US3905842A - Method of producing silicon-iron sheet material with boron addition and product - Google Patents

Abstract

The addition to silicon-iron of a small amount of boron in critical proportion to the nitrogen content of the metal enables preparation of oriented silicon-iron sheet of good magnetic properties from material which would otherwise be incapable of secondary recrystallization necessary to produce such properties.

Description

United States Patent [1 1 Grenoble 51 Sept. 16, 1975 METHOD OF PRODUCING SILICON-IRON SHEET MATERIAL WITH BORON ADDITION AND PRODUCT [75] Inventor: Herbert E. Grenoble, Amsterdam,

[73] Assignee: General Electric Company,

Schenectady, NY.

[22] Filed: Sept. 23, 1974 [21] Appl, No.: 508,330

Related US. Application Data [63] Continuation-in-part of Ser. No. 431,128, Jan. 7, 1974, abandoned, which is a continuation-in-part of Ser. No. 326,852, Jan. 27, 1973, abandoned.

[52] US. Cl. 148/111; 75/123 B; 75/123 L;

148/31.55; 148/112 [51] Int. Cl. HOlf l/04 [58] Field of Search 148/111, 110, 112, 31.55;

Primary Examiner-Walter R. Satterfield Attorney, Agent, or Firm-Charles T. Watts; Joseph T. Cohen; Jerome C. Squillaro 5 7 ABSTRACT The addition to silicon-iron of a small amount of boron in critical proportion to the nitrogen content of the metal enables preparation of oriented si1icon-iron sheet of good magnetic properties from material which would otherwise be incapable of secondary recrystallization necessary to produce such properties.

10 Claims, No Drawings METHOD OF PRODUCING SILIC( )N -IRON SHEET MATERIAL WITH BORON ADDITION AND PRODUCT This is a continuation-in-part ofmy copending patent i producing electrical steel and is more particular-ly-concerned with a novel method'of producing singly ori" ented siliconiron sheet through the use of small'but critical amounts of boron. and with a new cold-rolled silicon-iron sheet product. i I i I i CROSS-REFERENCES This invention is related tothe invention disclosed and claimed in patent application Ser. No 429,800, now abandoned, filed Jan 2, 1974 as a continuation-in part of patent application Ser. No. 320.668, filed Jan. 7

ducing Oriented Silicon-Iron Sheet Material With Boron Addition" in the name ofHoward C. Fiedler and assigned to the assignee hereof. directed to the novel concept of cold rolling hot-rolled silicon-iron sheet di'- rectly to final thickness without an intermediate heat treatment through the use of small but critical amounts of boron and by maintaining the ratio of manganese to sulfer in the metal at less than [.54

The invention disclosed and claimed herein also re lates to that disclosed and claimed in patent application Ser. No. 429.791 now abandoned, filedJan'. 2, I974, as a continuation-in-part of patent application Ser. No.

320.669, filed Jan; 2. 1973 (now abandoned )1 entitled Method of Producing Oriented Silicon-Iron Sheet Material With Boron Addition" in the name of Howard C. Fiedle r and assigned to the assignec hereof which per tains to the new concept of using small but critical 1973 (now abandoned). entitled Method of Pro-- ished sheet-or strip thickness. usually involving at least a 50 percent reduction in thickness, and given a final or texture-producing annealing treatment suMMARYoF THE INVENTION have discovered that under certain; conditions boronhas a beneficial effect on the secondary recrystallization of silicon-iron sheet material to develop the (l 1())[()Ul texture and the special mi tgne ticproperties associated with it. Particularly l liave found that the presence of a very small, but highly-' cri'ticzil, amount of boron in cold-rolled silicon-iron sheet during the final or textuie-developing anneal enables preparation of silicon iron sheet having a strong cube-on-edgetexture and correspondingly good magnetic properties In other words, the seemingly insignificant amount of boron makes secondaryrecrystallization possible, Conamounts of boron to enable the production of singly I oriented silicon-iron sheet of improved magnetic properties by subjecting silicon-iron sheet containing manganese and sulfcr in a ratio less than 2.] toa cold re duction sequence including an intermediate annealing step and a final heavy cold rolling reduction.

BACKGROUND OF-THE INVENTION I The sheet materials to which this invention is directed are usually referred to in the-art electricaf silicon steels or. more properly silicon-irons and are 7 ordinarily composed principally of iron alloyed ,with

about 2.2 to 4.5 percent silicon and relatively minor amounts of various impurities and very small amount of'carbo n. These products are of the cubeon-edgc type; more than about 70 percent of their crystal st rue ture being oriented in the (l l())[()()l] scribed in Miller Indices terms.

Such grain-or iented siliconiron sheet products are currently made commercially by thc sequence-of hot texture, as dcband. The hot-rolled band is then cold roll'e dtwith ap 1 propriate intermediate annealing treatinc H z seq u ently the use of manganese sulfide can be avoided ascan the necessity ahigh-temperature desulfu rizing heat treatment during the final processing operations. Thus th'e metalcan by reason of this invcntiori be desulfuriied at the melt stage with substantial time and cost savings. is quite surprising considering the fact that boron'lhas previously been recognized in our experienceas a detrimental impurity which it definitely is in amounts oiily moderately greater than those which I have found to be useful. In fact, except in the presence of otherwise dctrin'ientally high amounts of nitrogen the metal, boron in amount as small as 50 parts per inillion (ppm) is definitely detrimental in terms of dc sired magnetic characteristics". Thus. the important new results and advantages of this invention a're'ohtained through the presence ofboronin'amounts from about five to about 45 ppm duiing the texture anneal of' 'the cold-rolled sheet. I have found the optimum boron content tobe' in the range fr'om about five to It) pn This unique capability of boron was discovered during experiments involving the use of crucible'refract't')- rics containing boron as' a minor impurity. small amounts of boron were reduc-ed'from the refractories tothc-silicon-iron melts and exerted noticeable benefi cial effect on the texturede\'"eloping process. Suhse quently I demonstrated that the'boron content in sili coniron melts prepared in such" vessels could 'be' closely controlled by adjusting the melt carbon content by adding iron oxide-and thereby preventing the reductionof boron in thecruciblerefractory and conse quent pick-up ofboron by the melt. Ifurther found that the boron requirements can be met through the use of a boron-free crucible by adding a boron source to the melt. i

l have further found that the surprisingly sharp'criticali ty of such relatiyelyismall proportions presents no "all the boron is eliminated from the metal when.- in accordance w th this mvention therole of boron in promoting the desired secondary recrystallization texture development has terminated I have additionally discovered that the proportion of nitrogen to boron is also of critical importance to the new results and advantages of this invention. Unless the ratio of nitrogen to boron is in the range from two to four parts of nitrogen per part of boron, products having good magnetic properties can not be consistently produced even though the boron content of the melt is within the above stated critical range. Consequently, in accordance with this invention, the nitrogen content of the melt will be in the range from about 15 parts per million to about 95 parts per million.

The nitrogen requirement can be met in any convenient manner, but in preferred practice the metal in a vacuum furnace is provided with a 30-torr nitrogen atmosphere to which argon is added to bring the pressure up to one atmosphere for the pouring operation. The metal as poured contains about 30 ppm of nitrogen and in the neighborhood of ppm of boron. The pressure of nitrogen required in the furnace chamber will depend in any given circumstance upon the ratio of the volume of the chamber to the weight of the melt.

Another discovery which I have made is that the proportions of sulfur and manganese in the metal during final annealing treatment are critical in terms of the magnetic properties of the final product strip or sheet material. Particularly, it is essential that there be at least 0.007 percent sulfur in solute form at that stage of processing. That requirement can be met if both the sulfur and the manganese contents of the silicon iron are quite low and in fact if there is no more than about 0.007 percent sulfur in the metal. The tendency for the manganese to tie up the sulfur is negligible in highly dilute systems in which the manganese content is of the order of about 0.002 to 0.006 percent and. conse-.

quently, it is not necessary in the practice of this invention to reduce the manganese content of the metal to a trace amount under any circumstances.

From the foregoing it will be understood that this invention has both method and article or product aspects. Thus. the several discoveries and new concepts set forth above expressed in terms of manipulative steps add up to a novel process and when expressed in compositional terms define a unique silicon-iron sheet product. The product is a cold-rolled sheet of final gauge thickness which by virtue of its boron, nitrogen, manganese and sulfur content can be converted to the oriented state in which it will have valuable mangetic properties but will not contain the boron which enabled the development of those properties through secondary recrystallization. The process of producing this new intermediate cold-rolled sheet is also new as is the overall process of producing the final desired sheet material from a silicon-iron melt.

Briefly described in its article aspect, this invention comprises a cold-rolled silicon-iron sheet product containing 2.2 to 4.5 percent silicon. between about 5 and 45 ppm boron. between about and 95 ppm nitrogen with the nitrogen and boron being in'the ratio range of 2 to 4 parts of nitrogen per part of boron, between about 0.007 and 0.06 percent sulfur, and between about 0.002 and 0.01 percent manganese, and the pro portion of manganese to sulfur being such that the pres ence in the metal of at least 0.007 percent sulfur in solute form is assured during the final texture anneal.

jecting it to a final DETAILED DESCRIPTION OF THE INVENTION In the preferred practice of this invention, the amount of nitrogen in the metal will not exceed about ppm so that any tendency for nitrogen-induced slivering and blistering can be avoided. This requirement is readily met by commercial steel-producing practices when usual precautions are taken to limit nitrogen pick-up. Consequently, it is preferable to add boron to the melt after it has been tapped into the ladle for teeming. The amounts to be added will be l020 ppm of the melt weight.

In carrying out the method of this invention, one will prepare a silicon-iron melt of required chemistry and use it to produce ingots which are hot rolled to interme diate thickness. When it is poured, the melt will contain from 2.2 to 4.5 percent silicon, from 0.003 to 006 percent sulfur, from 0.001 to 0. 10 percent manganese and from about 5 to 45 parts per million boron, from about 15 to 95 parts per million nitrogen in the ratio range to boron between two and four parts to one, the remainder being iron and small incidental amounts of other elements including carbon, aluminum and oxygen. The resulting sheet is cold rolled to final gauge thickness and subjected to the final heat treatment for decarburi- Zation and development of the l l0)[00l] secondary recrystallization texture. Preferably, hot rolling will be carried out between l,l00 and 1,3S0C and the hotrolled sheet will be pickled and then may be heat treated suitably for several minutes at 900 to 1,000C before cold rolling. Cold rolling may be in one stage or in two stages with an intermediate anneal. Also, the decarburization heat treatment at final gauge will be carried out at 800C in hydrogen containing sufficient moisture to effect the removal of carbon. A heat treatment of l to 5 minutes is used for this purpose. In the final texture anneal, secondary grain growth to produce the desired texture is initiated at about 950C when heating at 50C per hour in pure nitrogen. Recrystallization should be completed by the time the temperature attains l,000C and a change of atmosphere to purified dry hydrogen can then be made. Heating can be continued to about l,025C for a low temperature anneal, or to higher temperatures such as l,lC for more complete removal of residual sulfur, carbon and nitrogen.

In mill operations, the sulfur content of silicon-iron melts normally is substantially greater than the tolerable level in finished electrical steel sheet products. Accordingly. taking full advantage of the unique opportunity afforded by this invention for use of a lower sulfur content during the texture-developing stage of the final heat treatment, one will subject the melt to a dcsulfurization step. Preferably, this is accomplished in the ladle prior to teeming through the addition of lime and fluorospar to the ladle so that the sulfur content of the metal is reduced to a level nearer the limit specified for the ultimate sheet product.

The following illustrative. but not limiting, examples of my novel method as I have actually carried it out will further inform those skilled in the art of the nature and special utility of this invention:

EXAMPLE I A vacuum furnace .used to prepare a silicon-iron melt of the following composition;

The furnace was charged with electrolytic iron and a carbon addition and the melt was held in the molten condition for as long as one hour to enable reduction of boron from the crucible. The ferrosilicon. ferrous sulfide and a final carbon addition were added and the melt was poured to produce an ingot l l X 5 /2 X 2% inches). The ingot was heated to 1.325C for 45 minutes under a hydrogen atmosphere and then hot rolled to a sheet of about 0.085 inch thickness using eight passes without reheating. Pieces were cut from the hotrollcd sheet for reduction by cold rolling after pickling to remove hot-rolling scale and normalizing for 5 minutes at 900C in hydrogen (dewpoint about 0F). The sheet was cold rolled without tension to 0.028 inch thickness and then normalized 3 minutes at 900C in hydrogen (dewpoint about 0F) and again cold rolled (but with tension) to ().()l l inch thickness. Test strips- 3 cm by 30.5 cm in size were sheared in the rolling direction from this strip. sufficient mam an Epstein test pack. The strips were decarburized by heating for three minutes at 800C in wet hydrogen (+70F dewpoint). They were then annealed as a pack by heating at 50C per hour in purified nitrogen to 975C. then in purified hydrogcn at the same rate of heating to l.024(. holding 3 hours at this temperature followed by cooling at 50% per hour in hydrogen to 600C to room temperature. cooling was accomplished by withdrawal of therctort to the cooling /onc of the furnace. Magnetic test results are given below. When this same pack was reanncalcd. heating in hydrogen to l.l75C. magnetic pro erties ere only slightly improved. Thus. a material re,

quiring only a rclati\ely low temperature anneal to de vclop good magnetic quality is demonstrated.

Magnetic Properties Silicon 3.18 per cent Sulfur 0.009 per cent Manganese 0.001 per cent Carbon 0.024 per cent Boron 6 parts per million Aluminum 47 parts per million Nitrogen 27 parts per million Oxygen 18 parts per million lron Remainder Again. as in Example'l, the resulting ingot was hot rolled and otherwise processed as described therein with the result that a product was obtained corresponding to that of Example I having-permeability of 1.865 gausses per .oersted (in' a l0-oersted field), and losses of 0.553 and 0.665 watts per pound at l5.000 and 16.300 gausses. respectively. following anneal at ].025C.

EXAMPLE III In the preparation of the :melt for this example, a change was made from the method of Example I. The melt was held in the crucible in molten Condition for only a few minutes in order to limit the reduction of boron fromthe cruciblev A boron addition as a 19 per cent grade ferroboron was made to the melt after the ferrosilicon. ferrous sulfide and final carbon additions had been made. The resulting composition as deter-. mined by analysis was as follows:

Remainder The procedure for hot rolling was modified fromthat of Example I in that the rolled billet at l /z inch thick ness was cooled to room temperature and divided into several pieces. These were reheated to one of several temperatures. used to continue hot rolling to 0.08 inch thick sheet. For the material of this example. a 1.300C reheat temperature was used. The total number of passes and the reduction for each pass were unchanged.

(old rolling was carried out in two stages with an intermediate thickness of 0.05 inch. The intermediate heat treatment was at 900C for 3 minutes in dry hydrogen as before. After cold rolling to a final thickness of 0.0ll inch, Epstein stripswere cut. deearburized at 800C in hydrogen of room temperature dewpoint. and annealed as inlixample l. Magnetic test values after annealing at l.025C. and again at l.l75C were as follows:

. 'l'hiekness A.('. Loss at o0 Hert/ lltill lrcatmcnt. (inches) 15.0mm motion 17.0mm lllll I025 anneal .0l0' 0. 47 0.050 0.748 1850 H7 .mnenl 0.0l0.\ (L503 0.6100 0.07] lXt'i7 EXAMPLE ll EXAMPLE l\" l'olltming the procedure described in lixamplc l. the silicon-iron melt of the following composition was prepared:

A melt of the following composition was prepared as described in Example lll:

iil'h on 3.25 per cent An ingot of the size already described was poured and u ur 0.008 per cent a Manganese W108 per mm hot and cold rolled with intermediate heat treatments (arhon 0.022 per cent as described in Example I. The resulting ll-mil strip Boron 12 parts per million 4 Nhmgun 22 mm per million when prepared as an Epstein pack and annealed as in Oxygen 37 parts per million 5 Example I developed the following magnetic properlron Remainder ies.

Heat Thickness A.(. Loss at 60 Hertz 'l reatment (mils) l5 000 gs. l6 300 gs. #IUH (watts/lb) (watts/lb) 10 MT 7 The resulting magentic properties after processing as Annual 107 1.075 L187 1463 set forth in Example lll, except that a reheat tempcra- I75C ture of l. l 50C was used in hot rolling, were: H43

A.(. Loss at 60 Hertz Thickness l5.000 gs. l6 300 gs. 17.000 gs. Heat Treatment (inches) (watts/lb) (HHS/lb) (watts/lb) p l0H 105C anneal 0.0107 0.50s 0.6] l 0.692 ism [175C reanneal 0.0[08 0.497 0.589 0.658 M82 EXAMPLE V EXAMPLE VI] A melt of the following composition was prepared in A full-scale mill heat of 159,000 pounds of siliconaccordance with thc procedure set forth in Example lll: 7s iron was prepared using metal from a basic oxygen furnace. The melt was desulfurized (sulfur. reduced from 0.020 to 0.007 percent) as it was tapped and poured ST 1 I into a ladle containing 2,000 pounds of burned lime I ICU" cr CC" Sulfur 0.0011 per cent and 600 pounds of fluorospar. lron sulfide was then Mimgmu m added to bring the sulfur content from 0.007 to 0.009 Carbon 0.002 per cent 50 puns mink, percent. and 5 pounds of 19 percent grade ferroboron Aluminum P P i f were added to the ladle for purposes of the experiment. Nitrogen 24 parts per million l I I I v 24 palm minim, The analysis of the metal in the ladle was then as follron Remainder lows;

The resulting ingot was hot and cold rolled and otherwise processed as described in Example Ill. The result- Siliwn 3-1071 Aluminum Manganese 0.030% Phosphorus 0.006% mg sheet product had magnetic properties after anneal Cum)" OM33 Titanium g of! Nickel 0.094% Nitrogen 0.0033); 40 Copper 0.247: Oxygen 0.005291 Tin 0.021% Sulfur 0.009% Chromium 0.043% Boron 0.000871 Heat 'l'hickness A.( Loss at ()(l Hertz Rcmumdur Treatment (mils) 15.000 gs. 16300 gs. p.l0H

(ms/lb) l lngots cast from the metal were hot rolled from 2,450F to 90 mils thickness and then pickled, de-

1-336 scribed in Example l, heat treated for 5 minutes at minim )7 H49 L266 1443 900C, cold rolled to 0.028 inch thickness, heat treated 3 minutes at 900C, and cold rolled to a final gauge of 0.01 1 inch. Test strips were sheared in the rolling direc- 50 tion to form an Epstein pack and were decarburized by EXAMPLE V] a 3-minute heat treatment in hydrogen of F dewh E l m h point. The strips were then annealed by heating at a opermon l to t d g f tg Z; erfzm rate of 50C per hour in nitrogen from 800C to 950C f x fl x y r 3 1 or uctlon then at the same rate in dry hydrogen to l,025C. After a no oron 'i 1 ion was O d {E t l t :3 f H holding 3 hours at this temperature. the strips were m a me o e o owin com osi ion ma L n c g p cooled at 50C per hour in hydrogen to 600C at which was re are p p temperature the annealing retort was withdrawn to the cooling chamber. The measured magnetic properties Silicon 3.5 per cent (,0 were: Sulfur 0.008 per cent Manganese 0.002 per cent (arhon 0.029 per cent 'Ihickness A.(. Loss at (\0 Hert/ Boron 2 parts per million (mils) 15.000 gauss l6 300 gauss ,ul0H Aluminum 27 parts per million (watts/H (mus/1h) Nitrogen 22 parts per million Oxygen 19 parts per million 5 i(i 4 0.500 0.739 1X05 lron Remainder l EXAMPLE V111 In another operation similar to that of Example 111. a melt of the following composition was prepared:

An ingot was poured and processed through hot and cold rolling stages and heat treatments as described in Example 1 and test strips of the resulting I l-mil material were usedto provide an Epstein pack. This pack was heated at 50C per hour in purified nitrogen to 975C where it was held for 3 hours and then cooled at the rate of 50C per hour at 600C, whereupon it was placed in a cooling zone of the furnace until the pack reached room temperature. The product proved to have good properties when tested as described above, permeability being 1.898 gausses per oersted (in a 10- oersted field). v

A series of experiments was performed for purposes of determining the effects of various boron and nitrogen ratios on the development of secondary recrystallization during the final anneal. Thus. a total of six separate heats were prepared, all of the following basic composition:

Silicon 3.25 per cent Sulfur 0.008 per cent ('arbon 0.025 per cent lron Remainder To four of the heats, ferroboron was added to provide a nominal composition of parts per million boron. while the boron content of the other two was nominally established at 50 and 75 parts per million. The nitrogen content ranged in these heats from 40 to 145 parts per million.

EXAMPLE 1X The partial pressure of nitrogen in the furnace was maintained at 30 mm, and the metal was poured from the ladle following the ferroboron addition. The resulting ingot was hot and cold rolled and heat treated as described in Example 111. Analysis of the cold-rolled strip indicated the boron content to be 30 ppm and the nitrogen content to be 41 ppm. Magnetic properties of the cold-rolled strip product are set out in Table A below together with those of the following examples.

EXAMPLE X Following the procedure of Example IX except that the nitrogen partial pressure in the furnace was 60 mm. a cold-rolled product was obtained which proved on analysis to contain 30 ppm boron and 53 ppm nitrogen.

EXAMPLE X1 7 Following the procedure of Examples IX and X. but still further increasing the partial pressure of nitrogen in the furnace to 100 mm. resulted. in a cold-rolled product which was similarly found to contain 32 ppm boron and 78 ppm nitrogen.

EXAMPLE x11 1 I Again. the procedure of Example IXwas followed with the exception that the partiallpressure of nitrogen in the .furnace was 400 mm. The cold-rolled product contained .34 ppm boron and 145 ppm nitrogen.

XAMPLE xm Following the Example IX procedure, but maintaining 200 mm nitrogen partial pressure in the furnace and adding still. more ferroboron to the ladle. resulted in a cold-rolled product containing 59 ppm :boron and 68 ppm nitrogen. l 1

EXAMPLE xiv A cold-rolled strip product which contained on anal ysis 44 ppm boron and 93 ppm nitrogen was made generally in the manner described in Example IX through the additionto the ladle offerrobOron in amount equivalent'to 50 ppm boron and by maintaining the nitrogen partial pressure in the melting furnace at 200 mm.

Whenever in this specification and in the appended claims reference is made to amounts. rates, percent ages, or proportions. the weight basis is intended unless otherwise expressly stated.

As used herein and in the appended claims, the term ingot means and refers to a body made by solidifying by any casting method a molten steel made by any suitable steel-making method, and this includes a slab-like ingot obtained by a continuous casting method.

What 1 claim as new and desire to secure by Letters Patent of the United States is: r

l. The method of producing grain-oriented siliconiron sheet which comprises the steps of providing a silicon-iron melt containing 2.2 to 4.5 percent silicon and lesser amounts of sulfur and manganese. incidental amounts of other elements including carbon, aluminum and oxygen, and balance iron, adding a source of boron to the melt. casting the melt and hot-rolling the resulting billet to form an elongated sheet-like body, coldrolling the hot-rolled sheet-like body to provide a sheet of final gauge thickness containing from 5 to 45 parts per million boron and from about 15 to 95 ppm nitrogen and the proportions of nitrogen and boron being in the ratio range of two to four parts of nitrogen to one part of boron. from 0.007 to 0 .06 percent sulfur and from 0.002 to 0.1 percent manganese and the proportions of the sulfur and manganese being such as to re sult in a minimum of about 0.007 percent sulfur in solute form during final annealing treatment, and subjecting the said cold-rolled sheet to a final heat treatment to decarburize it and to develop l 10) [001 secondary recrystallization texture in it.

2. The method of claim 1 in which the amount of boron in the cold-rolled sheet is between about 5 and about 20 ppm.

3. The method of claim 1 in which the cold-rolled sheet contains 12 to 20 parts per million of boron, 3.25 percent silicon, 0.008 percent manganese. 0.008 per cent sulfur, and 37 ppm oxygen. iron constituting the remainder, and in which the final anneal consists of heating in an atmosphere consisting primarily of nitrogen until secondary recrystallization is completed. and then completing the annealing treatment in pure hydrogen 4. The method of claim 1 which includes the preliminary step of reducing the sulfurand manganese con tents of the melt to less than about 0.01 percent.

5. The method of claim 1 which includes the preliminary step of adding a desulfurizing agent to the melt and thereby reducing the sulfur content of the melt from about 0.020 to 0.025 percent to about 0.005 to 0.010 percent.

6. The method of claim 1 in which the melt contains about 0.03 percent manganese and about 0.020 to 0.025 percent sulfur. and which includes a desulfurizing step comprising the addition of lime and fluorospar to the melt to reduce the sulfur content thereof to less than about 0.0[ percent.

7. The method of claim 1 in which the cold-rolled sheet contains about 30 parts per million boron and about 80 parts per million nitrogen.

8. The method of claim 1 in which the cold-rolled sheet contains about 45 ppm boron and about 95 ppm nitrogen.

9. The method of producing grain-oriented siliconiron sheet which comprises the steps of providing a cold-rolled sheet of the thickness of the desired final product and containing 2.2 to 4.5 percent silicon, from about 5 to about 45 ppm boron, about 15 to ppm nitrogen and the proportions of nitrogen and boron being in the ratio range of two to four parts of nitrogen to one part of boron. from about 0.007 to 0.06 percent sulfur, and from 0.002 to 0.1 percent manganese and the proportion of sulfur and manganese being such as to result in a minimum of about 0.007 percent sulfur in solute form during the final annealing treatment, and subjecting the said cold-rolled sheet to a final heat treatment to decarburize it and to develop l l0)[00l secondary recrystallization texture in it.

10. A cold-rolled silicon-iron sheet product containing 2.2 to 4.5 percent silicon, between about 5 and 45 parts per million boron, between about 15 and 95 ppm nitrogen, the amounts of nitrogen and boron being in the ratio range of two to four parts of nitrogen per part of boron. between about 0.007 and 0.06 percent sulfur, and between about 0.002 and OJ percent manganese. the proportion of sulfur to manganese being such as to result in a minimum of about 0.007 percent sulfur in solute form when the sheet is heated to about 950C during texture-developing heat treatment.

Claims (10)

1. THE METHOD OF PRODUCING GRAIN-ORIENTED SILCON-IRON SHEET WHICH COMPRISES THE STEPS OF PROVIDING A SILICON-IRON MELT CONTAINING 2.2 TO 4.5 PERCENT SILICON AN LESSER AMOUNTS OF SULFUR AND MANGANESE, INCIDENTAL AMOUNTS OF OTHER ELEMENTS INCLUDING CARBON, ALUMINUM AND OXYGEN, AND BALANCE IRON, ADDING A SOURCE OF BORON TO THE MELT, CASTING THE MELT AND HOT-ROLLING THE RESULTING BILLET TO FORM AN ELONGATED SHEETLIKE BODY, COLD-ROLLING THE HOT-ROLLED SHEET-LIKE BODY TO PROVIDE A SHEET OF FINAL GAUGE THICKNESS CONTAINING FROM 5 TO 45 PARTS PER MILLION BORON AND FROM ABOUT 15 TO 95 PPM NIROGEN AND THE PROPORTIONS OF NITROGEN AND BORON BEING IN THE RATIO RANGE OF TWO TO FOUR PARTS OF NITROGEN TO ONE ONE PART OF BORON, FROM 0.007 TO 0.06 PERCENT SULFUR AND FROM 0.002 TO 0.1 PERCET MANGANESE AND THE PROPORTIONS OF THE SULFUR AND MANGANESE BEING SUCH AS TO RESULT IN A MINIMUM OF ABOUT 0.007 PERCENT SULFUR IN SOLUTE FORM DURING FINAL ANNEALING TREATMENT AND SUBJECTING THE SAID COLD-ROLLED SHEET TO A FINAL HEAT TREATMENT TO DECARBURIZE IT AND TO DEVELOP (110) (001) SECONDARY RECRYSTALLIZATION TEXTURE IN IT.

2. The method of claim 1 in which the amount of boron in the cold-rolled sheet is between about 5 and about 20 ppm.

3. The method of claim 1 in which the cold-rolled sheet contains 12 to 20 parts per million of boron, 3,25 percent silicon, 0.008 percent manganese, 0.008 percent sulfur, and 37 ppm oxygen, iron constituting the remainder, and in which the final anneal consists of heating in an atmosphere consisting primarily of nitrogen until secondary recrystallization is completed, and then completing the annealing treatment in pure hydrogen.

4. The method of claim 1 which includes the preliminary step of reducing the sulfur and manganese contents of the melt to less than about 0.01 percent.

5. The method of claim 1 which includes the preliminary step of adding a desulfurizing agent to the melt and thereby reducing the sulfur content of the melt from about 0.020 to 0.025 percent to about 0.005 to 0.010 percent.

6. The method of claim 1 in which the melt contains about 0.03 percent manganese and about 0.020 to 0.025 percent sulfur, and which includes a desulfurizing step comprising the addition of lime and fluorospar to the melt to reduce the sulfur content thereof to less than about 0.010 percent.

7. The method of claim 1 in which the cold-rolled sheet contains about 30 parts per million boron and about 80 parts per million nitrogen.

8. The method of claim 1 in which the cold-rolled sheet contains about 45 ppm boron and about 95 ppm nitrogen.

9. The method of producing grain-oriented silicon-iron sheet which comprises the steps of providing a cold-rolled sheet of the thickness of the desired final product and containing 2.2 to 4.5 percent silicon, from about 5 to about 45 ppm boron, about 15 to 95 ppm nitrogen and the proportions of nitrogen and boron being in the ratio range of two to four parts of nitrogen to one part of boron, from about 0.007 to 0.06 percent sulfur, and from 0.002 to 0.1 percent manganese and the proportion of sulfur and manganese being such as to result in a minimum of about 0.007 percent sulfur in solute form during the final annealing treatment, and subjecting the said cold-rolled sheet to a final heat treatment to decarburize it and to develop (110)(001) secondary recrystallization texture in it.

10. A cold-rolled silicon-iron sheet product containing 2.2 to 4.5 percent silicon, between about 5 and 45 parts per million boron, between about 15 and 95 ppm nitrogen, the amounts of nitrogen and boron being in the ratio range of two to four parts of nitrogen per part of boron, between about 0.007 and 0.06 percent sulfur, and between about 0.002 and 0.1 percent manganese, the proportion of sulfur to manganese being such as to result in a minimum of about 0.007 percent sulfur in solute form when the sheet is heated to about 950*C during texture-developing heat treatment.