JP2001040417A - Manufacture of high permeability and high strength steel sheet for cathode-ray tube band - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel sheet for cathode-ray tube band, capable of being easily manufactured and having high strength and high magnetic permeability. SOLUTION: A steel slab, which has a composition containing 0.005-0.06% C, 0.05-1.5% Mn, <=0.02% S, 0.019-0.15% Al, and <=0.005% N and also containing, if necessary, either or both of <=0.9% Si and <=0.15% P, is hot rolled. The resultant steel plate is subjected to primary cold rolling at >=60% cold rolling rate, to primary annealing, and to secondary cold rolling at 5-60% cold rolling rate, followed by continuous annealing at 720-900 deg.C. The resultant steel sheet is used as a solid material or as a plated steel sheet prepared by the application of electroplating with Zn, Ni, Cr, or alloys thereof to improve corrosion resistance. It is preferable to coil the hot rolled steel strip at 500-700 deg.C at hot rolling. Moreover, the continuously annealed steel sheet or the continuously annealed and electroplated steel sheet can be subjected to temper rolling at <=2.5% elongation percentage and then to roller leveling at <=2.0% elongation percentage at sheet surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-permeability, high-strength steel sheet used as a CRT band for fastening around a panel portion of a cathode ray tube incorporated in a television, an OA apparatus, and the like.

[0002]

2. Description of the Related Art A cathode ray tube has a high vacuum inside.
Around the panel to prevent concave deformation of the panel surface and internal explosion.
The area is fastened with a CRT band. CRT van
As for the temperature, the perimeter of the panel part should be 0.2 ~
0.8-2.0m thickness with 0.6% shorter inner circumference
m steel plates are used. CRT band band
When wearing, thermal expansion by heating at 450-500 ° C
The CRT band around the panel,
To the panel due to heat shrinkage caused by rapid cooling
A tight shrink fit method is employed. CRT van
Tightening force generates tightening force. Tightening force is in the pipe
Is 10 ^-6100 to 100 tons due to high vacuum
The shape of the panel surface that was deformed into a concave shape
It has the function of compensating and eliminating concave deformation. Also, soft
CRT band made from steel plate which is magnetic material,
Permeability μ of about 200_{0. 35}(Magnetic field strength: 0.35 Els
Magnetic shield inside the cathode ray tube.
It also has the effect of

A material used for a cathode ray tube band having such a function is required to be excellent in both tensile properties and magnetic shielding properties. In particular, in accordance with the recent tendency for cathode ray tubes to be larger, flatter, lighter, and more precise, the demand for materials having both excellent tensile properties and magnetic shielding properties is increasing. The tension performance of the CRT band is an important characteristic for large size, flatness and light weight. For high definition, it is necessary to suppress landing fluctuation (geomagnetic drift) of the electron beam due to terrestrial magnetism which is one of the causes of color shift. Magnetic shielding performance is an important characteristic.

[0004] In steel plates used for CRT bands,
There is a contradictory relationship between the high strength required for improving the tensile properties and the high magnetic permeability required for improving the magnetic shield. By the way,
A CRT band using a high-strength steel plate for high strength deteriorates geomagnetic drift due to insufficient magnetic shielding performance and cannot be put to practical use. In order to obtain a cathode ray tube band having both contradictory characteristics of high strength and high magnetic permeability, a large amount of Si, which is a solid solution strengthening element, was added to a very low carbon steel composition of C: 0.005% by weight or less. A method of manufacturing a cathode ray tube band from a cold-rolled steel sheet, a so-called silicon steel sheet (electromagnetic steel sheet), is introduced in Japanese Patent Application Laid-Open Nos. 10-208670 and 10-214578. When this cold-rolled steel sheet is lightly cold-rolled with a rolling reduction of 3 to 15%, a magnetic field strength of 0.3 is obtained after a heating and cooling cycle equivalent to shrink fitting.
It is reported that the permeability μ _0.3 in Oersted is 250 or more and the yield stress is 400 N / mm ² or more.

[0005]

The addition of a large amount of Si aims at improving the magnetic permeability by lowering the magnetic anisotropy constant and improving the yield stress by solid solution strengthening. Light cold rolling has the effect of improving the yield stress of a steel sheet by work hardening. The addition of a large amount of Si is effective for achieving both high strength and high magnetic permeability in combination with light cold rolling, but introduces a new problem. In a steel type mass-produced by a steel maker, the extremely low carbon content of C: 0.005% by weight or less and the addition of a large amount of Si are causes of soaring steelmaking costs. Further, when a large amount of Si is added, not only does the cold rolling property, productivity, etc. decrease, the production cost increases, but also the material becomes very brittle, and the material may be broken even by light working such as bending. .

[0006] In this regard, the steel plates introduced in JP-A-10-208670 and JP-A-10-214578 are not general steel plates and correspond to special steel plates. Moreover, although light cold rolling is effective in improving the yield stress by work hardening, it is a cause of significantly lowering the magnetic permeability. Work in the direction to negate. It is said that the relative deterioration of magnetic permeability due to the increase in yield stress can be suppressed to a low level by properly combining the annealing conditions and the cold rolling rate during light cold rolling, but it is still sufficient to recover the deteriorated magnetic permeability. I have not been able to.

[0007]

SUMMARY OF THE INVENTION The present invention utilizes age hardening due to solid solution C for increasing strength, and uses cementite (Fe).
Precipitation form of ₃ C), by controlling the size and the ferrite crystal grain size in production conditions, without the need for addition of a large amount of ultra low carbon reduction and Si, using steels having a composition having the general material equivalent productivity To achieve both high strength and high permeability,
It is an object of the present invention to provide a steel plate for a CRT band having excellent formability.

In order to achieve the object of the production method of the present invention, C: 0.005 to 0.06% by weight, Mn: 0.0
5 to 1.5% by weight, S: 0.02% by weight or less, Al:
After hot rolling a steel slab containing 0.019 to 0.15% by weight, N: 0.005% by weight or less, and the balance being substantially Fe, the primary slab is subjected to a cold rolling reduction of 60% or more. Rolling,
After primary annealing, secondary cold rolling is performed at a cold rolling rate of 5 to 60%, and then continuous annealing is performed in a temperature range of 720 to 900 ° C. As a steel slab, Si: 0.9% by weight or less,
A compound containing one or two kinds of P: 0.15% by weight or less can also be used.

The obtained steel sheet can be used as a solid material or Z
It is used as a plated steel sheet having improved corrosion resistance by electroplating n, Ni, Cr or an alloy thereof. In the hot rolling, it is preferable to wind the hot-rolled steel strip at a temperature of 500 to 700 ° C. Alternatively, the continuously annealed steel sheet or the steel sheet electroplated after the continuous annealing may be subjected to temper rolling at an elongation of 2.5% or less, and then subjected to a roller leveler having an elongation of 2.0% or less.

[0010]

The present invention is directed to a steel having a normal composition which does not require extremely low carbon and a large amount of Si. And, among the material properties required for steel plates for CRT bands,
The improvement in strength (high yield stress) is improved by age hardening of solid solution C remaining in the matrix. Higher permeability can be improved by adjusting the precipitation form and size of cementite (Fe ₃ C) and increasing the ferrite crystal grain size.

In the present invention, which aims to increase the strength of a steel sheet by age hardening, a steel type containing 0.005% by weight or more of C is basically targeted, and prior to increasing the strength by using solid solution strengthening of Si. Unlike the technology, it does not require ultra-low carbonization of C: 0.005% by weight or less, so that the steelmaking cost does not increase. In order to utilize age hardening for high strength, the CRT band before being shrink-fitted to the panel portion is soft and has good workability. Therefore, when forming into a cathode ray tube band, forming is easy, and there is no occurrence of defects such as bending cracks. Then, when shrink-fitting the CRT band mounted on the panel portion, solid solution C precipitates at dislocations in the course of a heating / cooling cycle of about 450 to 500 ° C. The precipitated C acts as an inhibitor for fixing dislocations and increases the yield stress of the steel sheet.

Most of C dissolved in the matrix precipitates as cementite (Fe ₃ C). Generally speaking, the permeability decreases due to the precipitation of cementite (Fe ₃ C), but the effect on the degree of decrease in the permeability is greatest when finely dispersing cementite (Fe ₃ C) in ferrite crystal grains. When cementite (Fe ₃ C) precipitates and agglomerates at the ferrite crystal grain boundaries and the ferrite crystal grains grow large, the influence on the degree of decrease in magnetic permeability becomes extremely small. As a result, a high magnetic permeability characteristic required for a steel plate for a cathode ray tube band can be obtained. The preferred precipitation morphology and precipitation size of cementite (Fe ₃ C) and coarsening of ferrite crystal grains are achieved by hot rolling at high temperature winding, secondary cold rolling at a relatively low cold rolling reduction and high temperature as secondary annealing. This is achieved by combining continuous annealing.

[0013] The magnetic permeability is also reduced by the refining step after the secondary annealing or the temper rolling that is performed to secure the sheet shape after the electroplating. The temper rolling is generally light cold rolling with an elongation of about 0.5 to 3%, and the plastic strain and residual stress introduced at this time are causes of a decrease in magnetic permeability.
The magnetic permeability lowered by the temper rolling can be recovered by applying a roller leveler after the temper rolling.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The components and compositions of steel used in the present invention, manufacturing conditions, and the like will be described below. C: 0.005 to 0.06% by weight An alloy component effective for improving the strength. In the present invention, it is an essential component for increasing the strength required particularly for a steel plate for a cathode ray tube band. Part of C becomes solid solution C in the state of continuous annealing, and imparts a high yield stress to the steel sheet by age hardening during shrink fitting. For this, 0.005
It is necessary to contain C in an amount of at least% by weight, but if a large amount of C exceeding 0.06% by weight is included, the magnetic permeability μ _0.35 after shrink fitting tends to be deteriorated. Mn: 0.05 to 1.5% by weight An alloy component that fixes S inevitably mixed as MnS and improves hot workability. The effect of Mn becomes remarkable at 0.05% by weight or more, but when an excessive amount of Mn exceeding 1.5% by weight is included, the workability is deteriorated, and the magnetic permeability μ _0.35 after shrink fitting is also deteriorated.

S: 0.02% by weight or less S is a harmful component to the steel sheet, and if present as an inclusion in the steel sheet, adversely affects both the heat ductility and the magnetic permeability. However, excessively lowering the S content causes an increase in steelmaking costs,
In the present invention, the upper limit of the S content is set to 0.02% by weight so as not to adversely affect the magnetic permeability. Al: 0.019 to 0.15% by weight It is an alloy component effective as a deoxidizing agent for reducing inclusions in steel, and also has an effect of fixing N as AlN, and has an effect of 0.019%.
The effect is exhibited when Al is added in an amount of at least% by weight. However, the generated AlN inhibits the growth of ferrite crystal grains.
To suppress the growth of ferrite crystal grains, the Al content may be reduced to reduce the amount of generated AlN, or 0.15% by weight.
In addition, a method of adding a large amount of Al exceeding the above to sufficiently coarsen the AlN is adopted. In this regard, in the component system targeted by the present invention, even if the production of AlN is not particularly controlled,
Ferrite grains are coarsened to the target size. Therefore, the Al content is set at 0.1 with a primary focus on the reduction of inclusions in the steel.
It is regulated to 15% by weight or less. On the other hand, when a large amount of Al exceeding 0.15% by weight is contained, the surface quality of the steel sheet tends to deteriorate.

N: 0.005% by weight or less In order to generate AlN which inhibits the growth of ferrite crystal grains, it is preferable to reduce the content as much as possible. In the present invention, the upper limit of the N content is specified to be 0.005% by weight. . Si: 0.9% by weight or less An alloy component added as necessary, and increases the strength of the steel sheet by solid solution strengthening. However, if a large amount of Si is contained, the workability deteriorates. Therefore, in the present invention, the upper limit of the Si content is set to 0.9% by weight. P: 0.15% by weight or less An alloy component added as necessary, and exhibits an effect of increasing the strength of a steel sheet by solid solution strengthening. In addition, it is an effective alloy component for increasing the amount of solid solution C. However, it is easily segregated in the steel sheet, and a large amount of P content exceeding 0.15% by weight causes the steel sheet to be embrittled.

Hot Rolling: Winding Temperature 500-700 ° C. A steel slab having a predetermined composition is hot-rolled according to a conventional method.
It is wound around a coil at a removal temperature of 500 to 700 ° C. heat
Slab heating temperature and finishing temperature during hot rolling are particularly restricted
Although it is not a thing, 1100 ~ 1250 ℃
And a temperature range of 840 to 950 ° C.
No. The winding temperature is set to cementite (Fe _Three C) coarsening
500 ° C. or higher is preferable for promoting the temperature. But 7
At winding temperatures exceeding 00 ° C., cementite (Fe_Three 
Excessive coarsening of C), forming such as bending
Sometimes cracks originating from coarse cementite,
Processing cracks are likely to occur.

Primary Cold Rolling: Cold Rolling Rate of 60% or More Primary cold rolling is a necessary step for adjusting the cold rolling rate at the time of secondary cold rolling to an appropriate amount. There is no restriction. The thickness of the hot-rolled steel strip is usually about 2 to 5 mm, and when the product thickness becomes as thin as about 1 mm, the thickness of the hot-rolled steel strip and the product thickness are reduced in a single cold rolling production line. Since the cold rolling reduction is determined from the relationship, the cold rolling reduction must be high, and an appropriate low cold rolling reduction cannot be set.
In this regard, in order to make the cold rolling reduction during the secondary cold rolling an appropriate amount,
It is preferable to set the cold rolling ratio of the primary cold rolling to 60% or more. If the cold rolling reduction does not reach 60%, coarse ferrite grains cannot be obtained under stable conditions due to final annealing after secondary cold rolling.

Primary Annealing The cold rolled structure generated by the primary cold rolling is recrystallized by the primary annealing. For the primary annealing, ordinary recrystallization annealing conditions can be adopted. However, if the ferrite grains are grown large at this point, it is difficult to make the ferrite grains coarse by the final annealing. In order to suppress the growth of ferrite crystal grains, it is preferable to perform primary annealing in a temperature range of not lower than the recrystallization temperature and not higher than 780 ° C.

Secondary Cold Rolling: Cold Rolling Rate of 5 to 60% In the secondary cold rolling, a low cold rolling rate is employed in order to grow ferrite crystal grains coarsely. The cold rolling reduction greatly affects the ferrite crystal grain coarsening, and the higher the cold rolling reduction, the smaller the ferrite crystal grain tends to be. The magnetic permeability also changes in proportion to the size of the ferrite crystal grain. But 5%
If the cold rolling reduction is less than 1, it becomes difficult to obtain ferrite crystal grains that are coarse and stable. If the ferrite crystal grains are coarsened more than necessary, the magnetic permeability is improved but the yield stress is reduced. Conversely, at a cold rolling rate exceeding 60%, the ferrite crystal grains do not become coarse, and the magnetic permeability μ _0.35 ≧ 4
50 becomes difficult to obtain. For this reason, in the present invention, the cold rolling ratio of the secondary cold rolling is set to 5 to 60%, preferably 10 to 60%.
Set within the range of ~ 50%.

High-temperature continuous annealing (secondary annealing): annealing temperature 72
As the secondary annealing after the 0-900 ° C. secondary cold rolling, continuous annealing is employed in order to recrystallize and coarsen the ferrite crystal grains and leave solid solution C in the subsequent cooling process. The higher the annealing temperature, the more the ferrite crystal grains become coarser, and higher magnetic permeability characteristics can be obtained. The coarsening of ferrite crystal grains becomes remarkable at an annealing temperature of 720 ° C. or higher. However, if the annealing temperature exceeds 900 ° C., defects such as surface flaws and plate breakage are likely to occur.
By the way, in a normal continuous annealing line, an overaging zone is additionally provided. When using this continuous annealing line, there is no particular restriction on the overaging condition. However, at a low overaging temperature, fine cementite (Fe ₃ C) starts to precipitate in the ferrite crystal grains. Therefore, it is preferable to set the overaging temperature to 350 ° C. or higher to suppress the precipitation of cementite in the ferrite crystal grains. . In the cooling after the overaging treatment, a cooling rate of 60 ° C./min or more is preferable.

Temper rolling: elongation of 2.5% or less The steel sheet maintains a relatively predetermined sheet shape even after continuous annealing. However, if a good sheet shape is required, after continuous annealing or after continuous annealing. After the electroplating after annealing, it is temper rolled.
However, permeability decreases due to plastic deformation and residual stress introduced by temper rolling. Therefore, it is preferable that the temper rolling is performed at the lowest possible elongation so that the magnetic permeability does not significantly decrease. Investigation of the effect of temper rolling on the decrease in magnetic permeability revealed that temper rolling in which the elongation was set to 2.5% or less could reduce the degree of decrease in magnetic permeability.

Roller leveler: elongation of 2.0% or less The permeability lowered by temper rolling is recovered by reducing residual stress in the roller leveler after temper rolling. In a roller leveler, the maximum distortion of 2.0% or less on the plate surface is effective for the recovery of the magnetic permeability, and the recovery of the magnetic permeability cannot be expected with the distortion of more than 2.0%.

[0024]

Example 1 A steel slab having the composition shown in Table 1 was hot-rolled into a hot-rolled steel strip having a thickness of 4.2 mm under the conditions shown in Table 2, and primary cold-rolled and annealed at a cold-rolling rate of 72%. Through continuous annealing at a temperature of 720 ° C. and secondary cold rolling at a cold rolling rate of 15%, a sheet thickness of 1.0 mm
Of cold rolled steel strip. The obtained cold-rolled steel strip was passed through a continuous annealing furnace and annealed at 850 ° C., and was overaged at 490 ° C. in a cooling process after the annealing. Next, the sheet was passed through an electroplating line and subjected to electric Zn-Ni plating with an adhesion amount of 20 g / m ² .

[0025]

A test piece was cut out from each electroplated steel strip in a direction parallel to the rolling direction, and subjected to a contact bending test to evaluate workability by cracking during bending. After heat treatment equivalent to shrink fitting (500 ° C. × 5 seconds → air cooling), it was subjected to a tensile test and a magnetic property test. In the adhesion bending test, JI
Close bending was performed according to SZ2248, and the bendability was investigated based on the presence or absence of cracks. JI in the tensile test
JIS Z224 using No. 5 test piece of S Z2201
The tensile properties were measured according to 1. In the magnetic property test, a magnetic permeability μ _0.35 at a magnetic field strength of 0.35 Oe was measured according to JIS C2204.

As can be seen from the investigation results in Table 2, the steel types Nos. 3 to 6 according to the present invention have a yield stress of 270 N / mm.
² or more, the magnetic permeability was as high as μ _0.35 ≧ 450, indicating that the steel sheet had high strength and high magnetic permeability. On the other hand, steel grade numbers 1 and 2
(Comparative Example) showed good magnetic permeability μ _0.35 , but the yield stress was low and required high strength was not obtained. The low yield stress has a small C content in steel type No. 1 and a small C content in steel type No. 2 and also includes Ti for fixing C as TiC, so that there is no improvement in yield stress by age hardening. That is the cause.

In the case of steel type No. 7 containing a large amount of C, cementite (F) which is a precipitation site of solid solution C during continuous annealing is used.
e ₃ C) is dissolved C amount for abundant was decreased. Therefore, improvement of the yield stress by age hardening cannot be expected, but the effect of improving the yield stress by increasing the precipitation amount of cementite has been exhibited, and tentatively high yield stress has been exhibited. But,
A large amount of cementite (Fe ₃
Since C) was precipitated, the magnetic permeability μ _0.35 was low, and the required high magnetic permeability characteristics could not be obtained. Steel type No. 8 exhibits high yield stress and high magnetic permeability due to a high Si content, but cracks were generated in a close contact bending test due to a large solid solution strengthening effect of Si and poor workability.

[0029]

[0030]

Example 2 A hot-rolled steel strip having a thickness of 4.2 mm obtained from a steel slab having a steel type number 4 (Table 1) was subjected to primary cold rolling at a cold rolling reduction of 45 to 80%, and then subjected to an annealing temperature of 730 ° C. It was annealed continuously and then subjected to secondary cold rolling at various cold rolling reductions. The obtained cold-rolled steel strip was passed through a continuous annealing line, continuously annealed at an annealing temperature of 830 ° C., subsequently aged at 480 ° C., and then subjected to temper rolling at an elongation of 0.8%. Further, an electric Zn-Ni plating with an adhesion amount of 20 g / m ² was applied in an electroplating line,
Leveling was performed with a roller leveler having a maximum surface distortion of 1.0%. A test piece was cut out from each of the electroplated steel strips and subjected to the same contact bending test as in Example 1, and the workability was evaluated by the occurrence of cracks during bending. In addition, heat treatment equivalent to shrink fitting (5
(00 ° C. × 5 seconds → air cooling), and then subjected to the same tensile test and magnetic property test as in Example 1.

As can be seen from the examination results in Table 3, Test Nos. 2 to 5 in which the secondary cold rolling reduction was set within the range specified in the present invention.
Has a yield stress of 270 N / mm ² or more and a magnetic permeability of μ
_As high as _0.35 ≧ 450, a steel plate with high strength and high magnetic permeability was obtained. On the other hand, in Test No. 1 in which the secondary cold rolling reduction was as low as 2%, recrystallization was not completed and coarse ferrite crystal grains were not obtained, so that a high yield stress was exhibited. In Test No. 6 in which the secondary cold rolling reduction was too high as 80%, although the ferrite crystal grains were refined to obtain a high yield stress, the magnetic permeability showed an extremely low value of μ _0.35 = 210.

[0032]

[0033]

As described above, in the present invention, age hardening by solid solution C is utilized for increasing strength, and ferrite crystal grains and cementite (Fe ₃ C) are coarsened and cementite (Fe ₃ C). In order to increase the magnetic permeability by suppressing the precipitation in the ferrite crystal grains described in (1)). For this reason, there is no increase in steelmaking cost which is observed in a conventional ultra-low carbon steel sheet in which a large amount of Si is added, and a steel sheet suitable for a CRT band with good productivity can be obtained. In addition, since the required strength is given by age hardening in the heating and cooling cycle when shrink-fitting the CRT band to the panel part, workability is secured in the process until it is formed into a CRT band, and bending No cracks occur. As described above, according to the present invention, an age-hardened steel sheet for a high-permeability CRT band that sufficiently satisfies the required characteristics can be manufactured at low cost.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Seiichi Hamanaka 11-1 Showa-cho, Kure-shi, Hiroshima F-term in Nisshin Steel Co., Ltd. Technical Research Institute (reference) 4K037 EA01 EA04 EA05 EA11 EA13 EA15 EA18 EA20 EA23 EA25 EA27 EB08 EB09 FC04 FE01 FE02 FE03 FG01 FG03 FH01 FJ05 FL01 FM01 GA05 JA06 5C012 AA02 BB01 BB07 5C032 AA02 CC03 CC10

Claims (4)

[Claims] 1. C: 0.005 to 0.06% by weight, M
n: 0.05 to 1.5% by weight, S: 0.02% by weight or less, Al: 0.019 to 0.15% by weight, N: 0.00
After hot rolling a steel slab containing not more than 5% by weight, with the balance being substantially the composition of Fe, primary cold rolling at a cold rolling reduction of 60% or more, and after primary annealing, a cold rolling reduction of 5 to 60% The method for producing a high-strength steel plate for a high permeability CRT band, which is subjected to secondary cold rolling in a second step and then continuous annealing in a temperature range of 720 to 900 ° C. 2. The composition according to claim 1, further comprising: Si: 0.9% by weight or less;
The method for producing a high-strength steel sheet for a high-permeability CRT band according to claim 1, wherein a steel slab containing one or two kinds of not more than 15% by weight is used. 3. A method for producing a high-strength steel sheet for a high-permeability CRT tube band, wherein the steel slab according to claim 1 or 2 is hot-rolled at a winding temperature of 500 to 700 ° C. 4. The steel sheet subjected to continuous annealing or electroplated after continuous annealing is subjected to temper rolling at an elongation of 2.5% or less, and then subjected to a roller leveler having an elongation of 2.0% or less. Item 4. The method for producing a high-strength steel sheet for a high-permeability CRT band according to any one of Items 1 to 3.