JPS6366376B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to steel for shadow masks of color television cathode ray tubes. Conventional color TV CRT shadow masks are made of ultra-thin cold-rolled rimmed steel strip (thickness 0.2 mm or less) with a carbon content of 0.1% or less.The steel strip is perforated by photo etching, then annealed and leveled. It is manufactured by sequentially applying and then press molding. However, when the material is a rimmed steel strip, the following problems have conventionally existed in manufacturing. First, since rimmed steel has a high oxygen content and many nonmetallic inclusions, defects are likely to occur during etching and drilling. Even if the second rimmed steel is sufficiently decarburized, nitrogen is not fixed, so stretcher strain is likely to occur.To prevent this, the annealing temperature must be adjusted.
It is necessary to raise the temperature to 900-950°C to enlarge the crystal grains and increase the number of levelers. Thirdly, annealing is performed by cutting the etched hole and stacking the cut pieces to form a 900~
It is carried out at a high temperature of 950℃. For this reason, flatness defects such as sticking of the plates to each other and waviness tend to occur, and the yield is reduced due to annealing. Fourth, leveling is performed to improve flatness and prevent stretcher strain after annealing, but in the case of rimmed steel, the number of leveling must be increased. This caused distortion in the etched holes. It is already known that the above problems can be solved by using ultra-low carbon aluminum killed steel for the steel strip. However, when we investigated the coercive force of shadow masks made from ultra-low carbon aluminum killed steel, we found that the coercive force was often high and not constant.
After the shadow mask is incorporated into a cathode ray tube, it is temporarily demagnetized by a degaussing device, but if the magnetic coercive force is high, a large amount of power is required. Furthermore, if the coercive force is high, when a magnetic force is applied from the outside, the magnetism remains, causing disturbance in the polarization of the electron beam during imaging and causing color shift. For this reason, it is generally considered necessary that the coercive force of conventional shadow mask materials be 1.4 oersted (Oe) or less after annealing. Therefore, in manufacturing a shadow mask, it is necessary to reduce the coercive force in addition to improving the above-mentioned problems. The inventors of the present invention conducted various studies on this problem and found that the coercive force varies depending on the amount of N and O in the steel, and the smaller the amount of N and O, the lower the coercive force becomes. Thus, the present invention provides C:
0.01% or less, S: 0.014% or less, Mn: 0.15 to 0.50
%, Sol.Al: 0.020-0.080%, N: 50ppm or less,
The present invention provides a steel for shadow masks having an extremely low coercive force, characterized in that O: 70 ppm or less, the balance being iron and unavoidable impurities. The reasons for limiting the ingredients of the present invention will be described below. C: The amount of C affects photoetching properties, coercive force and elongation at yield point. In other words, as the amount of C increases, more carbides (Fe ₃ C) are produced,
Since this material is less likely to be etched than the iron substrate during photoetching, more of it remains after etching, and the coercive force also increases. In addition, the elongation at yield point increases, which impairs the shape of the hole during press forming. Therefore, taking these into consideration comprehensively, the C content was reduced by 0.01%. S: If there is a large amount of S, surface cracking will occur during hot rolling, and MnS-based inclusions will increase due to reaction with Mn, which is added to prevent this, which will impair the shape of the pores during photoetching and reduce the coercive force. It also becomes expensive. Such a situation becomes noticeable when the S content exceeds 0.014%, so the S content was set to 0.014% or less. In order to solve the problem of hot rollability due to Mn:S, the amount of Mn needs to be about Mn/S>10,
And since it is desirable to have less in order to lower the coercive force.
It was set at 0.15-0.5%. N: Figure 1 shows C: 0.002%, S: 0.010%,
Mn: 0.18%, Al: 0.035%, N: 20-90ppm,
This figure shows the relationship between the amount of N in the steel and the coercive force after an aluminium-killed cold-rolled steel strip with O: 30 ppm is annealed at 700°C, and the coercive force increases as the N amount increases.
In the case of a shadow mask, the coercive force must be less than 1.4 oersted, so from Figure 1, the amount of N is
It was set to 50ppm or less. If the amount of N is reduced in this way, the coercive force and elongation at yield point will be reduced, which is advantageous, but if the amount of N is too small, the crystal grains will become coarse and uneven elongation will occur during press forming, so the lower limit should be 20 ppm. It is preferable. Various experiments have shown that the amount of N is preferably 20 to 30 ppm in order to balance coercive force and press formability. Sol.Al: Al fixes solid solution N as AlN to reduce yield elongation, and also suppresses the formation of oxides that are difficult to off-etch by deoxidizing. For this purpose, the amount of Al needs to be 0.020% or more.
However, adding more than necessary will not change the effect and increase costs, so the upper limit was set at 0.080%. O: Figure 2 shows C: 0.001%, Mn: 0.19%, S:
0.008%, Al: 0.025%, N: 0.0025%, O:
This figure shows the relationship between the amount of O in the steel and the coercive force after an ultra-low carbon aluminum killed cold rolled steel strip of 0.0020 to 0.0100% is annealed at 700°C, and the coercive force increases as the amount of O increases. In particular, the coercive force increases rapidly above 70 ppm. This is considered to be because as the amount of O increases, the number of nonmetallic inclusions increases, which prevents the movement of magnetic domains. In the case of a shadow mask, the coercive force needs to be 1.4 oersted or less as mentioned above, so the amount of O is set to 70 ppm or less. However, since it is preferable that the amount of O be small, it is appropriate to set it to 20 ppm or less. Example Table 1 shows the above-mentioned shadow mask manufacturing method, in which steps up to photo-etching were carried out in the conventional manner, and subsequent annealing was carried out depending on the steel type, and the adhesion (seizing) between plates and the wavy shape due to annealing were investigated. At the same time, the number of passes through a leveler and the coercive force required to flatten the material after annealing were investigated.

[Table] (Note) Regarding the evaluation of annealing adhesion and waviness, cases where both of these are significant are judged as ×, and cases where they are not significant are judged as ○.
As is clear from Table 1, when the steel type is rimmed steel, the coercive force is low, but due to annealing, close contact between the plates and a wavy shape are observed. Also, even if the steel type is ultra-low carbon aluminum killed steel, the N amount is more than 50 ppm or the O amount is
If the amount is more than 70 ppm, the coercive force is high. On the other hand, the amount of N and O of ultra-low carbon aluminum killed steel is
When the coercive force is 50 ppm or less and 70 ppm or less, the coercive force is low and the fluctuation is small. As described above, by using the steel of the present invention, the coercive force of the shadow mask can be made low and stable, so a large amount of electric power is not required for degaussing, and color shift on a color TV screen does not occur during video images.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the amount of N in the steel and the coercive force of an aluminium-killed steel strip, and FIG. 2 is a graph showing the relationship between the amount of O in the steel and the coercive force in the same steel.

Claims (1)

[Claims] 1 C: 0.01% or less, S: 0.014% or less, Mn:
0.15~0.50%, Sol.Al: 0.020~0.080%, N:
A steel for shadow masks with an extremely low coercive force, characterized by comprising 50 ppm or less, O: 70 ppm or less, and the balance consisting of iron and unavoidable impurities. 2 N and O: 20 to 30 ppm and O:
The steel for shadow masks having an extremely low coercive force according to claim 1, characterized in that the coercive force is 20 ppm or less.