WO2009145562A2 - Tôle d'acier à haute résistance et excellente ductilité présentant un bord sans crique, tôle d'acier galvanisé à chaud et procédé de production correspondant - Google Patents

Tôle d'acier à haute résistance et excellente ductilité présentant un bord sans crique, tôle d'acier galvanisé à chaud et procédé de production correspondant 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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Korean (ko)
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WO2009145562A3 (fr
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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/ja
Priority to US12/991,003 priority patent/US20110064968A1/en
Publication of WO2009145562A2 publication Critical patent/WO2009145562A2/fr
Publication of WO2009145562A3 publication Critical patent/WO2009145562A3/fr

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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.

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Abstract

La présente invention concerne une tôle d'acier présentant une résistance à la traction de 780 à 980 MPa et un allongement supérieur ou égal à 28%, possédant un bord sans crique. La présente invention concerne une tôle d'acier à haute résistance contenant, en % en poids, C: 0,1 à 0,25%, Si: 1,0 à 1,9%, Mn: 1,5 à 2.5%, Al: 0,5 à 1.6%, Ti: 0,005 à 0,03%, B: 5 à 30 ppm, et Sb: 0,01 à 0,03%, le reste étant constitué de Fe et d'impuretés inévitables, 1,75≤Si+Al≤3,25. L'invention concerne également une tôle d'acier galvanisé à chaud et son procédé de production.
PCT/KR2009/002810 2008-05-29 2009-05-27 Tôle d'acier à haute résistance et excellente ductilité présentant un bord sans crique, tôle d'acier galvanisé à chaud et procédé de production correspondant WO2009145562A2 (fr)

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JP2011510432A JP5456026B2 (ja) 2008-05-29 2009-05-27 延性に優れ、エッジ部に亀裂のない高強度鋼板、溶融亜鉛メッキ鋼板及びその製造方法
US12/991,003 US20110064968A1 (en) 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

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KR10-2008-0050366 2008-05-29
KR1020080050366A KR101008099B1 (ko) 2008-05-29 2008-05-29 연성이 우수하고 에지부 균열이 없는 고강도 강판,용융아연도금강판 및 그 제조방법

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KR101359281B1 (ko) * 2011-12-20 2014-02-06 주식회사 포스코 점용접성, 강도 및 연신율이 우수한 자동차용 강판 및 그 제조방법
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KR101657784B1 (ko) * 2014-11-28 2016-09-20 주식회사 포스코 열간압연시 크랙 발생이 저감된 고연성 고강도 냉연강판 및 이의 제조방법
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JP5456026B2 (ja) 2014-03-26
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KR101008099B1 (ko) 2011-01-13
KR20090124264A (ko) 2009-12-03

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