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Патент USA US2412041

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2,412,041
Patented Dec. 3, 1946
6
UNITED STATES PATENT, OFFICE
2,412,041
PROCESS FOR FLATTENING SILICON
STEEL SHEETS
Carl E. Gi?z‘ord, Zanesville, Victor W. Carpenter,
Franklin, and Lowell L. Cook, Zanesville, Ohio,
assignors to The American Rolling Mill Com
pany, Middletown, Ohio, a corporation of Ohio
No Drawing. Application March 28, 1941,
Serial No. 385,756
10 Claims.
(Cl. 148-12)
2
1
' have not come into wide commercial usage due
There has been recently a considerable tight
ening in the requirements for ?atness in sheets
of electrical steel. It will be understood that the
?atness characteristics of magnetic sheet metals
vary considerably in accordance with the mode
of manufacture of the sheets, so that diiferent
standards of ?atness have been thought to apply
to differently processed materials. While cold re
duced strip has been developed to the point where
to their resulting in a material of extremely poor
?atness. It was hitherto supposed that the only
way of increasing the ?atness characteristics of
materials poor in these respects was by giving
them a carefully controlled box anneal. Even
here, however, the ?atness characteristics were
not fully satisfactory, and furthermore it is not
always desirable, either from the standpoint of
it is commonly quite ?at, light gage, hot rolled 10 resultant magnetic and physical characteristics
or from the standpoint of economy, to conclude
sheets are at best somewhat wavy and conse
certain manufacturing processes with a box an
quently are at a commercial disadvantage for
neal.
'
some applications.
We have discovered that under certain circum
It is an object of our invention, therefore, to
provide a means whereby the ?atness character 15 stances an open annealing treatment may be
caused to effect a marked improvement in the
istics of hot rolled sheets may be usefuly im
proved. While the degree of improvement will
vary somewhat with the ?atness of materials be
fore they have been given our treatment, it is
?atness characteristics without involving undue
expense; that our treatment, where desired, may
be practiced upon otherwise ?nished materials
forth above, an object of this invention to pro
vide a treatment which will impart ?atness char
acteristics substantially equal or better than the
best ?atness hitherto produced, to this material
hitherto characterized by notable lack of ?at 25
magnetic characteristics; and that where an open
annealing treatment is desired as part of the
processing treatment of the steel for the sake of
other characteristics (such as ductility, magnetic
characteristics and the like), the open annealing
for the production of these desired results can
nevertheless, following the general object set 20 without impairing their previously developed
ness, i. e. materials hot rolled to gauge.
It is an object of our invention to provide a
be so carried on as to respond to the invention
herein set forth without diminishing its e?ective
?atness treatment which in itself is not only rela
tively inexpensive, but which may be practiced
upon magnetic materials without impairing the 30
magnetic characteristics previously developed
materials while they are subject to a_ controlled
tension, greatly enhanced ?atness will be the re
sult without detriment to the materials in any
way. While it is possible, it would be very dif
?cult and costly to tension single hot rolled sheets
therein by other treatments. Further it is an
object of our invention to provide a treatment
which is capable, in some modes of manufacture,
of being substituted for a ?nal heat treatment
for the production of magnetic characteristics.
In this way further economies may be effected,
as will be set forth hereinafter.
Our invention has been found applicable to
all commercial grades of hot reduced electrical
steel sheets irrespective of the quantitative silicon
content, or the content of other alloying ingredi
ents, and the particular routing of the steel does
at an elevated temperature.
-
The objects set forth above, and others which
will be pointed out hereinafter or will be apparent
to one skilled in the art upon reading these speci
?cations, we accomplish bythat treatment and
process of which we shall now describe an exem
If the sheets are
carefully welded together, preferably end to end
to form a long band, the means of applying ten
siOn during a continuous annealing becomes rela
tively simple.
In forming a continuous supply from indi
vidual sheets or strips we prefer accurately to
butt weld the sheets or strips together by the
not form a limitation upon the invention herein
described.
ness for the said results.
We have found that if a heat treatment in an
open annealing furnace is carried on, on the
45 procedures and using the apparatus of the, fol
lowing patents: U. S. Letters Patents Nos.
‘2,172,080, 2,172,081, 2,219,493, 2,175,615, 2,175,616,
2,196,941, 2,282,611 and 2,254,314.
By these procedures, we secure very long lengths
60 of silicon steel characterized ‘by welds at inter
plary embodiment.
Hitherto a number of processes for the pro
duction of hot reduced silicon steel have been
proposed, which processes included an open an—
neal as a ?nal heat'treatment. Such processes 55
vals, the welds however being substantially no
thicker than the welded sheets, and being so
perfectly formed that the steel in the endless
strip is useful for'all of the purposes to which
the sheet material itself can be put, quite irre
2,412,041
3
4
spective of the position of the welds. Welded strip
hot rolled sheets is due to certain areas or sur
formed in this way, however, has not hitherto
faces being shorter than they should be, and that
the ?attening action is due to the effect of the
tension in elongating the short areas until they
been characterized by great ?atness.
Moreover, it would normally be supposed that
the strains introduced into the strip by .theweld
ing would be productive of a marked decrease in
are all the length required in a .?at sheet and the
stresses ‘set up by the lack of uniformity are
relieved.
?atness if the welded strip were subjected to an
open annealing,
An exact rule for the determination of the cor
We have found however, that
rect amount of tension to be employed to flatten
the heat treatment we can improve the ?atness 10 all wavy materials using all types of ‘annealing
apparatus cannot be arrived at on account of
to the point where it exceeds that produced by
the interplay of the many variables, but with any
a good box anneal.
given material, at any given temperature, it will
The tension required is not great. Indeed with
be within the skill of the worker in the art to
certain kinds of materials, where a fairly long
furnace is used, the desired degree of ?atness 15 select and apply an average tension which is
sufficient to give the ?atness desired without being
may be produced by the weight of the strip only,
great enough to produce longitudinal wrinkles or
the strip being supported both as it enters and
corrugations in the strip, or pulling it in two,
as it leaves the furnace. We prefer however, so
The temperature of the heat treatment to pro
to operate as to apply a positive tension to the
stripes it passes through the furnace. This is 20 duce ?atness is not at all critical; for example
by subjecting the welded strip to tension during
readily accomplished by providing feeding de
we most
In
havecases
usedthe-temperature
temperatures as
willlow
be governed
as l200° by
vices for the strip both at the entrance and at
the exit ends of the furnace and driving the feed
a consideration of the other results expected to
be produced, or desired, from the open annealing.
exit feeding device operates very slightly faster 25 Where the primary purpose of the treatment is
to produce ?atness, it is well to choose a tem
than the entrance feeding device, Pinch rolls
perature which is below the graphite solubility
may be used; and they may be driven at the re
temperature, so that the treatment ,does'not have
quired related speeds by a connecting chain or
the result of bringing the graphitic carbon into
shaft drive. In a type of open annealing furnace
currently being used ‘by us, continuous supports 30 solution. Under these circumstances, the mag
netic properties previously developed in the ma
have been eliminated, and the welded strip is
terial will not be impaired, and since there has
supported upon driven rollers spaced about two
not been a resolution of the graphitic carbon, the
feet apart. By means of synchronized pinch rolls,
treatment will not be productive of magnetic
we apply to the strip sufficient tension to keep it
ing devices in a synchronized way so that the
from sagging'to any great extent between the
aging.
interspaced supports, and such tension has been
found" suincient to produce excellent ?atness.
Such tension is obtained by operating our exit ‘
For example, when operating upon a silicon
steel containing say from 4.5 to 5.0% silicon,
which steel has already been given a high tem
rolls at a peripheral speed, usually 0.1 to 0.5%
perature box anneal for developing the required
faster than the-entrance rolls.
_
As indicated,vthe amount of tension required is
not great. The strength of the material at the
elevated temperature is low; for example, 4.5%
silicon steel has a tensile strength of about‘ 15,000
pounds per square inch at 1200’ F., 3,000 pounds
at 1500‘ F. and 1,500 pounds at 1800° F. While
more tension is required than merelythat suffi
cient to move the strip when supported substan
tially throughout its length on low friction sup
porting means, yet for some requirements the
weight of the material throughout a, fairly long
span is often su?icient. One reason we believe
‘ that the amount of tension required is relatively
low, is that this type of material at elevated tem
peratures has no de?nite yield point but begins
to creep at relatively low stresses, Consequently
the tensile strengths cited are only approximate
since the material permanently elongates some
what even with very low tension if enough time
is given.
Thus the amount of tension required will vary
with the composition and gage of the material,
'
‘
40 core loss and permeability, We carefully weld in
dividual sheets together and pass them under
tension through an open annealing furnace kept
at .1490 to 1500° F. or thereabouts, holding the
steel in the hot zone around one and one-half
minutes. Such a treatment greatly improves flat
ness while not harming the other properties of
the material and in some cases improving them.
In those cases where the carbon content is
quite low, such as when no carbide or graphite
particles are visible on microscopic examination,
much higher temperatures can be satisfactorily
used. 'Or if ?atness is the only consideration then
the maximum permissible temperature is pretty
muchdetermined by mechanical factors.
On the other hand, in processes for producing
magnetic steels, where an open anneal is desir
able for other reasons as one of the steps or as
the ?nal step of ‘a particular routing, tempera
tures appropriate to the said step may be used
60 and our ?atness attained by the use of proper
amounts of tension. For example, when operat
ing with a silicon steel of a silicon content be
low say 4.0%, which silicon steel has been de
carburized by box annealing it at an intermedi
ture. ‘ t will also vary somewhat with the degree 65 ate gauge in the presence of the hot ‘mill scale
(in accordance With the teachings of Patent
of waviness of the material -to be ?attened. ‘For
best results we have discovered that under what
2,242,334 to Carpenter) and has been reduced
ever conditions the process is used, the tension
to gauge, wecarefully weld thesheets into a strip
must be su?iciently great to permanently elongate
and givethe strip a final open annealing .under
the material slightly. For example, we common
tension at around 1500 to '2100° F. This treat
ly obtain a permanent elongation of 0.15 to 0.3%
ment not only produces the desired ?atness but
on ‘one grade of material when given our treat—
is an integral step in the production-of the de
ment.
sired magnetic properties.
While not ‘wishing to be limited .byva'ny-theory,
The tension bears a certain relation to gauge
we {believe that the zlacklo-f ?atness lofilight :ga'ge,
and temperature; ?but with ' material of any given
temperature to which the strip is heated, and the
length of time at which it is held at tempera
2,412,041
5
su?lcient to ?atten it, and produce a slight over
all elongation in the material, without producing
in the'material any detectable change in the crys
gauge, having selected a temperature for treat
ment as taught above, the skilled Worker can
then select a tension to give him the desired re
sult. As to the duration of the heat treatment,
our investigations have shown that no great hold
ing time is necessary if the material is brought
tal
orientation.
-
-
2. A process for increasing the ?atness offin
ished silicon steel in strip form, made by joining
together pieces of lesser length with transverse
butt welds, and which, in ?nished form, is char
tion of the tension. The length of time the ma
acterized by lack of ?atness, which comprises
terial is in the furnace and subjected to the tem
perature thereof will vary of course primarily with 10 bringing the material to a temperature at which
to a softening temperature during the applica
it is soft enough for the relief of strains but be
the length of the furnace and the speed of travel
low the graphite solution temperature, and sub
of the strip. The length of time it takes to
jecting the material to tension sufficient to ?at
bring material up to temperature is of course
ten it and produce therein a slight over-all elon
affected by the gauge. With silicon steel of or
dinary transformer gauges the material will usu 15 gation while at said temperature and while cool
ing said material to normal temperatures at a
ally reach temperature within one-half to one
rate slower than open cooling in air at room tem
minute. We have found it preferable not to cool
perature, without producing in the material any
the strip too abruptly as by bringing it immedi
detectable change in the crystal orientation.
ately out into the air from the hot zone.-~ We
3. The step of increasing the flatness of fin
prefer to attach to our furnaces a cooling hood 20
ished, hot rolled silicon steel sheets which com
whereby the temperature drop may be made
prises joining the sheets end to end to form a
somewhat more gradually. The atmosphere with
band, and subjecting the band to a softening
in the furnace does notaffect the ?atness, hence
temperature of the order of 1200° F., and higher,
forms no limitation on our process. The at
mosphere may be chosen in accordance with its 25 but insufficient to cause graphite solution, and
concurrently subjecting the band to tension suf
effect upon other qualities such as brightness,
ficient to increase ?atness and produce a slight
core loss, ductility and the like. We prefer to
over-all elongation in the band, without produc
use a neutral or reducing atmosphere to sub
ing in the material any detectable change in the
stantially prevent any scaling of the strip.
It will be seen that our process is much more 30 crystal orientation.
4. The step of increasing the ?atness of wavy,
hot rolled silicon sheet steel which comprises
joining sheets end to end to form a band and
subjecting the steel to a softening temperature
effective than those processes employing, for ex
ample, an open anneal and a light cold rolling
prior to a box anneal, because the products of
those processes have hitherto been characterized
by lack of ?atness. Thus where the ?atness of 35 while tensioning the band su?iciently to increase
flatness by passing the band through a continu
the product resulting from a box anneal to de
ous open annealing furnace including a cooling
velop magnetic properties is not satisfactory for
hood
and positively feeding the hand both into
a given use, the sheets may be weldedtogether
and out of the furnace at speeds interrelated to
and passed under tension through an open an
nealing furnace merely to increase their ?atness. 40 produce tension in the strip and a slight over-all
elongation therein, the value of the tension em
Again where an open anneal after a box anneal
is desired for any other purpose, the open an
nealing may be carried on at the appropriate
temperatures for these results, but under tension
in accordance with the present teachings. Yet 45
again, as where the material has, for example,
ployed being not greater than that required to
eliminate substantial sag in the material in a
span substantially equivalent to the furnace
length.
been decarburized at an intermediate gauge and
then hot rolled to ?nal gauge so that a ?nal 0pen
5. The step of increasing the flatness of wavy
silicon sheet steel which comprises joining sheets
end to end by butt welding to form a band, and
an added treatment for the speci?c purpose, or
can take the place of an annealing already a part
span substantially equivalent to the furnace
passing the band so formed through an open an
anneal is all that is required to develop its mag
netic properties, the said ?nal open anneal may 50 nealing furnace while controlling the entrance
speed of the band into the furnace and its exit
be made productive of ?atness in accordance with
speed therefrom to produce a tension and elonga
the present teachings.
tion in the band, while subjecting the band to a
The examples which we have given are not
softening temperature, the value of the tension
limiting since, as we have explained, our treat
ment for the production of ?atness can either be 55 employed being not greater than that required to
eliminate substantial sag in the material in a
length,
of the desired process for the production of the
6. A process as set forth in claim 5 in which
steel. Our treatment will thus be most generally
applied to material which has been reduced to 60 the temperature to which the silicon steel is heat
ed is above 1200“ F. but less than the graphite
?nal gauge.
‘
solubility temperature of the silicon steel.
Modi?cations may be made in our invention
7. A process as set forth in claim 5 in which
without departing from the spirit of it.
the silicon steel prior to the treatment for ?at
Having thus described our invention what we
claim as new and desire to secure by Letters Pat 65 ness is box annealed, and in which the tempera
ture to which the silicon steel is heated during
ent is:
1. A process for increasing the ?atness of ?n
ished silicon steel in strip form, made by joining
together pieces of lesser length with transverse
butt welds, and which is characterized by lack of
?atness, which comprises bringing the sheet ma
terial to a temperature at which it becomes soft
enough for the relief of strains but below the
graphite solution temperature, and while at said
temperature subjecting the material to tension
the treatment for ?atness is above 1200° F. but
somewhat less than the graphite solubility tem
perature of the silicon steel.
8. A process for ?attening silicon steel which
comprises forming silicon steel sheets character
ized by transverse waviness into a strip like sup
ply of inde?nite length and sheet gauge by butt
welding, and passing the said supply through an
75 open annealing furnace at a temperature between
2312;041
7
1200 and 1500° ,F., providing interspaced :feeding
‘10. In a process of ‘producing silicon steel in
the furnace, and operating said feeding devices
pcludingthe step of simultaneously producing the
reguiredmagnetic properties and increasing the
at di?erential speeds so related as to prevent cu
mulative sagging of the supply if it were unsup
flatness of the product, hot rolling silicon steel ‘to
an intermediate gauge, decarburizing it by box
portedin said furnace, whereby to produce a ten
sion substantially limited to the tension which
annealing it in the presence of the hot millscale,
pickling it and cold rolling it to ?nished gauge
sheets, welding said sheets end to end to form a
devices acting on the supply as it passes through
would be exerted on the vmaterial by its .own
weight if unsupported in said furnace.
'
supply of inde?nite length, passing said supply
9. A process for ?attening silicon steel which 10 through an open annealing furnace and subject
ing it therein to a temperature of between vsubcomprises forming silicon steel sheets character
stantially 1500 and substantially 2100° F. while
ized by transverse waviness into a strip like sup
.tensioning the supply to vproduce flatness therein
ply .of inde?nite length and sheet gauge by butt
by positively controlling its entrance'and exit
welding, and passing the said supply through an
open annealing furnace at a temperature of 15 speeds to substantially those differential speeds
which would be required to prevent cumulative
around 1200 to 1500° F. while subjecting the sup
sagging of the said supply under its own weight at
ply to tension limited to an amountsubstantially
the said temperatures if unsupported in the said
suilicient to compensate for sagging of the‘mate
rial under its own weight at the said temperatures
furnace.
'
CARL E. GIFFORD.
‘
if unsupported in a span of furnace length, the v20
VICTOR W. CARPENTER.
time duration of the heat treatment being of the
LOWELL-L. COOK.
order of 11/; minutes, and the heat treatment be~
,ing followed by a cooling slower than a free cool
ing in air at room temperature.
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