CN105734410A - High-strength cold-rolled steel sheet of excellent bending workability and hole-expanding property, hot-dip galvanized steel sheet and manufacturing method thereof - Google Patents

High-strength cold-rolled steel sheet of excellent bending workability and hole-expanding property, hot-dip galvanized steel sheet and manufacturing method thereof Download PDF

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CN105734410A
CN105734410A CN201510983281.1A CN201510983281A CN105734410A CN 105734410 A CN105734410 A CN 105734410A CN 201510983281 A CN201510983281 A CN 201510983281A CN 105734410 A CN105734410 A CN 105734410A
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bendability
steel sheet
high strength
steel plate
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韩成豪
韩箱浩
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Posco Holdings Inc
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Posco Co Ltd
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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
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • 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
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • 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
    • 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

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)

Abstract

The invention relates to a high-strength cold-rolled steel sheet of excellent bending workability and hole-expanding property. The high-strength cold-rolled steel sheet comprises the following components in weight percentage: 0.06 to 0.1% of C, 0.05 to 0.5% of Si, 2.0 to 2.5% of Mn, 0.001 to 0.10% of P, 0.010% or less of S, 0.01 to 0.10% of soluble Al, 0.010% or less of N, more than one selected from 0.003 to 0.08% of Ti and Nb, the balance of Fe and impurities. The fine structure of the steel material is composed of 40% or less of martensite, 30 to 40% of bainite and 20 to 30% of ferrite in area percentage. The hardness ratio of bainite to ferrite is over 0.7. The ferrite contains precipitates, wherein the density of the precipitates is 1.5*10<6> per mm2 and the size of the precipitates is smaller than 10 nm. In this way, the hardness ratio of bainite to ferrite is 2 or less.

Description

Bendability and the high strength cold rolled steel plate of hole expandability excellence, hot-dip galvanized steel sheet and manufacture method thereof
Technical field
The present invention relates to the manufacture method of the ultrahigh-strength steel plates that a kind of tensile strength is more than 980MPa level, described steel plate uses mainly as structural partsof automobiles.In more detail, while relating to a kind of area fraction by suitably controlling ferrite, bainite and martensite, control to change the hardness ratio of phase, size etc. and obtain processability and the cold-rolled steel sheet of excellent in bending workability, hot-dip galvanized steel sheet and manufacture method thereof.
Background technology
In recent years, for environment of preserving our planet, while the regulation about fuel efficiency is strengthened, also launching the lightweight to car body energetically.As counte-rplan, people are alleviating the weight of automotive material by the high strength of steel plate.Generally, high-strength vehicle material can be divided into precipitation strength steel, baking hardened steel, Solid Solution Strengthened Steel, transformation strengthening steel etc..Wherein, change strengthening steel and have dual phase steel (DualPhaseSteel), complex tissue steel (ComplexPhaseSteel), phase-change induced plastic (TransformationInducedPlasticity) steel etc..These change strengthening steel and are also referred to as AHSS (AdvanceHighStrengthSteel:AHSS).Described dual phase steel (DP) is the martensite being uniformly dispersed hard in soft ferrite, ensures that the steel of high intensity.Described complex tissue steel (CP) includes the biphase or three-phase of ferrite, martensite, bainite, is the steel of the precipitation-hardening element comprising Ti, Nb etc. to improve intensity.Phase-change induced plastic (TRIP) steel is at normal temperatures fine homodisperse retained austenite to be processed and produce martensite transfor mation, so that it is guaranteed that the steel grade of high-strength high-tractility.
Recently; in order to improve fuel efficiency and durability, it is necessary to have the automotive sheet of higher intensity, and; from the viewpoint of crashworthiness and protection passenger, increase with the ultrahigh-strength steel plates that tensile strength is more than 980MPa for self structure or as the consumption that makes of girth member.But, the high strength of steel plate can cause molding processibility and weldability to reduce, accordingly, it would be desirable to develop the material making up this defect.In this demand, the structural transformation steel plates such as duplex structure's steel, TRIP steel or complex tissue steel up to the present should be have developed.Such as, Japanese Patent Laid-fair 6-145892 discloses the amount of a kind of retained austenite by controlling chemical composition and steel plate and has the manufacture method of the steel plate of the mouldability of excellence, Japanese Patent No. 2660644 and a kind of manufacture method by controlling the micro organization of chemical composition and steel plate with the high-strength steel sheet of good extrusion forming disclosed in patent the 2704350th.It addition, the excellent in workability of a kind of retained austenite comprising more than 5%, steel plate that especially local elongation is excellent disclosed in Japanese Patent No. 3317303.But, these invention major parts are provided to improve ductility and develop, the bendability of major criterion when not taking into full account as processing physical unit or weldability etc..
In the characteristic required by steel plate, in body construction or girth member, the most important characteristic of the main ultrahigh-strength steel plates that tensile strength is more than 980MPa level used is bendability and hole expandability.Owing to needing that the position using these high strength steels is carried out main bending (bending) or stretch flange processing as the accessories such as curb girder (sillside), seat (seat), therefore, even if percentage elongation is excellent again, when bendability or stretch flange deteriorate, then cannot function as accessory and use.Bendability represents the ratio (R/t) of the minimum bending radius to unit thickness, and wherein, minimum bending radius ratio (R) represents after being curved test, the least radius that the outer ring portion of steel plate does not crack.Each motor corporation is more or less different for the requirement of bendability, to require that most stringent Toyota Motor is as standard, based on tensile strength 980MPa level cold-rolled steel sheet, it is desirable to meet the condition of R/t≤1.
Tested by hole expandability and evaluate stretch flange, employ the grade of Japan JSFT1001-1996.The requirement of hole expandability is not had definite standard, but for high strength steel more than 980MPa level, in order to prevent adding, at accessory, the crackle produced because of flange formation man-hour, at least requires the value of more than 20%.
As the method being used for improving this hole expandability and bendability, it is known that need suitably to control composition and the ratio of the transformation phase of existence in steel, and the strength ratio of soft phase and hard phase is more low, bendability more excellent (referring to Fig. 1).For this reason, it may be necessary to bainite or tempered martensite (TemperedMartensite) replace martensite.But, these transformations are met and are sharply increased yield strength and make percentage elongation significantly reduce (referring to Fig. 2), therefore, suitably guarantee that the ratio of components changing phase is particularly important.
Additionally, when actual operation manufactures the ultrahigh-strength steel plates that tensile strength is more than 980MPa level, owing to yield strength is very high, cold-rolling property is made to be substantially reduced because of the high intensity as the hot rolled plate of intermediate materials, and, owing to needing to use rapid cooling thermal treatment conditions when being annealed and processing, operability therefore can be made to be substantially reduced.It addition, for these materials, owing to the transformation existed in steel is very sensitive relative to annealing temperature, thus can change according to annealing temperature, therefore, annealing temperature is somewhat varied from, the kind and composition that change phase will be changed.Thus causing that yield strength produces significant change, percentage elongation can reduce, accordingly, it would be desirable to develop a kind of new product being able to ensure that stable material under broader annealing region.But, foregoing is studied by the known technology such as Japanese Patent Publication the 3729105th, Japanese Patent Publication 2010-90432 and Unexamined Patent 2005-105367 fully.
Summary of the invention
Solve the technical problem that
Therefore, the present invention proposes to solve above-mentioned problems of the prior art, its object is to, a kind of low yield strength ratio type high strength cold rolled steel plate and hot-dip galvanized steel sheet are provided, namely, when manufacturing the ultrahigh-strength thin steel sheet that tensile strength is more than 980Mpa level, by while the area fraction that suitably controls ferrite, bainite and martensite, controlling the when size of the hardness between each phase etc. provides a kind of ductility and bendability and the excellent low yield strength ratio type high strength cold rolled steel plate of hole expandability and hot-dip galvanized steel sheet.
Further, it is an object of the invention to, it is provided that the manufacture method of a kind of described cold-rolled steel sheet and hot-dip galvanized steel sheet.
But, the technical problem to be solved in the present invention is not limited to technical problem mentioned above, and those skilled in the art can be expressly understood that NM other technologies problem above according to set forth below.
Technical scheme
The present invention for realizing above-mentioned purpose relates to a kind of bendability and the high strength cold rolled steel plate of hole expandability excellence, described high strength cold rolled steel plate has following chemical composition: in weight %, C containing 0.06～0.1%, the Si of 0.05～0.5%, 2.0～2.5% Mn, 0.001～0.10% P, more than one in the S of less than 0.010%, Ti and the Nb of the solvable Al of 0.01～0.10%, the N of less than 0.010% and respectively 0.003～0.08% scope, and the Fe of surplus and impurity；The micro organization of steel is by with area fractionBe calculated as the martensite of less than 40%, the bainite of 30～40% and 20～30% ferrite constitute；The hardness ratio of bainite/martensite is more than 0.7；Described ferrite is formed with 1.5 × 106Individual/mm2The above precipitate being sized to below 10nm, to meet bainite/ferritic hardness ratio for less than 2.
Additionally, the described ferritic crystallization particle diameter in the present invention is preferably less than 10 μm, the mean size of martensite is preferably less than 5 μm.
Additionally, (bainite+martensite)/ferritic hardness ratio is preferably less than 4.
Moreover it is preferred that described cold-rolled steel sheet contains more than one in the Mo of Cr and 0.01～0.15% of 0.5～1.0% further.
Moreover it is preferred that described cold-rolled steel sheet contains the B of 0.0010～0.0060% further.
Moreover it is preferred that described cold-rolled steel sheet contains the Sb of less than 0.10% further.
Additionally, the present invention relates to a kind of bendability and the high strength hot dip galvanized steel sheet of hole expandability excellence, described high strength hot dip galvanized steel sheet is the high strength hot dip galvanized steel sheet being formed with molten zinc plating layer in above-mentioned surface of cold-rolled steel plate.
In addition, the present invention relates to a kind of bendability and the high-strength galvannealed sheet of hole expandability excellence, described high-strength galvannealed sheet is the high-strength galvannealed sheet being formed with hot dip alloyed zinc coat in above-mentioned surface of cold-rolled steel plate.
Additionally, the present invention relates to the manufacture method of the high strength cold rolled steel plate of a kind of bendability and hole expandability excellence, the manufacture method of described high strength cold rolled steel plate includes following operation: it is reheated after having the steel billet of alloy as above composition by preparation；For the described steel billet through reheating, under Ar3～Ar3+50 DEG C of temperature range, carry out hot finishing After, it is wound under 600～750 DEG C of temperature ranges；For through winding described hot rolled plate, with the cold rolling reduction ratio of 40～70% carry out cold rolling after, carry out continuous annealing process the temperature range of Ac1+30 DEG C～Ac3-30 DEG C；And the described steel plate for processing through continuous annealing, carry out first paragraph cooling, until it reaches 650～700 DEG C, then second segment cooling is carried out, until reaching the temperature range of 400～500 DEG C, then carry out Wetted constructures, until it reaches the temperature range of 300～400 DEG C.
In addition, the present invention relates to the manufacture method of the high strength hot dip galvanized steel sheet of a kind of bendability and hole expandability excellence, the manufacture method of described high strength hot dip galvanized steel sheet includes following operation: it is reheated after having the steel billet of alloy as above composition by preparation；For the described steel billet through reheating, after carrying out hot finishing under Ar3～Ar3+50 DEG C of temperature range, it is wound under 600～750 DEG C of temperature ranges；For through winding described hot rolled plate, with the cold rolling reduction ratio of 40～70% carry out cold rolling after, carry out continuous annealing process the temperature range of Ac1+30 DEG C～Ac3-30 DEG C；For the described steel plate processed through continuous annealing, carry out first paragraph cooling, until it reaches 650～700 DEG C, then carry out second segment cooling with the average cooling rate of 3～30 DEG C/s, until it reaches 600 DEG C of temperature below scopes；And under normal conditions to after overcooled described steel plate is annealed, carry out molten zinc plating.
In addition, the present invention relates to the manufacture method of the high-strength galvannealed sheet of a kind of bendability and hole expandability excellence, the manufacture method of described high-strength galvannealed sheet includes, after carrying out described molten zinc plating process, carrying out the operation of the Alloying Treatment of molten zinc plating under the temperature range of 450～600 DEG C.
In the present invention, for described cold-rolled steel sheet, hot-dip galvanized steel sheet or alloy galvanized steel plate, it is preferable that the micro organization of steel by be calculated as with area fraction the martensite of less than 40%, the bainite of 30～40% and 20～30% ferrite constituted；The hardness ratio of bainite/martensite is more than 0.7；Described ferrite is formed with 1.5 × 106Individual/mm2The above precipitate being sized to below 10nm, to meet bainite/ferritic hardness ratio for less than 2.
Additionally, in the present invention, described ferritic crystallization particle diameter is preferably less than 10 μm, and the mean size of described martensite is preferably less than 5 μm, and (bainite+martensite)/ferritic hardness ratio is preferably less than 4.
Additionally, more than one preferably comprising in described cold-rolled steel sheet in the Mo of Cr and 0.01～0.15% of 0.5～1.0%.
Moreover it is preferred that contain the B of 0.0010～0.0060% further.
Moreover it is preferred that contain the Sb of less than 0.10% further.
In the present invention, it is also possible under the reduction ratio scope of 0.2～1.0%, the steel plate cooled down through second segment is carried out roll-in press polish (skinpassrolling).
Beneficial effect
The present invention with composition as above can provide the cold-rolled steel sheet that tensile strength is more than 980Mpa level and the hot-dip galvanized steel sheet of a kind of bendability and hole expandability excellence effectively, its percentage elongation is more than 12%, yield tensile ratio is less than 0.7, and bendability (R/t) is that hole expandability is more than 30% while less than 0.5.
Accompanying drawing explanation
Fig. 1 is for illustrate the hardness ratio chart with the relation of reaming ratio (HER).
Fig. 2 is the chart illustrating percentage elongation with the relation of reaming ratio.
The chart of the microhardness distribution that the steel plate (grade of steel 1,1-1) that Fig. 3 is manufactured in one embodiment of the invention demonstrates according to different second segment cooling termination temperatures (RCS).
Fig. 4 is the micro organization's distribution photo under different RCS of the steel plate shown in Fig. 3.
Fig. 5 is the nano-scaled precipitate distribution photo of steel plate (example 1) manufactured in one embodiment of the invention.
Preferred implementation
Below, the present invention will be described.
The present inventor in order to obtain the tensile strength with more than 980Mpa, and the excellent high strength cold rolled steel plate of hole expandability or bendability and be repeatedly performed the result of research, it was found that herein below.(1) by after the compositional optimization of composition, in area fraction, containing the ferritic phase of 20～30%, the Bainite Phases of Some of 30～40% and less than 40% martensitic phase, and, in order to make structure refinement, preferably by ferritic size controlling below 10 μm, the mean size of martensite is controlled below 5 μm.(2) as the method being used for improving hole expandability and bendability, it is preferable that make micro organization in the intensity difference between each phase minimize, in order to increase the intensity in ferritic phase, by controlling the precipitate of nanosized 1.5 × 106Individual/mm2Above, so that the hardness ratio of Bainite Phases of Some/ferritic phase controls below 2.Additionally, in order to reduce the intensity difference as the martensitic phase and Bainite Phases of Some changing tissue, by the hardness ratio of Bainite Phases of Some/martensitic phase is controlled more than 0.7, so that martensitic phase maintains almost similar level with the intensity of Bainite Phases of Some.Wishing that carrying out such control by the hardness that transformation is organized makes the hardness ratio of (Bainite Phases of Some+martensitic phase)/ferritic phase be controlled in less than 4, changing phase and the ferritic difference of hardness as parent phase thus reducing as much as possible.The tensile strength of more than 980Mpa and the hole expandability of excellence or bendability it is capable of by such general knowledge.
Additionally, the micro organization of above-mentioned steel plate passes through when being annealed to heat/maintain under the temperature conditions of two phase region, so that it is guaranteed that after a certain amount of ferrite, (3) Slow cooling method is used for cold rolled annealed steel plate, described cooling means is, be cooled to the temperature province of 400～500 DEG C with the average cooling rate of 5～30 DEG C/s after, carry out the temperature province of Wetted constructures to 300～400 DEG C.(4) additionally, in order to manufacture hot-dip galvanized steel sheet, utilize the heat treatment method being cooled to 600 DEG C of temperature below regions with the average cooling rate of 3～30 DEG C/s.This cycle heat treatment is for guaranteeing the operation of suitable bainite when cooling.Alternate difference of hardness can be reduced by this method guaranteeing bainite.
Below, micro organization and the precipitate characteristic of the bendability (R/t) below HER and 1.0 for guaranteeing more than 30% of the presently claimed invention will be described in detail.
In order to ensure suitable ductility required in the present invention, it is necessary to made annealing treatment the ferrite obtaining 20～30% by two-phase section.Further, in order to realize intended intensity and flexural property etc., therefore, to assure that the Bainite Phases of Some of certain area fraction.When being made up of martensite and not containing bainite, cause percentage elongation high because producing intensity difference between martensitic phase and ferritic phase, but the problem of bendability and hole expandability deterioration.Therefore, known in order to improve bendability and hole expandability, therefore, to assure that a certain amount of Bainite Phases of Some, it is 30～40% that the present inventor confirms suitable bainite by experiment, and this result can be passed through, after annealing cooling, to carry out Wetted constructures at bainite range and obtain.Additionally, the austenite not changed after Wetted constructures translates into martensite, thus forming the martensite area fraction of more than 40%.
It addition, in the present invention, in order to make tissue miniaturization, it is possible to ferritic crystallization particle diameter is limited in less than 10 μm, the mean size of martensite is limited in less than 5 μm.That is, in order to improve hole expandability, bendability, it is important that guarantee that uniform tissue, this uniform tissue include alternate strength variance and reduce and tissue miniaturization.In order to realize good bendability and hole expandability in the region of more than 980Mpa, it is necessary to as much as possible the size of micro organization is controlled in low level.When the diameter of F is more than 10 μm, and when the mean diameter of hard transformation phase is more than 5.0 μm, because the inequality of tissue homogenizes, it is impossible to enough satisfied bendabilities that disclosed in this invention or hole expandability.
As mentioned above, the difference of hardness of each phase in the micro organization of reduction as much as possible is favourable to flexural property and hole expandability.Its reason is in that, when applying external stress, owing to crackle can transmit along alternate interface, therefore, in order to prevent the crackle produced along interphase interface, it is preferable that reduce each alternate intensity difference as much as possible.Guarantee that homogeneous structure is the most excellent.But, for single-phase ferritic steel, intended intensity cannot be guaranteed because of soft ferrite；For single-phase bainitic steel or single-phase martensite steel, although excellent strength, but have problems in guaranteeing intended percentage elongation.Therefore, in order to guarantee bendability and hole expandability while guaranteeing ductility, it is necessary to suitably control the area fraction of the micro organization generated in tissue, and, reduce each alternate difference of hardness as much as possible.Consider these, in the present invention, the hardness ratio of Bainite Phases of Some/martensitic phase is limited in more than 0.7, when these conditions are met, be then able to ensure that the bendability desired by the present invention and hole expandability.
Additionally, in order to reduce each alternate difference of hardness, it is necessary to improve the intensity of soft ferritic phase.Consider these, it is a feature of the present invention that and make in ferritic phase with 1.5 × 106Individual/mm2Above distribution forms the precipitate of below 10nm, with meet Bainite Phases of Some/ferritic phase hardness ratio for less than 2.It is possible to fully improve ferritic intensity, thus meeting bendability disclosed in this invention and hole expandability.
In order to have bendability excellent as described in the present invention and hole expandability, do not require nothing more than the hardness changing phase and improved, but also require to be improved as the ferritic hardness of parent phase simultaneously yet.In order to improve the intensity of ferritic phase, it is possible to interpolation solid solution element is used as a kind of method, but, when adding alloying element, meeting make because of the increase of intensity the area fraction of transformation tissue increase and also can with the deterioration etc. of weldability.Accordingly, as the another kind of method of the intensity improving ferritic phase, present inventor considered that the nano-scaled precipitate used in steel.According to the research that the present inventor carries out, if the ensuring that 1.5 × 106Individual/mm2The precipitate of above below 10nm, then can make ferritic intensity be improved fully such that it is able to meet bendability disclosed in this invention and hole expandability.
It is highly preferred that make the hardness ratio of (Bainite Phases of Some+martensitic phase)/ferritic phase control below 4, it is possible to guarantee more excellent bendability and hole expandability.
Below, the constituent of the steel of the present invention and such reason limiting composition are described in detail.
Carbon (C) in steel is to strengthen the very important element changing tissue and add.Carbon contributes to high strength, also the formation of the martensite in promotion complex tissue steel.If carbon content increases, then the amount of the martensite in steel can increase.But, if carbon content is more than 0.1%, although then can increase the intensity of martensite, but the ferritic intensity difference low with concentration of carbon can increase.Such intensity difference, when additional stress, can easily produce to break on interphase interface, therefore can reduce flexural property and stretch flange.Additionally, due to weldability is relatively poor, therefore, customer company can cause weld defect when processing component.On the other hand, if carbon content is down to less than 0.06%, then be very difficult to guarantee intended intensity, therefore, in the present invention preferably by carbon content control 0.06～0.1%.
Silicon (Si) in steel promotes ferritic transformation, and improves the carbon content not changing in austenite, so that the complex tissue of ferrite and martensite is readily formed, and causes the solid solution strengthening effect of silicon self.So, silicon is for ensuring that the element being highly useful of intensity and material, but, in surface characteristic, not only can cause surface scale defect, but also chemical convertibility (chemicalconversiontreatment) can be reduced, it is therefore preferable that control the interpolation scope of silicon.Therefore, it is within the contemplation of the invention that while guaranteeing a certain amount of ferrite and martensite area fraction, the content of silicon is controlled the scope will not reduce weldability 0.05～0.5%.When the content of silicon is less than 0.05%, owing to cannot ensure that sufficient ferrite, therefore, ductility may reduce；When the content of silicon is more than 0.5%, the while of dropping low intensive, weldability also can be made to deteriorate.
Manganese (Mn) in steel is the element playing following effect.Manganese, when not destroying ductility, makes particle miniaturization, and makes the sulfur in steel precipitate out with the form of MnS completely, thus the red brittleness brought by the generation of FeS can not only be prevented, but also steel can be played invigoration effect.Further, manganese can play the effect reducing the critical cooling rate obtaining martensitic phase in complex tissue steel such that it is able to is more easily formed martensite.But, when the content of manganese is less than 2.0%, it is difficult to guarantee the intensity desired by the present invention, on the other hand, when the content of manganese is more than 2.5%, the probability causing the problem such as weldability, hot rolling can be made to become big.In consideration of it, the content of Mn is preferably controlled in 2.0～2.5% scopes by the present invention.
Phosphorus (P) in steel, as the maximum substituted type alloying element of solid solution strengthening effect, plays and improves intra-face anisotropy and improve the effect of intensity.When the content of phosphorus is less than 0.001%, not only cannot ensure that its effect, but also the problem that manufacturing expense aspect can be caused.On the other hand, when addition is too much, extrusion forming can be made to deteriorate, and steel can be made to produce fragility, it is therefore preferable that control to be 0.001～0.10% by the content of P.
Sulfur (S) in steel is the impurity element in steel, is the element of ductility and the weldability hindering steel plate.When the content of sulfur is more than 0.010%, the ductility of obstruction steel plate and the probability of weldability are big, it is therefore preferable that the content by described S controls below 0.010%.
Soluble aluminum (Sol.Al) in steel is combined by the oxygen in steel and plays deoxidation, and the same with the Si effect played, and is that the carbon in ferrite is assigned as austenite, thus improving the effective ingredient of the quenching degree of martensite.When the content of soluble aluminum is less than 0.01%, it is impossible to guarantee the effect above, on the other hand, when the content of soluble aluminum is more than 0.10%, the effect above not only can be made saturated, but also can be more costly to manufacture.Therefore, the content of described soluble aluminum is preferably controlled in 0.01～0.10% scope by the present invention.
Nitrogen (N) in steel is the composition that austenitic stabilisation plays useful effect.But, when the content of nitrogen is more than 0.010%, austenitic stability can be greatly increased, thus the formation of the bainite of 30～40% levels desired by the present invention can be hindered, it is therefore preferable that controlled below 0.010% by its content.
Ti and Nb in steel is the effective element of miniaturization to the intensity and particle diameter improving steel plate, more preferably contains more than one in Ti and the Nb of respectively 0.003～0.08% scope in the present invention.When the content of described Ti and Nb is respectively less than 0.003%, it is difficult to guarantee this effect, when the content of described Ti and Nb is more than 0.08%, ductility can be substantially reduced because of the raising of manufacturing expense and too much precipitate.
The steel plate of the present invention is on the basis of above-mentioned composition of steel, it is possible to optionally comprise following compositions further.
First, the steel plate of the present invention more preferably contains more than one in the Mo of Cr and 0.01～0.15% of 0.5～1.0%.
Chromium (Cr) in steel is to improve the quenching degree of steel and the composition guaranteeing high intensity and adding, and it for promoting the element of bainite formation, is the element playing very important effect in the present invention.When the content of described chromium is less than 0.5%, it is difficult to guarantee the effect above, when the content of described chromium is more than 1.0%, its effect can be saturated, and unfavorable for economic aspect, it is therefore preferable that control the content of described Cr 0.5～1.0%.
It is to improve the quenching degree of steel and the composition guaranteeing high intensity and adding such as Cr, the Mo in steel.Further, Mo can generate Mo class fine carbide in steel, thus playing the effect of the intensity improving ferrite fundamental tissue.This effect can make transformation tissue and ferritic alternate intensity difference reduce, thus playing the effect that bendability is favourable.When the content of Mo is below 0.01%, it is difficult to obtain this effect, when the content of Mo is more than 0.15%, it is possible to manufacturing expense can be made excessively to increase.
Additionally, the steel plate of the present invention can comprise the B of 0.0010～0.0060% further.
B in steel is in the process of the cooling when being annealed, and is used for postponing austenite and is changed into ferritic composition, and it is added as the element of the ferritic formation of suppression and the formation promoting bainite.But, when the content of described B is less than 0.0010%, it is difficult to obtain the effect above, when the content of described B is more than 0.0060%, from the teeth outwards can concentrated many B, thus gold-plated adhering deterioration can be caused.Consider this problem, the content of described B is preferably controlled 0.0010%～0.0060% by the present invention.
Further, the steel plate of the present invention can comprise the Sb of less than 0.10% further.
Sb in steel is the composition added in order to ensure excellent resistance to impact (dentresistance) in the present invention.Described Sb is by suppressing for MnO, SiO2、Al2O3Concentrate reduce because of the surface defect brought of impact on the surface of oxide, suppress to be risen by temperature and in the coarsening of surface concentrate that hot-rolled process change brings effect notable.When the content of described Sb is more than 0.1%, even if its content continues to increase, this effect is without increasing too much, and also results in the problem such as manufacturing expense and processability deterioration, it is therefore preferable that the content by described Sb controls below 0.1%.
The steel plate of the present invention with constituent and the steel micro organization etc. of steel as above can demonstrate following effect, the percentage elongation of the steel plate of the present invention is more than 12%, yield tensile ratio is less than 0.7 simultaneously, and bendability (R/t) is less than 0.5, and hole expandability is more than 30%.
Below, the manufacture method of the cold-rolled steel sheet of the present invention, hot-dip galvanized steel sheet and alloy galvanized steel plate is specifically described.
In the present invention, after first preparation has the steel billet of constituent of steel as above, it is reheated.Reheating condition in the present invention is not particularly limited, it is possible to use conventional reheating condition is implemented.
Then, for the described steel billet through reheating, under Ar3～Ar3+50 DEG C of temperature range, hot finishing is carried out.If hot finishing temperature is less than Ar3, the probability that then thermal deformation resistance sharply increases is big, and, owing to the head (top) of hot rolled coil, afterbody (tail) and edge become monophase field, the anisotropy in face can be made to increase, and mouldability can be made to deteriorate.On the other hand, when the temperature of hot finishing is more than Ar3+50 DEG C, not only can produce blocked up oxide skin, and the probability of micro organization's coarsening of steel plate can become big.
Then, after terminating described hot finishing, it is wound under the temperature range of 600～750 DEG C.When described coiling temperature is less than 600 DEG C, owing to generating too much martensite or bainite, thus can cause that the intensity of hot rolled steel plate improves, the problem that therefore can cause the manufacture views such as the shape defect that brings because of load when cold rolling.On the other hand, when coiling temperature is more than 750 DEG C, the surface concentration caused by element of Si, Mn and the B etc. by the wettability reducing molten zinc plating can be deepened, it is therefore preferable that controlled by coiling temperature at 600～750 DEG C.
Then, it is possible under normal conditions the hot rolled plate of described winding is carried out follow-up pickling processes.
It addition, in the present invention, for the described steel plate through winding, carry out cold rolling with the cold rolling reduction ratio of 40～70%.When reduction ratio is less than 40%, recrystallization driving force can die down, and the probability come into question in obtaining good recrystal grain is high, and is very difficult to correction shape.But, when reduction ratio is more than 70%, the probability cracked at steel plate edge part is big, and rolling load can sharply increase.
Then, for carrying out continuous annealing process through cold rolling steel plate.Now, it is preferable that continuous annealing temperature is set as the temperature range of Ac1+30～Ac3-30 DEG C.When temperature when continuous annealing is less than Ac1+30 DEG C, the danger producing not recrystal grain can increase, and is difficult to be sufficiently formed austenite, thus being difficult to ensure that the target strength desired by the present invention.It addition, when annealing temperature is more than Ac3-30 DEG C, the amount of bainite can be made to sharply increase because forming too much austenite, thus the area fraction of bainite can not meet the scope of disclosed in this invention less than 10%.The increase of this bainite area fraction can cause yield strength excessively to increase and the deterioration of ductility.
Then, for described steel plate through equal thermal anneal process in continuous annealing operation, first paragraph cooling is carried out, until it reaches the temperature range of 650～700 DEG C.The cooling of described first paragraph is in order to by assuring that the operation implemented to improve the ductility of steel plate and intensity of the concentration of carbon of ferrite and austenitic balance, when described first paragraph cooling termination temperature is less than 650 DEG C or more than 700 DEG C, it is difficult to ensure that in the ductility desired by the present invention and intensity, it is therefore preferable that described first paragraph cooling termination temperature is controlled at 650～700 DEG C.In the present invention, it is preferable that rate of cooling now is set as the scope of 1～10 DEG C/s.
Then, for the described steel plate cooled down through first paragraph, carry out second segment cooling, until it reaches after the temperature range of 400～500 DEG C, between Bainite Region, carry out Wetted constructures, until it reaches the temperature range of 300～400 DEG C.Described second segment cooling termination temperature is the very important temperature conditions used to guarantee ductility and bendability simultaneously.When cooling termination temperature is below 400 DEG C, the time resting on bainite range when carrying out Wetted constructures is short, therefore, it is difficult to guarantee the sufficient bayesian scale of construction, when cooling termination temperature is more than 500 DEG C, the time mainly resting on bainite range when carrying out Wetted constructures is very long, yield strength can be made to increase because producing too much bainite, and make ductility deteriorate.In the present invention, it is preferable that second segment rate of cooling now is set as the scope of 5～20 DEG C/s.
Additionally, when this Slow cooling heat treatment, the ratio of ferrite, bainite and martensite is optimised, it is thus possible to produce highly stable steel, while bendability that described steel are required in meeting the present invention and ductility, even if the wide annealing temperature at ± 20 DEG C is interval, the change of yield strength also is able to as ± below 40Mpa.
In the present invention, the steel plate cooled down through second segment can being carried out skin pass rolling as required, reduction ratio now is preferably set to 0.2～1.0%.Generally, to change organization steel carry out skin pass rolling time, yield strength can rise more than 50Mpa, and tensile strength increases hardly.But, when reduction ratio is less than 0.2%, it is very difficult to when manufacturing heretofore described unimach control shape, when processing with the reduction ratio of more than 1.0%, excessive increase because of yield strength, thus yield tensile ratio can be made to exceed expection yield tensile ratio 0.7 disclosed in this invention, and the instability of operability can be caused because of high stretched operation.
It addition, for the hot-dip galvanized steel sheet manufacturing the present invention, under the manufacturing condition such as above-mentioned cold-rolled steel sheet, through hot rolling, cold rolling, continuous annealing and first paragraph refrigerating work procedure.Afterwards, in second segment refrigerating work procedure, cool down so that the average cooling rate of 3～30 DEG C/s carries out second segment cooling, until it reaches 600 DEG C of temperature below scopes.
At this moment, when average cooling rate is less than 3 DEG C/s, in carrying out the process cooled down, ferrite can change, thus the ratio of martensitic phase can be made to reduce, and then causes that intensity reduces, meanwhile, can cause the deterioration of material because of the ferritic phase of uneven generation.It addition, when average cooling rate is more than 30 DEG C/s, it is suppressed that the effect of ferritic transformation can be saturated, can cause the reduction of extension characteristics and hole expandability because the ratio of martensitic phase is superfluous simultaneously.
And, when cooling termination temperature is more than 600 DEG C, the ratio of martensitic phase can be made to significantly reduce because of the generation of ferritic phase or pearlite phase, thus, martensite area occupation ratio shared by global tissue is by less than 20%, thus not only can not obtain the TS of more than 780Mpa, and the ferritic phase of uneven generation or pearlite are met and are made percentage elongation reduce, and can cause the deterioration of the materials such as hole expandability.
It addition, in the present invention, it is possible to the reduction ratio of 0.2～1.0%, the described steel plate cooled down through second segment is carried out skin pass rolling as required.
Then, molten zinc plating process is carried out after the described steel plate cooled down through second segment being annealed process with conventional condition such that it is able to produce hot-dip galvanized steel sheet.After being annealed, conventional when, implement molten zinc plating process.
Further, in the present invention it is possible to the steel plate processed through molten zinc plating as above is carried out Alloying Treatment such that it is able to produce alloy galvanized steel plate.The Alloying Treatment of this molten zinc plating, under the temperature range of 450～600 DEG C, makes the concentration of the Fe in Gold plated Layer become 8～12% such that it is able to improve the corrosion resistance after gold-plated adhesiveness or coating.It addition, when described alloying temperature is less than 450 DEG C, not only make alloying not to be sufficiently carried out, but also the reduction or gold-plated adhering reduction that sacrificing protection (sacrificedprotection) acts on can be caused.Further, when described alloying temperature is more than 600 DEG C, alloying can excessively carry out and can reduce pulverability, or can cause the reduction of intensity deficiency or hole expandability because generating pearlite phase or Bainite Phases of Some in a large number.
In the present invention, the condition of other manufacture method is not particularly limited, but from the viewpoint of productivity, a series of process such as described annealing, molten zinc plating, Alloying Treatment are implemented preferably on continuous print molten zinc plating production line.Further, when carrying out molten zinc plating, it is preferred to use comprise the zinc plating solution of the Al of 0.10～0.20%.
The micro organization of the steel of the cold-rolled steel sheet of the present invention, hot-dip galvanized steel sheet or the alloy galvanized steel plate that are manufactured by above-mentioned manufacturing process by be calculated as with area fraction the martensite of less than 40%, the bainite of 30～40% and 20～30% ferrite constituted；The hardness ratio of bainite/martensite is more than 0.7；Described ferrite is formed with 1.5 × 106Individual/mm2The above precipitate being sized to below 10nm, to meet bainite/ferritic hardness ratio for less than 2.
Additionally, described ferrite crystallization particle diameter can be less than 10 μm, the mean size of martensite can be less than 5 μm, and (bainite+martensite)/ferritic hardness ratio can be less than 4.
It addition, described steel plate can demonstrate following characteristic.The percentage elongation of described steel plate is more than 12%, and yield tensile ratio is less than 0.7 simultaneously, and bendability (R/t) is less than 0.5, and hole expandability is more than 30%.
Detailed description of the invention
Below, by the preferred embodiments of the present invention, the present invention is described in detail.
Preparation is heated after having the steel billet of composition described in table 1 below in heating furnace, and described heating is to carry out at the reheating temperature of 1200 DEG C 1 hour.Then, the described steel billet through reheating is implemented hot rolling and produces hot rolled plate, then above-mentioned hot rolled plate is wound.Now, under the temperature range of 880～900 DEG C of more than Ar3, complete hot rolling, coiling temperature is set as 680 DEG C.Then, to, after the steel plate of hot rolling carries out pickling, carrying out cold rolling with the cold rolling reduction ratio of 50%.
Carry out continuous annealing process to through cold rolling described steel plate under the conditions shown in table 1, afterwards, the steel plate processed through continuous annealing is carried out first paragraph cooling, until reaching 650 DEG C, then, when shown in table 2, second segment cooling is carried out, thus finally preparing cold-rolled steel sheet.
Additionally, in order to manufacture hot-dip galvanized steel sheet, to after cold rolling described steel plate carries out continuous annealing process when shown in table 4, the steel plate processed through continuous annealing is carried out first paragraph cooling, until reaching 650 DEG C, then, second segment cooling is carried out, until it reaches the temperature range of 600 DEG C.Afterwards, by being impregnated in the galvanizing bath maintained at a certain temperature through overcooled described steel plate, thus producing the hot-dip galvanized steel sheet at above-mentioned surface of steel plate with molten zinc plating layer.Then, under the temperature range of 500 DEG C, the part in described hot-dip galvanized steel sheet is carried out alloying heat treatment, thus producing alloy galvanized steel plate.Further, for the steel of annealed process, skin pass rolling rate is finally fixed at 0.7%.
26～No. 34 steel in table 1 below are only in the manufacture of cold-rolled steel sheet, and other steel are simultaneously used in the manufacture of cold-rolled steel sheet and hot-dip galvanized steel sheet.It addition, table 2 below-3 is about cold-rolled steel sheet.It addition, No. 1-3 and No. 14-16 in table 4 below-5 about hot-dip galvanized steel sheet (GI), other steel are about alloy galvanized steel plate (GA).
In addition, table 2 below-3 show the mechanical property of the final cold-rolled steel sheet manufactured according to the method described above and changes the area fraction of phase, table 4 below-5 show the mechanical property of the hot-dip galvanized steel sheet manufactured according to the method described above and changes the area fraction etc. of phase.
It addition, produced JIS5 tension test sheet by the cold-rolled steel sheet processed through continuous annealing, thus determining material.Additionally, the bendability of display is evaluated in the following manner in table 2 and table 4.After test piece is processed into V-type bending (bending), make the radius (R inside bending section, radius) it is changed from 0 to 5, then observe surface whether to crack, and the final radius not cracked is expressed as the bendability R value of corresponding steel, then R value is represented bendability divided by thickness.Evaluation simultaneously for hole expandability (HER, HoleExpansionRatio) is that the grade using Japan JSFT1001-1996 carries out.It addition, for the phase area content of the transformation phase of display in Table 3 below and table 5, be after being measured by scanning electron microscope (SEM), utilize graphical analysis (Imageanalyzer) equipment to be measured.Additionally, for changing the hardness of tissue, utilize nano-hardness tester (Nano-Indenter, NT110) 100 points (point) of load measurement with 2g in square area, and use eliminate maximum and minima after remaining measured value.For the distribution density of nano-scaled precipitate, it is utilize image analysis equipment to be measured the precipitate macrograph measured by Flied emission transmission electron microscope (FE-TEM).
Table 1
Table 2
* in table 2, SS represents continuous annealing temperature (DEG C), and RCS represents second segment cooling termination temperature (DEG C).
Table 3
*, in table 3, F represents that ferrite, B represent bainite, and M represents martensite.It addition, nanometer ppt quantity represents (number * 106Individual/mm2)。
Table 4
*, in table 4, SS represents continuous annealing temperature (DEG C).
Table 5
*, in table 5, F represents that ferrite, B represent bainite, and M represents martensite.It addition, Nanoppt quantity represents (number * 106Individual/mm2)。
As shown in above-mentioned table 1-5, meet the composition of steel scope of the present invention and the example 1～13 and 23～32 of manufacturing process, meet the yield tensile ratio of less than 0.7 and the percentage elongation of more than 13%.Additionally, the measurement result of bendability and hole expandability also fully meets condition required in the present invention, described condition is, bendability (R/t) is less than 1, and hole expandability is more than 30%.The area fraction control of this material characteristic and transformation phase and transformation phase and the alternate hardness ratio of parent phase, nano-scaled precipitate distribution etc. have close relationship.That is, as shown in above-mentioned table 3 and table 5, it can be seen that the distribution etc. of the phase area content and size, hardness relation formula and nano-scaled precipitate that meet the compositional ranges of the present invention and the example 1～13 of manufacture method and 23-32 meets condition disclosed in this invention.
On the other hand, as shown in above-mentioned table 2, meet the steel constituent of the present invention, but second segment cooling termination temperature (RCS) below Ms temperature, such as 250 DEG C etc. and low-down comparative example 1-1,2-1,4-1,9-1,10-1 and 32-1, it is difficult to form sufficient bainite while Bainite Region carries out Slow cooling after first paragraph cools down, but directly generated martensite, so that the area fraction of martensite increases, alternate hardness ratio is thus caused to increase and hole expandability deterioration.
Fig. 3 is the hardness distribution of the micro organization under the second segment cooling termination temperature (RCS) that expression is different.There it can be seen that the alternate difference of hardness that RCS maintains the steel at 400 DEG C is greatly improved.As shown in figs. 4-5, this effect of improving is derived from maintaining the bainite range that RCS is 400 DEG C, bainite area fraction in micro organization is increased, and ferritic phase is formed the nano-scaled precipitate of countless substantial amounts of below 10nm so that caused by ferritic intensity improves.
Additionally, comparative example 14 is the Si content example well below the desired value that disclosed in this invention, owing to the Si content as ferrite former reduces, therefore being annealed, Wetted constructures time bainite area fraction increased, thus cause that percentage elongation reduces.Additionally, promote that carbon enters the ability step-down in martensitic phase by adding Si, thus causing that changing alternate hardness ratio also fails to meet the condition of the present invention.
It addition, the Si content of comparative example 22 is 1.0%, it is the situation excessively adding Si..Add substantial amounts of Si and can cause when carrying out the Slow cooling of first paragraph cooling, promote ferritic generation, and suppress the transformation of bainite when carrying out second segment cooling.Further, the effect improving martensite intensity is played.This effect shows the effect increasing alternate difference of hardness so that ductility is excellent, but causes bendability or hole expandability deterioration.
Comparative example 15-16 is the content example beyond the composition range of the present invention of carbon, Mn or Cr and Mo.These elements are used in the element of strengthening steel, play the effect of the transformation phase area content increasing annealed sheet.But, owing to excessively with the addition of alloying element, so that change the equal condition beyond the present invention, thus cause Material degradation.It addition, comparative example 17 is the low-down example of carbon content.The minimizing of carbon content causes the minimizing of intensity, thus tensile strength 980Mpa level required in the present invention can not be met.
It addition, the constituent that comparative example 18-19 is steel meets the scope of the present invention, but the example that annealing temperature is too low or too high.Such as the steel of comparative example 18, when annealing temperature non-normally low time, owing to recrystallization is insufficient and cause that ductility deteriorates.It addition, annealing temperature is 890 DEG C and very high comparative example 19, owing to generating too much austenite when annealing and making concentration of carbon reduce, when causing cooling down, the area fraction of bainite increases, and thus fails to the satisfied bainite area fraction standard that disclosed in this invention.
And, comparative example 20-21 is entirely without the example adding Ti, Nb.Formation nano-precipitation is played very important effect by Ti or Nb in steel.If without these elements, then the distribution of the nano-scaled precipitate in steel can not meet the standard of the present invention.That is, the deterioration of hole expandability and bendability is caused because alternate difference of hardness is not enough.
Although describing the present invention with reference to above example, but those skilled in the art should be understood that in the thought of the present invention and the scope in field recorded in without departing from claims, it is possible to the present invention is carried out multiple modifications and changes.

Claims (21)

1. the high strength cold rolled steel plate of a bendability and hole expandability excellence, it is characterized in that, described high strength cold rolled steel plate has following chemical composition: in weight %, C containing 0.06～0.1%, the Si of 0.05～0.5%, 2.0～2.5% Mn, 0.001～0.10% P, more than one in the S of less than 0.010%, Ti and the Nb of the solvable Al of 0.01～0.10%, the N of less than 0.010% and respectively 0.003～0.08% scope, and the Fe of surplus and impurity；The micro organization of steel by be calculated as with area fraction the martensite of less than 40%, the bainite of 30～40% and 20～30% ferrite constituted；
The hardness ratio of bainite/martensite is more than 0.7；
Described ferrite is formed with 1.5 × 106Individual/mm2The above precipitate being sized to below 10nm, to meet bainite/ferritic hardness ratio for less than 2.
2. the high strength cold rolled steel plate of bendability as claimed in claim 1 and hole expandability excellence, it is characterised in that described ferritic crystallization particle diameter is less than 10 μm, and, the mean size of described martensite is less than 5 μm.
3. the high strength cold rolled steel plate of bendability as claimed in claim 1 and hole expandability excellence, it is characterised in that (bainite+martensite)/ferritic hardness ratio is less than 4.
4. the high strength cold rolled steel plate of bendability as claimed in claim 1 and hole expandability excellence, it is characterised in that described cold-rolled steel sheet contains more than one in the Mo of Cr and 0.01～0.15% of 0.5～1.0% further.
5. the high strength cold rolled steel plate of bendability as claimed in claim 1 and hole expandability excellence, it is characterised in that described cold-rolled steel sheet contains the B of 0.0010～0.0060% further.
6. the high strength cold rolled steel plate of bendability as claimed in claim 1 and hole expandability excellence, it is characterised in that described cold-rolled steel sheet contains the Sb of less than 0.10% further.
7. the high strength hot dip galvanized steel sheet of a bendability and hole expandability excellence, it is characterized in that, described high strength hot dip galvanized steel sheet is the high strength hot dip galvanized steel sheet being formed with molten zinc plating layer in the surface of cold-rolled steel plate according to any one of claim 1 to 6.
8. the high-strength galvannealed sheet of a bendability and hole expandability excellence, it is characterized in that, described high-strength galvannealed sheet is the high-strength galvannealed sheet being formed with hot dip alloyed zinc coat in the surface of cold-rolled steel plate according to any one of claim 1 to 6.
9. the manufacture method of the high strength cold rolled steel plate of a bendability and hole expandability excellence, it is characterised in that the manufacture method of described high strength cold rolled steel plate includes following operation:
After preparation has the steel billet of following composition, it is reheated, the composition of described steel billet is: in weight %, C containing 0.06～0.1%, the Si of 0.05～0.5%, 2.0～2.5% Mn, 0.001～0.10% P, more than one in the S of less than 0.010%, Ti and the Nb of the solvable Al of 0.01～0.10%, the N of less than 0.010% and respectively 0.003～0.08% scope, and the Fe of surplus and impurity；
For the described steel billet through reheating, after carrying out hot finishing under the temperature range of Ar3～Ar3+50 DEG C, it is wound under 600～750 DEG C of temperature ranges；
For through winding described hot rolled plate, with the cold rolling reduction ratio of 40～70% carry out cold rolling after, carry out continuous annealing process the temperature range of Ac1+30 DEG C～Ac3-30 DEG C；And
For the described steel plate processed through continuous annealing, carry out first paragraph cooling, until it reaches 650～700 DEG C, then second segment cooling is carried out, until reaching the temperature range of 400～500 DEG C, then carry out Wetted constructures, until it reaches the temperature range of 300～400 DEG C.
10. the manufacture method of the high strength cold rolled steel plate of bendability as claimed in claim 9 and hole expandability excellence, it is characterized in that, the micro organization of described high strength cold rolled steel plate by be calculated as with area fraction the martensite of less than 40%, the bainite of 30～40% and 20～30% ferrite constituted；The hardness ratio of bainite/martensite is more than 0.7；Described ferrite is formed with 1.5 × 106Individual/mm2The above precipitate being sized to below 10nm, to meet bainite/ferritic hardness ratio for less than 2.
11. the manufacture method of the high strength cold rolled steel plate of bendability as claimed in claim 10 and hole expandability excellence, it is characterized in that, described ferritic crystallization particle diameter is less than 10 μm, the mean size of described martensite is less than 5 μm, further, (bainite+martensite)/ferritic hardness ratio is less than 4.
12. the manufacture method of the high strength cold rolled steel plate of bendability as claimed in claim 9 and hole expandability excellence, it is characterised in that described cold-rolled steel sheet contains more than one in the Mo of Cr and 0.01～0.15% of 0.5～1.0%.
13. the high strength cold rolled steel plate of bendability as claimed in claim 9 and hole expandability excellence, it is characterised in that described cold-rolled steel sheet contains the B of 0.0010～0.0060% further.
14. the high strength cold rolled steel plate of bendability as claimed in claim 9 and hole expandability excellence, it is characterised in that described cold-rolled steel sheet contains the Sb of less than 0.10% further.
15. the manufacture method of the high strength hot dip galvanized steel sheet of a bendability and hole expandability excellence, it is characterised in that the manufacture method of described high strength hot dip galvanized steel sheet includes following operation:
After preparation has the steel billet of following composition, it is reheated, the composition of described steel billet is: in weight %, C containing 0.06～0.1%, the Si of 0.05～0.5%, 2.0～2.5% Mn, 0.001～0.10% P, more than one in the S of less than 0.010%, Ti and the Nb of the solvable Al of 0.01～0.10%, the N of less than 0.010% and respectively 0.003～0.08% scope, and the Fe of surplus and impurity；
For the described steel billet through reheating, after carrying out hot finishing under the temperature range of Ar3～Ar3+50 DEG C, it is wound under 600～750 DEG C of temperature ranges；
For through winding described hot rolled plate, with the cold rolling reduction ratio of 40～70% carry out cold rolling after, carry out continuous annealing process the temperature range of Ac1+30 DEG C～Ac3-30 DEG C；And
For the described steel plate processed through continuous annealing, carry out first paragraph cooling, until it reaches 650～700 DEG C, then carry out second segment cooling with the average cooling rate of 3～30 DEG C/s, until it reaches 600 DEG C of temperature below scopes；And
Under normal conditions to after overcooled described steel plate is annealed, carry out molten zinc plating.
16. the manufacture method of the high strength hot dip galvanized steel sheet of bendability as claimed in claim 15 and hole expandability excellence, it is characterized in that, the micro organization of described high strength hot dip galvanized steel sheet by be calculated as with area fraction the martensite of less than 40%, the bainite of 30～40% and 20～30% ferrite constituted；The hardness ratio of bainite/martensite is more than 0.7；It is formed with 1.5 × 10 in described ferrite6Individual/mm2The above precipitate being sized to below 10nm, to meet bainite/ferritic hardness ratio for less than 2.
17. the manufacture method of the high strength hot dip galvanized steel sheet of bendability as claimed in claim 16 and hole expandability excellence, it is characterized in that, described ferritic crystallization particle diameter is less than 10 μm, the mean size of described martensite is less than 5 μm, further, (bainite+martensite)/ferritic hardness ratio is less than 4.
18. the manufacture method of the high strength hot dip galvanized steel sheet of bendability as claimed in claim 15 and hole expandability excellence, it is characterised in that described hot-dip galvanized steel sheet contains more than one in the Mo of Cr and 0.01～0.15% of 0.5～1.0%.
19. the manufacture method of the high strength hot dip galvanized steel sheet of bendability as claimed in claim 15 and hole expandability excellence, it is characterised in that described hot-dip galvanized steel sheet contains the B of 0.0010～0.0060% further.
20. the manufacture method of the high strength hot dip galvanized steel sheet of bendability as claimed in claim 15 and hole expandability excellence, it is characterised in that described hot-dip galvanized steel sheet contains the Sb of less than 0.10% further.
21. the manufacture method of the high-strength galvannealed sheet of a bendability and hole expandability excellence, it is characterized in that, the manufacture method of described high-strength galvannealed sheet includes after the manufacturing process of the hot-dip galvanized steel sheet carried out as according to any one of claim 15 to 20, carries out the operation of the Alloying Treatment of molten zinc plating under the temperature range of 450～600 DEG C.
CN201510983281.1A 2014-12-24 2015-12-24 High-strength cold-rolled steel sheet of excellent bending workability and hole-expanding property, hot-dip galvanized steel sheet and manufacturing method thereof Pending CN105734410A (en)

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