WO2024043606A1 - Tôle d'acier laminée à froid pour formage par pressage à chaud ayant une excellente qualité de surface, élément formé par pressage à chaud, et procédé de fabrication associé - Google Patents

Tôle d'acier laminée à froid pour formage par pressage à chaud ayant une excellente qualité de surface, élément formé par pressage à chaud, et procédé de fabrication associé Download PDF

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WO2024043606A1
WO2024043606A1 PCT/KR2023/012140 KR2023012140W WO2024043606A1 WO 2024043606 A1 WO2024043606 A1 WO 2024043606A1 KR 2023012140 W KR2023012140 W KR 2023012140W WO 2024043606 A1 WO2024043606 A1 WO 2024043606A1
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steel sheet
rolled steel
oxide layer
temperature
hot
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PCT/KR2023/012140
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English (en)
Korean (ko)
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이세웅
오진근
김성우
김상헌
이상철
김권일
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주식회사 포스코
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Publication of WO2024043606A1 publication Critical patent/WO2024043606A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C47/00—Winding-up, coiling or winding-off metal wire, metal band or other flexible metal material characterised by features relevant to metal processing only
    • B21C47/02—Winding-up or coiling
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • 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
    • 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
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment
    • 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
    • C22C38/34—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
    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel 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
    • C22C38/40—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

Definitions

  • the present invention relates to cold-rolled steel sheets for hot forming, hot-formed members, and methods for manufacturing them. More specifically, it relates to cold-rolled steel sheets for hot forming, hot-formed members with excellent surface quality, and methods for manufacturing them.
  • Patent Document 1 suggests that ultra-high strength with a tensile strength of 1600 MPa or more can be secured by heating an Al-Si plated steel sheet to 850°C or higher, then forming the structure of the member into martensite through hot forming and rapid cooling with a press. .
  • corrosion resistance and spot weldability can be secured without shot blast due to the alloying layer and diffusion layer formed by Fe diffusion from the base material to the plating layer during heat treatment.
  • Patent Document 1 U.S. Patent No. 6296805 (published on October 2, 2001)
  • the object is to provide a cold rolled steel sheet for hot forming with excellent surface quality, a hot forming member, and a method for manufacturing them.
  • One aspect of the present invention includes a base steel sheet and a first oxide layer on the base steel sheet,
  • the first oxide layer contains two or more types of Fe, Mn, Cr, and Si, and can provide a cold-rolled steel sheet with a thickness of 5 to 500 nm.
  • the above-mentioned steel plate has % by weight, C: 0.05-0.4%, Si: 0.5-3.0%, Cr: 0.3-5.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001 ⁇ 0.02%, N: 0.001 ⁇ 0.02%, may contain balance Fe and other unavoidable impurities.
  • the above-mentioned steel plate has Ti: 0.001 ⁇ 0.4%, Nb: 0.001 ⁇ 0.4%, Zr: 0.001 ⁇ 0.4%, V: 0.001 ⁇ 0.4%, B: 0.0001 ⁇ 0.01%, Mo: 0.001 ⁇ 1.0%, W: 0.001 ⁇ It may contain one or more of 1.0%, Cu: 0.005-2.0%, Ni: 0.005-2.0%, Sb: 0.001-1.0%, Sn: 0.001-1.0%, REM: 0.0001-0.02%.
  • the first oxide layer may have a total Si, Mn, and Cr content of 30% or more in weight percent.
  • the cold rolled steel sheet may contain ferrite and cementite in a microstructure of 5% by area or more.
  • Another aspect of the present invention includes a base steel sheet, a first oxide layer on the base steel sheet, and a second oxide layer on the first oxide layer,
  • the first oxide layer includes two or more types of Fe, Mn, Cr, and Si,
  • the second oxide layer is composed of Fe-based oxide and can provide a member with a thickness of 0.1 to 10 ⁇ m.
  • the steel sheet has a weight percentage of C: 0.05-0.4%, Si: 0.5-3.0%, Cr: 0.3% to less than 5.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05. %, S: 0.0001 ⁇ 0.02%, N: 0.001 ⁇ 0.02%, may contain balance Fe and other unavoidable impurities.
  • the above-mentioned steel plate has Ti: 0.001 ⁇ 0.4%, Nb: 0.001 ⁇ 0.4%, Zr: 0.001 ⁇ 0.4%, V: 0.001 ⁇ 0.4%, B: 0.0001 ⁇ 0.01%, Mo: 0.001 ⁇ 1.0%, W: 0.001 ⁇ It may contain one or more of 1.0%, Cu: 0.005-2.0%, Ni: 0.005-2.0%, Sb: 0.001-1.0%, Sn: 0.001-1.0%, REM: 0.0001-0.02%.
  • the sum of Si, Mn, and Cr contents in weight percent of the second oxide layer may be less than 30%.
  • the member may include martensite or bainite as a main phase as a microstructure.
  • the member may have a tensile strength of 500 MPa or more.
  • Another aspect of the invention includes reheating a steel slab
  • the temperature increase rate is 3.0 to 20.0°C/s at an ambient temperature of room temperature to 700°C
  • the temperature increase rate is 0.08 to 1.5°C/s at an ambient temperature of 700 to 800°C
  • the ambient temperature is 800 to 900°C. It is possible to provide a method of manufacturing a cold rolled steel sheet where the temperature increase rate is 0.01 to 1.5°C/s and the temperature increase rate is 0.01 to 1.0°C/s at an ambient temperature of 900 to 1000°C.
  • the steel slab has, in weight percent, C: 0.05-0.4%, Si: 0.5-3.0%, Cr: 0.3-5.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001 ⁇ 0.02%, N: 0.001 ⁇ 0.02%, may contain balance Fe and other unavoidable impurities.
  • the steel slab has Ti: 0.001 ⁇ 0.4%, Nb: 0.001 ⁇ 0.4%, Zr: 0.001 ⁇ 0.4%, V: 0.001 ⁇ 0.4%, B: 0.0001 ⁇ 0.01%, Mo: 0.001 ⁇ 1.0%, W: 0.001 ⁇ It may contain one or more of 1.0%, Cu: 0.005-2.0%, Ni: 0.005-2.0%, Sb: 0.001-1.0%, Sn: 0.001-1.0%, REM: 0.0001-0.02%.
  • the reheating is performed in a temperature range of 1000 to 1300°C,
  • the hot rolling is performed at a finish rolling temperature of Ar3 ⁇ 1000°C,
  • the winding is performed in a temperature range of Ms to 750°C,
  • the cold rolling may be performed at a reduction rate of 30 to 80%.
  • the continuous annealing is performed in the steel sheet temperature range of 700 to 900°C, and the continuous annealing time may be 1 to 1000 seconds.
  • Another aspect of the present invention includes heat treating a cold rolled steel sheet
  • T represents the heating temperature, the unit is °C, and t represents the total heating time, the unit is seconds.
  • the heat treatment it can be heated to the heating temperature at an atmospheric temperature increase rate of 1 to 1000°C/s.
  • the heating temperature may be 700 to 1000°C and the heating time may be 150 to 1000 seconds.
  • a cold rolled steel sheet for hot forming with excellent surface quality, a hot forming member, and a method for manufacturing them can be provided.
  • the present invention can be applied to automobile structural materials or reinforcement materials, and can provide cold-rolled steel sheets for hot forming, hot-formed members, and methods for manufacturing them, which have excellent surface quality and collision resistance characteristics without a plating process or a shot blast process. there is.
  • Figure 1 shows the surface quality of Inventive Example 2 and Comparative Example 10 after hot forming.
  • Figure 2 shows the phosphate coverage after hot forming of Inventive Example 1 and Comparative Example 2.
  • Figure 3 shows changes in surface quality according to hot forming conditions.
  • Figure 4 is a photograph observing the surfaces of Inventive Example 11 and Comparative Example 24 after hot forming.
  • the present inventors have solved the problem that, in the case of non-plated cold-rolled steel sheets for hot forming, excellent surface quality of the member cannot be secured due to the oxidation layer generated during heat treatment performed when manufacturing the hot formed member, and a shot blast process is essential to remove this layer.
  • a shot blast process is essential to remove this layer.
  • a cold rolled steel sheet according to one aspect of the present invention may include a base steel sheet and a first oxide layer formed on the base steel sheet.
  • the % indicating the content of each element is based on weight.
  • the base steel sheet of the cold rolled steel sheet according to one aspect of the present invention is, in weight percent, C: 0.05 to 0.4%, Si: 0.5 to 3.0%, Cr: 0.3 to 5.0%, Mn: 0.01 to 4.0%, Al: 0.001 to 0.4. %, P: 0.001 ⁇ 0.05%, S: 0.0001 ⁇ 0.02%, N: 0.001 ⁇ 0.02%, the remainder may contain Fe and other unavoidable impurities.
  • Carbon (C) is an essential element to increase the strength of heat-treated members, and needs to be added appropriately. If the carbon (C) content is less than 0.05%, there may be a problem in securing sufficient strength. On the other hand, if the content exceeds 0.4%, the strength of the hot rolled material is excessively high when cold rolling the hot rolled material, which not only deteriorates cold rolling properties, but also significantly reduces spot weldability. According to another aspect of the present invention, the lower limit may be 0.06%. According to another aspect of the present invention, the upper limit may be 0.38%, and according to another aspect, the upper limit may be 0.36%.
  • Silicon (Si) not only plays an important role in forming a silicon (Si)-based oxide layer by concentrating on the surface when annealing a cold-rolled steel sheet in a continuous annealing line, but also suppresses the formation of Fe, Mn, and Cr oxide layers during the hot forming process. It can play a role in ensuring the spot weldability of members. If the silicon (Si) content is less than 0.5%, the above-described effect may be insufficient. According to another aspect of the present invention, the lower limit may be 0.8%. On the other hand, if the content exceeds 3.0%, there may be a problem in that an excessively thick Si-based amorphous oxide layer is formed, which reduces spot weldability. According to another aspect of the present invention, the upper limit may be 2.8%.
  • Chromium (Cr) not only improves the hardenability of steel sheets, but also plays a role in stably forming a surface Si-based amorphous oxide layer through an appropriate reaction with Si. If the chromium (Cr) content is less than 0.3%, the above-mentioned effect may be insufficient. According to another aspect of the present invention, the lower limit may be 0.5%. On the other hand, if the content exceeds 5.0%, the effect may be saturated and manufacturing costs may increase. According to another aspect of the present invention, the upper limit may be 4.5%.
  • Manganese (Mn) needs to be added not only to ensure a solid solution strengthening effect, but also to lower the critical cooling rate for securing martensite in hot formed members. If the manganese (Mn) content is less than 0.01%, the above-mentioned effect may be insufficient. According to another aspect of the present invention, the lower limit may be 0.05%. On the other hand, if the content exceeds 4.0%, the strength of the steel sheet before the hot forming process increases excessively, which not only makes blanking work difficult, but also has the disadvantages of increased cost and poor spot weldability due to excessive addition of ferroalloy. You can. According to another aspect of the present invention, the upper limit may be 3.9%, and according to another aspect, the upper limit may be 3.8%.
  • Phosphorus (P) is an impurity, and controlling its content to less than 0.001% may require a lot of manufacturing costs, so the lower limit can be limited to 0.001%. On the other hand, if the content exceeds 0.05%, the weldability of the hot formed member may be greatly reduced. According to another aspect of the present invention, the upper limit may be 0.03%.
  • S Sulfur
  • the lower limit can be limited to 0.0001%.
  • the upper limit may be 0.01%.
  • Nitrogen (N) is an impurity, and controlling its content to less than 0.001% may require a lot of manufacturing costs, so the lower limit can be limited to 0.001%. On the other hand, if the content exceeds 0.02%, not only will the slab become susceptible to crack generation when playing, but the impact characteristics may also deteriorate. According to one aspect of the present invention, the upper limit may be 0.01%.
  • the steel material of the present invention may contain remaining iron (Fe) and inevitable impurities in addition to the composition described above. Since unavoidable impurities may be unintentionally introduced during the normal manufacturing process, they cannot be excluded. Since these impurities are known to anyone skilled in the field of steel manufacturing, all of them are not specifically mentioned in this specification.
  • the cold rolled steel plate according to one aspect of the present invention has Ti: 0.001 ⁇ 0.4%, Nb: 0.001 ⁇ 0.4%, Zr: 0.001 ⁇ 0.4%, V: 0.001 ⁇ 0.4%, B: 0.0001 ⁇ 0.01%, Mo: 0.001 ⁇ 1.0%, W: 0.001 ⁇ 1.0%, Cu: 0.005 ⁇ 2.0%, Ni: 0.005 ⁇ 2.0%, Sb: 0.001 ⁇ 1.0%, Sn: 0.001 ⁇ 1.0%, REM: 0.0001 ⁇ 0.02%. It can be included.
  • Titanium (Ti), niobium (Nb), zirconium (Zr), and vanadium (V) are effective in improving the strength of heat-treated members by forming fine precipitates, stabilizing retained austenite by refining grains, and improving impact toughness. If the content (meaning the sum of two or more types added) is less than 0.001%, the above-mentioned effect may be insufficient, and if the content exceeds 0.4%, the effect will not only be saturated, but excessive addition of ferroalloy may result. This may result in an increase in costs.
  • Boron (B) is an element that can not only improve hardenability even with a small amount of addition, but can also suppress embrittlement of hot-formed parts due to grain boundary segregation of P and/or S by segregating at the grain boundaries of prior austenite. If the boron (B) content is less than 0.001%, the above-described effect may be insufficient, and if the content exceeds 0.01%, the effect is not only saturated, but also may cause hot embrittlement during hot rolling.
  • the upper limit according to one aspect of the invention may be 0.005%.
  • Molybdenum (Mo) and tungsten (W) can be added to improve hardenability, improve strength through precipitation strengthening effects, and refine grains. If the content is less than 0.001%, the above-described effect is insufficient, and if the content exceeds 1.0%, the effect may be saturated and there may be a problem of increased costs.
  • Copper (Cu) can be added as an element to improve strength by forming fine precipitates. Additionally, nickel (Ni) may cause hot embrittlement when added alone to copper (Cu), so it may be added as needed. If the content is less than 0.005%, the above-mentioned effect may be insufficient, and if the content exceeds 2.0%, there is a risk of excessive cost increase.
  • Antimony (Sb) and tin (Sn) have the effect of suppressing the formation of oxides that may be formed at the surface grain boundaries of hot-rolled steels to which Si is added, and prevent dent defects caused by the separation of surface grain boundaries during annealing of cold-rolled steels. It can be suppressed. To achieve this effect, more than 0.001% can be added. On the other hand, if the content exceeds 1.0%, not only does the cost increase excessively, but it may also be dissolved in the slab grain boundaries and cause coil edge cracks during hot rolling.
  • Rare earth elements control the activity of Fe in steel and can control the formation thickness of surface Fe scale during hot forming. To obtain this effect, it is desirable to add 0.0001% or more of REM element. On the other hand, if the content exceeds 0.02%, the controllability of Fe activity may be lost, resulting in poor surface quality. According to one aspect of the present invention, it can be controlled to 0.01% or less.
  • the first oxide layer according to one aspect of the present invention includes two or more types of Fe, Mn, Cr, and Si, and may have a thickness of 5 to 500 nm.
  • the first oxide layer is a composite oxide layer containing two or more types of Fe, Mn, Cr, and Si, and is formed of two or more types of the corresponding elements, and is used in cold-rolled steel sheets to control the thickness of the second oxide layer of the member after hot forming.
  • precise thickness control is required by controlling the rate of increase in atmospheric temperature.
  • the sum of Si, Mn, and Cr contents in percent by weight relative to the first oxide layer may be 30% or more, and according to another aspect, the sum of the contents may be 90% or less.
  • the thickness of the first oxide layer is less than 5 nm, the second oxide layer is formed excessively thick after hot forming, and the effect of improving surface quality is minimal, making it difficult to secure excellent surface quality.
  • the thickness exceeds 500 nm it is not easy to form a second oxide layer after hot forming, and phosphate treatment properties are poor, making it difficult to secure excellent surface quality and sufficient paint corrosion resistance.
  • the upper thickness limit may be 490 nm, and according to another aspect, the lower thickness limit may be 5.5 nm.
  • the first oxide layer of the present invention may be formed continuously or discontinuously.
  • the first oxide layer according to one aspect of the present invention includes two or more types of Fe, Mn, Cr, and Si, and may have a thickness of 5.0 to 500.0 nm.
  • the % indicating the fraction of microstructure is based on area.
  • the cold rolled steel sheet according to one aspect of the present invention may include ferrite and cementite.
  • the area fraction is not particularly limited, but more preferably, ferrite and cementite may be 5 area% or more.
  • the microstructure feature may refer to the microstructure of the base steel sheet of the cold rolled steel sheet. If this is not taken into consideration, bainite, martensite, etc. may be included and are not excluded.
  • a member according to one aspect of the present invention may include a base steel plate, a first oxide layer formed on the base steel plate, and a second oxide layer formed on the first oxide layer.
  • composition of the base steel sheet of the member according to one aspect of the present invention is the same as the composition of the cold rolled steel sheet described above, it will not be described separately.
  • the second oxide layer according to one aspect of the present invention is composed of Fe-based oxide and may have a thickness of 0.1 to 10 ⁇ m.
  • the thickness of the second oxide layer exceeds 10 ⁇ m, there is a problem in securing excellent surface quality, such as peeling of surface oxide after hot forming, due to excessive oxide formation. On the other hand, if the thickness is less than 0.1 ⁇ m, phosphate treatment properties are poor and it may be difficult to secure excellent surface quality.
  • the sum of Si, Mn, and Cr contents in percent by weight relative to the second oxide layer may be less than 30%, and is preferably more than 0%.
  • the % indicating the fraction of microstructure is based on area.
  • the member according to one aspect of the present invention may include martensite or bainite as a main phase as a microstructure.
  • the hot formed member of the present invention may include martensite or bainite as the main phase to ensure high strength.
  • the microstructure feature may refer to the microstructure of the base steel plate of the member.
  • the main phase may refer to the phase with the largest area fraction among several phases that make up the microstructure.
  • the area fraction is not particularly limited, but according to one aspect of the present invention, it may be 5 area% or more.
  • the cold rolled steel sheet according to one aspect of the present invention can be manufactured by reheating, hot rolling, coiling, cold rolling, and continuous annealing a steel slab satisfying the above-described alloy composition.
  • Steel slabs satisfying the alloy composition of the present invention can be reheated to a temperature range of 1000 to 1300°C.
  • the reheating temperature is less than 1000°C, it is difficult to homogenize the slab structure, and if the temperature exceeds 1300°C, there is a risk of excessive oxide formation and increased manufacturing costs.
  • the reheated steel slab can be hot rolled at a finish rolling temperature of Ar3 ⁇ 1000°C.
  • finish rolling temperature is lower than Ar3, abnormal rolling is likely to occur, which may lead to a mixed structure occurring in the surface layer, and there may be difficulties in controlling the shape of the hot rolled steel sheet.
  • the temperature exceeds 1000°C, there is a risk that the crystal grains of the hot rolled steel sheet may become coarse.
  • the hot-rolled steel sheet can be cooled and wound in a temperature range of Ms to 750°C.
  • the strength of the hot rolled steel sheet may increase excessively, thereby reducing cold rolling properties.
  • Ms martensite transformation start temperature
  • the temperature exceeds 750°C the thickness of the oxide layer increases and surface grain boundary oxidation occurs, which not only deteriorates pickling properties, but also causes problems such as separation of surface grain boundaries during annealing in a continuous annealing furnace.
  • the cooling rate is not particularly limited, but air cooling may be performed.
  • the coiled steel sheet can be cold rolled.
  • the reduction rate of cold rolling is not specifically limited, but can be performed at a reduction rate of 30 to 80% to secure the target thickness.
  • cold rolling can be performed for more precise steel sheet thickness control, and pickling can be performed before cold rolling.
  • the cold rolled steel sheet can be continuously annealed, and during the continuous annealing, the temperature increase rate is 3.0 to 20.0°C/s at an ambient temperature of room temperature to 700°C, and the temperature increase rate is 0.08 to 1.5°C at an ambient temperature of 700 to 800°C. °C/s, and the temperature increase rate may be 0.01 to 1.5 °C/s at an ambient temperature of 800 to 900 °C, and the temperature increase rate may be 0.01 to 1.0 °C/s at an ambient temperature of 900 to 1000 °C.
  • the rate of increase in ambient temperature is more strictly controlled. If the temperature increase rate of the ambient temperature is below the suggested lower limit, an excessive first oxide layer is formed and exceeds 500 nm, and the second oxide layer of sufficient thickness cannot be secured after hot forming, resulting in poor phosphate treatment properties. Excellent surface quality may not be secured. On the other hand, if the temperature increase rate of the ambient temperature exceeds the suggested upper limit, the formation of the first oxide layer is minimal, and an excessive second oxide layer is formed after hot forming, which may result in poor surface quality such as surface scale peeling.
  • the continuous annealing can be performed in the steel sheet temperature range of 700 to 900°C. If the annealing temperature is less than 700°C, it may be difficult for the rolled structure created by cold rolling to recover and recrystallize. On the other hand, if the temperature exceeds 900°C, the annealing equipment may deteriorate, which may be a factor in increasing process costs due to frequent replacement of equipment.
  • the continuous annealing time may be 1 to 1000 seconds. If the annealing time is less than 1 second, it is difficult to obtain an annealing effect, whereas if the annealing time exceeds 1000 seconds, productivity may decrease.
  • the member according to one aspect of the present invention can be manufactured by heat treating, hot forming, and cooling the cold rolled steel sheet manufactured by the above-described method.
  • the cold rolled steel sheet according to one aspect of the present invention is heat treated, and the A value defined in the following relational equation 1 may be 0.6 to 1.0, and the heat treatment may be performed after heating at a temperature increase rate of 1 to 1000° C./s to the heating temperature.
  • the heating temperature and heating time can be controlled through relational equation 1 in order to precisely control the formation thickness of the second oxide layer. If the A value defined in Equation 1 is less than 0.6, when heat treatment is performed, the formation thickness of the second oxide layer is so small that it may be difficult to secure excellent surface quality, such as poor phosphate treatment properties. On the other hand, if the value exceeds 1.0, the thickness of the second oxide layer is excessive, making it difficult to secure excellent surface quality due to peeling of the oxide layer.
  • the temperature increase rate in the heat treatment step may refer to the temperature increase rate of the atmosphere of the continuous annealing furnace. If the temperature increase rate is less than 1°C/s, it may be difficult to secure sufficient productivity, and if the rate exceeds 1000°C/s, there may be a problem of requiring equipment that costs excessively.
  • the heating temperature may be 700°C or higher and may be 1000°C or lower.
  • the heating time according to one aspect of the present invention may be 150 seconds or more, and may be 1000 seconds or less.
  • T represents the heating temperature, the unit is °C, and t represents the total heating time, the unit is seconds.
  • the heat-treated steel sheet After hot forming, the heat-treated steel sheet can be cooled to the Mf temperature or lower at a cooling rate of 10 to 1000°C/s.
  • cooling rate is less than 10°C/s, unwanted ferrite and pearlite are formed, making it difficult to secure the desired level of tensile strength.
  • speed exceeds 1000°C/s, expensive special cooling equipment is required to control the speed, so productivity may decrease.
  • the hot formed member according to one aspect of the present invention manufactured in this way has a tensile strength of 500 MPa or more, and can secure excellent strength and collision resistance.
  • a 40 mm thick slab having the composition shown in Table 1 below was vacuum melted, heated in a furnace at 1200°C for 1 hour, and then hot rolled at a final rolling temperature of 900°C to produce a hot rolled steel sheet with a final thickness of 3 mm.
  • the hot-rolled steel sheet was air-cooled and wound at 600°C, and then the hot-rolled steel sheet was pickled and then cold-rolled at a cold rolling reduction rate of 50% to produce a cold-rolled steel sheet.
  • the cold rolled steel sheet manufactured as above was continuously annealed under the conditions shown in Table 2 below. At this time, continuous annealing was performed at a steel sheet temperature of 780°C.
  • heat treatment was performed under the conditions shown in Table 2 below, and cooling was performed after hot forming. During heat treatment, the temperature increase rate was 5°C/s, and after hot forming, it was cooled to room temperature at a cooling rate of 30°C/s.
  • T represents the heating temperature, the unit is °C, and t represents the total heating time, the unit is seconds.
  • Table 3 shows the measured thickness of the first oxide layer of the cold rolled steel sheet after continuous annealing, and also shows the measured thickness of the second oxide layer of the member after heat treatment, hot forming, and cooling.
  • the first oxide layer thickness was measured using a transmission electron microscope (TEM), and the second oxide layer thickness was measured at three locations using a transmission electron microscope (TEM) and electron beam microanalysis (EPMA), and the average result was obtained. indicated.
  • TEM transmission electron microscope
  • EPMA electron beam microanalysis
  • Phosphate coverage was determined by observing the tissue with a scanning electron microscope (SEM) and measuring the area of the area where phosphate crystals were not formed. At this time, if the phosphate crystal formation area exceeded 70%, the phosphate characteristics were judged to be good. In addition, the yield strength, tensile strength, and elongation of the manufactured member were measured and shown. Yield strength, tensile strength, and elongation were tested at room temperature using JIS-5 specimens in accordance with ISO6892 standards.
  • Cold-rolled steel sheets and members that satisfy the alloy composition and manufacturing conditions of the present invention formed a first oxide layer and a second oxide layer in the thickness range suggested by the present invention, and excellent surface quality was secured even after hot forming.
  • Figure 1 is a photograph showing the surface quality of Inventive Example 2 and Comparative Example 10 after hot forming.
  • Comparative Example 10 compared to Inventive Example 2, it can be confirmed that the quality is inferior due to the formation of a thick oxide.
  • Figure 2 shows the phosphate coverage after hot forming of Inventive Example 1 and Comparative Example 2. In Comparative Example 2, it was confirmed that less than 70% of phosphate crystals were formed.
  • Figure 3 shows the change in surface quality according to heat treatment temperature and time conditions.
  • the surface condition was observed by adjusting the hot forming temperature and time. If the heat treatment conditions are outside the range limited by Equation 1, surface scale peeling occurs due to excessive formation of a second oxide layer on the surface after heat treatment, or excessive first oxide It can be confirmed that the surface quality deteriorates, such as phosphate treatment properties, due to the formation of the layer.
  • Figure 4 is a photograph observing the surfaces of Inventive Example 11 and Comparative Example 24 after hot forming. Comparative Example 24 was heat treated exceeding the heat treatment conditions limited by Relation 1, and scale was confirmed when the surface was visually observed compared to Inventive Example 11.

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  • Metallurgy (AREA)
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  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
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Abstract

La présente invention concerne une tôle d'acier laminée à froid pour formage par pressage à chaud, un élément formé par pressage à chaud, et un procédé de fabrication associé et, plus spécifiquement, une tôle d'acier laminée à froid pour formage par pressage à chaud, ayant une excellente qualité de surface, un élément formé par pressage à chaud, et un procédé de fabrication associé.
PCT/KR2023/012140 2022-08-22 2023-08-17 Tôle d'acier laminée à froid pour formage par pressage à chaud ayant une excellente qualité de surface, élément formé par pressage à chaud, et procédé de fabrication associé WO2024043606A1 (fr)

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Publication number Priority date Publication date Assignee Title
JP2009091640A (ja) * 2007-10-11 2009-04-30 Jfe Steel Kk 缶用鋼板原板の製造方法
KR20160078851A (ko) * 2014-12-24 2016-07-05 주식회사 포스코 내식성이 우수한 열간성형 부재 및 그 제조방법
KR20170075046A (ko) * 2015-12-22 2017-07-03 주식회사 포스코 내식성이 우수한 열간 프레스 성형품 및 그 제조방법
KR101830527B1 (ko) * 2016-09-26 2018-02-21 주식회사 포스코 내식성 및 점용접성이 우수한 열간성형용 냉연강판, 열간성형부재 및 그들의 제조방법
KR101852277B1 (ko) * 2013-07-04 2018-06-04 아르셀러미탈 인베스티가시온 와이 데살롤로 에스엘 냉간 압연 강판, 제조 방법 및 차량
CN114045441A (zh) * 2021-11-16 2022-02-15 攀钢集团攀枝花钢铁研究院有限公司 800MPa级连退用增强塑性双相钢及其制备方法

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009091640A (ja) * 2007-10-11 2009-04-30 Jfe Steel Kk 缶用鋼板原板の製造方法
KR101852277B1 (ko) * 2013-07-04 2018-06-04 아르셀러미탈 인베스티가시온 와이 데살롤로 에스엘 냉간 압연 강판, 제조 방법 및 차량
KR20160078851A (ko) * 2014-12-24 2016-07-05 주식회사 포스코 내식성이 우수한 열간성형 부재 및 그 제조방법
KR20170075046A (ko) * 2015-12-22 2017-07-03 주식회사 포스코 내식성이 우수한 열간 프레스 성형품 및 그 제조방법
KR101830527B1 (ko) * 2016-09-26 2018-02-21 주식회사 포스코 내식성 및 점용접성이 우수한 열간성형용 냉연강판, 열간성형부재 및 그들의 제조방법
CN114045441A (zh) * 2021-11-16 2022-02-15 攀钢集团攀枝花钢铁研究院有限公司 800MPa级连退用增强塑性双相钢及其制备方法

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