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
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/06—Making non-ferrous alloys with the use of special agents for refining or deoxidising
• • 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
  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
• • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • 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
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • 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
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • 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
  • C21D2211/00—Microstructure comprising significant phases
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/004—Dispersions; Precipitations

Definitions

• the present invention relates to a high-strength thin steel sheet in which placing cracks and delayed fracture, which are particularly problematic in a high-strength thin steel sheet, are suppressed, a method of manufacturing the same, and a strength part for automobiles manufactured by using the same.
• high-strength steel is often used for applications such as ports, PC steel wires, and line pipes.However, when the strength exceeds 78 OMPa, delayed blasting occurs due to the penetration of hydrogen into the steel. It is known to occur.
• ultrahigh-strength steel sheets of 780 MPa or more are press-formed into reinforcing materials such as pumper-packed beam beams and sheet trails.
• the number of cases where pipe forming, bending, end face processing, or hole expansion processing is provided is increasing rapidly. Therefore, there is an urgent need to develop ultra-high strength thin steel sheets with delayed fracture resistance.
• Japanese Patent Application Laid-Open No. 11-293383 discloses that an oxide mainly composed of Ti and Mg is effective in preventing generation of hydrogen defects.
• delayed rupture of thin steel sheets it has been reported that delayed rupture was promoted due to the addition-induced transformation of the amount of retained austenite (for example, Yamazaki et al., CAMP—ISIJ vol. 5 p1839) ⁇ 1842 (1992), see).
• the above report relates to a high-strength thin steel sheet with a specific structure, and cannot be said to be a fundamental measure for improving delayed rupture resistance.
• the present inventors have come to find a method for fundamentally improving delayed fracture resistance by sufficiently considering the use environment of thin steel sheets and the production method using existing facilities.
• the delayed fracture resistance after forming can be improved without deteriorating the formability of the high-strength steel sheet. I found that it could be improved.
• the balance consists of iron and unavoidable impurities.
• the volume fraction of retained austenite in the structure of the steel sheet is 7% or less.
• At least one of Mg oxides, sulfides, complex precipitates and complex precipitates is at least one of Mg oxides, sulfides, complex precipitates and complex precipitates
• Average particle size d 0.01 to 5.0 // m
• Density (0: 100 to 100,000 per square mm, and distribution: the ratio of standard deviation ⁇ from average particle diameter to average particle diameter d ⁇ 1.0 is satisfied, and
• a high-strength thin steel sheet with excellent delayed fracture resistance after forming characterized in that the volume fraction V V (%) of residual austenite and the tensile strength T S (MP a) satisfy formula (A).
• V y Volume ratio of residual austenite (%)
• V 0.05 to 1%
• a high-strength thin steel sheet excellent in delayed fracture resistance after forming as described in (1) characterized by containing one or more of the following.
• N i 0.005 to 2.0%
• C o 0.05 to 2.0%
• the high-strength thin steel sheet having excellent delayed fracture resistance according to the above (1) to (7) is a hot-rolled steel sheet or a cold-rolled steel sheet. High strength thin steel sheet with excellent delayed fracture.
• a high-strength thin steel sheet having excellent delayed fracture resistance according to the above (1) to (7), wherein the steel sheet has been subjected to a surface treatment with zinc plating. High strength thin steel sheet with excellent delayed fracture resistance.
• a composition comprising the composition according to any one of (1) to (7).
• a piece is manufactured, hot-rolled at a finishing temperature of 3 points or more of Ar, wound up at 500 to 800 ° C, then pickled, and then cooled at a rolling reduction of 30 to 8 °%. Rolling, then soaking at a temperature of 600 ° C. or more to 950 ° C. or less, recrystallization annealing, and then temper rolling are performed.
• the steel sheet may have a temperature of 200 to 700 ° C after annealing.
• a high-strength component for automobiles which is made of a high-strength thin steel sheet having excellent delayed fracture resistance after the forming process according to (1) to (7).
• Figure 1 is a diagram showing the relationship between equation (A) and delayed rupture time.
• FIG. 2 is a diagram showing the relationship between equation (A) and residual austenite.
• FIG. 3 is a diagram showing the relationship between the formula (A) and the amount of Mg.
• FIG. 4 is a diagram showing the relationship between the equation (A) and the density.
• delayed blasting is thought to be caused by the accumulation of hydrogen at the former austenite grain boundaries and the like, and voids and the like originate from that portion.
• the hydrogen trap site is evenly and finely dispersed and hydrogen is trapped in that part, the diffusible hydrogen concentration decreases, and the sensitivity to delayed fracture decreases.
• the present inventors have developed various types of crystallization and precipitation to ensure or improve the use environment of thin steel sheets, that is, delayed rupture resistance even after forming.
• the effects of the materials were examined.
• the oxide or sulfide containing Mg in (i) and the compound crystallized or precipitated with them are present in the grains (excluding the phase interface of the microstructure such as the former austenite grain boundary). This is more effective for improving delayed blasting properties.
• the production conditions are specified, and oxides, nitrides, sulfides, and other crystallized or precipitated substances of various elements are trapped in hydrogen. It is also effective to control the form that can be a site.
• the delayed fracture resistance of the high-strength thin steel sheet can be sufficiently ensured even after the forming.
• Residual austenite amount Since the residual austenite increases the delayed fracture susceptibility when it becomes martensite due to work-induced transformation, the upper limit is set to 7% by volume.
• Average particle size The average particle size was limited to 0.5 ⁇ to 0.5 ⁇ . A certain size is required as a hydrogen trap site, and the presence of a large amount of fine particles is not preferable in terms of ensuring the ductility of a thin steel sheet, and makes production difficult.
• the lower limit of the average particle diameter was set to 0.1 ⁇ .
• coarse particles do not act as a trap site and can be a starting point for destruction. Therefore, 5.0 ⁇ was set as the upper limit of the average particle diameter.
• Density The particle density was set to 100 to: L 0000 particles mm 2 .
• the low particle density means that the number of trap sites is small, and the delayed fracture resistance after processing cannot be ensured. Therefore, the lower limit was set to 100 particles / mm 2 .
• the ratio of the standard deviation ⁇ from the average particle diameter to the average particle diameter d satisfies the equation ⁇ / d ⁇ 1.0.
• ⁇ ⁇ (1> 1.0) means that the particle distribution is wide-ranging, and the effect of improving delayed blasting is smaller than that of the same average particle size. Therefore, the upper limit of a Z d is set to 1.0.
• particle measurement use a thin film or extracted replica sample and observe it with a scanning or transmission electron microscope at a magnification of 50,000 to 100,000, and a minimum of 30 fields of view. Is the value obtained by measuring.
• the particle diameter is evaluated by the circle equivalent diameter by image analysis. When determining the density, multiple precipitates or crystals are counted as one.
• composition analysis was performed using EDX and EELS, and the structural analysis was performed by analyzing the diffraction pattern.
• Each composite compound is composed of a compound (Carbide, Nitride, Oxide or Sulfide) containing an alloying element (for example, Ti, Nb, V, Cr, Mo, REM, Ca, etc.) in addition to Mg. Things).
• an alloying element for example, Ti, Nb, V, Cr, Mo, REM, Ca, etc.
• the present invention relates to a high-strength thin steel plate, and mainly relates to a steel plate having a tensile strength of 780 MPa or more and a thickness of 0.5 mm to 4.0 mm. Things.
• equation (A) Based on the assumption that the volume fraction of residual austenite, the average particle size, the density, the amount of Mg, and the tensile strength can be cited as factors of delayed rupture resistance, FIG. ) It was set.
• V y Volume ratio of residual austenite (%)
• FIG. 2 is a diagram showing a correlation between f (V y) and the volume ratio V of retained austenite.
• the preconditions are as follows: Mg: 30 ppm, average particle diameter: 0.4 ⁇ m, density: 1500 pieces Zmm 2 , tensile strength: 1480 MPa.
• V ⁇ is high, the delayed fracture resistance deteriorates, but the invention steel with a high f (Vy) value shows good delayed fracture resistance when V0 is 7% or less.
• the comparative steel of X has f (V7) ⁇ 10 because Mg, particle size, and density are out of the ranges defined by the present invention, and the delayed fracture resistance is deteriorated. It is.
• FIG. 3 is a diagram showing a correlation between f (M g) and the amount of Mg added.
• the prerequisites are as follows: volume ratio of residual austenite: 3.0%, average particle diameter: 0.4 ⁇ m, density: 1500 / mm 2 , tensile strength: 148 MP .
• the Mg is in the range of 20 to 70 ppm, particularly, where the delayed blasting resistance is good.
• the residual austenite, particle size, and density are out of the range defined by the present invention. Is worse.
• FIG. 4 is a diagram showing the correlation between f ( P ) and the density of crystallized substances and precipitates.
• the preconditions are as follows: volume fraction of residual austenite: 3.0%, Mg: 30 ppm, tensile strength: 138 MPa. If the density is low, it can be said that delayed crushing resistance is poor.
• the density p is within the range defined by the present invention, that of X is the range where the residual austenite, Mg, and particle size are limited by the present invention. Since it was out of the surrounding area, it was f (p)-10 and the delayed rupture resistance was poor.
• C is an element that can increase the strength of a steel sheet.
• it produces a hard phase such as martensite-austenite and is an essential element for high strength.
• 0.055% or more is necessary, but conversely, if it is contained too much, the cementite, which is the starting point of brittle fracture, will increase, and hydrogen embrittlement will occur. Is likely to occur. Therefore, the upper limit was set to 0.3%.
• Si is a substitutional solid solution strengthening element that greatly hardens the material, is effective in increasing the strength of the steel sheet, and is an element that suppresses cementite precipitation.
• the upper limit is 3.0%.
• Mn is an element effective for increasing the strength of a steel sheet.
• the lower limit was set to 0.01%.
• the upper limit is 3.0%.
• P is an element that promotes grain boundary destruction due to grain boundary segregation, and it is preferable that P be low. However, extreme reduction is not preferable in terms of manufacturing cost.
• the upper limit is set to 0.02%.
• S is an element that promotes the absorption of hydrogen in a corrosive environment. It is desirable that S be low, but extremely reducing it is not preferable in terms of manufacturing cost. Particularly, in order to enhance the workability, the lower the better, the upper limit is set to 0.02%.
• A1 is added in an amount of 0.01% or more for deoxidation.However, if the addition amount increases, inclusions such as alumina increase, thereby deteriorating the workability and the weldability.
• the upper limit is 0%.
• the addition of 0.2% or more has an effect of suppressing the generation of residual austenite, and is therefore preferable.
• N contributes to the deterioration of workability and the occurrence of blowholes during welding, a smaller N is better. If the content exceeds 0.01%, the workability deteriorates. Therefore, the upper limit is set to 0.01%.
• Mg is not only effective in improving the delayed fracture resistance of the compound itself, but also forms complex precipitates or crystallized substances with other elements, and changes their morphology to delayed fracture resistance. Since it is an element necessary for controlling to contribute to improvement, it is added in an amount of 0.0002% or more.
• V, T i, N b, and Z r are strong carbide forming elements, which are elements necessary for forming precipitates and inclusions and improving strength and delayed fracture resistance.
• V is an element effective for increasing the strength of the steel sheet and reducing the grain size.
• the lower limit is set to 0.005%.
• the upper limit was set to 1%.
• Ti is an element effective for increasing the strength of the steel sheet and reducing the grain size.
• the lower limit is set to 0.02%.
• the upper limit was set at 1%.
• Nb is an element effective for increasing the strength and refining the steel sheet.
• these effects cannot be obtained at less than 0.002%, so the lower limit was made 0.002%.
• the content exceeds 1%, the precipitation of carbonitrides increases and the workability and delayed fracture resistance deteriorate, so the upper limit was made 1%.
• Zr is an element effective for increasing the strength and reducing the grain size of the steel sheet.
• the content is less than 0.02%, the number of precipitates decreases, so the lower limit was made 0.02%.
• the upper limit was set to 1%.
• Cr, Mo, and W are carbide forming elements and temper softening resistance elements, and are elements necessary for improving strength and delayed rupture resistance.
• Cr is an element effective for increasing the strength of the steel sheet.
• the lower limit was made 0.05%.
• the upper limit was set to 5%.
• Mo is not only an effective element for improving the hardenability of steel sheets and stably obtaining martensite in continuous annealing equipment, but also has the effect of strengthening grain boundaries and suppressing the occurrence of hydrogen embrittlement. It is an element that plays. However, these effects cannot be obtained at less than 0.005%, so the lower limit was made 0.05%. Also, if it exceeds 5%, these effects will saturate, The upper limit is set at 5%.
• W is an element effective for increasing the strength of the steel sheet.
• this effect cannot be obtained at less than 0.05%, so the lower limit was made 0.05%.
• the upper limit was set to 5%.
• Ni and Co are strengthening elements that enhance hardenability.
• Ni is an element that forms Ni sulfide to suppress hydrogen intrusion and improve delayed blasting properties, and to enhance the hardenability of the steel sheet to ensure the strength of the steel sheet.
• Co is effective for strengthening, it was added in an amount of 0.05% or more.
• the upper limit is set to 2.0%.
• B is an element effective in increasing the strength of the steel sheet.
• the lower limit is set to 0.0002%.
• the upper limit was made 0.1%.
• REM, Ca, and Y are effective for controlling the morphology of inclusions and contribute to delayed rupture resistance, so they were added in an amount of 0.0005% or more. On the other hand, 'excessive addition degrades hot workability, so the addition was made 0.01% or less. Next, the manufacturing method will be described.
• Finish rolling is performed at Ar 3 or more.
• the finish rolling temperature is desirably 940 ° C or lower.
• the higher the temperature the more recrystallization and grain growth are promoted, and workability can be expected to be improved.
• scale formation that occurs during hot rolling is promoted, and pickling properties are reduced. It should be below 0 ° C.
• the winding temperature is set to 500 ° C. or higher.
• the lower limit of the draft is set to 30%. Further, if rolling is performed at a rolling reduction exceeding 80%, cracks will occur at the edges of the steel sheet and shape irregularities will occur, so the upper limit is set to 80%.
• the continuous annealing temperature is too low, it will be in an unrecrystallized state and the steel structure will be hardened.On the other hand, if it is too high, the crystal grains may become coarse and the surface may be roughened during pressing. Not less than 950 ° C. Annealing is performed using continuous annealing equipment or box annealing equipment.
• the temperature may be maintained in a temperature range of 200 to 700 ° C. for 1 minute to 10 hours, and then cooled.
• alloy carbides or nitrides for example, carbonitrides containing V, Cr, Mo, W
• the production speed of the piece is preferably 0.05 to 20.OmZ. Furthermore, in order to stably utilize the delayed rupture property improving effect of the Mg compound, the content of 1.0 to 3.0 OmZ is preferable.
• the steel sheet of the present invention may be any of a hot-rolled steel sheet, a cold-rolled steel sheet, and a plated steel sheet. Further, the plating may be any of normal zinc plating and aluminum plating. The plating may be hot dip plating or electroplating, and may be subjected to an alloying heat treatment after plating, or may be multi-layer plating.
• a steel sheet that is not plated or a steel sheet that has been subjected to a film lamination treatment on a plated steel sheet does not depart from the scope of the present invention.
• a high-strength component for an automobile for example, a reinforcing member such as a bumper or a door impact beam
• a high-strength thin steel sheet for example, a steel sheet of 780 MPa or more
• cold rolling was performed after pickling, followed by recrystallization annealing, and then temper rolling of 0.4% to obtain a cold-rolled steel sheet.
• reference numeral I, J are basis weight and alloyed molten zinc plated steel sheet of single-sided 5 0 gZrn 2, for J, was further subjected to film lamination.
• Table 2 shows the steel sheet manufacturing methods and material properties.
• Table 3 shows the evaluation of the delayed fracture resistance of the steel sheet.
• the evaluation method was to bend a strip test of 80 mm x 30 mm, attach a water-resistant strain gauge to the surface, immerse it in 0.5 mo 1 Z1 sulfuric acid, and electrolyze by electric current. This is a method for invading hydrogen.
• the bending radii were 5 mm, 10 mm, and 15 mm, and the applied stress was 60 MPa and 90 MPa, respectively.
• reference numerals 1, 2, 3, 5, and 7 to 12 which are examples of the present invention, show sufficient tensile strength and ductility to be applied to reinforcing parts of automobiles. Also, the time until crack generation is long, and it is excellent in delayed rupture resistance.
• Symbols 4 and 6 indicate that the value of the formula (A) deviates from the range of the present invention, and that the time until crack generation is short.
• Reference numerals 13 to 15 deviate from the component range of the present invention, and the number of crystallized substances and precipitates serving as hydrogen trap sites is small, or conversely, cracks occur because hydrogen is trapped too much. Occur And the difference from the delayed fracture resistance obtained in the present invention is apparent.
• the Mg compound or the composite crystallization / precipitate which is a hydrogen trap site, is effectively dispersed, and the ductility and the delayed fracture resistance after the forming process are reduced. It is possible to balance soil properties.

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• 2003
  • 2003-05-27 EP EP03817075A patent/EP1637618B1/de not_active Expired - Lifetime
  • 2003-05-27 WO PCT/JP2003/006617 patent/WO2004106571A1/ja not_active Ceased
  • 2003-05-27 AU AU2003235443A patent/AU2003235443A1/en not_active Abandoned
  • 2003-05-27 DE DE60333400T patent/DE60333400D1/de not_active Expired - Lifetime
  • 2003-05-27 US US10/558,579 patent/US20070006948A1/en not_active Abandoned
• 2010
  • 2010-12-07 US US12/928,310 patent/US20110120598A1/en not_active Abandoned

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