WO2019088552A1 - Ultra-high strength cold-rolled steel sheet having excellent cold rolling property, and method for manufacturing same - Google Patents

Ultra-high strength cold-rolled steel sheet having excellent cold rolling property, and method for manufacturing same Download PDF

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WO2019088552A1
WO2019088552A1 PCT/KR2018/012595 KR2018012595W WO2019088552A1 WO 2019088552 A1 WO2019088552 A1 WO 2019088552A1 KR 2018012595 W KR2018012595 W KR 2018012595W WO 2019088552 A1 WO2019088552 A1 WO 2019088552A1
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steel sheet
less
cold
rolled steel
hot
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PCT/KR2018/012595
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French (fr)
Korean (ko)
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이제웅
한상호
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주식회사 포스코
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • 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
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to a cold-rolled steel sheet having an ultra-high strength of at least 2000 MPa and a method for manufacturing the steel sheet.
  • AHSS Advanced High Strength Steel
  • DP Dual Phase
  • TRIP Transformation Induced Plasticity
  • Complex Phase composite structure steel
  • hot press forming As a component capable of applying structural members to secure collision safety, hot press forming (hot press forming) which ensures final strength by heat treatment at high temperature and quenching after contact with a water-cooled die after molding, Although the steel is in the spotlight, it has the problems of additional capital investment, heat treatment and process cost increase.
  • a roll forming method is a method of producing a complicated shape through multi-step roll forming.
  • an ultra-high strength material having a low elongation Is being applied to the molding of parts of an automobile.
  • Such an ultra-high strength steel material generally has a tempered martensite microstructure which is tempered with martensite and martensite.
  • the cooling rate after annealing is very important, and therefore, continuous annealing It is easy to manufacture in furnace.
  • Patent Document 1 proposes a method for producing a cold rolled steel sheet having high temper- ature and high ductility at the same time by obtaining tempered martensite transformation by microstructure after heat treatment in a continuous annealing process and also having a high plate shape. It is impossible to ignore the possibility of induction of internal dent in an annealing furnace.
  • the cooling rate is inevitably deteriorated. Therefore, in order to obtain the above-mentioned martensite microstructure, it is a top priority to secure sufficient hardenability by adjusting the alloy component.
  • the carbon content is limited to 0.2% by weight or less.
  • the content of Mn is 3.0 to 4.0% by weight and the Mn content is quite high. .
  • Patent Document 1 Japanese Laid-Open Patent Application No. 2010-090432
  • Patent Document 2 Korean Patent Application No. 2015-0098217
  • the present invention has been made in order to overcome the above-described problems of the prior art, and it is an object of the present invention to provide a continuous annealing apparatus capable of using roll cooling, mist cooling, gas cooling, And an object of the present invention is to provide an ultra-high strength cold-rolled steel sheet, a coated steel sheet and a method of manufacturing the same, which are excellent in product shape and cold rolling property, which are manufactured using a hot-dip galvanizing system.
  • the present invention provides a steel sheet comprising, by weight, 0.4 to 0.6% of C, 1.5 to 3.0% of Mn, 0.7 to 2.0% of Cr, 0.03% or less of P Mo: not more than 1.0% (excluding 0%), and B: not more than 0.005% (excluding 0%), N: not more than 0.01% %), Remaining Fe and unavoidable impurities, and satisfies the following relational expression (1)
  • the present invention relates to a cold-rolled steel sheet having excellent cold-rolling properties, comprising a steel microstructure having an area fraction of 90% or more of martensite and 10% or less of a secondary phase.
  • the present invention relates to a method for producing an ultra-high strength cold rolled steel sheet excellent in cold rolling resistance.
  • an ultra-high-strength cold-rolled steel sheet of 2000 MPa or more can be produced by using a continuous annealing process using a conventional cooling facility, and it can have a superior surface shape quality as compared with the martensitic steel produced by using water cooling.
  • ultra-high strength cold-rolled steel sheets contain a large amount of alloy components, and therefore, the hot-rolled microstructure contains a hard microstructure such as bainite and martensite, there was.
  • the present invention provides a useful effect of manufacturing a cold-rolled steel sheet having improved cold rolling property and widthwise material deviation of an ultra-high strength steel material by securing 80% or more of pearlite by hot-rolled microstructure by utilizing an open-air component system or a corresponding alloy component system have.
  • Fig. 1 is a photograph of a microstructure observed by a transmission electron microscope (TEM) after the cold rolling and continuous annealing process of Specimen No. 2-1 in this embodiment.
  • TEM transmission electron microscope
  • the present inventors have found that there are problems such as variations in material in the width direction of a hot-rolled steel sheet having an ultra-high-strength steel mainly containing bainite and martensite microstructure and high cold rolling load, In order to solve the problems that were limited to As a result, it is possible to appropriately control the alloy composition and the manufacturing method to secure a full pearlite or a corresponding large amount of pearlite microstructure after hot rolling to reduce variations in material in the width direction of the hot-rolled steel sheet, It is possible to provide a steel sheet excellent in cold rolling resistance by reducing the load, and the present invention is presented.
  • an ultrahigh strength cold rolled steel sheet excellent in the lateral direction material deviation and cold rolling property comprising 0.4 to 0.6% of C, 1.5 to 3.0% of Mn, 0.7 to 2.0% P: not more than 0.03% (excluding 0%), S: not more than 0.01% (excluding 0%), N: not more than 0.01% (excluding 0%), sol.Al: not more than 0.1% , At least 90% of at least one of the steel microstructure and at least one of the residual Fe and unavoidable impurities, satisfying the following relational expression 1: And a second phase of 10% or less.
  • Carbon (C) is an important component in the production of a steel sheet having pearlite microstructure composed of ferrite and cementite after hot rolling in the present invention. Generally, as the C content increases, a high percentage of pearlite structure can be secured. Is an indispensable element to be added. In addition, since it is the largest element that contributes to the strength increase in the martensite microstructure after cold-rolling continuous annealing, it is indispensable to obtain an ultra-high strength of 2000 MPa or more.
  • the C content is less than 0.4%, it is difficult to sufficiently secure pearlite, and it is difficult to secure the strength of martensite to obtain an ultra-high strength of 2000 MPa or more.
  • the C content is more than 0.6%, the carbide in the pearlite is excessively formed and the phase-to-phase compatibility with the precipitate is lowered, so that the hot rolling property and the room temperature ductility can be lowered, .
  • Mn in steel is one of the representative elements that inhibits ferrite formation and facilitates the formation of austenite, and is an effective element for increasing the strength of martensite.
  • Mn content is less than 1.5%, the ferrite is easily formed during the continuous cooling process during the continuous annealing process and the strength becomes low.
  • Mn content exceeds 3.0%, the bending deterioration due to the formation of manganese bands due to segregation, And the content of the alloy is limited due to an increase in the cost of the alloy iron due to the excessive amount.
  • Cr is one of the essential elements added to obtain martensite transformation during the continuous annealing process of the cooling equipment because it exhibits the property of increasing the hardenability of the steel similar to Mn.
  • Cr plays a role in lowering the carbon content required for the formation of vacancies, allowing pearlite microstructure transformation during hot working even at low carbon content. It also promotes the formation of cementite and reduces the spacing of the pearlite laminates to promote cementite spheroidization. It also has the property of further improving the corrosion resistance of the steel sheet even by adding a small amount.
  • the mechanical properties may be adversely affected and the surface scale pickling property may be deteriorated during pickling.
  • Aluminum oxide (sol.Al) is an element to be added for grain refinement and deoxidation of steel.
  • content exceeds 0.1%, there is a possibility of occurrence of defective surface of hot-dip galvanized steel sheet due to over- There is a problem that not only the size is increased but also the manufacturing cost is increased.
  • the lower limit is not particularly limited, but 0% is excluded considering the level that is unavoidably added during the manufacturing process.
  • ⁇ P 0.03% or less (excluding 0%)
  • P (P) is an element favorable in securing strength.
  • P is an element favorable in securing strength.
  • 0% is excluded considering the level that is inevitably added during the manufacturing process.
  • ⁇ S 0.01% or less (excluding 0%)
  • S Sulfur
  • S in the steel has a problem of increasing the possibility of generating fumed brittleness. Therefore, it is preferable to control the content to 0.01% or less. However, 0% is excluded considering the level that is inevitably added during the manufacturing process.
  • ⁇ N 0.01% or less (excluding 0%)
  • Nitrogen (N) is an element which is inevitably added as an impurity element in the steel, and it is preferable to control the operating conditions to 0.01% or less, which is a possible range. However, 0% is excluded considering the level that is inevitably added during the manufacturing process.
  • At least one of Mo: 1.0% or less (excluding 0%) and B: 0.005% or less (excluding 0%) is included.
  • Mo plays an important role in enhancing the hardenability of steel such as C, Mn, and Cr, and is an element having a large effect of inhibiting ferrite and bainite phase transformation when added with Cr.
  • the content is more than 1.0%, it is limited to the increase of the amount of alloy iron due to the excessive amount of alloy.
  • 0% is excluded considering the level that is inevitably added during the manufacturing process.
  • Boron (B) has an advantage of suppressing ferrite formation, and has an advantage of suppressing the formation of ferrite upon cooling after annealing.
  • B has an advantage of suppressing ferrite formation, and has an advantage of suppressing the formation of ferrite upon cooling after annealing.
  • B exceeds 0.005%, but rather is a problem that ferrite is formed by promoting the precipitation of Fe 23 (C, B) 6 restrict the content according.
  • 0% is excluded considering the level that is inevitably added during the manufacturing process.
  • each element symbol represents the content of each element in weight%, and is calculated as 0 if not included.
  • the above-mentioned relational expression 1 is designed in consideration of the influence of each element for producing steel having a certain area fraction or more of pearlite required in the present invention after hot working and an alloy component system for obtaining a martensite structure after cold annealing.
  • the value defined by the relational expression 1 is less than 1.6, it is difficult to secure pearlite of 80% or more by area after hot rolling, and it is difficult to secure martensite of 90 area% or more after cold rolling continuous annealing. On the other hand, if the value is more than 3.52, elongation may be lowered due to addition of a large amount of alloying elements.
  • the remainder of the present invention is iron (Fe).
  • impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.
  • the cold-rolled steel sheet of the present invention can produce a cold-rolled steel sheet having a tensile strength of 2000 MPa or more including a martensite and a residual secondary phase of 90% or more in area fraction.
  • the secondary phase includes ferrite and bainite microstructure.
  • the steel sheet of the present invention may further have one of a zinc plating layer and a galvanized zinc plating layer formed thereon.
  • the method of manufacturing an ultra-high strength cold rolled steel sheet according to the present invention comprises the steps of: heating a steel slab having the above composition to 1100 to 1300 ⁇ ; Preparing a hot rolled steel sheet by subjecting the heated slab to finish hot rolling in a temperature range of Ar 3 + 5 ° C to Ar 3 + 95 ° C; Winding the hot rolled steel sheet at a temperature in the range of 550 to 700 ⁇ ⁇ to produce a hot rolled coil having a microstructure of 80% or more of pearlite and 20% or less of ferrite in an area fraction; Rolling the rolled hot-rolled steel sheet at a reduction ratio of 40 to 80%; And a step of subjecting the cold-rolled cold-rolled steel sheet to continuous annealing at 100 to 250 ° C to obtain an ultra-high-strength cold-rolled steel sheet having an area fraction of 90% or more of martensite and 10% or less of a second phase; .
  • the steel slab having the above-described alloy composition is heated to a temperature range of 1100 to 1300 DEG C for hot rolling.
  • the heating temperature is less than 1100 ° C, it is difficult to uniformize the structure and components of the slab, and if the heating temperature is more than 1300 ° C, problems of surface oxidation and equipment deterioration may occur.
  • the heated slab is subjected to finish hot-rolling the heated slab in a temperature range of Ar 3 + 5 ° C to Ar 3 + 95 ° C.
  • the final hot rolling temperature is lower than Ar3 + 5 deg. C, there is a possibility of an abnormal reverse rolling of ferrite and austenite, which may cause difficulty in control of mixed grain structure and plate shape in the steel surface layer, and may cause material nonuniformity.
  • the finishing hot rolling is preferably performed in a single phase of austenite which is in the range of Ar 3 + 5 ° C. to Ar 3 + 95 ° C.
  • the Ar3 temperature can be defined by the following relational expression (2).
  • the hot-rolled steel sheet is wound such that the microstructure contains 80% or more of pearlite and 20% or less of ferrite in an area fraction.
  • the microstructure of the hot-rolled coil according to the present invention contains 80% or more of pearlite and 20% or less of ferrite in an area fraction.
  • the pearlite is less than 80%, the material deviation in the width direction of the hot- It is difficult to induce the desired amount of martensite transformation after the heat treatment.
  • the cermetite in the pearlite is elongated in a lamellar form, but passes through a cold rolling and continuous annealing heat treatment process and is segmented and spheroidized. Therefore, the microstructure after the continuous annealing heat treatment contains spheroidized cementite in martensite.
  • the hot-rolled steel sheet of the present invention has a tensile strength of 1200 MPa or less and a high tensile strength, it exhibits a long elongation in the rolling direction due to the pearlite structure having elongated lamellar cementite. Which is superior to the light microstructure of bainite and martensite.
  • the winding temperature range is preferably limited to a temperature range of 550 to 700. If the coiling temperature is less than 550 ⁇ , a low-temperature transformed structure, that is, bainite or martensite is generated to cause excessive increase in the strength of the hot-rolled steel sheet, thereby causing problems such as defective shape due to excessive load during cold rolling, And it may be difficult to obtain pearlite microstructure for the purpose of the present invention.
  • the present invention may further include a step of performing batch annealing at 200 to 700 ° C after the winding step to reduce the rolling load before cold rolling as required.
  • the hot-rolled structure When the temperature is lower than 200 ° C, the hot-rolled structure is not sufficiently softened and does not significantly affect the reduction of the rolling load. If the temperature exceeds 700 ° C, pearlite decomposition may occur due to high temperature annealing.
  • the present invention is not particularly limited.
  • the rolled hot-rolled steel sheet is cold-rolled at a reduction ratio of 40 to 80% to obtain a cold-rolled steel sheet.
  • the reduction rate is less than 40%, it may be difficult to secure a target thickness.
  • the cold rolling can be performed at room temperature.
  • the cold-rolled steel sheet is continuously annealed in a temperature range of Ac 3 - 5 ° C to Ac 3 + 80 ° C to obtain a tensile strength of at least 2000 MPa after cold rolling.
  • the Ac3 temperature can be defined by the following equation (3).
  • spheroidized cementite (Fe 3 C) is present in the martensite and the size is limited to a size of 50 nm or more.
  • spheroidized cementite (Fe 3 C) generated during the heat treatment from the cermetite in pearlite, there may be another type of carbide in the final structure, martensite.
  • transition carbides have a diameter limited to 50 nm or less and can be produced by a tempering heat treatment or the like and are often called transition carbides. These transition carbides are often produced at low tempering temperatures (below 300 ° C), and their chemical equivalents depend on the temperature at which they are produced, usually in the order of a few nanometers.
  • the final microstructure subjected to the annealing heat treatment is characterized by an A value of not less than 3 according to the following relational expression (4).
  • A A X / A Y
  • a X denotes the number of cementite having an aspect ratio of not less than 1.5 in 1 mm 2 area
  • a Y denotes the number of cementite having an aspect ratio within the same area of less than 1.5.
  • the annealing temperature is less than Ac3-5 deg. C, the phase transformation to austenite is small and the martensite fraction obtained after the final continuous annealing is limited.
  • Ac3 + 80 deg. C the austenite grain size becomes large, There is a fear that the tensile strength is inhibited. Therefore, continuous annealing is preferable in the temperature range of Ac3-5 deg. C to Ac3 + 80 deg.
  • the method may further include plating the cold rolled steel sheet.
  • the plating method and plating type are not particularly limited because they do not greatly affect the material properties even under normal operating conditions.
  • plating can be performed with zinc or a zinc alloy, and plating can be performed using a hot-dip coating method, an alloying hot-dip coating, an electroplating method, or the like.
  • the cold-rolled steel sheet is tempered by heat treatment.
  • This additional tempering heat treatment is limited to a temperature range of 100 to 250 DEG C and the time is not particularly limited.
  • the reason for the additional tempering heat treatment is as follows. In order to obtain a tensile strength of at least 2000 MPa, it is very important to bring the microstructure of the steel sheet into the martensite, and it is only necessary to increase the strength of the martensite itself.
  • the strength of martensite is influenced by alloy composition, packet size, block size, etc. Among them, the effect of alloying elements is very high. Among the alloying elements, carbon is the biggest contributor to the strength increase. On the other hand, carbon plays a very large role in increasing the strength of martensite, and at the same time, toughness of martensite is lowered.
  • tempering heat treatment can precipitate carbons in the martensite in the form of carbide to give toughness again. If the tempering temperature is less than 100 ⁇ ⁇ , the carbon is hardly precipitated in the form of carbide, and redistribution into martensite defects (dislocation, vacancy, etc.) only occurs and the desired toughness effect is insignificant. When the temperature exceeds 250 ° C., martensite brittleness occurs and the ductility is greatly reduced. This phenomenon is often referred to as Tempered Martensite Embrittlement (TME). Therefore, the tempering heat treatment is preferably performed in a range of 100 ° C to 250 ° C.
  • the slabs having the composition shown in the following Table 1 were heat-treated in a 1200 ° C heating furnace for 1 hour and then subjected to finish hot-rolling at 880 ° C. Then, the hot rolled material was charged into a preheated furnace at 650 ° C and held for 1 hour to simulate hot-rolled coiling by cold rolling, followed by pickling and cold rolling.
  • annealing was carried out at various annealing temperature conditions as shown in Table 2 below, followed by gradual cooling to 3O < 0 > C and 650 < 0 > C per second and cooling to 440 & After over-heat treatment for 360 seconds, it was cooled to room temperature to 3 ° C per second.
  • the hot-rolled steel sheet was annealed at 3 ° C / sec to 650 ° C / sec, cooled to 660 ° C / 560 ° C / sec and annealed at 460 ° C.
  • the microstructure after cold rolling continuous annealing contains martensite of 90% or more in an area fraction,
  • the maximum tensile strength after tempering was more than 2000 MPa and the total elongation was 3% or more.
  • the maximum tensile strength after tempering may not satisfy the maximum tensile strength of more than 2000 MPa due to insufficient martensite, It was confirmed that the tensile strength was insufficient or the toughness was not given when the tempering temperature condition was not met, so that the total elongation was less than 3%.
  • the microstructure was observed after the application of the separating etching method using a scanning electron microscope (SEM). Specifically, the size (the length of the major axis / the minor axis length) for measuring the aspect ratio of the cementite in the microstructure in the cold- was measured using a transmission electron microscope (TEM) microstructure observation photograph as shown in Fig. Fig. 1 is a photograph of a microstructure observed by a transmission electron microscope (TEM) after the cold rolling and continuous annealing process of Specimen No. 2-1 in this embodiment.
  • TEM transmission electron microscope

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Abstract

Provided are an ultra-high strength cold-rolled steel sheet having an excellent cold rolling property, and a method for manufacturing the same. A cold-rolled steel sheet of the present invention includes, by weight %, at least one among 0.4-0.6% of C, 1.5-3.0% of Mn, 0.7-2.0% of Cr, 0.03% or less (exclusive of 0%) of P, 0.01% or less (exclusive of 0%) of S, 0.01% or less (exclusive of 0%) of N, 0.1% or less (exclusive of 0%) of sol.Al, 1.0% or less(exclusive of 0%) of Mo, and 0.005% or less (exclusive of 0%) of B, and a balance of Fe and inevitable impurities; satisfies relational formula 1; and has a steel microstructure comprising, by area fraction, 90% or higher of martensite and 10% or less of a secondary phase.

Description

냉간압연성이 우수한 초고강도 냉연강판 및 이의 제조방법Ultra-high strength cold-rolled steel sheet excellent in cold-rolling property and method for manufacturing the same
본 발명은 자동차의 경량화 및 충돌 성능 향상에 적용되는 초고강도 강판 및 이의 제조방법에 관한 것으로, 보다 상세하게는 인장 강도 2000MPa 이상의 초고강도를 갖는 냉연, 도금강판 및 이의 제조방법에 관한 것이다.More particularly, the present invention relates to a cold-rolled steel sheet having an ultra-high strength of at least 2000 MPa and a method for manufacturing the steel sheet.
최근 자동차 소재 경량화를 통한 연비 향상 및 승객 안전 등의 이유로 인한 자동차용 철강소재의 강도 향상 노력이 지속 되고 있다. 이를 위하여 AHSS(Advanced High Strength Steel)이 오랜 기간 개발, 발전되고 있으며 대표적으로는 Dual Phase(DP) steel(이상조직강), Transformation Induced Plasticity(TRIP) steel(변태유기소성강), Complex Phase(CP) steel(복합조직강) 등을 들 수 있다. 이들 강 종에서는 탄소 및 합금원소의 증가를 통해 강도를 높일 수 있으나 현재 약 1200MPa급의 인장 강도가 한계이다. Recently, efforts have been made to improve the strength of automotive steel due to improvements in fuel efficiency and passenger safety through weight reduction of automobiles. For this purpose, Advanced High Strength Steel (AHSS) has been developed and developed for a long time. Typical examples are Dual Phase (DP) steel, Transformation Induced Plasticity (TRIP) steel, Complex Phase ) steel (composite structure steel). In these steels, strength can be increased by increasing carbon and alloying elements, but the tensile strength is about 1200 MPa.
또한 충돌 안전성을 확보하기 위한 구조부재의 적용이 가능한 부품으로써, 고온에서 열처리 및 성형 후 수냉 다이(Water-cooled Die)와의 접촉을 통한 급냉에 의하여 최종 강도를 확보하는 열간 프레스 성형(Hot Press Forming)강이 각광받고 있으나, 추가 설비 투자비, 열처리 및 공정비용의 증가라는 문제점을 지니고 있다.In addition, as a component capable of applying structural members to secure collision safety, hot press forming (hot press forming) which ensures final strength by heat treatment at high temperature and quenching after contact with a water-cooled die after molding, Although the steel is in the spotlight, it has the problems of additional capital investment, heat treatment and process cost increase.
한편 일반 냉간 프레스 성형(Cold Press Forming) 및 열간 프레스 성형(Hot Press Forming)과 달리, 롤 포밍(Roll Forming) 공법은 다단 롤 포밍을 통하여 복잡한 형상을 제작하는 방법인데, 통상 연신율이 낮은 초고강도 소재의 부품 성형에 적용이 확대되고 있다. 이러한 초고강도 철강소재는 일반적으로 마르텐사이트 및 마르텐사이트를 템퍼링한 템퍼트 마르텐사이트(tempered martensite) 미세조직을 갖는데, 이를 위해서는 소둔 후의 냉각속도가 매우 중요하고, 이에 따라 주로 수냉각 설비를 갖춘 연속 소둔로에서 제조가 용이하다. 하지만 수냉각 시 제품의 폭 방향, 길이방향 냉각능 차이에 따른 온도편차로 인한 표면 형상 품질이 나빠지게 되어 롤 포밍 시 작업성이 나빠지고 위치별 재질 편차가 나는 단점을 나타낸다. Unlike ordinary cold press forming and hot press forming, a roll forming method is a method of producing a complicated shape through multi-step roll forming. Usually, an ultra-high strength material having a low elongation Is being applied to the molding of parts of an automobile. Such an ultra-high strength steel material generally has a tempered martensite microstructure which is tempered with martensite and martensite. For this purpose, the cooling rate after annealing is very important, and therefore, continuous annealing It is easy to manufacture in furnace. However, the quality of the surface shape due to the temperature variation due to the difference in the cooling properties of the product in the width direction and the longitudinal direction is deteriorated during the water cooling, which leads to deterioration in workability in roll forming and disadvantage in material deviation in each position.
특허문헌 1에서는 연속 소둔 공정 열처리 후, 미세조직으로 템퍼드 마르텐사이트 변태를 얻고, 이를 활용하여 고강도와 고연성을 동시에 얻으며 판 형상도 뛰어난 냉연강판의 제조방법을 제공하는데, Si다량 함유에 기인한 소둔로 내 덴트 유발 가능성을 무시할 수 없다.Patent Document 1 proposes a method for producing a cold rolled steel sheet having high temper- ature and high ductility at the same time by obtaining tempered martensite transformation by microstructure after heat treatment in a continuous annealing process and also having a high plate shape. It is impossible to ignore the possibility of induction of internal dent in an annealing furnace.
수냉각 설비가 없는 연속 소둔로 공정에서는 냉각속도가 나빠질 수밖에 없기 때문에 기 언급된 마르텐사이트 미세조직을 얻기 위해서는 합금성분 조정을 통한 충분한 경화능 확보가 최우선 과제이다. 특허문헌 2에서는 탄소 함량을 0.2 중량% 이하로 제한하였지만, 경화능 확보를 위하여 Mn의 함량은 3.0~4.0 중량%로 Mn 함량이 꽤 높으며, 이에 따른 Mn 편석대 등에 의하여 굽힘 성능 등이 나빠질 수 있다.In the continuous annealing furnace process without water cooling equipment, the cooling rate is inevitably deteriorated. Therefore, in order to obtain the above-mentioned martensite microstructure, it is a top priority to secure sufficient hardenability by adjusting the alloy component. In Patent Document 2, the carbon content is limited to 0.2% by weight or less. However, in order to secure the hardenability, the content of Mn is 3.0 to 4.0% by weight and the Mn content is quite high. .
또한 최근 초고강도 냉연강판을 제조하기 위해서 열간 압연판에서 냉간 압연판을 만드는 과정인 냉간압연 특성이 중요한데, 냉간압연 설비의 성능은 그대로이나 재료의 초고강도와 추세로 인하여 열간 압연판의 강도 자체가 매우 올라가고 있기 때문이다. 고합금 성분계의 재료들은 경화능이 매우 높아 열간압연 공정 후, 베이나이트 및 마르텐사이트 등의 매우 강도 높은 미세조직을 갖는 경우가 많으며, 열간공정 중 열연 판의 폭 방향 등의 위치에 따른 냉각능의 차이로 인하여 미세조직이 다르게되어 이에 따른 폭 방향 재질 편차는 재료의 냉간압연성을 나쁘게 하는 주된 원인이 되고 있다. 따라서, 수냉각 설비가 없는 연속 소둔로를 활용하여 초고강도의 냉연강판 제조를 위해서는 경화능 및 냉간압연성을 고려한 최적 합금성분계의 도출이 필요하다.In order to manufacture ultra-high-strength cold-rolled steel sheets, cold-rolling characteristics, which is a process of making cold-rolled plates in hot-rolled plates, are important. However, due to the ultrahigh strength and trend of materials, the strength of hot- It is very up. Since the high alloy materials have very high hardenability, they often have very high strength microstructures such as bainite and martensite after the hot rolling process, and the difference in the cooling ability depending on the position of the hot- And thus the deviation of the material in the width direction becomes a main cause of deteriorating the cold rolling property of the material. Therefore, in order to manufacture cold-rolled steel sheets having ultra-high strength by utilizing a continuous annealing furnace without water cooling equipment, it is necessary to derive an optimum alloy component system considering hardenability and cold rolling property.
(특허문헌 1) 일본공개특허 제2010-090432호(Patent Document 1) Japanese Laid-Open Patent Application No. 2010-090432
(특허문헌 2) 대한민국 특허출원 제2015-0098217호(Patent Document 2) Korean Patent Application No. 2015-0098217
따라서 본 발명은 상술한 종래기술의 한계를 해소하기 위하여 안출된 것으로서, 수 냉각에 설비에 비하여 서냉각 설비인 롤 냉각, mist 냉각, 가스 냉각의 이용이 가능한 연속소둔 설비와 연속소둔 용융아연도금설비 및 연속소둔 용융아연 합금화 도금설비를 이용하여 제조되는 제품 형상 및 냉간압연 특성이 매우 우수한 초고강도 냉연강판, 도금강판 및 이의 제조방법을 제공함에 그 목적이 있다. Accordingly, the present invention has been made in order to overcome the above-described problems of the prior art, and it is an object of the present invention to provide a continuous annealing apparatus capable of using roll cooling, mist cooling, gas cooling, And an object of the present invention is to provide an ultra-high strength cold-rolled steel sheet, a coated steel sheet and a method of manufacturing the same, which are excellent in product shape and cold rolling property, which are manufactured using a hot-dip galvanizing system.
한편, 본 발명의 과제는 상술한 내용에 한정하지 않는다. 본 발명의 과제는 본 명세서의 내용 전반으로부터 이해될 수 있을 것이며, 본 발명이 속하는 기술분야에서 통상의 지식을 가지는 자라면 본 발명의 부가적인 과제를 이해하는데 아무런 어려움이 없을 것이다.On the other hand, the object of the present invention is not limited to the above description. It will be understood by those of ordinary skill in the art that there is no difficulty in understanding the additional problems of the present invention.
상기 목적을 달성하기 위한 본 발명은, 중량%로, C: 0.4~0.6%, Mn: 1.5~3.0%, Cr: 0.7~2.0%, P: 0.03% 이하(0%는 제외), S: 0.01% 이하(0% 제외), N: 0.01% 이하(0% 제외), sol.Al: 0.1% 이하(0%제외), Mo: 1.0% 이하(0% 제외) 및 B: 0.005% 이하(0% 제외) 중 1종 이상, 잔여 Fe 및 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하고, In order to attain the above object, the present invention provides a steel sheet comprising, by weight, 0.4 to 0.6% of C, 1.5 to 3.0% of Mn, 0.7 to 2.0% of Cr, 0.03% or less of P Mo: not more than 1.0% (excluding 0%), and B: not more than 0.005% (excluding 0%), N: not more than 0.01% %), Remaining Fe and unavoidable impurities, and satisfies the following relational expression (1)
강 미세조직이 면적 분율로 90% 이상의 마르텐사이트와 10% 이하의 제 2차상으로 이루어진 냉간압연성이 우수한 초고강도 냉연 강판에 관한 것이다. The present invention relates to a cold-rolled steel sheet having excellent cold-rolling properties, comprising a steel microstructure having an area fraction of 90% or more of martensite and 10% or less of a secondary phase.
[관계식 1] [Relation 1]
1.6 ≤ C + Mn/2 + Cr/3 + Mo/4+ B*100 ≤ 3.521.6? C + Mn / 2 + Cr / 3 + Mo / 4 + B? 100? 3.52
또한 본 발명은,Further, according to the present invention,
중량%로, C: 0.4~0.6%, Mn: 1.5~3.0%, Cr: 0.7~2.0%, P: 0.03% 이하(0%는 제외), S: 0.01% 이하(0% 제외), N: 0.01% 이하(0% 제외), sol.Al: 0.1% 이하(0%제외), Mo: 1.0% 이하(0% 제외) 및 B: 0.005% 이하(0% 제외) 중 1종 이상, 잔여 Fe 및 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하는 강 슬라브를 1100~1300℃로 가열하는 단계; (Excluding 0%), S: not more than 0.01% (excluding 0%), N: not more than 0.03%, P: not more than 0.03% 0.01% or less (excluding 0%), sol.Al: 0.1% or less (excluding 0%), Mo: 1.0% or less (excluding 0%) and B: 0.005% or less And inevitable impurities, and heating a steel slab satisfying the following relational expression 1 to 1100 to 1300 캜;
상기 가열된 슬라브를 Ar3 + 5℃ ~ Ar3 + 95℃의 온도범위에서 마무리 열간압연함으로써 열연강판을 제조하는 단계;Preparing a hot rolled steel sheet by subjecting the heated slab to finish hot rolling in a temperature range of Ar 3 + 5 ° C to Ar 3 + 95 ° C;
상기 제조된 열연강판을 550~700℃의 온도범위로 권취함으로써 그 미세조직이 면적 분율로 80% 이상의 펄라이트 및 20% 이하의 페라이트를 포함하는 열연코일을 제조하는 단계; Winding the hot rolled steel sheet at a temperature in the range of 550 to 700 占 폚 to produce a hot rolled coil having a microstructure of 80% or more of pearlite and 20% or less of ferrite in an area fraction;
상기 권취된 열연코일을 압하율 40 ~ 80%로 냉간 압연하는 단계; 및Cold rolling the rolled coil to a rolling reduction of 40 to 80%; And
상기 냉간 압연된 냉연 강판을 연속 소둔 후 100~250℃에서 추가 템퍼링(tempering) 열처리함으로써 면적 분율로 90% 이상의 마르텐사이트와 10% 이하의 제 2차상으로 이루어진 초고강도 냉연강판을 제조하는 단계;를 포함하는 냉간압연성이 우수한 초고강도 냉연 강판의 제조방법에 관한 것이다.Further comprising the step of subjecting the cold-rolled cold-rolled steel sheet to continuous annealing at 100 to 250 ° C to prepare an ultra-high-strength cold-rolled steel sheet having an area fraction of 90% or more of martensite and 10% The present invention relates to a method for producing an ultra-high strength cold rolled steel sheet excellent in cold rolling resistance.
[관계식 1] [Relation 1]
1.6 ≤ C + Mn/2 + Cr/3 + Mo/4+ B*100 ≤ 3.521.6? C + Mn / 2 + Cr / 3 + Mo / 4 + B? 100? 3.52
본 발명에 의하면, 서냉각 설비를 활용한 통상의 연속 소둔공정을 활용하여 2000MPa 이상의 초고강도 냉연강판을 제조하며, 수냉각을 활용하여 제조된 마르텐사이트강에 비하여 우수한 표면 형상 품질을 가질 수 있다. According to the present invention, an ultra-high-strength cold-rolled steel sheet of 2000 MPa or more can be produced by using a continuous annealing process using a conventional cooling facility, and it can have a superior surface shape quality as compared with the martensitic steel produced by using water cooling.
일반적으로 초고강도 냉연 강판의 경우 합금성분을 다량 함유하고 이에 따라 열연 미세조직이 베이나이트, 마르텐사이트 등의 경한 미세조직을 필수적으로 함유하여 폭방향 재질 편차 열위 및 냉간압연시 부하가 크게 걸리는 문제점이 있었다. 그러나 본 발명은 공석 성분계 혹은 그에 상응하는 합금 성분계를 활용하여 열연 미세조직으로 80% 이상의 펄라이트를 확보하여 초고강도 철강소재의 냉간압연성 및 폭방향 재질편차를 개선한 냉연강판을 제조하는 유용한 효과가 있다. Generally, ultra-high strength cold-rolled steel sheets contain a large amount of alloy components, and therefore, the hot-rolled microstructure contains a hard microstructure such as bainite and martensite, there was. However, the present invention provides a useful effect of manufacturing a cold-rolled steel sheet having improved cold rolling property and widthwise material deviation of an ultra-high strength steel material by securing 80% or more of pearlite by hot-rolled microstructure by utilizing an open-air component system or a corresponding alloy component system have.
도 1은 본 실시예에서 시편번호 2-1의 냉간압연 및 연속소둔공정 후 미세조직을 투과전자현미경(TEM)으로 관찰한 사진이다.Fig. 1 is a photograph of a microstructure observed by a transmission electron microscope (TEM) after the cold rolling and continuous annealing process of Specimen No. 2-1 in this embodiment.
이하, 본 발명을 설명한다. Hereinafter, the present invention will be described.
본 발명자들은 종래의 베이나이트 및 마르텐사이트 미세조직을 주로 갖는 초고강도강이 갖는 열연강판의 폭방향 재질 편차 및 높은 냉간압연부하 등의 문제점과, 기존 초고강도 냉연강판의 최대 인장강도가 약 1500MPa급으로 제한되었던 문제점을 해결하기 위하여 깊이 연구하였다. 그 결과, 합금조성 및 제조방법을 적절하게 제어함으로써 열연 후에는 완전 펄라이트(full pearlite) 혹은 그에 상응하는 다량의 펄라이트 미세조직을 확보하여 열간압연강판의 폭 방향 재질 편차를 감소시키고, 냉간압연 시의 부하를 저감시켜 냉간압연성이 우수한 강판을 제공할 수 있음을 확인하고, 본 발명을 제시하는 것이다. DISCLOSURE OF THE INVENTION The present inventors have found that there are problems such as variations in material in the width direction of a hot-rolled steel sheet having an ultra-high-strength steel mainly containing bainite and martensite microstructure and high cold rolling load, In order to solve the problems that were limited to As a result, it is possible to appropriately control the alloy composition and the manufacturing method to secure a full pearlite or a corresponding large amount of pearlite microstructure after hot rolling to reduce variations in material in the width direction of the hot-rolled steel sheet, It is possible to provide a steel sheet excellent in cold rolling resistance by reducing the load, and the present invention is presented.
즉, 본 발명의 일 측면에 따른 폭방향 재질편차 및 냉간압연성이 우수한 초고강도 냉연 강판은, 중량%로, C: 0.4~0.6%, Mn: 1.5~3.0%, Cr: 0.7~2.0%, P: 0.03% 이하(0%는 제외), S: 0.01% 이하(0% 제외), N: 0.01% 이하(0% 제외), sol.Al: 0.1% 이하(0%제외), Mo: 1.0% 이하(0% 제외) 및 B: 0.005% 이하(0% 제외) 중 1종 이상, 잔여 Fe 및 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하며, 강 미세조직이 면적 분율로 90% 이상의 마르텐사이트와 10% 이하의 제 2차상으로 이루어진다. That is, according to one aspect of the present invention, there is provided an ultrahigh strength cold rolled steel sheet excellent in the lateral direction material deviation and cold rolling property, comprising 0.4 to 0.6% of C, 1.5 to 3.0% of Mn, 0.7 to 2.0% P: not more than 0.03% (excluding 0%), S: not more than 0.01% (excluding 0%), N: not more than 0.01% (excluding 0%), sol.Al: not more than 0.1% , At least 90% of at least one of the steel microstructure and at least one of the residual Fe and unavoidable impurities, satisfying the following relational expression 1: And a second phase of 10% or less.
[관계식 1] [Relation 1]
1.6 ≤ C + Mn/2 + Cr/3 + Mo/4+ B*100 ≤ 3.521.6? C + Mn / 2 + Cr / 3 + Mo / 4 + B? 100? 3.52
먼저, 본 발명에 따른 강 합금조성에 및 그 함량 제한 사유에 대하여 설명한다. 이하, 각 원소 함량의 단위는 특별한 언급이 없는 한 중량%이다. First, the composition of the steel alloy according to the present invention and the reason for its content limitation will be described. Hereinafter, the unit of each element content is expressed by weight% unless otherwise specified.
·C: 0.4~0.6%C: 0.4 to 0.6%
탄소(C)는 본 발명에서 열간압연 후 페라이트와 세멘타이트로 이루어진 펄라이트 미세조직을 갖는 강판을 제조하는데 중요한 성분으로서, 일반적으로 C 함량이 증가할수록 펄라이트 조직 분율을 높게 확보할 수 있으며 강의 강도를 확보하기 위해 첨가되는 필수적인 원소이다. 또한 냉연 연속 소둔 후의 마르텐사이트 미세조직에서 강도증가에 기여하는 효과가 가장 큰 원소이므로 2000MPa 이상의 초고강도를 얻기 위해서는 반드시 필요하다.Carbon (C) is an important component in the production of a steel sheet having pearlite microstructure composed of ferrite and cementite after hot rolling in the present invention. Generally, as the C content increases, a high percentage of pearlite structure can be secured. Is an indispensable element to be added. In addition, since it is the largest element that contributes to the strength increase in the martensite microstructure after cold-rolling continuous annealing, it is indispensable to obtain an ultra-high strength of 2000 MPa or more.
C 함량이 0.4% 미만인 경우에는 펄라이트를 충분히 확보하기 어려울 뿐 아니라 2000MPa 이상의 초고강도를 얻기 위한 마르텐사이트 강도 확보가 힘들다는 문제점이 있다. 반면에 C함량이 0.6% 초과인 경우에는 펄라이트 내 탄화물이 과다 형성되어 석출물과의 상간 정합성을 저하시켜 열간 압연성 및 상온 연성이 저하될 수 있을 뿐만 아니라, 입내 강도를 급격히 증가시켜 연성을 감소시킬 수 있다. When the C content is less than 0.4%, it is difficult to sufficiently secure pearlite, and it is difficult to secure the strength of martensite to obtain an ultra-high strength of 2000 MPa or more. On the other hand, when the C content is more than 0.6%, the carbide in the pearlite is excessively formed and the phase-to-phase compatibility with the precipitate is lowered, so that the hot rolling property and the room temperature ductility can be lowered, .
·Mn: 1.5~3.0%Mn: 1.5 to 3.0%
강 중 Mn은 페라이트 형성을 억제하고 오스테나이트 형성을 용이하게 하는 대표 원소 중 하나이며, 또한 마르텐사이트의 강도를 높이는 효과적인 원소이다. Mn이 1.5% 미만인 경우에는 연속 소둔공정 중 서냉각시 페라이트 생성이 용이하여 강도가 낮아지게 되고, Mn이 3.0%를 초과하는 경우에는 편석에 의한 망간 밴드형성에 따른 굽힘성 열화 및 전로 조업시 합금 투입량 과다에 의한 합금철 원가증가의 문제로 그 함량을 제한한다.Mn in steel is one of the representative elements that inhibits ferrite formation and facilitates the formation of austenite, and is an effective element for increasing the strength of martensite. When the Mn content is less than 1.5%, the ferrite is easily formed during the continuous cooling process during the continuous annealing process and the strength becomes low. When the Mn content exceeds 3.0%, the bending deterioration due to the formation of manganese bands due to segregation, And the content of the alloy is limited due to an increase in the cost of the alloy iron due to the excessive amount.
·Cr: 0.7~2.0%Cr: 0.7 to 2.0%
Cr은 Mn과 비슷하게 강의 경화능을 높이는 특성을 나타내기 때문에, 서냉각 설비의 연속 소둔공정 중 마르텐사이트 변태를 얻기 위해 첨가되는 필수 원소 중 하나이다. 또한 Cr은 공석 조성에 필요한 탄소함량을 낮추는 역할을 하여, 낮은 탄소함량에서도 열간 공정 중 펄라이트 미세조직 변태가 이루어질 수 있게 한다. 또한 세멘타이트의 형성을 조장하고 펄라이트의 라멜라 간격을 작게 하는 특성이 있어 세멘타이트 구상화를 촉진한다. 또한 미량의 첨가에 의해서도 강판의 내식성을 좀 더 개선하는 특성을 지니고 있다. Cr is one of the essential elements added to obtain martensite transformation during the continuous annealing process of the cooling equipment because it exhibits the property of increasing the hardenability of the steel similar to Mn. In addition, Cr plays a role in lowering the carbon content required for the formation of vacancies, allowing pearlite microstructure transformation during hot working even at low carbon content. It also promotes the formation of cementite and reduces the spacing of the pearlite laminates to promote cementite spheroidization. It also has the property of further improving the corrosion resistance of the steel sheet even by adding a small amount.
그러나 Cr 함량이 2.0% 초과인 경우에는 기계적 특성에 나쁜 영향을 미칠 수 있고, 산세 시 표면 스케일 산세성을 나빠지게 할 수 있는 문제점이 있다. However, when the Cr content exceeds 2.0%, the mechanical properties may be adversely affected and the surface scale pickling property may be deteriorated during pickling.
또한 Cr함량이 0.7% 미만인 경우에는 열연 상태에서 공석 펄라이트 형성을 위한 C함량이 높아져 C에 의한 점용접성이 크게 나빠질 뿐만 아니라 요구되는 경화능을 얻기 힘들수 있다. In addition, when the Cr content is less than 0.7%, the C content for forming vacancy pearlite increases in the hot rolled state, so that the spot weldability by C is greatly deteriorated and it is difficult to obtain the required hardenability.
·Sol.Al: 0.1% 이하(0%는 제외)· Sol.Al: 0.1% or less (excluding 0%)
산가용 알루미늄(sol.Al)은 강의 입도 미세화와 탈산을 위해 첨가되는 원소로서, 그 함량이 0.1%를 초과하게 되면, 제강 연주 조업시 개재물의 과다 형성으로 용융아연도금강판 표면 불량의 발생 가능성이 커질 뿐만 아니라, 제조원가의 상승을 초래하는 문제가 있다. Aluminum oxide (sol.Al) is an element to be added for grain refinement and deoxidation of steel. When the content exceeds 0.1%, there is a possibility of occurrence of defective surface of hot-dip galvanized steel sheet due to over- There is a problem that not only the size is increased but also the manufacturing cost is increased.
그 하한을 특별히 한정할 필요는 없으나, 제조과정 중에 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.The lower limit is not particularly limited, but 0% is excluded considering the level that is unavoidably added during the manufacturing process.
·P: 0.03% 이하(0%는 제외)· P: 0.03% or less (excluding 0%)
강 중 인(P)은 강도 확보에 이로운 원소이지만, 과잉 첨가할 경우 취성 파괴 발생 가능성이 증가하여 열간압연 도중 슬라브 파단 등의 문제점이 발생할 가능성이 증가하며, 도금표면 특성을 저해하는 원소로 작용하는 문제가 있다. 따라서 본 발명에서 P는 불순물로서 그 상한을 제어하는 것이 중요하며 0.03% 이하로 제어하는 것이 바람직하다. 다만, 제조과정 중에 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.P (P) is an element favorable in securing strength. However, when it is added excessively, the possibility of occurrence of brittle fracture increases, and there is an increased possibility of problems such as slab breakage during hot rolling. there is a problem. Therefore, in the present invention, it is important to control the upper limit of P as an impurity, and it is preferable to control P to 0.03% or less. However, 0% is excluded considering the level that is inevitably added during the manufacturing process.
·S: 0.01% 이하(0%는 제외)· S: 0.01% or less (excluding 0%)
황(S)은 강 중 불순물 원소로서 불가피하게 첨가되는 원소로서, 강 중 S은 적열 취성을 발생시킬 가능성을 높이는 문제가 있으므로, 그 함량을 0.01% 이하로 제어하는 것이 바람직하다. 다만, 제조과정 중에 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.Sulfur (S) is an element which is inevitably added as an impurity element in the steel. S in the steel has a problem of increasing the possibility of generating fumed brittleness. Therefore, it is preferable to control the content to 0.01% or less. However, 0% is excluded considering the level that is inevitably added during the manufacturing process.
·N: 0.01% 이하(0%는 제외)· N: 0.01% or less (excluding 0%)
질소(N)는 강 중 불순물 원소로서 불가피하게 첨가되는 원소이며, 조업조건이 가능한 범위인 0.01% 이하로 제어하는 것이 바람직하다. 다만, 제조과정 중에 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.Nitrogen (N) is an element which is inevitably added as an impurity element in the steel, and it is preferable to control the operating conditions to 0.01% or less, which is a possible range. However, 0% is excluded considering the level that is inevitably added during the manufacturing process.
본 발명에서는 상술한 성분 외에 Mo: 1.0% 이하(0% 제외) 및 B: 0.005% 이하(0% 제외) 중 1종 이상을 포함한다. In the present invention, in addition to the above-mentioned components, at least one of Mo: 1.0% or less (excluding 0%) and B: 0.005% or less (excluding 0%) is included.
Mo: 1.0% 이하(0%는 제외)Mo: 1.0% or less (excluding 0%)
Mo는 C, Mn, Cr등의 원소와 같이 강의 경화능을 높이는 역할을 하는 원소로서, 특히 Cr과 복합 첨가되었을 때 페라이트 및 베이나이트 상변태를 억제하는 효과가 큰 원소이다. 그러나 함량이 1.0% 초과인 경우에는 합금 투입량 과다에 의한 합금철 원가증가로 제한한다. 다만, 제조과정 중에 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.Mo plays an important role in enhancing the hardenability of steel such as C, Mn, and Cr, and is an element having a large effect of inhibiting ferrite and bainite phase transformation when added with Cr. However, if the content is more than 1.0%, it is limited to the increase of the amount of alloy iron due to the excessive amount of alloy. However, 0% is excluded considering the level that is inevitably added during the manufacturing process.
B: 0.005%이하(0% 제외)B: 0.005% or less (excluding 0%)
보론 (B)은 페라이트 형성을 억제하는 장점이 있어서, 소둔 후 냉각시에 페라이트의 형성을 억제하는 장점이 있다. 그러나 상기 B의 함량이 0.005%를 초과하게 되면 오히려 Fe23(C,B)6의 석출에 의하여 페라이트 형성이 촉진되는 문제가 있어서 그 함량을 제한한다. 다만 제조과정 중에 불가피하게 첨가되는 수준을 고려하여 0%는 제외한다.Boron (B) has an advantage of suppressing ferrite formation, and has an advantage of suppressing the formation of ferrite upon cooling after annealing. However, When the content of B exceeds 0.005%, but rather is a problem that ferrite is formed by promoting the precipitation of Fe 23 (C, B) 6 restrict the content according. However, 0% is excluded considering the level that is inevitably added during the manufacturing process.
이때, 본 발명에서는 상술한 각 원소 함량을 만족할 뿐만 아니라, C, Mn, Cr 및 Mo 함량이 하기 관계식 1을 만족할 필요가 있다.At this time, in the present invention, not only the content of each element described above is satisfied, but also the contents of C, Mn, Cr and Mo must satisfy the following relational expression (1).
[관계식 1] [Relation 1]
1.6 ≤ C + Mn/2 + Cr/3 + Mo/4+ B*100 ≤ 3.521.6? C + Mn / 2 + Cr / 3 + Mo / 4 + B? 100? 3.52
(상기 관계식 1에서 각 원소기호는 각 원소함량을 중량%로 나타낸 값이며, 포함되지 않는 경우 0으로 계산한다.) (In the above relational expression 1, each element symbol represents the content of each element in weight%, and is calculated as 0 if not included.)
상기 관계식 1은 본 발명에서 열간 공정 후 요구되는 일정 면적 분율 이상의 펄라이트와, 냉연 소둔 후의 마르텐사이트 조직을 얻기 위한 합금 성분계를 갖는 강을 제조하기 위한 각 원소의 영향도를 고려하여 설계한 것이다. The above-mentioned relational expression 1 is designed in consideration of the influence of each element for producing steel having a certain area fraction or more of pearlite required in the present invention after hot working and an alloy component system for obtaining a martensite structure after cold annealing.
만일 관계식 1에 의해 정의되는 값이 1.6 미만인 경우에는 열간압연 후 80 면적% 이상의 펄라이트를 확보하기 어려울 뿐 아니라, 냉연 연속 소둔후에 90 면적% 이상의 마르텐사이트를 확보하기 힘들다. 반면에, 그 값이 3.52 초과인 경우에는 다량의 합금원소 첨가로 인해 연신율이 저하될 수 있다. If the value defined by the relational expression 1 is less than 1.6, it is difficult to secure pearlite of 80% or more by area after hot rolling, and it is difficult to secure martensite of 90 area% or more after cold rolling continuous annealing. On the other hand, if the value is more than 3.52, elongation may be lowered due to addition of a large amount of alloying elements.
본 발명의 나머지 성분은 철(Fe)이다. 다만, 통상의 제조과정에서는 원료 또는 주위 환경으로부터 의도되지 않는 불순물들이 불가피하게 혼입될 수 있으므로, 이를 배제할 수는 없다. 이들 불순물들은 통상의 제조과정의 기술자라면 누구라도 알 수 있는 것이기 때문에 그 모든 내용을 특별히 본 명세서에서 언급하지는 않는다.The remainder of the present invention is iron (Fe). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing.
한편 본 발명의 냉연 강판은 면적 분율로 90% 이상의 마르텐사이트와 잔여 2차상을 포함하여, 인장강도 2000MPa이상의 초강도 냉연강판을 제조할 수 있다. 본 발명에서 상기 2차상으로는 페라이트 및 베이나이트 미세조직을 들 수 있다.  On the other hand, the cold-rolled steel sheet of the present invention can produce a cold-rolled steel sheet having a tensile strength of 2000 MPa or more including a martensite and a residual secondary phase of 90% or more in area fraction. In the present invention, the secondary phase includes ferrite and bainite microstructure.
또한, 본 발명의 강판은 표면에 아연도금층 및 합금화 아연도금층 중 하나가 추가로 형성되어 있을 수 있다. Further, the steel sheet of the present invention may further have one of a zinc plating layer and a galvanized zinc plating layer formed thereon.
다음으로, 본 발명의 일측면에 따른 인장강도 2000MPa 이상의 초고강도 냉연강판 제조방법에 대하여 설명한다.Next, a method for manufacturing an ultra-high strength cold rolled steel sheet having a tensile strength of at least 2000 MPa according to one aspect of the present invention will be described.
본 발명의 초고강도 냉연강판 제조방법은, 상기 조성의 강 슬라브를 1100~1300℃로 가열하는 단계; 상기 가열된 슬라브를 Ar3 + 5℃ ~ Ar3 + 95℃의 온도범위에서 마무리 열간압연함으로써 열연강판을 제조하는 단계; 상기 제조된 열연강판을 550~700℃의 온도범위로 권취함으로써 그 미세조직이 면적 분율로 80% 이상의 펄라이트 및 20% 이하의 페라이트를 포함하는 열연코일을 제조하는 단계; 상기 권취된 열연강판을 압하율 40 ~ 80%로 냉간 압연하는 단계; 및 상기 냉간 압연된 냉연 강판을 연속 소둔 후 100~250℃에서 추가 템퍼링(tempering) 열처리함으로써 면적 분율로 90% 이상의 마르텐사이트와 10% 이하의 제 2차상으로 이루어진 초고강도 냉연강판을 제조하는 단계;를 포함한다. The method of manufacturing an ultra-high strength cold rolled steel sheet according to the present invention comprises the steps of: heating a steel slab having the above composition to 1100 to 1300 캜; Preparing a hot rolled steel sheet by subjecting the heated slab to finish hot rolling in a temperature range of Ar 3 + 5 ° C to Ar 3 + 95 ° C; Winding the hot rolled steel sheet at a temperature in the range of 550 to 700 占 폚 to produce a hot rolled coil having a microstructure of 80% or more of pearlite and 20% or less of ferrite in an area fraction; Rolling the rolled hot-rolled steel sheet at a reduction ratio of 40 to 80%; And a step of subjecting the cold-rolled cold-rolled steel sheet to continuous annealing at 100 to 250 ° C to obtain an ultra-high-strength cold-rolled steel sheet having an area fraction of 90% or more of martensite and 10% or less of a second phase; .
슬라브 가열 단계Slab heating step
먼저, 본 발명에서는 상술한 합금조성을 갖는 강 슬라브를 열간압연 하기 위해 1100~1300℃ 온도범위로 가열한다. First, in the present invention, the steel slab having the above-described alloy composition is heated to a temperature range of 1100 to 1300 DEG C for hot rolling.
만일 상기 가열 온도가 1100℃ 미만이면 슬라브의 조직 및 성분을 균일화 처리하기 어렵고, 1300℃를 초과하면 표면 산화 및 설비 열화의 문제점이 발생할 수 있다. If the heating temperature is less than 1100 ° C, it is difficult to uniformize the structure and components of the slab, and if the heating temperature is more than 1300 ° C, problems of surface oxidation and equipment deterioration may occur.
열간압연 단계Hot rolling step
다음으로 본 발명에서는 상기 가열된 슬라브를 상기 가열된 슬라브를 Ar3 + 5℃ ~ Ar3 + 95℃의 온도범위에서 마무리 열간 압연한다.Next, in the present invention, the heated slab is subjected to finish hot-rolling the heated slab in a temperature range of Ar 3 + 5 ° C to Ar 3 + 95 ° C.
상기 마무리 열간압연 온도가 Ar3 + 5℃ 미만이면 페라이트와 오스테나이트의 이상역 압연 가능성이 있어 강 표층에 혼립 조직 및 판 형상 제어에 어려움을 야기할 수 있으며, 또한 재질 불균일성을 초래할 수 있다. If the final hot rolling temperature is lower than Ar3 + 5 deg. C, there is a possibility of an abnormal reverse rolling of ferrite and austenite, which may cause difficulty in control of mixed grain structure and plate shape in the steel surface layer, and may cause material nonuniformity.
반면에 마무리 열간압연 온도가 Ar3 + 95℃를 초과하면 열연재의 결정립 조대화 현상이 발생하기 쉽다. On the other hand, if the final hot rolling temperature exceeds Ar 3 + 95 ° C, crystal grain coarsening phenomenon of the thermal expansion material tends to occur.
따라서 본 발명에서는 상기 마무리 열간압연의 경우 Ar3 + 5℃ ~ Ar3 + 95℃ 온도 범위인 오스테나이트계 단상역에서 하는 것이 바람직하다. 상기 온도 범위에서 마무리 열간압연을 함으로써 단상 오스테나이트 결정립으로 구성되는 미세 조직에서 보다 균일한 변형을 가하여 조직 내 균일성을 증가시킬 수 있기 때문이다. Therefore, in the present invention, the finishing hot rolling is preferably performed in a single phase of austenite which is in the range of Ar 3 + 5 ° C. to Ar 3 + 95 ° C. By performing the hot rolling in the above-mentioned temperature range, it is possible to increase the uniformity in the structure by applying a more uniform deformation in the microstructure composed of single-phase austenite grains.
이때, 상기 Ar3 온도는 하기 관계식 2로 의해 정의될 수 있다. At this time, the Ar3 temperature can be defined by the following relational expression (2).
[관계식 2][Relation 2]
Ac3(℃) = 955-250*C-25*Mn+200*Al-11*Cr+90*MoAc3 (° C.) = 955-250 * C-25 * Mn + 200 * Al-11 * Cr + 90 * Mo
(상기 관계식 2에서 각 원소 기호는 각 원소 함량을 중량%로 나타낸 값이며, 포함되지 않는 경우 0으로 계산한다.) (In the above relational expression 2, the symbol of each element represents the content of each element in weight%, and is calculated as 0 if it is not included.)
권취 단계Winding step
이어, 본 발명에서는 그 미세조직이 면적 분율로 80% 이상의 펄라이트와 20% 이하의 페라이트를 포함하도록 상기 열연강판을 권취한다. Next, in the present invention, the hot-rolled steel sheet is wound such that the microstructure contains 80% or more of pearlite and 20% or less of ferrite in an area fraction.
본 발명에 따른 열연코일의 미세조직은 면적 분율로 80% 이상의 펄라이트 및 20% 이하의 페라이트를 포함하며, 펄라이트가 80% 미만인 경우에는 열연 강판의 폭방향 재질 편차가 심해질 수 있고, 이후의 연속 소둔공정 열처리 후 원하는 양의 마르텐사이트 변태를 유도하기 힘들다.The microstructure of the hot-rolled coil according to the present invention contains 80% or more of pearlite and 20% or less of ferrite in an area fraction. When the pearlite is less than 80%, the material deviation in the width direction of the hot- It is difficult to induce the desired amount of martensite transformation after the heat treatment.
열연강판의 펄라이트 분율이 높을수록 폭방향 재질 편차를 줄일 수 있기 때문에, 그 상한은 특별히 한정하지 않으며, 펄라이트 단상인 것이 보다 바람직하다. 상기 펄라이트 내 세멘타이트는 길쭉한 라멜라(lamellar) 형태이나, 냉간압연 및 연속소둔 열처리 공정을 통과하며 분절 및 구상화된다. 따라서 연속 소둔 열처리 후의 미세조직은 마르텐사이트 내 구상화된 세멘타이트를 포함하고 있다. The higher the pearlite fraction of the hot-rolled steel sheet, the smaller the variation in the material in the width direction. Therefore, the upper limit is not particularly limited, and it is more preferable that the pearlite single phase is used. The cermetite in the pearlite is elongated in a lamellar form, but passes through a cold rolling and continuous annealing heat treatment process and is segmented and spheroidized. Therefore, the microstructure after the continuous annealing heat treatment contains spheroidized cementite in martensite.
그리고 본 발명의 열연강판은 인장강도가 1200MPa 이하이며, 인장강도가 높다고 할 수 있으나 길쭉한 라멜라 형태의 세멘타이트를 갖는 펄라이트 구조로 인하여 냉간 압연 시 압연 방향으로 길게 연신되는 특성을 보여 냉간 압연성 측면에서는 베이나이트 및 마르텐사이트의 경한 미세조직보다 우수하다고 할 수 있다.Although the hot-rolled steel sheet of the present invention has a tensile strength of 1200 MPa or less and a high tensile strength, it exhibits a long elongation in the rolling direction due to the pearlite structure having elongated lamellar cementite. Which is superior to the light microstructure of bainite and martensite.
이러한 물성을 확보함으로써 종래 냉간압연 작업 범위에서 냉간압연을 하더라도 폭방향 재질편차에서 오는 각종 파단 및 냉간압연부하를 감소시켜 초고강도 냉연강판을 제조할 수 있다. By securing such physical properties, it is possible to manufacture various ultra-high-strength cold-rolled steel sheets by reducing various fracture and cold rolling load from a material deviation in the width direction even in cold rolling in the conventional cold rolling work range.
이때, 본 발명에서는 상기 권취온도 범위를 550~700의 온도 범위로 제한함이 바람직하다. 만일 상기 권취 온도가 550℃ 미만이면, 저온 변태조직 즉, 베이나이트 또는 마르텐사이트가 생성되어 열연강판의 과다한 강도 상승을 초래함으로써 냉간압연 시 과다한 부하로 인한 형상불량 등의 문제와, 폭방향 재질편차가 크게 발생할 수 있으며, 본 발명의 목적인 펄라이트 미세조직을 얻기 힘들 수 있다. At this time, in the present invention, the winding temperature range is preferably limited to a temperature range of 550 to 700. If the coiling temperature is less than 550 캜, a low-temperature transformed structure, that is, bainite or martensite is generated to cause excessive increase in the strength of the hot-rolled steel sheet, thereby causing problems such as defective shape due to excessive load during cold rolling, And it may be difficult to obtain pearlite microstructure for the purpose of the present invention.
반면에 상기 권취 온도가 700℃를 초과하면 과도한 열연재 입계 산화가 발생하기 쉬우며, 이에 따라 산세성이 나빠지는 문제가 발생할 수 있다. On the other hand, if the coiling temperature exceeds 700 ° C, excessive thermal transition grain boundary oxidation tends to occur, which may result in deteriorated pickling performance.
한편, 본 발명에서는 필요에 따라 냉간 압연 전 압연 부하를 줄이기 위해서 상기 권취하는 단계 후에 200~700℃에서 상소둔(batch annealing)을 행하는 단계를 추가로 포함할 수 있다. The present invention may further include a step of performing batch annealing at 200 to 700 ° C after the winding step to reduce the rolling load before cold rolling as required.
상소둔 온도가 200℃ 미만인 경우에는 열연 조직이 충분히 연화되지 못하여 압연 부하 감소에 큰 영향을 미치지 못하고, 700℃를 초과하게 되면 고온 소둔에 의한 펄라이트 분해가 발생될 수 있다. When the temperature is lower than 200 ° C, the hot-rolled structure is not sufficiently softened and does not significantly affect the reduction of the rolling load. If the temperature exceeds 700 ° C, pearlite decomposition may occur due to high temperature annealing.
한편, 상소둔 열처리 시간은 크게 영향을 주지 않기 때문에 본 발명에서 특별히 한정할 필요는 없다. On the other hand, since the heat treatment time is not greatly affected, the present invention is not particularly limited.
냉간압연 단계Cold rolling step
그리고 본 발명에서는 상기 권취된 열연강판을 압하율 40~80%로 냉간압연하여 냉연강판을 얻는다. In the present invention, the rolled hot-rolled steel sheet is cold-rolled at a reduction ratio of 40 to 80% to obtain a cold-rolled steel sheet.
상기 압하율이 40% 미만이면 목표로 하는 두께를 확보하기 어려울 수 있다. If the reduction rate is less than 40%, it may be difficult to secure a target thickness.
열연강판의 경우 펄라이트 변태시 성장 시간이 충분하다면 길쭉한 형태의 라멜라 세멘타이트를 갖는 것이 일반적이다. 다만 열간압연 후 권취 공정 조건에 따라 충분한 펄라이트 변태 시간이 주어지지 못한다면 열연강판에서도 일부분 분절된 형태의 세멘타이트가 나타날 수 있으나, 분절된 펄라이트를 충분히 확보할 수는 없다. 냉간압연 후 라멜라 형태의 세멘타이트들은 압연방향으로 연신 혹은 분절되어 나타나게 된다. 또한 냉간압하율에 따라 열간 압연재의 두께는 줄어들기 때문에 냉간압연 후에는 interlamellar spacing(라멜라 세멘타이트 간 거리)은 줄어들게 된다.In the case of a hot-rolled steel sheet, it is common to have an elongated lamellar cementite if the pearlite transformation time is sufficient. However, if a sufficient pearlitic transformation time is not given according to the rolling process conditions after hot rolling, a partially segmented cementite may appear in the hot-rolled steel sheet, but the segmented pearlite can not be sufficiently secured. After cold rolling, lamellar cementites are stretched or segmented in the rolling direction. In addition, the interlamellar spacing is reduced after cold rolling because the thickness of the hot rolled material decreases with cold reduction.
반면에 압하율이 80% 초과인 경우에는 냉연강판 에지(edge)부에서 크랙이 발생 가능성이 있고, 냉간압연의 부하가 높아질 수 있다. On the other hand, when the reduction rate is more than 80%, there is a possibility of cracking at the edge of the cold rolled steel sheet, and the load of cold rolling may be increased.
이때, 냉간압연은 상온에서 행할 수 있다.At this time, the cold rolling can be performed at room temperature.
연속 소둔 단계Continuous annealing step
본 발명에서는 냉간압연 후에 인장 강도 2000MPa 이상을 얻기 위해서 냉연강판을 Ac3 - 5℃ ~ Ac3 + 80℃의 온도범위에서 연속 소둔 한다. 이때, 상기 Ac3 온도는 하기 관계식 3에 의해 정의될 수 있다. In the present invention, the cold-rolled steel sheet is continuously annealed in a temperature range of Ac 3 - 5 ° C to Ac 3 + 80 ° C to obtain a tensile strength of at least 2000 MPa after cold rolling. At this time, the Ac3 temperature can be defined by the following equation (3).
[관계식 3][Relation 3]
Figure PCTKR2018012595-appb-I000001
Figure PCTKR2018012595-appb-I000001
(상기 관계식 3에서 각 원소 기호는 각 원소 함량을 중량%로 나타낸 값이며, 포함되지 않는 경우 0으로 계산한다.)(In the above formula (3), the symbol of each element represents the content of each element in weight%, and is calculated as 0 if it is not included.)
상기 온도범위에서 연속 소둔을 행함으로써 소둔 과정 중 일정량 이상의 오스테나이트 변태를 야기할 수 있고, 상기 오스테나이트가 냉각 중 마르텐사이트로 변태하여 90% 면적분율 이상의 마르텐사이트를 확보하여 2000MPa 이상의 인장강도를 얻을 수 있다. 또한 연속 소둔 열처리 과정에서 열간압연 시 형성된 라멜라(lamellar) 형태의 세멘타이트 및 냉간압연 후 형성된 분절 형태의 세멘타이트가 구형의 형태로 구상화될 수 있다. 세멘타이트의 구상화 열처리 방법은 크게 Ac1 온도 직하에서 수행하는 Subcritical annealing 방법과 Ac1~Ac3 온도 사이에서 행하는 Intercritical annealing 방법 두 가지가 있다. 본 기술에서는 후자의 방법이 적용되며 Intercritical annealing 시, 일정 분율의 페라이트가 오스테나이트로 변태가 개시되고, 펄라이트 내 세멘타이트 입자는 미고용 상태를 유지 즉, 오스테나이트와 미용해 세멘타이트 조직으로 구성되며, 이러한 미용해 세멘타이트를 핵으로 구상화가 진행된다. 따라서 본 발명에 따른 냉연 연속소둔 강판의 미세조직 내에는 구상화된 세멘타이트(Fe3C)가 마르텐사이트 내 존재하게 되며, 크기는 50 nm 이상의 사이즈로 제한한다. 펄라이트 내 세멘타이트로부터 열처리 도중 생성된 상기 구상화된 세멘타이트(Fe3C)와 별도로 최종 조직인 마르텐사이트 내 다른 종류의 탄화물이 존재할 수 있다. 이러한 탄화물은 그 직경을 50nm 이하로 제한을 하고, 템퍼링 열처리 등에 의해 생성될 수 있으며 흔히 천이 탄화물(transition carbides)이라 명명한다. 이러한 transition carbides은 흔히 낮은 템퍼링 온도(300℃ 이하) 열처리 조건에서 생성되며 생성온도에 따라 화학당량식이 달라지며, 일반적으로 그 크기는 수 nm이다. 상기 소둔 열처리된 최종 미세조직은 하기 관계식 4에 의한 A 값이 3 이상인 것을 특징으로 한다. By performing continuous annealing in this temperature range, a certain amount of austenite transformation can be caused in the annealing process, and the austenite is transformed into martensite during cooling to secure a martensite having a 90% area fraction or more to obtain a tensile strength of 2000 MPa or more . Also, lamellar type cementite formed in hot rolling in the continuous annealing process and spherical cementite formed in the shape after cold rolling can be spheroidized. There are two subcritical annealing methods which are performed under the temperature of Ac1 and intercritical annealing method which is performed between the temperatures of Ac1 and Ac3. In the present technology, the latter method is applied. In the intercritical annealing, a certain percentage of ferrite is transformed into austenite, and the cermetite particles in the pearlite remain unused, that is, austenite and unhardened cementite structure , And these unsolvated cementites are spheroidized. Therefore, in the microstructure of the cold-rolled continuous annealed steel sheet according to the present invention, spheroidized cementite (Fe 3 C) is present in the martensite and the size is limited to a size of 50 nm or more. Apart from the spheroidized cementite (Fe 3 C) generated during the heat treatment from the cermetite in pearlite, there may be another type of carbide in the final structure, martensite. These carbides have a diameter limited to 50 nm or less and can be produced by a tempering heat treatment or the like and are often called transition carbides. These transition carbides are often produced at low tempering temperatures (below 300 ° C), and their chemical equivalents depend on the temperature at which they are produced, usually in the order of a few nanometers. The final microstructure subjected to the annealing heat treatment is characterized by an A value of not less than 3 according to the following relational expression (4).
[관계식 4][Relation 4]
A=AX/AY A = A X / A Y
(상기 관계식 4에서, AX 는 1 mm2 면적 내 aspect ratio 가 1.5 이상인 세멘타이트의 개수, AY 는 동일면적 내 aspect ratio 가 1.5 미만인 세멘타이트 의 개수를 의미한다.)(In the above relational expression 4, A X denotes the number of cementite having an aspect ratio of not less than 1.5 in 1 mm 2 area, and A Y denotes the number of cementite having an aspect ratio within the same area of less than 1.5.)
만일 상기 소둔 온도가 Ac3-5℃ 미만이면 오스테나이트로의 상변태가 적어 최종 연속 소둔 후에 얻을 수 있는 마르텐사이트 분율이 제한적이며, Ac3+80℃ 초과인 경우에는 오스테나이트 입도 크기가 커져 최종 마르텐사이트의 인장 강도를 저해할 우려가 있다. 따라서 Ac3-5℃ ~ Ac3+80℃의 온도범위에서 연속 소둔하는 것이 바람직하다. If the annealing temperature is less than Ac3-5 deg. C, the phase transformation to austenite is small and the martensite fraction obtained after the final continuous annealing is limited. When Ac3 + 80 deg. C, the austenite grain size becomes large, There is a fear that the tensile strength is inhibited. Therefore, continuous annealing is preferable in the temperature range of Ac3-5 deg. C to Ac3 + 80 deg.
한편, 상기 냉연강판을 도금하는 단계를 추가로 포함할 수 있다. 도금방법 및 도금종류는 통상의 조업조건에 의해서도 재질 특성에는 큰 영향이 없으므로 특별히 한정하지 않는다. The method may further include plating the cold rolled steel sheet. The plating method and plating type are not particularly limited because they do not greatly affect the material properties even under normal operating conditions.
예를 들어, 아연, 아연합금 등으로 도금을 행할 수 있으며, 용융도금법, 합금화 용융도금, 전기도금법 등을 이용하여 도금을 행할 수 있다. For example, plating can be performed with zinc or a zinc alloy, and plating can be performed using a hot-dip coating method, an alloying hot-dip coating, an electroplating method, or the like.
Tempering 열처리 단계Tempering heat treatment step
마지막으로, 본 발명에서는 상기 냉연강판을 템퍼링 열처리한다. Finally, in the present invention, the cold-rolled steel sheet is tempered by heat treatment.
이러한 추가 템퍼링 열처리는 100~250℃의 온도범위로 한정하고 그 시간은 특별하게 한정하진 않는다. 추가 템퍼링 열처리가 필요한 이유는 다음과 같다. 인장강도 2000MPa 이상을 얻기 위해서는 강판의 미세조직을 마르텐사이트로 가져가는 것이 매우 중요하며, 또한 마르텐사이트 자체의 강도를 증가시켜야만 가능하다. 마르텐사이트의 강도는 합금성분, packet size, block size 등에 의하여 영향을 받는데, 그 중 합금성분의 영향도가 매우 크며, 합금성분 중에서도 탄소가 강도 증가에 기여하는 부분이 가장 크다고 할 수 있다. 반면, 탄소가 마르텐사이트의 강도를 높이는 데에 매우 큰 역할을 함과 동시에, 마르텐사이트의 인성을 떨어뜨리게 된다. 이러한 경우 추가적인 템퍼링 열처리를 통해 마르텐사이트 내 탄소를 탄화물의 형태로 석출시켜 다시 인성을 부여해 줄 수 있다. 템퍼링 온도가 100℃ 미만이면, 탄소의 탄화물 형태로의 석출을 거의 일어나지 않고 마르텐사이트 내 결함(전위, 공공 등) 등으로의 재분배만 일어나 원하는 인성부여 효과가 미미하다. 온도가 250℃ 초과가 되면 마르텐사이트 취화가 일어나 연성이 크게 감소하게 되는데 이 현상을 흔히 Tempered Martensite Embrittlement(TME)라 한다. 따라서 템퍼링 열처리는 100℃~250℃ 구간에서 행하는 것이 바람직하다.This additional tempering heat treatment is limited to a temperature range of 100 to 250 DEG C and the time is not particularly limited. The reason for the additional tempering heat treatment is as follows. In order to obtain a tensile strength of at least 2000 MPa, it is very important to bring the microstructure of the steel sheet into the martensite, and it is only necessary to increase the strength of the martensite itself. The strength of martensite is influenced by alloy composition, packet size, block size, etc. Among them, the effect of alloying elements is very high. Among the alloying elements, carbon is the biggest contributor to the strength increase. On the other hand, carbon plays a very large role in increasing the strength of martensite, and at the same time, toughness of martensite is lowered. In this case, additional tempering heat treatment can precipitate carbons in the martensite in the form of carbide to give toughness again. If the tempering temperature is less than 100 占 폚, the carbon is hardly precipitated in the form of carbide, and redistribution into martensite defects (dislocation, vacancy, etc.) only occurs and the desired toughness effect is insignificant. When the temperature exceeds 250 ° C., martensite brittleness occurs and the ductility is greatly reduced. This phenomenon is often referred to as Tempered Martensite Embrittlement (TME). Therefore, the tempering heat treatment is preferably performed in a range of 100 ° C to 250 ° C.
이하, 실시예를 통하여 본 발명을 보다 상세하게 설명한다. Hereinafter, the present invention will be described in more detail with reference to Examples.
(실시예)(Example)
하기 표 1에 나타낸 성분 조성을 갖는 슬라브를 1200℃ 가열로에서 1시간 동안 열처리 한 후, 880℃에서 마무리 열간 압연하였다. 이어, 열간 압연재를 650℃로 미리 가열된 로에 장입한 후 1 시간 유지하여 로냉함에 의하여 열연 권취를 모사하였으며, 이후, 이를 산세 후 냉간압연을 실시하였다. The slabs having the composition shown in the following Table 1 were heat-treated in a 1200 ° C heating furnace for 1 hour and then subjected to finish hot-rolling at 880 ° C. Then, the hot rolled material was charged into a preheated furnace at 650 ° C and held for 1 hour to simulate hot-rolled coiling by cold rolling, followed by pickling and cold rolling.
상기 냉간 압연 이후, 연속 소둔 모사의 경우에는 하기 표 2와 같이, 다양한 소둔 온도 조건에서 열처리한 후, 초당 3℃로 650℃까지 서냉하고 이를 통상의 냉각속도인 초당 20℃로 440℃까지 냉각하고 360초 동안 과시효 열처리후, 상온까지 초당 3℃로 냉각하였다. 연속소둔 용융도금을 모사하는 경우에는 소둔 열처리후 초당 3℃로 650℃까지 서냉하고, 초당 6℃로 560℃까지 냉각하고 과시효 열처리를 행하고, 이어, 460℃ 용융도금 포트에 침적하고 상온까지 초당 3℃로 냉각하였다. 이어, 강재에 인성을 부여하기 위하여 하기 표 2와 같이, 추가 템퍼링 열처리를 실시하였으며, 다양한 열처리를 행한 후, 강재 시편의 기계적 성질을 측정한 결과를 또헌 하기 표 2에 나타내었다. 한편, 하기 표 2에서 P는 펄라이트, F는 페라이트, B는 베이나이트, M은 마르텐사이트를 의미한다. 그리고 하기 표 1에서 각 원소 함량의 단위는 중량%이다. After the cold rolling, in the case of continuous annealing, annealing was carried out at various annealing temperature conditions as shown in Table 2 below, followed by gradual cooling to 3O < 0 > C and 650 < 0 > C per second and cooling to 440 & After over-heat treatment for 360 seconds, it was cooled to room temperature to 3 ° C per second. In the case of continuous hot-dip galvanizing, the hot-rolled steel sheet was annealed at 3 ° C / sec to 650 ° C / sec, cooled to 660 ° C / 560 ° C / sec and annealed at 460 ° C. 3 < 0 > C. Next, in order to impart toughness to the steel, additional tempering heat treatment was performed as shown in Table 2, and mechanical properties of the steel specimen after various heat treatments were measured, and the results are shown in Table 2 below. In the following Table 2, P means perlite, F means ferrite, B means bainite and M means martensite. In Table 1, the unit of each element content is% by weight.
　 CC MnMn CrCr MoMo AlAl SS BB NN 관계식 1Relationship 1 Ac3Ac3
발명강1Inventive Steel 1 0.510.51 2.122.12 1.481.48 0.650.65 0.0450.045 0.00250.0025 0.00210.0021 0.0040.004 2.442.44 774.7774.7
발명강2Invention river 2 0.530.53 2.452.45 1.521.52 0.870.87 0.0040.004 0.00320.0032 0.0050.005 0.00380.0038 2.982.98 770.6770.6
발명강3Invention steel 3 0.41 0.41 1.621.62 0.820.82 0.480.48 0.026 0.026 0.00480.0048 0.00050.0005 0.0038 0.0038 1.661.66 810.4810.4
발명강4Inventive Steel 4 0.43 0.43 1.751.75 1.381.38 0.62 0.62 0.025 0.025 0.00330.0033 0.0020 0.0020 0.0043 0.0043 2.122.12 806.4806.4
발명강5Invention steel 5 0.580.58 2.982.98 1.961.96 0.950.95 0.026 0.026 0.00420.0042 0.00460.0046 0.0039 0.0039 3.423.42 746.6746.6
비교강6Comparative Steel 6 0.180.18 0.850.85 1.651.65 0.510.51 0.025 0.025 0.0210.021 0.0020 0.0020 0.0055 0.0055 1.531.53 903.5903.5
비교강7Comparative Steel 7 0.090.09 0.150.15 1.851.85 0.780.78 0.020 0.020 0.0190.019 0.00320.0032 0.0057 0.0057 1.301.30 973.6973.6
비교강8Comparative Steel 8 0.350.35 1.361.36 1.251.25 0.280.28 0.024 0.024 0.0560.056 0.00140.0014 0.0054 0.0054 1.661.66 814.8814.8
비교강9Comparative Steel 9 0.110.11 0.850.85 0.310.31 0.540.54 0.031 0.031 0.00280.0028 0.0040.004 0.0040 0.0040 1.171.17 898.9898.9
강종Steel grade 시편번호Specimen Number 소둔 열처리 온도(℃)Annealing heat treatment temperature (캜) 냉연소둔 조직 면적분율(%)Area fraction of cold-rolled annealed structure (%) 연속소둔 후After continuous annealing 템퍼링 온도(℃)Tempering temperature (℃) 연속소둔+TemperingContinuous Annealing + Tempering 비고Remarks
인장강도(MPa)Tensile Strength (MPa) 연신율(%)Elongation (%) 인장강도(MPaTensile Strength (MPa 연신율(%)Elongation (%)
발명강1Inventive Steel 1 1-11-1 820820 M: 100M: 100 20652065 1.71.7 220220 22852285 6.26.2 발명예Honor
1-21-2 725725 P: 100P: 100 12251225 7.67.6 200200 11281128 8.38.3 비교예Comparative Example
발명강 2Invention river 2 2-12-1 845845 M: 100M: 100 21152115 2.22.2 190190 23872387 6.56.5 발명예Honor
2-22-2 680680 P: 100P: 100 13521352 7.17.1 230230 12741274 7.37.3 비교예Comparative Example
발명강 3Invention steel 3 3-13-1 830830 F: 6, M: 91F: 6, M: 91 18751875 1.71.7 200200 20842084 6.86.8 발명예Honor
3-23-2 820820 F: 8, M: 92F: 8, M: 92 19241924 2.22.2 550550 11651165 13.513.5 비교예Comparative Example
발명강4Inventive Steel 4 4-14-1 840840 F: 2, M: 98F: 2, M: 98 22112211 3.73.7 210210 23112311 5.95.9 발명예Honor
4-24-2 840840 F: 2, M: 98F: 2, M: 98 21852185 3.23.2 700700 10531053 15.715.7 비교예Comparative Example
발명강5Invention steel 5 5-15-1 800800 M: 100M: 100 20982098 0.80.8 200200 24852485 6.86.8 발명예Honor
5-25-2 810810 M: 100 M: 100 20892089 0.70.7 5050 20752075 0.60.6 비교예Comparative Example
비교강6Comparative Steel 6 66 910910 F: 71, B: 22, M: 7F: 71, B: 22, M: 7 812812 2222 200200 808808 2323 비교예Comparative Example
비교강 7Comparative Steel 7 77 985985 F: 81, B: 16, M: 3F: 81, B: 16, M: 3 789789 2525 240240 778778 2626 비교예Comparative Example
비교강 8Comparative Steel 8 88 830830 F: 15, B: 8, M: 77F: 15, B: 8, M: 77 17851785 5.65.6 200200 17141714 5.95.9 비교예Comparative Example
비교강 9Comparative Steel 9 99 900900 F: 30, B: 37, M: 33F: 30, B: 37, M: 33 11881188 17.217.2 195195 11701170 17.517.5 비교예Comparative Example
상기 표 1-2로부터 알 수 있는 바와 같이, 본 발명에서 제시한 합금조성 및 제조조건을 모두 만족하는 발명예들의 경우, 냉연 연속소둔 후 미세조직은 면적분율로 90% 이상의 마르텐사이를 포함하며, 템퍼링 후 최대 인장강도는 2000MPa 이상 및 총 연신율은 3% 이상을 확보할 수 있었다.As can be seen from Table 1-2, in the case of the inventions satisfying both the alloy composition and the manufacturing conditions proposed in the present invention, the microstructure after cold rolling continuous annealing contains martensite of 90% or more in an area fraction, The maximum tensile strength after tempering was more than 2000 MPa and the total elongation was 3% or more.
이에 반하여, 본 발명에서 제시한 합금조성 또는 제조조건을 만족하지 못한 비교예들의 경우, 마르텐사이트를 충분히 확보하지 못하여 템퍼링 후 최대 인장강도가 2000MPa 이상을 만족하지 못한 경우도 있으며, 충분한 양의 마르텐사이트를 확보하였더라도 템퍼링 온도 조건이 맞지 않는 경우에 인장강도가 미달하거나, 혹은 인성이 부여되지 않아 총 연신율이 3% 미만으로 나옴을 확인할 수 있었다.On the contrary, in the comparative examples which do not satisfy the alloy composition or the manufacturing conditions proposed in the present invention, the maximum tensile strength after tempering may not satisfy the maximum tensile strength of more than 2000 MPa due to insufficient martensite, It was confirmed that the tensile strength was insufficient or the toughness was not given when the tempering temperature condition was not met, so that the total elongation was less than 3%.
한편 미세조직은 주사전자현미경(SEM)을 이용해 나이탈 에칭법 적용 후 관찰하였으며, 구체적으로, 냉연강판에서의 미세조직 내 세멘타이트의 aspect ratio를 재기 위한 사이즈(장축의 길이/단축의 길이)는 도 1과 같은 투과전자현미경(TEM) 미세조직 관찰 사진을 이용하여 측정하였다. 도 1은 본 실시예에서 시편번호 2-1의 냉간압연 및 연속소둔공정 후 미세조직을 투과전자현미경(TEM)으로 관찰한 사진이다.On the other hand, the microstructure was observed after the application of the separating etching method using a scanning electron microscope (SEM). Specifically, the size (the length of the major axis / the minor axis length) for measuring the aspect ratio of the cementite in the microstructure in the cold- Was measured using a transmission electron microscope (TEM) microstructure observation photograph as shown in Fig. Fig. 1 is a photograph of a microstructure observed by a transmission electron microscope (TEM) after the cold rolling and continuous annealing process of Specimen No. 2-1 in this embodiment.
이상 실시예를 참조하여 설명하였지만, 해당 기술 분야의 숙련된 당업자는 하기의 특허 청구의 범위에 기재된 본 발명의 사상 및 영역으로부터 벗어나지 않는 범위 내에서 본 발명을 다양하게 수정 및 변경시킬 수 있음을 이해할 수 있을 것이다.It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (6)

  1. 중량%로, C: 0.4~0.6%, Mn: 1.5~3.0%, Cr: 0.7~2.0%, P: 0.03% 이하(0%는 제외), S: 0.01% 이하(0% 제외), N: 0.01% 이하(0% 제외), sol.Al: 0.1% 이하(0%제외), Mo: 1.0% 이하(0% 제외) 및 B: 0.005% 이하(0% 제외) 중 1종 이상, 잔여 Fe 및 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하고, (Excluding 0%), S: not more than 0.01% (excluding 0%), N: not more than 0.03%, P: not more than 0.03% 0.01% or less (excluding 0%), sol.Al: 0.1% or less (excluding 0%), Mo: 1.0% or less (excluding 0%) and B: 0.005% or less And inevitable impurities, and satisfies the following relational expression (1)
    강 미세조직이 면적 분율로 90% 이상의 마르텐사이트와 10% 이하의 제 2차상으로 이루어진 냉간압연성이 우수한 초고강도 냉연 강판. An ultra-high strength cold-rolled steel sheet having excellent cold-rolling properties, comprising a steel microstructure having an area fraction of 90% or more of martensite and 10% or less of a secondary phase.
    [관계식 1] [Relation 1]
    1.6 ≤ C + Mn/2 + Cr/3 + Mo/4+ B*100 ≤ 3.521.6? C + Mn / 2 + Cr / 3 + Mo / 4 + B? 100? 3.52
  2. 제 1항에 있어서, 상기 냉연강판의 표면에 전기아연도금층, 용융아연도금층 및 합금화 용융아연도금층 중 하나의 아연도금층이 형성되어 있음을 특징으로 하는 냉간압연성이 우수한 초고강도 냉연강판. The cold-rolled steel sheet according to claim 1, wherein one of an electro-galvanized layer, a hot-dip galvanized layer and a galvannealed hot-dip galvanized layer is formed on the surface of the cold-rolled steel sheet.
  3. 제 1항에 있어서, 상기 강은 하기 관계식 4에 의해 정의되는 A 값이 3 이상을 만족하는 강 미세조직을 가짐을 특징으로 하는 냉간압연성이 우수한 초고강도 냉연강판. The cold-rolled steel sheet according to claim 1, wherein the steel has a steel microstructure satisfying an A value of 3 or more as defined by the following formula (4).
    [관계식 4][Relation 4]
    A=AX/AY A = A X / A Y
    (여기에서, AX 는 1 mm2 면적 내 aspect ratio 가 1.5 이상인 세멘타이트의 개수, AY 는 동일 면적 내 aspect ratio 가 1.5 미만인 세멘타이트의 개수를 의미한다)(Where A X is the number of cementite with an aspect ratio of not less than 1.5 in 1 mm 2 area, and A Y means the number of cementite having an aspect ratio within the same area of less than 1.5)
  4. 중량%로, C: 0.4~0.6%, Mn: 1.5~3.0%, Cr: 0.7~2.0%, P: 0.03% 이하(0%는 제외), S: 0.01% 이하(0% 제외), N: 0.01% 이하(0% 제외), sol.Al: 0.1% 이하(0%제외), Mo: 1.0% 이하(0% 제외) 및 B: 0.005% 이하(0% 제외) 중 1종 이상, 잔여 Fe 및 불가피한 불순물을 포함하고, 하기 관계식 1을 만족하는 강 슬라브를 1100~1300℃로 가열하는 단계; (Excluding 0%), S: not more than 0.01% (excluding 0%), N: not more than 0.03%, P: not more than 0.03% 0.01% or less (excluding 0%), sol.Al: 0.1% or less (excluding 0%), Mo: 1.0% or less (excluding 0%) and B: 0.005% or less And inevitable impurities, and heating a steel slab satisfying the following relational expression 1 to 1100 to 1300 캜;
    상기 가열된 슬라브를 Ar3 + 5℃ ~ Ar3 + 95℃의 온도범위에서 마무리 열간압연함으로써 열연강판을 제조하는 단계;Preparing a hot rolled steel sheet by subjecting the heated slab to finish hot rolling in a temperature range of Ar 3 + 5 ° C to Ar 3 + 95 ° C;
    그 미세조직이 면적 분율로 80% 이상의 펄라이트와 20% 이하의 페라이트를 포함하도록 상기 제조된 열연강판을 권취하는 단계; Winding the prepared hot-rolled steel sheet so that the microstructure contains 80% or more of pearlite and 20% or less of ferrite in an area fraction;
    상기 권취된 열연강판을 압하율 40 ~ 80%로 냉간 압연하는 단계; 및Rolling the rolled hot-rolled steel sheet at a reduction ratio of 40 to 80%; And
    상기 냉간 압연된 냉연 강판을 Ac3 - 5℃ ~ Ac3 + 80℃의 온도범위에서 연속 소둔 후 100~250℃에서 추가 템퍼링(tempering) 열처리함으로써 면적 분율로 90% 이상의 마르텐사이트와 10% 이하의 제 2차상으로 이루어진 초고강도 냉연강판을 제조하는 단계;를 포함하는 냉간압연성이 우수한 초고강도 냉연강판의 제조방법.The cold-rolled cold-rolled steel sheet is subjected to continuous annealing at a temperature range of Ac 3 - 5 ° C to Ac 3 + 80 ° C and then subjected to additional tempering heat treatment at 100 to 250 ° C to obtain a steel sheet having an area fraction of 90% or more of martensite and 10% And a step of preparing an ultra high strength cold rolled steel sheet made of a second phase.
    [관계식 1] [Relation 1]
    1.6 ≤ C + Mn/2 + Cr/3 + Mo/4+ B*100 ≤ 3.521.6? C + Mn / 2 + Cr / 3 + Mo / 4 + B? 100? 3.52
  5. 제 4항에 있어서, 상기 냉연강판의 연속 소둔 후, 추가 템퍼링 처리 전에, 전기아연도금, 용융아연도금 및 합금화 용융아연도금 공정 중 하나의 아연도금공정을 이용하여 냉연간판의 표면에 아연도금층을 형성하는 것을 특징으로 하는 냉간압연성이 우수한 초고강도 냉연강판의 제조방법.The method according to claim 4, wherein a zinc plating layer is formed on the surface of the cold-rolled signboard by using one of zinc electroplating, hot dip galvanizing, and galvannealing hot dip galvanizing after the continuous annealing of the cold rolled steel sheet and before the additional tempering treatment Wherein the cold rolled steel sheet has an excellent cold rolling property.
  6. 제 4항에 있어서, 상기 연속 소둔 열처리된 강판의 최종 미세조직은 하기 관계식 4에 의해 정의되는 A 값이 3 이상인 것을 특징으로 하는 냉간압연성이 우수한 초고강도 냉연강판의 제조방법. 5. The method of manufacturing an ultra-high strength cold rolled steel sheet according to claim 4, wherein the final microstructure of the steel sheet subjected to the continuous annealing treatment has an A value of 3 or more defined by the following relational expression (4).
    [관계식 4][Relation 4]
    A=AX/AY A = A X / A Y
    (여기에서, AX 는 1 mm2 면적 내 aspect ratio 가 1.5 이상인 세멘타이트의 개수, AY 는 동일 면적 내 aspect ratio 가 1.5 미만인 세멘타이트의 개수를 의미한다)(Where A X is the number of cementite with an aspect ratio of not less than 1.5 in 1 mm 2 area, and A Y means the number of cementite having an aspect ratio within the same area of less than 1.5)
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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114829661A (en) * 2019-12-20 2022-07-29 株式会社Posco Steel wire rod having excellent spheroidizing heat treatment characteristics and method for manufacturing same

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20230089785A (en) * 2021-12-14 2023-06-21 주식회사 포스코 Ultra high strength steel sheet having excellent bendability, and method for manufacturing thereof

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100711445B1 (en) * 2005-12-19 2007-04-24 주식회사 포스코 A method for manu- facturing alloyed hot dip galvanized steel sheet for hot press forming having excellent plating adhesion and impact property, the method for manufacturing hot press parts made of it
KR20090124263A (en) * 2008-05-29 2009-12-03 주식회사 포스코 High strength steel sheet for hot forming with excellent heat treatment property, hot formed hardening member and manufacturing methods thereof
KR20100116608A (en) * 2008-01-31 2010-11-01 제이에프이 스틸 가부시키가이샤 High-strength steel sheet and process for production therof
KR20110062899A (en) * 2009-12-04 2011-06-10 주식회사 포스코 Steel sheet with excellent cold rolling property and coatability, method for manufacturing the same, high strength structural member for vehicles and method for manufacturing the same
WO2013051238A1 (en) * 2011-10-04 2013-04-11 Ｊｆｅスチール株式会社 High-strength steel sheet and method for manufacturing same

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5359168B2 (en) 2008-10-08 2013-12-04 Ｊｆｅスチール株式会社 Ultra-high strength cold-rolled steel sheet with excellent ductility and method for producing the same
JP6164113B2 (en) 2014-02-19 2017-07-19 味の素株式会社 Resin sheet with support

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR100711445B1 (en) * 2005-12-19 2007-04-24 주식회사 포스코 A method for manu- facturing alloyed hot dip galvanized steel sheet for hot press forming having excellent plating adhesion and impact property, the method for manufacturing hot press parts made of it
KR20100116608A (en) * 2008-01-31 2010-11-01 제이에프이 스틸 가부시키가이샤 High-strength steel sheet and process for production therof
KR20090124263A (en) * 2008-05-29 2009-12-03 주식회사 포스코 High strength steel sheet for hot forming with excellent heat treatment property, hot formed hardening member and manufacturing methods thereof
KR20110062899A (en) * 2009-12-04 2011-06-10 주식회사 포스코 Steel sheet with excellent cold rolling property and coatability, method for manufacturing the same, high strength structural member for vehicles and method for manufacturing the same
WO2013051238A1 (en) * 2011-10-04 2013-04-11 Ｊｆｅスチール株式会社 High-strength steel sheet and method for manufacturing same

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114829661A (en) * 2019-12-20 2022-07-29 株式会社Posco Steel wire rod having excellent spheroidizing heat treatment characteristics and method for manufacturing same
CN114829661B (en) * 2019-12-20 2023-10-13 株式会社Posco Steel wire rod having excellent spheroidizing heat treatment characteristics and method for manufacturing the same

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