U.S. patent application number 13/431051 was filed with the patent office on 2012-07-19 for process and plant for manufacturing steel plates without interruption.
Invention is credited to Giovanni Arvedi.
Application Number | 20120180975 13/431051 |
Document ID | / |
Family ID | 35385547 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120180975 |
Kind Code |
A1 |
Arvedi; Giovanni |
July 19, 2012 |
PROCESS AND PLANT FOR MANUFACTURING STEEL PLATES WITHOUT
INTERRUPTION
Abstract
Process and related plant for manufacturing steel plates with
thickness<100 mm and width of up to 4000 mm from a continuous
casting step for slabs, comprising a liquid core reduction step,
without interruptions until completion of a finishing rolling step
with high reduction ratios in at least one stand. The average
temperature when entering the rolling step is .gtoreq.1250.degree.
C., but can be reduced for unalloyed or low alloyed steel
greatest.
Inventors: |
Arvedi; Giovanni; (Cremona
CR, IT) |
Family ID: |
35385547 |
Appl. No.: |
13/431051 |
Filed: |
March 27, 2012 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11988334 |
Jan 4, 2008 |
8162032 |
|
|
PCT/IT2005/000412 |
Jul 19, 2005 |
|
|
|
13431051 |
|
|
|
|
Current U.S.
Class: |
164/263 |
Current CPC
Class: |
B21B 1/463 20130101;
B21B 1/46 20130101; Y10T 29/49991 20150115 |
Class at
Publication: |
164/263 |
International
Class: |
B22D 11/126 20060101
B22D011/126; B22D 11/12 20060101 B22D011/12; B22D 11/124 20060101
B22D011/124 |
Claims
1.-6. (canceled)
7. A plant for manufacturing steel plate having a thickness<100
mm and a width up to 4000 mm, from a continuous casting product for
slabs, comprising, after a continuous casting mold, a liquid core
reduction means to obtain a thickness.gtoreq.55 mm at the outlet at
an average temperature.gtoreq.1250.degree. C., without
interruptions until the last stand of a finishing rolling mill with
one or more stands being in line with the said continuous casting
under high reduction ratio, followed by cooling means and a shear
for cutting the plate at a desired length.
8. The plant according to claim 7, comprising a final straightening
machine.
9. The plant according to claim 7, comprising a descaler
immediately upstream of said rolling mill.
10. The plant according to claim 7, having a total length from
continuous casting mold until the last cooling means not greater
than 60 m.
11. The plant according to claim 7, wherein for unalloyed or low
alloyed steel requiring thermo-mechanical treatment additional
cooling means are provided at intermediate positions between the
rolling stands to reduce the a rolling temperature by
50-100.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This divisional patent application claims priority to the
parent U.S. application Ser. No. 11/988,334, filed Jan. 4, 2008,
which claims the benefit of priority under 35 U.S.C.
.sctn.119(a)-(d) to International Application No.
PCT/IB2005/000412, filed Jul. 19, 2005 and published in English;
the contents of both applications are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a process and related plant
for manufacturing steel plates without interruption from the
continuous casting to the last rolling stand.
[0004] 2. Description of Related Art
[0005] It is known that traditionally, in this field of
manufacturing, "reversible" rolling stands have been generally used
to roll, by means of several longitudinal and transversal passes,
in order to increase each time the product size in length and
width, an ingot, preferably of rectangular cross-section, or a slab
suitably heated upstream in a heating and temperature equalization
furnace, until obtaining a plate of desired thickness and width.
The dimensions of the ingot or slab, the latter being possibly
produced from continuous casting, are such to show a thickness
between 120 and 400 mm and a width between 1000 and 2000 mm
according to the type of steel and the technology employed for the
manufacturing.
[0006] It is also known that in this type of processing the ratio
between the thickness of the starting material, i.e. the ingot or
slab, and of the desired final plate should not be less than 1:4 in
order to ensure welding of possible pores present in the core or
middle zone, which are typical in ingots/slabs of great thickness.
This means, for a plate having final thickness of 50 mm, an initial
slab with minimum thickness of 200 mm.
[0007] With the subsequent development of the thin-medium thickness
slab technology, plants have been designed by which slabs with a
thickness of up to 150 mm are cast, having a width of up to 3600
mm. These slabs are subsequently cut and, upon passing through a
heating and temperature equalization furnace, are forwarded in line
to a reversible rolling mill which however is adapted to
longitudinally rolling only.
[0008] With these plants the thickness ratio between slab and final
plate can be as low as 1:3, whereby a minimum slab thickness of 150
mm would be required for a plate 50 mm thick. Of course it is also
possible with these plants to produce not only plates but also
strips wound in coils by making the same reversible stand to work
with two rails in a furnace ("plate/Steckel mill technology"). It
is clear that with a reduction ratio 1:3 between slab and final
plate, to obtain thicknesses of 40-50 mm for the finished plate it
is necessary that slabs of 120-150 mm are cast at a maximum speed
in the order of 2 m/min, that is insufficient for an in-line
rolling process without interruption, requiring on the contrary a
minimum speed of 3.5 m/min.
[0009] These considerations have prevented so far from adopting in
the plate manufacturing the "cast-rolling" technology already known
for manufacturing strips. From experimental tests, that however
have not made possible to obtain reductions higher than 35% owing
to the reduced torque value of the rolling stands, mathematic
simulating models have been developed. It has been understood from
these models that the same quality results can be reached with a
reduction coefficients even greater than 50% and even up to 60%,
bringing to more compact plants and further reducing the production
costs and investments.
BRIEF SUMMARY OF THE INVENTION
[0010] Therefore it is an object of the present invention to
provide a process and related plant for the manufacturing of plates
with thickness of up to 100 mm and width up to 4000 mm, with low
investment and production costs.
[0011] When adopting the technology employed for manufacturing
coils according to patents EP 0925132, EP 0946316 and EP 1011896,
all in the present applicant's name, it has been observed that,
starting at the outlet of the mold with a product 75 mm thick and
at the outlet of the continuous casting with a thickness of 55 mm,
after a liquid core reduction ("soft reduction"), an average
temperature higher than 1250.degree. C. at a speed of 5 m/min was
established. The in-line rolling was carried out with two stands
having high reduction ratio (33% at the first stand and 30% at the
second one) to obtain final plates 25 mm thick and consequently
with a thickness ratio slab/plate of about 1:2. The quality was
comparable to that of plates manufactured according to the prior
art, in particular free from pores and provided with a homogeneous
microstructure throughout the whole thickness.
[0012] The object of the present invention is thereby obtained with
a process for manufacturing steel plate having a thickness<100
mm and a width up to 4000 mm, from a slab continuous casting step,
wherein the method comprises a liquid core reduction step with a
thickness.gtoreq.55 mm at the outlet, an average
temperature.gtoreq.1250.degree. C., without interruptions up to the
end of a finishing rolling step with high reduction ratios, through
one or more stands, followed by a cooling step and cutting at the
desired length of the plate and relating plant for manufacturing
steel plate having a thickness<100 mm and width up to 4000 mm,
from a continuous casting product for slabs, characterized by
comprising, after a continuous casting mold, liquid core reduction
means to obtain a thickness.gtoreq.55 mm at the outlet at an
average temperature.gtoreq.1250.degree. C. , without interruptions
until the last stand of a finishing rolling mill with one or more
stands being in line with the said continuous casting under high
reduction ratio, followed by cooling means and a shear for cutting
the plate at a desired length.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)
[0013] These and other objects, advantages and features of the
present invention will be clearer from the following detailed
description of two embodiments thereof, given by non-limiting
example with reference to the annexed drawings. The foregoing
summary, as well as the following detailed description of preferred
embodiments of the invention, will be better understood when read
in conjunction with the appended drawings. For the purpose of
illustrating the invention, there is shown in the drawings
embodiments which are presently preferred. It should be understood,
however, that the invention is not limited to the precise
arrangements and instrumentalities shown. In the drawings:
[0014] FIG. 1 shows a schematic view of a plant according to the
present invention for manufacturing plates in stainless steel;
and
[0015] FIG. 2 shows a schematic view of a plant according to the
present invention for manufacturing plates in unalloyed or low
alloyed steel grade.
DETAILED DESCRIPTION OF THE INVENTION
[0016] With reference to FIG. 1 there is shown a plant on which the
mutual distances are quoted between the various components of the
plant with a whole distance, of about 60 m, between a continuous
casting machine 1 and the end of rolling step. There are also shown
thickness values, different from those mentioned in the example
given above, but anyhow falling within the claimed range of values.
Starting in fact with a thickness of 70 mm for a slab 10 from
continuous casting 1 with a speed of 3.5 m/min and average
temperature of 1250.degree. C., there follows a descaler 2 and
then, without interruptions, a rolling mill 3 placed in line with
the casting machine l without solution of continuity until
obtaining at the outlet a plate with a thickness even lower than 8
mm, According to the type of steel and desired thickness for the
plate, the rolling stands being represented in number of three
(M1-M3) can be reduced in number by omitting one or two thereof.
Thanks in fact to the temperature conditions claimed it is possible
to obtain the final plate even with only a single rolling stand and
suitable reduction ratio comprised between 1:1.5 and 1:2.5,
preferably of about 1:2.
[0017] It will be noted in fact that a favorable temperature
profile for a thin slab, with a temperature value in the core or
middle region that is rather high and near to 1350.degree. C.,
increases the average rolling temperature and allows for a high
thickness reduction, thus welding the inner pores with less rolling
passes with respect to a conventional plate rolling mill. As a
matter of fact, when exceeding a given reduction ratio or shape
factor at constant width, the hydrostatic stress or specific
pressure at the thin slab core reaches values which are high enough
to weld any existing pores. Moreover the high deformation
temperatures enhance recrystallization, i.e. the process by which
the grain is deformed and then, thanks to the high temperature,
recrystallizes completely, thus favorable the formation of uniform
microstructures, contrary to what occurs when rolling at lower
temperatures, e.g. from 1050 to 900.degree. C. as taught by patent
EP 0580062. These low temperatures generally give rise in fact to
mixed structures that are not completely recrystallized.
[0018] High rolling temperatures also enhance in stainless steel
the solubilization of chrome carbides, thus avoiding their
precipitation without having to make recourse to subsequent
specific solubilization treatments.
[0019] Referring again to FIG. 1, an accelerated cooling step then
follows in 4, which allows a further improvement of the
microstructures and characteristics of the plate profile.
[0020] Finally, after a shear 5 to cut the plate at the desired
length, a straightening step 6 can be provided.
[0021] With reference to FIG. 2, another embodiment of the plant
according to the present invention is instead represented, which is
particularly adapted for plates in unalloyed or low alloyed steel.
In this case, intermediate between the stands M2 and M3 there is
provided an interstand cooling 4' capable of lowering by
50-100.degree. C. the high rolling temperature, as it is required
for these types of steel, In these cases it is in fact necessary to
provide a thermo-mechanical rolling with a combined treatment of
mechanical deformation and cooling.
[0022] The distance between M2 and M3 is greater as a consequence
of the presence of an additional cooling system 4' between these
two stands. There could be also provided, still in view of the
above-mentioned thermo-mechanical treatment, as required for the
unalloyed or low alloyed steel, a lower distance between the first
stand M1 and the intensive cooling 4 on the outlet roller path.
[0023] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *