JP2004027303A - High strength, high toughness, high workability seamless steel tube for air bag and method of producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing a high strength, high toughness, high workability seamless steel tube for an air bag. <P>SOLUTION: A steel tube stock having a composition comprising 0.01 to 0.10% C, ≤0.5% Si, 0.10 to 2.00% Mn, >1.0 to 2.0% Cr and ≤0.5% Mo is made into a seamless steel tube. Thereafter, the seamless steel tube is subjected to quenching tempering treatment so as to be heated to a temperature in the range of an Ac<SB>3</SB>transformation point to 1050°C, be quenched, and be tempered at a temperature in the range of 450°C to an Ac<SB>1</SB>transformation point. The seamless steel tube is subsequently subjected to cold drawing into a steel tube having prescribed dimensions. The steel tube can comprise one or more kinds of metals selected from ≤1.0% Cu, ≤1.0% Ni,≤0.10% Nb, ≤0.10% V, ≤0.10% Ti and ≤0.005% B as well. <P>COPYRIGHT: (C)2004,JPO

Description

【００３４】
【表２】

【００３５】
本発明例はいずれも、表面性状に優れ、かつ９００ＭＰａ以上の引張強さと、高靭性とを有し、加工性に優れ、さらに、溶接性に優れた継目無鋼管となっている。一方、本発明の範囲を外れる比較例は、引張強さが８５０ＭＰａ未満であるか、靭性が低下しているか、あるいは加工性が低下しているかして、カーテン式エアバッグ用インフレータ向け鋼管として、十分な特性が得られていない。
【００３６】
【発明の効果】
以上のように、本発明によれば、高強度高靭性高加工性継目無鋼管を安定して製造でき、産業上格段の効果を奏する。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-strength seamless steel pipe, and particularly to a high-strength seamless steel pipe excellent in toughness and workability, suitable for use in airbags.
[0002]
[Prior art]
In recent years, there has been a keen desire to improve the safety of automobile collisions. In particular, safety devices for protecting occupants during collisions have been actively introduced. Above all, in the event of a collision, the deployment of airbags that are deployed between the occupant and the steering wheel or instrument panel to absorb the kinetic energy of the occupant and reduce occupant damage is becoming common. In particular, driver-side airbags installed in the steering wheel and passenger-side airbags installed in the instrument panel are becoming standard equipment. Furthermore, recently, in addition to these, in order to protect occupants in the event of a side collision, many vehicles are equipped with a side airbag or a curtain-type airbag covering a side window.
[0003]
2. Description of the Related Art Conventionally, airbags have often adopted a method of generating gas using explosives. However, recently, in consideration of recyclability and environmental consideration, a method of filling an inflator with an inert gas such as argon at a high pressure instead of using explosives has been adopted. In this method, since the inert gas must be constantly maintained at a high pressure in the inflator, it is desired that the inflator has sufficient strength.
[0004]
Generally, an inflator for an airbag is manufactured by processing a steel pipe. In an airbag of a type in which an inert gas is filled, the inert gas is filled into the inflator at a high pressure. Therefore, from the viewpoint of the reliability of the seam, a seamless steel pipe is used as the steel pipe for the inflator. Normally, a seamless steel pipe is subjected to cold drawing to a predetermined size and cut to a predetermined length, and then both pipe ends are processed by press working or the like, and a sealing plate is welded to obtain a product (inflator).
[0005]
For this reason, a seamless steel pipe having sufficient strength and toughness, excellent workability, and excellent weldability is demanded as a steel pipe for an inflator.
In response to such demands, for example, JP-A-10-140283 discloses that C: 0.01 to 0.20%, Si: 0.50% or less, Mn: 0.30 to 2.00%, : 0.020% or less, S: 0.020% or less, Al: 0.10% or less, or further Mo: 0.50% or less, V: 0.10% or less, Ni: 0.50% or less , Cr: 1.00% or less, Cu: 0.50% or less, Ti: 0.10% or less, Nb: 0.10% or less, B: 0.005% or less, the balance being Manufacture of high-strength, high-toughness airbag steel pipes that are made of steel consisting of Fe and unavoidable impurities, and then subjected to annealing, normalizing, or quenching and tempering after cold working or after cold working. A method has been proposed.
[0006]
Japanese Patent Application Laid-Open No. 10-140249 discloses that steel having a composition similar to that described in Japanese Patent Application Laid-Open No. 10-140283 is pipe-formed, then annealed at 850 to 1000 ° C., and then cooled to a predetermined size. There has been proposed a method for producing a steel pipe for a high-strength and tough airbag, which is subjected to a stress relief annealing, normalizing, or quenching and tempering treatment while a cold working is being performed.
JP-A-10-140250, after the pipe producing a steel having the same composition as the composition described in JP-A-10-140283, quenching at 850 to 1000 ° C., or even 450 ° C. or higher Ac ₁ A method for producing a steel pipe for a high-strength, high-toughness airbag that performs tempering at a temperature lower than the transformation point and then performs cold-working with predetermined dimensions or annealing after cold-working has been proposed. .
[0007]
According to the techniques described in JP-A-10-140283, JP-A-10-140249, and JP-A-10-140250, the workability and the weldability are excellent with high dimensional accuracy, and the tensile strength is 590. It is stated that a steel pipe for an airbag having high strength and toughness of N / mm ² or more can be manufactured.
[0008]
[Problems to be solved by the invention]
Recently, it has been required to reduce the size and weight of the airbag system, and further increase the strength of the seamless steel pipe for the inflator of the airbag. In particular, a curtain-type airbag requires a large volume of gas so that the airbag can cover the front and rear side windows, and a filling pressure of 50 MPa or more is required. In order to satisfy such demands, a seamless steel pipe that has been subjected to cold drawing, heat treatment, and the like, and finally has a tensile strength of 900 MPa or more as an inflator is demanded.
[0009]
The techniques described in JP-A-10-140283, JP-A-10-140249, and JP-A-10-140250 aim at manufacturing a 590 MPa class high-strength seamless steel pipe. There is a problem that it is not possible to cope with the demand for higher strength. When heat treatment after cold working is required in the techniques described in JP-A-10-140283, JP-A-10-140249, and JP-A-10-140250, the surface roughness due to scale generation is required. Deterioration, and furthermore, residual stress introduced during cold working is released by heat treatment, and there is a major problem in product characteristics that dimensional accuracy, especially roundness is reduced, and there is also a manufacturing problem due to bending. .
[0010]
The present invention advantageously solves the above-mentioned problems of the prior art, has high dimensional accuracy, is excellent in workability at the time of manufacturing an inflator, has excellent weldability, and is further divided into a half and a tensile strength of 900 MPa or more as an inflator. An object of the present invention is to propose a method for producing a high-strength, high-toughness, high-workability seamless steel pipe capable of obtaining high toughness showing ductility in a drop test at −60 ° C. on a steel pipe.
[0011]
[Means for Solving the Problems]
The present inventors have intensively studied various factors affecting strength, toughness, and workability in order to achieve the above object. As a result, to reduce the C content to a steel composition containing appropriate amounts of Cr and Mo, form a seamless steel pipe, then perform a quenching and tempering treatment or a normalizing treatment, and then perform cold drawing. It has been found that a seamless steel pipe having high dimensional accuracy and high strength can be achieved, and in particular, has a small decrease in circumferential strength and a small anisotropy.
[0012]
The present invention has been completed based on the above-mentioned findings and further studies. That is, the gist of the present invention is as follows.
(1) By mass%, C: 0.01 to 0.10%, Si: 0.5% or less, Mn: 0.10 to 2.00%, Cr: more than 1.0% to 2.0%, Mo: A steel pipe material having a composition containing 0.5% or less is formed into a seamless steel pipe, and then the seamless steel pipe is heated to a temperature within the range from the Ac ₃ transformation point to 1050 ° C. and then quenched. Then, a quenching and tempering treatment of tempering at a temperature in the range of 450 ° C. or more and the Ac ₁ transformation point or less is performed, and thereafter, the steel tube is cold drawn to obtain a steel pipe having a predetermined size. A method of manufacturing a tough, highly workable seamless steel pipe.
(2) In (1), in addition to the above composition, in mass%, Cu: 1.0% or less, Ni: 1.0% or less, Nb: 0.10% or less, V: 0.10% or less , Ti: 0.10% or less, B: 0.005% or less, a high-strength, high-toughness, high-workability seam for an airbag, characterized in that the composition contains one or more kinds selected from the group consisting of: Manufacturing method of steelless pipe.
(3) In the above (1) or (2), instead of the quenching and tempering treatment, the seamless steel pipe is subjected to a normalizing treatment of heating to a temperature in the range of 850 to 1000 ° C. and air cooling. For producing high strength, high toughness, high workability seamless steel pipes for airbags.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the reasons for limiting the composition of the steel pipe material used will be described. Hereinafter, mass% in the composition is simply referred to as%.
C: 0.01 to 0.10%
C is an element that contributes to an increase in the strength of the steel. However, if it is contained in excess of 0.10%, workability and weldability are reduced. On the other hand, if the content is less than 0.01%, it becomes difficult to secure a desired tensile strength. For this reason, in the present invention, C is limited to the range of 0.01 to 0.10%. In addition, it is preferably 0.03 to 0.08%.
[0014]
Si: 0.5% or less Si is an element that increases the strength of steel and is preferably contained at 0.1% or more. However, excessive content lowers ductility and workability. Limited to 5% or less. Incidentally, the content is preferably 0.1 to 0.4%.
Mn: 0.10-2.00%
Mn is an element for improving the strength, and in order to secure a desired strength, the content of Mn is required to be 0.10% or more in the present invention. On the other hand, if the content exceeds 2.00%, ductility is reduced, and workability and weldability are reduced. For this reason, Mn was limited to 2.00% or less. In addition, Preferably, it is 1.00 to 1.70%.
[0015]
Cr: more than 1.0% to 2.0%
Cr is an effective element for improving the strength and corrosion resistance of steel, and in the present invention, it is necessary to contain more than 1.0% mainly to secure high strength. On the other hand, when the content exceeds 2.0%, the ductility is reduced, and the workability, weldability and toughness are further reduced. For this reason, Cr is limited to a range of more than 1.0% to 2.0%. Incidentally, the content is preferably 1.1 to 1.5%.
[0016]
Mo: 0.5% or less Mo is an element that increases the strength of steel and improves the hardenability, and in the present invention, it is preferable to contain 0.1% or more. On the other hand, when the content exceeds 0.5%, the ductility is reduced and the resistance to weld cracking is reduced. For this reason, Mo was limited to 0.5% or less. Incidentally, it is preferably at most 0.3%.
[0017]
In the present invention, in addition to the above basic composition, Cu: 1.0% or less, Ni: 1.0% or less, Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10 % Or less, B: 0.005% or less.
Cu, Ni, Nb, V, Ti, and B all have the effect of increasing the strength, and one or more of them can be selected and contained as needed.
[0018]
Cu is an element that increases the strength of steel and also improves corrosion resistance. However, if the content exceeds 1.0%, the hot workability decreases. Therefore, Cu is preferably limited to 1.0% or less. Note that the content is more preferably 0.5% or less.
Ni is an element that increases the strength of the steel and improves the hardenability and toughness, but is expensive. Therefore, in the present invention, Ni is preferably limited to 1.0% or less. Note that the content is more preferably 0.5% or less.
[0019]
Nb is an element that increases the strength of the steel by precipitation hardening and refines the structure to improve the toughness. However, if it exceeds 0.10%, the toughness is degraded. Therefore, Nb is preferably limited to 0.10% or less. In addition, it is more preferably 0.01 to 0.05%.
V is an element that increases the strength of the steel by precipitation hardening and improves the hardenability, but if it is contained in excess of 0.10%, the toughness deteriorates. Therefore, V is preferably limited to 0.10% or less. In addition, more preferably, it is 0.01 to 0.05%.
[0020]
Ti is an element that increases the strength of steel by precipitation hardening and refines the structure to improve toughness. However, if it is contained in excess of 0.10%, the toughness is deteriorated. For this reason, it is preferable to limit Ti to 0.10% or less. Note that the content is more preferably 0.005 to 0.03%.
B is an element that contributes to an increase in strength through improvement in hardenability. However, if it is contained in excess of 0.005%, toughness decreases. Therefore, B is preferably limited to 0.005% or less. Note that the content is more preferably 0.0005 to 0.002%.
[0021]
The balance other than the components described above is Fe and inevitable impurities. As inevitable impurities, P: 0.03% or less, S: 0.01% or less, and Al: 0.10% or less are acceptable.
It is preferable to smelt the molten steel having the above composition by a known smelting method such as a converter or an electric furnace, and to form a steel pipe material such as a billet by a known casting method such as a continuous casting method or an ingot casting method.
[0022]
Next, the obtained steel pipe material is preferably formed using a normal Mannesmann-plug mill method or a Mannesman-mandrel mill method, and the seamless steel pipe is manufactured by a method other than the above. No problem. The formed seamless steel pipe is then subjected to a quenching and tempering treatment or a normalizing treatment.
[0023]
The heating temperature for quenching is a temperature in the range from the Ac ₃ transformation point to 1050 ° C. If the heating temperature is lower than the Ac ₃ transformation point, uniform austenitization cannot be performed. On the other hand, if the heating temperature is higher than 1050 ° C., the crystal grains become coarse and the toughness decreases. For this reason, in the present invention, the quenching heating temperature is in the range from the Ac ₃ transformation point to 1050 ° C. After heating to a temperature within the above range, the material is cooled (quenched) by water cooling or the like to obtain a quenched structure (martensite structure). Preferably, the quenching heating temperature is not lower than the Ac ₃ transformation point and not higher than 950 ° C.
[0024]
Tempering is performed at a temperature within the range of 450 ° C. or more and the Ac ₁ transformation point or less. As the tempering temperature, it is preferable to select a temperature at which the strength, toughness and workability are simultaneously optimized. If the tempering temperature is lower than 450 ° C., the tempering is insufficient and the desired toughness cannot be obtained. On the other hand, when the temperature exceeds the Ac ₁ transformation point, a quenched structure cannot be obtained, and the strength is reduced, so that a desired strength cannot be secured. For this reason, the tempering temperature is limited to a temperature within the range of 450 ° C. or more and the Ac ₁ transformation point or less. The temperature is preferably 500 to 700 ° C. The cooling after tempering is preferably performed at a speed higher than air cooling.
[0025]
The normalizing process is performed by heating to a temperature in the range of 850 to 1000 ° C. and air cooling. If the normalizing temperature is lower than 850 ° C., the austenite grains cannot be sufficiently homogenized. On the other hand, if the normalizing temperature is higher than 1000 ° C., the crystal grains become coarse and it is difficult to secure desired toughness. For this reason, it is preferable to limit the normalizing temperature to 850 to 1000 ° C. The temperature is preferably 850 to 950 ° C.
[0026]
The seamless steel pipe that has been subjected to the quenching and tempering treatment or the normalizing treatment is thereafter subjected to cold drawing to form a steel pipe having a predetermined size.
The cold drawing does not require a special device, and can be performed by using a generally known cold drawing device. The cold drawing condition is not particularly limited as long as the steel tube can have a predetermined size, but by adjusting the diameter reduction ratio to an appropriate range of 5 to 15% and the wall thickness reduction to 10 to 30%, A reduction in circumferential toughness can be suppressed, and a steel pipe with less anisotropy can be obtained.
[0027]
The seamless steel pipe manufactured by the above-described manufacturing method has high dimensional accuracy, high tensile strength of 900 MPa or more, and high ductility in a drop test at −60 ° C. for a half-split steel pipe. It is a steel pipe having toughness and excellent in workability and weldability and suitable for an inflator for a curtain type airbag.
[0028]
【Example】
A steel pipe material (billet: 140 mm φ) having the composition shown in Table 1 was heated to 1250 ° C., and drilled by a Mannesmann-mandrel mill system, stretch-rolled, and reduced-diameter roll to form a seamless steel pipe (outer diameter: 34.0 φ × (Thickness: 3.2 mm, outer diameter: 38.1φ × thickness: 3.3 mm). These seamless steel pipes were subjected to quenching and tempering or normalizing treatment under the conditions shown in Table 2. Next, these heat-treated seamless steel pipes were subjected to cold drawing with a diameter reduction ratio of 11.8% and 8.9% and a wall thickness reduction ratio of 21.9% and 18.2%, respectively, to obtain an outer diameter of 30%. A steel pipe (product) having a diameter of 0.0φ × 2.5 mm or an outer diameter of 34.7φ × 2.7 mm was used.
[0029]
A test piece was sampled from the obtained seamless steel pipe (product), a real pipe tensile test was performed, and a tensile property in a longitudinal direction was investigated. The actual pipe tensile test was performed in accordance with JIS Z 2241 by extracting a No. 11 test piece (tubular test piece: real pipe) specified in JIS Z 2201.
Furthermore, a hydraulic burst test was performed, and the tensile strength in the circumferential direction was converted from the burst pressure.
[0030]
Further, a drop test at −60 ° C. was performed on the obtained seamless steel pipe (product) to investigate toughness. In the drop test at -60 ° C, a 70 mm long seamless steel pipe (product) is divided into halves, and a 100 kgf (980 N) heavy drop is dropped from a height of 500 mm onto the half. At −60 ° C., the fracture surface was observed, and the presence or absence of brittle fracture was investigated. The test was repeated three times, and the case where no brittle fracture occurred at all in the three tests was evaluated as ○, the case where all brittle fractures occurred was evaluated as x, and the others were evaluated as Δ.
[0031]
Further, the obtained seamless steel pipe (product) was reduced in outer diameter to 20 mm and 25 mm by a spatula drawing, and a crack in a processed portion was observed to evaluate workability. The case where no crack occurred was defined as workability ○, and the case where cracks occurred was defined as workability ×.
After the pipe end was reduced to an outer diameter of 20 mm by spatula drawing, a sealing plate was welded to the pipe end, and the occurrence of cracks after welding was visually and microscopically examined to evaluate the weldability.
[0032]
Further, for the obtained seamless steel pipe (product), the surface roughness of the inner and outer surfaces of the product was measured using a surface roughness meter, and an arithmetic average roughness Ra specified in JIS B0601 was obtained. The case where Ra was less than 1 μm was evaluated as ○, and the case where Ra was 1 μm or more was evaluated as ×.
Table 2 shows the obtained results.
[0033]
[Table 1]

[0034]
[Table 2]

[0035]
Each of the examples of the present invention is a seamless steel pipe having excellent surface properties, a tensile strength of 900 MPa or more, and high toughness, excellent workability, and excellent weldability. On the other hand, a comparative example out of the scope of the present invention has a tensile strength of less than 850 MPa, a reduced toughness, or a reduced workability, as a steel pipe for an inflator for a curtain type airbag, Sufficient characteristics have not been obtained.
[0036]
【The invention's effect】
As described above, according to the present invention, a high-strength, high-toughness, and high-workability seamless steel pipe can be stably manufactured, and an industrially remarkable effect is achieved.

Claims (3)

In mass%,
C: 0.01 to 0.10%, Si: 0.5% or less,
Mn: 0.10 to 2.00%, Cr: more than 1.0% to 2.0%,
Mo: A steel pipe material having a composition containing 0.5% or less is formed into a seamless steel pipe, and then the seamless steel pipe is heated to a temperature within the range from the Ac ₃ transformation point to 1050 ° C. and then quenched. Then, a quenching and tempering treatment of tempering at a temperature in the range of 450 ° C. or more and the Ac ₁ transformation point or less is performed, and thereafter, the steel tube is cold drawn to obtain a steel pipe having a predetermined size. A method of manufacturing a tough, highly workable seamless steel pipe. In addition to the above composition, in mass%, Cu: 1.0% or less, Ni: 1.0% or less, Nb: 0.10% or less, V: 0.10% or less, Ti: 0.10% or less And B: a composition containing at least one member selected from the group consisting of 0.005% or less and a high-strength, high-toughness, and high-workability seamless steel tube for an airbag according to claim 1, characterized in that: Manufacturing method. 3. The airbag according to claim 1, wherein, instead of the quenching and tempering treatment, the seamless steel pipe is subjected to a normalizing treatment of heating to a temperature in a range of 850 ° C. to 1000 ° C. and air cooling. A method for manufacturing a high-strength, high-toughness, high-workability seamless steel pipe.