CA1042768A - Method of producing silicon-iron sheet material with boron addition and product - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
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 other-wise be incapable of secondary recrystallization necessary to produce such properties.

Description

~0~'~7~8 The present invention relates generally to the art of producing electrical ~teel and is more particularly concerned with a novel method of producing ~ingly-oriented silicon-iron sheet through the use of ~mall but critical amounts of boron, and with a new cold-rolled silicon-iron sheet product.
This invention is related to the invention disclosed and claimed in U.S. patent No.~3 ~/DSJ ~ y~ issued 5e~t~A'~r/~/Ç~s , entitled "Method of Producing Oriented Silicon-Iron Sheet Material With Boron Addition" in the na~e of ~oward C. Fiedler and a~igned to the assignee hereof, dir-cted to the novol concept of cold rolling hot-rolled ~ilicon-iron sheet direetly to final thiekness without an intermediato -~ heat treat~ent through the u~e of small but eritical amounts of boron and by maintaining the ratio of manganese to sulfur in the metal at les~ than 1.5~
The invention disclosed and claimed herein also relate~ to that diselosed and elai~ed in U.S. Patent No.
~- 3,~ , issued ~ ~ t~ 6 , entitled ~Method of Producing Oriented Silicon-Iron Sheet ~aterial With Boron AdditionU in the na~e of Howard C. Fiedler and as~igned to the assignee hereof, whieh pertains to the new eoneept of using small but eritieal amounts of boron to enable the produetion of singly-oriented ~ilieon-iron sheet of improved magnetie properties by ~ubjeeting ~ilieon-iron sheet eontaining manganese and sulfur in a ratio less than 2.1 to a eold reduetion ~eguence ineluding an int~nmodiate annoaling step and 2 final heavy eold rolling reduetion.
Tho ~heet materials to whieh this invention is direeted are u~ually referred to in tho art as ~eleetrieal~ ~ilieon ~teels or, moro prop-rly, ~ilieon-irons and are ordinarily eompo~ed prineipally of iron all~yad with about 2.2 to 4.5 RD-7~94 7~;8 per cent ~ilicon and r~lativoly minor amount~ of variou~
i~puritie~ and very ~mall amountJ of carbon The~e product~
ar~ of the "cube-on-edge~ type, ~ore th~n about 70 por cent of thsir cryatal ~tructure being oriented in the (110) 00 toxture, as de~cribed in Miller Indice~ ter~s Such grain-oriented ~ilicon-iron ~heet products are currently made com~ rcially by the sqquence of hot rolling, heat treating, cold rolling, heat treating, again cold rolling and then final he~t treating to decarburize, de~ulfuriz- and recrystallize Ingots are convontionally hot-worked into a strip or sheet-like configuration le~8 than 0 150 inch in thickne-~, referrod to as Uhot-rolled band " The hot-rolled band i~ thon cold rollod with appropriate intermediate ann-aling treat~ent to the finished sheet or Jtrip thicknes~ u~ually Lnvolving ~t l~ast a 50 p-r ce~t roduction in thickne-s, aad giv~n a final or texture-producing annealing treatment I hava discover-d that under certain conditions boroa ha~ a b neficial effect on the ~econdary recrystallization of si}icon-iron sh -t ~atorial to dov-lop the (110) LOO~ textura and the ~p~cial magnotic properti-~ a~ociated with it ; Particul~rly, I have found that th proaence of a vory snall, but highly ~ritical, amount of boron in cold-rolled Jilicon-iron ~heet during the final or texture-developing anneal enable~
preparation of ~ilicon-iron sheot having a Jtrong cubo-on-edge textur- and corre-pondingly good magnetic propertie~ In other `- word~, the seemingly insignificant amount of boron ~akes secondary recry~tallization possible Conseguently~ the u~e of ~angane~e sulfide can be avoided as can the neces~ity of a high-temperature de~ulfurizing heat treatmeat during the final processing operations Thu3, the metal can by reason of this invention be desulfuriz~d at the melt stage with 104;~7~
~ub~tantial time and co~t ~aving~. All thi~ i~ quite ~upris-ing considering the f~ct that boron hAs previou~ly been recognized in our experience a~ a detrimental impurity which it definitely i8 in amounts only moderately greater than those which I have found to be useful. In fact, ~xcept $n the pre~ence of otherwise detrimentally high amount~ of nitrogen in the metal, boron in amount a~ small as 50 parts per million (ppm) is definitely detrimental in terms of desired magnetic characteristics. ~hus, the important new re~ults and advantages of this invention are obtained through the presence of boron in amounts from about five to about 45 ppm during the texture anneal of the cold-rolled sheet. I h~ve found the optimum boron content to be in the range from about five to 20 ppm.
This unigue capability of bDron wa~ discovered during experiments involving the use of crucible refractories contain-ing boron a- a minor impurity. ~ all amounts of boron were reduced from the rofractories to the silicon-iron melts and exerted noticeable beneficial effect on the texture-developing processO Subsequently, I demonstrated that the boron content in silicon-iron melts prepared in such vessels could be closely controlled by ad~usting the melt carbon content as by adding iron oxide and thereby preventing the reduction of boron in the crucible refractory and consequent pick-up of boron by the melt. I further found that the boron requirements can be m~t through the use of a boron-free crucible by adding a boron source to the melt.
I have further found that the surprisingly ~harp criticality of such relatively ~mall proportions presents no substantial difficulty in either laboratory or mill~cale operations. Thus, boron in suitable form i-~ added in requi~ite 10 ~'~7 ~ ~
amount to the melt shortly befor~ ca~tinq. In mill practice, the boron JOUrce i~ suitably add~d to the ladle after the u~ual ferrosilicon addition. No significant lo~ of boron from the ~etal occur~ through hot and cold rolling and heat treating stages prior to the final heat treatment. Ho~ever, boron 108~ c~n bo substantial if the boron source is added well in advanco of ca~ting or if the ingot is ~oakod at high tonperature for a prolonged period. During the final anneal, es~entially all the boron i~ eliminated from the metal when in accordance with thi~ invontion the role of boron in promoting the d~ired secondary recrystallization texture develop~ont ha~ terminated.
I have additionally discovored that the proportion of nitrogen to boron i~ al~o of critical importance to the new result- and advantages of this invention. unles~ the ratio of nitrogen to boron i~ in the range-from two to four parts of nitrogen per part of boron, products having good magnetic propertioJ can not be consiJtently produced even though the boron content of the melt i8 within the above stated critical - 20 range. con~equently, in accordance with this invention, thenitrogen content of tho m lt will be in the range from about 15 part~ per million to about 95 parts per million.
The nitrogen requirement can be mot in any convenient man~er, but in proferred practice the motal in a vacuum furnace is provided with a 30-torr nitrogen atmosphere to which argon i~ added to bring the pressure up to one atmo~phere for the pouring operation. The metal as poured contains about 30 ppm of nitrogen and in the neighborhood of 10 ppm of boron. The pressurc of nitrogen required in the furnace chamber will dep~nd in any given circumstance upon the ratio of the volume of the chamber to the weight of the melt.

1~4~7~
Anothor di~covory which I havo made is that the proportions of ~ulfur and mangan~se in the ~etal duri~g final ~nnealing treatment are critlcal in t~rms of the magnetic propertie~ of the final product strip or sheet material. Particularly, it i9 essential that there be at lea~t 0.007 per cent ~ulfur in solute form at that stage of proce#sing. That re~uirement can be met if both th~ ~ulfur and the m~nga~ese contents of the ~ilicon iron are quite low ~nd in fact if there i8 no more than about 0.007 per cent sulfur in the metal. The tendency for the manganese to tie - up the sulfur i8 ~egligible in highly dilute systems in which the manganose content is of the order of about 0.002 to 0.006 per cent and, conseguently, it i8 not ~ecessary 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 di~coveries and new concepts set forth above expressed in terms of manipulative ~t~ps add up to a novel process and when expressed in co~positional terms de~ine a unigue silicon-iron sheet product. The product i8 a cold-rolled sheot of final gauge thickne~s which by virtue of its boron, nitrogen, mangane~e and sulfur content can be converted to the oriented state in which it will have valuable magnetic properties but will not contain the boron which enabled the develop~ent of thoJe properties through secondary recry~talliza~
ion. The process of producing this new intermediate cold-rolled ~heet i8 al~o new as i~ the overall process of producing the final dosired ~heet material fro~ a silicon-iron melt.
Briefly described in its article aspoct, this invention comprises a cold-rolled silicon-iron sheet product ~ 7 ~ ~
containing 2 2 to 4 5 per cent ~Llicon, between ~bout 5 and 45 ppm boron, between about 15 ~d 95 ppm nitrogen with the nitrogen and boron being in the ratio range of 2 to 4 parts of nitrogen per p~rt of boron, b~tween about 0 007 and 0 006 per cont ~ulfur, an~ between ~bout 0 002 and O Ol por cent ~angan-~e, and the proportion of ~angan~se to sulfur b-ing such that the presenco in tho ~ t~l of at loast 0 007 per cent sulfur in soluto forn is as~urod during the final textur~
anneal Similarly de~cribed, the ~ethod co~pri~es the steps of providing this intormediate ~hoot product and subjocting -~ it to a final heat treatm nt to develop (llO) rOOlJ secondary recrystallization t-xture in it In tha preferred practice of this invontion, the a~ount of nitrog n in th~ metal will not oxceed about 60 ppm 80 th~t any tendoncy for nitrogen-induced ~liv~ring and bli~toring can be avoided Thi~ r~guire~ent i- ro~dily met by con~orci~l ~teel-producing practice- when u~u~l precautions aro taken to limit nitrogen pick-up Con~eguently, it is pr-forable to add boron to th0 melt after it has been tapped into the ladlo for te-~ing The amounts to be added will bo 10-20 ppm of the ~elt weight In carrying out the ~othod this inv~ntion, ono will pr~par- a silicon-iron melt of roquired che~i~try and U8~ it to produce ingots whi~h are hot roll-d to interaediato thickness When it i8 poured, tbe ~elt will contain fro~ 2 2 to 4 5 per cent silicon, from 0 003 to 0 06 per cent sulfur, fro~ ~ 001 to 0 10 por c~nt mangane-e and from about 5 to 45 part~ per ~illion boron, fro~ about 15 to 95 parts per million nitrogen in the ratio range to boro~ bet~e-n two and four parts to one, the remainder being iron and sMall incidental amount~ of other 10~ 8 ele~ent~ including carbon, aluminum and oxygen. The resulting ~hoet is cold rolled to final gauge thickne~ and subjectod to the final heat treat~ent for decarburization and development of the ~110) L ool~ 3econdAry recrystallization texture.
Preferably, hot rolling will be carried out between 1100 and 1350 C and the hot-rolled sheet will bo pickled and th-n may be heat treated suitably for several minutes at 900C to looo& before cold rolling. cold rolling may be in one stage or m two stage~ 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 one to five minutes is used for this purpose. In the final texture anneal, ~econdary grain growth to produco the deRirea t~xture i8 initiated at about 950C when heating at 50C per hour in pure nitrogen. Recrystallization should be completed by the time the temperature attains 1000C and a change of atmosphere to purified dry hydrogen can then be made. Heating can be continued to about 1025& for a low temperature anneal, or to higher t~mperatures ~uch as 1175C 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 ~teel sheet products. Accordingly, taking full advantage of ~he unique opportunity afforded by thi3 invention for use of a lower sulfur content during the texture-developing stage of the final heat treatment, one will ~ubject the melt to a desulfurization step. Preferably, this i8 accomplished in the ladle prior to teeming through the addition of lime and fluorospar to the ladle ~o that the sulfur content of the metal is reduced to a level nearer the limit 104'~7~i8 specified for the ultLmate sheet product.
The ~ollowing illustrat:ive, but not li~iting, exa~ples of ~y novel method as I have actually c~rried it out will further inform tho~e skilled in the art of the nature and special utility of this invention:
EXAMP~E I
A vacuum furnace was used to prepare a silicon-iron melt of tho following compositions Silicon 3.25 per cent Sulfur 0.009 per cent Mang~nese 0.002 per cent carbon 0.021 per cent Boron 13 parts per million ;~ Alu~i~u~ 32 Nitrogen 32 u n Oxyge~ 23 n ~ n Iron Ro~ainder The furnace was charged with electrolytic iron and a carbon addition and the melt wa~ held in the ~olten condition .:
for as long as one hour to enable reduction of boron from the crucible. Tho ferrosilicon, ferrous sulfid- a~d a final carbon addition were added and the melt was poured to produce an ingot (11 x 5-1/2 x 2-5/8 inches). ~he ingot was heated to 1325C ~or 45 ~inutos under a hyd~ogen atmosphere and then hot rolled to a sheet of about 0.085 inch thickness using eight pa-Jo- without reheating. Pieces were cut fro~ the hot-roll~d sheet for reduction by cold rolling after pickling to r~ovo hot-rolling ~cale and normalizing for five ~inute~ at goo& in hydrogen (d~wpoint about 0F). The ~heet wa~ cold rolled without tension to 0.028 inch thickne~s and then nor~alized three minute~ at 90~C in hydrogen (dewpoiat about 1~4;~7~8 OOF) and again cold rolled tbut with tension) to 0.011 ifich thickne~ est ~trip~ 3 cm by 30.5 cm in ~ize wer~ sheared in the rolling direction fro~ this ~trip, ~ufficient to form an Ep~tein te~t pack. Tho ~trip~ were decarburized by hoating for three minutes at 800C in wet hydrogen (+70F dewpoint).
They were then annealed a~ a pack by heating at 50C per hour in purified nitrogen to 975C, th-n in purified hydrogon at the ~ame rate of heating to 1024 C, holding three hour~ at this temperature followed by cooling at 50C per hour in hydrogen to 600 &. From 600C to room temperature, cooling wa~ acco~pli~hed by withdrawal o~ ~he retort to the cooling zone of the furnaco. Magnetic te_t result~ are given below.
When this 8ame pack wa~ reannealed, heating in hydrogen to 1175C, magnetic properties were only slightly improved.
Thu~, a ~aterial requiring only a relatively low te~perature anneal to develop good magn-tic guality i8 demonstrated.
M-qn tic ProvertieR

A.C. Los~
Thickness at ~O Hertz ~eat Treatment (mil~) 15,00B 16,300B ~lOH
1025C anneal10.7 0.537 0.647 1856 1175C reanneal 10.7 0.529 0.644 1862 EXAMPLE II
Following the procedure described in ESa pl- I, the silicon-iron melt of the following composition was prepared:
Silicon 3.28 per cent Sulfur 0.OO9 n Manganese 0.002 Carbon 0.024 "
Boron 6 parts per million Aluminum 47 parts per million Nitrogen 27 n Oxygen 18 " " "
Iron Remainder _ g _ .

~04;~ 8 Again, as in Example I, the resulting ingot was hot rolled and otherwi~e processed a3 described therein with the result that a product wa~ obtained corresponding to that of Example I having permeability of 1865 gaus~es per oer~ted (in a l0-o~rsted field), and 1088e8 of 0.553 and 0.665 watts per pound at 15,000 and 16,300 gau88e~, respectively, following ann~al at 1025 C.
~XAMPLE III
In th~ preparation of the melt for this example, a change was made fro~ the method of Examplo ~. The melt was held in the crucible in molten condition for only a few minutes in order to limit the reduction of boron from the crucible. A boro~ additDn~as a 19 per cent grade ferroboron was made to the ~elt after the forrosilicon, ferrous sulfide and final carbon additions had been ~ade. Tho resulting compo~itio~ as determi~ed by analysis was as follows:
Silicon 3.25 per cent Sulfur 0. 008 n Manganese 0,003 n n Carbon 0. 02 ~ n Boron 12 parts per million Nitrog~n 37 ~ u N
Oxygen 30 "
Iron Remainder The procedura for hot rolling was ~odified from that of ~xample I in that the rolled billet at one and one-half inch thickness was coolod to room temperature and divided into sev~ral pieces. The~e were reheated to one of several te~peratures, used to continue hot rolling to 0.08 inch thick ~heet. For the material of this example, a 1300& roheat temperature wa~ used. The total number of pas~e~ and the . - 10 -i~4;~7t;~
roduction for each pa~ were unch~nged.
Cold rolling w~ c~rrled out in two 8tago8 with an intermediate thic~ne-~ of 0.05 inch. The int~rmediate h ~t treatm~nt was ~t 900C for thre~ ~i~utes in dry hydrogen as bofore. After cold rolling to ~ f~n~l thickness of 0.011 inch, ~p~toi~ ~trip~ wore cut, dec~rburized at 800C in hydrogen of roo~ te~perature dewpoint, and anneal~d a- in Ex~ple I. Magnetic test value~ after ~nnealing at 1025C, and again ~t 1175& were aq follows:

Thickn~s~ A.C. Loqa at 60 Hertz Hoat Treatm~nt (inches) 15,000B 16!000B 17,000B ~lOH
1025C anneal 0.0107 0.547 0.656 0.748 18S6 1175C ann~al 0.0108 0.503 0.600 0.671 1867 EXAMPLE IV
A melt of the following co~position wa~ prepared a8 describ~d in Exampl~ III:
Silicon 3.25 Per cent Sulfur 0.008 ~ n Mangan-~e 0.008 a n Carbon 0.022 u u Boron 12 parts per ~illion Nitrogen 22 ~ ~ ~
Oxygen 37 " u n The re~ulting magnetic propertie~ after procressing a~ set forth in Bxample III, xcept that a reheat temperature of 1150~
was used in hot rolling, were:

A.C. Lo~- at 60 Hertz Heat Thicknesa _,500 q~. 16 300 gs. 17,000 qa Treatment (inches) (watts/lb) (w;tts/lb)(~5~3 ann-~l 0.0107 0.508 0.611 0.692 1876 reann-al 0.0108 0.497 0.589 0.658 1882 ~V4*761~

EXA~P~ V
A ~lt of th~ following co~position waJ prepared in accordance with the proceduro ~et forth in ~xa~ple II}~
Silicon 3.3 p-r cent Sulfur 0. 006 n M~gi~l~l81~ o. 005 ~ n c~rbon 0.002 u Boron 50 parts per million 3 Aluminum 30 n ~ n ~ 10 ~itrogen 24 u n ~
Oxygen 24 ~ ~ n Iron Re~ainder ~ The resulting ingot was hot and cold rolled and otherwise :~ procos~ed a~ d~scribed in Example III. The r~sulting sheet product had magnetic propertie~ after annealing of 5 Thickne8 A.C. Loss at 60 ~ertz ~e~t Treatment (mil~)15,000 gs. 16,300 gs.~lOH
~watt~7Ib) ~watts/lb) 1025anneal 10.71.226 1. 379 1465 1175 reanneal 10.71.149 1.266 1443 EXAMP~E VI
I~ an operation si~ilar to that of Example III wherein - a minimum opportunity was provided for ~he reduction of boDDn fro~ the crucible, and no boron addition was made to the melt, a melt of the following composition wa~ prepared:
Silicon 3~5 per cent Sulfur 0. 008 n Manganese 0.002 "
Carbon 0.029 u -Boron 2 parts per million Aluminu~ 27 parts per million : 30 ~itrogen 22 " ~ "
~'xy~en~ 19 u u Iron Remainder ~6)4;~76~
An ingot of tho 8ize already d~cribed was poursd and hot and cold rolled with intermediate heat; treatments a~ de~cribed in Example I. The r~sulting ll-mil ~trip when prepared as an Epstein pack and annealed a~ in Exa~ple I d~veloped the following magnetic prop~rtie~s Thickne88 A.C. Log~ at 60 Hertz Heat Treatment (mils) 15,000 g~. 16,300 g~ lOH
1025C anneal 10.7 1.075 1.187 1463 1175C reanneal 10.7 1.143 1.256 1441 EXAMPLE VII
A full-~cale mill heat of 159,000 pounds of silicon-iron was prepared u~ing metal from a basic oxygen furnace.
The melt wa~ desulfurized (sulfur reduced from 0.020 to 0.007 per cent) a~ it was tapp~d and poured into a ladle containing 2000 pounds of burned li~e and 600 pound~ of fluorospar. Iron ~ulfide wa~ then added to bring the sulfur content from 0.007 to 0.009 per cent, and five pounds of 19 per cent grade ferroboron were added to the ladlo for purpo~es of the experiment. Tho analysi~ of the metal in the ladle wa~ then a~ follows:
Silicon 3.20% Alu~inum 0.00~%
Manganese 0.030X Phosphorus 0.00~%
carbon 0.033% Titanium 0.005~
Nickel O.Q94X ~itrogen 0.0033%
~opp~r 0.24~ Oxygen 0.0052%
Tin 0.021% Sulfur 0.009%
~ Chromium 0.043% Boron 0.0008%
Iron Remainder In~ots cast from the metal were hot rolled from 2450F
to 90 mils thickness and then pickled, a~ described in Example I, heat treated for five minute~ at 900C, cold rolled to 0.028 inch thicknes~, heat treated thr2e minute~ at 900C, and cold ~ 4;~76~
rolled to a final gauge of 0 011 inch Tost ~trip~ w re ~heared in the rolling direction to form an Ep~tein pack and wer~
decarburized by a three-minute heat treatm-nt in hydrog-n of 700F d~wpoint The strip~ w~re then ~nn~aled by h~ating at a rat- of 50 & p-r hour in nitrogen fro~ 800C to 950C th-n at the ~amo rate in dry hydrogen to 1025C After holding thr~o hour~ at this tomperature thc ~trip~ w ro cooled at 50 per hour in hydrogen to 600 & at which temp~r~ture the annealing retort Wa8 withdrawn to the cooling ch~b~r The meaRur~d magnotic propertie~ werOE

~hickne~s A C Los~ at 60 ~ertz (mil~ 15 000 qaus~ 16 300 gaus~ ~10H

EXAMPLE VIII
In anothor operation similar to that of ~xampl~ III
a melt of the following compo~ition wa~ prepar-ds Silicon 3 28 p-r cent ~angane~o 0 001 Sulfur 0 005 ~ n Carbon 0 018 H U
Aluninum 0 004 Boron 0 0007 H n Nitrogen 0 0019 H
Oxygen 0 0026 Iron Romainder An ingot wa~ poured and processed through hot and cold rolling stage~ and ~eat treatmonts a~ describ-d in Example 1 and te~t strips of the resulting ll-mil material w ra u~ed to provide an Ep~tein pack Thi~ pack wa~ h-ated at 50C per hour in purified nitrogon to 97 s& where it was held for three hours and then cooled at the rate of 50C per hour at 600 & whereupon it wa~ placed in a cooling zone of the furnace until the pack 1~)4~2~ti8 r~ach~d roo~ t~mp~r~turo The product prov~d to have good propertie~ whon teJted ~8 doscriblsd above, pormeability being 1898 gaus~e~ per oorsted (in a 10-oer~ted field) A ~orie~ of experiment~ was performed for purpo3es of determining the effects of various boron ~nd nitrogen ratios on th dev~lopment of ~econdary recrystallization during the final anneal Thus, a total of 8iX separat~ heat~ were prepared, all of tho same following basic compositions Silicon 3 25 per c~nt Sulfur 0 008 n carbon 0 025 ~ n Iron Remainder To four of the heat~, ferroboron was added to provide a nominal co~po~ition of 50 part~ per million boron, while the boron content of th~ other two was nominally established at 50 and 75 p rts por million The nitrogen content ranged in the~- heat~ from 40 to 145 parts per million EXANPLE IX
The partial pressure of nitrogen in the furnace was maintained at 30 ~m, and the metal was poured from the ladle following the ferroboron addition The resulting ingot wa~
hot and cold rollod and heat treated as described in Example III Analysis of the cold-rolled strip indicated the boron content to be 30 ppm and the nitrogen content to be 41 ppm Magnetic propertie~ of the cold-rolled serip product are set out in Table A below togethor with those of the following examples ~XAMPI.E X
Following the procedure of Example IX except that the nitrogen partial pressur~ in furnace was 60 ~m, a cold-rolled product was obtained which proved on analysis to contain - 30 ppm boron and 53 ppm nitrogen ~D-7794 1~)9,Z7ti~
E~CAMP~ XI
Following th~ procedure of E xampla~ IX and X, but ~till further increa~ing the partial pre~sure of nitrog-n in the furnace to 100 ~, re~ulted in a cold-rolled product which was similarly found to contain 32 ppm boron and 78 ppm nitrogen ~XAMPI13 XII
Again, tho procedure of Example IX wa~ followed with the exception that the partial pressuro of nitrogen in the furnace was 400 mm The cold-rolled product contained 34 ppm boron and 145 ppm nitrog~n EXANP~ XIII
Following th~ ~3xampl- IX procedur-, but maintaining 200 n~ nitrogen partial prel~Jure i~ the furnace and adding ~till mor- ferroboron to the ladl~, resulted in a cold-rolled product containing S9 ppm boron aDd 68 ppD~ nitrogen : I~XAMPLE: XIV
A cold-rolled strip p~oduct ~hich contain-d on ~aly~i~ 44 pp~ boron and 93 ppm nitrog-n Wa8 ~ade g-nera~ly in th- mann r d scribod in Exampl- IX through th~ ~ddition to th- ladle of ferroboron in amount eguivalent to 50 pp~ boron and by Dlaintaining the nitrogen partial pr-~ure in the r~olting furnac~ at 200 ~
TABI~ A

A C. Lo8~
Ex~Pl-Thickn-88 (in L ls~cB171cB lOH
D~OiQ8 1 271 --- 1421 XIIo0107 9301 255 1551 XIV0107 53~~12 1842 . .

1~4~7~j8 Whenev-r in this specification and in the append-d clai~s reforence i~ mado to a~ount~, r~t-~, p-rcentag~-, or proportion~, the weight ba~is i8 intendbd unlo~s otherwi~e expressly 3tatod As usod her-in and in the appendod claimn, the term ~ingot~ moans ~nd rofers to a body made by ~olidifying by any casting m-thod a Dolton Jte~l aade by any uitablo ~teel-makinq ~othod, and this includ~ a ~lab-liko ingot obtainod by a continuous c-sting m~thod - 1~7 -1.

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method of producing grain-oriented silicon-iron sheet which comprises the steps of providing a silicon-iron a melt containing 2.2 to 4.5 per cent 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, cold-rolling the hot-rolled sheet-like body to provide a sheet of final gauge thickness containing from five to 45 parts per million boron and from about fifteen 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 per cent sulfur and from 0.002 to 0.1 per cent manganese and the proportions of the sulfur and manganese being such as to result in a minimum of about 0.007 per cent 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 five and about 20 ppm.

3. The method of claim 1 in which the cold-rolled sheet contains twelve to 20 parts per million of boron, 3.25 per cent silicon, 0.008 per cent 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 sulfur and manganese contents of the melt to less than about 0.01 per cent.

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 per cent to about 0.005 to 0.010 per cent.

6. The method of claim 1 in which the melt contains about 0.03 per cent manganese and about 0.020 to 0.025 per cent 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 per cent.

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 per cent silicon, from about five to about 45 ppm boron, about fifteen 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 per cent sulfur, and from 0.002 to 0.1 per cent manganese and the proportion of sulfur and manganese being such as to result in a minimum of about 0.007 per cent 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 per cent silicon, between about five and 45 parts per million boron, between about fifteen 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 per cent sulfur, and between about 0.002 and 0.1 per cent manganese, the proportion of sulfur to manganese being such as to result in a minimum of about 0.007 per cent sulfur in solute form when the sheet is heated to about 950°C during texture-developing heat treatment.