a temperature of not less than 2000 F., it will be appreciated that such temperature may be as high as 2150 F. depending upon the speed of reduction from the initially heated ingot having a temperature in excess of 2300 F. In order to insure the outstanding consistent results of this invention, the mill operators should be instructed to process the heated ingot so that the reduced slab has a temperature of not less than-2025 F. so that any slight variation below such specfied temperature will still be above the critical 2000 F. temperature necessary to maintain the production of cold rolled strip having consistently outstanding magnetic characteristics.

The'process of this invention is not restricted to the mill equipment referred to so long as the heated ingot is directly processed to produce the reduced slab having a thickness of from A to 1 /2 inches and a temperature of not less than 2000 F. and is immediately and quickly reduced to a hot rolled strip having a thickness of 0.060

rectly to hot rolled strip.

We claim:

1. A process of producing highly grain oriented silicon steel for magnetic purposes, said steel containing substantially 2.5% to 4% silicon, including as steps, hot working the steel from ingot to hot rolled strip followed by a cold rolling treatment and a final high temperature anneal, the hot working being accomplished by heating the ingot to a temperature about 2300" F. and slabbing the heated steel to produce a hot slab having a thickness of from to 1 /2 inches and a temperature of not less than 2000 F., and immediately subjecting the hot slab to a series of hot reductions to produce a hot rolled strip having a thickness of 0.060 to 0.10 inch before the temperature of said hot rolled strip decreases to below 1600 F the direct hot working from heated ingot to hot rolled strip being a direct hot working without an intermediate reheating of the steel.

2. A process of producing highly grain oriented silicon steel for magnetic purposes having as steps, the heating of a silicon steel ingot to a temperature above 2300 F., said steel containing substantially 2.5% to 4% silicon, hot working the heated ingot into hot rolled strip form having a thickness of 0.060 to 0.10 inch before the temperature of said hot rolled strip decreases to below 1600 F., the hot working from heated ingot to hot rolled strip being a direct hot working without an intermediate reheating of the steel, and thereafter subjecting said hot rolled strip to at least one cold rolling treatment and a final high temperature box anneal.

3. A process of producing highly grain oriented silicon steel for magnetic purposes having as steps, the heating of a silicon steel ingot to a temperature above 2300 F., said steel containing substantially 2.5% to 4% silicon, hot working the heated ingot into hot rolled strip form having a thickness of 0.06 to 0.10 inch before the temperature of said hot rolled strip decreases to below 1600 F., the hot working from the heated ingot to hot rolled strip being a direct hot working without an intermediate reheating of the steel, and thereafter subjecting said hot rolled strip to two cold rolling stages and an intermediate anneal.

4. The process claimed in claim 3 in which the intermediate anneal is an open anneal at a temperature substantially between 1600 F. and 1850" F.

5. A process of producing highly grain oriented silicon steel for magnetic purposes, said steel containing substantially 2.5% to 4.0% silicon including as steps, hot working the steel from ingot to hot rolled strip followed by a cold rolling treatment and a final high temperature anneal, the hot working comprising, heating the ingot to a temperature above 2300 F., subjecting the heated ingot to a hot rolling operation to produce a slab having a thickness from to 8 inches and a temperature ofnot less than 2230 F., hot rolling the hot slab to produce a reduced slab having a thickness from A to 1 /2 inches and a temperature of not less than 2000 F., and immediately subjecting said reduced slab to a series of hot reductions to produce hot rolled strip having a thickness of 0.060 to 0.10 inch and a temperature of not less than 1600 F., the hot working from heated ingot to said hot rolled strip being a direct hot working without any intermediate reheating of the steel.

6. A process of producing highly grain oriented silicon steel for magnetic purposes, said steel containing substantially 2.5% to 4.0% silicon, including as steps, hot working the steel from ingot to hot rolled strip followed by two cold rolling stages and an intermediate anneal, the hot working comprising heating the ingot to a temperature between 2300 F. and 2450 F., subjecting the heated ingot to a hot rolling operation to produce a slab having a thickness from 5 to 8 inches and a temperature of not less than 2230 F., hot rolling the hot slab to produce a reduced slab having a thickness from to 1 /2 inches and a temperature between 2000 F. and 2150 F., and immediately subjecting said reduced slab to a 0nd cold rolling step is followed by a decarburizing treatment including an open anneal, and by a final box anneal.

9. The process claimed in claim 6 in which said inter mediate anneal is an open anneal at a temperature substantially between 1600 F. and 1850 F., and the second cold rolling step is followed by an open decarburizing anneal at a temperature substantially between 1400 F., and 1550 F and by a final box anneal in dry hydrogen at a temperature substantially between 2100 F. and 2200 F.

10. A process of producing highly grain oriented silicon steel for magnetic purposes having as steps, the heating of a silicon steel ingot to a temperature above 2300 F., said steel containing substantially 2.5% to 4% silicon, hot working the heated ingot into hot rolled strip form having a thickness of 0.060 to 0.10 inch, the hot working from heated ingot to hot rolled strip including the steps of slabbing and introducing the resulting slab at a temperature of not less than 2000 F. to a series of hot reductions to produce said hot rolled strip before the temperature of said hot rolled strip decreases to below 1600 F., said hot working from heated ingot to hot rolled strip being a direct hot working without an intermediate reheating of the steel, and thereafter subjecting said hot rolled strip to cold rolling and annealing treatments to develop the magnetic characteristics thereof.

11. The process claimed in claim 10 in which the cold rolling and annealing treatments include two cold rolling stages and an intermediate anneal.

12. The process claimed in claim 10 in which the cold rolling and annealing treatments include two cold rolling stages and an intermediate open anneal at a temperature substantially between 1600 F. and 1850 F.

References Cited in the file of this patent UNITED STATES PATENTS 1,852,836 Corson Apr. 5, 1932 2,084,337 Goss June 22, 1937 2,088,440 Ruder July 27, 1937 2,378,321 Pakkala June 12, 1945 2,599,340 Littmann June 3, 1952 2,618,843 Goodsell Nov. 25, 1952 FOREIGN PATENTS 474,544 Great Britain Nov. 3, 1937

Claims (1)

1. A PROCESS OF PRODUCING HIGHLY GRAIN ORIENTED SILICON STEEL FOR MAGNETIC PURPOSES, SAID STEEL CONTAINING SUBSTANTIALLY 2.5% TO 4% SILICON, INCLUDING AS STEPS, HOT WORKING THE STEEL FROM INGOT TO HOT ROLLED STRIP FOLLOWED BY A COLD ROLLING TREATMENT AND A FINAL HIGH TEMPERATURE ANNEAL, THE HOT WORKING BEING ACCOMPLISHED BY HEATING THE INGOT TO A TEMPERATURE ABOUT 2300* F. AND SLABBING THE HEATED STEEL TO PRODUCE A HOT SLAB HAVING A THICKNESS OF FROM 3/4 TO 11/2 INCHES AND A TEMPERATURE OF NOT LESS THAN 2000* F., AND IMMEDIATELY SUBJECTING THE HOT ROLLED STRIP TO A SERIES OF HOT REDUCTIONS TO PRODUCE A HOT ROLLED STRIP HAVING A THICKNESS OF 0.060 TO 0.10 INCH BEFORE THE TEMPERATURE OF SAID HOT ROLLED STRIP DECREASES TO BELOW 1600* F., THE DIRECT HOT WORKING FROM HEATED INGOT TO HOT ROLLED STRIP BEING A DIRECT HOT WORKING WITHOUT AN INTERMEDIATE REHEATING OF THE STEEL.