EP1338667A1 - Composite structure type high tensile strength steel plate, plated plate of composite structure type high tensile strength steel and method for their production - Google Patents
Composite structure type high tensile strength steel plate, plated plate of composite structure type high tensile strength steel and method for their production Download PDFInfo
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- EP1338667A1 EP1338667A1 EP01998666A EP01998666A EP1338667A1 EP 1338667 A1 EP1338667 A1 EP 1338667A1 EP 01998666 A EP01998666 A EP 01998666A EP 01998666 A EP01998666 A EP 01998666A EP 1338667 A1 EP1338667 A1 EP 1338667A1
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- deep drawability
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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
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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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
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- 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
- C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
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- 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
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- 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
- C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
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- 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
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
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- 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
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- 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
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- 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
- JP-A-55-100934 a method for lowering the high yield stress is disclosed in JP-A-55-100934.
- the box annealing is first carried out in order to obtain a high r-value, wherein the temperature in the box annealing is made to a two-phase region of ferrite ( ⁇ )-austenite ( ⁇ ) and Mn is enriched from ⁇ phase to ⁇ phase during the soaking.
- Mn enriched phase preferentially becomes ⁇ phase during the continuous annealing, the dual-phase microstructure is obtained even at a cooling rate as in the gas jet cooling, and further the yield stress becomes low.
- the high cooling rate of 100°C/s is difficult to attain in the gas jet cooling usually used in the continuous annealing line or continuous galvanizing line after the cold rolling, and is required to use an equipment for water-quenching, and also a problem becomes actual in the surface treatment of the water-quenched steel sheet, so that there are problems in the production equipment and the materials.
- JP-B-62-40405 there is proposed a method of producing the high-strength dual-phase galvanized steel sheet by defining the cooling rate after the annealing or the plating in the continuous galvanizing line.
- this method is not actual from the constraint on the equipment for the continuous galvanizing line and also the steel sheet obtained by this method is not said to have a sufficient ductility.
- galvanized steel sheet used herein means to include a galvanized steel sheet obtained by subjecting to a galvanization containing aluminum or the like in addition to zinc and an alloyed galvanized steel sheet obtained by subjecting to a heat (alloying) treatment for diffusing iron of the matrix steel sheet into the plated layer after the galvanization.
- the sheet after the finish rolling is subjected to a temperature holding treatment of 650°C ⁇ 1 hour as a coiling treatment. Subsequently, the sheet is subjected to a cold rolling at a rolling reduction of 70% to obtain a cold rolled steel sheet having a thickness of 1.2 mm. Next, the cold rolled steel sheet is subjected to a recrystallization annealing at 850°C for 60 seconds and cooled at a cooling rate of 30°C/s.
- an abscissa in FIGS. 1a and 1b is an atomic ratio ((V/51)/(C/12)) of V content to C content, and an ordinate is r-value in FIG. 1a and yield ratio (YR) in FIG. 1b.
- 2a and 2b is an atomic ratio (2 ⁇ Nb/93+2 ⁇ Ti/48)/(V/51) of Nb and Ti contents to V content, and an ordinate is tensile strength (TS) in FIG. 2a and r-value in FIG. 2b.
- the invention is accomplished by further examining based on the above knowledge.
- the summary of the invention is as follows.
- the cold rolled steel sheet and the galvanized steel sheet according to the invention are high-strength dual-phase steel sheets having a tensile strength (TS) of not less than 440 MPa and an excellent deep drawability.
- TS tensile strength
- C is an element for increasing the strength of the steel sheet and further promoting the formation of a dual-phase microstructure of ferrite and martensite, and is necessary to contain not less than 0.01%, preferably not less than 0.015% from a viewpoint of the formation of the dual-phase microstructure in the invention.
- the C content is preferable to be not less than 0.015% and not less than 0.03%, respectively.
- the invention limits the C content to 0.01-0.08%.
- it is particularly required to increase the strength of the steel sheet it is preferable to be 0.03-0.08%.
- Si is a useful reinforcing element capable of increasing the strength of the steel sheet without remarkably lowering the ductility of the steel sheet, if the content exceeds 2.0%, the deterioration of the deep drawability is caused, but also the surface properties are degraded. Therefore, Si is limited to not more than 2.0%. Moreover, if it is intended to increase the strength to TS: not less than 780 MPa, it is preferable to be not less than 0.1% for ensuring the required strength. And also, it is preferable to be not less than 0.01% for increasing the strength to TS: not less than 440 MPa which is a main object of the invention.
- Mn has an action reinforcing the steel and further has an action of lessening a critical cooling rate for the obtention of the dual-phase microstructure of ferrite and martensite to promote the formation of the dual-phase microstructure of ferrite and martensite, so that it is preferable to contain a content in accordance with the cooling rate after the recrystallization annealing.
- Mn is an effective element preventing the hot tearing through S, so that it is preferable to contain an appropriate content in accordance with S content.
- the Mn content exceeds 3.0%, the deep drawability and weldability are degraded. In the invention, therefore, the Mn content is limited to not more than 3.0%.
- the Mn content is preferable to be not less than 0.5% for remarkably developing the above effect, and particularly it is preferable to be not less than 1.0% for increasing the strength to TS: not less than 780 MPa. And also, it is preferable to be not less than 0.1% for increasing the strength to TS: not less than 440 MPa which is a main object of the invention.
- the P has an action reinforcing the steel and can be contained in a required amount in accordance with the desired strength.
- the P content exceeds 0.10%, the press formability is degraded. Therefore, the P content is limited to not more than 0.10%.
- the P content is preferable to be not more than 0.08%.
- the P content is preferable to be not more than 0.05% in order to prevent the degradation of the weldability.
- it is intended to increase the strength to TS: not less than 440 MPa it is preferable to be not less than 0.001%.
- S is existent as an inclusion in the steel sheet and is an element bringing about the degradation of the ductility and the formability of the steel sheet, particularly the stretch-flanging property. Therefore, it is preferable to be decreased as far as possible, and when it is decreased to not more than 0.02%, S does not exert a bad influence, so that the S content is 0.02% as an upper limit in the invention.
- the S content is preferable to be not more than 0.01%, more preferably not more than 0.005%.
- the S content is preferable to be not less than 0.0001% considering a cost for the removal of S in the steelmaking process.
- the Al is added to the steel as a deoxidizing element and is a useful element for improving the cleanliness of the steel, but the addition effect is not obtained at less than 0.005%.
- the addition effect is not obtained at less than 0.005%.
- the invention does not exclude a steelmaking method through deoxidization other than the Al deoxidization.
- Ti deoxidization or Si deoxidization may be conducted.
- the steel sheets made by these deoxidizing methods are included within a scope of the invention. In this case, even if Ca, REM and the like are added to the molten steel, the characteristics of the steel sheet according to the invention are not obstructed, so that the steel sheet including Ca, REM and the like is naturally included within the scope of the invention.
- V 0.01-0.5% and 0.5 ⁇ C/12 ⁇ V/51 ⁇ 3 ⁇ C/12
- V is a most important element in the invention.
- the solid-solute C is precipitated and fixed as V carbide to develop the ⁇ 111 ⁇ recrystallization texture, whereby a high r-value can be obtained.
- V dissolves the V carbide in the annealing at ⁇ - ⁇ two-phase region to enrich a large quantity of the solid-solute C in austenite phase, which is easily transformed into martensite at the subsequent cooling process, whereby the dual-phase steel sheet having a dual-phase microstructure of ferrite and martensite can be obtained.
- V content is not less than 0.01%, more preferably not less than 0.02% and satisfies 0.5 ⁇ C/12 ⁇ V/51 in relation to the C content.
- V content exceeds 0.5% or when it is V/51 > 3 ⁇ C/12 in relation to the C content, the dissolution of the V carbide at the ⁇ - ⁇ two-phase region hardly occurs and the dual-phase microstructure of ferrite and martensite is hardly obtained. Therefore, the V content is limited to 0.01-0.5% and to 0.5 ⁇ C/12 ⁇ V/51 ⁇ 3 ⁇ C/12.
- V/51 ⁇ 2 ⁇ C/12 is preferable for obtaining the dual-phase microstructure of ferrite and martensite.
- Nb not more than 0.3% in total of one or tow of Nb: more than 0% but not more than 0.3% and Ti: more than 0% but not more than 0.3%
- V, Nb, Ti and C satisfy 0.5 ⁇ C/12 ⁇ (V/51+2 ⁇ Nb/93+2 ⁇ Ti/48) ⁇ 3 ⁇ C/12
- the deep drawability is apt to be easily degraded by the addition of large quantities of solid-solution strengthening elements such as C, Mn and the like.
- the V, Nb and Ti contents are further desirable to be a range of 1.5 ⁇ (2 ⁇ Nb/93+2 ⁇ Ti/48)/ (V/51) ⁇ 15.
- (2 ⁇ Nb/93+2 ⁇ Ti/48)/ (V/51) is limited to not less than 1.5 is considered due to the fact that although the detail of the cause is not clear, the formation of carbide after the hot rolling is promoted to decrease the solid-solute C by adding large quantities of Nb and Ti as compared with V and hence the ⁇ 111 ⁇ recrystallization texture is easily developed.
- (2 ⁇ Nb/93+2 ⁇ Ti/48)/ (V/51) is desirable to be a range of not more than 15.
- A-group not more than 2.0% in total of one or two of Cr and Mo
- B-group not more than 2.0% in total of one or two of Cu and Ni
- B is an element having an action of improving the hardenability in the steel and may be included, if necessary.
- B is an element having an action of improving the hardenability in the steel and may be included, if necessary.
- the B content exceeds 0.003%, the above effect is saturated, so that the B content is preferable to be not more than 0.003%.
- a more desirable range is 0.001-0.002%.
- Ca and REM have an action of controlling the form of sulfide inclusion and also have an effect of improving the stretch-flanging property. Such an effect is saturated when one or two selected from Ca and REM exceed 0.01% in total. To this end, the content of one or two of Ca and REM is preferable to be not more than 0.01% in total. Moreover, a more preferable range is 0.001-0.005%.
- the reminder other than the above elements is Fe and inevitable impurities.
- the inevitable impurity are mentioned, for example, Sb, Sn, Zn, Co and the like.
- acceptable ranges of their contents are Sb: not more than 0.01%, Sn: not more than 0.1%, Zn: not more than 0.01% and Co: not more than 0.1%.
- the cold rolled steel sheet according to the invention has a microstructure consisting of ferrite phase as a primary phase and a secondary phase including not less than 1% of martensite phase at an area ratio with respect to a whole of the microstructure.
- the microstructure of the steel sheet according to the invention In order to provide the cold rolled steel sheet having a low yield stress (YS), a high ductility (El) and an excellent deep drawability, it is required to render the microstructure of the steel sheet according to the invention into a dual-phase microstructure consisting of a ferrite phase as a primary phase and a secondary phase including a martensite phase. It is preferable that the ferrite phase as a primary phase is not less than 80% at an area ratio and hence the secondary phase is not more than 20%. When the area ratio of the ferrite phase is less than 80%, it is difficult to ensure the high ductility and the press formability tends to lower.
- the ferrite phase is not less than 85% at the area ratio and hence the secondary phase is not more than 15%. Moreover, in order to utilize the advantage of the dual-phase microstructure, the ferrite phase is required to be not more than 99%.
- the secondary phase is required to include the martensite phase at the area ratio of not less than 1% with respect to the whole of the microstructure.
- the martensite is less than 1% at the area ratio, the low yield stress (YS) and the high ductility (El) can not be satisfied simultaneously. More preferably, the martensite phase is not less than 3% but not more than 20% at the area ratio. In case of requiring a good ductility, the martensite phase is preferable to be not more than 15% at the area ratio.
- the secondary phase may be constituted by only the martensite phase at the area ratio of not less than 1% or by mixed phases of the martensite phase at the area ratio of not less than 1% and any of a pearlite phase, a bainite phase and a retained austenite as an additional phase and is not especially limited.
- the pearlite phase, the bainite phase and the retained austenite are preferable to be not more than 50% in total at the area ratio with respect to the microstructure of the secondary phase in order to more effectively develop the effect of the martensite phase.
- composition of the steel slab used in the production method of the invention is the same as the compositions of the aforementioned cold rolled steel sheet and the galvanized steel sheet, so that the explanation on the reason of the limitation in the steel slab is omitted.
- the cold rolled steel sheet according to the invention is produced by using a steel slab having a composition of the above range as a starting material and successively subjecting this starting material to a hot rolling step of subjecting to a hot rolling to obtain a hot rolled steel sheet, a pickling step of pickling the hot rolled steel sheet, a cold rolling step of subjecting the hot rolled steel sheet to a cold rolling to obtain a cold rolled steel sheet, and a recrystallization annealing step of subjecting the cold rolled steel sheet to a recrystallization annealing to obtain a cold rolled annealed steel sheet.
- the galvanized steel sheet according to the invention is produced by using a steel slab having a composition of the above range as a starting material and successively subjecting this starting material to a hot rolling step of subjecting to a hot rolling to obtain a hot rolled steel sheet, a pickling step of pickling the hot rolled steel sheet, a cold rolling step of subjecting the hot rolled steel sheet to a cold rolling to obtain a cold rolled steel sheet, and a continuous galvanization step of subjecting the cold rolled steel sheet to a recrystallization annealing and a galvanizing to obtain a galvanized steel sheet. Furthermore, it is produced by subjecting the cold rolled steel sheet to a step of annealing and pickling before the continuous galvanization step, if necessary.
- the steel slab used is preferable to be produced by a continuous casting process in order to prevent the macro-segregation of the components, but may be produced by an ingot casting process or a thin slab casting process. Furthermore, in addition to the conventional process of cooling to a room temperature once after the production of the steel slab and again heating, energy-saving processes such as a process for inserting a hot steel slab into a heating furnace without cooling, a process for direct sending rolling or direct rolling immediately after slight heat-holding and the like can be applied without problems.
- the above starting material (steel slab) is subjected to the hot rolling step of forming the hot rolled steel sheet by heating and hot rolling.
- the hot rolling step there is particularly no problem even in the use of usual rolling conditions as.long as the hot rolled steel sheet having a desired thickness can be produced.
- preferable hot rolling conditions are mentioned below for the reference.
- the slab heating temperature is desirable to be made lower as far as possible in order to improve the deep drawability by coarsening the precipitate to develop the ⁇ 111 ⁇ recrystallization texture.
- the slab heating temperature is preferable to be not lower than 900°C.
- the upper limit of the slab heating temperature is more preferable to be 1300°C in terms of the lowering of the yield resulted from the increase of scale loss accompanied with the increase of the oxide weight.
- the utilization of a so-called sheet bar heater of heating the sheet bar in the hot rolling is an effective process from a viewpoint that the slab heating temperature is lowered and the troubles in the hot rolling are prevented.
- Finisher delivery temperature not lower than 700°C
- the finisher delivery temperature (FDT) is preferable to be not lower than 700°C in order to obtain a uniform microstructure of the hot rolled parent sheet for providing an excellent deep drawability after the cold rolling and the recrystallization annealing. That is, when the finish deformation temperature is lower than 700°C, not only the microstructure of the hot rolled parent sheet becomes nonuniform, but also the rolling load in the hot rolling becomes higher and the risk of causing the trouble in the hot rolling is increased.
- Coiling temperature not more than 800°C
- the coiling temperature is preferable to be not higher than 800°C. That is, when the coiling temperature exceeds 800°C, the scale increases and the yield tends to lower due to the scale loss. And also, when the coiling temperature is lower than 200°C, the shape of the steel sheet remarkably is disordered and the risk of causing problems in the actual use increases, so that the lower limit of the coiling temperature is more preferable to be 200°C.
- the steel slab is heated above 900°C, subjected to the hot rolling at the finish deformation temperature of not lower than 700°C, and coiled at the coiling temperature of not higher than 800°C.
- a lubrication rolling may be conducted in a part of the finish rolling or between passes thereof in order to reduce the rolling load in the hot rolling.
- the application of the lubrication rolling is effective from a viewpoint of the uniformization of the steel sheet shape and the homogenization of the material.
- the coefficient of friction in the lubrication rolling is preferable to be within a range of 0.10-0.25.
- the cold rolled steel sheet is formed by subjecting the hot rolled steel sheet to the cold rolling.
- the cold rolling conditions are not especially limited as long as the cold rolled steel sheet having desired size and shape can be obtained, but it is preferable that a rolling reduction in the cold rolling is not less than 40%. When the rolling reduction is less than 40%, the ⁇ 111 ⁇ recrystallization texture is not developed and the excellent deep drawability can not be obtained.
- the cold rolled steel sheet according to the invention is subjected to a recrystallization annealing in the subsequent recrystallization annealing step to obtain a cold rolled annealed steel sheet.
- the recrystallization annealing is carried out in a continuous annealing line.
- the galvanized steel sheet according to the invention is produced by subjecting the cold rolled steel sheet to recrystallization annealing and galvanizing in the continuous galvanization line after the cold rolling.
- the annealing temperature in the recrystallization annealing is required to be conducted at a ( ⁇ + ⁇ ) two-phase region within a temperature range from A C1 transformation point to A C3 transformation point.
- the annealing is carried out at ( ⁇ + ⁇ ) two-phase region to dissolve the carbides of V, Ti and Nb to thereby distribute an amount of solid-solute C sufficient to transform austenite to martensite into the austenite phase.
- the annealing temperature is lower than the A C1 transformation point, the microstructure is rendered into the ferrite single phase and the martensite can not be generated, while when it is higher than the A C3 transformation point, the crystal grains are coarsened and the microstructure is rendered into the austenite single phase and the ⁇ 111 ⁇ recrystallization texture is not developed and hence the deep drawability is deteriorated remarkably.
- the cooling in the recrystallization annealing is preferable to be conducted at a cooling rate of not less than 5°C/s in order to produce the martensite phase to obtain the dual-phase microstructure of ferrite and martensite.
- the galvanized steel sheet according to the invention it is preferable to quench to a temperature region of 380-530°C after the above recrystallization annealing.
- a stop temperature of the quenching is lower than 380°C, the defective plating easily occurs, while when it exceeds 530°C, the unevenness easily occurs on the plated surface.
- the cooling rate is preferable to be not less than 5°C/s in order to produce the martensite phase to obtain the dual-phase microstructure of ferrite and martensite.
- the galvanization is carried out by dipping in a galvanizing bath.
- the annealing is preferable to be conducted under a condition that a temperature of the steel sheet reaching in the continuous annealing line is not lower than the A C1 transformation point decided by the components in the steel. Because it is required to promote the enrichment of the alloying element on the surface of the steel sheet and to enrich the alloying element in the secondary phase by once forming the dual-phase microstructure in the continuous annealing line. In the steel sheet after the annealing in the continuous annealing line, there is a tendency that P among the components in the steel is diffused to segregate on the surface of the steel sheet and Si, Mn, Cr and the like enrich as an oxide, so that it is preferable to remove the enriched layer formed on the surface of the steel sheet by the pickling.
- the same annealing as in the above is performed in the continuous galvanization line.
- the annealing in the continuous galvanization line is preferable to be performed at ( ⁇ + ⁇ ) two-phase region within a temperature range of from the A C1 transformation point to the A C3 transformation point.
- the reason why the annealing is performed at not lower than the A C1 transformation point in both the continuous annealing line and the continuous galvanization line is due to the fact that the dual-phase microstructure is formed as mentioned above.
- the dual-phase microstructure as a final microstructure in the continuous annealing line
- the alloying element is further enriched in the secondary phase or ⁇ -phase and hence the ⁇ -phase easily transforms into the martensite phase during the cooling process.
- the invention develops an industrially remarkable effect that the high-strength cold rolled steel sheet and galvanized steel sheet having an excellent deep drawability can be produced stably.
- the cold rolled steel sheet and the galvanized steel sheet according to the invention are applied to vehicle parts, there are effects that the press forming is easy and they can sufficiently contribute to reduce the weight of the vehicle body.
Abstract
Description
Not more than 0.3% in total of one or tow of Nb: more than 0% but not more than 0.3% and Ti: more than 0% but not more than 0.3%, and V, Nb, Ti and C satisfy 0.5×C/12 ≤ (V/51+2×Nb/93+2×Ti/48) ≤ 3×C/12
Claims (24)
- A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability, characterized in that the steel sheet has a composition comprising C: 0.01-0.08 mass%, Si: not more than 2.0 mass%, Mn: not more than 3.0 mass%, P: not more than 0.10 mass%, S: not more than 0.02 mass%, Al: 0.005-0.20 mass%, N: not more than 0.02 mass% and V: 0.01-0.5 mass%, provided that V and C satisfy a relationship of 0.5×C/12 ≤ V/51 ≤ 3×C/12, and the remainder being Fe and inevitable impurities, and has a microstructure consisting of a ferrite phase as a primary phase and a secondary phase including martensite phase at an area ratio of not less than 1% to a whole of the microstructure.
- A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability, characterized in that the steel sheet has a composition comprising C: 0.01-0.08 mass%, Si: not more than 2.0 mass%, Mn: not more than 3.0 mass%, P: not more than 0.10 mass%, S: not more than 0.02 mass%, Al: 0.005-0.20 mass%, N: not more than 0.02 mass% and V: 0.01-0.5 mass% and further comprising not more than 0.3 mass% in total of one or two of Nb: more than 0 mass% but not more than 0.3 mass% and Ti: more than 0 mass% but not more than 0.3 mass%, provided that V, Nb, Ti and C satisfy a relationship of 0.5×C/12 ≤ (V/51+2×Nb/93+2×Ti/48) ≤ 3×C/12, and the remainder being Fe and inevitable impurities, and has a microstructure consisting of a ferrite phase as a primary phase and a secondary phase including martensite phase at an area ratio of not less than 1% to a whole of the microstructure.
- A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to claim 2, wherein the steel sheet comprises not more than 0.3 mass% in total of one or two of Nb: 0.001-0.3 mass% and Ti: 0.001-0.3 mass%.
- A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to claim 2, wherein the steel sheet comprises C: 0.03-0.08 mass%, Si: 0.1-2.0 mass%, Mn: 1.0-3.0 mass%, P: not more than 0.05 mass% and S: not more than 0.01 mass%, provided that V, Nb and Ti satisfy a relationship of 1.5 ≤ (2×Nb/93+2×Ti/48)/(V/51) ≤ 15.
- A high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to any one of claims 1-4, wherein the steel sheet further comprises one or two of the following A-group and B-group:A-group: not more than 2.0 mass% in total of one or two of Cr and Mo;B-group: not more than 2.0 mass% in total of one or two of Cu and Ni.
- A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability, which comprises hot rolling a steel slab having a composition comprising C: 0.01-0.08 mass%, Si: not more than 2.0 mass%, Mn: not more than 3.0 mass%, P: not more than 0.10 mass%, S: not more than 0.02 mass%, Al: 0.005-0.20 mass%, N: not more than 0.02 mass% and V: 0.01-0.5 mass%, provided that V and C satisfy a relationship of 0.5×C/12 ≤ V/51 ≤ 3×C/12, and the remainder being Fe and inevitable impurities, pickling, cold rolling and then subjecting to a continuous annealing at a temperature range from a AC1 transformation point to a AC3 transformation point.
- A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability, which comprises hot rolling a steel slab having a composition comprising C: 0.01-0.08 mass%, Si: not more than 2.0 mass%, Mn: not more than 3.0 mass%, P: not more than 0.10 mass%, S: not more than 0.02 mass%, Al: 0.005-0.20 mass%, N: not more than 0.02 mass% and V: 0.01-0.5 mass% and further comprising not more than 0.3 mass% in total of one or two of Nb: more than 0 mass% but not more than 0.3 mass% and Ti: more than 0 mass% but not more than 0.3 mass%, provided that V, Nb, Ti and C satisfy a relationship of 0.5×C/12 ≤ (V/51+2×Nb/93+2×Ti/48) ≤ 3×C/12, and the remainder being Fe and inevitable impurities, pickling, cold rolling and then subjecting to a continuous annealing at a temperature range from a AC1 transformation point to a AC3 transformation point.
- A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to claim 7, wherein the steel slab comprises not more than 0.3 mass% in total of one or two of Nb: 0.001-0.3 mass% and Ti: 0.001-0.3 mass%.
- A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to claim 7, wherein the steel slab comprises C: 0.03-0.08 mass%, Si: 0.1-2.0 mass%, Mn: 1.0-3.0 mass%, P: not more than 0.05 mass% and S: not more than 0.01 mass%, provided that V, Nb and Ti satisfy a relationship of 1.5 ≤ (2×Nb/93+2×Ti/48)/(V/51) ≤ 15.
- A method of producing a high-strength dual-phase cold rolled steel sheet having an excellent deep drawability according to any one of claims 6-9, wherein the steel slab further comprises one or two of the following A-group and B-group:A-group: not more than 2.0 mass% in total of one or two of Cr and Mo;B-group: not more than 2.0 mass% in total of one or two of Cu and Ni.
- A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in claim 1.
- A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in claim 2.
- A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in claim 3.
- A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in claim 4.
- A high-strength dual-phase galvanized steel sheet having an excellent deep drawability comprising a galvanized coating on the steel sheet as claimed in claim 5.
- A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability, characterized by subjecting to a galvanization after the continuous annealing at a temperature range from a AC1 transformation point to a AC3 transformation point in the method claimed in claim 6.
- A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to claim 16, characterized by further comprising a continuous annealing step between the cold rolling step and the continuous annealing step at a temperature range from a AC1 transformation point to a AC3 transformation point.
- A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability, characterized by subjecting to a galvanization after the continuous annealing at a temperature range from a AC1 transformation point to a AC3 transformation point in the method claimed in claim 7.
- A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to claim 18, characterized by further comprising a continuous annealing step between the cold rolling step and the continuous annealing step at a temperature range from a AC1 transformation point to a AC3 transformation point.
- A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability, characterized by subjecting to a galvanization after the continuous annealing at a temperature range from a AC1 transformation point to a AC3 transformation point in the method claimed in claim 8.
- A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to claim 20, characterized by further comprising a continuous annealing step between the cold rolling step and the continuous annealing step at a temperature range from a AC1 transformation point to a AC3 transformation point.
- A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability, characterized by subjecting to a galvanization after the continuous annealing at a temperature range from a AC1 transformation point to a AC3 transformation point in the method claimed in claim 9.
- A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to claim 22, characterized by further comprising a continuous annealing step between the cold rolling step and the continuous annealing step at a temperature range from a AC1 transformation point to a AC3 transformation point.
- A method of producing a high-strength dual-phase galvanized steel sheet having an excellent deep drawability according to any one of claims 16-23, wherein the steel slab further comprises one or two of the following A-group and B-group:A-group: not more than 2.0 mass% in total of one or two of Cr and Mo;B-group: not more than 2.0 mass% in total of one or two of Cu and Ni.
Applications Claiming Priority (9)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2000361273 | 2000-11-28 | ||
JP2000361273 | 2000-11-28 | ||
JP2000361274 | 2000-11-28 | ||
JP2000361274 | 2000-11-28 | ||
JP2001312687 | 2001-10-10 | ||
JP2001312688 | 2001-10-10 | ||
JP2001312687A JP4010131B2 (en) | 2000-11-28 | 2001-10-10 | Composite structure type high-tensile cold-rolled steel sheet excellent in deep drawability and manufacturing method thereof |
JP2001312688A JP4010132B2 (en) | 2000-11-28 | 2001-10-10 | Composite structure type high-tensile hot-dip galvanized steel sheet excellent in deep drawability and method for producing the same |
PCT/JP2001/010340 WO2002044434A1 (en) | 2000-11-28 | 2001-11-27 | Composite structure type high tensile strength steel plate, plated plate of composite structure type high tensile strength steel and method for their production |
Publications (3)
Publication Number | Publication Date |
---|---|
EP1338667A1 true EP1338667A1 (en) | 2003-08-27 |
EP1338667A4 EP1338667A4 (en) | 2005-08-17 |
EP1338667B1 EP1338667B1 (en) | 2011-01-19 |
Family
ID=27481823
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP01998666A Expired - Lifetime EP1338667B1 (en) | 2000-11-28 | 2001-11-27 | Composite structure type high tensile strength steel plate, plated plate of composite structure type high tensile strength steel and method for their production |
Country Status (9)
Country | Link |
---|---|
US (1) | US20030129444A1 (en) |
EP (1) | EP1338667B1 (en) |
KR (1) | KR20020073564A (en) |
CN (1) | CN1193110C (en) |
AU (1) | AU776043B2 (en) |
CA (1) | CA2398126A1 (en) |
DE (1) | DE60143907D1 (en) |
TW (1) | TW520398B (en) |
WO (1) | WO2002044434A1 (en) |
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- 2001-11-27 CA CA002398126A patent/CA2398126A1/en not_active Abandoned
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- 2001-11-27 DE DE60143907T patent/DE60143907D1/en not_active Expired - Lifetime
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Cited By (14)
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EP1682686A4 (en) * | 2003-11-04 | 2007-06-27 | Uec Technologies Llc | Dual phase steel strip suitable for galvanizing |
EP1682686A1 (en) * | 2003-11-04 | 2006-07-26 | UEC Technologies LLC | Dual phase steel strip suitable for galvanizing |
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US7442268B2 (en) | 2004-11-24 | 2008-10-28 | Nucor Corporation | Method of manufacturing cold rolled dual-phase steel sheet |
US7879160B2 (en) | 2004-11-24 | 2011-02-01 | Nucor Corporation | Cold rolled dual-phase steel sheet |
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US8337643B2 (en) | 2004-11-24 | 2012-12-25 | Nucor Corporation | Hot rolled dual phase steel sheet |
US7608155B2 (en) | 2006-09-27 | 2009-10-27 | Nucor Corporation | High strength, hot dip coated, dual phase, steel sheet and method of manufacturing same |
US8435363B2 (en) | 2007-10-10 | 2013-05-07 | Nucor Corporation | Complex metallographic structured high strength steel and manufacturing same |
US9157138B2 (en) | 2007-10-10 | 2015-10-13 | Nucor Corporation | Complex metallographic structured high strength steel and method of manufacturing |
WO2011036352A1 (en) * | 2009-09-24 | 2011-03-31 | Arcelormittal Investigación Y Desarrolllo Sl | Ferritic stainless steel having high drawability properties |
WO2011036351A1 (en) * | 2009-09-24 | 2011-03-31 | Arcelormittal Investigación Y Desarrollo Sl | Ferritic stainless steel having high drawability properties |
EP2636762A4 (en) * | 2010-11-05 | 2016-10-26 | Jfe Steel Corp | High-strength cold-rolled steel sheet having excellent deep-drawability and bake hardenability, and method for manufacturing same |
US10400301B2 (en) | 2014-12-10 | 2019-09-03 | Posco | Dual-phase steel sheet with excellent formability and manufacturing method therefor |
Also Published As
Publication number | Publication date |
---|---|
CN1193110C (en) | 2005-03-16 |
KR20020073564A (en) | 2002-09-27 |
DE60143907D1 (en) | 2011-03-03 |
AU2411802A (en) | 2002-06-11 |
CN1419607A (en) | 2003-05-21 |
US20030129444A1 (en) | 2003-07-10 |
CA2398126A1 (en) | 2002-06-06 |
TW520398B (en) | 2003-02-11 |
EP1338667B1 (en) | 2011-01-19 |
AU776043B2 (en) | 2004-08-26 |
EP1338667A4 (en) | 2005-08-17 |
WO2002044434A1 (en) | 2002-06-06 |
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