ELECTRICALLY RESISTANCE WELDED STEEL TUBE, METHOD OF MANUFACTURING THE SAME, AND AUTOMOBILE STRUCTURAL MEMBER

Abstract

An electrical resistance welded steel tube having excellent formability and torsional fatigue resistance is provided, and a method for manufacturing the same is provided. An electrical resistance welded steel tube (1) includes a joint region (3) and a base metal region (6), the joint region (3) having a range of ±10 degrees in a circumferential direction of the tube with respect to an electrical resistance welded joint (2) formed in a longitudinal direction of the tube, the base metal region (6) being a region distinct from the joint region (3), wherein the electrical resistance welded steel tube (1) has an r value in the longitudinal direction of the tube of 1.0 or greater, H (mm) and W (mm) satisfy formula (1) below, where H (mm) is a difference between Ts(MIN) (mm) and Tb(Ave) (mm) (Tb(Ave) - Ts MIN)), Ts MIN) (mm) is a minimum wall thickness value of the joint region (3), Tb((Ave) (mm) is an average wall thickness value of the base metal region (6), and W (mm) is an arc length of an internal surface of the tube in the joint region (3), and Ts(MAX) (mm) and Tb(Ave) (mm) satisfy formula (2) below, where Ts(MAX) (mm) is a maximum wall thickness value of the joint region (3). H / W = 0.10 formula (1) Ts(MAX) / Tb(Ave) = 1.05 formula (2).

Description

Electrically resistance welded steel tube, method of manufacturing the same, and structural member of an automobile. TECHNICAL FIELD The present invention relates to a technology for electrically resistance welded steel tubes that have excellent torsional fatigue resistance and are therefore suitable for automotive stabilizers. PREVIOUS TECHNIQUE In recent years, efforts have been made to reduce vehicle body weight in order to improve fuel efficiency. A stabilizer bar is one of the components that make up the vehicle body. Although steel bars have been used in the stabilizer bar in the past, there is a growing trend toward using electrically resistance-welded steel tubing, which offers excellent productivity, to create a hollow stabilizer bar. Since bending is carried out for automotive parts, such as the stabilizer, high formability is required, and furthermore, since bending and torsional stresses act continuously on the final product during its use, excellent fatigue property is also required (hereafter referred to as torsional fatigue strength). For example, Patent Literature 1 proposes an electrical resistance-welded steel pipe in which a region called the white layer is specified to satisfy the required torsional fatigue strength. This region is part of the electrical resistance-welded zone and has a low carbon content and, therefore, lower post-mitigation hardness than the surrounding area. Furthermore, Patent Literature 2 proposes an electrical resistance-welded steel pipe with improved torsional fatigue strength, achieved by defining and limiting an area of ​​weld defects. APPOINTMENT LIST Patent Literature PTL 1: Japanese Patent No. 5942572 PTL 2: Japanese Patent No. 5845623 BRIEF DESCRIPTION OF THE INVENTION Technical Problem Unfortunately, it cannot be said that the steel tubes proposed in Patent Literatures 1 and 2 have sufficient resistance to torsional fatigue. U04 To solve the problem, the present invention is aimed at providing a technology for an electrical resistance welded steel pipe that has excellent formability and resistance to torsional fatigue. Solution to the Problem The present inventors carried out an investigation relating to the torsional fatigue of steel tubes and discovered that reduction stretching rolling produces a change in the internal peripheral shape near an electrical resistance welded joint of a steel tube, and this change in shape affects the torsional fatigue property. Furthermore, to achieve the aforementioned objective, the present inventors diligently conducted studies on various schemes for improving the internal peripheral shape near the electrical resistance welded joint in relation to a method for performing stretch reduction rolling on a hot-rolled steel tube. As a result, it was found that the internal peripheral shape near the electrical resistance welded joint changes depending on the positions of the rolling rolls for the stretch reduction rolling process and the electrical resistance welded joint of the steel tube during the stretch reduction rolling process.Consequently, it was found that, for the stretch reduction rolling step, optimizing the feed position of the steel tube relative to the rolling rolls improves the internal peripheral shape and thus enables the realization of both high formability and improved fatigue properties. The present invention was completed based on the findings described above and with additional studies. Specifically, a summary of the present invention is as follows. [1] An electrical resistance welded steel pipe including a joint region and a base metal region, the joint region having a range of ± in a circumferential direction of the pipe with respect to an electrical resistance welded joint formed in a longitudinal direction of the pipe, the base metal region being a region distinct from the joint region, wherein the electrical resistance welded steel pipe has an r value in the longitudinal direction of the pipe of 1.0 or greater, H (mm) and W (mm) satisfy formula (1) below, where H (mm) is a difference between Ts(min) (mm) and Tb(Ave)(mm) (fb(Ave) - Tsímin), Ts (MiN)(mm) is a minimum wall thickness value of the joint region, Tb(Ave)(mm) is an average wall thickness value of the base metal region, and W (mm) is an arc length of an internal pipe surface of the joint section, and Ts(max) (mm) and Tb(Ave) (mm) satisfy formula (2) below, where Ts(max) (mm) is a maximum wall thickness value of the joining region. H / W < 0.10 formula (1) Ts <MAX) / Tb(Ave) < 1.05 fórmula(2) [2] The electrical resistance welded steel pipe according to [1], where Tb(Ave) (mm) and Db(Ave) (mm) satisfy the formula (3) below, where Db(Ave) (mm) is an average value of the pipe's outside diameter from the base metal region. (Tb(Ave) / Db(Ave)) * 100 > 15% formula (3) [3] The electrical resistance welded steel tube according to [1] or [2], wherein the r value is an r value in the longitudinal direction of the tube in the base metal region. [4] A method for manufacturing the electrical resistance welded steel tube in accordance with any of [1] to [3], the method includes: perform a forming operation on a steel strip to form an open pipe; Performing electric resistance welding on the open pipe to form a hollow pipe; and heating the hollow pipe to a heating temperature of 650°C or higher and performing stretch reduction rolling on the hollow pipe to a cumulative slow stretch reduction ratio of 30% or higher, wherein the stretch reduction rolling is performed so as to ensure that, on a rolling stand with a stretch reduction ratio of 5.0% or higher, the electric resistance welded joint does not move through a region of a roll, which region has a range of ±5.0° with respect to a calibration center of the roll, and the electric resistance welded joint also does not move through regions of the roll, the regions having a range of ±5.0° with respect to the respective positions 360° / (nx2) to the left and right of the calibration center, where n is the number of rolls per stand. [5] An automobile structural member in which electrical resistance welded steel tubing is used in accordance with any of [1] to [3]. Favorable Effects of the Invention The present invention provides a technology for an electrical resistance welded steel tube that has excellent formability and resistance to torsional fatigue. Specifically, the present invention enables the manufacture of a steel pipe with high formability, i.e., an r-value of 1.0 or greater, designed to prevent plug rubbing, and which also exhibits excellent torsional fatigue resistance compared to the related art. Therefore, the present invention produces a significant industrial benefit. Electrically resistance-welded steel pipes according to the present invention are suitable for automotive structural members, such as stabilizers, which require torsional fatigue resistance after bending and cross-sectional deformation. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of a cross-section of an electrical resistance welded steel tube. Figure 2 is a plan view of a joining region. Figure 3 is a plan view of the joint region in a case where a maximum wall thickness value Ts <max>of the joint region has exceeded an average wall thickness value Tb(Ave) of an average base metal region Tb(Ave) of a base metal region. Figures 4(a) and 4(b) are an external view of a manufacturing line for an electrical resistance welded steel tube of the present invention. The figure is an external view illustrating the position of an electrical resistance welded joint in a case where the electrical resistance welded steel tube is fed into the rolling mill rolls. Figure 6 is an external view illustrating the regions of a rolling mill roll where contact of the electrical resistance welded joint must be avoided, in the present invention. Figure 7 is a plan view of the rolling mill rolls illustrating a phase angle of a rolling mill roll. Figure 8 is a diagram illustrating a relationship between a feed position of the electrical resistance welded joint with respect to the rolling rolls and the regions of the rolling rolls where contact of the electrical resistance welded joint must be avoided, in relation to the Examples. DESCRIPTION OF THE MODALITIES Electrical Resistance Welded Steel Tubes A steel tube of the present invention is an electrical resistance welded steel tube comprising a joint region and a base metal region. The joint region has a range of ±10° in a circumferential direction of the tube with respect to an electrical resistance welded joint formed in a longitudinal direction of the tube. The base metal region is distinct from the joint region. The electrical resistance welded steel tube has an r value in the longitudinal direction of the tube of 1.0 or greater. H (mm) and W (mm) satisfy the formula (1) below, where H (mm) is the difference between Ts(min) (mm) and Tb(Ave) (mm) (Tb(Ave) - Ts(min)), Ts(min) (mm) is a minimum wall thickness value of the joint region, Tb(Ave) (mm) is an average wall thickness value of the base metal region, and W (mm) is an arc length of an internal surface of the tube in the joint region.Ts(max) (mm) and Tb(Ave) (mm) satisfy formula (2) shown below, where Ts(MAX)(mm) is a maximum wall thickness value of the joint region. The electrical resistance welded steel tube has a. U04 excellent resistance to torsional fatigue. H / W < 0.10 formula (1) Ts(MAX) / Tb(Ave) < 1.05 formula (2) The methods for measuring dimensions will now be described. Figure 1 illustrates a cross-section of an electrically resistance-welded steel tube (1), and Figure 2 is an enlarged view of a joint region (3). The joint region (3) is a region that has a range of ± 10° in the circumferential direction of the pipe with respect to an electrical resistance welded joint (2), where a center of the circle (O) is defined as a center of a cross-section perpendicular with respect to a direction of the pipe axis (the longitudinal direction). The average wall thickness value Tb(Ave) of a base metal region (6) is determined as follows. The wall thickness of the base metal region (6) is measured with a spherical-flat anvil micrometer at positions of 40°, 80°, 120°, 160°, 200°, 240°, 280° and 320°, with respect to an electrical resistance welded joint position, which is assumed to be at 0°, and an average of the values ​​is determined as Tb(Ave) (mm). The average value of the external diameter of the pipe Db(Ave) (mm) of the base metal region (6) is determined as follows. The external diameter of the pipe of the base metal region (6) is measured with an external micrometer at positions of 40°, 80°, 120° and 160°, with respect to the electrical resistance welded joint position (2), which is assumed to be at 0°, and an average of the values ​​is determined as Db(Ave) (mm). The arc length W (mm) of the inner surface of the tube of the joint region n (3) is defined according to formula (4) below. W (mm) = (Db(Ave) after the reduction of the stretch - 2 χ Tb(Ave)) χ 20 χπ / 360 formula (4) Ts(min) (mm) and Ts(max) (mm) are defined, respectively, as a minimum wall thickness value of the joint region (3) (in Figure 2, the position indicated by the number (5) defines the minimum wall thickness value) and a maximum wall thickness value of the joint region (3) (in Figure 2, the position indicated by the number (4) defines the maximum wall thickness value). It should be noted that Ts(min) (mm) and Ts(max) (mm) are the minimum and maximum values, respectively, of the wall thicknesses measured with a micrometer tip every 1° over the joint zone (3). In the electrical resistance welded steel tube of the present invention, the average wall thickness value Tb(Ave) of the base metal region (6) is not particularly limited and may preferably be from 4.0 to 8.0 mm. Furthermore, in the electrical resistance welded steel pipe of the present invention, the average value of the pipe's external diameter Db(Ave) is not particularly limited and can preferably be from 20.0 to 45.0 mm. r value: 1.0 or greater. The range of the r-value (Lankford value) will now be described. In the present invention, the r-value can be the longitudinal r-value of the pipe in the base metal section (6). When the longitudinal r-value of the steel pipe (1) is greater than or equal to 1.0, the formability required for manufacturing stabilizers is satisfied. On the other hand, when the r-value of the steel pipe (1) is less than 1.0, the steel pipe (1) buckles when subjected to bending, and consequently, the steel pipe (1) cannot be bent into a predetermined shape. Therefore, it is specified that the longitudinal r-value of the steel pipe (1) is greater than or equal to 1.0. Preferably, the r-value is greater than or equal to 1.3. While the upper limit of the r-value is not particularly restricted, the upper limit is preferably less than or equal to 2.0.This is because when the r value is exclusively high, the deformation is concentrated in the circumferential direction of the pipe and, therefore, in cases where bending is performed on the steel pipe (1), a cross-section of the steel pipe may be reduced in diameter, which may result in throttling; consequently, the desired shape may not be obtained. The r-value is determined as follows. A tensile test is performed in which a nominal strain of 5 to 10% is applied. The true strain in the width direction (eW) is then measured relative to the true strain in the longitudinal direction (eL), and the r-value is calculated according to the equation r-value = p / (-1 - p), where p is the slope obtained. In this case, for the tensile test, a JIS No. 12-A tensile test specimen is cut from the base metal region of the steel pipe, and a metric strain gauge with a length of 2 mm is attached to the tensile test specimen; the test is then performed accordingly. The r value can be adjusted by controlling a heating temperature and a cumulative stretch reduction ratio that are used for stretch reduction rolling. H / W < 0.10(1) formula (1) The reason for the limitation imposed on the H / W ratio of H (mm) with respect to the arc length W (mm) of the inner surface of the tube in the joint region (3) will now be described. H (mm) is the difference between the minimum wall thickness value Ts(min) (mm) of the bonding region (3) and the average wall thickness value Tb(Ave) (mm) of the base metal region (6) [Tb(Ave) Ts(min)]. That is, H = Tb(Ave) - Ts(min). When the internal peripheral shape of the electrical resistance welded steel pipe (1) has a pronounced recess, as illustrated in Figure 2 (see number (5) in Figure 2), the torsional fatigue strength is significantly reduced because the stress is concentrated in the recess. Research revealed that when H / W, which serves as an indicator of the slope of a recess in the joint region (3), is less than or equal to 0.10, the required torsional fatigue strength is met. When H is a negative value, i.e., when Ts(min) is greater than Tb(Ave), the bonding region (3) has no recesses that define a thickness of the bonding region (3) less than the thickness of the base metal region (6), and, consequently, the torsional fatigue resistance does not decrease. Accordingly, in the present invention, it is specified that the ratio between H(mm) and W (mm) (H / W) is less than or equal to 0.10, where H(mm) is defined by the difference between the value of the minimum wall thickness Ts(min) (mm) of the joining region (3) and the value of the average wall thickness Tb(Ave) (mm) of the base metal region (6) (Tb(Ave) - Ts(min)), and W (mm) is the arc length of the joining region (3). Preferably, H / W is less than or equal to 0.07, and more preferably, less than or equal to 0.05. Preferably, H / W is greater than or equal to -0.10, and more preferably, greater than or equal to 0.07. [H / W can be adjusted to be in any of the above-mentioned ranges, on a rolling stand in which the stretch reduction is carried out with a stretch reduction ratio per stand greater than or equal to a specified value, feeding a hollow tube (12) in such a way as to ensure that the electrical resistance welded joint (2) avoids regions of a roll, regions that have a specified range with respect to a gauge end or a roll calibration center. Ts <MAX) / Tb(Ave) < 1.05 fórmula (2) The reason for the limitation imposed on the ratio between the maximum wall thickness value Ts(max> (mm) of the bonding region (3) and Tb(Ave) (mm) (Ts(MAX) / Tb(Ave>) will now be described. Regarding torsional fatigue resistance, the greater the wall thickness of the bonding region relative to the wall thickness of the base metal region (6), the less likely a fracture initiated from the bonding region (3) will occur. Now, we refer to Figure 3. Figure 3 is a plan view of the bonding region (3) in a case where the maximum wall thickness value Ts(maxj of the bonding region (3) has exceeded the average wall thickness value Tb(Ave> of the base metal region (6). When Ts(max> (see item (4) in Figure 3) is greater than Tb(Ave), as illustrated in Figure 3, a problem can occur during the cold drawing that follows the draw-reduction rolling. Cold drawing is a process in which a plug is inserted into the steel pipe and drawn through a die. When a bulge forms on an inner periphery of the joint region (3), the inserted plug is damaged, and another problem arises that the inner periphery ends up having a portion with which the plug cannot make contact. In this sense, by ensuring that Ts(MAX) / Tb(Ave), which serves as an indicator of the increase in the wall thickness of the joint region (3), is less than or equal to 1.05, the occurrence of such problems can be inhibited. Accordingly, in the present invention, the ratio between the maximum value of the wall thickness Ts(max) (mm) of the joining region and Tb(Ave) (mm) (Ts(MAX; / Tb(Ave)) is specified to be less than or equal to 1.05. Preferably, Ts <MAX) / Tb(Ave) es menor a o igual a 1.04, y más preferiblemente, menor a o igual a 1.03. Preferably, Ts <MAX) / Tb(Ave) es mayor a o igual a 0.90, y más preferiblemente, mayor a o igual a 0.95. Ts(MAxj / Tb(ave) can be set to be in any of the ranges mentioned above, on a rolling stand in which the stretch reduction is carried out with a stretch reduction ratio per stand greater than or equal to a specific value, feeding the electrical resistance welded joint (2) to a position such that the electrical resistance welded joint (2) avoids regions of a roll, regions that have a specific range with respect to a gauge end or a roll calibration center. (Tb(Ave) / Db(Ave)) x 100 > 15% formula (3) Furthermore, in the steel pipe of the present invention, it is preferable that (Tb(Ave) / Db(Ave)) × 100 be greater than or equal to 15%, where (Tb(Ave) / Db(Ave)) is a ratio between Tb(Ave) (mm) and the average value of the external diameter of the pipe Db(Ave) (mm) of the base metal region. One reason for the limitation imposed on Tb(ave) / Db(ave) is the following. Reducing Tb(Ave) / Db(Ave) can reduce weight; however, when (Tb(Ave) / Db(Ave)) × 100 is less than 15%, the required stiffness and strength for a component may not be met. Consequently, it is preferable for a steel tube, as a substitute for a steel bar, to have dimensions that satisfy (Tb(Ave) / Db(Ave) × 100 > 15%). Preferably, (Tb(Ave) / Db(Ave)) × 100 is greater than or equal to 15.5%, and more preferably, greater than or equal to 16.0%. Preferably, (Tb(Ave) / Db(Ave)) × 100 is less than or equal to 45%, and more. Preferably, less than or equal to 40%. A suitable chemical composition for the steel tube used in the present invention will now be described. In the following description of the chemical composition, % by mass is simply indicated as % unless otherwise specified. C: 0.55% or less Carbon (C) is an element that contributes to increased strength, and its addition improves fatigue resistance. However, when the C content exceeds 0.55%, weldability is reduced, and consequently, a stable resistance weld quality cannot be achieved. Therefore, it is preferable for the C content to be less than or equal to 0.55%. More preferably, the C content is less than or equal to 0.45%. A C content greater than or equal to 0.2% is also preferable. Yes: 0.01 to 1.0% Silicon (Si) increases the strength of steel by deoxidizing and dissolving within it. For optimal effect, a Si content of 0.01% or greater is preferable. When the Si content exceeds 1.0%, the steel pipe may exhibit reduced hardenability. Therefore, a Si content between 0.01% and 1.0% is preferable. More preferably, the Si content should be 0.1% or greater. Furthermore, and even more preferably, the Si content should be less than or equal to 0.4%. Mn: 0.2 to 3.0% Manganese (Mn) has a hardening-enhancing effect. This effect occurs when Mn is present at a concentration of 0.2% or greater. However, when the Mn content exceeds 3.0%, the quality of the resistance weld may be degraded. Therefore, a Mn content of 0.2% to 3.0% is preferable. More preferably, the Mn content should be 0.5% or greater. Furthermore, even more preferably, the Mn content should be less than or equal to 0.4%. P: 0.01% or less Phosphorus (P) segregates at grain boundaries and the like, reducing hardness. Therefore, it is desirable that P be reduced as much as possible in the present invention; however, a P content of up to 0.01% is permitted. Accordingly, it is preferable that the P content be less than or equal to 0.01%. More preferably, the P content is less than or equal to 0.005%. S: 0.01% or less Sulfur (S) is an element present in steel as disulfide inclusions, reducing formability and fatigue strength. Therefore, it is desirable to reduce S as much as possible in the present invention; however, an S content of up to 0.01% is permitted. Accordingly, it is preferable that the S content be less than or equal to 0.01%. More preferably, the S content is less than or equal to 0.005%. Cr: 2.0% or less Chromium (Cr) is an element that enhances hardenability and is therefore effective in increasing the strength of steel, thus improving its fatigue properties. However, when Cr is present in an amount greater than 2.0%, a Cr oxide can remain in the resistance weld joint, and consequently, the quality of the resistance weld can degrade. Therefore, it is preferable that the Cr content be less than or equal to 2.0%. More preferably, the Cr content is less than or equal to 0.5%. Furthermore, preferably, the Cr content is greater than or equal to 0.001%. Ti: 0.1% or less Titanium (Ti) has the function of forming TN in steel, thus fixing N. However, when the Ti content exceeds 0.1%, the formability and hardness of the steel can be reduced. Therefore, it is preferable for the Ti content to be less than or equal to 0.1%. More preferably, the Ti content is less than or equal to 0.1%. 0.04%. In addition, preferably, the Ti content is greater than or equal to 0.01%. AL: 0.1% or less Aluminum (Al) is an effective deoxidizing element and is necessary to inhibit the growth of austenite grains during mitigation, thus ensuring the resulting strength. However, when the Al content exceeds 0.1%, the effects are no longer enhanced, and furthermore, the number of Al-containing inclusions increases, which can reduce fatigue strength. Therefore, it is preferable for the Al content to be less than or equal to 0.1%. More preferably, the Al content is less than or equal to 0.08%. Additionally, it is preferable for the Al content to be greater than or equal to 0.01%. V: 0.5% or less Zinc (V) is an element that forms fine carbides, thus contributing to increased steel strength. However, when the V content exceeds 0.5%, the effect no longer increases, and therefore, an effect commensurate with the content cannot be expected; in other words, an economic disadvantage arises. Consequently, it is preferable for the V content to be less than or equal to 0.5%. More preferably, the V content is less than or equal to 0.3%. Furthermore, preferably, the V content is greater than or equal to 0.01%. Nb: 0.1% or less Nitrogen (Nb) is an element that forms fine carbides, thus contributing to increased steel strength. However, when the Nb content exceeds 0.1%, the effect no longer increases, and therefore, an effect commensurate with the content cannot be expected; in other words, an economic disadvantage arises. Consequently, it is preferable for the Nb content to be less than or equal to 0.1%. More preferably, the Nb content is less than or equal to 0.03%. Furthermore, preferably, the Nb content is greater than or equal to 0.001%. Mo: 1.0% or less Molybdenum (Mo) is an element that improves hardenability, thus contributing to increased strength in steel. However, when the Mo content exceeds 1.0%, the effect no longer increases, and therefore a proportional effect cannot be expected, resulting in an economic disadvantage. Consequently, it is preferable for the Mo content to be less than or equal to 1.0%. More preferably, the Mo content is less than or equal to 0.3%. Furthermore, preferably, the Mo content is greater than or equal to 0.01%. Cu: 2.0% or less Copper (Cu) is an element that increases hardenability and is therefore effective in increasing the strength of steel, thus improving its fatigue resistance. However, when Cu is present in an amount greater than 2.0%, formability can be reduced. Consequently, it is preferable for the Cu content to be less than or equal to 2.0%. More preferably, the Cu content is less than or equal to 0.5%. Furthermore, preferably, the Cu content is greater than or equal to 0.001%. Ni: 2.0% or less Nickel (Ni) is an element that increases hardenability and is therefore effective in increasing the strength of steel, thus improving its fatigue resistance. However, when Ni is present in an amount greater than 2.0%, formability can be reduced. Therefore, it is preferable for the Ni content to be less than or equal to 2.0%. More preferably, the Ni content is less than or equal to 0.5%. Furthermore, preferably, the Ni content is greater than or equal to 0.001%. B: 0.005% or less Boron (B) is an element that increases the hardenability of steel even when present in small amounts. However, when the B content exceeds 0.005%, the effect is no longer enhanced, and fatigue resistance is reduced because B segregates at grain boundaries, promoting intergranular fracture. Therefore, it is preferable for the B content to be less than or equal to 0.005%. More preferably, the B content is less than or equal to 0.0050%. Furthermore, it is preferable for the B content to be greater than or equal to 0.0003%. N: 0.01% or less Nitrogen (N) is an unavoidable element in steel. N combines with nitride-forming elements in steel, thus helping to inhibit grain coarsening and increasing the strength resulting from hardening. However, when N is present in an amount greater than 0.01%, the toughness of the resistance weld joint can be reduced and formability can be degraded. Therefore, it is preferable for the N content to be less than or equal to 0.01%. More preferably, the N content is less than or equal to 0.005%. The balance, apart from the components described above, is Fe and incidental impurities. Method of Manufacturing Electrically Resistance Welded Steel Tubes A method for manufacturing the steel tube will now be described with reference to Figure 4. Figure 4 is a schematic illustration of a line for manufacturing the electrical resistance welded steel tube of the present invention. In the present invention, as illustrated in Figure 4(a), a continuous forming operation is first performed on a steel strip (7) using a continuous forming machine (8) or similar device to form an open tube (9), and then electrical resistance welding is performed on the open tube using welding means (10) to form the hollow tube (12). It should be noted that in the present invention, the hollow tube (12) can be obtained by electrical resistance welding on circumferential portions that are in contact with the steel strip (7) using the welding means (10) while the contacting portions are pressed together by compression rollers (11). Furthermore, the hollow tube (12) can be cut to predetermined dimensions using a cutting machine (13). Once the hollow tube (12) has been obtained, the hollow tube (tube body) (12) is heated to a U04 heating temperature of 650°C or higher with heating means (14), and then stretch reduction rolling is carried out on the hollow tube (12) to a cumulative stretch reduction ratio of 30% or higher by using rolling rolls (hereafter also referred to simply as rolls) (15), as illustrated in Figure 4(b). For the stretch reduction rolling carried out with the rolling rolls (15), a plurality of rolling stands (161), (16-2)..., and (16-N) (N being a natural number) can be used to progressively carry out the stretch reduction. It should be noted that the stretch reduction ratio is defined by formula (5) below. Stretch reduction ratio (%) = 100 χ (Db(Ave) before stretch reduction - Db(Ave) after stretch reduction) / Db(Ave) before stretch reduction formula (5) More specifically, the cumulative stretch reduction ratio can be determined using formula (6) below. Cumulative stretch reduction ratio (%) = 100 χ (Db(Ave) before stretch reduction on the first support-Db(Ave) after stretch reduction on the final support) / Db(Ave) before stretch reduction on the first support formula (6) By using a heating temperature of 650°C or higher for the stretch reduction rolling of steel pipe and using a cumulative stretch reduction ratio of 30% or higher for the stretch reduction rolling, it is possible to achieve an r value of the processed steel pipe of 1.0 or higher; consequently, in steel pipe bending, the steel pipe can be bent into a desired shape. The heating temperature is preferably greater than or equal to 700°C and more preferably greater than or equal to 800°C. Furthermore, the heating temperature is preferably less than or equal to 1050°C and more preferably less than or equal to 1000°C. The cumulative stretch reduction ratio is preferably greater than or equal to 35% and more preferably greater than or equal to 40%. Furthermore, the cumulative stretch reduction ratio is preferably less than or equal to 90% and more preferably less than or equal to 85%. In the present invention, the stretch reduction rolling is carried out such that, on a rolling stand with a stretch reduction ratio of 5.0% or greater, the electrical resistance welded joint (2) does not shift across a region of a roll, the region having a range of ±5.0° with respect to a calibration center of the roll, and the electrical resistance welded joint (2) also does not shift across regions of the roll, the regions having a range of ±5.0° with respect to the respective 360° / (nx2) positions to the left and right of the calibration center, where n is the number of rolls per stand. As mentioned herein, the stretch reduction ratio on a rolling stand N is determined by the formula (7) shown below. Stretch reduction ratio (%) = 100 χ (Db(Ave) before stretch reduction at support N - Db(Ave) after stretch reduction at support N) / Db(Ave) before stretch reduction at support N formula (7) The reason for the limitation imposed on a feed position of the electrical resistance welded joint (2) on the rolling stand will now be described. As mentioned herein, the feed position of the electrical resistance welded joint (2) is a circumferential position in a case where the steel pipe is fed onto the draw-reduction rolling rolls. The feed position is defined assuming that, viewed from a direction in which the steel pipe advances, the steel pipe rotates counterclockwise around a steel pipe center with respect to a roof direction. In this case, the roof direction is assumed to be 0°.Furthermore, the respective positions of 360° / (nx2) to the left and to the right of the calibration center can also be expressed as positions respective to ±360° / (nx2) of the calibration center. Figure 5 is a view illustrating the feed position of the electrically resistance welded steel tube. Furthermore, Figure 6 is an external view illustrating the positions of a rolling roll (15) where contact with the electrically resistance welded joint (2) must be avoided, in the present invention. The present inventors directed their attention to the fact that in a case where draw-reduction rolling is performed on a steel pipe by means of the rolls (15), a wall thickness corresponding to a region near a gauge end of the rolls (15) used for rolling is increased, and a wall thickness corresponding to a gauge center (17) thereof is reduced, in a cross-section of the steel pipe. The roll (15) is a roll for performing the reduction-stretch rolling of a steel tube and has a gauge formed in a circumferential direction of the roll. A plurality of rolls (15) hold the steel tube (hollow tube (12)) in the gauges while the rolls (15) rotate. As seen in a cross-section perpendicular to an axial (longitudinal) direction of the steel tube (cross-section perpendicular to the direction of the tube axis), the gauge has a curved shape that fits an outer periphery of the steel tube in the cross-section perpendicular to the tube axis. A gauge center (17) located on an arc where a gauge diameter (18) has a minimum value is a gauge bottom; the gauge diameter (18) is defined by having its center on an axis of rotation of the roll. The present inventors specified several positions in the circumferential direction for the electrical resistance welded joint (2) and introduced the hollow tube (12) into the stretch reduction rolling rolls (15) (16-1), as illustrated in Figure 5. As a result, it was found that a good internal peripheral shape can be maintained, with a low degree of deformation, in cases where the hollow tube (12) was fed, as illustrated in Figure 6, in a manner that ensures that, in a stretch reduction rolling stand with a stretch reduction ratio per stand of 5.0% or greater, the electrical resistance welded joint (2) avoided a region of one roll (15), the region having a range of ± 5.0° with respect to the calibration center (17), and the electrical resistance welded joint (2) also avoided regions of the roll (15), the regions having a range of ± 5.0° with respect to the respective 360° / (nx2) positions to the left and to the right of the calibration center (17), where n is the number of rollers per support. As used in this document, the expression ± 5.0° with respect to the center of the gauge (17) means a range of ± 5.0° in a sector shape where the center of the gauge (17) is assumed to be at 0 degrees. The sector shape is defined by assuming that an external peripheral portion of the gauge viewed in a cross-section perpendicular to the axis of the pipe (15) is sector-shaped, conforming to a cross-sectional circle of the steel pipe and being a sector shape whose circular center is the center of the cross-sectional circle of the steel pipe. Furthermore, the expression ±(5.0°) with respect to the respective positions at 360° / (nx2) from the center of the gauge (17), where n is the number of rolls per stand, has the following meanings, for example: in a case where rolling is done with 4 rolls, the expression means ranges of ± 5.0°.0° in a circumferential direction with respect to the respective positions 45° (= 360° / (4x2)) to the left and to the right of the center of the gauge (17), and in a case where rolling is done with 3 rollers, the expression means ranges of ±(5.0°) in the circumferential direction with respect to the respective positions 60° (= 360° / (3x2)) to the left and to the right of the calibration center (17). In the present invention, with respect to the rollers (15) adjacent to each other in the circumferential direction of the pipe, the region having a range of ± 5.0° of the left-side roller (15), with respect to the position of 360° / (nx2) distance from the calibration center (17), the position being on the right-end side, can overlap with the region having a range of ±5.0° of the right-side roller (15), with respect to the position of 360° / (nx2) distance from the calibration center (17), the position being on the left-end side.This may be possible in terms of feasibility. As described, to obtain an electrical resistance welded steel tube having excellent formability and torsional fatigue resistance, the stretch reduction rolling is carried out so as to ensure that, on a rolling stand with a stretch reduction ratio of 5.0% or greater, the electrical resistance welded joint does not move through a region of a roll, the region having a range of ± 5.0° with respect to the calibration center of the roll, and the electrical resistance welded joint also does not move through regions of the roll, the regions having a range of ± 5.0° with respect to the respective positions 360° / (nx2) to the left and right of the calibration center, where n is the number of rolls per stand. U04 Furthermore, methods exist for limiting the circumferential displacement of the electrical resistance welded joint (2) of the tube during the stretch reduction roll, thereby feeding the tube to a target feed position more reliably. Examples of such methods include, but are not limited to, a method in which a roller guide is installed between adjacent rolling stands (16) and used to limit the circumferential displacement of the tube as it passes between the stands (16); a method in which a tensile stress is applied from a rear side during the stretch reduction roll; and a method in which the electrical resistance welding and the stretch reduction roll are performed continuously. The resulting steel tube (1) can be subjected to an induction hardening process and an annealing process. The induction hardening process involves heating the steel tube (1) to a temperature of 850 to 1050°C for a holding time of 1 to 1800 seconds, followed by quenching with water. The annealing process involves holding the steel tube (1) at 150 to 450°C for 5 to 60 minutes, followed by air cooling. The electrical resistance welded steel tube (1) of the present invention, described above, can be used in automotive structural members, such as automotive stabilizers. EXAMPLES Now, the present invention will be further described in relation to the Examples. The open tubes were formed by continuous forming of steel strips of two grades, A and B, as shown in Table 1. Subsequently, the open tubes were resistance welded to form hollow tubes. The hollow tubes were then subjected to a stretch reduction rolling process, which was carried out at various cumulative stretch reduction ratios, heating temperatures, and feed positions onto a roll stand for the stretch reduction rolling. As a result, steel tubes Nos. A-1 to A-19 and B-1 to B-19 were obtained. Steel tubes Nos. A-1 to A-19 were manufactured from grade A steel strip, and steel tubes Nos. B-1 to B-19 were manufactured from grade B steel strip. Table 2 shows the stretch reduction schedule. Additionally, Figure 7 is a plan view of the rolling mill rolls illustrating a phase angle of a rolling mill roll shown in Table 2. The phase angle shown in Table 2 is an angle (°) that represents the position of the calibration center (gauge bottom) of a rolling roll (15) of each of the supports (16) in a circumferential direction with respect to a ceiling. As illustrated in Figure 7, for standards Aa D, U04 which are 4-roll patterns, the rolling roll (15) is one located in a region of 0 to 90° counterclockwise with respect to the ceiling, assuming the center of the steel tube is the axis. Furthermore, for pattern E, which is a 3-roll pattern, the phase angle shown in Table 2 is an angle (°) that represents a position of the bottom gauge of a rolling roll (15) of each of the supports (16) in the circumferential direction with respect to the ceiling, and the rolling roll (15) is one located in a region of 0 to 120° counterclockwise with respect to the ceiling. Table 3 and Table 4 show the stretch reduction conditions, including the stretch reduction patterns, used for the manufacture of steel tubes nos. A-1 to A-19 and B-1 to B-19. The feed position of each of the steel tubes for the rolling rolls, indicated in Table 3 and Table 4, is also shown in Figure 8 for each of the draw reduction patterns. Each of the angles was a counterclockwise angle determined with respect to the roof and a rolling direction (see also Figure 7). Specifically, with respect to the stretch reduction patterns A and B (n=4 for both), the cases in which the condition of the manufacturing conditions of the present invention, which is to ensure that the electrical resistance welded joint does not move through a region of a roller, the region having a range of ± 5.0° with respect to the calibration center of the roller, and the electrical resistance welded joint also does not move through regions of the roller, the regions having a range of ± 5.0° with respect to the respective 360° / (nx2) positions to the left and to the right of the calibration center, where n is the number of rollers per support, (the condition is hereafter referred to as condition P'j), was satisfied are as follows: for the respective supports nos. 5 to 10, which had a stretch reduction ratio of 5.0% or greater, cases in which the feed position of the joint n (electrical resistance welded joint) was not located within the regions having a range of ± 5.0° with respect to the respective phase angles of 11.25°, 56.25°, 78.75°, 33.75°, 0° and 45°, and furthermore, the feed position of the joint (electrical resistance welded joint) was not located within the regions having a range of ± 5.0° with respect to the respective phase angles of the above angles ±45° (= 360° / (4x2)), namely, -33.75° (considered as 56.25° (90° added to -33.75°) for its evaluation), 56.25°, 11.25°, 101.25° (considered as 11..25° (90° subtracted from 101.25°) for your evaluation), 33.75°, 123.75° (considered as 33.75° (90° subtracted from 123.75°) for your evaluation), -11.25° (considered as 78.75° (90° added to -11.25°) for your evaluation), 78.75°, -45° (considered as 45° (90° added to 45°) for evaluation), 45°, 0° and 90° (considered as 0° (90° subtracted from 90°) for evaluation). As for the steel tubes employing the A or B draw reduction pattern, the feed position of steel tubes Nos. A-1 and B-1 was 18°; as 18° was outside the ranges mentioned, steel tubes Nos. A-1 and B-1 met condition P. The feed position of steel tubes A-2 and B-2 was 113°. Since 23°, which was obtained by subtracting 90° from 113°, was outside the ranges mentioned, steel tubes A-2 and B-2 met condition P. The feed position of steel tubes A-3 and B-3 was 205°. Since 25°, which was obtained by subtracting 90°x2 from 205°, was outside the aforementioned ranges, steel tubes Nos. A3 and B-3 met condition P. The feed position of steel tubes A-4 and B-4 was 337°. Since 67°, which was obtained by subtracting 90°x3 from 337°, was outside the aforementioned ranges, steel tubes Nos. A4 and B-4 met condition P. The feed position of steel tubes A-5 and B-5 was 70°. Since 70° was outside the ranges mentioned, steel tubes A-5 and B-5 met condition P. The feed position of steel tubes A-6 and B-6 was 108°. Since 18°, which was obtained by subtracting 90° from 108°, was outside the ranges mentioned, steel tubes Nos. A-6 and B-6 met condition P. The feed position of steel tubes A-10 and B-10 was 113°. Since 23°, which was obtained by subtracting 90° from 113°, was outside the ranges mentioned, steel tubes A-10 and B-10 met condition P. The feed position of steel tubes A-9 and B-9 was 113°. Since 35° was within the ranges mentioned above, steel tubes A-9 and B-9 did not meet condition P (see REGION TO AVOID in Figure 8). The feed position of steel tubes A-11 and B-11 was 12°. Since 12° was within the ranges mentioned above, steel tubes A-11 and B-11 did not meet condition P. The feed position of steel tubes A-13 and B-13 was 255°. Since 75°, which was obtained by subtracting 90° from 255°, was within the ranges mentioned above, steel tubes A-13 and B-13 did not meet condition P. The feed position of the A-14 and B-14 steel tubes was 35°. Since 35° was within the ranges mentioned above, the A-14 and B-14 steel tubes did not meet condition P. The feed position of the A-15 and B-15 steel tubes was 46°. Since 46° was within the ranges mentioned above, the A-15 and B-15 steel tubes did not meet condition P. With regard to the stretch reduction patterns C and D (n=4 for both), the cases in which condition P of the manufacturing conditions of the present invention was met are as follows: for the respective supports nos. 5 to 8, which had a stretch reduction ratio of 5.0% or greater, the cases in which the feed position of the joint (electrical resistance welded joint) was not within the regions that had a range of ± 5.0° with respect to the respective phase angles of 11.25°, 56.25°, 78.75° and 33.75°, and furthermore, the advance position of the joint (electrical resistance welded joint) was not within regions that had a range of ± 5.0° with respect to the respective phase angles of the above angles ±45° (= 360° / (4x2)), namely, -33.75° (considered as 56.25° (90° added to -33.75°) for evaluation), 56.25°, 11.25°, 101.25° (considered as 11.25° (90° subtracted from 101.25°) for your evaluation), 33.75°, 123.75° (considered as 33.75° (90° subtracted from 123.75°) for your evaluation), -11.25° (considered as 78.75° (90° added to -11.25°) for your evaluation), and 78.75°. Regarding the steel tubes that employed the C or D draw reduction pattern, the feed position of steel tubes Nos. A-7 and B-7 was 180°; since 0°, which was obtained by subtracting 90°x2 from 180°, was outside the ranges mentioned, steel tubes Nos. A-7 and B-7 met condition P. The feed position of steel tubes A-8 and B-8 was 226°. Since 46°, which was obtained by subtracting 90°x2 from 226°, was outside the aforementioned ranges, steel tubes Nos. A8 and B-8 met condition P. The feed position of steel tubes A-12 and B-12 was 226°. Since 46°, which was obtained by subtracting 90°x2 from 226°, was outside the aforementioned ranges, steel tubes Nos. A-12 and B-12 met condition P. The feed position of the A-16 and B-16 steel tubes was 79°. Since 79° was within the ranges mentioned above, the A-16 and B-16 steel tubes did not meet condition P. With regard to the stretch reduction pattern E (n=3), the cases in which condition P of the manufacturing conditions of the present invention was met are the following: for the respective supports nos. 5 to 10, which had a stretch reduction ratio of 5.0% or greater, cases in which the feed position of the joint (electrical resistance welded joint) was not located within regions having a range of ± 5.0° with respect to the respective phase angles of 15°, 75°, 105°, 45°, 0° and 60°, and the feed position of the joint (electrical resistance welded joint) was not located within the regions of the respective phase angles of the above angles ± 60° (= 360° / (3χ2)), namely, -45° (considered as 75° (120° added to -45°) for its evaluation), 75°, 45°, 165° (considered as 45° (120° subtracted from 165°) for its evaluation), 0° and 120° (considered as 0° (120° subtracted from 120°) for evaluation). The feed position of the A-17 and B-17 steel tubes was 23°. Since 23° was outside the ranges mentioned, the steel tubes Nos. A-17 and B-17 met condition P. The feed position of the A-18 and B-18 steel tubes was 165°. Since 45°, which was obtained by subtracting 120° from 165°, was within the aforementioned ranges, the A-18 and B-18 steel tubes did not meet condition P. The feed position of steel tubes A-19 and B-19 was 342°. Since 102°, which was obtained by subtracting 120° from 342°, was within the ranges mentioned above, steel tubes A-19 and B-19 did not meet condition P. Furthermore, Table 3 and Table 4 show the target outer diameters and target sheet thicknesses for the final products, along with the actual outer diameters resulting from the reduction in stretch. Additionally, from a cross-section of each of the steel tubes, Ts(max), Ts(min), Tb(ave), and Db(ave) were measured, and W and H were calculated. Subsequently, these electrically resistance welded steel tubes underwent an induction hardening process and an annealing process. It should be noted that the induction hardening process involved heating the steel tubes to 950°C for 1 second, followed by quenching with water. In the annealing process, the steel tubes were held at 190°C for 1 hour and then cooled with air. After performing the strain reduction rolling and heat treatments, a tensile test was conducted to determine the tensile strength (TS) and the r-value. For the tensile test, a JIS No. 12-A tensile test specimen was cut from the base metal region of the steel pipe, and a 2 mm long strain gauge was attached to the specimen. The tensile strength (TS) was then determined from the tensile test result. The r-value was determined as follows: A tensile application was performed in which a nominal strain of 5 to 10% was applied. The true strain in the width direction (eW) was then measured relative to the true strain in the longitudinal direction (eL), and the r-value was calculated according to the equation r-value = p / (-1 - p), where p is the slope obtained. Furthermore, a torsional fatigue test specimen having a pipe shape (length: 450 mm) was cut from the obtained stretch-reduction rolled steel pipe, and a torsional fatigue test was performed. The torsional fatigue test was carried out under conditions that included an applied stress (external surface) of 600 MPa, a stress ratio of -1 (alternating), a frequency of 2 Hz, and a sinusoidal waveform. The number of cycles to failure was measured to evaluate fatigue strength. In the present invention, the determination that the torsional fatigue property was improved was made in cases where the number of cycles to failure was greater than or equal to 2.0 times that of a comparative example that had the same stretch reduction program, the same dimensions of the final product (the same combination of target wall thickness and target outside diameter), and the same grade of steel. For the evaluation of plug rub, the electrical resistance welded steel pipe, used as a hollow pipe, was drawn by cold drawing. Specifically, a plug was inserted into the steel pipe, and it was drawn through a die. In this case, when the inner periphery of the electrical resistance welded steel pipe protrudes and causes the formation of a scratch called plug rub, this scratch can cause a defect in the processing of other steel pipes. The evaluation was carried out as follows: After cold drawing, a visual inspection was performed to check the surface of the plug for any defects, and the presence or absence of defects was determined. It was determined that the steel pipes without defects have excellent formability. The results obtained are shown in Table 3 and Table 4. As mentioned above, Table 3 shows the results for the No. A steels, and Table 4 shows the results for the No. B steels. Table 3 and Table 4 demonstrate that in all Examples, H / W was less than or equal to 0.10, Ts(MAX) / Tb(Ave) was less than or equal to 1.05, and the r value was greater than or equal to 1.0. Furthermore, the steel tubes in the Examples did not cause surface defects on the plug, and therefore had excellent formability, and the steel tubes also exhibited improved torsional fatigue properties compared to the electrical resistance-welded steel tubes of the related technique in the high-load test. Furthermore, for steel tubes Nos. A-9 and B-9, which are comparative examples, the feed position of the joint (electric resistance welded joint) did not satisfy condition P, and as a result, H / W was outside the range of the present invention; consequently, the desired torsional fatigue strength was not achieved. Furthermore, in the case of steel tubes nos. A-10 and B-10, the heating temperature for the stretch reduction rolling was less than 650°C and consequently the r value was less than 1.0; therefore, the desired formability was not achieved. Furthermore, for steel tubes A-11 and B-11, the feed position of the joint (electric resistance welded joint) did not satisfy condition P, and as a result, Ts <MAX) / Tb(Ave) estaba fuera del rango de la presente invención; en consecuencia, se producía un defecto en el tapón durante el estirado en frío. Furthermore, in the case of steel tubes nos. A-12 and B-12, the cumulative stretch reduction ratio was less than 30% and, consequently, the r value was less than 1.0; therefore, the desired formability was not achieved. Furthermore, in the case of steel tubes A-13 and B-13, the feed position of the joint (electric resistance welded joint) did not satisfy condition P, and as a result, H / W was outside the range of the present invention; consequently, the desired torsional fatigue strength was not achieved. Furthermore, in the case of steel tubes Nos. A-14 and B-14, the feed position of the joint (electric resistance welded joint) did not satisfy condition P, and as a result, H / W and Ts(MAX) / Tb(Ave> were outside the ranges of the present invention; consequently, the desired torsional fatigue strength was not achieved, and a defect occurred in the plug during cold drawing. Furthermore, in the case of steel tubes A-15 and B-15, the feed position of the joint (electric resistance welded joint) did not satisfy condition P, and as a result, H / W was outside the range of the present invention; consequently, the desired torsional fatigue strength was not achieved. Furthermore, in the case of steel tubes A-16 and B-16, the feed position of the joint (electric resistance welded joint) did not satisfy condition P, and as a result, H / W was outside the range of the present invention; consequently, the desired torsional fatigue strength was not achieved. Furthermore, in the case of steel tubes A-18 and B-18, the feed position of the joint (electric resistance welded joint) did not satisfy condition P, and as a result, H / W was outside the range of the present invention; consequently, the desired torsional fatigue strength was not achieved. Furthermore, in the case of steel tubes A-19 and B-19, the feed position of the joint (electric resistance welded joint) did not satisfy condition P, and as a result, Ts(MAX) / Tb(Ave) was outside the range of the present invention; consequently, a defect occurred in the plug during cold drawing. Table 1 Steel No. Chemical Composition (% by mass) C Si Mn PS Cr Ti Al V Nb Mo Cu Ni BNA 0.35 0.22 1.25 0.001 0.003 0.152 0.035 0.035 0.003 0.001 0.21 0.313 0.317 0.0021 0.002 B 0.23 0.21 0.60 0.001 0.003 0.332 0.016 0.023 0.052 0.015 0.05 0.226 0.292 0.0026 0.003 The remainder, apart from the components mentioned above, is iron and incidental impurities. Table 2 U04 Stretch Reduction Schedule A (roller 4) B (roller 4) C (roller 4) D (roller 4) E (roller 3) Stretch Reduction Ratio (%) Phase Angle (°) Stretch Reduction Ratio (%) Phase Angle (°) Stretch Reduction Ratio (%) Phase Angle (°) Stretch Reduction Ratio (%) Phase Angle (°) 1 20 0 20 0 1.0 0 10 0 20 0 2 20 45 20 45 2.0 45 20 45 20 60 3 30 225 40 225 30 225 30 225 30 30 4 40 675 40 675 40 675 30 675 40 90 5 50 11 25 60 11 25 50 11 25 50 11 25 50 15 6 70 56.25 70 56 25 50 56 25 50 56 25 70 75 7 70 78 75 10.0 7875 50 7875 50 7875 70 105 Number of $ 50 33 75 10.0 33 75 50 33 75 50 3375 70 45 Support g 50 0 70 0 4.0 0 30 0 70 0 10 50 45 60 45 2.0 45 10 45 50 60 11 40 225 40 225 10 225 05 22 5 40 30 12 30 675 30 675 05 675 05 675 30 90 13 20 11.25 20 11 25 20 15 14 20 56.25 20 56 25 20 75 15 10 78 75 1 0 7875 10 105 16 05 33 75 05 33 75 05 45. Table 3 Notes Example | o £ ω LU Example | Example | Example | OE LU Example | o E o E gw § Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example o E Φ LU Comparative Example Comparative Example Plug friction O zozozoz O zozozozoz 00 ozoz 00 ozoz O zoz GO Fatigue test torsional Improvement ratio csi CM CM co CM CM CM CM CM Comparative example of same dimensions Yes Yes A-13 2 'T CO A-16 CO Torsional fatigue cycles (> 10Λ6) LO m 2 Ξ Yes CO s 2 Yes 2 to 2 O CO 2 o 'T Value-r CM CM co 2 LO co 2 LO or co 2 LO and 7 - co Tensile strength TS (MPa) 1844 | 1858 I § | 1916 I | 1855 | | 1872 I 1870 | 1858 | 05 05 3 CO 1870 1883 Yes Yes Yes 1897 2 1908 1894 yes É δ' 1— 3 ¿so 0 99 8 O 2 2 3 2 2 s 0 95 O 0 93 0 98 o 094 WH -0 02 90 0 0 07 -0 08 CM 00 0 εο o O oo zoo- ZOO 026 oo LO 20 0 oo (wiu) H ' 80 0- O -0 23 3 o 2 CM ΜΌ o -0 20 co oo LO LO O o 044 800 Binding region Ts(MAX) .(mm) § 5.94 | 6.32 | co cO | 4.60 I CM lo CO CO 4.56 co 7.76 5.68 8.05 σι 7.37 | 4.89 I LO CM Ts(min) (mm) co LO lO có 756 ¥ CM OO 4 08 4 48 co co LO ¡cí CM LO 722 395 674 co 3.98 4 55 W (mm) £ £ £ 2 CM co LO 2 2 2 Oí CM CM CM 2 O 2 2 Rgión metal base Tb(ave) (mm) 4.50 s | 6.08 I 75 / £ LO LO 4.52 5.48 £ 5.98 4.50 LO 4.66 442 458 Position of union Position of feeding C) Í2 m CM ¿00 O o § 2 LO $2 2 CM ¡o CM LO CQ 2 co 342 Thickness objective wall (mm) ost θ 009 | 6 00 I 750 | 4 50 I 09 / θ s 4 50 4 50 4 50 6 00 7 50 4 50 7 50 LO 4 50 4 50 Patrón de reducción de estiramiento Diámetro exterior objetivo (mm) 5 8Z7 co CM 3 3 877 27.8 27.8 45.9 27.8 27.8 2 44.3 | 26.6 I 26.6 266 Calendano de reducción de estiramiento c < co OO < < a < co LU LU LU Temp de calentamiento rc.i co fo 950 | 830 | | 680 I | 880 I θ | 850 | s LO LO 800 830 920 680 790 850 LO 950 800 Tb(Ave) / Db(Ave) > 10Ό (%) CO <£> CO 2 2 CO co CO 05 05 CO CO 27 2 LO CO o LO CO CO Extraction reduction ratioCumulative (%) 5 44.5 3 | 44.6 I CO OO CO lo 427 45.0 293 10 446 LO 05 CO CO CO co 463 Outside diameter after stretching reduction (mm) 27.83 <o CM | 27 92 I | 27 68 | | 2412 I 44 36 | 44.15 | 27 52 27 46 27.50 45 95 27.42 27.68 24 28 44.28 | 26 61 I 26 58 26 84 Diámetro exterior antes de la reducción de estiramiento (mm) LO o 50 0 | 50 0 | 0 09 | 50 0 | 65 0 CO LO LO CO S LO LO LO CO | 50 0 | 50 0 0 09 No de tubo de Acero 5 co 3 IO 3 3 co A-9 A-10 A-12 A-13 A-14 A-15 A-16 Zl-v A-18 A-19 U04 Table 4 Notes Example | Example | Example | Example | Example | Example | Example | Example | Example | Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example | Comparative Example Comparative Example Plug friction o _o .0 .0 .0 co .0 co co 03 O »2 Improvement ratio Csl CXJ un o O o Csl 03 CT QJ 03 OJ Comparative example of same dimensions αό σ> ώ ώ co CO co CD C¿ B-16 | B-19 a Torsional fatigue cycles (>10Λ6) 2 8 2 2 2 2 CD o Csl 2 CO CO o O LO r-value Csl co CD T CM CD 03 2 03 LO 2 LO 2 CD Tensile strength TS (MPa) 1601 | 1563 | 1582 I tt9l 1 1585 co 1621 | 1604 I 1588 1593 CD 1595 1574 1608 co C0 1604 1557 1524 1523 8 O 03 8 s 03 8 § CXI ss 03 co 03 CO 03 s LÍ3 03 2 1— o 0 03 O 3 0 02 0 03 0 02 I oo o £ o -0 05 0 05 0 25 o Csl Csl 0 02 O -0 08 H (mm) O o 03 O 900 C3 OI zo o I 0.52 Ο0Ό -0 15 0.29 69Ό 0.29 99 Ό 063 0.05 0.44 -0.25 •O Ts(MAX) (mm) 4.65 est 82 = | 6.22 I s 750 4.62 4.52 6.24 7.55 5.84 8 3 7.35 § 4.20 LO cu cz ;O QJ íi 1— 458 8 LO lO <D 5 | 4 45 I 5 CO O 4.48 567 03 533 03 3 99 687 398 483 C¿ W (mm) CO £ cq 2 2 2 LO LO ex 2 03 2 2 2 co LO O có có Región de metal base | Tb(ave) (mm) ΐ σ> 8 LO | 6 04 I LO 3 8 453 4 48 5 52 748 6 02 748 4 55 OS / 4 66 | CXI co Union position Clon power position C) co 3 LO CXI 288 θ O § | 226 | LO 2 Csl CD Csj CXI 255 LO co 8 LO CD 342 s 0. συ. objective wall (mm) 4.50 | 4.50 I 00'9 1 00'9 1 o | 4.50 I o 4.50 4.50 4.50 4.50 00'9 7.50 4.50 7.50 4.50 4.50 4.50 cu cu Ό c Ό OS £ Diámetro extenor objective (mm) co cs¡ £ Csl CM co Csj 5 278 278 278 459 278 278 Csl 44 3 266 26 6 26 6 2 Tn CU Extraction reducción calendar < < < < < CO OO < < < a < < O LU LU LU . <l e <l calentamiento (°c) 089 o 950 830 | 880 850 lo 800 920 680 790 s 8 008 ^e) db(avei 100(%) csl co 2 272 cd co 03 io ιο r- £ proporción de reduc- ción estiramiento acumula do (%) 44.5 i 84+ 44.6 7 293 u3 46.8 46.3 diámetro extenor después ae la reducción (mm) 27 83 76 cxi 92 89 28 24 12 44 36 15 52 46 50 45 95 42 68 26 61 58 84 exterior antes 50.0 65.0 0ό9 tubo acero có 3 8*8 m b-10 ώ b-12 b-13 b-14 b-15 b-16 zi-a b-19U04 List of Reference Signs (1) Electrical resistance welded steel tube (2) Electrical resistance welded seam (3) Joint region (4) Position defining the maximum wall thickness of the joint section (5) Position defining the minimum wall thickness of the joint region (6) Base metal region (7) Steel strip (8) Continuous forming machine (9) Open tube (10) Welding means (11) Squeeze roll (12) Hollow tube (13) Cutting machine (14) Heating means; (15) Rolling roll (16) Rolling stand (suffix numbers indicate stand numbers) (17) Calibration center (18) Gauge diameter< / l> < / max>

Claims

1. An electrical resistance welded steel pipe comprising a joint region and a base metal region, having in the joint region a range of ±10° in a circumferential direction of the pipe with respect to an electrical resistance welded joint formed in a longitudinal direction of the pipe, the base metal region being a region distinct from the joint region, wherein the electrical resistance welded steel pipe has a value r in the longitudinal direction of the pipe of 1.0 or greater, H (mm) and W (mm) satisfy formula (1) below, where H (mm) is a difference between Ts(min) (mm) and Tb(Ave) (mm) (Tb(Ave) - Ts(min>), Ts(min) (mm) is a minimum wall thickness value of the joint region, Tb(Ave) (mm) is an average wall thickness value of the base metal region, and W (mm) is an arc length of an internal surface of the pipe in the joint region, and Ts(max) (mm) and Tb(Ave) (mm) satisfy formula (2) below, where Ts(max) (mm) is a maximum wall thickness value of the joint region. H / W < 0.10 formula (1) Ts(MAX; / Tb(Ave) < 1.05 formula (2).

2. The electrically resistance welded steel pipe according to claim 1, wherein Tb(Ave) (mm) and Db(Ave) (mm) satisfy formula (3) below, wherein Db(Ave) (mm) is an average value of the pipe's outside diameter in the base metal region. (Tb(Ave) / Db(Ave)) x 100 > 15% formula (3) 3. The electrical resistance welded steel tube according to claim 1 or 2, wherein the r value is an r value in the longitudinal direction of the tube in the base metal region.

4. A method for manufacturing the electrical resistance welded steel tube according to any of claims 1 to 3, the method comprising: performing a forming operation on a steel strip to form an open pipe; performing electrical resistance welding on the open pipe to form a hollow pipe; and heating the hollow pipe to a heating temperature of 650°C or higher and performing stretch reduction rolling on the hollow pipe to a cumulative stretch reduction ratio of 30% or higher, wherein the stretch reduction rolling is performed so as to ensure that, on a rolling stand with a stretch reduction ratio of 5.0% or higher, the electrical resistance welded joint does not shift across a region of a roll, the region having a range of ± 5.0° with respect to a roller calibration center, and the electrical resistance welded joint also does not move through regions of the roller, the regions have a range of ± 5.0° with respect to the respective positions of 360° / (nx2) to the left and to the right of the calibration center, where n is the number of rollers per support.

5. An automotive structural member in which the electrical resistance welded steel tube is used in accordance with any of claims 1 to 3.

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