SE444186B - WAY TO IMPROVE CORE LOSS FEATURES OF KUB-PA OFFICE-OILED SILICONE ALLOY STEEL - Google Patents

Description

7 7805720-5 obtain very high permeability. U.S. Pat. No. 3,855,019 discloses one copper additive to a silicon steel melt, in which aluminum nitride is also present as a primary barley growth inhibitor, to obtain improved permeability values.

U.S. Patent 3,676,227 to F. Matsumoto et al Nippon Steel Corporation) describes a method of manufacturing cube-edge oriented silicon steel, containing less than 4% silicon and 0.010 - 0.065% acid-soluble aluminum, which has a lot high permeability and ‘low iron loss’ (i.e., low core lust), which includes the application of an annealing separator composition on the surfaces of cold-rolled carbonated silicon steel material, drying of the separator composition, and that the material is subjected to a ready annealing is carried out at a temperature above 1000 ° C for more than 5 hours in hydrogen or nitrogen. The annealing separator can be magnesium oxide, calcium oxide, alumina, titanium dioxide, or mixtures thereof, and contains 0.01 - 1.0 weight-8 boron or a boron compound, based on the weight of the annealing separator.

U.S. Pat. No. 3,700,506 discloses the addition of a boron compound. to a magnetic separator composition, which also contains titanium, manganese and sulfur, for use on a silicon steel containing aluminum nitride.

The addition of boron compounds to annealing separators compositions based on magnesium oxide are also described in GB-PS 1,398,504, in U.S. Patents 3,583,887 and 3,841,925, listed on Morton Norwich Products, Inc., in U.S. Patents 3,697,322, 3,785,879, 3,932,202, 3,941,621 and 3,945,862 on Merck & Co., Inc. and in U.S. Patent 4,010,050.

A number of the above-mentioned patents relate to the formation of the electrically insulating glass film and Franklin resistivity, by addition of boron compounds, in silicon steel which would have permeabilities less than 1850 at 796 Alm. Such materials do not normally contain sufficient amounts of acid-soluble aluminum, and consequently they does not have the same technology required for very high meability (i.e. greater than 1850 at 796 A / m), and for reasons such as explained below. ~. - Ü ~ = rL «»> ï ~,. v ** ff. * 'f-i-i = -f'ß-st ~ .r min:; . f ”. 4111-: vaosvzo-s It has been shown that a magnesium oxide from Japanese source, containing about 0.08% boron based on the weight of nesium oxide, produced excellent glass film coated silicon steels as well regarding the physical properties of the glass film as they the magnetic properties of the finished silicon steel material, in the production of cube-on-edge oriented material with much high permeability. However, it has proved impossible to reproduce these results, and to obtain high permeability small, low core loss and good glass film properties in magnesium oxide from other sources with additives of the same order of magnitude ning. Studies have shown that variations in sodium, calcium and the chloride contents of the magnesium oxides had little effect. Oh on the other hand, variations in citric acid activity and surface area have a pronounced effect.

Despite the fact that the degree of hydration and surface area as such were known to affect the behavior of magnesium oxide, it was found that the specification of a particular citric acid activity and a special surface area area is still not achieved came uniformly reproducible results in particular with respect to on magnesium oxides from various commercial sources. Also different batches of magnesium oxide from the same commercial source were shown cause difficulties in one type or another despite citric acid activity and surface area values which, according to previous nothing learning, would have been optimal.

In view of the above related background, it is obvious attempt to improve the magnetic properties of silicon steel with very high permeability by adding about 0.08% live to a commercial source of magnesium oxide at best were only temporarily successful, and the behavior was not predictable.

A main object of the present invention is to provide come a way that solves the above problems in manufacturing of silicon steel having a very high permeability in accordance with any of the above U.S. patents.

Roughly speaking, it is known that living, set to a magnetic silica coating, is volatile at the high temperature of ready annealing (at or around 1200 ° C), with part of the drill "t 'P1 ~ = ;;. ~: 1. ~, -_ g: ¿-W -« - ¿¶ = ,,. - .-. _4 7805720-5 i f '. diffusing inwardly through the surfaces of the silicon steel material, and that the residue disappears in the annealing atmosphere where it is effective. It has now been shown that the amount of boron which into the annealing atmosphere is a direct function of the density, or packing factor of the dried magnesium the oxide coating. (It should be understood that the coating is applied as an aqueous slamming by any common method such as dipping, spraying, dosing rollers, or the like, and then dried at relatively low heat.) Bulk density or packing density factor is in turn directly dependent on the particle size distribution and the degree of hydration of the magnesium oxide. Although the citric acid activity of magnesium oxide may produced, at least within wide limits, when it is produced especially in large quantities is the particle size distribution depending on the particular method of production and can not be included ease is varied by commercial producers. When looking of this is the new concept of the present invention to compensate for different particle size distributions by portioning the amount of additive in relation to the batch size distribution, surface area and citric acid activity. Heath in other words, the addition is made inversely proportional to the the density or packing factor of the dried magnesium the oxide coating.

Due to the thinness of the dried coating and the relative roughness of the surface of the silicon steel material, it is it is not possible to determine the bulk density of the dried coating with currently available equipment or technology.

Consequently, the off-addition is proportional to the three parameters most directly affecting the bulk density, namely size distribution, surface area and degree of hydration, such as sued by citric acid activity.

It has been found that good adhesion of a dried stomach Nesium oxide coating on silicon steel surfaces usually provides one coating with a high bulk density so that it will be require a relatively low additive.

It has further been found that the density or tensile the bonding in the gluing has a band ring during the final annealing at . w. - .m "ml; - vs f f _. 7805720-5 elevated temperature can affect the amount of boron required. Solve tabs or turns allow more boron to disappear into the annealing atmosphere.

In connection with hydration, it should be understood that magnesium hydroxide lowers the density and alters the morphine login of the original magnesium oxide particles. Hydrating the cooling water is not driven off by the relatively low heat was turned over when drying the coating. However, this is driven water by heating to a higher temperature, such as the behavior during the finished annealing, thus increasing the porosity of the magnesium oxide coating.

This is the reason for the direct effect of hydrating degree of bulk density.

Regarding the effect of the particle size distribution on the packing or bulk density can be referred to Fig. 3.2 of "Introduction to Ceramics" by W.D. Kingery, J. Wiley & Sons, Inc. (1960), the disclosure of which is incorporated herein by reference.

According to the present invention there is provided a method of improve the core loss properties of cube-on-edge-oriented silicon alloy steel in the form of strip and sheet material that comes to have a magnetic permeability greater than 1850 at 796 A / m after a final high temperature annealing in a reducing atmosphere, which involves adding a boron compound to the water magnesium oxide slurry in the range 0.07% to 6.30% based on the weight of the magnesium oxide, apply the slurry to the surfaces and dries the coating so applied before the final annealing.

The method is characterized by the addition of the boron compound in inverse proportion to the bulk density of the dried coating.

Reference is made to the accompanying drawings, in which Fig. 1 graphically shows the particle size distribution of prior art magnesium oxide from a first source, Fig. 2 graphically shows the particle size distribution for magnesium oxide from a second source and ._._- ¿v_-r-f. = W, <, - fmww »_, _-» fl mås-n »A» __, m .. i , _ _. _ 'ß' MW-pmm I 5 «. . 7805720-5 Fig. 3 graphically shows the particle size distribution of magnesium oxide from a third source.

A preferred method of the invention for preparing of silicon steel in the form of strips and sheet metal which may have a magnetic permeability greater than 1850 at 796 A / m after a ready annealing at high temperature, includes the steps of att a cold-rolled, charred silicon steel is produced in the form of strip and sheet containing 2 - 4% silicon, 0.01 - 0.15% manganese, 0.002 - 0.005% carbon, 0.01 - 0.03% sulfur, up to 0.010% boron, 0.005 - 0.010% nitrogen, 0.010 - 0.065 3 aluminum, with the remainder consisting of iron and impurities, that an aqueous solution is applied to the surfaces of the material slurry containing magnesium oxide, at least one boron compound, and up to 20% titanium dioxide based on the weight of magnesium oxide, the slurry thus applied dries by heating to a temperature sufficient to evaporate the water and leave one dried coating on the surfaces, and that the coated material is annealed. material in a non-oxidizing atmosphere at a temperature of about 1095 - 12600 C, to thereby form an insulator film and to produce a cube-on-edge orientation by se- customer recrystallization, which is characterized by the the boron compound in the slurry is proportional to get a total boron content of 0.07 - 0.30% by weight, based on the weight of magnesium oxide, according to particle size distribution, surface area and citric acid activity of the magnesium oxide. The way one- The invention will result in the production of a thin, cohesive glass film and will improve the core pleasure properties while maintaining the very high permeability the mobility of the material. _ It should be understood that a thin continuous glass film is beneficial for promoting improved magnetic quality, is better ratio between utilized effective area and the entire surface, better magnetostriction, and better adhesion. When applying brings a secondary coating such as the one described in US-PS In addition, a glass film must be thin and cohesive. in order to obtain good adhesion of the secondary coating and to allow the tensile-producing properties to At . t ¿V - ,.: = j- »ï; _. ¿,, ~, 7aos12o-sl IN- to be realized.

The thickness of the dried magnesium oxide coating can not be determined for exactly the same reasons as explained above with with respect to determining the bulk density of the coating.

Accordingly, the coating weight of the dried coating was used. for control purposes, and a dried coating that comes to form a continuous thin glass film with the above-described advantageous properties will be formed with a dry coating weight of 6.3 - 15.65 g / m2 for a magnesium oxide which has a citric acid activity greater than 50 seconds.

A cold-rolled charred silicon steel in the form of strip and sheet material can be produced by a conventional method where a suitable melt is cast as ingot or is cast continuously in slabs subject form. If the cast as cast, the steel is pre-rolled and platinum-rolled in the usual way, and the platinum is hot rolled to medium thickness from a temperature of about 1260 to about 1400 ° C, with annealing after hot rolling. The filament is then removed, and the The material is cold rolled to finished size in one or more steps, followed of decarburization in a hydrogen atmosphere.

If the steel is continuously cast into sheet metal form with a column crystal structure, preferably the method is written in U.S. Pat. No. 3,764,406. In this method, a continuous molded plate blank with a thickness of about 10 - 30 cm more a temperature between 750 and 220 ° C and hot rolled from the beginning with a thickness reduction of S - 50%, for reheating of the blank to a temperature between about 1260 and 140 ° C for ..nlig hot rolling, Hot rolling, annealing, cold rolling- one and the decarburization then follows in the manner described above.

The cold-rolled and charred material is then coated with an aqueous slurry of magnesium oxide by dipping, spraying, or dosing rollers and dried by heating to a temperature in the order of about 200 - 300 ° C to give a weight of dried coating of 6.3 - 15.6 g / m2. It be- laid strip or sheet material is then subjected to a finished high temperature annealing, which may be a coffin annealing or smiles an annealing with open band ring. f * - ä, .

. Rí- ä .'_. ï-.¿3.¿ - .. ¿ç if; Qff: jg ". á ß r _ 1: -: W Lä 'x 7805720-5 An appropriate concentration for aqueous slurry, when using dosing rollers, is between 0.096 and 0.192 g of magnesium oxide per milliliter of water with up to 20 8 titanium dioxide, and preferably about 5%, which can be added to sludge based on the weight of the magnesium oxide.

The high temperature annealing of the furnace during which the the on-edge orientation is achieved by secondary recrystallization. carried out in a known manner is carried out at about 1095 - 160 ° C in a educational atmosphere. It should be understood that the magnesium oxide reacts silicon in the steel to form a glass film in this annealing ning. The heating part of the finished annealing is carried out before in a nitrogen-hydrogen atmosphere in order to optimize the formation of that of nitrides which serve as barley plant inhibitors. Finished- part of the annealing, which involves heating at temperature turn and taper, is preferably carried out in hydrogen because This is known for purifying the steel to promote secondary recrystallization.

The type of boron compound and the time at which it is has been shown to be of no particular significance. Bor- acid, calcium borate, or any other of commonly available boron compounds can thus be used. The associations can be set to the magnesium oxide before or during the treatment thereof, or can be added after an aqueous slurry has formed.

It is also possible to add a drilling compound to the belt surfaces before applying the magnesium oxide slurry to the same. Follow- actually the term 'appointment of a drilling association to an aqueous magnesium oxide slurry 'used herein, that perceived as broad enough to cover the addition of application of the boron compound at any stage prior to application those of the slurry on the surfaces of the silicon steel material.

Figure 1 shows the particle size distribution of a magnesium oxide from a first source. It should be noted that two peaks or bumps occur with about 10% of the particles between 5 and 10 microns and about 22% between 0.8 and 2 microns.

Magnesium oxide from this source exhibits a typical particle size play distribution% if as follows, in weight-8: ä; - xx g -. :,. g É 7sos1zo-s 9 8 - 10% between S and 10 microns ao - -m s menan à and 2 microns 20 - 30% between 2 and 1 micron 18 - 40% less than a micron A particle size distribution of the type shown in _ Fig. 1 approaches a two-component system shown in Fig. 3.2 f at the above-mentioned 'Introduction to Ceramícs'. Consequently, 1 magnesium oxide according to Fig. 1 a relatively dense dried coating.

Magnesium oxide can be obtained from this source with a citric acid activity greater than 50 seconds. A nominal 0.08% over- kit has been shown to give excellent results.

Fig. 2 shows particle size distribution in a magnesium oxide from a second source in which there is a certain sizes around relatively large and relatively small, * lar, but with a large dominance less than 1 micron. Typical p r- item size distributions from this source are as follows: in weight-%: 0 - 5% between 5 and 10 microns 5 - 10% between 5 and 2 microns 5 - 10% between 2 and 1 micron 75 - 90% less than 1 micron, with 50 - 60 2 in between 0.3 and 0.5 microns.

A magnesium oxide of the type shown in Fig. 2 forms one less densely dried coating than that of Fig. 1. Consequently it has been found that about 0.10 - 0.15% live, based on magnesium oxide, is required for magnesium oxide of the type Fig. 2, with a citric acid activity greater than 50 seconds, in order to compensate for the boron loss in the annealing atmosphere during the annealing, when the particle size distribution is from 75 to 90% less than 1 micron. The citric acid activity can lie in a range of about 55 - 120 seconds for magnesium oxide from this source.

P19, 3 shows the particle size distribution of a magnetic silica from a third source. It should be noted that there is very small ‘scattering’ in relatively large and small particle sizes games and that a large dominance lies within the size range 2 to 5 microns. Typical particle size distribution for magnesium oxide from this source is as follows, in weight-1: at '1805120-s 0 - S S between 5 and 10 microns 80 - 90 Q between 5 and 2 microns 10 - 20% between 2 and 1 micron 0% less than 1 micron It was found that the bulk density of dried coatings Magnesium oxide emissions shown in Fig. 3 were relatively low and less than any of those of Figs. 1 and 2. Accordingly, a boron content of about 0.15 - 0.20% was necessary, together with a citric acid activity greater than 50 seconds, in order to compensate for boron loss to the annealing atmosphere, when the particle size distribution is from 80 to 90% between 2 and 5 microns. Citric acid activity may be in a range from about 60 to about 200 seconds for magnesium oxide from it source.

Although less critical than citric acid activity and size distribution, the surface area of the magnesium oxide is not nevertheless of importance in regulating the activity or hydration degree of titration of the magnesium oxide. Very finely divided material rial causing high surface area tend to hydrate rapidly with inevitable undesirable effect on the bulk density of it dried coating, as explained above. The material with all for coarse particle size and a very low surface area tend to dissipate from the aqueous slurry and do not undergo with ease reaction with the silica, during the final annealing at high temperature, to form a thin and cohesive glass film. It has been found that a surface area between about 10 and about 20 m2 / g gives excellent results, in combination with the others the parameters according to the present method.

The composition of the silicon steel indicated above is completely and has been shown to be critical in order to obtain added optimal and magnetic properties. The presence of manganese sulfide and aluminum nitride within the specified limits are necessary you for preferential grain growth during the final annealing at high temperature, which can have a total length of about 8 - 30 hours. Although not necessary, boron can be added to silicon steel together with nitrogen in critical amounts, in accordance with = 1. -_ «.:.;.« T '"ï #;: * .; zà; f ..-. ¿.: 2 = f: u *». = -. ¿Š - .. ~ f1f1 '-l .'- a' ~ 1 :: * '- * ɧï w ann » 1 ,, vaosvào-Si _, - .. p what is taught in U.S. Pat. No. 3,873,381. These boron and nitrogen additives looking at the steel melt has the purpose of regulating grain growth during the primary grain growth stage of the finished annealing. On the other hand, U.S. Pat. No. 3,700,506 discloses the addition of a boron compound for a magnetic separator composition, which also contains titanium, manganese, and sulfur or selenium, 1 purpose to regulate secondary grain growth during final annealing, 1 a silicon steel containing aluminum nitride as a primary grain growth inhibitor.

The presence of aluminum in the silicon steel results in the formation of a small amount of alumina on the surfaces of the silicon steel, which makes the formation of a thin, adhesive and cohesive man-hanging glass film more difficult. The addition of titanium dioxide within however, the range of about 5 - 20% reduces this difficulty.

A series of tests have been carried out, all of which was carried out with cold-rolled, charred silicon steel strip material with a composition in the range of about 2 - 4% silicon, about 0.01 - 0.15% manganese, about 0.002 - about 0.005% carbon, about 0.01 - 0.03% sulfur, about 0.005 - 0.010 S nitrogen, about 0.010 - 0.065% acid soluble aluminum, up to about 0.010% boron and residual iron plus impurities.

The magnesium oxide from the first source (Fig. 1) is used. were used in all tests as a standard for comparison because it had been used successfully for many years in a no- minimum boron content of about 0.08% (total).

Test data are shown in the following tables. Table I contains designations for the source, citric acid activity ' (C.A.A.), surface area, coating weight (dried coating) and boron content of the various samples. It should be understood that source designation refer to the three sources indicated by the figures na l - 3 with respect to particle size distribution.

Table II lists the magnetic properties of coated and annealed bandings of the samples according to Table I. All values listed in Table II represent averages of samples from the beginning of the ring and the end of the ring corrected to a thickness of 0.295 mm. contained 5% titanium dioxide, based on the weight of magnesium oxide, All magnesium oxide coating slurries are -fišr-fšf, -in-'f ... -w-vazußëf * ... q, * “Oh 7805720-5 and the slurry concentration ranged from 0.085 to 0.121 g of magnetic A * silica per milliliter of water. Q The citric acid activity is a measure of hydration the degree of magnesium oxide and is determined by measuring it then required time for a given weight of a magnesium oxide to provide sufficient hydroxyl ions to neutralize a given weight of citric acid. The test is the same as the report U.S. Pat. No. 3,841,925, namely: 1. 100 ml of 0,400 normal aqueous citric acid containing 2 ml of 1% phenolphthalein indicator was brought to 30 ° C in a jar holding 227 g. The jar was fitted with a screw cap and a magnetic stir bar. 2. Magnesium oxide weighing 2.00 g was introduced into the jar and a stopwatch was started at the same time. 3. As soon as the magnesium oxide sample additive was screwed lid on the jar at 5 seconds, the jar was shaken and contained kept strong. The shaking ended at the 10 second point. 4. At the 10 second point, the sample was placed on a magnetic stirrer unit. Mechanical agitation would provide one vortex about 2 cm deep at the center when the inner diameter of the bur the ken is about 6 cm. 5. The stopwatch was stopped as soon as the suspension expired in skärt, and the time was recorded. This time in seconds is lemon the acid activity.

It is clear that a low value represents a relative active active magnesium oxide, i.e. one that hydrates quickly.

The degree of hydration is of greater importance than the final one degree of hydration, although a high degree usually also includes indicates a high degree of hydration at equilibrium.

Sample B, from source 2, did not present any problems with respect to the coating The slurry wetted the belt and came a smooth even coating on both surfaces. Hydration of the stomach the magnesium oxide in the aqueous slurry did not occur lightness, and the adhesion of the dried coating was good.

The magnetic properties were comparable to those of the control sample A, from source 1, thus showing that the boron content of 0.12 S from sample B was close to optimum. '7805720-S3 13 Sample D, from source 3, which also contained 0.12% boron, did not cause any coating problems either. The sludge was wet both surfaces well and produced an excellent dried coating, although the adhesion of the dried coating was moderate rather than good. The glass film after finishing annealing was smooth, cohesive and light gray. The core loss of sample D responded not against that of its control sample C, from source 1, 0.047 watts / kg was considered significant. The permeability was also slightly lower than that of control sample C. It is therefore that the optimum boron content for sample D would be greater than g E ¥ å É ær % n * ä? å 5-f É is ß É % 0.12% boron. ¿ Samples F and G from source 2 were the same magnesium oxide f containing 0.07% boron placed at two different coating folds of 7.6 resp. 20.8 g / m2. This showed the coating weight is a variable that can affect the ultimate magnetic properties the creators. The low coating weight of sample F produced one thin, non-cohesive glass film containing only a few get small sulfide particles. The thicker glass film of sample G contained a large number of large sulfide particles, and the subsurface silica particles were large and relatively few in number. Emel- however, neither sample F nor G mimicked control sample B (from source 1) in core loss values or in permeability. This showed that the boron level of 0.07% was insufficient.

Table I Å Sample Source C.A.A. * surface area coating weight total% live base- É (sec.l (m2 / 9) (g / m2) rat by weight of 0 0 H90 3 A 1 67. 13.5 11.64 0.08 É B 2 65 24.0 '17 0.12 c 1 sv 13.5 11.64 o, os 1 n 3 57 1o 13 o, 1z -É B 1 67 13,5 '11,64 o, os} F 2 36 30.0 7.6 o, o7, § G 2 36 30.0 20.8 0.07 5 * C.A.A. = citric acid activity 7805720-5 14 Table II Sample Source Nuclear Loss -Permeability (watts / k9) at 796 A / m 1.7 Tesla A 1 1,388 1916 B 2 1,397 1918 c 1 1,388 1916 n 3 1,435 1910 s 1 1,418 1922 P 2 1,438 A. '1911 G 1 1.485 1916 Variation in the magnetic properties as a function of boron content (at several citric acid activity values) was shown by laboratory assessments of several magnesium oxides from the other the source, with a particle size distribution according to Fig. 2. These results are summarized in Table III. A magnesium oxide from it the first source (sample H, source 1) was used as a control for comparison with samples J and K, while another magnesium oxide batch from the first source (sample L) was used as a control for comparison with samples M through R.

Data according to Table III (average corrected to 0.295 m) showed that although 0.08% of the boron content of sample J (from the second source) provided similarity to the magnetic properties of the control sample H, significantly better magnetic properties was obtained at a boron level of 0.13% in sample K. samples M and P showed that a boron level of 0.077% did not was sufficient to give the same magnetic properties as at the control (sample L), and that a boron level of about 0.1 - 0.12 % is required. A comparison of samples N and 0 (C.A.A. of 80 seconds) with samples Q and R (C.A.A. of 36 seconds) shown however, that at a higher citric acid activity less required to mimic the magnetic properties of the the trolls. In the case of samples N and 0, better results were also obtained core loss at 0.1% boron level than at 0.12 8. This shows that an optimal range exists for any given citric acid activity. and particle size distribution, and that boron contents below få f fi smwmösg fi aaëäne 7805720 ° S 15 or above optimum, the magnetic properties adversely affect tigt. É rabe11 111 Sample Source Total C.A.A. (watts / kg) Permeability % live (sec.) 1.7 Tesla at 796 A / m 7 u 1 0.011 59 1.485 1918 É J 2 0.08 52 1.479 1920 å x 2 0.13 62 1.420 1930 É, L 1 0.08 62 1.535 1919 å M 2 0.011 80 1.605 1912 3- N _2 0.10 1 80 1.485 1932 ¿ 0 2 0.12 80 1.545 1927 j P 2 0.017 38 1,595 1915 * Q 2 0.10 38 1.519 1919 R 2 0.12 30 1.511 1931 Consequently, the drilling range 0.10 - 0.30% may be considered as critical, and this is dismantled by additional laboratory assessments carried out on a magnesium oxide from the second source which had a citric acid activity of 72 seconds, to which should be set in amounts of 0.03%, 0.08%, 0.15%, 0.20 8, 0.25% and 0.30%, respectively, based on the weight of magnesium oxide.

The magnetic properties of the samples were as follows: Total Core Loss Permeability % boron ~ (watts / kg) at 796 A / m 1.7 Tesla 0.03 - 1.488 g 1930 0.08 1.436 1936 0.15 1.450 1927 0.20 1.450 1917 0.25 1.462 1913 0.30 '1.608 1926 1805720-5 ,, l It is clear that the optimal drilling area for the said example was 0.08 - 0.2o s.

In addition to magnetic properties, a number of other factors are few of importance in the formation of an electrically insulating glass 3 Film. Among these is the viscosity of the magnesium oxide slurry, wettability of the material surfaces by means of the aqueous slurry the adhesion of the dried coating, and the thickness heat, smoothness and physical appearance of the glass film. viscosity is usually not a problem for sludge concentricne: between 3.096 and 0.192 grams of magnesium oxide per millilifcr of water, provided that the degree of hydration is not high.

Under these conditions, the viscosity gradually increases during the run of an experiment when the magnesium oxide is successively hydrated to to a greater extent. This results in too strong an- ignition losses of the dried coating and an undesirable worth thick glass film. This can be avoided when applying by ensuring a citric acid activity of re than 50 seconds, which will reduce the degree of hydration enough. when the velocity increases, it is more difficult to er- 1 keep a smooth even dried magnesium oxide coating. Stroke image coating may be the result of high viscosity.

Adhesion of the dried coating is apparently a function of porosity, which in turn is affected by particulate matter the size distribution and citric acid activity. When these meters are regulated in accordance with the present invention, has the adhesion of the dried coating has been shown to be satisfactory in all cases.

Thickness of the glass film and the reasons for regulating it have been discussed above. It should be sufficient to reiterate that particle size distribution and citric acid activity in in accordance with the present invention results in the formation of a desirable thin, cohesive glass film. Likewise, smooth of the intermediate surface glass-metal either directly or indirectly by regulating these parameters.

Regarding the physical appearance of the film, discoloration usually occurs as a result of iron oxide formation. Too much water present 1 coating below * 7805720-5 11: i F ' the finishing layer will usually provide a porous glass film which will not protect the steel and will not prevent iron oxide formation. Again, this is regulated in the of the present invention by providing a lemon juice. acid activity greater than 50 seconds, thereby hydration brought to a minimum.

In summary, excellent results are obtained for one magnesium oxide so has a particle size distribution typical of the one shown in Fig. 2 and a citric acid activity greater than SO customers to about 120 seconds, an away addition of about 0.10 - 0.15%, based on the weight of magnesium oxide. Excellent results obtained with a magnesium oxide having a particle size ratio division typical of that shown in Fig. 3 and a citric acid activator greater than 50 to about 200 seconds, an addition of about 0.15 - 0.20%, based on the weight of magnesium oxide.

In its broadest aspect, the present invention provides a method for producing silicon steel material in the form of tape and sheet metal with a magnetic permeability greater than 1850 at 796 A / m, including the steps of achieving a cold rolled, charred silicon steel material in the form of strip or sheet metal containing about 2 - 4% silicon and about 0.01 - 0.065% acid soluble aluminum, applying to the surfaces of the material an aqueous containing slurry consisting of magnesium oxide, at least one boron compound, and up to 20% by weight of titanium dioxide (based on magnesium oxide), drying of the sludge so applied to form a dried coating, and to expose it be- 1 laid the material for a ready annealing at high temperature, for é to thereby form a glass film and to induce in the material á in cube-on-edge orientation by secondary recrystallization, and proportioning of the total boron content within a range of 0.07 - 0.3% by weight, based on the weight of magnesium oxide, in one with particle size distribution and citric acid activity of the magnesium oxide, thereby achieving improvement in the .msmmwm fi sæmmmms Éi fi., »Xt the loss properties while obtaining a very high ethical permeability of the material. 07805120-s l¿V: fl l 1.0 Preferably, the final annealing is carried out at high temperature in a reducing atmosphere at a temperature of approx 1095 - 12 ° C, over a period of up to 30 hours. nen preferred silicon steel composition, in cold rolled and decarburized condition, consists essentially of, in% by weight, about 2 - 4 8 silicon, § about 0.01 - 0.15% manganese, about 0.002-% - 0.005 8 carbon, about : U 0.01 - 0.03% sulfur, about 0.005 - 0.010% nitrogen, about 0.010 - 0.065% acid-soluble aluminum, and raised iron with driver- g ; .._. . É ä » 5% * F nings. ¿ 1.L, ', -: "" -r 0 wvgg:' ~., ¿-.__ ;. ,

Claims (10)

É; ,, 0 7sos12o # s Patentkrav Ways to improve the core loss properties of cube-on-edge oriented silicon alloy steel in the form of strip and sheet material L) which will have a magnetic permeability greater than 1850 É at 796 Alm after a final high temperature annealing in a reducing atmosphere, which involves adding a boron compound to aqueous magnesium oxide slurry in the range of f0.07% to 0.30% based on the weight of the magnesium oxide, applying the slurry to the surfaces of the material and drying the coating so applied before final annealing, known as by adding the boron compound in inverse proportion to the bulk density of the dried coating. A method according to claim 1, comprising the steps of applying the water slurry to cold reduced, decarburized silicon alloy steel in strip or sheet form containing from 2% to 4% silicon and from 0.01% to 0.065% in acid soluble aluminum, wherein the slurry also contains up to 20% by weight of titanium dioxide based on the weight of the magnesium oxide and subjecting the coated material to a final annealing at high temperature, characterized in that the total boron content of the slurry is proportioned according to the particle size distribution and the magnesium oxide citric acid. 0 activity. 3. A method according to claim 1 or 2, characterized in that the silicon steel strip material consists essentially of 2 - 4% silicon, 0.01 - 0.15% manganese, 0.002 - 0.005% carbon, 0.01 - 0.03 sulfur, 0.005 - 0.010% nitrogen, 0.010 - 0.065% acid-soluble aluminum, and residual iron with impurities. 4. A method according to claim 1 or 2, characterized in that the slurry is applied to an extent sufficient to achieve a dried additive growth of 6.3 - 15.65 g / m 2, and that the citric acid activity of the magnesium oxide is greater than SO seconds. 5. A method according to claim 1 or 2, characterized in that boron is added with 0.10 - 0.15 3, based on the weight of magnesium oxide, when the citric acid activity is from greater than SO to about 120 seconds, and when the particle size distribution of the magnesium oxide is from 75 to 90 S less than 1 micron. 6. A method according to claim 1 or 2, characterized in that boron is added with 0.10 - 0.15 S, based on the weight of magnesium oxide, when the citric acid activity of the magnesium oxide is from greater than 50 to about 120 seconds, and when The size distribution thereof is as follows: 0 - 5% between 5 and 10 microns 5 - 10% between 5 and 2 microns S - 10% between 2 and 1 microns 75 - 90% less than 1 micron. A method according to claim 1 or 2, characterized in that boron is added with 0.15 - 0.20%, based on the weight of magnesium oxide, when the citric acid activity is from greater than 50 to about 200 seconds, and when the particle size distribution of magnesium oxide is from 80 to 90% between 2 and 5 microns. A method according to claim 1 or 2, characterized in that boron is added with 0.15 - 0.20%, based on the weight of magnesium oxide, when the citric acid activity of the magnesium oxide is from greater than 50 to about 200 seconds, and when The size distribution thereof is as follows: 0 - 5% between 5 and 10 microns 80 - 90% between 5 and 2 microns 10 - 20% between 2 and 1 microns 0% less than 1 micron. 9. A method according to claim 1 or 2, characterized in that the slurry contains S-20% titanium dioxide, based on the weight of magnesium oxide. 10. A method according to claim 1 or 2, characterized in that the surface area of the magnesium oxide is 10 - 20 m2 / g.