Classifications

• • 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
  • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/10—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
• • 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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/26—Methods of annealing
  • C21D1/28—Normalising

Definitions

• the airbag which is designed to expand between the crew and a steering wheel or an instrument panel, and absorb kinetic energy of the crew, thereby reduce the damage on the crew, is now being generalized.
• an airbag for a driver seat installed within the steering wheel, or an airbag for a passenger seat installed within the instrument panel is being included as standard equipment.
• an automobile having a side airbag in the seat or a curtain type airbag for covering a side window has been increased.
• the airbag inflator is produced by aprocessing steel pipe.
• a seamless steel pipe is mostly used as the pipe for the inflator.
• the seamless steel pipe is subjected to cold drawing process to have a predetermined size and cut into a predetermined length, then both pipe ends are processed by pressing and sealing plates are welded to the pipe ends, thereby products (inflator) are formed.
• JP-A-10-140283 proposes a method for manufacturing a high-strength, high-toughness steel pipe for the airbag inflator, in which the steel containing 0.01 to 0.20% of C, 0.50% or less of Si, 0.30 to 2.00% of Mn, 0.020% or less of P, 0.020% or less of S, and 0.10% or less of Al, or further containing at least one of 0.50% or less of Mo, 0.10% or less of V, 0.50% or less of Ni, 1.00% or less of Cr, 0.50% or less of Cu, 0.10% or less of Ti, 0.10% or less of Nb, and 0.005% or less of B, and Fe and unavoidable impurities as residue is used to manufacture a seamless steel pipe.
• the seamless steel pipe is remained as cold working, or subjected to normal
• JP-A-10-140250 proposes a method for manufacturing a high-strength, high-toughness steel pipe for the airbag inflator, wherein the steel having a same composition as the composition described in JP-A-10-140283 is used to manufacture a steel pipe.
• the steel pipe is quenched at 850 to 1000°C, or further tempered at 450°C or more and less than A c1 transformation point, then subjected to the cold working to have a predetermined size and remained as it is, or subjected to the normalizing after the cold working.
• a high-strength, high-toughness steel pipe for the airbag having high dimension accuracy, excellent formability, and weldability, and a tensile strength of 590 N/mm 2 or more can be manufactured according to the technique described in JP-A-10-140283, JP-A-10-140249, or JP-A-10-140250.
• JP-A-10-140283 JP-A-10-140249, or JP-A-10-140250, which aims to manufacture a 590 MPa class, high-strength, seamless steel pipe, there is a problem that the technique cannot meet the demand for further increase of strength desired for the steel pipe for the inflator.
• a seamless steel pipe having a steel composition containing a reduced content of C and proper amounts of Cr and Mo is manufactured.
• the seamless steel pipe is subjected to the cold drawing. Then the pipe is subjected to the quenching and tempering, or the normalizing.
• a seamless steel pipe having a steel composition containing the reduced amount of C content and the proper amounts of Cr and Mo is manufactured.
• the seamless steel pipe is subjected to the quenching and tempering, or the normalizing. Then the pipe is subjected to the cold drawing. It was found that by either of the methods (1), (2), increase of the strength can be designed, particularly, a seamless steel pipe with small decrease in circumferential strength and small anisotropy is obtained.
• C is an element that contributes to increase of the strength of steel.
• excessive C content of more than 0.10% causes decrease in formability and weldability.
• the C content is less than 0.01%, a desired tensile strength is hard to be ensured. Therefore, in the invention, C is limited within a range from 0.01 to 0.10%.
• the C content is 0.03 to 0.08%.
• Si 0.5% or less
• Si is an element that increases the strength of steel, and preferably contained at 0.1% ormore to obtain such an effect. However, since excessively large content of Si causes decrease in ductility and formability, the Si content was limited to 0.5% or less in the invention. Preferably, the Si content is 0.1 to 0.4%. Mn: 0.10 to 2.00%
• Mn is an element that improves the strength, and must be contained at 0.10% or more to ensure a desired strength in the invention.
• Mn was limited to 2.00% or less.
• the Mn content is 1.00 to 1.70%.
• Cr more than 1.0% and 2.0% or less
• Cr is an effective element for improving the strength and corrosion resistance of steel, and must be contained at more than 1.0% mainly for ensuring a high strength in the invention.
• Cr was limited within a range of more than 1.0% and 2.0% or less.
• the Cr content is 1.1 to 1.5%.
• Mo 0.5% or less
• Mo is an element that increases the strength of steel and improves the quenching characteristics, and preferably contained at 0.1% or more in the invention. On the other hand, when more than 0.5% of Mo is contained, the ductility is decreased, and weld crack resistance is lowered. Therefore, Mo was limited to 0.5% or less. Preferably, the Mo content is 0.3% or less.
• one or two or more selected from 1.0% or less of Cu, 1.0% or less of Ni, 0.10% or less of Nb, 0.10% or less of V, 0.10% or less of Ti, and 0.005% or less of B can be further contained.
• Each of Cu, Ni, Nb, V, Ti, and B acts to increase the strength, and one or two or more of them can be selectively contained as needed.
• Cu is an element that increases the strength of steel, in addition, improves corrosion resistance. However, whenmore than 1.0% of Cu is contained, hot working characteristics are lowered. Therefore, Cu is preferably limited to 1.0% or less. More preferably, the Cu content is 0.5% or less.
• Ni is an element that increases the strength of steel, and improves the quenching characteristics and the toughness. However, since Ni is expensive, it is preferable that Ni is limited to 1.0% or less in the invention. More preferably, the Ni content is 0.5% or less.
• V is an element that increases the strength of steel through precipitation hardening, and improves the quenching characteristics. However, when more than 0.10% of V is contained, the toughness is decreased. Therefore, V is preferably limited to 0.10% or less. More preferably, the V content is 0.01 to 0.05%.
• the residue other than the above components is Fe and the avoidable impurities.
• the avoidable impurities 0.03% or less of P, 0.01% or less of S, and 0.10% or less of Al are allowed.
• molten steel having the above composition is produced using a known steel making process such as a converter or an electric furnace, and then preferably made into a raw material for steel pipe such as billet using a known casting process such as a continuous casting process or an ingot making process.
• the slab, which is produced using the continuous casting process can be made into the billet by rolling.
• the resultant raw material for steel pipe is manufactured using a typical manufacturing process of Mannesmann-plug mill method or Mannesmann-mandrel mill method, thereby a seamless steel pipe is formed.
• the manufacturing process of the seamless steel pipe may include other method than the above methods.
• the manufactured seamless steel pipe is subjected to either one of the following two treatments. (1) After the quenching and tempering, or the normalizing, the cold drawing is performed. (2) After the cold drawing, the quenching and tempering, or the normalizing is performed.
• the cold drawing can be performed using a generally known cold drawing apparatus without requiring a particular apparatus.
• conditions of the cold drawing is not needed to be particularly limited as long as a predetermined size of pipe can be formed, it is preferable from a view of ensuring dimension accuracy to adjust the diameter reduction percentage to be within a range from 5 to 25% and the thickness reduction percentage to be within a range from 10 to 30%.
• Heating temperature for quenching is set to be a temperature in a range from A c3 transformation point to 1050°C.
• the heating temperature for the quenching was set to be 1050°C or less in the invention.
• cooling is performed by water cooling (quenching) to form a quenching microstructure (martensite microstructure).
• the heating temperature for quenching is the A c3 transformation point or more and 950°C or less.
• the tempering is performed at a temperature within a range of 450°C or more and A c1 transformation point or less.
• the tempering temperature is preferably selected to be a temperature at which the strength, toughness, and formability are best together. When the tempering temperature is less than 450°C, the tempering is inadequate, and thus a desired toughness cannot be obtained. On the other hand, when the temperature exceeds the A c1 transformation point, the quenching microstructure cannot be obtained, and the strength is decreased, thereby a desired strength cannot be ensured. Therefore, the tempering temperature was limited to a temperature in a range of 450°C or more and the A c1 transformation point or less. Preferably, the temperature is 500 to 700°C. Cooling after the tempering is preferably performed at a rate of air cooling rate or more.
• the seamless steel pipe subjected to the quenching and tempering or the normalizing is then preferably subjected to descaling by acid pickling, or bend straightening as needed, thereby pipe products (steel pipe) are formed.
• the seamless steel pipe manufactured by the above method has a high strength of 900 MPa in tensile strength and a high toughness or ductility exhibited in the drop weight test at -60°C for the halved steel pipe, and is formed into a steel pipe having excellent formability and weldability, thereby a steel pipe suitable for the inflator for the curtain type airbag is formed.
• a raw material for steel pipe (billet with a diameter of 140 mm) having a composition shown in Table 1 was heated to 1250°C, and formed into a seamless steel pipe (outer diameter of 34.0 mm and thickness of 3.2 mm, or outer diameter of 38.1 mm and thickness of 3.3 mm) by the Mannesmann-mandrel mill method. They are piercing, mandrel mill rolling, and reducer rolling.
• the seamless steel pipes were subjected to the quenching and tempering or the normalizing under conditions shown in Table 2. Then, each of the seamless steel pipes after the heat treatments was subjected to the cold drawing in a diameter reduction percentage of 11.8% or 8.9%, and a thickness reduction percentage of 21.9% or 18.2% under the conditions shown in Table 2, thereby a pipe product with the diameter of 30.0 mm and the thickness of 2.5 mm or the diameter of 34.7 mm and the thickness of 2.7 mm was formed.
• the seamless steel pipes were subj ected to the cold drawing in diameter reduction percentage of 11.8% or 8.9%, and thickness reduction percentage of 21.9% or 18.2% under conditions shown in Table 3, thereby a steel pipe with the diameter of 30.0 mm and the thickness of 2.5 mm or the diameter of 34.7 mm and the thickness of 2.7 mm was formed. Then, the steel pipes were subjected to the quenching and tempering or the normalizing under the conditions shown in Table 2. Then, the seamless steel pipes after the heat treatments were straightened to remove the bend, thereby the pipe products were formed.
• Test pieces were sampled from the resulting pipe products, and a tensile test was carried out, thereby longitudinal tensile characteristics were examined.
• the tensile test was carried out in accordance with JIS Z 2241 standard after sampling No. 11 test pieces (tubular test piece) defined by JIS Z 2201. Furthermore, a hydraulic burst test was achieved, and circumferential strength was converted from the burst pressure.
• the drop weight test was carried out at -60°C, and the toughness was examined.
• the drop weight test at -60°C was performed in such a way that the pipe products were semicircularly halved, then a test of dropping a weight of 100kgf from a height of 500 mm onto the pipes was carried out at -60°C. After the test, fractures were observed and occurrence of brittle failure was examined. The test was set to be repeated three times, and it was determined that a case that no brittle failure occurred in the three tests was O, a case that the brittle failure occurred in all tests was X, and other cases were ⁇ .
• Each of'the examples of the invention is a seamless steel pipe having a tensile strength of 900 MPa or more and high toughness, and having an excellent formability, in addition, an excellent weldability.
• the tensile strength is less than 900 MPa, the toughness is decreased, or the formability is decreased.
• sufficient properties as the steel pipe for the inflator for the curtain type airbag are not obtained.
• a seamless steel pipe having high dimension accuracy, in addition, high strength, high toughness, and high formability can be stablymanufactured, thereby industrially remarkable advantages are provided.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Articles (AREA)
• Heat Treatment Of Steel (AREA)

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• 2003
  • 2003-06-11 EP EP03733377A patent/EP1516935A4/de not_active Withdrawn
  • 2003-06-11 WO PCT/JP2003/007435 patent/WO2004003241A1/ja not_active Ceased
  • 2003-06-11 CA CA002476546A patent/CA2476546A1/en not_active Abandoned
  • 2003-06-11 US US10/514,765 patent/US20060070687A1/en not_active Abandoned
  • 2003-06-11 MX MXPA04010403A patent/MXPA04010403A/es active IP Right Grant

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