JPH059665A - Thin steel sheet for magnetic shield - Google Patents

Abstract

PURPOSE:To produce a thin steel sheet having excellent workability and spot weldability as well as excellent magnetic characteristics, also having excellent suitability to blackening treatment and release of residual gas after the treatment and utilizable as a magnetic shield material for CRT or a frame material having magnetic shielding property. CONSTITUTION:This steel sheet for a magnetic shield consists of, by weight, <=0.005% C, <=0.10% Si, <=0.5% Mn, <=0.02% P, <=0.005% S, 0.005-<0.015% sol. Al, <=0.004% N, <=0.003% O, <=0.002% B (0.1<= B/N<0.5) and the balance Fe with inevitable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic shield thin steel sheet having excellent magnetic properties, forming processability, gas releasing property, spot weldability and blackening processability, and particularly to a CRT for a color television receiver or the like. The present invention relates to a thin steel plate suitable for a magnetic shield material incorporated in a display device or a frame material having magnetic shield properties for holding them.

[0002]

2. Description of the Related Art In a CRT (Cathode Ray Tube, so-called CRT), a magnetic shield material is generally used in order to prevent the image and the color tone from being deviated due to the influence of external magnetism. The principle of the magnetic shield is to surround the space with a ferromagnetic material and allow external magnetism to flow along it to weaken the influence of magnetism inside the shielded space. The higher the magnetic permeability of the shield material and the thicker the wall thickness, the more easily the magnetism flows, but from the viewpoint of material saving and weight reduction, a material of high magnetic permeability is strongly desired. Further, if the shield material itself is magnetized, it also has an adverse effect such as disturbing the electron beam, so that the demagnetization coil erases the residual magnetism, but in this case, the coercive force of the shield material must be small. Magnetic properties such as high magnetic permeability and small coercive force are also required for the frame material for holding the shield material and the shadow mask.

On the other hand, the shield material and the frame material are formed into a predetermined shape and then spot-welded together with a shadow mask or the like into an integral structure, which is then incorporated in the CRT. Therefore, formability and spot weldability are also required as important material properties. In particular, in recent years, materials have been made thinner, and it has become necessary to process them into more complicated shapes than before in order to ensure the rigidity of the structure, and there is a strong demand for better moldability. ing. In addition, the material improves the thermal emissivity when absorbing the electron beam,
The surface is subjected to a blackening treatment to form a thin magnetite coating, and the adhesion and adsorbed gas releasing property of the coating are also important factors controlling the performance of CRT. Particularly, the adsorbed gas releasing property is emphasized as a factor controlling the life of the CRT.

By the way, iron is an inexpensive and excellent ferromagnetic material, but an ordinary iron plate has insufficient magnetic characteristics and cannot provide a satisfactory magnetic shield property. In order to shield weak magnetism such as geomagnetism with a CRT, the magnetic permeability μ around 0.35 Oe
Of 1000 G / Oe or more is desirable, whereas the level of ordinary iron plate is only 200-300 G / Oe. In order to improve the demagnetization efficiency, the coercive force is 10O.
It is required to be 1 Oe or less in the magnetic field of e, but it is as high as about 3 Oe in the ordinary iron plate. Silicon steel sheets have improved magnetic properties, but high-grade products with a high Si content show considerably good low magnetic field properties, but the formability and blackening processability are extremely poor. On the other hand, low grade products with low Si content have poor properties in low magnetic fields. Further, since silicon steel sheets are mainly used as a core material for transformers and motors after being laminated after being punched, and no consideration is given to formability, it is difficult to apply them to shield materials and frame materials.

Speaking only of magnetic properties, permalloy-based Ni
Alloys and amorphous alloys are well known as materials having excellent magnetic permeability and coercive force, but they are extremely expensive. In mass-produced products such as television sets, high and low material costs are a major factor in selecting materials. Moreover, since these alloys are extremely difficult to form and blacken and have a low saturation magnetic flux density, they are not suitable for shielding in a strong magnetic field. Due to such drawbacks and high price, there is no example applied to a CRT shield material or the like.

Japanese Patent Publication No. 63-65743 proposes a steel sheet for magnetic shield containing Ti. However, the subject of the method is to prevent the blackened film from peeling off, and although there is some mention of bending workability, no consideration is given to magnetic properties, spot weldability, or gas release properties.
In general, carbonitride-forming elements such as Ti and Nb form fine precipitates and deteriorate the magnetic properties, so it is common to avoid adding them.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention An object of the present invention is to provide a comprehensively excellent material as a magnetic shield material for CRTs and a frame material having magnetic shield properties, that is, in addition to magnetic properties, workability and spots. An object of the present invention is to provide a thin magnetic shield steel sheet which is excellent in weldability, blackening treatment property, and residual gas release property thereafter, and is inexpensive and can be used as a material for mass-produced products.

[0008]

First of all, it is necessary to consider an iron-based material containing no expensive alloying elements from the viewpoint of economy. This is also necessary in order to increase the saturation magnetic flux density and secure the shielding property against a strong magnetic field.

However, in general, magnetic properties of iron and other properties such as moldability are often incompatible.
Si and Al added to improve magnetic properties in silicon steel sheets
The alloying elements such as have a strong tendency to deteriorate the workability and the blackening processability. The deterioration of the workability is because the addition of these alloying elements hardens the steel and increases large-sized precipitates.
Further, these elements are apt to undergo internal oxidation and not only deteriorate the adhesion of the blackening treatment film, but also deteriorate the gas releasing property. On the other hand, in drawing steel sheets with excellent workability, the fine texture of carbonitride is used to control the desirable texture (orientation of crystal grains) for workability. Has an adverse effect, and the resulting texture is also extremely undesirable for magnetic properties.

As described above, the concept of the composition and the metallurgical structure are completely different between the magnetic characteristics and the workability.
Conventionally, no steel has been obtained that simultaneously satisfies these various properties.

In view of the above situation, the present inventors have conducted research to find a composition of steel that is compatible with magnetic properties and workability, and as a result, it is possible within a limited composition range. I found that.

Here, the gist of the present invention is a thin steel sheet having the following composition.

% By weight, C: 0.005% or less, Si: 0.10%
Below, Mn: 0.5% or less, P: 0.02% or less, S: 0.005%
Below, Sol.Al: 0.005 to 0.015%, N: 0.004% or less,
O: 0.003% or less, B: 0.002% or less, and B / N
Is 0.1 or more and less than 0.5, and the balance is Fe and inevitable impurities.

[0014]

[Function] For melting steel, Si and Al are usually used as deoxidizing agents.
Is used. As a result of first studying these elements, the present inventors have found that it is necessary to control the addition amount of these elements within a specific range. Since these elements are deoxidized, it is necessary to add them to some extent.However, if the content of both of these elements is small, the oxygen level in the steel becomes high due to insufficient deoxidation, and large oxide-based precipitates are formed. The moldability is remarkably deteriorated by increasing the number of cracks during bending. On the other hand, when only the Si content is excessively large, the residual gas emission after the blackening treatment increases, and the adhesion of the blackening treatment film decreases. I'm not sure why, but
This is probably because the internal oxidation by Si is increased. Also,
If only the Si content is too large, the strength of the steel increases and workability tends to deteriorate. When only the Al content becomes excessive, the precipitation amount of AlN increases, the characteristics in a low magnetic field deteriorate, and the texture which is disadvantageous to the magnetic characteristics easily develops.
Since Al promotes internal oxidation like Si, if the amount of Al increases, the amount of residual gas released increases and the adhesion of the blackening treatment film deteriorates. Therefore, it is necessary to add Al and Si within an appropriate range so that these properties are not impaired.

Next, as a result of an examination focusing on B, which is considered to have a relatively small adverse effect on the magnetic properties among the nitride-forming elements, when a trace amount of B is contained, AlN and BN are complex-precipitated. It was clarified that the precipitates in No. 1 became larger and the magnetic properties were improved, and that the hardenability of the weld was improved and the strength of the weld was increased. However, B /
If the ratio of N exceeds a certain value, a texture, which is disadvantageous to the moldability, develops, so the amount thereof needs to be adjusted according to the amount of N.

By the above composition determined by combining these findings, a thin steel sheet having excellent magnetic properties, forming workability, spot weldability, blackening treatment property and gas releasing property can be obtained.

The reasons for limiting the content of each component will be described below. In addition, all "%" regarding a component content means "weight%."

C, S, N, O (oxygen): C is a carbide, S
Is a sulfide, N is a nitride, and O is an oxide in the steel, which deteriorates magnetic properties and workability. Especially for C to avoid magnetic aging,
It should be 0.005% or less, preferably 0.003% or less. S is 0.
It is 005% or less, preferably 0.003% or less, N is 0.004% or less, preferably 0.003% or less, and O is 0.003% or less.

P: P increases the strength of steel and deteriorates formability, so its content is made 0.02% or less.

Si: Si is added as a deoxidizer, but 0.10%
When the content exceeds 0.10%, not only the residual gas emission after the blackening treatment remarkably increases, but also the adhesion of the blackening treatment film is deteriorated and the workability is deteriorated. Therefore, the content is set to 0.10% or less.

Mn: Mn is weaker than Si but has an effect of deoxidizing and also has an effect of preventing hot embrittlement due to S.
Add within the range where the content does not exceed 0.5%. If it exceeds 0.5%, the magnetic properties and workability will deteriorate, so the content should be 0.5% or less. The desirable content is 0.3% or less.

Sol.Al: Al is a strong deoxidizer, but Sol.Al.
If the Al content is less than 0.005%, the deoxidation will be insufficient, the oxygen level will increase, and oxide precipitates will increase, deteriorating workability and magnetic properties, so the lower limit is made 0.005%. On the other hand, So
If the Al content exceeds 0.015%, a large amount of fine AlN precipitates, deteriorating the magnetic properties, so the upper limit is made 0.015%.

B: B has the effect of fixing N as BN to prevent the deterioration of formability due to aging, and also has the effect of improving the strength of the spot welded portion. Further, in the present invention, B is a necessary element in order to avoid the deterioration of the magnetic characteristics due to a small amount of Sol.Al. However, its content is 0.0
If it exceeds 02%, the magnetic properties may rather deteriorate due to an increase in precipitates, so the content is made 0.002% or less.

B / N ratio: If the B / N ratio is less than 0.1, the above effect of adding B cannot be obtained. On the other hand, the B / N ratio is 0.5
% Or more, a texture, which is disadvantageous to moldability, develops,
The B / N ratio is set to 0.1 or more and less than 0.5 in order to impair the formability.

The desirable production conditions of the thin steel sheet of the present invention having the above composition will be illustrated below.

First, the slab heating temperature in the hot rolling step is appropriately 1100 to 1250 ° C. If the heating temperature is too high, fine MnS precipitates during hot rolling, impairing magnetic properties.
On the other hand, if the heating temperature is too low, it becomes difficult to secure the following hot rolling finishing temperature. Higher hot rolling finish temperature generally improves magnetic properties and workability, so 800 ° C or higher is desirable. The coiling temperature after hot rolling may be selected in the range of 400 to 700 ° C. Generally, low temperature winding is better for moldability, and high temperature winding is better for magnetic characteristics. Taking these harmony into consideration, a coiling temperature of 550 to 650 ° C is suitable.

The cold rolling reduction ratio may be in the range of 40 to 80%. Particularly, if the rolling reduction is about 60 to 70%, the balance between magnetic properties and workability is improved. If necessary, cold rolling including intermediate annealing may be performed twice or more, but sufficient performance can be obtained even by a single cold rolling method with a simple manufacturing process.

Annealing after cold rolling is preferably carried out in the range of 700 to 950 ° C. This lower limit is the temperature required for recrystallization,
The upper limit is the temperature determined by the Ac ₃ transformation point of the material. Outside this range, both formability and magnetic properties deteriorate. The annealing may be box annealing, but continuous annealing is preferable in consideration of economic efficiency and process shortening. After annealing, the rolling reduction is 1.5 to adjust the surface texture.
% Or less skin pass rolling may be performed.

[0029]

EXAMPLE Steels having the compositions shown in Table 1 were melted and hot-rolled and cold-rolled under the following conditions to obtain thin steel plates having a thickness of 0.5 mm. The heating temperature for hot rolling was 1200 ° C, the finishing temperature for rolling was 850 ° C, and cooling was performed in a pattern corresponding to coil winding at 550 ° C. After pickling, cold rolling was performed at a reduction rate of 80%. Then, after annealing at 850 ° C for 1 minute, various characteristics were investigated.

The magnetic characteristics were obtained by punching out a ring-shaped test piece.
After stress relief annealing at 600 ℃ × 15 minutes, the magnetic permeability (0.35O
The value at e) and the coercive force (at 10 Oe) were measured.

The workability is the Rankford value in the tensile test.
(r value) and a flat plate bending test. The larger the r value, the more complicated the molding process can be. That is, the larger the r value, the better. In the bending test, the presence or absence of cracks in 180 ° contact bending was examined.

The spot weldability was determined by measuring the shear tensile strength by a tensile test after overlaying and welding steel sheets having the same composition.

The blackening property is 600 ° C. in a CO--CO ₂ atmosphere.
After the treatment for 15 minutes, the magnetite coating on the surface was peeled off with an adhesive tape and evaluated.

The gas releasing property is 400 to 500 ° C. by subjecting the material after blackening treatment under the above conditions to gas chromatography.
The emission peak of the residual gas in was measured and evaluated.

The test results are shown in Table 2. Invention Steels A to D
It can be seen that each of them shows extremely excellent performance. On the other hand, the comparative steel E having a low Al has poor workability, particularly bending workability. In Comparative Steel F with high Si, the amount of gas released was large, the adhesion of the blackening film was poor, and the workability was poor. In Comparative Steel G containing a large amount of Al, the magnetic properties were slightly poor and the amount of gas released was large. In Comparative Steel H containing too much B, the Rankford value is low and complicated forming is difficult. Comparative Steel I, which does not contain B, is inferior in magnetic properties and spot welding strength.

If the range of the present invention is deviated in this way, it is not possible to completely satisfy all of the performances required for the magnetic shield material for CRT and the frame material. On the other hand, the steel of the present invention satisfies all the performances without any loss.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

The thin steel sheet of the present invention has not only the magnetic characteristics required as a magnetic shield material, but also the characteristics required as a CRT material such as workability and gas releasing property. Moreover, it does not contain expensive alloying elements other than a trace amount of B, and the manufacturing method is substantially the same as that of a normal cold-rolled steel sheet, and can be manufactured at low cost. It goes without saying that the steel sheet of the present invention can be used for various magnetic shields other than CRTs.

Claims (1)

[Claims] [Claim 1] C: 0.005% or less by weight%, Si: 0.10%
Below, Mn: 0.5% or less, P: 0.02% or less, S: 0.005%
Below, Sol.Al: 0.005 to 0.015%, N: 0.004% or less,
O: 0.003% or less, B: 0.002% or less, a B / N ratio of 0.1 or more and less than 0.5, and the balance consisting of Fe and unavoidable impurities.