Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~01~63
This invention relates to the production o~ grain
oriented silicon steel sheet or strip of low core loss which
is used as magnetic core material in electric machines such
as transormers and the like. Such material has a preferred
grain orientation or texture defined in Miller indice~ as
~110) 001, that is to say the individual grains making up
the sheet or strip have their (110) crys-tallographic planes
predominantly parallel to the sheet or trip surface and their
001 crystallographic directions predominantly paralle:L to the
rolling diréction of the sheet or stripO
.. According to one aspect of the present invention
a procéss for producing grain oriented silicon steel for
; electromagnetic applicati.ons comprises producing by a conven-
tional refining process a steel yielding a slab having a
carbon content of up to 0.08% by weight and a silicon content
lying between 2~5% and 3.5%, hot rolling the slab to strip,
which is annealed at a temperature lying within the range
8S0C to 1050C, cold rolling the annealed strip to sub-
stantially final gauge, subjecting the cold rolled strip
to a decarburising anneal at a temperature within the range
850C -to 1050C so as to reduce carbon concentration to less
than 005% and subjecting the strip to a final anneal at a
temperature up to 1200C. .
; Preferably the slab is reduced to hot band within
the thickness range 1.5mm - 3.0mm.
The final anneal conveniently is a box anneal which
preferably is within the range 1150C to 1200C.
.In one embodiment of the invention the steel of the
slab suitably contains manganese and sulphur which subse~uent-
-~ 30 ly combine to produce manganese sulphide precipitates in the
. hot rolled sheet or strip, such manganese sulphide precipita-
;~ tes subsequently acting as a grain growth inhibitor effective
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to produce material displaying good core loss characteristics.
The manganese sulphide is obtained by adding manganese in
concentrations of up to 0.1% by weight to the steel melt at
any suitable stage up to casting of the ingot for slabbing. -
In this embodiment of the invention the ingot may
be derived from a melt produced by any conventional steel-
making process and typically having a composition adjusted
to 0.02% to 0,035% carbon, 2.8% to 3.5% silicon, 0~02% to
0.03% sulphur, and 0.05% to 0.09% manganese, the balance
being iron and incidental impurities. Slabs obtained from such
a melt either by ingot casting and hot rolling or directly
by continuous slab casting are reheated at a temperature
within the range 1350C to-1400C and hot rolled into strip
conveniently of about 1.9mm thickness. The hot rolliny
parameters may be those conventionally used in the art.
The hot band so produced may be annealed at between
850C to 1000C typically for a few minutes and then cold ~
rolied to substantially final gauge without intermediate ,
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annealing. The cold rolled strip is then continuously
annealed in wet hydrogen or other decarburising atmosphere, -~
preferably between 900C to 1000C although any temperature
within the range 850C to 1050C may be used. ;
The decarburising temperature whi~h is higher than
that conventionally used may be maintained substantially ;~
constant during the period the strip or sheet remains in the ;~
annealing furnace. However the annealing furnace may be
arranged to heat the strip through two distinct temperature
ranges respectively effective to reduce carbon concentration
and to develop the final magnetic characteristics required~
`30 Conveniently the strip is heated in a typical annealing
furnace over two temperature plateaux extending batween
800C to 850C and between 900C to 1000C. The sequence
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~OS0~363
of low temperature and high temperature plateaux may h~wever
be reversed if so required.
The use of a decarburising anneal temperature of up
to 1050C which is higher than that conventionally employed
allows good secondary recrystallisation to occur during
subsequent box annealing which conveniently is for about 24
hours at a temperature of up to 1190C. It is believed that
such secondary recrystallisation would not occur with single
stage cold rolled material which is decarburised within the
normal temperature range of between 800C to 850CC at present
employed in conventional processes for producing grain
; oriented silicon steels.
In an alternative embodiment of the invention the
steel may include aluminium nitride as a grain growth inhibitor
in addition to manganese sulphide. In this case the aluminium
nitride is pro-
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duced ~y inoculating the steeL with aluminium at any stage up to
casting of the ingot so that the final concentration of acid solu-
ble aluminlum is up to ~.065% by weight. In this alternative em-
bodiment the steel again is produced from a melt arising rom any
conventional steelmaking process and typically adjusted to contain
0.02% to 0.06% carbon, 2.5% to 3.5% silicon~ 0.01% to 0.06% acid
soluble aluminLum, 0.05% to 0;1% manganese and 0.02% to 0.03% sul-
phur, the balance being iron and other incidental impurities.
After casting lnto ingots and rolling to slabs, the slabs are re-
heated wlthin the temperature range 1350C to 1400C and hot rolled
to strip of about 2.8mm thickness.
In accordance with the present invention the hot band so pro~
duced is annealed at a temperature between 850C to 1000C that
is to say at a considerably lower temperature than conventional
r~15 finishing processes involving aluminium nitride as a grain growth --
inhibitor and is after picking cold rolled directly to substan-
tially final gauge.
The cold rolled strip is subject to a decarburisation anneal
at a temperature wit~in the range 850C to 1050C and is subse~
quently box annealed for about 24 hours at about 1190C. As
previou~ly, the annealing may be achieved in a suitable furnace ;~
which may display a temperature gradient including two temperature
plateaux.
It is believed that ~he non-conventional comblnation of hot
. . . . . .
~5 band annealing and decarburisation temperature produces grain
' orlented material having magnetic characteristics at least equi-
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valent to those produced by more costly alternative processes.
Embodiment of the invention will now be particularly
described by way of the following examples.
EXAMPLE 1
An open hearth steel of pit analysis 0.~29%C,
0.079/~Mn, 0.028%S, 3.18%Si, 0.007%P, 0.0065/~, 0.116%Cu,
0 . 044~Ni ~ and 0.018%Sn was cast into ingots which were sub-
sequently rolled into slabs. The slabs after reheating
to about 1400C were rolled on a continuous hot strip mill to
produce hot rolled strip 1.92mm thlck. Sheets of this hot
rolled strip were annealed at 910C for a total residence
time of 5 minutes. After pickling these sheets were cold
rolled to 0.337mm thick in several passes without intermediate
annealing. The cold rolled sheets were then decarburisation
annealed at 950C for about 5 minutes in hydrogen with a
dewpoint of 60C. After coating with magnesia the decarburi~ed
sheets were annealed at about 1190C for about 24 hours.
Epstein samples cut from the annealed material gave, after
stress relief annealing, core loss values of 1.03 to 1.09 W/kg
at 1.5T and 50Hz. These values are all within the M6 grade
specification of l.llW/kg for this thickness of material.
EXAMPLE 2
A basic oxygen converter, vacuum degassed melt was
cast into ingots which were subsequently hot rolled into
slabs. The slabs after reheating to about 1400C were rolled
on a continuous hot strip mill to produce hot rolled strip
2.97mm thicko The hot rolled strip analysed 0.041%C~ 0.080/~n,
; 2.94%Si~ 0.024%S, 0.013%P, 7/~2' and 0.025% acid soluble
` Al. Sheets of this hot rolled strip were annealed at 900C
to 910C for a total residence time of 5 minutes. After
pickling these sheets were cold rolled to 0.337mm thick in
several passes without intermediate annealing. The cold
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rolled sheets were then decarburisation annealed at 950C
for about 5 minutes in hydrogen with a clewpoint of 60C.
After coating with magnesia the decarburised sheets were
annealed at about 1190C for about 24 hours~ The material
thus produced had excellent orientation of the (110) 00~ ;
type and gave the following magnetic test results:-
Core loss at 1.5T, 50Hz - 0.91 to 1.00 W/kg, mean 0.96 W/kg
Core loss at 1.7T, 50Hz - 1.16 to 1.36 W/kg, mean 1.28 W/kg
B at H = lkA/m - 1.90 to 1.94T, mean 1.92T
EXAMPLE 3
An open hearth steel pit analysis 0.024%C, 0.087/~Mn,
0.027%S, 3.08%Si, 0.008YoPl 7/~2' 0.142%Cu, 0.0580/oNil
0.018%Sn were cast into ingots which were subsequently rolled
to slabs. After reheating to 1400C the slabs were rolled on
a continuous hot strip mill to produce hot rolled strip 2.28mm
thick. Sheets of this hot rolled strip were annealed at ~-
, 1000C for a to-tal residence time of 5 minutes. After pickli~g, ~`
- these sheets were cold rolled to 0.337mm thick in several
passes without intermediate annealing. The cold rolled sheets
were then decarburised at 900C for about 5 minutes in hydrogen
~dewpoint + 60C). After coating with magnesia the decarburised
sheets were annealed at about 1190C for 24 hours. Epstein
samples cut from the annealed material gave, after stress
relief annealing, core loss values of 1.06 to 1.07 at 1.5T
and 50Hz and permeabilities of B = 1.78 to 1.81 at H = lkA/m.
EXAMPLE 4
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A basic oxygen converter, vacuum degassed melt was
cast into ingots which were subsequently hot rolled in slabs.
The slabs after reheating to about 1400C were rolled on a
continuous hot strip mill to produce hot rolled strip 2.03 mm
: .
-` thick. The hot rolled strip analysed 0.029%C, 3.14%Si,
O.02S%S, 0.008%P, 0.067~/~Mn, O.015~i, 0.042%Cu, 0.008%Sn,
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0.0042%N, 0.004f~1. This hot rolled strip was processed
through a work continuous annealing furnace at 900C for
a total time in furnace of 5 minutes~ After pickling, the .
strip was cold rolled to 0.354mm in several passes without
intermediate annealing. The cold rolled sheets were then
decarburisation annealed in a continuous annealing line at
950C for about 5 minutes in hydrogen (dewpoint + 60C).
After magnesia coating the decarburised strip was
coiled and annealed at 1190C for 24 hours. The material thus ~.
produced had an excellent orientation of the (110) 001 type
and gave the following magnetic test results after stress relief
annealing:-
Core loss at 1.5T, 50Hz - 1.03 - 1.13 mean 1.07
Core loss at 1.7T, 50Hz - 1.47 - 1.61 mean 1.53
Permeability B at H = lkA/m 1.76 - 1.82 mean 1.79
~o significant variation of magnetic properties was detected ~:
between those embodiments in which the strip was or was not
allowed to cool toward ambient between the decarburisation
anneal and the final anneal.
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