WO2024043606A1 - Cold rolled steel sheet for hot-press forming having excellent surface quality, hot-press-formed member, and method for manufacturing same - Google Patents

Cold rolled steel sheet for hot-press forming having excellent surface quality, hot-press-formed member, and method for manufacturing same Download PDF

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Publication number
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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French (fr)
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/en

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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.

Abstract

The present invention relates to a cold rolled steel sheet for hot-press forming, a hot-press-formed member, and a method for manufacturing same and, more specifically, to a cold rolled steel sheet for hot-press forming, having excellent surface quality, a hot-press-formed member, and a method for manufacturing same

Description

표면품질이 우수한 열간 성형용 냉연강판, 열간 성형 부재 및 그들의 제조방법Cold rolled steel sheets for hot forming with excellent surface quality, hot forming members, and their manufacturing methods
본 발명은 열간 성형용 냉연강판, 열간 성형 부재 및 그들의 제조방법에 관한 것으로, 보다 상세하게는, 표면품질이 우수한 열간 성형용 냉연강판 및 열간 성형 부재 및 그들의 제조방법에 관한 것에 관한 것이다.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.
최근 자동차 경량화를 통한 연비 향상 및 고강도화를 통한 내충돌성 향상을 위하여 자동차 구조 부재에 대하여 많은 연구가 행해지고 있다. 특히, 자동차 구조 부재로 열간 성형으로 제조되는 부재가 많이 적용이 되고 있다. Recently, much research has been conducted on automobile structural members to improve fuel efficiency by reducing the weight of automobiles and improving crash resistance through increased strength. In particular, members manufactured by hot forming are widely used as automobile structural members.
특허문헌 1에서는 Al-Si 도금강판을 850℃ 이상 가열 후, 프레스로 열간 성형 및 급냉을 통해 부재의 조직을 마르텐사이트로 형성함으로써, 인장강도가 1600MPa 이상인 초고강도를 확보할 수 있음을 제시하고 있다. 또한, 열처리 중 모재에서 도금층으로 Fe 확산에 의해 형성되는 합금화층 및 확산층으로 인해 샷 블래스트(shot blast) 없이도 내식성 및 점용접성을 확보할 수 있음을 개시하고 있다.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. . In addition, it is disclosed that 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.
그러나, Al-Si 도금강판은 Al-Si 도금층을 형성해야 하므로, 별도의 도금공정이 필요하여 경제성 및 생산성이 저하되는 문제점이 있다.However, since Al-Si plated steel sheets must form an Al-Si plating layer, a separate plating process is required, which reduces economic efficiency and productivity.
한편, 비도금재의 경우, 열처리 시 생성되는 산화층으로 인해 점용접성을 확보할 수 없고, 이를 제거하기 위한 샷 블래스트 공정이 반드시 필요할 뿐만 아니라, 내식성을 확보하기 어려운 문제점이 있다.Meanwhile, in the case of non-plated materials, spot weldability cannot be secured due to the oxidation layer generated during heat treatment, and a shot blast process is necessary to remove it, and there is a problem in that it is difficult to secure corrosion resistance.
따라서, 도금공정 및 샷 블래스트 공정 없이도 우수한 내식성 및 점용접성을 확보할 수 있는 열간 성형용 냉연강판, 열간 성형 부재 및 그들의 제조방법에 대한 개발이 요구되는 실정이다.Accordingly, there is a need for the development of cold-rolled steel sheets for hot forming, hot-formed members, and their manufacturing methods that can secure excellent corrosion resistance and spot weldability without the plating process and shot blast process.
[선행기술문헌][Prior art literature]
(특허문헌 1) 미국 등록특허 제6296805호(2001.10.02 공개)(Patent Document 1) U.S. Patent No. 6296805 (published on October 2, 2001)
본 발명의 일 측면에 따르면 표면품질이 우수한 열간 성형용 냉연강판, 열간 성형 부재 및 그들의 제조방법을 제공하고자 하는 것이다.According to one aspect of the present invention, 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.
본 발명의 과제는 상술한 내용에 한정되지 않는다. 통상의 기술자라면 본 명세서의 전반적인 내용으로부터 본 발명의 추가적인 과제를 이해하는데 아무런 어려움이 없을 것이다.The object of the present invention is not limited to the above-described content. A person skilled in the art will have no difficulty in understanding the additional problems of the present invention from the overall content of the present specification.
본 발명의 일 측면은, 소지강판 및 상기 소지강판 상의 제1 산화물층을 포함하고,One aspect of the present invention includes a base steel sheet and a first oxide layer on the base steel sheet,
상기 제1 산화물층은 Fe, Mn, Cr, Si 중 2종 이상을 포함하고, 5~500nm의 두께를 가지는 냉연강판을 제공할 수 있다.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.
상기 소지강판은 중량%로, 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%, 잔부 Fe 및 기타 불가피한 불순물을 포함할 수 있다.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.
상기 소지강판은 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% 중 1종 이상을 포함할 수 있다.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%.
상기 제1 산화물층은 중량%로 Si, Mn 및 Cr 함량의 합이 30% 이상일 수 있다.The first oxide layer may have a total Si, Mn, and Cr content of 30% or more in weight percent.
상기 냉연강판은 미세조직으로 페라이트 및 세멘타이트를 5면적% 이상 포함할 수 있다.The cold rolled steel sheet may contain ferrite and cementite in a microstructure of 5% by area or more.
본 발명의 다른 일 측면은, 소지강판, 상기 소지강판 상의 제1 산화물층 및 상기 제1 산화물층 상의 제2 산화물층을 포함하고,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,
상기 제1 산화물층은 Fe, Mn, Cr, Si 중 2종 이상을 포함하고,The first oxide layer includes two or more types of Fe, Mn, Cr, and Si,
상기 제2 산화물층은 Fe계 산화물로 구성되며, 0.1~10μm의 두께를 가지는 부재를 제공할 수 있다.The second oxide layer is composed of Fe-based oxide and can provide a member with a thickness of 0.1 to 10 μm.
상기 소지강판은 중량%로, C: 0.05~0.4%, Si: 0.5~3.0%, Cr: 0.3% 이상 5.0% 미만, 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%, 잔부 Fe 및 기타 불가피한 불순물을 포함할 수 있다.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.
상기 소지강판은 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% 중 1종 이상을 포함할 수 있다.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%.
상기 제2 산화물층은 중량%로 Si, Mn 및 Cr 함량의 합이 30% 미만일 수 있다.The sum of Si, Mn, and Cr contents in weight percent of the second oxide layer may be less than 30%.
상기 부재는 미세조직으로 마르텐사이트 또는 베이나이트를 주상으로 포함할 수 있다.The member may include martensite or bainite as a main phase as a microstructure.
상기 부재는 인장강도가 500MPa 이상일 수 있다.The member may have a tensile strength of 500 MPa or more.
본 발명의 다른 일 측면은, 강 슬라브를 재가열하는 단계;Another aspect of the invention includes reheating a steel slab;
상기 재가열된 강 슬라브를 열간압연하는 단계;hot rolling the reheated steel slab;
상기 열간압연된 강판을 냉각하여 권취하는 단계;Cooling and winding the hot-rolled steel sheet;
상기 권취된 강판을 냉간압연하는 단계; 및Cold rolling the rolled steel sheet; and
상기 냉간압연된 강판을 연속소둔하는 단계를 포함하고,Continuously annealing the cold rolled steel sheet,
상기 연속소둔 시, 상온~700℃의 분위기 온도에서 승온속도가 3.0~20.0℃/s이고, 700~800℃의 분위기 온도에서 승온속도가 0.08~1.5℃/s이고, 800~900℃의 분위기 온도에서 승온속도가 0.01~1.5℃/s이고, 900~1000℃의 분위기 온도에서 승온속도가 0.01~1.0℃/s인 냉연강판 제조방법을 제공할 수 있다.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, the temperature increase rate is 0.08 to 1.5°C/s at an ambient temperature of 700 to 800°C, and 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.
상기 강 슬라브는 중량%로, 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%, 잔부 Fe 및 기타 불가피한 불순물을 포함할 수 있다.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.
상기 강 슬라브는 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% 중 1종 이상을 포함할 수 있다.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%.
상기 재가열은 1000~1300℃의 온도범위에서 행하고,The reheating is performed in a temperature range of 1000 to 1300°C,
상기 열간압연은 Ar3~1000℃의 마무리 압연온도로 행하며,The hot rolling is performed at a finish rolling temperature of Ar3~1000℃,
상기 권취는 Ms~750℃의 온도범위에서 행하고,The winding is performed in a temperature range of Ms to 750°C,
상기 냉간압연은 30~80%의 압하율로 행하는 것일 수 있다.The cold rolling may be performed at a reduction rate of 30 to 80%.
상기 연속소둔은 강판온도가 700~900℃인 온도범위에서 행하고, 연속소둔 시간은 1~1000초일 수 있다.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.
본 발명의 다른 일 측면은, 냉연강판을 열처리하는 단계; 및Another aspect of the present invention includes heat treating a cold rolled steel sheet; and
상기 열처리된 강판을 열간 성형 후 냉각하는 단계를 포함하고,Comprising the step of cooling the heat-treated steel sheet after hot forming,
상기 열처리 시, 하기 관계식 1에서 정의되는 A 값이 0.6~1.0인 부재 제조방법을 제공할 수 있다.During the heat treatment, it is possible to provide a method of manufacturing a member in which the A value defined in the following relational equation 1 is 0.6 to 1.0.
[관계식 1][Relationship 1]
A = (T + 0.2t)/1210A = (T + 0.2t)/1210
(식에서, T는 가열온도를 나타내며, 단위는 ℃이고, t는 총 가열시간을 나타내며, 단위는 초이다.)(In the formula, T represents the heating temperature, the unit is ℃, and t represents the total heating time, the unit is seconds.)
상기 열처리 시, 가열온도까지 1~1000℃/s의 분위기 승온속도로 가열할 수 있다.During the heat treatment, it can be heated to the heating temperature at an atmospheric temperature increase rate of 1 to 1000°C/s.
상기 열처리 시, 가열온도는 700~1000℃이고, 가열시간은 150~1000초일 수 있다.During the heat treatment, the heating temperature may be 700 to 1000°C and the heating time may be 150 to 1000 seconds.
상기 열간 성형 후 냉각 시, 10~1000℃/s의 냉각속도로 Mf 온도 이하까지 냉각할 수 있다.When cooling after the hot forming, it can be cooled to the Mf temperature or lower at a cooling rate of 10 to 1000°C/s.
본 발명의 일 측면에 따르면 표면품질이 우수한 열간 성형용 냉연강판, 열간 성형 부재 및 그들의 제조방법을 제공할 수 있다.According to one aspect of the present invention, 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.
본 발명의 일 측면에 따르면 자동차 구조 보재 또는 보강재 등에 적용될 수 있으며, 도금공정 및 샷 블래스트 공정 없이도 표면품질 및 내충돌성 특성이 우수한 열간 성형용 냉연강판, 열간 성형 부재 및 그들의 제조방법을 제공할 수 있다.According to one aspect of the present invention, it 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.
도 1은 발명예 2와 비교예 10의 열간 성형 후 표면품질을 나타낸 것이다.Figure 1 shows the surface quality of Inventive Example 2 and Comparative Example 10 after hot forming.
도 2는 발명예 1과 비교예 2의 열간 성형 후 인산염 커버리지를 나타낸 것이다.Figure 2 shows the phosphate coverage after hot forming of Inventive Example 1 and Comparative Example 2.
도 3은 열간 성형 조건에 따른 표면 품질의 변화를 나타낸 것이다.Figure 3 shows changes in surface quality according to hot forming conditions.
도 4는 발명예 11과 비교예 24의 열간 성형 후 표면을 관찰한 사진이다.Figure 4 is a photograph observing the surfaces of Inventive Example 11 and Comparative Example 24 after hot forming.
이하에서는 본 발명의 바람직한 구현예들을 설명하고자 한다. 본 발명의 구현예들은 여러 가지 형태로 변형될 수 있으며, 본 발명의 범위가 아래에서 설명되는 구현예들에 한정되는 것으로 해석되어서는 안된다. 본 구현예들은 당해 발명이 속하는 기술분야에서 통상의 기술자에게 본 발명을 더욱 상세하게 설명하기 위하여 제공되는 것이다.Below, preferred embodiments of the present invention will be described. Embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as limited to the embodiments described below. These embodiments are provided to explain the present invention in more detail to those skilled in the art.
본 발명자들은 열간 성형용 비도금 냉연강판의 경우, 열간 성형 부재 제조 시 행해지는 열처리 중 생성되는 산화층으로 인해 부재의 우수한 표면품질을 확보할 수 없고, 이를 제거하기 위한 샷 블래스트 공정이 반드시 필요한 문제점을 인지하고, 이를 해결하면서도 우수한 표면품질을 확보하기 위하여 깊이 연구하였다.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. We recognized this and conducted in-depth research to solve this problem and secure excellent surface quality.
그 결과, 합금조성 및 제조조건, 특히 Cr, Si, Mn 함량 및 소둔 시 분위기 온도의 변화속도를 정밀하게 제어함으로써 소둔 시, 목표하는 두께로 복합 산화물층을 형성시키고, 열간 성형 공정 조건을 제어함으로써 샷 블래스트 공정 없이도 우수한 표면품질을 확보할 수 있음을 확인하고, 본 발명을 완성하기에 이르렀다.As a result, by precisely controlling the alloy composition and manufacturing conditions, especially the Cr, Si, and Mn contents, and the rate of change of the ambient temperature during annealing, a composite oxide layer is formed to the target thickness during annealing, and the hot forming process conditions are controlled. It was confirmed that excellent surface quality could be secured without the shot blast process, and the present invention was completed.
이하, 본 발명에 대하여 상세히 설명한다.Hereinafter, the present invention will be described in detail.
이하에서는, 본 발명의 냉연강판에 대해 자세히 설명한다.Below, the cold rolled steel sheet of the present invention will be described in detail.
본 발명의 일 측면에 따르는 냉연강판은 소지강판 및 상기 소지강판 상에 형성된 제1 산화물층을 포함할 수 있다.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.
이하에서는,본 발명의 일 측면에 따르는 냉연강판의 소지강판 조성에 대해 자세히 설명한다.Hereinafter, the composition of the base steel sheet of the cold rolled steel sheet according to one aspect of the present invention will be described in detail.
본 발명에서 특별히 달리 언급하지 않는 한 각 원소의 함량을 표시하는 %는 중량을 기준으로 한다.In the present invention, unless otherwise specified, the % indicating the content of each element is based on weight.
본 발명의 일 측면에 따르는 냉연강판의 소지강판은 중량%로, 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%, 나머지 Fe 및 기타 불가피한 불순물을 포함할 수 있다.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.
탄소(C): 0.05~0.4%Carbon (C): 0.05~0.4%
탄소(C)는 열처리 부재의 강도를 상향시키기 위하여 필수적인 원소로서, 적절히 첨가될 필요가 있다. 탄소(C) 함량이 0.05% 미만인 경우, 충분한 강도를 확보하기 곤란한 문제점이 있을 수 있다. 반면, 그 함량이 0.4%를 초과하면 열연재를 냉간압연할 때 열연재 강도가 과도하게 높아 냉간 압연성이 크게 열위하게 될 뿐만 아니라, 점용접성을 크게 저하시킬 수 있다. 본 발명의 다른 일 측면에 따르면 하한은 0.06%일 수 있다. 본 발명의 다른 일 측면에 따르면 상한은 0.38%일 수 있으며, 다른 일 측면에 따르면 상한은 0.36%일 수 있다. 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%.
실리콘(Si): 0.5~3.0%Silicon (Si): 0.5~3.0%
실리콘(Si)은 냉연강판을 연속 소둔 라인에서 소둔 시, 표면으로 농화되어 실리콘(Si)계 산화층을 형성하는 중요한 역할을 할 뿐만 아니라, 열간 성형 공정에서 Fe, Mn, Cr 산화물층 형성을 억제하여 부재의 점용접성을 확보하는 역할을 할 수 있다. 실리콘(Si) 함량이 0.5% 미만인 경우, 상술한 효과가 불충분할 수 있다. 본 발명의 다른 일 측면에 따르면 하한은 0.8%일 수 있다. 반면, 그 함량이 3.0%를 초과하면 과도하게 두꺼운 Si계 비정질 산화층을 형성하여 점용접성이 오히려 저하되는 문제점이 있을 수 있다. 본 발명의 다른 일 측면에 따르면 상한은 2.8%일 수 있다.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%.
크롬(Cr): 0.3~5.0%Chromium (Cr): 0.3~5.0%
크롬(Cr)은 강판의 경화능을 향상시킬 뿐만 아니라, Si과 적절한 반응을 통하여 표층 Si계 비정질 산화물층 형성을 안정적으로 도와주는 역할을 할 수 있다. 크롬(Cr) 함량이 0.3% 미만인 경우, 상술한 효과가 불충분할 수 있다. 본 발명의 다른 일 측면에 따르면 하한은 0.5%일 수 있다. 반면, 그 함량이 5.0%를 초과하면 그 효과가 포화되고, 제조비용이 상승하는 문제점이 있을 수 있다. 본 발명의 다른 일 측면에 따르면 상한은 4.5%일 수 있다.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%.
망간(Mn): 0.01~4.0%Manganese (Mn): 0.01~4.0%
망간(Mn)은 고용강화 효과를 확보할 수 있을 뿐만 아니라, 열간 성형 부재에 있어서, 마르텐사이트를 확보하기 위한 임계 냉각 속도를 낮추기 위하여 첨가될 필요가 있다. 망간(Mn) 함량이 0.01% 미만인 경우, 상술한 효과가 불충분할 수 있다. 본 발명의 다른 일 측면에 따르면 하한은 0.05%일 수 있다. 반면, 그 함량이 4.0%를 초과하면, 열간 성형 공정 전 강판의 강도가 과도하게 올라가기 때문에 블랭킹 작업이 어려워질 뿐만 아니라, 과다한 합금철 첨가에 따른 원가 상승 및 점용접성을 열위하게 하는 단점이 있을 수 있다. 본 발명의 다른 일 측면에 따르면 상한은 3.9%일 수 있으며, 다른 일 측면에 따르면 상한은 3.8%일 수 있다.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%.
알루미늄(Al): 0.001~0.4%Aluminum (Al): 0.001~0.4%
알루미늄(Al)은 Si과 더불어 제강에서 탈산 작용을 하여 강의 청정도를 높일 수 있다. 알루미늄(Al) 함량이 0.001% 미만인 경우, 상술한 효과가 불충분할 수 있다. 본 발명의 다른 일 측면에 따르면 하한은 0.005%일 수 있다. 반면, 그 함량이 0.4%를 초과하면 Ac3 온도가 과다하게 상승하여 가열온도를 높여야 하는 문제점이 있을 수 있다. 본 발명의 다른 일 측면에 따르면 상한은 0.3%일 수 있으며, 다른 일 측면에 따르면 상한은 0.2%일 수 있다.Aluminum (Al), along with Si, can increase the cleanliness of steel by acting as a deoxidizer in steelmaking. If the aluminum (Al) content is less than 0.001%, the above-described effect may be insufficient. According to another aspect of the present invention, the lower limit may be 0.005%. On the other hand, if the content exceeds 0.4%, the Ac3 temperature may increase excessively, which may cause a problem in that the heating temperature must be increased. According to another aspect of the present invention, the upper limit may be 0.3%, and according to another aspect, the upper limit may be 0.2%.
인(P): 0.001~0.05%Phosphorus (P): 0.001~0.05%
인(P)은 불순물로서, 그 함량을 0.001% 미만으로 제어하기 위해서는 많은 제조비용이 들 수 있으므로 그 하한을 0.001%로 한정할 수 있다. 반면, 그 함량이 0.05%를 초과하면 열간 성형 부재의 용접성을 크게 저하시킬 수 있다. 본 발명의 다른 일 측면에 따르면 상한은 0.03%일 수 있다.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%.
황(S): 0.0001~0.02%Sulfur (S): 0.0001~0.02%
황(S)은 불순물로서, 그 함량을 0.0001% 미만으로 제어하기 위해서는 많은 제조비용이 들 수 있으므로 그 하한을 0.0001%로 한정할 수 있다. 반면, 그 함량이 0.02%를 초과하면 부재의 연성, 충격특성 및 용접성을 저해할 우려가 있다. 본 발명의 다른 일 측면에 따르면 상한은 0.01%일 수 있다.Sulfur (S) is an impurity, and controlling its content to less than 0.0001% may require a lot of manufacturing costs, so the lower limit can be limited to 0.0001%. On the other hand, if the content exceeds 0.02%, there is a risk that the ductility, impact properties, and weldability of the member may be impaired. According to another aspect of the present invention, the upper limit may be 0.01%.
질소(N): 0.001~0.02%,Nitrogen (N): 0.001~0.02%,
질소(N)는 불순물로서, 그 함량을 0.001% 미만으로 제어하기 위해서는 많은 제조비용이 들 수 있으므로 그 하한을 0.001%로 제한할 수 있다. 반면, 그 함량이 0.02%를 초과할 경우, 슬라브 연주 시, 크랙 발생에 민감해질 뿐만 아니라, 충격특성이 저하될 수 있다. 본 발명의 일 측면에 따르면 상한은 0.01%일 수 있다.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%.
본 발명의 강재는, 상술한 조성 이외에 나머지 철(Fe) 및 불가피한 불순물을 포함할 수 있다. 불가피한 불순물은 통상의 제조공정에서 의도되지 않게 혼입될 수 있으므로, 이를 배제할 수는 없다. 이러한 불순물들은 통상의 철강제조분야의 기술자라면 누구라도 알 수 있는 것이기 때문에 그 모든 내용을 특별히 본 명세서에서 언급하지는 않는다.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.
본 발명의 일 측면에 따르는 냉연강판 소지강판은 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% 중 1종 이상을 포함할 수 있다.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.
티타늄(Ti), 니오븀(Nb), 지르코늄(Zr), 바나듐(V): 0.001~0.4%Titanium (Ti), niobium (Nb), zirconium (Zr), vanadium (V): 0.001~0.4%
티타늄(Ti), 니오븀(Nb), 지르코늄(Zr), 바나듐(V)은 미세 석출물 형성으로 열처리 부재의 강도 향상과 결정립 미세화에 의한 잔류 오스테나이트 안정화 및 충격인성 향상에 효과가 있다. 그 함량(2종 이상 첨가된 경우, 그들의 합계를 의미함)이 0.001% 미만이면 상술한 효과가 불충분할 수 있으며, 그 함량이 0.4%를 초과하면 그 효과가 포화될 뿐만 아니라, 과다한 합금철 첨가에 따른 원가 상승을 초래할 수 있다.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.
붕소(B): 0.0001~0.01%Boron (B): 0.0001~0.01%
붕소(B)는 소량의 첨가로도 경화능을 향상시킬 수 있을 뿐만 아니라, 구오스테나이트 결정립계에 편석되어 P 및/또는 S의 입계 편석에 의한 열간 성형 부재의 취성을 억제할 수 있는 원소이다. 붕소(B) 함량이 0.001% 미만인 경우, 상술한 효과가 불충분할 수 있으며, 그 함량이 0.01%를 초과할 경우, 그 효과가 포화될 뿐만 아니라, 열간압연 시, 열간 취성을 초래할 수 있다. 본 발명의 일 측면에 따르는 상한은 0.005%일 수 있다.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%.
몰리브덴(Mo), 텅스텐(W): 0.001~1.0%Molybdenum (Mo), tungsten (W): 0.001~1.0%
몰리브덴(Mo), 텅스텐(W)은 경화능 향상과 석출강화 효과를 통한 강도 향상 및 결정립 미세화를 위하여 첨가할 수 있다. 그 함량이 0.001% 미만인 경우, 상술한 효과가 불충분하고, 그 함량이 1.0%를 초과하면 그 효과가 포화될 뿐만 아니라 비용상승의 문제가 있을 수 있다.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.
구리(Cu), 니켈(Ni): 0.005~2.0%Copper (Cu), Nickel (Ni): 0.005~2.0%
구리(Cu)는 미세 석출물을 형성시켜 강도를 향상시키는 원소로서 첨가될 수 있다. 또한, 니켈(Ni)은 구리(Cu) 단독으로 첨가될 때 열간 취성을 초래할 수 있으므로 필요에 따라 첨가될 수 있다. 그 함량이 0.005% 미만에서는 상술한 효과가 불충분할 수 있고, 그 함량이 2.0%를 초과하면 과다한 비용 상승을 초래할 우려가 있다.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.
안티몬(Sb), 주석(Sn): 0.001~1.0%Antimony (Sb), Tin (Sn): 0.001~1.0%
안티몬(Sb), 주석(Sn)은 Si이 첨가된 강재의 열연재 표층 결정립계에 생성될 수 있는 산화물 생성을 억제하는 효과를 가져, 냉연재 소둔 시, 표층 결정립계 탈락에 의한 덴트(dent) 결함을 억제할 수 있다. 이와 같은 효과를 얻기 위해서는 0.001% 이상 첨가할 수 있다. 반면, 그 함량이 1.0%를 초과하면 과다한 비용 상승뿐 아니라, 슬라브 입계에 고용되어 열간압연 시, 코일 에지(edge) 크랙을 유발시킬 수 있다.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.
희토류 원소(REM): 0.0001~0.02%Rare Earth Elements (REM): 0.0001-0.02%
희토류 원소(REM)는 강 내 Fe의 활동도를 제어하여 열간 성형 시, 표층 Fe 스케일의 형성 두께를 제어할 수 있다. 이러한 효과를 얻기 위해서는 0.0001% 이상의 REM 원소의 첨가가 바람직하다. 반면, 그 함량이 0.02%를 초과하면 Fe 활동도의 제어능을 상실하여 표면 품질이 열위해질 수 있다. 본 발명의 일 측면에 따르면 0.01% 이하로 제어할 수 있다.Rare earth elements (REM) 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.
본 발명의 일 측면에 따르는 제1 산화물층은 Fe, Mn, Cr, Si 중 2종 이상을 포함하고, 5~500nm의 두께를 가질 수 있다.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.
제1 산화물층은 Fe, Mn, Cr, Si 중 2종 이상을 함유하는 복합 산화물층으로, 해당 원소가 2종 이상 형성되어 있으며, 열간 성형 후 부재의 제2 산화층의 두께를 제어하기 위하여 냉연강판 제작 시, 분위기 온도 승온속도 제어를 통해 정밀한 두께 제어가 필요하다. 본 발명의 일 측면에 따르면, 제1 산화물층에 대한 자체 중량%로 Si, Mn 및 Cr 함량의 합이 30% 이상일 수 있으며, 다른 일 측면에 따르면 그 함량의 합이 90% 이하일 수 있다.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. When manufacturing, precise thickness control is required by controlling the rate of increase in atmospheric temperature. According to one aspect of the present invention, 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.
상기 제1 산화물층의 두께가 5nm 미만인 경우, 열간 성형 후 제2 산화물층이 과도하게 두껍게 형성되어 표면품질의 향상 효과가 미미하여 우수한 표면품질을 확보하기 어려울 수 있다. 반면, 그 두께가 500nm를 초과하면, 열간 성형 후 제2 산화물층 형성이 용이하지 않아, 인산염 처리성이 열위해져 우수한 표면품질의 확보가 어려우며, 충분한 도장 내식성을 확보하기 어려울 수 있다. 본 발명의 일 측면에 따르는 두께 상한은 490nm일 수 있으며, 다른 일 측면에 따르면 두께 하한은 5.5nm일 수 있다. 본 발명의 제1 산화물층은 연속적 또는 불연속적으로 형성될 수 있다.If 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. On the other hand, if 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. According to one aspect of the present invention, 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.
본 발명의 일 측면에 따르는 제1 산화물층은 Fe, Mn, Cr, Si 중 2종 이상을 포함하고, 5.0~500.0nm의 두께를 가질 수 있다.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.
이하에서는, 본 발명의 냉연강판 미세조직에 대해 자세히 설명한다.Below, the microstructure of the cold rolled steel sheet of the present invention will be described in detail.
본 발명에서 특별히 달리 언급하지 않는 한 미세조직의 분율을 표시하는 %는 면적을 기준으로 한다.In the present invention, unless specifically stated otherwise, the % indicating the fraction of microstructure is based on area.
본 발명의 일 측면에 따르는 냉연강판은 페라이트 및 세멘타이트를 포함할 수 있다. 본 발명에서는 특별히 그 면적분율을 한정하지 않으나, 보다 바람직하게는 페라이트 및 세멘타이트가 5면적% 이상일 수 있다.The cold rolled steel sheet according to one aspect of the present invention may include ferrite and cementite. In the present invention, the area fraction is not particularly limited, but more preferably, ferrite and cementite may be 5 area% or more.
냉연강판을 열간 성형 부재를 제조하기 위하여 블랭크(blank)를 만들 때, 그 강도가 과도하면 금형 마모가 쉽게 발생할 수 있다. 보다 구체적으로는, 상기 미세조직 특징은 냉연강판의 소지강판의 미세조직을 의미할 수 있다. 이를 고려하지 않는 경우에는 베이나이트, 마르텐사이트 등을 포함할 수 있으며, 이를 배제하는 것은 아니다.When making a blank from a cold-rolled steel sheet to manufacture a hot-formed member, if the strength is excessive, mold wear can easily occur. More specifically, 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.
이하에서는, 본 발명의 부재에 대해 자세히 설명한다.Below, the elements of the present invention will be described in detail.
본 발명의 일 측면에 따르는 부재는 소지강판, 상기 소지강판 상에 형성된 제1 산화물층 및 상기 제1 산화물층 상에 형성된 제2 산화물층을 포함할 수 있다.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.
본 발명의 일 측면에 따른 부재의 소지강판의 조성은 상술한 냉연강판의 조성과 동일하므로 별도로 설명하지 않는다.Since the 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.
본 발명의 일 측면에 따르는 제2 산화물층은 Fe계 산화물로 구성되며, 0.1~10μm의 두께를 가질 수 있다.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 μm.
상기 제2 산화물층의 두께가 10μm를 초과하면 과도한 산화물 형성으로 열간 성형 후 표면 산화물 박리 등 우수한 표면품질을 확보하기 어려운 문제점이 있다. 반면, 그 두께가 0.1μm 미만이면, 인산염 처리성이 열위해져 우수한 표면품질을 확보하기 어려울 수 있다. 본 발명의 일 측면에 따르면, 제2 산화물층에 대한 자체 중량%로 Si, Mn 및 Cr 함량의 합이 30% 미만일 수 있으며, 0% 초과인 것이 바람직하다.If the thickness of the second oxide layer exceeds 10 μm, 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 μm, phosphate treatment properties are poor and it may be difficult to secure excellent surface quality. According to one aspect of the present invention, 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%.
이하에서는, 본 발명의 부재 미세조직에 대해 자세히 설명한다.Below, the microstructure of the member of the present invention will be described in detail.
본 발명에서 특별히 달리 언급하지 않는 한 미세조직의 분율을 표시하는 %는 면적을 기준으로 한다.In the present invention, unless specifically stated otherwise, the % indicating the fraction of microstructure is based on area.
본 발명의 일 측면에 따르는 부재는 미세조직으로 마르텐사이트 또는 베이나이트를 주상으로 포함할 수 있다.The member according to one aspect of the present invention may include martensite or bainite as a main phase as a microstructure.
본 발명의 열간 성형 부재는 고강도를 확보하기 위하여 마르텐사이트 또는 베이나이트를 주상으로 포함할 수 있다. 보다 구체적으로는, 상기 미세조직 특징은 부재의 소지강판의 미세조직을 의미할 수 있다. 본 발명에서 주상은 미세조직을 이루는 여러 상(phase) 중에서 가장 큰 면적분율을 가지는 상을 의미할 수 있다. 특별히 그 면적분율을 한정하지 않으나, 본 발명의 일 측면에 따르면 5면적% 이상일 수 있다.The hot formed member of the present invention may include martensite or bainite as the main phase to ensure high strength. More specifically, the microstructure feature may refer to the microstructure of the base steel plate of the member. In the present invention, 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.
이하에서는, 본 발명의 냉연강판 및 부재 제조방법에 대해 자세히 설명한다.Below, the cold-rolled steel sheet and member manufacturing method of the present invention will be described in detail.
본 발명의 일 측면에 따르는 냉연강판은 상술한 합금조성을 만족하는 강 슬라브를 재가열, 열간압연, 권취, 냉간압연 및 연속소둔하여 제조될 수 있다.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.
재가열reheat
본 발명의 합금조성을 만족하는 강 슬라브를 1000~1300℃의 온도범위로 재가열할 수 있다.Steel slabs satisfying the alloy composition of the present invention can be reheated to a temperature range of 1000 to 1300°C.
재가열 온도가 1000℃ 미만인 경우, 슬라브 조직을 균질화 하기 어려운 문제점이 있으며, 그 온도가 1300℃를 초과하는 경우, 과다한 산화물 형성 및 제조비용 상승이 발생할 우려가 있다.If 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.
열간압연hot rolling
상기 재가열된 강 슬라브를 Ar3~1000℃의 마무리 압연온도로 열간압연할 수 있다.The reheated steel slab can be hot rolled at a finish rolling temperature of Ar3~1000°C.
마무리 압연온도가 Ar3 미만인 경우, 이상역 압연이 되기 쉬어 표층에 혼립 조직이 발생할 우려가 있으며, 열연강판의 형상 제어에 어려움이 있을 수 있다. 반면, 그 온도가 1000℃를 초과하는 경우, 열연강판의 결정립이 조대화될 우려가 있다.If the 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. On the other hand, if the temperature exceeds 1000°C, there is a risk that the crystal grains of the hot rolled steel sheet may become coarse.
냉각 및 권취Cooling and Winding
상기 열간압연된 강판을 냉각하여 Ms~750℃의 온도범위에서 권취할 수 있다.The hot-rolled steel sheet can be cooled and wound in a temperature range of Ms to 750°C.
권취온도가 Ms(마르텐사이트 변태 개시 온도) 미만인 경우, 열연강판의 강도가 과도하게 높아져 냉간압연성을 저하시킬 수 있다. 반면, 그 온도가 750℃를 초과하면 산화층의 두께가 증가 및 표층 입계산화를 야기시켜 산세성이 열위해질 뿐만 아니라, 연속소둔로에서 소둔 시, 표층 입계 탈락을 야기시키는 문제점이 발생할 수 있다. 냉각 시, 냉각속도에 대하여 특별히 한정하지 않으나, 공냉을 행할 수 있다.If the coiling temperature is less than Ms (martensite transformation start temperature), the strength of the hot rolled steel sheet may increase excessively, thereby reducing cold rolling properties. On the other hand, if 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. When cooling, the cooling rate is not particularly limited, but air cooling may be performed.
냉간압연cold rolling
상기 권취된 강판을 냉간압연할 수 있다.The coiled steel sheet can be cold rolled.
본 발명에서는 냉간압연의 압하율을 특별히 한정하지 않으나, 목표 두께를 확보하기 위하여 압하율 30~80%로 행할 수 있다.In the present invention, 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.
본 발명에서는 보다 정밀한 강판 두께 제어를 위하여 냉간압연을 행할 수 있으며 냉간압연 전 산세를 실시할 수 있다.In the present invention, cold rolling can be performed for more precise steel sheet thickness control, and pickling can be performed before cold rolling.
연속소둔Continuous Annealing
상기 냉간압연된 강판을 연속소둔할 수 있으며, 상기 연속소둔 시, 상온~700℃의 분위기 온도에서 승온속도가 3.0~20.0℃/s이고, 700~800℃의 분위기 온도에서 승온속도가 0.08~1.5℃/s이고, 800~900℃의 분위기 온도에서 승온속도가 0.01~1.5℃/s이고, 900~1000℃의 분위기 온도에서 승온속도가 0.01~1.0℃/s일 수 있다.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. ℃/s, and the temperature increase rate may be 0.01 to 1.5 ℃/s at an ambient temperature of 800 to 900 ℃, and the temperature increase rate may be 0.01 to 1.0 ℃/s at an ambient temperature of 900 to 1000 ℃.
연속소둔 시, 표층 제1 산화층의 두께를 정밀히 제어하기 위하여 본 발명에서는 분위기 온도의 승온속도를 더욱 엄격히 제어한다. 분위기 온도의 승온속도가 제안하는 하한에 미달될 경우, 과도한 제1 산화물층이 형성되어 500nm를 초과하게 되고, 열간 성형 후 충분한 두께의 제2 산화물층을 확보하지 못하므로, 인산염 처리성이 열위해져 우수한 표면품질을 확보하지 못할 수 있다. 반면, 분위기 온도의 승온속도가 제안하는 상한을 초과할 경우, 제1 산화물층의 형성이 미미하여, 열간성형 후 과도한 제2 산화물층이 형성되어 표면 스케일 박리 등 표면품질이 열위해질 수 있다.In order to precisely control the thickness of the surface first oxide layer during continuous annealing, in the present invention, 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.
본 발명의 일 측면에 따르면, 상기 연속소둔은 강판온도 700~900℃의 온도범위에서 행할 수 있다. 소둔온도가 700℃ 미만이면, 냉간압연에 의해 생성된 압연조직이 회복 및 재결정이 일어나기 어려울 수 있다. 반면, 그 온도가 900℃를 초과하면, 소둔 설비를 열화시킬 수 있어 설비의 잦은 교체 등으로 공정비용 상승의 요인이 될 수 있다.According to one aspect of the present invention, 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.
본 발명의 일 측면에 따르면 연속소둔 시간은 1~1000초일 수 있다. 소둔시간이 1초 미만이면, 소둔 효과를 얻기 어려운 반면, 그 시간이 1000초를 초과하면, 생산성이 저하될 수 있다.According to one aspect of the present invention, 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.
본 발명의 일 측면에 따르는 부재는 상술한 방법으로 제조되는 냉연강판을 열처리, 열간 성형 및 냉각하여 제조될 수 있다.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.
열처리heat treatment
본 발명의 일 측면에 따르는 냉연강판을 열처리하되, 하기 관계식 1에서 정의되는 A 값이 0.6~1.0일 수 있으며, 가열온도까지 1~1000℃/s의 승온속도로 가열한 후 열처리할 수 있다. 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.
본 발명에서는 제2 산화층의 형성 두께를 정밀히 제어하기 위하여 관계식 1을 통하여 가열온도 및 가열시간을 제어할 수 있다. 관계식 1에서 정의되는 A 값이 0.6 미만이면, 열처리를 진행하는 경우 제2 산화물층의 형성 두께가 미미하여 인산염 처리성이 열위해지는 등 우수한 표면품질의 확보가 어려울 수 있다. 반면, 그 값이 1.0을 초과하면 제2 산화물층의 두께가 과도하여 산화물층의 박리로 우수한 표면품질을 확보하기 어려운 문제점이 있다.In the present invention, 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.
열처리 단계에서의 승온속도는 연속소둔로(爐)의 분위기의 승온속도를 의미할 수 있다. 상기 승온속도가 1℃/s 미만인 경우, 생산성을 충분히 확보하기 어려울 수 있으며, 그 속도가 1000℃/s를 초과하는 경우, 과다한 비용이 드는 설비를 필요로 하는 문제점이 있을 수 있다. 본 발명의 일 측면에 따르면 가열온도를 700℃ 이상으로 행할 수 있으며, 1000℃ 이하로 행할 수 있다. 본 발명의 일 측면에 따르는 가열시간은 150초 이상일 수 있으며, 1000초 이하로 행할 수 있다.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. According to one aspect of the present invention, 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.
[관계식 1][Relationship 1]
A = (T + 0.2t)/1210A = (T + 0.2t)/1210
(식에서, T는 가열온도를 나타내며, 단위는 ℃이고, t는 총 가열시간을 나타내며, 단위는 초이다.)(In the formula, T represents the heating temperature, the unit is ℃, and t represents the total heating time, the unit is seconds.)
열간 성형 및 냉각Hot forming and cooling
상기 열처리된 강판을 열간 성형 후 10~1000℃/s의 냉각속도로 Mf 온도 이하까지 냉각할 수 있다.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.
상기 냉각속도가 10℃/s 미만인 경우, 원치 않는 페라이트 및 펄라이트가 형성되어 목적하는 수준의 인장강도를 확보하기에 어려움이 있다. 반면, 그 속도가 1000℃/s를 초과하면, 그 속도를 제어하기 위해서 고가의 특별한 냉각설비가 필요하므로, 생산성이 저하될 수 있다.If the 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. On the other hand, if the speed exceeds 1000°C/s, expensive special cooling equipment is required to control the speed, so productivity may decrease.
냉각종료온도가 Mf (마르텐사이트 변태 종료 온도)를 초과하여 냉각 정지한 후 다시 상온까지 냉각할 경우, 열간 성형 부재의 형상 동결성을 확보하기 어려울 수 있다. When cooling is stopped because the cooling end temperature exceeds Mf (martensite transformation end temperature) and then cooled back to room temperature, it may be difficult to secure the shape freezing of the hot formed member.
이와 같이 제조된 본 발명의 일 측면에 따르는 열간 성형 부재는 인장강도가 500MPa 이상으로, 강도 및 내충돌성이 우수한 특성을 확보할 수 있다.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.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명한다. 다만, 아래의 실시예는 본 발명을 예시하여 보다 상세하게 설명하기 위한 것일 뿐, 본 발명의 권리범위를 제한하기 위한 것이 아니라는 점에 유의할 필요가 있다.Hereinafter, the present invention will be described in more detail through examples. However, it is important to note that the examples below are only for illustrating and explaining the present invention in more detail, and are not intended to limit the scope of the present invention.
이하, 실시예를 통하여 본 발명을 보다 구체적으로 설명한다. 다만, 아래의 실시예는 본 발명을 예시하여 보다 상세하게 설명하기 위한 것일 뿐, 본 발명의 권리범위를 제한하기 위한 것이 아니라는 점에 유의할 필요가 있다.Hereinafter, the present invention will be described in more detail through examples. However, it is important to note that the examples below are only for illustrating and explaining the present invention in more detail, and are not intended to limit the scope of the present invention.
(실시예)(Example)
하기 표 1의 조성을 가지는 두께 40mm 슬라브를 진공 용해하고, 가열로에서 1200℃, 1시간 동안 가열한 후, 마무리 압연온도 900℃로 열간압연하여 최종 두께 3mm의 열연강판을 제조하였다. 상기 열연강판을 공냉하여 600℃에서 권취한 후, 이어 상기 열연강판을 산세 후 50%의 냉간압하율로 냉간압연을 실시하여 냉연강판을 제조하였다.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.
강종steel grade 합금조성(wt%)Alloy composition (wt%)
CC SiSi MnMn PP SS AlAl CrCr MoMo TiTi BB NN
AA 0.330.33 1.931.93 3.463.46 0.00560.0056 0.00820.0082 0.0020.002 4.894.89 0.4890.489 0.0210.021 0.00250.0025 0.00240.0024
BB 0.320.32 0.940.94 2.002.00 0.00660.0066 0.00150.0015 0.0090.009 0.850.85 0.0850.085 0.0150.015 0.00200.0020 0.00230.0023
CC 0.060.06 2.662.66 2.182.18 0.00460.0046 0.00010.0001 0.0080.008 0.650.65 0.0650.065 0.0250.025 0.00110.0011 0.00210.0021
DD 0.160.16 1.211.21 2.432.43 0.00330.0033 0.00260.0026 0.0070.007 1.401.40 0.1400.140 0.0170.017 0.02300.0230 0.00410.0041
EE 0.100.10 2.152.15 1.661.66 0.00270.0027 0.00860.0086 0.0010.001 3.903.90 0.3900.390 0.0180.018 0.00000.0000 0.00280.0028
FF 0.180.18 2.922.92 1.781.78 0.00900.0090 0.00430.0043 0.0050.005 0.330.33 0.0330.033 0.0210.021 0.00180.0018 0.00450.0045
GG 0.330.33 1.521.52 1.701.70 0.00550.0055 0.00830.0083 0.0020.002 0.460.46 0.0120.012 0.0100.010 0.00000.0000 0.00490.0049
HH 0.100.10 0.060.06 3.623.62 0.00920.0092 0.00710.0071 0.0010.001 4.904.90 0.4900.490 0.0950.095 0.00200.0020 0.00370.0037
II 0.360.36 1.931.93 0.420.42 0.00270.0027 0.00360.0036 0.0080.008 5.125.12 0.5120.512 0.0040.004 0.00000.0000 0.00470.0047
JJ 0.250.25 1.441.44 0.860.86 0.00160.0016 0.00450.0045 0.0050.005 5.755.75 0.5750.575 0.0720.072 0.00040.0004 0.00280.0028
KK 0.240.24 1.391.39 0.630.63 0.00380.0038 0.00470.0047 0.0040.004 0.210.21 0.0210.021 0.1000.100 0.00240.0024 0.00480.0048
LL 0.320.32 0.350.35 1.001.00 0.00790.0079 0.00700.0070 0.0070.007 1.621.62 0.1620.162 0.0610.061 0.00000.0000 0.00430.0043
MM 0.070.07 1.091.09 2.502.50 0.00800.0080 0.00850.0085 0.0080.008 6.666.66 0.6660.666 0.0690.069 0.00150.0015 0.00210.0021
NN 0.190.19 0.260.26 2.322.32 0.01200.0120 0.00140.0014 0.0070.007 0.050.05 0.0130.013 0.0530.053 0.00190.0019 0.00500.0050
OO 0.080.08 2.452.45 3.813.81 0.00330.0033 0.00950.0095 0.0070.007 0.200.20 0.4100.410 0.0410.041 0.00230.0023 0.00480.0048
PP 0.390.39 3.023.02 3.893.89 0.00350.0035 0.00030.0003 0.0070.007 7.867.86 0.2500.250 0.0510.051 0.00000.0000 0.00340.0034
QQ 0.140.14 0.900.90 0.0090.009 0.00500.0050 0.00070.0007 0.0060.006 1.801.80 0.1800.180 0.0570.057 0.00090.0009 0.00310.0031
RR 0.140.14 0.900.90 4.234.23 0.00500.0050 0.00070.0007 0.0060.006 1.751.75 0.1750.175 0.0570.057 0.02500.0250 0.00250.0025
상기와 같이 제조된 냉연강판을 하기 표 2의 조건으로 연속소둔을 행하였으며, 이 때, 780℃의 강판온도로 연속소둔을 행하였다. 더하여, 하기 표 2의 조건으로 열처리를 행하였으며, 열간 성형 후 냉각하였다. 열처리 시, 승온속도는 5℃/s를 적용하였으며, 열간 성형 후 상온까지 30℃/s의 냉각속도로 냉각하였다.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. In addition, 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℃/s, and after hot forming, it was cooled to room temperature at a cooling rate of 30℃/s.
시
편
번
호city
side
th
like 		강
종river
bell 		연속소둔Continuous annealing 열처리heat treatment
온도구간에 따른 분위기 온도 승온속도(℃/s)Ambient temperature increase rate according to temperature section (℃/s) 온도
(℃)temperature
(℃) 		시간
(s)hour
(s) 		관계식 1Relation 1
상온~700(℃)Room temperature ~ 700 (℃) 700~800(℃)700~800(℃) 800~900(℃)800~900(℃) 900~1000(℃)900~1000(℃)
1One AA 18.018.0 1.191.19 1.201.20 0.500.50 900.0900.0 300.0300.0 0.7930.793
22 BB 7.37.3 1.391.39 0.120.12 0.130.13 900.0900.0 300.0300.0 0.7930.793
33 CC 9.29.2 0.120.12 1.341.34 0.980.98 900.0900.0 300.0300.0 0.7930.793
44 DD 9.09.0 1.441.44 1.421.42 0.900.90 900.0900.0 300.0300.0 0.7930.793
55 EE 4.44.4 0.160.16 0.920.92 0.490.49 900.0900.0 300.0300.0 0.7930.793
66 FF 3.83.8 0.100.10 0.880.88 0.880.88 900.0900.0 300.0300.0 0.7930.793
77 GG 6.76.7 0.970.97 0.250.25 0.300.30 900.0900.0 300.0300.0 0.7930.793
88 HH 6.86.8 0.250.25 0.050.05 0.700.70 900.0900.0 300.0300.0 0.7930.793
99 II 10.110.1 0.920.92 0.510.51 0.240.24 900.0900.0 300.0300.0 0.7930.793
1010 JJ 5.65.6 1.021.02 0.610.61 0.410.41 900.0900.0 300.0300.0 0.7930.793
1111 KK 10.410.4 0.840.84 1.291.29 0.550.55 900.0900.0 300.0300.0 0.7930.793
1212 LL 4.44.4 1.451.45 0.390.39 0.210.21 900.0900.0 300.0300.0 0.7930.793
1313 MM 9.79.7 0.740.74 0.130.13 0.140.14 900.0900.0 300.0300.0 0.7930.793
1414 NN 17.417.4 0.430.43 0.580.58 0.880.88 900.0900.0 300.0300.0 0.7930.793
1515 OO 3.23.2 0.380.38 0.190.19 0.090.09 900.0900.0 300.0300.0 0.7930.793
1616 PP 5.65.6 0.130.13 1.091.09 0.160.16 900.0900.0 300.0300.0 0.7930.793
1717 QQ 6.56.5 1.431.43 0.630.63 0.590.59 900.0900.0 300.0300.0 0.7930.793
1818 RR 9.69.6 1.181.18 0.850.85 0.560.56 900.0900.0 300.0300.0 0.7930.793
1919 AA 18.0418.04 1.191.19 1.201.20 0.500.50 900.0900.0 300.0300.0 0.7930.793
2020 AA 6.786.78 0.130.13 1.821.82 0.780.78 900.0900.0 300.0300.0 0.7930.793
2121 AA 8.748.74 0.070.07 0.290.29 0.390.39 900.0900.0 300.0300.0 0.7930.793
2222 AA 8.738.73 0.760.76 0.0060.006 0.200.20 900.0900.0 300.0300.0 0.7930.793
2323 AA 8.438.43 0.210.21 1.121.12 1.221.22 900.0900.0 300.0300.0 0.7930.793
2424 CC 9.229.22 0.120.12 1.341.34 0.980.98 900.0900.0 300.0300.0 0.7930.793
2525 CC 1.771.77 0.960.96 1.441.44 0.300.30 900.0900.0 300.0300.0 0.7930.793
2626 CC 8.348.34 1.961.96 0.840.84 0.020.02 900.0900.0 300.0300.0 0.7930.793
2727 CC 7.637.63 0.100.10 2.462.46 0.180.18 900.0900.0 300.0300.0 0.7930.793
2828 CC 5.175.17 0.900.90 0.610.61 0.0080.008 900.0900.0 300.0300.0 0.7930.793
2929 DD 8.988.98 1.441.44 1.421.42 0.900.90 900.0900.0 300.0300.0 0.7930.793
3030 DD 25.025.0 0.190.19 0.070.07 0.640.64 900.0900.0 300.0300.0 0.7930.793
3131 DD 1.921.92 0.190.19 1.201.20 2.182.18 900.0900.0 300.0300.0 0.7930.793
3232 DD 5.505.50 1.771.77 0.000.00 0.540.54 900.0900.0 300.0300.0 0.7930.793
3333 BB 7.37.3 1.391.39 0.120.12 0.130.13 900.0900.0 300.0300.0 0.790.79
3434 BB 7.37.3 1.391.39 0.120.12 0.130.13 700700 1010 0.580.58
3535 BB 7.37.3 1.391.39 0.120.12 0.130.13 10001000 24002400 1.221.22
3636 EE 4.44.4 0.160.16 0.920.92 0.490.49 900.0900.0 300.0300.0 0.790.79
3737 EE 4.44.4 0.160.16 0.920.92 0.490.49 720720 1010 0.590.59
3838 EE 4.44.4 0.160.16 0.920.92 0.490.49 980980 28002800 1.271.27
3939 FF 3.83.8 0.100.10 0.880.88 0.880.88 900.0900.0 300.0300.0 0.790.79
4040 FF 3.83.8 0.100.10 0.880.88 0.880.88 690690 1010 0.570.57
4141 FF 3.83.8 0.100.10 0.880.88 0.880.88 10201020 20002000 1.171.17
4242 GG 6.76.7 0.970.97 0.250.25 0.300.30 900.0900.0 300.0300.0 0.790.79
4343 GG 6.76.7 0.970.97 0.250.25 0.300.30 670670 100100 0.570.57
4444 GG 6.76.7 0.970.97 0.250.25 0.300.30 970970 36003600 1.401.40
[관계식 1]A = (T + 0.2t)/1210[Relation 1]A = (T + 0.2t)/1210
(식에서, T는 가열온도를 나타내며, 단위는 ℃이고, t는 총 가열시간을 나타내며, 단위는 초이다.)(In the formula, T represents the heating temperature, the unit is ℃, and t represents the total heating time, the unit is seconds.)
하기 표 3에는 연속소둔 후 냉연강판의 제1 산화물층 두께를 측정하여 나타내었으며, 이후 열처리, 열간성형 및 냉각 후 부재의 제2 산화물층 두께 또한 측정하여 나타내었다. 여기서, 제1 산화물층 두께는 투과전자현미경(TEM)을 이용하여 측정하였으며, 제2 산화물층 두께는 투과전자현미경(TEM) 및 전자빔 미세 분석법(EPMA)을 이용하여 3군데 측정 후 평균한 결과치를 나타내었다. 또한, 품질열위 항목에 대하여 스케일 박리 여부를 육안으로 관찰하여 나타내었으며, 육안관찰 시, 면적 5mm2 이상의 스케일이 10점 이상 박리가 발생하면 열위하다고 판단하였다. 인산염 커버리지는 전자주사현미경(SEM)으로 조직 관찰 후 인산염 결정이 생성되지 않은 부분의 면적을 측정하여 품질열위 여부를 판단하였다. 이때, 인산염 결정 형성부가 70%를 넘으면 인산염 특성이 양호하다고 판단하였다. 또한, 제조된 부재에 대하여 항복강도, 인장강도 및 연신율을 측정하여 나타내었다. 항복강도, 인장강도 및 연신율은 JIS-5호 시편으로 ISO6892 규격에 의거 상온 인장시험이 진행되었다.Table 3 below 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. Here, 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. In addition, for quality inferiority items, scale peeling was visually observed and indicated, and when peeling of more than 10 points occurred on a scale with an area of 5 mm 2 or more during visual observation, it was judged to be inferior. 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.
시
편
번
호city
side
th
like 		강
종river
bell 		냉연강판cold rolled steel plate 부재absence 부재absence 구분division
제1산화물층first oxide layer 제2산화물층Second oxide layer 품질
열위
항목quality
inferior
item 		인산염
커버리지
(%)phosphate
coverage
(%) 		물성Properties
두께
(nm)thickness
(nm) 		두께
(μm)thickness
(μm) 		항복강도
(MPa)yield strength
(MPa) 		인장강도
(MPa)tensile strength
(MPa) 		연신율
(%)elongation
(%)
1One AA 474.4474.4 0.190.19 -- 86.186.1 14101410 20122012 5.35.3 발명예1Invention Example 1
22 BB 8.38.3 8.538.53 -- 98.298.2 13521352 20092009 66 발명예2Invention Example 2
33 CC 36.036.0 7.597.59 -- 92.992.9 425425 639639 15.215.2 발명예3Invention Example 3
44 DD 151.8151.8 4.604.60 -- 75.075.0 715715 11091109 9.89.8 발명예4Invention Example 4
55 EE 291.1291.1 2.622.62 -- 81.181.1 826826 10841084 13.513.5 발명예5Invention Example 5
66 FF 149.4149.4 5.585.58 -- 90.890.8 979979 12101210 12.612.6 발명예6Invention Example 6
77 GG 5.15.1 9.669.66 -- 95.195.1 14951495 21622162 4.84.8 발명예7Invention Example 7
88 HH 3.93.9 12.1512.15 스케일scale -- 908908 11271127 1313 비교예1Comparative Example 1
99 II 641.1641.1 0.0800.080 인산염phosphate 58.358.3 13471347 19821982 4.34.3 비교예2Comparative example 2
1010 JJ 965.5965.5 0.0320.032 인산염phosphate 61.861.8 11251125 16101610 6.26.2 비교예3Comparative example 3
1111 KK 4.24.2 11.8611.86 스케일scale -- 10591059 14771477 7.47.4 비교예4Comparative example 4
1212 LL 1.71.7 22.5822.58 스케일scale -- 14551455 19621962 4.74.7 비교예5Comparative Example 5
1313 MM 933.1933.1 0.0420.042 인산염phosphate 57.757.7 853853 10661066 17.117.1 비교예6Comparative Example 6
1414 NN 2.52.5 17.1517.15 스케일scale -- 988988 10771077 19.319.3 비교예7Comparative example 7
1515 OO 713.3713.3 0.0600.060 인산염phosphate 67.167.1 10011001 12251225 7.87.8 비교예8Comparative example 8
1616 PP 999.4999.4 0.0110.011 인산염phosphate 55.155.1 14651465 20622062 4.54.5 비교예9Comparative Example 9
1717 QQ 1.451.45 30.9730.97 스케일scale -- 894894 12501250 11.511.5 비교예10Comparative Example 10
1818 RR 726.5726.5 0.0570.057 인산염phosphate 68.068.0 901901 12671267 12.312.3 비교예11Comparative Example 11
1919 AA 474.4474.4 0.190.19 -- 86.186.1 14181418 20102010 5.25.2 발명예8Invention Example 8
2020 AA 2.12.1 19.1019.10 스케일scale -- 14761476 20532053 5.35.3 비교예12Comparative Example 12
2121 AA 761.2761.2 0.050.05 인산염phosphate 48.348.3 14001400 20722072 3.43.4 비교예13Comparative Example 13
2222 AA 686.7686.7 0.050.05 인산염phosphate 57.857.8 13981398 20252025 5.35.3 비교예14Comparative Example 14
2323 AA 4.74.7 16.9716.97 스케일scale -- 14151415 20072007 5.25.2 비교예15Comparative Example 15
2424 CC 36.036.0 7.597.59 -- 92.992.9 421421 637637 14.414.4 발명예9Invention Example 9
2525 CC 604.7604.7 0.080.08 인산염phosphate 53.553.5 411411 633633 13.913.9 비교예16Comparative Example 16
2626 CC 4.64.6 15.6715.67 스케일scale -- 471471 654654 1616 비교예17Comparative Example 17
2727 CC 3.93.9 17.8417.84 스케일scale -- 486486 699699 16.216.2 비교예18Comparative Example 18
2828 CC 717.0717.0 0.050.05 인산염phosphate 63.563.5 493493 696696 13.613.6 비교예19Comparative Example 19
2929 DD 151.8151.8 4.604.60 -- 75.075.0 728728 11601160 9.39.3 발명예10Invention Example 10
3030 DD 540.0540.0 0.090.09 인산염phosphate 48.548.5 723723 10171017 9.69.6 비교예20Comparative Example 20
3131 DD 861.2861.2 0.040.04 인산염phosphate 54.054.0 712712 11431143 9.59.5 비교예21Comparative Example 21
3232 DD 848.0848.0 0.040.04 인산염phosphate 60.060.0 736736 10371037 9.69.6 비교예22Comparative example 22
3333 BB 8.38.3 8.538.53 -- 98.298.2 13621362 20562056 5.95.9 발명예11Invention Example 11
3434 BB 8.38.3 0.0690.069 인산염phosphate 47.747.7 13341334 19981998 5.25.2 비교예23Comparative example 23
3535 BB 8.38.3 27.3627.36 스케일scale -- 13661366 20162016 5.25.2 비교예24Comparative example 24
3636 EE 291.1291.1 2.622.62 -- 81.181.1 862862 10231023 13.813.8 발명예12Invention Example 12
3737 EE 291.1291.1 0.0790.079 인산염phosphate 55.855.8 855855 10121012 12.612.6 비교예25Comparative Example 25
3838 EE 291.1291.1 29.7029.70 스케일scale -- 861861 10171017 12.112.1 비교예26Comparative example 26
3939 FF 149.4149.4 5.585.58 -- 90.890.8 974974 12741274 11.111.1 발명예13Invention Example 13
4040 FF 149.4149.4 0.060.06 인산염phosphate 64.964.9 963963 12371237 11.611.6 비교예27Comparative example 27
4141 FF 149.4149.4 17.8417.84 스케일scale -- 955955 12311231 12.712.7 비교예28Comparative example 28
4242 GG 5.15.1 9.669.66 -- 95.195.1 15161516 21362136 4.44.4 발명예14Invention Example 14
4343 GG 5.15.1 0.050.05 인산염phosphate 42.742.7 15261526 21962196 4.64.6 비교예29Comparative example 29
4444 GG 5.15.1 35.1635.16 스케일scale -- 14381438 21582158 4.54.5 비교예30Comparative Example 30
본 발명의 합금조성 및 제조조건을 만족하는 냉연강판 및 부재는 본 발명에서 제안하는 두께 범위의 제1 산화물층 및 제2 산화물층을 형성하였으며, 열간 성형 후에도 우수한 표면품질을 확보하였다.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.
도 1은 발명예 2와 비교예 10의 열간 성형 후 표면품질을 사진으로 나타낸 것이다. 비교예 10은 발명예 2와 비교하여 두꺼운 산화물이 형성되어 열위한 품질을 확인할 수 있다.Figure 1 is a photograph showing the surface quality of Inventive Example 2 and Comparative Example 10 after hot forming. In 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.
도 2는 발명예 1과 비교예 2의 열간 성형 후 인산염 커버리지를 나타낸 것이다. 비교예 2는 인산염 결정이 70% 미만으로 형성된 것을 확인할 수 있었다.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.
도 3은 열처리 온도 및 시간 조건에 따른 표면 품질의 변화를 나타낸 것이다. 열간 성형 온도 및 시간을 조절함에 따라 표면 상태를 관찰한 것으로, 열처리 조건이 관계식 1이 제한한 범위를 벗어나게 되면 열처리 후 표층에 과도한 제2 산화물층 형성으로 표층 스케일 박리가 발생하거나, 과도한 제1 산화물층의 형성에 기인하여 인산염 처리성이 열위해지는 등 표면 품질이 열위해지는 것을 확인할 수 있다.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.
도 4는 발명예 11과 비교예 24의 열간 성형 후 표면을 관찰한 사진이다. 비교예 24는 관계식 1에 의해 제한된 열처리 조건을 초과하여 열처리된 것으로, 발명예 11과 비교하여 표면을 육안으로 관찰하였을 때 스케일이 확인되었다.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.
비교예 1, 4, 5, 7 및 10은 각 원소의 함량이 본 발명이 제안하는 요구 범위에 미달하여 제1 산화물층의 형성이 적절치 못하여, 도 1에 보여지는 바와 같이, 열간 성형 후 제2 산화층의 두께가 10μm을 초과하여 열간 성형 후 표면 스케일이 과도하게 생겨 우수한 표면품질을 확보하지 못하였다.In Comparative Examples 1, 4, 5, 7, and 10, the content of each element was below the required range proposed by the present invention, so the formation of the first oxide layer was not appropriate, and as shown in Figure 1, the second oxide layer was formed after hot forming. As the thickness of the oxide layer exceeded 10 μm, excessive surface scale occurred after hot forming, and excellent surface quality was not secured.
비교예 2, 3, 6, 8, 9 및 11은 각 성분의 함량이 본 발명이 제안하는 요구 범위를 초과하여 소둔 후 과도한 제1 산화물층의 형성되었다. 이로 인해, 열간 성형 시 충분한 제2 산화물층이 형성되지 못하여, 70% 미만의 인산염 결정을 형성하여 표면품질이 열위하였다.In Comparative Examples 2, 3, 6, 8, 9, and 11, the content of each component exceeded the required range proposed by the present invention, and an excessive first oxide layer was formed after annealing. As a result, a sufficient second oxide layer was not formed during hot forming, and less than 70% of phosphate crystals were formed, resulting in poor surface quality.
또한, 연속소둔 시, 각 구간별 승온속도 중 본 발명에서 제안하는 범위를 하나라도 초과한 비교예 12, 15, 17, 18 및 20의 경우, 제1 산화물층이 충분히 형성되지 못하여, 열간 성형 후 과도한 제2 산화물층 형성으로 표층 스케일 박리 등 우수한 표면 품질을 확보하지 못하였다.In addition, in the case of Comparative Examples 12, 15, 17, 18, and 20, in which any one of the temperature increase rates for each section exceeded the range proposed in the present invention during continuous annealing, the first oxide layer was not sufficiently formed, and after hot forming Due to excessive formation of the second oxide layer, excellent surface quality, such as surface scale peeling, could not be secured.
비교예 13, 14, 16 및 19의 경우, 각 구간별 분위기 온도 승온속도가 본 발명에서 제한하는 승온속도 하한에 미달하여 과도한 제1 산화물층 형성으로 인산염 처리성이 열위해져 우수한 표면 품질을 확보하지 못하였다.In the case of Comparative Examples 13, 14, 16, and 19, the rate of increase in atmospheric temperature in each section was below the lower limit of the rate of increase in temperature limited by the present invention, resulting in poor phosphate treatment properties due to excessive formation of the first oxide layer, making it impossible to secure excellent surface quality. I couldn't do it.
또한, 각 구간별 분위기 온도가 일부 하한 값에 미달하거나 상한 값을 초과한 비교예 21 및 22의 경우에도 과도한 제1 산화물층이 형성되어, 열간 성형 후 제2 산화물층의 형성이 용이하지 않아 인산염 처리성이 열위해져 우수한 표면 품질을 확보하지 못하였다.In addition, in Comparative Examples 21 and 22 in which the ambient temperature for each section was below some lower limit or exceeded the upper limit, an excessive first oxide layer was formed, making it difficult to form a second oxide layer after hot forming, resulting in phosphate Processability was poor and excellent surface quality could not be secured.
비교예 23, 25, 27 및 29의 경우, 관계식 1에 제한된 조건의 하한에 미달되어 제2 산화물층이 충분히 형성되지 못하여 열위한 인산염 처리성을 보였으며, 제안하는 범위의 상한을 초과한 비교예 24, 26, 28 및 30의 경우, 제2 산화물층 형성 두께가 두꺼워 Fe 스케일이 다량 발생하여 표면품질이 열위하였다.In the case of Comparative Examples 23, 25, 27, and 29, the lower limit of the conditions limited in relational equation 1 was not met and the second oxide layer was not sufficiently formed, showing poor phosphate treatability, and the comparative example exceeded the upper limit of the proposed range. In the case of 24, 26, 28, and 30, the second oxide layer was formed thick and a large amount of Fe scale was generated, resulting in inferior surface quality.
이상에서 실시예를 통하여 본 발명을 상세하게 설명하였으나, 이와 다른 형태의 실시예들도 가능하다. 그러므로, 이하에 기재된 청구항들의 기술적 사상과 범위는 실시예들에 한정되지 않는다.Although the present invention has been described in detail through examples above, other forms of embodiments are also possible. Therefore, the technical spirit and scope of the claims set forth below are not limited to the embodiments.

Claims (20)

  1. 소지강판 및 상기 소지강판 상의 제1 산화물층을 포함하고,It includes a base steel plate and a first oxide layer on the base steel plate,
    상기 제1 산화물층은 Fe, Mn, Cr, Si 중 2종 이상을 포함하고, 5~500nm의 두께를 가지는 냉연강판.The first oxide layer contains two or more types of Fe, Mn, Cr, and Si, and has a thickness of 5 to 500 nm.
  2. 청구항 1에 있어서,In claim 1,
    상기 소지강판은 중량%로, 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%, 잔부 Fe 및 기타 불가피한 불순물을 포함하는 냉연강판.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%, cold rolled steel sheet containing the balance Fe and other inevitable impurities.
  3. 청구항 2에 있어서,In claim 2,
    상기 소지강판은 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% 중 1종 이상을 포함하는 냉연강판.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~ Cold rolled steel sheet containing 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%.
  4. 청구항 1 내지 3 중 어느 한 항에 있어서,The method of any one of claims 1 to 3,
    상기 제1 산화물층은 중량%로 Si, Mn 및 Cr 함량의 합이 30% 이상인 냉연강판.The first oxide layer is a cold-rolled steel sheet in which the sum of Si, Mn, and Cr contents in weight percent is 30% or more.
  5. 청구항 1 내지 4 중 어느 한 항에 있어서,The method of any one of claims 1 to 4,
    상기 냉연강판은 미세조직으로 페라이트 및 세멘타이트를 5면적% 이상 포함하는 냉연강판.The cold-rolled steel sheet is a cold-rolled steel sheet containing more than 5% by area of ferrite and cementite as a microstructure.
  6. 소지강판, 상기 소지강판 상의 제1 산화물층 및 상기 제1 산화물층 상의 제2 산화물층을 포함하고,It includes a base steel plate, a first oxide layer on the base steel plate, and a second oxide layer on the first oxide layer,
    상기 제1 산화물층은 Fe, Mn, Cr, Si 중 2종 이상을 포함하고,The first oxide layer includes two or more types of Fe, Mn, Cr, and Si,
    상기 제2 산화물층은 Fe계 산화물로 구성되며, 0.1~10μm의 두께를 가지는 부재.The second oxide layer is composed of Fe-based oxide and has a thickness of 0.1 to 10 μm.
  7. 청구항 6에 있어서,In claim 6,
    상기 소지강판은 중량%로, C: 0.05~0.4%, Si: 0.5~3.0%, Cr: 0.3% 이상 5.0% 미만, 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%, 잔부 Fe 및 기타 불가피한 불순물을 포함하는 부재.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 to 0.02%, N: 0.001 to 0.02%, free of residual Fe and other unavoidable impurities.
  8. 청구항 7에 있어서,In claim 7,
    상기 소지강판은 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% 중 1종 이상을 포함하는 부재.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~ 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%.
  9. 청구항 6 내지 8에 있어서,The method of claims 6 to 8,
    상기 제2 산화물층은 중량%로 Si, Mn 및 Cr 함량의 합이 30% 미만인 부재.The second oxide layer is a member in which the sum of Si, Mn, and Cr contents in weight percent is less than 30%.
  10. 청구항 6 내지 9 중 어느 한 항에 있어서,The method of any one of claims 6 to 9,
    상기 부재는 미세조직으로 마르텐사이트 또는 베이나이트를 주상으로 포함하는 부재.The member is a member whose microstructure includes martensite or bainite as the main phase.
  11. 청구항 6 내지 10 중 어느 한 항에 있어서,The method of any one of claims 6 to 10,
    상기 부재는 인장강도가 500MPa 이상인 부재.The member has a tensile strength of 500 MPa or more.
  12. 강 슬라브를 재가열하는 단계;Reheating the steel slabs;
    상기 재가열된 강 슬라브를 열간압연하는 단계;hot rolling the reheated steel slab;
    상기 열간압연된 강판을 냉각하여 권취하는 단계;Cooling and winding the hot-rolled steel sheet;
    상기 권취된 강판을 냉간압연하는 단계; 및Cold rolling the rolled steel sheet; and
    상기 냉간압연된 강판을 연속소둔하는 단계를 포함하고,Continuously annealing the cold rolled steel sheet,
    상기 연속소둔 시, 상온~700℃의 분위기 온도에서 승온속도가 3.0~20.0℃/s이고, 700~800℃의 분위기 온도에서 승온속도가 0.08~1.5℃/s이고, 800~900℃의 분위기 온도에서 승온속도가 0.01~1.5℃/s이고, 900~1000℃의 분위기 온도에서 승온속도가 0.01~1.0℃/s인 냉연강판 제조방법.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, the temperature increase rate is 0.08 to 1.5°C/s at an ambient temperature of 700 to 800°C, and the ambient temperature is 800 to 900°C. A method of manufacturing a cold-rolled steel sheet in which 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.
  13. 청구항 12에 있어서,In claim 12,
    상기 강 슬라브는 중량%로, 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%, 잔부 Fe 및 기타 불가피한 불순물을 포함하는 냉연강판 제조방법.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%, Method for manufacturing cold rolled steel sheets containing S: 0.0001~0.02%, N: 0.001~0.02%, remainder Fe and other unavoidable impurities.
  14. 청구항 13에 있어서,In claim 13,
    상기 강 슬라브는 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% 중 1종 이상을 포함하는 냉연강판 제조방법.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~ A method of manufacturing a cold rolled steel sheet containing 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%.
  15. 청구항 12 내지 14 중 어느 한 항에 있어서,The method of any one of claims 12 to 14,
    상기 재가열은 1000~1300℃의 온도범위에서 행하고,The reheating is performed in a temperature range of 1000 to 1300°C,
    상기 열간압연은 Ar3~1000℃의 마무리 압연온도로 행하며,The hot rolling is performed at a finish rolling temperature of Ar3~1000℃,
    상기 권취는 Ms~750℃의 온도범위에서 행하고,The winding is performed in a temperature range of Ms to 750°C,
    상기 냉간압연은 30~80%의 압하율로 행하는 것인 냉연강판 제조방법.A method of manufacturing a cold rolled steel sheet, wherein the cold rolling is performed at a reduction ratio of 30 to 80%.
  16. 청구항 12 내지 15 중 어느 한 항에 있어서,The method of any one of claims 12 to 15,
    상기 연속소둔은 강판온도가 700~900℃인 온도범위에서 행하고, 연속소둔 시간은 1~1000초인 냉연강판 제조방법.The continuous annealing is performed in a temperature range of 700 to 900 ° C., and the continuous annealing time is 1 to 1000 seconds.
  17. 청구항 12 내지 16 중 어느 한 항의 냉연강판을 열처리하는 단계; 및Heat treating the cold rolled steel sheet of any one of claims 12 to 16; and
    상기 열처리된 강판을 열간 성형 후 냉각하는 단계를 포함하고,Comprising the step of cooling the heat-treated steel sheet after hot forming,
    상기 열처리 시, 하기 관계식 1에서 정의되는 A 값이 0.6~1.0인 부재 제조방법.A method of manufacturing a member in which, during the heat treatment, the A value defined in Equation 1 below is 0.6 to 1.0.
    [관계식 1][Relational Expression 1]
    A = (T + 0.2t)/1210A = (T + 0.2t)/1210
    (식에서, T는 가열온도를 나타내며, 단위는 ℃이고, t는 총 가열시간을 나타내며, 단위는 초이다.)(In the formula, T represents the heating temperature, the unit is ℃, and t represents the total heating time, the unit is seconds.)
  18. 청구항 17에 있어서,In claim 17,
    상기 열처리 시, 가열온도까지 1~1000℃/s의 분위기 승온속도로 가열하는 부재 제조방법.During the heat treatment, a method of manufacturing a member is heated at an atmospheric temperature increase rate of 1 to 1000°C/s to the heating temperature.
  19. 청구항 17 또는 18에 있어서,The method of claim 17 or 18,
    상기 열처리 시, 가열온도는 700~1000℃이고, 가열시간은 150~1000초인 부재 제조방법.During the heat treatment, the heating temperature is 700 to 1000°C and the heating time is 150 to 1000 seconds.
  20. 청구항 17 내지 19 중 어느 한 항에 있어서,The method of any one of claims 17 to 19,
    상기 열간 성형 후 냉각 시, 10~1000℃/s의 냉각속도로 Mf 온도 이하까지 냉각하는 부재 제조방법.A method of manufacturing a member that cools to the Mf temperature or lower at a cooling rate of 10 to 1000°C/s when cooling after hot forming.
PCT/KR2023/012140 2022-08-22 2023-08-17 Cold rolled steel sheet for hot-press forming having excellent surface quality, hot-press-formed member, and method for manufacturing same WO2024043606A1 (en)

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