JP3405339B2 - Color CRT mask frame, steel plate used therefor, method for manufacturing the steel plate, and color CRT provided with the frame - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a color CRT (color cathode ray tube) (also referred to as a color picture tube) used for a television receiver, a display and the like. More specifically, the present invention relates to a mask frame (hereinafter referred to as a color CRT mask frame) that is a member that supports a tension type shadow mask arranged in a color CRT under tension, and a mask frame of the mask frame. The present invention relates to a steel plate used for manufacturing and a manufacturing method thereof.

[0002]

2. Description of the Related Art A color CRT internally has three electron guns for red, blue and green, and a fluorescent screen (screen) on which electron beams emitted from these collide. On the surface of the phosphor screen, phosphor dots emitting the above three colors are formed, which are arranged in a regular order.

In the shadow mask system, which occupies most of the color CRT, a rectangular shadow mask having a large number of aligned beam passage holes is arranged immediately before the fluorescent screen. The shadow mask is a member that aligns the electron beams and the phosphor dots so that each electron beam irradiates the phosphor dots of the corresponding color.

A conventional ordinary shadow mask has a thickness of 0.15
It consists of cold-rolled steel sheets of ~ 0.28 mm with fine holes formed at regular intervals by etching. After the shadow mask is curved by press molding, its four sides are welded and fixed to the mask frame. The curvature of the mask is necessary so that the mask absorbs thermal expansion of the mask and vibrations transmitted from the outside so that the displacement of the holes of the mask does not occur. Therefore, this type of mask cannot sufficiently cope with the flattening of the mask surface.

More recently developed is a tension type shadow mask. A typical tension-type shadow mask consists of a thin steel plate with a thickness of 0.05 to 0.15 mm with fine holes through which the beam passes, and is attached to the mask frame with tension applied vertically.
Since the thermal expansion and vibration of the mask can be absorbed by the tension, the mask can be planarized. It is also possible to use a tension type shadow mask in which tension is applied in both the vertical direction and the horizontal direction.

The mask frame for supporting the above-described typical tension type shadow mask has two horizontal long side frame members constituting upper and lower frame portions and two vertical direction frame members constituting left and right frame portions. The short side frame member is usually joined by welding for assembly. The long-side frame member is generally composed of a press-formed or roll-formed steel plate. The plate thickness of the steel plate is in the range of 3 to 6 mm, and is selected according to the size of the CRT. A round or square pipe or steel bar is usually used for the short-side frame member.

Before the shadow mask is attached to the mask frame, the mask frame is blackened. The blackening treatment is a treatment for forming a blackening film made of Fe ₃ O _{4 on the} steel surface by heat treatment. The blackened film has the effect of increasing the thermal emissivity of the material surface, increasing the absorption and heat dissipation of electron beams, and preventing the generation of secondary electrons and the generation of rust. The heating conditions for this blackening treatment are usually 450 to 680 ° C x 10 to 30 minutes.

The tension type shadow mask is attached to the mask frame by compressing the upper frame part and the lower frame part of the mask frame composed of the long side frame members from the outside inward, and at the same time, simultaneously applying the shadow mask. Also, while pulling in the vertical direction, the upper and lower edges of the shadow mask are welded to the upper frame portion and the lower frame portion of the frame, respectively. After that, when the pressure applied to the upper frame portion and the lower frame portion of the frame is removed, the shadow mask is supported by the frame in a vertically pulled state by the repulsive force of the frame. The left and right edges of the shadow mask are not fixed to the left and right frame portions (consisting of short-side frame members) of the mask frame.

In the structure in which the shadow mask is attached to the mask frame in this manner (hereinafter, also referred to as the shadow mask / frame structure), the upper frame portion and the lower frame portion of the mask frame are in a state in which bending stress is applied, and The shadow mask is in a state of being vertically tensioned. The left and right frame parts of the mask frame serve to support the upper and lower frame parts under bending stress.

Finally, the shadow mask / frame structure is subjected to strain relief annealing to remove the strain when the mask is attached. The strain relief annealing is generally performed by heating at a temperature of 400 to 680 ° C for 10 to 30 minutes.

The order of the steps of the above-mentioned process (hereinafter referred to as process A) is as follows: molding of the mask frame member → assembly of the mask frame → blackening treatment of the mask frame → sealing of the frame.
Adhesion of a mask, then stress relief annealing .

In the above process sequence, the blackening process and the stress relief annealing process can be reversed. In that case, in the strain relief annealing step, the strain of the mask frame due to forming and welding is removed. In the blackening process step, the mask frame and the shadow mask are blackened together, and during the blackening process, distortion at the time of attaching the shadow mask is also removed. The process sequence of this process (hereinafter referred to as process B) is as follows: molding → assembly → strain relief annealing → shadow mask
Paste → Blackening process

[0013]

In any of the processes, it is required to form a blackened film having good adhesion in the blackening treatment step. If the adhesion of the blackening film is poor, the blackening film may peel off during use of the color CRT, and fragments of the blackening film may drop into the CRT, blocking the beam passage hole of the shadow mask, etc. This is because the image receiving characteristics may be significantly impaired.

In the heat treatment process (strain relief annealing in process A and blackening process in process B) performed after attaching the shadow mask, bending stress is applied to the upper and lower frame portions of the mask frame, and the shadow mask is tensioned. It is a heat treatment that is performed under the special circumstances of receiving the heat. If the bending stress in the upper and lower frame portions of the mask frame is remarkably relaxed by this heat treatment, the mask frame may be deformed. Since tension is applied to the shadow mask in the vertical direction by the mask frame, the deformation of the upper and lower frame portions of the mask frame lowers the tension of the shadow mask and causes surface distortion. As a result, wrinkles and unevenness of the hole pitch may occur in the shadow mask, and performance deterioration such as color impurity may occur. Therefore, it is important to suppress the deformation of the mask frame during this heat treatment.

In order to reduce the deformation of the mask frame during the above-mentioned heat treatment process, which causes a decrease in tension and surface distortion of the tension type shadow mask, upper and lower frame portions of the mask frame for supporting the shadow mask under tension are provided. The long-sided frame member is made of 36Ni, which has high temperature creep strength.
Manufactured from steel or 42Ni steel. These steels contain 36% or 42% of expensive Ni, respectively, which makes the mask frame expensive.

Further, recent televisions tend to be large in size, and mask frames are also becoming large. In order to reduce the weight of televisions, it is also required to increase the strength of the steel material used as a mask frame material so that the thickness can be reduced.

An object of the present invention is to provide a steel plate for a color CRT mask frame which is relatively inexpensive, has excellent high-temperature strength, and has small creep strain at high temperatures. As a result, deformation of the frame during heat treatment such as stress relief annealing performed after attaching the tension type shadow mask to the mask frame can be minimized, and wrinkles of the shadow mask and hole pitch unevenness due to this heat treatment can be suppressed. Occurrence can be prevented.

Another object of the present invention is to form a blackened film having high strength, sufficient workability so as to reduce the weight of the mask frame and having a good adhesion by the blackening treatment. It is to provide a steel plate for a color CRT mask frame that can be used.

Another object of the present invention is the above color CRT.
A method of manufacturing a steel plate for a mask frame is provided.

[0020]

The present invention is based on the following findings found by the present inventors. (1) Deformation of the mask frame during heat treatment performed under bending stress generally tends to be suppressed by using a steel material having high high-temperature yield strength. However, even with steel materials having the same high-temperature yield strength, the amount of deformation will differ considerably.

(2) Regarding the above deformation of the mask frame, 1 is performed under the condition that the stress is 196 N / mm ² or more and the temperature is 400 ° C. or more.
By measuring the amount of creep strain over time, the superiority or inferiority of the steel material with respect to deformation can be determined.

(3) In addition to Mo, which has the effect of improving high-temperature strength, V and N are added to control the ferrite grain size and ferrite volume ratio to below a certain level. Steel sheets do not contain a large amount of expensive Ni. However, it shows a small amount of creep strain under the above conditions.

In one aspect, the present invention is, in mass%, C: 0.03 to 0.30%, Si: 0.30% or less, Mn: 0.05 to 1.5%, P: 0.05% or less, S: 0.02% or less, Mo: 0.02. ~ 0.50%, V: 0.02 to 0.20%, Al: 0.10% or less, N: 0.0040 to 0.0200%, and in some cases Cu: 1.0% or less,
Ni: 1.0% or less, Cr: 2.0% or less, W: 1.0% or less,
B: 0.003% or less, Ti: 0.030% or less, Nb: 0.030% or less, one or more, and the balance is steel and inevitable impurities, and has a steel composition of Al ≦ 7.0N, and Ferrite grain size is 15μm or less, ferrite volume ratio is
It is a steel plate for a color CRT mask frame having a metal structure of 90% or less.

[0024] In another aspect, the present invention is a rectangular color CRT mask frame in which four frame members are joined, at least a part of the frame members being formed from the above steel plate. It is a mask frame.

The present invention also relates to a color CRT equipped with this mask frame. In yet another aspect,
The present invention is a method for producing a steel plate for a color CRT mask frame, which includes the following steps: C: 0.03 to 0.30%, Si: 0.30% or less, Mn: 0.05 to 1.5%, P: 0.05% or less in mass%. , S: 0.02% or less, Mo: 0.02 to 0.50%, V: 0.02 to 0.20%, Al: 0.10% or less, N: 0.0040 to 0.0200%, and further, Cu: 1.0%
Below, Ni: 1.0% or less, Cr: 2.0% or less, W: 1.0% or less, B: 0.003% or less, Ti: 0.030% or less, Nb: 0.030
% Or less, one or two or more, the balance consisting essentially of iron and unavoidable impurities, the step of producing a slab having a steel composition with Al ≦ 7.0 N, and a finishing temperature of this slab of 820-950 ° C. , A step of forming a hot-rolled steel sheet by hot rolling at a winding temperature of 400 to 700 ° C.

The above method may further include a step of subjecting the hot rolled steel sheet obtained in the hot rolling step to cold rolling at a rolling rate of 0.2 to 15%. In that case, before the cold rolling step, a step of performing softening annealing on the hot rolled steel sheet under the conditions of an annealing temperature of 600 to 750 ° C. and an annealing soaking time of 1 to 25 hours may be further included.

The present invention also provides a color CRT mask frame manufactured by a method including the following steps:
Forming the above-mentioned steel sheet to form a color CRT mask frame member; joining four mask frame members, at least a part of which is the mask frame member, to form a color CRT mask frame; and a color CRT mask A step of blackening the frame to form a blackening film in the temperature range of 450 to 680 ° C, or a step of strain relief annealing of this mask frame in the temperature range of 400 to 680 ° C.

The present invention is also manufactured from the above color CRT mask frame by a method including the following steps:
A tension type color CRT shadow mask / frame structure is also provided: fixing the shadow mask to the color CRT mask frame so that tension is applied to the shadow mask to form a shadow mask / frame structure; Step of strain relief annealing in the temperature range of ~ 680 ℃, or process of blackening this structure in the temperature range of 450 ~ 680 ℃ to form a blackened film.

The steel sheet according to the present invention is excellent in mechanical strength, but the first heat treatment (blackening treatment in the process A) causes the solutioned metal element to precipitate, and the steel sheet is mechanically treated at room temperature and high temperature. Strength and creep properties are further improved. Therefore, the mask frame manufactured from this steel sheet is less likely to be deformed during the heat treatment (strain relief annealing in the process A) performed under bending stress after attaching the shadow mask. As a result, the decrease in the tension of the shadow mask due to this deformation can be minimized, and wrinkles and unevenness in the hole pitch of the shadow mask due to this heat treatment can be prevented.

Japanese Unexamined Patent Publication (Kokai) No. 8-67945 discloses a steel plate for an aperture frame which supports an aperture grill which is a shadow mask composed of many ribbons. The steel sheet is described as maintaining high high temperature strength after stress relief annealing. However, the high temperature strength in this case is the yield strength, which is realized by adding Mo. There is no suggestion on the composite addition of V and N, the influence of the ferrite structure, and the high temperature creep property in the present invention.

The steel sheet according to the present invention is excellent not only in high temperature yield strength but also in creep strength at high temperature, and exhibits low creep strain at high temperature. In the following description, the term “high temperature strength” is used to mean both high temperature yield strength and high temperature creep strength.

[0032]

The present invention is described in more detail below. In the following description,% is unless otherwise specified.
It is% by mass.

The steel plate for a color CRT mask frame according to the present invention is C: 0.03 to 0.30%, Si: 0.30% or less, Mn: 0.05 to 1.5%, P: 0.05% or less, S: 0.02% or less, Mo: 0.02. -0.50%, V: 0.02-0.20%, Al: 0.10% or less, N: 0.0040-0.0200%, Cu: 1.0% or less, Ni: 1.0% or less, Cr: 2.
0% or less, W: 1.0% or less, B: 0.003% or less, Ti: 0.
030% or less, Nb: 0.030% or less, one or more, and the balance essentially consists of iron and inevitable impurities,
It has a steel composition with Al ≦ 7.0N.

C is an element effective for increasing the strength of steel, and is contained in an amount of 0.03% or more in order to secure the strength of the mask frame. The upper limit of the C content is set to 0.30% because the addition of a larger amount of C impairs the formability and weldability of the steel plate required for manufacturing the mask frame. Preferably, the lower limit of the C content is 0.05% and the upper limit thereof is 0.20%.

Si is effective as a deoxidizer during the melting of steel, and is also effective for increasing the strength of steel. On the other hand,
Si tends to deteriorate the surface texture of the hot-rolled steel sheet and also impair the adhesion of the blackened coating. Therefore, Si is set to 0.30% or less. Desirably, Si is 0.25% or less.

Mn is also an element required as a deoxidizer and is also effective in increasing the strength of steel. Further, Mn has a function of fixing S which is an impurity as MnS and preventing hot brittleness. Therefore, Mn is contained by 0.05% or more. The upper limit of the Mn content is 1.5% because the addition of a larger amount of Mn impairs the formability and weldability. Preferably, the lower limit of the Mn content is 0.2% and the upper limit is 1.0%.

P is an element that improves the strength of steel.
However, since P tends to segregate, the inclusion of a large amount of P causes a large strength variation in the steel sheet, impairing the formability and weldability of the steel sheet. Therefore, the P content is 0.05% or less, preferably 0.03% or less.

If the content of S is large, the amount of inclusions such as MnS increases, and the formability is impaired. Therefore, the S content is preferably as low as possible, but 0.02% is acceptable. Mo is an important element that contributes to the high temperature strength of the steel sheet of the present invention. Mo
Almost does not form a solid solution in cementite, but forms a solid solution in ferrite. When the steel is subjected to heat treatment, Mo dissolved in this ferrite precipitates as Mo ₂ C separately from cementite during the temperature rising process. This Mo ₂ C finely precipitates on the new nuclei formed on the dislocations of the ferrite matrix phase by coherent precipitation, and is therefore effective in increasing the high temperature strength of the steel.

In the steel sheet of the present invention, such fine Mo ₂
Coincident precipitation of C occurs in the first heat treatment that the steel sheet receives (blackening treatment in process A, but as described later, another heat treatment such as softening annealing may be performed before that), and high temperature strength is improved. The mask frame can be manufactured. As a result, during heat treatment (strain relief annealing in process A) performed after attaching the shadow mask, the mask frame to which bending stress is applied exhibits low creep strain, and the tension of the shadow mask can be maintained.

In order to utilize such an effect of Mo, Mo
Is contained in an amount of 0.02% or more. Considering that excessive Mo content impairs formability and weldability, and that Mo is an expensive element, the upper limit of Mo content is 0.50%. Preferably, the Mo content has a lower limit of 0.30% and an upper limit of 0.40%.

V is also an important element along with Mo in the steel composition of the present invention. Similar to Mo, V does not form a solid solution in cementite and forms plate-like V ₄ C _{3 in} the dislocation portion of ferrite in the temperature rising process of the first heat treatment of the steel plate. This increases the high temperature strength of the mask frame and contributes to prevention of deformation during stress relief annealing.

To obtain the above effect, V is contained in an amount of 0.02% or more. For the same reason as Mo, the upper limit of V content is 0.20%
And Preferably, the V content has a lower limit of 0.04% and an upper limit of
It is 0.15%.

N can form a nitride with V. Therefore, in the first temperature rising process of the heat treatment of the steel sheet, V is coherently precipitated as VN in addition to the above carbides, which contributes to the improvement of the high temperature strength of the mask frame.

To obtain this effect, N is contained in an amount of 0.0040% or more. The upper limit of the N content is set to 0.0200% because the addition of a larger amount of N tends to cause pinhole-like defects on the slab surface during casting. Preferably, the lower limit of the N content is 0.0050%.

Although N is generally contained in steel as an impurity,
For steels of the type according to the invention, the content of N as an impurity is usually less than 0.0040%. Al is an element effective as a deoxidizer, and has a function of fixing N, which is generally an impurity, as AlN. However, in the present invention, N is positively added in an amount of 0.0040 to 0.0200% in order to precipitate VN, and precipitation of AlN is not desirable. Also, a large amount
The inclusion of Al easily causes surface defects of the steel sheet, which makes it easier for the blackened film to peel off. Furthermore, although Al is more stable than VN, when a large amount of Al is contained, N is fixed by Al during winding slow cooling after the end of hot rolling, and the effective solid solution N decreases. For these reasons, the Al content is 0.10% or less. Preferably, the Al content is 0.05% or less.

In order to obtain the improvement of the high temperature strength of the mask frame by the addition of N according to the present invention, it has been found that the content of Al for fixing N needs to be relatively limited with respect to the content of N. . Specifically, when the Al content is more than 7.0 times the N content, the high temperature strength of the steel sheet after heat treatment decreases. Therefore, Al ≦ 7.0N. Preferably, Al ≦ 6.0N.

The steel sheet according to the present invention may optionally contain Cu, Ni,
It may further contain one or more of Cr, W, B, Ti and Nb, whereby the high temperature strength of the steel sheet after heat treatment, and hence the mask, can be further enhanced.

Cu dissolves in the steel at the end of hot rolling and finely precipitates during the blackening treatment to increase the strength at room temperature and high temperature. However, if the added amount is too large, the formability and weldability are impaired, so the Cu content should be 1.0% or less.

Ni also enhances high temperature strength, but addition of a large amount impairs formability and weldability. Ni is also an element effective in preventing hot brittleness caused by Cu. Therefore, when Cu is added, it is preferable to add Ni together, and it is appropriate that the addition amount of Ni at that time is substantially the same as Cu. Considering that Ni is an expensive element, the Ni content is set
1.0% or less.

Cr and W increase the high temperature strength, but if contained in a large amount, formability and weldability are impaired. Therefore, Cr is
2.0% or less and W is 1.0% or less. B has the effect of strengthening the crystal grain boundaries, improving the rolling property, and refining the crystal grains to increase the high temperature strength. However, the addition of a large amount of B reduces the amount of VN precipitation necessary for improving the high temperature strength by fixing N as BN. Therefore, the upper limit of B content is 0.003%.

Ti and Nb form precipitates of TiC, NbC, etc., and the room temperature and high temperature strength can be increased by the grain refining action. However, both Ti and Nb combine with N to form a nitride, thereby reducing the amount of VN precipitation necessary for improving the high temperature strength. Therefore, when adding these elements, it is desirable to reduce the addition amount.
Both Nb and Nb are 0.030% or less.

The steel sheet of the present invention having the above-mentioned steel composition has a metallic structure composed of two phases of ferrite-pearlite, ferrite-bainite, and ferrite-martensite. The steel sheet of the present invention is characterized by having a ferrite grain size of 15 μm or less and a ferrite volume ratio of 90% or less in this metal structure.

As the ferrite grain size of the metal structure increases, the strength of the steel sheet tends to decrease. Even if the steel composition is within the above range, if the ferrite grain size becomes larger than 15 μm, the high temperature strength required for the mask frame can be obtained by the improvement of the high temperature strength due to the precipitation of fine carbonitride by the above-mentioned first heat treatment. Becomes difficult. The ferrite grain size is preferably 14 μm or less. The ferrite grain size can be adjusted by hot rolling conditions, particularly finishing temperature and winding temperature.

When the coiling temperature of the steel sheet becomes higher or the C content in the steel composition becomes lower, the second phase other than ferrite (pearlite, baylite, martensite) in the above two-phase structure becomes less than 10% by volume. May decrease. In such a metal structure having a small amount of second phase, it becomes difficult to obtain a desired high temperature strength after the first heat treatment even if the Mo, V and N contents are controlled to appropriate values. Therefore, the volume ratio of ferrite is 90% or less, preferably 88% or less.

The steel plate for a color CRT mask frame of the present invention is manufactured as a slab of steel having the above-mentioned composition.
It is manufactured by hot rolling under the conditions of. This as-hot-rolled steel sheet can be used for a mask frame, but may be further cold-rolled at a rolling rate of 0.2 to 15%. As is well known to those skilled in the art, cold rolling with a rolling ratio of 2% or less is called skin pass rolling (or temper rolling). Therefore, this cold rolling includes skin pass rolling.

From the production of slabs to the finishing of hot rolling,
There is no particular limitation and it may be performed according to the conventional technique. The finishing temperature of hot rolling is 820 ° C or more and 950 ° C or less in order to make the crystal grains finer, and is basically just above the Ar ₃ transformation point. This finishing temperature also applies when performing cold rolling after hot rolling. If the finishing temperature is less than 820 ° C, the hot rolling is in the α phase region, and if it exceeds 950 ° C, the hot rolling is in the high temperature γ phase region. In both cases, the crystal grains become coarse and the ferrite grain size becomes large. As a rough guideline for setting the ferrite grain size to 15 μm or less, the finishing temperature in the temperature range of 820 to 930 ° C. is preferable.

If the coiling temperature is lower than 400 ° C., the shape of the steel sheet after rolling becomes poor. When the coiling temperature exceeds 700 ° C, the volume fraction of ferrite exceeds 90%, and the grain size of ferrite is 15 μm.
May exceed. In addition, the scale becomes thick and the descaling property by pickling deteriorates.

The finishing temperature of hot rolling and the coiling temperature may be set within the above ranges so that the metal structure has a ferrite grain size of 15 μm or less and a ferrite volume ratio of 90% or less. M with the effect of suppressing recrystallization and ferrite transformation during hot
When the contents of o, Nb, Cr, V, etc. increase, the restrictions on finishing temperature and winding temperature are alleviated.

The hot-rolled steel sheet thus obtained has sufficient properties as it is as the steel sheet for mask frame of the present invention. However, when the light cold rolling is performed, the room temperature strength and the high temperature strength are improved more by the first heat treatment, and the creep strain of the mask frame during the stress relief annealing can be further reduced.

It is considered that the effect of this cold rolling can be attributed to the introduction of dislocations. When dislocations are introduced by cold rolling, MoC, V that occur during the first heat treatment of the steel sheet
Precipitation of fine carbonitrides such as ₄ C ₃ , VN and Cu is promoted. In addition to the action of these fine precipitates, the action of dislocation movement is prevented by these precipitates, and the room temperature and high temperature strength of the steel sheet after heat treatment are improved.

In order to obtain this effect, the rolling ratio in cold rolling is set to 0.2% or more, preferably 0.3% or more. The upper limit of the rolling ratio is set to 15% because if it exceeds this value, the formability deteriorates.

Prior to this cold rolling, the surface is descaled if necessary, and then the annealing temperature is 600 to 750 ° C.
The softening annealing may be performed under the condition of soaking time of 1 to 25 hours.
In that case, the room temperature and high temperature strength is improved during the softening annealing by the precipitation of fine carbonitrides described above. Descaling can be performed by pickling, but other methods may be used. Even when softening annealing is not carried out, it is generally preferable to carry out pickling and descaling after the rolling step.

As described above, the color CRT mask frame steel plate according to the present invention is used for the color CRT.
Mask frames and shadow mask / frame structures can be manufactured. In the following, the process order of the process A described above will be described, but the process B can also be adopted.

First, a steel plate is formed by press forming or roll forming to produce a mask frame member. It is also possible to make all four frame members of the mask frame from the steel sheet according to the invention. However, the short-side frame members forming the left and right frame portions of the mask frame are usually round or square rods or pipes. Therefore, it is usual to manufacture at least a part of the frame member, particularly two long side frame members constituting the upper and lower frame parts from the steel sheet of the present invention.

A mask frame is assembled by joining four frame members, usually by welding. The assembled mask frame is then heated in a hot gas furnace for blackening treatment.
The blackening process can be performed in the same manner as the conventional one. The heating conditions are usually 450 to 680 ° C for 10 to 30 minutes. The preferred blackening temperature is 500 to 650 ° C.

When the first heat treatment of the steel sheet is this blackening treatment, Mo ₂ C or VN is initially used during this blackening treatment, as described with respect to the steel composition and metallographic structure of the steel sheet of the present invention. Precipitates fine carbonitrides and improves the room temperature and high temperature strength (including high temperature creep properties) of the steel sheet.
As a result, the deformation of the mask frame when subjected to strain relief annealing under bending stress is minimized, and the tension of the shadow mask can be maintained. Further, the steel sheet of the present invention can form a blackened film having good adhesion on the surface of the frame in the blackening treatment.

A tension type shadow mask is attached to the blackened mask frame. As mentioned above, the shadow mask is applied by applying an inward pressure to the upper and lower parts of the mask frame and, if necessary, applying a vertical pulling force to the shadow mask as well. After the upper and lower edges of the shadow mask are welded to the frame portion, the force applied to the frame or the frame and the mask is released. This results in a shadow mask / frame structure in which the shadow mask is supported by the mask frame under tension.

Finally, the shadow mask / frame structure is subjected to strain relief annealing. The strain relief annealing can be performed in a temperature range of 400 to 680 ° C, preferably 450 to 650 ° C. The heating time is usually 10 to 30 minutes. In the present invention, the high-temperature strength (both the yield strength and the creep strength) of the heat-treated mask frame is high, and the deformation of the frame during the stress relief annealing is suppressed. Therefore, the tension of the shadow mask is maintained even after the strain relief annealing, and it is possible to prevent the occurrence of defects such as color impurity due to the wrinkles of the shadow mask and the deviation of the hole pitch.

This shadow mask / frame structure is placed immediately in front of the phosphor screen of the color CRT. Color CRT
The configuration other than the shadow mask / frame structure is not particularly limited, and may be any known or later-developed configuration.

[0070]

The following examples are given to illustrate the invention and are not intended to limit the invention.

Steel slabs having the steel compositions shown in Tables 1 and 2 were melted, and these slabs were hot-rolled under the conditions shown in Tables 3 and 4.
Hot rolling at (finishing temperature and coiling temperature) yields a sheet thickness of 4.50
A hot-rolled steel sheet of ~ 5.00 mm was obtained. Some of the hot-rolled steel sheets were skin-pass rolled or cold-rolled at the rolling rates shown in Table 3. Each steel sheet obtained by hot rolling or hot rolling + cold rolling was pickled after the completion of rolling.

A part of each of the obtained steel sheets was heated at 570 ° C. for 30 minutes in a hot gas furnace to be blackened. The following characteristics were investigated for these steel sheets. The test results are also shown in Tables 3 and 4.
Are also shown.

(1) Tensile Properties Steel Sheets without Blacking (referred to as "rolled" steel sheets)
From both the blackened steel sheet and JIS Z220 in the rolling direction.
The No. 5 tensile test piece of 1 was sampled and a room temperature tensile test was performed according to JIS Z2241.

For the blackened steel sheet, a tensile test at a high temperature of 460 ° C. corresponding to the strain relief annealing temperature was conducted according to the JI method.
It carried out according to S G0567. Tables 3 and 4 show the tensile properties of as-rolled steel sheet (0.2% yield stress <YS>, tensile strength <TS>,
Total elongation <El>) and room temperature and 460 ° C of blackened steel
The 0.2% yield stress <YS> is shown.

(2) Metal structure: The test material of the as-rolled steel plate was etched with a nital solution, and then observed by SEM at 2000 times to determine the grain size and volume ratio of ferrite. In addition, the ferrite volume ratio was obtained by obtaining the ratio of the area of ferrite from a plurality of SEM observation results and averaging the ratios.

(3) Creep test: The high temperature creep strain of a test piece taken from a blackened steel sheet was measured with a gauge length of 30 m.
It was measured using an m extensometer. I measured the test piece
It was the amount of elongation when kept at 460 ° C. for 1 hour under a tensile stress of 294 N / mm ² . The temperature of 460 ° C. corresponds to the strain relief annealing temperature as described above.

Based on the measured creep strain amount, the high temperature creep characteristics were evaluated as follows: ○: 0.10% or less, △: more than 0.10%, 0.
Evaluation was made in 3 stages of less than 15% and x: 0.15% or more. ○ means good, Δ means good, and × means bad.

(4) Surface quality: The surface of the steel sheet after pickling was visually observed and the surface quality was evaluated by the presence or absence of severe scale scratches (scale remaining, scale indentation). ○ means that there is no severe scale scratch, and × means that there is severe scale scratch.

(5) Formability: The as-rolled steel sheet specimen was subjected to right-angle bending, and the presence or absence of cracks on the bent end face was visually observed to evaluate the formability. ○ means that there is no clear crack on the bent end surface, and × means that there is clear crack on the bent end surface.

(6) Weldability: Two specimens of the same rolled steel sheet were TIG welded and the welded portion was bent similarly to the formability. Weldability was evaluated by the presence or absence of large cracks in the weld. ○ means that there is no large crack in the weld, and × means that there is a large crack in the weld.

(7) Adhesion of blackening film: A test piece of a blackened steel plate was bent as in the formability test. At the bent portion, a film peeling test was performed using a transparent adhesive tape, and the adhesion of the blackened film was evaluated by the peeling state of the film. ○ indicates that the blackened film did not peel off or was very slight, ×
Means that a clear strip is confirmed.

[0082]

[Table 1]

[0083]

[Table 2]

[0084]

[Table 3]

[0085]

[Table 4]

As can be seen from Tables 3 and 4, the steel sheet having the steel composition and metallurgical structure according to the present invention has good tensile properties as it is rolled, and has good formability, weldability, and surface condition after pickling. It was good. In addition, they showed improved yield stress at room temperature after undergoing heat treatment by blackening treatment, and showed good high temperature strength at the strain relief annealing temperature. Therefore, the creep strain amount at high temperature was as small as 0.10% or less, and the high temperature creep property was excellent. Further, the blackening treatment made it possible to form a blackened film having good adhesion. Therefore, it is apparent that the present invention provides a relatively inexpensive steel plate having all the various characteristics required for a mask frame for a tension type shadow mask.

The steel sheets of Comparative Examples having a steel composition and / or a metallographic structure outside the scope of the present invention had insufficient at least one property. Especially, like No.31, 42, 44, 45,
The steel sheet to which a large amount of Cr, Mo or W was added was inferior in performance to the steel sheet of the present invention even though the cost was high.

Regarding Nos. 2 to 4, 6, 32 and 33 of Tables 3 and 4, yield stress and creep strain amount at 460 ° C (460 ° C x
1 hr) is shown as a graph in FIGS. 1 to 4 as a relationship with the ferrite grain size and the ferrite volume ratio. From this figure, it is clear that according to the present invention, the criticality of setting the ferrite grain size to 15 μm or less and the ferrite volume ratio to 90% or less.

[0089]

According to the present invention, various characteristics (surface quality, moldability, weldability, room temperature and high temperature strength, low temperature and high temperature) required for a mask frame for holding a tension type color CRT shadow mask under tension are obtained. Creep strain,
A relatively inexpensive steel sheet having a blackened film adhesion) is provided.

The present invention includes a television,
Color CRT for crystallizing tension type shadow mask
It is a technology that contributes to cost reduction and weight reduction. The steel sheet of the present invention can be used not only in the type in which the tension is applied only in one direction in the vertical direction, but also in the mask frame of a tension type shadow mask in which the tension is applied in two directions, the vertical direction and the horizontal direction. The steel sheet of the present invention can also be used for a mask frame that supports a conventional shadow mask that is not of the tension type.

[Brief description of drawings]

FIG. 1 is a graph showing the results of Examples.

FIG. 2 is a graph showing the results of Examples.

FIG. 3 is a graph showing the results of Examples.

FIG. 4 is a graph showing the results of Examples.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C21D 9/46 C21D 9/46 NT C22C 38/12 C22C 38/12 38/54 38/54 C23C 8/14 C23C 8/14 H01J 9/14 H01J 9/14 G 29/07 29/07 Z (72) Inventor Shinji Tsuge 4-533 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) Hideharu Ohmae No. 1-1 Sachimachi, Takatsuki City, Osaka Prefecture Matsushita Electronics Industrial Co., Ltd. (56) Reference JP 10-158788 (JP, A) JP 8-67945 (JP, A) JP 10-226821 (JP, A) JP 3-249149 (JP, A) JP 3-53045 (JP, A) JP 9-180647 (JP, A) JP 2000-38641 (JP, A) JP JP-A-55-133735 (JP, A) JP-A-11-213879 (JP, A) JP-A-4-4 7631 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00 C21D 1/26 C21D 6/00 C21D 9/46 C23C 8/14 H01J 9/14 H01J 29/07

Claims (11)

(57) [Claims] 1. In mass%, C: 0.03 to 0.30%, Si: 0.30% or less, Mn: 0.05 to 1.5%, P: 0.05% or less, S: 0.02% or less, Mo: 0.02 to 0.50%, V: 0.02 to 0.20%, Al: 0.10% or less, N: 0.0040 to 0.0200%, the balance being iron and unavoidable impurities, and having a steel composition of Al ≦ 7.0N, and having a ferrite grain size of 15 μm or less, ferrite Having a metal structure with a volume ratio of 90% or less,
Steel plate for color CRT mask frame. 2. The steel composition, in mass%, Cu: 1.0% or less, Ni: 1.0% or less, Cr: 2.0% or less, W: 1.0% or less, B: 0.003% or less, Ti: 0.030% or less, Nb: 0.030
% Or less, 1 type or 2 types or more are further contained, The steel plate for color CRT mask frames of Claim 1 characterized by the above-mentioned. 3. Four frame members are joined together,
A rectangular color CRT mask frame, wherein at least a part of the frame member is formed of the steel plate according to claim 1 or 2. 4. A color CRT provided with the color CRT mask frame according to claim 3. 5. A method for manufacturing a steel plate for a color CRT mask frame, which comprises the following steps: C: 0.03 to 0.30%, Si: 0.30% or less, Mn: 0.05 to 1.5%, P: 0.05% or less in mass%. S: 0.02% or less, Mo: 0.02 to 0.50%, V: 0.02 to 0.20%, Al: 0.10% or less, N: 0.0040 to 0.0200%, with the balance being iron and unavoidable
Steel composition of Al ≦ 7.0N,
In addition to the above steel composition, Cu: 1.0% or less, Ni: 1.0% or less, Cr: 2.0% or less, W: 1.0% or less, B: 0.003% or less, Ti: 0.030% or less, Nb: 0.030% or less 1 For producing a slab having a steel composition containing two or more kinds, and a finishing temperature of 820 to 950 ° C and a winding temperature of 400 to 70
A step of forming a hot rolled steel sheet by hot rolling under the condition of 0 ° C. 6. The method further comprises the step of subjecting the hot-rolled steel sheet obtained in the hot-rolling step to cold rolling at a rolling ratio of 0.2 to 15%.
The method of claim 5. 7. The hot-rolled steel sheet is annealed at a temperature of 600 to 750 ° C. and an annealing soaking time of 1 to 25 before cold-rolling the hot-rolled steel sheet.
The method according to claim 6, further comprising the step of performing softening annealing under the condition of time. 8. A color CRT mask frame manufactured by a method including the following steps: a step of forming a color CRT mask frame member by molding the steel plate according to claim 1 or 2, wherein at least a part of the mask frame member is formed. The step of joining the four mask frame members to form a color CRT mask frame, and blackening the formed color CRT mask frame in the temperature range of 450 to 680 ° C to form a blackening film on the surface of the frame. Forming process. 9. A color CRT mask frame manufactured by a method including the following steps: a step of forming the color CRT mask frame member by forming the steel plate according to claim 1 or 2, wherein at least a part of the mask frame member is formed. And the step of joining the four mask frame members to form a color CRT mask frame, and the step of strain relief annealing the formed color CRT mask frame in the temperature range of 400 to 680 ° C. 10. A tension type color CRT shadow mask / frame structure manufactured by a method including the following steps: A shadow mask is fixed to a color CRT mask frame according to claim 8 so that tension is applied to the shadow mask. The process of forming the shadow mask / frame structure and the process of strain relief annealing this structure in the temperature range of 400-680 ° C. 11. A tension type color CRT shadow mask / frame structure manufactured by a method including the following steps: A shadow mask is fixed to a color CRT mask frame according to claim 9 so that tension is applied to the shadow mask. A step of forming a shadow mask / frame structure, and a step of blackening this structure in a temperature range of 450 to 680 ° C to form a blackened film on the surface of the structure.