WO2022145924A1 - Composant estampé à chaud et procédé de fabrication de celui-ci - Google Patents

Composant estampé à chaud et procédé de fabrication de celui-ci Download PDF

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Publication number
WO2022145924A1
WO2022145924A1 PCT/KR2021/019945 KR2021019945W WO2022145924A1 WO 2022145924 A1 WO2022145924 A1 WO 2022145924A1 KR 2021019945 W KR2021019945 W KR 2021019945W WO 2022145924 A1 WO2022145924 A1 WO 2022145924A1
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Prior art keywords
hot stamping
carbide
less
blank
stamping part
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PCT/KR2021/019945
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English (en)
Korean (ko)
Inventor
김혜진
황규연
정현영
이진호
정승필
Original Assignee
현대제철 주식회사
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Priority to EP21915722.9A priority Critical patent/EP4268986A1/fr
Priority to CN202180086821.XA priority patent/CN116783013A/zh
Priority to JP2022575420A priority patent/JP7453424B2/ja
Publication of WO2022145924A1 publication Critical patent/WO2022145924A1/fr
Priority to US18/077,064 priority patent/US20230107817A1/en

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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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02—Stamping using rigid devices or tools
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/16—Heating or cooling
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • 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
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0252—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment with application of tension
    • 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
    • C21D2211/008—Martensite

Definitions

  • Embodiments of the present invention relate to hot stamping parts and methods of manufacturing the same.
  • High-strength steel for weight reduction and stability is applied to parts used in automobiles.
  • high-strength steel can secure high-strength properties compared to its weight, but as the strength increases, press formability deteriorates, causing material breakage during processing or springback phenomenon, making it difficult to form products with complex and precise shapes. There are difficulties.
  • the hot stamping method is a molding technology for manufacturing high-strength parts by heating a boron steel sheet to an appropriate temperature, forming it in a press mold, and then rapidly cooling it.
  • problems such as crack generation or shape freezing defect during forming, which are problems in high-strength steel sheet, are suppressed, so that it is possible to manufacture parts with good precision.
  • Embodiments of the present invention are to solve various problems including the above-described problems, and to provide a hot stamping part and a manufacturing method thereof that can control the residual stress of the hot stamping part to secure excellent mechanical properties and hydrogen embrittlement.
  • these problems are exemplary, and the scope of the present invention is not limited thereto.
  • the residual stress analysis value is the magnitude of the XRD value quantifying the residual stress by X-ray diffraction (XRD) and backscattered electron diffraction pattern analysis (EBSD; electron backscatter diffraction) is the product of the magnitude of the EBSD value quantifying the orientation
  • the preset condition is 2.85 * 10 -4 (Degree * MPa / ⁇ m 2 ) or more and 0.05 (Degree * MPa / ⁇ m 2 ) or less.
  • the heating of the blank includes a multi-stage heating step of heating the blank while passing sections in which the temperature range is increased stepwise among a plurality of sections provided in the heating furnace, and heating the blank to a temperature of Ac3 or higher It may include a crack heating step of heating with a furnace.
  • the ratio of the length of the section for heating the blank in multiple stages in the plurality of sections to the length of the section for heating the blank by cracking may be 1:1 to 4:1.
  • the temperatures of the plurality of sections may increase in a direction from the entrance of the heating furnace to the exit direction of the heating furnace.
  • the temperature increase rate of the blank in the multi-stage heating step may be 6 °C / s to 12 °C / s.
  • a temperature of a section in which the blank is heated by cracking among the plurality of sections may be higher than a temperature of sections in which the blank is heated in multiple stages.
  • the blank may stay in the furnace for 180 seconds to 360 seconds.
  • the step of cooling the molded body to form the hot stamping part may include maintaining the molded body in a press mold at a temperature below the temperature at which martensitic transformation starts for 3 seconds to 20 seconds. have.
  • the molded body may be cooled at an average cooling rate of 15 °C/s or more to a temperature at which martensitic transformation is terminated in the press mold.
  • the hot stamping part is located in the martensite phase having an area fraction of 80% or more and the martensite phase, and having an area fraction of less than 5% based on the martensite phase, iron-based carbide.
  • the iron-based carbide may have a needle-like shape, and the needle-like shape may have a diameter of less than 0.2 ⁇ m and a length of less than 10 ⁇ m.
  • the martensite phase includes a lath phase
  • the iron-based carbide includes ferrous carbide horizontal to the longitudinal direction of the lath phase and ferric carbide perpendicular to the longitudinal direction of the lath phase. and a reference area fraction of the iron-based carbide of the ferrous carbide may be greater than an area fraction of the iron-based carbide of the ferric carbide.
  • an angle formed with the longitudinal direction of the lath may be 0° or more and 20° or less, and the reference area fraction of the iron-based carbide may be 50% or more.
  • an angle formed with the longitudinal direction of the lath may be 70° or more and 90° or less, and the reference area fraction of the iron-based carbide may be less than 50%.
  • the residual stress analysis value in the hot stamping parts in which the residual stress analysis value satisfies a preset condition, is an X-ray diffraction analysis (XRD; X-ray diffraction) to quantify the residual stress. It is the product of the magnitude of the XRD value and the magnitude of the EBSD value quantified by the orientation by electron backscatter diffraction (EBSD), and the preset condition is 2.85 * 10 -4 (Degree * MPa / ⁇ m 2 ) More than 0.05 (Degree * MPa / ⁇ m 2 ) or less, a hot stamping part is provided.
  • XRD X-ray diffraction analysis
  • a martensite phase having an area fraction of 80% or more and an iron-based carbide having an area fraction of less than 5% based on the martensite phase and located inside the martensite phase may be provided.
  • the iron-based carbide may have a needle-like shape, and the needle-like shape may have a diameter of less than 0.2 ⁇ m and a length of less than 10 ⁇ m.
  • the martensite phase includes a lath phase
  • the iron-based carbide includes ferrous carbide horizontal to the longitudinal direction of the lath phase and ferric carbide perpendicular to the longitudinal direction of the lath phase. and a reference area fraction of the iron-based carbide of the ferrous carbide may be greater than an area fraction of the iron-based carbide of the ferric carbide.
  • an angle formed with the longitudinal direction of the lath may be 0° or more and 20° or less, and the reference area fraction of the iron-based carbide may be 50% or more.
  • an angle formed with the longitudinal direction of the lath may be 70° or more and 90° or less, and the reference area fraction of the iron-based carbide may be less than 50%.
  • FIG. 1 is a plan view illustrating a portion of a hot stamping part according to an embodiment of the present invention.
  • FIG. 2 is a plan view illustrating a portion of a hot stamping part according to an embodiment of the present invention.
  • FIG. 3 is a flowchart schematically illustrating a method of manufacturing a hot stamping part according to an embodiment of the present invention.
  • FIG. 4 is a graph illustrating a temperature change when a blank is heated in multiple stages in a method of manufacturing a hot stamping part according to an embodiment of the present invention.
  • 5 is a graph showing a comparison of the temperature change when the blank is heated in multiple stages and when the blank is heated in single stages.
  • a specific process sequence may be performed different from the described sequence.
  • two processes described in succession may be performed substantially simultaneously, or may be performed in an order opposite to the order described.
  • a and/or B refers to A, B, or A and B. And, “at least one of A and B” represents the case of A, B, or A and B.
  • a film, region, or component when a film, region, or component is connected, when the film, region, or component is directly connected, or/and in the middle of another film, region, or component It includes cases where they are interposed and indirectly connected.
  • a film, region, component, etc. when it is said that a film, region, component, etc. are electrically connected, when the film, region, component, etc. are directly electrically connected, and/or another film, region, component, etc. is interposed therebetween. This indicates an indirect electrical connection.
  • FIG. 1 is a plan view illustrating a portion of a hot stamping part according to an embodiment of the present invention.
  • a hot stamping part according to an embodiment of the present invention includes a steel plate 10 .
  • the steel sheet 10 may be a steel sheet manufactured by performing a hot rolling process and/or a cold rolling process on a slab cast to include a predetermined alloying element in a predetermined content. Such a steel sheet 10 may exist as a full austenite structure at a hot stamping heating temperature, and then may be transformed into a martensitic structure upon cooling.
  • the steel sheet 10 is carbon (C), manganese (Mn), boron (B), phosphorus (P), sulfur (S), silicon (Si), chromium (Cr), and the remainder iron (Fe) ) and other unavoidable impurities.
  • the steel sheet 10 may further include at least one alloy element of titanium (Ti), niobium (Nb), and vanadium (V) as an additive.
  • the steel plate 10 may further include a predetermined amount of calcium (Ca).
  • Carbon (C) acts as an austenite stabilizing element in the steel sheet 10 .
  • Carbon is a main element that determines the strength and hardness of the steel sheet 10, and after the hot stamping process, the purpose of securing the tensile strength (eg, tensile strength of 1,350 MPa or more) of the steel sheet 10, and securing the hardenability characteristics is added as Such carbon may be included in an amount of 0.19 wt% to 0.38 wt% based on the total weight of the steel sheet 10 .
  • the carbon content is less than 0.19 wt%, it is difficult to secure a hard phase (martensite, etc.), so it is difficult to satisfy the mechanical strength of the steel sheet 10 .
  • the carbon content exceeds 0.38 wt%, brittleness of the steel sheet 10 or a reduction in bending performance may occur.
  • Manganese (Mn) acts as an austenite stabilizing element in the steel sheet 10 .
  • Manganese is added to increase hardenability and strength during heat treatment.
  • Such manganese may be included in 0.5wt% to 2.0wt% based on the total weight of the steel sheet 10 .
  • the content of manganese exceeds 2.0 wt%, ductility and toughness due to manganese segregation or pearlite bands may be reduced, which may cause deterioration in bending performance and may cause a heterogeneous microstructure.
  • Boron (B) is added for the purpose of securing the hardenability and strength of the steel sheet 10 by suppressing the transformation of ferrite, pearlite, and bainite to secure a martensitic structure.
  • boron segregates at grain boundaries to increase hardenability by lowering grain boundary energy, and has an effect of grain refinement due to an increase in austenite grain growth temperature.
  • Such boron may be included in an amount of 0.001 wt % to 0.005 wt % based on the total weight of the steel sheet 10 . When boron is included in the above range, it is possible to prevent the occurrence of brittleness at the hard phase grain boundary, and secure high toughness and bendability.
  • Phosphorus (P) may be included in an amount greater than 0 and 0.03 wt% or less based on the total weight of the steel sheet 10 in order to prevent deterioration of the toughness of the steel sheet 10 .
  • the phosphorus content exceeds 0.03 wt%, a phosphide compound is formed to deteriorate toughness and weldability, and cracks may be induced in the steel sheet 10 during the manufacturing process.
  • S may be included in an amount greater than 0 and 0.003 wt% or less based on the total weight of the steel sheet 10 . If the sulfur content exceeds 0.003 wt%, hot workability, weldability, and impact properties are deteriorated, and surface defects such as cracks may occur due to the formation of large inclusions.
  • Silicon acts as a ferrite stabilizing element in the steel sheet 10 .
  • Silicon improves the strength of the steel sheet 10 as a solid solution strengthening element, and improves the carbon concentration in austenite by suppressing the formation of carbides in the low-temperature region.
  • silicon is a key element in hot rolling, cold rolling, hot pressing, homogenizing the structure (perlite, manganese segregation zone control), and fine dispersion of ferrite. Silicon serves as a martensitic strength heterogeneity control element to improve collision performance.
  • Such silicon may be included in an amount of 0.1 wt% to 0.6 wt% based on the total weight of the steel sheet 10 .
  • Chromium (Cr) is added for the purpose of improving the hardenability and strength of the steel sheet 10 . Chromium makes it possible to refine grains and secure strength through precipitation hardening. Such chromium may be included in 0.05wt% to 0.6wt% based on the total weight of the steel sheet 10 . When the content of chromium is less than 0.05wt%, the precipitation hardening effect is low, and on the contrary, when the content of chromium exceeds 0.6wt%, the Cr-based precipitates and matrix solid solution increase to decrease toughness, and production cost due to increased cost may increase.
  • unavoidable impurities may include nitrogen (N) and the like.
  • Nitrogen may be included in an amount greater than 0 and 0.001 wt% or less based on the total weight of the steel sheet 10 . When the content of nitrogen exceeds 0.001 wt%, impact properties and elongation of the steel sheet 10 may be deteriorated.
  • the additive is a carbide generating element that contributes to the formation of precipitates in the steel sheet 10 .
  • the additive may include at least one of titanium (Ti), niobium (Nb), and vanadium (V).
  • Titanium (Ti) forms precipitates such as TiC and/or TiN at a high temperature, thereby effectively contributing to austenite grain refinement.
  • Such titanium may be included in an amount of 0.001 wt% to 0.050 wt% based on the total weight of the steel plate 10 .
  • When titanium is included in the content range poor performance and coarsening of precipitates can be prevented, and physical properties of the steel can be easily secured, and defects such as cracks can be prevented on the steel surface.
  • the content of titanium exceeds 0.050 wt%, the precipitates are coarsened, and elongation and bendability may decrease.
  • Niobium (Nb) and vanadium (V) may increase strength and toughness according to a decrease in martensite packet size.
  • Each of niobium and vanadium may be included in an amount of 0.01 wt% to 0.1 wt% based on the total weight of the steel sheet 10 .
  • the crystal grain refinement effect of the steel sheet 10 is excellent in the hot rolling and cold rolling process, and it prevents cracks in the slab and brittle fracture of the product during steelmaking/playing, It is possible to minimize the formation of precipitates.
  • Calcium (Ca) may be added to control the inclusion shape. Such calcium may be included in an amount of 0.003 wt% or less with respect to the total weight of the steel plate 10 .
  • the 'residual stress' means a stress that exists in the hot stamping part in a state where no external force acts on the steel sheet 10 .
  • Residual stresses can result from defects in the material.
  • point defects such as vacancy, interstitials, impurities, etc.
  • line defects such as dislocations, etc. and external surfaces, grain boundaries, etc.
  • twin boundaries, stacking faults, and interfacial defects such as phase boundaries may be due to the generation of residual stress. That is, it can be understood that the more defects are present in the steel sheet 10, the greater the internal residual stress.
  • the tensile strength of the hot stamping part is, when defects inside the steel sheet 10 exist at an appropriate level, the more defects (or the greater the residual stress), the higher the tensile strength, and the fewer the defects (or the smaller the residual stress). more), the tensile strength may be lowered. This is because the more defects there are, the more irregular the elements are, making it difficult to move dislocations that cause material deformation.
  • the hydrogen embrittlement of the steel sheet 10 may be decreased as the number of internal defects (or the larger residual stress) decreases, and the smaller the number of internal defects (or the smaller the residual stress) is, the better.
  • the amount of activated hydrogen is reduced, and hydrogen embrittlement of the product may be improved.
  • fine precipitates present therein eg, nitrides or carbides of titanium (Ti), niobium (Nb), and vanadium (V)
  • defects existing therein may also serve as hydrogen trap sites.
  • the hot stamping part may include at least one bent portion according to an applied position in the structure of the vehicle, and the bent portion is a portion that is formed excessively compared to a flat area during the hot stamping process. That is, since the stress caused by the press is relatively concentrated during the hot stamping process and the residual stress may increase, it may act as a hydrogen embrittlement weakness.
  • the residual stress analysis value quantifying the residual stress present in the steel plate 10 to satisfy a preset condition, defects existing in the steel plate 10 and the residual stress resulting therefrom are appropriately adjusted. level can be controlled.
  • the residual stress analysis value is the magnitude of the XRD value quantifying the residual stress by X-ray diffraction (XRD) (or the absolute value of the XRD value), and the backscattered electron diffraction pattern analysis (EBSD). ; It can be the product of the magnitude of the EBSD value (or the absolute value of the EBSD value) that quantifies the orientation with electron backscatter diffraction.
  • the preset condition may be 2.85*10 -4 (Degree*MPa/ ⁇ m 2 ) or more and 0.05 (Degree*MPa/ ⁇ m 2 ) or less.
  • the residual stress analysis value satisfies the range of 2.95*10 -4 (Degree*MPa/ ⁇ m 2 ) or more and 0.01 (Degree*MPa/ ⁇ m 2 ) or less. is controlled, and when the size of the XRD value is 15 MPa or more and less than 55 MPa, the residual stress analysis value is controlled to satisfy the range of 9.31*10 -4 (Degree*MPa/ ⁇ m 2 ) or more and 0.035(Degree*MPa/ ⁇ m 2 ) or less.
  • the residual stress analysis value can be controlled to satisfy the range of 3.96*10 -3 (Degree*MPa/ ⁇ m 2 ) or more and 0.043(Degree*MPa/ ⁇ m 2 ) or less. .
  • XRD X-ray diffraction analysis
  • the peak position of the changed diffraction line is taken as the vertical axis
  • sin 2 ⁇ of the incident angle of the X-ray is taken as the horizontal axis
  • the slope is obtained by linear regression by the least squares method
  • the obtained slope is multiplied by the stress constant obtained from the Young's modulus and Poisson's ratio.
  • the stress value (XRD value) can be calculated
  • Such X-ray diffraction analysis has excellent representativeness because it targets a relatively wide range, but has a disadvantage in that the deviation is large and the uniformity is not good. In addition, the deviation of these XRD values tends to increase as the residual stress inside the product increases. Therefore, there is a problem in that it is difficult to accurately analyze and control the residual stress of a material only with the XRD value obtained by quantifying the residual stress by X-ray diffraction analysis (XRD).
  • EBSD backscattered electron diffraction pattern analysis
  • an electron beam is irradiated to a specimen in a scanning electron microscope (SEM)
  • SEM scanning electron microscope
  • the incident electron beam is scattered within the specimen, and a diffraction pattern appears in the direction of the specimen surface.
  • This is called an electron back scattered diffraction pattern (EBSP), and this pattern responds to the crystal orientation of the area irradiated with the electron beam, and can measure the crystal orientation of a material with an accuracy of less than 1°.
  • EBSD backscattered electron diffraction pattern analysis
  • Embodiments of the present invention apply a differentiated residual stress analysis value in order to compensate for the disadvantages of the aforementioned X-ray diffraction analysis (XRD) and backscattered electron diffraction pattern analysis (EBSD), respectively.
  • the residual stress analysis value the magnitude of the XRD value (or the absolute value of the XRD value) in which the residual stress is quantified by X-ray diffraction analysis (XRD), and the orientation by the backscattered electron diffraction pattern analysis (EBSD)
  • the product of the magnitude of the EBSD value (or the absolute value of the EBSD value) may be applied.
  • the deviation which is a disadvantage of the XRD value
  • the representativeness which is a disadvantage of the EBSD value
  • the XRD value is supplemented by the XRD value
  • the residual stress analysis value may be expressed as in Equation 2 below.
  • Such residual stress analysis value may be substantially proportional to the defect in the hot stamping part and the resulting residual stress. Specifically, it can be understood that the larger the residual stress analysis value is, the more defects exist and the residual stress is large inside the product, and the smaller the residual stress analysis value is, the fewer defects exist inside the product and the residual stress is small. Furthermore, it can be understood that the higher the residual stress analysis value, the higher the tensile strength of the product, but the hydrogen embrittlement is not excellent, and the smaller the residual stress analysis value, the lower the tensile strength of the product but the hydrogen embrittlement is excellent. Therefore, by controlling the residual stress analysis value to satisfy the preset condition, it is possible to properly secure the mechanical properties and hydrogen embrittlement of the product.
  • defects and residual stress may be caused by a temperature difference existing in the width direction or length direction of the steel sheet 10 during the manufacturing process.
  • a differentiated process condition for example, a heating condition and/or a cooling condition during the manufacturing process
  • the above-described residual stress analysis value may be controlled to satisfy a preset condition.
  • FIG. 2 is a plan view illustrating a portion of a hot stamping part according to an embodiment of the present invention.
  • the steel sheet 10 may be made of a component system having a microstructure including a martensite phase of 80% or more by area fraction.
  • the steel sheet 10 may include a bainite phase of less than 20% by area fraction.
  • the martensitic phase is the result of diffusionless transformation of austenite ⁇ below the onset temperature (Ms) of martensitic transformation during cooling.
  • Martensite may have a rod-shaped lath phase oriented in one direction (d) in each initial grain of austenite.
  • the steel plate 10 may have iron-based carbide positioned inside the martensite phase.
  • the iron-based carbide may be in the form of needles.
  • the diameter of the iron-based carbide may be less than 0.2 ⁇ m, and the length of the iron-based carbide may be less than 10 ⁇ m.
  • the 'diameter of the iron-based carbide' may mean a minor axis length of the iron-based carbide, and the 'length of the iron-based carbide' may mean a major axis length of the iron-based carbide.
  • the diameter of the iron-based carbide is 0.2 ⁇ m or more or the length is 10 ⁇ m or more, it remains without melting even at a temperature of Ac3 or more in the annealing heat treatment process, and the bendability and yield ratio of the steel sheet 10 may be reduced.
  • the diameter of the iron-based carbide is less than 0.2 ⁇ m and the length is less than 10 ⁇ m, the balance between strength and formability of the steel sheet 10 may be improved.
  • Such iron-based carbides may have an area fraction of less than 5% based on the martensite phase.
  • the area fraction of the iron-based carbide is 5% or more based on the martensite phase, it may be difficult to secure the strength or bendability of the steel sheet 10 .
  • the iron-based carbide may include a ferrous carbide (C1) and a ferric carbide (C2).
  • the ferrous carbide C1 may be an iron-based carbide horizontal to the longitudinal direction d of the lath
  • the ferric carbide C2 may be an iron-based carbide perpendicular to the longitudinal direction d of the lath.
  • 'horizontal' includes forming an angle of 0° or more and 20° or less with the longitudinal direction (d) of the lath
  • 'vertical' refers to an angle of 70° or more and 90° or less with the longitudinal direction (d) of the lath.
  • the ferrous carbide (C1) may form an angle of 0° or more and 20° or less with the longitudinal direction (d) of the lath, and the ferric carbide (C2) is 70° or more with the longitudinal direction (d) of the lath. Angles of 90° or less can be achieved.
  • the iron-based carbide reference area fraction of the ferrous carbide C1 may be greater than the iron-based carbide reference area fraction of the ferric ferrous carbide. Through this, the bendability of the steel plate 10 may be improved.
  • the iron-based carbide reference area fraction of the ferrous carbide (C1) forming an angle of 0° or more and 20° or less with the longitudinal direction (d) of the lath may be 50% or more, preferably 60% or more.
  • the iron-based carbide reference area fraction of the ferric carbide (C2) forming an angle of 70° or more and 90° or less with the longitudinal direction (d) of the lath may be less than 50%, preferably less than 40%.
  • Cracks generated during bending deformation may be generated as dislocations move in the martensite phase.
  • the local strain rate among the given plastic deformations has a larger value, the degree of energy absorption for the plastic deformation of martensite increases, so that the collision performance is improved.
  • the iron-based carbide reference area fraction of the ferrous carbide (C1) horizontal to the longitudinal direction (d) of the lath phase is higher than the iron-based carbide reference area fraction of the ferric carbide (C2) perpendicular to the longitudinal direction (d) of the lath phase.
  • DSA dynamic strain aging
  • Indentation dynamic deformation aging is a concept of plastic deformation absorption energy, and since it means resistance to deformation, the more frequent the indentation dynamic deformation aging phenomenon, the better the resistance performance to deformation.
  • the iron-based carbide reference area fraction of the ferrous carbide (C1) forming an angle of 20° or less with the longitudinal direction (d) of the lath is 50% or more, and the longitudinal direction (d) of the lath is formed.
  • the ferric carbide reference area fraction of ferric carbide (C2) forming an angle of 70° or more and 90° or less is formed to be less than 50%, so indentation dynamic deformation aging phenomenon may occur frequently, and through this, V- By securing a bending angle of 50° or more, bendability and collision performance can be improved.
  • the bainite phase having an area fraction of less than 20% in the steel sheet 10 has a uniform hardness distribution, it has an excellent balance between strength and ductility. However, since bainite is softer than martensite, in order to secure the strength and bendability of the steel sheet 10, it is preferable that the bainite has an area fraction of less than 20%.
  • the aforementioned acicular iron-based carbide may be precipitated inside the bainite phase. Since the iron-based carbide inside bainite increases the strength of bainite and reduces the strength difference between bainite and martensite, the yield ratio and bendability of the steel sheet 10 can be increased. In this case, the iron-based carbide may be present in an amount of less than 20% in the bainite phase, based on the bainite phase. If the iron-based carbide is 20% or more based on the bainite phase, voids may be generated, which may lead to a decrease in bendability.
  • FIG. 3 is a flowchart schematically illustrating a method of manufacturing a hot stamping part according to an embodiment of the present invention
  • FIG. 4 is a case in which a blank is heated in multiple stages in the manufacturing method of a hot stamping part according to an embodiment of the present invention It is a graph showing the temperature change
  • FIG. 5 is a graph showing the comparison of the temperature change when the blank is heated in multiple stages and when the blank is heated in single stages.
  • the method for manufacturing a hot stamping part may include a blank input step ( S110 ), a multi-stage heating step ( S120 ), and a crack heating step ( S130 ).
  • the hot stamping part manufacturing method may further include a transfer step (S140), a forming step (S150), and a cooling step (S160) performed after the crack heating step (S130).
  • the blank input step ( S110 ) may be a step of inputting the blank into a heating furnace having a plurality of sections.
  • the blank input into the heating furnace may be formed by cutting a plate for forming a hot stamping part.
  • the plate material may be manufactured by performing hot rolling or cold rolling on a steel slab, followed by annealing heat treatment.
  • a plating layer may be formed on at least one surface of the annealing heat treated plate material.
  • the plating layer may be an Al-Si-based plating layer or a Zn plating layer.
  • the multi-stage heating step (S120) and the crack heating step (S130) may be sequentially performed.
  • the blank introduced into the heating furnace may be heated while passing through a plurality of sections provided in the heating furnace.
  • the blank introduced into the heating furnace may be mounted on a roller and transported along a transport direction.
  • the heating furnace may include a plurality of sections sequentially arranged in the heating furnace.
  • the plurality of sections included in the heating furnace include sections in which the temperature range is increased step by step from the inlet of the furnace in which the blank is input to the outlet of the furnace in which the blank is taken out, and sections in which the temperature range is maintained uniformly .
  • the multi-stage heating step ( S120 ) is a step of heating the blank while passing the sections in which the temperature range is increased step by step among a plurality of sections provided in the heating furnace.
  • the uniform heating step (S130) is a step of heating the multi-stage heated blank through sections in which the temperature range is maintained uniformly among a plurality of sections provided in the heating furnace.
  • the temperature range of a plurality of sections provided in the heating furnace increases stepwise from the entrance of the heating furnace into which the blank is input to the exit direction of the furnace where the blank is taken out to the target temperature (Tt) range, and then increases the target temperature (Tt) range. It can be maintained in a uniform temperature range, that is, the target temperature (Tt) range from the section having the furnace to the exit of the heating furnace.
  • the number of sections in which the temperature range is increased in stages, the number of sections in which the temperature range is maintained uniformly, and the temperature range of each section are not limited.
  • the heating furnace includes a first section P1 having a first temperature range T1 , a second section P2 having a second temperature range T2 , and a third A third section P3 having a temperature range T3, a fourth section P4 having a fourth temperature range T4, a fifth section P5 having a fifth temperature range T5, a sixth temperature range A sixth section P6 having T6 and a seventh section P7 having a seventh temperature range T7 may be provided.
  • the heating furnace may have 6 or less or 8 or more sections, and the temperature range of each of the sections may also be variously changed.
  • FIG. 4 will be described.
  • the first section P1 to the seventh section P7 may be sequentially disposed in the heating furnace.
  • the first section (P1) having the first temperature range (T1) is adjacent to the inlet of the furnace into which the blank is put, and the seventh section (P7) having the seventh temperature range (T7) is the furnace through which the blank is discharged.
  • the first section P1 having the first temperature range T1 may be the first section among a plurality of sections included in the heating furnace, and the seventh section P7 having the seventh temperature range T7. It may be the last section among a plurality of sections provided in this heating furnace.
  • the blank may be heated by sequentially moving the first section (P1) to the seventh section (P7) provided in the heating furnace.
  • the temperature range of the sections from the first section P1 to the fifth section P5 increases stepwise to the target temperature Tt range, and the sixth section P6 and the seventh section P7 may be maintained in the same temperature range as the target temperature Tt range, which is the temperature range of the fifth section P5 .
  • the number of sections in which the temperature range is increased in stages and sections in which the temperature range is uniformly maintained may be variously changed.
  • a temperature difference between two adjacent sections among a plurality of sections provided in the heating furnace may be 0°C or more and 100°C or less.
  • the temperature difference between the first section P1 and the second section P2 may be 0 °C or more and 100 °C or less.
  • the first temperature range T1 of the first section P1 may be 840 °C to 860 °C, and 835 °C to 865 °C.
  • the second temperature range T2 of the second section P2 may be 870 °C to 890 °C, and 865 °C to 895 °C.
  • the third temperature range T3 of the third section P3 may be 900 °C to 920 °C, and 895 °C to 925 °C.
  • the fourth temperature range T4 of the fourth section P4 may be 920 °C to 940 °C, or 915 °C to 945 °C.
  • the fifth temperature range T5 of the fifth section P5 may be Ac3 to 1,000 °C.
  • the fifth temperature range T5 of the fifth section P5 may be 930 °C or more and 1,000 °C or less. More preferably, the fifth temperature range T5 of the fifth section P5 may be 950 °C or more and 1,000 °C or less.
  • the sixth temperature range T6 of the sixth section P6 and the seventh temperature range T7 of the seventh section P7 may be the same as the fifth temperature range T5 of the fifth section P5.
  • the multi-stage heating step (S120) is performed in the first section (P1) to the fourth section (P4), and the uniform heating step (S130) is performed in the fifth section (P5) to the seventh section (P7).
  • the uniform heating step S130 is performed in the temperature range of the fifth section P5, and the temperature range of the fifth section P5 is the target temperature Tt range, and may be a temperature of Ac3 or higher. That is, in the crack heating step ( S130 ), the blank heated in multiple stages passing through the first section ( P1 ) to the fourth section ( P4 ) can be crack-heated at a temperature of Ac3 or higher.
  • the multi-stage heated blank may be crack-heated at a temperature of 930 °C or more and 1,000 °C or less. More preferably, in the crack heating step (S130), the multi-stage heated blank may be crack-heated at a temperature of 950 °C or more and 1,000 °C or less.
  • the heating furnace may have a length of 20m to 40m along the transport path of the blank.
  • the heating furnace may have a plurality of sections having different temperature ranges, the length of the section for multi-stage heating of the blank among the plurality of sections (D1, see FIG. 4) and the section for crack heating the blank among the plurality of sections
  • the ratio of the length (D2, see FIG. 4) of may satisfy 1:1 to 4:1. That is, the length D2 of the uniform heating section among the plurality of sections provided in the heating furnace may have a length corresponding to 20% to 50% of the total length (D1+D2) of the heating furnace.
  • the ratio of the length (D1) of the section for heating the blank in multiple stages (D1) to the length (D2) of the section for heating the blank by cracking is less than 4:1 because the length of the section for crack heating the blank is reduced, the crack heating section (time) This is not sufficiently ensured, so the strength of the hot stamping part manufactured by the manufacturing process of the hot stamping part may be non-uniform.
  • the blank in the multi-stage heating step (S120) and the crack heating step (S130), may have a temperature increase rate of about 6 °C/s to 12 °C/s, and the cracking time is about 3 minutes to It can be 6 minutes. More specifically, when the thickness of the blank is about 1.6 mm to 2.3 mm, the temperature increase rate is about 6 °C/s to 9 °C/s, and the soaking time may be about 3 to 4 minutes. In addition, when the thickness of the blank is about 1.0 mm to 1.6 mm, the temperature increase rate is about 9 °C / s to 12 °C / s, and the soaking time may be about 4 to 6 minutes.
  • the blank B' is single heated.
  • the temperature of the furnace is set so that the internal temperature of the furnace is kept equal to the target temperature (Tt) of the blank.
  • the target temperature Tt of the blank B' may be equal to or greater than Ac3.
  • the target temperature (Tt) of the blank (B') may be 930 °C. More preferably, the target temperature (Tt) of the blank (B') may be 950 °C.
  • the temperature of the blank B' in the single heating step may reach the target temperature Tt faster than the temperature of the blank B in the multi-step heating step.
  • the temperature increase rate of the blank (B') in a single heating step may be faster than the temperature increase rate of the blank (B) in a multi-stage heating stage by about 2°C/s or more. Since the single heating step reaches the target temperature Tt faster than the multi-stage heating step, the cracking time ET2 of the single heating step may be formed longer than the cracking time ET1 of the multi-step heating step. As in the case of a single heating step, if the cracking time ET2 is long, the size of the grain boundary is not formed uniformly, and the aforementioned defects may be excessively formed more than necessary.
  • the hot stamping parts manufactured by applying the multi-stage heating method can be controlled to have defects and residual stress within a preset range, and whether the preset range is satisfied can be checked through the residual stress analysis value described above.
  • the crack heating step ( S130 ), the transferring step ( S140 ), the forming step ( S150 ), and the cooling step ( S160 ) may be further performed.
  • the transferring step ( S140 ) may be a step of transferring the heated blank from the heating furnace to the press mold.
  • the heated blank may be air-cooled for 10 to 15 seconds.
  • the forming step ( S150 ) may be a step of hot stamping the transferred blank to form a molded body.
  • the cooling step ( S160 ) may be a step of cooling the formed body.
  • a final product After being molded into a final part shape in a press mold, a final product may be formed by cooling the molded body.
  • a cooling channel through which a refrigerant circulates may be provided in the press mold. It is possible to rapidly cool the heated blank by circulating the refrigerant supplied through the cooling channel provided in the press mold. At this time, in order to prevent a spring back phenomenon of the plate material and maintain a desired shape, rapid cooling may be performed while the press mold is closed while pressing. That is, the forming process (or forming step, S150) and the cooling process (or cooling step, S160) may be simultaneously performed while the blank is disposed in the press mold.
  • the blank in performing the forming process and the cooling process for the heated blank, is a preset time in the press mold at a temperature below the temperature at which martensitic transformation starts (MS temperature), for example, 3 seconds to 20 It can be held for seconds.
  • the blank may be cooled while maintaining the average cooling rate at 15 °C/s or more until the temperature at which martensitic transformation is terminated (Mf temperature).
  • the holding time in the press mold is less than 3 seconds, the material may not be sufficiently cooled, and thermal deformation may occur due to the residual heat of the product and the temperature deviation for each part.
  • the time the blank is maintained in the press mold exceeds 20 seconds, more than necessary defects and residual stress resulting therefrom may occur, and the retention time in the press mold may be prolonged, thereby reducing productivity.
  • the tensile strength of the hot stamping part manufactured by the manufacturing method of the hot stamping part may be 1350 MPa or more, and the amount of activated hydrogen may be 0.7 wppm or less.
  • Psalter XRD value The tensile strength (MPa) amount of activated hydrogen (wppm) A-1 -5.1 ⁇ 3.2 1369 0.581 A-2 -26.2 ⁇ 11.3 1373 0.652 A-3 -44.8 ⁇ 15.1 1410 0.667 A-4 -59.1 ⁇ 13.7 1434 0.681 A-5 -69.1 ⁇ 17.5 1481 0.689 A-6 -4.8 ⁇ 3.8 1331 0.573 A-7 -4.2 ⁇ 3.1 1332 0.571 A-8 -70.3 ⁇ 19.6 1448 0.739 A-9 -73.9 ⁇ 18.1 1508 0.751
  • Table 1 shows the results of measuring the XRD value, tensile strength, and the amount of activated hydrogen for each of specimens A-1 to A-9. Specifically, Table 1 confirms whether the size of the XRD value measured for the specimens satisfies the range of 5 MPa or more and 70 MPa or less, and compares the tensile strength and the amount of activated hydrogen in the case of satisfying the range and the case of dissatisfaction Data for analysis are presented.
  • the XRD value is a value obtained by quantifying the residual stress by the aforementioned X-ray diffraction analysis (XRD).
  • the XRD value was measured by removing the coating layer of the specimen and irradiating X-rays after electropolishing to a target position (eg, 1/4 point).
  • the electrolytic polishing is an electrolytic polishing solution containing 5% of 2-butoxyethanol (2-Butoxyethanol), 20% of perchloric acid, 35% of ethanol (Ethanol) and 40% of water (water) was performed with
  • the amount of activated hydrogen can be measured using a thermal desorption spectroscopy method.
  • the heating degassing analysis method is to measure the amount of hydrogen released from the specimen at a specific temperature or lower while heating the specimen at a preset heating rate to increase the temperature. It can be understood as activated hydrogen that affects destruction. That is, if the amount of hydrogen measured as a result of thermal degassing analysis is large, it means that a large amount of activated hydrogen that can cause delayed destruction of uncaptured hydrogen is included.
  • the amount of activated hydrogen in Table 1 is a value obtained by measuring the amount of hydrogen emitted from the specimen at 350 °C or less while raising the temperature from room temperature to 500 °C at a heating rate of 20 °C/min for each of the specimens.
  • Specimens A-1 to A-5 satisfy the range of the measured XRD value of 5 MPa or more and 70 MPa or less. That is, it can be understood that an appropriate level of defects and residual stress are present in the specimens A-1 to A-5. Accordingly, it can be confirmed that the tensile strength of specimens A-1 to A-5 satisfies 1350 MPa or more, and the activated hydrogen amount of specimens A-1 to A-5 satisfies 0.7 wppm or less.
  • the magnitude of the measured XRD value is less than 5 MPa. That is, it can be seen that defects exist less than the required level inside specimens A-6 and A-7, and the resulting residual stress is too small. Accordingly, it can be seen that the amount of activated hydrogen of each of specimens A-6 and A-7 satisfies 0.7 wppm or less, while the tensile strength is less than 1350 MPa.
  • the magnitude of the measured XRD value exceeds 70 MPa. That is, it can be seen that defects exist more than necessary inside specimens A-8 and A-9, and the resulting residual stress is too large. Accordingly, the tensile strength of each of specimens A-8 and A-9 satisfies 1350 MPa or more, while the amount of activated hydrogen exceeds 0.7 wppm, confirming that hydrogen embrittlement is reduced.
  • Psalter EBSD value (degree/ ⁇ m 2 ) The tensile strength (MPa) amount of activated hydrogen (wppm) B-1 5.72*10 -5 ⁇ 0.001 1359 0.579 B-2 9.82*10 -5 ⁇ 0.007 1391 0.591 B-3 2.33*10 -4 ⁇ 0.003 1402 0.635 B-4 7.14*10 -4 ⁇ 0.012 1492 0.661 B-5 5.62*10 -5 ⁇ 0.006 1327 0.589 B-6 3.13*10 -5 ⁇ 0.004 1321 0.581 B-7 7.28*10 -4 ⁇ 0.015 1495 0.761 B-8 8.67*10 -4 ⁇ 0.011 1491 0.775
  • Table 2 shows the results of measuring the EBSD value, tensile strength, and amount of activated hydrogen for each of specimens B-1 to B-8. Specifically, Table 1 confirms whether the size of the EBSD value measured for the specimens satisfies the range of 5.71*10 -5 (degree/ ⁇ m 2 ) or more and 7.14*10 -4 (degree/ ⁇ m 2 ) or less, and , shows data for comparative analysis of tensile strength and activated hydrogen amount, respectively, when satisfying and dissatisfied with the range.
  • the EBSD value is a value obtained by quantifying the orientation by the above-described backscattered electron diffraction pattern analysis (EBSD; electron backscatter diffraction).
  • EBSD backscattered electron diffraction pattern analysis
  • the EBSD value was measured by scanning a sample area of 4000 times and 25 ⁇ m*70 ⁇ m in 50 nm steps. In addition, these measurements were performed for 5 observation surfaces.
  • the amount of activated hydrogen was measured using a thermal desorption spectroscopy method under the same conditions as in Table 1.
  • Specimens B-1 to B-4 satisfy the range of the measured EBSD value of 5.71*10 -5 (degree/ ⁇ m 2 ) or more and 7.14*10 -4 (degree/ ⁇ m 2 ) or less. That is, it can be understood that an appropriate level of defects and residual stress are present in the specimens B-1 to B-4. Accordingly, it can be confirmed that the tensile strength of specimens B-1 to B-4 satisfies 1350 MPa or more, and the activated hydrogen amount of specimens B-1 to B-4 satisfies 0.7 wppm or less.
  • the size of the measured EBSD value is less than 5.71*10 -5 (degree/ ⁇ m2).
  • the amount of activated hydrogen of each of specimens B-5 and B-6 satisfies 0.7 wppm or less, while the tensile strength is less than 1350 MPa.
  • the magnitude of the measured EBSD value exceeds 7.14*10 -4 (degree/ ⁇ m 2 ). That is, it can be seen that defects exist more than necessary inside specimens B-7 and B-8, and the resulting residual stress is too large. Accordingly, the tensile strength of each of specimens B-7 and B-8 satisfies 1350 MPa or more, while the amount of activated hydrogen exceeds 0.7 wppm, confirming that hydrogen embrittlement is reduced.
  • Table 3 shows XRD values, EBSD values, residual stress analysis values, tensile strength, activated hydrogen amount, and 4-point bending test results for each of specimens C-1 to C-12.
  • XRD value, EBSD value, tensile strength, and the amount of activated hydrogen were measured under the same conditions and methods as in Tables 1 and 2.
  • the residual stress analysis value was calculated as the product of the magnitude (or absolute value) of the XRD value and the magnitude (or absolute value) of the EBSD value.
  • the 4-point bending test is a test method to check whether stress corrosion cracking occurs by applying a stress level below the elastic limit to a specific point on a specimen manufactured by reproducing the state in which the specimen is exposed to a corrosive environment.
  • stress corrosion cracking means a crack that occurs when corrosion and continuous tensile stress act simultaneously.
  • results of the four-point bending test in Table 1 are results of checking whether fracture occurs by applying a stress of 1,000 MPa in air for 100 hours to each of the specimens.
  • the residual stress inside the product is more It can be accurately analyzed and controlled.
  • the residual stress analysis value is controlled to satisfy the range of 2.85*10 -4 (Degree*MPa/ ⁇ m 2 ) or more and 0.05 (Degree*MPa/ ⁇ m 2 ) or less.
  • the residual stress analysis value can be more precisely controlled according to the range of the XRD value. Specifically, when the size of the XRD value is 5 MPa or more and less than 15 MPa, the residual stress analysis value is controlled to satisfy the range of 2.95*10 -4 (Degree*MPa/ ⁇ m 2 ) or more and 0.01(Degree*MPa/ ⁇ m 2 ) or less, , when the size of the XRD value is 15 MPa or more and less than 55 MPa, the residual stress analysis value is controlled to satisfy the range of 9.31*10 -4 (Degree*MPa/ ⁇ m 2 ) or more and 0.035(Degree*MPa/ ⁇ m 2 ) or less, and XRD When the magnitude of the value is 55 MPa or more and 70 MPa or less, the residual stress analysis value may be controlled to satisfy the range of 3.96*10 -3 (Degree*MPa/ ⁇ m 2 ) or more and 0.043(Degree*MPa/ ⁇ m 2 ) or
  • Specimens C-1 to C-6 are hot stamping parts manufactured through steps S110 to S160 by applying the above-described process conditions. That is, the specimens C-1 to C-6 apply the conditions applied to the above-described multi-stage heating step (S120) and uniform heating step (S130), and the temperature (Mf) at which the martensitic transformation of the blank is terminated in the cooling step (S160). Specimens manufactured by applying an average cooling rate of 15 °C/s or more to the temperature), and maintaining them for 3 to 20 seconds in a press mold at a temperature below the temperature at which martensite transformation starts (MS temperature).
  • the size of the measured XRD value satisfies the range of 5 MPa or more and 70 MPa or less
  • the size of the measured EBSD value is 5.71*10 -5 (degree/ ⁇ m2) or more and 7.14*10 It satisfies the range of -4 (degree/ ⁇ m2) or less.
  • the residual stress analysis values (the product of the size of the XRD value and the size of the EBSD value) of specimens C-1 to C-6 are also 2.85*10 -4 (Degree*MPa/ ⁇ m 2 ) or more and 0.05 (Degree*MPa) / ⁇ m 2 ) satisfies the following ranges.
  • the size of the XRD value is 5 MPa or more and less than 15 MPa
  • the residual stress analysis value is 2.95*10 -4 (Degree*MPa/ ⁇ m 2 ) or more and 0.01 (Degree*MPa/ ⁇ m 2 ) satisfies the following ranges.
  • the size of the XRD value was 15 MPa or more and less than 55 MPa
  • the residual stress analysis value was 9.31*10 -4 (Degree*MPa/ ⁇ m 2 ) or more and 0.035 (Degree*MPa/ ⁇ m 2 ) The following ranges are satisfied.
  • specimens C-5 and C-6 had an XRD value of 55 MPa or more and 70 MPa or less, and a residual stress analysis value of 3.96*10 -3 (Degree*MPa/ ⁇ m 2 ) or more and 0.043 (Degree*MPa/ ⁇ m 2 ) The following ranges are satisfied.
  • specimens C-1 to C-6 not only the magnitude of the XRD value and the magnitude of the EBSD value, but also the residual stress analysis value satisfies the preset conditions. It can be understood that there is a defect and the resulting residual stress. Accordingly, it can be confirmed that the tensile strength of the specimens C-1 to C-6 satisfies 1350 MPa or more, and the activated hydrogen content satisfies 0.7 wppm or less. In addition, it can be confirmed that the specimens C-1 to C-6 did not break as a result of the four-point bending test. That is, specimens C-1 to C-6 were manufactured by applying the above-described process conditions, and by controlling the residual stress analysis value to satisfy preset conditions, appropriate levels of tensile strength and hydrogen embrittlement were secured.
  • specimens C-7 to C-12 are hot stamping parts manufactured by applying different process conditions to at least some of the aforementioned process conditions.
  • the size of the measured XRD value satisfies the range of 5 MPa or more and 70 MPa or less, and the size of the measured EBSD value is 5.71*10 -5 (degree/ ⁇ m 2 ) More than 7.14*10 -4 (degree/ ⁇ m 2 ) It satisfies the following range. Accordingly, it can be confirmed that the tensile strength of specimens C-7 to C-12 satisfies 1350 MPa or more, and the activated hydrogen amount of specimens C-7 to C-12 satisfies 0.7 wppm or less.
  • Specimen C-7 has an XRD value of 5 MPa or more and less than 15 MPa, and the residual stress analysis value is less than 2.95*10 -4 (Degree*MPa/ ⁇ m 2 ). That is, it can be understood that there are fewer defects in the specimen C-7 than necessary and the resulting residual stress is too small. Accordingly, it can be confirmed that the specimen C-7 was fractured as a result of the four-point bending test.
  • Specimen C-8 has an XRD value of 5 MPa or more and less than 15 MPa, and the residual stress analysis value exceeds 0.01 (Degree*MPa/ ⁇ m 2 ). That is, it can be understood that defects exist more than necessary inside specimen C-8, and the resulting residual stress is too large. Accordingly, it can be confirmed that the specimen C-8 was fractured as a result of the four-point bending test.
  • Specimen C-9 has an XRD value of 15 MPa or more and less than 55 MPa, and the residual stress analysis value is less than 9.31*10 -4 (Degree*MPa/ ⁇ m 2 ). That is, it can be understood that there are fewer defects in the inside of specimen C-9 than necessary, and the resulting residual stress is too small. Accordingly, it can be confirmed that the specimen C-9 was fractured as a result of the four-point bending test.
  • Specimen C-10 has an XRD value of 15 MPa or more and less than 55 MPa, and the residual stress analysis value exceeds 0.035 (Degree*MPa/ ⁇ m 2 ). That is, it can be understood that defects exist more than necessary inside specimen C-10, and the resulting residual stress is excessively large. Accordingly, it can be confirmed that the specimen C-10 was fractured as a result of the four-point bending test.
  • Specimen C-11 has an XRD value of 55 MPa or more and 70 MPa or more, and the residual stress analysis value is less than 3.96*10 -3 (Degree*MPa/ ⁇ m 2 ). That is, it can be understood that there are fewer defects in the specimen C-11 than the required level, and the resulting residual stress is too small. Accordingly, it can be confirmed that the specimen C-11 was fractured as a result of the four-point bending test.
  • Specimen C-12 has an XRD value of 55 MPa or more and 70 MPa or more, and the residual stress analysis value exceeds 0.043 (Degree*MPa/ ⁇ m 2 ). That is, it can be understood that defects exist more than necessary inside specimen C-12, and the resulting residual stress is too large. Accordingly, it can be confirmed that the specimen C-12 was fractured as a result of the four-point bending test.
  • Specimens C-7 to C-12 were fractured as a result of a four-point bending test because the residual stress analysis value did not satisfy the preset conditions, although each of the size of the XRD value and the size of the EBSD value satisfies the preset conditions. It can be understood that it is difficult to completely control defects inside hot stamping parts and the resulting residual stresses only by XRD analysis or EBSD analysis.
  • the residual stress analysis value determines the internal defects of hot stamping parts and It can be confirmed that the residual stress can be analyzed and controlled more accurately.

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Abstract

Selon un aspect de la présente invention, l'invention concerne un procédé de fabrication d'un composant estampé à chaud dont la valeur d'analyse de contrainte résiduelle satisfait à une condition prédéfinie, le procédé comprenant les étapes de : chauffage d'une ébauche ; estampage à chaud de l'ébauche pour former un corps moulé ; et refroidissement du corps moulé pour former un composant estampé à chaud, la valeur d'analyse de contrainte résiduelle étant le produit de l'amplitude d'une valeur XRD qui est une contrainte résiduelle quantifiée par diffraction des rayons X (XRD) et l'amplitude d'une valeur EBSD qui est un azimut quantifié par diffraction de rétrodiffusion d'électrons (EBSD), et la condition prédéfinie est supérieure ou égale à 2.85*10-4 (Degré*MPa/㎛2) et inférieure ou égal à 0,05 (Degré*MPa/㎛2).
PCT/KR2021/019945 2020-12-28 2021-12-27 Composant estampé à chaud et procédé de fabrication de celui-ci WO2022145924A1 (fr)

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CN202180086821.XA CN116783013A (zh) 2020-12-28 2021-12-27 热冲压部件及其制造方法
JP2022575420A JP7453424B2 (ja) 2020-12-28 2021-12-27 ホットスタンピング部品及びその製造方法
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