TW201217199A - Process for producing steel pipe for air bag - Google Patents

Abstract

A process for producing a high-strength and high-toughness steel pipe for air bags is disclosed with which it is possible to simplify the step of cold drawing and reduce alloy cost. The process comprises: forming a seamless steel pipe from a steel which contains, in terms of mass%, 0.04-0.20% C, 0.10-0.50% Si, 0.10-1.00% Mn, up to 0.025% P, up to 0.005% S, up to 0.10% Al, 0.01-0.50% Cr, 0.01-0.50% Cu, and 0.01-0.50% Ni, with the remainder comprising Fe and incidental impurities; subjecting this seamless steel pipe to cold drawing at least once so as to result in a reduction of area exceeding 40%, thereby making the steel pipe have a given size; heating the drawn steel pipe to a temperature which is the Ac3 point or higher at a rate of 50 C/s or higher; subsequently cooling the heated steel pipe so that the cooling rate in the temperature range of at least 850-500 C is 50 C/s or higher, thereby quench-hardening the steel pipe; and then tempering the steel pipe at a temperature which is the Ac1 point or lower.

Description

201217199 VI. Description of the Invention: [Technical Field of the Invention] The present invention relates to a high strength of a tensile strength of 900 MPa or more and a vTrslOO (a ductile breaking rate of 1%) The conversion temperature is related to the inexpensive manufacturing method of the seamless steel pipe having a high degree of twist of 60 ° C or less. [Prior Art] In recent years, in the automotive industry, devices for seeking safety have been actively introduced. One of the devices developed is the airbag system, and most of the cars are currently being carried. The airbag system is a system that uses a gas to expand the airbag between the occupant and the occupant before the collision of the steering wheel or the instrument panel, and absorbs the kinetic energy of the occupant to reduce the damage. The airbag system was originally developed using explosive drugs. However, in recent years, the use of high-pressure gas-filled gas has been developed and its scope of application has been promoted. An air bag system that uses a high-pressure gas-filled gas is a gas for unfolding, for example, an inert gas (for example, argon) that is blown into a balloon during a collision, and is constantly held at a high pressure in a pressure accumulating container (accumulator) connected to the air bag. Inside, at the moment of the collision, gas is injected from the accumulator into the airbag to deploy the airbag. The accumulator is generally cut into a steel pipe of an appropriate length, and after being subjected to reduction processing, the both ends of the cover are welded to be manufactured. Therefore, the steel pipe used as an accumulator of the airbag system (hereinafter referred to as an airbag accumulator or simply an accumulator) is subjected to a stress at a large strain of -5 - 201217199 in a very short time. Therefore, such a steel pipe, unlike conventional structures such as pipes, requires high dimensional accuracy, processability, and also requires higher strength and excellent burst resistance. Recently, there has been a strong demand for lightweight vehicles. From this point of view, it is also desirable for the airbag steel pipe for vehicles to be thinner and lighter to ensure high burst pressure, so that the tensile strength is above 9 〇OMPa or even higher than 10 MPa. An accumulator manufactured without the strength is applied to the airbag system. For example, when a pressure accumulator made of a jointless steel pipe having an outer diameter and a thickness of 3.55 mm is used, the burst pressure of 800 MPa ' is as high as about 100 MPa. On the other hand, lOO MPa and the burst pressure rise to i3 〇 MPa. At the same time, 20% thin meat can be achieved when the outer diameter of the airbag and the required burst pressure are constant. Further, for example, in order to avoid the occurrence of two disasters in the case of a brittle fracture of a pressure device in a cold region, the accumulator must have excellent low temperature toughness. From this point of view, the seamless steel pipe for the accumulator can be tempered by fire to achieve high strength and high toughness. Specifically, for the storage requirement -60 °C, the breakage of the Charpy impact test exhibits ductility (vTrslOO is below -6 0 °C), and the elongation at -80 °C is ductile. (vTrSlOO is preferably - 8 (TC or less). It is the same as the jointless steel pipe for the high-strength and high-toughness airbag system, as in the production of the seamless steel pipe for the airbag described in Patent Document 1. •~r~r ecu and mesh, the strength is 60mm for the seam steel pipe TS is TS for the degree of the accumulator because the storage has a quenching device, ie, the shell impact low temperature toughness, example method, 201217199 In order to produce a seamless steel pipe by using a steel material having a chemical composition of a specific range, the seamless steel pipe is subjected to cold drawing processing to be a steel pipe of a specific size, and then heated to Ac3 or higher. Quenching is carried out at a temperature in the range of 1 050 ° C or lower, and then quenching and tempering is carried out at a temperature within a range of 45 ° C or higher and below the AC | point to perform quenching and tempering treatment. Processability and melting in an inflator The joint has excellent jointability. In addition, the inflator has a tensile strength of 900 MPa or more, and a high-toughness seamless steel pipe exhibiting a ductility of -60 ° C drop weight test for a half-section steel pipe. However, at -60 ° The ductility exhibited by the C weight drop test does not necessarily represent the ductility of the burst test at -6 0 ° C. Patent Document 2 describes the production of tensile strength by performing high frequency induction heating quenching and fine granulation by rapid heating. A method of using a steel pipe for an airbag system having a strength of more than 1000 MPa. For example, when a seamless steel pipe is used as a plain pipe, a steel material of a specific range of chemical composition is used, and a joint of a seamless steel pipe is used for heat, and then The seamless steel pipe is subjected to cold drawing processing to form a steel pipe of a specific size. After the steel pipe is heated, quenching is performed, and secondly, tempering is performed at a temperature lower than the ACl transformation point. After quenching, tempering treatment is performed to obtain a desired The burst test at -80 ° C or lower also exhibits high ductility. However, the methods shown in Patent Documents 1 and 2, as shown in the specific examples, are used to obtain tensile strength and high toughness of 100 MPa or more. Steel, must contain large amounts such as Cr, Mo alloy of Patent Document 1 is expensive, Cr + Mo:. 1.0~2.5 mass% in Patent Document 2, usually 201,217,199

Cr + Mo: 0. 92% by mass of steel. When a large amount of Cr or Mo is contained, in particular, high-priced Mo not only leads to an increase in the cost of raw materials, but also, after the heat pipe of the seamless steel pipe, the strength of the steel pipe tends to become high, and the subsequent cold drawing process is performed. It has become more difficult. Therefore, before the cold drawing process, softening annealing must be performed to complicate the process, which leads to an increase in manufacturing cost. Patent Document 3 using a steel of Cr + Mo: 1_〇 to 1.18 mass% has the same problem as in Patent Document 1 '2. Patent Document 4 describes a steel composition containing Cr, Mo, Cu, and Ni for a seamless steel pipe excellent in burst resistance, but the evaluation of its characteristics is based on Cr+Mo: 0.76 mass% or more. The seam steel pipe is also the tensile strength of 947 MPa. Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-76034 Patent Document 2: WO 2004/104255A1 Patent Document 3: US 2005/0076975A1 Patent Document 4: WO 2002/079526 A1 SUMMARY OF THE INVENTION A conventional steel pipe for airbags is required to ensure high strength and high strength. Toughness is enhanced by adding Cr and Mo. However, this method not only increases the alloy cost, but also makes it difficult to perform cold drawing after pipe making. Therefore, if the difference between the size of the seamless steel pipe of the prime tube and the size of the steel pipe for the final product airbag is too large, the cold drawing process must be repeated several times in the cold drawing process. This -8-201217199' is based on the degree of cold drawing processing, and is trimmed to a desired product size while performing intermediate softening annealing. Overall, the manufacturing cost is high, and the object of the present invention is to provide a manufacturing method. By the simplification of the cold drawing process or the reduction of the alloy cost, it is cheaper than the conventional one, that is, a steel pipe for high strength and high toughness is manufactured by a means cheaper than the conventional method. On the other hand, the object of the present invention is to provide a method for producing a steel pipe for an air bag which is equivalent to a conventional product or a thinner and smaller diameter by using a material/manufacturing method which is lower than the conventional cost. The inventors of the present invention have focused on the conventional steel tubes for high-strength airbags, which have been strengthened by Cr and Mo, and have resulted in high strength after the completion of the hot pipe, reduced productivity in cold drawing, and increased alloy cost. In order to suppress the use of these alloying elements as much as possible, it is possible to ensure an alloy composition and a manufacturing method of high tensile strength of 900 MPa or more and excellent low-temperature toughness of vTrslOO of -60 ° C or less. As a result, it is possible to obtain the following findings, and to realize the present invention, (a) in the production of a steel pipe for airbags which are subjected to cold drawing and tempering after cold drawing, and appropriately set the heating conditions and cooling conditions at the time of quenching. Even if it does not contain a large amount of Cr and Mo, it can ensure high strength and low temperature | In particular, it is extremely effective to contain special Cr and Mo in combination with Cu and Ni. (b) Reducing Cr and Mo and replacing it with steel containing Cu and Ni. The cold drawing after hot pipe is easier, and the cold drawing process is once cold-drawing and the processing degree of 201217199 is reduced. The rate can be larger, which in turn can simplify the cold drawing process. The feature of the method for producing a steel pipe for an air bag according to the present invention includes: C: 004 to 0_20%, si: 0·10 to 0.50%, Μη: 0.10 to 1.00%, P: 〇.025% or less, S: 0.005 % or less, A1: 0.10% or less, Cr: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Ni: 0.01 to 0.50%, and the balance being Fe and unavoidable impurities The steel constituting the steel pipe to implement the heat pipe manufacturing process of the seamless steel pipe; for the obtained seamless steel pipe, the shrinkage rate of the cold drawing process of at least one time is more than 40% Stretching process to obtain a cold drawing process of a steel pipe of a specific size; and heating the steel pipe subjected to cold drawing to a temperature of at least 50 ° C / s to a temperature of Ac3 or higher, at least 850 to 500 ° The quenching is carried out by cooling in a temperature range of 50 ° C/s or more in the temperature range of C, and second, a tempering heat treatment process is performed at a temperature equal to or lower than the ACl point temperature. A good embodiment of the method for producing a steel pipe for gas enthalpy of the present invention is as follows. The steel may further contain one or more of the following elements as needed. • Mo: less than 0.10%, • Nb: 0.050% or less, Ti: 0.050% or less, and V: 0.2〇% or less, • Ca: 0·005% or less, and B: 0.0030% or less. Kind. The concentration of Cu, Ni, Cr, and Mo in the steel is preferably in accordance with the following formula (1 -10- 201217199).

Cu+Ni^(Cr+Mo)2+〇.3 · (1) The element mark of the formula (1) represents the number 値 when the content of the element 2 is expressed by mass%. However, when Mo is not contained, Mo = 0 (zero) ^ After the cold drawing process is completed, the thickness of the steel pipe is preferably 2.0 mm in terms of γ. The cold drawing process is preferably carried out once by cold stretching. The heating for the purpose of quenching in the heat treatment process is preferably carried out by high-frequency induction _ heating. In this case, it is preferred to first correct the cold drawing process before heating for the purpose of quenching. According to the present invention, it is possible to suppress the amount of high-priced Mo to 0 or a small amount, and to manufacture a steel pipe for airbags having high strength of tensile strength of 900 MPa or more and excellent low-temperature toughness of vTrs 100 of -60 °C or less. In addition, since the strength of the seamless steel pipe obtained by the hot pipe is not too high, the processing rate of the subsequent cold drawing process can be increased more than the conventional one, and the intermediate softening annealing during the period can be reduced. The number of cold stretches. Therefore, with the present invention, both the alloy cost and the manufacturing cost of the steel pipe for airbags can be made lower than the conventional one. [Embodiment] Hereinafter, the chemical composition and manufacturing process of the steel pipe for an air bag of the present invention will be described more specifically. (A) Chemical composition of steel -11 - 201217199 In this specification, the "%" associated with the chemical composition of steel is used to indicate "% by mass". The remainder of the chemical composition of the steel other than the elements described below is Fe and unavoidable impurities. C : 0_04 ～0.20% C is an effective element that is inexpensive and can increase the strength of steel. When the content is 0.04% or less, it is difficult to obtain high strength (tensile strength), and when it exceeds 0.20%, workability and weldability are lowered. Therefore, the content of C is 0.04% or more and 0.20% or less. The content of the C content is preferably 0.07% or more and 0.20% or less, and more preferably 0.12% or more and 0.17% or less. When the tensile strength of 1 〇〇〇 MPa or more is targeted, the C content should be 0.06% or more.

Si : 0· 1 0~0.50%

Si is an element which has a deacidification effect and can improve the hardenability of steel and increase the strength. For the above purpose, the content of Si is 0.10% or more. However, since the content exceeds 0.50%, the toughness is lowered, and if the content of si is 〇·50% or less. The favorable range of the Si content is 0.20% or more and 0.45% or less. Μη: 0.10 ～1.00% Μη, an effective element that has deacidification and improves the hardenability of steel and improves strength and toughness. However, if the content is less than 1%, the 'intensive strength and toughness cannot be obtained. On the other hand, if the amount exceeds 丨〇〇%, the -12-201217199 words will be coarsened. The hot pressing delay occurs and the blade edge is lowered. Therefore, the content of Μη is 〇·10% or more ' 丨.00% or less. The content of Μη is preferably 0.30% or more and 〇·80% or less. Ρ: 0.025% or less Ρ, which is contained in steel in the form of impurities, which causes a decrease in toughness due to grain boundary segregation. In particular, if the content of ρ exceeds 025·025%, the degree of f-edge is remarkably lowered. Therefore, the content of ’ is 〇 5 2 5 % or less. The content of P is preferably 0.020% or less, preferably 0.015% or less, S: 0,005% or less, S, which is also formed in the steel by the formation of impurities. In particular, it causes the T direction of the steel pipe (perpendicular to the rolling direction of the steel pipe). The toughness of the direction (longitudinal direction). When the content of s exceeds 0.005%, the toughness in the T direction of the steel pipe is remarkably lowered, so the content of S is 0.005% or less. The content of S is preferably 0.003% or less. A1 : 0.1 0 % or less A1 is an effective element which has a deacidification effect and can improve the toughness and workability of steel. However, if A1 is contained in an amount exceeding 0.10%, strip cracks are apparent. Therefore, the content of A1 is 〇·10% or less. Since the A1 content may also be an impurity level, the lower limit thereof is not particularly limited, but it is preferably 0.005% or more. The content of A1 in the present invention means the content of the acid A13 (2012), which is dissolved in A1 (so-called "sol. Al").

Cr : 0.0 1 ~ 0.50%

Cr is an effect of high steel strength and toughness by improving the hardenability and temper softening resistance of steel. The effect is as long as Cr is 〇. However, because the quenching property is improved, the cooling process after the hot pipe will cause the hardening of the steel to limit the degree of processing once, so the cold drawing process must be performed with a plurality of softening annealings. The possibility of stretching. This increase in the content also leads to an increase in the cost of the alloy. The content of Cr is 0.01+% or more and 0.50% or less based on the above. The amount of Cr is preferably 0.15% or more and 0.45% or less, and the content is preferably % or more and 〇3.55% or less.

Mo: less than 0~0.10%

Mo improves the strength and toughness of steel by improving the hardenability and temper softening resistance of steel. The effect can be found as long as it contains 0. However, in the present invention, the necessary strength and toughness are ensured by Ni and Cu, so that it is not necessary to add Mo. That is, it can be 〇%. Even when Mo is added, its content is less than 0.10%. If the amount is high, the seamless steel pipe obtained by the hot pipe will have a tendency to be too high in the strength of the seamless steel pipe. As a result, the cold drawing process must be subjected to softening annealing before processing. In addition, it has a Ti of 1% of Cr and is cold-stretched with I, and the content of Cr is 0·18 and has 01% to ' Because Mo also contains air-cooled in the next cold stretching -14-201217199 processing processing (shrinking rate) is limited, when used to form steel pipes of a specific size, 'the necessary cold drawing process and softening before it The number of annealings increases. This tends to be very obvious when Mo is more than 10%. In addition, since Mo ’ is a very expensive metal, an increase in the Mo content causes a significant increase in alloy cost. That is, more than 10% of Mo is harmful for achieving the object of the present invention. Therefore, the Mo content in the case of containing Mo is less than 0.10%, however, the content is preferably 0.01% or more and 0.05% or less.

Cu : 0.01 ~ 0.50%

Cu has the effect of improving the hardenability of steel and increasing its strength and toughness. The effect is found when it contains 0.01% or more, preferably 0.03% or more of Cu. However, containing more than 0.50% of Cu leads to an increase in alloy cost. Therefore, the content of Cu is 0.01% or more and 0.50% or less. The Cu content is preferably 0.03% or more, particularly preferably 0.05% or more, more preferably 0.15% or more. The upper limit of the Cu content is preferably 0.40%, more preferably 〇·35%.

Ni: 0.01 to 0.50%

Ni has the effect of improving strength and toughness by improving the hardenability of steel. The effect is found when it contains 0.01% or more, preferably 0.03% or more of Ni. However, the inclusion of more than 〇·50% of Ni' results in an increase in the cost of the alloy. Therefore, the content of Ni is 〇.01% or more and 0.50% or less. The Ni content is preferably 0.03% or more, particularly preferably 0.05% or more, and more preferably 0.15% or more. The upper limit of the Ni content is preferably 0.40 -15 - 201217199 %', preferably 0.35 %.

The sum of the contents of Cu and Ni (Cu + Ni ) should be 0.20% or more and 0.65% or less, preferably 〇, 28% or more and 0.60% or less. In a preferred embodiment of the present invention, the amount of Cu, Ni, Cr, and Mo contained in the steel is adjusted so as to satisfy the following formula (1).

Cu + Ni ^ (Cr + Mo) 2+ 0.3 · · · (1) The meaning of the element symbol of the formula (1) is the number 値 when the content of each element is expressed by mass%. When Mo is not contained, Mo is zero.

Cr, Mo, hinder the spheroidization of cementite precipitated during tempering, especially steel containing B, because the compound of B (boride) is easily formed at the grain boundary, which is particularly likely to cause toughness of high-strength material. The reduction. By suppressing Cr and Mo and containing Cu and Ni in a manner satisfying the formula (1), it is easier to manufacture a high-strength and high-toughness airbag steel pipe. In a preferred embodiment of the present invention, at least one element selected from one or both of the following two groups (i) and (Π) may be further included.

(i) Nb, Ti, V (ii ) Ca, B

Nb: 0·050% or less

Nb is dispersed in steel by fine carbides and has a crevice effect of strengthening the grain boundary. As a result, the finer the granulation of the crystal grains, the higher the toughness of the steel. However, if the content of Nb exceeds 0.050%, the carbide is coarsened and the toughness is lowered. Therefore, when added, the content of Nb is 0.050% or less. In addition, the above-mentioned effect of Nb can be confirmed in a very small amount of -16 to 201217199. However, in order to obtain sufficient effects, it is preferable to contain 〇. 〇 〇 5 % or more.

Ti : 0.05 0% or less

The Ti' system fixes N in steel and has an effect of improving the toughness. The fine Ti nitride is dispersed by the crevices to strengthen the grain boundaries, and the finer the crystal grains, the higher the toughness of the steel. However, if Ti is contained in an amount of more than 0.050%, the nitride is coarsened and the toughness is lowered. Therefore, the content of Ti when added is 0.050% or less. The effect of Ti can also be confirmed in a small amount, however, in order to sufficiently obtain an effect, it is preferably 0.005% or more. The content of Ti is preferably 0.008 to 0.035 % V: 0 · 2 0 % or less V' not only ensures toughness but also enhances strength by strengthening precipitation. However, if the content of V exceeds 0.20% Will cause a decrease in toughness. Therefore, when added, the content of V is 0.20% or less. The effect of V on a trace amount can also be confirmed. However, in order to sufficiently obtain an effect, it is preferable to contain 0.02% or more. The range of the V content is preferably 0.03 to 0.10%.

Ca: 0.005% or less

Ca is used to fix the S of the unavoidable impurities present in the steel in the form of a sulfide to improve the anisotropy of the toughness, thereby improving the T-direction toughness of the 17-201217199 steel pipe, and improving The role of burst resistance. However, containing more than 0.005% of Ca will result in an increase in inclusions and a decrease in toughness. Therefore, when added, the content of Ca is 0.005% or less. The effect of Ca described above can also be confirmed in a very small amount, but it is preferable to contain 0.0005% or more in order to obtain sufficient effects. B: 0.0030% or less B ' can cause grain boundary segregation in steel by a slight addition, and the hardenability of steel is remarkably improved. However, when 0.003% or more of B is contained, coarse boride is precipitated at the crystal grain boundary, and it is confirmed that the toughness tends to decrease. Therefore, when added, the content of B is 0.0030% or less. The effect of B is also confirmed in a trace amount, however, in order to secure a sufficient effect, it is preferably 0.0005% or more. In the present invention, when the tensile strength of 1 0 0 ο Μ P a or more is targeted, it is preferable to blend B to improve the hardenability and thereby increase the strength. Further, if B is not contained in a solid solution state, segregation does not occur at the crystal boundary. Therefore, it is preferable that the N' of the compound which is likely to generate B is preferably fixed by Ti to be contained in an amount of more than or equal to N. The meaning of the 'B content' is from the chemical quantity ratio of B, Ti, and N. It is better to satisfy the relationship of the following formula (2). B_(NT i/3. 4) X (1 〇 8/1 4)^0. 〇〇〇1 (2) B, N, and Ti in the formula (2) are the numbers 値 when the content of each element is expressed by mass%. -18- 201217199 (B) Control procedure A seamless steel pipe is obtained by using a hot pipe which is made of a steel block composed of steel having a chemical composition as described in the above (A) as a material. The form and production method of the steel block as the material of the hot steel pipe are not particularly limited. For example, it is also possible to use a continuous casting machine having a cylindrical mold to cast each sharp (circular CC steel) or to make a rectangular shape and then hot forge into a cylindrical steel soul. In the steel used in the present invention, since the addition of the ferrite iron stabilizer element of Cr and Mo is suppressed, and the relationship between the stabilizer of the Vostian iron of Cu and Ni is added, and the round CC billet is continuously cast into a spherical shape, It is quite large to prevent the cracking of the center, so it has high applicability to the round CC. Therefore, it is possible to omit the processing of the ball slab by the block rolling or the like which is required for casting into a rectangular shape. The hot pipe method for forming the seamless steel pipe is not particularly limited. For example, a mandrel-Mannesmann method is employed. The cooling of the hot pipe, the cooling rate of the radiant cooling or the like is small, and the shape of the seamless steel pipe obtained by the cold drawing is preferable, and is not particularly limited. However, for example, the diameter is 32. It is preferably about 50 mm and a thickness of 2.5 to 3.0 mm. (C) Cold drawing process The seamless steel pipe obtained by the hot pipe generally has a large thickness and a large diameter and an insufficient dimensional accuracy. In order to obtain a specific size (outer diameter and thickness of the steel pipe) and surface properties, the seamless steel pipe was used as a plain tube and subjected to cold drawing. In the present invention, in order to utilize the characteristics of the steel to be used, the degree of processing (reduction ratio) of at least one cold drawing process performed by the cold drawing process is -19-201217199, which is more than 4%. When the degree of processing of the cold drawing is more than 50%, the inside is prone to crepe or cracking, so the degree of processing is preferably 42 to 48%, preferably 43 to 46%. When the cold drawing process is carried out for two or more cold drawing processes, the degree of processing of at least one cold drawing may be 40% or more, and the cold working of less than 40% is allowed. The degree of cold drawing is synonymous with the shrinkage ratio (profile reduction rate) defined by the following formula. Shrinkage ratio (%) = (S〇-Sf) X 1 〇〇/s0 However, S. : sectional area of steel pipe before cold drawing process s f : sectional area of steel pipe after completion of cold drawing process "sectional area of steel pipe" is the sectional area of only the wall portion of the hollow portion of the pipe section. "The degree of processing (or shrinkage ratio) of one cold drawing" is performed without softening annealing in the middle, and the total processing degree of the multiple cold drawing operations is also regarded as "the degree of processing of one cold drawing". . When the steel of the present invention is used, since the degree of processing of one cold drawing exceeds 40%, as long as the trimming size of the seamless steel pipe obtained by the hot pipe is appropriately selected, a specific size of thin meat can be produced by one cold drawing. Steel Pipe. Therefore, the conventionally required two-stage cold drawing process and the thin-skinned steel pipe which needs to be soft-annealed in the middle are greatly simplified. The processing method of the cold drawing is carried out by a conventional method which is well known. For example, the seamless steel pipe made by the mandrel-Mannesmann method as described above is used as a plain tube, and after the radiation is cooled to room temperature, the drawing is carried out by using a mold -20-201217199 and a pipe plug, whereby the drawing is performed. Reduce the diameter and thin meat. For example, a steel having a diameter of 30 mm or less and a thickness of 2 mm or less can be obtained from a seamless steel pipe of a plain tube, and the processing method is not particularly limited. However, it is preferable in the above manner. The steel used in the present invention is processed by one cold drawing, for example, by a shrinkage ratio of 46%. Therefore, when the steel pipe for airbags has a thickness of 1.7 mm and an outer diameter of 25 mm, if it is subjected to cold drawing and has a size of, for example, an outer diameter of 31.8 mm and a thickness of 2.5 mm, it can be stretched to obtain a product of a specific size. (D) Correcting the steel pipe for airbags manufactured by the present invention, since the resistance is i 900 MPa or more, and the shrinkage ratio of cold drawing is 40% or more, the strength tends to be higher than that of the conventional steel, however, sometimes, it is also The steel tube after the cold drawing process is bent by the bomb or the like. As shown in the following description, in order to ensure the high-strength and high-speed blade is stretched into a steel pipe of a specific size, it is heated to the point of the Ac3 transformation point for the purpose of quenching. However, the rapid application of the typical high frequency is used. Induction heating is implemented. If the quenched steel is to be applied, it has to worry about the problem that the high cycle used for high-frequency induction heating can pass straight through the steel pipe. Therefore, it is good to carry out corrective processing after cold stretching to eliminate the bending of the steel pipe. The correction method is not particularly limited, and it is only necessary to use a steel pipe in a conventional method. As long as the cold drawing of the tube is stretched, it is possible to use the cold-strength tension of the final size of the tube to be cold-stretched. It is possible to cause the bending speed to be caused by the cold-speed heating, heat, and the tube. The system can be implemented. "21 - 201217199 It is preferable to arrange, for example, about 4 rows of 2 roller type brackets to make the center positions of the roller gaps of the respective columns offset from each other (that is, offset). The amount of the gap is such that the steel pipe passes between the rollers to perform a processing method of bending and bending back. The higher the degree of processing of the bending and bending back at this time, the higher the correction effect. From this point of view, the offset amount (the amount of deviation between the adjacent roller pairs) is less than or equal to 外径% of the outer diameter of the steel pipe and less than 1% of the outer diameter of the steel pipe. good. On the other hand, in order to avoid problems such as cracking of the steel pipe, the offset amount is preferably 50% or less of the outer diameter of the steel pipe and more than 5% of the outer diameter of the steel pipe. (E) Heat treatment After the above-mentioned (D) correction processing is carried out, the required tensile strength is imparted to the steel pipe, and the steel pipe is heat-treated in order to improve the T-direction toughness and ensure burst resistance. In order to provide a steel pipe with high tensile strength of 900 MPa or more, excellent low-temperature toughness and burst resistance, it is heated to a temperature equal to or higher than the Ac3 (metamorphic) point to carry out quenching. Second, tempering is carried out at a temperature below the ACl (metamorphic) point. If the heating temperature before quenching is lower than the Ac3 point of the single phase of Vostian Iron, good T-direction toughness (and good burst resistance) cannot be ensured. On the other hand, if the above-mentioned heating temperature is too high, the Worthite iron particles start to rapidly grow to become coarse particles, which results in a decrease in toughness, so that it is preferably 0.45 °C or lower. l 〇〇〇 ° C or less is better. At the time of quenching, the heating up to the temperature of Ac3 or higher is carried out by heating at a rapid rate of 50 ° C /s or more at a temperature of -22 - 201217199. The heating rate can be 値 of an average heating rate in a temperature range of a heating temperature of 200 ° C or more. When the heating rate is less than 50 ° C /s, the particle size of the Worthite iron cannot be made fine, and the tensile properties, low-temperature toughness or burst resistance are lowered. In order to obtain a steel pipe having a tensile strength of 100 MPa or more and a vTrs100 of -80 ° C or less, the heating rate is preferably 8 (TC / s or more, preferably 100 ° C / s or more. Such rapid heating can be utilized. In this case, the heating rate can be adjusted by the stepping speed of the steel pipe passing through the high-frequency coil, etc. The steel pipe heated to a temperature of Ac3 or higher by rapid heating is kept at Ac3 or higher for a short time. After the temperature, rapid cooling for quenching is carried out, and the holding time is preferably in the range of 0.5 to 8 seconds, preferably 1 to 4 seconds. If the holding time is too short, the uniformity of mechanical properties may be deteriorated. If the holding time is too long, in particular, when the temperature is kept high, the particle size of the Worthite iron is likely to be coarsened. Fine particle granulation is necessary for ensuring extremely high toughness. Cooling for the purpose of quenching Speed, the cooling rate in the temperature range of at least 850~500 °C should be controlled above 50 °C / s. The cooling rate is preferably l 〇〇 ° C / s or more. In order to make the tensile strength lOOOOMPa or more, Make vTrslOO into -80 ° C or less, the cooling rate is preferably 150 ° C / s or more. If the cooling rate is too small, the quenching is incomplete, the ratio of martensite is lowered, and sufficient tensile strength is not obtained. It is cooled and cooled to In order to give a tensile strength of 900 MPa or more and sufficient burst resistance, the steel pipe near normal temperature is tempered at a temperature of -23 to 201217199 below the ACl point. If the temperature of the tempering exceeds the ACl point, it is difficult to obtain the purpose with certainty and stability. The tensile strength and the low-temperature toughness are not particularly limited. For example, the heat treatment furnace such as a Haas Roller type continuous furnace or high-frequency induction heating may be subjected to soaking heating and then cooled. The soaking condition of the heat treatment furnace is preferably at a temperature of 305 to 500 ° C and a holding time of 20 to 30 minutes. After tempering, the method of (D) may be used to appropriately correct the bending by a straightener or the like. In order to process the steel pipe for airbags manufactured in this manner into a gas pressure accumulator, the steel pipe is cut into a specific length to form a short pipe, and at least one end thereof is subjected to press working, spinning, or the like as needed. The diameter processing (referred to as the bottle mouth processing), and finally processing it into the necessary shape for mounting the starter, etc. Therefore, the specific size and dimensional accuracy of the steel pipe for airbags referred to in this specification means the tube thickness and Diameter-related dimensions and dimensional accuracy. Finally, the cover is welded to both ends of the steel pipe. The embodiment melts the steel having the chemical composition shown in Table 1 in a converter (the ACl point is in the range of 720 to 735 °C, The AC3 point is in the range of 835 to 860 ° C), and a cylindrical billet having an outer diameter of 191 mm is produced by continuous casting (circular CC). The round CC billet is cut into a desired length and heated to 1500 ° C. The first element tube having an outer diameter of 31.8 mm and a thickness of 2.5 mm and an outer diameter of 42.7 mm and a meat thickness of 2.7 mm are obtained by perforation and rolling using a conventional Mannesmann perforated mandrel mill. The second element tube. The two types of plain tubes obtained in this way are refurbished by one or two times of cold drawing processing (cold drawing processing) by using a mold and a tube into a normal method of stretching from -24 to 201217199. Steel pipe with a diameter of 25.0 mm and a thickness of 1. 7 mm. In the comparative steels G and Η of Table 1, the first-stage tube of the outer diameter of 3 1.8 mm and the thickness of 2.5 mm was used to test the steel pipe of the above shape in one drawing, and as a result, cracking occurred and the production was impossible. In Comparative Examples 9 and 10, a second tube was used, and a steel tube having an outer diameter of 32.0 mm and a thickness of 2.2 mm was formed by the first stretching, and a softening annealing was performed at 63 ° C for 20 minutes. It was stretched twice to form an outer diameter of 25.0 mm and a meat thickness of 1.7 mm. The steel pipe subjected to the cold drawing process is corrected by a straightener, and then heated to a temperature of 300 ° C / s (the average temperature in the temperature range of 200 to 900 ° C) by a high frequency induction heating device to After holding at 920 ° C for 2 seconds at 920 ° C, water quenching (average cooling rate of 150 ° C / s in the temperature range of 850 to 500 ° C) was carried out to carry out water quenching. Next, in order to temper the steel pipe, a heat treatment was performed in a glow annealing furnace at 350 to 50 CTC for 30 minutes, and the steel pipe for the gas capsule was obtained by cooling in the furnace by natural cooling and radiant cooling to room temperature. A tube of a certain length was cut out from each of the obtained steel pipes, and cut and expanded from the length of the tube at room temperature. A 2 mm V dimple was formed as a test piece from a rectangular material having a length of 55 mm, a height of 10 mm, and a width of 1.7 mm taken from the unfolded tube in the T direction, and a Charpy impact test was performed at various temperatures below -4 (TC). The lower limit temperature (vTrslOO) of the ductile fracture rate of 100% is obtained. In addition, the π test piece specified in JIS Z 2201-25-201217199 taken from the L direction of the steel pipe is used, according to the IS Z 224 1 The tensile test is carried out by the specified tensile test method for metallic materials. The above test results are shown in Table 2 together with the manufacturing conditions of the steel pipe. -26- 201217199 [Oi i 1 m 翳a (Cr+Mo)2 + 0.3 ooooo CO o LO CO 〇5 os 3 z 3 oso CM L〇o CM CO o O' 〇> mo CM LO 〇so W 毅 cone Η amp&Μ W chain 骊CO |0.00141 0.00131 |〇. 00141 0.00151 0.0010 | 0.00031 0.0002 Ιο. 00161 0.0011 0.00151 | 0.00131 1 1 | 0.0015| 0.0022 Isol.AI | •r— so ΙΩ CO oo 9 oooo 甘 so O oo <〇so CO so > 1 1 1 oo oo 1 1 1 1 - soosoo CO s o' CO CM 〇O' 1 CM S 〇S 〇00 oo € \r&gt ; CM ooaoo Si oo 1 1 1 CO S 〇aooz CO CNi o' oo CS4 d in Cs| ogo ir> Cvl o another o L〇04 o 〇3 L〇CM o <〇CM o K o CO CM 〇C ^lo σ> CSJ o K o σ> eg ooo 1 oos 〇1 S o 箐oo CM 〇i> CO O ώ another o σ> CM ooo <〇CO o CM CM om CQ o and Ξ o Γ Γ - o CO soogoooosoo CM 〇osoo SO o CM 〇〇a. CM oo CN oo CO oo T— 5 o CJ so CO Ξ o oo CO 5 oso 笃o CM in oo CO ooo 箐σ> cm SO CO O) OJ o oo Csj o eg om CSJ o ς〇CM O <〇CM o tn CM O CO cvl oo to omo inch o CO o CO y-^ o in o CM 〇o RBT 骊卿-< OQ oo LU u. C9 * -27- 201217199 [s] Remarks Inventive Example Comparative Example vTrslOO (°c) s rj· s 8 f2 o tj- o T—· 1 I orTM· o TS (Mpa) 1098 | 1070 I 〇1022 1 1028 I CO g T-" 1 I mgog cooling speed (°C/s) s 1 IS v— III 920°Cx2s frequency induction heating) * $ ! 920°Cx2s (high frequency induction heating) total processing (3⁄4) CO CO CO <〇first stretch g 1 1 1 sleep 1 1 I i Contraction (f) rate 1 1 瞧1 1 1 I s 1 39.6 t1 3 es \ 1 1 1 1 1 1 I 0D: 25. Omm 1 x1. 7mm t First stretch κπ tET 0 〇 Ooo 0 XXO 0 Shrinkage ratio (%) CO I 39.3 Si 0D : 25,0mm xl. 7mm t OD :32. Omm x2. 2mm t Tube size 0D: 31.8mm x2.5mm t 0D: 42.7imi1 x2. 7mm t ilTWtl 职-- GD oo LU Ll. CD O 3: Sincerity: i CsJ CO to <〇r-» 00 σ> o -28- 201217199 It can be seen from Table 2 that the use has the invention according to the invention When steels A to F of the chemical composition of steel are all free of expensive Mo, or only a small amount of 0.10% or less, although the alloy cost is reduced, the degree of work with a shrinkage ratio of 46% '1 cold stretching can also be used. The product is processed into a specific product size, and rapid heating and rapid cooling are performed in the subsequent quenching process to achieve a high level of product performance as a steel pipe for airbags. In particular, when steels A to C, E, and F having the composition of the above formula (1) are used, vTrslOO is -10 ° C or less, and the low temperature toughness is extremely high, so that it is expected to be excellent in a low temperature environment. Burst resistance. On the other hand, the steels F and G of the comparative examples have a high alloy cost because they contain a large amount of Mo. Further, when cold drawing processing having a shrinkage ratio of 40% or more is performed, cracking occurs. Therefore, it is necessary to carry out cold drawing processing of a shrinkage ratio of less than 40% twice or more, and it is necessary to perform softening annealing in the middle, which also leads to an increase in the manufacturing cost of the steel pipe for airbags. -29-

Claims (1)

201217199 VII. Scope of application for patents: 1. A method for manufacturing a steel pipe for gas venting, characterized in that it comprises: a control process, which is composed of mass% C: 〇. 〇 4 to 0.20%, Si: 0.10 ～ 0.50%, Μη: 0.10 ～1.00%, P: 0.025% or less, S: 0.005% or less, Α1: 0.10% or less, Cr: 〇.〇1 to 0.50%, Cu: 0·01 to 0·50%, Ni: 〇· 〇1~0·50%, the rest of which is made of Fe and unavoidable impurities to carry out the hot tube of the seamless steel pipe; the cold drawing process, which is performed on the obtained seamless steel pipe, at least One-time cold drawing process with a shrinkage ratio of more than 40% for cold drawing to obtain a steel pipe of a specific size: and a heat treatment process 'for a cold-drawn steel pipe, 50 ° C / s or more After the heating rate is increased to a temperature of Ac3 or higher, the quenching is performed by cooling at a cooling rate of at least 8 50 to 500 ° C in a temperature range of 50 ° C/s or more, and secondly, at a temperature lower than the ACl point temperature. Implement tempering. The method for producing a steel pipe for an air bag according to claim 1, wherein the steel further contains Mo: less than 0.10%. The method for producing a steel pipe for an air bag according to the first or second aspect of the invention, wherein the steel steel is selected from the group consisting of Nb: 0.050% or less, Ti: 0.050% or less, and V: 〇_2〇% or less. At least one species. The method for producing a steel pipe for an airbag according to the first or second aspect of the invention, wherein the steel includes at least one selected from the group consisting of Ca: 0.005% or less and B: 0.0030% or less. 5. The method for producing a steel pipe for an air bag according to claim 1, wherein the concentration of Cu, Ni, Cr, and Mo of the steel satisfies the following formula (1): C u + N i ^ (C r +Mo)2 +0. 3 ( 1 ) The meaning of the element symbol of the formula (1) is the number 値 when the content of the elements is expressed by mass %, but when Mo is not contained, Mo = 〇〇 6. The method for producing a steel pipe for an air bag according to claim 1 or 2, wherein the steel pipe after the cold drawing process has a meat thickness of 2.0 mm or less 〇7 as described in claim 6 The method for producing a steel pipe for an air bag, wherein the cold drawing process is carried out by one cold drawing. 8. The method for producing a steel pipe for an air bag according to the first or second aspect of the invention, wherein, in the heat treatment process, heating for the purpose of quenching is performed by high-frequency induction heating. 9. The method for producing a steel pipe for an air bag according to the invention of claim 8, wherein the steel pipe obtained by the cold drawing process is subjected to a correction before the heating for the purpose of the quenching. -31 - 201217199 Four designated representatives: (1) The representative representative of the case is: No (2) The symbol of the representative figure is simple: No 201217199 If there is a chemical formula in the case, please disclose the chemical formula that best shows the characteristics of the invention: no