CA1240592A - Processing for cube-on-edge oriented silicon steel - Google Patents
Processing for cube-on-edge oriented silicon steel Download PDFInfo
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- CA1240592A CA1240592A CA000451247A CA451247A CA1240592A CA 1240592 A CA1240592 A CA 1240592A CA 000451247 A CA000451247 A CA 000451247A CA 451247 A CA451247 A CA 451247A CA 1240592 A CA1240592 A CA 1240592A
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
- C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
- C21D8/1272—Final recrystallisation annealing
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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Abstract
ABSTRACT OF THE DISCLOSURE
A method is provided for final texture annealing silicon steel to produce a cube-on-edge grain orientation having lower core losses and higher magnetic permeability. The method includes using a controlled heating cycle including an isothermal hold at a selected recrystallization temperature of about 1650°F to improve secondary recrystallization and the Goss texture (110)[001].
A method is provided for final texture annealing silicon steel to produce a cube-on-edge grain orientation having lower core losses and higher magnetic permeability. The method includes using a controlled heating cycle including an isothermal hold at a selected recrystallization temperature of about 1650°F to improve secondary recrystallization and the Goss texture (110)[001].
Description
3~241C~S~
PROCESSING FOR CUBE-ON-EDG~
O~IENTED SII.ICON STEEL
~CKGROUND OF THE INVENTION
This invention relates to a final texture annealing cycle to promote improved secondary recrystallizationO Parti-cularly, the invention relates to a substantially isothermal anneal at a selected recrystallization tempexature.
In the manufacture of' grain-oriented silicon steel, it is known that if improved secondary recrystallization texture, e.g., Goss texture (110)[001], is achieved, the magnetic properties, particularly permeability and core loss, will be correspondingly improved. The Goss texture (l:L0)[001], in accordance with ~iller's indices, refers to the body-centered cubes making up the grains or crystals being oxiented in the cube-on-edge position.
The texture or grain orientations of this type refers to the cube edges being parallel to the rolling direction and in the plane of rolling, and the cube face diagonals being perpendicula~ to the rolling direction and in the rolling plane. As is well known, steel having this orientation is characterized by a relatively ; high permeability in the rolling direction and a relatively low permeability in a direction at right angles thereto.
The development of a cube-on-edge orientation is dependent upon a mechanism known as secondary recrystallization.
During secondary recrystallization, secondary cube-on-edge oriented grains are pref'erentially grown at the expense of primary grains having a different and undesirable orientation. The steel composition, particularly the impurity contents, the processing operations including hot rolling and the degree of deformation in each cold-rolling operation, intermediate and final continuous annealing time and temperature cycles, and the final texture annealing procedure must all be carefully controlled to attain the optimum texture development. A steel that has not obtained optimum texture development may have a substantially uniform but inadequate grain size and structure and resulting poor mag-netic properties or may exhibit a "banding" of inferior grain structure. Generally, banding means areas or bands of inferior grain structure extending across the width of the coil surrounded by areas of well-textured steel. Generally, the initial phases of secondary recrystallization occur at about 1550F (843C), however, secondary grain growth proceeds much faster and mor~
efficiently at temperatures of about 1600F (871C) or more.
The operation through which the secondary grains are preferentially grown and consume the primary grains is known as final texture annealing.
In the manufacture of grain-oriented silicon steel, the typical steps include subjecting the melt of 2.5-4% silicon steel through a casting operation, such as a continuous casting process, hot rolling the steel, cold rolling the steel to final gauge with an intermediate annealing when two or more cold rollings are used, decarburizing the steel, applying a refractory oxide base coating to the steel, and final texture annealing the steel, such as in a hydrogen atmosphere, to produce the desired secondary recrystallization, and purification treatment to remove impurities, such as nitrogen and sulfur. The final texture annealing is typically performed at a temperature in excess of 2000F (1093C) and held for an extended time period of at least 4 hours and generally longer to remove impurities.
~L~Ai359Z
A typical thermal cycle of the final texture ann*aling practice may include a reasonably continuous heating rate of approximately 50F/hour (27.8C/hour) from the charge temperature of the coated strip to a temperature high enough to effect purification. The charge temperature in mill practice, typically, is on the order of room temperature of 80F (26.7C) or more and the purification temperature may range from 2000F (1093C) up to a maximum of about 2300F (1260C) and preferably up to 2250F (1232C). The steel is generally subjected to a soaking at the purification temperature to remove the impurities for a long time, typically on the order of about 20 hours at or higher than 2100F (1150C).
Numerous attempts by others have been made to improve the final texture. U.S. Patent 2,534,141 - Morrill et al discloses a two-stage final texture anneal to improve the orientation.
First, the cold-rolled decarburized sheet is held for 4-24 hours at 850-900C (1560-1650F), and preferably at 875C (1605F), in a reducing or nGnoxidi~ing atmosphere to encourage and permit nucleation of well-oriented crystals and their growth. Second, the steel is then held at a temperature at 900 to 1200C
(1650-2192F), and preferably 1175C (2147F) in a reducing atmosphere to permit completion of the growth of the well-oriented crystals and to relieve mechanical strain.
U.S. Patent 4,157,925 - Malagari et al discloses a process for producing a cube-on-edge orientation in a boron-inhibited silicon steel. The process includes heating the steel from a temperature of 1700 to 1900F (926 to 1038C) at an average rate of less than 30F/hour (]6.7C/hour) so as to provide a minumum time period for the selective grairi-growth process to occur and to final texture anneal the steel by heating 1;24~3S~Z
to a temperature in excess of 2000F (1093C) and to a maximum temperature o~ ~300F (1260C) for purification of the steel.
U.S. Patent 4,318,758 - Kuroki et al discloses in Example 3 a method for producing grain-oriented silicon steel containing aluminum wherein the decarburized and coated sheet is heated up to 900C (1650F) in a 75% H2 and 25% N2 atmosphere with a heating rate of 20C/hour (36F/hour), then heating between 900 to 1050C (1650-1922F) in the same atmosphere at a heating rate of 5C/hour (9F/hour), between 1050 and 1200C
(1922-2192F) in 100~ ~2 atmosphere at a heating ratio o~
20C/hour (36F/hour) where the steel is maintained at 1200C
(2192F) for 20 hours in the 100% H2 atmosphere.
None of these patents disclose the present invention.
What is needed is an improved final texture annealing process wherein improved cube-on-edge orientation of the secondary grains may be achieved during secondary recrystallization to result in improved permeability and core loss values. The improved final texture annealing process should include control of the heating cycle and result in improved productivity as measured by an overall improvement in quality.
It is known that variations occur in magnetic properties within a given coil of silicon steel. The variations can be measured by taking samples from the coil ends and measuring the core loss values of those samples. A convenient measure of quality improvement is the percentage of coils having a poor end core loss at 60 Hz equal to or less than 0.714 WPP at 17 KG (1.57 WPKg at 1.7 Tesla). It is desirable to improve pro-ductivi~y so that an increasing percentage, and preferably the majority, of the coils produced satisfy minimum core loss val~es, such as that above.
It is also an objective to develop a process which substantially eliminates the "banding" problem.
SUMMARY OF THE INVENTION
In accordance with the present invention, a process is provided for producing electromagnetic silicon steel having cube-on-edge orientation wherein the process incluaes the con-ventional steps of preparing a steel melt containlng 2.5-4~ silicon, casting the steel, hot rolling the steel, cold rolling the steel to final gauge, decarburizing the steel, applying a refractory ; 10 oxide base coating to the steel, and final texture annealing the steel by heating to and maintaining at a temperature in excess of 2000F. The improvement comprises heating the steel during the final texture annealing to a selected recrystallization temper-ature within the range of 1600 to 1700F, isothermally heating the steel at that temperature for about 6 to 20 hours to sub-stantially compLete secondary recrystallization, and heating the ; steel from that isothermal hold temperature to a temperature in excess of 2000F to effect purification.
BRIEF DESCRIPTION OF THE DRAWINGS
:
Figures la and lb are plots of core loss and permeability, respectively, versus hold temperature for ll-mil steel; and Figures 2a and 2b are plots of core loss and permeability, respectively, versus hold temperature for 9-mil steel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
_ The final texture annealing process of the present invention includes a controlled heating cycle wherein the steel is substantially isothermally annealed at selected temperatures for particular periods of time to effect substantially complete secondary recrystallization. As used herein, isothermal heating or annealing du:ring recrystallization means heating at a very low ,, ~
~ , :: :
12~(~S9;~
heating rate. The heating rate need not be zero, but preferably should be less than about 10F/hour (5.5C/hour), and more preferably less than 5F/hour ~2.8C/hour~. As a practical con-sideration, it is difficult to isothermally hold at a particular temperature in a production furnace, but very small variations in heating rate about a selected recrystallization temperature is within the scope of the invention. Most preferably such an isothermal hold shall mean a heating rate of less than 5F/hour.
Specific processing of the steel up to final texture annealing may ~e conventional and is not critical to the present inventlon. The specific processing may include a number of conventional steps which include preparing a melt of the steel, casting the steel, hot rolling the steel, cold rolling the steel to final gauge with intermediate annealing steps, decarburizing the steel, applying a refractory oxide base coating, and then final texture annealing the steel in excess of 2000F.
Although the texture annealing method of the invention described in detail hereinafter has utility with grain-oriented silicon steel generally, the following typical composition is one example of a silicon steel composition adapted for use with the method of this invention:
C Mn S Cu Si Fe 0.030 0.065 0.025 0.22 3.15 Balance To illustrate the several aspects of the final texture annealing process of the present invention, various samples of a silicon steel having a composition similar to the above~described typical composition were processed and the results of the tests are shown in the following Table I.
~24~S92 TABLE I
Averaqe HoldHold WPP ,~
Sample No. of Temp.Time at at 10 H
GrouP Samples (F)(Hrs.) 17 KG (Gauss~
A 18 None - .754 1812 B 2S None - .746 1820 C 25 None - .726 1819 D 25 1600 6 .706 1833 E 25 1650 6 .711 1830 F 25 1700 6 .728 1824 G 25 1750 6 .736 1816 H 17 None - .730 1821 I 17 1460 6 .724 , 1828 J 17 1540 6 .724 1823 K 17 1650 ~ .706 1834 17 1600 6 .719 1828 17 160012 .717 1827 N 15 None - .727 1820 O 15 155012 .731 1816 P 15 1600 6 .737 1820 Q 15 1650 6 .718 1832 R 15 170012 .736 1815 S 11 1600S0 .707 1831 T 15 155050 .744 1812 U 15 1600 6 .731 1821 V 15 160020 .695 1838 W 15 1650 6 .703 1833 X 15 165020 .708 1832 Y 15 1700 6 .740 1812 Z 15 170020 .738 1814 AA 15 155012 .731 1816 BB 15 160012 .717 1833 CC 15 165012 .709 1837 DD 15 170012 .736 1815 59;2 All the Sample Groups of Table I were obtained from various heats of nominally ll-mil gauge silicon steel having the above-identified typical composition. The samples were all coated with MgO slurry and heated from a charge temperature at a relatively constant heating rate of about 50F/hour (27.7C/hour) or greater. Groups D-G and I-M and O-DD were all heated from charge temperature up to the speci~ied hold temperature. 5ample Groups A, B, C, H and N were not isothermally annealed and so were not held at any temperature, but were heated from the charge temperature up to a purification soak temperature. All the Sample Groups were texture annealed in a hydrogen atmosphere at a soak temperature of 2150F (1177C). Groups A-Z were held at 2150F
for 20 hours, and Groups AA-DD for 10 hours.
The magnetic properties listed in Table I represent an average value for core loss and permeability for the number of samples for that group. The distribution of 60 Hz core losses at 17 KG (1.7 Tesla~ and permeability at 10 Oersteds for those samples are shown in Figures la and lb.
The data show that generally the samples which were held for time at a temperature within the recrystallization range of 1600 to 1700F have improved properties over those samples not held at temperature (Samples A, B, C, H and N). The data demonstrate that annealed samples demonstrate incomplete recrystalliz~tion if the hold temperature is 1550F. All samples were completely recrystallized at about 1650F hold temperature.
The data also suggest that within the 1600-1700F range, there may be a range of temperatures within which substantial recrystal-lizaticn occurs so as to result in improved magnetic ~roperties.
The range of about 1600-1650F is preferred.
~2~5~Z
The hold time for the isothermal anneal is also critical. Insufficient time results in incomplete recrystal-lization. Too much time will generally result in some deterioration of magnetic properties, as shown by Groups S and T at 50 hours hold time. Results of tests have shown that the hold times of 6 to 20 hours provide good properties with a practical preferred time ~eing about 12 hours.
TABLE II
Avera~e HoldHold WPP _4~
SampleNo. of Temp.Time at at 10 H
GroupSamples (F)(Hrs.) 17 XGiGauss) A 25 lS50 12 .731 1808 B 25 1600 12 .728 1808 C 25 1650 12 .686 1853 D 25 1700 12 .706 1829 E 6 None - .738 1800 F 6 1650 12 .682 1825 G 6 1550 12 .733 1789 6 1550 50 1.010 1640 1 6 1650 50 .681 1818 J 6 1600 50 .796 1761 K 6 1700 12 .693 1817 L 6 1600 12 .716 1809 M 9 1600 12 .717 1804 N 9 1650 40 .675 1827 O 9 1650 40 .662 1834 P 25 1550 12 .726 1815 Q 25 1650 12 .691 1851 R 25 1650 12 .683 1838 S 25 1700 12 o706 1829 _g .
All the Sample Groups of Table II were obtained from various heats of nominally 9-mil gauge silicon steel having the same nominal composition as for the ll-mil samples of Table I. The samples were all coated with MgO slurry and heated from a charge temperature at a relatively constant heating rate of about 50F/hour (27.7C/hour) or greater. All of the Sample Groups, except Group E, were heated from charge temperature up to the specified hold temperature. Sample Group E was not isothermallv annealed and so was not held at temperature, but was heated from the charge temperature up to a purification soak temperature. All the Sample Groups were texture annealed in a hydrogen atmosphere at a soak temperature of 2150F
~1177C) and held for 10 hours.
The magnetic properties listed in Table II represent an average value for core loss and permeability for the number of samples for that group. The distribution of 60 Hz core losses at 17 KG (1.7 Tesla) and permeability at 10 Oersteds for those samples are shown in Figures 2a and 2b.
The data show that for 9-mil gauge, as with the ll-mil gauge, the annealed samples were incompletely recrystallized at 1550F, but completely recrystallized at about 1650F hold tem-perature. The data also suggest that within the 1600-1700F
range, there may be a range of temperatures within which sub-stantial recrystallization occurs with a corresponding improvement in magnetic properties. ~he range of about 1650-1700F is preferred and is slightly higher than the range for the thicker, ll-mil steel.
The data also confirm that the hold times for the isothermal anneal are critical. As with the ll-mil data, the 9-mil samples demonstrate some deterioration of magnetic properties 1~4~359Z
at 50 hours hold time, as shown by Groups H, I and J. Groups H and J show such poor properties that ~hey are not plotted in Figures 2a and 2b. It appears that the thin gauge 9-mil material is even more sensitive to hold times than the ll-mil material.
Results of tests have shown that hold times up to 20 hours provide good results, preferably 6 to 20 hours, and a practical preferred time of about 12 hours.
The overall results show that a dramatic improvement in overall magnetic properties of core loss and permeability result from both 9-mil and ll-mil steel when processed by an isothermal anneal for 6-20 hours within the range 1600-1700F.
The preferred ranges for each differ within that range, but the best combination of properties and complete secondary recrystal-lization occurs at about 1650F for both gauges.
The method of the present invention relates to an improved final texture annealing process wherein the steel is heated to a recrystallization temperature within the range of 1600 to 1700F. The heating rate may be on the order of a con-ventional 50F per hour and the selected isothermal hold temperature be about 1650F. The steel is then isothermally heated by holding the steel at that temperature for about 6 to 20 hours, preferably about 12 hours, to substantially complete secondary recrystallization. Thereafter the steel is heated from that temperature to a purification temperature in excess of 2000F, preferably about 2200F, at a heating rate such as 50F per hour and held at that temperature to effect purification. Generally, the heating rate up to the hold tem-per-ture and up to the purification temperature are relatively constant heating rates. The heating rate, however, does not appear to be critical to significantly affect the properties.
12~5~2 An advantage of the method of the present invention is that secondary recrystallization is essentially completed during the isothermal portion of the heat treatment, rather than being completed in accordance with conventional practice during heating to the higher purification temperature. As has been demonstrated, the effect of the present invention is to improve both magnetic permeability and core loss values. The method of the present invention is able to improve the magnetic properties in a manner not heretofore recognized in the art.
Although preferred and alternative embodiments have been described, it will be apparent to one s~illed in the art that changes can be made therein without departing from the scope of the in~ention.
PROCESSING FOR CUBE-ON-EDG~
O~IENTED SII.ICON STEEL
~CKGROUND OF THE INVENTION
This invention relates to a final texture annealing cycle to promote improved secondary recrystallizationO Parti-cularly, the invention relates to a substantially isothermal anneal at a selected recrystallization tempexature.
In the manufacture of' grain-oriented silicon steel, it is known that if improved secondary recrystallization texture, e.g., Goss texture (110)[001], is achieved, the magnetic properties, particularly permeability and core loss, will be correspondingly improved. The Goss texture (l:L0)[001], in accordance with ~iller's indices, refers to the body-centered cubes making up the grains or crystals being oxiented in the cube-on-edge position.
The texture or grain orientations of this type refers to the cube edges being parallel to the rolling direction and in the plane of rolling, and the cube face diagonals being perpendicula~ to the rolling direction and in the rolling plane. As is well known, steel having this orientation is characterized by a relatively ; high permeability in the rolling direction and a relatively low permeability in a direction at right angles thereto.
The development of a cube-on-edge orientation is dependent upon a mechanism known as secondary recrystallization.
During secondary recrystallization, secondary cube-on-edge oriented grains are pref'erentially grown at the expense of primary grains having a different and undesirable orientation. The steel composition, particularly the impurity contents, the processing operations including hot rolling and the degree of deformation in each cold-rolling operation, intermediate and final continuous annealing time and temperature cycles, and the final texture annealing procedure must all be carefully controlled to attain the optimum texture development. A steel that has not obtained optimum texture development may have a substantially uniform but inadequate grain size and structure and resulting poor mag-netic properties or may exhibit a "banding" of inferior grain structure. Generally, banding means areas or bands of inferior grain structure extending across the width of the coil surrounded by areas of well-textured steel. Generally, the initial phases of secondary recrystallization occur at about 1550F (843C), however, secondary grain growth proceeds much faster and mor~
efficiently at temperatures of about 1600F (871C) or more.
The operation through which the secondary grains are preferentially grown and consume the primary grains is known as final texture annealing.
In the manufacture of grain-oriented silicon steel, the typical steps include subjecting the melt of 2.5-4% silicon steel through a casting operation, such as a continuous casting process, hot rolling the steel, cold rolling the steel to final gauge with an intermediate annealing when two or more cold rollings are used, decarburizing the steel, applying a refractory oxide base coating to the steel, and final texture annealing the steel, such as in a hydrogen atmosphere, to produce the desired secondary recrystallization, and purification treatment to remove impurities, such as nitrogen and sulfur. The final texture annealing is typically performed at a temperature in excess of 2000F (1093C) and held for an extended time period of at least 4 hours and generally longer to remove impurities.
~L~Ai359Z
A typical thermal cycle of the final texture ann*aling practice may include a reasonably continuous heating rate of approximately 50F/hour (27.8C/hour) from the charge temperature of the coated strip to a temperature high enough to effect purification. The charge temperature in mill practice, typically, is on the order of room temperature of 80F (26.7C) or more and the purification temperature may range from 2000F (1093C) up to a maximum of about 2300F (1260C) and preferably up to 2250F (1232C). The steel is generally subjected to a soaking at the purification temperature to remove the impurities for a long time, typically on the order of about 20 hours at or higher than 2100F (1150C).
Numerous attempts by others have been made to improve the final texture. U.S. Patent 2,534,141 - Morrill et al discloses a two-stage final texture anneal to improve the orientation.
First, the cold-rolled decarburized sheet is held for 4-24 hours at 850-900C (1560-1650F), and preferably at 875C (1605F), in a reducing or nGnoxidi~ing atmosphere to encourage and permit nucleation of well-oriented crystals and their growth. Second, the steel is then held at a temperature at 900 to 1200C
(1650-2192F), and preferably 1175C (2147F) in a reducing atmosphere to permit completion of the growth of the well-oriented crystals and to relieve mechanical strain.
U.S. Patent 4,157,925 - Malagari et al discloses a process for producing a cube-on-edge orientation in a boron-inhibited silicon steel. The process includes heating the steel from a temperature of 1700 to 1900F (926 to 1038C) at an average rate of less than 30F/hour (]6.7C/hour) so as to provide a minumum time period for the selective grairi-growth process to occur and to final texture anneal the steel by heating 1;24~3S~Z
to a temperature in excess of 2000F (1093C) and to a maximum temperature o~ ~300F (1260C) for purification of the steel.
U.S. Patent 4,318,758 - Kuroki et al discloses in Example 3 a method for producing grain-oriented silicon steel containing aluminum wherein the decarburized and coated sheet is heated up to 900C (1650F) in a 75% H2 and 25% N2 atmosphere with a heating rate of 20C/hour (36F/hour), then heating between 900 to 1050C (1650-1922F) in the same atmosphere at a heating rate of 5C/hour (9F/hour), between 1050 and 1200C
(1922-2192F) in 100~ ~2 atmosphere at a heating ratio o~
20C/hour (36F/hour) where the steel is maintained at 1200C
(2192F) for 20 hours in the 100% H2 atmosphere.
None of these patents disclose the present invention.
What is needed is an improved final texture annealing process wherein improved cube-on-edge orientation of the secondary grains may be achieved during secondary recrystallization to result in improved permeability and core loss values. The improved final texture annealing process should include control of the heating cycle and result in improved productivity as measured by an overall improvement in quality.
It is known that variations occur in magnetic properties within a given coil of silicon steel. The variations can be measured by taking samples from the coil ends and measuring the core loss values of those samples. A convenient measure of quality improvement is the percentage of coils having a poor end core loss at 60 Hz equal to or less than 0.714 WPP at 17 KG (1.57 WPKg at 1.7 Tesla). It is desirable to improve pro-ductivi~y so that an increasing percentage, and preferably the majority, of the coils produced satisfy minimum core loss val~es, such as that above.
It is also an objective to develop a process which substantially eliminates the "banding" problem.
SUMMARY OF THE INVENTION
In accordance with the present invention, a process is provided for producing electromagnetic silicon steel having cube-on-edge orientation wherein the process incluaes the con-ventional steps of preparing a steel melt containlng 2.5-4~ silicon, casting the steel, hot rolling the steel, cold rolling the steel to final gauge, decarburizing the steel, applying a refractory ; 10 oxide base coating to the steel, and final texture annealing the steel by heating to and maintaining at a temperature in excess of 2000F. The improvement comprises heating the steel during the final texture annealing to a selected recrystallization temper-ature within the range of 1600 to 1700F, isothermally heating the steel at that temperature for about 6 to 20 hours to sub-stantially compLete secondary recrystallization, and heating the ; steel from that isothermal hold temperature to a temperature in excess of 2000F to effect purification.
BRIEF DESCRIPTION OF THE DRAWINGS
:
Figures la and lb are plots of core loss and permeability, respectively, versus hold temperature for ll-mil steel; and Figures 2a and 2b are plots of core loss and permeability, respectively, versus hold temperature for 9-mil steel.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
_ The final texture annealing process of the present invention includes a controlled heating cycle wherein the steel is substantially isothermally annealed at selected temperatures for particular periods of time to effect substantially complete secondary recrystallization. As used herein, isothermal heating or annealing du:ring recrystallization means heating at a very low ,, ~
~ , :: :
12~(~S9;~
heating rate. The heating rate need not be zero, but preferably should be less than about 10F/hour (5.5C/hour), and more preferably less than 5F/hour ~2.8C/hour~. As a practical con-sideration, it is difficult to isothermally hold at a particular temperature in a production furnace, but very small variations in heating rate about a selected recrystallization temperature is within the scope of the invention. Most preferably such an isothermal hold shall mean a heating rate of less than 5F/hour.
Specific processing of the steel up to final texture annealing may ~e conventional and is not critical to the present inventlon. The specific processing may include a number of conventional steps which include preparing a melt of the steel, casting the steel, hot rolling the steel, cold rolling the steel to final gauge with intermediate annealing steps, decarburizing the steel, applying a refractory oxide base coating, and then final texture annealing the steel in excess of 2000F.
Although the texture annealing method of the invention described in detail hereinafter has utility with grain-oriented silicon steel generally, the following typical composition is one example of a silicon steel composition adapted for use with the method of this invention:
C Mn S Cu Si Fe 0.030 0.065 0.025 0.22 3.15 Balance To illustrate the several aspects of the final texture annealing process of the present invention, various samples of a silicon steel having a composition similar to the above~described typical composition were processed and the results of the tests are shown in the following Table I.
~24~S92 TABLE I
Averaqe HoldHold WPP ,~
Sample No. of Temp.Time at at 10 H
GrouP Samples (F)(Hrs.) 17 KG (Gauss~
A 18 None - .754 1812 B 2S None - .746 1820 C 25 None - .726 1819 D 25 1600 6 .706 1833 E 25 1650 6 .711 1830 F 25 1700 6 .728 1824 G 25 1750 6 .736 1816 H 17 None - .730 1821 I 17 1460 6 .724 , 1828 J 17 1540 6 .724 1823 K 17 1650 ~ .706 1834 17 1600 6 .719 1828 17 160012 .717 1827 N 15 None - .727 1820 O 15 155012 .731 1816 P 15 1600 6 .737 1820 Q 15 1650 6 .718 1832 R 15 170012 .736 1815 S 11 1600S0 .707 1831 T 15 155050 .744 1812 U 15 1600 6 .731 1821 V 15 160020 .695 1838 W 15 1650 6 .703 1833 X 15 165020 .708 1832 Y 15 1700 6 .740 1812 Z 15 170020 .738 1814 AA 15 155012 .731 1816 BB 15 160012 .717 1833 CC 15 165012 .709 1837 DD 15 170012 .736 1815 59;2 All the Sample Groups of Table I were obtained from various heats of nominally ll-mil gauge silicon steel having the above-identified typical composition. The samples were all coated with MgO slurry and heated from a charge temperature at a relatively constant heating rate of about 50F/hour (27.7C/hour) or greater. Groups D-G and I-M and O-DD were all heated from charge temperature up to the speci~ied hold temperature. 5ample Groups A, B, C, H and N were not isothermally annealed and so were not held at any temperature, but were heated from the charge temperature up to a purification soak temperature. All the Sample Groups were texture annealed in a hydrogen atmosphere at a soak temperature of 2150F (1177C). Groups A-Z were held at 2150F
for 20 hours, and Groups AA-DD for 10 hours.
The magnetic properties listed in Table I represent an average value for core loss and permeability for the number of samples for that group. The distribution of 60 Hz core losses at 17 KG (1.7 Tesla~ and permeability at 10 Oersteds for those samples are shown in Figures la and lb.
The data show that generally the samples which were held for time at a temperature within the recrystallization range of 1600 to 1700F have improved properties over those samples not held at temperature (Samples A, B, C, H and N). The data demonstrate that annealed samples demonstrate incomplete recrystalliz~tion if the hold temperature is 1550F. All samples were completely recrystallized at about 1650F hold temperature.
The data also suggest that within the 1600-1700F range, there may be a range of temperatures within which substantial recrystal-lizaticn occurs so as to result in improved magnetic ~roperties.
The range of about 1600-1650F is preferred.
~2~5~Z
The hold time for the isothermal anneal is also critical. Insufficient time results in incomplete recrystal-lization. Too much time will generally result in some deterioration of magnetic properties, as shown by Groups S and T at 50 hours hold time. Results of tests have shown that the hold times of 6 to 20 hours provide good properties with a practical preferred time ~eing about 12 hours.
TABLE II
Avera~e HoldHold WPP _4~
SampleNo. of Temp.Time at at 10 H
GroupSamples (F)(Hrs.) 17 XGiGauss) A 25 lS50 12 .731 1808 B 25 1600 12 .728 1808 C 25 1650 12 .686 1853 D 25 1700 12 .706 1829 E 6 None - .738 1800 F 6 1650 12 .682 1825 G 6 1550 12 .733 1789 6 1550 50 1.010 1640 1 6 1650 50 .681 1818 J 6 1600 50 .796 1761 K 6 1700 12 .693 1817 L 6 1600 12 .716 1809 M 9 1600 12 .717 1804 N 9 1650 40 .675 1827 O 9 1650 40 .662 1834 P 25 1550 12 .726 1815 Q 25 1650 12 .691 1851 R 25 1650 12 .683 1838 S 25 1700 12 o706 1829 _g .
All the Sample Groups of Table II were obtained from various heats of nominally 9-mil gauge silicon steel having the same nominal composition as for the ll-mil samples of Table I. The samples were all coated with MgO slurry and heated from a charge temperature at a relatively constant heating rate of about 50F/hour (27.7C/hour) or greater. All of the Sample Groups, except Group E, were heated from charge temperature up to the specified hold temperature. Sample Group E was not isothermallv annealed and so was not held at temperature, but was heated from the charge temperature up to a purification soak temperature. All the Sample Groups were texture annealed in a hydrogen atmosphere at a soak temperature of 2150F
~1177C) and held for 10 hours.
The magnetic properties listed in Table II represent an average value for core loss and permeability for the number of samples for that group. The distribution of 60 Hz core losses at 17 KG (1.7 Tesla) and permeability at 10 Oersteds for those samples are shown in Figures 2a and 2b.
The data show that for 9-mil gauge, as with the ll-mil gauge, the annealed samples were incompletely recrystallized at 1550F, but completely recrystallized at about 1650F hold tem-perature. The data also suggest that within the 1600-1700F
range, there may be a range of temperatures within which sub-stantial recrystallization occurs with a corresponding improvement in magnetic properties. ~he range of about 1650-1700F is preferred and is slightly higher than the range for the thicker, ll-mil steel.
The data also confirm that the hold times for the isothermal anneal are critical. As with the ll-mil data, the 9-mil samples demonstrate some deterioration of magnetic properties 1~4~359Z
at 50 hours hold time, as shown by Groups H, I and J. Groups H and J show such poor properties that ~hey are not plotted in Figures 2a and 2b. It appears that the thin gauge 9-mil material is even more sensitive to hold times than the ll-mil material.
Results of tests have shown that hold times up to 20 hours provide good results, preferably 6 to 20 hours, and a practical preferred time of about 12 hours.
The overall results show that a dramatic improvement in overall magnetic properties of core loss and permeability result from both 9-mil and ll-mil steel when processed by an isothermal anneal for 6-20 hours within the range 1600-1700F.
The preferred ranges for each differ within that range, but the best combination of properties and complete secondary recrystal-lization occurs at about 1650F for both gauges.
The method of the present invention relates to an improved final texture annealing process wherein the steel is heated to a recrystallization temperature within the range of 1600 to 1700F. The heating rate may be on the order of a con-ventional 50F per hour and the selected isothermal hold temperature be about 1650F. The steel is then isothermally heated by holding the steel at that temperature for about 6 to 20 hours, preferably about 12 hours, to substantially complete secondary recrystallization. Thereafter the steel is heated from that temperature to a purification temperature in excess of 2000F, preferably about 2200F, at a heating rate such as 50F per hour and held at that temperature to effect purification. Generally, the heating rate up to the hold tem-per-ture and up to the purification temperature are relatively constant heating rates. The heating rate, however, does not appear to be critical to significantly affect the properties.
12~5~2 An advantage of the method of the present invention is that secondary recrystallization is essentially completed during the isothermal portion of the heat treatment, rather than being completed in accordance with conventional practice during heating to the higher purification temperature. As has been demonstrated, the effect of the present invention is to improve both magnetic permeability and core loss values. The method of the present invention is able to improve the magnetic properties in a manner not heretofore recognized in the art.
Although preferred and alternative embodiments have been described, it will be apparent to one s~illed in the art that changes can be made therein without departing from the scope of the in~ention.
Claims (11)
1. In a process for producing electromagnetic silicon steel having a cube-on-edge orientation, which process includes the steps of preparing a steel melt containing 2.5 to 4% silicon, casting the steel, hot rolling the steel, cold rolling the steel to final gauge, decarburizing the steel, applying a refractory oxide base coating to the steel, and final texture annealing the steel by heating to and maintaining a temperature in excess of 2000°F, the improvement comprising the steps of during final texture annealing, heating the steel to a recrystallization temperature within the range of 1600 to 1700°F;
heating the steel at about 10°F/hour or less in the recrystallization temperature range at temperatures depending upon the thickness of the steel with higher temperatures for thinner steel for about 6 to 20 hours to substantially complete secondary recrystallization; and heating the steel from the selected recrystallization temperature range to a temperature in excess of the 2000°F, said steel having improved magnetic permeability and core loss values.
heating the steel at about 10°F/hour or less in the recrystallization temperature range at temperatures depending upon the thickness of the steel with higher temperatures for thinner steel for about 6 to 20 hours to substantially complete secondary recrystallization; and heating the steel from the selected recrystallization temperature range to a temperature in excess of the 2000°F, said steel having improved magnetic permeability and core loss values.
2. The process as set forth in claim 1 wherein the recrystallization temperature range is about 1600 to 1650°F
for steel having a gauge of about 11 mils.
for steel having a gauge of about 11 mils.
3. The process as set forth in claim 1 wherein the recrystallization temperature range is about 1650 to 1700°F
for steel having a gauge of about 9 mils.
for steel having a gauge of about 9 mils.
4. The process as set forth in claim 1 wherein the steel is substantially isothermally heated at about 1650°F
for about 12 hours.
for about 12 hours.
5. The process as set forth in claim 1 wherein the heating in the recrystallization range occurs at about 5°F/hour or less.
6. In a process for producing electromagnetic silicon steel having a cube-on-edge orientation, which process includes the steps of preparing a steel melt containing 2.5 to 4% silicon, casting the steel, hot rolling the steel, cold rolling the steel to final gauge, decarburizing the steel, applying a refractory oxide base coating to the steel, and final texture annealing the steel by heating to and maintaining at a temperature in excess of 2000°F, the improvement comprising heating the steel during final texture annealing at a relatively constant heating rate of about 1600-1700°F;
substantially isothermally heating the steel at about 1600-1650°F for steel having a gauge of about 11 mils, and about 1650-1700°F for thinner steel for about 6 to 20 hours to sub-stantially complete secondary recrystallization; and then heating the steel at a relatively constant heating rate to a temperature in excess of the 2000°F, said steel having improved permeability and core loss values.
substantially isothermally heating the steel at about 1600-1650°F for steel having a gauge of about 11 mils, and about 1650-1700°F for thinner steel for about 6 to 20 hours to sub-stantially complete secondary recrystallization; and then heating the steel at a relatively constant heating rate to a temperature in excess of the 2000°F, said steel having improved permeability and core loss values.
7. A process for producing electromagnetic silicon steel having a cube-on-edge orientation comprising the steps of preparing a steel metal containing 2.5 to 4% silicon; casting the steel; hot rolling the steel; cold rolling the steel to final gauge; decarburizing the steel; applying a refractory oxide base coating to the steel; heating the coated steel to a recrystallization temperature range of 1600 to 1700°F; heating the steel at about 10°F/hour or less in the recrystallization temperature range at temperatures depending upon the thickness of the steel, and being about 1650°F or more for steels having a gauge of 11 mils or thinner for about 6 to 20 hours to sub-stantially complete secondary recrystallization; and thereafter to complete final texture annealing, further heating the steel from the selected recrystallization temperature range to a tem-perature in excess of 2000°F, said steel having improved magnetic permeability and core loss values.
8. The process as set forth in claim 7 wherein the recrystallization temperature range is about 1600 to 1650°F
for steel having a gauge of about 11 mils.
for steel having a gauge of about 11 mils.
9. The process as set forth in claim 7 wherein the recrystallization temperature range is about 1650 to 1700°F
for steel having a gauge of about 9 mils.
for steel having a gauge of about 9 mils.
10. The process as set forth in claim 7 wherein the steel is substantially isothermally heated at about 1650°F
for about 12 hours.
for about 12 hours.
11. The process as set forth in claim 7 wherein the steel is heated at about 5°F/hour or less.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US51084483A | 1983-07-05 | 1983-07-05 | |
| US510,844 | 1983-07-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1240592A true CA1240592A (en) | 1988-08-16 |
Family
ID=24032438
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000451247A Expired CA1240592A (en) | 1983-07-05 | 1984-04-04 | Processing for cube-on-edge oriented silicon steel |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0130674A3 (en) |
| JP (1) | JPS6036619A (en) |
| CA (1) | CA1240592A (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4662954A (en) * | 1985-08-13 | 1987-05-05 | Allegheny Ludlum Corporation | Method for improving base coating formation on silicon steel by controlling winding tension |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2534141A (en) * | 1948-01-14 | 1950-12-12 | Gen Electric | Heat-treatment of cold rolled silicon steel strip |
| JPS50116998A (en) * | 1974-02-28 | 1975-09-12 | ||
| JPS535800A (en) * | 1976-07-05 | 1978-01-19 | Kawasaki Steel Co | Highhmagneticcflux density oneeway siliconnsteellfolstellite insulator film and method of formation thereof |
| JPS53129116A (en) * | 1977-04-18 | 1978-11-10 | Nippon Steel Corp | Oriented electromagnetic steel sheet with excellent magnetic characteristic s |
| US4157925A (en) * | 1978-04-12 | 1979-06-12 | Allegheny Ludlum Industries, Inc. | Texture annealing silicon steel |
| US4213804A (en) * | 1979-03-19 | 1980-07-22 | Allegheny Ludlum Industries, Inc. | Processing for cube-on-edge oriented silicon steel |
-
1984
- 1984-04-04 CA CA000451247A patent/CA1240592A/en not_active Expired
- 1984-05-02 EP EP84302946A patent/EP0130674A3/en not_active Withdrawn
- 1984-07-02 JP JP13705484A patent/JPS6036619A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| EP0130674A2 (en) | 1985-01-09 |
| JPH0447010B2 (en) | 1992-07-31 |
| JPS6036619A (en) | 1985-02-25 |
| EP0130674A3 (en) | 1985-05-15 |
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