METHOD FOR PRODUCING ORIENTED SILICON STEEL HAVING IMPROVED MAGNETIC PROPERTIES

METHODE DE PRODUCTION DE L'ACIER SILICIEUX ORIENTE A PROPRIETES MAGNETIQUES ACCRUES

English Abstract

METHOD FOR PRODUCING ORIENTED SILICON STEEL HAVING
IMPROVED MAGNETIC PROPERTIES

Abstract of the Disclosure


An improvement in the manufacture of oriented
silicon steel to improve the magnetic properties, and
specifically to achieve improved core loss; the improvement
comprises removing at least 3.3µ? from each surface of said
steel and normalizing said steel to effect decarburization
prior to final texture annealing.


* * * * *

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 is desirable to have reduced core loss, because the
consumption of electrical energy decreases as core loss decreases.

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Claims

1. In 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, the
improvement comprising removing at least 3.3µ? from each
surface of said steel after cold-rolling and prior to
normalizing said steel.


2. The method of claim 1 wherein at least 3.3µ?
is removed from each surface of said steel by acid pickling.


3. The method of claim 2 wherein said pickling
is performed by the use of an HC1 solution.
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Description

~L 1006


1 METHOD FOR PRODUCING ORIENTED SILICON STEEL HAVING
IMPROVED MAGNETIC PROPERTIES

Abstract of the Disclosure

An improvement in the manufacture of oriented
silicon steel to improve the magnetic properties~ an
specifically to achieve improved core 105s; the improvement
comprises removing at least 3O3~t~ from each surface of said
steel and normalizing said steel to effect decarburization
prior to final texture annealing.

1 0

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 inlthe direction of
rolling. In applications for this material and specifically
when used in the manufacture of transformer cores the
material is desirable to have reduced core loss, because the
consumption of electrical energy decreases as core loss decreases.

3~



1 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.

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, whi.ch achieves reduced core loss~

This and other objects of the invention, as well
as a more complete understanding thereof, may be obtained
from the following description, specific examples and
drawings, in which:

Figure 1 is a sc~ematic representation of specific
examples of the practice of the invention;

Figure 2 is a curve showing the permeability
achieved with respect to the specific examples set forth in
Figure l; and

Fiyure 3 is a curve showing the core loss
determinations with respect to the specific examples of
Figure 1.

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

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1 examples hereinafter, if oriented silicon steel is subjected
to an operation such as acid pickling to remove at least
3.3~ 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 preEerably by the use of a
hydrochloric acid solution.


By way of a specific example to demonstrate
the invention samples of oriented silicon steels of the
following compositions were employed:


Heat C Mn S Si Cu B Nz
__
494 030 034 020 3.12 .35 .0011 .0043
495 043 035 020 3.24 .34 .00~4 .00~9


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 l. As may be seen from this
Figure 1 samples of the steel were subject to pickling
beforet after and between final normalizing steps. In
Figure l the symbols N, Q and P indicate the following

treatrnents:


N = Norma:L final normalizing cycle, 1475F, 6 in./min.
in 80N2/20H2 at 50F d.~.
Q = Quick heat to 1800F for l min. in BON2/20H2
at 50F dopo

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3~


1 P = Pickle in 50~ HCl, removing about 1/2 mil. from
each side of strip.

Prior to texture annealing all the sample ctrips
were coated with MgO + .75%B and thereafter final texture
annealed in H2 at 2150F. 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 calculaterd gauge of the strips, By
way of comparison with conventionally processed material no~
subjected to pickling in accordance with the examples set
forth in Figure l; 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 kexture annealing.

TABLE I

Heat # Final Norm. Cycle Coating 10H WPP 17KB
14S4~4 1475~F,/6l' min., Mag5 + .8~B 1890 .711
80N2/20H2 at 60F d.p.
148495 1475F,/5" min., MagS ~ .8~B 1897 ~681
80N2/20H2 at 60F d.p.

F'rom the magnetic properky data presented in
Figures 2 and 3, when compared with the Table I data Eor
conventionally processed material, it is evident that
pickling in accordance with the invention prior to final
normalizing results in an appreciable improvement in

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~$q~ 3~


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 be seen from the Table I
data.
We claim: