Method for manufacturing a strip having a variable thickness and associated strip
The present invention relates to a method for manufacturing a strip with variable
thickness along its length, made of an iron-based alloy.
Cryogenic Invar8, notably lnvar8 M93, are alloys which have low thermal
5 expansion coeff~cients, which makes them notably attractive for transporting cryogenic
fluids.
In such applications, elements made of cryogenic lnvai8 of different thicknesses
may be assembled, for example by welding.
The thereby obtained assemblies do not give entire satisfaction. Indeed, the welds
10 form weakened areas of the structures formed by the assembled elements. The presence
of these weakened areas may result in a reduction of the fatigue strength.
An object of the invention is to solve this problem by proposing a method for
manufacturing a strip mainly, based on iron and nickel which gives the possibility of
producing structures that are reinforced from a mechanical point of view.
15 For this purpose, the invention relates to a manufacturing method according to
claim 1.
According to particular embodiments, the manufacturing method has one or
several of the characteristics of claims 2 to 11, taken individually or according to all the
technically possible combinations.
20 The invention also relates to a method for manufacturing a blank according to
claim 12 or 13.
The invention also relates to a method for manufacturing a cryogenic tube
segment according to claim 14
The invention also relates to a variable thickness strip according io claims 15 to
25 17.
The invention also relates to a blank according to claims 18 to 20.
The invention also relates to a cryogenic tube segment according to claims 21 and
22.
The invention also relates to an assembly according to claims 23 to 25.
30 The invention will be better understood upon reading the description which follows,
only given as an example, and made with reference to the appended drawings, wherein:
- Fig. 1 is a schematic longitudinal sectional view of an initial strip;
- Fig. 2 is a schematic longitudinal sectional view of an intermediate strip;
- Fig. 3 is a schematic longitudinal sectional view of a variable thickness strip ;
35l - Fig. 4 is a schematic illustration of a blank obtained by the manufacturing method
according to the invention;
L
- Fig. 5 is a schematic longitudinal sectional illustration of a first assembly of a
blank with a second part;
- Fig. 6 is a schematic longitudinal sectional illustration of two blanks assembled
end to end; and
5 - Fig. 7 is a schematic sectional illustration of a cryogenic tube.
An exemplary method for manufacturing a strip having a variable thickness along
its length made of an alloy mainly based on iron and nickel according to the invention will
now be described.
In a first step of this method, an initial strip 1 obtained by hot rolling is provided
10 The initial strip 1 is a strip made of an alloy of the cryogenic lnvar type. This alloy
comprises by weight.
34.5% 5 Ni 5 53.5%
0.15% r Mn r 1.5%
0 2 Si 2 0.35%, preferably 0.1% 5 Si 5 0.35%
15 0 S: C 5 0.07%
optionally:
0 5C0<20%
0 sTi50.5%
0.01 %5Cr50.5%
20 the remainder being iron and impurities necessarily resulting from the elaboration
The silicon notably has the function of allowing deoxidation and of improving the
corrosion resistance of the alloy.
An alloy of the cryogenic lnvar type is an alloy which has three main properties:
- It is stable towards the martensitic transformation until below the liquefaction
25 temperature TL of a cryogenic fluid. This cryogenic fluid is for example liquid butane,
propane, methane, nitrogen or bxygen. The contents of gammagenic elements, nickel
(Ni), manganese (Mn) and carbon (C), of the alloy are adjusted so that the onset
temperature of the martensitic transformation is strictly less than the liquefaction
temperature TL of the cryogenic fluid.
30 - It has a low average thermal expansion coefficient between room temperature
and the liquefaction temperature TLOth~e cryogenic fluid.
,,, - It does not exhibit any "ductile-fragile" resilience transition.
, ..
The alloy used preferably has:
- an average thermal expansion coefficient between 20°C and 100°C of less than
35 or equal to 10.5~10K-~', ~in particular less than or equal to 2.5x10-@K -';
3
- an average thermal expansion coefficient between -180°C and 0°C of less than
or equal to lox 10-%-', in particular less than or equal to 2x10-%-'; and
- a resilience greater than or equal to 100 joule/cm2, in particular greater than or
equal to 150 joule/cm2, at a temperature greater than or equal to -196°C.
5 Preferably, the alloy used has the following composition, in weight %:
34.5 5 Ni 5 42.5%
0.15% 5 Mn s 0.5%
0 5 Si 5 0.35%, preferably 0.1% 2 Si 5 0.35%
0.010% 5 C 5 0.050%
10 optionally:
0 5C0520%
0 5Tir0.5%
0.01 %5Cr50.5%
the remainder being iron and impurities necessarily resulting from the elaboration.
15 In this case, the alloy used preferably has:
- an average thermal expansion coefficient between 20°C and 100°C of less than
or equal to 5.5 x 10.~K -';
- an average thermal expansion coefficient between -180°C and 0°C of less than
or equal to 5 x 1 0-6 K-'; and
20 - a resilience greater than or equal to 100 joule/cm2, in particular greater than or
equal to 150 joulelcm2, at a temperature greater than or equal to -196°C.
Still more particularly,
35% 5 NI 5 36.5%
0.2% r Mn 5 0.4%
25 0.02 5 C 5 0.04%
0.15 5 Si 5 0.25%
optionally
0 SC0520%
0 sTis0.5%
the remainder being iron and impurities necessarily resulting from the elaboration.
In this case, the alloy preferably has:
- an average thermal expansion coefficient between 20°C and 100°C of less than
or equal to 1.5 x 10' K-';
35 - an average thermal expansion coefficient between -180°C and 0°C of less than
or equal to 2x10.~ K-';
4
- a resilience greater than or equal to 200 joule/cm2 at a temperature greater than
or equal to -196°C.
Such an alloy is an alloy of the cryogenic lnvar8 type. The trade name of this alloy
is lnvar8-~93.
5 Conventionally, the alloys used are elaborated in an electric arc furnace or an
induction vacuum furnace. -
After operations of refining in a ladle, which allow adjusting the contents of residual
alloy elements, the alloys are cast as semi-finished products, which are subjected to hot
processing, in particular by hot rolling, in order to obtain strips.
10 These semi-finished products are for example ingots. Alternatively, they are
formed by slabs continuously cast by means of an installation for continuous casting of
slabs.
The thereby obtained strip is stripped and polished in a continuous process in
order to limit its defects: calamine, oxidized penetration, flakes and thickness
15 inhomogeneities in the direction of the length and of the width of the strip.
The polishing is notably achieved by means of grinders or abrasive papers. One
function of the polishing is to remove the stripping residues.
At the end of this polishing step, the initial strip 1 provided in the first step of the
method according to the invention is obtained.
20 Optionally, before the homogenous cold rolling step, annealing is carried out on
the strip for homogeneization of the microstructure. This microstructure homogeneization
annealing is notably a continuous annealing in a heat treatment oven, called
microstructure homogeneization annealing oven in the subsequent description, with a
dwelling time in the microstructure homogeneization annealing oven comprised between 2
25 minutes and 25 minutes and a temperature of the strip during the microstructure
homogeneization annealing comprised between 850°C and 1200°C.
The initial strip 1 has a constant thickness E, comprised between 1.9 mm and 18
mm (see Fig. 1).
The initial strip 1 is then rolled during a homogenous cold rolling step. The
30 homogenous rolling is carried out along the length of the initial strip 1.
By homogenous rolling, is meant a rolling which transforms a strip having a
constant thickness into a thinner strip also having a constant thickness.
More particularly, the homogenous rolling step comprises one or several passes
performed in a mill wherein the strip passes into a rolling gap delimited between working
35 rolls. The thickness of this rolling gap remains constant during each pass of the
homogenous rolling step.
5
This homogenous rolling step results in an intermediate strip 3 having a constant
thickness E, along the rolling direction, i.e. along the length of the intermediate strip 3 (see
Fig. 2). .
Optionally, the homogenous rolling step comprises at least one intermediate
5 recrystallization annealing.
When it is present, the intermediate recrystallization annealing is carried out
between two successive homogenous rolling passes. Alternatively or optionally, it is
carried out before the flexible rolling step at the end of the homogenous rolling step, i.e.
after all the rolling passes carried out during the homogenous rolling step.
10 For example, the intermediate recrystallization annealing is a continuous annealing
carried out in an intermediate annealing oven with a temperature of the strip during the
intermediate annealing comprised between 850°C and 1200°C and a dwelling time in the
intermediate annealing oven comprised between 30 seconds and 5 minutes.
The intermediate recrystallization annealing, or when several intermediate
15 recrystallization annealings are carried out, the last intermediate recrystallization
annealing of the homogenous rolling step, is carried out when the strip has a thickness Ei
comprised between the thickness E, of the initial strip 1 and the thickness E, of the
intermediate strip 3.
When the intermediate recrystallization annealing is carried out at the end of the
20 homogenous rolling step, the thickness Ei of the strip during the intermediate
recrystallization annealing is equal to the thickness E, of the intermediate strip 3 at the
beginning of the flexible rolling step.
Advantageously, in the embodiment in which at least one intermediate
recrystallization annealing is carried out, a single intermediate recrystallization annealing
25 is carried out. In particular, this single intermediate recrystallization annealing is carried
out between two successive homogeneous rolling passes when the strip has a thickness
Ei strictly greater than the thickness E, of the intermediate strip 3.
Preferably, the homogenous rolling step does not comprise any intermediate
annealing.
30 The intermediate strip 3 having a thickness E, obtained at the end of the
homogenous rolling step is then subjected to a flexible cold rolling step.
The flexible rolling is carried out along a rolling direction extending along the length
of the intermediate strip 3.
Flexible rolling allows obtaining a strip having a variable thickness along its length.
6
For this, the thickness of the rolling gap of the mill used is continuously varied.
This variation depends on the desired thickness of the area of the strip being rolled so as
to obtain a strip having a variable thickness along its length.
More particularly, and as illustrated in Fig. 3, at the end of the flexible rolling step a
5 variable thickness strip 4 comprising first areas 7 having a first thickness e+s and second
areas 10 having a second thickness e, smaller than the first thickness e+s. The first
thickness e+s and the second thickness e each correspond to a given rolling gap
thickness.
The first areas 7 and the second areas 10 each have a substantially constant
10 thickness, e+s and e, respectively.
They are connected together through connecting areas 11 having a non-constant
thickness along the length of the variable thickness strip 4 . The thickness of the
connecting areas 11 varies between e and e+s. According to an example, it varies
linearly between e and e+s.
15 The homogenous rolling step and the flexible rolling step generate in the first areas
7, i.e. in the thickest areas of the strip 4, a plastic deformation ratio z,, after an optional
intermediate recrystallization annealing, which is greater than or equal to 30%, more
particularly comprised between 30% and 98%, still more particularly comprised between
30% and 80%. In the aforementioned ranges, the plastic deformation ratio z, is
20 advantageously greater than or equal to 35%, more particularly greater than or equal to
40%, and still more particularly greater than or equal to 50%.
The plastic deformation ratio z, generated in the first areas 7 is defined as follows:
- If no intermediate recrystallization annealing is carried out during the
homogenous rolling step, the plastic deformation ratio z, is' the total reduction ratio
25 generated in the first areas 7 of the strip 4 by the homogenous rolling step and the flexible
rolling step, i.e. resulting from the reduction in thickness from the initial thickness E, to the
thickness e+s.
In this case, the plastic+deformation ratioz, , in percentage, is given by the following
E ( e + ~ )
formula: T, = x 100 (1).
Eo
30 Thus, in the case when no intermediate recrystallization annealing is carried out, '
the plastic deformation ratio z, is equal to the total reduction ratio generated in the first
areas 7 by the homogenous rolling step and the flexible rolling step.
7
- If at least one intermediate recrystallization annealing is carried out during the
homogenous rolling step, the plastic deformation ratio T, is the reduction ratio generated
in the f~rsta reas 7 by the reduction in thickness of the strip from the thickness E, which it
has during the last intermediate recrystallization annealing carried out during the
5 homogenous rolling step to thickness ets.
In this case, the plastic deformation ratio^, , in percentage, is given by the following
E, - ( E + s )
formula: T , = x I00 (2)
E,
Thus, in the case when one or several intermediate annealings are carried out
during the homogenous rolling step, the plastic deformation ratio T, is strictly smaller than
10 the total reduction ratio generated in the first areas 7 by the homogenous rolling step and
the flexible cold rolling step:
The plastic deformation ratio T , , afler an optional intermediate recrystallization
annealing, generated in the second areas 10, is strictly greater than the plastic
deformation ratio T, in the first areas 7. It is calculated in a similar way, by replacing ets
15 with e in the formulae (1) and (2) above.
The difference AT of the plastic deformation ratio between the second areas 10
and the first areas 7 is given by the relationship AT = T, -T, .
This difference AT is advantageously smaller than or equal to 13% if the thickness
Eo is strictly greater than 2 mm. It is advantageously smaller than or equal to 10% if the
20 thickness Eo is less than or equal to 2 mm.
More particularly, the difference AT is less than or equal to 10% of Eo is strictly
greater than 2mm, and the difference AT is less than or equal to 8% if Eo is less than or
equal to 2mm.
Advantageously, the thickness E, of the intermediate strip 3 before the flexible
25 rolling step is in particular equal to the thickness e of the second areas 10 multiplied by a
reduction coefficient k comprised between 1.05 and 1.5. Advantageously, k is equal to
about 1.3.
Advantageously, the thicknesses e+s and e of the first and second areas 7, 10
observe the equation:
30 e+s=(n+l).e
wherein n is a constant coefficient comprised between 0.05 and 0.5.
In other words, the first thickness e+s is equal to the second thickness e multiplied
by a multiplication coefficient comprised between 1.05 and 1.5.
8
This equation can be rewritten in the following way: s = n.e , i.e. the over-thickness
s of the first areas 7 relatively to the second areas 10 is equal to the coefficient n
multiplied by the thickness e of the second areas 10.
The thickness e of the second areas 10 is comprised between 0.05 mm and 10
5 mm, more particularly between 0.15 mm and 10 mm, still more particularly between 0.25
mm and 8.5 mm. When sheets are made, the thickness e is less than or equal to 2 mm,
advantageously comprised between 0.25 mm and 2 mm. When plates are made, the
thickness e is strictly greater than 2 mm, in particular comprised between 2.1 mm and
IOmm, more particularly comprised between 2.1 mm and 8.5 mm.
10 Next the variable thickness strip 4 resulting from the flexible rolling step is
subjected to a final recrystallization annealing.
The final recrystallization annealing is a continuous annealing carried out in a final
annealing oven. The temperature of the final annealing oven is constant during the final
recrystallization annealing. The temperature of the strip 4 during the final recrystallization
15 annealing is comprised between 850°C and 1200°C.
The dwelling time in the final annealing oven is comprised between 20 seconds
and 5 minutes, more particularly between 30 seconds and 3 minutes.
The running speed of the strip 4 in the final annealirlg oven is constant. For
example it is comprised between 2mlmin and 20mlmin for a final annealing oven with a
20 heating length equal to 10m.
Advantageously, the temperature of the strip 4 during the final annealing is
1025°C. In this case, the dwelling time in the final annealing oven is for example
comprised between 30 seconds and 60 seconds for a variable thickness strip 4 having
second areas 10 with a thick~esse of less than or equal to 2 mm. The dwelling time in
25 the final annealing oven is for example comprised between 3 minutes and 5 minutes for a
variable thickness strip 4 having second areas 10 with a thickness e strictly greater than 2
mm.
The dwelling time in the final annealing oven, as well as the final annealing
temperature are selected so as to obtain after the final recrystallization annealing a strip 4
30 having quasi-homogenous mechanical properties and grain sizes between the first areas
7 and the second areas 10. Subsequent description specifies the meaning of "quasihomogenous".
Preferably, the final annealing is carried out in a reducing atmosphere, i.e. for
example in pure hydrogen or in a Hz-NZ atmosphere. The frost temperature is preferably
35 less than -40°C. In the case of a Hz-NZ atmosphere, the content of N2 may be comprisedi
9
between 0% and 95%. The atmosphere Hz-N2for example comprises approximately 70%
of H2 and 30% of N,.
According to an embodiment, the variable thickness strip 4 continuously passes
from the flexible rolling mill to the final annealing oven, i.e. without any inte~mediatec oiling
5 of the variable thickness strip 4.
Alternatively, at the end of the flexible rolling step, the variable thickness strip 4 is
coiled so as to transport it to the final annealing oven, and then it is uncoiled and
subjected to the final recrystallization annealing.
According to this alternative, the coiled strip 4 for example has a length comprised
10 between 100 m and 2500 m, notably if the thickness e of the second areas 10 of the strip
4 is approximately 0.7 mm.
At the end of the final recrystallization annealing, a strip 4 having a variable
thickness along its length is obtained having the following characteristics.
It comprises first areas 7 having a thickness of e+s and second areas of thickness
15 e, optionally connected together through connecting areas 11 with a thickness varying
between e and e+s.
Preferably, the absolute value difference between the average size of the grains of
the first areas 7 and the average size of the grains of the second areas 10 is less than or
equal to 0.5 numbers according to the ASTM E l 12-10 standard. The average grain size in
20 ASTM numbers is determined by using the method of comparison with typical images as
described in the ASTM E112-10 standard. According to this method, in order to
determine the average grain size of a sample, an image of the structure of the grains on
the screen obtained by means of an optical microscope at a given magnification of the
sample having been subjected to contrast etching is compared with typical images
25 illustrating twinned grains of different sizes having been subject to contrast etching '
(corresponding to plate Ill of the standard). The average grain size number of the sample
is determined as being the number corresponding to the magnification used borne on the
typical image which looks the most like the image seen on the screen of the microscope.
If the image seen on the screen of the microscope is intermediate between two
30 successive typical images of grain sizes, the average grain size number of the image
seen in the microscope is determined as being the arithmetic mean between the numbers
corresponding to the magnification used borne on each of the two typical images.
More particularly, the average grain size number GIAsrM of the first areas 7 is at
most 0.5 less than the average size number G&sTM of the second areas 10.
35 The variable thickness strip 4 may have quasi-homogenous mechanical properties.
In particular:
10
- the absolute value difference between the yield strength at 0.2% of the first areas
7 noted as Rpl and the yield strength at 0.2% of the second areas 10 noted as Rp2 is
less than or equal to 6MPa, and
- the absolute value difference between the ultimate tensile strength of the first
5 areas 7 noted as Rml and the ultimate tensile strength of the second areas 10 noted as
Rm2 is less than or equal to 6MPa.
By yield strength at 0.2%, is conventionally meant the stress value at a plastic
deformation of 0.2%.
Conventionally, the ultimate tensile strength corresponds to the maximum stress
10 before striction of the test sample.
In the illustrated example, the variable thickness strip 4 has a pattern periodically
repeated over the whole length of the strip 4. This pattern successively comprises one
I,
half of a first area 7 with a length A, a connecting area 11 of length L3, a second area
2
10 of length L2, a connecting area 11 of length L3 and one half of a first area 7 with a
L
15 length of 2.
2
Advantageously, the length L2 of the second area 10 is substantially greater than
the length L1 of the first area 7. As an example, the length L2 is comprised between 20
and 100 times the length Ll.
Each sequence formed by a first area 7 surrounded by two connecting areas 11
20 forms an over-thickness area of the variable thickness strip 4 , i.e. an area with a .
thickness greater than e. Thus, the variable thickness strip 4 comprises second areas 10
of length L2 with a thickness e, separated between them by over-thickness areas.
After the final recrystallization annealing, the variable thickness strip 4 is cut out in
the over-thickness areas, preferably in the middle of the over-thickness areas.
25 Blanks 12 illustrated in Fig. 4 are thereby obtained, comprising a second area of
length L2 surrounded at each of its longitudinal ends by a connecting area 11 of length L3
L1
and by a half of a first area 7 of length -
2
At the end of the cutting step, the blanks 12 are leveled according to a known
leveling method.
30 The blanks 12 are then wound into unit coils.
According to an alternative of the manufacturing method described above, the
leveling of the variable thickness strip 4 is carried out after the final recrystallization
annealing and before the cutting out of the blanks 12.
11
According to this alternative, the leveled variable thickness strip 4 is cut out in the
over-thickness areas in order to form the blanks 12. Preferably, the strip 4 is cut out in the
middle of the over-thickness areas.
The cutting out is for example performed on the leveler used for leveling the strip
5 4. Alternatively, the leveled strip 4 is wound into a coil, and then cut out on a machine
different from the leveler.
The blanks 12 are then wound as unit coils.
By means of the manufacturing method described above, blanks 12 formed in one
piece comprising a central area 13 of thickness e, surrounded by reinforced ends 14, i.e.
10 with a thickness greater than the thickness e of the central area 13, are obtained. The
ends 14 correspond to over-thickness areas of the variable thickness strip 4 and the
central area 13 corresponds to a second area 10 of the variable thickness strip 4 from
which the blank 12 has been but out.
These blanks 12, which have a variable thickness along their length while being
15 formed with one part, do not have the weaknesses of the welded assemblies of the state
of the art. Further, their reinforced ends 14 allow assembling them by welding with other
parts while minimizing the mechanical weaknesses due to this assembling by welding.
According to alternatives, the blanks 12 may for example be obtained by cutting
out the strip 4 at other locations than in two successive over-thickness areas. For
20 example, they may be obtained by alternately cutting them in an over-thickness area and .
in a second area 10. In this case, blanks 12 are obtained having a single reinforced end
14 with a thickness greater than e.
They may also be obtained by cutting out in two successive second areas 10.
As an example, and as illustrated in Fig. 5, a blank 12 according to the invention
25 may be assembled with a second part 16 by welding one of the reinforcedends 14 of the
blank 12 to an edge of the second part 16. The thickness of the second part 16 is
preferably greater than the thickness of the central area 13 of the blank 12. The weld
performed is more particularly a lap weld.
The part 16 may be a blank 12 as described above.
30 Thus, in Fig. 6, two blanks 12 assembled end to end by welding are illustrated.
These two blanks 12 are welded together through their reinforced ends 14.
In the examples illustrated in figs. 5 and 6:
- the length of the central area 13 is for example comprised between 40 m and 60
m; and
35 - the length of each reinforced end 14 is for example comprised between 0.5 m
and 2 m.
12
The second thickness e is notably about equal to 0.7 mm
The first thickness e+s is about equal to 0.9 mm.
Alternatively, a non-planar part is formed from the blank 12
Thus, in the example illustrated in Fig. 7, a tube segment 18 is formed from the
5 blank 12.
The edges of the blank 12 extending along the length of the blank 12 are called
longitudinal edges.
In order to manufacture the tube segment 18, the blank 12 is rolled up along its
width, i.e. around a longitudinal axis L so as to form a rolled up blank 12. The longitudinal
10 edges of the rolled up blank 12 are then welded together so as to form the tube segment
18. This tube segment 18 has a cylindrical central area 20 of thickness e and cylindrical
reinforced ends 22 with a thickness greater than the thickness e, and in particular equal to
e+s.
A tube 24 is then made by welding at least two tube segments 18 together through
15 their reinforced ends 22. heh held is an orbital weld, in particular a weld of the end-to-end
type.
The thickness e+s of the reinforced ends 22 is defined depending on the traction
forces which the tube 24 has to undergo during its mounting and during its use.
Such a tube 24 is for example a cryogenic tube suitable for conveying liquefied
20 natural gas and intended to form for example the main tube coated with a material
protecting it against the corrosion of a cryogenic under-water conduit for conveying
liquefied natural gas or the inner tube of such a conduit.
In this case, for example:
-the thickness e is equal to about 8.2 mm;
25 -the thickness e+s is equal to about 9.43 mm.
The length L2 of the central area 20 of a tube segment 18 is equal to about 8m.
The manufacturing method according to the invention is particularly advantageous.
Indeed, it allows obtaining a strip made of an alloy mainly based on iron and nickel having
the chemical composition defined above having areas with different thicknesses but quasi-
30 homogeneous mechanical properties. These properties are obtained by the use of a
plastic deformation ratio after an optional intermediate recrystallization annealing
generated by the homogenous rolling and flexible rolling steps in the thickest areas
greater than or equal to 30%.
The following experimental examples illustrate the significance of the range of
35 plastic deformation ratio claimed for this type of alloy.
13
In a first series of experiments, variable thickness sheets were made, i.e. variable
thickness strips 4 having a thickness e of the second areas 10 is less than or equal to 2
mm.
Table 1 hereafter illustrates tests for manufacturing sheets having variable
thickness without any intermediate recrystallization annealing. ,
Table 2 hereafter contains characteristics of the sheets obtained by the tests of
Table 1.
Table 3 hereafter illustrates tests for manufacturing sheets with variable thickness
with an intermediate recrystallization annealing at thickness E,.
Table 4 hereafter contains characteristics of the sheets obtained by the tests of
Table 3.
In a second series of sxperiments, variable thickness plates were manufactured,
i.e. variable thickness strips 4 having a thickness e of the second areas 10 is strictly
greater than 2 mm.
Table 5 illustrates tests for manufacturing variable thickness plates with or without
any intermediate annealing.
Table 6 hereafter contains characteristics of the plates obtained by the tests of
Table 5.
In all the tables, the tests according to the invention are underlined.
It is seen that when the plastic deformation ratio T, after an optional intermediate
recrystallization annealing is greater than or equal to 30% (tests 1 to 7 of Table 1, 1 to 3 of
Table 3 and 1 to 9 of Table 5), the obtained variable thickness strip 4 has an average
grain size difference between the average size of the grains of the first areas 7 (thickness
e+s) and the size of the grains of the second areas 10 (thickness e) of less than or equal
to 0.5 ASTM numbers in absolute value. This small average grain size difference
between the first areas 7 and the second areas 10 results in quasi-homogenous
mechanical properties, i.e. a difference in yield strength at 0.2%, beltaRp between the first
areas 7 and the second areas 10 of less than or equal to 6 MPa in absolute value, and a
difference between the ultimate tensile strength DeltaRm of the first areas 7 and of the
second areas 10 of less than or equal to 6 MPa in absolute value.
It is thus possible to obtain a variable thickness strip 4 , having quasi-homogenous
mechanical properties and grain sizes at the end of a very simple recrystallization
annealing, since it is carried out at a constant temperature and constant running speed.

16
DeltaGasm
12
(%)
60
60
-67
25
25
L1
(m)
1.20
- -1.20 -
-1.20
1.50
1.50
Delta Rp
Test (MPa)
z2-rl
(%I
-10
-6
-5
19
----11 -
Ec
(mm)
08
08
07
1.95
1.73
Test
-1
-2 .
-3
4
5
6
Delta Rm
(MPa)
Properties at thickness e
Final annealing
T"C; duration
1025°C: 40s
1025°C: 40s
1025°C; 30s
1025°C; 60s
1025'C; 60s
19 -
10
11
L2
(m)-
- - -1.5-0 - -
1.50 - - . - - - - - - - - - - .
-1.50
1.90
1.90
El
(mm)
1.5
1.5
1.5
2.00
2.00
G2-TM
Properties at thickness e+s
1025°C; 60s
1025°C; 605
1025°C; 40s
(mm)
Q&
, Q&
0.5
1.5
1.5
Annealing at
Ei
TsC; dur6e
1025°C: 50s
1025°C: 50s
1025"C;50s
1025°C; 80s
1025°C; 80s
Wavelength
(m)
-50
-- -50
-60
50
50
, 5 0 .
GI-TM
L3
(m)
45.8
@
-55.8
44.7
44.7
RP
(MPa)
TI
(%I
50
54
-62
6
14
113518
u
Cm
-0.15
0.25
0.15
Eo
(mm)
2.6
2.6
2.6
4.2
4.2
, 3.2
-
7
8
Rm
(MPa)
RP
(MPa)
e+s
(mm)
0.75
0.69
-0.58
1.88
1.73
- -1.3 -
-1.3
- -1.3 -
1.30
1.15
1.30 1.30 1025°C; 50s 1.30 1.0 0.25 1.25 1.50 1.90 44.7 4 23
1.15
1.15
Rm
(MPa)
50
60
1.50
1.00
-
3.2
2.6
1025'C; 60s
lOOO"C:4Os
1.15
0.81
1.0
0.7
0.15
0.15
1.15
0.81
1.00
1.00
1.50 .
1.50
46.0
56.0
23
20
33
30
Wavelength
T 1 L )
, Anne;? at
(mm) PC; duration PC; duration
8.2 1050°- C: 5 min
Test Properties at thickness e+s Properties at thickness e
1 G I 1 Rp (MPa) I Rm (MPa) / GZmm / Rp (MPa) / Rm (MPa)
Delta Rp (MPa) Delta Rm (MPa) DeltaGmm
CLAIMS
1 .-A method for manufacturing a strip having a variable thickness along its length,
made of an iron-based alloy, the strip being made of an alloy comprising by weight:
5 34.5% r Ni 5 53.5%
0.15% 5 Mn S 1.5%
0 r Si < 0.35%, preferably 0.1% 5 Si < 0.35%
0 r C 5 0.07%
optionally:
10 0