EP1960562A1 - Tole d'acier laminee a froid de haute resistance possedant une excellente propriete de formabilite et de revetement, tole d'acier plaquee de metal a base de zinc fabriquee a partir de cette tole et procede de fabrication de celle-ci - Google Patents

Tole d'acier laminee a froid de haute resistance possedant une excellente propriete de formabilite et de revetement, tole d'acier plaquee de metal a base de zinc fabriquee a partir de cette tole et procede de fabrication de celle-ci

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Publication number
EP1960562A1
EP1960562A1 EP06824061A EP06824061A EP1960562A1 EP 1960562 A1 EP1960562 A1 EP 1960562A1 EP 06824061 A EP06824061 A EP 06824061A EP 06824061 A EP06824061 A EP 06824061A EP 1960562 A1 EP1960562 A1 EP 1960562A1
Authority
EP
European Patent Office
Prior art keywords
steel sheet
content
range
less
acier
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP06824061A
Other languages
German (de)
English (en)
Other versions
EP1960562A4 (fr
EP1960562B1 (fr
Inventor
Yeon-Sang Ahn
Jin-Keun Oh
Il-Ryoung Sohn
Seong-Ju Kim
Kwang-Geun Chin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Posco Holdings Inc
Original Assignee
Posco Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from KR1020050120407A external-priority patent/KR100711358B1/ko
Priority claimed from KR1020050128666A external-priority patent/KR100711468B1/ko
Application filed by Posco Co Ltd filed Critical Posco Co Ltd
Publication of EP1960562A1 publication Critical patent/EP1960562A1/fr
Publication of EP1960562A4 publication Critical patent/EP1960562A4/fr
Application granted granted Critical
Publication of EP1960562B1 publication Critical patent/EP1960562B1/fr
Active legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • 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

Definitions

  • the present invention relates to a steel sheet which is primarily used as structural members and reinforcement of the car body, a zinc-based metal plated steel sheet(zinc-coated steel sheet) made of it and a method for manufacturing the same. More specifically, the present invention relates to a high-strength, cold rolled steel sheet having tensile strength of more than 490 MPa and excellent coating properties, a zinc -based metal plated steel sheet(zinc-coated steel sheet) made of it and a method for manufacturing the same.
  • the automotive steel sheet also requires high corrosion resistance
  • hot-dip galvanized steel sheets having excellent corrosion resistance have been conventionally used as the automotive steel sheet. That is, such steel sheets can be manufactured with excellent corrosion resistance at low production costs, since they are manufactured through a continuous hot-dip galvanizing line where recrystallization annealing and coating are carried out in the same line.
  • alloyed hot-dip galvanized steel sheets, which were subjected again to heat treatment after hot-dip galvanizing are widely used in terms of excellent weldability and formability, in addition to excellent corrosion resistance.
  • Japanese Unexamined Patent Publication No. 2004-292891 suggests a method of manufacturing a high tensile strength steel sheet.
  • This conventional art is directed to a steel sheet composed of a composite structure containing ferrite as a primary phase, the retained austenite as a secondary phase, and bainite and martensite as low temperature transformation phases, and suggests a method of manufacturing a steel sheet having improved ductility and stretch flangeability.
  • this conventional art suffers from a difficulty to achieve desired coating quality due to the addition of large amounts of silicon (Si) and aluminum (Al), and a difficulty to secure desired surface quality upon steel-making and continuous casting. Further, this art also suffers from a difficulty to secure flatness of the steel sheet due to the risk of partial deformation of the steel sheet upon cooling, since cooling of the steel sheet should be carried out at a rate of more than 100°C/sec in order to obtain high strength.
  • Japanese Unexamined Patent Publication No. 2002-088447 which relates to a steel sheet composed of a composite structure including ferrite as a primary phase, and discloses a method of obtaining good workability and coating properties.
  • this patent suffers from difficulties in practical application thereof, due to increased production costs resulting from one or more heat treatment processes prior to coating, in order to obtain good workability.
  • the present invention has been made in view of the above problems, and the present invention provides advantages capable of achieving excellent coating properties and high tensile strength of more than 490 MPa, by the addition of antimony (Sb) to a steel material. Further, the present invention provides advantages of securing desired formability of a steel sheet. In addition, the present invention provides advantages of securing bake hardenability after coating of the steel sheet.
  • Sb antimony
  • a cold rolled steel sheet comprising 0.01-0.2 wt% of carbon (C), 0.01-2.0 wt% of silicon (Si), 0.5-4.0 wt% of manganese (Mn), less than 0.1 wt% of phosphorous (P), less than 0.03 wt% of sulfur (S), less than 1.0 wt% of soluble aluminum (SoLAl), 0.001-0.1 wt% of nitrogen (N), 0.005-1.0 wt% of antimony (Sb), and the balance of iron (Fe) with inevitable impurities.
  • the cold rolled steel sheet may satisfy the following inequality of (Si/28+Al/27)/(N/14)>10, for Si, Al and N.
  • contents of the soluble aluminum (SoLAl) and nitrogen (N) in the cold rolled steel sheet are preferably in a range of 0.01 to 1.0%, and in a range of 0.001 to 0.03%, respectively.
  • contents of the soluble aluminum (SoLAl) and nitrogen (N) in the cold rolled steel sheet are preferably in a range of less than 0.2%, and in a range of 0.01 to 0.1%, respectively.
  • the cold rolled steel sheet may further comprise at least one selected from the group consisting of:
  • [20] a) 0.001-0.1% of at least one of titanium (Ti), niobium (Nb) and vanadium (V);
  • a steel structure of the cold rolled steel sheet may have ferrite as a primary phase and a martensite fraction of 2 to 70% as a secondary phase.
  • a zinc-coated steel sheet includes the above cold rolled steel sheet as a base steel sheet and has a zinc-coating layer on at least one surface of top and bottom surfaces of the base steel sheet.
  • the zinc-coated steel sheet may have one coating layer of zinc coating and alloying hot-dip zinc coating, without being limited thereto.
  • a method for manufacturing a cold rolled steel sheet comprising re -heating a steel slab satisfying the steel composition of the present invention at a temperature of 1100 0 C to 1300 0 C; subjecting the steel slab to hot finish rolling at a temperature ranging from the Ar transformation point to 1000 0 C; winding the steel slab at a temperature of 45O 0 C to 75O 0 C; pickling and cold-rolling the steel slab; continuously annealing the steel slab at a temperature of 75O 0 C to 900 0 C for 10 to 1000 sec; cooling the steel slab to 600 0 C to 72O 0 C at a rate of 1 to 10°C/sec (primary cooling); and cooling the steel slab to 100 0 C to 400 0 C at a rate of 1 to 100°C/sec (secondary cooling).
  • the cold rolled steel sheet is subjected to hot-dip galvanizing at a temperature of 45O 0 C to 500 0 C for less than 10 sec.
  • a steel sheet secures high tensile strength of more than 490 MPa, in conjunction with improvement of coating properties.
  • excellent formability of the steel sheet is also secured.
  • bake hard- enability after coating of the steel sheet is enhanced. Therefore, the steel sheet of the present invention can be applied as structural members and reinforcement of au- tomotives.
  • FIG. 1 is a graph showing a relationship between (Si/28+Al/27)/(N/14) and TS*E1 in the present invention
  • FIG. 2 is a graph showing a relationship between N* and TS*E1 and between N* and BH in the present invention.
  • FIG. 3 is a photograph showing surface-enriching properties with addition of Sb in the present invention.
  • N* (N/14)/(Al/27+Ti/48+Nb/93+V/51+B/l l)>0.2 (2)
  • the bake hardenability is also increased due to solute nitrogen (N) after coating of the steel sheet, when the solute nitrogen is secured.
  • Carbon (C) is a very important component to increase strength of a steel sheet and to secure a composite structure composed of ferrite and martensite. Where the carbon content is lower than 0.01%, it is impossible to obtain the steel strength which is desired by the present invention. On the other hand, where the carbon content is higher than 0.2%, the steel may be highly susceptible to deterioration of toughness and weldability. Therefore, the carbon content is preferably limited to the range of
  • Silicon (Si) is a useful element which is capable of securing desired strength of a steel sheet while not causing deterioration of ductility of the steel sheet.
  • silicon is an element promoting the formation of martensite by promoting the formation of ferrite and facilitating the enrichment of carbon into the untransformed austenite.
  • the silicon content is lower than 0.01%, it is difficult to secure the above-mentioned effects.
  • the silicon content is higher than 2.0%, surface properties and weldability may be deteriorated. Therefore, the silicon content is preferably limited to the range of 0.01 to 2.0%.
  • Manganese (Mn) is an element having significant solid-solution strengthening
  • the manganese content is lower than 0.5%, it is difficult to secure the steel strength which is desired by the present invention.
  • the manganese content is higher than 4.0%, this may result in high susceptibility to problems associated with the weldability and hot-rolling performance. Therefore, the manganese content is preferably limited to the range of 0.5 to 4.0%.
  • Phosphorus (P) serves to strengthen a steel sheet, but an excessive amount thereof may result in degradation of the press formability. Therefore, the phosphorus content is preferably limited to a range of less than 0.1%.
  • S is an impurity element present in the steel, and is likely to inhibit the ductility and weldability of a steel sheet. Therefore, the sulfur content is preferably limited to a range of less than 0.03%.
  • Soluble aluminum is an element which combines with oxygen in the steel to thereby exert deoxidation effects, and, in conjunction with silicon (Si), is effective to improve the martensite hardenability by distribution of carbon in ferrite into austenite. If the content of Sol.Al exceeds 1.0%, the deoxidation effects and improvement of the martensite hardenability are saturated and production costs are increased. Therefore, the content of Sol.Al is limited to the range of less than 1.0%. The content of Sol.Al is preferably in the range of 0.01 to 1.0%, more preferably less than 0.2%.
  • Nitrogen (N) is a component effective to stabilize austenite. Where the nitrogen content is lower than 0.001%, it is difficult to achieve such stabilizing effects. On the other hand, where the nitrogen content is higher than 0.1%, there is no significant increase in stabilizing effects of austenite, in conjunction with problems associated with the weldability and increased production costs. Therefore, the nitrogen content is limited to the range of 0.001 to 0.1%.
  • the nitrogen content is in the range of 0.01 to 0.1%.
  • Nitrogen combines with titanium (Ti), niobium (Nb) and aluminum (Al) to form nitrides, thereby increasing yield strength of steel.
  • sufficient amounts of nitrogen are added so as to increase the yield strength of steel after coating.
  • Nitrogen serves as a primary cause for a sharp increase of the yield strength of steel, in a manner that nitrogen remains in the form of solute N within crystal grains prior to coating, and then interferes with the dislocation movement after coating to thereby elevate a yield point. If the nitrogen content is lower than 0.01%, it is difficult to achieve such effects. On the other hand, if the nitrogen content exceeds 0.1%, there is no significant increase in the yield strength-improving effects, in conjunction with problems associated with the weldability and increased production costs.
  • the nitrogen content is preferably in the range of 0.001 to 0.03%, even though it may not secure sufficient strength by solute nitrogen.
  • Antimony (Sb) is a very important element in the present invention, and is an
  • Sb as shown in FIG. 2, reduces surface defects by inhibiting surface enrichment of oxides such as MnO, SiO and Al O , and exhibits excellent effects on inhibition of coarsening of surface- enriched materials resulting from elevation of temperatures and changes of the hot- rolling process.
  • the antimony content is lower than 0.005%, it is difficult to secure the above effects.
  • a continuing increase of the antimony content does not lead to further significant increase of such effects and may also present problems associated with production costs and degradation of the workability. Therefore, the antimony content is preferably limited to the range of 0.005 to 1.0%.
  • one or more elements selected from titanium (Ti), niobium (Nb) and vanadium (V), and chromium (Cr), molybdenum (Mo) and boron (B) may be further added to the steel.
  • Titanium (Ti), niobium (Nb) and vanadium (V) are elements effective to increase the strength of the steel sheet and to achieve grain refinement. Where the content of Ti, Nb and V is lower than 0.001%, it is difficult to achieve desired effects. On the other hand, where the content of Ti, Nb and V exceeds 0.1%, this may result in increased production costs, and decreased ductility of ferrite due to excessive amounts of precipitates. Therefore, the Ti, Nb and V content is preferably limited to the range of 0.001 to 0.1%.
  • Chromium (Cr) is a component added to improve the hardenability of the steel and to secure high strength. Where the chromium content is lower than 0.01%, it is difficult to secure such effects. On the other hand, where the chromium content exceeds 2.0%, this may result in saturation of such effects and deterioration of the ductility.
  • the chromium content is preferably limited to the range of 0.01 to 2.0%.
  • Molybdenum (Mo) is a component added to retard transformation of austenite into pearlite and simultaneously to achieve ferrite refinement and improve the strength. Where the molybdenum content is lower than 0.001%, it is difficult to obtain such effects. On the other hand, where the molybdenum content exceeds 1.0%, this may result in saturation of such effects and deterioration of the ductility. Therefore, the molybdenum content is preferably limited to the range of 0.001 to 1.0%.
  • Boron (B) is a component which retards transformation of austenite into pearlite upon cooling of the steel during an annealing process. Where the boron content exceeds 0.01%, this may result in degradation of the coating adhesion, due to excessive enrichment of boron on the steel sheet surface. Therefore, the boron content is preferably limited to the range of less than 0.01%.
  • Si, Al and N satisfy the inequality 1 of (Si/28+Al/27)/(N/14)>10.
  • contents of the soluble aluminum (Sol. Al) and nitrogen (N) in the steel sheet are preferably in a range of 0.01 to 1.0%, and in a range of 0.001 to 0.03%, respectively.
  • Inequality 1 is a very important equation in terms of the formability of the present invention. As shown in FIG. 1, where the inequality value is smaller than 10, it is difficult to secure excellent TS * El balance. On the other hand, where the inequality value is 10 or higher, it is possible to secure TS * El balance of more than 15,000.
  • ferrite-formation promoting elements Si and Al are appropriately added to actively induce formation of ferrite, thereby facilitating enrichment of carbon into austenite and improving the hardenability to promote martensitic transformation.
  • the ratio of Al and N is controlled to appropriately form AlN precipitates, thereby preventing pearlite band formation during the hot rolling process to induce refining and dispersion of pearlite, consequently achieving fine dispersion of martensite in the final annealing process. As a result, it is possible to secure high strength and high ductility of the steel.
  • N* (N/14)/(Al/27+Ti/48+Nb/93+V/51+B/l l)>0.2.
  • contents of the soluble aluminum (Sol.Al) and nitrogen (N) in the steel sheet are preferably in the range of less than 0.2%, and in a range of 0.01 to 0.1%, respectively.
  • N* means a content of nitrogen remained after the formation of nitrides by
  • N* referring to the remaining nitrogen after formation of nitrides, serves as an austenite-stabilizing element, similar to carbon, and therefore promotes martensitic transformation during a cooling process.
  • nitrogen enriched within the martensite leads to increased strength of the steel. As a result, an improved elongation ratio can be obtained at the same strength. Further, the bake hardenability is also improved by the solute nitrogen (N) after coating of the steel sheet.
  • the steel of the present invention is composed of the above-mentioned components and the balance of iron (Fe) with inevitable impurities. If necessary, other alloying elements may also be added. Therefore, it should be understood that the steel of the present invention does not exclude steels with addition of other alloying elements, although not mentioned in embodiments of the present invention.
  • a cold rolled steel sheet as composed above.
  • a zinc-coated steel sheet having a zinc coating layer on at least one surface of top and bottom surfaces of the cold rolled steel sheet.
  • the steel composed as above may be subjected to heat treatment suited for the cold rolled steel sheet and hot-dip galvanized steel sheet to control a microstructure of the steel, thereby imparting desired physical properties.
  • the steel sheet in the present invention is made to have ferrite as a primary phase and a martensite fraction of 2 to 70% as a secondary phase. Where the martensite fraction is lower than 2%, it is difficult to obtain high tensile strength which is desired by the present invention. On the other hand, where the martensite fraction is higher than 70%, this may result in a sharp decrease of an elongation ratio. Therefore, the martensite fraction is preferably limited to the range of 2 to 70%. Further, in the present invention, it is also possible to secure physical properties which are desired by the present invention, when bainite as the secondary phase is contained in a content of less than 5%, in addition to martensite.
  • the re-heating temperature is preferably limited to the range of 1100 0 C to 1300 0 C.
  • the steel slab is subjected to hot finish rolling at a temperature ranging from the Ar transformation point to 1000 0 C.
  • the hot finish rolling temperature is lower than the Ar transformation point, this may lead to high possibility of a dramatic increase in the hot deformation resistance and problems associated with manufacturing processes.
  • the hot finish rolling temperature is higher than 1000 0 C, this may probably result in high risk of excessively thick oxide scales and coarsening of the steel sheet structure. Therefore, the hot finish rolling temperature is preferably limited to a temperature ranging from the Ar transformation point to 1000 0 C.
  • the thus-rolled steel slab was wound at a temperature of 45O 0 C to 75O 0 C.
  • the winding temperature is lower than 45O 0 C, excessive formation of martensite or bainite leads to excessively increased strength of the hot rolled steel sheet, thereby resulting in problems associated with manufacturing processes such as imperfect shapes due to heavy load upon cold rolling.
  • the winding temperature is higher than 75O 0 C, this may result in severe surface enrichment by elements such as Si, Mn and B, which lower the wettability of hot-dip galvanizing. Therefore, the winding temperature is preferably limited to a range of 45O 0 C to 75O 0 C.
  • the hot rolled steel sheet may be processed into a cold rolled steel sheet by cold rolling, if necessary.
  • the cold rolling is preferably carried out at a reduction ratio of 30 to 80%. Where the cold-rolling reduction ratio is lower than 30%, it is difficult to achieve a desired thickness of the steel sheet and it is also difficult to achieve shape correction of the steel sheet. On the other hand, where the cold-rolling reduction ratio is higher than 80%, this may result in high susceptibility to the occurrence of cracks in edges of the steel sheet, and increased cold rolling load.
  • the thus-cold rolled steel sheet may be subjected to annealing treatment, if
  • the cold rolled steel sheet may be subjected to continuous annealing at a
  • the continuous annealing temperature is intended to perform recrystallization, simultaneously with formation of ferrite and austenite and distribution of carbon.
  • the continuous annealing temperature is lower than 75O 0 C, it is difficult to achieve sufficient recrystallization and sufficient formation of austenite, and it is therefore difficult to obtain the steel strength which is desired by the present invention.
  • the continuous annealing temperature exceeds 900 0 C, this may result in decreased productivity and excessive formation of austenite, thereby decreasing the ductility. Therefore, the continuous annealing temperature is preferably limited to the range of 75O 0 C to 900 0 C.
  • the continuous annealing time is shorter than 10 sec, it is difficult to form sufficient amounts of austenite.
  • the continuous annealing time is longer than 1000 sec, this may result in decreased productivity and excessive formation of austenite. Therefore, the continuous annealing time is preferably limited to the range of 10 to 1000 sec.
  • the thus-continuously annealed steel sheet is cooled to 600 0 C to 72O 0 C at a rate of 1 to 10°C/sec (primary cooling).
  • the primary cooling step is intended to increase the ductility and strength of the steel sheet by securing an equilibrium carbon concentration of ferrite and austenite.
  • the primary cooling termination temperature is lower than 600 0 C or higher than 72O 0 C, it is difficult to obtain the steel ductility and strength which are desired by the present invention. Therefore, the primary cooling termination temperature is preferably limited to the range of 600 0 C to 72O 0 C.
  • the primary cooling rate is lower than l°C/sec, this may result in susceptibility to the formation of pearlite during the cooling process.
  • the primary cooling rate is higher than 10°C/sec, it is difficult to achieve the equilibrium carbon concentration, thus making it difficult to obtain desired ductility and strength of the steel sheet. Therefore, the primary cooling rate is preferably limited to the range of 1 to 10°C/sec.
  • the steel sheet is cooled to 100 0 C to 400 0 C at a rate of 1 to
  • the secondary cooling rate is lower than l°C/sec, this results in formation of largely pearlite or bainite as the secondary phase, thus making it difficult to secure the desired ductility and strength.
  • the secondary cooling rate is higher than 100°C/sec, there is necessary excessive facility investment. Therefore, the secondary cooling rate is preferably limited to the range of 1 to 100°C/sec.
  • the secondary cooling termination temperature is lower than 100 0 C, it is difficult to stably secure a composite structure composed of ferrite and martensite.
  • the secondary cooling termination temperature is higher than 400 0 C, pearlite and bainite are largely formed as the secondary phase, thus making it difficult to secure the desired ductility and strength. Therefore, the secondary cooling termination temperature is preferably limited to the range of 100 0 C to 400 0 C.
  • the hold time after secondary cooling is shorter than 10 sec, it is difficult to stably secure a composite structure steel.
  • the hold time is longer than 1000 sec, this may result in decreased productivity and a difficulty to desired steel strength. Therefore, the hold time is preferably limited to the range of 10 to 1000 sec.
  • annealed cold-rolled steel sheet (hereinafter, referred to simply as "steel sheet") may be coated.
  • zinc coating or alloyed zinc coating may be applied to coating of the steel sheet.
  • coating methods There is no particular limit to coating methods and for example, mention may be made of hot-dip coating, electrolytic coating, evaporation deposition coating and cladding. From a productivity point of view, hot-dip coating is preferred. Even though the coating method will be described according to the most preferred embodiment, the present invention is not limited thereto.
  • Hot-dip galvanizing of a steel sheet is preferably carried out at a coating
  • the coating temperature is preferably limited to the range of 45O 0 C to 500 0 C.
  • the hot-dip galvanizing time is longer than 10 sec, this may result in excessive zinc coating. Therefore, the coating time is preferably limited to the range of less than 10 sec. After the hot-dip galvanizing was complete, the steel sheet is cooled to room temperature.
  • the steel sheet may be cooled to room temperature to manufacture a galvanized steel sheet, or otherwise the steel sheet may be subjected to alloy coating treatment to manufacture an alloyed galvanized steel sheet.
  • the alloyed galvanized steel sheet may be subjected to alloying heat treatment at a temperature of 44O 0 C to 58O 0 C for less than 30 sec. Where the alloying heat treatment temperature is lower than 44O 0 C or higher than 58O 0 C, this may result in unstable alloying. Further, where the alloying heat treatment time exceeds 30 sec, this may result in excessive alloying.
  • the continuously-annealed steel sheets manufactured as above were heated to 46O 0 C, subjected to hot-dip galvanizing for 5 sec and alloying treatment at 500 0 C for 10 sec, and cooled to room temperature, followed by observation of whether the steel sheets were coated or not by naked eyes.
  • composition and manufacturing method specified in the present invention exhibited a value of Inequality 1 of more than 10. That is, as shown in FIG. 1, Inventive materials could secure the formability which is desired by the present invention, as evidenced by TS x El balance of more than 15,000 at a value of Inequality 1 of more than 10.
  • Inventive materials exhibited high tensile strength of more than 490 MPa, and exhibited, as shown in FIG. 3, excellent coating properties with the addition of antimony (Sb). Therefore, steel materials of the present invention can be used as automotive structural members and reinforcement having high tensile strength of more than 490 MPa, high ductility and excellent coating properties.
  • JIS 5 test pieces were taken from the annealed cold rolled steel sheet and examined for the quality of material thereof. Further, in order to simulate the quality of the material after coating in automotive parts, 2% strain was applied to the thus-prepared JIS 5 test pieces which were then boiled in oil at 17O 0 C for 20 min, followed by the tensile test.
  • a BH value was calculated from the following equation:
  • the continuously-annealed steel sheets manufactured as above were heated to 46O 0 C, subjected to hot-dip galvanizing for 5 sec and alloying treatment at 500 0 C for 10 sec, and cooled to room temperature, followed by observation of whether the steel sheets were coated or not by naked eyes.
  • Sb antimony

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  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Coating With Molten Metal (AREA)
  • Metal Rolling (AREA)

Abstract

La présente invention concerne une tôle d'acier laminée à froid de haute résistance et une tôle d'acier revêtue de zinc de haute résistance qui sont principalement utilisées comme élément structurel et comme renfort de carrosserie de voitures et, qui possèdent d'excellentes propriétés de formabilité et de revêtement et, des procédés de fabrication de celles-ci. Cette tôle d'acier comprend entre 0,01 % et 0,2 % en masse de carbon (C), entre 0,0 1 % et 2 % en masse de silicium (Si), entre 0,5 % et 4,0 % en masse de manganèse (Mn), moins de 0,1 % en masse de phosphore (P), moins de 0,0 3 % en masse de soufre (S), moins de 1 % en masse d'aluminium soluble (Al sol.), de 0,001 % à 0,1 % en masse d'azote (N), de 0,005 % à 1, 0 % en masse d'antimoine (Sb), et le solde en fer (Fe) avec des impuretés inévitables. Cette invention concerne aussi une tôle d'acier revêtue de zinc et la préparation de celle-ci au moyen de cette tôle d'acier. Selon la présente invention, d'excellentes propriétés de revêtement et une résistance à la traction élevée > 490 MPa peuvent être obtenues. Par ailleurs, la formabilité de l'équilibre TS *EL présentant 15,000 MPaD % au minimum peut être assurée. De plus une dureté de cuisson excellente d'une valeur de BH de 80 Mpa au moins peut être obtenue.
EP06824061.3A 2005-12-09 2006-12-08 Tole d'acier laminee a froid de haute resistance possedant une excellente propriete de formabilite et de revetement, tole d'acier plaquee de metal a base de zinc fabriquee a partir de cette tole et procede de fabrication de celle-ci Active EP1960562B1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
KR1020050120407A KR100711358B1 (ko) 2005-12-09 2005-12-09 성형성, 소부경화성 및 도금특성이 우수한 고강도 냉연강판및 용융아연도금강판, 그리고 이들의 제조방법
KR1020050128666A KR100711468B1 (ko) 2005-12-23 2005-12-23 성형성과 도금특성이 우수한 고강도 냉연강판 및용융아연도금강판, 그리고 이들의 제조방법
PCT/KR2006/005355 WO2007067014A1 (fr) 2005-12-09 2006-12-08 Tole d'acier laminee a froid de haute resistance possedant une excellente propriete de formabilite et de revetement, tole d'acier plaquee de metal a base de zinc fabriquee a partir de cette tole et procede de fabrication de celle-ci

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EP1960562A1 true EP1960562A1 (fr) 2008-08-27
EP1960562A4 EP1960562A4 (fr) 2012-01-25
EP1960562B1 EP1960562B1 (fr) 2015-08-26

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EP (1) EP1960562B1 (fr)
JP (1) JP5042232B2 (fr)
CN (1) CN104264075B (fr)
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EP3231887A4 (fr) * 2014-12-08 2017-11-22 Posco Tôle d'acier obtenue par galvanisation à chaud à très haute résistance présentant une excellente qualité de surface et une excellente adhérence du revêtement, et son procédé de fabrication
EP3730636A4 (fr) * 2017-12-22 2020-10-28 Posco Tôle d'acier à haute résistance présentant une excellente aptitude au façonnage, et procédé de fabrication de celle-ci

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KR101353787B1 (ko) * 2011-12-26 2014-01-22 주식회사 포스코 용접성 및 굽힘가공성이 우수한 초고강도 냉연강판 및 그 제조방법
JP5982905B2 (ja) 2012-03-19 2016-08-31 Ｊｆｅスチール株式会社 高強度溶融亜鉛めっき鋼板の製造方法
JP5982906B2 (ja) 2012-03-19 2016-08-31 Ｊｆｅスチール株式会社 高強度溶融亜鉛めっき鋼板の製造方法
KR101716728B1 (ko) 2013-03-04 2017-03-15 제이에프이 스틸 가부시키가이샤 고강도 강판 및 그의 제조 방법 그리고 고강도 용융 아연 도금 강판 및 그의 제조 방법
JP5884196B2 (ja) 2014-02-18 2016-03-15 Ｊｆｅスチール株式会社 高強度溶融亜鉛めっき鋼板の製造方法
KR101561008B1 (ko) 2014-12-19 2015-10-16 주식회사 포스코 구멍확장능이 우수한 용융아연도금강판, 합금화 용융아연도금강판 및 그 제조방법
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KR101647224B1 (ko) * 2014-12-23 2016-08-10 주식회사 포스코 표면품질, 도금밀착성 및 성형성이 우수한 고강도 용융아연도금강판 및 그 제조방법
CN105088103A (zh) * 2015-08-25 2015-11-25 广西南宁智翠科技咨询有限公司 一种抗低温脆性合金钢及其制备方法
WO2017168991A1 (fr) * 2016-03-31 2017-10-05 Ｊｆｅスチール株式会社 Tôle d'acier mince, tôle d'acier plaquée, procédé de fabrication de tôle d'acier laminée à chaud, procédé de fabrication de tôle d'acier dure laminée à froid, procédé de fabrication de tôle d'acier mince et procédé de fabrication de tôle d'acier plaquée
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EP3231887A4 (fr) * 2014-12-08 2017-11-22 Posco Tôle d'acier obtenue par galvanisation à chaud à très haute résistance présentant une excellente qualité de surface et une excellente adhérence du revêtement, et son procédé de fabrication
US10344361B2 (en) 2014-12-08 2019-07-09 Posco Ultra-high strength, hot-dip galvanized steel sheet having excellent surface quality and coating adhesion
EP3730636A4 (fr) * 2017-12-22 2020-10-28 Posco Tôle d'acier à haute résistance présentant une excellente aptitude au façonnage, et procédé de fabrication de celle-ci
US11519051B2 (en) 2017-12-22 2022-12-06 Posco Co., Ltd High-strength steel sheet having excellent processability and method for manufacturing same
US11827950B2 (en) 2017-12-22 2023-11-28 Posco Co., Ltd Method of manufacturing high-strength steel sheet having excellent processability

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JP2009518541A (ja) 2009-05-07
WO2007067014A8 (fr) 2014-03-13
EP1960562A4 (fr) 2012-01-25
EP1960562B1 (fr) 2015-08-26
CN104264075A (zh) 2015-01-07
JP5042232B2 (ja) 2012-10-03
CN104264075B (zh) 2018-01-30
WO2007067014A1 (fr) 2007-06-14

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