JP2018094599A - Tube material and manufacturing method of the tube material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce energy consumption in manufacturing a steel pipe with high rigidity.SOLUTION: A tube material 20 is formed of a steel material comprising, by weight, 0.15% or less of C, 0.15-0.35% of Si, 0.3-1.5% of Mn, and 0.030% or less of S, and containing at least one kind out of 0.005-0.05% of Nb, 0.040-0.10% of V, and 0.01-0.08% of Ti, and the balance Fe with inevitable impurities. An average crystal grain size of a ferrite structure in a cross section vertical to a length direction of the tube material 20 is 5 μm or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for manufacturing a steel pipe having high strength.

  In an air bag system that improves the collision safety of an automobile, it is necessary to rapidly deploy the airbag when the automobile collides. Therefore, in the airbag system, a dedicated gas supply device (inflator) that can supply a sufficient amount of gas in a short time is used. As the inflator, a gas storage container that stores a high-pressure filling gas and a gunpowder storage container that stores explosives are used. In such an inflator, when the airbag is deployed, the gunpowder is ignited, and the sealing material is destroyed by a shock wave generated by the ignited gunpowder exploding. And the combustion gas of a gunpowder and filling gas are supplied to an airbag through the destroyed sealing material. At this time, the gas storage container (inflator gas storage container) is required to have high strength because a high pressure of the filling gas and a shock wave when the explosive explodes are applied to the inner peripheral surface. Therefore, in the production of the gas container for an inflator, the composition is appropriately adjusted, and heat treatment such as quenching and tempering is performed on the steel pipe formed in a desired shape in advance to increase the strength (for example, , See Patent Document 1).

JP 2004-76034 A

  However, when heat treatment such as quenching and tempering is performed, it is essential to heat the steel pipe, so that the amount of energy consumed when manufacturing the inflator gas storage container is increased. This problem is not limited when manufacturing a gas container for an inflator, but is common when manufacturing various steel pipes that require high strength.

  This invention is made | formed in order to solve the conventional subject mentioned above, and it aims at providing the technique which reduces the energy consumption at the time of manufacturing a steel pipe with high intensity | strength.

  In order to achieve at least a part of the above object, the present invention can be realized as the following forms or application examples.

[Application example]
Containing 0.15 wt% or less of C, 0.15 to 0.35 wt% of Si, 0.3 to 1.5 wt% of Mn and 0.030 wt% or less of S; A steel material containing at least one of 0.05% by weight of Nb, 0.040 to 0.10% by weight of V and 0.01 to 0.08% by weight of Ti, with the balance being Fe and inevitable impurities And a tube material having an average crystal grain size of a ferrite structure in a cross section perpendicular to the length direction of 5 μm or less.

  In the steel material used in this application example, the tensile strength of the pipe material can be sufficiently increased by setting the average grain size of the ferrite structure in the cross section perpendicular to the length direction to 5 μm. Such refinement of the ferrite structure proceeds by cold working the raw material (original pipe material) made of the steel material. Therefore, since heat treatment can be omitted in the manufacture of the pipe material of this application example, it is possible to reduce energy consumption when manufacturing a pipe material that is a steel pipe having high strength.

  Note that the present invention can be realized in various modes. For example, it is realizable in aspects, such as a pipe material, the manufacturing method of a pipe material, the pipe material manufactured with the manufacturing method, various members using those pipe materials, and a manufacturing method.

Process drawing which shows a part of manufacturing process of the gas storage container for inflators. Explanatory drawing which shows the mode of pilger rolling. Explanatory drawing which shows the stress added to an intermediate pipe material at the time of pilger rolling. The graph which shows the relationship between content of S and a crack generation limit. The graph which shows the relationship between an area reduction rate and tensile strength. The graph which shows the relationship between an area reduction rate and hardness. The graph which shows the relationship between an area reduction rate and ductility. Explanatory drawing which shows the evaluation result of the refinement | miniaturization condition of a ferrite structure.

Hereinafter, modes for carrying out the present invention will be described in the following order.
A. Embodiment:
A1. Manufacturing process of inflator gas container:
A2. Pilger rolling:
A3. Steel composition:
B. Example:
B1. Steel composition evaluated:
B2. Strength after diameter reduction:
B3. Tissue after diameter reduction:
C. Variations:

A. Embodiment:
A1. Manufacturing process of inflator gas container:
FIG. 1 is a process diagram showing a part of a manufacturing process of a gas storage container for an inflator. An inflator is a device that supplies gas used to deploy an airbag in an airbag system. The inflator gas storage container is a container for storing a high-pressure filling gas that is part of the gas supplied to the airbag, and is manufactured using a steel pipe. The inflator is formed by storing a high-pressure filling gas in an inflator gas storage container and attaching an explosive storage container containing explosives to the inflator gas storage container. When the airbag system is operated, the gunpowder is ignited, and the sealing material is destroyed by a shock wave generated by the explosion of the ignited gunpowder. The airbag is developed by supplying the combustion gas of the explosive and the filling gas to the airbag through the broken sealing material. As described above, the inflator gas storage container is required to have high strength because a high pressure of the filling gas and a shock wave when the explosive explodes are applied to the inner peripheral surface.

  In the manufacture of an inflator gas storage container, first, as shown in FIG. 1A, a steel pipe (original pipe material) 10 that is a raw material of the inflator gas storage container is prepared. As the raw pipe material 10, for example, a seamless steel pipe manufactured by the Mannesmann method or the like is used. In preparing the raw pipe material 10, a long steel pipe is cut into an appropriate length.

  Next, by performing pilger rolling (described later) on the prepared raw pipe material 10, as shown in FIG. 1 (b), the inner diameter and the outer diameter (hereinafter referred to as “pipe diameter”) than the original pipe material 10 are obtained. A small pipe material (small diameter pipe) 20 having a small wall thickness is manufactured. In the process of manufacturing the small-diameter pipe 20, pilger rolling is performed so that the area reduction rate is 70% to 85%. Here, the area reduction rate refers to a reduction rate of the cross-sectional area with respect to the cross-sectional area of the raw pipe material 10 in a plane perpendicular to the length direction.

  As shown in FIG. 1, when the small-diameter pipe 20 is manufactured from the raw pipe material 10, the small-diameter pipe 20 is longer than the original pipe material 10 because the cross-sectional area in a plane perpendicular to the length direction decreases. Therefore, the length of the raw pipe material 10 is shorter than the small-diameter pipe 20 having substantially the same length as the inflator gas storage container.

  Work hardening occurs by performing pilger rolling when manufacturing the small-diameter pipe 20 from the raw pipe material 10. By this work hardening, the tensile strength of the small-diameter pipe 20 can be increased without performing heat treatment or surface treatment. Therefore, in this embodiment, in order to sufficiently increase the tensile strength by work hardening, the composition of the steel material used as the raw pipe material 10 is adjusted as described later. In general, when work hardening occurs, ductility decreases. Therefore, the composition of the steel material is adjusted so as to suppress an excessive decrease in ductility due to work hardening.

  The small-diameter pipe 20 manufactured in this way is subjected to drawing, which is a kind of cold working, as shown in FIG. Thereby, the tube material (container tube) 30 before being finally processed into the inflator gas storage container is manufactured. Then, if necessary, the container base tube 30 is subjected to processing such as drilling and cutting, and other parts are welded to the appropriately processed container base tube 30 to manufacture an inflator gas storage container. . Note that the tensile strength obtained in the small-diameter pipe 20 is also maintained by drawing the small-diameter pipe 20 in this way. Further, since the tensile strength does not decrease even when drilling, cutting, welding or further cold working is performed, the strength of the finally obtained gas container for inflator can be sufficiently increased.

  Thus, in the manufacturing process of the inflator gas storage container, after manufacturing the small-diameter pipe 20, cold processing, drilling, cutting, and the like are performed. In these processes, when the hardness (Vickers hardness) of the small-diameter pipe 20 is increased, the life of a tool for performing the process is shortened. Moreover, welding is also performed after manufacture of the small diameter pipe 20. Considering these points, the composition of the steel material is adjusted so as to suppress an excessive increase in hardness due to work hardening and sufficiently increase the weldability. In the present specification and the present invention, various processes (drawing, drilling, cutting, welding, etc.) that are performed on the manufactured small-diameter pipe 20 and performed for the manufacture of the gas container for an inflator are collectively named, Also called post-processing.

A2. Pilger rolling:
FIG. 2 is an explanatory diagram showing a state of pilger rolling performed when the small-diameter pipe 20 is manufactured from the raw pipe material 10. FIG. 2 shows a state in which the Pilger rolling mill 100, the original pipe material 10, the small-diameter pipe 20, and the pipe material (intermediate pipe material) 90 being rolled are cut along a plane that includes the axis c and is perpendicular to the roll shaft 114 (described later). Show.

  The pilger rolling mill 100 shown in FIG. 2 includes a pair of roll dies 110, a mandrel 120, and a rod 130. The roll die 110 has a roll body 112 and a roll shaft 114, and the roll body 112 is rotatable around the roll shaft 114. The roll body 112 is provided with a substantially semicircular groove (caliber) 119 provided from the outer peripheral side toward the roll shaft 114. The caliber 119 is formed so that its inner diameter gradually changes in the circumferential direction of the roll body 112.

  The mandrel 120 is a truncated cone-shaped member formed such that the outer diameter decreases from the raw pipe material 10 side (upstream side) toward the small diameter pipe 20 side (downstream side). The mandrel 120 is attached to the rod 130 on the upstream side thereof, and the mandrel 120 is also rotated by rotating the rod 130 about the axis c.

  As shown in FIG. 2, the roll main body 112 is disposed on the outer peripheral side of the intermediate tube member 90, and the mandrel 120 is disposed on the inner peripheral side of the intermediate tube member 90. Then, with the inner surface of the caliber 119 pressed against the outer peripheral surface of the intermediate tube member 90, the pair of roll dies 110 are simultaneously reciprocated in both directions, upstream and downstream. Thereby, the intermediate tube material 90 is deformed until the inner surface thereof contacts the mandrel 120. In this way, the roll die 110 is reciprocated, and the mandrel 120 is rotated to rotate the original tube material 10, the intermediate tube material 90, and the small diameter tube 20 (material to be processed). By repeating the reciprocating movement of the roll die 100 and the rotation of the workpiece, the small diameter tube 20 is obtained.

  FIG. 3 is an explanatory diagram showing stress applied to the intermediate tube 90 during pilger rolling (represented by white arrows). FIG. 3A shows the cross section shown in FIG. 2 in an enlarged manner near the position (contact position) where the inner surface of the caliber 119 and the outer peripheral surface of the intermediate tube 90 are in contact with each other, and FIG. The cross section cut by a plane passing through the position and perpendicular to the axis c is shown enlarged.

  As shown in FIG. 3, by performing the pilger rolling, the intermediate pipe member 90 is subjected to compressive stress in the vertical direction on the paper surface on the inner peripheral surface and the outer peripheral surface thereof. Further, since the inner diameter of the caliber 119 changes in the circumferential direction of the roll main body 112, when the roll main body 112 (roll die 110) is moved toward the downstream side as indicated by the black arrow, The intermediate tube material 90 is contacted. As a result, the intermediate pipe member 90 is subjected to stress in an oblique direction on the paper surface on the inner and outer peripheral surfaces thereof. By applying the compressive stress in this way, the ferrite structure (crystal grains) of the intermediate tube member 90 and the small diameter tube 20 is refined in a cross section perpendicular to the axis c direction (length direction).

A3. Steel composition:
As described above, the ferrite structure of the small-diameter tube 20 is refined in a cross section perpendicular to the length direction by pilger rolling. Thus, by reducing the average crystal grain size of the ferrite structure in the cross section perpendicular to the length direction (hereinafter, also simply referred to as “average crystal grain size”), the tensile strength can be obtained without performing heat treatment or surface treatment. Can be made high enough. In addition, a decrease in ductility can be suppressed by reducing the average crystal grain size and increasing the tensile strength. These effects are remarkably exhibited when the average crystal grain size is 5 μm or less. Therefore, the composition of the steel material is determined so that the average crystal grain size is 5 μm or less in the small diameter tube 20.

  In pilger rolling, it is difficult to reduce the area reduction rate to 90% or more. Generally, when the area reduction rate is low, it is difficult to refine the ferrite structure. In consideration of such characteristics, in the present embodiment, the composition of the steel material was determined so that the average grain size was 5 μm or less even in the area reduction ratio of 70 to 85%.

  Further, as described above, when manufacturing the gas storage container for an inflator, cold working, drilling, cutting, or welding is performed after pilger rolling. Therefore, the composition of the steel material was determined so that the excessive increase in hardness was suppressed by pilger rolling and the weldability was sufficiently high. Specifically, the steel material contains the contained elements as shown below, with the balance being iron (Fe) and inevitable impurities. In addition, below, content of each containing element is represented by weight%.

  Carbon (C) is an element that increases the tensile strength. However, when the content is increased, the weldability is lowered, and the hardness is rapidly increased by work hardening and the ductility is lowered. Therefore, the C content is 0.15% or less. In addition, when the target tensile strength of the small diameter pipe 20 is about 800 MPa, the content is preferably set to 0.10% or less.

  Manganese (Mn) is an element that increases the tensile strength like C, and complements the effect of C. Therefore, to make the tensile strength sufficiently high, the Mn content is set to 0.3 to 1.5%. The content of Mn is preferably adjusted depending on the presence or absence of chromium (Cr) and molybdenum (Mo) that are selectively added as will be described later. When adding Cr and Mo, the Mn content is preferably 0.30 to 0.85%. On the other hand, when Cr and Mo are not added, the Mn content is preferably 0.60 to 1.5%.

  Cr is an element that promotes improvement in tensile strength by work hardening, and is selectively added. The Cr content is 0.85 to 1.25%. Mo, like Cr, is an element that promotes improvement of tensile strength by work hardening, and is added simultaneously with the addition of Cr. The Mo content is 0.15 to 0.35%.

  Sulfur (S) is an effective element for improving machinability. However, since S reduces ductility, there is a possibility that cracks may occur during pilger rolling and during subsequent cold working. Therefore, the upper limit of the S content was determined experimentally.

  FIG. 4 is a graph showing the relationship between the S content (S content) and the limit processing rate (cracking limit) at which cracking occurs during cold working. The graph of FIG. 4 shows the evaluation result of the crack generation limit by the ring compression test in which the ring-shaped test material is upset and forged. The horizontal axis represents the S content, and the vertical axis represents the crack generation limit. Represents. The crack generation limit is an upsetting rate when a crack occurs on the outer peripheral surface in the ring compression test.

  In the evaluation, materials to be tested having different S contents based on SCM415 were prepared. One set of prepared materials to be tested was subjected to normal annealing, and the other set was subjected to spheroidizing annealing. And the ring compression test was done about each test material, and the crack generation limit was evaluated. As a result, even in the test material subjected to spheroidizing annealing with a low crack generation limit, the crack generation limit became about 70% or more by setting the S content to 0.015% or less. Based on the evaluation result of the crack generation limit, the S content was set to 0.015% or less. Note that when the S content is 0.010% or less, the price of the steel material increases rapidly. Therefore, the practical lower limit of the S content is 0.010%.

  Silicon (Si) is an element that promotes ferrite transformation, and in order to facilitate cold working, the lower limit of the content is set to 0.15%. On the other hand, when the Si content increases, ductility decreases. Therefore, the upper limit of the Si content is 0.35%.

  Titanium (Ti) and niobium (Nb) suppress the growth of crystals having a ferrite structure of nitride. Therefore, by adding at least one of Ti and Nb, the ferrite structure can be refined and the variation in the crystal grain size of the ferrite structure can be reduced (homogenized). Thereby, at the time of cold processing, a fracture | rupture and a crack can be suppressed and a processing limit can be raised. In addition, when adding any one of Ti and Nb, it is preferable to add Ti from a viewpoint of availability and reduction of the price of steel materials.

  In order to express the effect of refining and homogenizing the ferrite structure, when Ti is added, the content is 0.01 to 0.08%, and when Nb is added, the content is 0. 0.005 to 0.05%. Furthermore, in order to more reliably express the effect of refining and homogenizing the ferrite structure, the Ti content is more preferably 0.03 to 0.06%, and the Nb content is 0.02. It is preferable to set it to -0.03%.

  Vanadium (V) is an element that improves yield stress (yield strength) and is selectively added. V also suppresses the growth of crystals in which the carbide is a ferrite structure. Therefore, the ferrite structure can be refined by adding V. When adding V, in order to express these effects, the V content is set to 0.040 to 0.10%.

  In the present invention, among the elements Cr, Mo, Ti, Nb, and V that are selectively added, any one of the elements Ti, Nb, and V having an effect of refining the ferrite structure is an essential additive element. It is. Moreover, as mentioned above, Cr and Mo are added simultaneously.

  Thus, in the present embodiment, work hardening is generated by performing pilger rolling on the thick tube material 10 having a large tube diameter, and the tensile strength of the obtained small-diameter tube 20 is increased. Thereby, the small diameter pipe | tube 20 which has sufficient tensile strength as a gas storage container for inflators can be manufactured, without performing heat processing, such as hardening and tempering. Therefore, according to this embodiment, since energy is not required for heat processing, consumption of energy at the time of manufacturing the gas storage container for inflators can be suppressed. Further, by omitting the heat treatment, the occurrence of bending is suppressed even when the small diameter tube 20 is lengthened. Therefore, the process of correcting the generated bending can be omitted.

  Furthermore, by determining the composition of the steel material as the material as described above, pilger rolling with a reduction in area of 70 to 85% is performed, and the average crystal grain size is set to 5 μm or less. Therefore, the tensile strength can be sufficiently increased while suppressing a decrease in ductility of the obtained small-diameter pipe 20. In addition, the tensile strength achieved in the present embodiment corresponds to 8.8 (tensile strength: 800 MPa, yield strength 640 MPa) to 10.9 (tensile strength: 1000 MPa, yield strength 900 MPa) or more in the strength category. .

  In the present embodiment, the composition of the steel material is determined in consideration of post-processing (drawing, drilling, cutting, welding, etc.) when manufacturing the inflator gas storage container from the small-diameter pipe 20. Therefore, it is possible to more easily manufacture the inflator gas storage container from the small diameter tube 20. In particular, in this embodiment, since the excessive rise in the hardness by pilger rolling is suppressed, it can suppress that the lifetime of the tool for processing shortens.

B. Example:
B1. Summary of evaluation:
In order to confirm the effect of the present invention, a test material comprising two types of steel materials (steel material A and steel material B) was prepared. And after work hardening the prepared to-be-tested material, the mechanical characteristic and the refinement | miniaturization condition of a ferrite structure were evaluated. The composition of the steel used for the prepared material to be tested is shown in Table 1 below.

  The mechanical properties to be evaluated are tensile strength, hardness (Vickers hardness) and ductility (drawing). In the evaluation of mechanical characteristics, the reduction in area due to processing was changed from 10% to 90%, and the change in each mechanical characteristic due to the reduction in area was investigated.

  The fineness of the ferrite structure was evaluated by cutting the material to be tested on a surface perpendicular to the length direction and taking a structure photograph of the cross section. Evaluation of the refinement state of the ferrite structure was performed using a material to be tested in which the area reduction rate by processing was 70%.

B2. Evaluation of mechanical properties:
5 to 7 show the evaluation results of the mechanical characteristics. FIG. 5 is a graph showing the relationship between the area reduction rate and the tensile strength. As shown in FIG. 5, the material under test (steel material) with a low C content in the unprocessed state (the area reduction rate is 0%) and in all areas where the area reduction rate is 10% to 90% A) had a lower tensile strength than the material to be tested (steel material B) having a high C content. However, even when the steel material A was used, the tensile strength could be 800 MPa or more by setting the area reduction rate to 70% or more. On the other hand, when the steel material B was used, the tensile strength could be 1000 MPa or more by making the area reduction rate 70% or more. From this, it has been confirmed that even if any of the steel material A and the steel material B is used, the tensile strength can be sufficiently increased by setting the area reduction rate to 70% or more.

  FIG. 6 is a graph showing the relationship between the area reduction rate and the hardness (Vickers hardness). In FIG. 6, the numerical value shown in the vicinity of the mark represents the amount of increase in hardness due to processing. As shown in FIG. 6, the material under test (steel material) having a high C content in the unprocessed state (the area reduction rate is 0%) and in the entire area where the area reduction rate is 10% to 90%. B) had higher hardness than the material to be tested (steel material A) having a low C content. Further, the amount of increase in hardness was higher for steel B than for steel A. However, even in the steel material B having a high hardness increase amount, the hardness increase amount was 212 HV when the area reduction rate was 85%. From this, it was confirmed that even if any of the steel materials A and B was used, an excessive increase in hardness due to work hardening could be sufficiently suppressed by setting the area reduction rate to 85% or less.

  FIG. 7 is a graph showing the relationship between the area reduction rate and ductility (drawing). As shown in FIG. 7, the material to be tested (steel material) having a high C content in the unprocessed state (the area reduction rate is 0%) and in all areas where the area reduction rate is 10% to 90% B) had lower ductility than the material to be tested (steel material A) having a low C content. However, even in the steel material B having low ductility, the drawing at the area reduction rate of 85% was about 65%. From this, it was confirmed that even if any of the steel material A and the steel material B is used, the reduction in ductility due to work hardening can be sufficiently suppressed by setting the area reduction rate to 85% or less.

B3. Evaluation of refinement of ferrite structure:
FIG. 8 is an explanatory view showing the evaluation results of the state of refinement of the ferrite structure. FIG. 8A is a structural photograph of the material to be tested (steel material A) with a low C content, and FIG. 8B is a structural photograph of the material to be tested (steel material B) with a high C content. is there. As shown in FIG. 8A and FIG. 8B, the average crystal grain size of the ferrite structure was 5 μm or less in both the steel materials A and B. In general, the refinement of the ferrite structure proceeds as the area reduction rate increases. Therefore, from the evaluation results shown in FIG. 8, it can be confirmed that the average crystal grain size can be reduced to 5 μm or less by setting the area reduction rate to 70% or more regardless of whether the steel material A or the steel material B is used. It was.

C. Variations:
The present invention is not limited to the above-described embodiments and examples, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

C1. Modification 1:
In the above embodiment, the raw pipe material 10 is pilger-rolled in order to manufacture the small-diameter pipe 20, but in general, the small-diameter pipe 20 has a larger pipe diameter and a thicker wall than the small-diameter pipe 20. It can manufacture by giving the pipe material 10 cold processing (cold diameter reduction processing). For example, it is possible to produce the small-diameter pipe 20 by drawing the raw pipe material 10. Even in this case, the area reduction rate is preferably 70 to 85%. Even if it does in this way, since the average crystal grain diameter of a ferrite structure can be 5 micrometers or less, tensile strength can be made high enough. However, as described above, by performing pilger rolling, compressive stress is applied to the intermediate tube member 90 being processed on both the outer peripheral side and the inner peripheral side. This compressive stress promotes refinement of the ferrite structure. Therefore, by performing pilger rolling, the average crystal grain size of the ferrite structure of the small-diameter tube 20 can be more reliably set to 5 μm or less, and the tensile strength of the small-diameter tube 20 can be sufficiently increased.

C2. Modification 2:
In the above embodiment, the small-diameter pipe 20 is manufactured from the original pipe material 10 by one pilger rolling, but it is also possible to manufacture the small-diameter pipe 20 from the original pipe material 10 by performing pilger rolling a plurality of times. . Moreover, it is good also as what manufactures the small diameter pipe | tube 20 from the raw pipe material 10 by performing various cold diameter reduction processes including a pilger rolling in multiple times. However, in this case, in order to ensure that the average crystal grain size of the ferrite structure of the small diameter tube 20 is 5 μm or less and the tensile strength of the small diameter tube 20 is sufficiently high, the final cold diameter reduction processing is called pilger rolling. It is preferable to do this. Further, in drawing or the like, it is difficult to increase the area reduction rate in one process, and it may be necessary to perform a number of processes more than pilger rolling. Also in this respect, it is preferable to perform pilger rolling as the cold diameter reduction processing.

C3. Modification 3:
In the said embodiment, although this invention is applied to the gas storage container for inflators, this invention can be applied to the various steel pipe by which high intensity | strength is requested | required. The present invention can be applied to various members such as a side door beam that is stored in a side door of an automobile and protects an occupant from a side collision, and a steering shaft that transmits rotation of a handle in an automobile. Further, the present invention is not limited to various members for automobiles, but can be applied to members for moving bodies such as railway vehicles and airplanes, members used for various mechanical devices, and the like.

DESCRIPTION OF SYMBOLS 10 ... Original pipe material 20 ... Small diameter pipe 30 ... Container base pipe 90 ... Intermediate pipe material 100 ... Pilger rolling mill 110 ... Roll die 112 ... Roll main body 114 ... Roll shaft 119 ... Caliber 120 ... Mandrel 130 ... Rod

Claims (7)

Containing 0.15 wt% or less of C, 0.15 to 0.35 wt% of Si, 0.3 to 1.5 wt% of Mn and 0.030 wt% or less of S; A steel material containing at least one of 0.05% by weight of Nb, 0.040 to 0.10% by weight of V and 0.01 to 0.08% by weight of Ti, with the balance being Fe and inevitable impurities Consists of
The average grain size of the ferrite structure in the cross section perpendicular to the length direction is 5 μm or less,
Tube material. The pipe according to claim 1,
The steel material further contains 0.85 to 1.25% by weight of Cr and 0.15 to 0.35% by weight of Mo,
The Mn content in the steel is 0.30 to 0.85% by weight,
Tube material.   The pipe material according to claim 1, wherein the Mn content in the steel material is 0.60 to 1.5% by weight.   The tube material is manufactured by subjecting an original tube material having an inner diameter and an outer diameter larger than those of the tube material and a wall thickness larger than that of the tube material to a cold reduction process so that the area reduction ratio is 70 to 85%. The pipe material according to any one of claims 1 to 3, wherein   The tube material according to claim 4, wherein the cold diameter reduction processing is pilger rolling.   The said pipe material is a pipe material in any one of Claims 1 thru | or 5 which is a container raw tube for manufacturing the gas storage container for inflators. A method of manufacturing a pipe material,
Containing 0.15 wt% or less of C, 0.15 to 0.35 wt% of Si, 0.3 to 1.5 wt% of Mn and 0.030 wt% or less of S; A steel material containing at least one of 0.05% by weight of Nb, 0.040 to 0.10% by weight of V and 0.01 to 0.08% by weight of Ti, with the balance being Fe and inevitable impurities The inner diameter and the outer diameter larger than the pipe material, and preparing a thick original pipe material than the pipe material, and
A step of cold-reducing the prepared raw pipe material so that the area reduction ratio is 70 to 85%;
Comprising
Manufacturing method of pipe material.