WO1996013618A1 - Cold rolled sheet steel for shadow mask, and manufacturing method therefor - Google Patents

Cold rolled sheet steel for shadow mask, and manufacturing method therefor Download PDF

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Publication number
WO1996013618A1
WO1996013618A1 PCT/KR1995/000138 KR9500138W WO9613618A1 WO 1996013618 A1 WO1996013618 A1 WO 1996013618A1 KR 9500138 W KR9500138 W KR 9500138W WO 9613618 A1 WO9613618 A1 WO 9613618A1
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WIPO (PCT)
Prior art keywords
shadow mask
less
steel sheet
rolling
carried out
Prior art date
Application number
PCT/KR1995/000138
Other languages
French (fr)
Inventor
Woo Chang Jeong
Chang Hyun Park
Tae Yup Park
Tae Won Kim
Seong Ho HAN
Bong Taek Hwang
Original Assignee
Pohang Iron & Steel Co., Ltd.
Research Institute Of Industrial Science & Technology
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Application filed by Pohang Iron & Steel Co., Ltd., Research Institute Of Industrial Science & Technology filed Critical Pohang Iron & Steel Co., Ltd.
Priority to RU96116986A priority Critical patent/RU2109839C1/en
Priority to JP8514462A priority patent/JPH09503825A/en
Priority to DE19581414A priority patent/DE19581414C1/en
Publication of WO1996013618A1 publication Critical patent/WO1996013618A1/en

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    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • CCHEMISTRY; METALLURGY
    • C22METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22CALLOYS
    • C22C38/00Ferrous alloys, e.g. steel alloys
    • C22C38/18Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226Hot rolling
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C21D9/48Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236Cold rolling
    • CCHEMISTRY; METALLURGY
    • C21METALLURGY OF IRON
    • C21DMODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273Final recrystallisation annealing

Definitions

  • the present invention relates to a cold rolled steel sheet for making a shadow mask of a cathode ray tube of a color TV and a manufacturing method therefor, in which the etchability and the formability are superior.
  • the shadow mask type cathode ray tube of the color TV was developed by the RCA of the United States, and was put to the practical use.
  • the cathode ray tube of the color TV is attached with a shadow mask which has several hundred thousands of apertures. Therefore, electron beams which are emitted from an electron gun are made to pass the apertures of the shadow mask, so that the electron beams would exactly land on the red, blue and green phosphorescent dot films.
  • the shadow mask has a color defining function.
  • the shadow mask has a thermal expansion correcting function, and a magnetic shielding function.
  • the cold rolled steel sheet for making the shadow mask is generally composed of a Cr-added low carbon aluminum killed steel. This steel is melted in a converter, and continuously cast. The cast steel is subjected to a hot rolling followed by an acid pickling and a first cold rolling, then a first decarburization annealing is carried out to an extremely low carbon level. The annealed steel is secondly cold rolled and is shipped to a photo etching company. The photo-etched shadow mask is made to undergo a second annealing at a temperature of 700 - 750°C, and then, is press-formed into a curved face. The formed shadow mask is put to a blackening treatment, before installed to the cathode ray tube.
  • Such a shadow mask has to have superior etchability and surface characteristics. If the shadow mask is to have a superior etchability, the steel sheet as the raw material has to have a uniform thickness, and its shape has to be superior. Further its surface has to have a proper surface roughness, and the steel sheet has to have a low level of non-metallic inclusion content so as to have a high cleanness.
  • the low carbon rimmed steel which was superior in the surface characteristics was widely used as the material for the shadow mask.
  • the non-metallic inclusion content was higher in the upper portion than the lower portion of the ingot, and therefore, deviations in the product quality could not be reduced.
  • the low carbon aluminum killed steel is bad in the surface characteristics compared with the rimmed steel, and therefore, the killed steel was known to be unacceptable for the shadow mask.
  • the surface characteristics of the killed steel has become almost same as that of the rimmed steel.
  • the killed steel is uniform in the material quality in the lengthwise direction of the coil, and therefore, the use of the killed steel has become advantageous in view of the shape ensuring and the uniformity of the sheet thickness after the cold rolling process. Further, the cleanness of the killed steel is superior over the rimmed steel, and therefore, the killed steel has come to be widely used for the shadow mask recently.
  • a typical manufacturing method for the killed steel is disclosed in Japanese Patent Application Laid-open No. Sho- 61-16324.
  • a hot rolled sheet of a low carbon aluminum killed steel is subjected to a first cold rolling, an annealing, and a second rolling in the cited sequence.
  • the steel is composed of: less than 0.03% of C, 0.20 - 0.60% of Mn, less than 0.03% of Si, less than 0.10% of P, less than 0.10% of S, 0.01 - 0.05% of Soluble Al, 0.01 - 0.05% of Cr, and a balance of Fe and other unavoidable impurities.
  • the oxide film adherence which had been problematic was improved by adding Cr.
  • the steel manufacturing techniques such as the vacuum degassing has briskly advanced, and therefore, a high cleanness low carbon steel has been made to be manufactured in the steel manufacturing process. Therefore, the shadow mask came to be manufactured using the extremely low carbon steel as the starting material.
  • the yield strength becomes high after an etching and a second annealing due to the solute carbon. Consequently, the shape holding ability during a press forming is aggravated, and a stretcher strain occurs, with the result that it becomes difficult to obtain a shadow mask having a uniform curved surface. Therefore it is the key of the technique to design the alloy system in such a manner that the yield strength should be lowered, and the stretcher strain should not occur after the second annealing.
  • the cold rolled steel sheet for making a shadow mask is composed of: less than 0.005% of C, 0.05 - 0.50% of Mn, less than 0.010% of S, 0.01 -0.08% of soluble Al, less than 0.005% of N, more than 7 of Mn%/S%, more than 6 of (soluble Al % - 0.003%)/N%, a balance of Fe and other unavoidable impurities.
  • the rimmed steel or the Cr-added low carbon aluminum killed steel is subjected to a hot rolling, an acid pickling, a first cold rolling, a decarburization annealing and a second cold rolling under the general conditions. Therefore, an OCA furnace (open coil annealing furnace) is required for decarburizing a low carbon steel to an extremely low carbon steel. Further, a second cold rolling facility having a superior thickness and shape control capability is required for obtaining a high thickness precision and a superior shape. That is, conventionally, in manufacturing the cold rolled steel sheet for making the shadow mask, invest enrs in facilities such as decarburizing furnace and the second cold rolling apparatus are required, and further, the manufacturing process is more complicated, with the result that the manufacturing cost is increased.
  • the present invention is intended to overcome the above described disadvantages of the conventional techniques.
  • a cold rolled steel sheet for making a shadow mask and a manu acturing method therefor in which an extremely low carbon aluminum killed steel containing a tiny amount of Nb for precipitating a solute carbon of the initial material in the form of a carbide and containing a tiny amount of Cr for improving the oxide film adherence is subjected to a hot rolling, and a single round of cold rolling is carried out into the final thickness, whereby, without carrying out a decarburization annealing, the yield strength of the second annealed steel sheet after an etching becomes less than 11 kgf/m 2 , and the yield point elongation becomes less than 0.2%, so as to obtain a cold rolled steel sheet for use in a shadow mask having a superior etchability and a superior formability.
  • the cold rolled steel sheet for making a shadow mask having superior etchability and formability according to the present invention is composed of in weight %: less than 0.004% of C, 0.1 - 0.4% of Mn, less than 0.02% of P, less than 0.02% of Si, 0.02 - 0.08% of soluble Al, less than 0.004% of N, 0.02 - 0.06% of Cr, 0.0050 - 0.030% of Nb, and a balance of Fe and other unavoidable impurities.
  • the method for manufacturing the cold rolled steel sheet for making a shadow mask includes the steps of: homogenizing the extremely low carbon aluminum killed steel having the above described composition at a temperature of 1200 - 1250°C; carrying out a hot finish rolling at a temperature of 900 - 940°C; coiling the steel sheet at a temperature of 550 - 650°C; carrying out a cold rolling down to the final thickness at a reduction ratio of 85 - 90%; carrying out a continuous annealing at a temperature of 640 - 680°C; and carrying out a temper rolling, whereby a cold rolled steel sheet for making a sha ⁇ ow mask having superior etchability and formability is manufactured.
  • FIG. 1A is a photograph showing a cross section of a slot of a shadow mask which is manufactured by photo- etching the cold rolled steel sheet according to the present invention
  • FIG. IB is a sectional photograph taken along a line A-A' of FIG. 1A;
  • FIG. 1C is a sectional photograph taken along a line B-B' of FIG. 1A.
  • FIG. 2 is a graphical illustration showing the stress- strain curves obtained in tensile tests after carrying out a second annealing on an inventive steel and a comparative steel.
  • the carbon content becomes more than 0.004 weight % (to be called '%' below), then the amounts of carbides are increased, with the result that the etchability is aggravated. Further, the amount of the solute carbon is increased, leading to increase in the yield strength and the yield point elongation after the final annealing, with the result that the press formability is aggravated. Therefore it is preferable to limit the carbon content to less than 0.004%, and more preferably, the carbon content should be limited to less than 0.003%, because it is better to reduce the carbon content as low as possible.
  • Mn prevents the red shortness (caused by FeS) by precipitating sulphur in the form of MnS. Therefore, Mn needs to be added at least in the amount of 0.1%. However, if Mn is added by more than 0.4%, the steel becomes too hard, or the formability of the steel is aggravated due to the solid solution hardening by Mn. Therefore it is desirable to limit the content of Mn to 0.1 - 0.4%.
  • phosphorus is a substitutional alloy element having a large solid solution hardening, and therefore, if it is added by more than 0.02%, the steel is too much hardened, thereby aggravating the formability.
  • sulphur forms sulfide type non-metallic inclusions, aggravating the etchability, and therefore, it is desirable to limit sulphur to less than 0.02%.
  • aluminum is added for deoxidization in steel making, and for precipitating nitrogen in the form of A1N, so that the increase of the yield strength due to the solute nitrogen as well as the stretcher strain can be inhibited.
  • aluminum is added by 0.02% or more.
  • aluminum is excessively added by more than 0.08%, the steel may be too much hardened, and therefore, it is desirable to limit aluminum to a range of 0.02 - 0.08%.
  • Cr is an element for improving the oxide film adherence. If the oxide film adherence is aggravated, the small chips of the oxide film degrades the quality of the TV picture, and the voltage resistant property is also aggravated. Therefore, if a tiny amount of Cr is added, the adherence can be improved. However, if the Cr content is less than 0.02%, its effect is insufficient, while if its content is more than 0.06%, not only the oxide film adherence is saturated, but also the manufacturing cost is increased, as well as too much hardening the steel.
  • Nb precipitates the solute carbon in the form of NbC, leading to decrease in the yield point elongation and the yield strength after the second annealing, so that the stretcher strain can be inhibited.
  • the yield strength after the second annealing and the stretcher strain caused during the forming are increased proportionally to the solute carbon.
  • Nb performs the function of eliminating the stretcher strain and lowering the yield strength after the second annealing, without carrying out a decarburization annealing, unlike the conventional method in which a decarburization annealing is carried out to reduce the carbon content down to an extremely low carbon steel.
  • the Nb content becomes lower than 0.005%, then the solute carbon cannot be effectively precipitated.
  • the etchability is rather aggravated due to a large amount of precipitation of NbC. Therefore, it is desirable to limit the Nb content to 0.005 - 0.03%.
  • the extremely low carbon aluminum killed steel is melted by using a converter and a vacuum degassing facility. Then slabs are formed by applying a continuous casting process, and then, the slabs are heated to a temperature of 1200 - 1250°C, so that the austenitic structure can be sufficiently homogenized before carrying out hot rollings. Then, near 920°C just above the Ar 3 temperature, hot rollings are completed down to a thickness of 2.0 mm.
  • the hot rolling finish temperature is below 900°C, then the top, the tail and the edges of the hot rolled steel sheet become a ferrite single phase, so that a non-uniformity in the mechanical properties of the steel would be generated.
  • the hot rolling finish temperature of the general hot rolling process is below 940°C, and therefore, it is desirable to carry out the finish hot rolling at a temperature of 900 - 940°C.
  • the hot rolled steel sheet be coiled at a temperature of 550 - 650°C, and the reason is as follows. That is, if the coiling temperature is above 650°C, then the amount of Nb precipitates is increased, with the result that the etchability is aggravated. Further, the quality deviations between the coils of the hot rolled steel sheets in the lengthwise direction become severe, with the result that the acid pickling characteristics becomes aggravated. On the other hand, if the coiling temperature comes down to below 550°C, the temperature becomes not uniform, and therefore, not only severe deviations occur in the lengthwise direction, but also the shape of the shadow mask is aggravated, because a thin sheet of about 2.0 mm is coiled at below 550°C.
  • a hot rolled steel sheet which has undergone an acid pickling is subjected to a first cold rolling with a reduction ratio of about 70%. Then a recrystallization annealing is carried out to decarburize the steel sheet down to an extremely low carbon steel, and then, a second cold rolling is carried out down to the final thickness.
  • a recrystallization annealing is carried out to decarburize the steel sheet down to an extremely low carbon steel, and then, a second cold rolling is carried out down to the final thickness.
  • the hot rolled steel sheet which has undergone the usual acid pickling is subjected to a single round of cold rolling with a reduction ratio of 85 - 90%. Then a recovery annealing is carried out, and then, a temper rolling is carried out in the normal manner.
  • the cold rolling reduction ratio becomes different depending on the required thickness of the shadow mask, and therefore, the cold rolling is carried out by taking into account the thickness of the shadow mask. If the cold rolling is carried out with a reduction ratio of above 90%, the process is not only overloaded, but also the shape or the thickness precision is aggravated.
  • the cold rolling is carried out with a reduction ratio of below 85%, it is meant that the hot rolled steel sheet has to be thin in obtaining the same thickness of the cold rolled steel sheet. Therefore, an extra load is imposed on the hot rolling process, and the shape of the hot rolled steel sheet is aggravated. Therefore, it is desirable to carry out the cold rolling with a reduction ratio of 85 - 90%. Meanwhile, it is very difficult to provide a proper surface roughness required for the shadow mask during the cold rolling. Therefore, a temper rolling is required for providing the required surface roughness. However, the cold rolled steel sheet is too much hardened to such a degree that it is difficult to carry out the temper rolling.
  • a continuous annealing is carried out at a temperature of 640 - 680°C for recovery annealing the steel.
  • the annealing temperature is above 680°C, the structure becomes a completely recrystallized ferrite, with the result that the etchability can be aggravated in the etching process.
  • the annealing temperature is below 640°C, the structure becomes same as that of the cold rolled sheet, with the result that an exact surface roughness cannot be provided during the temper rolling.
  • the steel sheet which has undergone the recovery annealing is made to undergo a temper rolling, thereby providing the required surface roughness, and correcting the shape.
  • a temper rolling ratio 1.0%.
  • a thick shadow mask sheet may be temper rolled with work rolls surface-textured by electro discharge texturing method. In this way the surface roughness can be varied, so that the etchability can be improved. That is, the product in which the surface roughness is provided by a shot blast in the usual way shows a small number of peaks per inch (PPI) and a large peak-to-peak interval (Sm), thereby aggravating the etchability.
  • PPI peaks per inch
  • Sm peak-to-peak interval
  • Example 1 Extremely low carbon Al killed steels having the compositions of Table 1 were melted in converters, and were subjected to a vacuum degassing treatment. Then the steels were subjected to a continuous casting, thereby preparing steel slabs.
  • inventive steels 1 - 3 and the comparative steels 4 - 6 of Table 1 a vacuum degassing treatment was carried out on all of them.
  • the comparative steel 7 a steel having a carbon content of 0.02% was made to undergo a decarburizing process, and the final composition is shown in the table.
  • the Nb content exceeds the composition range of the present invention, while the comparative steel 5 is a can making steel. Further, the comparative steel 6 does not contain Nb at all.
  • the cold rolling reduction ratio, the annealing temperature and the temper rolling ratio were as shown in
  • Comparative material 7 First cold rolling- decarburization annealing (recrystallization annealing)- temper rolling-second cold rolling. Table 3
  • Comparative material 6 75.0 760 75.0 1.30 - Goo ⁇ Good
  • the comparative materials 1A and IB correspond to the steel which is annealed at a temperature at which recrystallization completely occurs and recrystallization does not occur at all, respectively.
  • the comparative material 5 corresponds to a can making steel (the comparative steel 5) on which the process for the inventive materials was carried out. However, it is somewhat different from the inventive materials which was recovery annealed at 640-680°C because the material 5 was completely recry ⁇ tallized at a high temperature of 730 - 750°C.
  • the etchability was assigned with "good” or “no good” based on a collective judgment by considering the straightne ⁇ s of the slot portion, the distortion and the uniformity of the slots shape.
  • the oxide film adherence was assigned with "good” or “no good” in accordance with whether the oxide film was dropped in small chips when carrying out a bending test at an angle of 120°C after putting a piece of scotch tape on the shadow mask.
  • the oxide film adherence was aggravated due to the lack of Cr content.
  • the results of the property evaluations were superior.
  • a continuous annealing or a decarburization annealing was carried out after carrying out a first cold rolling to completely recrystallize them, and then, a second rolling was carried out. Therefore they have the disadvantage that a decarburization annealing or the like is required.
  • the yield strength of the steel sheet is less than 13 Kgf/mm 2 (with the cross head speed of 10 mm/min) .
  • a tiny amount of Nb is added to an extremely low carbon Al killed steel so as to precipitate the solute carbon in the form of a carbide, and the hot rolling and cold rolling conditions are properly controlled.
  • a cold rolling is carried out, then a recovery annealing was carried out in a continuous annealing furnace in the usual manner, and then, a temper rolling is carried out.
  • a steel sheet for making a shadow mask is manufactured, in which the yield strength of the second annealed sheet after an etching is less than 11 Kgf/mm 2 , and the yield point elongation is less than 0.2%. Therefore, the etchability and formability of the steel sheet of the present invention are found to be improved.
  • the continuous annealing which is carried out in the present invention corresponds to the usual continuous annealing other than a decarburization annealing, and therefore, the process of the present invention excludes the decarburization annealing and the second cold rolling, with the result that the manufacturing cost can be saved to a significant degree.

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Abstract

A cold rolled steel sheet for making a shadow mask and a manufacturing method therefor are disclosed, in which an extremely low carbon aluminum killed steel containing a tiny amount of Nb for precipitating a solute carbon of the initial material in the form of a carbide and containing a tiny amount of Cr for improving the oxide film adherence is subjected to a hot rolling, and a single round of cold rolling is carried out into the final thickness, whereby, without carrying out a decarburization annealing, the yield strength of the second annealed steel sheet after an etching becomes less than 11 kgf/mm2, and the yield point elongation becomes less than 0.2 %, so as to obtain a cold rolled steel sheet for making a shadow mask having a superior etchability and a superior formability. The method for manufacturing the cold rolled steel sheet for a shadow mask according to the present invention includes the step of: homogenizing the extremely low carbon aluminum killed steel at a temperature of 1200 - 1250 °C, the steel being composed of in weight %: less than 0.004 % of C, 0.1 - 0.4 % of Mn, less than 0.02 % of P, less than 0.02 % of Si, 0.02 - 0.08 % of soluble Al, less than 0.004 % of N, 0.02 - 0.06 % of Cr, 0.0050 - 0.030 % of Nb, and a balance of Fe and other unavoidable impurities. Then a hot finish rolling is carried out at a temperature of 900 - 940 °C. Then the steel sheet is coiled at a temperature of 550 - 650 °C. Then a cold rolling down to the final thickness is carried out at a reduction ratio of 85 - 90 %. Then a continuous annealing is carried out at a temperature of 640 - 680 °C, and a usual temper rolling is carried out, whereby a cold rolled steel sheet for making a shadow mask having superior etchability and formability is manufactured.

Description

COLD ROLLED SHEET STEEL FOR SHADOW MASK, AND MANUFACTURING METHOD THEREFOR
FIELD OF THE INVENTION The present invention relates to a cold rolled steel sheet for making a shadow mask of a cathode ray tube of a color TV and a manufacturing method therefor, in which the etchability and the formability are superior.
BACKGROUND OF THE INVENTION
The shadow mask type cathode ray tube of the color TV was developed by the RCA of the United States, and was put to the practical use. The cathode ray tube of the color TV is attached with a shadow mask which has several hundred thousands of apertures. Therefore, electron beams which are emitted from an electron gun are made to pass the apertures of the shadow mask, so that the electron beams would exactly land on the red, blue and green phosphorescent dot films. Thus the shadow mask has a color defining function. Besides the color defining function, the shadow mask has a thermal expansion correcting function, and a magnetic shielding function.
The cold rolled steel sheet for making the shadow mask is generally composed of a Cr-added low carbon aluminum killed steel. This steel is melted in a converter, and continuously cast. The cast steel is subjected to a hot rolling followed by an acid pickling and a first cold rolling, then a first decarburization annealing is carried out to an extremely low carbon level. The annealed steel is secondly cold rolled and is shipped to a photo etching company. The photo-etched shadow mask is made to undergo a second annealing at a temperature of 700 - 750°C, and then, is press-formed into a curved face. The formed shadow mask is put to a blackening treatment, before installed to the cathode ray tube. Such a shadow mask has to have superior etchability and surface characteristics. If the shadow mask is to have a superior etchability, the steel sheet as the raw material has to have a uniform thickness, and its shape has to be superior. Further its surface has to have a proper surface roughness, and the steel sheet has to have a low level of non-metallic inclusion content so as to have a high cleanness.
Meanwhile, in the early time's, a low carbon rimmed steel which was superior in the surface characteristics was widely used as the material for the shadow mask. However, in the case of the rimmed steel, the non-metallic inclusion content was higher in the upper portion than the lower portion of the ingot, and therefore, deviations in the product quality could not be reduced. On the other hand, the low carbon aluminum killed steel is bad in the surface characteristics compared with the rimmed steel, and therefore, the killed steel was known to be unacceptable for the shadow mask. However, owing to the progress in the technique of the continuous casting, the surface characteristics of the killed steel has become almost same as that of the rimmed steel. Further, the killed steel is uniform in the material quality in the lengthwise direction of the coil, and therefore, the use of the killed steel has become advantageous in view of the shape ensuring and the uniformity of the sheet thickness after the cold rolling process. Further, the cleanness of the killed steel is superior over the rimmed steel, and therefore, the killed steel has come to be widely used for the shadow mask recently.
A typical manufacturing method for the killed steel is disclosed in Japanese Patent Application Laid-open No. Sho- 61-16324. According to this invention, a hot rolled sheet of a low carbon aluminum killed steel is subjected to a first cold rolling, an annealing, and a second rolling in the cited sequence. The steel is composed of: less than 0.03% of C, 0.20 - 0.60% of Mn, less than 0.03% of Si, less than 0.10% of P, less than 0.10% of S, 0.01 - 0.05% of Soluble Al, 0.01 - 0.05% of Cr, and a balance of Fe and other unavoidable impurities. In this killed steel for manufacturing the shadow mask, the oxide film adherence which had been problematic was improved by adding Cr.
Recently, the steel manufacturing techniques such as the vacuum degassing has briskly advanced, and therefore, a high cleanness low carbon steel has been made to be manufactured in the steel manufacturing process. Therefore, the shadow mask came to be manufactured using the extremely low carbon steel as the starting material. However, when the shadow mask steel is manufactured by using a Cr-added extremely low carbon aluminum killed steel as the initial material, the yield strength becomes high after an etching and a second annealing due to the solute carbon. Consequently, the shape holding ability during a press forming is aggravated, and a stretcher strain occurs, with the result that it becomes difficult to obtain a shadow mask having a uniform curved surface. Therefore it is the key of the technique to design the alloy system in such a manner that the yield strength should be lowered, and the stretcher strain should not occur after the second annealing.
U.S. Patent 4,609,412 (filed on September 2, 1986) is another example, and according to this patent, the cold rolled steel sheet for making a shadow mask is composed of: less than 0.005% of C, 0.05 - 0.50% of Mn, less than 0.010% of S, 0.01 -0.08% of soluble Al, less than 0.005% of N, more than 7 of Mn%/S%, more than 6 of (soluble Al % - 0.003%)/N%, a balance of Fe and other unavoidable impurities. However, in manufacturing the steel sheet for the shadow mask according to the above described patent, the rimmed steel or the Cr-added low carbon aluminum killed steel is subjected to a hot rolling, an acid pickling, a first cold rolling, a decarburization annealing and a second cold rolling under the general conditions. Therefore, an OCA furnace (open coil annealing furnace) is required for decarburizing a low carbon steel to an extremely low carbon steel. Further, a second cold rolling facility having a superior thickness and shape control capability is required for obtaining a high thickness precision and a superior shape. That is, conventionally, in manufacturing the cold rolled steel sheet for making the shadow mask, invest enrs in facilities such as decarburizing furnace and the second cold rolling apparatus are required, and further, the manufacturing process is more complicated, with the result that the manufacturing cost is increased.
SUMMARY OF THE INVENTION The present invention is intended to overcome the above described disadvantages of the conventional techniques.
Therefore it is the object of the present invention to provide a cold rolled steel sheet for making a shadow mask and a manu acturing method therefor, in which an extremely low carbon aluminum killed steel containing a tiny amount of Nb for precipitating a solute carbon of the initial material in the form of a carbide and containing a tiny amount of Cr for improving the oxide film adherence is subjected to a hot rolling, and a single round of cold rolling is carried out into the final thickness, whereby, without carrying out a decarburization annealing, the yield strength of the second annealed steel sheet after an etching becomes less than 11 kgf/m 2, and the yield point elongation becomes less than 0.2%, so as to obtain a cold rolled steel sheet for use in a shadow mask having a superior etchability and a superior formability.
In achieving the above object, the cold rolled steel sheet for making a shadow mask having superior etchability and formability according to the present invention is composed of in weight %: less than 0.004% of C, 0.1 - 0.4% of Mn, less than 0.02% of P, less than 0.02% of Si, 0.02 - 0.08% of soluble Al, less than 0.004% of N, 0.02 - 0.06% of Cr, 0.0050 - 0.030% of Nb, and a balance of Fe and other unavoidable impurities.
In another aspect, the method for manufacturing the cold rolled steel sheet for making a shadow mask according to the present invention includes the steps of: homogenizing the extremely low carbon aluminum killed steel having the above described composition at a temperature of 1200 - 1250°C; carrying out a hot finish rolling at a temperature of 900 - 940°C; coiling the steel sheet at a temperature of 550 - 650°C; carrying out a cold rolling down to the final thickness at a reduction ratio of 85 - 90%; carrying out a continuous annealing at a temperature of 640 - 680°C; and carrying out a temper rolling, whereby a cold rolled steel sheet for making a shaαow mask having superior etchability and formability is manufactured.
BRIEF DESCRIPTION OF THE DRAWINGS
The above object and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention with reference to the attached drawings in which:
FIG. 1A is a photograph showing a cross section of a slot of a shadow mask which is manufactured by photo- etching the cold rolled steel sheet according to the present invention; FIG. IB is a sectional photograph taken along a line A-A' of FIG. 1A;
FIG. 1C is a sectional photograph taken along a line B-B' of FIG. 1A; and
FIG. 2 is a graphical illustration showing the stress- strain curves obtained in tensile tests after carrying out a second annealing on an inventive steel and a comparative steel.
DESCRIPTION OF THE PREFERRED EMBODIMENT If the carbon content becomes more than 0.004 weight % (to be called '%' below), then the amounts of carbides are increased, with the result that the etchability is aggravated. Further, the amount of the solute carbon is increased, leading to increase in the yield strength and the yield point elongation after the final annealing, with the result that the press formability is aggravated. Therefore it is preferable to limit the carbon content to less than 0.004%, and more preferably, the carbon content should be limited to less than 0.003%, because it is better to reduce the carbon content as low as possible.
Meanwhile, Mn prevents the red shortness (caused by FeS) by precipitating sulphur in the form of MnS. Therefore, Mn needs to be added at least in the amount of 0.1%. However, if Mn is added by more than 0.4%, the steel becomes too hard, or the formability of the steel is aggravated due to the solid solution hardening by Mn. Therefore it is desirable to limit the content of Mn to 0.1 - 0.4%.
Meanwhile, phosphorus is a substitutional alloy element having a large solid solution hardening, and therefore, if it is added by more than 0.02%, the steel is too much hardened, thereby aggravating the formability.
Meanwhile, sulphur forms sulfide type non-metallic inclusions, aggravating the etchability, and therefore, it is desirable to limit sulphur to less than 0.02%. Meanwhile, aluminum is added for deoxidization in steel making, and for precipitating nitrogen in the form of A1N, so that the increase of the yield strength due to the solute nitrogen as well as the stretcher strain can be inhibited. For this purpose, aluminum is added by 0.02% or more. However, if aluminum is excessively added by more than 0.08%, the steel may be too much hardened, and therefore, it is desirable to limit aluminum to a range of 0.02 - 0.08%. Meanwhile, if nitrogen is added by more than 0.004%, then AlN or the solute nitrogen is increased, with the result that the yield strength is increased after the second annealing, or that a stretcher strain is generated. Therefore, it is desirable to control its upper limit to 0.004%.
Meanwhile, Cr is an element for improving the oxide film adherence. If the oxide film adherence is aggravated, the small chips of the oxide film degrades the quality of the TV picture, and the voltage resistant property is also aggravated. Therefore, if a tiny amount of Cr is added, the adherence can be improved. However, if the Cr content is less than 0.02%, its effect is insufficient, while if its content is more than 0.06%, not only the oxide film adherence is saturated, but also the manufacturing cost is increased, as well as too much hardening the steel.
Meanwhile, Nb precipitates the solute carbon in the form of NbC, leading to decrease in the yield point elongation and the yield strength after the second annealing, so that the stretcher strain can be inhibited. Generally, the yield strength after the second annealing and the stretcher strain caused during the forming are increased proportionally to the solute carbon. In the present invention, Nb performs the function of eliminating the stretcher strain and lowering the yield strength after the second annealing, without carrying out a decarburization annealing, unlike the conventional method in which a decarburization annealing is carried out to reduce the carbon content down to an extremely low carbon steel. However, if the Nb content becomes lower than 0.005%, then the solute carbon cannot be effectively precipitated. On the other hand, if the Nb content becomes higher than 0.03%, the etchability is rather aggravated due to a large amount of precipitation of NbC. Therefore, it is desirable to limit the Nb content to 0.005 - 0.03%.
Now the method for manufacturing a cold rolled steel sheet having the above described composition according to the present invention will be described. The extremely low carbon aluminum killed steel is melted by using a converter and a vacuum degassing facility. Then slabs are formed by applying a continuous casting process, and then, the slabs are heated to a temperature of 1200 - 1250°C, so that the austenitic structure can be sufficiently homogenized before carrying out hot rollings. Then, near 920°C just above the Ar3 temperature, hot rollings are completed down to a thickness of 2.0 mm.
Under this condition, if the hot rolling finish temperature is below 900°C, then the top, the tail and the edges of the hot rolled steel sheet become a ferrite single phase, so that a non-uniformity in the mechanical properties of the steel would be generated. On the other hand, in the case where the slab heating temperature is above 1200 - 1250°C, the hot rolling finish temperature of the general hot rolling process is below 940°C, and therefore, it is desirable to carry out the finish hot rolling at a temperature of 900 - 940°C.
It is desirable that the hot rolled steel sheet be coiled at a temperature of 550 - 650°C, and the reason is as follows. That is, if the coiling temperature is above 650°C, then the amount of Nb precipitates is increased, with the result that the etchability is aggravated. Further, the quality deviations between the coils of the hot rolled steel sheets in the lengthwise direction become severe, with the result that the acid pickling characteristics becomes aggravated. On the other hand, if the coiling temperature comes down to below 550°C, the temperature becomes not uniform, and therefore, not only severe deviations occur in the lengthwise direction, but also the shape of the shadow mask is aggravated, because a thin sheet of about 2.0 mm is coiled at below 550°C.
In the conventional method, a hot rolled steel sheet which has undergone an acid pickling is subjected to a first cold rolling with a reduction ratio of about 70%. Then a recrystallization annealing is carried out to decarburize the steel sheet down to an extremely low carbon steel, and then, a second cold rolling is carried out down to the final thickness. However, in the present invention, it is possible to skip the decarburization annealing and the second cold rolling.
For this purpose, in the present invention, the hot rolled steel sheet which has undergone the usual acid pickling is subjected to a single round of cold rolling with a reduction ratio of 85 - 90%. Then a recovery annealing is carried out, and then, a temper rolling is carried out in the normal manner.
Under this condition, the cold rolling reduction ratio becomes different depending on the required thickness of the shadow mask, and therefore, the cold rolling is carried out by taking into account the thickness of the shadow mask. If the cold rolling is carried out with a reduction ratio of above 90%, the process is not only overloaded, but also the shape or the thickness precision is aggravated.
On the other hand, if the cold rolling is carried out with a reduction ratio of below 85%, it is meant that the hot rolled steel sheet has to be thin in obtaining the same thickness of the cold rolled steel sheet. Therefore, an extra load is imposed on the hot rolling process, and the shape of the hot rolled steel sheet is aggravated. Therefore, it is desirable to carry out the cold rolling with a reduction ratio of 85 - 90%. Meanwhile, it is very difficult to provide a proper surface roughness required for the shadow mask during the cold rolling. Therefore, a temper rolling is required for providing the required surface roughness. However, the cold rolled steel sheet is too much hardened to such a degree that it is difficult to carry out the temper rolling. Therefore, a continuous annealing is carried out at a temperature of 640 - 680°C for recovery annealing the steel. However, if the annealing temperature is above 680°C, the structure becomes a completely recrystallized ferrite, with the result that the etchability can be aggravated in the etching process. On the other hand, if the annealing temperature is below 640°C, the structure becomes same as that of the cold rolled sheet, with the result that an exact surface roughness cannot be provided during the temper rolling.
Then the steel sheet which has undergone the recovery annealing is made to undergo a temper rolling, thereby providing the required surface roughness, and correcting the shape. For these two purposes, it is preferable to apply a temper rolling ratio of 1.0%.
Generally, in a shadow mask, the etchability is more aggravated, as the thickness is increased. A thick shadow mask sheet may be temper rolled with work rolls surface-textured by electro discharge texturing method. In this way the surface roughness can be varied, so that the etchability can be improved. That is, the product in which the surface roughness is provided by a shot blast in the usual way shows a small number of peaks per inch (PPI) and a large peak-to-peak interval (Sm), thereby aggravating the etchability.
Now the present invention will be described based on actual examples.
<Example 1> Extremely low carbon Al killed steels having the compositions of Table 1 were melted in converters, and were subjected to a vacuum degassing treatment. Then the steels were subjected to a continuous casting, thereby preparing steel slabs. As to the inventive steels 1 - 3 and the comparative steels 4 - 6 of Table 1, a vacuum degassing treatment was carried out on all of them. In the case of the comparative steel 7, a steel having a carbon content of 0.02% was made to undergo a decarburizing process, and the final composition is shown in the table. Further, in the case of the comparative steel 4, the Nb content exceeds the composition range of the present invention, while the comparative steel 5 is a can making steel. Further, the comparative steel 6 does not contain Nb at all.
Table 1
Figure imgf000014_0001
The steel slabs having the compositions of Table 1 above were homogenized at a temperature of 1230°C. Then
35 at a temperature of 920°C which is the temperature just above the Ar3, a hot finish rolling was carried out down to a thickness of 2.0 mm. Then a coiling was carried out at a temperature of 600°C, and then, an acid pickling was carried out in the usual manner.
40 Then the processes as shown in Table 2 below were carried out, thereby obtaining final cold rolled steel sheets having a thickness of 0.25 mm.
The cold rolling reduction ratio, the annealing temperature and the temper rolling ratio were as shown in
45 Table 3 below. Table 2
Example Manufacturing process
Inventive material 1. Cold rolling-continuous annealing
(recovery annealing)- temper rolling Comparative material 1A. Cold rolling-continuous annealing (completely recrystallizing annealing)- temper rolling Comparative material IB. Cold rolling-continuous annealing (non-recrystallizing annealing)-temper rolling Inventive material 2. Cold rolling-continuous annealing
(recovery annealing)-temper rolling Inventive material 3. Cold rolling-continuous annealing
(recovery annealing)-temper rolling Comparative material 4. Cold rolling-continuous annealing (recovery annealing)- temper rolling Comparative material 5. Cold rolling-continuous annealing(recrystallization annealing) -temper rolling Comparative material 6. First cold rolling-continuous annealing (recrystallization annealing)-temper rolling-second cold rolling
Comparative material 7. First cold rolling- decarburization annealing (recrystallization annealing)- temper rolling-second cold rolling. Table 3
Material First Anneal¬ Second Temper cold ing cold rolling Property evaluation 5 rolling temper¬ rolling ratio reduc¬ ature reduc¬ (%) Temper Etcha¬ Oxide tion (°c) tion rolla- bility film ratio(%) ratio(%) bility adherence
10 Inventive material 1 87.5 650 0 0.75 Good Good Good
Comparative No material 1A 87.5 720 0 0.75 Good Good Good ι ς
Comparative No No material IB 87.5 630 0 0.75 Good Good Good
Inventive 20 material 2 87.5 655 0 0.80 Good Good Good
Inventive material 3 87.5 660 0 0.90 Good Good Good
25 Comparative No material 4 87.5 660 0 0.90 Good Good Good
Comparative No material 5 86.0 740 0 1.30 Good Good Good
Comparative material 6 75.0 760 75.0 1.30 - Gooα Good
Comparative 1 35 material 7 70.0 700 75.0 1.30 Good j Good
As shown in Tables 2 and 3 above, for the inventive materials, a first cold rolling was carried out to the
40 final thickness, and then, a recovery annealing was carried out, so that providing the roughness would be facilitated at the temper rolling step, and so that the etching would be improved at the etching step. Then a temper rolling was carried out.
45 On the other hand, the comparative materials 1A and IB correspond to the steel which is annealed at a temperature at which recrystallization completely occurs and recrystallization does not occur at all, respectively. The comparative material 5 corresponds to a can making steel (the comparative steel 5) on which the process for the inventive materials was carried out. However, it is somewhat different from the inventive materials which was recovery annealed at 640-680°C because the material 5 was completely recryεtallized at a high temperature of 730 - 750°C.
Meanwhile, in the cases of the comparative materials 6 and 7, a first cold rolling was carried out, and then, a continuous annealing or decarburization annealing was carried out for a complete recrystallization. Then a second cold rolling was carried out.
On the steels on which the above described process steps had been carried out, a temper rolling was carried out, and then, the temper rollability was evaluated. Then an etching and a blackening treatment were carried out, and then, the respective characteristics for them were evaluated. The evaluation results are shown in Table 3 above. The evaluation results of Table 3 were obtained in the following manner. That is, based on the usual practice, the temper rollability was assigned with "good" or "no good" in accordance with whether the shape correction and the proper roughness transfer from work roll to the steel sheet were possible at the usual rolling loads of the temper rolling mill (first stand: 700 - 1000 tons, and second stand: 350 - 600 tons).
The etchability was assigned with "good" or "no good" based on a collective judgment by considering the straightneεs of the slot portion, the distortion and the uniformity of the slots shape.
The oxide film adherence was assigned with "good" or "no good" in accordance with whether the oxide film was dropped in small chips when carrying out a bending test at an angle of 120°C after putting a piece of scotch tape on the shadow mask.
As shown in Table 3 above, in the cases of the inventive materials, it was confirmed that the surface roughness could be easily provided during the temper rolling, and that eatching characteristics and oxide film adherence was superior.
On the other hand, in the case of the comparative material 1A which was obtained by annealing the inventive steel 1, providing the roughness was easy, but the etchability and the workability during the etching were aggravated.
Meanwhile, in the case of the comparative material IB which was obtained by annealing the inventive steel 1 at 630°C which is the non-recrystallizing temperature, it showed the same rolling structure as 87.5% cold-reduced steel. Therefore, it was difficult to provide the roughness during the temper rolling, and the shape was aggravated, as well aggravating the etchability.
In the case of the comparative material 4, carbides were precipitated due to the excessive content of Nb, with the result that the etchability was aggravated.
In the case of the comparative material 5, the oxide film adherence was aggravated due to the lack of Cr content. In the cases of the comparative materials 6 and 7, the results of the property evaluations were superior. However, unlike the steels of the present invention, a continuous annealing or a decarburization annealing was carried out after carrying out a first cold rolling to completely recrystallize them, and then, a second rolling was carried out. Therefore they have the disadvantage that a decarburization annealing or the like is required.
Meanwhile, for the inventive material 1 on which the temper rolling had been completed, a photo etching step was carried out in the usual manner, and then, the cross section of the slot of the etched shadow mask was observed by means of a microscope. The result showed that a good slot was formed as shown in FIG. 1.
<Example 2>
On the inventive materials 1 - 3 and the comparative materials 6 - 7 which showed superior temper rollability, etchability and oxide film adherence, a second annealing was carried out. This was for evaluating the formability after the second annealing, because the formability is an important property of the steel sheet for making a shadow mask.
The second annealing was carried out at a temperature of 750°C for 10 minutes under an atmosphere composed of 20% of H2 + 80% of N2. Then a tensile test was carried out on the second annealed sheet at the normal temperature at a cross head speed of 0.5 - 10 mm/min. The test results are shown in Table 4 below, while stress-strain curves for the inventive material 1 and the comparative material 6 are shown in FIG. 2.
Table 4
Example Cross Mechanical properties of head second annealed sheet
3 = No. speed (mm/min) Yield Tensile Elon¬ Yield strength strength gation point (kgf/mm2) (kgf/mm2) elonga- i n tion )
1U
1 0.5 8.5 27.9 49.9 0.1
15 Inventive 1 1.0 9.0 28.6 48.5 0.1 material
1 10.0 10.7 29.1 45.7 0.1
20
2 10.0 10.3 29.0 47.8 0.1
3 10.0 10.5 28.8 48.6 0.1 =;
Compara¬ 6 10.0 15.7 24.3 52.0 5.0 tive material 30 7 1.0 8.2 26.5 48.9 0.1
7 10.0 10.3 27.9 47.3 0.1
35
In order to inhibit the generation of the stretcher strain, it is required that the steel sheet for making a shadow mask has a yield point elongation of less than 1.0%.
40 Further, in order to ensure the shape holding ability of a shadow mask, it is required that the yield strength of the steel sheet is less than 13 Kgf/mm2 (with the cross head speed of 10 mm/min) .
As shown in Table 4 and in FIG 2, the inventive
45 materials 1 - 3 satisfied the above mentioned two requirements, whereas in the case of the comparative material 6, the yield strength and the yield point elongation were too high to ensure an acceptable press forming. Therefore, forming defects are expected. Meanwhile, in the case of the comparative material 7, the mechanical properties were found to be of the same level as that of the inventive steels. However, unlike the present invention, this comparative material required a decarburization annealing and a second cold rolling, this being a serious disadvantage.
According to the present invention as described above, a tiny amount of Nb is added to an extremely low carbon Al killed steel so as to precipitate the solute carbon in the form of a carbide, and the hot rolling and cold rolling conditions are properly controlled. Thus a cold rolling is carried out, then a recovery annealing was carried out in a continuous annealing furnace in the usual manner, and then, a temper rolling is carried out. Thus, a steel sheet for making a shadow mask is manufactured, in which the yield strength of the second annealed sheet after an etching is less than 11 Kgf/mm2, and the yield point elongation is less than 0.2%. Therefore, the etchability and formability of the steel sheet of the present invention are found to be improved. Further, the continuous annealing which is carried out in the present invention corresponds to the usual continuous annealing other than a decarburization annealing, and therefore, the process of the present invention excludes the decarburization annealing and the second cold rolling, with the result that the manufacturing cost can be saved to a significant degree.

Claims

What is claimed is:
1. A cold rolled steel sheet for making a shadow mask having superior etchability and formability, comprising in weight %: less than 0.004% of C, 0.1 - 0.4% of Mn, less than 0.02% of P, less than 0.02% of Si, 0.02 - 0.08% of soluble Al, less than 0.004% of N, 0.02 - 0.06% of Cr, 0.0050 - 0.030% of Nb, and a balance of Fe and other unavoidable impurities.
2. A method for manufacturing a cold rolled steel sheet for a shadow mask, comprising the steps of: homogenizing an extremely low carbon aluminum killed steel at a temperature of 1200 - 1250°C, said steel having a composition of in weight %: less than 0.004% of C, 0.1 -
0.4% of Mn, less than 0.02% of P, less than 0.02% of Si,
0.02 - 0.08% of soluble Al, less than 0.004% of N, 0.02 -
0.06% of Cr, 0.0050 - 0.030% of Nb, and a balance of Fe and other unavoidable impurities; carrying out a hot finish rolling at a temperature of
900 - 940°C; coiling the steel sheet at a temperature of 550 - 650°C; carrying out a cold rolling down to a final thickness at a reduction ratio of 85 - 90%; carrying out a continuous annealing at a temperature of 640 - 680°C; and carrying out a usual temper rolling, whereby a cold rolled steel sheet for making a shadow mask having superior etchability and formability is manu actured.
PCT/KR1995/000138 1994-10-28 1995-10-26 Cold rolled sheet steel for shadow mask, and manufacturing method therefor WO1996013618A1 (en)

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US6544356B2 (en) 1996-12-05 2003-04-08 Nisshin Steel Co., Ltd. Steel sheet for use as an electrode-supporting frame member of a color picture tube and manufacturing method thereof
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EP0964073A1 (en) * 1996-12-05 1999-12-15 Nisshin Steel Co., Ltd. A steel sheet for use as an electrode-supporting frame member of a color picture tube and manufacturing method thereof
US6544356B2 (en) 1996-12-05 2003-04-08 Nisshin Steel Co., Ltd. Steel sheet for use as an electrode-supporting frame member of a color picture tube and manufacturing method thereof
WO2002038818A1 (en) * 2000-11-08 2002-05-16 Thyssenkrupp Stahl Ag Method for producing a cold rolled strip that is cold formed with low degrees of deformation
CN100430511C (en) * 2005-06-30 2008-11-05 宝山钢铁股份有限公司 Cold rolled strip steel for shadow mask and its making process
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