WO2013160928A1 - Tôle d'acier à haute résistance et procédé de fabrication de cette dernière - Google Patents

Tôle d'acier à haute résistance et procédé de fabrication de cette dernière Download PDF

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WO2013160928A1
WO2013160928A1 PCT/JP2012/002775 JP2012002775W WO2013160928A1 WO 2013160928 A1 WO2013160928 A1 WO 2013160928A1 JP 2012002775 W JP2012002775 W JP 2012002775W WO 2013160928 A1 WO2013160928 A1 WO 2013160928A1
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less
strength
steel sheet
rolling
steel
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PCT/JP2012/002775
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English (en)
Japanese (ja)
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金晴 奥田
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Ｊｆｅスチール株式会社
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Priority to BR112014025955-0A priority Critical patent/BR112014025955B1/pt
Priority to CN201280072616.9A priority patent/CN104284995B/zh
Priority to PCT/JP2012/002775 priority patent/WO2013160928A1/fr
Priority to RU2014146942/02A priority patent/RU2587102C1/ru
Priority to MYPI2014703110A priority patent/MY172403A/en
Publication of WO2013160928A1 publication Critical patent/WO2013160928A1/fr
Priority to ZA2014/07626A priority patent/ZA201407626B/en

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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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—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

Definitions

  • the present invention relates to a high-strength steel sheet for automobiles, home appliances and the like, which is used through a press forming process, and a method for manufacturing the same.
  • Patent Document 1 For example, if the tensile strength (TS) of the steel sheet is up to 440 MPa, the Ti and Nb are dissolved in the solute carbon and solid solution in the steel.
  • a method of adding a solid solution strengthening element such as Si, Mn and P based on a steel that has been converted to IF (Interstitial free) by adding a sufficient amount to fix nitrogen is disclosed (for example, Patent Documents) 1).
  • This Patent Document 1 has a composition of C: 0.002 to 0.015%, Nb: C% ⁇ 3 to C% ⁇ 8 + 0.020%, Si: 1.2%, Mn: 0.04 to 0.8%, and P: 0.03 to 0.10%.
  • a technique for obtaining a high-tensile cold-rolled steel sheet having a non-aging property with a tensile strength of 35 to 45 kg / mm 2 class (340 to 440 MPa class) and excellent formability is disclosed.
  • TS tensile strength
  • DP steel sheets having a two-phase structure of ferrite-martensite and TRIP steel sheets utilizing residual ⁇ are known.
  • the former has a feature of high work hardening ability while having low yield strength due to residual strain around martensite.
  • the latter has the feature that the uniform elongation of the steel sheet is increased by performing plasticity-induced martensitic transformation.
  • the mechanical properties of high-tensile steel sheets are often evaluated with tensile properties in a specific direction, such as a direction perpendicular to the rolling direction, and in part, the in-plane anisotropy ( ⁇ r) of the r value is a problem.
  • evaluation may be made based on r values in the rolling direction, 45 ° direction, and 90 ° direction.
  • the formability of the press is determined by the properties in the direction of lower ductility than the direction in which the mechanical properties are evaluated, particularly the elongation value. I understood that.
  • Patent Document 2 discloses a method of obtaining a cold-rolled steel sheet for an automotive outer panel component having excellent bake hardenability and small in-plane anisotropy.
  • the in-plane anisotropy and dent resistance of a steel sheet are defined by defining the in-plane anisotropy of the r value, that is, ⁇ r, according to the amount of C and the cold pressure ratio. It is said that both can be achieved.
  • the cooling is started within 2 seconds after the hot rolling and that the cooling is performed at a cooling rate of 70 ° C./s or more and in a temperature range of 100 ° C. or more.
  • Patent Document 3 discloses a steel sheet excellent in shape freezing property. According to this, ferrite or bainite is used as the largest phase in volume fraction, and volume fraction: 1 % As a composite structure steel containing martensite in a range of 25% to 25%.
  • the average value (A) of the X-ray random intensity ratio of the ⁇ 100 ⁇ ⁇ 011> to ⁇ 223 ⁇ ⁇ 110> orientation groups is 4.0 or more
  • the average value (B) of the X-ray random intensity ratios of the three crystal orientations of ⁇ 554 ⁇ ⁇ 225>, ⁇ 111 ⁇ ⁇ 112> and ⁇ 111 ⁇ ⁇ 110> is 5.5 or less
  • (Iv) ⁇ 100 ⁇ ⁇ 011> X-ray reflection random intensity ratio is equal to or greater than ⁇ 211 ⁇ ⁇ 011> X-ray random intensity ratio;
  • the above conditions (i) to (iv) are all satisfied, and at least one of the r value in the rolling direction and the r value in the direction perpendicular to the rolling direction is 0.7 or less, and the anisotropy ⁇ uE1 of uniform elongation is 4 % Or less, the local elongation anisotropy
  • ⁇ uE1 and ⁇ LE1 are obtained by the following equations.
  • ⁇ uEl ⁇
  • ⁇ LEl ⁇
  • the uniform elongation in the direction parallel to the rolling direction (L direction), vertical (C direction), and 45 ° is uEl (L), uEl (C), and uEl (45 °), respectively, and the rolling direction
  • the local elongations in the parallel (L direction), vertical (C direction), and 45 ° directions are LEl (L), LEl (C), and LEl (45 °), respectively.
  • the present invention advantageously solves the above-mentioned problems, and proposes a high-strength steel sheet capable of reducing ductility anisotropy and suppressing cracking during press forming together with its advantageous manufacturing method. With the goal.
  • the inventors have intensively studied to solve the above-mentioned problems, and by defining a reduction ratio according to the contents of Ti and Nb and developing a certain texture, ductility In particular, the in-plane anisotropy of uniform elongation was successfully reduced.
  • the present invention has been completed based on the above findings.
  • the gist configuration of the present invention is as follows. 1. In mass%, C: more than 0.0005% and less than 0.10%, Si: 1.5% or less, Mn: 0.1% or more and 3.0% or less, P: 0.080% or less, S: 0.03% or less, sol.Al: 0.01% or more and 0.50% or less And N: 0.005% or less, and Nb: 0.20% or less and Ti: 0.2% or less selected from one or two kinds, the balance is composed of Fe and inevitable impurities,
  • the steel structure is a ferrite phase with a volume fraction of 60% or more, Intensity of ODF ⁇ 0 °, 0 °, 45 ° ⁇ when ⁇ is 0 °, ⁇ 1 is 0 °, and ⁇ 2 is 45 ° in the density function (ODF) ⁇ OD1, ⁇ , ⁇ 2 ⁇ of the three-dimensional crystal orientation Is a high-strength steel sheet in which the strength of ODF ⁇ 0 °, 35 °, 45
  • the steel sheet is further mass%, V: 0.40% or less, Cr: 0.50% or less, Mo: 0.50% or less, W: 0.15% or less, Zr: 0.10% or less, Cu: 0.50% or less, Ni: 0.50%
  • the following 1 containing at least one selected from B: 0.0050% or less, Sn: 0.20% or less, Sb: 0.20% or less, Ca: 0.010% or less, Ce: 0.01% or less, and La: 0.01% or less
  • the steel slab having the component composition described in 1 or 2 above is hot-rolled at a finishing temperature of 820 ° C. or higher and 950 ° C. or lower, and the rolling reduction (X%) satisfies the relationship of the following formula (1):
  • a method for producing a high-strength steel sheet which is subjected to cold rolling under satisfying conditions, then subjected to continuous annealing in a temperature range from the recrystallization temperature to 900 ° C., and then cooled. Record 0.30 ⁇ ⁇ 1.6 ⁇ ([% Ti] +2 ⁇ [% Nb]) + 0.004X ⁇ ⁇ 0.36 (1)
  • [% A] indicates the content (mass%) of element A in steel.
  • the in-plane anisotropy of uniform elongation can be effectively reduced, even if the strength and ductility in the direction perpendicular to the rolling direction are the same as in conventional steel, the occurrence of press cracks It is possible to obtain a high-strength steel sheet that further suppresses
  • (a) and (b) are graphs showing the results of evaluating the influence of the rolling reduction on strength and the relationship with the in-plane anisotropy of uniform elongation.
  • (C) is a graph showing the relationship between strength and uniform elongation.
  • the ductility anisotropy can be reduced regardless of the accumulation of ⁇ -fiber, which is said to be related to other orientations, for example, the r value which is an index of deep drawability.
  • % Representing the content of each component element means “% by mass” unless otherwise specified.
  • C more than 0.0005% and less than 0.10% C is an element necessary for increasing the strength of the steel sheet while suppressing the area ratio of the second phase.
  • the lower limit of the C amount is set to more than 0.0005%, which is normally possible with a melting technique.
  • the C content is less than 0.10%, preferably less than 0.08%.
  • Si 1.5% or less Si improves the surface quality by delaying scale formation during hot rolling, and moderately delays the alloying reaction between the iron and zinc in the plating bath or alloying process. Furthermore, since it has various effects such as an effect of increasing the work hardening ability of ferrite, the Si content is preferably 0.01% or more, more preferably 0.05% or more. However, if the Si content exceeds 1.5%, the appearance quality deteriorates and the ⁇ ⁇ ⁇ transformation point rises, hot rolling cannot be performed in the ⁇ region, and the texture changes greatly. For this reason, the in-plane anisotropy of the uniform elongation of the steel sheet cannot be controlled. Therefore, the Si content is 1.5% or less. Preferably it is 1.2% or less.
  • Mn 0.1% to 3.0% Mn not only suppresses hot ductility due to FeS, but can also be used as a solid solution strengthening element. Therefore, addition of 0.1% or more is necessary. On the other hand, if the Mn content is less than 0.1%, the grain growth is improved, which is not preferable from the viewpoint of controlling the in-plane anisotropy. Note that Mn is an element effective for increasing the strength by making martensite present in the second phase because it enhances hardenability. From the viewpoint of such complex organization, addition of 1.0% or more is preferable.
  • the Mn content is 3.0% or less. In order to control the in-plane anisotropy of uniform elongation to a higher degree, 2.5% or less is preferable.
  • the amount of P is preferably 0.005% or more, more preferably 0.010% or more, and even more preferably 0.015% or more.
  • the P content is 0.080% or less, preferably 0.050% or less.
  • the S content is preferably 0.01% or less, and more preferably 0.002% or less.
  • sol.Al 0.01% or more and 0.50% or less
  • Al is useful as a deoxidizing element for steel and has the effect of fixing solid solution N to improve normal temperature aging resistance. Shall be allowed to.
  • the addition exceeding 0.50% increases the manufacturing cost and further induces surface defects in the steel sheet. Therefore, Al is 0.50% or less, preferably 0.08% or less.
  • N 0.005% or less N is preferably reduced as much as possible because if it is too much, the room temperature aging resistance deteriorates and a large amount of Al or Ti needs to be added. Therefore, the upper limit is made 0.005%.
  • Nb is capable of controlling the in-plane anisotropy of uniform elongation after cold rolling annealing by refining the structure and suppressing recrystallization of austenite in the hot rolling process. This is an important element in the present invention. However, if added over 0.20%, not only the cost is increased, but the texture in hot rolling is excessively developed, and the in-plane anisotropy of uniform elongation cannot be controlled due to excessive increase in the recrystallization temperature. Therefore, Nb needs to be 0.20% or less. Preferably it is 0.12% or less. In order to obtain the above effect, Nb is preferably contained in an amount of 0.005% or more.
  • Ti 0.20% or less Ti, like Nb, refines the structure, suppresses recrystallization of austenite in the hot rolling process, and controls the in-plane anisotropy of uniform elongation after cold rolling annealing. This is an important element in the present invention. However, if added over 0.20%, not only the cost is increased, but the texture in hot rolling is excessively developed, and the in-plane anisotropy of uniform elongation cannot be controlled due to excessive increase in the recrystallization temperature. Therefore, Ti needs to be 0.20% or less. Preferably it is 0.12% or less. In addition, when obtaining the said effect, it is preferable to contain Ti 0.005% or more.
  • V 0.40% or less
  • V is an element that improves hardenability, and since it hardly reduces the plating quality and corrosion resistance, it can be used as a substitute for Mn and Cr. However, if added over 0.40%, the cost will increase significantly, so it is desirable to add V at 0.40% or less.
  • Cr 0.50% or less Cr, like Mn, is an element that contributes to high strength by forming a composite structure of a steel sheet. In order to acquire this effect, it is preferable to contain 0.10% or more. However, excessive addition of Cr not only saturates the above effect, but also causes high alloy costs, so the upper limit is made 0.50%.
  • Mo 0.50% or less Mo is an element that improves hardenability, suppresses the formation of pearlite, and contributes to high strength. However, since Mo is an extremely expensive element, a large amount of addition leads to a significant cost increase. Therefore, the amount of Mo added is preferably 0.50% or less.
  • W 0.15% or less W can be used as a hardenability improving element and a precipitation strengthening element. However, if the added amount is too large, ductility is reduced, so the added amount of W is preferably 0.15% or less.
  • Zr 0.10% or less Zr can be used as a hardenability improving element and a precipitation strengthening element. However, if the added amount is too large, ductility is lowered, so it is desirable to add Zr at 0.10% or less.
  • Cu 0.50% or less By allowing contamination, Cu can be used as a raw material, and manufacturing costs can be reduced. In consideration of improving corrosion resistance, it is desirable to add 0.03% or more when Cu is added. However, if the content is too large, it may cause surface defects, so the upper limit is preferably 0.50%.
  • Ni 0.50% or less
  • Ni is an element that improves corrosion resistance, and has the effect of reducing surface defects that are likely to occur when Cu is contained. Therefore, from the viewpoint of improving the surface quality while improving the corrosion resistance, it is desirable to add Ni by 0.02% or more. On the other hand, if the amount of Ni added is too large, scale generation in the heating furnace becomes non-uniform, causing surface defects and a significant cost increase. Therefore, the upper limit is desirably 0.50%.
  • B 0.0050% or less B is an element that improves the hardenability of steel.
  • B is an element that improves the hardenability of steel.
  • the content exceeds 0.0050%, the effect is saturated. Therefore, when added, the content is preferably 0.0050% or less.
  • Sn 0.20% or less
  • Sn is preferably added from the viewpoint of suppressing nitridation and oxidation of the steel sheet surface, or decarburization and deboronization (de-B) of the steel sheet surface layer caused by oxidation. From the viewpoint of suppressing nitriding and oxidation, it is desirable to add 0.005% or more, but if it exceeds 0.20%, excessive yield strength (YP) will be increased and toughness will be deteriorated, so Sn should be contained at 0.20% or less. Is desirable.
  • Sb 0.20% or less
  • Sb is desirably added from the viewpoint of suppressing nitridation and oxidation of the steel sheet surface, or decarburization and de-B of the steel sheet surface layer caused by oxidation, as with Sn.
  • Sb is desirable to add 0.005% or more.
  • Sb is desirably contained at 0.20% or less.
  • Ca 0.010% or less Ca has the effect of fixing S in steel as CaS, further increasing the pH in corrosive organisms, and improving the corrosion resistance around the hem-processed part and spot welded part. Moreover, the production
  • Ce 0.01% or less Ce can be added for the purpose of fixing S in steel. However, since it is an expensive element, adding a large amount increases the cost. Therefore, it is desirable to add Ce at 0.01% or less.
  • La 0.01% or less La can be added for the purpose of fixing S in steel. However, since it is an expensive element, adding a large amount increases the cost. Therefore, it is desirable to add La at 0.01% or less.
  • the balance other than the above elements is Fe and inevitable impurities.
  • the ferrite texture is controlled, but when confirming the texture, the X-ray diffraction method is generally used.
  • the main phase of ferrite cannot be clearly distinguished from the second phase such as martensite and bainite
  • the main point of the present invention is when the second phase fraction becomes high. It becomes impossible to control the anisotropy of uniform elongation by texture control.
  • the second phase when the second phase increases, the second phase surrounds the periphery of the ferrite in a network shape, and the macroscopic plastic behavior of the steel sheet does not depend on the crystal orientation of the ferrite.
  • the ferrite needs to be 60% or more in volume fraction.
  • the volume fraction is preferably 75% or more.
  • the volume fraction of the ferrite phase can be obtained on the basis of the volume fraction of the second phase by regarding the area ratio of the second phase obtained by the following procedure as the volume fraction of the second phase.
  • the area ratio of the second phase is obtained from a photograph of the structure taken after polishing the L cross section (vertical cross section parallel to the rolling direction) of the steel plate, corroding with nital, observing 10 fields of view with a SEM at a magnification of 4000 times.
  • the ferrite is observed as a slightly black contrast region, the region where the carbides are formed in a lamellar or dotted pattern is pearlite and bainite, and the particles with white contrast are martensite or residual ⁇ . is there.
  • the fine dot-like particles having a diameter of 0.4 ⁇ m or less recognized on the SEM photograph are mainly carbides, and since their area ratio is very small, it is considered that the material is hardly affected.
  • the area ratio of the second phase is obtained from the ratio of the second phase existing on the lattice using a square mesh (point count method).
  • the area ratio (%) of the second phase thus determined is directly used as the volume fraction (%) of the second phase.
  • the volume fraction (%) of the ferrite phase can be obtained by subtracting the volume fraction (%) of the second phase from 100%.
  • ODF three-dimensional crystal orientation density function
  • ODF density function
  • ⁇ 1, ⁇ , ⁇ 2 ⁇ ⁇ 0 °, 35 °, 45 ° ⁇
  • the rolling direction and the direction perpendicular to the rolling direction are relatively low, so press cracks occur. This is because it becomes easier.
  • the strength exceeds 4.5, the uniform elongation in the D direction (a direction that forms 45 ° with the rolling direction) is relatively low. This is because the texture of the steel sheet is related to the anisotropy of the yield strength, so the yield strength and ductility are in a trade-off relationship, the direction of high strength has a low uniform elongation, and Ti and Nb are rolled.
  • the azimuth strength in the present invention is determined as follows. First, the pole figures of the three surfaces (200), (211), and (110) are measured by the reflection method to obtain three incomplete pole figures. Next, these three incomplete pole figures are converted into a three-dimensional crystal orientation density function by the series expansion method, and the strength of the desired orientation is obtained.
  • the steel slab used in the production method of the present invention is preferably produced by a continuous casting method in order to prevent macro segregation of components, but is not particularly limited, and is produced by an ingot-making method or a thin slab casting method. Also good.
  • direct feed rolling in which the steel slab is charged without being cooled and charged in a heating furnace and hot-rolled, or a little heat retention After carrying out, energy saving processes such as direct feed rolling and direct rolling that are immediately hot rolled can be applied without any problem.
  • the slab heating temperature is not particularly limited, but it is desirable that the slab heating temperature is low in order to improve the deep drawability by developing a ⁇ 111 ⁇ recrystallization texture by coarsening the precipitates. However, if the heating temperature is less than 1000 ° C., the rolling load increases and the risk of trouble during hot rolling increases, so the slab heating temperature is preferably 1000 ° C. or higher. Note that the upper limit of the slab heating temperature is preferably 1300 ° C. in view of an increase in scale loss accompanying an increase in oxidized weight.
  • ⁇ Hot rolling for rough rolling and finish rolling is performed on the steel slab heated under the above conditions.
  • the steel slab is made into a sheet bar by rough rolling.
  • the conditions for rough rolling need not be specified, and may be performed according to a conventional method. From the viewpoint of lowering the slab heating temperature and preventing problems during hot rolling, it is an effective method to use a so-called sheet bar heater that heats the sheet bar.
  • Finishing temperature 820 ° C or more and 950 ° C or less Finishing and rolling the sheet bar to make a hot-rolled sheet.
  • the finishing temperature that is, the finish rolling outlet temperature (hereinafter referred to as FT) is 820 ° C. or higher and 950 ° C. or lower. This is to obtain a texture preferable for in-plane anisotropy of uniform elongation after cold rolling and recrystallization annealing.
  • FT finish rolling outlet temperature
  • lubrication rolling may be performed between some or all passes of finish rolling.
  • Performing the lubrication rolling is effective from the viewpoint of homogenizing the shape of the steel plate and homogenizing the material.
  • the coefficient of friction between the roll and the steel sheet is preferably in the range of 0.10 to 0.25.
  • the coil winding temperature (CT) in the present invention is not particularly specified, but is preferably 400 ° C. or higher and 720 ° C. or lower.
  • CT coil winding temperature
  • the crystal grains are coarsened, resulting in a decrease in strength and an increase in r value after cold rolling annealing.
  • the hot-rolled sheet is subjected to pickling and cold rolling to perform a cold rolling process to obtain a cold-rolled sheet.
  • Pickling may be performed under normal conditions.
  • Ti and Nb are important elements for rolling in the austenite non-recrystallized region of hot rolling. Rolling due to the development of ⁇ texture due to non-recrystallizing rolling and the variant restrictions during the subsequent transformation. Greatly involved in the texture. Further, the rolling reduction is an important condition for developing the rolling texture.
  • the inventors balance the texture because the texture due to the coarsening of the ferrite grain size and the texture due to the non-recrystallized ⁇ rolling have opposite effects on the in-plane anisotropy of elongation.
  • the in-plane anisotropy of uniform elongation and the strength f ( ⁇ 35 °) of ODF ⁇ 0 °, 35 °, 45 ° ⁇ were investigated for steels with varying Ti, Nb and rolling reduction. .
  • the amount of Nb is the amount of Ti ([% Ti]) from the viewpoint of the recrystallization suppression effect in the solid solution state with the precipitate and the difference in atomic weight.
  • the anisotropy was evaluated by uniform elongation ⁇ UEL normalized by UEL L using the following formula (2).
  • the uniform elongation of the L, D, C direction of a steel plate be UEL L , UEL D , UEL C , respectively.
  • the recrystallization temperature is set. This is because the ductility is reduced.
  • the recrystallization temperature is obtained by subjecting the cold-rolled plate to a predetermined temperature by changing the annealing temperature, immediately after cooling (with a holding time within 1 s), and immediately quenching into cold water. The temperature may be determined as a temperature at which unrecrystallization is not observed.
  • the annealing temperature may be changed at a pitch of 10 ° C. from 650 ° C., for example.
  • the average cooling rate in the temperature range from the annealing temperature to 500 ° C is 5 ° C / s to 15 ° C / s. It is preferable to cool in the following range. If the average cooling rate in this temperature range is less than 5 ° C./s, martensite is hardly formed, and a ferrite single phase structure may be formed, resulting in insufficient structure strengthening.
  • the average cooling rate up to 500 ° C. is equal to or higher than the critical cooling rate. In order to achieve this, 5 ° C / s or more is necessary.
  • the cooling at 500 ° C. or lower is not particularly limited because the ⁇ phase is stabilized to some extent by the cooling so far, but subsequently, the temperature range up to about 300 ° C. is maintained at an average cooling rate of 5 ° C./s or more. It is preferable to cool, and when performing an overaging treatment, it is preferable that the average cooling rate is 5 ° C./s or more up to the overaging treatment temperature.
  • the steel sheet can be galvanized as required.
  • martensite is formed as the second phase in the hot dip galvanizing line, it is usually 450 to 500 from the annealing temperature after soaking.
  • the average cooling rate to the temperature of the galvanizing bath maintained in the temperature range up to 0 ° C. is desirably 2 to 30 ° C./s.
  • the cooling rate is slower than 2 ° C./s, a large amount of pearlite is generated in the temperature range of 500 to 650 ° C., and a hard second phase cannot be obtained.
  • the cooling rate is higher than 30 ° C./s, the ⁇ ⁇ ⁇ transformation proceeds remarkably in the vicinity of 500 ° C. before and after being immersed in the plating bath, so that the second phase becomes finer and ductility decreases.
  • the cold-rolled annealed plate and the plated steel plate can be subjected to temper rolling or leveler processing for the purpose of shape correction, surface roughness adjustment and the like.
  • the total elongation of temper rolling or leveler processing is preferably in the range of 0.2 to 15%. If it is less than 0.2%, the intended purpose of shape correction and roughness adjustment cannot be achieved. On the other hand, if it exceeds 15%, the ductility is significantly reduced.
  • the processing form differs between temper rolling and leveler processing, it has been confirmed that there is no significant difference between the two. Note that temper rolling and leveler processing are effective even after plating.
  • the obtained cold-rolled annealed sheet was subjected to temper rolling with an elongation of 0.5%.
  • the recrystallization temperature of each steel plate was 700 to 760 ° C., which was obtained by observation of the structure after heat-quenching for a short time, and was above the recrystallization temperature under all conditions.
  • the No. 5 steel sheet was subjected to a cold-rolled sheet annealing process in a continuous hot dip galvanizing line, followed by in-line hot dip galvanizing (plating bath temperature: 480 ° C.) to obtain a hot dip galvanized steel sheet.
  • Test pieces were collected from the obtained cold-rolled annealed sheet and hot-dip galvanized steel sheet, and the microstructure, tensile properties, and density function (ODF) of three-dimensional crystal orientation were determined by the following methods.
  • the in-plane anisotropy of uniform elongation was evaluated by obtaining a value of ⁇ UEL by the following equation (2).
  • the in-plane anisotropy of uniform elongation is excellent when the value of ⁇ UEL obtained by the following equation (2) is in the range of -0.020 to 0.020.
  • Table 2 The obtained results are also shown in Table 2.
  • ⁇ UEL ⁇ UEL L + UEL C ⁇ 2 ⁇ UEL D ⁇ / (2 ⁇ UEL L ) (2) Note that the microstructure (ferrite volume fraction) was determined based on the area ratio (volume ratio) of the second phase determined by the point counting method from the SEM photograph as described above.
  • the texture is not included in the scope of the present invention, and as a result, the anisotropy of uniform elongation is large. It has become a steel plate.

Abstract

La présente invention se rapporte à une tôle d'acier à haute résistance qui ne se fissure pas facilement pendant le formage sous pression et qui présente une faible anisotropie d'allongement, ladite tôle d'acier pouvant être obtenue en utilisant une composition qui comprend, en % en masse, une quantité de carbone (C) supérieure à 0,0005 % mais inférieure à 0,10 %, une quantité de silicium (Si) égale ou inférieure à 1,5 %, une quantité de manganèse (Mn) comprise entre 0,1 % et 3,0 %, une quantité de phosphore (P) égale ou inférieure à 0,080 %, une quantité de soufre (S) égale ou inférieure à 0,03 %, une quantité d'aluminium (Al) soluble comprise entre 0,01 % et 0,50 %, et une quantité d'azote (N) égale ou inférieure à 0,005 %, et qui contient une quantité de niobium (Nb) égale ou inférieure à 0,02 % et/ou une quantité de titane (Ti) égale ou inférieure à 0,20 %, le reste étant du fer (Fe) et des impuretés inévitables, et en configurant la structure d'acier de telle sorte que 60 % ou plus de cette dernière par fraction volumique soit une phase ferrite et que, dans la fonction de densité d'orientation (fonction ODF) des cristaux en trois dimensions {φ1, Φ, φ2}, la résistance de la fonction ODF {0°, 0°, 45°} lorsque Φ vaut 0°, φ1 vaut 0° et φ2 vaut 45°, est égale ou inférieure à 3,0 et la résistance de la fonction ODF {0°, 35°, 45°} lorsque Φ vaut 35°, φ1 vaut 0° et φ2 vaut 45°, se situe dans la plage allant de 2,5 à 4,5.
PCT/JP2012/002775 2012-04-23 2012-04-23 Tôle d'acier à haute résistance et procédé de fabrication de cette dernière WO2013160928A1 (fr)

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BR112014025955-0A BR112014025955B1 (pt) 2012-04-23 2012-04-23 chapa de aço com alta resistência e método para fabricar a mesma
CN201280072616.9A CN104284995B (zh) 2012-04-23 2012-04-23 高强度钢板及其制造方法
PCT/JP2012/002775 WO2013160928A1 (fr) 2012-04-23 2012-04-23 Tôle d'acier à haute résistance et procédé de fabrication de cette dernière
RU2014146942/02A RU2587102C1 (ru) 2012-04-23 2012-04-23 Высокопрочный стальной лист и способ его изготовления
MYPI2014703110A MY172403A (en) 2012-04-23 2012-04-23 High-strength steel sheet and method for manufacturing same
ZA2014/07626A ZA201407626B (en) 2012-04-23 2014-10-21 High-strength steel sheet and method for manufacturing same

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CN107287505A (zh) * 2017-08-04 2017-10-24 蒙城信和汽车有限公司 一种汽车面板用钢及其制备方法
CN109594012A (zh) * 2018-11-05 2019-04-09 包头钢铁（集团）有限责任公司 一种700MPa级稀土耐腐蚀车用钢带及其制备方法
CN110117756B (zh) * 2019-05-21 2020-11-24 安徽工业大学 一种Cu合金化深冲双相钢板及其制备方法
CN112048674B (zh) * 2020-09-17 2022-02-15 南京奇纳金属材料科技有限公司 低屈强比含磷高强无间隙原子钢及其制备方法
CN113061816B (zh) * 2021-03-25 2022-04-12 德龙钢铁有限公司 一种抑制带钢三次渗碳体沿晶界析出的低碳加硼钢
CN113234996A (zh) * 2021-04-15 2021-08-10 首钢集团有限公司 一种高强if的冶炼方法
CN114657459B (zh) * 2022-02-21 2022-11-18 长沙东鑫环保材料有限责任公司 一种氮钒钛铌稀土微合金化高强深冲冷轧钢板及其生产方法
CN114959444B (zh) * 2022-03-22 2023-04-28 湖南华菱涟源钢铁有限公司 耐低温酸露点钢材及其制备方法

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