METHOD FOR PRODUCING CUBE-ON-EDGE ORIENTED SILICON STEEL

Abstract: An improvement in the manufacture of cube-on-edge oriented silicon steel; the improvement comprises normaliz­ ing said steel followed by cold deformation prior to final texture annealing, whereby reduced watt loss is achieved.

Description: METHOD OF PRODUCING CUBE-ON-EDGE ORIENTED SILICON STEEL This invention relates to a method of producing cube-on-edge oriented silicon steel. Cube-on-edge oriented silicon steel, in the form of sheets, is known for use in various electrical applications, including the manufacture of transformer cores. With cubeon-edge silicon steel - the alloy is characterized by secondary recrystallization in the (110) (001) position, which is termed the cube-on-edge position. This material in sheet form has the direction of easy magnetization in the direction of rolling. In applications for this material, and specifically when used in the manufacture of transformer cores, the material is required to have reduced watt loss, because the consumption of electrical energy decreases as iron loss decreases. Reduced watt loss may be promoted by achieving fine secondary grain size during texture annealing. It is accordingly an object of the present invention to provide a method whereby cube-on-edge silicon steel may be provided with a fine secondary grain or crystal structure after texture annealing, which achieves reduced watt loss. The present invention provides a method of producing cube-on-edge oriented silicon steel, characterized by reduced watt loss, including the steps of hot-rolling, coldrolling with intermediate annealing and a final texture annealing which comprises normalizing said steel to effect decarburization and primary recrystallization followed by cold-deformation prior to said final texture annealing. With respect to cube-on-edge silicon steel to which the present invention is directed, this steel is conventionally processed by hot rolling followed by one or more cold rolling operations with intermediate anneals. After cold rolling the steel is subjected to a normalizing operation to achieve primary recrystallization and decarburization. Typically, normalizing is conducted at temperatures within the range of 704 to 8710C (1300 to 16000F). In accordance with the invention, after normalizing the steel is subjected to cold deformation as by a cold-rolling operation. After cold deformation, the steel is final texture annealed in the conventional manner to achieve secondary recrystallization. It has been found that by cold deforming in accordance with the invention following normalizing and prior to texture annealing secondary grain growth is inhibited during final texture annealing, which results in reduced watt loss. For this purpose, cold rolling to achieve an elongation within the range of 5 to 15% has been found to be effective for the purpose. It has been found that by varying the amount of cold reduction the grain size after texture annealing may be regulated. Although the practice of the invention finds utility with cube-on-edge silicon steels generally it is particularly adapted to steels of this type within the following composition limits in percent by weight: Steel Mn C S Si B Fe SX-14 .025-.045 .020-.060 .005-.040 2.70-3.50 .0005-.0030BaL SX-ll .050-.080 .020-.060 .020-.035 3.00-3.70 - BaL By way of specific example two heats of the alloy identified SX-14 (Heat Nos. 154684 and 153595) were melted to the following composition in percent by weight: Heat No Mn S C Si B Fe 154684 .036 .019 .028 3.21 .0011 Balance 153595 .038 .020 .025 3.25 .0013 Balance This material was processed in the conventional manner by hot rolling followed by a cold-rolling operation. Then it was subjected to a final normalizing treatment comprising continuous annealing at a temperature of 8000C (14750F) which served to decarburize the steel and effect primary recrystallization. The normalized steel in strip form was cut to lengths suitable for cold rolling and rolled in a 4high cold rolling mill at ambient temperature. The extent of plastic deformation was determined by measuring the percent elongation over a 610mm (24") span scribed on the steel strip before cold rolling. For control purposes samples of the steel were retained prior to cold rolling. The material was cut into standard Epstein strip samples and roller coated with a water slurry of MgO+ .75%B. Texture annealing was performed in dry hydrogen. The anneal cycle consisted of charging the steel into a furnace at 14000F (7600C), heating at 500F (280C) per hour to 21500F (1175 C), holding 20 hours at 21500F (11750C) and furnace cooling. Magnetic testing and grain size measurements were made after this texture annealing operation. Table I lists the magnetic properties and grain size of the material tested. TABLE I MAGNETIC PORPERTIES AND GRAIN SIZE (SX-14) Elonga- Gauge WPP W/KG # at B &commat; Grain tion Mils &commat; &commat; 10 Oe 796 A/m Size Heat Code in % (mm) 17KG 1.7T in G/Oe in T in mm 153595 A 0 13.1 .759 1.67 1913 1.91 16 (control) (.33) B .5 13.2 .777 1.71 1903 1.90 12 (.33) C 1.3 13.1 .773 1.70 1893 1.89 8 (.33) D 3.1 12.8 .796 1.76 1831 1.83 3 (.33) E 4.7 12.8 .877 1.93 1788 1.79 3 (.33) F 17.7 11.4 - - 1442 1.44 Mixed (.29) 154684 A 0 10.3 .683 1.51 1928 1.93 14 (control) (.26) B .5 10.5 .717 1.58 1866 1.87 5 (.27) C 1.5 10.1 .736 1.62 1842 1.84 4 (.26) D 3.7 10.1 .820 1.81 1774 1.77 2 (.26) E 4.6 9.9 .988 2.18 1678 1.68 1 (.25) F 8.1 9.6 1.30 2.89 1519 1.52 .4 (.24) The method of the present invention reduces both the permeability at high induction levels and the size of the grains formed during final texture annealing. The current trend in electrical steel usage is toward lower inductions and significant improvements have been made in lowering core losses or watt losses by reducing the sheet thickness. Commercially available material typically ranges from .014 to .011 inch (.35 to .28mm), and may be .009 inch (.23mm) and lower. As such materials are used at lower inductions, of the order of 15 kilogauss or lower, the reduction in permeability at high inductions becomes less important in electrical equipment. Also, as the sheet thicknesses are reduced, core losses arising from eddy currents appear to be more dependent upon the material grain size, i.e., core losses decrease with decreasing grain size. The advantages of the present invention establish that it is of substantial importance in the manufacture of thin sheet, of the order of less than .015 inch to .004 inch (.38 to .lmm) thick, and suitable for use in transformers.

Claims: CLAIMS 1. A method of producing cube-on-edge oriented silicon steel, characterized by reduced watt loss, including the steps of hot-rolling, cold-rolling with intermediate annealing and a final texture annealing, characterized in normalizing said steel to effect decarburization and primary recrystallization followed by cold-deformation prior to said final texture annealing. 2. A method according to claim 1, characterized in that said cold-deformation includes at least one coldrolling operation. 3. A method according to claim 2, characterized in that said cold-rolling operation effects an elongation of said steel within the range of 5 to 15%. 4. A method according to claim 1, 2 or 3, characterized in that the steel is normalized at a temperature 'within the range of 704 to 8710C (1300 to 16000F). 5. A cube-on-edge oriented silicon steel of less than 0.38mm (0.015-inch) thick made in accordance with the method of any one of claims 1 to 4.

Inventors: MILLER, ROBERT FREDERICK
Applicants: ALLEGHENY LUDLUM STEEL CORPORATION
Application year: 1983
Main classification: C21D8
IPC codes: C22C38, H01F1, C21D8