The invention relates to a method for manufacturing of strips of stainless
steel, comprising rolling in cold condition of strips which in a foregoing process
have been manufactured through strip casting and/or have been hot rolled. The invention
also relates to an integrated rolling mill line to be used at the carrying out of
BACKGROUND OF THE INVENTION
Cold rolling of stainless steel strips is performed for one or several
purposes. The basic purpose is generally to reduce the thickness of the starting
strips, which normally have been hot rolled in a foregoing hot rolling line to a
thickness of the hot rolled strips, which is not less than 1.5 mm and normally is
in the order of 2-4 mm, but can be up to 6 mm. A main purpose or a secondary purpose
of the cold rolling also may be to increase the strength of the strip material.
Usually, it is also a purpose of the treatment of the steel strip
in the integrated rolling mill line to afford the strip certain surface features.
The cold rolling, the annealing, and the pickling in this respect cooperate and
have in different ways influence on the end result It should in this connection
be pointed out that the level of ambition as far as desired surfaces are concerned
may vary very much. In some cases, a very fine, high gloss surface, a so called
2B-surface or finer, is desired. In other cases, a considerably more raw surface
may be good enough, i.e. a beautifully pickled surface. The removal of scales, and
pickling play an important role in this respect, whether the purpose is to produce
a high gloss strip with a very fine surface, or a final product having that surface
structure which is achieved after pickling but without subsequent skin-pass rolling,
or other surface of good quality. It is particularly important that the scale residues
can be easily removed without heavy blasting. The surface structure would generally
be significantly impaired, if, e.g. a very powerful blasting would be required prior
to the pickling
Conventionally, initial annealing, cooling, and descaling through
shot-blasting as well as pickling in one or more steps precede the cold rolling,
for the achievement of a starting material for the cold rolling without oxides and
scale residues from the foregoing hot rolling but often with defects because of
powerful, scale-breaking shot blasting.. As an alternative the hot rolling can completely
or partly be replaced by manufacturing of strips through casting, which strips may
have a thickness down to what is normal for hot rolled strips or be a few millimetres
thicker, but also in this case the cold rolling normally is preceded by initial
annealing, cooling, scale-breaking shot-blasting, and pickling, to the extent the
technique has been implemented at all. At the cold rolling, which conventionally
is carried out in a plurality of consecutive cold rolling operations, possibly alternating
with annealing, cooling, descaling, and pickling operations, the thickness can be
reduced down to 1 mm and in some cases to even thinner gauges. At the same time
it is possible to produce, in these conventional cold rolling mills, strips with
a very fine surface, a so called 2B-surface, if the rolling is finished by heat
treatment, pickling, and skin-pass-rolling, or even finer if bright annealing is
employed. Further is it known - US 5 197 179 and EP 0 837 147 - to perform at least
a first cold rolling operation on the cooled hot rolled strip or on the cooled cast
strip prior to heat treatment, pickling, and possible further cold rolling operations
in order to bring the strip to desired final gauge.
It is also known from EP A 0 738 781 that cold-rolling can be performed
on a hot-rolled strip on which oxide scale still remains on the surfaces thereof.
The hot-rolled strip is cold-rolled with an at least 10% thickness reduction and
the cold-rolled strip is annealed at a temperature of between 1050 °C and 1200 °C.
It is also disclosed in EP A 0 738 781 that annealed strip can be pickled. Furthermore,
it is disclosed in EP A 0 738 781 that a manufacturing line may comprise a cold
rolling mill, an annealing furnace, a cooling box, a shot-blasting machine, a pickling
bath, a cold-stretching mill and a recoiler.
It is, however, characteristic for methods and rolling mill lines
known so far that they are expensive and/or difficult to adapt to widely disparate
requirements as far as strip thickness, surface conditions, and strength of the
final product are concerned. This particularly applies when hot rolling and subsequent
cold rolling, as well as operations in connection with the hot rolling and the cold
rolling, are considered as an integrated process of production.
DISCLOSURE OF THE INVENTION
It is a purpose of the invention to attack and solve the above complex
of problems. More particularly, the invention aims at facilitating the removal of
oxides and scales from the cast and/or hot rolled steel strip, in which process
the pickling constitutes an integrated part, by a treatment of the cast and/or hot
rolled stainless steel strip prior to descaling and pickling, which treatment is
characteristic for the invention. The invention is, however, not connected to any
particular pickling technique. Generally, any pickling method, which is suited for
pickling of stainless steels, can be employed in the method and the production line
according to the invention.
These and other objectives can be achieved therein that the cast and/or
hot rolled strip, which is dark coloured by oxides on the surfaces of the strips,
remaining from the foregoing manufacturing of the said cast and/or hot rolled strip,
is cold rolled in one ore more consecutive cold rolling passes reducing the strip
thickness by 10-75 % and crackling the oxide scales, i.e. so that cracks are produced
in the oxide scales, that the strip then is annealed in a furnace having a furnace
atmosphere obtainable by heating the furnace by means of a burner, which consumes
a liquid or gaseous fuel, which is combusted by means of a gas which contains at
least 85 vol-% oxygen and not more than 10 vol-% nitrogen, whereafter the strip
is cooled and subjected to at least any descaling operation and is pickled.
The initial cold rolling of the strip, which is dark coloured by oxides
on the surfaces of the strip, remaining from the foregoing manufacture of the cast
and/or hot rolled stainless steel strip, can be considered as an initial descaling
operation, which can facilitate the efficient descaling that is performed later,
after the annealing, but before the strip is pickled. In order that the said initial
crackling shall be possible to be utilised efficiently in order to facilitate later
descaling and pickling it is desirable that it as far as possible is not eliminated
in connection with the annealing, i.e. so that fissures or cracks in the oxide layers
do not heal up at the annealing. This desirable effect is to a considerable degree
achieved therein that the strips are annealed in the specific atmosphere of the
annealing furnace, which contains max 10 vol-% oxygen, preferably max 6 vol-% oxygen,
while the main part consists of carbon dioxide, steam and a minor amount of nitrogen,
which substantially emanates from air that possibly may leak in. A furnace atmosphere
of that type can be achieved, e.g. through the technique which is disclosed in WO95/24509.
In the atmosphere of the furnace, which is poor of oxygen, the strip can be annealed
at a temperature of 1050-1200°C during such a long period of time that the strip
will be through-heatened and be recrystallized without at the same time oxidising
the metal surfaces, which are exposed because of the crackling, to an extent that
it would make the subsequent descaling and pickling more difficult.
Different techniquesof descaling can be employed without damaging
the strip surfaces, because of the crackling of the scales in connection with the
initial cold rolling of the strips in combination with the annealing in the furnace
atmosphere that is poor of oxygen Conventionally, descaling is carried out through
powerful shot blasting in one or more steps, a treatment which however would cause
the non-desired damages of the strip surfaces, if employed. According to an aspect
of the invention, the descaling instead is carried out by bending the strip repeatedly
in different directions about rolls, at the same time as the strip is cold-stretched,
so that it is permanently elongated 2-10 % prior to pickling according to a technique,
which is known per se through EP 0 738 781. Through this treatment an efficient
descaling is achieved without impairing the strip surfaces This descaling can be
completed by a mild blasting, which can be performed before or after the descaling,
preferably before, aiming at removing only loose oxides in order, through accumulation
of oxides, not do disturb subsequent descaling. If the blasting is carried out subsequent
to the descaling it is correspondingly achieved that loose oxides are removed, the
blasting in each case being carried out in such a mild way that the metallic surfaces
of the strip are not impaired. Typically therefore, the descaling after annealing
is completed through cold-stretching, wherein the strip is bent repeatedly about
rolls, in combination with a gentle, not surface damaging, blasting before or after
the cold stretching. Since the scales still are crackled after annealing and therefore
easy to break, it is also conceivable to carry out the descaling through only a
light blasting and brushing, or through cold stretching the strip plus brushing,
or through only brushing.
Further characteristic features and aspects of the invention will
be apparent from the appending claims and from the following detailed description
of the invention. In this description will be explained how the invention can be
employed in a number of different variants of rolling mill lines, in which the initial
cold rolling of hot rolled strips or corresponding and the treatment of the strips
between said initial cold rolling and pickling, as has been described in the foregoing,
is an integrated part. It should, however, be pointed out that the usability of
the invention is not restricted to any of the described applications that can be
used generally in connection with cold rolling of stainless steel strips.
BRIEF DESCRIPTION OF DRAWINGS
In Fig 1 the invention and the said integrated rolling mill line is
illustrated semi-schematically, and in Fig. 2 a preferred embodiment of the method
for manufacturing cold rolled stainless strips, in which the method of the invention
is an integrated part, is illustrated very schematically.
DETAILED DESCRIPTION OF THE INVENTION
In the drawings, A schematically illustrates some different methods
to manufacture the stainless strips, preferably strips of austenitic or ferritic
stainless steel, which constitute starting material for the process in the subsequent
rolling mill line B which is used for the carrying out of the method according to
the invention. Also ferritic-austenitic steels are conceivable. Three methods of
manufacturing the starting material are illustrated in the left hand part A of the
drawings. According to method I, slabs 1 are hot rolled in a hot rolling mill line
for the manufacturing of hot rolled strips with a thickness which can be normal
for hot rolled strips, i.e. 1.5-6 mm. According to one aspect of the invention,
however, the hot rolling is stopped before or at the latest when the thickness has
been reduced to 2.5 mm, i.e. so that the strips obtain a thickness within the gauge
range 3-6 mm, preferably a thickness between 3 and 5 mm. The hot rolled strips are
quench-cooled to a temperature lower than 500°C at a rate of at least 15°C/s in
a quench-cooling section 3, suitably through intense water-spraying. Thereupon the
strips are coiled into coils 4, which are caused to cool further to 100°C or lower.
Through the rapid cooling to below 500°C, precipitation of grain boundary carbides
in the stainless steel strips are essentially avoided. Another effect attained through
the rapid cooling is that those oxide layers which unavoidably are formed on the
surfaces of the steel strip become thinner than what is normal in connection with
hot rolling and slower cooling, particularly in connection with cooling after the
strips have been coiled to form coils at a higher temperature.
According to method II stainless steel strips are cast to the shape
of strips according to any technique which may be known per se and which as far
as its specific mode of operation is concerned, does not form part of this invention
and will therefore not be described more in detail. By way of example, however,
there can be utilised so called stainless steel strip casting by twin rolls, which
is a technique known by people skilled in the art. The cast stainless steel strip
is hot rolled in a hot rolling mill line 2' to a thickness which is conventional
for stainless, hot rolled strips, or somewhat larger, 3-6 mm, see above, whereupon
the hot rolled strip immediately is quench-cooled in a cooling section 3 and is
coiled to form a coil 4.
According to method III the stainless steel strip is cast in the shape
of a strip having a thickness which is normal for stainless steel strips, or possibly
somewhat larger, i.e. about 2.5-6 mm, whereupon the strip is quench-cooled in a
cooling section 3' to a temperature below 500°C at a rate which is sufficient to
essentially avoid the formation of grain boundary carbides and for avoiding undesirably
thick oxide scales on the surfaces of the strip, i.e. at a rate of at least 15°C/s.
The thus produced strips are warned up on coils 4'.
The starting material for the subsequent operation in the rolling
mill line B thus consists of the cast and/or hot rolled, stainless steel strips
4, 4'. Such a coil 4, 4' of a stainless steel strip is shown in the drawings as
it is being decoiled from a decoiler 6. An auxiliary decoiler is designated 6A.
A welding machine for splicing strips, a first strip looper, and a first multi-roll
S-mill are designated 7, 8, and 9, respectively. Then follows an initial cold rolling
section 10, consisting of three cold rolling mills 11, 12, and 13, which mills are
of so called Z-high- or 6-high type, which means that each of them has a pair of
working rolls and two support rolls over and under respective working roll.
After the initial cold rolling section 10 there follows a degreasing
equipment 14, a second multi-roll S-mill 15 and a second strip looper 16.
The strip which has been decoiled from the coil 6 is designated 5
in the drawings. After having passed the initial cold rolling section 10, the strip
is designated 5'. From the strip looper 16, the strip 5' is fist fed through a washing
equipment 17 before it is fed into and through an annealing furnace 18 and a cooling
section comprising two cooling chambers 19 and 20. Then there follows a third multi-roll
S-mill 21, a shot blasting step 22 and a descaler 24. On each side of descaler 24
there is a fourth and a fifth multi-roll S-mill 23 and 25, respectively.
The furnace atmosphere in the furnace 18 may contain e.g. max 10 %
oxygen, preferably max 6 % oxygen. A furnace atmosphere of that type can be obtained
and maintained in different ways, e.g. and suitably by heating the furnace by means
of burners which consume a liquid or gaseous fuel, which is combusted by means of
a gas which contains at least 85 vol-% and not more than 10 vol-% nitrogen, as is
disclosed in WO95/24509. Preferably, the combustion gas according to the known technique
contains 99.5 % oxygen. If propane is used as fuel and is combusted by means of
a gas, which contains 99.5 vol-% oxygen, there will be obtained a furnace atmosphere,
which contains about 40 vol-% carbon dioxide, 50 vol-% steam and totally 10 % nitrogen
and oxygen. In one case it was achieved according to this technique, which is known
per se, a furnace gas which contained 39 vol-% CO2, 51 vol-% H2O, 6 vol-% N2, wherein
the nitrogen emanated from air that was leaking in.
The descaler 24 consists of a cold stretch mill, the design of which
is shown in detail in Fig. 3 in said EP 0 738 781, which herein is incorporated
in the present description by reference. A cold stretch mill of that type comprises
a series of rolls which force the strip to be bent alternatively in different directions,
at the same time as the strip is permanently elongated through cold stretching.
One has found that by means of a cold stretch mill of that type it is possible to
achieve an efficient descaling without impairing the surfaces of the strip beneath
the oxide layers.
After the descaler 24 there follows a pickling section, which e.g.
can consist of an initial neolyte- or other electrolytic pickling section 26 and
a mixed acid pickling section 27.
The acid mixture e.g. may consist of a mixture of nitric acid, HNO3,
and hydrofluoric acid, HF. The pickled strip, which is designated 5", then can be
stored in a third strip looper 28.
A further, terminating cold rolling mill is designated 32. This mill,
according to the embodiment, consists of a four-high mill, i.e. a rolling mill with
a couple of working rolls and a supporting roll over and under the working roll,
respectively, allowing rolling with reductions by up to 15 to 20 % depending on
the type of stainless steel (austenitic or ferritic, the ferritic steels normally
being possible to be rolled with a higher degree of reduction than austenitic steels).
Alternatively the finishing cold rolling mill may consist of a two-high mill intended
only for skin-pass-rolling. Subsequent to the rolling mill 32 there are provided
a sixth multi-roll S-mill 33, a straightening mill 34, a drying unit 36, a seventh
S-mill 36, and an edge cutting unit 37 before the strip 5''' is wound up to form
a coil 40 on a coiler 38. An auxiliary coiler has been designated 38A.
According to the various aspects of the invention, the stainless steel
strip shall pass once or twice through the rolling mill line B. This will now be
disclosed more in detail with reference to Fig. 2, in which only the most essential
equipment have been shown, while other parts, such as a welding machine, S-mills,
deflecting- and guide rollers, loopers, etc., have been left out in order that the
principles of the invention shall be more clear. Reference numerals within brackets
indicate strip material that is being processed as the material is passing the rolling
mill line B for the second time.
The rolling in the rolling mill line B is initiated by unwinding the
hot rolled or cast strip 5 of stainless steel from the coil 4, 4' of strip material.
It then still has its dark, oxidic coating which it has obtained in the foregoing
process in part A. This strip is cold rolled with a thickness reduction of totally
at least 10 % and max 75 % in one, two, or all the three of the rolling mills 11,
12, 13 in the initial cold rolling section 10, preferably with 20-50 % area reduction.
The comparatively thin, dark oxide layers on the strip surfaces obtained at the
quench-cooling after hot rolling or casting are so ductile that they are not broken
apart through the cold rolling operations in the initial cold rolling section 10
to such a degree that they get loose from the substrate, i.e. from the metal surface.
However, cracks are formed in the oxide layers, i.e. the scales on the steel strips
crackle. This appears to be of essential importance for the subsequent pickling,
the efficiency of which therein being promoted, which in its turn is important for
the achievement of fine surfaces on the final product.
In the annealing furnace 18 the thus cold rolled strip 5' is annealed
through heating to a temperature within the temperature range 1050-1200°C for so
long a period of time that the strip is through heated and recrystallised. As mentioned
above, the furnace contains max 10 vol-% oxygen, preferably max 6 vol-% oxygen,
but at the same time also a low content of nitrogen. More particularly, the furnace
atmosphere consists substantially of carbon dioxide and steam due to the fact that
the furnace is heated by means of burners which consume a liquid or gaseous fuel
which is combusted by means of a gas which contains at least 85 vol-% oxygen and
not more than 10 vol-% nitrogen. In this atmosphere in the furnace 18, those surface
of the steel strips which are exposed through the fissures in the oxide, , which
have been established through the cold rolling in the initial cold rolling section
10, are oxidised only to an insignificant degree, which is favourable for the subsequent
In the cooling chambers 20 the strip 5' is cooled to below 100°C,
before it is mildly shot-blasted in the shot-blasting section 22, which is a first
measurement for the removal of oxides and scales from the strip surfaces. More particularly,
oxides which lay loosely are removed through the shot-blasting in order not to spoil
the subsequent descaling through accumulation of oxides.
The strip is passed and is stretch-elongated in the descaler 24 between
a plurality of rolls under repeated bending, wherein the oxide scales are broken
as another, preparatory measurement prior to the pickling in the pickling units
26 and 27, where the oxide scales are completely removed.
The thus pickled strip 5" then is cold rolled also in the terminating,
additional cold rolling mill 32, which is dimensioned such that it can reduce the
thickness additionally by up to 20 %. Preferably the strip gauge reduction in the
finishing cold rolling mill 32 is at least 2 % and normally not more than 15 %,
suitably at least 8 % and max 12 %. The strip 5''' then is wound up to form a strip
According to a first aspect of the invention then the strip is passed
one more time through the rolling mill line B in the same direction as during the
first pass. According to another aspect of the invention the obtained product may
be the final product
According to the first aspect of the invention the strip coil 40,
after a period of time, which depends, among other things, on the logistic planning
of the production in the plant, is transported to the decoiler 6 or 6A in the starting
position of the rolling mill line, where the strip (5''') again is decoiled for
the second passage of the strip through the rolling mill line B. While the strip
during the first passage possibly only was rolled in one or two of the rolling mills
11-13 in the initial cold rolling section 10, it is this time rolled in two or three
of the mills 11-13 so that it essentially achieves the desired final gauge of the
strip. The total thickness reduction in the rolling mill section 10 at the second
passage of the strip through this section depends on the desired final gauge and
can amount to totally 60 % and to at least 20 %, preferably to at least 30 %. After
having passed the cold rolling section 10 for the second time, the cold rolling
of the strip, now designated (5IV), is finished. The final treatment
consists of again passing the strip through the annealing furnace 18, the cooling
chambers 19 and 20 and the pickling sections 26 and 27. However, it is this time
not at all treated in the shot-blasting unit 22 or in the descaler 24 according
to an aspect of the invention. According to another aspect of the invention it is,
however, also during the second passage through the rolling mill line treated in
the descaler 24, the purpose in this case being to increase the yield strength of
the strip through cold stretching. In the terminating cold rolling mill 32 it is
then possibly rolled one more time, but this time it is only skin-pass rolled with
a reduction thickness of 0.2-1.5 %, preferably about 0.5 %, in order to provide
desired fine surfaces. The treatment of the strip (5VI) then is finished
and the strip is coiled again. As an alternative, the strip (5V), instead
of being skin-pass rolled, is rolled with the same heavy thickness reduction as
when the strip was rolled for the first time in the terminating cold rolling mill
32, if the aim is to produce a strip with a very high yield strength.
The above description describes preferred embodiments according to
different aspects of methods of using the rolling mill line B. It is a particular
advantage of the design of the rolling mill line B that the rolling mill line or
parts of it also can be used for processes which aims at manufacturing not only
strips with very fine, bright surfaces but also strips with features which for some
applications are of more significant importance than very bright surfaces, such
as strips with high strength or strips with a lower degree of improvement but with
advantages from a cost point of view. For the latter purpose, the treatment e.g.
can be stopped already after the strip 5" has passed the pickling sections 26, 27
after the first passage of the first cold rolling section 10, the annealing and
cooling sections, and the pickling sections. In the descaler 24 the strip can be
cold stretched 2-10 %, which provides a significant improvement of the strength
This treatment, however, also can be omitted, if such increase of the strength/yield
strength is not desired. As an alternative the cold stretching can be replaced or
completed by 2-20 % cold rolling in the terminating cold rolling mill 32, which
in that case is performed on non-lubricated surfaces, as the strip passes the terminating
cold rolling mill a first time, whereafter the process is finished by coiling the
strip. These examples and alternatives illustrate the versatility and adaptability
of the rolling mill line to various wants as far as the final product is concerned.
A slab of stainless austenitic steel of grade ASTM 304 is hot rolled
in a Steckel-mill to achieve a strip with a breadth of 1530 mm and a thickness of
4.0 mm. Immediately upon rolling, the strip is quench-cooled from a final rolling
temperature of about 900°C to below 500°C for about 10 s by water spraying, whereafter
the strip is coiled. Through the fast cooling prior to coiling, formation of grain
boundary carbides are essentially avoided. At the same time also the dark oxide
layers on the surfaces of the strip become comparatively thin.
The strip coil then is transported to the rolling mill line of the
invention, is decoiled, and is first cold rolled with its dark oxide layers in two
of the rolling mills 11-13 in the initial cold rolling section 10 to the thickness
of 2.05 mm, wherein the oxide layers crackle, however without loosening. Thereafter
the strip is annealed in the annealing furnace 18 in the atmosphere poor of oxygen,
which has been previously described, at a temperature of 1120°C for a sufficiently
long period of time in order to be completely recrystallised, whereafter the strip
is cooled to below 100°C in the cooling chambers 19 and 20. Then the surfaces of
the strip is shot-blasted in the shot-blasting unit 22 very mildly with steel shots,
whereafter the strip is subjected to descaling in the stretch mill 24, before it
is pickled, first through electrolytic pickling in the section 26 and then in mixed
acid (mixture of nitric acid, HNO3, and hydrofluoric acid, HF) in the
pickling section 27. In the finishing cold rolling mill 32 the pickled strip then
is cold rolled with a thickness reduction of 9.8 % to gauge 1.85 mm, whereafter
the strip is wound up on a coil.
The strip then is transported back to the start position. Due to the
heavy cold rolling which the strip has been subjected to in the terminating cold
rolling operation in the rolling mill 32 it has been deformation hardened to a considerable
degree and it is therefore not easily damaged and can therefore be transported and
handled without a risk that the strip surfaces shall be damaged. The strip thus
again is decoiled and it is this time rolled in all the three rolling mills 11-13
in the initial cold rolling mill 10 with a total thickness reduction of 45.9 % to
gauge 1.0 mm. The strip is annealed, cooled, and then pickled in the same way as
during the first passage through the rolling mill line but is not shot-blasted or
cold stretched prior to pickling according to the example. Finally the strip is
skin-pass rolled in the terminating cold roll mill 32, adding a further thickness
reduction of about 0.5 %, wherein the strip achieves a surface fineness Ra 0.12
µm, i.e. very well corresponding to 2B-surface.
As is apparent from the foregoing, the cold rolling mill of the invention
is extremely versatile as far as its use for the manufacturing of stainless strips
with very fine surfaces and/or for strips with other desirable qualities or desired
features are concerned. In the following table, there will be listed a number ofthese
alternative ways of manufacturing strips with reference to the utilisation of the
various thickness reducing units which are included in the rolling mill line, i.e.
the initial cold rolling mills, the descaler/cold stretching mill, which also can
be used for reducing the thickness of the strip, and the cold rolling mill, or possibly
a plurality of cold rolling mills, which terminate the line.
Verfahren zur Herstellung rostfreier Stahlbänder, umfassend das Kaltwalzen eines
Bandes, das in einem vorangegangenen Verfahren durch Gießen einer Schmelze
unter Ausbildung eines Gussbandes und/oder heiß gewalzt hergestellt worden
ist, und wobei das gegossene und/oder heiß gewalzte Band, das durch Oxide
auf den Oberflächen der Bänder dunkel gefärbt ist, die von der vorangegangenen Herstellung
des gegossenen und/oder heiß gewalzten Streifens stammen, in einem oder mehreren
aufeinander folgenden Kaltwalzdurchläufen (11-13) kalt gewalzt wird, wodurch die
Banddicke zu 10 bis 75% verringert und die Oxidhäute aufgespalten werden, d.h. dass
in den Oxidhäuten Risse erzeugt werden, und wobei das Band danach in einem Ofen
(18) ausgeglüht wird, der eine Ofenatmosphäre besitzt, die durch Heizen des Ofens
mittels Brennern erhältlich ist, die eine Flüssigkeit oder gasförmigen Brennstoff
verbrauchen, der mittels eines Gases verbrannt wird, das mindestens 85 Vol.-% Sauerstoff
und nicht mehr als 10% Stickstoff enthält, wonach das Band abgekühlt und gebeizt
Verfahren nach Anspruch 1, dadurch gekennzeichnet, dass die Ofenatmosphäre
maximal 10 Vol.-% Sauerstoff, vorteilhafterweise maximal 6 Vol.-% Sauerstoff enthält.
Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, dass das Band
in der Ofenatmosphäre bei einer Temperatur von 1.050 bis 1.200°C während so einer
langen Zeitspanne ausgeglüht wird, dass das Band durchgeglüht und rekristallisiert
Verfahren nach irgendeinem der Ansprüche 1 bis 3, dadurch gekennzeichnet,
dass die Dicke des rostfreien Bandes um 20 bis 50% beim anfänglichen Kaltwalzabschnitt
(10) verringert wird.
Verfahren nach irgendeinem der Ansprüche 1 bis 4, dadurch gekennzeichnet,
dass das Band nach dem Ausglühen abgekühlt und in mindestens einer Entzunderungseinheit
(24) entzundert wird, wobei das Band vielfach in unterschiedlichen Richtungen um
die Walzen zur gleichen Zeit abgebogen wird, wie das Band kalt gestreckt wird, so
dass es permanent verlängert wird, wodurch die Häute aufgebrochen werden, bevor
das Band gebeizt wird.
Verfahren nach Anspruch 5, dadurch gekennzeichnet, dass das Band in mindestens
einer Entzunderungseinheit (24) kalt gestreckt wird, so dass es permanent um 2 bis
10% verlängert wird.
Integrierte Walzstrasse, umfassend mindestens einen Ausglühabschnitt (18), mindestens
einen Beizabschnitt (26,27), und als Anfangsteil der Strasse mindestens einen Kaltwalzwerk
(11-13) zum anfänglichen Kaltwalzen der rostfreien Stahlbänder mit dunklen, oxidischen
Oberflächen, erhalten in Verbindung mit einem vorangegangenen Gießen und/oder
Heißwalzen der rostfreien Stahlbänder, nach dem anfänglichen Kaltwalzwerk,
den Ausglühabschnitt, der einen Ausglühofen (18) umfasst, der mittels Brennern erwärmt
wird, die eine Flüssigkeit oder gasförmigen Brennstoff verbrauchen, der mittels
eines Gases verbrannt wird, das mindestens 85 Vol.-% Sauerstoff und nicht mehr als
10 Vol.-% Stickstoff enthält, und nach dem Ausglühabschnitt, einen Kühlabschnitt
und mindestens einen Beizabschnitt umfasst.
Integrierte Walzstrasse nach Anspruch 7, gekennzeichnet durch eine Kaltwalzstrasse
(10) als Anfangsteil der Strasse, umfassend mindestens zwei Kaltwalzwerke (11-13)
Integrierte Kaltwalzstrasse nach irgendeinem der Ansprüche 7 bis 8,
dadurch gekennzeichnet, dass mindestens die anfängliche oder mindestens zwei
anfängliche Kaltwalzwerke in Reihe vorgesehen werden, die dazu in der Lage sind,
die Dicke eines gegossenen und/oder heiß gewalzten rostfreien Stahlbandes
um insgesamt mindestens 10, vorteilhafterweise mindestens 20 und maximal 75% zu
Integrierte Walzstrasse nach irgendeinem der Ansprüche 7 bis 9, dadurch gekennzeichnet,
dass jedes Kaltwalzwerk als Anfangsteil der Strasse ein Paar Arbeitswalzen und
mindestens zwei Stützwalzen über und unter der entsprechenden Arbeitswalze umfasst.
Integrierte Kaltwalzstrasse nach irgendeinem der Ansprüche 7 bis 10,
dadurch gekennzeichnet, dass eine Entzunderungsvorrichtung (24) zwischen
dem Ausglüh- und dem Beizabschnitt in Form eines Kaltstreckwerkes vorgesehen ist,
wobei das Band abwechselnd in unterschiedlichen Richtungen um eine Vielzahl von
Walzen zur gleichen Zeit abgebogen wird, wie das Band permanent gestreckt wird.
Integrierte Walzstrasse nach irgendeinem der Ansprüche 7 bis 11, gekennzeichnet
durch ein Kaltwalzwerk im abschließenden Teil der Strasse, das entweder
aus vier Hochwalzwerken besteht, die ein Paar Arbeitswalzen und mindestens eine
Stützwalze ober- und unterhalb der entsprechenden Arbeitswalze, oder zwei Hochwalzwerke
zum Kaltnachwalzen der Gusshaut besitzen.
Method for the manufacturing of strips of stainless steel, comprising cold rolling
of a strip which in a foregoing process has been manufactured through casting a
melt to form a cast strip and/or has been hot rolled and wherein the cast and/or
hot rolled strip, which is dark coloured by oxides on the surfaces of the strips,
remaining from the foregoing manufacturing of the said cast and/or hot rolled strip,
is cold rolled in one or more consecutive cold rolling passes (11-13) reducing the
strip thickness by 10-75 % and crackling the oxide scales, i.e. so that cracks are
produced in the oxide scales, and wherein the strip then is annealed in a furnace
(18) having a furnace atmosphere obtainable by heating the furnace by means of burners
which consume a liquid or gaseous fuel which is combusted by means of a gas which
contains at least 85 vol-% oxygen and not more than 10 vol-% nitrogen, whereafter
the strip is cooled and pickled.
Method according to claim 1, characterised in that the furnace atmosphere
contains max 10 vol-% oxygen, preferably max 6 vol-% oxygen.
Method according to claim 1 or 2, characterised in that the strip is
annealed in the furnace atmosphere at a temperature of 1050-1200°C during such a
long period of time that the strip is through-heated and re-crystallised.
Method according to any of claims 1 to 3, characterised in that the thickness
of the stainless strip is reduced by 20-50 % in said initial cold rolling section
Method according to any of claims 1 to 4, characterised in that the strip
after annealing is cooled and subjected to descaling in at least one descaling unit
(24), in which the strip is bent a plurality of times in different directions about
rolls, at the same time as the strip is cold-stretched so that it is permanently
elongated, causing the scales to break prior to pickling the strip.
Method according to claim 5, characterised in that the strip is cold-stretched
in said at least one descaling unit (24), so that it is permanently elongated 2-10
Integrated rolling mill line comprising at least one annealing section (18),
at least one pickling section (26, 27), and, in the initial part of the line, at
least one cold rolling mill (11-13) for initial cold rolling of stainless steel
strips with dark, oxidic surfaces obtained in connection with a foregoing casting
and/or hot rolling of stainless steel strips;
after said initial cold rolling mill, said annealing section, which includes an
annealing furnace (18), which is heated by means of burners which consume a liquid
or gaseous fuel which is combusted by means of a gas which contains at least 85
vol-% oxygen and not more than 10 vol-% nitrogen; and
after the annealing section, a cooling section and at least one pickling section.
Integrated rolling mill line according to claim 7, characterised by,
in the initial part of the line, a cold rolling line (10) comprising at least two
cold rolling mills (11-13) in series.
Integrated rolling mill line according to any of claims 7-8, characterised
in that said at least initial, or said at least two initial cold rolling mills
in series, are provided to be able to reduce the thickness of a cast and/or hot
rolled stainless steel strip by totally at least 10, preferably at least 20, and
max 75 %.
Integrated rolling mill line according to any of claims 7-9, characterised
in that each of the cold rolling mills in the initial part of the line comprises
a pair of working rolls and at least two supporting rolls over and under respective
Integrated rolling mill line according to any of claims 7-10, characterised
in that a descaler (24) is provided between the annealing and pickling sections
in the form of a cold-stretching mill, in which the strip is provided to be bent
alternatingly in different directions about a plurality of rolls at the same time
as the strip is permanently being stretched.
Integrated rolling mill line according to any of claims 7-11, characterised
by a cold rolling mill in the terminating part of the line, which consists either
of a four-high rolling mill, comprising a pair of working rolls and at least one
supporting roll over and under respective working roll, or consists of a two-high
rolling mill for skin pass rolling.
Procédé pour la fabrication de bandes d'acier inoxydable, comprenant le laminage
à froid d'une bande qui, au cours d'un processus précédent a été fabriquée en coulant
une masse fondue pour former une bande coulée et/ou qui a été laminée à chaud et
dans lequel la bande coulée/ou laminée à chaud, dont la couleur est assombrie par
des oxydes sur les surfaces des bandes, restant de la fabrication précédente de
la bande coulée et/ou laminée à chaud, est laminée à froid au cours d'une ou plusieurs
passes consécutives de laminage à froid (11-13) réduisant l'épaisseur de la bande
de 10 à 75 % et craquelant la calamine, c'est-à-dire de sorte que des craquelures
soient produites dans la calamine et dans lequel la bande est ensuite soumise à
un recuit dans un four (18) ayant une atmosphère que l'on peut obtenir en chauffant
le four au moyen de brûleurs consommant un combustible liquide ou gazeux entrant
en combustion au moyen d'un gaz contenant au moins 85 % en volume d'oxygène et au
maximum 10 % en volume d'azote, après quoi la bande est refroidie et décapée.
Procédé selon la revendication 1, caractérisé en ce que l'atmosphère
du four contient au maximum 10 % en volume d'oxygène, de préférence au maximum 6
% en volume d'oxygène.
Procédé selon la revendication 1 ou 2, caractérisé en ce que la bande
est soumis à un recuit dans l'atmosphère du four à une température de 1050 à 1200°C
pendant une durée telle que la bande soit chauffée à coeur et recristallisée.
Procédé selon l'une quelconque des revendications 1 à 3, caractérisé en ce
que l'épaisseur de la bande d'acier inoxydable est réduite de 20 à 50 % dans
ladite partie de laminage à froid initial (10).
Procédé selon l'une quelconque des revendications 1 à 4, caractérisé en ce
que la bande, après avoir été soumise au recuit, est refroidie et soumise à
un décalaminage dans au moins une unité de décalaminage (24), dans lequel la bande
est pliée plusieurs fois dans différents sens par rapport aux rouleaux, en même
temps que la bande est étirée à froid de sorte qu'elle soit allongée de façon permanente,
ce qui amène la calamine à se rompre avant le décapage de la bande.
Procédé selon la revendication 5, caractérisé en ce que la bande est
étirée à froid dans ladite au moins une unité de décalaminage (24), de sorte qu'elle
soit allongée de façon permanente de 2 à 10 %.
Chaîne de laminoir intégré comprenant au moins une partie de recuit (18), au
moins un partie de décapage (26, 27), et, dans la partie initiale de la chaîne,
au moins un laminoir à froid (11-13) pour le laminage à froid initial de bandes
d'acier inoxydable à surfaces d'oxyde sombres, obtenues par suite d'une coulée précédente
et/ou d' un laminage à chaud précédent de bandes d'acier inoxydable ; après ledit
laminoir à froid initial, ladite partie de recuit, qui comprend un four de recuit
(18), chauffé au moyen de brûleurs consommant un combustible liquide ou gazeux entrant
en combustion au moyen d'un gaz contenant au moins 85 % en volume d'oxygène et au
maximum 10 % en volume d'azote ; et après la partie de recuit, une partie de refroidissement
et au moins une partie de décapage.
Chaîne de laminoir intégré selon la revendication 7, caractérisée par,
dans la partie initiale de la chaîne, un laminoir à froid (10) comprenant au moins
deux laminoirs à froid (11-13) en série.
Chaîne de laminoir intégré selon l'une quelconque des revendications 7 et 8,
caractérisée en ce que ledit au moins un laminoir initial ou lesdits au moins
deux laminoirs à froid initiaux en série, sont prévus afin de pouvoir réduire l'épaisseur
d'une bande d'acier inoxydable coulée et/ou laminée à chaud d'au moins 10 % au total,
de préférence 20 % au total, et au maximum de 75 % au total.
Chaîne de laminoir intégré selon l'une quelconque des revendications 7 à 9,
caractérisée en ce que chaque laminoir à froid dans la partie initiale de
la chaîne comprend deux rouleaux de travail et au moins deux rouleaux porteurs sur
et sous le rouleau de travail correspondant.
Chaîne de laminoir intégré selon l'une quelconque des revendications 7 à 10,
caractérisé en ce qu'une décalamineuse (24) est prévue entre les parties
de recuit et de décapage sous la forme d'un laminoir étireur à froid, dans lequel
la bande est prévue pour être pliée alternativement dans différentes directions
par rapport à plusieurs rouleaux en même temps que la bande est étirée. de façon
Chaîne de laminoir intégré selon l'une quelconque des revendications 7 à 11,
caractérisée par un laminoir à froid dans la partie terminale de la chaîne,
qui est constituée soit d'un laminoir quarto, comprenant deux rouleaux de travail
et au moins un rouleáu porteur sur et sous le rouleau de travail correspondant,
soit d'un laminoir duo pour une légère passe de laminage à froid.