CS212706B2 - Method of improving the permeability of silicon steel with goss orientation - Google Patents

Abstract

1452699 Processing silicon steel sheet ARMCO STEEL CORP 22 Feb 1974 1 March 1973] 8078/74 Headings C7A and C7N Silicon steel with a cube-on-edge orientation is produced from a steel containing in percentage by weight: - by re-heating the cast material to 1260-1400‹C, - hot-rolling to 0À05-0À1 inch, annealing at 815- 1150‹C, cold-rolling and decarburizing. The sheet is then coated with a separator e.g. CaO, MgO or Al 2 O 3 , and finally box annealed at 1093-1260‹C for 8-30 hours in dry hydrogen. Preferably the separator incorporates an inhibitor to prevent grain growth during the primary stage of the final anneal, examples being S, Se or their compounds, particularly 1-6% of S, while the heating up stage of the final anneal may be carried out in nitrogen, particularly at less than 70‹C/hour.

Description

The invention relates to a method for improving the permeability of silicon steel with a Goss orientation.

Silicon steel sheets for use in magnets to which the invention relates have an orientation in which the elemental cubes of which the grains or crystals are composed are oriented in an edge position, which is indicated by the symbol! (110) Miller, [001]. As is known, sheets with this orientation are characterized by a relatively high permeability in the rolling direction and a relatively low permeability in the direction perpendicular to the rolling direction. Goss-oriented silicon steel sheets have a number of applications, the main one being their application to cores of electromagnetic equipment such as transformers, etc.

Silicon steels with Goss grain orientation were first produced by Goss according to U.S. Pat. 1965 559. However, from the very beginning, silicon steels with this orientation with permanently good magnetic properties were difficult to produce on an industrial scale. Therefore, much effort and time has been devoted to the development of these silicon steels.

Gradually, rapid progress has been made in the industrial production of Goss-oriented silicon steels. For example, in Patent ¹ Pat. No. 2,287,467 discloses a method of wet hydrogen oůuhličení allow ..............

removing carbon and unwanted magnetic aging.

It has long been known that the formation of the Gossian orientation is related to the energy at the grain boundary. Furthermore, it is known that an inhibitor such as sulfur in the form of sulfides, dispersing appropriately at the grain boundary during the primary grain growth stage at final annealing, can prevent the primary grain structure from causing grain growth that interferes with following secondary grain growth. As a result, a fine-grained structure is maintained in the steel until the secondary grains with a Goss orientation begin to absorb the grains with other orientations. Then, as the temperature continues to rise during the final annealing, the secondary grain growth will continue with energy at the grain boundary and transform the fine-grained structure into a perfectly developed Goss-oriented structure. It was initially believed that the amount of inhibitor at the grain boundary during the primary grain growth stage at the final annealing depends on the amount of inhibitor in the original taventone and the amount of inhibitor lost during processing prior to the final annealing. Therefore, many of these processing steps were considered critical in order to avoid loss of inhibitor.

212700

U.S. Pat. No. 2,599,340 teaches that higher permeability can be achieved with silicon steels which are hot rolled to an intermediate thickness of high slab temperature of 1260 to 1400 ° C. It has been found that the high temperature during hot rolling causes, at least in part, the dissolution and subsequent elimination of an inhibitor, such as manganese sulphide, in silicon steel.

U.S. Pat. No. 2,906,645 discloses the use of magnesium oxide as a high temperature separator for annealing to form an insulating glass layer on finished silicon steel as part of the treatment. Such a glass coating is very advantageous in many applications because it imparts electrical resistance to the steel and protects it against oxidation and carburization.

According to U.S. Pat. Nos. 3,333,991, 3,333,992 and 3,333,993, the inhibitor can be added to the silicon steel environment immediately before or during the primary grain growth stage of the final annealing and allowed to diffuse into the grain boundary. Therefore, it was no longer necessary to rely solely on the amount of inhobitor present in the. the original melting and many of the processing steps · before final annealing could be considered less critical. According to the latter patents, sulfur and its compounds and -selen and compounds thereof may serve as the inhibitor.

The inhibitor can be supplied to the environment around - silicon steel - during the primary grain growth stage in the final annealing in various ways. For example, sulfur or a sulfur compound that dissociates -or decomposes at primary grain-growth temperatures-may be added to the high temperature separator during annealing. Alternatively, hydrogen sulphide or any other suitable gaseous sulfur compound may be introduced into the annealing environment. In yet another method, hydrogen sulfide or any other suitable gaseous sulfur compound can be added to the decarburizing atmosphere before final annealing. The sulfur compound reacts with the surface of the iron to form a layer of iron sulphide on the surface of the material, which is then a source of force at the stage of primary grain growth at the final annealing.

Finally, the research has progressed so far that it is possible to produce on an industrial scale silicon steel with Goss orientation and good magnetic properties, including permeability at an average value of about 1820 at a magnetic field strength H = -796 A. m “ ¹ . Since then, the focus has been on improving these magnetic properties. U.S. Pat. No. 3,287,183 discloses a process for producing silicon steel having a Goss orientation, wherein the steel produced has a permeability of at least 1800 to about 1910 at a magnetic field strength Ή = 796 A. m -1. According to this patent, the composition of the melt is critical and the melt must contain - in a concentration by weight of 0.025 to 0.085 -% - carbon, 2.5 to 4.0% silicon,

0.005 to 0.050% sulfur and, most importantly, 0.010 to 0.065% acid-soluble aluminum, the remainder being iron and admixed impurities. After hot rolling and pickling, the silicon steel is rolled to a final thickness by at least one cold rolling. In addition to the composition of the melt, it is crucial that the last rolling cold. a thickness reduction of 81-95% is achieved and that prior to the final cold rolling, the silicon iron is subjected to high temperature annealing, so that aluminum nitrides are formed in the steel sheet in such an amount that more than 0.00-20-20% nitrogen is present in the steel in the form of aluminum nitride.

Although the magnetic properties of Goss-oriented silicon steel produced according to U.S. Pat. No. 3,287,183 are excellent, this method has some disadvantages. For example, the measurement does not proceed as easily as with other methods due to the presence of aluminum. Said process requires that the annealing immediately before the final cold rolling is carried out at high temperature followed by relatively rapid cooling or turbidity. Finally, due to the presence of alumina on the surface of the silicon steel, it is difficult to form an ordinary insulating glass sheet thereon.

U.S. Patent No. 700,506 discloses the use of a special high temperature annealing insulation in the process described in the aforementioned U.S. Patent 3,287,183. The high temperature separator used is magnesium oxide to which a titanium compound has been added and manganese compound. The boron compound is then added to the high-temperature annealing separator in addition to the sulfur or sulfur compound or selenium or selenium compound. According to this patent, the addition of boron or boron compound, when added with sulfur or sulfur, results in improved core loss in the resulting product and formation of a thin uniform glassy layer on the silicon steel. According to this patent, boron or boron compound is used to control secondary grain growth during final annealing, while aluminum nitrides control grain growth at the primary growth stage at final annealing.

The present invention relates to a process for the production of silicon steel with Goss orientation which has excellent magnetic properties including permeability at a magnetic field strength of H-796 A. m "1, which is higher than about 1820 and up to 1'90Ό · or more. No annealing at an unusually high temperature is required before final annealing; pickling can be easily carried out in the usual manner; boron and nitrogen are added to control grain growth during the primary growth stage, the final anneal grain; and a conventional glass protective layer may be formed on the silicon steel, the formation of which is part of the conventional manufacturing process for this steel.

Accordingly, the present invention provides a method for improving the permeability of a silicon steel having a Goss orientation, the melt of which contains at a concentration of 2 to 4% silicon by weight, 0.01 to 0.15 percent manganese, 0.02 to 0.05% carbon, 0.01 to 0% , ^{03 0} / o sulfur, up to 0.008% aluminum, the balance being iron and impurities inherent steelmaking, in which the melted silicon steel is cast, hot rolled to an intermediate thickness of from 1.25 -to 2.5 4 mm, hot-rolled silicon steel anneals at temperatures ranging from -815 to 1115 QC, anneals silicon steel-seas and cold-rolled to a final thickness, cold-rolled steel is decarburized and then subjected to final annealing at The process is carried out in a pot, in which at least the last part of the annealing is carried out in dry hydrogen at a temperature ranging from 10-93 to 1260 ° C for 8 to 30 hours. The principle of the invention consists in adding to the silicon steel melt in a weight concentration of 0.002 to 0.012, preferably 0.003 to 0.010% boron and 0.003 to 0.010, preferably 0.004 to 0.008% nitrogen, the cast silicon steel being reheated to a temperature in the range of 1260 ° to 1400 ° C and to the decarburized silicon steel, the annealing separator is applied in the pots before said final annealing.

The process according to the invention can be used for steels melted by any suitable process. The melt can be cast into either ingots or continuously cast slabs. Before hot rolling, the silicon steel is heated to a temperature of 1260 to 1400 ° C for a time sufficient to dissolve the inhibitor, whereupon the steel is hot rolled to a hot strip, i.e. a hot-rolled strip of sheet thickness. After hot rolling, the silicon steel is annealed at a temperature range of 815 to 1150 ° C, the annealing temperature being inversely proportional to the final thickness of the silicon steel. The annealing is followed by conventional pickling and cold rolling to a final thickness, which can be carried out in one or more stages.

The cold-rolled and subsequently decarburized material is covered with MgO as the annealing separator. Although not required, a grain growth inhibitor from the group consisting of sulfur, sulfur compounds, selenium and selenium compounds can be added to the environment around the silicon steel during the primary grain growth stage of the final anneal to achieve optimal permeability values. E.g. 1 to 8% sulfur may be added to the magnesium oxide forming the high temperature annealing separator.

The decarburized and high temperature annealed coated steel separator is then subjected to final annealing in a dry hydrogen atmosphere at temperatures ranging from 1093 to 1260 ° C. Although not necessary, heating at the final annealing in a nitrogen atmosphere can be performed to achieve optimum permeability values, the temperature being raised at a rate of less than -70 ° C / h, preferably about 28 ° C / h.

Silicon steel having a Goss orientation according to the invention is characterized by a permeability at a magnetic field strength of 796 A. m ^-1 , which is higher than about 18210 and up to 1900 and higher.

The steel melt according to the invention can be produced by any suitable known method, for example in a Martin furnace, in a converter, in an electric furnace, in a vacuum melting furnace or below.

The initial composition of the melt is conventional as used in silicon steel with a Goss orientation in terms of silicon, manganese, carbon and sulfur. However, critical amounts of boron and nitrogen are added to this melt composition. The melt may have the following composition: 2 to 4% silicon, 0.01 to 0.15%, preferably 0.03% to 0.15% manganese, 0.02 to 0.05% carbon, 0.01 to 0.03% sulfur, 0.002 to 0.012%, preferably -0.003 to 0.010% boron, -0.003 to 0.010%, preferably 0.004 to 0.008% nitrogen, the remainder iron and random impurities inherent in the manufacturing process. Although not necessary, aluminum (as a deoxidizing agent or impurity in an amount of up to about 0.008% by weight) may be present in the above melt. The optimum amount of boron is considered to be 0.007% and the optimal weight nitrogen content -0.007%.

The boron content of the original melt can be achieved by any suitable known method, including the addition of a boron-containing compound, for example ferroboride, to the original melt. Similarly, the nitrogen content of the original melt can be achieved by any suitable method known in the art. For example, nitrogen may be added in the form of a nitrogen compound such as manganese nitride. The addition of nitrogen can also be achieved by blowing. It is also possible to obtain the desired nitrogen content by using a melt process which typically results in a corresponding nitrogen content, for example by using an electric furnace to produce a low carbon melt.

Silicon steel can be either cast into ingots or continuous slabs can be cast from it. If the steel is cast, the ingots can either be hot rolled immediately onto a hot strip or slabs of intermediate thicknesses can be rolled out of the hot rolls, which are then reheated and hot rolled into a hot strip. In hot rolling or continuous casting slabs, the slabs should be reheated to a temperature in the range of 1260 to 1400 ° C, preferably to 1370 ° C according to the aforementioned patent specification, prior to hot rolling. US No. 2,599,340 ·. The resulting warm strip will generally have a thickness of 1.25 to 2.54 mm.

After hot rolling to a hot strip, the silicon steel is annealed as previously mentioned at a temperature of 815 - 1150 ° C, preferably 927 - 1093 ° C for about 3.5 minutes in a suitable atmosphere such as air, combustion products or an inert gas. It has been found that to achieve optimal permeability values, the annealing temperature should be inversely proportional to the desired resultant silicon steel thickness. Therefore, if thinner sheets are to be produced as the final product, the annealing temperature should be at the upper end of the above range. Similarly, if thicker sheets are to be produced, the annealing temperature should be at the lower end of the above range. The annealed hot rolled silicon steel can be turbid by spraying with water or cooled by air. Then the silicon steel is pickled in a conventional manner and cold rolled in a single stage (or in two or more stages with intermediate heating) to a final thickness.

After reducing the thickness of the cold, the silicon steel is decarburized in a humid hydrogen atmosphere at a temperature of 815 ° C and a dew point of 57 ° C according to the aforementioned U.S. Patent No. 2,287,467.

After carbonization, a suitable high temperature annealing separator, such as magnesium oxide, aluminum oxide, calcium oxide or mixtures of these compounds, is applied to the silicon steel. If it is desired that the resulting product be provided with a glass layer on the surface, magnesium oxide according to U.S. Pat. No. 2,906,645 may be used as the high temperature annealing separator. in a known way.

The silicon steel with the applied high temperature annealing separator is subjected to final annealing in pots at a temperature of 1093 to 1260 ° C, preferably at a temperature of 1205 ° C for 8 to 30 hours. This annealing, hereinafter referred to as " final annealing " for greater accuracy, is the annealing in which the Goss orientation is achieved during the secondary grain growth stage. The annealing is carried out in an atmosphere of dry hydrogen.

It has been found that although this is not necessary to achieve good permeability values, to obtain optimal permeability values, a grain growth inhibitor should be present in the silicon steel environment immediately before or during the primary grain growth stage at the final anneal. Sulfur, selenium and their compounds are excellent inhibitors; these materials can be introduced into the silicon steel environment by any of the methods described in U.S. Patent Nos. 3,333,991, 3,333,992 and 3,333,993. For example, very good results are obtained when magnesium oxide is used as a high temperature separator for annealing about 1 to about 6% sulfur.

Although not again necessary for the purposes of the present invention, it has nevertheless been found, although not also necessary to achieve optimal magnetic properties, that a nitrogen atmosphere should be used during the heating stage of the final annealing, while the remaining annealing stage should be used. use dry hydrogen instead of nitrogen. At the heating stage of the annealing, the temperature should rise relatively slowly, i.e. less than about 70 ° C / h, preferably about 28 ° C / h.

The invention is illustrated by the following examples.

Example 1 A laboratory melt was prepared under reduced pressure having the following composition by weight in%:

C 0,03.3% Mn 0.094% with 0,029% Si 3.24% В 0.006% N 0,068% AI 0.002%

Cast the ingot and heat to 1260 ° C. Then, the material is hot rolled to a thickness of 2.54 mm and annealed at 1038 ° C for 3.5 minutes. After this annealing, the silicon steel is cooled in air, seas and cold rolled in N 0.0068% to reduce its thickness to 0.30 µm.

Then, the cold rolled silicon steel is decarburized at a temperature of 815 ° C in humid hydrogen at a dew point of 57 ° C, and then covered with magnesium oxide as a high temperature annealing separator containing 6% by weight of sulfur. Subsequently, the coated silicon steel is annealed in pots under a hydrogen atmosphere at 1205 ° C for 30 hours. The finished material is characterized by a permeability of 1921 at a magnetic field strength of 796 A. m ^_1 .

This example illustrates the high permeability that can be achieved when both boron and nitrogen are added to the melt in the previously mentioned ranges and the silicon steel is produced by the process of the invention.

Example 2

A laboratory melting having the following composition by weight is produced. %:

C 0.032% Mn 0.100% WITH 0,025 Si 3.35% В 0.0052% N 0.0077% AI 0.004%

25.4 mm thick ingots are cast from the melted material, which are heated to a temperature of 1260 ° C and hot rolled to a thickness of approximately 2.29 mm. The first and second samples of this material are calcined for 3.5 minutes at 927 ° C, while the third sample is annealed

212708 is also calcined for 3.5 minutes at 1150 ° C. The first sample is air cooled and cold rolled to a thickness of 0.356 mm. The second and third samples are quenched by spraying with water and rolled to coldness to a thickness of 0.254 mm.

All three samples are decarburized at 815 ° C in humid conditions. hydrogen with a dew point of 57 ° C. Magnesium oxide was applied to all samples as. high temperature separator for. annealing containing 6% by weight of sulfur. The coated samples are calcined in boxes at a temperature of 1205 ° C and for 27 hours at a heating rate of 28 ° C / h. The heating portion of the final annealing is carried out under a 'nitrogen atmosphere', while the 'rest of the' final annealing 'is carried out under a hydrogen atmosphere.

The first, second, and third samples are characterized by permeabilites 1889, 1864, and 1896 at a magnetic field strength of 796 A. m -1 Samples 2 a. 3 clearly illustrate the opposite relationship between the annealing temperature after cold rolling and the resulting thickness. '·

Example 3

Melt the laboratory 'melting' having the following% by weight:

C 0.030% Mn 0.100 '% WITH 0.025% Si 3.29% (B) 0.0072% N 0.0078 '% AI 0.007%

25.4 mm thick ingots are cast from the melted material, heated to a temperature of 1260 ° C, and rolled to a thickness of 2.29 mm. Ingots are annealed at temperature. 927 ° C for

3.5 minutes, cooled by air, sea and cold rolled to a thickness of 0.356 mm. The cold rolled silicon steel is then decarburized at a temperature of 815 ° C in a humid state. of hydrogen at a dew point of 57 ° C and applied as a high temperature separator for annealing magnesium oxide containing 6 wt. % sulfur. The silicon steel having coating thereon is subjected to a final annealing at 1,205 ° C for 27 hours with a heating rate of 28 'C ⁰ / h. During the heating portion of the final annealing, a nitrogen atmosphere is used, while the rest of the annealing is carried out under a hydrogen atmosphere. The final product is characterized by a permeability of 1889, with a magnetic field strength of 796 A.m -1.

Claims (4)

A method of determining the permeability of a silicon steel with Goss. orientation. the melt contains from 2 to 4% by weight of silicon, from 0.01 to 0.15% of manganese, from 0.02 to 0.05% of carbon, from 0.01 to 0.03% of sulfur; 0.008 percent of aluminum and the remainder 'formed by iron and impurities of their own'. production of steel, 'in which' is melted. Silicon steel is cast, hot rolled to an intermediate thickness ranging from 1.25. up to 2.54 mm, hot rolled silicon. The steel is annealed at a temperature ranging from 0d 815 to 1115 ° C, the annealed silicon steel is pickled and cold rolled. . 'Final thickness of the cold rolled' .ocel decarburizing and ^e. then 'undergo final' pot annealing, at least last '. Part of the annealing - done 'in dry. Hydrogen 'at. a temperature in the range of from 1093 to 1260 ° C for 8 to <hours, characterized by a temperature of 10 to 1260 ° C. The composition of claim 1, wherein the weight of the silicon steel is added to the 'melt'. Concentrations of 0.002-0.022, preferably 0.003-0.010% boron and 0.003-0.010, preferably 0.004-0.08% nitrogen, cast silicon steel. reheated to a temperature in the range of 1260 to 1400 ° C and to decarburized silicon steel. before. by final annealing in pots, apply a annealing separator. 2. A process as claimed in claim 1, characterized in that it is:. a grain growth inhibitor from the group consisting of sulfur, sulfur compounds, selenium and selenium compounds is added to the environment at the final annealing step. 3. Method. according to 1 or 2, characterized in that:. The composition of claim 1, wherein magnesium oxide containing magnesium oxide is added as the annealing separator. in a concentration by weight of 1 to 6% sulfur. 4. A process according to any one of claims 1 to 3, wherein the final heating comprises a heating step which is carried out under a nitrogen atmosphere while the rest. The pot annealing is carried out in an atmosphere of dry hydrogen.