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(11) | EP 0 074 715 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method for producing oriented silicon steel having improved magnetic properties |
| (57) An improvement in the manufacture of oriented silicon steel to improve the magnetic
properties, and specifically to achieve improved core loss; the improvement comprising
removing as by acid pickling at least 3.3 µm from each surface of said steel and normalizing
said steel to effect decarburization prior to final texture annealing. |
[0001] The present invention relates to a method for producing oriented silicon steel having improved magnetic properties and particularly improved core loss.
[0002] Oriented silicon steel in the form of sheets is known for use in various electrical applications, including the manufacture of transformer cores. The steel is produced by hot-rolling followed by cold-rolling with or without.intermediate annealing. Normalizing treatments are then conducted during which both decarburization and recrystallization are achieved. The steel is then conventionally coated and texture annealed. With oriented silicon steel after final texture annealing the alloy is characterized by a secondary recrystallization texture in the (110) (001) position, which is termed the cube-on-edge orientation. This alloy in sheet form has a single 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 desirably has reduced core loss, because the consumption of electrical energy decreases as core loss decreases. Reduced core loss may be promoted by achieving improved cube-on-edge orientation or grain structure, which in turn results in improved magnetic properties, specifically improved core loss.
[0003] It is accordingly an object of the present invention to provide a method whereby oriented silicon steel may be provided with an improved orientation with regard to the secondary grain or crystal structure after texture annealing, which achieves reduced core loss.
[0004] The present invention provides a method for producing oriented silicon steel characterized by improved core loss, including the steps of hot-rolling, cold-rolling with intermediate annealing, normalizing and final texture annealing, wherein at least 3.3µm is removed from each surface of said steel after cold-rolling and prior to normalizing said steel.
[0005] The invention will be more particularly described with reference to the accompanying drawings, in which:-
Figure 1 is a schematic representation of specific examples of the practice of the present invention;
Figure 2 is a curve showing the permeability achieved with respect to the specific examples set forth in Figure 1; and
Figure 3 is a curve showing the core loss determinations with respect to the specific examples of Figure 1.
[0006] In accordance with the invention it was determined better oriented secondary grains are produced in the interior of a strip as opposed to the surface portions thereof. In accordance with the practice of the invention it was determined that, and as will be shown by specific examples hereinafter, if oriented silicon steel is subjected to an operation such as acid pickling to remove at least 3.3µm from each surface of the steel after cold-rolling and prior to normalizing and final texture annealing the surface portion thereof will be characterized by an improved secondary recrystallization or grain orientation which is the substantial equivalent of that typically occurring in the interior of the strip. This removal operation is performed by acid pickling and preferably by the use of a hydrochloric acid solution.
[0007] By way of a specific example to demonstrate the invention samples of oriented silicon steels of the following compositions were employed:-
Samples in the form of strips of the above compositions were processed to determine the effect of surface removal brought about by pickling on the final magnetic properties after texture annealing. The processing sequences for these samples are set forth in Figure 1. As may be seen from this Figure 1 samples of the steel were subject to pickling before, after and between final normalizing steps. In Figure 1 the symbols N, Q and P indicate the following treatments:
N = Normal final normalizing cycle, 802°C (1475°F), 152.4 (6 in)/min., in 80N2/20H2 at 10°C (50°F) d.p.
Q = Quick heat to 982°C (1800°F) for 1 min. in 80N2/20H2 at 10°C (50°F)d.p.
P = Pickle in 50% HC1, removing about b mil. from each side of strip.
[0008] Prior to texture annealing all the sample strips were coated with MgO + .75%B and thereafter final texture annealed in H2 at 1177°C (2150°F). The magnetic properties of the samples after final texture annealing with respect to permeability and core loss are set forth in Figures 2 and 3, respectively. The number after each data point in Figures 2 and 3 represents the calculated gauge of the strips. By way of comparison with conventionally processed material not subjected to pickling in accordance with the examples set forth in Figure 1, the permeability and core loss data for conventionally processed materials are set forth in Table I.. The material of Table I is of the same composition as that subjected to the testing as reported in Figure 1 and likewise was similarly coated after a similar normalizing treatment and prior to texture annealing.
[0009] From the magnetic property data presented in Figures 2 and 3, when compared with the Table I data for conventionally processed material, it is evident that pickling in accordance with the invention prior to final normalizing results in an appreciable improvement in magnetic properties after texture annealing. More specifically, the treatment for the samples as set forth in Figure 1 designated at P + Q treatment yields the lowest core loss; whereas, the sample subjected to the N + P treatment produces the highest core loss. The N + P treatment samples with respect to core loss approximate the core loss values achieved with conventional processing, absent a pickling treatment, as may been seen form the Table I data.
1. A method for producing oriented silicon steel characterised by improved core loss,
including the steps of hot-rolling, cold-rolling with intermediate annealing, normalizing
and final texture annealing, characterised in that at least 3.3µm is removed from
each surface of said steel after cold-rolling and prior to normalizing said steel.
2. A method according to claim 1, characterised in that at least 3.3µm is removed
from each surface of said steel by acid pickling.
3. A method according to claim 2, characterised in that said pickling is performed
by the use of an HCl solution.