Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~040~160
This invention relates to lamination steel and
methods of making it, and more particularly to such lamina-
tion steel killed with sufficient silicon to impart the
desired magnetic, punching or casting properties. The
steel can be processed by a number of routings to obtain
the desired magnetic or mechanical properties and to pro-
vide a semi-processed or a fully-processed lamination steel.
The steel of the present invention has many uses.
While not intended to be limiting, it is well suited for use
in the manufacture of the magnetic parts of low horsepower
electric motors.
Heretofore, various grades of non-oriented sili-
con steel were used in the manufacture of such magnetic
parts. In recent years, however, many improvements have
been made in the decarburization of motor laminations and in
j the design of the motors themselves enabling the manufacturers
thereof to turn to ordinary plain carbon steels for the fabri-
cation of the magnetic parts. While plain carbon steel is
less expensive than non-oriented silicon steel, its magnetic
properties are not as good. For example~ greater heat losses
are generated within the plain carbon steel when magnetized.
Such heat losses are the result of hysteresis, eddy current
and anomalous losses. Eddy current losses, in particular,
are higher in carbon steel than in non-oriented silicon steel.
Heretofore, a 60 hertz core loss of 5 to 5.5 watts per pound
at 14 kilogausses in a .025 in. (0.65 mm) thick sample of
- ordinary carbon steel was considered normal for a sample
given a proper anneal by the customer and 7 watts per
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pound was considered good for a sample not annealed arter
shearing or punchine-
Prior art workers have expended much time andenergy in an attempt to improve core losses in lamination
steel Or the carbon steel type. Numerous patent~ teach the
benerit of processing with a critical amount of strain so that
critical grain growth,is obtainèd in the customer's anneal.
Examples o~ this are United States patent 2,672,429; German
patent DT 2,219,059; l~ritish patent 1,114,4l18; Canadian patents
- A ~~fe~f /~ caf"",~//0S.
~, 10 642,689 and 707,731 and Japanese-pato~Ss 4139/1965 and 8556/1963.
-, Critical ~rain growth can reduce co're loss by about 10~, but the,
process (including the customer's'anneal) must be carerully
controlled; the results can be variable; and the punched lamina-
tions must be annealed because Or the high stress level necessary ,
for critical grain growth.
In United States Patent 3,180,767, ~aston and
Carpenter teach that core loss under 5 watts per pound can be
obtained conslstently in a carbon steel or'normal melt composi-
, tion by decarburizing the pickled hot band ahead Or cold reduction
but thls process also is limited to production o~ a semi-processed
grade because it must be cold rolled in order to provide sufricien
hardness for good punchability. British Patent 1,100,771 teaches
the errects Or manganese. The manganese' level throughout the
industry has ranged rrom about .15% to approaching 1%, but ror
, 25 motor laminations it is generally over about .4%.
Silicon-killed grades have been made ror other types
applications but they normally have relatively high oxygen
contents and contain many inclusions. They have not b~en very
~, satisfactory in magnetlc applicatlons. It has been found that
3o ir motor laminatlon steel contained about .1% phosphorus and had
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a carbon content of about .06% or less, the requirements for a
decarburizing anneal practlced by the customer were less stringent
and a core loss o~ 4.5 to 5.0 watts per pound could be achieved,
and much steel Or this type has been produced by the industry,
although not in combination with a low-oxy~en, sllicon-killed
steel. German Patent 1,931,4?0 teaches vacuum degassing,
deoxidation with manganeæe and/or silicon, the use Or .05% to
.25% phosphorus, and decarburization in a process anneal.
Veoxidation with manganese or silicon does not mean that a low
total oxide or inclusion content has been achieved, even though
such deoxidation can be used to avold the rlmming actlon. The
remainin~ oxides and lnclusions act as barriers for grain growth
and for domain-wall movement.
'rhe present inventlon is dlrected to a laminatlon
steel c~laracterized by the fact that a core loss Or about
ll watts per pound can be consistently achieved in a semi-
processed grade and about 4.5 watts per pound in a fully-
processed grade. The laminatlon steel of the present invention
is quite versatile in that it may be processed b~ a number of
different routings to obtain the particular magnetic or
mechanical properties desired and, as indicated above, can
be provided to the customer in a fully-processed form or a
semi-processed rorm. As used herein and in the claims, the
term "rully processed" relates to a lamination steel which
does not require an anneal to be practiced by the customer
althouKh a stress relief anneal would improve the magnetic
propcrties and can be optionally practiced. The term "semi-
processed", as used herein and in the claims, refers to a lamina-
tion steel which does require an anneal by the customer. The
annealing Or semi-processed ~rades may or may not involve
decarburization depending upon the amount of carbon rcmoval
prior to receipt by the customer.
.
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The lamination steel of the present invention is competitive
in price with plain carbon steels used heretofore, but exhibits improved
magnetic characteristics while being cheaper than non-oriented silicon
steels. This is accomplished by reducing the number of inclusions and in-
creasing the amount of silicon as compared to that found heretofore in plain
carbon steel motor laminations. As will be explained hereinafter, the upper
limit of the silicon content is based not on metallurgical reasons but on
economic reasons to assure that the steel of the present invention is not
classified as a silicon steel and subjected to the rates and standards applied
by the industry to silicon steel.
According to the invention there is provided a steel of the
carbon steel type for magnetic uses and producible by the manufacturer in
fully-processed and semi-processed grades, said steel consisting of, in
weight percent, up to 0.1% carbon, from 0.05% to 1.0% manganese, 0.02% maxi-
mum sulfur, from 0.05% to 0.6% silicon, about 0.008% maximum nitrogen, about
0.02~ maximum oxygen, about 0.15% maximum phosphorus, the balance being iron
and those impurities incident to the mode of manufacture, said steel having
a 60 hertz core loss of about 4 watts per pound at 15 kilogausses at a thick-
ness of 0.025 inch (0.64 mm) in said semi-processed grade and a 60 hertz core
` 20 loss of about 4.5 watts per pound at 15 kilogausses at a thickness of 0.025
inch (0.64 mm) in said fully-processed grade,
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When the product of the present invention has a carbon
content greater than about 0.010%, it will be necessary for the customer
to perform a decarburizing anneal.
The process of the invention will provide either a fully-
processed lamination steel requiring no further annealing by the customer,
or a semi-processed lamination steel requiring further annealing by the
customer which may or may not involve decarburization.
According to the invention there is provided a process of
making a fully-processed grade steel of the carbon steel type having a 60
hertz core loss of about 4.5 watts per pound at 15 kilogausses at a thick-
ness of 0.025 inch (0.64 mm), comprising the steps of providing a steel
melt having in weight percent, a carbon content up to 0.1% maximum, reducing
the nitrogen content to 0.008% maximum and reducing the oxygen content to
0.01% maximum, adding to said melt from 0.05% to 1.0% manganese and from
0.05% to 0.15% phosphorus and up to 0.6% silicon, casting said steel melt,
hot rolling said steel to hot band, pickling said steel, cold rolling said
steel to strip and sheet, subjecting said steel to a heat treatment, and
reducing sait carbon content to 0.010% maximum in at least one of said melt,
sait hot band and said strip and sheet during said process.
The melt is ingot cast or strand cast, hot rolled to hot
band, pickled, cold rolled to final strip
y
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and sheet thicknesses and subjected to an anneal to develop the magnetic
properties, but leaving the strip with sufficient hardness to permit punching
into laminations.
Ordinary carbon steel, heretofore used for magnetic purposes, is
well known in the art. Such ordinary carbon steel generally has the following
analysis in weight percent:
C .06% to .08%
Mn .30% to .50%
P less than about .005%
S .025% maximum
Si under .005%
N .008% or less
O from about .03% to about .05%.
The present invention is based upon the discovery that if the above
chemistry is modified, a lamination steel can be achieved consistently having
a 60 hertz core loss of about 4 watts per pound at 15 kilogausses and at a
thickness of .025 in. if semi-processed and tested as annealed and about 4.5
watts per pound if fully-processed and tested as sheared. The core loss
values given above and hereinafter are based on tests using equal numbers of
samples cut parallel to and transversely of the rolling direction, a common
testing technique in the industry.
In accordance with the present teachings, the amount of manganese
may be raised; oxygen is removed to as low a value as possible; and the la-
mination steel is killed with sufficient silicon to impart desired magnetic,
punching or casting properties but not in an amount such as to class the steel
as a silicon steel. In its simplest form, the present invention contemplates
a steel having from less than .010% to about .1% carbon as desired, from
about .05% to about 1.0% (and preferably about .45%) manganese, about .020%
maximum (and preferably under .010%) sulfur, from about .05% up to .60%
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(and preferably about .10% to about .15%) silicon, nitrogen as low as pos-
sible (about .008% or less and preferably under about .005%), oxygen as low
as possible (about .02% or less and preferably under about .005%) and from
- residual to .15% phosphorus as desired, the balance being iron and those
impurities incident to the mode of manufacture.
In its final form, the steel should contain about .010% maxinum
carbon, and preferably less. The above noted range of .010% to .1% is given
because the carbon may be reduced to the desired .010% or less value in the
melt, during processing (before or after cold rolling) or in an anneal prac-
ticed by the customer. In some applications, the economics are such that the
customer toes not wish to practice a decarburizing anneal. In other appli-
cations, better magnetics are achieved if at least some decarburization is
practiced by the customer to achieve the desired final carbon content of
.010% or less.
If some or all of the decàrburizing is to be achieved in the melt,
it can be accomplished by vacuum degassing, as is well known in the art. If
some or all of the decarburizing is to be achieved during the steel manu-
facturer's processing of the steel, a decarburizing anneal may be performed
on the hot band after pickling or after cold rolling. If performed after
... .
cold rolling, the decarburizing anneal may constitute a part of an anneal to
achieve the desired magnetic characteristics of the steel. Decarburizing
anneals are well known in the art. An exemplary technique taught by
Carpenter et al in United States Patent 2,287,467 may be used before or
after cold rolling, subjecting the steel to an anneal at a temperature of
about 1350F in a 20%-40% hydrogen atmosphere, the balance being nitrogen, at
a dewpoint of 120F. Other atmospheres containing more or less hydrogen can
be used with higher or lower dewpoints, or the decarburizing atmosphere can
be produced by partially combusting fuel gases. The decarburization can be
carried out over a range of temperatures. Hot bands can be decarburized by
:
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annealing with the hot mill scale on the strip, as taught by Carpenter in
United States Patents 2,236,519 and 2,242,234 and by British patent 1,037,396.
However, the carbon may not be as low or as uniform as desired and the re-
; duced scale is difficult to remove by pickling.
; The silicon, added to the melt as high purity ferrosilicon, iron-
manganese-silicon alloy, or metallic silicon, is used to kill the steel and
to raise its volume resistivity, thereby improving the magnetics. The
silicon addition also reduces segregation generally obta1ned with rimmed or
capped steel
By present standards recognized in the industry and outlined in the
AISI Flat Rolled Electrical Sheet Manual, 1972 Edition (pp. 6 and 7), steels
with a silicon content greater than .60% are classed as Silicon Alloy Steels;
those having .60% or less are classed as Nonoriented Carbon Steels; and those
containing .15% or less are classed as Cold Rolled Carbon Sheet (or Motor
Lamination Steel). Each of the above classifications has its own pricing
structure. The teachings of this patent apply to any of the above classi-
fications. The upper limit of the silicon content of the steel of the present
invention is the highest possible silicon content without causing the steel to
be classified as a silicon steel and to be subject to silicon steel stan-
dards and rates (i.e. .60%), with the preferred upper limit being the .15%
of the cold rolled carbon steel sheet.
The upper silicon limit, and the preferred upper silicon limit,
are based strictly on commercial reasons. If classified as a silicon steel
the steel of the present invention could not be competitive pricewise with
motor lamination steels currently in use. There is no metallurgical reason
why more silicon could not be added and some magnetic properties might be
improved through further reduction in the eddy current and hysteresis com-
ponents of core loss.
The desired low oxygen content may be obtained in the melt by
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argon stirring or vacuum degassing, by providing the proper balance of
carbon and oxygen in the melt before degassing or stirring, and by proper
additions of aluminum or other deoxidizing agents to the ladle, all as is
well known in the art. Depending upon whether the carbon content is to be
reduced to the final desired level or some higher level in the melt, the
melt should be provided with an appropriate carbon-oxygen ratio to reduce the
carbon content as desired and the oxygen level to as low a value as possible.
In addition, other elements can be added or substituted to improve the magne-
tic properties. For example, manganese, aluminum, chromium and the like can
be added for the purpose of increasing the volume resistivity and phosphorus
may be added to increase both the volume resistivity and the hardness.
The manganese in the above given composition (as does silicon)
increases volume resistivity - i.e., reduces eddy currents and thus diminishes
core loss. Within the above given range the quantity of manganese used de
pends upon the desired magnetic characteristics of the final product. If it
is desired magnetic characteristics of the final product. If it is desired to
have a lower silicon content within the above given range, volume resistivity
can be increased by adding more manganese within the above given range and
vice versa.
As indicated above, phosphorus also increases the volume resistivity
and contributes to the hardness of the material. Again, within the above
given range the quantity of phosphorus added will depend upon the magnetic
and physical characteristics desired in the final product.
The melt can be ingot cast or strand cast. In all instances, the
steel is hot rolled to hot band and pickled in the conventional manner. From
this point on, however, variations may be made in the routing depending upon
,
the type of product desired to be received by the customer, the additional
processing steps practiced by the cutomer and the ultimate application for
the steel.
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104046(~
The following is a list of eleven exemplary routings following hot
rolling and pickling which may be practiced:
1. The steel may be decarburized in the hot band after pickling,
cold rolled and shipped to the customer in the full hard condition.
2. The steel may be decarburized in the hot band after pickling,
cold rolled, box annealed (to achieve recrystallization, relieve stresses
and soften the steel) and temper rolled.
3. The steel may be decarburized in the hot band after pickling,
cold rolled, strip normalized and temper rolled.
4. The steel may be decarburized in the hot band after pickling,
cold rolled, strip normalized and shipped for use as stamped.
5. The steel may be colt rollèd, box annealed and temper rolled
without decarburization.
6. The steel may be cold rolled, strip normalized and temper rolled
without decarburization.
7. The steel may be cold rolled, strip normalized and shipped for
use as stamped, the des~red low carbon content having been achieved in the
melt.
8. The steel may be cold rolled, strip annealed and temper rolled
with no decarburization step.
9. The steel may simply be cold rolled, strip annealed and shipped
for use as stamped. The desired low carbon content can be achieved in the
melt or additional carbon can be removed in the strip anneal.
10. The steel may simply be cold rolled and shipped.
11. The steel may be cold rolled, decarburized (by strand anneal
or open coil anneal) and temper rolled.
In rout1ngs 1, 2, 3, 5, 6, 8, 10 and 11 the customer should ~ubject
the steel to an anneal after shearing or punching to develop the magnetic
properties and to decarburize to .010% or less if not achieved in the
.
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routing or the melt.
Routings 4, 7 and 9 provide the customer with a fully-processed
product. While not required, a stress relief anneal after shearing or
punching will improve the magnetic properties.
In routings 7 and 9 low carbon is achieved in the melt. Additional
carbon can be removed in the process anneals, if desired.
In routings 5, 6, 8, and 10 decarburization may be complete in the
melt or partially achieved in the melt to reduce the decarburizing required
of the customer. Otherwise the customer must perform the entire decarburiza-
tion.
In routings 1 through 3 and 11 decarburization in the melt may
reduce the amount of decarburization required in the routing and if the
product received by the customer has a carbon content of .010% or less, no
decarburizing is required of the customer.
`~ It will be understood that in the above listed routings the steps
of hot rolling, pickling, cold rolling, box annealing, strip normalizing,
strip annealing and temper rolling are individually conventional and well
known in the art. When strip annealing best results have been achieved at a
temperature of about 1600F. As between routings 7 and 9, routing 9 is pre-
ferred, having been found to yield better all around properties due to the
lower temperature used and additional decarburization.
In any of the above routings ending with a temper roll pass, the
amount of reduction may be such as to produce critical grain growth in the
customer's anneal if desired, thereby improving the magnetic properties.
It will be understood by one skilled in the art that not all of
the above listed routings give equal results. In general, however, if the
final carbon content is .010% or less, the resultant steel will be charac-
terized by a core loss of about 4 watts per pound in a semi-processed grade
and about 4.5 watts per pound in a fu1l-processed grade. A steel is pro-
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duced which has an inclusion content sufficiently low to permit it to act as
a member of the silicon steel family, although the silicon content is such
that it cannot properly be classified as a silicon steel.
If the steel of the present invention is to be provided to the
customer in fully-processed form, i.e., if the customer desires not to have
to perform an anneal, there is a preferred chemistry for the steel. Under
these circumstances the steel should contain about .010% maximum carbon (and
preferably about .006% or lower); from about .05% to about 1.0% manganese
(and preferably about .45%), from about .05% to about .15% phosphorus (and
preferably about .10%), about .010% maximum sulfur (and preferably as low a
9ulfur content as possible), up to the largest silicon content achievable
without causing the steel to be classified as a silicon steel (and preferably
from about .10% to about .15%); about .008% or less nitrogen (and preferably
under about .005%) and about .01% or less oxygen (and preferably under about
.005%); the balance being iron and those impurities incitent to~the mode
of manufacburo.
The low carbon and low oxygen indicated above may be achieved in
the melt by vacuum degassing and by making the proper aluminum additions to
the ladle. To this end, the carbon and oxygen content of the melt is ad-
justed so that these elements combine for the maximum removal of both by the
vacu o degassing. Manganese, silicon and phosphorus are added to the melt
after the decarburization in the liquid state. The silicon is added for the
same purposes given above, i.e., primarily to improve the magnetics. Nor-
mally, if ordinary carbon steel is decarburized during plant processing to a
`~ point where the magnetic properties can be fully teveloped, the steel is so
soft as to be difficult to punch. If hardness is increased by mechanical
working, the magnetic properties are severely impaired. The above noted
`~ phosphorus additions, along with the silicon, enable the magnetic properties
of the steel of the present invention to be developed while at the same time
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~040460
maintaining sufficient hardness for good punchability. Again the manganese
serves to increase the volume resistivity.
If the steel of the present invention is to be provided to the
customer in the fully-processed form, it can be supplied with either an
organic or an inorganic insulative coating, if desired. Such coatings may be
applied by either the manufacturer or the customer.
The melt can be ingot cast or strand cast as desired. The steel
is hot rolled to hot band, pickled, cold rolled to final gauge and finished
with an anneal to develop the magnetic properties. The anneal is conducted
in a protective atmosphere at a temperature of from about 1400F to about
2000F (and preferably about 1600F) for a period of about 3-1/2 minutes.
Such an anneal will permit the development of the desired magnetic properties,
.'J
but will leave ~he strip with sufficient hardness to permit punching into
laminations or the like. The finished product possesses good punching
characteristics and may be used as stamped without a customer's stress relief
anneal, although a stress relief anneal may optionally be performed. It is
further characterized by a 60 hertz core loss of about 4.5 watts per pound
at 15 kilogausses measured at a thickness of .025 in. and has good penmeabili-
ty and exciting current.
EXAMPLES
Five steels designed A, B, C, D and E were produced with the
chemistries given in Table I below. In this table "Routing" refers to those
listed above and IlF-P'l and "S-P" refer to "fully-processed" and "semi-pro-
cessed", respectively.
'
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~'
~,.
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TABLE I
CHEMISTRY IN WEIGHT-PERCENT
Mate- Rout- Hard-
rial ng C Mn P S Si N 0 Gradeness
r M Sample R
~: A 9 .009 .002 .48 .12 .011 .15 .0046 .014 F-P 55-60
B 7 .009 .009 .48 .12 .011 .15 .0046 .014 F-P 55-60
C 1 .079 .001 .55 .11 .017 .12 .0034 .0032 S-P 90-95
D 1 .050 .001 .35 .007 .014 .12 .0026 .0097 S-P 90-95
: E 11 .040 .0024 .36 .003 .015 .14 .006 .011 S-P 60
Steel A was hot rolled to .09~', pickled, cold rolled to .024",
strip annealed for 3-1/2 minutes at 1600F in a dissociated a~monia atmosphere
- with +130F dewpoint and tested as sheared (Routing 9 above). Steel B was the
same as Steel A except it was normalized at 1850F instead of 1600F.
Steel C was hot rolled to .oga~, pickled, decarburized at 1300F
in an atmosphere of 15% hydrogen, 85% nitrogen with a dewpoint of 120F for
several hours, cold rolled to .025" and given a simulated customer anneal
:! at 1550F in a partially-combusted natural gas atmosphere for 30 minutes
(Routing 1). Steel D received the same processing and simulated customer
anneal as Steel C but differed in chemistry, including higher oxygen (see
.~ Table I).
; Steel E was hot rolled to .e~o", pickled, cold rolled to a nominal
. thickness of .025", and opened-coil annealed at 1100F in a dry atmosphere
of 8% hydrogen and 92% nitrogen, the furnace power having been shut off when
the charge reached 1100F. Steel E was then temper rolled 0.7% and given a
;~
simulated decarburizing customer anneal at 1450F in a wet, partially-
combusted natural gas atmosphere for 1-1/2 hours (Routing 11).
~` Table II below gives the magnetic properties of steels A, B, C, D
and E. The values given in Table II are average values for several samples,
each sample consisting of equal numbers of strips of each steel cut parallel
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to and transversely of the rolling direction.
TABLE II
MAGNETIC PROPERTIES
Exciting
Core LossCurrent Permeability
Mate-Thickness (2/lb, (AT/inch, 15 KGa 10 Oersteds
rial(Inches) 15 KGa) 15 KGa)
A .0239 4.40 8.0 1900 1530
B .0239 4.95 15.6 955 1370
C .025 4.05 5.54 3345 1595
D .025 4.60 6.60 2845 1570
E .0255 3.95 6.73 2060 1525
Modifications may be made in the invention without departing from
the spirit of it.
