WO2015059903A1 - Feuille d'acier haute résistance présentant une faible anisotropie d'allongement dans le plan et son procédé de fabrication - Google Patents

Feuille d'acier haute résistance présentant une faible anisotropie d'allongement dans le plan et son procédé de fabrication Download PDF

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WO2015059903A1
WO2015059903A1 PCT/JP2014/005228 JP2014005228W WO2015059903A1 WO 2015059903 A1 WO2015059903 A1 WO 2015059903A1 JP 2014005228 W JP2014005228 W JP 2014005228W WO 2015059903 A1 WO2015059903 A1 WO 2015059903A1
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steel sheet
elongation
less
plane anisotropy
rolling
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Japanese (ja)
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藤田　耕一郎
雄介 木俣
長谷川　浩平
耕造 原田
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Ｊｆｅスチール株式会社
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Priority to CN201480058323.4A priority Critical patent/CN105899696A/zh
Priority to MX2016005137A priority patent/MX2016005137A/es
Priority to KR1020167013339A priority patent/KR101813914B1/ko
Publication of WO2015059903A1 publication Critical patent/WO2015059903A1/fr

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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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0436—Cold rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/004—Heat treatment in fluid bed
    • 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
    • C21D2201/00—Treatment for obtaining particular effects
    • C21D2201/05—Grain orientation
    • 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
    • C21D2211/003—Cementite
    • 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
    • C21D2211/009—Pearlite

Definitions

  • the present invention relates to a high-strength steel sheet having a small in-plane anisotropy of elongation that is useful for use in automobiles, electric machines, and the like, and a method for producing the same.
  • a high strength steel plate for example, when the yield strength (YP) is 440 MPa class, Ti and Nb are added to an extremely low carbon steel plate having excellent formability to fix solute C and solute N, and IF is formed (Interstitial free). ), And a steel plate to which a solid solution strengthening element such as Si, Mn, or P is added.
  • the yield strength (YP) is 500 MPa or more
  • a composite structure steel sheet is put into practical use, and there are a DP steel sheet having a two-phase structure of ferrite and martensite, and a TRIP steel sheet utilizing residual austenite.
  • the former is characterized by low yield strength and high work hardening ability due to residual strain around the martensite.
  • the latter is characterized by high uniform elongation due to plasticity-induced martensitic transformation.
  • the mechanical properties of high-strength steel plates are evaluated by the tensile properties in a specific direction such as the direction perpendicular to rolling.
  • part formability for example, the height that can be formed by stretch forming or the Erichsen test, is greatly influenced by the in-plane anisotropy of elongation. Therefore, improvement in press formability can be expected by reducing the in-plane anisotropy of elongation.
  • Patent Document 1 discloses a cold-rolled steel sheet having excellent bake hardenability and a small in-plane anisotropy and a manufacturing method thereof.
  • ⁇ r is defined by the amount of C and the rolling reduction during cold rolling, and both in-plane anisotropy and dent resistance can be achieved.
  • it is necessary to start cooling within 2 seconds after hot rolling and to cool at a cooling rate of 70 ° C./s or more over a temperature range of 100 ° C. or more.
  • the in-plane anisotropy here is ⁇ r and does not necessarily match the in-plane anisotropy of elongation.
  • Patent Document 2 discloses a high-strength steel sheet having a small in-plane anisotropy of elongation and a method for producing the same.
  • a steel sheet is a composite structure steel containing martensite having a ferrite phase area ratio of 85% to 99% and an area ratio of 1% to 13%, and the ODF of the plate surface at the 1/4 sheet thickness position of the steel sheet.
  • the composite steel containing martensite has a problem in that the yield strength (YP) is low, so that the effect of suppressing deformation at the time of product transportation or accidental dropping becomes small. Even if martensite is included, if the tensile strength (TS) is increased by high alloying, the yield strength (YP) also increases. However, in this case, there is a problem that the manufacturing cost increases.
  • Patent Document 4 As a technique for improving the in-plane anisotropy while utilizing the residual ⁇ structure, for example, Patent Document 4 is disclosed. However, all of them are expensive because there are many alloy components. Further, since TS has a remarkably high strength of 590 MPa or more, the load required for molding is high, and a large-scale press is required, resulting in high costs.
  • the present invention advantageously solves the above-mentioned problems.
  • the yield strength (YP) suitable for automobile parts and electrical parts is as high as 400 MPa or more, and the in-plane anisotropy of elongation is reduced to perform press molding.
  • An object of the present invention is to provide a high-strength cold-rolled steel sheet having excellent properties and a method for producing the same.
  • the rolled texture of a cold-rolled steel sheet develops an ⁇ fiber whose ⁇ 100> direction is parallel to the rolling direction and a ⁇ fiber whose ⁇ 111> direction is parallel to the normal direction.
  • the ⁇ fiber becomes weaker and the ⁇ fiber becomes stronger. Since ⁇ -fiber reduces the elongation in the 45 ° direction with respect to the rolling direction, the cold-rolled steel sheet produced by a normal process has a low elongation in the 45 ° direction with respect to the rolling direction and a strong elongation anisotropy. Become.
  • the present invention has been made based on the above findings, and the gist thereof is as follows. [1] By mass%, C: 0.060 to 0.099%, Si: 0.09% or less, Mn: 1.0 to 1.49%, P: 0.050% or less, S: 0.03 % Or less, sol.
  • a steel slab having the component composition described in [1] or [2] is prepared, the steel slab is heated, and kept in a temperature range of 1150 ° C. or higher for 60 minutes or more, followed by rough rolling. After that, finish rolling is performed at a finish rolling temperature of 820 to 920 ° C. and a final pass rolling ratio of 15 to 25% of finish rolling, and water cooling is started within 2 seconds after the finish rolling to cool the hot rolled steel sheet. After the production, the hot-rolled steel sheet is pickled and cold-rolled, and then subjected to continuous annealing, and is kept at a temperature range of 830 ° C. or higher for 10 to 250 seconds. Manufacturing method.
  • the present invention it is possible to obtain a high-strength steel sheet having a small in-plane anisotropy of elongation and excellent press formability. Moreover, since the yield strength (YP) is high, deformation at the time of product transportation or accidental dropping is suppressed.
  • the high-strength steel sheet of the present invention can be applied to automotive parts and electrical parts, and is extremely useful.
  • C 0.060 to 0.099% C is an element necessary for refining the crystal and increasing the strength. Moreover, it has the effect of forming a precipitate with Nb, which will be described later, and increasing the yield strength (YP). If the amount of C is less than 0.060%, the effect of increasing the strength due to the fine graining is low, so it is necessary to contain 0.060% or more. On the other hand, when the amount of C exceeds 0.099%, it becomes easy to form the second phase, and the elongation decreases. Therefore, the C content is in the range of 0.060 to 0.099%. Preferably it is 0.060 to 0.090% of range.
  • Si 0.09% or less
  • Si has an effect of improving the surface quality by delaying the scale generation in hot rolling in a small amount.
  • the Si content is 0.09% or less.
  • Mn 1.0-1.49%
  • Mn is an element useful for increasing the strength of a steel sheet through solid solution strengthening and crystal grain refining effects. If the amount of Mn is less than 1.0%, the effect of solid solution strengthening and refining is low, so 1.0% or more is required. On the other hand, when the amount of Mn exceeds 1.49%, it becomes easy to form a martensite phase and the yield strength (YP) decreases. Therefore, the Mn content is in the range of 1.0 to 1.49%.
  • the P content is 0.050% or less. Preferably, it is 0.040% or less.
  • S 0.03% or less S has an effect of improving the peelability of the primary scale of the steel sheet and improving the appearance quality.
  • the amount of S increases, the amount of MnS precipitated in the steel increases.
  • ductility such as elongation of a steel plate and stretch flangeability, is reduced, and press formability is reduced.
  • the hot ductility at the time of hot-rolling a slab is reduced, and surface defects are likely to occur.
  • the S amount is set to 0.03% or less.
  • it is 0.01% or less, More preferably, it is 0.005% or less, More preferably, it is 0.002% or less.
  • sol. Al 0.01 to 0.09% sol.
  • Al has the effect of fixing solid solution N present as an impurity and improving formability. For this reason, sol.
  • the amount of Al is 0.01% or more.
  • the Al content is in the range of 0.01 to 0.09%. Preferably, the content is 0.02 to 0.07%.
  • N 0.005% or less If the amount of N is too large, the moldability is deteriorated and a large amount of Al is required to fix the solid solution N. For this reason, it is preferable to reduce as much as possible. From such a viewpoint, the N amount is set to 0.005% or less.
  • Nb 0.035 to 0.080% Nb is an element necessary for refining the crystal and increasing the strength. Moreover, the above-mentioned C and precipitates are formed, and in particular, it has the effect of increasing the yield strength (YP). Furthermore, since Nb precipitates are finely precipitated in the finish rolling step of the hot rolling process to partially suppress recrystallization of the steel, and Nb has the effect of increasing the ⁇ fiber after cold rolling and annealing. It is the most important element of the invention. In order to acquire such an effect, it is necessary to contain 0.035% or more of Nb amount.
  • the Nb amount is set to a range of 0.035 to 0.080% or less. Preferably, it is 0.060% or less.
  • Ti 0.010 to 0.050% Ti has the effect of increasing the yield strength (YP) by forming precipitates. For this reason, it is desirable to contain 0.010% or more.
  • Nb as an essential component
  • the Ti amount is set to a range of 0.010 to 0.050% or less. Preferably it is 0.029% or less.
  • the following elements may be further contained.
  • the following elements are elements that have particularly high hardenability and facilitate the formation of a martensite phase. Therefore, the following range is preferable.
  • Cr 0.05% or less Cr, like Mn, is an element that easily forms a martensite phase, and yield strength (YP) decreases when the martensite phase is generated. For this reason, the Cr content is 0.05% or less. Preferably it is 0.02% or less, More preferably, it is 0.01% or less. Since excessive reduction causes an increase in cost, the lower limit is preferably set to 0.001%.
  • Mo 0.05% or less Mo, like Mn, is an element that easily forms a martensite phase. When a martensite phase is generated, yield strength (YP) decreases. For this reason, the Mo amount is 0.05% or less. Preferably it is 0.02% or less, More preferably, it is 0.01% or less. Since excessive reduction causes an increase in cost, the lower limit is preferably set to 0.001%.
  • the components other than the above are Fe and inevitable impurities. However, as long as the effects of the present invention are not impaired, the inclusion of components other than those described above is not rejected.
  • the microstructure of the steel sheet of the present invention is a structure composed of ferrite + pearlite or further cementite, and in the present invention, it does not include the martensite phase and the retained austenite phase. Means less than 1%. Moreover, it can control by a manufacturing condition mentioned later that a martensite phase and a retained austenite phase are not included.
  • the pole figure represents a statistical crystal orientation distribution regarding a large number of crystal grains, and is therefore a method suitable for determining the preferred orientation.
  • the texture of polycrystalline materials often exhibits a number of preferred orientations as well as a single preferred orientation.
  • a fiber texture such as an ⁇ fiber or ⁇ fiber that is an orientation group rotated around a crystal axis
  • the evaluation of the three-dimensional crystal orientation distribution function it is obtained by the series expansion method from the incomplete pole figures (200), (211), and (110) obtained by the reflection method.
  • FIG. 1 shows the relationship between the average crystal orientation densities I ⁇ and I ⁇ thus obtained and the absolute value of ⁇ E1 (hereinafter sometimes simply referred to as
  • ⁇ El shown by the following formula (1) is ⁇ 2% or more and 2% or less.
  • El 0 , El 45 and El 90 are values of elongation at break measured in directions of 0 °, 45 ° and 90 ° with respect to the rolling direction of the steel sheet.
  • the yield strength YP is preferably 400 MPa or more.
  • the yield ratio YR is preferably 0.79 or more. If the tensile strength is higher than the yield strength, the press load becomes higher than necessary, and a large press must be introduced. For this reason, it is preferable that the tensile strength TS is 580 MPa or less.
  • the steel slab to be used is preferably manufactured by a continuous casting method in order to prevent macro segregation of components.
  • the slab is manufactured and then cooled to room temperature and then reheated, it is charged directly into the heating furnace without being cooled and placed in a heating furnace and hot rolled, or a little heat retention
  • an energy saving process such as direct rolling which is immediately hot rolled can be applied without any problem.
  • Slab heating temperature Hold for 60 minutes or more in a temperature range of 1150 ° C or higher
  • Nb precipitates are completely dissolved and finely precipitated in the finish rolling step of the hot rolling process to recrystallize the steel.
  • the heating temperature is high and the holding time is long. From such a viewpoint, in the present invention, the slab heating temperature is maintained for 60 minutes or more in a temperature range of 1150 ° C. or more.
  • the heating temperature is preferably 1300 ° C. or less, and the holding time is 500 minutes or less. It is preferable.
  • the steel slab heated under the above conditions is subjected to hot rolling consisting of rough rolling and finish rolling.
  • 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.
  • it is effective to use a so-called sheet bar heater or edge heater that heats the sheet bar for the purpose of preventing troubles during hot rolling or improving temperature unevenness in the width direction.
  • the finish rolling entry temperature is preferably 1050 ° C. or lower.
  • the sheet bar is preferably water-cooled before finish rolling in order to cool to 1050 ° C. on the finish rolling entry side.
  • excessively low temperature increases the load during hot rolling, and is preferably 930 ° C. or higher.
  • Finish rolling temperature 820-920 ° C
  • the sheet bar is finish-rolled to obtain a hot-rolled steel sheet.
  • the finish rolling temperature that is, the finish rolling exit temperature (FT) is set to 820 to 920 ° C. This is for obtaining a texture preferable for in-plane anisotropy of elongation after cold rolling and recrystallization annealing.
  • the FT is less than 820 ° C., not only the load during hot rolling becomes high, but in some component systems, rolling occurs in the ferrite region, and the texture changes greatly.
  • the finish rolling temperature is 820 to 920 ° C., more preferably 820 to 890 ° C.
  • Final rolling ratio of finish rolling 15-25% Texture formation by rolling in the austenite region during finish rolling enhances the ⁇ fiber after cold rolling and annealing. This effect is most strongly influenced by the final pass of finish rolling.
  • the final pass rolling ratio of the finish rolling is less than 15%, the texture formation by rolling in the austenite region is insufficient, and the ⁇ fiber after cold rolling and annealing does not become strong, so the content is made 15% or more.
  • it exceeds 25% the load during rolling becomes high, so it is 25% or less.
  • Time until start of water cooling after finish rolling within 2 seconds Since it is necessary to transform austenite in a partially recrystallized state after finish rolling, holding in the austenite region is not preferable. Therefore, water cooling is started within 2 seconds after finish rolling. More preferably, it is within 0.5 seconds.
  • the cooling rate from finish rolling to coil winding is not particularly specified. In order to suppress recrystallization in the austenite region during cooling, it is preferably 20 ° C./second or more. Moreover, since excessive cooling tends to cause temperature unevenness in the plate thickness direction and in-plane direction, it is preferably 200 ° C./second or less. More preferably, it is 99 degrees C / second or less, More preferably, it is 40 degrees C / second or less.
  • the coil winding temperature is not particularly specified.
  • CT coil winding temperature
  • CT exceeds 720 ° C., the crystal grains are coarsened, which may lead to a decrease in strength.
  • Pickling is not particularly specified and is performed by a conventional method. In order to suppress scale defects, shot blasting or leveling may be performed before pickling.
  • Cold rolling is not particularly specified.
  • the rolling rate is preferably 30 to 80%. If the rolling rate is less than 30%, recrystallization at the time of annealing may become unstable, leading to a decrease in elongation. On the other hand, if the rolling rate exceeds 80%, the load during rolling increases.
  • Annealing Continuous annealing and holding for 10 to 250 seconds in a temperature range of 830 ° C. or higher
  • the steel sheet of the present invention has a slow recrystallization due to the large amount of Nb added, and an unrecrystallized structure remains when annealed at a low temperature. Therefore, the elongation will decrease.
  • it is necessary to heat to the austenite single phase region during annealing For this reason, it is necessary to heat at a heating temperature of 830 ° C. or more for 10 seconds or more.
  • annealing time shall be 250 seconds or less.
  • the cooling after annealing is fast, a martensite phase is likely to be generated, and therefore it is desirable to cool at an average cooling rate of 50 ° C./sec or less.
  • a plating layer may be formed on the surface of the steel sheet by adding a surface treatment such as electroplating or hot dipping after the cold-rolled steel sheet annealing process.
  • the plating layer is not limited to pure zinc plating or zinc-based alloy plating, but may be various plating layers conventionally applied to the surface of a steel sheet, such as Al plating or Al-based alloy plating. Moreover, you may apply
  • temper rolling or leveler processing may be applied to the cold-rolled annealed sheet or plated steel sheet produced as described above for the purpose of adjusting the shape correction, surface roughness, 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. More preferably, it is 1.3% or more. On the other hand, if it exceeds 15%, it tends to cause a significant decrease in ductility, which is not preferable.
  • Molten steel having various compositions shown in Table 1 was melted in a converter and made into a steel slab by a continuous casting method. These steel slabs were hot rolled under the conditions shown in Table 2 to obtain 3.2 mm thick hot rolled steel sheets. These hot-rolled steel sheets were pickled and then made into 1.6 mm thick as roll material by cold rolling at a reduction rate of 50%. Next, these as roll materials were subjected to continuous annealing in the continuous annealing line under the conditions shown in Table 2. Furthermore, the obtained cold-rolled annealed steel sheet was subjected to temper rolling with an elongation of 1.3%. Further, some as roll materials were subjected to hot dip galvanization after annealing under the conditions shown in Table 2 in a continuous hot dip galvanizing line, and subjected to temper rolling with an elongation rate of 1.3%.
  • the thus obtained cold-rolled annealed sheet and hot-dip galvanized steel sheet were examined for tensile properties, steel structure and texture.
  • ⁇ El was used as an index of in-plane anisotropy of elongation. This ⁇ El indicates the in-plane anisotropy of elongation, and was calculated from the following equation (1).
  • ⁇ El (El 0 ⁇ 2El 45 + El 90 ) / 2 (1)
  • El 0 , El 45 , and El 90 indicate the elongation at break of the test specimens taken from 0 ° (L direction), 45 ° (D direction), and 90 ° (C direction) directions. If ⁇ El is ⁇ 2% to 2%, it can be said that the in-plane anisotropy of elongation is excellent.
  • volume fraction of phase The volume fraction of each phase is determined by measuring the area ratio of each phase by the point count method (according to ASTM E562-83 (1988)). The rate was defined as the volume fraction.
  • the area ratio of each phase was obtained by collecting a test piece from each of the obtained cold-rolled annealed plates, and corroding the vertical section (L section) parallel to the rolling direction with nital after polishing, and using a scanning electron microscope (SEM).
  • SEM scanning electron microscope
  • the type of phase was identified by observation at 4000 times, and the area ratio (martensite fraction) of the martensite phase was determined. In the structure photograph, particles with white contrast were martensite.
  • the abundance ratio of residual austenite phase is obtained by performing X-ray diffraction of the plate surface at the 1/4 thickness, and integrating the ⁇ phase (ferrite phase) (211) and the ⁇ phase (220). The strength was measured and standardized.
  • a steel sheet having I ⁇ of 2.0 or more and 4.0 or less and I ⁇ of 2.0 or more and 10.0 or less has low in-plane anisotropy of elongation.
  • steel types D, E, F, H, I, and N which are the scope of the present invention, are high strength and high yield ratio steel plates with YP ⁇ 400 MPa and YR ⁇ 0.79. And it has the structure which consists of ferrite + pearlite + cementite, does not contain martensite phase and residual ⁇ phase, I ⁇ is 2.0 or more and 4.0 or less, I ⁇ is 2.0 or more and 10.0 or less.
  • ⁇ El is ⁇ 2% to 2% and the in-plane anisotropy of elongation is small.
  • steel sheet E having a hot rolling finish entry side temperature of 1050 ° C.
  • steel type N has lower strength and lower ductility, although it is the same component. This is presumably because the hot rolling cooling rate is high and the structure is non-uniform.
  • steel types A and O whose component or annealing time is out of the present invention have a low strength of YP of less than 400 MPa.
  • the steel types G, P, and Q deviating from the component range of the present invention lose the texture balance and increase the anisotropy.
  • the steel type G which is a steel sheet including a martensite phase and a retained austenite phase, not only has a large anisotropy but also has a low YR.
  • the steel types B, C, J, L, and M satisfying the component range of the present invention satisfy the scope of the present invention in terms of slab heating conditions, annealing temperature, cooling start time, final pass rolling rate of finish rolling, and the like. Therefore, the texture balance is lost and the anisotropy is increased.

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Abstract

L'invention vise à fournir une feuille d'acier haute résistance laminée à froid et son procédé de fabrication, la feuille d'acier étant idéale pour des composants automobiles et des pièces de machines électriques, présentant une résistance élevée avec une limite d'élasticité apparente (YP) de 400 MPa ou plus, et présentant une excellente aptitude au formage à la presse en raison de la réduction de l'anisotropie d'allongement dans le plan. La feuille d'acier haute résistance à faible anisotropie d'allongement dans le plan contient en % en masse, C : 0,060 - 0,099 %, Si : 0,09% ou moins, Mn : 1,0 - 1,49 %, P : 0,050% ou moins, S : 0,03 % ou moins, sol. Al : 0,01 - 0,09 %, N : 0,005 % ou moins, Nb : 0,035 - 0,080 %, le reste étant constitué de Fe et d'impuretés inévitables, et ne contenant pas de phases martensitiques ou de phases austénitiques résiduelles. Dans la texture de la surface de la plaque, à ¼ de l'épaisseur de la feuille d'acier, la densité d'orientation cristalline moyenne (Iα) dans la gamme de ϕ = 25° - 35° de fibres α représentée par la fonction de distribution d'orientation cristalline ODF (ϕ1 = 0°, ϕ2 = 45° et ϕ = 0° - 55°) est 2,0 à 4,0 et la densité d'orientation cristalline moyenne (Iγ) de fibres γ (ϕ1 = 0° - 60°, ϕ2 = 45° et ϕ = 55°) est 2,0 à 10,0.
PCT/JP2014/005228 2013-10-22 2014-10-15 Feuille d'acier haute résistance présentant une faible anisotropie d'allongement dans le plan et son procédé de fabrication WO2015059903A1 (fr)

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CN201480058323.4A CN105899696A (zh) 2013-10-22 2014-10-15 伸长率的面内各向异性小的高强度钢板及其制造方法
MX2016005137A MX2016005137A (es) 2013-10-22 2014-10-15 Lamina de acero de alta resistencia que tiene una pequeña anisotropia planar de elongacion y metodo para la produccion de la misma.
KR1020167013339A KR101813914B1 (ko) 2013-10-22 2014-10-15 연신의 면내 이방성이 작은 고강도 강판 및 그의 제조 방법

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JP2013218833A JP5817805B2 (ja) 2013-10-22 2013-10-22 伸びの面内異方性が小さい高強度鋼板およびその製造方法

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CN109355583A (zh) * 2018-11-09 2019-02-19 唐山钢铁集团有限责任公司 一种低各向异性低合金高强冷轧退火钢带及其生产方法
JP7355994B2 (ja) * 2019-03-29 2023-10-04 日本製鉄株式会社 高炭素鋼板およびその製造方法
CN111621712A (zh) * 2020-05-22 2020-09-04 武汉钢铁有限公司 一种屈服强度≥420MPa的汽车用低合金电镀锌钢板的生产方法

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MX2016005137A (es) 2016-07-18
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JP2015081360A (ja) 2015-04-27
KR20160074623A (ko) 2016-06-28
KR101813914B1 (ko) 2018-01-02

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