FR2733767A1 - FE-CO-NI ALLOY AND USE FOR MAKING A SHADOW MASK - Google Patents

Abstract

Fe-Ni-Co alloy whose chemical composition includes, by weight: 32% = <Ni = <34%, 3.5% = <Co = <6.5%, 0% = <Mn = <0.1% , 0% = <Si = <0.1%, 0% = <Cr = <0.1%, 0.005% = <C = <0.02%, S = <0.001%, 0.0001% = <Ca = <0.002%, 0.0001% = <Mg = <0.002%, the remainder being iron and impurities resulting from the production; the chemical composition of the alloy also satisfying the relationships: Co + Ni = <38.5%, Co + 0.5 x Ni> = 20%, Co + 5 x Ni> = 165.5% and S = < 0.02 x Mn + 0.8 x Ca + 0.6 x Mg. Use of the alloy for the manufacture of a shadow mask for a viewing cathode ray tube.

Description

FE-CO-NI ALLOY

AND USE FOR MAKING A SHADOW MASK

The present invention relates to a Fe-Ni-Co alloy having a low coefficient of expansion as well as its use for the manufacture of a shadow mask for a viewing cathode ray tube. Low coefficient of expansion Fe-Ni-Co alloys, commonly referred to as SUPERINVAR, are well known. These alloys are used in particular for the manufacture of shadow masks as indicated, for example, the European patent application EP 05340460 which proposes to use for the manufacture of shadow masks an Fe-Ni-Co alloy containing, by weight, in addition to iron, from 28% to 34% of nickel, from 2% to 7% of cobalt, from 0.1% to 1% of manganese, less than 0.1% of silicon and less than 0.01 % of carbon; the remainder being impurities resulting from the production. But this alloy sometimes has the drawback of having a point Ms at the start of martensitic transformation close to ambient temperature so that, either during the forming of the shadow mask, or during its storage at low temperature, the martensitic transformation starts, which causes permanent deformations of the shadow mask. In addition, due in particular to the manganese content, considered necessary for the alloy to have good hot-rolling ability, the alloy has a slightly too high coefficient of expansion.

to sufficiently reduce the shadow mask blistering defect.

The aim of the present invention is to provide an Fe-Ni-Co alloy which has a martensitic transformation start point of less than -50 C, an average thermal expansion coefficient between 20 C and 100 C of less than 0.7x10-6 / K and an average thermal expansion coefficient between 80 C

and 130 C less than lxlo-6 / K.

To this end, the invention relates to an Fe-Ni-Co alloy whose chemical composition comprises, by weight: 32% <Ni <34% 3.5% <Co <6.5% 0% <Mn <0 , 1% 0% <if <0.1% 0% <Cr <0.1%

0.005% <C <0.02%

S <0.001%

0.0001% <Ca <0.002% 0.0001% <Mg <0.002% the remainder being iron and impurities resulting from the production; the chemical composition of the alloy also satisfying the relationships: Co + Ni <38.5% Co + 0.5 x Ni> 20% Co + 5 x Ni> 165.5% and S <0.02 x Mn + 0.8 x Ca + 0.6 x Mg Preferably, the contents of copper, molybdenum, vanadium and niobium should each be less than 0.1%. And better still, the sum of the contents of manganese, silicon, chromium, copper, molybdenum,

vanadium and niobium must be less than 0.30%.

Finally, it is preferable that the oxygen content is less than or equal to 0.01%, that the nitrogen content is less than or equal to 0.005% and

that the phosphorus content is less than or equal to 0.005%.

A subject of the invention is also the use of the alloy according to the invention for the manufacture of a shadow mask as well as the mask.

shade thus obtained.

The invention will now be described more precisely but

non-limiting.

While it is known that the deformations of a shadow mask are generated mainly by an average heating up to a temperature below 100 ° C. and typically 80 ° C., the inventors have estimated, in a novel way, that image defects were generated by local heating of the shadow mask at temperatures of up to 130 C. To reduce the image defects as much as possible, it is necessary to use, for the manufacture of the shadow mask, a alloy which not only has an average coefficient of expansion between 20 C and 100 C as low as possible, but which also has an average coefficient of expansion between 80 C and 130 C as low as possible. In addition, this alloy must have a micrographic structure stable up to a temperature

sufficiently low, i.e. down to at least -50 C.

The alloy according to the invention is an Fe-Ni-Co alloy, the chemical composition of which is adjusted so that, at the same time, its average coefficient of expansion between 20 C and 100 C is less than or equal to 0.7x10-6 / K, its average coefficient of expansion between 80 C and 130 C is less than or equal

at 1x10-6 / K and their Ms point is less than -50 C.

The chemical composition of the alloy comprises, by weight, at least 32% and at most 34% of nickel as well as at least 3.5% and at most 6.5% of cobalt, the nickel and cobalt contents being such that : Co + Ni <38.5% so that the mean coefficient of expansion between 20 C and 100 C is less than 0.7x10-6 / K; Co + 0.5 x Ni> 20% so that the average coefficient of expansion between 80 C and 130 C is less than 1x0l-6 / K; Co + 5 x Ni> 165.5%

so that the point Ms is less than -50 C.

But, so that the average coefficient of expansion between 20 C and C is less than 0.7x10-6 / K, it is necessary that the manganese contents,

silicon and chromium are less than or equal to 0.1%.

In order for the Ms point to remain below -50 ° C., the alloy must contain at least 0.005% carbon, however, in order not to deteriorate the drawformability, the content of

carbon should not exceed 0.02%.

However, industrial alloys always contain residual elements such as copper, molybdenum, vanadium or niobium, and, for the coefficient of expansion to be as low as possible, it is desirable that the contents of each of these elements remain less than or equal to 0.1% and, preferably, that: Mn + Si + Cr + Mo + V + Nb + Cu <0.30% Finally, and in order to obtain better hot ductility, it is preferable that the oxygen content remains less than or equal to 0.01%, the nitrogen content remains less than or equal to 0.005% and the

phosphorus remains less than or equal to 0.005%.

With this alloy, it is possible, in particular, to manufacture shadow masks. For this, the alloy is produced, it is cast into an ingot or slab, it is hot-rolled to form a strip approximately 4mm thick; the strip is then cold rolled to obtain a cold strip approximately 0.15 mm thick. This cold strip has a plastic flow limit RpO, 2 to 20 C of the order of 600 MPa which is much too high to allow easy shaping, also, after machining of the mask blanks by chemical cutting, one submits these blanks at an annealing between 700 C and 850 C which reduces the plastic yield point RpO, 2 at 20 C to about 320Mpa. Then each blank is shaped, for example

by stamping, to obtain a shadow mask.

By way of example, the alloys A to D according to the invention were manufactured, the chemical compositions of which were, in% by weight: rep Ni Co Mn Si Cr C S Ca Mg Fe

A 32.7 4.5 0.06 0.08 0.04 0.014 0.0006 0.0005 0.0015 comp.

B 33.5 4.5 0.05 0.08 0.07 0.014 0.0009 0.0012 0.0009 comp.

C 33.5 3.5 0.05 0.08 0.05 0.011 0.0007 0.0008 0.0007 comp.

D 33.3 4.2 0.05 0.09 0.06 0.018 0.0008 0.0011 0.0011 comp.

The characteristics of these alloys were: RpO, 2 RpO, 2 Rpo, 2 aa ai Mpa Mpa Mpa rep 20 0/100 20 0/80 80/130 Ms 20 C 20 C 200 C -6 / K 10-6 / K 10 -6 / KC hardened annealed * annealed *

A 0.31 0.23 0.78 - 90 615 320 141

B 0.65 0.65 0.80 <-186 615 318 137

C 0.49 0.45 0.90 <-186 607 304 133

D 0.51 0.49 0.77 <-186 629 322 148

annealing 780 C - 15 mn With these alloys it is possible to manufacture shadow masks consisting in particular of a sheet pierced with holes and shaped by stamping. These shadow masks have a fully austenitic structure even after shaping or after storage in a cold environment, and they exhibit a local blistering defect that is at least 40% lower than the local blistering defect of alloy shadow masks.

Iron-Nickel according to the prior art.

Claims (4)

1 - Fe-Ni-Co alloy whose chemical composition comprises, by weight: 32% <Ni <34% 3.5% <Co <6.5% 0% <Mn <0.1% 0% <Si <0 , 1% 0% <Cr <0.1% o10 0.005% <C <0.02% S <0.001% 0.0001% <Ca <0.002% 0.0001% <Mg <0.002% the remainder being iron and impurities resulting from the production; the chemical composition of the alloy also satisfying the relationships: Co + Ni <38.5% Co + 0.5 x Ni> 20% Co + 5 x Ni> 165.5% and S <0.02 x Mn + 0, 8 x Ca + 0.6 x Mg 2 - Alloy according to claim 1 characterized in that the copper, molybdenum, vanadium and niobium contents are each less than 0.1%. 3 Alloy according to claim 2 characterized in that the sum of the contents of manganese, silicon, chromium, copper, molybdenum, vanadium and niobium is less than 0.3%. 4 - Alloy according to any one of claims 1 to 3 characterized in that the oxygen content is less than or equal to 0.01%, the nitrogen content is less than or equal to 0.005% and the content of phosphorus is less than or equal to 0.005%. 5 - Use of the alloy according to any one of claims 1 to 4 for making a shadow mask. 6 - Shadow mask characterized in that it comprises at least one sheet pierced with holes made of an alloy according to any one of claims 1 to 4.