JP2005281853A - Steel pipe having superior electromagnetic property and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel pipe having superior electromagnetic properties, and to provide a manufacturing method therefor. <P>SOLUTION: This steel pipe has a composition including, by mass%, 0.5% or less C and 85% or more Fe. The manufacturing method comprises: heating the base steel pipe having the above composition; and rolling it to reduce a diameter at a diameter reduction rate of 15% or more and at a rolling-finishing temperature of (Ar<SB>3</SB>transformation temperature -10)°C or lower. Thereby, the steel pipe acquires a structure having the three-dimensional random intensity ratio of crystals having the orientation of <100> in a circumferential direction and of <110> in a rolling direction in an amount of 3.0 or larger, when measured with an X-ray diffraction method; an enhanced r-value; and improved electromagnetic properties. Annealing treatment at 550°C or higher but the Ac<SB>1</SB>transformation temperature or lower after rolling for diameter reduction increases the grain size and further improves the electromagnetic properties. The steel pipe may be cold-drawn before being annealed. The electromagnetic properties are further improved by using a steel pipe having the high-purity composition including less than 0.01% C and 95% or more Fe, for the base steel pipe. It is preferable to contain a proper amount of Si and Al for further improving the electromagnetic properties. The electromagnetic properties in a high-frequency area are improved by containing the proper amount of Cr. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a steel pipe excellent in electromagnetic characteristics suitable for the use of a magnetic shield, a stator for a motor, a rotor, and the like, and a method for manufacturing the steel pipe.

Conventionally, steel plates and thick plates having excellent electromagnetic characteristics have been used for magnetic shields, motor stators, rotors, and the like. 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. Further, when used for a stator or a rotor of a motor, these steel plates are punched and a plurality of sheets are laminated and used, and processes such as punching and lamination are required. 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 portion such as a welded portion is formed, resulting in deterioration of electromagnetic characteristics. In order to avoid such a problem, it is also considered to use a steel pipe as a material.

It is conceivable to make a steel pipe with excellent electromagnetic characteristics by electro-welding the electrical steel sheet, but the electrical steel sheet has a high Si content and is difficult to electro-welded, and also has the problem that the electro-magnetic characteristics of the electro-resistance weld are deteriorated. is there. In addition, although it is conceivable to use a billet of electromagnetic steel to make a seamless steel pipe, the electromagnetic steel has low ductility and 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 a magnetic shield can be obtained. However, in this technique, the orientation of crystal orientation is merely achieved by grain growth by heat treatment. Therefore, there is a problem that the characteristics are insufficient for the purpose of use that requires higher electromagnetic characteristics.
JP-A-2-236226 Japanese Examined Patent Publication No. 7-68579

  An object of the present invention is to solve the above-described problems of the prior art, and to propose a steel pipe excellent in electromagnetic characteristics and suitable for a magnetic shield or a motor and a method for manufacturing the steel pipe.

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 <110> direction in the rolling direction are strongly oriented;
(B) The crystal grain size should be a relatively coarse grain, preferably a grain of 20 μm or more,
(C) Eliminating unsteady parts such as ERW welds,
Found that is important. And for further improvement of electromagnetic characteristics,
(D) the C content is less than 0.01% by mass,
I found that is desirable.

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 steel pipe having a composition containing, by mass%, C: 0.5% or less, and Fe containing 85% or more, wherein the <100> direction is oriented in the circumferential direction and the <110> direction is oriented in the rolling direction. A steel pipe excellent in electromagnetic characteristics, characterized by having a structure with a three-dimensional random intensity ratio of X-rays of 3.0 or more in an orientation.
(2) The steel pipe according to (1), wherein the r value in the circumferential direction is 1.2 or more and the r value in the rolling direction is (r value +1.0 in the circumferential direction) or more.
(3) The steel pipe according to (1) or (2), wherein the structure is a structure having an average crystal grain size of 20 μm or more.
(4) In any one of (1) to (3), the composition contains, by mass%, C: 0.5% or less, 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, and a steel pipe characterized by being composed of the balance Fe and inevitable impurities.
(5) In (4), in addition to the above-mentioned composition, the following A to C groups: A group: Ti: 0.05% or less, Nb: 0.05% or less, B: 0.005% or less, or 2 or more types,
Group B: Cr: 15% or less, Ni: 0.5% or less, Mo: 0.3% or less, 1 type or 2 types or more,
Group C: A steel pipe containing one group or two or more groups selected from one or two of Ca: 0.005% or less and REM: 0.05% or less.
(6) When a steel pipe having a composition containing C: 0.5% or less and containing Fe of 85% or more in mass% is heated and then subjected to reduction rolling, the reduction rolling is performed at a reduction ratio of 15%. %, And a rolling end temperature is (Ar ₃ transformation point −10) ° C. or less.
(7) In (6), the composition contains, by mass%, C: 0.5% or less, Si: 0.45% or less, Mn: 0.1-1.4%, S: 0.01% or less, P: 0.025% or less, A method for producing a steel pipe, comprising Al: 0.01 to 0.06%, N: 0.005% or less, and having a balance Fe and inevitable impurities.
(8) In (7), in addition to the above-mentioned composition, the following groups A to C: Group A: Ti: 0.05% or less, Nb: 0.05% or less, B: 0.005% or less, or 2 or more types,
Group B: Cr: 15% or less, Ni: 0.5% or less, Mo: 0.3% or less, 1 type or 2 types or more,
C group: Ca: 0.005% or less, REM: One or two or more selected from one or two of 0.05% or less.
(9) In any one of (6) to (8), after the diameter reduction rolling or further processing into a desired shape, an annealing treatment is performed at a temperature of 550 ° C. or higher and Ac ₁ transformation point or lower. Steel pipe manufacturing method.
(10) A method for manufacturing a steel pipe according to (9), wherein cold drawing is performed after the diameter reduction rolling and before the annealing treatment.
(11) The method for manufacturing a steel pipe according to any one of (6) to (10), wherein the reduced diameter rolling is reduced diameter rolling with a thickness increase rate of 40% or less.
(12) The method for manufacturing a steel pipe according to any one of (6) to (10), wherein the reduced diameter rolling is reduced diameter rolling with a reduction ratio of 40% or less.
(13) A steel pipe having a composition containing less than 0.01% by mass and containing less than 0.01% by mass and containing 95% or more of Fe, wherein the crystal is oriented in the <100> direction in the circumferential direction and the <110> direction in the rolling direction A steel pipe excellent in electromagnetic characteristics, characterized by having a structure with a three-dimensional random intensity ratio of X-rays of 3.0 or more in an orientation.
(14) The steel pipe according to (13), wherein the r value in the rolling direction is 2.0 or more.
(15) The steel pipe according to (13) or (14), wherein the structure is a structure having an average crystal grain size of 20 μm or more.
(16) In any one of (13) to (15), the composition includes, by mass%, C: less than 0.01%, Si: 0.45% or less, Mn: 0.1 to 1.4%, S: 0.01% or less , P: 0.025% or less, Al: 0.01 to 0.06%, N: 0.005% or less, and a steel pipe characterized by being composed of the balance Fe and inevitable impurities.
(17) In any one of (13) to (15), the composition contains, by mass%, C: less than 0.01%, Si: more than 0.45%, 3.5% or less, Mn: 0.1 to 1.4%, S: A steel pipe characterized by containing 0.01% or less, P: 0.025% or less, Al: more than 0.06% and 0.5% or less, N: 0.005% or less, and the balance consisting of Fe and inevitable impurities.
(18) In (16) or (17), in addition to the above composition, in mass%, the following groups D to F: Group D: Ti: 0.05% or less, Nb: 0.05% or less, B: 0.005% or less One or more of
Group E: Cr: 5% or less, Ni: 5% or less, Mo: 0.05% or less
Group F: Ca: 0.005% or less, REM: 0.05% or less, 1 type or 2 types
A steel pipe characterized by containing one group or two or more groups selected from the group.
(19) When a steel pipe having a composition containing less than 0.01% by mass and Fe of 95% or more is heated and then subjected to diameter reduction rolling, the diameter reduction rolling is performed at a diameter reduction ratio of 15%. %, And a rolling end temperature of 730 ° C. or higher and 900 ° C. or lower is used.
(20) In (19), the composition contains, by mass%, C: less than 0.01%, Si: 0.45% or less, Mn: 0.1 to 1.4%, S: 0.01% or less, P: 0.025% or less, A method for producing a steel pipe, comprising Al: 0.01 to 0.06%, N: 0.005% or less, and having a balance Fe and inevitable impurities.
(21) In (19), the composition contains, by mass%, 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: more than 0.06%, 0.5% or less, N: 0.005% or less, and a composition comprising the balance Fe and inevitable impurities.
(22) In (20) or (21), in addition to the above composition, in mass%, the following groups D to F: Group D: Ti: 0.05% or less, Nb: 0.05% or less, B: 0.005% or less One or more of
Group E: Cr: 5% or less, Ni: 5% or less, Mo: 0.05% or less
F group: Ca: 0.005% or less, REM: One or two or more groups selected from one or two of 0.05% or less.
(23) In any one of (19) to (22), after the diameter reduction rolling or further processing into a desired shape, an annealing treatment is performed at a temperature not lower than 750 ° C. and not higher than the Ac ₁ transformation point. Steel pipe manufacturing method.
(24) The method for manufacturing a steel pipe according to (23), wherein cold drawing is performed after the diameter reduction rolling and before the annealing treatment.
(25) The method for manufacturing a steel pipe according to any one of (19) to (24), wherein the reduced diameter rolling is reduced diameter rolling with a thickness increase rate of 40% or less.
(26) The method of manufacturing a steel pipe according to any one of (19) to (24), wherein the reduced diameter rolling is reduced diameter rolling with a reduction ratio of 40% or less.

  ADVANTAGE OF THE INVENTION According to this invention, the steel pipe excellent in the electromagnetic characteristic which has sufficient soft magnetic characteristics as a magnetic shielding material or a motor material can be manufactured easily and inexpensively, and there is a remarkable industrial effect.

The steel pipe of the present invention is a steel pipe having a composition containing C: 0.5% or less and Fe containing 85% or more by mass%. First, the reasons for limiting the composition of the steel pipe of the present invention will be described. Hereinafter, mass% in the composition is simply referred to as%.
C: 0.5% or less C is an element that increases the strength, and is desirably contained in a predetermined amount according to the desired steel pipe strength. However, the content exceeding 0.5% lowers the growth of crystal grains. For this reason, C was limited to 0.5% or less. In addition, since C lowers the electromagnetic characteristics, it is desirable to reduce as much as possible from the viewpoint of electromagnetic characteristics, considering the deterioration with time due to magnetic aging, 0.01% or less, and from the viewpoint of further improving the electromagnetic characteristics, 0.01% It is preferable to make it less than. When the C content is 0.01% or more, the amount of metal element (carbide forming element) added to fix C as a precipitate increases, and it may be difficult to improve electromagnetic characteristics. More 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: 85% or more As the impurities increase, the inhibition factors of the crystal grain growth increase and the magnetic properties deteriorate, so it is desirable to have a high purity with few impurities. In the present invention, the content of Fe is set to 85% or more in order to regulate the amount of impurities and increase the purity. In addition, Preferably it is 95% or more, More preferably, it is 98% or more.

Although the basic composition of the present invention is as described above, in order to further improve electromagnetic characteristics, it is contained by mass%, including C: 0.5% or less, 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, and preferably a composition comprising the balance Fe and inevitable impurities.
For uses that require further improvement in electromagnetic characteristics, it is preferable to have a high-purity composition in which C is less than 0.01%, other components are reduced as much as possible, and Fe: 95% or more. Further, Si and Al may be added as necessary to improve the electromagnetic characteristics, or Cr, Ni and the like may be added to further improve the electromagnetic characteristics in the high frequency range. For applications where such excellent electromagnetic 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, and a high-purity composition consisting of the balance Fe and inevitable impurities, or mass%, including C: less than 0.01%, and Si: Contains 0.45% or more and 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, the remainder Fe and inevitable impurities It is preferable to have a high-purity composition comprising

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 characteristics, particularly iron loss characteristics, and increases the strength of the steel pipe by solid solution. However, if its content exceeds 0.45%, there is a tendency to lower the ERW weldability. For this reason, it is preferable to limit Si to 0.45% or less. In addition, when particularly excellent electromagnetic characteristics are required, Si can be made 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 steel pipe by solid solution, and it is desirable to contain it according to the desired steel pipe strength, but if it exceeds 1.4%, the toughness deteriorates. 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 characteristics 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 steel pipe strength and improves electromagnetic properties, but P has a strong tendency to segregate at grain boundaries and has the adverse effect of preventing the domain wall from moving. 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 characteristics. 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 characteristics. In particular, when excellent electromagnetic characteristics in a low H (magnetic field) region are required, Al may be contained more than 0.06% and 0.5% or less. it can. 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 characteristics, and forms AlN to adversely affect the electromagnetic characteristics. 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. When a large amount of Al is contained to improve electromagnetic characteristics, it is desirable to reduce N to 0.0025% or less so as not to cause deterioration of electromagnetic characteristics due to AlN.

In addition to the above-described components, the following groups A to C: Group A: Ti: 0.05% or less; Nb: 0.05% or less; B: 0.005% or less;
Group B: Cr: 15% or less, Ni: 0.5% or less, Mo: 0.3% or less, 1 type or 2 types or more,
Group C: Ca: 0.005% or less, REM: One or two groups selected from one or two of 0.05% or less may be contained. In the case of a high-purity composition, the following groups D to F: Group D: Ti: 0.05% or less; Nb: 0.05% or less; B: 0.005% or less;
Group E: Cr: 5% or less, Ni: 5% or less, Mo: 0.05% or less
Group F: It is preferable to contain one group or two or more groups selected from one or two of Ca: 0.005% or less and REM: 0.05% or less.

Ti, Nb, and B in Group A or Group D are elements that form carbides, nitrides, and the like to increase the strength of the steel pipe, and can be selected and contained as necessary. Ti: 0.05%, Nb: 0.005%, and B: More than 0.005% often deteriorate the magnetic properties, so Ti: 0.05%, Nb: 0.05%, B: 0.005% may be the upper limit. preferable.
Group B or Group E: Cr, Mo, Ni are elements that improve hardenability and corrosion resistance, and can be selected and contained as necessary. If the content exceeds Cr: 15%, Mo: 0.3%, Ni: 0.5%, the electromagnetic characteristics are deteriorated, so Cr: 15%, Mo: 0.3%, and Ni: 0.5% are preferably set as upper limits, respectively. Note that Cr is an element that particularly improves the corrosion resistance, and a large amount of up to 15% is limited to the case where the corrosion resistance needs to be remarkably improved. When the purpose is to improve hardenability, it is preferably 0.05% or less. Moreover, in the use which requires the further improvement of electromagnetic characteristics, it is preferable to set Cr: 0.05% or less, Mo: 0.05% or less, and Ni: 0.05% or less. When it is necessary to further improve the electromagnetic characteristics in the high frequency range, Cr: 5% or less, Ni: 5% or less, Mo under the condition of a high purity composition of Fe: 95% or more, Mo : 0.05% or less can be contained.

  Group C or Group F: 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 of the present invention has an X-ray three-dimensional random intensity ratio of 3.0 or more in a crystal orientation in which the <100> direction in the circumferential direction and the <110> direction in the rolling direction are oriented. Have an organization.
By setting the crystal orientation to a crystal orientation in which the <100> direction that is the easy axis of magnetization in the circumferential direction of the steel pipe and the <110> direction in the rolling direction are oriented, the electromagnetic characteristics of the steel pipe are 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 <110> 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 characteristics cannot be obtained. In addition, Preferably it is 8.0 or more, More preferably, it is 10 or more.

Here, the three-dimensional random intensity ratio is an index indicating the presence or absence of orientation of a specific crystal orientation. The crystal orientation in the case of no orientation (random) is set to 1, and the strength of a specific crystal orientation with orientation. Is normalized in a random case. A larger value means stronger orientation.
Specifically, an incomplete pole figure by the 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 is oriented in the circumferential direction and the <110> direction is oriented in the rolling direction) 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.

  The “excellent electromagnetic characteristics” as used in the present invention means that the maximum relative magnetic permeability is larger than that of an electric resistance welded steel pipe that is not subjected to subsequent treatment, and the magnetic flux density is low under a low magnetic field condition with a magnetizing force of 200 A / m. This means that it is larger than the ERW steel pipe. However, it is necessary to consider that the high-purity component is better because the maximum relative permeability in the state of the ERW steel tube and the magnetic flux density at 200 A / m are affected by the chemical component. is there. Therefore, for example, when the electromagnetic characteristics in a system containing a lot of additive elements are slightly better than the state of a high-purity ERW steel pipe, the electromagnetic characteristics of the steel pipe are considerably improved. Can be seen.

  Note that “excellent electromagnetic characteristics” in a steel tube having a high-purity composition preferably has a maximum relative permeability of 2500 or more, more preferably 7500 or more, and a magnetic flux density of 0.8 T under a low magnetic field condition with a magnetizing force of 200 A / m. As described above, more preferably 1.0T or more, and when the steel pipe remains in the diameter-reduced rolling, the characteristics of the same as the ERW steel pipe are used as a reference, and when the heat treatment is performed after the diameter-reduced rolling, the ERW steel pipe Based on the characteristics of the heat-treated materials as they are, the superior relative magnetic permeability and magnetic flux density are used as the judgment criteria for “excellent electromagnetic characteristics”.

  Furthermore, the steel pipe of the present invention preferably has a structure with an average crystal grain size of 5 μm or more. When the average crystal grain size is less than 5 μm, it is not possible to ensure excellent electromagnetic characteristics even if <100> is oriented in the circumferential direction and <110> is oriented in the rolling direction. In the present invention, it is preferable that the crystal grains are relatively coarse from the viewpoint that excellent electromagnetic characteristics can be obtained. More preferably, the average crystal grain size is 10 μm or more, further preferably the average crystal grain size is 20 μm or more, and desirably 40 μm or more. 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 characteristics can be obtained.

  In the steel pipe of the present invention, it is preferable that the r value in the circumferential direction is 1.2 or more and the r value in the rolling direction is (r value +1.0 in the circumferential direction) or more. In the steel pipe of the present invention having a high purity composition, the r value in the rolling direction is preferably 2.0 or more. The r value in the circumferential direction is 1.2 or more, the r value in the rolling direction is (r value in the circumferential direction +1.0) or more, or the r value in the rolling direction is 2.0 or more in a high purity steel pipe. Therefore, excellent electromagnetic characteristics can be secured. When the r value is less than the above value, it is difficult to ensure excellent electromagnetic characteristics. Note that the r value in the rolling direction is preferably 4.0 or more, more preferably 8.0 or more in a steel pipe having a high purity composition.

The r value is conventionally used as an index of formability, but the steel pipe of the present invention has a crystal orientation in which <100> is oriented in the circumferential direction and <110> is oriented in the rolling direction. In conjunction with the improvement, the correspondence between the r value in the rolling direction and the electromagnetic characteristics is good, and the r value can be used as an index of the electromagnetic 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 : Calculated 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 this invention steel pipe is demonstrated.
In the present invention, the steel pipe having the above composition is heated and subjected to reduction rolling.
The manufacturing method of the steel pipe used 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.

There is no need to specifically limit the method of heating the steel pipe during the diameter reduction rolling. 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. The heating temperature is preferably 700 ° C. or higher, and is preferably 750 ° C. or higher when a steel pipe having a high purity composition is used. When using a steel pipe of less than 700 ° C or a high-purity composition, if it is less than 750 ° C, the deformation resistance becomes high and it is difficult to ensure a diameter reduction ratio of a predetermined value or more. Remains and electromagnetic characteristics deteriorate. Note that, in a steel pipe having a welded portion such as an electric resistance welded steel pipe, it is preferable that the heating temperature is set to the Ac ₃ transformation point or higher from the viewpoint of removing the unsteady portion and improving the electromagnetic characteristics of the entire steel pipe. 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.

The diameter reduction rolling is preferably a rolling with a reduction ratio of 15% or more and a rolling end temperature of (Ar ₃ transformation point −10) ° C. or less. In the case of a steel pipe having a high-purity composition, it is preferable to perform rolling with a diameter 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 <110> direction is oriented in the rolling direction, and 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 (Ar ₃ transformation point −10) ° C. or lower, and 900 ° C. or lower in the case of a steel pipe having a high purity composition. When the rolling end temperature of the reduced diameter rolling becomes higher than (Ar ₃ transformation point−10) ° C. (900 ° C. in the case of a steel pipe having a high purity composition), the reduced diameter rolling is completed in the austenite region. As a result, it is not oriented in the desired crystal orientation described above, but random orientation is obtained, and the magnetic properties are not improved. In addition, the temperature measured on the steel pipe surface shall be used for the rolling completion temperature here. Note that the rolling end temperature is preferably 400 ° C. or higher (730 ° C. or higher in the case of a steel pipe having a high purity composition). Less than 400 ° C. (less than 730 ° C. in the case of a steel tube with a high-purity composition), the strain of reduced diameter rolling remains, and the crystal orientation in which the <100> orientation is oriented in the circumferential direction and the <110> orientation is oriented in the rolling direction It becomes difficult to obtain, and the magnetic properties deteriorate. More preferably, it is 600 ° C. or higher (750 ° C. or higher in the case of a steel pipe having a pure iron composition).

  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 the range in this way, the orientation in the <100> orientation in the circumferential direction is strengthened, and accordingly, the electromagnetic 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 550 ° C. and not higher than the Ac ₁ transformation point after the above-described reduction rolling or after further processing into a desired shape. The annealing temperature is preferably 750 ° C. or more and Ac ₁ transformation point or less in the case of a steel pipe having a high purity composition.

By annealing at a temperature of 550 ° C or higher and below the Ac ₁ transformation point, and in the case of a high purity steel pipe at a temperature of 750 ° C or higher and below the Ac ₁ transformation point, crystal grains further grow and electromagnetic characteristics are improved. More improved. When the annealing temperature is less than 550 ° C. (less than 750 ° C. in the case of a steel pipe having a high purity composition), 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 becomes higher than the Ac ₁ transformation point, the crystal orientation starts to collapse. For this reason, the annealing treatment is performed at a temperature of 550 ° C. or more and Ac ₁ transformation point or less (in the case of a steel pipe having a high purity composition, it is 750 ° C. or more and Ac ₁ transformation point or less). Note that the cooling after annealing is preferably slow cooling from the viewpoint of electromagnetic 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 property. 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 is roll-formed to form an open pipe, and an ERW steel pipe obtained by electro-welding the ends and a slab having the composition shown in Table 1 are manufactured by the Mannesmann method. The seamless steel pipe obtained in this way was used as the raw steel pipe.
After these steel tubes were heated to 900 to 1000 ° C., they were subjected to reduction rolling under the conditions shown in Table 2 (reduction ratio, thickness reduction (−) ratio / thickening (+) ratio, rolling end temperature). A part of the obtained steel pipe was further subjected to cold drawing and / or annealing. The cold drawing process was performed with a surface reduction rate of 30%. The annealing treatment was performed at a temperature in the range of 500 to 900 ° C.

The obtained steel pipe was subjected to measurement of electromagnetic characteristics, structure investigation, and r value measurement. The measurement method was as follows.
(1) Electromagnetic characteristics The obtained steel pipe was cut into a length of 5 to 10 mm, the cut surface was polished, and then the direct current magnetization characteristics were measured with a primary winding number of 250 and a secondary winding number of 100. The magnetic force was measured up to 10000 A / m, the magnetic permeability was measured to obtain the maximum value (maximum magnetic permeability), and the maximum relative magnetic permeability was calculated. Further, the magnetic flux density at a magnetizing force of 200 A / m was obtained. The measurement was carried out after removing the scale by pickling. The maximum relative permeability was evaluated as a ratio (maximum relative permeability ratio) with respect to the reference, with the electric resistance welded steel pipe not subjected to the subsequent treatment (steel pipe No. 1) as the reference (1.0).
(2) Structure investigation The obtained steel pipe was measured for crystal grain size and crystal orientation.

  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 <110> direction in the rolling direction were oriented was normalized by the random strength to obtain a three-dimensional random strength ratio. Note that CuKα was used as the X-ray source.
(3) Measurement of 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 also shown in Table 2.

  In all of the examples of the present invention, the <100> direction in the circumferential direction and the <110> direction in the rolling direction are strongly oriented, the X-ray three-dimensional random intensity ratio is 3.0 or more, and the maximum relative permeability ratio Is higher than that of ERW steel pipes (steel pipe No. 1) and shows excellent characteristics. Moreover, in the example of this invention, the magnetic flux density in a low magnetic field (200 A / m) is also large compared with an electric-resistance-welded steel pipe (steel No. 1).

  Particularly in the present invention examples (steel pipe Nos. 11, 13 to 16, 19, 20, 22, 23, 25), the crystal orientation X is oriented in the <100> direction in the circumferential direction and the <110> direction in the rolling direction. The line three-dimensional random intensity ratio is 8.0 or more, and the electromagnetic characteristics are particularly improved. Further, in the inventive examples (steel pipe Nos. 13, 16, and 25), the value is 10.0 or more, which shows more excellent characteristics. In addition, after shrinking rolling, the crystal grains are coarsened by annealing at 550 ° C or higher (steel pipe Nos. 15 and 16), or cold drawing and annealing at 550 ° C or higher (steel pipe No. 13). In addition, the electromagnetic characteristics are further remarkably improved. Moreover, in the present invention examples (steel pipe Nos. 19 to 21) in which the annealing treatment is performed after the diameter reduction rolling, the electromagnetic characteristics are further improved by performing the thickness reduction rolling by 10 to 25% compared to the case where there is no increase or decrease in the thickness. Yes. On the other hand, in the case where only the diameter reduction rolling is performed and the annealing treatment is not performed, the electromagnetic characteristics are further improved by increasing the thickness to 10 to 25% as compared with the case without increasing or decreasing the thickness. If the thickness change rate exceeds 25%, the effect of improving electromagnetic characteristics is reduced. Moreover, all the steel pipes in which the r value in the circumferential direction is 1.2 or more and the r value in the rolling direction is (circumferential r value + 1.0) or more are <100> directions in the circumferential direction and the rolling direction. Furthermore, the X-ray three-dimensional random intensity ratio of the crystal orientation in which the <110> direction is oriented is 3.0 or more, and exhibits excellent electromagnetic characteristics.

On the other hand, in the comparative example out of the scope of 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 <110> direction is oriented in the rolling direction is less than 3.0. Improvement is not recognized.
In the comparative example (steel pipe No. 7) in which the C content is out of the range of the present invention, the maximum relative permeability ratio is as low as 0.8 of the comparative example (steel pipe No. 1). Further, the reduction ratio of the reduction rolling is out of the preferred range of the present invention, and the three-dimensional random intensity ratio of X-rays is less than 3.0.

  In addition, the maximum relative permeability ratio of the comparative example (steel pipe No. 10) in which the reduction ratio of the reduced diameter rolling falls outside the preferred range of the present invention is at the same level as the comparative example (steel pipe No. 1) as the raw steel pipe. No improvement is observed. In addition, the maximum relative permeability ratio of the comparative example (steel pipe No. 12) in which the rolling end temperature of the reduced diameter rolling deviates from the preferred range of the present invention remains at the same level as the raw steel pipe (steel pipe No. 1), No improvement is recognized. Moreover, in the comparative examples (steel pipe Nos. 17 and 18) in which the annealing treatment temperature after diameter reduction is far from the preferred range of the present invention, the grains grow and the maximum relative permeability is higher than that of the raw steel pipe (steel pipe No. 1). Although the ratio is high, the three-dimensional random strength ratio is less than 3.0, and it can be seen that the crystal orientation formed during the diameter reduction rolling collapses and is randomized. Therefore, the magnetic flux density at 200 A / m of steel pipes Nos. 17 and 18 (comparative example) is almost the same as that of the raw steel pipes (steel pipe No. 1), and electromagnetic waves as in steel pipes Nos. 15 and 16 (examples of the present invention). There is no noticeable improvement in properties.

A thin steel strip having a high-purity composition shown in Table 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 these steel tubes were heated to 900 to 1000 ° C., they were subjected to reduction rolling under the conditions shown in Table 4 (reduction ratio, thickness reduction (−) ratio / thickening (+) ratio, rolling end temperature). A part of the obtained steel pipe was further subjected to cold drawing and / or annealing. The cold drawing process was performed with a surface reduction rate of 30%. The annealing treatment was carried out at a temperature in the range of 500 to 950 ° C.

The obtained steel pipe was subjected to measurement of electromagnetic characteristics, structure investigation, and r value measurement. The measurement method was as follows in substantially the same manner as in Example 1.
(1) Electromagnetic characteristics The obtained steel pipe was cut into a length of 5 to 10 mm, the cut surface was polished, and then the direct current magnetization characteristics were measured with a primary winding number of 250 and a secondary winding number of 100. The magnetic force was measured up to 10000 A / m, the magnetic permeability was measured to obtain the maximum value (maximum magnetic permeability), and the maximum relative magnetic permeability was calculated. Further, the magnetic flux density at a magnetizing force of 200 A / m was evaluated. The measurement was carried out after removing the scale by pickling.
(2) Structure investigation The obtained steel pipe was measured for crystal grain size and crystal orientation.

  The crystal grain size was calculated using a straight line segment method for the C cross section of the steel pipe, etching with a corrosive solution and observing with a microscope. The corrosive solution was nital and a saturated aqueous solution of picral or picric acid, and the test piece was immersed in the two corrosive solutions alternately to reveal the structure and measure the particle size. In the measurement of the particle size, only the grain boundaries that were clearly identifiable (large tilt grain boundaries) were used, and the grain boundaries that were corroded very thinly such as “spider yarn” were ignored.

  The measurement position was the center of the plate thickness excluding the outermost layer of 100 μm. The line segment length of 200 crystal grains was measured in the direction along the steel pipe surface layer, the length of the line segment was divided by the number of ferrite grains, and the particle size was calculated to obtain the average crystal grain size. When the average crystal grain size clearly exceeded 100 μm, the exact grain size was not measured and displayed as more than 100 μm (> 100 μm). In steel pipes that have been annealed, the crystal grains are sized, but in high-purity steel pipes, the as-rolled structure is a structure in which the crystal grains extend in the thickness direction (from the outside to the inside of the steel pipe). It has become.

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 <110> direction in the rolling direction were oriented was normalized by the random strength to obtain a three-dimensional random strength ratio. Note that CuKα was used as the X-ray source.
(3) Measurement of r value Using an arc-shaped test piece (JIS No. 12 test piece) cut out from the obtained steel pipe, a strain gauge was attached to the test piece by the same method as described above, and the circumferential direction and rolling Directional strain was measured and the r value was evaluated. In addition, it calculated using the distortion at the time of elongation 7 to 8%.

  The obtained results are also shown in Table 4.

  Each of the inventive examples has a high purity composition of C: less than 0.01% and Fe: 95% or more, and the <100> direction in the circumferential direction and the <110> direction in the rolling direction are strongly oriented. The three-dimensional random strength ratio is 3.0 or more, the maximum relative permeability is 2500 or more, and the magnetic flux density in a low magnetic field (200 A / m) is 0.8 T or more. Further, all of the examples of the present invention have an average crystal grain size of 20 μm or more and an r value in the rolling direction of 2.0 or more. When the average grain size is 20 μm or more and the r value in the rolling direction is 2.0 or more, generally good electromagnetic characteristics are shown.

In particular, the invention examples (steel pipe No. 2-2 to No. 2-4, No. 2-7 to No. 2-10, No. 2-18 to No. 2- 20, No. 2-22, No. 2-26, No. 2-27, No. 2-28, No. 2-29) have a maximum relative permeability of 7500 or more in a low magnetic field (200 A / m). It shows very excellent magnetic properties with a magnetic flux density of 1.0T or more.
In addition, the present invention example (steel pipe No. 2-28) having a high Si and Al content has a maximum magnetic permeability of 61280, a magnetic flux density of 1.9 T in a low magnetic field (200 A / m), and the electromagnetic characteristics are remarkably improved. ing. In addition, the present invention example (steel pipe No. 2-29) containing 1.5% of Cr is the present invention example (steel pipe No. 2-29) containing no Cr at the maximum relative magnetic permeability and the magnetic flux density in a low magnetic field (200 A / m). 2-2 to No.2-4, No.2-7 to No.2-10), but the iron loss at a magnetic flux density of 0.1 T at 400 Hz is a steel pipe No. 2 containing Cr. It can be seen that steel pipe No. 2-10 that does not contain Cr is 2.48 W / kg, and the electromagnetic characteristics in the high frequency region are significantly improved by containing Cr, while -29 is 2.01 W / kg. In addition, the present invention example (steel pipe No. 2-27) subjected to the drawing process has both the maximum relative permeability and the magnetic flux density improved compared to the comparative example without the drawing process (steel pipe No. 2-26). .

  Moreover, in the present invention examples (steel pipes No. 2-12, No. 2-13, 2-17) in which the rolling end temperature of the diameter reduction rolling is outside the preferable range in the high purity composition steel pipe, the electromagnetic characteristics are slightly lowered. Yes. Moreover, in the present invention example (steel pipe No. 2-21) in which the diameter reduction ratio of the diameter reduction rolling is outside the preferable range of the present invention, the electromagnetic characteristics are slightly deteriorated. Further, in the present invention examples (steel pipe Nos. 2-6 and 2-11) in which the annealing temperature after the diameter reduction rolling is out of the preferable range in the high purity composition steel pipe, the electromagnetic characteristics are slightly lowered.

  In addition, the present invention example (steel pipe No. 2-1) as it is in the reduced diameter rolling has a maximum relative permeability of 20% or more, compared with the comparative example (steel pipe No. 2-14) as it is as an electric resistance welded pipe of the same composition. The magnetic flux density in a low magnetic field (200 A / m) is improved to 200% or more. In addition, examples of the present invention (for example, steel pipe No. 2-7 to No. 2-10, steel pipe No. 2-17 to No. 2-22) subjected to annealing treatment after diameter reduction rolling have the same composition. Compared to comparative examples (for example, steel pipe No. 2-15 and steel pipe No. 2-24) subjected to post-annealing annealing, the maximum relative permeability is 20% or more, and the magnetic flux density in a low magnetic field (200 A / m) Has improved to over 200%.

  In addition, steel pipe No. 2-6 in which the annealing temperature of reduced diameter rolling deviates from the preferred range is lower in electromagnetic characteristics than the comparative example (steel pipe No. 2-14) with the same composition as an electric resistance welded pipe. However, compared with comparative examples (for example, steel pipe No. 2-15 and steel pipe No. 2-16), which have a fine crystal grain size and are subjected to post-annealing processing of the same composition, the improvement in electromagnetic characteristics is Few. Further, in the present invention example (steel pipe subjected to annealing treatment after diameter reduction rolling) (steel pipe No. 2-17) in which the rolling end temperature of the diameter reduction rolling deviates from the preferred range of the present invention, the electric resistance welded pipe structure having the same composition Compared with the comparative example (steel pipe No. 2-25) subjected to post-tube normalization, the maximum relative permeability is slightly reduced, but the magnetic flux density is improved. In steel pipe No.2-25, the crystal grains are grown by heat treatment (annealing treatment) after forming the ERW pipe, but since the diameter reduction rolling is not performed, the orientation of the crystal grains is insufficient. It is thought that it is because it is doing.

On the other hand, in the comparative example in which the three-dimensional random intensity ratio of X-rays is less than 3.0 and out of the scope of the present invention, the maximum relative permeability or the magnetic flux density at a low magnetic field (200 A / m) is reduced as compared with the present invention example. The electromagnetic characteristics are degraded.
In the steel pipe No. 2-5 and the steel pipe No. 2-11 which are comparative examples, the annealing treatment heating temperature after the diameter reduction rolling deviated from the preferred range of the present invention, and was heated to the austenite single phase region. Occasionally, the crystal orientation is randomized, and the three-dimensional random intensity ratio of X-rays is less than 3.0, and electromagnetic characteristics are degraded. Moreover, in steel pipe No.2-23 which is a comparative example, the rolling end temperature of diameter reduction rolling is high, the three-dimensional random intensity ratio of X-rays is less than 3.0, and electromagnetic characteristics are degraded.

Claims (26)

  A steel pipe having a composition containing, in mass%, C: 0.5% or less and Fe containing 85% or more, and having a crystal orientation in which the <100> direction is oriented in the circumferential direction and the <110> direction is oriented in the rolling direction, A steel pipe excellent in electromagnetic characteristics, characterized by having a structure having a three-dimensional random intensity ratio of X-rays of 3.0 or more.   2. The steel pipe according to claim 1, wherein the r value in the circumferential direction is 1.2 or more and the r value in the rolling direction is (r value in the circumferential direction +1.0) or more.   The steel pipe according to claim 1 or 2, wherein the structure is a structure having an average crystal grain size of 20 µm or more.   The composition contains, by mass%, C: 0.5% or less, 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 The steel pipe according to any one of claims 1 to 3, wherein the steel pipe contains 0.005% or less and has a balance of Fe and inevitable impurities. The steel pipe according to claim 4, further comprising one group or two or more groups selected from the following groups A to C in mass% in addition to the composition.
Group A: Ti: 0.05% or less, Nb: 0.05% or less, B: One or more of 0.005% or less,
Group B: Cr: 15% or less, Ni: 0.5% or less, Mo: 0.3% or less, 1 type or 2 types or more,
Group C: Ca: 0.005% or less, REM: 0.05% or less, 1 type or 2 types In mass%, C: 0.5% or less, and a steel pipe having a composition with Fe of 85% or more is heated, and then subjected to diameter reduction rolling, the diameter reduction rolling is performed at a reduction ratio of 15% or more, A method for producing a steel pipe excellent in electromagnetic characteristics, characterized in that the rolling end temperature is (Ar ₃ transformation point −10) ° C. or less.   The composition contains, by mass%, C: 0.5% or less, 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 The method for producing a steel pipe according to claim 6, wherein the composition contains 0.005% or less and the balance is Fe and inevitable impurities. The method for manufacturing a steel pipe according to claim 7, further comprising one group or two or more groups selected from the following groups A to C in mass% in addition to the composition.
Group A: Ti: 0.05% or less, Nb: 0.05% or less, B: One or more of 0.005% or less,
Group B: Cr: 15% or less, Ni: 0.5% or less, Mo: 0.3% or less, 1 type or 2 types or more,
Group C: Ca: 0.005% or less, REM: 0.05% or less, 1 type or 2 types The method for manufacturing a steel pipe according to any one of claims 6 to 8, wherein annealing treatment is performed at a temperature not lower than 550 ° C and not higher than the Ac ₁ transformation point after the diameter reduction rolling or further processing into a desired shape. .   The method for manufacturing a steel pipe according to claim 9, wherein cold drawing is performed after the diameter reduction rolling and before the annealing treatment.   The method for manufacturing a steel pipe according to any one of claims 6 to 10, wherein the reduced diameter rolling is reduced diameter rolling with a thickness increase ratio of 40% or less.   The method of manufacturing a steel pipe according to any one of claims 6 to 10, wherein the reduced diameter rolling is reduced diameter rolling with a reduction ratio of 40% or less.   A steel pipe having a composition containing less than 0.01% by mass and C: less than 95% by mass and having Fe of 95% or more, having a crystal orientation in which the <100> direction is oriented in the circumferential direction and the <110> direction is oriented in the rolling direction, A steel pipe excellent in electromagnetic characteristics, characterized by having a structure having a three-dimensional random intensity ratio of X-rays of 3.0 or more.   The steel pipe according to claim 13, wherein the r value in the rolling direction is 2.0 or more.   The steel structure according to claim 13 or 14, wherein the structure is a structure having an average crystal grain size of 20 µm or more.   The composition contains, by mass%, 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 The steel pipe according to any one of claims 13 to 15, wherein the steel pipe has a composition containing 0.005% or less, the balance being Fe and inevitable impurities.   The composition contains, by mass%, 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: more than 0.06% The steel pipe according to any one of claims 13 to 15, wherein the steel pipe contains 0.5% or less, N: 0.005% or less, and is composed of the remaining Fe and inevitable impurities. The steel pipe according to claim 16 or 17, further comprising one group or two or more groups selected from the following groups D to F in mass% in addition to the composition.
Group D: Ti: 0.05% or less, Nb: 0.05% or less, B: 0.005% or less, 1 type or 2 types or more,
Group E: Cr: 5% or less, Ni: 5% or less, Mo: 0.05% or less
Group F: Ca: 0.005% or less, REM: 0.05% or less, 1 type or 2 types   When the steel pipe having a composition containing less than 0.01% by mass and Fe of 95% or more is heated and then subjected to reduction rolling, the reduction rolling is performed at a reduction ratio of 15% or more. A method for producing a steel pipe excellent in electromagnetic characteristics, characterized in that the rolling finish temperature is 730 ° C. or higher and 900 ° C. or lower.   The composition contains, by mass%, 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 20. The method for producing a steel pipe according to claim 19, wherein the steel pipe contains 0.005% or less, and has a balance of Fe and inevitable impurities.   The composition contains, by mass%, 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: more than 0.06% 20. The method for manufacturing a steel pipe according to claim 19, wherein the composition contains 0.5% or less, N: 0.005% or less, and the balance is Fe and inevitable impurities. The method for manufacturing a steel pipe according to claim 20 or 21, further comprising one group or two or more groups selected from the following groups D to F in mass% in addition to the composition.
Group D: Ti: 0.05% or less, Nb: 0.05% or less, B: 0.005% or less, 1 type or 2 types or more,
Group E: Cr: 5% or less, Ni: 5% or less, Mo: 0.05% or less
Group F: Ca: 0.005% or less, REM: 0.05% or less, 1 type or 2 types The method for manufacturing a steel pipe according to any one of claims 19 to 22, wherein annealing treatment is performed at a temperature not lower than 750 ° C and not higher than the Ac ₁ transformation point after the diameter reduction rolling or further processing into a desired shape. .   The method of manufacturing a steel pipe according to claim 23, wherein cold drawing is performed after the diameter reduction rolling and before the annealing treatment.   The method for manufacturing a steel pipe according to any one of claims 19 to 24, wherein the reduced diameter rolling is reduced diameter rolling with a thickness increase ratio of 40% or less.   The method of manufacturing a steel pipe according to any one of claims 19 to 24, wherein the reduced diameter rolling is reduced diameter rolling with a reduction ratio of 40% or less.