WO2014129327A1 - Moulage par pressage à chaud et procédé de fabrication s'y rapportant - Google Patents

Moulage par pressage à chaud et procédé de fabrication s'y rapportant Download PDF

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WO2014129327A1
WO2014129327A1 PCT/JP2014/052948 JP2014052948W WO2014129327A1 WO 2014129327 A1 WO2014129327 A1 WO 2014129327A1 JP 2014052948 W JP2014052948 W JP 2014052948W WO 2014129327 A1 WO2014129327 A1 WO 2014129327A1
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area
region
less
molding
hot press
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PCT/JP2014/052948
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English (en)
Japanese (ja)
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純也 内藤
村上　俊夫
池田　周之
圭介 沖田
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株式会社神戸製鋼所
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Priority to US14/650,712 priority Critical patent/US20160010171A1/en
Priority to CN201480009284.9A priority patent/CN105026065A/zh
Publication of WO2014129327A1 publication Critical patent/WO2014129327A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D8/0294—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a localised treatment
    • 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
    • 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
    • B21D22/20—Deep-drawing
    • B21D22/208—Deep-drawing by heating the blank or deep-drawing 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
    • C21D1/62—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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—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
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C21D2211/002—Bainite
    • 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
    • C21D2221/00—Treating localised areas of an article

Definitions

  • the present invention relates to a hot press-formed product which is used for a structural member of an automobile part and can adjust strength and ductility according to different regions in the molded product, and a manufacturing method thereof. More specifically, when a preheated steel plate (blank) is formed into a predetermined shape, hot press forming can be performed at the same time as shape imparting to obtain strength and ductility according to different regions. Articles and a useful method for producing such hot pressed articles.
  • the steel sheet is heated to a predetermined temperature (for example, a temperature at which it becomes an austenite phase) to reduce the strength (that is, to facilitate forming), and then at a lower temperature than the thin steel sheet (
  • a predetermined temperature for example, a temperature at which it becomes an austenite phase
  • a hot press molding method that secures the strength after molding by forming a mold with a room temperature mold and performing a quenching heat treatment (quenching) using the temperature difference between the two at the same time as giving the shape. It has been adopted.
  • FIG. 1 is a schematic explanatory view showing a mold configuration for carrying out the above hot press molding (hereinafter may be represented by “hot stamp”).
  • 3 is a blank holder
  • 4 is a steel plate (blank)
  • BHF is a crease pressing force
  • rp is a punch shoulder radius
  • rd is a die shoulder radius
  • CL is a punch / die clearance.
  • the punch 1 and the die 2 are formed with passages 1a and 2a through which the cooling mediums 5a and 6a (for example, water) can pass, respectively.
  • the cooling mediums 5a and 6a for example, water
  • a steel sheet for hot stamping As a steel sheet for hot stamping that is currently widely used, a steel sheet made of 22MnB5 steel is known. This steel sheet has a tensile strength of 1500 MPa and an elongation of about 6 to 8%, and is applied to an impact resistant member (a member that is not deformed as much as possible at the time of collision and does not break).
  • an impact resistant member a member that is not deformed as much as possible at the time of collision and does not break.
  • the development of increasing the C content and further increasing the strength (1500 MPa or higher, 1800 MPa class) based on 22MnB5 steel is also in progress.
  • B pillars center pillars
  • rear side members rear side members
  • front side members are considered in the case of side collisions and rear collisions (compatibility: a function that protects the other party when a small car collides).
  • both functions such as an impact resistant part and an energy absorbing part are provided in the parts.
  • 980 MPa class high-strength ultra high tensile steel and 440 MPa class high tensile steel are laser-welded (tailored weld blank, Tailor Welded Blank: TWB), and then cold pressed. The method to do was mainstream.
  • TWB Tailored weld blank
  • the tensile strength is 600 MPa or less and the elongation is about 12 to 18% on the energy absorption site side, but it is necessary to perform laser welding (tailored weld blank: TWB) in advance, As the number increases, the cost increases. Moreover, the energy absorption site
  • Non-Patent Documents 3 and 4 have also been proposed as techniques for creating different strengths within the parts.
  • the technique of Non-Patent Document 3 is to make a temperature difference (distribution) in a blank in a heating furnace, but is based on 22MnB5 steel, and is affected by the effect of boron addition.
  • the strength robustness after quenching is poor with respect to heating, the strength control on the energy absorption site side is difficult, and the elongation is only about 15%.
  • Non-Patent Document 4 the process is performed by changing the cooling rate within the mold (a part of the mold is heated by a heater or a material having a different thermal conductivity is used).
  • 22MnB5 steel which is not rational in terms of controlling the 22MnB5 steel with good hardenability so as not to be quenched (die cooling control).
  • the present invention has been made in view of the above circumstances, and the object thereof is to have at least areas corresponding to an impact resistant part and an energy absorbing part in a single molded article without applying a welding method, respectively. It is an object of the present invention to provide a hot press-formed product capable of achieving a high balance between high strength and elongation at a high level, and a useful method for manufacturing such a hot press-formed product.
  • the hot press-formed product of the present invention that has achieved the above object is a hot press-formed product obtained by forming a thin steel plate by a hot press forming method, and is martensite: 80 to 97 area%, retained austenite.
  • the chemical component composition is not limited.
  • the first molding region and the second molding region have the same chemical component composition, and the steel in each component region has C: 0. 15 to 0.3% (meaning mass%, hereinafter the same for chemical composition), Si: 0.5 to 3%, Mn: 0.5 to 2%, P: 0.05% or less (0% S: 0.05% or less (excluding 0%), Al: 0.01 to 0.1%, Cr: 0.01 to 1%, B: 0.0002 to 0.01% Ti: [N] ⁇ 4 to 0.1% [where [N] is the N content (%)] and N: 0.001 to 0.01%, the balance being iron and inevitable The thing which consists of impurities is mentioned.
  • the steel further contains, as another element, (a) one or more selected from the group consisting of Cu, Ni and Mo: 1% or less in total ( (B) does not include 0%), (b) it is also useful to include at least one of V and Nb: 0.1% or less (excluding 0%) in total, depending on the type of element contained Thus, the properties of the hot press-formed product are further improved.
  • the method of the present invention is a method for producing a hot press-formed product as described above by dividing a thin steel plate into a plurality of regions including at least a first and a second region, and the thin steel plate is formed into Ac 3.
  • a temperature not lower than the transformation point and not higher than 1000 ° C. at least the first molding region and the second molding region are both cooled with an average cooling rate of 20 ° C./second or more by pressing with a mold. Molding is started, and the molding is finished at a temperature lower than 50 ° C. below the martensite transformation start temperature in the first molding region, and the temperature lower than 100 ° C. below the bainite transformation start temperature is below the martensite transformation start temperature in the second molding region. While cooling to the above temperature range, it has a gist in the point which finishes shaping
  • the metal structure of each region can be adjusted while the appropriate amount of retained austenite is present. It is possible to achieve a hot press-molded product with a higher ductility (residual ductility) inherent in the molded product than when using conventional 22MnB5 steel, and the strength and Elongation can be appropriately controlled according to each region.
  • the inventors of the present invention after heating a thin steel plate to a predetermined temperature, when producing a molded product by hot press forming, after forming, good strength is ensured according to the required characteristics of each different region In order to realize a hot press-formed product that also exhibits ductility (elongation), examination was performed from various angles.
  • the area fraction of martensite needs to be 80 area% or more. However, if this fraction exceeds 97 area%, the area fraction of retained austenite (residual austenite fraction) becomes insufficient, and the ductility (residual ductility) decreases.
  • a preferred lower limit of the martensite fraction is 83 area% or more (more preferably 85 area% or more), and a preferred upper limit is 95 area% or less (more preferably 93 area% or less).
  • Residual austenite has the effect of increasing the work hardening rate (transformation-induced plasticity) and improving the ductility of the molded product by transforming into martensite during plastic deformation.
  • the retained austenite fraction needs to be 3 area% or more.
  • the ductility the higher the retained austenite fraction, the better.
  • the retained austenite that can be secured is limited, and the upper limit is about 20 area%.
  • a preferred lower limit of the retained austenite fraction is 5 area% or more (more preferably 7 area% or more).
  • ferrite, pearlite, bainite and the like may be included as the remaining structure.
  • these structures are softer than martensite and contribute less to the strength than other structures, and are preferably as small as possible. However, up to 5 area% is acceptable.
  • the remaining structure is more preferably 3 area% or less, and still more preferably 0 area%.
  • a portion having a strength (tensile strength TS) of 1500 MPa or more and an elongation (total elongation EL: total10elongation) of 10% or more (for example, resistance of automobile parts) Impact site) can be formed.
  • the area fraction of bainitic ferrite (bainitic ferrite fraction) needs to be 70 area% or more. However, if this fraction exceeds 97 area%, the retained austenite fraction becomes insufficient and the ductility (residual ductility) decreases.
  • the preferable lower limit of the bainitic ferrite fraction is 75 area% or more (more preferably 80 area% or more), and the preferable upper limit is 95 area% or less (more preferably 90 area% or less).
  • the martensite area fraction (martensite fraction) needs to be 27 area% or less.
  • a preferred lower limit of the martensite fraction is 5 area% or more (more preferably 10 area% or more), and a preferred upper limit is 20 area% or less (more preferably 15 area% or less).
  • the retained austenite fraction is set to 3 area% or more and 20 area% or less.
  • the preferable lower limit of the retained austenite fraction is also the same as in the first molding region.
  • ferrite, pearlite, bainite and the like may be included as the remaining structure.
  • these structures are softer than martensite and contribute less to the strength than other structures, and are preferably as small as possible. However, up to 5 area% is acceptable.
  • the remaining structure is more preferably 3 area% or less, and still more preferably 0 area%.
  • a portion having a strength (tensile strength TS) of 1100 MPa or more and an elongation (total elongation EL) of 15% or more (for example, an energy absorbing portion of an automobile part) ) can be formed.
  • the molded product of the present invention has at least a first molding region and a second molding region, but is not necessarily limited to two molding regions, and may have a third or fourth molding region. Good. In forming such a molding region, it is possible to make it in accordance with the manufacturing method described later.
  • a thin steel plate (the chemical component composition is the same as that of the formed product) may be divided into a plurality of regions including at least a first and a second. Specifically, after heating the thin steel sheet to a temperature not lower than the Ac 3 transformation point and not higher than 1000 ° C., at least the first forming region and the second forming region are both averaged by pressing with a mold. Cooling and molding at a cooling rate of 20 ° C./second or more are started, and in the first molding region, the temperature is 50 ° C. lower than the martensite transformation start temperature (hereinafter sometimes referred to as “Ms point ⁇ 50 ° C.”).
  • the temperature is 100 ° C. lower than the bainite transformation start temperature (hereinafter sometimes referred to as “Bs point ⁇ 100 ° C.”), and the martensite transformation start temperature (Ms point) or higher.
  • the residence time in the said temperature range should just be 10 second or more, and should just complete
  • molding The reasons for specifying each requirement in this method are as follows. Note that “finishing the molding” basically means a state where the bottom dead center of the molding (the time when the punch tip is located at the deepest part: the state shown in FIG. 1) has been reached. When it is necessary to cool the mold until the mold is cooled, this means that the mold is released after the mold is cooled and held.
  • the above method divides the steel sheet into at least two forming regions (for example, a high-strength side region and a low-strength side region), and controls the manufacturing conditions according to each region, whereby strength-ductility corresponding to each region. A molded product that exhibits a balance can be obtained. Manufacturing conditions for forming each region will be described.
  • ⁇ Cooling conditions during molding and molding end temperature need to be controlled appropriately for each region.
  • first steel plate region a steel plate region corresponding to the first forming region of the molded product (this region may be referred to as “first steel plate region”)
  • an average cooling rate of 20 ° C./second or more in the mold during forming. It is necessary to finish the molding at a temperature of (Ms point ⁇ 50 ° C.) or less while securing the above.
  • the average cooling rate during molding is 20 ° C./second or more, and the molding end temperature is (Ms point ⁇ 50 ° C.) or less.
  • the average cooling rate during molding is preferably 30 ° C./second or more (more preferably 40 ° C./second or more).
  • the forming end temperature in the first steel plate region may be finished while cooling to room temperature at the above average cooling rate, but is not higher than (Ms point ⁇ 50 ° C.) (preferably up to Ms point ⁇ 50 ° C.). ) After cooling, cooling to 200 ° C. or less may be performed at an average cooling rate of 20 ° C./second or less (two-stage cooling). By adding such a cooling step, carbon in martensite can be concentrated in untransformed austenite and the amount of retained austenite can be increased. When performing such two-stage cooling, the average cooling rate during the second stage cooling is preferably 10 ° C./second or less (more preferably 5 ° C./second or less).
  • a steel plate region corresponding to the second forming region (this region may be referred to as a “second steel plate region”). )
  • Heating temperature must be controlled within a predetermined range. By appropriately controlling this heating temperature, in the subsequent cooling process, it is transformed into a structure mainly composed of bainitic ferrite while securing a predetermined amount of retained austenite, and the final hot press-formed product is used to obtain a desired temperature. Can be built into the organization.
  • the heating temperature of the thin steel sheet is less than the Ac 3 transformation point, a sufficient amount of austenite cannot be obtained during heating, and a predetermined amount of retained austenite cannot be ensured in the final structure (structure of the molded product).
  • the heating temperature of a thin steel plate exceeds 1000 degreeC, it will become the same as a 1st steel plate area
  • the average cooling rate during molding is 20 ° C./second or more
  • the cooling stop temperature is (Bs point ⁇ 100 ° C.) or less
  • the martensite transformation start temperature (Ms point) or more this temperature range is changed to “cooling rate change”. It may be called "temperature”).
  • the average cooling rate is preferably 30 ° C./second or more (more preferably 40 ° C./second or more).
  • Cooling is temporarily stopped within the above temperature range (cooling rate changing temperature) and allowed to stay for 10 seconds or more in the temperature range (ie, (Bs point ⁇ 100 ° C.) or lower, temperature range of martensite transformation start temperature Ms point or higher).
  • the bainite transformation proceeds from supercooled austenite, and a structure mainly composed of bainitic ferrite can be obtained.
  • the staying time at this time is preferably 50 seconds or more (more preferably 100 seconds or more), but if the staying time becomes too long, austenite starts to decompose and a retained austenite fraction cannot be secured, so 1000 seconds. Or less (more preferably 800 seconds or less).
  • the staying step as described above may be any of isothermal holding, monotonous cooling, and reheating step as long as it is within the above temperature range.
  • the above stay may be added at the stage of finishing molding, but a holding step may be added within the above temperature range in the middle of finishing molding. . After the molding is completed in this way, it may be allowed to cool to room temperature by cooling or at an appropriate cooling rate.
  • Control of the average cooling rate during molding can be achieved by means such as (a) controlling the temperature of the molding die (cooling medium shown in FIG. 1), (b) controlling the thermal conductivity of the die. (The same applies to cooling in the following method). Further, in the method of the present invention, the cooling conditions during forming differ depending on each steel plate region, but the control means such as (a) and (b) above are separately formed in a single mold. The cooling control corresponding to each steel plate region may be performed in a single mold.
  • a simple shape hot press-formed product as shown in FIG. 1 is manufactured (direct method) as well as a relatively complicated shape.
  • the present invention can also be applied to manufacturing products.
  • a method of performing cold press forming in a pre-process of hot press forming (this method is called “indirect method”) can be employed.
  • This method is a method in which a portion that is difficult to be molded is preliminarily molded to an approximate shape by cold working, and the other portions are hot press molded. If such a method is adopted, for example, when a part having three uneven portions (peaks) of a molded product is formed, the two parts are formed by cold press molding, and then the third part is formed. Will be hot pressed.
  • the present invention is made assuming a hot press-formed product made of a high-strength steel plate, and its steel type may be of a normal chemical composition as a high-strength steel plate, but C, Si, About Mn, P, S, Al, Cr, B, Ti, and N, it is good to adjust to an appropriate range. From such a viewpoint, the preferable ranges of these chemical components and the reasons for limiting the ranges are as follows.
  • C is an important element for improving the strength by making the bainitic ferrite produced in the cooling process fine and increasing the dislocation density in the bainitic ferrite (low strength side region). Further, it is an important element in controlling the strength of the martensite structure (high strength side region). If the C content is reduced, the strength is insufficient even with full martensite. C is an element strongly related to hardenability, and exhibits an effect of suppressing the formation of other soft structures such as ferrite during cooling after heating by increasing the content. Furthermore, it is an element necessary for securing retained austenite. If the C content is less than 0.15%, the bainite transformation start temperature Bs rises, and the high strength of the hot press-formed product cannot be ensured.
  • a more preferable lower limit of the C content is 0.18% or more (more preferably 0.20% or more), and a more preferable upper limit is 0.27% or less (more preferably 0.25% or less).
  • Mn is an element useful for suppressing the formation of ferrite and pearlite during primary cooling. Also, it is useful to increase the strength of bainitic ferrite by reducing (Bs point –100 ° C) to refine the structural unit of bainitic ferrite or increase the dislocation density in bainitic ferrite. Element. Furthermore, it is an element effective for stabilizing austenite and increasing the amount of retained austenite. In order to exhibit these effects, it is preferable to contain Mn 0.5% or more. When only the characteristics are considered, it is preferable that the Mn content is large, but it is preferable to make it 2% or less because the cost of alloy addition increases.
  • P 0.05% or less (excluding 0%)
  • P is an element inevitably contained in the steel, but it deteriorates ductility, so it is preferable to reduce P as much as possible.
  • extreme reduction leads to an increase in steelmaking cost, and since it is difficult to make it 0%, it is preferable to make it 0.05% or less (not including 0%).
  • a more preferable upper limit of the P content is 0.045% or less (more preferably 0.040% or less).
  • S 0.05% or less (excluding 0%)
  • S is an element inevitably contained in steel, and deteriorates ductility. Therefore, S is preferably reduced as much as possible.
  • extreme reduction leads to an increase in steelmaking cost, and since it is difficult to make it 0%, it is preferable to make it 0.05% or less (not including 0%).
  • a more preferable upper limit of the S content is 0.045% or less (more preferably 0.040% or less).
  • Al 0.01-0.1%
  • Al is useful as a deoxidizing element, and also fixes solid solution N present in steel as AlN, which is useful for improving ductility.
  • the Al content is preferably 0.01% or more.
  • a more preferable lower limit of the Al content is 0.013% or more (more preferably 0.015% or more), and a more preferable upper limit is 0.08% or less (more preferably 0.06% or less).
  • Cr 0.01-1%) Since Cr has an action of suppressing ferrite transformation and pearlite transformation, it is an element that prevents formation of ferrite and pearlite during cooling and contributes to securing retained austenite. In order to exert such an effect, Cr is preferably contained in an amount of 0.01% or more, but even if it is contained in excess of 1%, the cost increases. In addition, Cr significantly increases the strength of austenite, which increases the load of hot rolling and makes it difficult to manufacture a steel sheet. Therefore, it is not preferable to contain more than 1% in terms of productivity. A more preferable lower limit of the Cr content is 0.02% or more (more preferably 0.05% or more), and a more preferable upper limit is 0.8% or less (more preferably 0.5% or less).
  • Ti [N] x 4 to 0.1%) Ti fixes N and allows B to be maintained in a solid solution state, thereby exhibiting an effect of improving hardenability. In order to exhibit such an effect, it is preferable to contain Ti at least four times the N content [N]. However, if the Ti content becomes excessive and exceeds 0.1%, a large amount of TiC is formed, and the strength increases due to precipitation strengthening, but the ductility deteriorates. A more preferable lower limit of the Ti content is 0.05% or more (more preferably 0.06% or more), and a more preferable upper limit is 0.09% or less (more preferably 0.08% or less).
  • N (N: 0.001 to 0.01%) N is an element that reduces the hardenability improving effect by fixing B as BN, and it is preferable to reduce it as much as possible. However, since there is a limit to reducing it in the actual process, 0.001% A preferable lower limit was set. Further, when the N content is excessive, coarse TiN is formed, and this TiN acts as a starting point of fracture and the ductility deteriorates, so the preferable upper limit was made 0.01%. The upper limit with more preferable N content is 0.008% or less (more preferably 0.006% or less).
  • substantially iron means a trace component that does not inhibit the properties of the steel material of the present invention other than iron (for example, Mg, Ca, Sr, Ba, REM such as La, and Zr, Hf). , Ta, W, Mo and other carbide-forming elements) may be acceptable, and inevitable impurities other than P and S (for example, O, H, etc.) may also be included.
  • the press-formed product of the present invention if necessary, (a) one or more selected from the group consisting of Cu, Ni and Mo: 1% or less in total (excluding 0%), (b) V and It is also useful to contain at least one type of Nb: 0.1% or less in total (excluding 0%), etc., and the properties of hot press-formed products are further improved depending on the type of elements contained Is done.
  • the preferable range when these elements are contained and the reason for limiting the range are as follows.
  • the press forming conditions heat forming conditions (heating temperature and cooling rate according to each steel plate region)
  • characteristics such as strength and elongation for each forming region in the molded product
  • a hot-pressed product having high ductility residual ductility
  • the molded product obtained by the present invention has a larger residual ductility than a molded product whose structure is adjusted by performing normal annealing after cold press molding.
  • a steel material having the chemical composition shown in Table 1 below was vacuum-melted to obtain a slab for experiment, then hot rolled, and then cooled and wound up. Furthermore, it cold-rolled and made it the thin steel plate.
  • the Ac 3 transformation point, Ms point, and (Bs point ⁇ 100 ° C.) in Table 1 were determined using the following formulas (1) to (3) (for example, “Leslie Steel Material Gakuzen Maruzen, (1985)).
  • the obtained steel sheet was subjected to forming / cooling treatment by changing the heating temperature in each steel sheet region.
  • press molding was performed using a hat channel-shaped (HAT-shaped) bending mold shown in FIG.
  • 10 indicates an upper die (corresponding to the punch 1 shown in FIG. 1)
  • 11 indicates a lower die (corresponding to the die 2 shown in FIG. 1).
  • this molding die is provided with a pad 12 and is configured to perform press molding while sandwiching the steel plate 4 with the upper mold 11 while applying pressure (pad pressure) (pad pressure is 9800 N). ing.
  • the heating temperature and average cooling rate in each steel plate region are shown in the following Table 2 (the forming end temperature (mold release temperature) is 200 ° C. in all regions).
  • the steel plate size at the time of forming and cooling was 220 mm ⁇ 500 mm (plate thickness: 1.4 mm) (the area ratio of the first steel plate region and the second steel plate region was 1: 1).
  • the shape of the molded press-molded product is shown in FIG. 3 (FIG. 3A is a perspective view, and FIG. 3B is an explanatory diagram schematically showing a cross section).
  • 15 indicates a first steel plate region (corresponding to the first forming region in the formed product)
  • 16 indicates a second steel plate region (corresponding to the second forming region in the formed product). Yes.
  • the “average cooling rate 1” of the first steel plate region shown in Table 2 is the average cooling rate from the heating temperature to (Ms point ⁇ 50 ° C.) or less (forming end temperature), and “average cooling rate 1” of the first steel plate region is “ “Average cooling rate 2” indicates the average cooling rate from the molding end temperature to 200 ° C. or less.
  • the press-formed product of the present invention includes a first forming region showing a metal structure containing martensite: 80 to 97 area%, retained austenite: 3 to 20 area%, and a remaining structure of 5 area% or less, and a bay Nitic ferrite: 70 to 97 area%, martensite: 27 area% or less, and retained austenite: 3 to 20 area%, respectively, and a second forming region showing a metal structure having a remaining structure of 5 area% or less Have.
  • the single molded article has at least areas corresponding to the impact resistant part and the energy absorbing part, and the balance between high strength and elongation is high at a high level according to each area. Can be achieved.

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Abstract

L'invention porte sur un moulage par pressage à chaud comprenant : une première zone de formage présentant une structure métallique, qui contient 80-97 % en surface de martensite et 3-20 % en surface d'austénite résiduelle, respectivement, et dans laquelle la structure résiduelle représente 5 % en surface ou moins; et une seconde zone de formage présentant une structure métallique, qui contient 70-97 % en surface de ferrite bainitique, 27 % en surface ou moins de martensite et 3-20 % en surface d'austénite résiduelle, respectivement, et dans laquelle la structure résiduelle représente 5 % en surface ou moins. En conséquence, des moulages par pressage à chaud, qui ont au moins une zone correspondant à une zone résistante au choc et une zone correspondant à une zone absorbant l'énergie dans un seul moulage et dans lesquels un niveau élevé d'équilibre entre la résistance élevée et l'allongement selon la zone respective peut être atteint, sont obtenus sans utilisation d'une méthode de soudage.
PCT/JP2014/052948 2013-02-21 2014-02-07 Moulage par pressage à chaud et procédé de fabrication s'y rapportant WO2014129327A1 (fr)

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JP6428282B2 (ja) * 2015-01-15 2018-11-28 新日鐵住金株式会社 プレス成形品の製造方法
WO2017098304A1 (fr) 2015-12-09 2017-06-15 Arcelormittal Procédé de production d'une pièce de structure automobile comprenant un bas de caisse de côté inférieur et un montant avant inférieur
DE102016201936A1 (de) * 2016-02-09 2017-08-10 Schwartz Gmbh Wärmebehandlungsverfahren und Wärmebehandlungsvorrichtung
CN110199044B (zh) 2017-01-17 2021-10-12 日本制铁株式会社 热冲压用钢板
JP6589928B2 (ja) * 2017-04-13 2019-10-16 Ｊｆｅスチール株式会社 ホットプレス部材およびその製造方法
US11141769B2 (en) * 2017-06-16 2021-10-12 Ford Global Technologies, Llc Method and apparatus for forming varied strength zones of a vehicle component
KR20220071545A (ko) * 2020-11-24 2022-05-31 현대자동차주식회사 Twb 공법을 이용한 핫스탬핑 성형체 및 그 제조방법
WO2022215228A1 (fr) 2021-04-08 2022-10-13 日本製鉄株式会社 Feuille d'acier pour estampage à chaud et élément estampé à chaud

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