FR2849061A1 - Iron-nickel alloy, used for shadow mask, cryogenic storage and electron canon applications, has low cobalt content and very low coefficient of thermal dilation - Google Patents

Abstract

An iron-nickel alloy has the following chemical composition (by wt %): (a) 35 at most Ni at most 37; (b) 0.001 at most C at most 0.05; (c) Mn at most 0.10; (d) Si at most 0.15; (e) Co at most 0.5; (f) S less than 0.002; (g) P less than 0.006; (h) B at most 0.0005; (i) Al+Mo+Cu+Cr at most 0.15; (j) 0.15 at most 2(V+Ti)+Nb+Zr+Ta+Hf at most 0.2; (k) 0.0025 at most N+O at most 0.015; (l) possibly some calcium and/or magnesium with a total content between 0.0001 and 0.005; (m) a balance of iron and inevitable production impurities. An Independent claim is also included for the fabrication of a strip of the above alloy by hot rolling.

Description

Ref IY 01/008

  The present invention relates to an alloy based on iron and nickel with a very low coefficient of expansion, which can in particular be used for the manufacture of masks. shadows for CRTs. In order to avoid the local deformation by thermal expansion of shadow masks for color display cathode ray tubes, it is desirable to use an alloy with the lowest thermal expansion coefficient possible for their manufacture. For example, an Fe Ni alloy containing about 36% nickel and about 0.3% manganese, well known as lnvar, is used. Such an alloy has a coefficient of thermal expansion between 20 ° C and 100 ° C. order of 1 x 10-6 / K.

  However, this coefficient of expansion is still too high for certain applications, such as the application to flat screens, and it has been proposed to use a Fe Ni alloy of which some nickel is replaced by cobalt This alloy has the advantage to have a coefficient of thermal expansion of the order of 0.4 x 10-6 / K, which leads to a gain of 60%, but it has the disadvantage of containing cobalt Indeed, the masks of Shade are metal foils pierced with very fine holes obtained by chemical etching, and cobalt generates an embarrassing pollution of chemical etching baths. In addition, cobalt is a very expensive element and it is desirable to reduce its content as much as possible.

  Also, it has been proposed to use a low-content residual cobalt-free Fe Ni alloy containing in particular less than 0.1% of manganese. This alloy has the advantage, on the one hand, of not containing cobalt, and of on the other hand to have a coefficient of thermal expansion of the order of 0.8 x 10-6 / K, lower than that of the alloy Fe Ni (Invar) conventional However, the coefficient of expansion is still too high , especially for large flat screens. In addition, it is desirable to use thinner masks to reduce their cost of manufacture and to improve the quality and accuracy of the images Gold alloys of the prior art do not have sufficient mechanical characteristics in order to allow the thickness of the masks to be reduced while maintaining a resistance of the masks to the deformations that may appear during the different stages of transport and handling.

  The object of the present invention is to overcome the drawbacks of alloys of the prior art by proposing an alloy that can be used especially for the manufacture of shadow masks, containing little or no cobalt, whose coefficient of thermal expansion is lower. that of Fe Ni alloys known and having an elastic limit in improved annealed state.

  For this purpose, the invention firstly relates to an alloy whose 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 + Hf < 0.2% 0.0025% <N + O <0.015% optionally calcium and / or magnesium in a total content of between 0.0001 and 0.005%, the remainder being iron and unavoidable impurities resulting from development. In a preferred embodiment, the alloy has a coefficient of thermal expansion between 20 C and 100 C of less than 0.70 x 10-6 / K, and preferably less than 0.65 x 10-6 / K in all cases, the coefficient of expansion obtained is less than 0.75 x 10-6 / K.

  In another preferred embodiment, the alloy has a 0.2% yield strength in an annealed state of greater than 280 M Pa, preferably greater than 300 M Pa, and more preferably greater than 310 M Pa.

  In another preferred embodiment, the niobium and carbon contents of the alloy composition are such that: Nb x C <0.01.

  This embodiment makes it possible to improve the elastic limit of the grade in the annealed state and makes it possible to avoid the formation of micrometric size carbides because the inventors have found that the presence of fine precipitates of niobium makes it possible to refine the grain. more easily.

  In another preferred embodiment, the titanium and nitrogen contents of the alloy composition are such that: Ti x N <0.00006 This embodiment avoids the presence of too much titanium nitrides, which have a size of the order of a few hundred nanometers or even a few microns, and which pose a problem during the manufacture by etching shadow masks.

  In another embodiment, the alloy contains precipitates based on titanium, and / or niobium, and / or vanadium, and / or tantalum, and / or zirconium and / or hafnium, the average size is less than or equal to 100 nm, preferably less than or equal to 70 nm.

  The subject of the invention is a process for manufacturing an alloy strip according to the invention comprising the steps according to which: a semi-finished product of this alloy is hot-rolled after reheating at a temperature greater than 850.degree. 1350 C, such that the rolling temperature is higher than the resoldering temperature of the titanium and / or niobium and / or vanadium and / or zirconium and / or tantalum and and / or hafnium and that the end-of-lamination temperature is lower than the precipitation start temperature of said precipitates, in order to obtain a hot strip, the hot strip is cold rolled in one or more passes, to obtain a cold band with possibly one or more intermediate annealing between two passes, the temperature of the intermediate annealing (s) being lower than the temperature of the dissolution of said precipitates.

  In a preferred embodiment, the hot rolling end temperature is less than or equal to 850 ° C, which results in finer grains.

  The third object of the invention is the use of the alloy described above for the manufacture of shade masks for color display cathode ray tubes, for the manufacture of shadow masks stretched in the vertical or horizontal direction for television sets. with flat screens, for the manufacture of support frames of shadow masks, for the manufacture of cryogenic storage containers, but also for the manufacture of electron gun grids, thanks to its very good aptitude for mechanical cutting. The invention is based on the fact that the inventors have found in a new and surprising way 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 carbon, oxygen and / or nitrogen on the other hand, causes a substantial lowering of the coefficient of expansion when the alloy has a low content of Si and Mn. The precise analysis of the compounds formed is delicate, but there are in particular carbides, nitrides, carbonitrides, oxides and / or oxynitrides of the metals mentioned above.

  Without wishing to be bound by theory, the inventors believe that this effect could be due to the fact that these various compounds have for the most part a cubic crystal structure, and form precipitates whose size is generally of the order of several tens of nanometers when formed in solid phase These small precipitates precipitate in the matrix and not at the grain boundaries, as is conventionally the case.

  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 ° C., as a function of the sum of the oxygen and nitrogen contents, for an alloy whose the composition comprises titanium at levels of 0.01 to 0.05%, less than 5 ppm boron, less than 5 ppm sulfur and no aluminum.

  The alloy according to the invention contains, in% by weight of 35% to 37% of nickel, and preferably between 35.5% and 36.5%, in order to obtain a low coefficient of thermal expansion between 20 C and 10 100 C, from 0.001% to 0.05% carbon to form fine carbide precipitates The formation of nanoscale carbide precipitates has the effect of reducing the coefficient of expansion and improving the mechanical properties of the product. its content at 0.05% to prevent the formation of large inclusions of insoluble carbides. less than 0.1% of manganese, since this element increases the coefficient of expansion of the alloy and must be limited to less than 0.15% of silicon, since this element increases the coefficient of expansion of the alloy and must be limited, less than 0.5% of cobalt, so as not to pollute the chemical etching baths of shadow masks, possibly from 0.0001 to 0.005% of at least one element taken from calcium and magnesium so to trap the sulfur which still exists as an impurity and thus to ensure a good heat distortion capability, possibly sulfur content of less than 0.002% in order not to deteriorate the heat-transformability of the catalyst. alloy, optionally phosphorus in a content of less than 0.006% in order not to deteriorate the heat-transformability of the alloy, optionally boron in a content of less than 0.0005%, and preferably of 0 %: indeed, the inventors have co It was found that in the presence of boron the coefficients of thermal expansion significantly increased, possibly aluminum, molybdenum, copper or chromium. in a total content of less than 0.15%, since these elements increase the coefficient of thermal expansion of the alloy.

  titanium, vanadium, niobium, tantalum, zirconium and / or hafnium in such quantities that the sum of 2 (V + Ti) + Nb + Ta + Zr + Hf is between 0.015% and 0.2 %, in order to form precipitates based on these elements, these precipitates preferably having a mean size of less than 100 nm, and particularly preferably less than 70 nm, oxygen and / or nitrogen in quantities such that the sum of their contents is between 0.0025% and 0.015%, because the inventors have found in a new way that the presence of oxygen and / or nitrogen in these contents in the alloy makes it possible to lower the coefficient of expansion when 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% to avoid the formation of large oxides or nitrides.

  the rest of the composition consists of iron and impurities resulting from the preparation.

  The alloy can be produced for example in an arc furnace with a refining phase at the AOD or VOD converters; it can also be developed in vacuum induction furnace This development must be conducted in order to obtain the desired residual contents.

  The alloy is then cast in the form of a semi-finished product such as an ingot, a billet or a reflow electrode. It can also be cast directly in the form of a thin slab or thin strip with a thickness of less than 15 mm. and preferably of thickness between 8 and 12 mm.

  When the alloy is cast as a reflow electrode, it is remelted electroslag slag to obtain a better homogeneity of the chemical composition and the solidification structure.

  The semi-finished product, or the thin strip obtained by direct pouring, is then hot-rolled at a temperature greater than 850 ° C., and preferably greater than 1150 ° C., but less than 1350 ° C. to obtain a hot strip of thickness in general, between 2 mm and 6 mm, and preferably between 3 and 5 mm, which is cold rolled in one or more passes with possibly annealing above 800 ° C. The heating temperature of the strip applied between Hot rolling or cold rolling steps may be chosen so that the precipitates of oxides, carbides or nitrides may possibly be returned to solution. Rapid cooling may also be applied to maintain a solid solution in the solution. alloy these elements likely to form precipitates Equilibrium precipitation treatments can then be made by maintaining at temperatures compr ises between 750 C and 1200 C (but preferably less than 1050 C).

  The invention will now be described in a more precise but nonlimiting manner and illustrated by examples.

  EXAMPLES By way of example, the alloys marked 1 to 15 according to the invention and 16 to 22 were prepared for comparison, the composition of which is described in Table 1 below. Chemical compositions and expansion coefficients a and 100 C, were measured on specimens taken from the hot-rolled strips. Each of these specimens was annealed for 30 minutes at 950 ° C, and cooled in the ambient air before making the measurements of thermal expansion coefficient. The results of the tests are summarized in Table 2, in which the coefficient of expansion a is expressed as 106 / K.

  The etch tests were carried out on cold rolled products of the experimental castings, partially coated with photoresist.

  The etchings were carried out at 60 ° C. with a solution of Fe CI 3 having a density of 45.5 °. The quality of the etchings was evaluated by measurements of the regularity of the cut out contours, as well as by the presence of defects related to the presence of particles.

  Table 1: No Ni Mn Si AI Co CSNO Nb V Ti B 1 35.80 0.048 <0.007 0.009 0.011 0.003 0.0010 0.0036 0.0019 <0.005 <0.05 0.023 <0.0005 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 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 o 4 36.13 0.027 0.011 <0.005 0.009 0.003 <0.00050,00200.0016 <0.005 <0.005 0, 034 <0.0005 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> 56 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: 6 36.0916 0, 02730 0.078 <0.005 0.01021 0.003 0.0005 0.0031 0.0012 <0.05 <0.005 0.06148 <0.0005 7 36.09 0.03127 0.02048 <0.04405 0.00121 0.003 0, 0008 0.0032 0.0018 <0.05 <0.005 0.02261 <0.0005 8 36.09 0.031 0.020 0.05544 0.009 0.003 <0.005 0.0026 0.0013 <0.005 <0.005 0.022 <0.0005 D 9 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 c ,, 0 10 36.10 0.040 0.045 0.008 0.050 0.004 0.0009 0.0023 0.0018 0.030 <0.005 0.016 0.00.000 (0.035 0.040 0.005 0.048 0.004 0.0008 0, 0030 0.0015 <0.005 0, 020 0.010 <0.0005

E

  O 12 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 x W 13 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 14 36.15 0.041 0.032 <0.005 0.050 0.003 0.0010 0.0026 0.0017 0.035 <0.05 0.013 <0.0005 15 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 16 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 g 17 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 18 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 E m 19 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 x E 20 35.95 0.042 0.021 <0.005 0.068 0.003 0.0029 0.0013 0 , 0012 0.051 <0.005 <0.005 <0.0005 WL OO 21 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 22 36.2 0.045 0.041 <0.005 0.050 0.002 0.0008 0.00 03 <0.001 0.040 <0.005 0.007 <0.0005

Table 2:

  N Yield strength Coefficient of expansion Quality of conventional to 0.2% average thermal between etchings * 2 (M Pa) * l 20 and 100 C 1 300 0.53 B 2 297 0.57 P 3 307 0.52 P 4 300 0.52 B 298 0.56 B 6 292 0.61 B 7 289 0.50 B 8 301 0.62 B 9 291 0.59 B 332 0.57 P 11 327 0.54 P 12 320 0, 49 P 13 328 0.56 P 14 322 0.50 P 325 0.61 P 16 289 0.80 P 17 298 1.01 B 18 295 0.76 B 19 275 0.75 P 302 0.75 P 21 290 0.77 B 22 313 0.78 P * 1 Values measured after a heat treatment of 15 minutes at 850 C.

  * 2 B: engravings considered good P: presence of defects related to the presence of particles.

  In view of this table, it is found that all the bands according to the invention have an expansion coefficient of less than 0.70 × 10 -6 / K and even less than 0.65 × 10 -6 / K in most cases. case.

  On the other hand, the strips given for comparison have expansion coefficients substantially greater than 0.70 × 10 -6 / K. he

  Counterexamples 16 and 17 show the harmful effect of boron on the coefficient of expansion. Examples 18 and 20 show the harmful influence of sulfur on the coefficient of expansion. These counterexamples also show the importance of oxygen contents. and nitrogen on the coefficient of expansion.

  The counterexample 19 which corresponds to the conventional low manganese Fe Ni alloy gives the reference showing the advantages of the invention. In fact, in the absence of compounds allowing the formation of solid phase precipitates, the measured expansion coefficients are more important.

  Counterexample 20 shows the detrimental effect of sulfur on the coefficient of expansion.

  Counterexamples 21 and 22 show the importance of nitrogen and oxygen contents on the coefficient of expansion.

  The alloy according to the invention can also be used for the production of shadow mask support frames. This alloy has a good behavior in chemical etching related to the low controlled presence of residuals of C, S, N type in solid solution. and because of its small amounts of inclusions of micrometric sizes. gg

12 2849061

Claims (6)

  1 Alloy whose 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 + Hf <0.2% 0.0025% <N + O <0.015% optionally calcium and / or magnesium in a total content of between 0.0001 and 0.005%, the balance being iron and unavoidable impurities resulting from the elaboration. 2 Alloy according to claim 1, characterized in that it has a coefficient of thermal expansion between 20 C and 100 C less than 0.7 x 10-6 / K.   3. Alloy according to claim 1 or 2, characterized in that its 0.2% yield strength in annealed state is greater than 280 M Pa.   4. An alloy according to claim 3, further characterized in that its 0.2% yield strength in an annealed state is greater than 300 M Pa.   An alloy according to any one of claims 1 to 4, further characterized in that the niobium and carbon contents are such that 30 Nb x C <0.01 6 Alloy according to any one of claims 1 to 5, characterized in that the titanium and nitrogen contents are such that: ## STR1 ## The alloy according to any one of claims 1 to 6, characterized in that it contains precipitates based on titanium, and / or niobium, and / or vanadium, and / or tantalum, and / or zirconium and / or hafnium, the average size of which is less than or equal to 100 nm. An alloy according to any one of claims 1 to 7, comprising the steps of: hot-rolling a semi-finished product of said alloy after reheating to a temperature above 850 C and below 1350 C, such that the temperature of rolling is greater than the temperature of resuspension of precipitates based on titanium and / or niobium, and / or vanadium and / or zirconium, and / or tantalum and / or hafnium and that the end-of-rolling temperature is lower than the starting temperature of precipitating said precipitates, in order to obtain a hot strip, the hot strip is cold rolled in one or more passes, to obtain a cold band with possibly one or more intermediate annealing between two passes, the temperature of the Intermediate anneals being less than the redissolving temperature of said precipitates.   9 Process according to claim 8, characterized in that the end temperature of hot rolling is less than or equal to 850 C.   10.The use of an alloy according to any one of claims 1 to 7 for the manufacture of shadow masks for color display cathode ray tubes.   11.Utilization of an alloy according to any one of claims 1 to 7 for the manufacture of cryogenic storage containers.   12.Utilization of an alloy according to any one of claims 1 to 7, for the manufacture of gates electron guns.   13 Use of an alloy according to any one of claims 1 to 7 for the manufacture of shadow masks stretched in the vertical or horizontal direction for flat screen televisions.   14. Use of an alloy according to any one of claims 1 to 7 for the manufacture of shadow mask support frames.