CA2054331A1 - Method of making regular grain oriented silicon steel without a hot band anneal - Google Patents
Method of making regular grain oriented silicon steel without a hot band annealInfo
- Publication number
- CA2054331A1 CA2054331A1 CA 2054331 CA2054331A CA2054331A1 CA 2054331 A1 CA2054331 A1 CA 2054331A1 CA 2054331 CA2054331 CA 2054331 CA 2054331 A CA2054331 A CA 2054331A CA 2054331 A1 CA2054331 A1 CA 2054331A1
- Authority
- CA
- Canada
- Prior art keywords
- silicon steel
- anneal
- conducting
- temperature
- per minute
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 229910000976 Electrical steel Inorganic materials 0.000 title claims abstract description 50
- 238000004519 manufacturing process Methods 0.000 title description 5
- 238000001816 cooling Methods 0.000 claims abstract description 38
- 238000000034 method Methods 0.000 claims abstract description 27
- 230000008569 process Effects 0.000 claims abstract description 20
- 238000000137 annealing Methods 0.000 claims abstract description 14
- 238000005097 cold rolling Methods 0.000 claims abstract description 12
- 238000010583 slow cooling Methods 0.000 claims abstract description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 7
- 238000010791 quenching Methods 0.000 claims abstract description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 15
- 229910052799 carbon Inorganic materials 0.000 claims description 15
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 14
- 229910052710 silicon Inorganic materials 0.000 claims description 14
- 239000010703 silicon Substances 0.000 claims description 14
- 239000000463 material Substances 0.000 claims description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 6
- 238000001953 recrystallisation Methods 0.000 claims description 5
- BUGBHKTXTAQXES-UHFFFAOYSA-N Selenium Chemical compound [Se] BUGBHKTXTAQXES-UHFFFAOYSA-N 0.000 claims description 4
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 claims description 4
- 229910052782 aluminium Inorganic materials 0.000 claims description 4
- 239000010949 copper Substances 0.000 claims description 4
- 230000000694 effects Effects 0.000 claims description 4
- 229910052711 selenium Inorganic materials 0.000 claims description 4
- 239000011669 selenium Substances 0.000 claims description 4
- 229910052717 sulfur Inorganic materials 0.000 claims description 4
- 239000011593 sulfur Substances 0.000 claims description 4
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 3
- 238000007792 addition Methods 0.000 claims description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 3
- 229910052796 boron Inorganic materials 0.000 claims description 3
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 229910052742 iron Inorganic materials 0.000 claims description 3
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 claims description 3
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 230000000171 quenching effect Effects 0.000 claims description 3
- 229910001566 austenite Inorganic materials 0.000 description 20
- 229910000859 α-Fe Inorganic materials 0.000 description 13
- 229910000831 Steel Inorganic materials 0.000 description 9
- 239000010959 steel Substances 0.000 description 9
- 230000035699 permeability Effects 0.000 description 8
- 230000032683 aging Effects 0.000 description 5
- 229910001567 cementite Inorganic materials 0.000 description 5
- 238000000354 decomposition reaction Methods 0.000 description 5
- 239000002244 precipitate Substances 0.000 description 5
- 238000001556 precipitation Methods 0.000 description 5
- CPLXHLVBOLITMK-UHFFFAOYSA-N Magnesium oxide Chemical compound [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 238000005266 casting Methods 0.000 description 4
- 239000012467 final product Substances 0.000 description 4
- 229920006395 saturated elastomer Polymers 0.000 description 4
- 229910000734 martensite Inorganic materials 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 229910052840 fayalite Inorganic materials 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 239000000395 magnesium oxide Substances 0.000 description 2
- 239000011572 manganese Substances 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910001562 pearlite Inorganic materials 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 239000006104 solid solution Substances 0.000 description 2
- 229910052582 BN Inorganic materials 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 229920001074 Tenite Polymers 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- -1 aluminum nitrides Chemical class 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000001143 conditioned effect Effects 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 229910052839 forsterite Inorganic materials 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000003966 growth inhibitor Substances 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- HCWCAKKEBCNQJP-UHFFFAOYSA-N magnesium orthosilicate Chemical compound [Mg+2].[Mg+2].[O-][Si]([O-])([O-])[O-] HCWCAKKEBCNQJP-UHFFFAOYSA-N 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- VCTOKJRTAUILIH-UHFFFAOYSA-N manganese(2+);sulfide Chemical class [S-2].[Mn+2] VCTOKJRTAUILIH-UHFFFAOYSA-N 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000001226 reprecipitation Methods 0.000 description 1
- 150000003346 selenoethers Chemical class 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
Landscapes
- Soft Magnetic Materials (AREA)
- Manufacturing Of Steel Electrode Plates (AREA)
Abstract
ABSTRACT
A process of producing regular grain oriented silicon steel having a final thickness of from 7 mils (0.18 mm) to about 18 mils (0.45 mm) including the steps of providing a silicon steel hot band, removing hot hand scale, cold rolling to intermediate gauge without an anneal of the hot band, performing an intermediate anneal at a soak temperature of about 1650° F (900° C) to about 1700° F (930° C), subjecting said annealed silicon steel to a first stage slow cooling at a rate of about 500° F (250° C) to about 1050° F (585° C) per minute down to about 1100° F ? 50° F (595° C ? 30° C), thereafter subjecting said silicon steel to a second stage fast cooling down to from about 600° F (315° C) to about 1000° F (540° C) at a cooling rate of from about 2500° F (1390° C) to about 3500° F (1945° C) per minute followed by a water quench, cold rolling to final gauge, decarburizing, applying an annealing separator and final annealing.
A process of producing regular grain oriented silicon steel having a final thickness of from 7 mils (0.18 mm) to about 18 mils (0.45 mm) including the steps of providing a silicon steel hot band, removing hot hand scale, cold rolling to intermediate gauge without an anneal of the hot band, performing an intermediate anneal at a soak temperature of about 1650° F (900° C) to about 1700° F (930° C), subjecting said annealed silicon steel to a first stage slow cooling at a rate of about 500° F (250° C) to about 1050° F (585° C) per minute down to about 1100° F ? 50° F (595° C ? 30° C), thereafter subjecting said silicon steel to a second stage fast cooling down to from about 600° F (315° C) to about 1000° F (540° C) at a cooling rate of from about 2500° F (1390° C) to about 3500° F (1945° C) per minute followed by a water quench, cold rolling to final gauge, decarburizing, applying an annealing separator and final annealing.
Description
3 3 ~
METHOD ~F MA~lNG REGUI~R
GRAIN ORIENTED SILICO~ STEEL
WITHOUT A H()T BAND A~iJEAL
Jerr~ W. Schoen ECHNICAL FIELD
The present invention relates to a process o producing regular grain oriented silicon steel in thicknesses ranging from about 18 mils (0.45 mm) to about 7 mils ~0.18 mm) without a hot band anneal, and to such a process wherein the intermediate anneal following the first cold rolling stage has a very lS short soak time and a two-part temperature-controlled cooling cycle to control carbide precipitation.
BACRGROUND ART
The teachings of the present invention are applied to silicon steel having a cube-on-edge orientation, designated (110) [001~ by Miller's Indices. Such silicon steels are generally referred to as grain oriented silicon steels. Grain oriented silicon steels are divided into two basic categories: regular grain oriented silicon steel and high permeability grain oriented silicon steel.
Regular grain oriented silicon steel utilizes manganese and sulfur (and/or selenium) as the 0 principle grain growth inhibitor and generally has a permeability at 796 A/m o less than 1870. High permeability silicon steel relies on aluminum nitrides, boron nitrides or other species known in the art made in addit;on to or in place of manganese sulphides and/or selenides as grain growth - 2 ~ 3 ~ ~
1 inhibitors and has a permeability greater than 1870.
The teachings of the present invention are applicable to regular grain oriented silicon steel.
Conventional processing of regular grain oriented silicon steel comprises the steps of preparing a melt of silicon steel in conventional facilities, refining and casting the silicon steel in the form of ingots or strand cast slabs. The cast silicon steel preferably contains in weight percent less than about 0.1% carbon, ~bout 0.025% to about 0.25% manganese, ahout 0.01% to 0.035% sulfur and/or selenium, about 2.5% to about 4.0~ silicon with an aim silicon content of about 3.15%, less than about 50 ppm nitrogen and less than about 100 ppm total aluminum, the balance being essentially iron. Additions of boron and/or copper can be made, if desired.
If cast into ingots, the steel is hot rolled into slabs or directly rolled from ingots to strip. If continuous cast, the slabs may be pre-rolled in accordance with U.SO Patent 4,713,951. If developed commercially, strip casting would also benefit from the process of the present invention. The slabs are hot rolled at 2550 F (1400 C) to hot band thickness and are subjected to a hot band anneal of about 1850 F (1010 C) wi~h a soak of about 30 seconds.
The hot band i5 air cooled to ambient temperature.
Thereafter, the material is cold rolled to intermediate gauge and subjected to an intermediate anneal at a temperature of about 1740 F (950 C) with a 30 second soak and i5 cooled as by air cooling to ambient temperature. Following the intermediate anneal, silicon steel is cold rolled to final gauge.
The silicon steel at final gauge is subjected to a conventional decarburizing anneal which serves to 2 ~ 3 ~ ~
1 recrystallize the steel, to reduce the carbon content to a non-aging level and to form a fayalite surface oxide. The decarburizing anneal is generally conducted at a temperature of from about 1525 F to about 1550 ~ (about 830 C to about 845 C3 in a wet hydrogeD bearing atmosphere for a time sufficient to bring the carbon content down to a~out 0.003% or lower. Thereafter, the silicon steel is coated with an annealing separator such as magnesia and is bo~
annealed at a temperature of about 2200 F (1200 C~
for twenty-four hours. This final anneal brings about secondary recrystalliæation. A forsterite or "mill" glass coating is formed by reaction of the fayalite layer with the separator coating.
Representative processes for producing regular grain oriented (cube-on-edge) silicon steel are taught in U.S. Patent Nos. 4,202,711; 3,764,406; and 3,843,422.
The present invention is based upon the discovery that in the conventional routing given above, the hot band anneal can be eliminated if the intermediate anneal and cool;ng practice of the present invention is ~oll~wed. The intermediate anneal and cooling procedure of the present invention contemplates a very short soak preferàbly at lower temperatures, toyether with a temperature controlled, two-stage cooling cycle~ as will be fully described hereinafter The teachings of the present invention yield a number o~ advantages over the prior art. At all final gauges within the above stated range, magnetic guality is achieved which is at least equal to and 3 ~ ~
l often better than that achieved by the conventional routing. The magnetic quality is also more consistent. The teachings of the present invention shorten the annealing cycle by from 20% or more, thereby increasing line capacity. The process of the present invention enables for the first time the manufacture of thin gauge, typically about 9 mils ~0.23 mm) to about 7 mils (0.18 mm), regular grain oriented silicon steel having good magnetic characteristics without a hot band anneal following hot rolling to hot band. This enables thin gauge regular grain oriented silicon steel to be manufactured where hot band annealing can not be practic~d. The lower tempPrature of the intermediate anneal of the present invention increases the mechanical strength of the silicon steel during the anneal, which previously was marginal at high annealing temperatures.
European Patent 0047129 teaches the use of rapid coolin~ from 1300 F to 400 F (705 C to 205 C) for the production of high permeability electrical steel. This rapid cooling enables the achievement of smaller secondary grain size in the final product.
U.S. Patent 4,517,932 teaches rapid cooling and controlled carbon loss in the intermediate ann~al for the production of high permeability electrical steel, including an aging treatment at 200 F to 400 F
(95 C to 205 C) for from lO to 60 seconds to condition the carbide These high permeability silicon steel references employ a very low temperature and lengthy intermediate anneal cycle having a 120 second soak at 1600 F (870~ C) followed by rapid ~ooling from 2 ~
1 1300 F (705 C) and an aging treatment to condition the carbide precipitates. It has been found, however, that in the intermediate anneal of the present invention, rapid cooling from above about 1150 F (620 C) or higher produces poorer maqnetic quality owing to the formation of martensite which increases hardness, degrades mechanical properties for subsequent cold rolling, and contributes to poorer magnetic quality in the final product.
In the above-noted U.S. Patent 4,517,032, a low temperature aging treatment following rapid cooling is employed. This practice, if used for regular grain oriented materials, has been found to produce enlarged secondary grain size and poorer magnetic quality in the final product since it impaires the fine iron carbide precipitates. Lower tamperature annealing at about 1640 F (895 C~ or lower, to avoid the formation of austenite, could be used to provide adequate solution of iron carbide without forming a second phase which must be conditioned out of the microstructure. However, this procedure requires much longer annealing times to effect carbide solution. Such a procedure would permit direct rapid cooling from soak temperature without the two-~tage cooling cycle of the present invention.
U.S. Patent 4,478,653 teaches that a higher intermediate anneal temperature can be used to produce 9 mil (0.23 mm~ regular grain oriented silicon steel without hot band annealing. It has been found, however, that 9 mil (0.23 mm) regular grain oriented silicon steel made in accordance with this patent has more variable magnetic quality than when a routing utilizing a hot band anneal i.s used.
2 ~ 3 f' ~
1 It has further been found that the no hot band anneal-high temperature intermediate anneal practice taught in this reference provides generally poor magnetic quality at thinner gauges of 9 mils (0.23 mm) or less, when compared to the above noted practice employing a hot band anneal. Finally, the very high temperature of the intermediate anneal of U.S. Patent 4,478,653 results in low mechanical strength of the silicon steel, making processing more ~ifficult.
DISCL~SUR~ OF THE I~VE~TIO~
According to the invention, there is provided a method ~or processing regular grain oriented silicon steel having a thickness in the range of from about 18 mils (0.45 mm) to about 7 mils (0.18 mm) comprising the steps of providing silicon steel consisting essentially of, in weight percent, of less than about 0.1% carbon, about 0.025% to 0.25%
manganese, about 0.01% to 0.035% sulfur and~or selenium, about 2.5% to 9.0% silicon, less than about 100 ppm total aluminum, less than about 50 ppm nitrogen, the balance being essentially iron.
Additions o boron and/or copper can be made, i~
de~ired.
The silicon steel is cold rolled from hot band to intermediate thickness without a hot band anneal.
The cold rolled intermediate thickness silicon steel is subjected to an intermediat~ anneal at about 1650 F to about 2100 F (about 900 C to about 1150 C) and preferably from about 1650 F to about 1700 F (from about 900 C to about 930 C) for a soak time of from about 1 to about 30 seconds, and 2 ~
1 preferably for about 3 to 8 seconds. Following this soak, the silicon steel is cooled in two stages. The first is a slow cooling stage from soak temperature to a t~mperature of from 1000 F to 1200 F (540 C
to 650 C), and preferably to a temperature of 1100 F ~ 50 F (595 C ~ 30 C) at a rate less than about 1500 F ~835 C) per minute, and preferably at a rate of from about 500 F (280 C~ to 1050 F
(585 C) per minute. The second stage is a fast cooling stage at a rate of greater than 1500 F
(835 C) per minute, and preferably at a rate of 2500 F to 3500 F (1390 C to 1945 C) per minute followed by a water quench at about 600 F to about 700 F (about 315 C to about 370 C). Following the intermediate anneal, the silicon steel is cold rolled to final thickness,- decarburized, coated with an annealing separator, and subjected to a final anneal to effect secondary recrystallization.
o BRIEF_DESCRIPTI~ OF T~IE DRAWI~IG
The Figure is a graph illustrating th~
intermediate anneal time/temperature cycle of the present invention and that of a typical prior art intermediate anneal.
DESCRIPTIO~ O~ THE PRE:E'ERPcED EMBODIME~T~;
In the practice of the present invention, the routing for the regular grain oriented silicon steel is conventional and is the same as that given above with two exceptions. The first e~ception is that there is no hot band anneal. The second exception is the development of the intermediate anneal and cooling cycle of the present invention, following the first stage of cold rolling.
2~J ~: 3 rJ ~
To this end, the starting material referred to as "hot band" can be produced by a number of methods known in the art such as ingot casting/continuous casting and hot rolling, or by strip casting~ The silicon steel hot band scale is removed, but no hot band anneal prior to the first stage of cold rolling is practiced.
Following the first sta~e of cold rolling, the silicon steel is subjected to an intermediate anneal in accordance with the teachings of the present inv~ntion. Reference is made to the Figure, which is a sch~matic of the time/temperature cycle for the intermediate anneal of th~ present invention. The Figure also shows, with a broken line, the time/temperature cycle for a typical, prior art intermediate anneal.
A primary thrust of the present invention is the discovery that the intermediate anneal and its cooling cycle can be adjusted to provide a fine carbide dispersion. The refinement of the carbide enables production of regular grain oriented silicon steel over a wide range of melt carbon, even at final gauges of 7 mils (O.lB mm) and less, having good and consistent magnetic properties in the final product without the necessity of a hot band annealing step.
During the heat-up portion of the intermediate annealt recrystallization occurs at about 1250 F
(675 C~, roughly 20 seconds after entering the furnace, after which normal grain growth occurs. The start of recrystallization is indicated at "0" in the Figure, Above about 1280 F (690 C) carbides will 3 ~ ~
1 begin dissolving, as indicated at "A" in the Figure.
This event continues and accelerates as the temperature increases. Above about 1650 F (900 C~, a small amount of ferrite transforms to austenite.
The austenite provides for more rapid solution o carbon and restricts normal grain growth, thereby establishing the intermediate annealed grain size.
Prior art intermediate anneal practice provided a soak at about 1740 F (950 C~ for a period of from 25 to 30 seconds. The intermediate anneal procedure of the present invention provides a soak time of from about 1 to 30 seconds, and preferably from about 3 to 8 seconds. The soak temperature has been determined not to be critical. The soak can be conducted at a temperature of from about 1650 F (900 C~ to about 2100 F (1150 C). Preferably, the soak is conducted at a temperature of from about 1650 F (900 C) to about 1700 F (930 C), and more prefarably at about 1680 F (915 C). The shorter soak time and the lower soak temperature are preferred because less austenite is formed. The austenite present in the form of dispersed islands at the prior ferrite grain boundaries is finer. Thus, the austenite is easier to decompose into ferrite with carbon in solid solution for subsequent precipitation of fine iron carbide. To e~tend either the soak temperature or time results in the enlargement of the austenite islands which rapidly become carbon-rich compared to the prior ferrite matri~. Both growth and carbon enrichment of the austenite hinder its decomposition during cooling. The desired structure exiting the furnace consists of a recrystallized matri~ of ferrite having less than about 5~ austenite uniformly dispersed throughout the material as fine islands.
At the end of the anneal, the carbon will 2 ~
1 be in solid solution and ready ~or reprecipitation on cooling. The primary reason behind the redesign of the intermediate anneal time and temperature at soak is the control of the growth of the austenite islands. The lower temperature reduces the equilibrium volume fraction of austenite which forms. The shorter time reduces carbon diffusion, thereby inhibiting growth and undue enrichment of the austenite. The lower strip tempPrature, the reduced volume fraction and the finer morphology of the austenite makes it easier to decompose during the cooling cycle.
Immediately after the soak, the cooling cycle is initiated. The cooling cycle o~ the present invention contemplates two stages. The first stage e~tending from soak to the point "E" on the Figure is a slow cool from soak temperatllre to a temperature of from about 1000 F (540 C) to about 1~00 F (650 C) and preferably to about 1100 F + 50 F
(595 C ~ 30 C). This first slow cooling stage provides for the decomposition of austenite to carbon-saturated ferrite. Under equilibrium conditions, au~tenite decomposes to carbon-saturated ferrite between from about 1650 F (900 C) and 1420 F (770 C). However, the kinetics of the cooling process are such that austenite decomposition does not begin in earnest until the mid 1500 F
(815 C) range and contînues somewhat below 1100 F
(595 C).
Failure to decompose the austenite in the first cooling stage will result in the formation of mart~nsite and/or pearlite. Martensite, i~ present, will cause an enlargement of the secondary grain 1 size, and the deterioration of the quality of the (110)[001~ orientation. Its presence adversely affects energy storage in the second stage of cold rolling, and results in poorer and more variable magnetic quality of the final silicon steel product.
Lastly, martensite degrades the mechanical properties, particularly the cold rolling characteristics. Pearlite is more benign, but still tieæ up carbon in an undesired form.
As indicated above, austenite decomposition begins at about point "C" in the Figure and continues to about point "E". At point "D" fine iron carbide begins to precipitate from the carbon-saturated ferrite. Under eguilibrium conditions, carbides begin to precipitate rom carbon-saturated ferrite at temperatures balow 1280 F (690 C). HoweYsr, the actual process requires some undercooling to start precipitation, which begins in earnest at about 1200 F (650 C). It wil:i be noted that the austenite decomposition to carbon~rich ferrite and carbide precipitation from the ferrite overlap somewhat. The carbide is in two forms. It is present as an intergranular film and as a fine intragranular precipitate. The former precipitates at temperatures above about 1060 F (570 C). The latter precipitates below about 1060 F (570 C).
The slow cooling first stage, e~tending from point "C" to point "E" of the Figure has a cooling rate of less than 1500 F (835 C) per minute, and preferably from about 500 F to abou~ 1050 F t280 C to 585 C) per minute.
The second stage of the cooling cycle, a fast cooling stage, begins at point "E" in the Figure and 1 extends to point "G" between 600 F and 1000 F
(315 C and 540 C) at which point the strip can be water quenched to complete the rapid cooling stage.
The strip temperature after water quenching is 150 F
(65 C) or less, which is shown in the Figure as room temperature (75 F or 25 C). During the second cooling stage, the cooling rate is preferably from about 2500 F to about 3500 F (1390 C to 1945 C) per minute and more preferably greater than 3000 F
per minute (1665 C) per mlnute. This assures the precipitation of fine iron carbide.
It will be evident from the above that the entire intermediate anneal and cooling cycle oE the present invention is required in the process of oh$aining the desired microstructure, and precise controls are critical. The prior art cycle time shown in the Figure required at least 3 minutes, terminating in a water bath, not shown, at a strip speed of about 220 feet pex minute (57 meters per minute)O The intermediate anneal cycle time of the present invention requires about 2 minutes, 10 seconds which enabled a strip speed of about 260 feet per minute (80 meters per minute) to be used. It will therefore be noted that the annealing cycle of the present invention enables greater productivity of the line.
No aging treatment after the anneal is either needed or desired, since it has been found $o cause the`
formation of an enlarged secondary grain size which degrades the magnetic quality of the final silicon steel product.
The intermediate anneal is followed by the second stage of cold rolling where the silicon steel is reduced to the desired final gauge. The silicon 2 ~ ,e 3 1 steel is thereafter decarburized, coated with an annealing separator and subjected to a final anneal to effect secondary recrystallization.
In the plant, two regular grain oriented silicon steel heats having an aim silicon content of 3.15%, were processed. The chemistries for these two heats in weight percent are given in TABLE I below.
TA~LE I
C Mn S S; Al N ~_ A 0.02800.0592 0.02153.163 0.0016 0.0033 0.094 B 0.02880.0587 0.02163.175 0.0013 0.0029 0.083 The processing was without a hot band anneal and each of the two heats were separated and processed to to final gauges of 11 mils (0.28 mm), 9 mils (0-.23 mm) and 7 mils (0.18 mm3 each using three different intermediate gauges. The three intermediate gauges for each of the 7, 9 and 11 mil (0.18 mm, 0.23 mm and 0.28 mm) materials are given in TABLE II below.
TABLE II
Final Intermediate Gau~e Gauqe (inch)(mm~ _ 7-mil (0.18 mm~ 0.019 O.g8 0.021 0.53 0.023 0.58 9-mil (0.23 mm) 0.021 0.53 0.023 0.58 0O025 0.63 ll-mil (O.28 mm) 0.022 0.56 0.024 0.61 0.026 0`.64 The standard prior art aim gauges for 7 mil (0.18 mm), 9 mil (0.23 mm) and 11 mil (0.28 mm) materials were, respectively, 0.021 inch (0.53 mm), 0.023 inch (0.58 mm), and 0.024 inch (0.61 n~). The silicon steels were given an intermediate anneal and cooling cycle according to the present invention. To this end they were soaked for about 8 seconds at about 1680 F (915 C). Thereafter they were cooled to about 1060 F (570 C~ at a rate of from about 850 F
to about 1200 F (from about 470C to about 670 C) per minute. They were then cooled to about 600 F
(350 C) at a rate of about 1500~ F to about ~000 F
(about 830 C to about 1100 C) per minute, followed by water quenching to less than 150 F (65 C). The silicon steels were cold rolled to final gauge, ~ecarburized at 1525 F (830 C) in wet hydrogen bear;ng atmosphere, magnesia coated, and given a final box anneal at 2200 F (1200 C) for 24 hours in wet hydrogen.
The coil front and back average results of both heats A and B are summarized in TABLE III below.
O h~
_1 q`
:c ~
- o ~ o 3 o o O
_ ~_ e P~ ~ ,, 00 ~
E _~ ~o r-- r`
oo ~ ~ ~ ~
g _ O o o _ o~
~ _~ ~ U~ ~o a _ ~ ~
_ O o O
ei ~`1 1~ 3 o o o o o 1~ CO ~
C ~ ~ ~
~1 u~ ~ ~ o ~1 ~ l ~, o~ ~ ~ ~
_ *~ _~
_~
Z 01~
:9 ~ o o O
~a o ~ ~ ~1 O O O
1:~ ~ o o o ~ .
b ~1 3 u~
~ IQ . ~ ~
E _ OE~ ct~ oo 0: 31 t~
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_ ~
I ~U. ~ ~ CO
r P ~ ~ u~ ~
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H ~ O O O
1 Based upon prior art results, the aim 15 kGa core loss values for the 7-mil (0.18 mm), 9-mil (0.23 mm) and ll-mil (0.2B mm) material, respectively, were .390 W/lb (0.867 W/Kg), .420 W/lb (0.933 W/Kg) and .480 W/lb (1.067 W/Kg~. It will be noted that for each of the 7, 9 and 11 mil (0.18 mm, 0~23 mm, and 0.28 mm) materials a slight core loss improvement was achieved at the prior art intermediate gauges. Even greatex improvement was achieved at heavier intermediate gauyes. This clearly shows that the optimum intermediate gauge has shifted upwardly with the adoption of the intermediate anneal cycle of the present invention. It will be noted that the H-10 permeability also improves at the heavier intermediate gauges.
The present invention has thus far been described in its application to partially austenitic grades o regular grain oriented silicon steel. Fully ferritic grades undergo no transformation from bcc type crystal structure to fcc. This can be determined from the ferrite stability index calculated as:
FSI = 2.54~40.53*(C+N)+0.43*(Mn+Ni~+0.22*Cu -2.65*Al-3.95*P-1.26*(Cr~Mo)-Si Compositions having a value equal to or less than 0.0 are fully ferritic. Increasing positive ferrite stability inde~ values represent increasing volume fractions of austenite will be present. For fully ferritic compositions, rapid cooling can be initiated directly at the end of the soak since there is no austenite present, and thus a stage one slow cooling is not required.
- 17 - ~ i3~
l Modifications may be made in the invention wi~hout departing from the spirit of it.
METHOD ~F MA~lNG REGUI~R
GRAIN ORIENTED SILICO~ STEEL
WITHOUT A H()T BAND A~iJEAL
Jerr~ W. Schoen ECHNICAL FIELD
The present invention relates to a process o producing regular grain oriented silicon steel in thicknesses ranging from about 18 mils (0.45 mm) to about 7 mils ~0.18 mm) without a hot band anneal, and to such a process wherein the intermediate anneal following the first cold rolling stage has a very lS short soak time and a two-part temperature-controlled cooling cycle to control carbide precipitation.
BACRGROUND ART
The teachings of the present invention are applied to silicon steel having a cube-on-edge orientation, designated (110) [001~ by Miller's Indices. Such silicon steels are generally referred to as grain oriented silicon steels. Grain oriented silicon steels are divided into two basic categories: regular grain oriented silicon steel and high permeability grain oriented silicon steel.
Regular grain oriented silicon steel utilizes manganese and sulfur (and/or selenium) as the 0 principle grain growth inhibitor and generally has a permeability at 796 A/m o less than 1870. High permeability silicon steel relies on aluminum nitrides, boron nitrides or other species known in the art made in addit;on to or in place of manganese sulphides and/or selenides as grain growth - 2 ~ 3 ~ ~
1 inhibitors and has a permeability greater than 1870.
The teachings of the present invention are applicable to regular grain oriented silicon steel.
Conventional processing of regular grain oriented silicon steel comprises the steps of preparing a melt of silicon steel in conventional facilities, refining and casting the silicon steel in the form of ingots or strand cast slabs. The cast silicon steel preferably contains in weight percent less than about 0.1% carbon, ~bout 0.025% to about 0.25% manganese, ahout 0.01% to 0.035% sulfur and/or selenium, about 2.5% to about 4.0~ silicon with an aim silicon content of about 3.15%, less than about 50 ppm nitrogen and less than about 100 ppm total aluminum, the balance being essentially iron. Additions of boron and/or copper can be made, if desired.
If cast into ingots, the steel is hot rolled into slabs or directly rolled from ingots to strip. If continuous cast, the slabs may be pre-rolled in accordance with U.SO Patent 4,713,951. If developed commercially, strip casting would also benefit from the process of the present invention. The slabs are hot rolled at 2550 F (1400 C) to hot band thickness and are subjected to a hot band anneal of about 1850 F (1010 C) wi~h a soak of about 30 seconds.
The hot band i5 air cooled to ambient temperature.
Thereafter, the material is cold rolled to intermediate gauge and subjected to an intermediate anneal at a temperature of about 1740 F (950 C) with a 30 second soak and i5 cooled as by air cooling to ambient temperature. Following the intermediate anneal, silicon steel is cold rolled to final gauge.
The silicon steel at final gauge is subjected to a conventional decarburizing anneal which serves to 2 ~ 3 ~ ~
1 recrystallize the steel, to reduce the carbon content to a non-aging level and to form a fayalite surface oxide. The decarburizing anneal is generally conducted at a temperature of from about 1525 F to about 1550 ~ (about 830 C to about 845 C3 in a wet hydrogeD bearing atmosphere for a time sufficient to bring the carbon content down to a~out 0.003% or lower. Thereafter, the silicon steel is coated with an annealing separator such as magnesia and is bo~
annealed at a temperature of about 2200 F (1200 C~
for twenty-four hours. This final anneal brings about secondary recrystalliæation. A forsterite or "mill" glass coating is formed by reaction of the fayalite layer with the separator coating.
Representative processes for producing regular grain oriented (cube-on-edge) silicon steel are taught in U.S. Patent Nos. 4,202,711; 3,764,406; and 3,843,422.
The present invention is based upon the discovery that in the conventional routing given above, the hot band anneal can be eliminated if the intermediate anneal and cool;ng practice of the present invention is ~oll~wed. The intermediate anneal and cooling procedure of the present invention contemplates a very short soak preferàbly at lower temperatures, toyether with a temperature controlled, two-stage cooling cycle~ as will be fully described hereinafter The teachings of the present invention yield a number o~ advantages over the prior art. At all final gauges within the above stated range, magnetic guality is achieved which is at least equal to and 3 ~ ~
l often better than that achieved by the conventional routing. The magnetic quality is also more consistent. The teachings of the present invention shorten the annealing cycle by from 20% or more, thereby increasing line capacity. The process of the present invention enables for the first time the manufacture of thin gauge, typically about 9 mils ~0.23 mm) to about 7 mils (0.18 mm), regular grain oriented silicon steel having good magnetic characteristics without a hot band anneal following hot rolling to hot band. This enables thin gauge regular grain oriented silicon steel to be manufactured where hot band annealing can not be practic~d. The lower tempPrature of the intermediate anneal of the present invention increases the mechanical strength of the silicon steel during the anneal, which previously was marginal at high annealing temperatures.
European Patent 0047129 teaches the use of rapid coolin~ from 1300 F to 400 F (705 C to 205 C) for the production of high permeability electrical steel. This rapid cooling enables the achievement of smaller secondary grain size in the final product.
U.S. Patent 4,517,932 teaches rapid cooling and controlled carbon loss in the intermediate ann~al for the production of high permeability electrical steel, including an aging treatment at 200 F to 400 F
(95 C to 205 C) for from lO to 60 seconds to condition the carbide These high permeability silicon steel references employ a very low temperature and lengthy intermediate anneal cycle having a 120 second soak at 1600 F (870~ C) followed by rapid ~ooling from 2 ~
1 1300 F (705 C) and an aging treatment to condition the carbide precipitates. It has been found, however, that in the intermediate anneal of the present invention, rapid cooling from above about 1150 F (620 C) or higher produces poorer maqnetic quality owing to the formation of martensite which increases hardness, degrades mechanical properties for subsequent cold rolling, and contributes to poorer magnetic quality in the final product.
In the above-noted U.S. Patent 4,517,032, a low temperature aging treatment following rapid cooling is employed. This practice, if used for regular grain oriented materials, has been found to produce enlarged secondary grain size and poorer magnetic quality in the final product since it impaires the fine iron carbide precipitates. Lower tamperature annealing at about 1640 F (895 C~ or lower, to avoid the formation of austenite, could be used to provide adequate solution of iron carbide without forming a second phase which must be conditioned out of the microstructure. However, this procedure requires much longer annealing times to effect carbide solution. Such a procedure would permit direct rapid cooling from soak temperature without the two-~tage cooling cycle of the present invention.
U.S. Patent 4,478,653 teaches that a higher intermediate anneal temperature can be used to produce 9 mil (0.23 mm~ regular grain oriented silicon steel without hot band annealing. It has been found, however, that 9 mil (0.23 mm) regular grain oriented silicon steel made in accordance with this patent has more variable magnetic quality than when a routing utilizing a hot band anneal i.s used.
2 ~ 3 f' ~
1 It has further been found that the no hot band anneal-high temperature intermediate anneal practice taught in this reference provides generally poor magnetic quality at thinner gauges of 9 mils (0.23 mm) or less, when compared to the above noted practice employing a hot band anneal. Finally, the very high temperature of the intermediate anneal of U.S. Patent 4,478,653 results in low mechanical strength of the silicon steel, making processing more ~ifficult.
DISCL~SUR~ OF THE I~VE~TIO~
According to the invention, there is provided a method ~or processing regular grain oriented silicon steel having a thickness in the range of from about 18 mils (0.45 mm) to about 7 mils (0.18 mm) comprising the steps of providing silicon steel consisting essentially of, in weight percent, of less than about 0.1% carbon, about 0.025% to 0.25%
manganese, about 0.01% to 0.035% sulfur and~or selenium, about 2.5% to 9.0% silicon, less than about 100 ppm total aluminum, less than about 50 ppm nitrogen, the balance being essentially iron.
Additions o boron and/or copper can be made, i~
de~ired.
The silicon steel is cold rolled from hot band to intermediate thickness without a hot band anneal.
The cold rolled intermediate thickness silicon steel is subjected to an intermediat~ anneal at about 1650 F to about 2100 F (about 900 C to about 1150 C) and preferably from about 1650 F to about 1700 F (from about 900 C to about 930 C) for a soak time of from about 1 to about 30 seconds, and 2 ~
1 preferably for about 3 to 8 seconds. Following this soak, the silicon steel is cooled in two stages. The first is a slow cooling stage from soak temperature to a t~mperature of from 1000 F to 1200 F (540 C
to 650 C), and preferably to a temperature of 1100 F ~ 50 F (595 C ~ 30 C) at a rate less than about 1500 F ~835 C) per minute, and preferably at a rate of from about 500 F (280 C~ to 1050 F
(585 C) per minute. The second stage is a fast cooling stage at a rate of greater than 1500 F
(835 C) per minute, and preferably at a rate of 2500 F to 3500 F (1390 C to 1945 C) per minute followed by a water quench at about 600 F to about 700 F (about 315 C to about 370 C). Following the intermediate anneal, the silicon steel is cold rolled to final thickness,- decarburized, coated with an annealing separator, and subjected to a final anneal to effect secondary recrystallization.
o BRIEF_DESCRIPTI~ OF T~IE DRAWI~IG
The Figure is a graph illustrating th~
intermediate anneal time/temperature cycle of the present invention and that of a typical prior art intermediate anneal.
DESCRIPTIO~ O~ THE PRE:E'ERPcED EMBODIME~T~;
In the practice of the present invention, the routing for the regular grain oriented silicon steel is conventional and is the same as that given above with two exceptions. The first e~ception is that there is no hot band anneal. The second exception is the development of the intermediate anneal and cooling cycle of the present invention, following the first stage of cold rolling.
2~J ~: 3 rJ ~
To this end, the starting material referred to as "hot band" can be produced by a number of methods known in the art such as ingot casting/continuous casting and hot rolling, or by strip casting~ The silicon steel hot band scale is removed, but no hot band anneal prior to the first stage of cold rolling is practiced.
Following the first sta~e of cold rolling, the silicon steel is subjected to an intermediate anneal in accordance with the teachings of the present inv~ntion. Reference is made to the Figure, which is a sch~matic of the time/temperature cycle for the intermediate anneal of th~ present invention. The Figure also shows, with a broken line, the time/temperature cycle for a typical, prior art intermediate anneal.
A primary thrust of the present invention is the discovery that the intermediate anneal and its cooling cycle can be adjusted to provide a fine carbide dispersion. The refinement of the carbide enables production of regular grain oriented silicon steel over a wide range of melt carbon, even at final gauges of 7 mils (O.lB mm) and less, having good and consistent magnetic properties in the final product without the necessity of a hot band annealing step.
During the heat-up portion of the intermediate annealt recrystallization occurs at about 1250 F
(675 C~, roughly 20 seconds after entering the furnace, after which normal grain growth occurs. The start of recrystallization is indicated at "0" in the Figure, Above about 1280 F (690 C) carbides will 3 ~ ~
1 begin dissolving, as indicated at "A" in the Figure.
This event continues and accelerates as the temperature increases. Above about 1650 F (900 C~, a small amount of ferrite transforms to austenite.
The austenite provides for more rapid solution o carbon and restricts normal grain growth, thereby establishing the intermediate annealed grain size.
Prior art intermediate anneal practice provided a soak at about 1740 F (950 C~ for a period of from 25 to 30 seconds. The intermediate anneal procedure of the present invention provides a soak time of from about 1 to 30 seconds, and preferably from about 3 to 8 seconds. The soak temperature has been determined not to be critical. The soak can be conducted at a temperature of from about 1650 F (900 C~ to about 2100 F (1150 C). Preferably, the soak is conducted at a temperature of from about 1650 F (900 C) to about 1700 F (930 C), and more prefarably at about 1680 F (915 C). The shorter soak time and the lower soak temperature are preferred because less austenite is formed. The austenite present in the form of dispersed islands at the prior ferrite grain boundaries is finer. Thus, the austenite is easier to decompose into ferrite with carbon in solid solution for subsequent precipitation of fine iron carbide. To e~tend either the soak temperature or time results in the enlargement of the austenite islands which rapidly become carbon-rich compared to the prior ferrite matri~. Both growth and carbon enrichment of the austenite hinder its decomposition during cooling. The desired structure exiting the furnace consists of a recrystallized matri~ of ferrite having less than about 5~ austenite uniformly dispersed throughout the material as fine islands.
At the end of the anneal, the carbon will 2 ~
1 be in solid solution and ready ~or reprecipitation on cooling. The primary reason behind the redesign of the intermediate anneal time and temperature at soak is the control of the growth of the austenite islands. The lower temperature reduces the equilibrium volume fraction of austenite which forms. The shorter time reduces carbon diffusion, thereby inhibiting growth and undue enrichment of the austenite. The lower strip tempPrature, the reduced volume fraction and the finer morphology of the austenite makes it easier to decompose during the cooling cycle.
Immediately after the soak, the cooling cycle is initiated. The cooling cycle o~ the present invention contemplates two stages. The first stage e~tending from soak to the point "E" on the Figure is a slow cool from soak temperatllre to a temperature of from about 1000 F (540 C) to about 1~00 F (650 C) and preferably to about 1100 F + 50 F
(595 C ~ 30 C). This first slow cooling stage provides for the decomposition of austenite to carbon-saturated ferrite. Under equilibrium conditions, au~tenite decomposes to carbon-saturated ferrite between from about 1650 F (900 C) and 1420 F (770 C). However, the kinetics of the cooling process are such that austenite decomposition does not begin in earnest until the mid 1500 F
(815 C) range and contînues somewhat below 1100 F
(595 C).
Failure to decompose the austenite in the first cooling stage will result in the formation of mart~nsite and/or pearlite. Martensite, i~ present, will cause an enlargement of the secondary grain 1 size, and the deterioration of the quality of the (110)[001~ orientation. Its presence adversely affects energy storage in the second stage of cold rolling, and results in poorer and more variable magnetic quality of the final silicon steel product.
Lastly, martensite degrades the mechanical properties, particularly the cold rolling characteristics. Pearlite is more benign, but still tieæ up carbon in an undesired form.
As indicated above, austenite decomposition begins at about point "C" in the Figure and continues to about point "E". At point "D" fine iron carbide begins to precipitate from the carbon-saturated ferrite. Under eguilibrium conditions, carbides begin to precipitate rom carbon-saturated ferrite at temperatures balow 1280 F (690 C). HoweYsr, the actual process requires some undercooling to start precipitation, which begins in earnest at about 1200 F (650 C). It wil:i be noted that the austenite decomposition to carbon~rich ferrite and carbide precipitation from the ferrite overlap somewhat. The carbide is in two forms. It is present as an intergranular film and as a fine intragranular precipitate. The former precipitates at temperatures above about 1060 F (570 C). The latter precipitates below about 1060 F (570 C).
The slow cooling first stage, e~tending from point "C" to point "E" of the Figure has a cooling rate of less than 1500 F (835 C) per minute, and preferably from about 500 F to abou~ 1050 F t280 C to 585 C) per minute.
The second stage of the cooling cycle, a fast cooling stage, begins at point "E" in the Figure and 1 extends to point "G" between 600 F and 1000 F
(315 C and 540 C) at which point the strip can be water quenched to complete the rapid cooling stage.
The strip temperature after water quenching is 150 F
(65 C) or less, which is shown in the Figure as room temperature (75 F or 25 C). During the second cooling stage, the cooling rate is preferably from about 2500 F to about 3500 F (1390 C to 1945 C) per minute and more preferably greater than 3000 F
per minute (1665 C) per mlnute. This assures the precipitation of fine iron carbide.
It will be evident from the above that the entire intermediate anneal and cooling cycle oE the present invention is required in the process of oh$aining the desired microstructure, and precise controls are critical. The prior art cycle time shown in the Figure required at least 3 minutes, terminating in a water bath, not shown, at a strip speed of about 220 feet pex minute (57 meters per minute)O The intermediate anneal cycle time of the present invention requires about 2 minutes, 10 seconds which enabled a strip speed of about 260 feet per minute (80 meters per minute) to be used. It will therefore be noted that the annealing cycle of the present invention enables greater productivity of the line.
No aging treatment after the anneal is either needed or desired, since it has been found $o cause the`
formation of an enlarged secondary grain size which degrades the magnetic quality of the final silicon steel product.
The intermediate anneal is followed by the second stage of cold rolling where the silicon steel is reduced to the desired final gauge. The silicon 2 ~ ,e 3 1 steel is thereafter decarburized, coated with an annealing separator and subjected to a final anneal to effect secondary recrystallization.
In the plant, two regular grain oriented silicon steel heats having an aim silicon content of 3.15%, were processed. The chemistries for these two heats in weight percent are given in TABLE I below.
TA~LE I
C Mn S S; Al N ~_ A 0.02800.0592 0.02153.163 0.0016 0.0033 0.094 B 0.02880.0587 0.02163.175 0.0013 0.0029 0.083 The processing was without a hot band anneal and each of the two heats were separated and processed to to final gauges of 11 mils (0.28 mm), 9 mils (0-.23 mm) and 7 mils (0.18 mm3 each using three different intermediate gauges. The three intermediate gauges for each of the 7, 9 and 11 mil (0.18 mm, 0.23 mm and 0.28 mm) materials are given in TABLE II below.
TABLE II
Final Intermediate Gau~e Gauqe (inch)(mm~ _ 7-mil (0.18 mm~ 0.019 O.g8 0.021 0.53 0.023 0.58 9-mil (0.23 mm) 0.021 0.53 0.023 0.58 0O025 0.63 ll-mil (O.28 mm) 0.022 0.56 0.024 0.61 0.026 0`.64 The standard prior art aim gauges for 7 mil (0.18 mm), 9 mil (0.23 mm) and 11 mil (0.28 mm) materials were, respectively, 0.021 inch (0.53 mm), 0.023 inch (0.58 mm), and 0.024 inch (0.61 n~). The silicon steels were given an intermediate anneal and cooling cycle according to the present invention. To this end they were soaked for about 8 seconds at about 1680 F (915 C). Thereafter they were cooled to about 1060 F (570 C~ at a rate of from about 850 F
to about 1200 F (from about 470C to about 670 C) per minute. They were then cooled to about 600 F
(350 C) at a rate of about 1500~ F to about ~000 F
(about 830 C to about 1100 C) per minute, followed by water quenching to less than 150 F (65 C). The silicon steels were cold rolled to final gauge, ~ecarburized at 1525 F (830 C) in wet hydrogen bear;ng atmosphere, magnesia coated, and given a final box anneal at 2200 F (1200 C) for 24 hours in wet hydrogen.
The coil front and back average results of both heats A and B are summarized in TABLE III below.
O h~
_1 q`
:c ~
- o ~ o 3 o o O
_ ~_ e P~ ~ ,, 00 ~
E _~ ~o r-- r`
oo ~ ~ ~ ~
g _ O o o _ o~
~ _~ ~ U~ ~o a _ ~ ~
_ O o O
ei ~`1 1~ 3 o o o o o 1~ CO ~
C ~ ~ ~
~1 u~ ~ ~ o ~1 ~ l ~, o~ ~ ~ ~
_ *~ _~
_~
Z 01~
:9 ~ o o O
~a o ~ ~ ~1 O O O
1:~ ~ o o o ~ .
b ~1 3 u~
~ IQ . ~ ~
E _ OE~ ct~ oo 0: 31 t~
_ ~_ O o O
_ ~
I ~U. ~ ~ CO
r P ~ ~ u~ ~
C: o o o o o ~-r .
H ~ O O O
1 Based upon prior art results, the aim 15 kGa core loss values for the 7-mil (0.18 mm), 9-mil (0.23 mm) and ll-mil (0.2B mm) material, respectively, were .390 W/lb (0.867 W/Kg), .420 W/lb (0.933 W/Kg) and .480 W/lb (1.067 W/Kg~. It will be noted that for each of the 7, 9 and 11 mil (0.18 mm, 0~23 mm, and 0.28 mm) materials a slight core loss improvement was achieved at the prior art intermediate gauges. Even greatex improvement was achieved at heavier intermediate gauyes. This clearly shows that the optimum intermediate gauge has shifted upwardly with the adoption of the intermediate anneal cycle of the present invention. It will be noted that the H-10 permeability also improves at the heavier intermediate gauges.
The present invention has thus far been described in its application to partially austenitic grades o regular grain oriented silicon steel. Fully ferritic grades undergo no transformation from bcc type crystal structure to fcc. This can be determined from the ferrite stability index calculated as:
FSI = 2.54~40.53*(C+N)+0.43*(Mn+Ni~+0.22*Cu -2.65*Al-3.95*P-1.26*(Cr~Mo)-Si Compositions having a value equal to or less than 0.0 are fully ferritic. Increasing positive ferrite stability inde~ values represent increasing volume fractions of austenite will be present. For fully ferritic compositions, rapid cooling can be initiated directly at the end of the soak since there is no austenite present, and thus a stage one slow cooling is not required.
- 17 - ~ i3~
l Modifications may be made in the invention wi~hout departing from the spirit of it.
Claims (11)
1. A process for producing regular grain oriented silicon steel having a thickness of from 7 to 18 mils (0.18 to 0.46 mm) comprising the steps of providing a hot band of silicon steel containing in weight percent from about 2.5% to about 4.0% silicon, removing the hot band scale if present, cold rolling to intermediate gauge without an anneal. of said hot band, subjecting said intermediate gauge material to an intermediate anneal at a soak temperature from about 1650° F (900° C) to about 2100° F (1150° C) for a soak time of from about 1 second to about 30 seconds, conducting a slow cooling stage from said soak temperature to a temperature of from about 1000° F (540° C) to about 1200° F (650° C) at a cooling rate less than 1500° F (835° C) per minute, thereafter conducting a fast cooling stage to a temperature of from about 600° F (315° C) to about 1000° F (540° C) at a rate greater than 1500° F
(835° C) per minute followed by water quenching, cold rolling said silicon steel to final gauge, decarburizing, coating said decarburized silicon steel with an annealing separator, and subjecting said silicon steel to a final anneal to effect secondary recrystallization.
(835° C) per minute followed by water quenching, cold rolling said silicon steel to final gauge, decarburizing, coating said decarburized silicon steel with an annealing separator, and subjecting said silicon steel to a final anneal to effect secondary recrystallization.
2. The process claimed in claim 1 wherein said silicon content in weight percent is about 3.15%.
3. The process claimed in claim 1 including the step of conducting said intermediate anneal with a soak time of from about 3 to 8 seconds.
4. The process claimed in claim 1 including the step of conducting said intermediate anneal at a soak temperature of from about 1650° F (900° C) to about 1700° F (930° C).
5. The process claimed in claim 1 including the step of conducting said intermediate anneal at a soak temperature of about 1680° F (915° C).
6. The process claimed in claim 1 including the step of terminating said slow cooling stage at a temperature of about 1100° F ? 50° F (595° C ? 30° C).
7. The process claimed in claim 1 including the step of conducting said slow cooling stage at a cooling rate of from about 500° F (280° C) to about 1050° F (585° C) per minute.
8. The process claimed in claim 1 including the step of conducting said fast cooling stage at a cooling rate of about 2500° F (1390° C) to about 3500° F (1945° C) per minute.
9. The process claimed in claim 1 including the steps of conducting said intermediate anneal with a soak temperature of about 1680° F (915° C) for a soak time of about 3 to 8 seconds, conducting said slow cooling stage at a cooling rate of about 500° F
(280° C) to about 1050° F (585° C) per minute, terminating said slow cooling stage at a temperature of about 1100° F ? 50° F (595° C + 30° C), and conducting said fast cooling stage at a rate of from about 2500° F (1390° C) to about 3500° F (1945° C) per minute.
(280° C) to about 1050° F (585° C) per minute, terminating said slow cooling stage at a temperature of about 1100° F ? 50° F (595° C + 30° C), and conducting said fast cooling stage at a rate of from about 2500° F (1390° C) to about 3500° F (1945° C) per minute.
10. The process claimed in claim 1 wherein said silicon steel consists essentially of, in weight percent, up to about 0.10% carbon, about 0.025% to 0.25% manganese, about 0.01% to 0.035% sulfur and/or selenium, about 2.5% to about 4.0% silicon, less than about 100 ppm aluminum, less than about 50 ppm nitrogen, additions of boron and or copper, if desired of, the balance being essentially iron.
11. The process claimed in claim 9 wherein said weight percent of silicon is about 3.15%.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA 2054331 CA2054331A1 (en) | 1991-10-28 | 1991-10-28 | Method of making regular grain oriented silicon steel without a hot band anneal |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA 2054331 CA2054331A1 (en) | 1991-10-28 | 1991-10-28 | Method of making regular grain oriented silicon steel without a hot band anneal |
Publications (1)
Publication Number | Publication Date |
---|---|
CA2054331A1 true CA2054331A1 (en) | 1993-04-29 |
Family
ID=4148646
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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CA 2054331 Abandoned CA2054331A1 (en) | 1991-10-28 | 1991-10-28 | Method of making regular grain oriented silicon steel without a hot band anneal |
Country Status (1)
Country | Link |
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CA (1) | CA2054331A1 (en) |
-
1991
- 1991-10-28 CA CA 2054331 patent/CA2054331A1/en not_active Abandoned
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