JP2007066970A - Electromagnetic shield material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tubular electromagnetic shield material employing a steel pipe. <P>SOLUTION: A steel pipe having a composition containing 0.01% or less of C, 95% or more of Fe, or further containing a proper amount of Si and Al, or a proper amount of Cr is preferably subjected to shrink rolling or further subjected to annealing treatment, thus obtaining a steel pipe having such a composition as the three-dimensional random strength ratio of X ray is 3.0 or above, the r value is 2.0 or above, and the average crystal grain size is 20 μm or above in the crystal orientation in which <100> is oriented in the circumferential direction and <011> is oriented in the rolling direction. When a tubular electromagnetic shield material is composed using that steel pipe, electromagnetic shield characteristics are enhanced remarkably. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electromagnetic shielding material, and more particularly, to an electromagnetic shielding material having a pipe shape that is excellent in electromagnetic shielding characteristics.

Conventionally, a thin plate or a thick plate made of a material excellent in electromagnetic characteristics has been used as an electromagnetic shielding material. Examples of a material having excellent electromagnetic characteristics include a non-oriented electrical steel sheet in which the easy magnetization direction <100> is oriented in the in-plane direction, and a directionality in which the easy magnetization direction <100> is strongly oriented parallel to the rolling direction. There are silicon steel sheets.
However, when these steel plates having excellent electromagnetic characteristics are used for, for example, magnetic shielding, a process is required in which these steel plates are processed, joined by welding or the like, and assembled into a desired shape. As described above, when a steel plate is used as a raw material, there is a problem that a complicated process is required and an unsteady part such as a welded part is formed, resulting in deterioration of electromagnetic shielding characteristics. In order to avoid such a problem, it is conceivable to use a steel pipe having excellent electromagnetic characteristics as a material.

Making a steel pipe excellent in electromagnetic characteristics by electro-magnetic welding of an electromagnetic steel sheet has a problem that the electromagnetic steel sheet has a high Si content and is difficult to be electro-welded, and the electromagnetic characteristics of the ERW weld are deteriorated. Although it is conceivable to use a billet of electromagnetic steel to make a seamless steel pipe excellent in electromagnetic characteristics, there is a problem that the electromagnetic steel has low ductility and it is difficult to make a pipe.
To deal with such problems, for example, Patent Document 1 uses a steel with a high Si and Al composition, and adjusts the hot extrusion conditions and hot rolling conditions to appropriate ranges to make seamless pipes. There has been proposed a method for manufacturing an electromagnetic material tube, in which rolling is performed at a temperature lower than the crystal temperature and further final annealing is performed. However, the technique described in Patent Document 1 has a problem that the hot extrusion process is an essential process and the manufacturing cost is high.

Also, in Patent Document 2, a steel slab or slab having a steel composition containing 99.5% or more Fe and the balance being impurities is heated to 1100 to 1350 ° C. and hot-rolled to obtain a raw material. And the manufacturing method of the electromagnetic steel pipe heat-processed at 500-1000 degreeC is proposed. According to the technique described in Patent Document 2, it is said that a steel pipe having sufficient characteristics for an electromagnetic shield can be obtained. However, this technique merely aims at grain growth by heat treatment, and the orientation of crystal orientation. Therefore, there is a problem that the characteristics are insufficient for the purpose of use that requires higher electromagnetic shielding characteristics.
JP-A-2-236226 Japanese Examined Patent Publication No. 7-68579

The object of the present invention is to solve the above-described problems of the prior art and to propose a pipe-shaped electromagnetic shielding material using a steel pipe that is excellent in electromagnetic shielding characteristics.
In the present invention, “excellent in electromagnetic shielding characteristics” means that the influence of an external magnetic field is not easily received inside the electromagnetic shielding material, and that the magnetic field inside the electromagnetic shielding material is difficult to be exposed to the outside. To do. It is difficult to receive the influence of an external magnetic field inside the electromagnetic shielding material because the magnetic field strength ratio (internal magnetic field) / (external magnetic field) is small, and the magnetic field inside the electromagnetic shielding material is exposed to the outside. What is difficult is that (external magnetic field) / (internal magnetic field) is small.

In the present invention, the magnetic field strength ratio is the value obtained by measuring the internal magnetic field of the electromagnetic shielding material with the external magnetic field strength being 50 gauss, and using the same thickness of the electromagnetic shielding material (reference material). The electromagnetic shielding characteristics shall be evaluated in comparison with the magnetic field strength ratio. In addition, as a reference material, in this invention, the material as it is made as a pipe which does not add an additional process (as an electric resistance steel pipe) shall be used.
The electromagnetic shielding properties qualitatively improve as the thickness of the electromagnetic shielding material increases. Therefore, when the thickness is different, the value of the magnetic field strength ratio itself is not important. In the present invention, when the magnetic field strength ratio is small compared to the magnetic field strength ratio of the electromagnetic shielding material (reference material) having the same thickness, the electromagnetic shielding material is “excellent in electromagnetic shielding characteristics”.

  In the present invention, the magnetic field strength ratio is determined with the external magnetic field strength being 50 gauss and the electromagnetic shielding properties are evaluated, but the electromagnetic shielding characteristics only in the 50 gauss region are not evaluated. When the external magnetic field is changed to around 0 to 100 gauss, the electromagnetic shielding properties are gradually improved when the external magnetic field strength is 20 gauss or more. Therefore, in the present invention, the electromagnetic shielding property is evaluated by using an external magnetic field strength of 50 gauss to represent the region.

  The electromagnetic shielding property from the viewpoint of generating a magnetic field inside the electromagnetic shielding material and not leaking the magnetism to the outside also shows the same tendency as when evaluated using an external magnetic field. Therefore, in the present invention, the external magnetic field strength is set to 50 gauss, the external magnetic field is added, the internal magnetic field of the electromagnetic shielding material is measured, and the electromagnetic shielding property is evaluated.

In order to achieve the above-mentioned problems, the present inventors diligently studied various factors affecting the electromagnetic characteristics of steel pipes. As a result, in order to further improve the electromagnetic properties of steel pipes, especially soft magnetic properties,
(B) adjusting the crystal structure in which the <100> direction in the circumferential direction of the steel pipe and the <011> direction in the rolling direction are strongly oriented;
(B) making the crystal grain size relatively coarse, preferably 20 μm or more;
(C) Eliminating unsteady parts such as ERW welds,
(D) the C content is less than 0.01% by mass,
Found that is important. And for further improvement of electromagnetic characteristics,
(E) Annealing treatment is performed at a temperature of 750 ° C. or more and Ac ₁ transformation point or less after the steel pipe is reduced in diameter or processed into a desired shape.
I found that is desirable. It has been found that the use of such a steel pipe improves the electromagnetic shielding characteristics of the pipe-shaped electromagnetic shielding material.

The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) A pipe-shaped electromagnetic shielding material using a steel pipe, wherein the steel pipe contains, by mass%, C: less than 0.01%, Fe containing 95% or more, and <100> direction in the circumferential direction. An electromagnetic shielding material excellent in electromagnetic shielding properties, characterized by being a steel pipe having a structure in which the three-dimensional random intensity ratio of X-rays is 3.0 or more in a crystal orientation in which the <011> direction is oriented in the rolling direction.

(2) The electromagnetic shielding material according to (1), wherein an r value in the rolling direction of the steel pipe is 2.0 or more.
(3) The electromagnetic shielding material according to (1) or (2), wherein the structure of the steel pipe is a structure having an average crystal grain size of 20 μm or more.
(4) In any one of (1) to (3), the composition of the steel pipe is, by mass%, including C: less than 0.01%, Si: 0.45% or less, Mn: 0.1-1.4%, S: 0.01 %, P: 0.025% or less, Al: 0.01 to 0.06%, N: 0.005% or less, and the composition comprising the balance Fe and unavoidable impurities.

(5) In any one of (1) to (3), the composition of the steel pipe includes, by mass%, C: less than 0.01%, Si: more than 0.45%, 3.5% or less, Mn: 0.1 to 1.4%, An electromagnetic shielding material comprising: S: 0.01% or less, P: 0.025% or less, Al: more than 0.06%, 0.5% or less, N: 0.005% or less, and the remaining Fe and inevitable impurities.
(6) In (4) or (5), in addition to the composition of the steel pipe, by mass%, the following groups A to C: Group A: Ti: 0.05% or less, Nb: 0.05% or less, B: 0.005% or less One or more of these,
Group B: Cr: 5% or less, Ni: 5% or less, Mo: 0.05% or less
Group C: Ca: 0.005% or less, REM: 0.05% or less, 1 type or 2 types
An electromagnetic shielding material comprising one group or two or more groups selected from among the above.

  ADVANTAGE OF THE INVENTION According to this invention, the electromagnetic shield material excellent in electromagnetic shielding property can be manufactured easily and cheaply, and there exists a remarkable effect on industry. In addition, according to the present invention, there is no unsteady portion, and there is an effect that there is little deterioration of the electromagnetic shielding characteristics.

The electromagnetic shielding material of the present invention is a tubular electromagnetic shielding material using a steel pipe. The steel pipe to be used is a steel pipe having a composition containing less than 0.01% C: less than 95% Fe and 95% Fe or more.
First, the reasons for limiting the composition of the steel pipe used in the present invention will be described. Hereinafter, mass% in the composition is simply referred to as%.
C: Less than 0.01% Since C is an element that deteriorates electromagnetic characteristics, it is desirable to reduce it as much as possible from the viewpoint of electromagnetic shielding properties, and it is limited to less than 0.01%. In addition, Preferably it is 0.004% or less. In addition, since the reduction of C of 0.001% or less causes the refining time to be abnormally prolonged and increases the refining cost, the lower limit is desirable from an economical viewpoint.

Fe: 95% or more As the impurities increase, the hindrance to crystal grain growth increases and the magnetic shielding property decreases, so it is desirable to have a high purity with few impurities. In the present invention, the content of Fe is set to 95% or more in order to regulate the amount of impurities and increase the purity. In addition, Preferably it is 98% or more.
The basic composition of the present invention is as described above. However, in order to further improve electromagnetic shielding properties, Si and Al are added as necessary, or Cr and Ni are further improved in order to improve electromagnetic characteristics in a high frequency range. Etc. may be included. For applications where such excellent electromagnetic shielding properties are required, it is contained in mass%, including C: less than 0.01%, Si: 0.45% or less, Mn: 0.1-1.4%, S: 0.01% or less, P : 0.025% or less, Al: 0.01 to 0.06%, N: 0.005% or less, the composition of high-purity system consisting of the balance Fe and unavoidable impurities, or mass%, C: less than 0.01%, and Si : More than 0.45%, 3.5% or less, Mn: 0.1 to 1.4%, S: 0.01% or less, P: 0.025% or less, Al: more than 0.06%, 0.5% or less, N: 0.005% or less, balance Fe and inevitable A high-purity composition composed of impurities is preferable.

Si: 0.45% or less, or more than 0.45% and 3.5% or less
Si acts as a deoxidizer and contains at least 0.01% or more. Si is an element that improves electromagnetic properties, especially iron loss properties, and increases the strength of shield materials (steel pipes) by solid solution, but inclusion exceeding 0.45% reduces ERW weldability. Tend. For this reason, it is preferable to limit Si to 0.45% or less. In addition, when particularly excellent electromagnetic shielding properties are required, Si can be more than 0.45% and 3.5% or less. When Si exceeds 3.5%, the magnetic flux density (B) in the low H (magnetic field) region is excellent, but the saturation magnetic flux density B in the high H region is lowered, and the electric resistance weldability is remarkably deteriorated.

Mn: 0.1-1.4%
Mn is an element that combines with S to form MnS, removes the adverse effects of S and improves hot workability, and is preferably contained according to the S content. It is preferable to make it. Mn is an element that increases the strength of the shield material (steel pipe) by solid solution, and it is desirable to contain it according to the strength of the desired shield material (steel pipe), but inclusion over 1.4% deteriorates toughness. Let For this reason, it is preferable to limit Mn to the range of 0.1 to 1.4%. In addition, More preferably, it is 0.3 to 0.6%.

S: 0.01% or less S is present as an inclusion in steel, lowers workability and inhibits electromagnetic shielding properties as MnS, so it is desirable to reduce it as much as possible. For these reasons, S is preferably limited to 0.01% or less. However, excessive reduction of S leads to an increase in refining costs, so 0.001% or more is desirable. In addition, when Si and Al are contained in a large amount for improving electromagnetic characteristics, it is preferable to reduce S to 0.001% or less for improving punchability.

P: 0.025% or less P is an element that dissolves and contributes to an increase in the strength of the shielding material (steel pipe) and improves the electromagnetic shielding properties. However, P has a strong tendency to segregate at the grain boundary and moves the domain wall. In the present invention, it is preferably limited to 0.025% or less. In addition, since excessive reduction leads to a rise in smelting cost, it is desirable to set the lower limit to about 0.005%.

Al: 0.01 to 0.06%, or more than 0.06% and 0.5% or less
Al is an element that acts as a deoxidizer and forms AlN to reduce the amount of dissolved N. Such an effect is recognized at a content of 0.01% or more, but depending on the N content, a content exceeding 0.06% often increases the amount of inclusions and lowers the electromagnetic shielding properties. For this reason, it is preferable to limit Al to the range of 0.01 to 0.06%. More preferably, it is 27 / 14N or more and 3 × 27 / 14N or less in relation to the N content. In the case of containing a strong nitride-forming element such as Ti or b, the amount of Al may be small. Al, together with Si, is an element that improves electromagnetic shielding properties. In particular, when excellent electromagnetic shielding properties in a low H (magnetic field) region are required, Al is contained more than 0.06% and 0.5% or less. be able to. However, Al content exceeding 0.5% may cause deterioration of electromagnetic characteristics.

N: 0.005% or less N increases the strength as an interstitial solid solution element in steel, but increases the internal stress and decreases the electromagnetic shielding properties, and forms AlN to adversely affect the electromagnetic shielding properties. For this reason, it is desirable to reduce N as much as possible, but it is acceptable up to 0.005%. For this reason, it is preferable to limit N to 0.005% or less. The lower limit is about 0.001% in relation to smelting costs. In the case where a large amount of Al is contained for improving electromagnetic shielding properties, it is desirable to reduce N to 0.0025% or less so as not to cause deterioration of electromagnetic shielding properties due to AlN.
In addition to the above-mentioned components, the following groups A to C: Group A: Ti: 0.05% or less, Nb: 0.05% or less, B: 0.005% or less, or one or more of the following:
Group B: Cr: 5% or less, Ni: 5% or less, Mo: 0.05% or less
It is preferable to contain 1 group or 2 groups or more selected from 1 type or 2 types in C group: Ca: 0.005% or less and REM: 0.05% or less.

Group A Ti, Nb, and B are elements that form carbides, nitrides, and the like to increase the strength of the shielding material (steel pipe), and can be selected and contained as necessary. Ti: 0.05%, Nb: 0.005%, B: If the content exceeds 0.005%, the electromagnetic shielding properties are often deteriorated. Therefore, Ti: 0.05%, Nb: 0.05%, B: 0.005% should be the upper limit. Is preferred.
Group B: Cr, Mo, and Ni are elements that improve hardenability and corrosion resistance, and can be selected and contained as necessary. If the content exceeds Cr: 5%, Ni: 5%, and Mo: 0.05%, the electromagnetic shielding properties are deteriorated, so Cr: 5%, Mo: 0.05%, and Ni: 5% are preferably set as upper limits, respectively.

  Group C: Ca and REM are elements that control the form of inclusions and improve corrosion resistance, and can be selected and contained as necessary. When used in an environment where even a slight amount of water comes into contact, it is preferable to contain Ca and REM, and the corrosion resistance is improved. In addition, the content exceeding Ca: 0.005% and REM: 0.05% deteriorates the magnetic properties. For this reason, it is preferable to make Ca: 0.005% and REM: 0.05% the upper limit.

The balance other than the above components is Fe and inevitable impurities.
In addition to the above composition, the steel pipe used in the present invention has a three-dimensional random intensity ratio of X-rays of a crystal orientation in which the <100> direction in the circumferential direction and the <011> direction in the rolling direction are oriented. Having an organization that is more than that.
Electromagnetic shield of a steel pipe used as an electromagnetic shield material by making the crystal orientation the crystal orientation in which the <100> direction which is the easy axis of magnetization in the circumferential direction and the <011> direction is oriented in the rolling direction of the steel pipe The property is remarkably improved. In the present invention, the X-ray three-dimensional random intensity ratio of the crystal orientation in which the <100> direction is oriented in the circumferential direction and the <011> direction is oriented in the rolling direction is 3.0 or more. If the three-dimensional random orientation strength is less than 3.0, excellent electromagnetic shielding properties cannot be obtained. In addition, Preferably it is 8.0 or more, More preferably, it is 10 or more.

In the tube-shaped electromagnetic shielding material, the magnetic field application direction does not necessarily coincide with the easy magnetization crystal orientation of the steel pipe, but the crystal in the circumferential direction and rolling direction of the steel pipe has the crystal orientation described above. By using the adjusted steel pipe, the electromagnetic shielding characteristics are remarkably improved.
Here, the three-dimensional random intensity ratio is an index indicating the presence / absence of orientation of a specific crystal orientation. The crystal orientation in the case of no orientation (random) is defined as 1, and the specific crystal orientation with orientation. Is standardized in a random case. A larger value means stronger orientation.

Specifically, an incomplete pole figure by a reflection method is measured, and the integrated intensity of a specific crystal orientation (in the present invention, a crystal orientation in which the <100> direction in the circumferential direction and the <011> direction in the rolling direction are oriented) is obtained. Standardized with random strength. The same value can be obtained from the measurement of a complete pole figure using both the reflection method and the transmission method.
Furthermore, the steel pipe used in the present invention has the above-described crystal orientation and a structure having an average crystal grain size of preferably 5 μm or more, more preferably 10 μm or more, further preferably 20 μm or more, and desirably 40 μm or more. When the average crystal grain size is less than 5 μm, it is not possible to ensure excellent electromagnetic shielding characteristics even if <100> is oriented in the circumferential direction and <011> is oriented in the rolling direction. In the present invention, the crystal grains are preferably relatively coarse from the viewpoint of obtaining excellent electromagnetic shielding characteristics. In particular, when the average crystal grain size is 20 μm or more, further 40 μm or more, a steel pipe having more excellent electromagnetic shielding characteristics can be obtained.

The steel pipe used in the present invention preferably has an r value in the rolling direction of 2.0 or more. When the r value in the rolling direction is 2.0 or more, excellent electromagnetic shielding characteristics can be secured. When the r value is less than the above value, it is difficult to ensure excellent electromagnetic shielding characteristics. The r value in the rolling direction is preferably 4.0 or more, more preferably 8.0 or more.
The r value is conventionally used as an index of formability, but the steel pipe used in the present invention has a crystal orientation in which <100> is oriented in the circumferential direction and <011> is oriented in the rolling direction. In conjunction with the improvement of the shield characteristics, the r value in the rolling direction and the electromagnetic shield characteristics are well matched, and the r value can also be used as an index of the electromagnetic shield characteristics.

In the present invention, the r value is measured by attaching a strain gauge in the tensile direction of the test piece and in the direction perpendicular thereto, conducting a tensile test, taking in the displacement in each direction one by one, and extending around 6 to 7%. The r value is calculated using the displacement at. The reason why the r value is calculated at an elongation of 6 to 7% is that the calculation is performed in a plastic deformation region exceeding the yield point elongation region. The r value is the following equation: r value = −1 / {1 + ln (L ₀ / L) / ln (W ₀ / W)}
Where L: length of the specimen in the tensile direction
L ₀ : initial length of the specimen in the tensile direction
W: Length of the specimen in the width direction
W ₀ : Calculate using the initial length in the width direction of the test piece. When the yield point elongation exceeds 7%, the r value is measured at the plastically deformed portion. In addition, it may be evaluated with a JIS No. 12 piece (arc-shaped test piece) or with a flat plate test piece obtained by flattening a steel pipe, and if the area where the strain gauge can be attached is secured in the parallel part of the test piece The test piece itself is not particularly limited, such as JIS No. 5 or No. 13 B. However, when measuring the r value in the circumferential direction, it must be flattened.

Below, the preferable manufacturing method of the steel pipe used by this invention is demonstrated.
In the present invention, a steel pipe having the above composition is heated as a raw material and subjected to reduction rolling.
The manufacturing method of the steel pipe used as a raw material in the present invention is not particularly limited except that it has the above-described composition. Either a seamless steel pipe manufactured by a generally known method or a welded steel pipe such as an ERW steel pipe manufactured by a generally known method can be suitably used.

The method for heating the steel pipe as the raw material during the diameter reduction rolling need not be particularly limited. Either heating by a heating furnace, heating by induction heating, or the like can be used. In addition, what is pipe-formed and manufactured hot like a seamless steel pipe can be directly sent to a reduced diameter rolling apparatus and reduced in diameter after the production. It is also possible to reduce the diameter after reheating.
In the case of reheating, the heating temperature of the reduced diameter rolling is preferably 1100 ° C. or less. When the heating temperature exceeds 1100 ° C, the surface properties of the steel pipe deteriorate. When using after rolling or polishing or etching, it is not necessary to limit the upper limit of the heating temperature. In addition, it is preferable that heating temperature shall be 750 degreeC or more. When the heating temperature is less than 750 ° C., the deformation resistance becomes high and it becomes difficult to secure a diameter reduction ratio equal to or higher than a predetermined value, and the distortion of the diameter reduction rolling remains in the cooled steel pipe, and the electromagnetic shielding characteristics are deteriorated. The lower limit value of the heating temperature described above is necessary to ensure the rolling end temperature of the reduced diameter rolling equal to or higher than the predetermined temperature. Note that, in a steel pipe having a welded portion such as an electric resistance steel pipe, it is preferable that the heating temperature is set to the Ac ₃ transformation point or more from the viewpoint of removing the unsteady portion and improving the electromagnetic shielding characteristics of the entire steel pipe.

The reduction rolling is preferably a rolling with a reduction ratio of 15% or more and a rolling end temperature of 730 ° C. or more and 900 ° C. or less. As a result, the steel pipe structure can be made to have a crystal orientation in which the <100> direction is oriented in the circumferential direction and the <011> direction is oriented in the rolling direction, and the grains grow and have relatively coarse crystals.
When the diameter reduction ratio is less than 15%, the amount of diameter reduction is insufficient, and the crystal is difficult to be oriented in the desired crystal orientation described above. On the other hand, the upper limit of the diameter reduction rate is determined by the product size and the capability of the rolling mill and is not particularly limited, but is preferably about 85 to 90%. More preferably, the diameter reduction rate is 45 to 80%.

  The rolling end temperature of the reduced diameter rolling is preferably 900 ° C. or lower. When the rolling end temperature of the reduced diameter rolling becomes higher than 900 ° C., the reduced diameter rolling is completed in the austenite region, the orientation is not oriented in the desired crystal orientation described above, the random orientation is obtained, and the electromagnetic characteristics are increased. Does not improve. In addition, the temperature measured on the steel pipe surface shall be used for the rolling completion temperature here. The rolling end temperature is preferably 730 ° C. or higher. If the temperature is lower than 730 ° C., the strain of reduced diameter rolling remains, and it becomes difficult to obtain a crystal orientation in which the <100> orientation is oriented in the circumferential direction and the <011> orientation is oriented in the rolling direction, and electromagnetic characteristics are deteriorated. More preferably, it is 750 ° C. or higher.

  In the present invention, it is more preferable that the diameter reduction rolling be reduced diameter rolling with a reduction ratio of 40% or less, or a reduction ratio of 40% or less. When the thickness reduction ratio or the thickness increase ratio exceeds 40%, the rotation of the crystal orientation becomes too large, affecting the orientation of the crystal orientation, and the desired orientation of the crystal orientation cannot be obtained. For this reason, it is more preferable that the thickness reduction ratio of the reduced diameter rolling is limited to 40% or less, or the thickness increase ratio is limited to 40% or less. In addition, when using it in the state as reduced diameter rolling, it is more preferable to make the thickness increase rate 10 to 25%. On the other hand, when the annealing treatment is performed after the diameter reduction rolling, it is more preferable to set the thickness reduction rate to 10 to 25%. By limiting to the range as described above, the orientation in the <100> direction in the circumferential direction is strengthened, and accordingly, the electromagnetic shielding characteristics are further improved.

The thickness reduction rate, the rate of increase of wall thickness, that is, the rate of change in thickness is the following formula: rate of change in thickness = [{(thickness of reduced diameter rolling) − (thickness of blank tube)} / (thickness of blank tube) )] X 100 (%)
The value calculated in is used.
In the present invention, it is preferable to perform an annealing treatment at a temperature not lower than 750 ° C. and not higher than the Ac ₁ transformation point after the above-described reduction rolling or after further processing into a desired shape.

By performing the annealing treatment at a temperature of 750 ° C. or more and below the Ac ₁ transformation point, crystal grains further grow and electromagnetic shielding characteristics are further improved. When the annealing temperature is less than 750 ° C., the growth of crystal grains is slow, and it takes a long time to grow to crystal grains having a desired grain size. On the other hand, when the annealing temperature rises beyond the Ac ₁ transformation point, the crystal orientation is broken and randomization begins. For this reason, the annealing treatment was performed at a temperature of 750 ° C. or higher and Ac ₁ transformation point or lower.

The cooling after annealing is preferably slow cooling from the viewpoint of electromagnetic shielding characteristics. The effect of the annealing treatment is the same both after the reduced diameter rolling and after being processed into a desired product shape. By optimizing the conditions for the annealing treatment, the average crystal grain size can be easily made 20 μm or more, preferably 40 μm or more.
In addition, it is preferable to perform a cold drawing process after the diameter reduction rolling and before the above-described annealing treatment. Thereby, it becomes a steel pipe which has the further outstanding electromagnetic shielding characteristic. This is probably because cold strain is applied in a state in which the rotation of crystal grains is restricted to some extent by cold drawing, so that crystal grain orientation and grain growth are promoted during annealing. In addition, it is preferable that the cold drawing process is a process with a reduction in area of 15% or more and 60% or less. The area reduction ratio is the following formula: Area reduction ratio (%) = {(steel pipe cross-sectional area before drawing)-(steel pipe cross-sectional area after drawing)} /
(Cross-sectional area of steel pipe before drawing) × 100
It shall be calculated in

A thin steel strip having the composition shown in Table 1 was roll-formed to form an open pipe, and an ERW steel pipe obtained by electro-welding the end portion was used as a material steel pipe.
After heating these steel pipes to 900-1000 ° C, they were subjected to reduction rolling under the conditions shown in Table 2 (diameter reduction rate, wall thickness fluctuation rate: thinning (-) / thickening (+), rolling end temperature). The outer diameter was 34 mmφ and the inner diameter was 25 mmφ. When the wall thickness variation rate was within 2%, the steel pipes having the same wall thickness were regarded as being evaluated. Some steel pipes were further annealed. The annealing treatment was a treatment held at 875 ° C. In addition, the electric resistance welded steel pipe (raw material steel pipe) as it was made into a pipe without performing diameter reduction rolling or annealing treatment was used as a comparative material.

The obtained steel pipe was subjected to measurement of electromagnetic shielding characteristics, investigation of structure, and measurement of r value. The measurement method was as follows.
(1) Electromagnetic shielding characteristics A test material having a length of 300 mm was cut out from the obtained steel pipe and used as an evaluation material for evaluating the electromagnetic shielding characteristics. In the magnetization application method, (a) a magnetic field is applied in a direction parallel to the longitudinal direction of the tube (FIG. 1), and (b) a magnetic field is applied in a direction orthogonal to the longitudinal direction of the tube (FIG. 1). 2). The external magnetic field was changed in the range of 0 to 90 gauss. As shown in FIGS. 1 and 2, the internal magnetic field is measured by installing a gauss meter probe 3 inside the test material 1 and measuring it according to the external magnetic field generated by the exciting coil 2. (Internal magnetic field) / (External magnetic field)). It is also displayed in dB (= −20 × log (magnetic field strength ratio)) indicating the shielding effect.
(2) Structure A test material was sampled from the obtained steel pipe, and the crystal grain size and crystal orientation were measured.

  The crystal grain size was calculated using a straight line segment method for the L direction cross section of the steel pipe, etching with a corrosive solution: nital and observing with a microscope. The measurement position was the center of the plate thickness excluding the outermost layer of 100 μm. The lengths of 500 crystal grains along the L direction are measured, and the lengths of 500 crystal grains are similarly measured along the plate thickness direction. After dividing the length by the number of ferrite grains and calculating the grain size, the average was taken as the average grain size.

The crystal orientation was determined by measuring a three-dimensional random intensity ratio using an X-ray diffraction method. About the specimen obtained by flattening the steel pipe, a surface layer of 500 μm or more was removed by polishing, and a specimen having a mirror finish was collected from the vicinity of the thickness center of the steel pipe. These test pieces were further subjected to chemical polishing (corrosive solution: 2-3% hydrofluoric acid + hydrogen peroxide solution) in order to remove processing distortion during polishing.
About the obtained test piece for a measurement, the incomplete pole figure by the reflection method was measured using the X-ray diffraction apparatus. From the obtained results, the integrated strength of the crystal orientation in which the <100> direction in the circumferential direction of the steel pipe and the <011> direction in the rolling direction were oriented was normalized with the random strength to obtain a three-dimensional random strength ratio. Note that CuKα was used as the X-ray source.
(3) r value The r value was evaluated using a test piece obtained by flattening the obtained steel pipe or a test piece cut out from the steel pipe (JIS No. 12 test piece). The r value was measured in the same manner as described above.

  The obtained results are shown in Table 2.

The obtained electromagnetic shielding characteristics are shown in FIG. 3 (magnetic field applied in parallel to the longitudinal direction of the tube) and FIG. 4 (direction orthogonal to the longitudinal direction of the tube) in relation to the shielding effect (dB), the magnetic field strength ratio and the external magnetic field. Shows magnetic field application).
In all of the inventive examples, the <100> direction in the circumferential direction and the <011> direction in the rolling direction are strongly oriented, the X-ray three-dimensional random intensity ratio is 3.0 or more, the r value is 2.0 or more, and the average particle size is As shown in Fig. 3 and Fig. 4, it remains as an electric-welded steel pipe with an X-ray three-dimensional random intensity ratio of 1.0, an r value of 0.9, and an average particle diameter of 18 µm (steel pipe No. 103) Excellent electromagnetic shielding characteristics. In particular, the electromagnetic shielding properties of steel pipe (steel pipe No. 102) subjected to annealing treatment in addition to reduced diameter rolling are superior to those of ERW steel pipe (steel pipe No. 103).

  From Fig. 3, steel pipe No. 101 has an electromagnetic shielding effect with a magnetic field strength ratio of 0.1 or less (shielding effect: 20 dB or more) in an area where the magnitude of the external magnetic field is 10 gauss or more, and an area of 50 gauss or more. Then, the magnetic field strength ratio: 0.03 or less (shielding effect: 30 dB or more) has an electromagnetic shielding effect. Steel tube No. 102 has a magnetic field in the region where the magnitude of the external magnetic field is 10 gauss or more. Strength ratio: 0.03 or less (shielding effect: 30 dB or more) Electromagnetic shielding effect of 50 gauss or more, Magnetic field strength ratio: 0.01 or less (shielding effect: 40 dB or more) Is clear. Furthermore, steel pipe No. 101 and steel pipe No. 102 always have an electromagnetic shielding effect that is twice or more in an external magnetic field of 50 gauss or more as compared with an electric resistance steel pipe (steel pipe No. 103). . Also in FIG. 4 in the case where the external magnetic field application direction is orthogonal to the tube longitudinal direction, the electromagnetic shielding effect is slightly inferior to that in FIG.

That is, the material steel pipe having the composition within the scope of the present invention is preferably subjected to reduced diameter rolling or further annealing treatment to form a pipe-shaped electromagnetic shielding material using the steel pipe having a structure within the scope of the present invention. It can be set as the electromagnetic shielding material which has an electromagnetic shielding characteristic.
3 and 4, there is a tendency for the magnetic field strength ratio to smoothly transition in a region where the external magnetic field is 10 gauss or more, and that the magnetic field strength ratio is good when the external magnetic field is 50 gauss or more. This direction tends to be substantially saturated. For this reason, the electromagnetic shielding characteristics were evaluated using the magnetic field strength ratio when the external magnetic field was 50 gauss.
(Example 2)
A thin steel strip having the composition shown in Tables 1 and 3 was roll-formed to form an open pipe, and an electric-welded steel pipe obtained by electro-welding the ends was used as a material steel pipe.

  After heating these steel pipes to 900-1000 ° C., they were subjected to reduction rolling under the conditions shown in Table 4 (reduction rate, thickness fluctuation rate: thickness reduction (−) / thickening increase (+), rolling end temperature). did. A part of the obtained steel pipe was further subjected to cold drawing to obtain a steel pipe of the same size (outer diameter: 34 mmφ, inner diameter 25 mmφ). When the wall thickness variation rate was within 2%, the steel pipes having the same wall thickness were regarded as being evaluated. Moreover, when the thickness fluctuation exceeding 30% occurred, the steel pipe size after the diameter reduction rolling was considered to be the same by using the material pipe thickness changed in advance. Some steel pipes were further annealed. The annealing treatment was performed at a temperature in the range of 750 to 920 ° C.

The obtained steel pipe was subjected to measurement of electromagnetic shielding characteristics, investigation of structure, and measurement of r value. The measurement method was basically the same as in Example 1.
(1) Electromagnetic shielding characteristics A test material having a length of 300 mm was cut out from the obtained steel pipe and used as an evaluation material for evaluating the electromagnetic shielding characteristics. As shown in FIG. 1, the magnetization application method applied a magnetic field in a direction parallel to the longitudinal direction of the tube. The external magnetic field was 50 gauss. As shown in FIG. 1, the internal magnetic field is measured by installing a gauss meter probe 3 inside the test material 1 and measuring it according to the external magnetic field generated by the exciting coil 2, and measuring the magnetic field strength ratio (= (internal Magnetic field) / (external magnetic field)). The ratio of the obtained magnetic field strength ratio to the magnetic field strength ratio of the as-made ERW steel pipe (steel pipe No. 103) not subjected to the reduction rolling or annealing treatment obtained in Example 1, “the ratio of the magnetic field strength ratio” The electromagnetic shielding characteristics of each test material were evaluated.

Note that (2) the examination of the structure and (3) the measurement of the r value were the same as in Example 1.
The obtained results are also shown in Table 4.

  In all of the inventive examples, the <100> direction in the circumferential direction and the <011> direction in the rolling direction are strongly oriented, the X-ray three-dimensional random intensity ratio is 3.0 or more, the r value is 2.0 or more, and the average particle size is The ratio of the magnetic field strength ratio is 1.5 times higher than that of ERW steel pipe (steel pipe No. 103) (reference material), and it has excellent electromagnetic shielding characteristics. On the other hand, in the comparative example outside the scope of the present invention, the ratio of the magnetic field strength ratio is as low as less than 1.5 times, and no improvement in electromagnetic shielding characteristics is observed.

  Examples of the present invention (steel pipes No. 203, No. 204, No. 205, No. 208) have a three-dimensional random intensity ratio of X-rays of 7.6 or more, especially in the case of steel pipes No. 203, No. 204, No. 205. The X-ray three-dimensional random strength ratio is 8.0 or higher, and the ratio of magnetic field strength ratio is more than double that of ERW steel pipe (steel pipe No. 103) (reference material), and it has excellent electromagnetic shielding characteristics. is doing. Steel pipe No. 208 is an example in which the cold drawing after the diameter reduction rolling is performed, but it is shown that a good electromagnetic shielding effect can be secured even if the cold drawing is performed.

On the other hand, the comparative examples (steel pipes No. 201 and No. 206) are examples in which annealing treatment was performed in the austenite region exceeding the Ac ₁ transformation point after the diameter reduction rolling, and the rolling formed during the diameter reduction rolling. Since the texture collapses and is randomized, the X-ray three-dimensional random intensity ratio is low, the r value is low, the average particle size is large, and no improvement in electromagnetic shielding characteristics is observed.
Moreover, the comparative example (steel pipe No. 202) is an example in which only the annealing process is applied to the steel pipe as-is-sewn. Even if the annealing process is performed without performing the diameter reduction rolling, there is no formation of a rolling texture. The coarsening of the grains only occurs, the X-ray three-dimensional random intensity ratio is low, and the r-value is low, and no improvement in electromagnetic shielding characteristics is observed.

The comparative examples (steel pipes No. 206 and No. 207) are examples with a large wall thickness fluctuation rate. The increase and decrease of the thickness exceeding 40% is the structure in which the crystal rotates and the rolling texture during the diameter reduction rolling is optimal. Therefore, the three-dimensional random intensity ratio of X-rays is lowered and no improvement in electromagnetic shielding characteristics is observed. It should be noted that the steel pipe No.206 has performed an annealing treatment in the austenite region that exceeds the Ac ₁ transformation point, the organization has been randomized.

  Thus, according to the present invention, an electromagnetic shielding material excellent in electromagnetic shielding characteristics can be easily obtained.

It is a schematic diagram which shows the outline of the electromagnetic sealing characteristic measuring method. It is a schematic diagram which shows the outline of the electromagnetic sealing characteristic measuring method. It is a graph which shows the relationship between magnetic field strength ratio, a sealing effect, and external magnetic field strength. It is a graph which shows the relationship between magnetic field strength ratio, a sealing effect, and external magnetic field strength.

Explanation of symbols

1 Test piece 2 Excitation coil 3 Gauss meter probe

Claims (6)

  A tube-shaped electromagnetic shielding material using a steel pipe, wherein the steel pipe contains, by mass%, C: less than 0.01%, a composition containing Fe of 95% or more, a <100> direction in the circumferential direction, and rolling An electromagnetic shielding material excellent in electromagnetic shielding characteristics, characterized by being a steel pipe having a structure in which a three-dimensional random intensity ratio of X-rays is 3.0 or more in a crystal orientation in which the <011> direction is oriented in the direction.   2. The electromagnetic shielding material according to claim 1, wherein an r value in the rolling direction of the steel pipe is 2.0 or more.   The electromagnetic shielding material according to claim 1 or 2, wherein the structure of the steel pipe is a structure having an average crystal grain size of 20 µm or more.   The composition of the steel pipe is mass%, including C: less than 0.01%, Si: 0.45% or less, Mn: 0.1-1.4%, S: 0.01% or less, P: 0.025% or less, Al: 0.01-0.06% N: 0.005% or less, The composition which consists of remainder Fe and an unavoidable impurity, The electromagnetic shielding material in any one of Claim 1 thru | or 3 characterized by the above-mentioned.   The composition of the steel pipe is by mass%, including C: less than 0.01%, Si: more than 0.45%, 3.5% or less, Mn: 0.1 to 1.4%, S: 0.01% or less, P: 0.025% or less, Al: 0.06 The electromagnetic shielding material according to any one of claims 1 to 3, wherein the electromagnetic shielding material contains more than 0.5% and 0.5% or less, N: 0.005% or less, and is composed of the remaining Fe and inevitable impurities. The electromagnetic shielding material according to claim 4 or 5, further comprising one group or two or more groups selected from the following groups A to C in mass% in addition to the composition of the steel pipe.
Group A: Ti: 0.05% or less, Nb: 0.05% or less, B: One or more of 0.005% or less,
Group B: Cr: 5% or less, Ni: 5% or less, Mo: 0.05% or less
Group C: Ca: 0.005% or less, REM: 0.05% or less, 1 type or 2 types

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