Note: Descriptions are shown in the official language in which they were submitted.
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A STEEL SHEET SUITABLE FOR ENAMELLING AND METHOD FOR
PRODUCING SUCH A SHEET
Field of the Invention
[0001] The present invention is related to a steel
sheet suitable for enamelling, and to a method for the
superficial decarburization of a steel sheet, as a
preparation for enamelling the steel.
State of the art.
[0002] The carbon level of a steel sheet has an
important influence on the results in terms of surface
quality of an enamel layer applied on the surface of the
sheet. A high carbon level at the steel surface may give
rise to CO-gas bubble formation, which shows up as black
spots and craters in the enamel surface. On the other
hand, when a sufficiently high carbon level is present
initially in the bulk, this carbon forms coarse cementite
during hot rolling which cracks upon cold rolling. These
cracks are capable of capturing hydrogen which enters the
steel during the enamelling process. When hydrogen is
insufficiently captured, pressure will rise at the
steel/enamel surface which gives rise to the so-called
'fish-scale' deformation of the enamel.
[0003] It is therefore advantageous to decarburize
the steel only in a layer at the surface of the steel, i.e.
to conduct a superficial decarburization. Document JP-A-
2282421 describes such a method, wherein a continuously
cast and annealed non-aging steel sheet for enamelling is
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produced, characterized in that a continuous-cast steel
slab containing C between 0.0025 and 0.0050wt%, Si max.
0.03wt%, Mn between 0.1 and 0.6wt%, P between 0.005 and
0.03wt%, S between 0.005 and 0.03wt%, Al max. 0.01wt%, N
max. 0.004wt%, Cu between 0.01 and 0.06wt%, 0 between 0.02
and 0.06wt%, V between 0.01 and 0.06wt%, the balance Fe and
inevitable impurities, is hot-rolled with a finishing
temperature higher than or equal to 800 C, and a coiling
temperature of 600-800 C, cold-rolled with a reduction
ratio higher than or equal to 60% and subjected to a
decarburization annealing at 700-900 C for 30sec-3min,
carried out in a continuous annealing furnace having a
decarburizing atmosphere composed of 1-20% water vapour,
gaseous hydrogen in an amount higher than or equal to twice
the water vapour amount, and the balance being mainly
gaseous nitrogen, so as to reduce the C-level to be less
than or equal to 0.002wt%. JP-
A-6116634 describes a
similar method, but wherein the starting material has no
vanadium and the initial C level is up to 0.015wt% and B is
added instead of V for H-trapping.
[0004]
Both prior art methods result in fully or
superficially decarburized steel sheets which are suitable
for enamelling by Direct White Enamelling (DWE), wherein
one white enamel coating is applied on the surface,
followed by one firing step. As the initial carbon level
is quite low, fish-scale resistance due to cementite
formation is not achieved. To compensate for this, a steel
with a high oxygen level and a limited Al-level is used in
the prior art together with specific alloying elements such
as B, V. Thanks
to the limited Al-content, oxides of Si
and Mn and nitrides of B and V are formed within the bulk
of the steel which are beneficial against fish-scaling.
However, this alloying involves extra costs and leads to
some technical difficulties, e.g. involving casting with V.
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Furthermore, the prior art decarburized sheets have rather
low formability as testified by the values of the Lankford
coefficient (rm). These values do not exceed 1.8 which is a
concern when deep-drawing is foreseen. In particular,
figure 1 of JP6116634 shows that rm values between 1.6 and
1.8 are only achieved for a very narrow range of carbon
level before decarburizing annealing. Below 0.0050wt%C and
above 0.0150wt%C, the rm value is deteriorated.
[0005]
Summary of the invention
[0006] The invention is related to steel sheets and
products and to a production method as disclosed
below.
The invention is related to a
rolled steel sheet suitable for enamelling, said sheet
having a carbon profile, defined by a gradient in the C-
level from a level Csurface at at least one surface of the
sheet, to a level Cbulk in the bulk of the sheet, Cbuik being
higher than Csurface and with :
- Cbuik higher than 0 and lower than or equal to
0.08wt%,
¨ Csurface between 0 and 0.015wt%,
- Al between 0.012wt% and 0.07wt%,
- Mn between 0.12wt% and 0.45wt%,
- 0 lower than 0.01wt%
and optionally :
- Cu between 0.025wt% and 0.1wt%,
- S between 0.008wt% and 0.04wt%,
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¨ Ca between 0.0005wt% and 0.005wt%
the balance being Fe and incidental impurities,
and wherein the
depth where the C-level reaches
(Cmulk+Csurface) /2, is higher than 75 m.
[0007] According to a
preferred embodiment, the
steel sheet of the invention has an rm value between 1.8
and 2.1.
[0008] According to
specific embodiments, Csurface is
between 0.005wt% and 0.015wt%, or between 0 and 0.005wt%.
[0009] According to
other specific embodiments, Cbulk
is between 0.02wt% and 0.08wt%, or between 0.025wt% and
0.08wt% or between 0.025wt% and 0.06wt%.
[0010] According to
another embodiment, the Al-level
is between 0.02wt% and 0.06wt%.
[0011] According to a
further embodiment, said depth
is between 130 m and 200 m.
[0012] The invention
is equally related to an
enamelled steel sheet consisting of a steel sheet according
to any of the above paragraphs, provided with an enamel
layer.
[0013] The invention
is further related to a steel
product produced from a sheet according to the invention,
and to an enamelled steel product consisting of a such a
product, provided with an enamel layer.
[0014] The invention is
also related to a method for
producing a rolled steel sheet for enamelling, comprising
the steps of :
¨ subjecting a steel slab to hot rolling followed by
coiling, and cold rolling, so as to obtain a cold-rolled
steel sheet, said slab comprising the following initial
composition :
¨ C between 0.02wt% and 0.08wt%,
¨ Al between 0.012wt% and 0.07wt%,
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¨ Mn between 0.12wt% and 0.45wt%,
¨ 0 lower than 0.01wt%
and optionally :
¨ Cu between 0.025wt% and 0.1wt%,
5 ¨ S between 0.008wt% and 0.04wt%,
¨ Ca between 0.0005wt% and 0.005wt%,
¨ the balance being Fe and incidental impurities,
¨ subjecting said cold-rolled sheet to continuous annealing
step, wherein said sheet is exposed during a
decarburizing time to a decarburizing atmosphere
comprising water vapour and hydrogen gas, wherein the H2
content is between 1vol% and 95vo1%, the H20 content
between 0.04vol% and 33vo1%, the remainder being mainly
nitrogen gas, the ratio pH20/pH2 being between 0.04 and
0.5.
[0015] According to a
preferred embodiment, said
continuous annealing takes place at an anneal temperature
between 760 C and 850 C, and during a decarburizing time
between 45s and 300s.
[0016] According to a
specific embodiment, the
anneal temperature is between 800 C and 850 C.
[0017] According to
specific embodiments of the
method of the invention, the initial C-level is between
0.025wt% and 0.08wt% or between 0.025wt% and 0.06wt%.
[0018] According to a
further embodiment, the
initial Al-level is between 0.02wt% and 0.06wt%.
[0019] According to a
specific embodiment, the ratio
pH20/pH2 is between 0.04 and 0.25.
[0020] The method of
the invention may further
comprise an over-ageing step at a temperature between 350 C
and 450 C during a timespan between 100s and 500s. The
method may further comprise a skinpass step with a
reduction of between 0.3% and 1.5%.
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Brief description of the figures
[0021]
Figure 1 illustrates the carbon profile in a
steel sheet according to the invention.
[0022]
Figure 2 illustrates an example of an
annealing step usable in the method of the invention.
Detailed description of the invention
[0023] The
steel sheet of the invention has a C-
profile, defined by a gradient in the C-level from a lower
value Csurface at the surface to a higher value Cbulk in the
bulk. The sheet is obtainable by a method which includes a
continuous decarburization step, as will be described
further in this text. Figure 1 illustrates the carbon-
distribution across the thickness of two sheets according
to the invention, with a thickness of 0.7mm. Curve 10
illustrates a sheet which comprises a bulk portion 11,
where the C-level Cbulk is substantially constant, and two
surface portions 12 (one on each side of the sheet), each
surface portion exhibiting the C-profile. The
surface
level is defined as the minimum value of the C-profile,
measured by a suitable measurement technique (e.g. Glow
Discharge Optical Emission Spectroscopy (GD-OES), which
allows composition measurement as depth analysis). In
a
steel sheet according to the invention, the C-level at the
surface is maximum 0.015wt%, whereas Cbulk is higher than
zero and lower than or equal to 0.08wt%. At the same time,
Cbulk is higher than Csurface = According to an embodiment,
Csurface is between 0.005wt% and 0.015wt%. According to
another embodiment, Cõr fa, is between 0 and 0.005wt%.
[0024]
Curve 10 is an example of a sheet where the
decarburization has not taken place over the entire
thickness of the sheet. This means that the level Cbulk is
equal to the initial C-level applied in the production
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method (described further in more detail).
According to
embodiments which correspond to embodiments of the method
of the invention (see further), Cbulk is then between
0.02wt% and 0.08wt%, or between 0.025wt% and 0.08wt, or
between 0.025wt% and 0.06wt% or between 0.025wt% and
0.05wt%.
Curve 13 illustrates the case where
decarburization has continued until the middle plane of the
sheet. In
this case, Cbulk is smaller than the initial C-
level of the method, and the C-profile extends over each
half-width of the sheet.
[0025] The
decarburized sheet according to the
invention further comprises Al, Mn and possibly S, Cu and
Ca. Contrary to the prior art references, the oxygen level
is to be kept lower than 0.01wt%. According to a preferred
embodiment of the steel sheet of the invention, oxygen is
not added deliberately to the composition, but is allowed
only at impurity levels.
Fish scaling resistance is
ensured by the higher initial C-level, so no oxide
formation is required for this purpose. This means that no
special alloying elements such as V are included. Also, N
is kept as low as possible.
[0026] The
Al-level in the sheet of the invention is
between 0.012wt% and 0.07wt%, which is higher than the
allowed Al-level in the prior art references cited above.
In the cited prior art documents Al needs to be limited to
avoid deoxidation, so as to ensure the formation of the
oxides that will work against fish-scaling. In
the method
of the invention (see further), Al is mandatory for
deoxidation and binding of free N to avoid the ageing of
the mechanical properties. When
the Al-level is lower
than 0.012wt%, insufficient deoxidation takes place, and
binding of N is required through other means. Adding Al at
levels higher than 0.07wt% means an increase in cost of the
process, and a deterioration of the enamelling quality. A
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more preferred range for the Al-level, related to more
optimized conditions in terms of deoxidation and
cost/enamelling quality is between 0.02wt% and 0.06wt%.
[0027] Mn
is present between 0.12wt% and 0.45wt%.
This element is added to control the strength properties of
the steel and to avoid the formation of free sulphur.
[0028]
Copper, Sulphur and Calcium may optionally be
added above the impurity level, more precisely in the
ranges 0.025wt% to 0.1wt%, 0.008wt% to 0.04wt% and
0.0005wt% to 0.005wt% respectively. These
elements
improve the enamelling quality.
[0029] The
balance of the composition of the steel
sheet according to the invention consists of Fe and
incidental impurities. The
following elements may be
present as impurities at levels which are preferably lower
than the values (in wt%) given in table 1 :
Si < 0.1
P < 0.03
Ti < 0.01
Cr <0.2
Ni <0.2
As < 0.02
Sn < 0.02
Nb < 0.01
/ <0.01
Sb < 0.02
Mo < 0.03
B < 0.0005
N < 0.007
Table 1 : impurity levels
[0030] In
a steel sheet of the invention, the depth
of the C-profile, being defined as the depth where the C-
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level reaches (Cmmi_k + Csurface) /2, is higher than 75 m, to
ensure good enamelling capability.
According to an
embodiment, said depth is between 130 m and 200 m.
[0031]
Steel sheets according to the invention,
i.e. with a C-level at the surface between 0 and 0.015wt%
are suitable for 2C/1F enamelling, i.e. enamelling by
applying a ground coat enamel, followed by an outer enamel
coating, both coatings being subjected to one firing step,
and for 1C/1F enamelling, i.e. enamelling by applying one
enamel layer subjected to one firing step. Steel sheets
with low C-levels (i.e. 0.005wt% and less) at the surface
may be suitable also for Direct White Enamelling (DWE).
[0032]
According to a preferred embodiment, the rm
value of a steel sheet according to the invention is
between 1.8 and 2.1. This means that the steel sheet has
better formability than the prior art steel sheets referred
to above. In
the present description, the 'rf value
refers to the plastic strain ratio (also known as the
anisotropy factor), being the ratio of the true strain in
the width direction to the true strain in the thickness
direction when a sheet material is pulled in uniaxial
tension beyond its elastic limit. The
'rmf value is
defined as 14(r90 + 2*r45 + ro), with r90, r.45 and ro the r-
values as defined above, measured on samples oriented
respectively at 90 , 45 and 0 with respect to the rolling
direction. In
a steel sheet according to the invention,
fish scaling resistance is ensured by the higher initial C-
level applied in the method (see further).
[0033] The
steel sheet of the invention can be
produced by subjecting a steel slab with a specific initial
steel composition to hot rolling, coiling and cold rolling,
and by subjecting the cold-rolled sheet to continuous
superficial decarburization. The initial composition is
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mainly characterized by a higher C-level compared to the
prior art, and by a higher Al-level and a lower oxygen
level. No deliberate addition of elements like V, Nb or B
is done, while still allowing to produce enamelled steel
5 sheets with a high fish scale resistance and good enamel
surface quality. The
initial C-level is between 0.02wt%
and 0.08wt%, more preferably between 0.025wt% and 0.08wt%.
This is higher than the initial C-levels disclosed in the
prior art references referred to above.
Despite such
10 higher initial C-levels, the method of the invention allows
to obtain steel sheets with
improved formability
characteristics compared to the prior art.
Whereas
JP6116634 indicates that above 0.015wt% of initial carbon,
it is not possible to obtain acceptable decarburization and
good formability, the starting composition of the invention
does not encounter these problems.
Decarburization is
possible down to an acceptable level, while formability is
excellent. When the initial C-level is lower than 0.02wt%,
insufficient cementite formation occurs which deteriorates
fish scale resistance. C-levels above 0.08wt% lead to too
high strength levels and thus reduced formability.
Specific ranges for the initial C-level, related to more
optimized characteristics in terms of fish scale resistance
and strength/formability are between 0.025wt% and 0.06wt%
and between 0.025wt% and 0.05wt%.
[0034] The
initial steel composition according to
the method of the invention further comprises Al, Mn and
possibly 0, S, Cu and Ca in the same ranges as the
decarburized sheet described above, the balance being Fe
and the incidental impurities listed in Table 1. A more
preferred range for the initial Al-level, related to more
optimized conditions in terms of deoxidation and
cost/enamelling quality is between 0.02wt% and 0.06wt%.
According to a preferred embodiment of the method of the
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invention, oxygen is not added deliberately to the
composition, but is allowed only at impurity levels.
[0035] The
method of the invention comprises
standard steps of hot rolling and cold rolling a steel slab
of the above composition. According to the preferred
embodiment, the slab is (re)heated at a temperature above
1050 C, subjected to hot rolling with a finishing
temperature between 850 C and 950 C, and coiling at coiling
temperature between 620 C and 770 C.
Still according to
the preferred embodiment, cold rolling is performed with a
reduction of minimum 50%. The final thickness of the cold
rolled sheet is preferably between 0.2 and 2mm.
[0036] The
decarburization anneal is done in an
annealing furnace for continuous annealing (i.e. annealing
while the cold-rolled sheet moves through the furnace at a
given speed, said speed determining the anneal time, i.e.
the time spent at the annealing temperature) as known in
the art, possibly provided with a vapour injection device
for applying a given annealing atmosphere.
[0037] Figure
2 shows an example of a lay-out of an
annealing furnace usable in the method of the invention,
starting with heating phase 1 wherein the temperature rises
to the annealing temperature. Phase 2 represents the
actual annealing (soaking) phase. Phase 3 is an overageing
step. Phase
2 can consist of one or more periods with a
different (constant or average) annealing temperature and a
different annealing atmosphere in each period. Practically
speaking, the different periods at different conditions can
be obtained by dividing the annealing zone in subsections
and by injecting H20 vapour into an atmosphere comprising
H2, at various points along the annealing line (see example
further in this description).
[0038]
According to the invention, the superficial
decarburization is done under a decarburizing atmosphere
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comprising water vapour and hydrogen gas, the remainder
being essentially nitrogen gas, with the H2 content between
1vol% and 95vo1%, the H20 content between 0.04vol% and
33vo1%, the ratio of partial pressures pH20/pH2 being
between 0.04 and 0.5, more preferably between 0.04 and
0.25. The
above composition describes the atmosphere at
the start of the decarburizing time. It is clear that
during decarburization, the atmosphere composition will
change, primarily due to the decarburization reaction
taking place (formation of H2 and CO). Also at the start
of the decarburizing time, small amounts of other gases may
already have formed or may be present as impurities in the
atmosphere. The total pressure under which the superficial
decarburization anneal takes place may be atmospheric
pressure, or a pressure different from atmospheric but
within generally known boundaries applied in this type of
annealing process.
[0039]
According to one embodiment, the
decarburizing atmosphere can be prepared with a mixture of
H2 and N2 with between 1,5 and 5% H2 in which H20 vapour is
injected so that pH20/pH2 is between 0.04 and 0.5. The
minimum value of this ratio ensures that sufficient H20 is
present to obtain decarburization according to the formula
C + H20 ' CO + H2. The maximum of said range ensures that
oxidation of Fe and of the furnace is avoided. A more
preferred range for pH20/pH2, related to more optimized
conditions in terms of sufficient decarburization and
avoiding the occurrence of Fe-oxidation is between 0.04 and
0.25.
[0040] In the
method of the invention, the
decarburizing atmosphere is applied during at least one of
said periods with a different (constant or average)
annealing temperature and a different annealing atmosphere
in each period, preferably during the totality of phase 2.
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In the following, the 'decarburizing time' refers to the
time spent under the conditions of the decarburizing
atmosphere.
[0041] The
decarburizing time and the anneal
temperature are chosen so as to obtain a steel sheet
according to the invention. It is within the skilled
person's knowledge to find suitable combinations of
decarburizing time and anneal temperature based on the
examples given further in this description. According to a
preferred embodiment, the decarburizing time is between 45s
and 300s and the anneal temperature between 760 C and
850 C. When the ratio pH20/pH2 is lower than about 0.1,
the decarburizing time is preferably higher than 70s. A
more preferred range of the anneal temperature, applicable
in combination with any decarburizing time between 45s and
300s is between 800 C and 850 C. The
temperature is not
necessarily constant during the decarburizing time.
Fluctuations of the temperature may occur due to variations
in the line speed for example. An over-ageing step may be
applied at a temperature between 350 C and 450 C during a
timespan between 100s and 500s. A skinpass may further be
applied with a reduction of between 0.3% and 1.5%.
Examples
[0042]
Results from industrial trials performed by
the applicant will be described hereafter, as well as a
number of laboratory trials. All tested samples were
produced from starting compositions according to the
invention. The coiling temperature was 725 C. Two
industrial trials were conducted. The
thickness of the
cold rolled sheet subjected to decarburization annealing in
industrial trial 1 was 0.6mm; in the second industrial
trial the thickness was lmm.
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[0043] The
continuous annealing line in which the
industrial trials were conducted consists of a heating
section, two soaking areas, a cooling and an overaging
part. The
annealing atmosphere consisted mainly of a
mixture of H2 and N2 , with H20 vapour being injected in the
first and/or the second soaking area. In the first trial,
H20 vapour was injected only in the second soaking area.
In the second trial, H20 was injected in the first and the
second soaking area.
Overageing was performed in both
trials at 400 C. The overageing time depended on the line
speed, e.g. at 180m/min line speed, the overageing time was
232s.
Table 2 shows the annealing conditions for both
trials (numbered trial 1 and trial 2).
Table 3 shows the
composition besides C, for a number of the samples shown in
table 1.
[0044] In
industrial trial 1, the pH20/pH2 ratio is
below the range of 0.04-0.5 in the first soaking area (due
to the fact that no H20 injection is done). The
decarburizing time in this trial is the time spent in the
second soaking area, where the pH20/pH2 is within said
range. This is an example therefore of a process wherein
phase 2 as shown in figure 1 comprises a first period
wherein the conditions of the present invention are not
met, and a second period wherein these conditions are met.
Such a process falls within the scope of the present
invention.
[0045] In
industrial trial 2, H20-injection was
performed in both soaking areas. The
decarburizing time
indicated here is the time spent in soaking areas 1 and 2.
The anneal temperature is the average of the temperatures
in soaking areas 1 and 2. The pH20/pH2 values indicated in
table 1 are the average values in soaking area 1 in which
more H20 was injected.
However, the pH20/pH2 in soaking
area 2 is estimated to be also within the range of 0.04-
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0.5. In
industrial trial 2, longer decarburizing times
could be achieved as compared to the first trial, for
similar line velocities, leading to
stronger
decarburization.
5 [0046] The
laboratory trials (marked 'trial 3' in
table 2), were conducted on samples which were subjected to
a simulation of the continuous annealing step, at the
conditions shown in table 2. These trials were conducted
in an atmosphere of HNx with 5% H2, with H20 added to obtain
10 pH20/pH2 in the range [0.04-0.5].
[0047]
Samples from all three trials were subjected
to an enamelling process wherein a ground coat enamel is
deposited, this enamel being designed especially to
determine the role of C in the enamel characteristics. It
15 was found that the adhesion of the enamelling layer was
good for all tested samples. The enamelling aspect was
good for C-levels at the surface of maximum 0.015wt%, and
for profile depths of 75 m up to 250 m, as shown in table
1. There is no reason to conclude from the results however
that the enamelling quality deteriorates at higher depth
values than 250 m. Such higher depth values are therefore
not excluded from the scope of the invention. All tested
samples showed a good fish scale resistance.
[0048]
Table 2 summarizes the results after
decarburization in terms of the C-level at the surface
(i.e. minimum level of the C-profile, measured by GD-OES),
the depth of the C-profile, and the quality of an enamel
layer produced on the surface of the samples. Samples 25
to 35 yielded a bad enamelling aspect, which can be
ascribed to either an insufficient depth of the C-profile
(as determined by the depth where the C-level reaches
(Csurface+Cbuld 2), and/or a C level at the surface which is
too high. The reason for these negative results can be
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ascribed to the test conditions, either the anneal
temperature which is too low, the decarburizing time too
short, or the pH20/pH2 ratio too low, or a combination of
these factors.
[0049] Table
4 shows the mechanical properties of a
number of samples taken from the sheets of the industrial
trials 1 and 2.
Importantly, the formability in terms of
the rm value is excellent, despite the initial C-level
which is higher than in the prior art : rm is between 1.8
and 2.1. These
results prove that the method of the
invention allows to produce steel sheets suitable for
enamelling, starting from an initial C-level higher than
0.02wt%, the resulting sheets allowing good enamelling
quality and fish scale resistance, and having very good
formability characteristics.
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decarb
initial urizing anneal Acc. to
Sam- Trial C time temp. 020/ C_surf depth enameling invention
pie N nr (ppm) (s) ( C) 012 (-) (ppm) (pm)
aspect ?
1 1 362 45 807 0,12 126 90 good Y
2 3 330 70 770 0,05 123 92 good Y
3 3 330 70 770 0,12 108 100 good Y
4 3 330 70 770 0,24 47 94* good Y
1 367 90 782 0,16 132 123 good Y
6 1 367 90 785 0,16 133 130 good Y
7 2 330 90 810 0,13 87 130* good Y
8 2 346 90 817 0,09 89 116* good Y
9 2 386 105 801 0,12 106 130 good Y
2 348 105 809 0,11 88 145* good Y
11 2 316 105 817 0,12 78 180 good Y
12 2 346 105 824 0,09 81 142* good Y
13 2 360 126 799 0,09 106 138* good Y
14 2 348 126 814 0,09 78 124* good Y
2 375 126 824 0,09 76 140* good Y
16 3 330 155 840 0,05 51 94* good Y
17 3 330 155 840 0,12 61 94* good Y
18 3 330 155 840 0,24 35 94* good Y
19 2 391 209 815 0,08 68 121* good Y
2 437 209 817 0,08 70 145* good Y
21 2 340 209 821 0,07 71 222 good Y
22 1 500 45 795 0,08 211 40 bad n
23 1 491 45 796 0,09 164 75 bad n
24 1 490 45 800 0,09 177 49 bad n
1 360 45 793 0,09 150 70 bad n
26 1 360 45 794 0,09 167 75 bad n
27 1 360 45 795 0,09 176 68 bad n
28 3 330 70 770 0,01 198 57 bad n
29 2 363 105 743 0,17 187 135 bad n
2 370 105 752 0,16 165 120 bad n
31 3 330 155 840 0,01 192 89 bad n
Table 2 : Overview of experimental conditions and results
1 : lwt% = 104 ppm
The depth-values given in table 1 are values of the depth
where the C-level reaches (Csurface+Cblalk) /2 . The
depth
5 measurements indicated with "F show the
maximum depth
which could be measured with the applied equipment. The
real value is thus higher than this value.
CA 02832357 2013-10-04
WO 2012/136270 PCT/EP2011/055477
18
Sample
n Al(wt%) Mn(wt%) Cu (wt%) S (wt%)
1 0.024 0.18 0.022 0.0049
0.03 0.18 0.028 0.0046
6 0.028 0.19 0.041 0.0052
9 0.035 0.18 0.029 0.0088
11 0.034 0.17 0.028 0.0077
Table 3 : composition of samples (C-level in table 1,
remaining elements are beneath impurity level, the
remainder is Fe)
initial Anneal Anneal
sample C-level Temp time pH20/pH2 Rp0.2 Rm Thickness
no (ppm) ( C) (s) (-) (MPa) (MPa) r_m (mm)
23 490 796 209 0,09 189 318 1,8 0,6
1 362 807 126 0,12 182 318 1,9 0,6
5 367 782 105 0,16 189 319 1,8 0,6
19 391 821 105 0,08 185 320 1,8 1
375 824 45 0,09 187 331 2,0 1
11 316 817 45 0,12 188 329 1,8 1
9 386 801 90 0,12 183 319 1,9 1
5 Table 4 : mechanical properties
