WO2009145562A2 - High-strength steel sheet with excellent ductility and crackless edge portion, hot-dip galvanized steel sheet, and manufacturing method thereof - Google Patents

High-strength steel sheet with excellent ductility and crackless edge portion, hot-dip galvanized steel sheet, and manufacturing method thereof Download PDF

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WO2009145562A2
WO2009145562A2 PCT/KR2009/002810 KR2009002810W WO2009145562A2 WO 2009145562 A2 WO2009145562 A2 WO 2009145562A2 KR 2009002810 W KR2009002810 W KR 2009002810W WO 2009145562 A2 WO2009145562 A2 WO 2009145562A2
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steel sheet
rolled steel
temperature range
cooling
hot
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PCT/KR2009/002810
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French (fr)
Korean (ko)
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WO2009145562A3 (en
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김성일
진영훈
곽재현
진광근
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주식회사 포스코
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Priority to JP2011510432A priority Critical patent/JP5456026B2/en
Priority to US12/991,003 priority patent/US20110064968A1/en
Publication of WO2009145562A2 publication Critical patent/WO2009145562A2/en
Publication of WO2009145562A3 publication Critical patent/WO2009145562A3/en

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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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following 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
    • C21D8/0247—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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0436—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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0463—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment following 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12785—Group IIB metal-base component
    • Y10T428/12792—Zn-base component
    • Y10T428/12799—Next to Fe-base component [e.g., galvanized]

Definitions

  • the present invention relates to a steel sheet for automobiles excellent in strength and workability mainly used in various structural members of automobiles, and a method of manufacturing the same.
  • Steel plate used as structural member among automobile components should be able to absorb external shocks well and improve the stability of passengers when the vehicle crashes.
  • steel sheets that are excellent in both strength and formability have been mainly used for such components as tensile strength of 780 MPa or more and elongation of 25% or more, and have high tensile strength, high elongation and low yield ratio (ratio of yield strength / tensile strength). .
  • Automotive high strength steels include Transformation Induced Plasticity (TRIP) and Dual Phase (DP).
  • TRIP Transformation Induced Plasticity
  • DP Dual Phase
  • the manufacturing process of ultra high strength steel with excellent workability is divided into slab manufacturing, hot rolling, cooling and winding of hot rolled sheet, cold rolling, and annealing.
  • the sheet having the structure of ferrite and pearlite is cold rolled.
  • this steel After annealing at a temperature above A 1 transformation point and below A 3 , and then transforming the austenite formed during the annealing process into martensite by controlling the cooling rate during cooling, this steel is called an abnormal texture.
  • the abnormal tissue steel has a strength determined by the fraction of martensite and ferrite. As the ratio of martensite in the whole structure increases, strength increases and ductility decreases, and therefore, the ratio of martensite must be appropriate.
  • Korean Patent Publication No. 2002-0045212 discloses that the steel containing C: 0.15 ⁇ 0.30wt%, Si: 1.5 ⁇ 2.5wt%, Mn: 0.5 ⁇ 2.0wt%, Al: 0.02 ⁇ 0.1wt% has a strength of 780MPa or more. Provides steel with elongation greater than 30%.
  • steels containing C: 0.06 ⁇ 0.6wt%, [Si + Al]: 0.5 ⁇ 3.0wt%, Mn: 0.5 ⁇ 3.0wt% have 800MPa grade strength and 40% elongation. Provide the river.
  • the amount of [Al + Si] is less than 1.5wt%.
  • Si is added to 0.5 wt%. Therefore, 1.5wt% is the correct expression, not [Si + Al] which is 0.5 ⁇ 3.0wt%.
  • the manufacturing process is classified into two types: first, manufacturing process of annealing or plating after hot rolling, and second, manufacturing process of performing two stage annealing after hot rolling and cold rolling.
  • first manufacturing process of annealing or plating after hot rolling
  • second manufacturing process of performing two stage annealing after hot rolling and cold rolling.
  • martensite is formed in the base structure by the first stage annealing
  • second stage annealing annealing is performed in a conventional metamorphic organic-plastic steel, which is economically lost and has low applicability.
  • the other technologies are only 490MPa and 780MPa, respectively, and because the manufacturing process is complicated, it is economically advantageous and highly applicable manufacturing technology to secure tensile strength of 780MPa or more and elongation of 28% or more simultaneously. need.
  • the present invention controls the composition, and adjusts the cooling step during hot rolling to control the martensite fraction 30 ⁇ 70% to have a tensile strength of 780 ⁇ 980MPa and elongation of 28% or more and at the same time (Edge) It is to provide a high strength steel sheet, a hot-dip galvanized steel sheet and a method of manufacturing the same without cracks of the site.
  • the present invention is in the weight%, C: 0.1 ⁇ 0.25%, Si: 1.0 ⁇ 1.9%, Mn: 1.5 ⁇ 2.5%, Al: 0.5 ⁇ 1.6%, Ti: 0.005 ⁇ 0.03%, B: 5 ⁇ 30ppm, Sb: It comprises 0.01 ⁇ 0.03%, the remainder is made of Fe and unavoidable impurities, to provide a high strength steel sheet and hot-dip galvanized steel sheet characterized by satisfying 1.75 ⁇ Si + Al ⁇ 3.25%.
  • the present invention is in the weight%, C: 0.1 ⁇ 0.25%, Si: 1.0 ⁇ 1.9%, Mn: 1.5 ⁇ 2.5%, Al: 0.5 ⁇ 1.6%, Ti: 0.005 ⁇ 0.03%, B: 5 ⁇ 30ppm, Sb: 0.01 to 0.03%, the remainder is composed of Fe and unavoidable impurities, hot-rolled steel slab that satisfies 1.75 ⁇ Si + Al ⁇ 3.25% in the temperature range of A 3 or more and a cooling rate of 30 ⁇ 200 °C / s Primary cooling to a temperature range of 600 ⁇ 800 °C;
  • It provides a method for producing a high strength hot rolled steel sheet comprising a.
  • the present invention is a weight%, C: 0.1 ⁇ 0.25%, Si: 1.0 ⁇ 1.9%, Mn: 1.5 ⁇ 2.5%, Al: 0.5 ⁇ 1.6%, Ti: 0.005 ⁇ 0.03%, B: 5 ⁇ 30ppm, Sb: 0.01 to 0.03%, the remainder is composed of Fe and unavoidable impurities, hot-rolled steel slab that satisfies 1.75 ⁇ Si + Al ⁇ 3.25% in the temperature range of A 3 or more and 30 ⁇ 200 °C / s First cooling to a temperature range of 600 to 800 ° C. at a cooling rate;
  • It provides a method for producing a high strength cold-rolled steel sheet and a hot-dip galvanizing step further comprising the step of hot-dip galvanized steel sheet comprising a.
  • the present invention has a tensile strength of 780 ⁇ 980MPa and elongation of 28% or more by controlling the composition of components and manufacturing conditions can be used in structural parts with high strength and workability, and at the same time by preventing the cracking of the edge portion There is an effect to increase the economics.
  • Figure 1 shows the test results of the tensile strength according to the [Si] + [Al] content vs. martensite volume fraction pre-tested for the present invention.
  • Figure 2 shows the test results of the elongation according to the martensite volume fraction after [Si] + [Al] content vs. hot rolling pre-tested for the present invention.
  • Figure 3 shows the crack length of the edge after cold rolling according to the [Si] + [Al] content vs. hot rolled Martensite volume fraction pre-tested for the present invention.
  • composition range of the present invention will be described in detail (hereinafter,% by weight).
  • the content of carbon (C) is 0.1 to 0.25%.
  • C is the most important component and is closely related to all physical and chemical properties such as strength and ductility.
  • the amount of carbon is less than 0.1%, the fraction and stability of the retained austenite decreases, and if it exceeds 0.25%, the weldability is lowered, and the workability is lowered due to excessive increase of the second phase fraction. Therefore, the composition range of C was limited to 0.1 to 0.25%.
  • Si silicon
  • Si is a component that stabilizes ferrite by solid solution in ferrite. In this cold-rolled steel sheet, it is dissolved in ferrite to increase the activity of carbon, thereby increasing the concentration of carbon in the austenite phase and suppressing the formation of the bite phase, thereby maintaining the stability of the retained austenite. It serves to raise the And employment increases the strength. If the amount of Si is less than 1.0%, the strength of the steel is lowered, and the carbide formation inhibitory effect such as carbide phase is reduced, and if it exceeds 1.9%, the hot rolled scale is caused, the plating property is deteriorated, and the weldability is also deteriorated. have. Therefore, the composition range of Si was limited to 1.0 to 1.9%.
  • Mn manganese
  • Mn is a component that stabilizes austenite as a component that increases hardenability by facilitating the formation of low temperature transformation phases such as acicular ferrite and bainite by increasing the hardenability. Therefore, when less than 1.5% is added, the above effect cannot be expected, and when excessively added in excess of 2.5%, weldability is lowered, and segregation zones are formed at the center of the sheet during hot rolling, and hydrogen embrittlement is caused by inclusions. Let's do it. Therefore, the content of Mn is 1.5 to 2.5%.
  • the content of aluminum (Al) is 0.5 to 1.6%.
  • Al is inferior in solid solution strengthening effect to Si, but exhibits a solid solution strengthening effect as a ferrite stabilizing element, suppresses the formation of carbides such as carbides, and increases stability by increasing the carbon concentration of residual austenite. If the content of Al is less than 0.5%, the stability of austenite is reduced and it is difficult to suppress the formation of carbides. If the content of Al is more than 1.6%, the fraction of austenite is lowered, so the ductility is relatively lowered, and the surface properties are deteriorated. Therefore, the content of Al is 0.5 ⁇ 1.6%.
  • Ti titanium
  • Ti is a component that forms TiN to inhibit AlN nitride formation through Al-bonding with N, and it is difficult to play such a role at less than 0.005% and more than 0.03% Since the effect of addition cannot be expected, the content of Ti was limited to 0.005 to 0.03%.
  • the content of boron (B) is 5 to 30 ppm.
  • B is a component that improves the hardenability even when a small amount is added to the steel, and when it is added 5 ppm or more, it is segregated at the austenite grain boundary at high temperature to suppress the formation of ferrite, which contributes to the increase of the hardenability, but when excessively added in excess of 30 ppm, the recrystallization temperature is increased. It lowers drawing property and deteriorates weldability. Therefore, the content of B is limited to 5 ⁇ 30ppm.
  • the content of antimony (Sb) is 0.01 to 0.03%.
  • Sb antimony
  • Sb is added in an appropriate amount of 0.01 to 0.03%, the surface properties are improved.
  • Sb is added in excess of 0.03%, thickening occurs on the surface, resulting in poor surface properties.
  • Sb is a kind of impurity that can be inevitably included in steel materials. If the content is less than 0.01%, it can be obtained even when steel is manufactured without a specific purpose. If the content of Sb is less than 0.01%, the surface is thickened. It is set to 0.01% or more because it is too small to generate a change in surface properties. Therefore, the content of Sb is limited to 0.01 ⁇ 0.03%.
  • both Si and Al play a role of inhibiting carbide formation in steel to increase the content of solid solution carbon in residual austenite and to improve the residual austenite stability, thereby controlling the contents of both components together when considering the strength and elongation of TRIP steel. It is necessary to do If the content of the two components exceeds 3.25%, the surface quality such as plating property due to the surface oxide over-formation decreases, and the strength and ductility may decrease due to the decrease of the austenite fraction during the two-phase annealing heat treatment.
  • the content of Si + Al is 1.75 ⁇ 3.25%.
  • the present invention comprises the above composition and the remainder consists of Fe and unavoidable impurities.
  • the steel slab that satisfies the above composition is first cooled at a cooling rate of 30 to 200 ° C / s after hot rolling in an austenite region of A 3 or more.
  • the cooling rate is less than 30 °C / s, it is difficult to secure the target material because the pearlite structure can be formed, and if it exceeds 200 °C / s, the distortion of the material may occur due to residual stress caused by the temperature deviation of the steel sheet It limits to 30-200 degreeC / s.
  • the primary cooling is maintained for 5 to 20 seconds in a temperature section of 600 ⁇ 800 °C. This means that it is cooled by natural convection in the atmosphere at room temperature without forced cooling. Below 600 ° C it is difficult to secure the ferrite phase formation fraction and above 800 ° C excess ferrite may be formed or pearlite tissue may be formed.
  • the secondary cooling rate is 50 ⁇ It limits to 200 degree-C / s.
  • the coiling temperature exceeds 300 °C, it is difficult to secure the target tissue by the formation of bainite phase, and when wound at room temperature ⁇ 300 °C, the matrix structure has a lattice-like fine martensite structure After hot rolling, it has high dislocation density and uniform distribution of solid carbon. Therefore, the coiling temperature is limited to room temperature ⁇ 300 °C.
  • cold rolling is performed at a rolling reduction of 30 to 50%.
  • cold rolling is performed at a reduction ratio of 30 to 50%. This can sufficiently increase the dislocation density in the martensite structure and the ferrite structure after winding through the cold rolling, and the reusability of carbon and an austenite phase formation uniformly occur during annealing. If the cold reduction rate is less than 30%, the dislocation density in the ferrite structure is not sufficient, so that it is difficult to obtain the target structure. If the cold reduction rate exceeds 50%, microcracking occurs easily at the boundary between the martensite phase and the ferrite phase. Crack defects are generated in the. Therefore, the cold reduction rate is limited to 30-50%.
  • the present invention is hot rolled and hot dip galvanized or alloyed hot dip galvanized.
  • the plated layer is attached to the surface layer by passing the steel plate through a plating bath containing molten zinc.
  • the temperature of the plating bath is preferably 450 ⁇ 500 °C and to produce a hot-dip galvanized steel sheet by a slow cooling process at a rate of 30 °C / s or less.
  • the plated steel sheet passed through the plating bath is immediately heated to a temperature range of 500 ⁇ 600 °C to alloy the heat treatment of the hot-dip galvanized layer to produce an alloyed hot-dip galvanized steel sheet fixed by slow cooling at a rate of less than 30 °C / s.
  • Hot rolled steel sheet after hot rolling in the present invention is characterized in that the martensite fraction is 30 ⁇ 70%.
  • Lath-like fine martensite structure produced by primary and secondary cooling after hot rolling induces uniform austenite transformation during annealing after cold rolling and increases the fraction of stabilized residual austenite .
  • the hot rolled steel sheet is manufactured by only one cooling process, and the hot rolled steel sheet contains pearlite structure in which coarse carbides are present. Coarse carbides are re-used during annealing after cold rolling. The carbides are coarse in size, so they are not reusable even at high temperatures above 700 ° C. During the annealing, austenite begins to form mainly near carbides with high carbon concentration.
  • austenite formation is less likely to occur. Therefore, the austenite fraction is lowered during the two-phase annealing and a local deviation also occurs, thereby reducing the residual austenite fraction generated during the cooling after annealing.
  • the martensite phase in the hot rolled steel sheet can alleviate this drawback.
  • the hot rolled steel sheet when the martensite phase is formed through the first and second cooling processes, the hot rolled steel sheet may be manufactured with almost no carbide.
  • the hot rolled steel sheet including the martensite phase is formed of fine carbide in the martensite structure having a high dislocation density during annealing heat treatment, and is re-applied immediately so that the variation in carbon concentration is considerably reduced compared with the case of the pearlite structure. Therefore, the austenite phase formed during annealing is formed evenly distributed in the vicinity of the grain boundary and the near-martensite structure, so that the residual austenite fraction and stability can be improved.
  • the martensite fraction of the hot rolled steel sheet is less than 30%, the effect of increasing the retained austenite fraction is insignificant. If the martensite fraction of the hot rolled steel sheet is more than 70%, fine cracks are generated at the edges during cold rolling. Limited to 70%.
  • the cold rolled steel sheet After the cold rolling and annealing process of the present invention, the cold rolled steel sheet generates residual austenite in the ferrite and bainite structure. At this time, the fraction of retained austenite in the present invention has 5 to 15%. The residual austenite phase appears in the form of a wrestle due to the influence of the wedge shaped martensite structure on the hot rolled steel sheet and is more stable than the remaining austenite of other shapes. In addition, the fraction of bainite tissue has 20 to 40% and the remainder consists of ferrite.
  • a high strength cold rolled steel sheet having a tensile strength of 780 to 980 MPa and an elongation of 28% or more having excellent workability can be produced.
  • Table 1 shows the composition ranges of the steels used in the examples and in the present invention proper adjustment of the components is important to obtain the desired tensile strength and elongation.
  • the steel slab having the composition shown in Table 1 was cold rolled and annealed after cooling and winding through a hot rolling process, and the cooling conditions, cold rolling rate, and tensile test results are shown in Table 2 below.
  • Tensile properties among the mechanical properties of the material, depend on the composition and the fabrication conditions of the microstructure.
  • the steel sheet of the present invention induces a uniform austenite transformation during annealing by lath-shaped fine martensite structure produced immediately after hot rolling, and increases the fraction of stabilized residual austenite therefrom, when subjected to deformation. This is to obtain excellent mechanical properties through transformation.
  • Table 2 shows the results of the cooling process, hot martensite fraction, cold rolling ratio, mechanical properties and edge cracking after hot rolling.
  • Comparative materials 9 to 15 do not satisfy the basic component requirements, it can be seen that even if the cooling conditions, martensite fraction and cold rolling rate conditions during the manufacturing process is properly adjusted, the strength and ductility targeted by the present invention are not obtained.
  • Comparative Materials 2-2, 2-3, 3-2, 3-3, 4-2, 4-3, 5-2, 7-2, 7-3, and 8-2 met the component requirements, but cooling conditions It can be seen that the target mechanical properties cannot be obtained due to failure to meet the requirements such as martensite fraction, cold reduction rate, or microcracks at the edges.
  • the crack length of the edge was measured by using a 200-magnification optical microscope to measure the martensite fraction, and the result was measured by an image analyzer after etching the microstructure at the thickness t / 4 position with 2% Nital etchant.
  • the fine cracks generated at were randomly selected at the edges of the cold rolled rolled plate and were averaged after selecting at least 30 of the longest cracks occurring within the length of 100 mm.

Abstract

An object of the present invention is to provide a steel sheet with a tensile strength of 780 to 980 MPa and an elongation of 28% or higher, and a crackless edge portion. The present invention provides a high-strength steel sheet, a hot-dip galvanized steel sheet and a method for manufacturing these steel sheets, the steel sheet comprising: by weight %, C: 0.1 to 0.25%, Si: 1.0 to 1.9%, Mn: 1.5 to 2.5%, Al: 0.5 to 1.6%, Ti: 0.005 to 0.03%, B: 5 to 30 ppm, and Sb: 0.01 to 0.03%, and the remainder consisting of Fe and inevitable impurities, wherein 1.75≤Si+Al≤3.25.

Description

연성이 우수하고 에지부 균열이 없는 고강도 강판, 용융아연도금강판 및 그 제조방법High strength steel plate with excellent ductility and no edge cracking, hot dip galvanized steel sheet and manufacturing method thereof
본 발명은 자동차의 각종 구조부재에 주로 사용되는 강도 및 가공성이 우수한 자동차용 강판 및 그 제조방법에 관한 것이다.The present invention relates to a steel sheet for automobiles excellent in strength and workability mainly used in various structural members of automobiles, and a method of manufacturing the same.
보다 상세하게는 인장강도 780~980MPa의 강도를 가지면서 동시에 연신율이 최소 28% 이상이고, 냉간압연 후 압연판 에지(Edge)부위의 균열발생이 없는 고강도 냉연강판 및 용융아연도금강판을 제조하는 방법에 관한 것이다. More specifically, a method of manufacturing a high strength cold rolled steel sheet and hot dip galvanized steel sheet having a strength of 780 to 980 MPa at the same time and an elongation of at least 28% and no cracking at the edge of the rolled plate after cold rolling. It is about.
자동차의 구성품 중 구조부재로 사용되는 강판은 외부의 충격을 잘 흡수하여 차량의 충돌시 승객의 안정성을 향상시킬 수 있어야 한다. 최근에는 이와 같은 부품으로 인장강도 780MPa 이상, 연신율 25% 이상의 강도와 성형성이 모두 우수한 강판이 주로 사용되고 있으며, 높은 인장강도와 높은 연신율, 낮은 항복비(항복강도/인장강도의 비율)를 가져야 한다.Steel plate used as structural member among automobile components should be able to absorb external shocks well and improve the stability of passengers when the vehicle crashes. Recently, steel sheets that are excellent in both strength and formability have been mainly used for such components as tensile strength of 780 MPa or more and elongation of 25% or more, and have high tensile strength, high elongation and low yield ratio (ratio of yield strength / tensile strength). .
최근에는 자동차 배기가스에 의한 환경오염문제가 대두되면서 연비를 더욱 향상 시키기 위한 기술개발의 방향으로 인장강도 780MPa 이상의 초고강도강을 사용하여 자동차 경량화를 이루기 위한 연구가 증가되고 있다. Recently, as the environmental pollution problem caused by automobile exhaust gas has emerged, research to achieve light weight of automobiles by using ultra high strength steel with tensile strength of 780 MPa or more in the direction of technology development to further improve fuel economy has been increasing.
자동차용 고강도강은 대표적으로 변태유기소성변형강(TRIP: Transformation Induced Plasticity)과 이상조직강(DP: Dual Phase)이 있다.Automotive high strength steels include Transformation Induced Plasticity (TRIP) and Dual Phase (DP).
가공성이 우수한 초고강도강의 제조공정은 크게 슬라브제조, 열간압연, 열간압연 판재를 냉각하여 권취하는 공정, 냉간압연 그리고 소둔공정으로 구분되는데, 열간압연 후 페라이트와 펄라이트의 조직을 갖는 판재를 냉간압연을 하여 가공한 후 A1 변태점 이상 A3 이하의 온도로 소둔을 한 후, 냉각 시 냉각속도를 조절하여 소둔과정에서 형성된 오스테나이트를 마르텐사이트로 변태시키는 경우 이 강을 이상조직상이라고 한다. 상기의 이상조직강은 마르텐사이트와 페라이트의 분율에 의해 강도가 결정이 되는데, 전체 조직 중에서 마르텐사이트의 비율이 증가할수록 강도가 증가하고 연성이 감소하게 되므로, 적정한 마르텐사이트의 비율을 가져야만 한다. 한편, 상기 이상조직강을 제조하는 방법과 같이 소둔과정에서 오스테나이트를 형성한 후 냉각과정에서 냉각속도와 종료되는 냉각온도를 제어하므로써 상온에서 일부 오스테나이트를 잔류시킴으로써 강도와 연성을 동시에 증가시키는 방법이 있다. 이렇게 생성된 잔류 오스테나이트를 소성변형 중에 마르텐사이트로 변태하도록 해서 강도증가와 함께 소성유기변태에 의해 응력집중을 완화시킴으로써 연성을 증가시키는데 이를 변태유기소성강(TRIP)이라고 부르며, 높은 강도와 연성을 갖는 고강도강으로 사용되고 있다.The manufacturing process of ultra high strength steel with excellent workability is divided into slab manufacturing, hot rolling, cooling and winding of hot rolled sheet, cold rolling, and annealing. After hot rolling, the sheet having the structure of ferrite and pearlite is cold rolled. After annealing at a temperature above A 1 transformation point and below A 3 , and then transforming the austenite formed during the annealing process into martensite by controlling the cooling rate during cooling, this steel is called an abnormal texture. The abnormal tissue steel has a strength determined by the fraction of martensite and ferrite. As the ratio of martensite in the whole structure increases, strength increases and ductility decreases, and therefore, the ratio of martensite must be appropriate. On the other hand, after forming austenite in the annealing process, such as the method for manufacturing the abnormal tissue steel, by controlling the cooling rate and the end of the cooling temperature in the cooling process by increasing the strength and ductility at the same time by remaining austenite at room temperature There is this. The residual austenite thus formed is transformed into martensite during plastic deformation, thereby increasing the strength and relieving stress concentration by plastic organic transformation. This is called ductile organic plastic steel (TRIP). It is used as the high strength steel which has.
상기의 변태유기소성강은 준안정한 잔류 오스테나이트를 변형 시 상온에서 마르텐사이트로의 변태를 억제하여 일정한 분율 이상을 유지하는 것이 강도와 연성을 높이는 데 매우 중요하다. 이를 위해 Si, Al 등을 첨가하여 페라이트 내 탄소의 활동도를 높여서 탄화물 생성을 억제하여 오스테나이트상 내에 탄소의 농도를 증가시킴으로써 잔류 오스테나이트의 안정성을 확보한다.In the metamorphic organic plastic steels, it is very important to increase the strength and ductility by maintaining metabolic stable austenite at a constant fraction or more by suppressing transformation to martensite at room temperature. To this end, by adding Si, Al, etc. to increase the activity of the carbon in the ferrite to suppress the formation of carbides to increase the concentration of carbon in the austenite phase to ensure the stability of the retained austenite.
이러한 높은 강도와 연신율을 확보하기 위한 기 공지된 기술로는 일본 특개평 6-1458920이 있다. 이 기술에 의하면 C:0.6~0.22wt%, Si:0.05~1.0wt%, Mn:0.5~2.0wt%, Al:0.25~1.5wt% 를 함유한 강에 경우에 따라 Mo:0.03~0.3wt% 를 첨가하여 490MPa 이상의 가도와 35% 이상의 연신율을 갖는 강을 제공한다.As a known technique for securing such high strength and elongation, there is Japanese Patent Laid-Open No. 6-1458920. According to this technique, Mo: 0.03 ~ 0.3wt% in the case of steel containing C: 0.6 ~ 0.22wt%, Si: 0.05 ~ 1.0wt%, Mn: 0.5 ~ 2.0wt%, Al: 0.25 ~ 1.5wt% Is added to provide steel having a ductility of at least 490 MPa and an elongation of at least 35%.
또한 한국 특허공개공보 2002-0045212호에서는 C:0.15~0.30wt%, Si:1.5~2.5wt%, Mn:0.5~2.0wt%, Al:0.02~0.1wt% 를 함유한 강이 780MPa이상의 강도와 30%이상의 연신율을 갖는 강을 제공한다.In addition, Korean Patent Publication No. 2002-0045212 discloses that the steel containing C: 0.15 ~ 0.30wt%, Si: 1.5 ~ 2.5wt%, Mn: 0.5 ~ 2.0wt%, Al: 0.02 ~ 0.1wt% has a strength of 780MPa or more. Provides steel with elongation greater than 30%.
일본특개 2005-336526호 공보에 의하면 C:0.06~0.6wt%, [Si+Al]:0.5~3.0wt%, Mn:0.5~3.0wt% 를 함유한 강이 800MPa급 강도와 40% 연신율을 갖는 강을 제공한다. 그러나 성분에서는 실제 내용을 보면 [Al+Si]의 양이 1.5wt% 이하인 것을 알 수 있다. 예를 들어 Al이 1wt%가 첨가되면 Si는 0.5wt%가 첨가되는 형식이다. 그러므로 성분범위가 0.5~3.0wt%인 [Si+Al]가 아니라 1.5wt%가 정확한 표현이다. 그리고 내용 중 제조공정을 두가지로 분류하는데, 첫째는 열간압연 후 소둔이나 도금을 하는 제조공정, 둘째는 열간압연, 냉간압연 후 2단 소둔을 하는 제조공정으로 분류를 했다. 2단 소둔시 냉간압연 이후 1단계 소둔에 의해 기지조직에 마르텐사이트를 형성하고, 2단계 소둔에서 통상적인 변태유기소성강에서 실시하는 소둔을 하여 제조를 하는데 이는 경제적으로 손실이며 적용가능성이 낮다.According to Japanese Laid-Open Patent Publication No. 2005-336526, steels containing C: 0.06 ~ 0.6wt%, [Si + Al]: 0.5 ~ 3.0wt%, Mn: 0.5 ~ 3.0wt% have 800MPa grade strength and 40% elongation. Provide the river. However, from the actual content of the component it can be seen that the amount of [Al + Si] is less than 1.5wt%. For example, when 1 wt% of Al is added, Si is added to 0.5 wt%. Therefore, 1.5wt% is the correct expression, not [Si + Al] which is 0.5 ~ 3.0wt%. In the contents, the manufacturing process is classified into two types: first, manufacturing process of annealing or plating after hot rolling, and second, manufacturing process of performing two stage annealing after hot rolling and cold rolling. In the second stage annealing, after cold rolling, martensite is formed in the base structure by the first stage annealing, and in the second stage annealing, annealing is performed in a conventional metamorphic organic-plastic steel, which is economically lost and has low applicability.
상기의 타 기술들은 각각 강도가 490MPa, 780MPa 급 정도의 강도에 불과하며, 제조공정이 복잡하므로 780MPa 이상의 인장강도와 28%이상의 연신율을 동시에 확보하기 위해서는 경제적으로도 유리하고 적용가능성이 높은 제조기술이 필요하다.The other technologies are only 490MPa and 780MPa, respectively, and because the manufacturing process is complicated, it is economically advantageous and highly applicable manufacturing technology to secure tensile strength of 780MPa or more and elongation of 28% or more simultaneously. need.
본 발명은 조성성분을 제어하고, 열간압연시에 냉각단계를 조정하여 마르텐사이트 분율을 30~70% 포함하도록 제어하여 780~980MPa 의 인장강도를 갖고 28%이상의 연신율을 가짐과 동시에 에지(Edge)부위의 크랙이 없는 고강도 강판, 용융아연도금강판 및 그 제조방법을 제공하고자 하는 것이다.The present invention controls the composition, and adjusts the cooling step during hot rolling to control the martensite fraction 30 ~ 70% to have a tensile strength of 780 ~ 980MPa and elongation of 28% or more and at the same time (Edge) It is to provide a high strength steel sheet, a hot-dip galvanized steel sheet and a method of manufacturing the same without cracks of the site.
본 발명은 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하는 것을 특징으로 하는 고강도 강판 및 용융아연도금강판을 제공한다.The present invention is in the weight%, C: 0.1 ~ 0.25%, Si: 1.0 ~ 1.9%, Mn: 1.5 ~ 2.5%, Al: 0.5 ~ 1.6%, Ti: 0.005 ~ 0.03%, B: 5 ~ 30ppm, Sb: It comprises 0.01 ~ 0.03%, the remainder is made of Fe and unavoidable impurities, to provide a high strength steel sheet and hot-dip galvanized steel sheet characterized by satisfying 1.75≤Si + Al≤3.25%.
본 발명은 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하는 강 슬라브를 A3이상의 온도범위에서 열간압연하고 30~200℃/s의 냉각속도로 600~800℃의 온도범위까지 1차 냉각하는 단계;The present invention is in the weight%, C: 0.1 ~ 0.25%, Si: 1.0 ~ 1.9%, Mn: 1.5 ~ 2.5%, Al: 0.5 ~ 1.6%, Ti: 0.005 ~ 0.03%, B: 5 ~ 30ppm, Sb: 0.01 to 0.03%, the remainder is composed of Fe and unavoidable impurities, hot-rolled steel slab that satisfies 1.75≤Si + Al≤3.25% in the temperature range of A 3 or more and a cooling rate of 30 ~ 200 ℃ / s Primary cooling to a temperature range of 600 ~ 800 ℃;
상기 1차 냉각한 열연강판을 600~800℃의 온도범위에서 공냉하는 단계;Air-cooling the first cooled hot rolled steel sheet in a temperature range of 600 to 800 ° C;
상기 공냉한 열연강판을 50~200℃/s의 냉각속도로 상온~300℃의 온도범위까지 2차 냉각하는 단계; 및Secondly cooling the air-cooled hot rolled steel sheet to a temperature range of room temperature to 300 ° C at a cooling rate of 50 to 200 ° C / s; And
상기 2차 냉각한 열연강판을 상온~300℃의 온도범위에서 권취하는 단계Winding the secondary cooled hot rolled steel sheet in a temperature range of room temperature to 300 ° C
를 포함하는 것을 특징으로 하는 고강도 열연강판을 제조하는 방법을 제공한다.It provides a method for producing a high strength hot rolled steel sheet comprising a.
또한, 본 발명은 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하는 강 슬라브를 A3이상의 온도범위에서 열간압연하고 30~200℃/s의 냉각속도로 600~800℃의 온도범위까지 1차 냉각하는 단계;In addition, the present invention is a weight%, C: 0.1 ~ 0.25%, Si: 1.0 ~ 1.9%, Mn: 1.5 ~ 2.5%, Al: 0.5 ~ 1.6%, Ti: 0.005 ~ 0.03%, B: 5 ~ 30ppm, Sb: 0.01 to 0.03%, the remainder is composed of Fe and unavoidable impurities, hot-rolled steel slab that satisfies 1.75≤Si + Al≤3.25% in the temperature range of A 3 or more and 30 ~ 200 ℃ / s First cooling to a temperature range of 600 to 800 ° C. at a cooling rate;
상기 1차 냉각한 열연강판을 600~800℃의 온도범위에서 공냉하는 단계;Air-cooling the first cooled hot rolled steel sheet in a temperature range of 600 to 800 ° C;
상기 공냉한 열연강판을 50~200℃/s의 냉각속도로 상온~300℃의 온도범위까지 2차 냉각하는 단계;Secondly cooling the air-cooled hot rolled steel sheet to a temperature range of room temperature to 300 ° C at a cooling rate of 50 to 200 ° C / s;
상기 2차 냉각한 열연강판을 상온~300℃의 온도범위에서 권취하는 단계; 및 Winding the secondary cooled hot rolled steel sheet in a temperature range of room temperature to 300 ° C .; And
상기 권취한 열연강판을 30~50%의 압하율로 냉간압연하고 소둔하는 단계Cold rolling and annealing the wound hot rolled steel sheet at a reduction ratio of 30 to 50%
를 포함하는 것을 특징으로 하는 고강도 냉연강판을 제조하는 방법 및 용융아연도금하는 단계를 더 포함하는 고강도 용융아연도금강판을 제조하는 방법을 제공한다.It provides a method for producing a high strength cold-rolled steel sheet and a hot-dip galvanizing step further comprising the step of hot-dip galvanized steel sheet comprising a.
본 발명은 성분구성과 제조조건을 제어함으로써 780~980MPa 의 인장강도와 28% 이상의 연신율을 갖게 되어 높은 강도와 가공성을 가진 구조용 부품에 이용될 수 있고, 동시에 에지부위의 크랙이 발생하는 것을 방지함으로써 경제성을 높일 수 있는 효과가 있다.The present invention has a tensile strength of 780 ~ 980MPa and elongation of 28% or more by controlling the composition of components and manufacturing conditions can be used in structural parts with high strength and workability, and at the same time by preventing the cracking of the edge portion There is an effect to increase the economics.
도1은 본 발명을 위해 예비 시험된 [Si]+[Al]함량 vs 열연 후 마르텐사이트 부피분율에 따른 인장강도의 시험결과를 나타낸 것이다.Figure 1 shows the test results of the tensile strength according to the [Si] + [Al] content vs. martensite volume fraction pre-tested for the present invention.
도2는 본 발명을 위해 예비 시험된 [Si]+[Al]함량 vs 열연 후 마르텐사이트 부피분율에 따른 연신율의 시험결과를 나타낸 것이다.Figure 2 shows the test results of the elongation according to the martensite volume fraction after [Si] + [Al] content vs. hot rolling pre-tested for the present invention.
도3은 본 발명을 위해 예비 시험된 [Si]+[Al]함량 vs 열연 후 마르텐사이트 부피분율에 따른 냉간압연 후의 에지(Edge)부위 균열길이를 나타낸 것이다.Figure 3 shows the crack length of the edge after cold rolling according to the [Si] + [Al] content vs. hot rolled Martensite volume fraction pre-tested for the present invention.
도4는 본 발명에 따라 제조된 발명강과 비교강의 [Si]+[Al]함량 vs 열연 후 마르텐사이트 부피분율에 따른 인장강도, 연신율 및 냉간압연 후 에지(Edge)부위 균열길이를 나타낸 것이다.4 shows tensile strength, elongation, and edge crack length after cold rolling according to [Si] + [Al] content vs. martensite volume fraction of inventive steel and comparative steel prepared according to the present invention.
이하, 본 발명의 조성범위에 대하여 상세히 설명한다(이하, 중량%).Hereinafter, the composition range of the present invention will be described in detail (hereinafter,% by weight).
탄소(C)의 함량은 0.1~0.25%로 한다. C는 가장 중요한 성분으로 강도 및 연성 등 모든 물리적, 화학적 특성에 밀접한 관계를 갖는다. 본 발명에서는 탄소의 양이 0.1% 미만이 되면 잔류 오스테나이트의 분율과 안정성이 감소하며, 0.25%를 초과하게 되면 용접성이 저하되며, 제2상 분율의 과대한 증가로 인하여 가공성이 저하되는 단점이 있으므로, C의 조성범위를 0.1~0.25%로 제한하였다.The content of carbon (C) is 0.1 to 0.25%. C is the most important component and is closely related to all physical and chemical properties such as strength and ductility. In the present invention, if the amount of carbon is less than 0.1%, the fraction and stability of the retained austenite decreases, and if it exceeds 0.25%, the weldability is lowered, and the workability is lowered due to excessive increase of the second phase fraction. Therefore, the composition range of C was limited to 0.1 to 0.25%.
실리콘(Si)의 함량은 1.0~1.9%로 한다. Si는 페라이트에 고용되어서 페라이트를 안정화 시키는 성분이며, 본 냉연강판에서는 페라이트 내에 고용되어 탄소의 활동도를 높임으로써 오스테나이트 상 내에 탄소의 농도를 증가시키고, 카바이트상의 생성을 억제시켜서 잔류 오스테나이트의 안정성을 높이는 역활을 한다. 그리고 고용됨으로써 강도 증가효과가 있다. Si의 양이 1.0% 미만이 되면 강의 강도가 저하되며, 카바이드상과 같은 탄화물 생성억제 효과가 저하되고, 1.9%르 초과하게 되면 열연스케일을 유발시키며, 도금성이 나빠지고 용접성도 열화되는 특성이 있다. 따라서 Si의 조성범위를 1.0~1.9%로 제한하였다.The content of silicon (Si) is 1.0 to 1.9%. Si is a component that stabilizes ferrite by solid solution in ferrite. In this cold-rolled steel sheet, it is dissolved in ferrite to increase the activity of carbon, thereby increasing the concentration of carbon in the austenite phase and suppressing the formation of the bite phase, thereby maintaining the stability of the retained austenite. It serves to raise the And employment increases the strength. If the amount of Si is less than 1.0%, the strength of the steel is lowered, and the carbide formation inhibitory effect such as carbide phase is reduced, and if it exceeds 1.9%, the hot rolled scale is caused, the plating property is deteriorated, and the weldability is also deteriorated. have. Therefore, the composition range of Si was limited to 1.0 to 1.9%.
망간(Mn)의 함량은 1.5~2.5%로 한다. Mn은 경화능을 크게하여 침상형 페라이트 및 베이나이트와 같은 저온 변태상의 생성을 용이하게 하며 강도를 증가시키는 성분으로 오스테나이트를 안정화시키는 성분이다. 따라서 1.5% 미만을 첨가하는 경우에는 상기 효과를 기대할 수 없고, 2.5%를 초과하여 과도하게 첨가되는 경우 용접성이 저하되고, 열간 압연시 판재의 중앙에 편석대를 형성하며 개재물 형성으로 수소취성을 야기시킨다. 따라서 Mn의 함량은 1.5~2.5%로 한다. The content of manganese (Mn) is 1.5 to 2.5%. Mn is a component that stabilizes austenite as a component that increases hardenability by facilitating the formation of low temperature transformation phases such as acicular ferrite and bainite by increasing the hardenability. Therefore, when less than 1.5% is added, the above effect cannot be expected, and when excessively added in excess of 2.5%, weldability is lowered, and segregation zones are formed at the center of the sheet during hot rolling, and hydrogen embrittlement is caused by inclusions. Let's do it. Therefore, the content of Mn is 1.5 to 2.5%.
알루미늄(Al)의 함량은 0.5~1.6%로 한다. Al은 Si에 비해서는 고용강화 효과가 떨어지지만 페라이트 안정화 원소로서 고용강화 효과를 나타내고, 카바이드와 같은 탄화물의 생성을 억제하며, 잔류 오스테나이트의 탄소농도를 증가시켜서 안정성을 높이는 성분이다. Al의 함량이 0.5% 미만에서는 오스테나이트의 안정성이 저하되고 탄화물의 생성을 억제하기가 힘들며, 1.6% 초과에서는 오스테나이트의 분율이 저하되어서 연성이 상대적으로 저하되며 표면 특성이 나빠지게 된다. 따라서 Al의 함량은 0.5~1.6%로 한다.The content of aluminum (Al) is 0.5 to 1.6%. Al is inferior in solid solution strengthening effect to Si, but exhibits a solid solution strengthening effect as a ferrite stabilizing element, suppresses the formation of carbides such as carbides, and increases stability by increasing the carbon concentration of residual austenite. If the content of Al is less than 0.5%, the stability of austenite is reduced and it is difficult to suppress the formation of carbides. If the content of Al is more than 1.6%, the fraction of austenite is lowered, so the ductility is relatively lowered, and the surface properties are deteriorated. Therefore, the content of Al is 0.5 ~ 1.6%.
티타늄(Ti)의 함량은 0.005~0.03%로 한다. Ti는 Al성분의 N과의 결합을 통한 AlN 질화물을 형성을 억제하여 Al이 본연의 작용을 할 수 있게 TiN을 형성하는 성분으로 0.005% 미만에서는 그러한 역활을 하기 힘들며, 0.03%를 초과해서는 더 이상 첨가하는 효과을 기대할 수 없으므로, Ti의 함량은 0.005~0.03%로 한정하였다.The content of titanium (Ti) is 0.005 to 0.03%. Ti is a component that forms TiN to inhibit AlN nitride formation through Al-bonding with N, and it is difficult to play such a role at less than 0.005% and more than 0.03% Since the effect of addition cannot be expected, the content of Ti was limited to 0.005 to 0.03%.
붕소(B)의 함량은 5~30ppm으로 한다. B는 강 중에 소량을 첨가해도 경화능을 향상시키는 성분이고, 5ppm 이상 첨가되면 고온에서 오스테나이트 입계에 편석되어 페라이트 형성을 억제하여 경화능 향상을 기여하지만 과다하게 30ppm 초과하여 첨가되면 재결정 온도를 상승시켜서 드로잉성을 저하시키며 용접성을 열화시킨다. 따라서 B의 함량은 5~30ppm 으로 한정한다.The content of boron (B) is 5 to 30 ppm. B is a component that improves the hardenability even when a small amount is added to the steel, and when it is added 5 ppm or more, it is segregated at the austenite grain boundary at high temperature to suppress the formation of ferrite, which contributes to the increase of the hardenability, but when excessively added in excess of 30 ppm, the recrystallization temperature is increased. It lowers drawing property and deteriorates weldability. Therefore, the content of B is limited to 5 ~ 30ppm.
안티몬(Sb)의 함량은 0.01~0.03%로 한다. Sb는 적정한 양의 0.01~0.03%를 첨가하면 표면특성을 개선시키나, 0.03% 초과하여 과다하게 첨가되면 표면에 농화가 발생하여 표면특성이 나빠지게 된다. Sb는 철강재료에 불가피하게 포함될 수 있는불순물의 일종으로 그 함량이 0.01%미만이면 특정한 목적없이 강을 제조한 경우에도 얻어질 수 있는 함량이며, Sb의 함량이 0.01%미만인 경우에는 표면에 농화가 발생하여 표면특성의 변화를 일으키기에는 너무 적기 때문에 0.01%이상으로 한다. 따라서 Sb의 함량은 0.01~0.03%로 한정한다.The content of antimony (Sb) is 0.01 to 0.03%. When Sb is added in an appropriate amount of 0.01 to 0.03%, the surface properties are improved. However, when Sb is added in excess of 0.03%, thickening occurs on the surface, resulting in poor surface properties. Sb is a kind of impurity that can be inevitably included in steel materials. If the content is less than 0.01%, it can be obtained even when steel is manufactured without a specific purpose. If the content of Sb is less than 0.01%, the surface is thickened. It is set to 0.01% or more because it is too small to generate a change in surface properties. Therefore, the content of Sb is limited to 0.01 ~ 0.03%.
본 발명에서는 1.75≤Si+Al≤3.25 를 만족한다. Si와 Al은 모두 강의 탄화물 형성을 억제하는 역활을 하여 잔류 오스테나이트내 고용탄소의 함량을 높여주고 잔류 오스테나이트 안정성을 개선시키는 역활을 함으로써 TRIP강의 강도와 연신율을 고려할 때 두 성분의 함량을 함께 제어하는 것이 필요하다. 두 성분이 함량이 3.25%를 초과하면 표면 산화물 과다형성에 의한 도금성 등의 표면품질이 저하하며 2상역 소 둔 열처리 중 오스테나이트 분율 감소로 강도 및 연성이 감소할 수 있다. 또한 1.75% 미만이면 목표로 한 인장강도 780MPa 이상의 TRIP강을 제조하는데 필요한 기본 고용강화 효과가 감소하며 잔류 오스테나이트 안정성을 확보하기 어렵게 된다. 따라서 Si+Al의 함량은 1.75~3.25%로 한다.In the present invention, 1.75 ≦ Si + Al ≦ 3.25 is satisfied. Both Si and Al play a role of inhibiting carbide formation in steel to increase the content of solid solution carbon in residual austenite and to improve the residual austenite stability, thereby controlling the contents of both components together when considering the strength and elongation of TRIP steel. It is necessary to do If the content of the two components exceeds 3.25%, the surface quality such as plating property due to the surface oxide over-formation decreases, and the strength and ductility may decrease due to the decrease of the austenite fraction during the two-phase annealing heat treatment. In addition, if it is less than 1.75%, the basic solid solution strengthening effect required for manufacturing TRIP steel with a target tensile strength of 780 MPa or more is reduced, and it is difficult to secure residual austenite stability. Therefore, the content of Si + Al is 1.75 ~ 3.25%.
본 발명은 상기의 조성을 포함하고 나머지는 Fe 및 불가피한 불순물로 구성된다.The present invention comprises the above composition and the remainder consists of Fe and unavoidable impurities.
이하, 본 발명의 제조방법을 상세히 설명한다. Hereinafter, the manufacturing method of the present invention will be described in detail.
본 발명은 상기의 조성을 만족하는 강 슬라브를 A3 이상의 오스테나이트 영역에서 열간압연 후 30~200℃/s의 냉각속도로 1차 냉각한다. 이때 냉각속도가 30℃/s 미만에서는 펄라이트 조직이 형성될 수 있어서 목표로 하는 재질을 확보하기 어려우며, 200℃/s 초과하면 강판의 온도편차 발생에 의해 잔류 응력 발생으로 소재의 뒤틀림이 발생할 수 있으므로 30~200℃/s로 한정한다. In the present invention, the steel slab that satisfies the above composition is first cooled at a cooling rate of 30 to 200 ° C / s after hot rolling in an austenite region of A 3 or more. At this time, when the cooling rate is less than 30 ℃ / s, it is difficult to secure the target material because the pearlite structure can be formed, and if it exceeds 200 ℃ / s, the distortion of the material may occur due to residual stress caused by the temperature deviation of the steel sheet It limits to 30-200 degreeC / s.
상기 1차 냉각하고 600~800℃의 온도구간에서 5~20초간 유지한다. 이는 강제냉각 없이 상온의 대기에서 자연대류에 의해 냉각됨을 의미한다. 600℃ 미만에서는 페라이트 상형성 분율 확보가 어렵고 800℃ 초과에서는 과도한 페라이트가 형성되거나 펄라이트 조직이 형성될 수 있다. The primary cooling is maintained for 5 to 20 seconds in a temperature section of 600 ~ 800 ℃. This means that it is cooled by natural convection in the atmosphere at room temperature without forced cooling. Below 600 ° C it is difficult to secure the ferrite phase formation fraction and above 800 ° C excess ferrite may be formed or pearlite tissue may be formed.
상기 공냉한 후에 50~200℃/s의 냉각속도로 2차 냉각한 후 상온~300 ℃ 에서 권취한다. 냉각속도 50℃/s 미만에서는 베이나이트상 형성에 의해 목표로 하는 조직을 얻기 어려우며 200℃/s 초과에서는 과도한 마르텐사이트상이 형성될 수 있으며 압연판의 형상 뒤틀림 발생할 수 있어 2차 냉각속도는 50~200℃/s로 한정한다.After the air cooling, after the second cooling at a cooling rate of 50 ~ 200 ℃ / s and wound at room temperature ~ 300 ℃. If the cooling rate is less than 50 ℃ / s, it is difficult to obtain the target structure by the bainite phase formation, and if it exceeds 200 ℃ / s, excessive martensite phase may be formed and the shape of the rolled plate may occur, the secondary cooling rate is 50 ~ It limits to 200 degree-C / s.
또한 권취온도가 300℃를 초과하게 되면 베이나이트상 형성에 의해 목표로 한 조직을 확보하기 어렵고 상온~300℃로 권취를 하게 되면 기지조직이 레쓰(lath)형상의 미세한 마르텐사이트 조직을 갖지게 되므로 열연 후 높은 전위밀도와 균일한 고용탄소 분포를 갖게 된다. 따라서 권취온도는 상온~300℃로 한정한다.In addition, if the coiling temperature exceeds 300 ℃, it is difficult to secure the target tissue by the formation of bainite phase, and when wound at room temperature ~ 300 ℃, the matrix structure has a lattice-like fine martensite structure After hot rolling, it has high dislocation density and uniform distribution of solid carbon. Therefore, the coiling temperature is limited to room temperature ~ 300 ℃.
권취 후 30~50%의 압하율로 냉간압연 한다. 통상적으로 60%의 압하율로 하는데 반해, 본 발명에서는 30~50%의 압하율로 냉간압연한다. 이는 냉간압연을 통해서 권취 후 생긴 마르텐사이트 조직과 페라이트 조직 중 페라이트 조직에 전위밀도를 충분히 증가시킬 수 있으며, 소둔 중 탄소의 재고용과 오스테나이트상 형성이 균일하게 발생하게 된다. 냉간압하율이 30% 미만이면 페라이트 조직내 전위밀도가 충분하지 않아 목표로 하는 조직을 얻기 어려우며 50% 초과하면 마르텐사이트상과 페라이트상 경계에서 미세균열이 쉽게 발생하여 특히 압연판 에지(edge)부위에 균열 결함이 발생하게 된다. 따라서 냉간압하율을 30~50%로 제한한다. After winding, cold rolling is performed at a rolling reduction of 30 to 50%. In general, in the present invention, cold rolling is performed at a reduction ratio of 30 to 50%. This can sufficiently increase the dislocation density in the martensite structure and the ferrite structure after winding through the cold rolling, and the reusability of carbon and an austenite phase formation uniformly occur during annealing. If the cold reduction rate is less than 30%, the dislocation density in the ferrite structure is not sufficient, so that it is difficult to obtain the target structure. If the cold reduction rate exceeds 50%, microcracking occurs easily at the boundary between the martensite phase and the ferrite phase. Crack defects are generated in the. Therefore, the cold reduction rate is limited to 30-50%.
상기 냉간압연 후 통상적인 소둔공정을 한다. After the cold rolling, a conventional annealing process is performed.
본 발명은 냉간압연한 후에 용융아연도금 또는 합금화 용융아연도금한다. 소둔공정 이후에 용융아연이 담겨진 도금욕에 강판을 통과시켜 표면층에 도금층을 일정한 두께로 부착시킨다. 이 때 도금욕의 온도는 450~500℃가 바람직하며 30℃/s 이하의 속도로 서냉시키는 공정으로 용융아연도금강판을 제조한다.The present invention is hot rolled and hot dip galvanized or alloyed hot dip galvanized. After the annealing process, the plated layer is attached to the surface layer by passing the steel plate through a plating bath containing molten zinc. At this time, the temperature of the plating bath is preferably 450 ~ 500 ℃ and to produce a hot-dip galvanized steel sheet by a slow cooling process at a rate of 30 ℃ / s or less.
또한 도금욕조를 통과한 도금강판을 곧바로 500~600℃의 온도구간으로 가열하여 용융아연도금층의 합금화 열처리를 한 후 30℃/s 이하의 속도로 서냉시키는 고정으로 합금화 용융아연도금강판을 제조한다. In addition, the plated steel sheet passed through the plating bath is immediately heated to a temperature range of 500 ~ 600 ℃ to alloy the heat treatment of the hot-dip galvanized layer to produce an alloyed hot-dip galvanized steel sheet fixed by slow cooling at a rate of less than 30 ℃ / s.
이하, 본 방법에 의해서 제조되는 강판의 조직에 대하여 상세히 설명한다. Hereinafter, the structure of the steel plate manufactured by this method is demonstrated in detail.
본 발명에서 열간압연 후의 열연강판은 마르텐사이트 분율이 30~70%인 것을 특징으로 한다. 열간압연 후 1차 및 2차 냉각과정으로 생성된 레쓰(lath)형상의 미세한 마르텐사이트 조직은 냉간압연 후 소둔과정에서 균일한 오스테나이트 변태를 유도하고 이로부터 안정화된 잔류 오스테나이트의 분율을 증가시킨다. 통상적으로 한번의 냉각과정만으로 열연강판을 제조하는데 이때의 열연강판은 조대한 탄화물이 존재하는 펄라이트 조직을 함유하게 된다. 조대한 탄화물은 냉간압연 후 소둔과정에서 재고용되는데 탄화물의 크기가 조대하여 700℃이상의 고온에서도 재고용되지 않고 잔류하기 쉬우며 소둔 중 오스테나이트는 탄소의 농도가 높은 탄화물 근처에서 주로 형성되기 시작하며 상대적으로 탄화물이 없는 영역에서는 오스테나이트 형성이 잘 이루어지지 않게 된다. 따라서 2상역 소둔 중에 오스테나이트 분율이 낮아지고 국부적인 편차도 발생하여 소둔 후 냉각과정에서 발생하는 잔류 오스테나이트 분율이 감소하게 된다. 열연강판에서의 마르텐사이트상은 이러한 단점을 개선할 수 있다. Hot rolled steel sheet after hot rolling in the present invention is characterized in that the martensite fraction is 30 ~ 70%. Lath-like fine martensite structure produced by primary and secondary cooling after hot rolling induces uniform austenite transformation during annealing after cold rolling and increases the fraction of stabilized residual austenite . Typically, the hot rolled steel sheet is manufactured by only one cooling process, and the hot rolled steel sheet contains pearlite structure in which coarse carbides are present. Coarse carbides are re-used during annealing after cold rolling. The carbides are coarse in size, so they are not reusable even at high temperatures above 700 ° C. During the annealing, austenite begins to form mainly near carbides with high carbon concentration. In the region without carbides, austenite formation is less likely to occur. Therefore, the austenite fraction is lowered during the two-phase annealing and a local deviation also occurs, thereby reducing the residual austenite fraction generated during the cooling after annealing. The martensite phase in the hot rolled steel sheet can alleviate this drawback.
본 발명에서는 1차 및 2차 냉각과정을 거쳐 마르텐사이트상을 형성시키면 탄화물이 거의 형성되지 않은 채 열연강판을 제조할 수 있다. 이와 같은 마르텐사이트상을 포함한 열연강판은 소둔 열처리중에 전위밀도가 높은 마르텐사이트 조직에서 미세탄화물이 형성되었다가 곧바로 재고용되므로 탄소농도의 편차가 펄라이트 조직을 갖는 경우에 비해 상당히 감소한다. 따라서 소둔 중 형성되는 오스테나이트 상은 결정립계 부근과 레쓰 마르텐사이트 조직이었던 부근 등에 골고루 분포하여 형성되므로 잔류 오스테나이트 분율과 안정성을 높일 수 있다.In the present invention, when the martensite phase is formed through the first and second cooling processes, the hot rolled steel sheet may be manufactured with almost no carbide. The hot rolled steel sheet including the martensite phase is formed of fine carbide in the martensite structure having a high dislocation density during annealing heat treatment, and is re-applied immediately so that the variation in carbon concentration is considerably reduced compared with the case of the pearlite structure. Therefore, the austenite phase formed during annealing is formed evenly distributed in the vicinity of the grain boundary and the near-martensite structure, so that the residual austenite fraction and stability can be improved.
또한 마르텐사이트상에 의해 높아진 전위밀도를 활용하여 비교적 낮은 냉간압하율을 적용하여 냉간압연 후 에지(Edge)부위에 쉽게 발생하는 미세균열 형성을 억제할 수 있다. 이때 열연강판의 마르텐사이트 분율이 30%미만이면 잔류 오스테나이트 분율 증가 효과가 미약하고, 70%이상이면 냉간압연시 에지부위에 미세균열이 발생하므로 본 발명에서는 열연강판의 마르텐사이트 조직 분율을 30~70%로 제한한다.In addition, by utilizing the dislocation density increased by the martensite phase, by applying a relatively low cold reduction rate, it is possible to suppress the formation of microcracks that easily occur in the edge area after cold rolling. At this time, if the martensite fraction of the hot rolled steel sheet is less than 30%, the effect of increasing the retained austenite fraction is insignificant. If the martensite fraction of the hot rolled steel sheet is more than 70%, fine cracks are generated at the edges during cold rolling. Limited to 70%.
본 발명의 냉간압연 및 소둔공정을 거친 후의 냉연강판은 페라이트와 베이나이트 조직에 잔류 오스테나이트가 생성된다. 이때 본 발명에서의 잔류 오스테나이트의 분율은 5~15%를 갖는다. 열연강판에서의 레쓰 형상의 마르텐사이트 조직의 영향으로 잔류 오스테나이트 상이 레쓰 형상으로 나타나며 다른 형상의 잔류 오스테나이트에 비해 안정된 것이다. 또한 베이나이트 조직의 분율은 20~40%를 갖고 나머지는 페라이트로 이루어진다. After the cold rolling and annealing process of the present invention, the cold rolled steel sheet generates residual austenite in the ferrite and bainite structure. At this time, the fraction of retained austenite in the present invention has 5 to 15%. The residual austenite phase appears in the form of a wrestle due to the influence of the wedge shaped martensite structure on the hot rolled steel sheet and is more stable than the remaining austenite of other shapes. In addition, the fraction of bainite tissue has 20 to 40% and the remainder consists of ferrite.
본 방법에 의하면 가공성이 우수한 780~980MPa 의 인장강도와 28% 이상의 연신율을 갖는 고강도 냉연강판을 제조할 수 있다.According to this method, a high strength cold rolled steel sheet having a tensile strength of 780 to 980 MPa and an elongation of 28% or more having excellent workability can be produced.
이하 본 발명의 실시예를 통하여 본 발명을 상세히 설명한다.Hereinafter, the present invention will be described in detail through examples of the present invention.
(실시예)(Example)
표1은 실시예에서 사용된 강의 조성범위이고 본 발명에서는 목적으로 하는 인장강도와 연신율을 얻기 위해 성분의 적절한 조정이 중요하다. Table 1 shows the composition ranges of the steels used in the examples and in the present invention proper adjustment of the components is important to obtain the desired tensile strength and elongation.
표 1
Figure PCTKR2009002810-appb-T000001
 Table 1
Figure PCTKR2009002810-appb-T000001
표1의 조성을 갖는 강슬라브를 열연공정을 거쳐 냉각 및 권취 후 냉간압연, 소둔하였으며 이에 대한 냉각조건과 냉간 압하율 및 인장시험결과 등을 표 2에 나타내었다.The steel slab having the composition shown in Table 1 was cold rolled and annealed after cooling and winding through a hot rolling process, and the cooling conditions, cold rolling rate, and tensile test results are shown in Table 2 below.
재료의 기계적 특성 중 인장 특성은 성분과 미세조직의 제조조건에 따라 달라진다. 본 발명의 강판은 열연 직후에 생성된 레쓰(lath)형상의 미세한 마르텐사이트 조직에 의해 소둔 과정에서 균일한 오스테나이트 변태를 유도하고 이로부터 안정화된 잔류 오스테나이트의 분율을 증가시켜서, 변형을 받을 때 변태를 통해 우수한 기계적 특성을 얻고자 하는 것이다.Tensile properties, among the mechanical properties of the material, depend on the composition and the fabrication conditions of the microstructure. The steel sheet of the present invention induces a uniform austenite transformation during annealing by lath-shaped fine martensite structure produced immediately after hot rolling, and increases the fraction of stabilized residual austenite therefrom, when subjected to deformation. This is to obtain excellent mechanical properties through transformation.
또한 마르텐사이트상에 의해 높아진 전위밀도를 활용하여 비교적 낮은 냉간압하율을 적용하여 냉간압연 후 에지(Edge)부에 쉽게 발생하는 미세균열 형성을 억제하고자 하였다. 이와 같은 특성을 얻기 위해서는 기본적으로 본 발명에서 제안한 성분을 만족시켜야 하며 열연 직후 냉각과정과 마르텐사이트 분율 그리고 냉간압하율이 최적으로 조율되어야 한다.In addition, by applying a relatively low cold reduction rate by utilizing the dislocation density increased by the martensite phase, it was intended to suppress the formation of microcracks easily occurring at the edge part after cold rolling. In order to obtain such characteristics, basically, the components proposed in the present invention should be satisfied, and the cooling process, the martensite fraction, and the cold reduction rate should be optimally adjusted immediately after hot rolling.
표 2
Figure PCTKR2009002810-appb-T000002
 TABLE 2
Figure PCTKR2009002810-appb-T000002
표2에 열연 직후 냉각과정과 마르텐사이트 분율, 냉간압하율 그리고 기계적 성질과 에지(Edge)부위 균열발생 정도를 측정하여 그 결과를 도시하였다. Table 2 shows the results of the cooling process, hot martensite fraction, cold rolling ratio, mechanical properties and edge cracking after hot rolling.
비교재 9 내지 15는 기본적인 성분요건을 충족하지 못하여 제조과정 중 냉각조건과 마르텐사이트 분율 및 냉간 압하율 조건이 적절하게 조절되어도 본 발명에서 목표로 하는 강도와 연성을 얻지 못하였음을 알 수 있다. Comparative materials 9 to 15 do not satisfy the basic component requirements, it can be seen that even if the cooling conditions, martensite fraction and cold rolling rate conditions during the manufacturing process is properly adjusted, the strength and ductility targeted by the present invention are not obtained.
또한 비교재 2-2, 2-3, 3-2, 3-3, 4-2, 4-3, 5-2, 7-2, 7-3, 8-2 는 성분요건을 충족하였지만 냉각조건, 마르텐사이트 분율, 냉간압하율 등의 요건을 충족시키지 못하여 목표로 하는 기계적 성질을 얻지 못하거나 에지부위에 미세균열이 발생한 것을 알 수 있다. In addition, Comparative Materials 2-2, 2-3, 3-2, 3-3, 4-2, 4-3, 5-2, 7-2, 7-3, and 8-2 met the component requirements, but cooling conditions It can be seen that the target mechanical properties cannot be obtained due to failure to meet the requirements such as martensite fraction, cold reduction rate, or microcracks at the edges.
표2에서 에지부위의 크랙길이 측정은 마르텐사이트 분율을 200배율 광학 현미경으로 관찰한 것으로, 두께 t/4 위치에서의 미세조직을 2% Nital 에칭액으로 에칭한 후 화상분석기로 측정한 결과이며 에지부위에 발생한 미세한 균열은 냉간압연된 압연판 에지부위를 무작위로 선정하여 길이 100mm 내에서 발생한 가장 길이가 긴 균열을 30개이상 선택한 후 평균한 값으로 하였다.In Table 2, the crack length of the edge was measured by using a 200-magnification optical microscope to measure the martensite fraction, and the result was measured by an image analyzer after etching the microstructure at the thickness t / 4 position with 2% Nital etchant. The fine cracks generated at were randomly selected at the edges of the cold rolled rolled plate and were averaged after selecting at least 30 of the longest cracks occurring within the length of 100 mm.

Claims (8)

  1. 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하는 것을 특징으로 하는 고강도 강판.By weight%, C: 0.1-0.25%, Si: 1.0-1.9%, Mn: 1.5-2.5%, Al: 0.5-1.6%, Ti: 0.005-0.03%, B: 5-30 ppm, Sb: 0.01-0.03 A high strength steel sheet comprising%, the remainder being made of Fe and inevitable impurities, and satisfying 1.75 ≦ Si + Al ≦ 3.25%.
  2. 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하고, 열간압연 후 미세조직의 분율은 마르텐사이트가 30~70%이고 나머지는 페라이트인 것을 특징으로 하는 고강도 열연강판.By weight%, C: 0.1-0.25%, Si: 1.0-1.9%, Mn: 1.5-2.5%, Al: 0.5-1.6%, Ti: 0.005-0.03%, B: 5-30 ppm, Sb: 0.01-0.03 %, The remainder is composed of Fe and inevitable impurities, satisfies 1.75≤Si + Al≤3.25%, the fraction of the microstructure after hot rolling is characterized in that the martensite is 30 ~ 70% and the rest is ferrite High strength hot rolled steel sheet.
  3. 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하고, 냉간압연 후 미세조직의 분율은 잔류 오스테나이트 5~15%, 베이나이트 20~40%이고, 나머지는 페라이트인 것을 특징으로 하는 고강도 냉연강판.By weight%, C: 0.1-0.25%, Si: 1.0-1.9%, Mn: 1.5-2.5%, Al: 0.5-1.6%, Ti: 0.005-0.03%, B: 5-30 ppm, Sb: 0.01-0.03 %, The remainder is composed of Fe and inevitable impurities, satisfies 1.75≤Si + Al≤3.25%, the fraction of microstructure after cold rolling is 5-15% residual austenite, 20-40% bainite and High strength cold rolled steel sheet, characterized in that the rest is ferrite.
  4. 제 3 항에 있어서, 상기 냉연강판은 780~980MPa 의 인장강도와 28% 이상의 연신율을 갖는 것을 특징으로 하는 고강도 강판.The high strength steel sheet according to claim 3, wherein the cold rolled steel sheet has a tensile strength of 780 to 980 MPa and an elongation of 28% or more.
  5. 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하고, 용융아연도금층을 갖는 것을 특징으로 하는 고강도 용융아연도금강판.By weight%, C: 0.1-0.25%, Si: 1.0-1.9%, Mn: 1.5-2.5%, Al: 0.5-1.6%, Ti: 0.005-0.03%, B: 5-30 ppm, Sb: 0.01-0.03 A high strength hot dip galvanized steel sheet comprising%, the remainder being made of Fe and inevitable impurities, satisfying 1.75 ≦ Si + Al ≦ 3.25%, and having a hot dip galvanized layer.
  6. 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하는 강 슬라브를 A3이상의 온도범위에서 열간압연하고 30~200℃/s의 냉각속도로 600~800℃의 온도범위까지 1차 냉각하는 단계;By weight%, C: 0.1-0.25%, Si: 1.0-1.9%, Mn: 1.5-2.5%, Al: 0.5-1.6%, Ti: 0.005-0.03%, B: 5-30 ppm, Sb: 0.01-0.03 include% and the remainder Fe and unavoidable impurities, consists of, 1.75≤Si + a steel slab satisfying the Al≤3.25% and the hot rolling in the temperature range a 3 or more at a cooling rate of 30 ~ 200 ℃ / s 600 ~ Primary cooling to a temperature range of 800 ° C .;
    상기 1차 냉각한 열연강판을 600~800℃의 온도범위에서 공냉하는 단계;Air-cooling the first cooled hot rolled steel sheet in a temperature range of 600 to 800 ° C;
    상기 공냉한 열연강판을 50~200℃/s의 냉각속도로 상온~300℃의 온도범위까지 2차 냉각하는 단계; 및Secondly cooling the air-cooled hot rolled steel sheet to a temperature range of room temperature to 300 ° C at a cooling rate of 50 to 200 ° C / s; And
    상기 2차 냉각한 열연강판을 상온~300℃의 온도범위에서 권취하는 단계Winding the secondary cooled hot rolled steel sheet in a temperature range of room temperature to 300 ° C
    를 포함하는 것을 특징으로 하는 고강도 열연강판의 제조방법.Method for producing a high strength hot rolled steel sheet comprising a.
  7. 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하는 강 슬라브를 A3이상의 온도범위에서 열간압연하고 30~200℃/s의 냉각속도로 600~800℃의 온도범위까지 1차 냉각하는 단계;By weight%, C: 0.1-0.25%, Si: 1.0-1.9%, Mn: 1.5-2.5%, Al: 0.5-1.6%, Ti: 0.005-0.03%, B: 5-30 ppm, Sb: 0.01-0.03 include% and the remainder Fe and unavoidable impurities, consists of, 1.75≤Si + a steel slab satisfying the Al≤3.25% and the hot rolling in the temperature range a 3 or more at a cooling rate of 30 ~ 200 ℃ / s 600 ~ Primary cooling to a temperature range of 800 ° C .;
    상기 1차 냉각한 열연강판을 600~800℃의 온도범위에서 공냉하는 단계;Air-cooling the first cooled hot rolled steel sheet in a temperature range of 600 to 800 ° C;
    상기 공냉한 열연강판을50~200℃/s의 냉각속도로 상온~300℃의 온도범위까지 2차 냉각하는 단계;Secondly cooling the air-cooled hot rolled steel sheet to a temperature range of room temperature to 300 ° C at a cooling rate of 50 to 200 ° C / s;
    상기 2차 냉각한 열연강판을 상온~300℃의 온도범위에서 권취하는 단계; 및Winding the secondary cooled hot rolled steel sheet in a temperature range of room temperature to 300 ° C .; And
    상기 권취한 열연강판을 30~50%의 압하율로 냉간압연하고 소둔하는 단계Cold rolling and annealing the wound hot rolled steel sheet at a reduction ratio of 30 to 50%
    를 포함하는 것을 특징으로 하는 고강도 냉연강판의 제조방법.Method for producing a high strength cold rolled steel sheet comprising a.
  8. 중량%로, C:0.1~0.25%, Si:1.0~1.9%, Mn:1.5~2.5%, Al:0.5~1.6%, Ti:0.005~0.03%, B:5~30ppm, Sb:0.01~0.03% 를 포함하고, 나머지는 Fe 및 불가피한 불순물로 이루어지며, 1.75≤Si+Al≤3.25 % 를 만족하는 강 슬라브를 A3이상의 온도범위에서 열간압연하고 30~200℃/s의 냉각속도로 600~800℃의 온도범위까지 1차 냉각하는 단계;By weight%, C: 0.1-0.25%, Si: 1.0-1.9%, Mn: 1.5-2.5%, Al: 0.5-1.6%, Ti: 0.005-0.03%, B: 5-30 ppm, Sb: 0.01-0.03 include% and the remainder Fe and unavoidable impurities, consists of, 1.75≤Si + a steel slab satisfying the Al≤3.25% and the hot rolling in the temperature range a 3 or more at a cooling rate of 30 ~ 200 ℃ / s 600 ~ Primary cooling to a temperature range of 800 ° C .;
    상기 1차 냉각한 열연강판을 600~800℃의 온도범위에서 공냉하는 단계;Air-cooling the first cooled hot rolled steel sheet in a temperature range of 600 to 800 ° C;
    상기 공냉한 열연강판을 50~200℃/s의 냉각속도로 상온~300℃의 온도범위까지 2차 냉각하는 단계;Secondly cooling the air-cooled hot rolled steel sheet to a temperature range of room temperature to 300 ° C at a cooling rate of 50 to 200 ° C / s;
    상기 2차 냉각한 열연강판을 상온~300℃의 온도범위에서 권취하는 단계; Winding the secondary cooled hot rolled steel sheet in a temperature range of room temperature to 300 ° C .;
    상기 권취한 열연강판을 30~50%의 압하율로 냉간압연하고 소둔하는 단계; 및Cold rolling and annealing the wound hot rolled steel sheet at a reduction ratio of 30 to 50%; And
    상기 소둔한 냉연강판을 용융아연도금하는 단계Hot-dip galvanizing the annealed cold rolled steel sheet
    를 포함하는 것을 특징으로 하는 고강도 용융아연도금강판의 제조방법.Method for producing a high strength hot dip galvanized steel sheet comprising a.
PCT/KR2009/002810 2008-05-29 2009-05-27 High-strength steel sheet with excellent ductility and crackless edge portion, hot-dip galvanized steel sheet, and manufacturing method thereof WO2009145562A2 (en)

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