KR20040041454A - Method for manufacturing inner shield cold rolling steel for braun tube with excellent magnetic shielding effect - Google Patents

Abstract

PURPOSE: A method is provided to reduce manufacturing costs by eliminating the necessity of adding an alloy element and installing a decarbonization device. CONSTITUTION: A method comprises a step of hot-rolling the steel slab made of carbon(C) 0.0025 weight% or lower, Mn 0.05 to 0.25 weight%, Si 0.003 to 0.015 weight%, Al 0.015 weight% or lower, N 0.025 weight% or lower, P 0.015 weight% or lower, S 0.01 weight% or lower, Fe, and impurities; a step of performing a primary cold-rolling process on the resultant structure; a step of performing an annealing process on the resultant structure at the temperature higher than the re-crystallization temperature; and a step of performing a secondary cold-rolling process on the resultant structure at a draft percentage of 25 to 40%.

Description

Method for manufacturing inner shield cold rolled steel sheet for cathode ray tube having excellent magnetic shielding {Method for manufacturing inner shield cold rolling steel for braun tube with excellent magnetic shielding effect}

The present invention relates to a method of manufacturing an inner shield cold rolled steel sheet for cathode ray tube having excellent self-shielding properties, and more particularly, by installing a special decarburization facility or adding expensive alloying elements to the magnetic body through low temperature hot rolling and two cold rolling. The present invention relates to a method for economically manufacturing an inner shield cold rolled steel sheet having excellent shielding properties.

1 schematically shows the structure of a typical CRT. The inner shield 11 used for the CRT 10 shields an external magnetic field inside the CRT 10 to prevent the electron beam 13 emitted from the electron gun 12 from escaping the orbit. The inner shield 11 is fixed to the shadow mask 16 installed in front of the CRT 10 and the frame 14 installed at both ends of the fluorescent screen 16 to the rear of the CRT 10 provided with the electron gun 12. Is extended. Accordingly, the electron beam 13 emitted from the electron gun 12 passes through the inner space of the CRT 10 formed by the inner shield 11 to reach the fluorescent screen 16 representing the color through the shadow mask 16. do. In this case, if the magnetic shielding property of the inner shield is not good, when the CRT is exposed to an external magnetic field, as shown in FIG. 2, the electron beam deviates from a predetermined path by the external magnetic field, resulting in poor image quality such as screen shaking or color bleeding. do.

Therefore, the inner shield should be a material having high external magnetic shielding which is easy to pass by magnetic flux, and this magnetic property is better for materials having high permeability and low coercive force. The main factor influencing these magnetic properties is the size of impurities and grains. The higher the purity and the coarser the grains, the better the magnetic autism with high magnetic permeability and low magnetic susceptibility.

A conventional technique for producing an inner shield cold rolled steel sheet excellent in magnetic shielding is a decarbonization annealing method disclosed in Japanese Laid-Open Patent Publication No. 60-255924. This technique is performed by hot rolling and primary cold rolling using steel with a carbon content of 0.08% or less, followed by decarbonization annealing to re-crystallize a recrystallized product having a final carbon content of 0.01% or less in a range of 5 to 17%. It is a method of performing cold rolling, performing secondary annealing in the range of 680-800 degreeC, and performing 3rd cold rolling finally on the conditions of 50% or more of reduction ratio. However, the magnetic properties of the products produced by this technology are good, but because of the complicated process, the manufacturing cost is high and there are many disadvantages in the manufacturing process.

A technique proposed to solve this problem is the decarbonization annealing method disclosed in Japanese Patent Laid-Open No. 62-280329. In this technology, hot rolling is carried out by lowering the slab heating temperature during hot rolling using steel with a carbon content of 0.02% or less, followed by primary cold rolling with a reduction ratio of 60% or more, and decarbonization annealing to bring the carbon content to 0.003% or less. After lowering, secondary cold rolling is further performed in the range of 60% or less of the reduction ratio, followed by annealing at a temperature of 650 ° C or higher. Although this technique is shortened because the third cold rolling process is omitted compared to the above-described conventional technique, it still includes a decarbonization annealing process so that special decarburization such as open coil annealing (hereinafter referred to as "OCA") is performed. It has the disadvantage of requiring an annealing facility.

A technique proposed to solve the problem of the decarbonization annealing method is a low temperature hot rolling method disclosed in Japanese Patent Laid-Open No. 2-166230. This technique is a method of adding 0.005 to 0.08% of titanium (Ti) to a steel having a carbon content of 0.005% or less, followed by low temperature hot rolling, and annealing at a temperature of 620 ° C. or higher after cold rolling. This technology has the advantage that the final product can be manufactured by only one cold rolling, but because the stored energy is large due to the cold rolling due to the high rolling rate, the recrystallization occurs quickly. The disadvantage is that the characteristics are not very good. That is, as shown in the embodiment, the steel sheet having a coercive force of 1.75e or less cannot be manufactured. In addition, since titanium, an expensive alloying element, must be added, manufacturing cost is high.

A technique for compensating the above-mentioned disadvantages of the decarbonization annealing method and the low temperature hot rolling method is disclosed in Korean Patent Publication No. 2000-40620. This technique is a method of hot rolling a steel with a carbon content of 0.0025% or less at a temperature of 910 ° C. or higher, followed by primary cold rolling, followed by annealing at a recrystallization temperature or higher, and secondarily cold rolling at a reduction ratio in the range of 25 to 50%. According to this technique, an inner shield with magnetic properties of 1.050e coercivity can be manufactured without using special decarburization equipment such as OCA and expensive alloying elements such as titanium.

However, in order to cope with the trend of CRTs which are becoming larger and more flat, materials with higher magnetic properties are required. Especially, CRTs require more excellent magnetic shielding properties because they have more openings than conventional CRTs. Since the above-described prior art does not meet such a demand, there is an increasing need for a method of manufacturing a cold rolled steel sheet having better magnetic properties.

The present invention has been proposed to satisfy this need, and is expensive by performing hot rolling in a specific temperature range, followed by primary cold rolling, followed by annealing above a recrystallization temperature, and then performing secondary cold rolling in a specific rolling reduction range. Its purpose is to provide a method of manufacturing an inner shield cold rolled steel sheet having excellent self-shielding properties without installing special decarburization equipment without adding an alloying element to meet the recent trend of enlargement and planarization of CRT.

1 is a schematic view showing the structure of a CRT.

2 is a schematic diagram showing electron beam departure by an external magnetic field;

3 is a partial state diagram of Fe-Fe ₃ C.

4 is a graph showing a rolling load according to hot rolling temperature.

5 is a graph showing hot rolling conditions according to the present invention;

6 is a flow chart showing a manufacturing method according to the present invention.

※ Explanation of symbols about main part of drawing ※

10: CRT 11: Inner shield

12: electron gun 13: electron beam

14: Frame 15: Shadow Mask

16: fluorescent screen

The present invention for achieving the above object is C: 0.0025% or less, Mn: 0.05 to 0.25%, Si: 0.003 to 0.015%, Al: 0.015% or less, N: 0.025% or less, P: 0.015% by weight Hereafter, S: 0.01% or less, the steel slab consisting of the remaining Fe and other impurity elements hot-rolled at 720 ~ 800 ℃ corresponding to A _r1 temperature or less, followed by primary cold rolling, followed by annealing above the recrystallization temperature Secondary cold rolling is carried out at a reduction ratio in the range of 25 to 40%.

Hereinafter, a method of manufacturing an inner shield cold rolled steel sheet according to the present invention will be described in detail with reference to the accompanying drawings.

First, the chemical composition of the steel used in the production method according to the present invention.

Carbon (C) is most important as the carbon content increases and the magnetic permeability is lowered as well as to a rolling possible temperature of A _r1 temperature in the ferrite region feature of the present invention the magnetic deterioration of the magnetic aging occurs down the hot rolling from the river chemical composition Since this possible temperature range becomes narrower, the lower the content is, the more advantageous it is, but it is limited to within 0.0025%, which is the industrial temperature range for mass production.

The manganese (Mn) is preferably added at 0.05% or more in order to prevent red shortness due to sulfur (S), which is inevitably included in the manufacturing process, but when the amount of manganese is increased, the permeability decreases and the coercivity is increased. Since the magnetism deteriorates such as to increase, the upper limit thereof is limited to 0.25%.

Since the silicon (Si) is an element added as a deoxidizer, it is preferable to contain at least 0.003% or more since the magnetic property is improved as the amount is increased. However, when excessively added, there is a disadvantage in that the blackening film is inferior in adhesion in the blackening treatment step performed before mounting of the CRT, and the upper limit thereof is limited to 0.015%.

The aluminum (Al) is also an element added as a deoxidizer, and the added aluminum combines with nitrogen (N) to form fine AlN precipitates. The AlN formed as described above limits the upper limit to 0.015% because the size of the crystal grains is reduced to decrease the magnetic properties. In addition, components such as phosphorus (P), sulfur (S), and nitrogen (N) deteriorate their magnetic properties as grain growth inhibiting elements.

The steel according to the present invention having such a chemical composition is clearly distinguished from the addition of titanium, which is an expensive alloying element, in the prior art published in Japanese Patent Laid-Open No. 2-166230. Titanium has a good effect on recrystallization behavior and aging, but TiC precipitates are not added because TiC precipitates at the grain boundary and prevents coarsening of grains, thereby degrading magnetic properties.

Slab is manufactured by continuous casting or ingot casting of molten steel having the chemical composition as described above, and then subjected to hot rolling after homogenizing treatment at a temperature of 1100 to 1250 ° C. Features of the hot rolling phase of the manufacturing method according to the present invention will be described with reference to FIG. 3, which shows a part of the Fe-Fe ₃ C state diagram. Conventionally, hot rolling is generally performed at a temperature higher than A _r3 , but according to the present invention, hot rolling is performed at a temperature below A _r1 . This low-temperature hot rolling is distinguished as the prior art published in the Republic of Korea Patent Application No. 2000-40620, published hot rolling at least 910 ℃ temperature less than A _r3 temperature. In general, it is known that when the hot rolling temperature is lowered, the deformation resistance of the metal is increased to increase the rolling load. However, in the case of steel, it becomes austenite (γ), which is the surface centered cubic structure (FCC) above A _r3 temperature, and ferrite (α), which is the body center cubic structure (BCC), below A _r1 temperature. Since it is determined by the relative size of the dynamic recovery, the ferrite, which is a body-centered cubic structure, has a lower atomic filling rate than the austenite, which is a face-centered cubic structure, so that the dynamic recovery occurs more easily. The rolling load hardly increases in comparison with the lower rolling temperature than the region. Therefore, even if hot rolling in the ferrite region in accordance with the present invention it is not necessary to apply more power than in the prior art.

On the other hand, when the hot rolling in the ferrite region (A _r1 temperature or less) according to the present invention as shown in Figure 5 hot rolling in the austenite region (A _r3 temperature or more) and the cooling process after hot rolling in the prior art Unlike the phase transformation of γ → γ + α at, no phase transformation occurs, so newly formed tissue grows more coarsely. As described above, the coarser grains of steel become better in magnetic properties such as permeability, so that the present inventors can improve the magnetic properties through coarsening of grains without burden of cost if hot rolling in the ferrite region. Noticed.

As shown in FIG. 3, the temperature of A _r1 varies depending on the chemical composition of the steel, but is about 840 ° C. or less in the chemical composition according to the present invention. If hot rolling is carried out in the two-phase coexistence area of austenite and ferrite between A _r1 and A _r3 temperatures, the structure is uneven and difficult to control the shape and thickness during rolling. There is a problem that the load is too high. Therefore, it is preferable to perform the temperature of hot rolling at 720-800 degreeC which can industrially stabilize operation.

The hot rolled steel sheet is subjected to the first cold rolling after the pickling process, and then subjected to the first annealing above the recrystallization temperature, and the second cold rolling at a cold rolling rate of 25 to 40%. Secondary cold rolling is another feature of the present invention, which is distinguished from the conventional technique disclosed in Japanese Patent Laid-Open No. 2-166230 only performing primary cold rolling. When the second cold rolling according to the present invention is performed, recrystallization occurs in the blackening treatment process to be described later due to accumulated energy due to the cold rolling, thereby further enhancing the magnetic properties by coarsening the crystal grains. However, if the cold reduction rate is less than 25%, the recrystallization does not occur in the blackening process and the deformation due to the cold rolling is not completely recovered, and the magnetic properties are deteriorated. If the cold reduction rate is greater than 40%, the recrystallization is not performed. Since the magnetic properties are deteriorated by the rapid progress and the finer the grains, the secondary cold rolling is preferably performed in the above-described 25 to 40% reduction ratio.

As such, the steel sheet completed by the second cold rolling is produced through the blackening treatment process, which is the final heat treatment step, and the blackening treatment is heat treated for 10 to 20 minutes at a temperature range of 570 to 600 ° C. . However, the hard material for bending processing does not have an annealing process after the second cold rolling, but forms an inner shield and recrystallizes in the blackening treatment process to secure magnetic properties, whereas the soft material for deep drawing is recrystallized after the second cold rolling. After annealing, it is molded into an inner shield and blackened. The recrystallization annealing is preferably 600 to 700 ° C. for continuous annealing and 550 to 600 ° C. for ordinary annealing. Such soft materials may have excellent processability, but have a disadvantage in that manufacturing costs increase due to additional processes.

6 shows a summary and arrangement of a method of manufacturing an inner shield cold rolled steel sheet according to the present invention. In short, the technical features of the present invention compared to the prior art is that by performing hot rolling in a ferrite region below the temperature of A _r1 , the crystal grains can be coarsened without new phase transformation during cooling, and 25 to 40% after the first annealing. By performing secondary cold rolling at a reduction ratio in the range, the grains can be coarsened by recrystallization, thereby securing magnetic properties of higher permeability and lower coercivity.

Look at the experimental results according to an embodiment according to the present invention. After dissolving the steel having the chemical composition as shown in Table 1, and manufacturing a cold rolled steel sheet under the conditions as shown in Table 2, after performing blackening treatment at 590 ℃ for 15 minutes, the characteristics were evaluated and the results are shown in Table 2.

ingredient C Mn Si Al S P Furtherance 0.0018 0.14 0.005 0.007 0.008 0.009

Steel grade Hot Rolling Temperature (℃) Primary rolling reduction rate (%) Primary Annealing Temperature (℃) Secondary rolling reduction rate (%) Hot Rolling Workability Coercivity Maximum Permeability Comparative Steel 1 700 ℃ (*) 88% 740 ℃ 25 Bad 1.04 4992 Comparative Steel 2 780 ℃ 20 (*) Good 1.88 2641 Comparative Steel 3 780 ℃ 55 (*) Good 1.42 3543 Comparative Steel 4 850 ℃ (*) 25 Bad 1.28 4011 Comparative Steel 5 915 ° C (*) 25 Good 1.18 4728 Inventive Steel 1 730 ℃ 25 Good 0.98 5310 Inventive Steel 2 780 ℃ 25 Good 0.91 5487 Invention Steel 3 780 ℃ 30 Good 0.99 5270 Inventive Steel 4 780 ℃ 35 Good 1.07 4981

* Mark is outside the condition of the present invention

As can be seen from Table 2, it can be seen that the magnetic properties of the final product differ depending on the hot rolling temperature and the reduction ratio of the secondary cold rolling. This is because the structure growth such as phase transformation is different according to the hot rolling temperature, and the recrystallization growth behavior in the blackening process is different according to the reduction rate of the secondary cold rolling.

In more detail, the comparative steel 1 has a hot rolling temperature of 700 ℃ lower than the temperature range of the present invention, the high rolling load during hot rolling, poor workability, and the comparative steel 2 has a too low secondary reduction rate during the blackening process Insufficient recrystallization caused the magnetic properties to deteriorate. In Comparative Steel 3, the secondary reduction ratio was so high that the recrystallized grains became fine and the magnetic properties deteriorated. In addition, Comparative steel 4 was hot rolling was performed in the two-phase region section, hot workability was poor, Comparative steel 5 was manufactured according to the prior art published in the Republic of Korea Patent Publication No. 2000-40620 the same secondary It can be seen that the magnetic properties are inferior to that of the inventive steel 2 manufactured by the rolling reduction rate. Inventive steels 1 to 4 are manufactured within the scope of the present invention, it can be seen that the magnetic properties are excellent and the workability during hot rolling is also excellent. However, even within the scope of the present invention, there is a difference in magnetic properties according to the hot rolling temperature and the secondary reduction rate. Therefore, when the present invention is applied to industrial production, the optimum conditions can be set in consideration of the conditions and magnetic properties suitable for production facilities.

As described above, in the present invention, by manufacturing a cold rolled steel sheet for inner shield through low temperature hot rolling and two cold rolling, there is no need to install expensive decarburization equipment without adding expensive alloy elements, thereby reducing manufacturing costs. In addition, it can provide a cold rolled steel sheet for inner shield with better magnetic properties in response to the recent trend of enlargement and planarization of the CRT.

Claims (3)

By weight% C: 0.0025% or less, Mn: 0.05-0.25%, Si: 0.003-0.015%, Al: 0.015% or less, N: 0.025% or less, P: 0.015% or less, S: 0.01% or less, remaining Fe and A steel slab made of other impurity elements is hot rolled at 720 to 800 ° C., first cold rolled, and then annealed at a recrystallization temperature or higher, followed by secondary cold rolling at a reduction ratio of 25 to 40%. Method for manufacturing inner shield cold rolled steel sheet for cathode ray tube with excellent shielding property. The method of claim 1, A method for producing an inner shield cold rolled steel sheet having excellent magnetic shielding, characterized in that the cold-rolled steel sheet prepared as described above is continuously annealed at 600 to 700 ° C., or is subjected to phase annealing at 550 to 600 ° C. The method according to claim 1 and 2, A method for producing an inner shield cold rolled steel sheet for a cathode ray tube having excellent self-shielding property, wherein the cold rolled steel sheet manufactured as described above is subjected to blackening treatment in a range of 570 to 600 ° C. for 10 to 20 minutes.