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US20050000601A1 - Steel pipe for an airbag system and a method for its manufacture - Google Patents

Steel pipe for an airbag system and a method for its manufacture Download PDF

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Publication number
US20050000601A1
US20050000601A1 US10/848,119 US84811904A US2005000601A1 US 20050000601 A1 US20050000601 A1 US 20050000601A1 US 84811904 A US84811904 A US 84811904A US 2005000601 A1 US2005000601 A1 US 2005000601A1
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Prior art keywords
steel
pipe
steel pipe
heating
airbag system
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US10/848,119
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Yuji Arai
Kunio Kondo
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Nippon Steel Corp
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Individual
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Assigned to SUMITOMO METAL INDUSTRIES, LTD. reassignment SUMITOMO METAL INDUSTRIES, LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ARAI, YUJI, KONDO, KUNIO
Publication of US20050000601A1 publication Critical patent/US20050000601A1/en
Priority to US11/266,265 priority Critical patent/US7727463B2/en
Abandoned legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
    • B60R21/00—Arrangements or fittings on vehicles for protecting or preventing injuries to occupants or pedestrians in case of accidents or other traffic risks
    • B60R21/02—Occupant safety arrangements or fittings, e.g. crash pads
    • B60R21/16—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags
    • B60R21/26—Inflatable occupant restraints or confinements designed to inflate upon impact or impending impact, e.g. air bags characterised by the inflation fluid source or means to control inflation fluid flow
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies

Definitions

  • This invention relates to a steel pipe which is suitable for use with an airbag system and which has a high tensile strength of at least 1000 MPa along with a high toughness. It also relates to a method for the manufacture of such a steel pipe.
  • the present invention relates to a steel pipe for au airbag system and to a method for its manufacture, the pipe having a high strength and high toughness to such a degree that when a pipe sample having a small wall thickness is subjected to an internal pressure bursting test at ⁇ 40° C. and even at ⁇ 80° C., it does not undergo brittle fracture
  • An example of such equipment is an airbag system, which causes an airbag to be inflated with gas between passengers and the steering wheel, the dashboard, or other portions of the vehicle interior before the passengers can impact therewith at the time of a collision and thereby absorbs the kinetic energy of the passengers so as to decrease the likelihood and severity of injuries.
  • An airbag system of the latter type normally maintains an inflating gas at a high pressure in an accumulator.
  • the inflating gas in the accumulator is discharged all at once into an airbag.
  • a steel pipe which is used as an accumulator for the high pressure inflating gas undergoes stress in an extremely short period of time at a high strain rate. Therefore, in contrast to a simple structural member such as a conventional pressure cylinder or line pipe, the steel pipe used as the inflating gas accumulator in such an airbag system is required to have high dimensional accuracy, workability, and weldability, and it is also required to have high strength and excellent resistance to bursting.
  • a steel pipe which is suitable for use with an airbag system to form an inflating gas accumulator and a method for its manufacture are described in the following published Japanese patent applications: JP P10-140238A, JP P10-140249A, JP P10-140250A, JP P10-140283A, JP P10-212549A, JP P2002-294339A, JP P11-199929A, JP P2001-49343A, and JP P2002-194501A.
  • the above-listed patent applications aim at providing a high strength, high toughness steel pipe suitable for use with an airbag system
  • the target tensile strength described in those applications is on the level of 590 MPa or above, and the values of tensile strength obtained in the examples of those applications are no higher than 947 MPa.
  • the present invention provides a high strength, high toughness steel pipe suitable for use with airbag systems (i.e., for use in forming inflating gas accumulators for airbag systems) which can satisfy properties which are demanded today as described above.
  • the present invention also provides a method for the manufacture of such a steel pipe.
  • the present inventors found that in order to provide a steel pipe for airbag systems with a high tensile strength and excellent resistance to bursting so as to meet the demand for higher accumulator pressures and smaller wall thicknesses, it is necessary for the steel pipe to have the following properties:
  • the steel pipe From the standpoint of safety, it is also important for the steel pipe to have good resistance to bursting, which is demonstrated in an internal pressure bursting test under hydrostatic pressure at ⁇ 40° C. by there being no occurrence of brittle fracture and there being no cracks which extend over the entire length of the steel pipe. It is still more desirable that such resistance to bursting be demonstrated in an internal pressure bursting test at ⁇ 80° C.
  • a steel pipe having a high strength of at least 1000 MPa and a high toughness as evidenced by 100% ductile fracture at ⁇ 40° C. in a Charpy impact test as well as the above-described good resistance to bursting can be obtained by selecting a specific steel composition.
  • a steel pipe suitable for use with an airbag system (to form an inflating gas accumulator for the airbag system) is made of a steel having a composition which consists essentially, in mass %, of: C: 0.05-0.20%, Si: 0.1-1.0%, P: at most 0.025%, S: at most 0.010%, Cr: 0.05-1.0 %, Al: at most 0.10%, one or both of Ti and Mn in amounts sufficient to satisfy the following equations (1) and (2), and a remainder of Fe and impurities: Ti ⁇ 0.02% (1) 0.4% ⁇ Mn+40Ti ⁇ 1.2% (2).
  • the steel pipe has a tensile strength of at least 1000 MPa.
  • the steel composition may further comprise one or more of Mo: 0.05-0.50%, Ni: 0.05-1.5%, V: 0.01-0.2%, and B: 0.0003-0.005%.
  • the steel composition may further comprise one or two of Cu: 0.05-0.5% and Nb: 0.003-0.1%.
  • the steel composition may further comprise one or more of Ca: 0.0003-0.01%, Mg: 0.0003-0.01%, and REM: 0.0003-0.01%.
  • a method of manufacturing a steel pipe for an airbag system comprises forming a pipe having prescribed dimensions from a steel having the above-described composition by a process including pipe making and subsequent cold working, then heating the cold-worked pipe to at least the Ac 1 transformation point of the steel followed by quenching, and tempering the quenched pipe at a temperature no higher than the Ac 1 transformation point of the steel.
  • the cold-worked steel pipe is heated to at least the Ac 3 transformation point of the steel and more preferably from 900° C. to 1000° C.
  • This heating is preferably performed by rapid heating at a rate of temperature increase of at least 10° C./sec by means of high frequency induction heating, for example.
  • the subsequent quenching is preferably performed such that the cooling rate at least in the temperature range of from 850° to 500° C. is at least 20° C./sec.
  • a steel pipe having an as-quenched fine microstructure with a ⁇ grain size number of 11 or larger (the larger the number, the finer the ⁇ grain size).
  • Such a steel pipe exhibits extremely good resistance to bursting as demonstrated by no cracks progressing significantly even in an internal pressure bursting test at ⁇ 80° C.
  • FIG. 1 is a graph showing the tensile strength in the circumferential direction of a steel pipe as a function of the value of vTrs100, which is defined below, and
  • the content of either one of Ti and Mn may be zero percent.
  • Carbon (C) is an element which is effective for inexpensively increasing the strength of steel. If the content thereof is less than 0.05%, it is difficult to obtain a desired tensile strength of at least 1000 MPa, while if its content exceeds 0.20%, workability and weldability decrease. A preferred range for the C content is 0.08-0.20%, and a more preferred range is 0.12-0.17%.
  • Phosphorus (P) brings about a decrease in toughness caused by grain boundary segregation.
  • the decrease in toughness becomes particularly marked when the P content exceeds 0.025%.
  • the P content is preferably at most 0.020% and more preferably at most 0.015%.
  • S Sulfur decreases toughness particularly in the T direction, i.e., the circumferential direction of a steel pipe.
  • the S content is preferably at most 0.005%, and still more preferably at most 0.003%.
  • Aluminum (Al) is an element which has a deoxidizing action and which is effective for increasing toughness and workability. However, if the content thereof exceeds 0.10%, the occurrence of scratch marks in the steel during rolling becomes marked.
  • the Al content may be on the level of an impurity, so there is no particular lower limit, but it is preferably at least 0.005%. A preferred range for the Al content is 0.005-0.05%.
  • the Al content refers to the content of acid soluble Al (so called sol. Al).
  • Ti titanium
  • the content is at most 0.02% so as to satisfy Equation (1).
  • Manganese (Mn) is an element which has a deoxidizing action and which is effective for increasing the hardenability of steel and for increasing strength and toughness, so Mn may be present in an amount of up to 1.0%. A sufficient hardness and toughness are not obtained when the content thereof is less than 0.20%, so the Mn content is preferably at least 0.20%. On the other hand, if the Mn content exceeds 1.0%, coarse MnS grains may form in the steel and they may be extended during hot rolling, thereby causing toughness to decrease. Therefore, the Mn content is preferably 0.20-1.0% and more preferably 0.4-0.8%.
  • the Ti and Mn content is controlled so as to satisfy Equation (2). If the value of (Mn+40Ti) is less than 0.4% or greater than 1.2%, the desired high tensile strength and/or high toughness cannot be obtained.
  • the value of (Mn+40Ti) is preferably in the range of 0.4-0.8%.
  • one or more of Mo, Ni, Cu, V, Nb, B, Ca, Mg, and REM may optionally be added within their respective ranges described below to the steel composition for a steel pipe according to the present invention.
  • molybdenum (Mo), nickel (Ni), boron (B), and vanadium (V) has the effect of increasing hardenability, and one or more of these elements may be added as optional elements.
  • Mo also has the effect of increasing strength through solid-solution hardening and precipitation hardening. These effects of Mo are obtained even when its content is on the level of an impurity, but in order to obtain a more marked effect, the content of Mo is preferably at least 0.05%. However, if the content of Mo exceeds 0.50%, welded portions are hardened and toughness decreases. Therefore, when it is added, the content of Mo is preferably 0.05-0.50% and more preferably 0.1-0.35%.
  • Ni also has the effect of increasing toughness. This effect of Ni is obtained even when its content is on the level of an impurity, but in order to obtain a more marked effect, the content of Ni is preferably at least 0.05%. However, Ni is an expensive element, and costs increase markedly when the content thereof exceeds 1.5%. Therefore, when Ni is added, its content is preferably 0.05-1.5% and more preferably 0.1-1.0%.
  • the content of B is preferably at least 0.0003%. However, if the content of B exceeds 0.005%, toughness decreases. Therefore, when B is added, its content is preferably 0.0003-0.005%. A more preferred range for the B content is 0.0003-0.002%.
  • V also has the effect of increasing strength through precipitation hardening. This effect of V is obtained when its content is at least 0.01%, but if the V content exceeds 0.2%, toughness decreases. Accordingly, when V is added, its content is preferably 0.01-0.2%. A more preferred range for the content of V is 0.03-0.10%.
  • Each of copper (Cu) and niobium (Nb) has the effect of increasing toughness, is and one or both of these elements may be added as optional elements.
  • the Cu content is preferably at least 0.05% and more preferably at least 0.1%.
  • Cu decreases the hot workability of steel, so when Cu is added, Ni is preferably also added in order to guarantee hot workability. If the content of Cu exceeds 0.5%, it may not be possible to guarantee good hot workability even if Ni is also added. Accordingly, the content of Cu when it is added is preferably 0.05-0.5%.
  • Nb has the effect of increasing toughness even when present on the level of an impurity, but in order to obtain a more marked effect, its content is preferably at least 0.003% and more preferably at least 0.005%. However, if the content of Nb exceeds 0.1%, toughness ends up decreasing. Accordingly, when Nb is added, its content is preferably 0.003-0.1%. A more preferred range for the Nb content is 0.003-0.03% and a still more preferred range is 0.005-0.02%.
  • one or more of calcium (Ca), magnesium (Mg), and rare earth metals (REM) may be added as optional elements.
  • each of these elements improves the anisotropy of toughness, and increases the toughness in the T direction of a steel pipe, and as a result they have the effect of further increasing the resistance to bursting.
  • This effect can be obtained even when the content is on the level of an impurity, but in order to obtain a more marked effect, the content of any of these elements which is added is preferably at least 0.0003%. However, if the content of any of these elements exceeds 0.01%, the formation of inclusions in the form of clusters occurs, leading to the occurrence of scratch marks. Accordingly, when any of these elements is added, the content of each added element is preferably 0.0003-0.01% and more preferably 0.0005-0.003%.
  • a seamless steel pipe or a welded steel pipe is made from a steel having the above-described chemical composition.
  • a seamless steel pipe is preferred from the standpoint of reliability. There are no particular limitations on a method of manufacturing a seamless pipe or a welded pipe.
  • a seamless or welded steel pipe made from the above steel is subjected to cold working under conditions selected so as to provide the pipe with a prescribed dimensional accuracy and surface quality.
  • the cold working may be any type as long as it can provide a prescribed dimensional accuracy and surface quality. Examples of useful types of cold working are cold drawing and cold rolling. There are no particular restrictions on the degree of cold working, but it is preferably at least 3% in terms of reduction in area. In order to decrease the working force during cold working, softening heat treatment may be performed prior to cold working.
  • the steel pipe After the cold working described above in (C), the steel pipe is subjected to heat treatment in order to guarantee that the steel pipe has the necessary tensile strength and in order to increase toughness in the T direction so as to also guarantee resistance to bursting.
  • the steel pipe In order to provide the steel pipe with a high strength in the form of a tensile strength of 1000 MPa and resistance to bursting, the steel pipe is quenched after heating at a temperature of at least the Ac 1 transformation point of the steel, and then tempering is carried out at a temperature no higher than the Ac 1 transformation point of the steel.
  • the heating temperature prior to quenching is less than the Ac 1 transformation point, good toughness in the T direction and therefore a good resistance to bursting cannot be guaranteed.
  • the heating temperature is preferably a temperature of at least the Ac 3 transformation point of the steel, which is in the austenite region.
  • Heating at a high temperature for a long period causes a large amount of scale to be formed on the surface of a steel pipe and decreases the dimensional accuracy and surface quality and also leads to a decrease in resistance to bursting. Therefore, the heating is preferably rapid heating to a predetermined temperature followed by a short retention period at that temperature.
  • the rapid heating is preferably carried out such that the rate of temperature increase is at least 10° C./sec.
  • Such rapid heating can be achieved by high frequency induction heating or direct resistance heating, although there are no particular restrictions on the heating method.
  • a particularly preferred heating method is high frequency induction heating.
  • a preferred heating temperature is in the range of from 900° C. to 1000° C. and more preferably from 900° C. to 960° C. If the heating temperature is lower than 900° C., complete autstenitization may not be achieved during the short-term heating, thereby making it impossible to form a desired microstructure. Heating to a temperature exceeding 1000° C. may cause the ⁇ grains to be coarsened to such a degree that the toughness is decreased.
  • the heating to a temperature of at least the Ac 1 transformation point of the steel is preferably performed in an atmosphere having as low an oxygen potential as possible from the standpoint of suppressing the formation of surface scale during heating.
  • a reducing atmosphere is even more preferred.
  • the steel pipe After the steel pipe is heated at a temperature of at least the Ac 1 transformation point and preferably at least the Ac 3 transformation point of the steel, it is then quenched in order to obtain a desired tensile strength of at least 1000 MPa in a stable and reliable manner.
  • the cooling rate for quenching is at least approximately 5° C./sec in the temperature range of 850-500° C.
  • the cooling rate is at least 20° C./sec.
  • Such quenching may be performed by water quenching.
  • Rapid heating to a temperature in the range of 900-1000° C. by high frequency induction heating followed by quenching at a cooling rate of at least 20° C./sec in the temperature range of 850-500° C. makes it possible to form a dense as-quenched microstructure characterized by the the size of ⁇ grains (size of pre-existing austenite grains as measured by the Bechet-Beaujard method according to JIS G0551) having a size number of 11 or larger in a stable manner.
  • a steel pipe having such a microstructure has a particularly improved toughness and exhibits an excellent resistance to bursting as demonstrated by no cracks progressing significantly even in an internal pressure bursting test performed at ⁇ 80° C.
  • a steel pipe which is cooled to approximately room temperature by quenching is then tempered at a temperature of no higher than the Ac 1 transformation point of the steel in order to provide the pipe with the desired tensile strength of at least 1000 MPa and resistance to bursting.
  • the ⁇ grain size does not vary by such tempering. It is difficult to obtain the above-described characteristics in a stable and a reliable manner if the temperature of tempering exceeds the Ac 1 transformation point.
  • the tempering is preferably carried out by maintaining the steel pipe for at least 10 minutes at a temperature in the range of 450-700° C. After tempering, bends can be removed by a suitable straightener or similar device.
  • a steel pipe for an airbag system which has a tensile strength of at least 1000 MPa and which has a high toughness as indicated by 100% ductile fracture at ⁇ 40° C., preferably at ⁇ 60° C., and more preferably at ⁇ 80° C. in a Charpy impact test and by no cracks progressing significantly in an internal pressure bursting test at ⁇ 40° C. and preferably at ⁇ 80° C.
  • the steel pipe can adequately cope with the recent trend in steel pipes for airbag systems towards higher accumulator pressures and lower wall thicknesses.
  • the following examples illustrate the present invention and demonstrate the effects thereof. These examples are to be considered in all respects as illustrative and not restrictive.
  • the steels used in the examples had an Ac 1 transformation point in the range of from 700° C. to 760° C. and an Ac 3 transformation point in the range of from 820° C. to 880° C.
  • a seamless steel pipe having nominal dimensions of an outer diameter of 70 mm and a wall thickness of 4.1 mm was manufactured from each billet by a hot working process which included heating the billet to 1250° C. and performing piercing and rolling by a conventional Mannesmann piercer-mandrel mill system.
  • Each seamless steel pipe was then finished by cold drawing so as to have an outer diameter of 60.33 mm and a wall thickness of 3.35 mm.
  • the pipe was then heated to 920° C. in a conventional walking beam furnace (heating rate: about 0.3° C.
  • a certain length of each steel pipe was cut open and unrolled at room temperature by cutting the pipe in a longitudinal direction thereof.
  • a V-notch Charpy test piece having a width of 2.5 mm in accordance with JIS Z 2002 was taken from the opened pipe in the T direction, and a Charpy impact test was then performed on the test piece.
  • a tensile test in accordance with the tensile test method for metallic materials set forth in JIS Z 2241 was carried out using a Number 11 test piece in accordance with JIS Z 2201, which was also taken from the opened pipe in the T direction.
  • the lower temperature limit for guaranteeing a ductile fracture rate of 100% in the Charpy impact test (referred to below as vTrs 100) and the tensile strength of each pipe are shown in Table 2 and FIG. 1 .
  • Steel Numbers 1 - 22 in Table 3 are steels for which the steel compositions is satisfy the conditions prescribed by the present invention, and Steel Numbers 23 - 27 are comparative steels for which the contents of some elements do not satisfy the conditions prescribed for the present invention.
  • Each steel pipe which had been subjected to cold drawing was heated to 920° C. in a conventional walking beam furnace, and it was held in the furnace for 10 minutes and then water quenched, after which it was heated at a temperature of lower than the Ac 1 transformation point of the steel for 30 minutes in a conventional walking beam furnace to perform tempering.
  • the Charpy impact test was carried out using a V-notch Charpy test piece with a width of 2.5 mm as prescribed by JIS Z 2202 taken in the circumferential direction (the T direction) from a sample of each steel pipe, which was cut open at room temperature in the same manner as described in Example 1, and toughness was evaluated based on vTrs100.
  • the tensile test was performed in accordance with the tensile test method prescribed by JIS Z 2241 using a Number 11 test piece prescribed by JIS Z 2201 taken in the same manner as for the Charpy impact test.
  • a steel pipe which had been finished by piercing, hot rolling, and cold working as described in Example 2, was heated to 920° C. using a high frequency induction heating apparatus at a heat-up rate of about 20° C./sec, and the induction heating was continued for 5 seconds after the temperature of the steel pipe reached 920° C. Thereafter, using the same procedure as in Example 2, the heated steel pipe was water quenched and tempered at a temperature of lower than the Ac 1 transformation point of the steel for 30 minutes in a conventional walking beam furnace.
  • the ⁇ grain size number of the steel was determined by the Bechet-Beaujard method according to JIS G0551.
  • the tensile strength and vTrs100 of the steel pipe were determined in the same manner as described in Example 2.
  • An internal pressure bursting test was performed in the same manner as described in Example 1 but at a temperature of ⁇ 80° C. rather than ⁇ 40° C., and the resistance to bursting was evaluated based on the presence or absence of a crack progressing to either end of the burst pipe. The results are also shown in Table 4.
  • the steel pipe generally had an increased tensile strength, and its toughness was also further improved as demonstrated by the value of vTrs100, which was ⁇ 90° C. or lower. As a result, no crack progression was found in the bursting test at ⁇ 80° C.
  • the hardenability was superior compared to when these elements were not present, so a uniform hardened-tempered structure was easily obtained, and there was an excellent balance between strength and toughness. As a result, the strength could be further increased without a decrease in toughness.
  • vTrs 100 was lower compared to when these elements were not present, and the toughness was even better.
  • the Cr content was lower than the range for the present invention, and the hardenability was decreased. Therefore, a non-uniform structure resulted, and even when the tempering temperature was adjusted, a strength of 1000 MPa could not be obtained. In addition, the resistance to bursting was not satisfactory.
  • FIG. 2 shows the relationship between the value of (Mn+40Ti) in Equation (2) and the tensile strength for examples of the present invention and examples of the prior art in the above-mentioned patent documents having the specific steel composition according to the present invention except for Equation (2).
  • Equation (2) when Equation (2) is satisfied, the strength can be increased to an extremely high level of 1000 MPa.
  • Example 2 quenching by furnace heating (920° C. ⁇ 10
  • Example 3 quenching by high frequency minutes) induction heating (920° C. ⁇ 5 seconds) Results of ⁇ grain Results of Steel TS vTrs100 bursting test size TS vTrs100 bursting test No. (MPa) (° C.) at ⁇ 40° C. 1) number (MPa) (° C.) at ⁇ 80° C.

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  • Heat Treatment Of Steel (AREA)
  • Heat Treatment Of Articles (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
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US20090238714A1 (en) * 2006-10-27 2009-09-24 Sumitomo Metal Industries, Ltd. Seamless Steel Tube for an Airbag Accumulator and Process for its Manufacture
US20110067787A1 (en) * 2008-05-13 2011-03-24 The Japan Steel Works, Ltd. High-strength low-alloy steel excellent in high-pressure hydrogen environment embrittlement resistance characteristics and method for producing the same
EP1983065A4 (en) * 2006-02-09 2013-05-01 Nippon Steel & Sumitomo Metal Corp METHOD FOR PRODUCING A BOTTLE ELEMENT FOR AN AIRBAG INFLATION DEVICE
US20150283855A1 (en) * 2012-10-10 2015-10-08 The Yokohama Rubber Co., Ltd. Pneumatic Tire
EP2371982A4 (en) * 2008-11-26 2017-03-29 Nippon Steel & Sumitomo Metal Corporation Seamless steel pipe and method for manufacturing same
EP2578705A4 (en) * 2010-06-03 2017-06-14 Nippon Steel & Sumitomo Metal Corporation Process for producing steel pipe for air bag
DE102018106546A1 (de) * 2018-03-20 2019-09-26 Benteler Steel/Tube Gmbh Rohrelement für Gasdruckbehälter und Gasdruckbehälter

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EP1983065A4 (en) * 2006-02-09 2013-05-01 Nippon Steel & Sumitomo Metal Corp METHOD FOR PRODUCING A BOTTLE ELEMENT FOR AN AIRBAG INFLATION DEVICE
US20090238714A1 (en) * 2006-10-27 2009-09-24 Sumitomo Metal Industries, Ltd. Seamless Steel Tube for an Airbag Accumulator and Process for its Manufacture
US8496763B2 (en) 2006-10-27 2013-07-30 Sumitomo Metal Industries, Ltd. Seamless steel tube for an airbag accumulator and process for its manufacture
US20110067787A1 (en) * 2008-05-13 2011-03-24 The Japan Steel Works, Ltd. High-strength low-alloy steel excellent in high-pressure hydrogen environment embrittlement resistance characteristics and method for producing the same
US8974612B2 (en) * 2008-05-13 2015-03-10 The Japan Steel Works, Ltd. High-strength low-alloy steel excellent in high-pressure hydrogen environment embrittlement resistance characteristics and method for producing the same
US10227682B2 (en) 2008-05-13 2019-03-12 The Japan Steel Works, Ltd. High-strength low-alloy steel excellent in high-pressure hydrogen environment embrittlement resistance characteristics and method for producing the same
EP2371982A4 (en) * 2008-11-26 2017-03-29 Nippon Steel & Sumitomo Metal Corporation Seamless steel pipe and method for manufacturing same
EP2578705A4 (en) * 2010-06-03 2017-06-14 Nippon Steel & Sumitomo Metal Corporation Process for producing steel pipe for air bag
US20150283855A1 (en) * 2012-10-10 2015-10-08 The Yokohama Rubber Co., Ltd. Pneumatic Tire
DE102018106546A1 (de) * 2018-03-20 2019-09-26 Benteler Steel/Tube Gmbh Rohrelement für Gasdruckbehälter und Gasdruckbehälter
US11913101B2 (en) 2018-03-20 2024-02-27 Benteler Steel/Tube Gmbh Pipe element for gas pressure vessel, and gas pressure vessel

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ES2605739T3 (es) 2017-03-16
JP4529901B2 (ja) 2010-08-25
JPWO2004104255A1 (ja) 2006-07-20
WO2004104255A1 (ja) 2004-12-02
US7727463B2 (en) 2010-06-01
CA2525062C (en) 2009-08-04
CN100415922C (zh) 2008-09-03
US20060130945A1 (en) 2006-06-22
AR044546A1 (es) 2005-09-21
PL1637619T3 (pl) 2017-05-31
TWI243212B (en) 2005-11-11
KR100711612B1 (ko) 2007-04-27
CA2525062A1 (en) 2004-12-02
MXPA05012511A (es) 2006-02-08
TW200426224A (en) 2004-12-01
KR20060012310A (ko) 2006-02-07
EP1637619A1 (en) 2006-03-22
CN1791694A (zh) 2006-06-21
EP1637619B1 (en) 2016-11-02

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