JP2008255397A - Method for producing electric resistance welded tube for hollow stabilizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an electric resistance welded tube for a hollow stabilizer imparted with high strength and having excellent bendability in the stage of a steel tube, and further exhibiting desired strength without annealing treatment after bending into a stabilizer shape. <P>SOLUTION: A steel having a component comprising, by mass, 0.15 to 0.30% C, ≤0.5% Si, 1.0 to 2.5% Mn, ≤0.03% P, ≤0.01% S, 0.5 to 1.5% Cr, 0.1 to 0.5% Mo, 0.0005 to 0.010% B, 0.01 to 0.1% Ti, ≤0.01% N and 0.02 to 0.08% Al, and the balance Fe with inevitable impurities is subjected to hot rolling, and is pickled, so as to be an electric resistance welded tube. At this time, the electric resistance weld zone is subjected to annealing under specified conditions, and is successively subjected to annealing satisfying the conditions in inequality; (T+273)/33+log(t)≥23; wherein, T: arrival temperature (°C); and t: holding time (s) at the arrival temperature, and further, the arrival temperature T: 380 to 710°C; and the holding time at the arrival temperature: ≥0.1 s. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention provides an electric sewing machine that can be manufactured with high productivity without requiring a quenching and tempering process after bending the stabilizer into the shape of the stabilizer when manufacturing a hollow stabilizer that maintains the running stability of an automobile. The present invention relates to a method for manufacturing a steel pipe.

A stabilizer which is an automobile part is a part for relaxing rolling of a vehicle body at cornering and ensuring running stability of the vehicle body at high speed. Steel bars (solid materials) are used as the material, but recently, steel pipes are frequently used from the viewpoint of weight reduction.
In addition, since the stabilizer is used for a long time in a state where it is attached to an automobile, it is required to have excellent fatigue durability. For this reason, the stabilizer member is required to have a tensile strength of 1000 N / mm ² or more. ing.

By the way, a hollow stabilizer is usually made of a steel pipe having an appropriate composition and size (diameter, plate thickness, etc.), processed at the end of the pipe, bent into a required shape at room temperature, and then quenched and tempered. It is manufactured by applying the process. Bending is performed prior to quenching and tempering because steel pipes that have become strong due to quenching and tempering generally have poor workability and it is difficult to perform strong processing with a bending angle of 90 degrees. This is because a predetermined shape is obtained and then the strength is increased by quenching and tempering while maintaining the predetermined shape. Further, after that, shot peening or painting for improving fatigue characteristics is performed as necessary.
Carbon steel of about 0.20% C is used as the material steel in order to exhibit a quenching effect in order to obtain a desired strength. Moreover, as a shape of a stabilizer, there are many U-shapes, and a bending process is often given to several places. And the steel pipe which receives a bending process is required to have a strict bending workability of a bending angle of 90 degrees.

The quenching and tempering process is a process performed to increase the strength in order to ensure fatigue durability as a stabilizer. And in patent document 1, in order to fully exhibit the quenching tempering effect, using what added B to raw material carbon steel is proposed.
Further, Patent Document 2 proposes that bending be performed warmly during the tempering step after quenching.
JP 58-197218 A JP 58-188518 A

As described above, in the conventional technique, a quenching and tempering process with a large energy consumption is indispensable for increasing the strength, resulting in an increase in cost.
The technique proposed in Patent Document 1 is also effective in increasing the strength and increasing the fatigue durability, but because the quenching and tempering process is performed, the number of processes is large and the energy consumption is also increased. The technique proposed in Patent Document 2 is also a significant technique in that the bending resistance is warm during the tempering process, so that the deformation resistance of the material is small and easy to process, and the time can be shortened. Consumption is the same as above.
The present invention has been devised to solve such problems, and has high strength and workability at the stage of the steel pipe, and can omit the quenching and tempering treatment performed after bending into a stabilizer shape. An object of the present invention is to provide a method of manufacturing an electric resistance welded steel pipe for a stabilizer that can reduce the number of processes and reduce energy consumption to secure a required strength at low cost.

In order to achieve the object, the method for producing a steel pipe for a hollow stabilizer of the present invention includes C: 0.15 to 0.30 mass%, Si: 0.5 mass% or less, Mn: 1.0 to 2.5 mass. %, P: 0.03 mass% or less, S: 0.01 mass% or less, Cr: 0.5-1.5 mass%, Mo: 0.1-0.5 mass%, B: 0.0005- 0.010% by mass, Ti: 0.01 to 0.1% by mass, N: 0.01% by mass or less and Al: 0.02 to 0.08% by mass, with the balance being Fe and inevitable impurities After finishing and hot-rolling a steel having a component composition in a temperature range of 800 to 950 ° C., winding it in a temperature range of 400 to 600 ° C. to form a hot rolled coil exhibiting a bainite-based metal structure, and further pickling When the hot-rolled coil is made into an ERW steel pipe, the ERW weld is cooled to a temperature below the Ms point. An ERW steel pipe manufactured by continuously annealing the ERW welded part in a temperature range of (Ac1 transformation point) to (Ac1 transformation point−100 ° C.) was used as a base pipe, and then the following formulas (1) to (3) It is the manufacturing method of the electric resistance welded steel pipe for hollow stabilizers characterized by cooling after performing annealing which satisfy | fills these conditions.
(T + 273) / 33 + log (t) ≧ 23 (1)
Here, T: ultimate temperature (° C.), t: retention time (second) at the ultimate temperature, and
Achieving temperature T: 380 to 710 ° C. (2)
Holding time at ultimate temperature: 0.1 second or longer (3)

In addition, as a steel pipe used as a raw pipe, what was set as the dimension range of plate thickness 1.5-6.0mm and outer diameter 10-40mm is preferable.
Moreover, the base plate is not a bainite-based hot-rolled coil manufactured under the above strict conditions, but an austenitic steel pipe having the same composition as described above is maintained in a temperature range of 800 to 950 ° C. to be austenitic. Then, after cooling to a temperature range of 400 to 600 ° C. at a cooling rate of 10 ° C./second or more and maintaining the temperature range and isothermal transformation to obtain an electric resistance steel pipe exhibiting a bainite-based metal structure, the steel pipe As the raw tube, after annealing that satisfies the conditions of the above formulas (1) to (3), it is cooled to form an electric-welded steel pipe for a hollow stabilizer, and then a hollow stabilizer may be manufactured by bending at room temperature. .

  The electric resistance welded steel pipe for hollow stabilizer provided in the present invention has its components adjusted to have high strength at the stage of the steel pipe before being processed into the shape of the stabilizer, and is subjected to hot rolling conditions, pipe forming conditions, and annealing after pipe forming. The conditions are adjusted, and bending is possible at room temperature after annealing. For this reason, quenching and tempering treatment can be omitted, and the number of steps and energy consumption for manufacturing the electric resistance welded steel pipe for hollow stabilizer can be reduced. In particular, since the annealing is performed before the bending process, the process is easy. In addition, since it is not necessary to heat-treat after processing into the shape of the stabilizer, it is not necessary to provide heat treatment equipment at the factory that processes the stabilizer, and to produce a high-strength hollow stabilizer having the same strength as the conventional product at a low cost. Can do.

  First, in order to develop a hollow stabilizer material that satisfies the required characteristics, the present inventors have made many studies on the effects of hot rolling conditions on the alloying elements and mechanical properties of steel that constitutes the ERW steel pipe that is the base pipe. The experiment was conducted. As a result, it is possible to manufacture an ERW steel pipe using a hot rolled coil wound at a temperature of 400 to 600 ° C. as a raw material after hot rolling the steel having the components specified in the present invention at a finishing temperature of 800 to 950 ° C. I found it effective.

Since the electric-welded welded portion of the steel pipe is rapidly cooled from the molten state, it is in a so-called quenched state. For this reason, the welded part is harder and less stretched than the base metal part. Therefore, the bending workability is poor as compared with the base material portion, and it is easy to cause processing cracks.
In order to improve the workability of such a welded part, when the welded part is annealed and the hardness is softened to the same level as that of the base material and the elongation is recovered, the overall strength of 1000 N / mm ² or more is good. It was able to demonstrate workability. In this annealing, heating that causes the entire base material to be annealed should be avoided.

By the way, when manufacturing a hollow stabilizer, it is necessary to perform bending until the bending angle reaches 90 degrees on the material steel pipe. In general, it is difficult to bend a high-strength steel pipe to which a large strain is applied to a bending angle of 90 degrees at room temperature.
Therefore, in the present invention, the bending process is performed after the elongation of the entire steel pipe is improved by annealing not only the welded part but also the entire steel pipe. In general, annealing improves the elongation, but the strength tends to decrease. For this reason, in this invention, the element which raises softening resistance like Cr, Mo, Ti is added appropriately, and it adjusts so that a strength fall may be suppressed even if it heats. Note that the annealing may be performed on the entire steel pipe, or only the part to be bent and the vicinity thereof may be partially heated and annealed.

Details will be described below.
First, alloy components, heat treatment conditions and the like defined in the present invention will be described.
C: 0.15-0.30 mass%
It is an alloy element necessary for obtaining the strength required as a hollow stabilizer. If the C content is less than 0.15% by mass, the required strength of 1000 N / mm ² or more cannot be obtained. However, when the C content exceeds 0.30% by mass, bending workability and toughness are deteriorated.
Si: 0.5% by mass or less When a large amount of Si is contained, the weldability deteriorates and scale flaws are easily generated. Moreover, the bad influence which degrades the surface quality of a hot-rolled sheet and inhibits toughness is also seen. Therefore, in the present invention, the upper limit of the Si content is regulated to 0.5% by mass.

Mn: 1.0 to 2.5% by mass
It is an alloying element that is important for improving the hardenability and strengthening of steel sheets. Mn suppresses ferrite transformation during cooling in hot rolling, and exhibits the effect of forming a bainite-based metal structure even at an extremely slow cooling rate. In order to exert the effect, at least 1.0% by mass is required. On the other hand, when a large amount of Mn exceeding 2.5% by mass is contained, the strength increasing effect and hardenability are saturated, and the weldability and toughness are deteriorated.
P: 0.03% by mass or less P is an element that deteriorates bending workability and toughness. When the P content exceeds 0.03% by mass, these properties are remarkably deteriorated.

S: 0.01% by mass or less An element that easily binds to Mn, and forms MnS that is an inclusion in steel, resulting in deterioration of bending workability. Therefore, in this invention, S content was controlled to 0.01 mass% or less.
Cr: 0.5 to 1.5% by mass
It is an element that increases the softening resistance (tempering softening resistance) during annealing. In order to acquire the effect, at least 0.5 mass% is required. However, if a large amount of Cr is contained so as to exceed 1.5% by mass, bending workability is lowered.

Mo: 0.1 to 0.5% by mass
It is an alloy element that is effective in improving strength and hardenability, and exhibits an effect of generating a tough bainite-based metal structure even at a low cooling rate. Moreover, the effect | action which raises the softening resistance at the time of annealing (tempering softening resistance) is also exhibited. In order to exert these actions, at least 0.1% by mass is required. However, even if a large amount of Mo exceeding 0.5% by mass is contained, further improvement in characteristics cannot be expected, and on the contrary, a large amount of expensive Mo is consumed, which is economically disadvantageous.

B: 0.0005-0.010 mass%
It is an alloy element that is effective in preventing the deterioration of toughness by significantly improving the hardenability of the steel material with a very small amount of addition, lowering the strain energy of the grain boundary and strengthening the grain boundary. Such an effect becomes remarkable when B is contained in an amount of 0.0005 mass% or more. However, even if the B content exceeds 0.010% by mass, the effect of addition of B is saturated and the toughness is deteriorated.

Ti: 0.01 to 0.1% by mass
It is also an important alloying component for fixing N dissolved in steel as nitride. That is, the amount of B consumed for fixing N is suppressed, and the quenching improving effect by B is efficiently exhibited. In addition, it has the effect of increasing the softening resistance during annealing (tempering softening resistance). Such an effect becomes remarkable when the Ti content is 0.01% by mass or more. However, if a large amount of Ti exceeding 0.05% by mass is contained, coarse nitrides are formed, resulting in deterioration of toughness.

N: 0.010% by mass or less Combined with Ti to produce TiN, exhibiting the effect of increasing the strength of the steel material and refining the crystal grains. However, when a large amount of N exceeding 0.010% by mass is contained, excess N is combined with B to reduce the effect of improving the hardenability of B.
Al: 0.020-0.080 mass%
It is an element added as a deoxidizer for molten steel, and 0.020% by mass or more is necessary. However, if the Al content exceeds 0.080% by mass, the cleanliness of the steel is impaired and surface defects are likely to occur.

Hot rolling finishing temperature: 800-950 ° C
In hot rolling, finish hot rolling is performed in a temperature range of 800 to 950 ° C. When the finishing temperature is less than 800 ° C., the deformation resistance increases, and the plate passing property such as narrowing of the steel plate is hindered. In addition, at a low finishing temperature, two-phase rolling occurs, and processed ferrite is easily generated. On the other hand, when the finishing temperature exceeds 950 ° C., the hot rolled structure becomes coarse, the workability deteriorates, the cooling strain in hot rolling increases, the shape of the steel sheet deteriorates, and water riding and uneven cooling occur in hot rolling. It becomes easy to do. As a result, the stability of the mechanical properties is impaired.

Winding temperature: 400-600 ° C
The steel strip after hot rolling is wound in a temperature range of 400 to 600 ° C. in order to obtain a high-strength coil with a metal structure mainly composed of bainite. When the coiling temperature is less than 400 ° C., the strength rises remarkably, and the stability of mechanical properties is impaired due to fluctuations in hot rolling conditions. In addition, in order to reduce the influence of the fluctuation | variation of the hot rolling conditions in an actual operation, it is preferable to set it as 450 degreeC or more. In addition, a coiling temperature that is too low causes cooling distortion and causes a shape defect in the steel sheet. On the other hand, when the coiling temperature exceeds 600 ° C., strength of 1000 N / mm ² or more may not be obtained due to fluctuations in hot rolling conditions, and grain boundary oxidation is likely to occur, and fatigue characteristics may be deteriorated.

Annealing of electric-welded welded parts Generally, in a hollow stabilizer, bending is performed from the torsion part to the arm part. The degree is a bending radius of 30 mm or more and a bending angle of 90 degrees or less on the neutral line. In general, when bending ERW pipes, welds that are not sufficiently annealed are harder and less ductile than the base metal, so if possible, place the welds near the neutral line of the bend. For example, measures are taken to prevent the weld from being strained as much as possible. However, in the case of a stabilizer, the shape is complicated and bent portions are often formed at a plurality of locations, and such measures as described above are often not always taken. For this reason, it is necessary to soften the ERW weld and impart elongation.

  In the method for producing an electric resistance steel pipe according to the present invention, the hot rolled coil is pickled and welded by a conventional method to obtain an electric resistance steel pipe. Usually, the electric-welded welded portion is rapidly cooled from a molten state to a so-called quenching state, and thus is harder and less stretched than the base material portion. Therefore, in the present invention, the ERW welded part is actively quenched to the Ms point or lower, and then only the welded part is annealed. A method of locally heating only the welded part by high-frequency heating or the like can be applied to the annealing process. This annealing process is performed only on the welded portion.

  According to the experiments by the present inventors, if the welded portion is annealed in a temperature range of (Ac1 transformation point) to (Ac1 transformation point−100 ° C.), the welded portion is softened to be equal to or lower than the base metal portion. I understood that. When the annealing temperature exceeds the Ac1 transformation point, it becomes austenite, so that it is quenched by subsequent cooling, and the purpose of softening cannot be achieved. Moreover, it does not fully soften at a temperature below the Ac1 transformation point of −100 ° C. If the annealing temperature is low, the time required for softening becomes long and the productivity is lowered, so the lower limit is preferably set to (Ac1 transformation point -70 ° C.).

Annealing As described above, it is difficult to bend a high-strength steel pipe that imparts a great strain to a bending angle of 90 degrees at room temperature. Therefore, in the present invention, bending can be performed at room temperature by annealing as a measure for improving the elongation of the steel pipe.
According to experiments by the inventors, the steels of the component systems indicated in the claims can be bent at a bending angle of 90 degrees when annealed at a temperature of 380 ° C. or higher. Further, even when elements having high softening resistance such as Cr, Mo, Ti were appropriately added, when the annealing temperature exceeded 710 ° C., the strength was lower than the target strength even if the holding time was short.

  In this annealing, the entire steel pipe may be annealed, or only the part where the bending process is performed and the vicinity thereof may be partially annealed. As a method of annealing the entire steel pipe, for example, an ERW steel pipe is inserted into a furnace that has reached a predetermined temperature and heated, or electrodes are connected to both ends of the ERW steel pipe, By energizing as a conductor, the entire ERW steel pipe can be heated. As a method of partially annealing, it is possible to use means such as high-frequency heating in which a high-frequency coil is placed outside the part to be annealed and heated.

Furthermore, from such a preliminary experiment, in order to express both required strength and bending workability, it is necessary to adjust the combination of the ultimate temperature of the annealing and the holding time. It has been found that the following relationship can be arranged when annealing is performed at the temperature.
(T + 273) / 33 + log (t) ≧ 23 (4)
Regarding the holding time t, if the annealing temperature is high, the steel pipe can be sufficiently annealed even if the holding time is short, but it is difficult to manage the holding time to less than 0.1 seconds practically. In the present invention, t ≧ 0.1 seconds or more.

The basis of the formula (4) will be described.
As a means for predicting the softening behavior accompanying tempering of carbon steel from the tempering conditions, as described in Non-Patent Document 1, the tempering parameter given by equation (5) as a function of the tempering temperature T and the tempering time t is known. ing.
T (C + logt) (5)
Here, C is a constant, and generally a value around 20 is used.
The tempering of carbon steel is a phenomenon related to the precipitation of carbides or their aggregation, and is a phenomenon related to the diffusion of each element in iron, so it can be expressed by the relationship between temperature and time as shown in the above equation, It is known that this parameter is applicable not only to carbon steel but also to special steel with a large amount of carbon and alloy elements added, and also applicable to tempering of bainite.

In the present invention, since the hardness after tempering is determined by the tempering temperature and time, practically, if the tempering conditions are such that the value of this tempering parameter is equal, the hardness will be the same and equivalent workability will be achieved. Take advantage of demonstrating. That is, in the steel component of the present invention, conditions for the annealing temperature and holding time at which bending for hollow stabilizers is possible are obtained by preliminary tests, and these are replaced with the values of the tempering parameters. After that, even if the specific annealing temperature and holding time change, if this value is more than the value obtained by preliminary experiments, it has been tempered sufficiently, and the ERW steel pipe can be used for hollow stabilizers, Is determined.
"Steel Materials Science" revised edition, by Kazama Kazo, Jikkyo Publishing Co., Ltd. (1994), p.179

Here, since it is cumbersome to use the above-described tempering parameter equation (5) as it is, the inventors have simplified and considered the ultimate temperature and holding time range of the annealing treatment practically used in the present invention. Found that can be used. As an example, when the ultimate temperature is 500 ° C. and the holding time is 5 seconds, the value of Equation (5) is 16,000. In that case, as shown in FIG. 1, although the relationship of Formula (5) draws a hyperbola, if it limits to the range of 380-710 degreeC which is the temperature used for the annealing process of this invention, as shown in FIG. A straight line approximation is possible. In that case, equation (5) can be modified as follows.
α (T + 273) + logt = B (6)
Where T: ultimate temperature (° C.)
t: Holding time at the ultimate temperature (seconds)
α, B: Constants Two constants can be determined experimentally.

Bending In the method for producing an electric resistance welded steel pipe for a hollow stabilizer according to the present invention, an annealing treatment is applied to the electric resistance welded steel pipe to be a base pipe as described above in order to improve elongation.
For this reason, bending at a bending angle of 90 degrees is possible even by bending at room temperature. By performing a bending process by a conventional method, it can be used as a stabilizer without being subjected to a second heat treatment after forming the stabilizer shape by the bending process.

In addition, if the whole manufacturing method of the electric resistance steel pipe for hollow stabilizers of this invention uses what shows the metal structure mainly of bainite, the intensity | strength of 1000 N / mm < ² > or more is favorable even if it does not perform the process of quenching and tempering. An electric-welded steel pipe that can be used as a blank pipe for a hollow stabilizer having processability is obtained.
In addition to the ones that specify the manufacturing conditions in order to obtain an ERW steel pipe exhibiting a bainite-based metal structure, even a previously manufactured ERW steel pipe should have a bainite-based metal structure by subsequent heat treatment. If it is a steel pipe, it can be easily bent into a stabilizer shape at room temperature by applying a predetermined annealing treatment.

By the way, since a hollow stabilizer generally used as an automobile part has a plate thickness of 1.5 to 6.0 mm and an outer diameter of 10 to 40 mm, even in the present invention, a plate thickness of 1.5 to 6 is used. It is preferable to produce an electric-welded steel pipe having an outer diameter of 10 to 40 mm using a 0.0 mm hot-rolled coil and bend it into a stabilizer shape using this steel pipe as a raw material.
In addition, in the normal stabilizer manufacturing process, coating for shot peening and rust prevention for improving fatigue characteristics is performed, but also in the method for manufacturing a hollow stabilizer in the present invention, shot peening and coating are not performed. Needless to say, it may be applied.

Various steels having the compositions shown in Table 1 were melted. Next, hot rolling was performed under conditions of a finish rolling temperature of 880 ° C. and a winding temperature of 500 ° C. to obtain a hot rolled steel strip having a plate thickness of 1.6 to 6.0 mm.
Subsequently, after skin pass rolling and pickling, pipe making was performed by a roll forming method, followed by electric resistance welding to obtain a steel pipe having an outer diameter of 19.1 to 38.1 mm. Table 2 shows the thickness, outer diameter, and the like of the obtained ERW steel pipe. The outer surface of the steel pipe was bead cut, and the welded part was water-cooled to 150 ° C, which is below the Ms point immediately after welding, and then the welded part was annealed at 680 ° C by high-frequency heating.
Thereafter, high-frequency heating was performed on a part of the steel pipe as annealing. The annealing conditions are as shown in Table 2. The rating of the high frequency power source used for heating is a frequency of 3 kHz and an output of 400 kW. The temperature of the steel pipe was measured using a thermocouple brought into contact with the steel pipe surface.

Next, each electric resistance welded steel pipe subjected to annealing was subjected to a bending test and a tensile test at room temperature.
In the bending test, a steel pipe cut to a length of 1 m so as to include the above-described annealed portion by high-frequency heating is prepared, and the annealed portion is positioned at the bending position by using a pipe bender device, and the bending is performed. It was bent by the method. The bending radius at the bending neutral line was set to 35 mm, and the bending angle was set to 90 degrees. The evaluation was made based on the presence or absence of cracks in the bent part (bending outside), and it was evaluated that cracks were generated even if cracks that did not lead to breakage were observed.
In the tensile test, a test piece having a length of 50 cm was cut out so as to include the above-mentioned annealed portion by high-frequency heating, and a bar-shaped jig having a diameter substantially equal to the inner diameter was inserted into the tube of the both-end gripping portion in accordance with JIS Z2241. It carried out in. Table 2 also shows the presence or absence of cracks in the bending test and the test results of tensile strength.

According to Table 2, the test piece obtained by subjecting the steel pipe having the prescribed component to the prescribed annealing had a tensile strength of 1000 N / mm ² or more and excellent bending workability.
On the other hand, No. 1 and 7 whose annealing temperature was lower than 380 ° C., and No. 12 where annealing was insufficient because the combination of annealing time and annealing temperature did not satisfy the formula (1). Although the strength exceeded 1000 N / mm ² , cracks occurred in the bent portion, and the bending workability was poor. Furthermore, since the steel components of Nos. 19 to 22 were outside the scope of the present invention, even when annealing was performed under appropriate conditions, both strength and bending workability could not be achieved.

FIG. 2 shows the relationship between the annealing conditions (arrival time T, holding time t) of each test piece and the presence or absence of cracks in the bending test. It has been shown that if the ultimate temperature is high or the holding time is long, sufficient cracking will not result in processing cracks. And the broken line in the figure shows that if an annealing condition corresponding to the right side of this broken line is selected, the processing crack does not occur. By determining two constants by the least square method, It can be expressed as
(T + 273) / 33 + log (t) ≧ 23 (4)
What annealed on the conditions within the range which satisfies (1)-(3) according to this invention did not generate | occur | produce the crack by a bending test, and showed favorable bending workability.

The figure which shows the relationship between the annealing process conditions (attainment temperature and holding time) in which a tempering parameter value shows a certain fixed value Figure showing the relationship between annealing conditions (annealing temperature, holding time) and the presence or absence of work cracks in a bending test

Claims (2)

C: 0.15-0.30 mass%, Si: 0.5 mass% or less, Mn: 1.0-2.5 mass%, P: 0.03 mass% or less, S: 0.01 mass% or less , Cr: 0.5 to 1.5 mass%, Mo: 0.1 to 0.5 mass%, B: 0.0005 to 0.010 mass%, Ti: 0.01 to 0.1 mass%, N : 0.01% by mass or less and Al: 0.02 to 0.08% by mass, and the steel having a composition composed of Fe and unavoidable impurities in the balance was finished and hot rolled in a temperature range of 800 to 950 ° C. Thereafter, the hot rolled coil exhibiting a bainite-based metal structure is wound by winding in a temperature range of 400 to 600 ° C., and when the hot rolled coil is made into an electric resistance steel pipe after pickling, the electric resistance welding portion is made Ms. After cooling to a temperature below the point, the ERW welded portion is continuously (Ac1 transformation point) to (Ac1 transformation point−100 ° C.). An electric-welded steel pipe manufactured by annealing in the temperature range of the above is used as a base pipe, and subsequently cooled after performing annealing satisfying the conditions of the following formulas (1) to (3): Production method.
(T + 273) / 33 + log (t) ≧ 23 (1)
Here, T: ultimate temperature (° C.), t: retention time (second) at the ultimate temperature, and
Achieving temperature T: 380 to 710 ° C. (2)
Holding time at ultimate temperature: 0.1 second or longer (3)   The method for producing an electric-welded steel pipe for a hollow stabilizer according to claim 1, wherein a dimension range of the steel pipe to be a raw pipe is a plate thickness of 1.5 to 6.0 mm and an outer diameter of 10 to 40 mm.

Images