Method for producing a grain-orientated electric strip

Abstract

The invention relates to a method for producing a grain-orientated electric steel which is coated with a phosphate layer and in which there is applied to the electric steel a phosphate solution which contains a colloid component and at least one colloid stabilizer (A) and/or at least one pickling inhibitor (B), the phosphate solution containing at least one compound which has chromium in the oxidation stage III (chromium (III) compound). Grain-orientated electric steel produced with the method according to the invention is distinguished by excellent optical properties and a high tensile stress.

Claims

1. A method for producing a grain-orientated electric steel which is coated with a phosphate layer, the method comprising applying to the electric steel a phosphate solution, wherein the phosphate solution comprises: a phosphate component; a colloid component; a colloid stabilizer and a pickling inhibitor; and at least one compound comprising chromium (III), which is soluble in the phosphate solution, wherein the phosphate solution comprises less than about 0.2% by weight of hexavalent chromium, and wherein the phosphate solution has a pH of less than about 3, and wherein the colloid stabilizer comprises at least one of a phosphoric acid ester and a phosphonic acid ester, and wherein the pickling inhibitor is selected from the group consisting of a thiourea derivative, a C2-10-alkynol, a triazine derivative, thioglycolic acid, a C1-4-alkylamine, a hydroxy-C2-8-thiocarboxylic acid, a fatty alcohol polyglycol ether, diethylthiourea, prop-2-in-1-ol, butin-1,4-diol, hexamethylenetetramine, and any combination thereof.

2. The method of claim 1, wherein the compound comprising chromium (III) comprises a chromium (III) salt.

3. The method of claim 2, wherein the chromium (III) salt is selected from the group consisting of chromium (III) nitrate, chromium (III) chloride, chromium (III) sulphate, chromium (III) acetate, chromium (III) sulphonate, and any combination thereof.

4. The method of claim 1 wherein the compound comprising chromium (III) is present in a quantity selected from about 0.2% to about 30% by weight, from about 5% to about 20% by weight, or from about 8% to about 15% by weight, with respect to the overall weight of the phosphate solution.

5. The method of claim 1 wherein the phosphate solution comprises less than about 0.1% by weight of hexavalent chromium.

6. The method of claim 1, wherein the colloid stabilizer comprises a phosphoric acid ester.

7. The method of claim 1, wherein the phosphoric acid ester is selected from the group consisting of monoethylphosphate, diethylphosphate, and any combination thereof.

8. The method of claim 1, wherein the phosphate solution further comprises a wetting agent.

9. The method of claim 8, wherein the wetting agent comprises a fluorosurfactant.

10. The method of claim 9, wherein the fluorosurfactant comprises tetraethyl ammonium perfluorooctane sulphonate.

11. The method of claim 1, wherein the colloid stabilizer is present in a quantity of from about 0.001% to about 20% by weight with respect to the overall weight of the phosphate solution.

12. The method of claim 1, wherein the pickling inhibitor is present in a quantity of from about 0.001% to about 10% by weight with respect to the overall weight of the phosphate solution.

13. The method of claim 8, wherein the wetting agent is present in a quantity of from about 0.0001% to about 5% by weight with respect to the overall weight of the phosphate solution.

14. The method of claim 1, wherein the phosphate component comprises aluminum phosphate, magnesium phosphate, or a combination thereof.

15. The method of claim 1, wherein the phosphate solution has a pH of between about 1 and about 2.

16. The method of claim 1, further comprising burning the electric steel at a temperature of more than about 800 C.

17. A method for producing a grain-orientated electric steel which is coated with a phosphate layer, the method comprising applying to the electric steel a phosphate solution, wherein the phosphate solution comprises: a) aluminum phosphate, magnesium phosphate, or a combination thereof; b) colloidal silica dioxide; c) monoethylphosphate, diethylphosphate, or a combination thereof; d) a thiourea derivative, a C.sub.2-10-alkynol, a triazine derivative, thioglycolic acid, a C.sub.1-4-alkylamine, a hydroxy-C.sub.2-8-thiocarboxylic acid, a fatty alcohol polyglycol ether diethylthiourea, prop-2-in-1-ol, butin-1,4-diol, hexamethylenetetramine, or any combination thereof; e) a fluorosurfactant; and f) a compound comprising chromium (III) which is soluble in the phosphate solution.

Description

Example 1: Effect of Chromium Nitrate in the Phosphate Solution on the Chemical Interaction

(1) The following phosphate solutions were prepared.

(2) TABLE-US-00004 TABLE 4 With With chromium chromium (III) Without (III) nitrate and Solution component chromium nitrate DETH Monoaluminium phosphate g 90 90 90 solution 50% Silica sol 30% g 110 110 110 Diethylthiourea g 0.06 Chromium (III) nitrate g 24 24

(3) Phosphate/silica sol admixtures without Cr (VI) and without pickling inhibitor according to WO 2009/101129 show a clearly marked interaction with free iron surfaces. Owing to the addition of chromium (III) nitrate, an again clearly increased interaction is produced. The combination of the additives chromium (III) nitrate and diethylthiourea (DETH) leads to a clear inhibition of the chemical interaction.

(4) The inhibition of the chemical interaction enables use in industrial coating plants since the contamination of the phosphating solution with iron ions is prevented.

(5) FIG. 10 illustrates the effect of Cr (III) nitrate and DETH on the pickling reaction with iron surfaces.

Example 2: Effect of Chromium Nitrate in the Insulation Solution According to the Invention on the Colloid Stability

(6) In order to clarify the advantages according to the present invention, the following phosphate solutions were prepared.

(7) TABLE-US-00005 TABLE 5 Solutions Solution component 1 2 3 4 5 Monoaluminium phosphate g 150 150 150 150 150 solution 50% Silica sol 30% g 183 183 183 183 183 Water g 22.5 10 12.5 22.5 Chromium trioxide g 7.7 Diethylthiourea g 0.1 0.1 Ethylphosphate g 12.5 12.5 Chromium (III) nitrate g 40 40

(8) The insulation solutions were subjected to a measurement of the time development of the viscosity at 50 C. FIG. 11 shows the results.

(9) The insulation solution with chromium (VI) has very good solution stability. The omission of the chromium (VI) compound without any replacement (solution 1) leads to a drastic impairment of the solution stability, which makes use in industrial production processes impossible. The replacement of chromium (VI) with chromium (III) also leads to an impairment of the solution stability. Such solutions are as unsuitable in practice as the solution 1. However, if chromium (III) is used in a solution which contains a colloid stabiliser (A), the solution stability is retained. Such solutions are suitable for industrial production processes.

Example 3: Effect of Chromium Nitrate in the Phosphate Solution on the Tensile Stress

(10) Owing to the burnt-in insulation layer, a tensile stress is intended to be transmitted to the ferromagnetic base material and is intended to have a positive influence on the domain structure and further lowers the magnetisation reversal loss.

(11) In order to demonstrate the advantages of the insulation solution according to the invention, the following solutions were prepared.

(12) TABLE-US-00006 TABLE 6 Solutions Solution component 1 2 3 Monoaluminium phosphate g 150 150 150 solution 50% Silica sol 30% g 183 183 183 Water g 40 40 14 Diethylthiourea g 0.1 0.1 Ethylphosphate g 12.5 12.5 Chromium (III) nitrate g 40 Chromium (VI) oxide g 14

(13) The solutions were applied to GO electric steel samples of the size 305 mm60 mm and burnt-in at 850 C. for 2 minutes. The layer application in the burnt-in state was in all cases 3.5 g/m.sup.2. Subsequently, the tensile stress test was carried out. FIG. 12 summarises the results.

Example 4: Influence of Chromium (III) Nitrate in the Phosphate Solution on the Layer Appearance

(14) The following phosphate solutions were prepared.

(15) TABLE-US-00007 TABLE 7 According to WO 2009/ the invention 101129 Solution component 1 2 Monoaluminium phosphate g 150 150 solution 50% Silica sol 30% g 183 183 Water g 40 40 Diethylthiourea g 0.1 0.1 Ethylphosphate g 12.5 12.5 Chromium (III) nitrate 40

(16) The solutions were applied to GO electric steel samples with glass film and burnt-in for approximately 2 minutes at 850 C. The layer appearance was subsequently evaluated (cf. FIG. 13).

(17) The layer appearance of the insulation according to the invention clearly shows more brilliance than that according to WO 2009/101129. The layer appearance of the insulation according to the invention can no longer be differentiated from an insulation which was produced using hexavalent chromium (VI).

Example 5: Effect of Chromium Acetate in the Phosphate Solution on the Tensile Stress

(18) Owing to the burnt-in insulation layer, a tensile stress is intended to be transmitted to the ferromagnetic base material, and is intended to have a positive effect on the domain structure and further lowers the magnetisation reversal loss.

(19) In order to demonstrate the advantages of the phosphate solution used in the method according to the invention, the following solutions were prepared.

(20) TABLE-US-00008 TABLE 8 Solutions Solution component 1 2 3 Monoaluminium phosphate g 150 150 150 solution 50% Silica sol 30% g 183 183 183 Water g 40 40 14 Diethylthiourea g 0.1 0.1 Ethyl phosphate g 12.5 12.5 ChromdlO-Acetate g 15 Chromium (VI) oxide g 14

(21) The solutions were applied to GO electric steel samples of the size 305 mm60 mm and burnt-in at 850 C. for 2 minutes. The layer application in the burnt-in state was in all cases 3.5 g/m.sup.2. Subsequently, the tensile stress test was carried out. FIG. 14 summarises the results.

(22) Using chromium (III) acetate, the tensile stress transmitted to the base material is influenced in a positive manner with respect to the chromium-free insulation but the effect is substantially less pronounced than that of chromium (VI).

Example 6: Effect of Chromium Chloride in the Insulation Solution According to the Invention on the Tensile Stress

(23) In order to demonstrate the advantages of the phosphate solution used in the method according to the invention, the following solutions were prepared.

(24) TABLE-US-00009 TABLE 9 According to Reference the invention Solution component 1 2 Monoaluminium phosphate g 150 150 solution 50% Silica sol 30% g 183 183 Water g 40 40 Diethylthiourea g 0.1 0.1 Ethyl phosphate g 12.5 12.5 Chromium (III) Chlond g 80

(25) The solutions were applied to GO electric steel samples of the size 305 mm60 mm and burnt-in at 850 C. for 2 minutes. The layer application in the annealed state was in all cases 3.5 g/m.sup.2. Subsequently, the tensile stress test was carried out. FIG. 15 summarises the results.

(26) From the chromium (III) chloride, there is obviously the same effect on the layer appearance as with chromium (III) nitrate and hexavalent chromium (VI) (cf. FIG. 16). However, when chromium (III) chloride is used, considerable layer defects occur which can probably be attributed to the acid residue of the relevant salt. Chromium (III) chloride can thus be used to achieve the objective. Advantageously, the entire solution system is then specifically tailored thereto (type of pickling, inhibition, etc.).

Example 7: Effect of Chromium (III) Sulphonate in the Phosphate Solution on the Tensile Stress

(27) In order to demonstrate the advantages of the phosphate solution used in the method according to the invention, the following solutions were prepared.

(28) TABLE-US-00010 TABLE 10 According to Reference the invention Solution component 1 2 Monoaluminium phosphate g 150 150 solution 50% Silica sol 30% g 183 183 Water g 40 40 Diethylthiourea g 0.1 0.1 Ethyl phosphate g 12.5 12.5 Chromium (III) sulphonate g 50

(29) The solutions were applied to GO electric steel samples of the size 305 mm60 mm and burnt-in at 850 C. for 2 minutes. The layer application in the burnt-in state was in all cases 3.5 g/m.sup.2. Subsequently, the tensile stress test was carried out. FIG. 17 summarises the results.