U.S. patent application number 10/539448 was filed with the patent office on 2006-08-03 for iron- nickel alloy with low coefficient of thermal expansion for making shade masks.
Invention is credited to Olena Danytola, Fabien Gaben, Sylvain Witzke.
Application Number | 20060171840 10/539448 |
Document ID | / |
Family ID | 32406240 |
Filed Date | 2006-08-03 |
United States Patent
Application |
20060171840 |
Kind Code |
A1 |
Gaben; Fabien ; et
al. |
August 3, 2006 |
Iron- nickel alloy with low coefficient of thermal expansion for
making shade masks
Abstract
The invention concerns an alloy whereof the chemical composition
comprises, by weight: 35%=Ni=37%. 0.001% %=C=0.05, % Mn=0.10%,
Si=0.15%, Co=0.5%, S<0.002%, P=0.006%, B=0.0005%,
Al+Mo+Cu+Cr=0.15% 0.015%=2(V+Ti)+Nb+Zr+Ta+III=0.2%,
0.0025%=N+O=0.015% optionally calcium and/or magnesium with total
content ranging beween 0.001 and 0.005%, the rest consisting of
iron and unavoidable impurities resulting from preparation, and a
method for making a strip of said alloy.
Inventors: |
Gaben; Fabien;
(Fourchambault, FR) ; Witzke; Sylvain; (Sauvigny
Les Bois, FR) ; Danytola; Olena; (Nevers,
FR) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Family ID: |
32406240 |
Appl. No.: |
10/539448 |
Filed: |
December 18, 2003 |
PCT Filed: |
December 18, 2003 |
PCT NO: |
PCT/FR03/03785 |
371 Date: |
February 15, 2006 |
Current U.S.
Class: |
420/94 ;
148/621 |
Current CPC
Class: |
C22C 38/004 20130101;
C22C 38/105 20130101; C21D 8/0205 20130101; C21D 8/0226 20130101;
C22C 38/08 20130101; C22C 38/12 20130101; C23F 1/02 20130101; H01J
1/48 20130101; C22C 38/14 20130101; H01J 2229/0733 20130101; H01J
9/142 20130101; H01J 29/07 20130101; H01J 9/14 20130101 |
Class at
Publication: |
420/094 ;
148/621 |
International
Class: |
C22C 38/08 20060101
C22C038/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2002 |
FR |
0216266 |
Claims
1. An alloy, the chemical composition of which comprises, by
weight: 35%.ltoreq.Ni.ltoreq.37% 0.001%.ltoreq.C.ltoreq.0.05%
Mn.ltoreq.0.10% Si.ltoreq.0.15% Co.ltoreq.0.5% S<0.002%
P<0.006% B.ltoreq.0.0005% Al+Mo+Cu+Cr.ltoreq.0.15%
0.015%.ltoreq.2(V+Ti)+Nb+Zr+Ta+Hf.ltoreq.0.2%
0.0025%.ltoreq.N+O.ltoreq.0.015% possibly calcium and/or magnesium
in a total content of between 0.0001 and 0.005%, the remainder
consisting of iron and inevitable impurities resulting from the
production process.
2. The alloy as claimed in claim 1, which furthermore has a niobium
content of below 0.1%.
3. The alloy as claimed in claim 1 or 2, which furthermore has a
carbon content of above 0.0035%.
4. The alloy as claimed in any one of claims 1 to 3, and the grain
size of which is below 10 (in accordance with G ASTM E112).
5. The alloy as claimed in any one of claims 1 to 4, and which
exhibits a coefficient of thermal expansion between 20.degree. C.
and 100.degree. C. of below 0.7.times.10.sup.-6/K.
6. The alloy as claimed in any one of claims 1 to 5, and of which
the conventional elastic limit at 0.2% OYS in the annealed state is
above 280 MPa.
7. The alloy as claimed in claim 6, and of which the conventional
elastic limit at 0.2% OYS in the annealed state is furthermore
above 300 MPa.
8. The alloy as claimed in any one of claims 1 to 7, wherein the
niobium and carbon contents are furthermore such that:
Nb.times.C.ltoreq.0.01.
9. The alloy as claimed in any one of claims 1 to 8, wherein the
titanium, niobium and nitrogen contents of the alloy composition
are furthermore such that: Ti.times.N.ltoreq.0.00006
Nb.times.N.ltoreq.0.001.
10. The alloy as claimed in any one of claims 1 to 9, and which
contains precipitates based on titanium and/or on niobium and/or on
vanadium and/or on tantalum and/or on zirconium and/or on hafnium,
the mean size of which is equal to 100 nm or smaller.
11. A method of manufacturing a strip of alloy as claimed in any
one of claims 1 to 10, comprising the steps whereby: a
semi-finished version of said alloy is hot-rolled after reheating
to a temperature of above 850.degree. C. and below 1350.degree. C.
so that the rolling temperature is above the solutionizing
temperature of the titanium- and/or niobium- and/or vanadium-
and/or zirconium- and/or tantalum- and/or hafnium-based
precipitates and so that the temperature at the end of rolling is
below the temperature at which said precipitates begin to
precipitate, so as to obtain a hot-rolled strip, the hot-rolled
strip is cold-rolled in one or more passes to obtain a cold-rolled
strip, possibly with one or more intermediate annealing operations
between two passes.
12. The method as claimed in claim 11, wherein the temperature of
the intermediate annealing operation or operations performed during
the cold-rolling is below the solutionizing temperature of said
precipitates.
13. The method as claimed in claim 11, wherein the temperature of
the intermediate annealing operation or operations performed during
the cold-rolling is above the solutionizing temperature of said
precipitates.
14. The method as claimed in claim 11 or 12, wherein the
temperature at the end of hot-rolling is equal to 850.degree. C. or
lower.
15. The use of an alloy as claimed in any one of claims 1 to 10 for
the manufacture of shadow masks for color display cathode ray
tubes.
16. The use of an alloy as claimed in any one of claims 1 to 10 for
the manufacture of cryogenic storage containers.
17. The use of an alloy as claimed in any one of claims 1 to 10 for
the manufacture of electron gun grids.
18. The use of an alloy as claimed in any one of claims 1 to 10 for
the manufacture of shadow masks held in the vertical or horizontal
direction for flat screen monitors.
19. The use of an alloy as claimed in any one of claims 1 to 10 for
the manufacture of shadow mask support frames.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an iron and nickel based
alloy with a very low coefficient of expansion that can be used in
particular for manufacturing shade or shadow masks for color
display cathode ray tubes.
PRIOR ART
[0002] In order to avoid the local deformation through thermal
expansion of the shadow masks used for color display cathode ray
tubes, it is desirable for their manufacture to employ an alloy
that has the lowest possible coefficient of thermal expansion.
Thus, for example, use is made of an FeNi alloy containing about
36% nickel and about 0.3% manganese, well known by the name of
Invar. Such an alloy has a coefficient of thermal expansion between
20.degree. C. and 100.degree. C. of the order of
1.times.10.sup.-6/K.
[0003] However, this coefficient of expansion is still too high for
certain applications, such as application to flat screens, and it
has been proposed that use be made of an FeNi alloy in which a few
% of the nickel are replaced with cobalt. This alloy has the
advantage of having a coefficient of thermal expansion of the order
of 0.4.times.10.sup.-6/K, which leads to a saving of 60%, but has
the disadvantage of containing cobalt. The problem with this is
that shadow masks are metal sheets pierced with very fine holes
obtained by chemical etching, and the cobalt leads to troublesome
contamination of the chemical etching baths. Furthermore, cobalt is
a very expensive element and it is desirable to reduce its content
as far as possible.
[0004] Hence, it has been proposed that use be made of an FeNi
alloy with a low residual and cobalt content, containing in
particular under 0.1% manganese. This alloy has the advantage, on
the one hand, of containing little or no cobalt and, on the other
hand, of having a coefficient of thermal expansion of the order of
0.8.times.10.sup.-6/K, which is lower than that of the conventional
FeNi alloy (Invar). However, the coefficient of expansion is still
too high, particularly for large format or slimline flat
screens.
[0005] Furthermore, it is desirable to use thinner masks so as to
reduce their cost of manufacture and so as to improve the quality
and precision of the images. Now, the mechanical properties of the
alloys of the prior art are not good enough to allow the thickness
of the masks to be reduced while at the same time keeping the masks
to withstand the deformations that may arise during the various
transport and handling steps.
SUMMARY OF THE INVENTION
[0006] The object of the present invention is to remedy the
disadvantages of the alloys of the prior art by proposing an alloy
that can be used in particular for the manufacture of shadow masks,
that contains little or no cobalt, of which the coefficient of
thermal expansion is lower than that of the known FeNi alloys, and
which has an elastic limit in the annealed state that is maintained
or even improved.
[0007] To this end, a first subject of the invention is an alloy,
the chemical composition of which comprises, by weight:
35%.ltoreq.Ni.ltoreq.37% 0.001%.ltoreq.C.ltoreq.0.05%
Mn.ltoreq.0.10% Si.ltoreq.0.15% Co.ltoreq.0.5% S<0.002%
P<0.006% B.ltoreq.0.0005% Al+Mo+Cu+Cr.ltoreq.0.15%
0.015%.ltoreq.2(V+Ti)+Nb+Zr+Ta+Hf.ltoreq.0.2%
0.0025%.ltoreq.N+O.ltoreq.0.015%
[0008] possibly calcium and/or magnesium in a total content of
between 0.0001 and 0.005%,
[0009] the remainder consisting of iron and inevitable impurities
resulting from the production process.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0010] In a preferred embodiment, the alloy furthermore exhibits a
niobium content of below 0.1%, or even below 0.07%.
[0011] In another preferred embodiment, the alloy exhibits a carbon
content of above 0.0035%.
[0012] In another preferred embodiment, the alloy exhibits a grain
size below 10, or even below 9 (in accordance with G ASTM E
112).
[0013] In another preferred embodiment, the alloy has a coefficient
of thermal expansion between 20.degree. C. and 100.degree. C. of
below 0.70.times.10.sup.-6/K, and preferably of below
0.65.times.10.sup.-6/K. In any case, the coefficient of expansion
obtained is below 0.75.times.10.sup.-6/K.
[0014] In another preferred embodiment, the alloy exhibits a
conventional elastic limit at 0.2% OYS, in the annealed state, of
above 250 MPa, preferably above 280 MPa, and as a more particular
preference, above 300 MPa, or even 310 MPa.
[0015] In another preferred embodiment, the niobium and carbon
contents of the alloy composition are such that:
Nb.times.C.ltoreq.0.01.
[0016] This embodiment allows the elastic limit of the grade in the
annealed state to be improved through the formation of carbides on
a sub-micron scale.
[0017] In another preferred embodiment, the titanium, niobium and
nitrogen contents of the alloy composition are such that:
Ti.times.N.ltoreq.0.00006 Nb.times.N.ltoreq.0.001.
[0018] This embodiment makes it possible to avoid the presence of
excessive quantities of niobium and/or titanium nitrides, which
have a size of the order of a few hundred nanometers or even a few
microns, and which present problems when manufacturing the shadow
masks by etching.
[0019] In another embodiment, the alloy contains precipitates based
on titanium and/or on niobium and/or on vanadium and/or on tantalum
and/or on zirconium and/or on hafnium, the mean size of which is
equal to 100 nm or smaller, preferably equal to 70 nm or smaller
and as a more particular preference, smaller than 50 nm.
[0020] A second subject of the invention is a method of
manufacturing a strip of alloy, according to the invention
comprising the steps whereby: [0021] a semi-finished version of
said alloy is hot-rolled after reheating to a temperature of above
850.degree. C. and below 1350.degree. C. so that the rolling
temperature is above the solutionizing temperature of the titanium-
and/or niobium- and/or vanadium- and/or zirconium- and/or tantalum-
and/or hafnium-based precipitates and so that the temperature at
the end of rolling is below the temperature at which said
precipitates begin to precipitate, so as to obtain a hot-rolled
strip; [0022] the hot-rolled strip is cold-rolled in one or more
passes to obtain a cold-rolled strip, possibly with one or more
intermediate annealing operations between two passes.
[0023] In a first preferred embodiment, the temperature of the
intermediate annealing operation or operations performed during the
cold-rolling is below the solutionizing temperature of said
precipitates.
[0024] In a second preferred embodiment, the temperature of the
intermediate annealing operation or operations performed during the
cold-rolling is above the solutionizing temperature of said
precipitates.
[0025] These two different embodiments allow the formation of
precipitates and the grain size to be altered. By way of
nonlimiting indication, a grain size larger than 7 is generally
obtained for the first embodiment, whereas grain sizes smaller than
7.5 are generally obtained in the second embodiment.
[0026] In another preferred embodiment, the temperature at the end
of hot-rolling is equal to 850.degree. C. or lower, which makes it
possible to obtain finer grains.
[0027] A third subject of the invention is the use of the alloy
described hereinabove for the manufacture of shadow masks for color
display cathode ray tubes, for the manufacture of shadow masks held
in the vertical or horizontal direction for flat screen monitors,
for the manufacture of shadow mask support frames, for the
manufacture of cryogenic storage containers, and also for the
manufacture of electron gun grids, by virtue of its very strong
suitability for mechanical cutting.
[0028] The invention is based on the fact that the inventors
discovered, in a novel way and surprisingly, that the precipitation
of compounds formed from titanium and/or niobium and/or vanadium
and/or zirconium and/or tantalum and/or hafnium, on the one hand,
and from carbon, oxygen and/or nitrogen, on the other, leads to an
appreciable reduction in the coefficient of expansion when the
alloy has a low Si and Mn content. Precise analysis of the
compounds formed is tricky, but in particular carbides, nitrides,
carbonitrides, oxides and/or oxynitrides of the abovementioned
metals are found.
[0029] Without wishing to be tied to a theory, the inventors
believe that this effect could be due to the fact that these
various compounds, for the most part, have a crystalline structure
of the cubic type, and form precipitates the size of which is
generally of the order of several tens of nanometers when they are
formed in the solid phase. These small-sized precipitates
precipitate in the matrix and not at the grain boundaries, as is
conventionally the case.
[0030] This effect on the coefficient of expansion of the alloy is
particularly visible in FIG. 1, which represents the variations of
this coefficient between 20 and 100.degree. C. as a function of the
sum of the oxygen and nitrogen contents, for an alloy the
composition of which contains titanium at contents ranging between
0.01 and 0.05%, less than 5 ppm of boron, less than 5 ppm of sulfur
and no aluminum. The same effect is obtained with an alloy
containing niobium completely or partially replacing the titanium,
within the limits set by claim 1.
[0031] The alloy according to the invention contains, as % by
weight: [0032] from 35% to 37% nickel, and preferably between 35.5%
and 36.5%, so as to obtain a low coefficient of thermal expansion
between 20.degree. C. and 100.degree. C., [0033] from 0.001% to
0.05% of carbon, so as to form fine carbide precipitates. The
formation of nanometer-scale carbide precipitates has the effect of
reducing the coefficient of expansion and of improving the
mechanical properties of the product. Its content is limited to
0.05% so as to avoid the formation of large insoluble carbide
inclusions. It is preferable for the carbon content to be above
0.0035% so as to have enough of a carbon content by volume to
obtain improved mechanical characteristics. It is also preferable
for the carbon content to be kept to a value below 0.010%, or even
below 0.007% so as to further limit the size of the carbides
formed. [0034] under 0.1% manganese because this element increases
the coefficient of expansion of the alloy and needs to be limited,
[0035] under 0.15% silicon, because this element increases the
coefficient of expansion of the alloy and needs to be limited,
[0036] under 0.5% cobalt, so as not to contaminate the chemical
etching baths used to etch the shadow masks, [0037] possibly 0.0001
to 0.005% of at least one element taken from among calcium and
magnesium so as to trap the sulfur which always exists by way of an
impurity and thus ensure good hot-deformation ability, [0038]
possibly sulfur at a content of below 0.002% so as not to impair
the hot-conversion ability of the alloy, [0039] possibly phosphorus
in a content of below 0.006% so as not to impair the hot-conversion
ability of the alloy, [0040] possibly boron at a content of less
than 0.0005%, and preferably of 0%: this is because the inventors
have found that with boron present, the coefficients of thermal
expansion increase appreciably, [0041] possibly aluminum,
molybdenum, copper or chromium in a total content of less than
0.15%, because these elements increase the coefficient of thermal
expansion of the alloy, [0042] titanium, vanadium, niobium,
tantalum, zirconium and/or hafnium in quantities such that the sum
2(V+Ti)+Nb+Ta+Zr+Hf lies between 0.015% and 0.2% so as to be able
to form precipitates based on these elements, these precipitates
preferably exhibiting a mean size smaller than 100 nm, and as a
preference smaller than 70 nm, and as a particular preference,
smaller than 50 nm. It is furthermore preferable for the niobium
content to be below 0.1%, or even below 0.07%, so as to further
reduce the coefficient of expansion and the size of the
precipitates, [0043] oxygen and/or nitrogen in quantities such that
the sum of their contents lies between 0.0025% and 0.015%, because
the inventors have found, in a novel way, that the presence of
oxygen and/or of nitrogen in these contents in the alloy allows the
coefficient of expansion to be lowered when it is associated with
the presence of titanium and/or niobium and/or vanadium and/or
tantalum and/or zirconium and/or hafnium. The sum of these contents
is limited to 0.015% so as to avoid the formation of large oxides
or nitrides, [0044] the remainder of the composition is made up of
iron and of impurities resulting from the production process.
[0045] The alloy may be formulated, for example, in an arc furnace
with an AOD or VOD converter refining phase; it may also be
formulated in an induction furnace under vacuum. This formulation
must be carried out in such a way as to obtain the desired residual
contents.
[0046] The alloy is then cast into the form of a semi-finished
product such as an ingot, a billet or a remelting electrode. It may
also be cast directly in the form of a thin slab or thin strip less
than 15 mm thick, and preferably with a thickness of between 8 and
12 mm.
[0047] When the alloy is cast in the form of a remelting electrode,
this electrode is remelted under electrically-conducting slag so as
to obtain better homogeneity of the chemical composition and of the
solidification structure.
[0048] The semi-finished product or the thin strip obtained by
direct casting is then hot-rolled at a temperature of above
850.degree. C., and preferable above 1150.degree. C. but below
1350.degree. C. to obtain a hot-rolled strip with a thickness of
generally between 2 mm and 6 mm, and preferably between 3 and 5 mm,
which is then cold-rolled in one or more passes, possibly with
annealing operations above 800.degree. C. The temperature to which
the strip is heated between the hot-rolling or cold-rolling steps
may be chosen in such a way that the precipitates of oxides,
carbides, or nitrides may possibly be returned to solution. Rapid
coolings may also be applied in order to keep these elements likely
to form precipitates in solid solution within the alloy.
Equilibrium precipitation treatments may then be carried out by
temperature soaks at between 750.degree. C. and 1200.degree. C.
(but preferably below 1050.degree. C.).
[0049] The invention will now be described in greater detail but
without implying limitation, and illustrated by examples.
Tests
[0050] By way of example, the alloys identified 1 to 16 according
to the invention and 17 to 23 by way of comparison and the
composition of which is described in Table 1 below were produced.
The chemical compositions and the coefficients of expansion a
between 20 and 100.degree. C. were measured on test specimens taken
from the hot-rolled strips. Each of these test specimens was
annealed for 30 minutes at 950.degree. C., and cooled in ambient
air before the coefficient of thermal expansion measurements were
taken. The results of the tests are collated in Table 2, in which
the coefficient of expansion .alpha. is expressed in
10.sup.-6/K.
[0051] The etching tests were performed on cold-rolled products
from the experimental castings, partially coated with
photosensitive resin. The etchings were performed at 60.degree. C.
with an FeCl.sub.3 solution having a density of 45.5.degree.Be. The
quality of the etching was evaluated by measuring the regularity of
the cut contours, and through the presence of defects associated
with the presence of particles. TABLE-US-00001 TABLE 1 No. Ni Mn Si
Al Co C S N O Nb V Ti B Examples 1 35.80 0.048 <0.007 0.009
0.011 0.003 0.0010 0.0036 0.0019 <0.005 <0.005 0.023
<0.0005 according 2 35.84 0.044 <0.007 <0.005 0.010 0.003
0.0010 0.0016 0.0024 <0.005 <0.005 0.017 <0.0005 to the 3
36.08 0.027 0.021 <0.005 0.010 0.002 <0.0005 0.0023 0.0041
<0.005 <0.005 0.012 <0.0005 invention 4 36.13 0.027 0.011
<0.005 0.009 0.003 <0.0005 0.0020 0.0016 <0.005 <0.005
0.034 <0.0005 5 36.08 0.029 0.053 <0.005 0.011 0.003 0.0005
0.0030 0.0024 <0.005 <0.005 0.024 <0.0005 6 36.16 0.030
0.078 <0.005 0.010 0.003 0.0005 0.0031 0.0012 <0.005
<0.005 0.048 <0.0005 7 36.09 0.031 0.020 0.044 0.009 0.003
<0.0005 0.0026 0.0013 <0.005 <0.005 0.022 <0.0005 8
36.06 0.030 0.021 0.055 0.010 0.002 <0.0005 0.0028 0.0010
<0.005 <0.005 0.052 <0.0005 9 36.10 0.040 0.045 0.008
0.050 0.004 0.0009 0.0023 0.0018 0.030 <0.005 0.016 <0.0005
10 36.10 0.045 0.040 <0.005 0.048 0.004 0.0008 0.0030 0.0015
<0.005 0.020 0.010 <0.0005 11 36.15 0.040 0.030 <0.005
0.050 0.004 0.0008 0.0032 0.0017 0.040 <0.005 0.005 <0.0005
12 36.20 0.042 0.033 <0.005 0.035 0.003 0.0009 0.0030 0.0015
0.028 <0.005 0.015 <0.0005 13 36.15 0.041 0.032 <0.005
0.050 0.003 0.0010 0.0026 0.0017 0.035 <0.005 0.009 <0.0005
14 36.18 0.051 0.027 0.008 0.014 0.004 0.0009 0.0021 0.0012 0.060
<0.005 0.015 <0.0005 15 36.0 0.06 0.03 <0.005 0.28 0.0044
0.0007 0.0031 0.0012 0.051 <0.005 <0.005 <0.0005 16 36.1
0.03 0.025 0.006 0.05 0.0048 0.0005 0.0025 0.0015 0.055 <0.005
<0.005 <0.0005 Comparative 17 35.84 0.052 <0.007 0.013
<0.005 0.003 0.0008 0.0042 <0.001 <0.005 <0.005 0.013
0.0010 Examples 18 35.83 0.053 0.011 0.019 0.011 0.006 0.0006
0.0034 0.0012 <0.005 <0.005 0.025 0.0024 19 35.79 0.049
<0.007 0.038 0.012 0.002 0.0028 0.0021 <0.001 <0.005
<0.005 0.045 <0.0005 20 36.00 0.071 0.076 <0.005 0.049
0.005 0.0007 0.0025 0.0012 <0.005 <0.005 <0.005 <0.0005
21 35.95 0.042 0.021 <0.005 0.068 0.002 0.0029 0.0013 0.0012
0.051 <0.005 <0.005 <0.0005 22 35.80 0.039 <0.007 0.006
<0.005 0.002 0.0005 0.0010 0.0013 0.009 0.012 0.080 <0.0005
23 36.2 0.045 0.041 <0.005 0.050 0.002 0.0008 0.0003 <0.001
0.040 <0.005 0.007 <0.0005
[0052] TABLE-US-00002 TABLE 2 Mean Conventional coefficient elastic
of thermal Grain limit at expansion size*.sup.3 0.2% OYS between 20
Quality of (annealed No. (MPa)*.sup.1 and 100.degree. C. the
etching*.sup.2 state) 1 300 0.53 P 8 2 297 0.57 G 8 3 307 0.52 G
8.5 4 300 0.52 P 8 5 298 0.56 P 8 6 292 0.61 P 7.5 7 301 0.62 P 8.5
8 291 0.59 P 7.5 9 332 0.57 G 9.5 10 327 0.54 G 9 11 320 0.49 G 8.5
12 328 0.56 G 9.5 13 322 0.50 G 9 14 325 0.61 G 9 15 285 0.54 G 6.5
16 289 0.51 G 6.5 17 289 0.80 G 8.5 18 298 1.01 P 8.5 19 295 0.76 P
8.5 20 275 0.75 G 8 21 302 0.75 G 8.5 22 290 0.77 P 8.5 23 313 0.78
G 9 *.sup.1Values measured after a heat treatment for 15 minutes at
850.degree. C. *.sup.2G: etching deemed to be good - P: presence of
faults associated with the presence of particles. *.sup.3Grain size
measured in accordance with G ASTM E 112, to plus or minus 0.5 of a
unit.
[0053] In the light of this table, all the strips according to the
invention can be seen to have a coefficient of expansion of below
0.70.times.10.sup.-6/K and even of below 0.65.times.10.sup.-6/K in
most cases.
[0054] By contrast, the strips given by way of comparison have
coefficients of expansion appreciably higher than
0.70.times.10.sup.-6/K.
[0055] The comparative examples 17 and 18 show the detrimental
effect of boron on the coefficient of expansion. The comparative
examples 19 and 21 show the detrimental influence of sulfur on the
coefficient of expansion. These comparative examples also show the
importance that the oxygen and nitrogen contents have on the
coefficient of expansion.
[0056] The comparative example 20 which corresponds to the
conventional low-manganese FeNi alloy provides the reference that
demonstrates the advantages of the invention. Specifically, in the
absence of compounds allowing solid phase precipitates to form, the
coefficients of expansion measured are higher.
[0057] Comparative example 21 shows the detrimental effect of
sulfur on the coefficient of expansion.
[0058] Comparative examples 22 and 23 show the importance of the
nitrogen and oxygen contents on the coefficient of expansion.
[0059] The alloy according to the invention can also be used for
the manufacture of shadow mask support frames. This alloy has good
behavior during chemical etching and this is associated with the
controlled weak presence of residuals of the C,S,N type in solid
solution, and because of its small amounts of micron-scale
inclusions.
* * * * *