EP4534719A1 - Heissprägeteil - Google Patents

Heissprägeteil Download PDF

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Publication number
EP4534719A1
EP4534719A1 EP22945039.0A EP22945039A EP4534719A1 EP 4534719 A1 EP4534719 A1 EP 4534719A1 EP 22945039 A EP22945039 A EP 22945039A EP 4534719 A1 EP4534719 A1 EP 4534719A1
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EP
European Patent Office
Prior art keywords
hot stamping
amount
less
stamping part
steel plate
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP22945039.0A
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English (en)
French (fr)
Inventor
Byung Gil Yoo
Seok Hyeon Kang
Je Woo Soo KIM
Seong Kyung Han
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Hyundai Steel Co
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Hyundai Steel Co
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Publication date
Application filed by Hyundai Steel Co filed Critical Hyundai Steel Co
Publication of EP4534719A1 publication Critical patent/EP4534719A1/de
Pending legal-status Critical Current

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    • 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
    • B21D37/01—Selection of materials
    • 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
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02—Stamping using rigid devices or tools
    • B21D22/022—Stamping using rigid devices or tools by heating the blank or stamping associated with heat treatment
    • 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
    • C21D1/62—Quenching devices
    • C21D1/673—Quenching devices for die quenching
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • 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
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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
    • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • 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
    • 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
    • C21D2211/005—Ferrite
    • 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
    • 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
    • C21D2211/009—Pearlite

Definitions

  • Embodiment s of the present disclosure relate to a hot stamping part, and more particularly, to a hot stamping part of which a molded part after hot stamping exhibits excellent mechanical properties, such as high strength and high toughness.
  • high strength steel is applied to parts for vehicles. Meanwhile, high strength steel may obtain high strength properties compared with weight, but as strength increases, press formability deteriorates, causing a material to break during processing or causing a springback phenomenon and thus making it difficult to form products with complex and precise shapes.
  • Hot stamping is a method to improve these problems, and as interest in the method increases, research on materials for hot stamping is also actively being conducted.
  • the hot stamping method is a forming technique for manufacturing a high-strength part by heating a steel plate for hot stamping to a high temperature and then rapidly cooling the steel plate while forming the steel plate in a press mold.
  • boron steel 22MnB5 containing carbon (C), and manganese (Mn), boron (B), or the like, as an element for improving heat treatment performance, is used as a typical example of a steel plate for hot stamping.
  • embodiments of the present disclosure are directed to provide a hot stamping part of which a molded part after hot stamping exhibits excellent mechanical properties, such as high strength and high toughness.
  • a hot stamping part of which a molded part after hot stamping exhibits excellent mechanical properties such as high strength and high toughness.
  • a steel plate for hot stamping of which a molded part after hot stamping exhibits excellent mechanical properties, such as high strength, high toughness, and the like, and a manufacturing method thereof, may be implemented. According to an embodiment of the present disclosure, the scope of the disclosure is not limited by the above effects.
  • an average particle size of the precipitates may be 10 nm or less.
  • the average number of the precipitates per unit area may be 10,000/100 ⁇ m 2 to 35,000/100 ⁇ m 2 .
  • an average gap between the precipitates may be 0.1 nm to 100 nm.
  • the hot stamping part may satisfy a bending angle of 50° or more.
  • Silicon (Si) operates as a ferrite stabilizing element in a steel plate. Silicon, as a solid-solution strengthening element, increases strength of a steel plate, and restricts formation of low-temperature carbide so as to increase carbon thickening in austenite. Furthermore, silicon is a core element in hot-rolling, cold-rolling, and hot-press structure homogenization and ferrite fine dispersion. Silicon operates as a martensite strength inhomogeneous control element to improve crashworthiness. The silicon may be included in an amount of 0.02 to 2.0 wt% to the total weight of a steel plate.
  • the silicon content is less than 0.02 wt%, it may be difficult to obtain the effect described above, and cementite formation and coarseness may occur in martensite structure of a molded part after hot stamping.
  • the silicon content exceeds 2.0 wt%, load on hot rolling and cold rolling may increase, and the plating properties of a steel plate may deteriorate.
  • the pearlite region may be formed within the hot stamping steel plate with a minimum content.
  • Phosphorus (P) is an element that contributes to strength improvement.
  • the phosphorus may be included in an amount of greater than 0 to 0.03 wt% or less to the total weight of a steel plate, to prevent deterioration of toughness of a steel plate.
  • an iron phosphide compound is formed so that toughness and weldability deteriorate, and cracks may be generated in a steel plate during a manufacturing process.
  • S is an element that contributes to improvement of machinability.
  • the sulfur may be included in an amount of greater than 0 to 0.008 wt% or less to the total weight of a steel plate.
  • the sulfur content exceeds 0.008 wt%, hot machinability, weldability, and shock-resistant properties may deteriorate, and due to generation of large inclusions, surface defects, such as cracks and the like, may be generated.
  • Chromium (Cr) is added for the purpose of increasing hardenability and strength during heat treatment. Chromium enables grain refinement and strength securement through precipitation hardening.
  • the chromium may be included in an amount of 0.05 wt% to 0.9 wt% to the total weight of a steel plate. When the chromium content is less than 0.05 wt%, precipitation hardening effect may be reduced. In contrast, when the chromium content exceeds 0.9 wt%, Cr-based precipitates and matrix solid content increase so that toughness is reduced, and production costs may increase due to an increased cost.
  • Boron (B) which secures a martensite structure by restricting ferrite, pearlite, and bainite transformation, is added for the purpose of obtaining hardenability and strength during heat treatment. Furthermore, boron is segregated at grain boundaries and lowers grain boundary energy so as to increase hardenability, and has a grain refinement effect by increasing the austenite grain growth temperature.
  • the boron may be included in an amount of 0.0005 wt% to 0.01 wt% to the total weight of a steel plate. When the boron is included in the range described above, occurrence of hard phase grain boundary brittleness may be prevented, and high toughness and bendability may be secured. When the boron content is less than 0.0005 wt%, the hardenability effect is insufficient.
  • Calcium (Ca) may be added for control of precipitates. Calcium has a high bonding strength with sulfur so as to form CaS precipitates, which may suppress the generation of MnS that impedes weldability.
  • the calcium may be included in an amount of 0.00001 wt% to 0.006 wt% to the total weight of a steel plate. When the calcium content is less than 0.00001 wt%, a MnS control effect deteriorates. When the calcium content exceeds 0.006 wt%, continuous casting properties may deteriorate.
  • Titanium (Ti) may effectively contribute to grain refinement by forming precipitates at high temperature.
  • the titanium may be included in an amount of 0.001 wt% to 0.095 wt%, in particular 0.005 wt% to 0.06 wt%, to the total weight of a steel plate.
  • the titanium is included in the content range, continuous casting defects and precipitate coarseness may be prevented, the physical properties of structural steel may be easily secured, and defects, such as crack generation and the like, on a surface of structural steel may be prevented.
  • the titanium content falls below the lower limit, the effect may not be appropriately achieved.
  • the titanium content exceeds the upper limit precipitates become coarse so that an elongation rate and bendability may be dropped.
  • Niobium (Nb) and vanadium (V) may increase strength and toughness according to a decrease in the martensite packet size.
  • the niobium and vanadium may each be included in an amount of 0.005 wt% to 0.06 wt% to the total weight of a steel plate.
  • the niobium is included in the above range, in hot rolling and cold rolling processes, grain refinement effect of a steel plate is excellent, during steel making/continuous casting, occurrence of cracks in a slab and brittle fracture of products may be prevented, and generation of coarse precipitates in steel making may be minimized.
  • the niobium content is less than 0.005 wt%, the effect may not be appropriately achieved.
  • niobium content exceeds 0.06 wt%
  • strength and toughness do not improve further with increasing niobium content, and the niobium exists as a state employed in ferrite so that there is a risk that impact toughness may be rather reduced.
  • Vanadium may also have a tendency similar to the niobium described above.
  • the shape of a microstructure formed in a steel plate may be controlled.
  • the microstructure may include, for example, an area where a pearlite structure is locally accumulated (hereinafter, referred to as the pearlite region).
  • the area where a pearlite structure is accumulated affects a size of a grain and fraction coarseness after hot stamping, which may deteriorate hydrogen embrittlement and bending angle (e.g., V-bending angle) performance of a hot stamping part after hot stamping.
  • the microstructure of a steel plate before hot stamping may include ferrite and pearlite.
  • a steel plate may include ferrite: 50-99% and pearlite: 0.1-50% at an area fraction.
  • a steel plate may include other inevitable structures.
  • a steel plate may include other inevitable structures of 0% or more and less than 5%.
  • an average grain size of ferrite included in a steel plate before hot stamping may be controlled to satisfy a range of 2 ⁇ m or more and 10 ⁇ m or less.
  • Carbon (C) and/or manganese (Mn) may be segregated in the pearlite, and thus, the microstructure of a steel plate for hot stamping may include pearlite with relatively high carbon content and/or manganese content. Furthermore, the pearlite with relatively high carbon content and/or manganese content is locally accumulated in a steel plate so as to form a pearlite region.
  • the steel plate before hot stamping may be controlled such that the size, density, and area fraction of a pearlite region that a steel plate for hot stamping has satisfy preset conditions, while including carbon and manganese as much as the content optimized as described above. Accordingly, the mechanical properties, such as tensile strength, yield strength, bending properties, an elongation rate, and the like, of a molded part after hot stamping may be controlled.
  • the tensile strength of a hot stamping part formed by hot stamping a steel plate may satisfy a range of 1,700 MPa or more, in particular 1,760 MPa or more and 1,950 MPa or less. Furthermore, the yield strength of a hot stamping part may satisfy a range of 1,150 MPa or more, in particular 1,200 MPa or more and 1,350 MPa or less. Furthermore, a hot stamping part may satisfy a bending angle of 50° or more, and may have an elongation rate of 5% or more.
  • the "bending angle” may mean a V-bending angle in a rolling direction (a rolling direction, RD).
  • the degree of influence on the mechanical properties of a hot stamping part after hot stamping may vary depending on the content of carbon (C) and the content of manganese (Mn) included in the pearlite accumulated in a pearlite region in a steel plate before hot stamping.
  • C carbon
  • Mn manganese
  • what affects the mechanical properties of a hot stamping part is an area where pearlite including carbon of 0.27 wt% or more and manganese of 1.0 wt% or more is locally concentrated.
  • the effect of an area where pearlite having a carbon content of less than 0.27 wt% or a manganese content of less than 1.0 wt% is locally concentrated area on the mechanical properties of a hot stamping part is minimal.
  • a steel plate for hot stamping is controlled such that the size, density, and area fraction of an area where pearlite including carbon of 0.27 wt% or more and manganese of 1.0 wt% or more is locally concentrated satisfy preset conditions.
  • the steel plate for hot stamping may include a pearlite region in which pearlite including carbon (C) of 0.27 to 0.70 wt% and/or manganese (Mn) of 1.0 to 5.0 wt% locally accumulated.
  • the size, shape, and area fraction of the pearlite region may be controlled to satisfy preset conditions.
  • the average length of the pearlite region may be controlled to satisfy a range of 0.01 ⁇ m or more and 500 ⁇ m or less, in particular 0.1 ⁇ m or more and 100 ⁇ m or less.
  • the average thickness of the pearlite region may be controlled to satisfy a range of 0.01 ⁇ m or more and 30 ⁇ m or less.
  • an average gap between pearlite regions may be controlled to be 0.01 ⁇ m or more and 10 ⁇ m or less.
  • an area fraction of a pearlite region in a steel plate for hot stamping may be controlled to satisfy a range of 0.1% or more and 15% or less.
  • the pearlite region may contain an area fraction of 50% or more pearlite and 5% or less ferrite. Furthermore, selectively, a low temperature phase structure, such as precipitate, martensite, and/or bainite, and the like may be included up to 5%.
  • FIG. 2 is an image showing the structure of a hot stamping part formed by hot stamping the steel plate according to FIG. 1 .
  • the hot stamping part may include microstructure including austenite grains.
  • a steel plate may include an area fraction of 70% or more martensite phase, the austenite grains may be generally distributed in the martensite phase.
  • an average size of austenite grains in the hot stamping part may be about 15 ⁇ m or less, in particular 13 ⁇ m or less.
  • AGS austenite grain size
  • the austenite grain size may be controlled through an element that forms precipitate within a steel plate.
  • the steel plate may further include vanadium (V) other than niobium (Nb), titanium (Ti), and molybdenum (Mo).
  • specimen 1 and specimen 2 according to comparative examples are formed such that a fraction of an austenite grain size of about 20 ⁇ m or more exceeds 10%. Specimen 1 and specimen 2 according to comparative examples have fracture occurring during hydrogen embrittlement evaluation, and thus, it can be seen that specimen 1 and specimen 2 according to comparative examples fall short of the performance to be implemented by the present disclosure.
  • specimen 3 and specimen 4 according to the present embodiment are formed such that a fraction of an austenite grain size of about 20 ⁇ m or more is 10% or less. Specimen 3 and specimen 4 according to the present embodiment do not have fracture occurring during hydrogen embrittlement evaluation, and thus, it can be seen that the performance to be implemented by the present disclosure is satisfied.
  • the average size of austenite grains in the hot stamping part is about 15 ⁇ m or less, and furthermore, the specimen is formed such that a fraction of an austenite grain size of about 20 ⁇ m or more is 10% or less, hydrogen embrittlement and bending angle performance may be satisfied.
  • Specimen 3 and specimen 4 according to the present embodiment may be formed such that the average size of austenite grains in the hot stamping part is 13 ⁇ m or less.
  • the hot stamping part may include precipitates including at least one of at least one of niobium (Nb), titanium (Ti), molybdenum (Mo), and vanadium (V).
  • Niobium (Nb), titanium (Ti), molybdenum (Mo), and vanadium (V) included in a steel plate are carbide generating elements that contribute to the formation of precipitates. Titanium (Ti), niobium (Nb), and molybdenum (Mo) form carbon (C)-based precipitates, and thus, strength, hydrogen embrittlement, and bendability of a hot stamping part may be secured.
  • the elements may function as a hydrogen trap site effective for improving delayed fracture resistance.
  • the precipitates may be distributed within a steel plate to trap hydrogen.
  • the precipitates provide a trap site to hydrogen introduced into the interior of a steel plate before hot stamping, and thus, hydrogen delayed fracture properties of the hot stamping part may be improved.
  • the precipitation behavior of the precipitates may be measured by a method of analyzing a transmission electron microscopy (TEM) image.
  • TEM images for certain regions as many as a preset number may be obtained with respect to specimen, precipitates may be extracted from the obtained images through an image analysis program and the like, and the number of precipitates, an average distance between precipitates, diameters of precipitates, and the like may be measured for the extracted precipitates.
  • niobium (Nb), titanium (Ti), and vanadium (V) are each included exceeding 0.06 wt%, or molybdenum (Mo) is included to be less than 0.05 wt%, the average particle size of precipitates exceeds 10 nm so that the probability of hydrogen embrittlement occurring in hot stamping part may increase.
  • the component (that is, an average component) of precipitates may include 50 wt% or less of titanium (Ti) and 30 wt% or more of molybdenum (Mo).
  • the component of precipitates satisfies 50 wt% or less of titanium (Ti) and 30 wt% or more of molybdenum (Mo).
  • the component of precipitates includes titanium (Ti) exceeding 50 wt%, or molybdenum (Mo) to be less than 30 wt%, the coarseness of precipitates occurs, and thus, designed strength may not be secured.
  • a gap between adjacent precipitates may be controlled to satisfy a preset range.
  • the "average distance” may be measured through a mean free path of precipitates.
  • the average distance between precipitates may be calculated using a particle area fraction and the number of particles per unit length.
  • a method of measuring the precipitation behavior of the precipitates is not limited to the example described above, and various methods may be employed therefor.
  • the average distance between precipitates may be 0.1 nm or more 100 nm or less, in particular 0.1 nm or more and 50 nm or less, or 0.1 nm or more 10 nm or less.
  • the average distance between microprecipitates is less than 0.1 nm, formability to bendability may deteriorate.
  • the average distance between microprecipitates exceeds 100 nm, strength may deteriorate.
  • the average number of precipitates per unit area may be controlled to satisfy preset conditions.
  • refinement of precipitates may be carried out.
  • the average number of precipitates per unit area may be 10,000/100 ⁇ m 2 to 35,000/100 ⁇ m 2 .
  • coarseness of precipitates is carried out.
  • the average number of precipitates per unit area may be formed to be less than 10,000/100 ⁇ m 2 .
  • Table 1 shows the composition of a steel plate for hot stamping
  • Table 2 shows measurement values for evaluation of an austenite grain size and hydrogen embrittlement of specimens corresponding to a hot stamping part.
  • Comparative Example 1 to Comparative Example 12 are specimens that do not satisfy the value of [Inequality 1] among the composition of Table 1, and Embodiment 1 to Embodiment 8 are specimens corresponding to a hot stamping part formed by hot stamping a steel plate having such a composition as Table 1.
  • An evaluation for hydrogen embrittlement of each specimen employs the ASTM G39-99 reference (4-point bending test) test method.
  • a specimen is loaded in a 4-point bending tester, and a yield strength (YP) of stress 100% is applied thereto.
  • the specimen is dipped in 0.1 N HCl of an aqueous solution for 100 hours, and then, it is measured whether a crack, that is, fracture, has occurred in a surface of the specimen.
  • Comparative Example 13 to Comparative Example 16 are specimens that satisfy the composition of Table 1, but do not satisfy the conditions of precipitate and the like due to a difference in the process control conditions.
  • Comparative Example 13 to Comparative Example 16 a fraction of an austenite grain size of 10 ⁇ m or more is formed to exceed 67%, and a fraction of an austenite grain size of 20 ⁇ m or more is formed to exceed 10%.
  • fracture occurs in the hydrogen embrittlement evaluation so that the design conditions of the present disclosure are unsatisfied.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Articles (AREA)
EP22945039.0A 2022-05-31 2022-12-01 Heissprägeteil Pending EP4534719A1 (de)

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