Shadow mask support member having high strength and thermal deformation resistant low-expansion alloy plate and high expansion alloy plate and method of producing the same

There is disclosed a shadow mask support member for supporting a shadow mask of a Braun tube which member comprises a parallel bonded-type bimetal, and has a high strength and an excellent resistance to thermal resistance. There is also disclosed a method of producing such a support member. The shadow mask support member includes a high-strength, low-expansion alloy plate, and a high-expansion alloy plate which are bonded together on their marginal surfaces, the low-expansion alloy plate having an excellent resistance to thermal deformation, the low-expansion alloy plate consisting essentially, by weight, of 0.1-0.5% C, not more than 1.0% Si, not more than 2.0% Mn, 30-40% Ni, 1.0-5.0% Mo and the balance Fe and incidental impurities, the low-expansion alloy plate having an average thermal expansion coefficient of not more than 6 .times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. C. and a tensile strength of not less than 100 kgf/mm.sup.2 at a room temperature, and the high-expansion alloy plate having an average thermal expansion coefficient of not less than 14.times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. C. and a tensile strength of not less than 110 kgf/mm.sup.2 at a room temperature. Optionally, the low-expansion alloy plate may further contain not more than 10.0% Cr and not more than 10.0% Co, and the content of (Ni+Co) is 30-40%.

BACKGROUND OF THE INVENTION 
This invention relates to a shadow mask support member (e.g. a spring 
comprising parallel bonded sheets) for supporting a shadow mask in a color 
Braun tube (cathode ray tube) so as to correct a color drift, and also 
relates to a method of producing such a support member. 
In a color Braun tube of a television set, when a shadow mask is heated by 
electron beams, the shadow mask is thermally expanded to produce a color 
drift trouble. Therefore, there has heretofore been used a support member 
for resiliently support the shadow mask relative to a glass container, 
such a support member comprising a spring of a bimetal composed of two 
metal plates, which have thermal expansion coefficients different to each 
other, bonded parallel together on their marginal surfaces. Typically, 
such a spring has been formed by stamping and shaping a bimetal (or a 
trimetal) which has a low-expansion plate of an invar alloy (Fe-36Ni) and 
a high-expansion plate of austenitic stainless steel such as SUS304 
(Fe-18Cr-8Ni). 
Recently, with an increased size of television sets, there is a tendency 
for a Braun tube to increase in size and to become flatter. On the other 
hand, a shadow mask support member has been required to have a 
high-strength, compact design. In the case of the conventional parallel 
bonded-type bimetal formed by combining SUS 304 and a Fe-36% Ni invar 
alloy together, the tensile strengths of SUS304 and the invar alloy at a 
room temperature are about 120 kgf/mm.sup.2 and about 80 kgf/mm.sup.2, 
respectively, even if an aging treatment is effected after cold working. 
Particularly, the strength of the invar alloy is low. Thus, the 
conventional support member is not sufficiently high in strength to have a 
compact design, and therefore there has been encountered a problem that 
the support member can not be of a sufficiently small size. Under the 
circumstances, the parallel bonded-type bimetal, constituting the support 
member, has now been required to have a higher strength, and therefore the 
metal plates, constituting the parallel bonded-type bimetal, have been 
required to have a high strength. 
When the shadow mask is to be incorporated into the Braun tube, the support 
member, while subjected to a strain, undergoes a heat history several 
times at temperatures ranging from 400.degree. C. to 600.degree. C. If the 
support member is formed into a small size, there is a possibility that 
the support member is permanently deformed by the heat of this heat 
history. The support member, constituted by the conventional parallel 
bonded-type bimetal (i.e., the combination of SUS304 and the Fe36%Ni invar 
alloy), does not possess a sufficient resistance to thermal deformation, 
and therefore there has been encountered a problem that the support member 
can not have a small-size design. Therefore, the parallel bonded-type 
bimetal, constituting the support member, has also been required to have 
an excellent resistance to thermal deformation, and to achieve this, it 
has been desired that the metal plates, constituting the parallel 
bonded-type bimetal, should have an excellent resistance to thermal 
deformation. 
As described above, in order that the Braun tube can have a large-size, 
flat design, there has been a demand for the type of shadow mask support 
member having a high strength and an excellent resistance to thermal 
deformation. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a shadow mask support member 
having a high strength and an excellent resistance to thermal resistance, 
the support member being formed by bonding a high-strength, low-expansion 
alloy plate (having a high strength and an excellent thermal deformation 
resistance) and a high-expansion alloy plate (having a high strength) 
together. 
In order to impart a high strength to a shadow mask support member, it is 
necessary that both of two metal plates (that is, a high-expansion metal 
plate and a low-expansion metal plate), constituting this support member, 
should be increased in strength. Therefore, it has been thought effective 
particularly to increase the strength of the one of the two metal plates 
of the conventional parallel bonded-type bimetal having a lower strength, 
that is, the Fe-36%Ni invar alloy. A study of the resistance of the 
Fe-36%Ni invar alloy (which defines the low-expansion material of the 
conventional parallel bonded-type bimetal) to thermal deformation has 
indicated that its thermal deformation resistance is very poor, and 
therefore it has also been found necessary to enhance its resistance to 
thermal deformation. 
In view of the foregoing, the inventors of the present invention have made 
an extensive study of Fe-Ni invar alloys in order to obtain an alloy 
having a high tensile strength at a room temperature, a low average 
thermal expansion coefficient at 30.degree.-100.degree. C., and a good 
thermal deformation resistance at 400.degree.-600.degree. C., and as a 
result there have been obtained the following findings based on which the 
present invention has been made. More specifically, it has been newly 
found that by the addition of C, Cr and Mo to a Fe-Ni invar alloy, the 
tensile strength at a room temperature, as well as the thermal deformation 
resistance at 400.degree.-600.degree. C., can be greatly enhanced, and 
that by suitably balancing the (Ni +Co) content, the average thermal 
expansion coefficient at 30.degree.-100.degree. C. can be kept low. 
It has been newly found that these properties required for the 
low-expansion material of the shadow mask support member, such as a high 
strength, a low thermal expansion property and an excellent thermal 
deformation resistance, can be obtained by optimizing conditions of cold 
working and an aging treatment. 
Further, it has been found that when a high-expansion alloy plate of 
Fe-high Mn-Cr-Ni-N or Fe-Mn-Ni-V-(Cr, Mo, W) is combined with the above 
low-expansion alloy plate, there can be obtained a shadow mask support 
member more excellent in thermal deformation resistance. 
More specifically, according to a first aspect of the present invention, 
there is provided a shadow mask support member comprising a high-strength, 
low-expansion alloy plate, and a high-expansion alloy plate which are 
bonded together on their marginal surfaces, the low-expansion alloy plate 
having an excellent resistance to thermal deformation, the low-expansion 
alloy plate consisting essentially, by weight, of 0.1-0.5% C, not more 
than 1.0% Si, not more than 2.0% Mn, 30-40% Ni, 1.0-5.0% Mo and the 
balance Fe and incidental impurities, the low-expansion alloy plate having 
an average thermal expansion coefficient of not more than 
6.times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. C. and a tensile 
strength of not less than 100 kgf/mm.sup.2 at a room temperature, and the 
high-expansion alloy plate having an average thermal expansion coefficient 
of not less than 14.times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. 
C. and a tensile strength of not less than 110 kgf/mm.sup.2 at a room 
temperature. 
According to a second aspect of the present invention, there is provided a 
shadow mask support member comprising a high-strength, low-expansion alloy 
plate, and a high-expansion alloy plate which are bonded together on their 
marginal surfaces, the low-expansion alloy plate having an excellent 
resistance to thermal deformation, the low-expansion alloy plate 
consisting essentially, by weight, of 0.1-0.5% C, not more than 1.0% Si, 
not more than 2.0% Mn, not more than 10.0% Cr, 30-40% Ni, 1.0-5.0% Mo and 
the balance Fe and incidental impurities, the low-expansion alloy plate 
having an average thermal expansion coefficient of not more than 
10.times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. C. and a tensile 
strength of not less than 100 kgf/mm.sup.2 at a room temperature, and the 
high-expansion alloy plate having an average thermal expansion coefficient 
of not less than 14.times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. 
C. and a tensile strength of not less than 110 kgf/mm.sup.2 at a room 
temperature. 
According to a third aspect of the present invention, there is provided a 
shadow mask support member comprising a high-strength, low-expansion alloy 
plate, and a high-expansion alloy plate which are bonded together on their 
marginal surfaces, the low-expansion alloy plate having an excellent 
resistance to thermal deformation, the low-expansion alloy plate 
consisting essentially, by weight, of 0.1-0.5% C, not more than 1.0% Si, 
not more than 2.0% Mn, 30-40% Ni, not more than 10.0% Co, 1.0-5.0% Mo and 
the balance Fe and incidental impurities, Ni+Co being 30-40%, the 
low-expansion alloy plate having an average thermal expansion coefficient 
of not more than 6.times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. 
C. and a tensile strength of not less than 100 kgf/mm.sup.2 at a room 
temperature, and the high-expansion alloy plate having an average thermal 
expansion coefficient of not less than 14.times.10.sup.-6 /.degree. C. at 
30.degree.-100.degree. C. and a tensile strength of not less than 110 
kgf/mm.sup.2 at a room temperature. 
According to a 4th aspect of the present invention, there is provided a 
shadow mask support member comprising a high-strength, low-expansion alloy 
plate, and a high-expansion alloy plate which are bonded together on their 
marginal surfaces, the low-expansion alloy plate having an excellent 
resistance to thermal deformation, the low-expansion alloy plate 
consisting essentially, by weight, of 0.1-0.5% C, not more than 1.0% Si, 
not more than 2.0% Mn, not more than 10.0% Cr, 30-40% Ni, not more than 
10.0% Co, 1.0-5.0% Mo and the balance Fe and incidental impurities, Ni+Co 
being 30-40%, the low-expansion alloy plate having an average thermal 
expansion coefficient of not more than 10.times.10.sup.-6 /.degree. C. at 
30.degree.-100.degree. C. and a tensile strength of not less than 100 
kgf/mm.sup.2 at a room temperature, and the high-expansion alloy plate 
having an average thermal expansion coefficient of not less than 
14.times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. C. and a tensile 
strength of not less than 110 kgf/mm.sup.2 at a room temperature. 
According to a 5th aspect of the present invention, there is provided a 
shadow mask support member comprising a high-strength, low-expansion alloy 
plate as defined in any one of the 1st to 4th aspects of the invention, 
and a high-expansion alloy plate which are bonded together on their 
marginal surfaces, the high-expansion alloy plate consisting essentially, 
by weight, of not more than 0.2% C, not more than 1.0% Si, 10-20% Mn, 
10-20% Cr, 2-10% Ni, not more than 0.4% N and the balance Fe and 
incidental impurities, and the high-expansion alloy plate having an 
average thermal expansion coefficient of not less than 14.times.10.sup.-6 
/.degree. C. at 30.degree.-100.degree. C. and a tensile strength of not 
less than 110 kgf/mm.sup.2 at a room temperature. 
According to a 6th aspect of the present invention, there is provided a 
shadow mask support member comprising a high-strength, low-expansion alloy 
plate as defined in any one of the 1st to 4th aspects of the invention, 
and a high-expansion alloy plate which are bonded together on their 
marginal surfaces, the high-expansion alloy plate consisting essentially, 
by weight, of not more than 0.2% C, not more than 1.0% Si, 10-20% Mn, 
10-20% Cr, 2-10% Ni, not more than 0.4% N, at least one selected from the 
group consisting of not more than 3.0% Mo and not more than 1.0% V, and 
the balance Fe and incidental impurities, and the high-expansion alloy 
plate having an average thermal expansion coefficient of not less than 
14.times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. C. and a tensile 
strength of not less than 110 kgf/mm.sup.2 at a room temperature. 
According to a 7th aspect of the present invention, there is provided a 
shadow mask support member comprising a high-strength, low-expansion alloy 
plate as defined in any one of the 1st to 4th aspects of the invention, 
and a high-expansion alloy plate which are bonded together on their 
marginal surfaces, the high-expansion alloy plate consisting essentially, 
by weight, of 0.2-1.0% C, not more than 1.0% Si, 2-10% Mn, 8-20% Ni, 
0.1-1.5% V, at least one selected from the group consisting of not more 
than 6.0% Cr, not more than 4% Mo and not more than 4% W, and the balance 
Fe and incidental impurities, and the high-expansion alloy plate having an 
average thermal expansion coefficient of not less than 16.times.10.sup.-6 
/.degree. C. at 30.degree.-100.degree. C. and a tensile strength of not 
less than 110 kgf/mm.sup.2 at a room temperature. 
According to an 8th aspect of the present invention, there is provided a 
shadow mask support member comprising a high-strength, low-expansion alloy 
plate as defined in any one of the 1st to 4th aspects of the invention, 
and a high-expansion alloy plate which are bonded together on their 
marginal surfaces, the high-expansion alloy plate consisting essentially, 
by weight, of 0.2-1.0% C, not more than 1.0% Si, 2-10% Mn, 8-20% Ni, 
0.1-1.5% V, not more than 0.1% N, at least one selected from the group 
consisting of not more than 6.0% Cr, not more than 4% Mo and not more than 
4% W, and the balance Fe and incidental impurities, and the high-expansion 
alloy plate having an average thermal expansion coefficient of not less 
than 16.times.10.sup.-6 /.degree. C. at 30.degree.- 100.degree. C. and a 
tensile strength of not less than 110 kgf/mm.sup.2 at a room temperature. 
According to a 9th aspect of the present invention, there is provided a 
shadow mask support member comprising a high-strength, low-expansion alloy 
plate as defined in any one of the 1st to 4th aspects of the invention, 
and a high-expansion alloy plate which are bonded together on their 
marginal surfaces, the high-expansion alloy plate consisting essentially, 
by weight, of 0.2-1.0% C, not more than 1.0% Si, 2-10% Fin, 8-20% Ni, 
0.1-1.5% V, not more than 0.5% Nb, at least one selected from the group 
consisting of not more than 6.0% Cr, not more than 4% Mo and not more than 
4% W, and the balance Fe and incidental impurities, and the high-expansion 
alloy plate having an average thermal expansion coefficient of not less 
than 16.times.10.sup.-6 /.degree. C. at 30.degree.-100.degree. C. and a 
tensile strength of not less than 110 kgf/mm.sup.2 at a room temperature. 
According to a 10th aspect of the present invention, there is provided a 
shadow mask support member comprising a high-strength, low-expansion alloy 
plate as defined in any one of the 1st to 4th aspects of the invention, 
and a high-expansion alloy plate which are bonded together on their 
marginal surfaces, the high-expansion alloy plate consisting essentially, 
by weight, of 0.2-1.0% C, not more than 1.0% Si, 2-10% Mn, 8-20% Ni, 
0.1-1.5% V, not more than 0.5% Nb, not more than 0.1% N, at least one 
selected from the group consisting of not more than 6.0% Cr, not more than 
4% Mo and not more than 4% W, and the balance Fe and incidental 
impurities, and the high-expansion alloy plate having an average thermal 
expansion coefficient of not less than 16.times.10.sup.-6 /.degree. C. at 
30.degree.-100.degree. C. and a tensile strength of not less than 110 
kgf/mm.sup.2 at a room temperature. 
According to an 11th aspect of the present invention, there is provided a 
method of producing a shadow mask support member having an excellent 
resistance to thermal deformation, comprising the steps of: 
cold working a high-strength, low-expansion alloy plate as defined in any 
one of claims 1 to 4 at a reduction of not less than 40%, and subsequently 
subjecting the low-expansion alloy plate to an aging treatment at a 
temperature not more than 650.degree. C.; and 
subsequently bonding the low-expansion alloy plate to a high-expansion 
alloy plate on their marginal surfaces. 
As described above, one of the most significant features of the support 
member of the present invention is that the low-expansion alloy plate and 
the high-expansion alloy plate both have a high tensile strength of not 
less than 100-110 kgf/mm.sup.2, and are bonded or joined together on their 
marginal surfaces by welding or the like to form the shadow mask support 
member. Such a combination has never been known or proposed in the prior 
art, and this support member is totally novel. 
Effects of the elements of the low-expansion alloy of the support member of 
the present invention will now be described. 
C is a very effective element which is, together with Cr and Mo, in a 
solid-solution state in the alloy of the invention to greatly enhance cold 
work hardenability, thereby increasing the strength at a room temperature, 
and also during the aging treatment, C forms carbides together with Cr and 
Mo, and finely precipitates, thereby increasing the strength at high 
temperatures to greatly enhance a thermal deformation resistance necessary 
for the material constituting the shadow mask support member. The C 
content should be at least 0.1%, but the addition of C in an excessive 
amount not only invites an increased thermal expansion coefficient, but 
also forms coarse carbides to adversely affect the cold workability. 
Therefore, this content should be not more than 0.5%. 
Si is added in a small amount as a deoxidizer. The addition of this 
substance in an excessive amount lowers ductility, and therefore this 
content has been decided to be not more than 1.0%. 
Mn is also added in a small amount as a deoxidizer. The addition of this 
substance in an excessive amount increases the thermal expansion 
coefficient, and therefore this content has been decided to be not more 
than 2.0%. 
Ni is a very important element for obtaining a low thermal expansion 
property, and need to be added in an amount of 30-40% in order to maintain 
the low thermal expansion property required for the low-expansion material 
of the shadow mask support member. If the Ni content is less than 30%, a 
martensite transformation temperature rises, so that the martensite 
transformation is liable to occur during the cold working, and the thermal 
expansion coefficient rises. In contrast, if this content is more than 
40%, the thermal expansion coefficient at lower temperatures rises 
although the inflection temperature rises. Thus, in either case, the 
intended low thermal expansion property can not be obtained, and therefore 
this content should be 30-40%. 
Mo, when added in combination with C, enhances the hardenability by the 
cold working to increase the strength. Moreover, Mo is a very important 
element for greatly enhancing the thermal deformation resistance required 
for the shadow mask support member. It is thought that this is 
attributable to a mutual action between Mo and C in the solid solution 
state and also to the precipitation of fine carbides of a part of Mo. The 
Mo content need to be at least 1.0%, but the addition of Mo in an amount 
of more than 5.0% forms a large amount of carbides to lower the ductility. 
Therefore, the Mo content should be 1.0-5.0%. 
In the alloy of the invention, it is not always necessary to add Cr. 
However, the addition of this substance is quite effective in enhancing 
the thermal deformation resistance required for the shadow mask support 
member. If this content is more than 10.0%, the austenitic structure 
becomes unstable, and the thermal expansion coefficient becomes too high. 
Therefore, the Cr content should be not more than 10.0%. 
Co, like Ni, is an effective element for obtaining the low thermal 
expansion property, and its effect is greater than that of Ni. If Co is 
added in an amount of more than 10%, the martensite transformation 
temperature rises although the inflection temperature is not changed so 
much, so that a martensite transformation liable to occur during the cold 
working, and the thermal expansion coefficient rises. Therefore, this 
content should be not more than 10%. Moreover, Co achieves a similar 
effect, as attained by Ni, for obtaining the low thermal expansion 
property, and therefore can substitute for Ni in an equivalent amount, and 
hence an arrangement can be made in terms of the (Co+Ni) content. If the 
(Co+Ni) content is less than 30%, the martensite transformation 
temperature rises, so that a martensite transformation is liable to occur 
during the cold working, and the thermal expansion coefficient rises. In 
contrast, if this content is more than 40%, the thermal expansion 
coefficient at the lower temperatures rises. In either case, the intended 
low thermal expansion property can not be obtained, and therefore this 
content should be 30-40%. 
The tensile strength need to be high so as to impart a high strength to the 
shadow mask support member. Further, the shadow mask support member need 
to have an excellent thermal deformation resistance in addition to a high 
tensile strength. In order to impart an excellent thermal deformation 
resistance to the shadow mask support member, the low-expansion alloy of 
the support member of the invention, having an excellent thermal 
deformation resistance, first need to be used instead of the conventional 
low-expansion alloy (Fe36%Ni alloy), and then the tensile strength level 
need to be increased. The tensile strength can be greatly increased by 
cold working the low-expansion alloy of the support member of the 
invention. It is advantageous that the tensile strength of the 
low-expansion alloy of the support member of the invention be higher than 
that of the conventional low-expansion alloy (the Fe-36% Ni invar alloy), 
and therefore the tensile strength of the low-expansion alloy of the 
invention has been decided to be not less than 100 kgf/mm.sup.2. 
In the shadow mask support member, the thermal expansion coefficient is 
significant in the range of from a room temperature to 100.degree. C. at 
the most. In order that the shadow mask support member can operate to 
correct a color drift by the difference in thermal expansion between the 
two metal plates constituting the shadow mask support member, the 
low-expansion material has been decided to have a thermal expansion 
coefficient (the average value in the range of from a room temperature to 
100.degree. C.) of not more than 10.times.10.sup.-6 /.degree. C. 
Preferably, this thermal expansion coefficient is not more than 
6.times.10.sup.-6 /.degree. C. 
Where other deoxidizing elements, such as Al, Ti, Mg, Ca and B, are 
incidentally contained as impurities, or added in a trace amount, they 
will not affect the properties at all in so far as their content is in the 
following range, and therefore this falls within the range of the present 
invention. 
Al, Ti.ltoreq.0.1% 
Mg, Ca, B.ltoreq.0.02% 
Next, a method of producing the low-expansion alloy of the support member 
of the invention will now be described. 
The low-expansion alloy of the support member of the invention, having a 
composition falling within the range of the present invention, is first 
prepared, and the cold working is effected for enhancing the tensile 
strength at a room temperature and the thermal deformation resistance. 
Even if the composition of the low-expansion alloy of the present support 
member falls within the range of the invention, an adequate tensile 
strength can not be obtained if the reduction is less than 40%. Therefore, 
the reduction should be not less than 40%. 
The aging treatment after the cold working is carried out for the purpose 
of enhancing the tensile strength, the tensile ductility, the thermal 
deformation resistance and the spring property. However, if the aging 
treatment is effected at a temperature of more than 650.degree. C., the 
tensile strength at a room temperature is greatly lowered. Therefore, the 
aging treatment should be carried out at not more than 650.degree. C. 
The shadow mask support member, formed by bonding the low-expansion alloy 
plate, produced by this method, and the high-expansion alloy plate 
together on their marginal surfaces by welding or the like, has a high 
tensile strength and an excellent thermal deformation resistance, and is 
suitable for a large-size design of a Braun tube and a flat face-design 
thereof. 
Next, effects of the elements of the high-expansion alloy of the support 
member of the invention, recited in claims 5 and 6, will now be described. 
C is present in the solid-solution state in the austenitic matrix to 
strengthen the matrix. However, if this substance is added in an amount of 
more than 0.2%, this decreases the solid solubility of N, thus affecting 
the solid solution of N which is effective in enhancing the thermal 
deformation resistance. Therefore, this content should be not more than 
0.2%. 
Si is added in a small amount as a deoxidizer. However, the addition of 
this substance in an excessive amount lowers the ductility, and therefore 
this content has been decided to be not more than 1.0%. 
Mn is an important element which increases the solid solubility of N to 
enhance the strength at a room temperature and the thermal deformation 
resistance, and also stabilizes the austenitic matrix to maintain a high 
thermal expansion property. However, if this content is less than 10%, the 
solid solubility of N is not adequate, and in contrast if this content is 
more than 20%, the workability is adversely affected. Therefore, this 
content should be 10-20%. 
Cr is an important element which, like Mn, increases the solid solubility 
of N to enhance the strength at a room temperature and the thermal 
deformation resistance. If this content is less than 10%, the solid 
solubility of N is not adequate, and in contrast if this content is more 
than 20%, the austenitic matrix becomes unstable, and the thermal 
expansion coefficient is lowered. Therefore, this content should be 
10-20%. 
Not less than 2% Ni is necessary for stabilizing the austenitic matrix to 
obtain a high thermal expansion coefficient as described above for Mn. If 
this content is more than 10%, the solid solubility of N is lowered to 
lower the strength at a room temperature and the thermal deformation 
resistance. Therefore, this content should be 2-10%. 
N is an important element which is contained in the solid solution state in 
the austenitic matrix to stabilize the austenite to increase the thermal 
expansion coefficient, and also greatly contributes to the strengthening 
of the solid solution to greatly improve the strength at a room 
temperature and particularly the thermal deformation resistance. If this 
content is more than 0.4%, the castability and weldability are adversely 
affected, and therefore this content should be not more than 0.4%. 
V and Mo are present in the solid solution state in the austenitic matrix, 
or precipitates as fine carbides in the austenitic matrix, thereby further 
enhancing the thermal deformation resistance. One or both of the two 
elements can be added according to the need. If the content of V is more 
than 1.0%, it forms coarse primary carbides to adversely affect the 
workability. If the content of Mo is more than 3%, it makes the austenitic 
matrix unstable to lower the thermal expansion coefficient. Therefore, the 
V content should be not more than 1.0%, and the Mo content should be not 
more than 3.0%. 
In the shadow mask support member, the thermal expansion coefficient is 
significant in the range of 30.degree.-100.degree. C. at the most. In 
order that the shadow mask support member can operate to correct a color 
drift by the difference in thermal expansion between the two metal plates 
constituting the shadow mask support member, the high-expansion material 
has been decided to have a thermal expansion coefficient (the average 
value in the range of from 30.degree.-100.degree. C.) of not less than 
14.times.10.sup.-6 /.degree. C. 
It is preferred that the tensile strength be high to impart a high strength 
to the shadow mask support member, and if the high-expansion alloy plate 
is greater in strength than the low-expansion alloy plate, the shadow mask 
support plate can be further increased in strength. Therefore, the tensile 
strength of the high-expansion alloy has been decided to be not less than 
110 kgf/mm.sup.2. 
Next, effects of the elements of the high-expansion alloy of the support 
member of the invention, recited in claims 7 to 10, will now be described. 
C is very effective in stabilizing the austenitic structure to maintain the 
high-expansion property, and also is very effective in greatly enhancing 
the cold work hardenability to increase the strength at a room 
temperature, and further forms carbides together with V, Cr, Mo and W, and 
finely precipitates to increase the strength at high temperatures, thereby 
greatly enhancing the thermal deformation resistance required for the 
material constituting the shadow mask support member. To achieve these 
effects, C need to be added in an amount of not less than 0.2%. However, 
if this content is more than 1.0%, coarse primary carbides are formed to 
lower the ductility, thereby adversely affecting the workability of the 
material and the shaping ability of the shadow mask support member. 
Therefore, this content should be 0.2-1.0%. 
Si is added in a small amount as a deoxidizer. If this substance is added 
in an excessive amount, the ductility is lowered, and therefore this 
content has been decided to be not more than 1.0%. 
Mn is very effective in stabilizing the austenitic structure to maintain 
the high-expansion property, and also is effective in greatly enhancing 
the cold work hardenability to increase the strength at a room 
temperature. If this content is less than 2%, its effect is not 
satisfactory, and in contrast if this content is more than 10%, the hot 
workability as well as the oxidation resistance during the heat treatment 
are adversely affected greatly. Therefore, this content should be 2-10%. 
Ni is most effective and essential for stabilizing the austenitic structure 
to maintain the high thermal expansion property. If this content is less 
than 8%, its effect is not satisfactory, and in contrast if this content 
is more than 20%, the austenitic structure is stabilized too much to lower 
the hardenability during the cold working, thus failing to provide a 
sufficiently high strength at a room temperature. Therefore, this content 
should be 8-20%. 
V is an effective element which forms primary carbides to thereby make the 
crystal grains fine to increase the strength at a room temperature, and 
also is partially contained in the solid solution state in the austenitic 
matrix, or precipitates as fine carbides in the austenitic matrix during 
the aging treatment, thereby enhancing the thermal deformation resistance 
and the strength at a room temperature. If this content is less than 0.1%, 
the above effects are not satisfactory, and in contrast if this content is 
more than 1.5%, a large amount of coarse primary carbides are formed to 
adversely affect the workability of the material and the shaping ability 
of the shadow mask support member. Therefore, this content should be 
0.1-1.5%. 
Cr, Mo and W are effective elements which are contained in the solid 
solution state in the austenitic matrix, or precipitate as fine carbides 
in the austenitic matrix during the aging treatment, thereby increasing 
the strength at a room temperature and particularly greatly enhancing the 
thermal deformation resistance. At least one selected from the group 
consisting of these elements is added. However, all of these are 
ferrite-forming elements, and therefore if the Cr content is more than 
6.0%, the Mo content is more 4.0%, and the W content is more than 4.0%, 
the austenitic matrix becomes unstable, which makes it difficult to 
maintain the high thermal expansion property. Therefore, the Cr content 
should be not more than 6.0%, the Mo content should be not more than 4.0%, 
and the W content should be not more than 4.0%. 
Nb is an effective element which forms primary carbides to thereby make the 
crystal grains fine to increase the strength at a room temperature. This 
element can be suitably added according to the need. However, if this 
content is more than 0.5%, a large amount of coarse primary carbides are 
formed to adversely affect the workability of the material and the shaping 
ability of the shadow mask support member. Therefore, this content should 
be not more than 0.5%. 
N is an effective element which is contained in the solid solution state in 
the austenitic matrix to solid-solution-strengthen the austenitic matrix, 
thereby increasing the strength at a room temperature and particularly 
enhancing the thermal deformation resistance. This element can be added 
according to the need, but if this content is more than 0.1%, the 
weldability is adversely affected. Therefore, this content should be not 
more than 0.1%. 
In the present invention, the high-strength, low-expansion alloy plate with 
an excellent thermal deformation resistance and the high-expansion alloy 
plate are combined together, that is, bonded together, on their marginal 
surfaces by butt welding to form a parallel bonded-type bimetal (or a 
parallel bonded-type trimetal), thereby providing the shadow mask support 
member. The shadow mask support member thus obtained has a high strength 
and an excellent thermal deformation resistance, and is far greater in 
strength than the conventional shadow mask support member formed by a 
combination of a Fe-36%Ni invar alloy and SUS304.