JP4273657B2 - Cold rolled steel sheet for color cathode ray tube magnetic shield - Google Patents

Description

【００４４】
［実施例２］
重量％で、Ｃ：０．０２％、Ｓｉ：０．０１％、Ｍｎ：０．４５％、Ｐ：０．０３％、Ｓ：０．００３％、ｓｏｌ．Ａｌ：０．０６％、Ｎ：０．００３％、Ｔｉ：０．００２％、Ｖ：０．００３％、Ｎｂ：０．００２％、Ｃｕ：０．０１１％、Ｓｎ：０．００４％、Ｎｉ：０．０３％、Ｃｒ：０．０２％、Ｍｏ：０．０２％を含み、残部が実質的にＦｅからなり、Ａｌ_２Ｏ_３／（Ａｌ_２Ｏ_３＋ＣａＯ＋ＭｎＯ＋ＳｉＯ_２）＝０．３５であるスラブを１２００℃で加熱し、仕上げ温度８８０℃、巻取温度６４０℃で熱間圧延して板厚１．８ｍｍとした後、酸洗し、次いで冷間圧延で板厚０．１ｍｍとした。これを窒素＋水素雰囲気中で５５０℃〜８８０℃の温度で５０秒間焼鈍し、さらに１．８％以下の伸長率の調質圧延を行うか、あるいは調質圧延を行わずに、鋼板表面にＣｒめっきを施してＮｏ．２３〜３３の供試材を得て、透磁率、保持力および非履歴透磁率を実施例１と同様の方法により測定した。それぞれの供試材の焼鈍温度、再結晶の有無、調質圧延の伸長率、透磁率、保持力および非履歴透磁率を表２に併せて示す。なお、この供試材のＡｃ_１点はフォーマスターで測定した結果、７５０℃付近であった。
【００４５】
表２に示すように、Ａｃ_１点以下で再結晶焼鈍を行い、かつ、伸長率１．５％以下の調質圧延を施した実施例であるＮｏ．２４〜２８，３０，３１の供試材は、７５００以上の非履歴透磁率および２３９Ａ／ｍ未満の保磁力を有しており、磁気特性が極めて優れていた。これに対して、どちらかの条件が本発明の範囲を外れた比較例であるＮｏ．２３，２９，３２，３３の供試材は、いずれかの磁気特性が劣っていた。具体的には、焼鈍温度がＡｃ_１点を超えていたＮｏ．３２および３３の供試材においては、調質圧延を施さなかったにも関わらず、非履歴透磁率がＮｏ．３２では６０００、Ｎｏ．３３では５８００であり、どちらも低い値を示した。また、焼鈍温度が５５０℃であったＮｏ．２３の供試材は、再結晶が起こらず、非履歴透磁率が５５００と低い値を示した。さらに、調質圧延の伸長率が本発明の範囲を超えたＮｏ．２９の供試材は、非履歴透磁率が７０００まで低下した。
【００４６】
【表２】

【００４７】
【発明の効果】
以上述べたように、本発明によれば、地磁気による色ずれを抑制して高精細な画像を得るために有効な、地磁気シールド性に優れ、かつ安価で資源の有効利用に対応可能なカラー陰極線管磁気シールド用冷延鋼板を得ることができる。本発明に係る鋼板をカラー陰極線管の磁気シールドとして用いることによって、消磁後、十分な磁気シールド性が確保され、さらに地磁気ドリフトによる色ずれが抑制される。よって、本発明の鋼板を用いることによりＴＶやコンピュータ等の高精細な画質を得るために有効な磁気シールドを得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic shield steel plate, particularly a magnetic shield steel plate suitable as a material for a magnetic shield component that is installed inside or outside a color cathode ray tube so as to cover the electron beam passing direction from the side surface. And a manufacturing method thereof.
[0002]
[Prior art]
The basic configuration of the color cathode ray tube includes an electron gun that emits an electron beam and a fluorescent screen that emits light by electron beam irradiation to form an image. Since the electron beam is deflected by the influence of geomagnetism, resulting in color shift in the image, an internal magnetic shield (also referred to as an inner shield or inner magnetic shield) is generally installed as a means for preventing the deflection. Yes. An external magnetic shield (also referred to as an outer shield or an outer magnetic shield) may be installed outside the color cathode ray tube. Hereinafter, the inner magnetic shield and the outer magnetic shield are collectively referred to as a magnetic shield.
[0003]
In recent years, consumer TVs have been increased in size, widened, and flattened screens. As a result, the traveling distance and scanning distance of electron beams have increased and are easily affected by geomagnetism. That is, since the deviation (referred to as geomagnetic drift) of the arrival point of the electron beam deflected by geomagnetism from the point where the electron beam should originally reach is larger than before, suppression thereof is desired. In addition, since a monitor cathode ray tube such as a personal computer requires a higher-definition still image, color shift due to geomagnetic drift must be suppressed as much as possible.
[0004]
Under such circumstances, conventionally, the characteristics of a steel sheet used as a magnetic shield of a color cathode ray tube have often been evaluated using the permeability in a low magnetic field corresponding to geomagnetism as an index. In this case, in order to prevent the magnetic permeability from remarkably deteriorating due to impurities, precipitates, etc., a steel plate having impurities reduced as much as possible has been used as the magnetic shield material.
[0005]
[Problems to be solved by the invention]
However, in order to produce such a high permeability steel sheet, it is essential to adjust the components with high precision at the steel making stage, resulting in poor production yield and increased cost. Furthermore, it is necessary to promote the effective use of resources due to social demands for environmental issues in recent years, and the production of high-permeability steel, which is used as a magnetic shield material, is expected in spite of an increase in the amount of scrap iron used. Is becoming increasingly difficult.
[0006]
On the other hand, even if a high permeability steel sheet is actually used, it is difficult to say that color shift due to geomagnetism is sufficiently suppressed at present. Several studies have been made on the relationship between geomagnetic shielding properties and material properties. For example, according to IEICE Transactions, Vol.J79-C-II No.6, p311-319, '96 .6 In general, a steel plate for magnetic shielding applied to a color cathode ray tube is demagnetized in the geomagnetism. In this case, the magnitude of magnetization after demagnetization or the magnitude of geomagnetism rather than the magnetic permeability. The so-called non-historic permeability, which is the value obtained by dividing, is considered to be an important factor representing the geomagnetic shielding performance. However, no consideration has been given to the means for obtaining a material having an increased non-historical permeability.
[0007]
For these reasons, there is a strong demand for magnetic shielding steel plates having higher performance magnetic shielding properties.
[0008]
The present invention has been made in view of such circumstances, and is effective for obtaining a high-definition image by suppressing color misregistration due to geomagnetism. An object of the present invention is to provide a cold-rolled steel sheet for a color cathode ray tube magnetic shield and a method for producing the same.
[0009]
[Means for Solving the Problems]
The present inventors have obtained the following knowledge as a result of repeated studies to solve the above problems.
In general, a steel plate, which is a ferromagnetic material, is used inside, in some cases, inside and outside the color cathode ray tube. Since the color cathode ray tube is normally exposed to geomagnetism, the steel plates inside and outside the color cathode ray tube are magnetized non-uniformly, which causes a color shift. In recent color cathode ray tubes, an AC demagnetization circuit is incorporated in order to remove the magnetization remaining in these ferromagnetic materials.
[0010]
By the way, since this demagnetization is performed in the geomagnetism, relatively high magnetization is generated along the direction of geomagnetism on the steel plates inside and outside the color cathode ray tube after demagnetization. The demagnetizing field formed by this magnetization erases the terrestrial magnetism in the color cathode ray tube, so that a high terrestrial shielding property is exhibited. In general, it is known that the magnetization of a material after demagnetization in a DC magnetic field converges to non-history magnetization (or ideal magnetization) corresponding to the DC magnetic field, and the magnetic flux density in this non-history magnetization state is converted to the DC The value divided by the magnitude of the magnetic field is called non-history permeability. As described in the aforementioned IEICE Transactions, Vol.J79-C-II No.6, p311 to 319, '96 .6, steel sheets suitable for magnetic shield applications are referred to as “non-history permeability”. Is considered to be a high steel plate. Based on this knowledge, the present inventors investigated the conditions for increasing the non-historical permeability in a DC bias magnetic field of 27.9 A / m equivalent to geomagnetism, and as a result of examining a steel sheet excellent for magnetic shielding, The following (1) to (5) were found.
[0011]
(1) In ordinary magnetic shield materials, the grain size is increased by reducing precipitates and heat treatment at high temperature in order to increase the permeability. Differently, there are some precipitates, and high values can be obtained even if the crystal grains are fine. (2) Active use of magnetization of materials generated by AC demagnetization in geomagnetism, such as color cathode ray tubes In the magnetic shield system, if a steel plate having a non-history permeability of 7500 or more is used as a shield material, the influence of geomagnetism can be effectively suppressed. (3) Non-history permeability can be improved by adding an appropriate amount of B (4) When the coercive force is increased more than 239A / m, the demagnetizing power increases required to reach the original anhysteretic magnetization, it is not preferable from the viewpoint of consumption power _{▲ 5 ▼ Al 2 O 3 /} (Al 2 By adjusting the ₃ + CaO + MnO + ratio of SiO _2), [0012] it is possible to lower the coercive force while maintaining a high anhysteretic magnetic permeability
The present invention has been completed based on such findings, and provides the following (1) to ( 2 ).
(1) A steel plate having a thickness of 0.05 mm or more and 0.5 mm or less used for a magnetic shield of a color cathode ray tube, and by weight%, C: 0.06% or less, Si: 1% or less, Mn: 0.00. 1% or more and 2% or less, P: 0.1% or less, S: 0.02% or less, sol. Al: 0.001% to 1%, N: 0.006% or less, Ti: 0.01% or less, V: 0.01% or less, Nb: 0.01% or less, Cu: 0.005% or more 0.5% or less, Sn: 0.001% to 0.3%, Ni: 0.005% to 2%, Cr: 0.004% to 0.2%, Mo: 0.3% or less A cathode cathode tube characterized by comprising a balance Fe and inevitable impurities , satisfying a relationship of Al ₂ O ₃ / (Al ₂ O ₃ + CaO + MnO + SiO ₂ ) ≧ 0.1, and having a non-historical permeability of 7500 or more Cold rolled steel sheet for magnetic shield.
[0014]
( 2 ) A cold-rolled steel sheet for a magnetic cathode ray tube magnetic shield according to (1), wherein the steel sheet surface has Cr and / or Ni plating.
[0017]
In addition, in this specification, all% which shows the component of steel is weight%. The non-history permeability in the present invention is the magnetic flux density obtained by alternating current demagnetization in a bias magnetic field (27.9 A / m equivalent to geomagnetism) divided by the bias magnetic field (27.9 A / m). Further, it is a value divided by the vacuum permeability for non-dimensionalization.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described.
First, the component composition of steel will be described.
The steel sheet for magnetic shielding according to the present invention is, by weight, C: 0.06% or less, Si: 1% or less, Mn: 0.1% or more and 2% or less, P: 0.1% or less, S: 0.00. 02% or less, sol. Al: 0.001% to 1%, N: 0.006% or less, Ti: 0.01% or less, V: 0.01% or less, Nb: 0.01% or less, Cu: 0.005% or more 0.5% or less, Sn: 0.001% to 0.3%, Ni: 0.005% to 2%, Cr: 0.004% to 0.2%, Mo: 0.3% or less It consists of the balance Fe and inevitable impurities . Hereinafter, the reason why each component is defined in this way will be described.
[0019]
C: 0.06% or less Even if a relatively large amount of carbide exists, it is possible to achieve a high non-historical permeability. However, if the C content exceeds 0.06%, the coercive force becomes 239 A / m or more. When used as a cathode ray tube shield material, a large amount of electric power is required in the demagnetization process, which is not preferable from the viewpoint of energy saving of home appliances. Therefore, the C amount is set to 0.06% or less.
[0020]
Si: 1% or less Si is an inexpensive element that increases the strength of the steel sheet, and is effective for improving the handleability when assembling the shield plate. However, addition of Si exceeding 1% deteriorates the weldability and plating performance. Therefore, the Si amount is set to 1% or less.
[0021]
Mn: 0.1% or more and 2% or less Mn is an element that increases the strength of the steel sheet and improves the hot ductility, and its effect is effectively exhibited at 0.1% or more. On the other hand, if added over 2%, a hardened structure is likely to be formed, and the non-historical permeability may be lowered, and the cost is increased. For this reason, the amount of Mn is made 0.1% or more and 2% or less.
[0022]
P: 0.1% or less An element effective for increasing the strength of a steel sheet, but if it is too much, embrittlement of the steel sheet is caused by knitting, and the defect rate during cold working is increased. Therefore, the P content is 0.1% or less.
[0023]
S: 0.02% or less S is an element that decreases hot ductility, and the S content is 0.02% or less from the viewpoint of not adversely affecting hot ductility.
[0024]
sol. Al: 0.001% or more and 1% or less Al is an element that increases the strength of the steel sheet, and has an effect of reducing the coercive force by increasing the Al ₂ O ₃ ratio in the oxide. These effects are sol. Although effective when the Al content is 0.001% or more, the addition of a large amount causes an increase in cost. Therefore, sol. Al amount is 1% or less.
[0025]
N: 0.006% or less N is an element that increases the strength of the steel sheet, but excessive addition causes surface blistering, so the N content is 0.006% or less.
[0026]
Ti: 0.01% or less V: 0.01% or less Nb: 0.01% or less Ti, V, and Nb fix C and N as carbides and nitrides, and stretcher strain generated during processing. It is effective to suppress. However, excessive addition causes problems such as an increase in recrystallization temperature or excessive hardening, and also increases costs, so that Ti: 0.01% or less, V: 0.01% or less, and Nb: 0, respectively. .01% or less.
[0027]
Cu: 0.005% or more and 0.5% or less Recently, in various electric parts and automobile parts, for example, Cu is contained as a winding of a motor. When these scraps are used as a material, In this case, the Cu content is 0.005% or more exceeding the general Cu content (for example, less than 0.005%). On the other hand, the non-history permeability does not change greatly with the increase or decrease of the Cu content, but a large amount of Cu addition exceeding 0.5% causes an increase in coercive force and an increase in surface defects. For this reason, the amount of Cu shall be 0.005% or more and 0.5% or less.
[0028]
Sn: 0.001% or more and 0.3% or less Sn is contained in tin cans for food cans and is an element mixed when these are used as scrap materials. Conventionally, it was less than 0.001%, but the lower limit is made 0.001% from the viewpoint of scrap utilization. However, if it is contained in a large amount, the coercive force is increased, so the upper limit is made 0.3%.
[0029]
Ni: 0.005% or more and 2% or less Ni is an element mixed from stainless steel or the like. Conventionally, it was less than 0.005%, but the lower limit is made 0.005% from the viewpoint of scrap utilization. Further, even if the Ni content is increased to 2%, almost no change in non-historical permeability and coercive force is observed, so the upper limit is made 2%.
[0030]
Cr: 0.004% or more and 0.2% or less Cr, like Ni, is an element mixed from stainless steel or the like. Conventionally, it was less than 0.004%, but the lower limit is made 0.004% from the viewpoint of scrap utilization. Further, if the Cr content increases excessively, the coercive force is deteriorated, so the upper limit is made 0.2%.
[0031]
Mo: 0.3% or less Mo is an element mixed from stainless steel or the like in scrap. If it exceeds 0.3%, the coercive force is increased, so the content is made 0.3% or less.
[0033]
In the present invention, the oxide in the steel satisfies Al ₂ O ₃ / (Al ₂ O ₃ + CaO + MnO + SiO ₂ ) ≧ 0.1. If this value is less than 0.1, the coercive force is increased and desired magnetic properties cannot be obtained. As an effective means for controlling the value of Al ₂ O ₃ / (Al ₂ O ₃ + CaO + MnO + SiO ₂ ) to be 0.1 or more, although it is a known method, after decarburization in vacuum degassing treatment in steelmaking, A method of adding a deoxidizer such as Mn, Si, etc. after first deoxidizing with Al when adding sol. There is a method of adding 0.001% or more of Al as the amount of Al.
[0034]
Next, the plate thickness will be described.
The lower limit of the thickness of the magnetic shield steel plate is too thin, even if it is a steel plate with high non-historical permeability, the magnetic shielding properties will be insufficient, and the rigidity as a magnetic shield component will not be obtained. 0.05 mm or more. On the other hand, in order to improve the magnetic shielding property, it is desirable that the plate thickness is large. However, with the recent increase in size and width of color televisions, the weight of television sets is desired, so the upper limit is 0.5 mm. To do.
[0035]
Next, a manufacturing method will be described.
First, steel having the above composition is melted and cast by continuous casting or the like to form a slab, which is hot-rolled. Hot rolling may be performed, for example, directly on the continuously cast slab or after slightly heating, or may be performed after reheating the slab once cooled.
[0036]
Next, the hot-rolled steel sheet is pickled, cold-rolled, and then recrystallized and annealed at a temperature below the ferrite single phase region or Ac ₁ transformation point. Thus, non-hysteresis magnetic permeability of 7500 or more can be obtained by recrystallization annealing at a temperature below the ferrite single-phase temperature range or Ac ₁ transformation point.
[0037]
After recrystallization annealing, temper rolling is performed as necessary. In order to ensure high non-history permeability, it is preferable that the elongation rate of temper rolling is small, and it is desirable not to perform temper rolling from the viewpoint of magnetic properties. However, when temper rolling is unavoidable for the purpose of correcting the shape of the steel sheet, the elongation ratio should be as small as possible. For this reason, the upper limit is 1.5%. When the problem with respect to the shape of the steel sheet is minor, it is preferably 1.0% or less, and more preferably 0.5% or less.
[0038]
The cold-rolled steel sheet for a color cathode ray tube magnetic shield obtained as described above may be subsequently subjected to Cr plating and / or Ni plating in order to improve corrosion resistance. These platings may be used in a single layer or in multiple layers, and the surface on which the plating layer is formed may be one surface or both surfaces of the steel sheet. By forming the plating layer, the generation of rust on the steel sheet can be suppressed, and the gas generation from the steel sheet can be suppressed when incorporated in the cathode ray tube, which is effective. The adhesion amount of the plating layer is not particularly limited, and an adhesion amount that can substantially cover the surface of the steel sheet is appropriately selected. Alternatively, the steel plate surface may be covered by applying a chromate treatment after partial Ni plating.
[0039]
【Example】
[Example 1]
After melting the test steel having the components shown in Table 1, it was cast into a slab, hot-rolled to a thickness of 1.8 mm, cold-rolled at a cold rolling rate of 83 to 94%, and the thickness was reduced to 0 0.1 to 0.3 mm. Subsequently, the obtained cold-rolled steel sheet was subjected to recrystallization annealing at 700 ° C. for 50 seconds in a nitrogen + hydrogen atmosphere, and then Cr plating was performed on both surfaces of the steel to obtain No. 1 1-No. 22 test materials were obtained. In the Cr plating, the lower layer was a metal Cr layer having an adhesion amount of 95 to 120 mg / m ² , and the upper layer was a hydrated oxide Cr layer having an adhesion amount (converted to metal Cr) of 12 to 20 mg / m ² . Incidentally, the column of _Al 2 _{O 3} ratio of Table 1 shows the values of the weight ratio of _Al 2 _O 3 _/ obtained _{(Al 2 O 3 + CaO +} MnO + SiO 2) by chemical analysis.
[0040]
No. obtained as described above. A strip sample of 30 mm × 280 mm was cut out from the specimens 1 to 22 in the coil rolling direction and the vertical direction, and the permeability and coercive force were measured by the Epstein test method based on JISC2550. In addition, a bias magnetic field coil was added to the Epstein test frame, and the non-history permeability was measured by the following procedure. The magnetic permeability, coercive force and non-historical permeability measured in this way are also shown in Table 1.
[0041]
Non-history permeability measurement method 1) Attenuating an alternating current is passed through the exciting coil to completely demagnetize the test piece.
2) In a state where a direct current is passed through the bias magnetic field coil to generate a 27.9 A / m direct current magnetic field, a decaying alternating current is passed through the exciting coil again to demagnetize the test piece.
3) While the bias magnetic field is applied, the BH loop is measured at the maximum magnetization force of 3180 A / m.
4) The non-history permeability is calculated from the asymmetry of the BH loop.
[0042]
As shown in Table 1, No. 1 which is an example having the steel composition of the present invention. Each of the test materials 1, 3 to 7, 9, 11, 13, 15, 17, and 21 has an excellent non-historical permeability of 7500 or more and a coercive force of less than 239 A / m. It had geomagnetic shielding properties. On the other hand, No. which is a comparative example in which any of the components deviates from the scope of the present invention. The test materials of 2, 8, 10, 12, 14, 16, 18 to 20, 22 were inferior in any of the characteristics, and an excellent magnetic shielding property was not obtained. Specifically, no. The specimen No. 2 had a high Mn amount exceeding the range of the present invention, and was inferior in non-history permeability. No. Sample No. 8 has a high Ti amount exceeding the range of the present invention. Sample No. 10 has a high V amount exceeding the range of the present invention. No. 12 specimen has a high Nb amount exceeding the range of the present invention. Sample No. 14 has a high Cu amount exceeding the range of the present invention. Sample No. 16 has a high Cr amount exceeding the range of the present invention. Sample No. 18 has a high Sn content exceeding the range of the present invention. No. 19 specimen has a high Mo amount exceeding the range of the present invention. No. 20 has an Al ₂ O ₃ ratio lower than the range of the present invention. No. 22 had a high C amount exceeding the range of the present invention, and in all cases, the coercive force exceeded 239 A / m.
[0043]
[Table 1]

[0044]
[Example 2]
% By weight, C: 0.02%, Si: 0.01%, Mn: 0.45%, P: 0.03%, S: 0.003%, sol. Al: 0.06%, N: 0.003%, Ti: 0.002%, V: 0.003%, Nb: 0.002%, Cu: 0.011%, Sn: 0.004%, Ni : 0.03%, Cr: 0.02%, Mo: 0.02%, the balance being substantially made of Fe, Al ₂ O ₃ / (Al ₂ O ₃ + CaO + MnO + SiO ₂ ) = 0.35 The slab was heated at 1200 ° C., hot-rolled at a finishing temperature of 880 ° C. and a coiling temperature of 640 ° C. to a plate thickness of 1.8 mm, pickled, and then cold-rolled to a plate thickness of 0.1 mm. This is annealed in a nitrogen + hydrogen atmosphere at a temperature of 550 ° C. to 880 ° C. for 50 seconds, and further subjected to temper rolling with an elongation of 1.8% or less, or without temper rolling, After applying Cr plating, no. Sample materials 23 to 33 were obtained, and the magnetic permeability, coercive force, and non-historical magnetic permeability were measured in the same manner as in Example 1. Table 2 shows the annealing temperature, presence / absence of recrystallization, elongation rate of temper rolling, magnetic permeability, coercive force and non-hysteretic magnetic permeability of each specimen. In addition, Ac ₁ point of this test material was about 750 degreeC as a result of measuring with a four master.
[0045]
As shown in Table 2, No. 1 is an example in which recrystallization annealing was performed at Ac ₁ point or less and temper rolling was performed with an elongation rate of 1.5% or less. The test materials of 24 to 28, 30, and 31 had a non-history permeability of 7500 or more and a coercive force of less than 239 A / m, and extremely excellent magnetic characteristics. On the other hand, in the comparative example No. 1 in which either condition is out of the scope of the present invention. The test materials 23, 29, 32, and 33 were inferior in any magnetic property. Specifically, No. whose annealing temperature exceeded Ac ₁ point. In the specimens 32 and 33, the non-history permeability was No. in spite of the fact that temper rolling was not performed. 32, 6000, no. 33 was 5800, and both showed low values. Moreover, No. whose annealing temperature was 550 degreeC. The test material No. 23 did not recrystallize, and the non-historical permeability showed a low value of 5500. Furthermore, the elongation rate of temper rolling exceeded the scope of the present invention. In the 29 test material, the non-history permeability decreased to 7000.
[0046]
[Table 2]

[0047]
【The invention's effect】
As described above, according to the present invention, a color cathode ray that is effective for suppressing a color shift due to geomagnetism and obtaining a high-definition image, has excellent geomagnetic shielding properties, is inexpensive, and can be used effectively for resources. A cold-rolled steel sheet for a pipe magnetic shield can be obtained. By using the steel plate according to the present invention as a magnetic shield of a color cathode ray tube, a sufficient magnetic shielding property is ensured after demagnetization, and further, color shift due to geomagnetic drift is suppressed. Therefore, by using the steel plate of the present invention, a magnetic shield effective for obtaining a high-definition image quality of a TV or a computer can be obtained.

Claims (2)

A steel plate having a thickness of 0.05 mm or more and 0.5 mm or less used for a magnetic shield of a color cathode ray tube, and by weight, C: 0.06% or less, Si: 1% or less, Mn: 0.1% or more 2% or less, P: 0.1% or less, S: 0.02% or less, sol. Al: 0.001% to 1%, N: 0.006% or less, Ti: 0.01% or less, V: 0.01% or less, Nb: 0.01% or less, Cu: 0.005% or more 0.5% or less, Sn: 0.001% to 0.3%, Ni: 0.005% to 2%, Cr: 0.004% to 0.2%, Mo: 0.3% or less A cathode cathode tube characterized by comprising a balance Fe and inevitable impurities , satisfying a relationship of Al ₂ O ₃ / (Al ₂ O ₃ + CaO + MnO + SiO ₂ ) ≧ 0.1, and having a non-historical permeability of 7500 or more Cold rolled steel sheet for magnetic shield. The cold rolled steel sheet for a magnetic cathode ray tube magnetic shield according to claim 1 , wherein the steel sheet surface has Cr and / or Ni plating.