JP2007092130A - High-strength steel sheet having excellent rigidity and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-strength steel sheet having excellent rigidity in which tensile strength is ≥590 MPa, a Young's modulus in the 90° direction to the rolling direction is ≥230 GPa, and the average Young's modulus in the 0°, 45° and 90° directions to the rolling direction is ≥215 GPa, and to provide its production method. <P>SOLUTION: The high-strength steel sheet having excellent rigidity has a composition comprising, by mass, 0.02 to 0.15% C, ≤0.3% Si, 1.0 to 3.5% Mn, ≤0.05% P, ≤0.01% S, ≤1.0% Al, ≤0.01% N and 0.1 to 1.0% Ti, and in which the contents of C, N, S and Ti satisfy equation (1), and the balance Fe with inevitable impurities, and has the microstructure of a ferrite single phase, and, in which the average ODF (Orientation Distribution Function) analysis strength in the (111)[1-10] to (111)[-1-12] orientation of the sheet face in the 1/4 sheet thickness is ≥5, and the average ODF analysis strength in the (113)[1-10] to (223)[1-10] orientation is ≥3. The equation (1) is: C-(12/47.9)×Ti<SB>-1</SB>≤0 ... (1), wherein, Ti<SB>-1</SB>=Ti-(47.9/14)×N-(47.9/32.1)×S, and each atomic symbol in the equation denotes the content of each element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention mainly relates to a high-strength thin steel sheet excellent in rigidity suitable for a columnar structural member having a rigidity thickness sensitivity index close to 1, such as a side sill, a center pillar, a side frame, and a cross member of an automobile, and a manufacturing method thereof. .

  In recent years, the weight reduction of automobile bodies in automobiles has become an extremely important issue, such as the exhaust gas regulations of automobiles being implemented in response to increasing interest in global environmental problems. In order to reduce the weight of the car body, it is an effective method to reduce the plate thickness by increasing the strength of the steel plate (thinning), but recently, as a result of remarkable progress in increasing the strength of the steel plate, the plate thickness is 2.0 mm. The use of thin steel sheets that are below the limit is increasing.

  However, in order to reduce the weight by further increasing the strength, it has become indispensable to simultaneously suppress the decrease in the vehicle body rigidity due to the thinning. Since the vehicle body structure has the greatest influence on the rigidity, it is effective to suppress the decrease in rigidity structurally, but it is not easy to change the basic structure. In addition, it is effective to change the welding conditions, such as increasing the number of welding points, switching to weld bonding, or switching to laser welding, for members that are spot-welded, but this involves the problem of increased costs. . Furthermore, there is a method of attaching a resin or the like to a portion where rigidity is required, but this increases the cost. Furthermore, although it is effective to change the shape of the cross section of the member, there are design problems and pressing problems.

  Therefore, if the rigidity of the steel plate used for the member is increased, the rigidity of the member can be increased without changing the member shape or welding conditions. In particular, for columnar structural members of automobiles, a bending load is applied while the automobile is running, so it is necessary to increase the bending rigidity. For this purpose, it is effective to increase the Young's modulus of the steel sheet.

  The Young's modulus is largely governed by the texture, and in the case of steel with a body-centered cubic lattice, it is known that the Young's modulus is high in the <111> direction, which is the atomic dense direction, and conversely small in the <100> direction where the atomic density is low. It has been. It is known that the Young's modulus of normal iron with no crystal orientation anisotropy is about 210 GPa, but by adding anisotropy to the crystal orientation and increasing the atomic density in a specific direction, that direction Can increase the Young's modulus. However, when considering the bending rigidity of an automobile body, since a load is applied from various directions, a steel sheet having a high Young's modulus in each direction is required in addition to a specific direction.

Regarding the Young's modulus of a steel sheet, various studies have been made on steel sheets that have a higher Young's modulus in a specific direction by controlling the texture. For example, Patent Document 1 uses ultra-low carbon steel to which Nb or Ti is added, and the rolling rate from Ar ₃ transformation point to (Ar ₃ transformation point + 150 ° C.) during hot rolling is 85% or more. By promoting ferrite transformation from recrystallized austenite, {311} <011> and {332} <113> were developed after hot rolling, and then {211} <011> by cold rolling and recrystallization annealing Has been developed to increase the Young's modulus in a direction perpendicular to the rolling direction. In Patent Document 2, low carbon steel with Nb added and having a C content of 0.05% by mass or less, finish rolling start temperature of 950 ° C. or less, (Ar ₃ transformation point −50 ° C.) to (Ar ₃ transformation point +100) (° C) finish rolling at the finishing finish temperature, suppressing the recrystallization of austenite, suppressing the development of {100}, which reduces the Young's modulus, and increasing the Young's modulus in the direction perpendicular to the rolling direction. A method for producing a hot-rolled steel sheet is disclosed. In Patent Document 3, a low carbon steel with an amount of C of 0.05 mass% or less in which the Ar ₃ transformation point is increased by adding Si and Al is hot-rolled with a reduction rate of 60% or more at the Ar ₃ transformation point or less. And the manufacturing method of the hot-rolled steel plate which raised the Young's modulus of the direction orthogonal to a rolling direction by developing {211} <110> is disclosed. In Patent Document 4, steel having a solid solution (C + N) of 10 ppm or more is rolled at a reduction rate of 20% or more in a temperature range of 200 to 500 ° C., and subjected to recrystallization annealing, (110) [ 001] orientation is developed to increase the Young's modulus in the direction of 45-67.5 ° with respect to the rolling direction. Patent Document 5 discloses a high-tensile cold-rolled steel sheet with excellent deep drawability in which Ti, Mo, and W are added to steel having a C content of 0.01 to 0.1% by mass to precipitate fine carbides of 10 to 30 nm. Has been.

Non-Patent Document 1 below relates to an ADC method for ODF analysis described in [Best Mode for Carrying Out the Invention] described later.
Japanese Patent Laid-Open No. 5-255804 Japanese Patent Laid-Open No. 5-27530 JP-A-9-53118 JP 58-9932 A JP 2003-321733 A Phys. Status Solid (b), 134 (1986) 447

  However, the above prior art has the following problems. That is, in the techniques of Patent Documents 1 to 4, it is effective to increase the Young's modulus in only one direction of the steel sheet, but to improve the rigidity of the structural member of an automobile that requires a steel sheet having a high Young's modulus in each direction. Not applicable. In the technique of Patent Document 5, since the precipitation is fine, the rolling load during cold rolling is high, and it is difficult to achieve high Young's modulus in addition to operational difficulties.

  In addition, in the technique of Patent Document 1, the tensile strength is as low as about 450 MPa at most because it uses an ultra-low carbon steel having a C content of 0.01% by mass or less, and it is difficult to further increase the strength. In order to perform rolling in the ferrite region, the crystal grains become coarse and the workability is remarkably reduced. In Patent Document 4, it is necessary to perform warm rolling at 200 to 500 ° C. In comparison, the rolling load becomes very high, and there is a problem that the manufacturing cost increases.

  In the present invention, the tensile strength is 590 MPa or more, the Young's modulus in the 90 ° direction with respect to the rolling direction is 230 GPa or more, and the average Young in the rolling direction, 45 ° direction with respect to the rolling direction, and 90 ° direction with respect to the rolling direction. An object of the present invention is to provide a high-strength thin steel sheet excellent in rigidity with a rate of 215 GPa or more and a method for producing the same.

  When the present inventors examined high Young's modulus of a high-strength thin steel sheet having a tensile strength of 590 MPa or more, using a steel in which the amount of C and Ti is appropriately controlled, the steel is rolled up at a high temperature after hot rolling. Is precipitated as carbides and free of solid solution C, and in the subsequent cold rolling, (113) [1-10] to (223) [1-10] orientation and (111) [1-10] (111) [1-10] to (111) [-1-] by developing the texture of the (111) [-1-12] orientation and using the fact that solid solution C is free during annealing 12] The texture in the rolling direction is developed by developing the texture in the (113) [1-10] to (223) [1-10] orientation by controlling the precipitate and annealing temperature. On the other hand, it was found that the Young's modulus in all directions can be improved while improving the Young's modulus in the 90 ° direction. Here, [1-10] and [-1-12] represent directions of (1, -1,0) and (-1, -1,2), respectively.

The present invention has been made based on these findings, and in mass%, C: 0.02 to 0.15%, Si: 0.3% or less, Mn: 1.0 to 3.5%, P: 0.05% or less, S: 0.01% or less , Al: 1.0% or less, N: 0.01% or less, Ti: 0.1 to 1.0%, C, N, S, Ti content satisfies the following formula (1), the balance is Fe and inevitable impurities The average of the (111) [1-10] to (111) [-1-12] orientations of the plate surface at a 1/4 thickness of the steel plate The ODF analysis strength f is 5 or more, and the average ODF analysis strength f in the (113) [1-10] to (223) [1-10] orientation is 3 or more. Provide high strength thin steel sheet.
C- (12 / 47.9) × Ti _-1 ≦ 0 ... (1)
Here, Ti ₋₁ = Ti− (47.9 / 14) × N− (47.9 / 32.1) × S, and each element symbol in the formula represents the content (% by mass) of each element.

The high-strength thin steel sheet of the present invention can further contain at least one element selected from Nb: 0.005 to 0.2% and V: 0.01 to 1.0% by mass. In that case, instead of the above formula (1), the contents of C, N, S, Ti, Nb, and V must satisfy the following formula (2).
C- (12 / 47.9) × Ti _-1- (12 / 92.9) × Nb- (12 / 50.9) × V ≦ 0 ... (2)
However, each element symbol in the formula represents the content (% by mass) of each element.

  In the high-strength thin steel sheet of the present invention, further, in mass%, Cr: 0.05-1.0%, Mo: 0.05-1.0%, Ni: 0.05-1.0%, B: 0.0005-0.0030%, Cu: 0.1-2.0%, W: At least one element selected from 0.1 to 2.0% can be contained.

The high-strength thin steel sheet of the present invention is obtained by, for example, casting a steel having the above composition, hot rolling at a finish rolling end temperature not lower than the Ar ₃ transformation point, and winding at a winding temperature of 500 ° C. or higher. , Pickling, after performing cold rolling at a reduction rate in the range of 20 to 85%, when performing annealing, heating from room temperature to 820 ° C at an average rate of 1 ° C / s or more, 820 It can be produced by a method for producing a high-strength thin steel sheet having excellent rigidity, characterized in that the residence time v (s) satisfying the following expression (3) is maintained in a temperature range of ˜900 ° C.

Here, F (w) is the temperature (° C) at an arbitrary time w (s) within the time v (s) that the steel sheet stays in the temperature range of 820 to 900 ° C after it reaches 820 ° C. To express.

  According to the present invention, the tensile strength is 590 MPa or more and 90 ° with respect to the rolling direction, which is suitable for a columnar structural member having a rigidity thickness sensitivity index close to 1, such as an automobile side sill, center pillar, side frame, and cross member. Manufactures high-strength steel sheets with excellent rigidity with a Young's modulus in the direction of 230 GPa or more and an average Young's modulus of 215 GPa or more in the rolling direction, 45 ° direction with respect to the rolling direction, and 90 ° direction with respect to the rolling direction. I can do it now.

  Below, the high-strength thin steel sheet and its manufacturing method which are this invention are demonstrated in detail.

1) Component (“%” below represents “% by mass”)
C: C forms precipitates with Ti, thereby controlling grain growth during annealing and contributing to higher rigidity, and can also contribute to higher strength by precipitation strengthening. In order to obtain such an effect, the C amount needs to be 0.02% or more. Also, by reducing the amount of solute C, it is possible to develop an orientation that is advantageous for high rigidity during cold rolling and annealing, so the left side of the above equation (1) representing the amount of solute C is 0 or less. There is a need to. On the other hand, if the amount of C increases, it is necessary to increase the amount of Ti accordingly, but since the carbide effect is saturated and the alloy cost increases, the amount of C is 0.15% or less, preferably 0.10% or less. There is a need to.

If the amount of Si: Si exceeds 0.3%, the Ar ₃ transformation point is raised, and rolling above the Ar ₃ transformation point becomes difficult. Further, it deteriorates the weldability of the steel sheet, promotes the formation of firelite on the surface of the slab during hot rolling, and promotes the generation of surface defects on the hot rolled steel sheet called so-called red scale. Furthermore, when used as a cold-rolled steel sheet, the Si oxide produced on the surface deteriorates the chemical conversion property, and when used as a hot-dip galvanized steel sheet, the Si oxide produced on the surface is not plated. To trigger. Therefore, the Si amount needs to be 0.3% or less. In addition, since Si contributes to high strength by solid solution strengthening, the Si content is preferably 0.1% or more.

  Mn: Mn acts as a solid solution strengthening element and contributes to increasing the strength of steel. In order to obtain such an effect, the Mn content needs to be 1.0% or more. On the other hand, if the amount of Mn exceeds 3.5%, the weldability of the steel sheet is deteriorated, and the rolling load during hot rolling or cold rolling is increased, leading to an increase in manufacturing cost. Therefore, the amount of Mn needs to be 3.5% or less.

  When P: P is contained in an amount exceeding 0.05%, it segregates at the grain boundaries to lower the ductility and toughness of the steel sheet and deteriorate the weldability. Moreover, when alloying hot dip galvanizing to the steel plate of this invention, P delays alloying speed | rate. Therefore, the P content is 0.05% or less. Note that P is an element effective for increasing the strength as a solid solution strengthening element, and also has an action of suppressing the occurrence of red scale in steel to which Si is added, so the P content is preferably 0.01% or more.

  When S: S is contained in a large amount exceeding 0.01%, hot ductility is remarkably lowered, hot cracking is induced, and the surface properties of the steel sheet are remarkably deteriorated. Moreover, it not only contributes to the strength, but also precipitates as coarse MnS, reducing the ductility such as hole expandability. Therefore, the S amount needs to be 0.01% or less. Note that the smaller the amount of S, the better, but 0.005% or less is more preferable from the viewpoint of further improving the hole expandability.

Al: Al is a ferrite stabilizing element, and if it exceeds 1.0%, the Ar ₃ transformation point of the steel is greatly increased, so that rolling above the Ar ₃ transformation point becomes difficult. Therefore, the Al amount needs to be 1.0% or less. In addition, since Al contributes to high strength by solid solution strengthening, the Al content is desirably 0.2% or more for this purpose.

  If N: N is contained in a large amount exceeding 0.01%, slab cracking may be induced during hot rolling, and surface flaws may occur in the steel sheet. Furthermore, since Ti and coarse nitrides are formed at a high temperature, the effect of adding Ti is reduced and the manufacturing cost is increased. Therefore, the N content needs to be 0.01% or less, preferably 0.005% or less.

  Ti: Ti forms carbides and contributes to higher rigidity and higher strength by reducing the amount of solid solution C, so the Ti amount needs to be 0.1% or more. On the other hand, if the Ti amount exceeds 1.0%, the effect is saturated, so the Ti amount needs to be 1.0% or less.

  The balance is preferably Fe and inevitable impurities, but even if it contains other trace elements, the effect of the present invention is not impaired. Examples of other trace elements include Ca and REM, and these elements contribute to improving the stretch flangeability of the steel sheet by controlling the form of sulfide inclusions. Therefore, although not particularly limited, in order to obtain this effect, it is preferable to include one or more of Ca and REM and to make the total of these contents 0.001% or more. Further, since the effect is saturated when the total content of Ca and REM exceeds 0.01%, the total of these contents is preferably 0.01% or less, and more preferably 0.005% or less. Examples of the impurity element include Sb, Sn, Zn, Co, etc., and the allowable ranges of these contents are Sb: 0.01% or less, Sn: 0.1% or less, Zn: 0.01% or less, Co: 0.1% or less.

  In addition to the above component elements, at least one element selected from the following elements can be contained.

  Nb, V: Nb and V contribute to high rigidity and high strength by forming carbides and reducing the amount of dissolved C. For this purpose, the Nb content must be 0.005% or more and the V content must be 0.01% or more. On the other hand, when the Nb amount exceeds 0.2% or the V amount exceeds 1.0%, the effect is saturated, and the rolling load during hot rolling or cold rolling is increased. Therefore, the Nb content must be 0.2% or less and the V content must be 1.0% or less. When Nb and V are added, the solid solution C calculated using the left side of the above equation (2) instead of the above equation (1) needs to be 0 or less.

Cr, Mo, Ni, B: Cr, Mo, Ni, and B contribute to high strength by increasing hardenability and making the structure finer. In order to obtain such an effect, it is necessary that the Cr content is 0.05% or more, the Mo content is 0.05% or more, the Ni content is 0.05% or more, and the B content is 0.0005% or more. On the other hand, when the Cr content exceeds 1.0%, the Mo content exceeds 1.0%, the Ni content exceeds 1.0%, and the B content exceeds 0.00030%, the effect is saturated, and hot rolling and Increase the rolling load during cold rolling. Therefore, it is necessary that the Cr content is 1.0% or less, the Mo content is 1.0% or less, the Ni content is 1.0% or less, and the B content is 0.00030% or less. Further, if Mo is more than Ti, a composite carbide of Ti and Mo is formed and the effect of quenching of Mo is reduced. Therefore, it is preferable to add Mo so as to satisfy Mo <Ti ₋₁ /0.6.

  Cu: Cu contributes to high strength by forming fine precipitates. In order to obtain this effect, the Cu content needs to be 0.1% or more. On the other hand, if the amount of Cu exceeds 2.0%, the hot ductility is lowered, surface defects accompanying cracks during hot rolling are induced, and the effect of hardenability is saturated. Therefore, the amount of Cu needs to be 2.0% or less. In addition, when adding Cu, although the crack at the time of hot rolling tends to generate | occur | produce, in order to prevent this, it is preferable to add together the above-mentioned Ni.

  W: W improves rigidity by existing as a solid solution element or carbide. In order to obtain this effect, the W amount needs to be 0.1% or more. On the other hand, if the amount of W exceeds 2.0%, the alloy cost increases, so the amount of W needs to be 2.0% or less.

2) Microstructure By making the microstructure a ferrite single phase, the average Young's modulus in the rolling direction, the 45 ° direction with respect to the rolling direction, and the 90 ° direction with respect to the rolling direction can be improved.

3) Texture
Stiffness is improved by developing textures in the (111) [1-10] to (111) [-1-12] and (113) [1-10] to (223) [1-10] orientations Therefore, the average ODF (Orientation Distribution Function) analysis strength f in the (111) [1-10] to (111) [-1-12] orientations of the plate surface at 1/4 thickness of the steel plate is 5 In addition, the average ODF analysis strength f in the (113) [1-10] to (223) [1-10] directions needs to be 3 or more.

Here, the average ODF analysis strength f in the (111) [1-10] to (111) [-1-12] and (113) [1-10] to (223) [1-10] orientations is I asked for it. In other words, after reducing the thickness to 1/4 by chemical polishing in order to remove the influence of processing strain, (110), (200), (211) pole figures were obtained by the Schulz method and described in Non-Patent Document 1. ODF analysis using the ADC method, φ ₁ = 0 °, φ = 55 °, φ ₂ = 0 °, 5 °, 10 °, ... 90 ° (φ ₂ is 5 from 0 ° to 90 ° The average value of the analysis intensity at (°) is the average ODF analysis intensity f in the (111) [1-10] to (111) [-1-12] direction, φ ₁ = 0 °, φ ₂ = 45 °, the average value of the analysis intensity when Φ is 25 °, 30 °, 35 °, 45 ° is the average ODF in the (113) [1-10] to (223) [1-10] orientations It was set as analysis strength f.

  In addition to hot-rolled steel sheets and cold-rolled steel sheets, steel sheets subjected to surface treatment such as hot-dip galvanized materials including alloying and electrogalvanized materials are also included in the thin steel plates targeted by the present invention.

4) Manufacturing method The high-strength thin steel sheet of the present invention is, for example, slab casted steel having the above composition, hot-rolled into a hot-rolled steel sheet, wound up, pickled, cooled It is cold rolled steel sheet by hot rolling and is manufactured by annealing, the details of which will be described below.

4-1) Finish rolling finish temperature When the finish rolling temperature of finish rolling during hot rolling (the temperature immediately after finish rolling) falls below the Ar ₃ transformation point, the ferrite grains become coarse or the coiling temperature is low. Becomes an unrecrystallized structure and cannot develop a texture that improves rigidity. Therefore, the finish rolling finish temperature needs to be higher than the Ar ₃ transformation point.

When performing the finish rolling, if the rolling is performed immediately above the Ar ₃ transformation point, the structure can be refined, and a texture that is advantageous for improving the rigidity can be developed in cold rolling. For this purpose, finish rolling is carried out with the total rolling reduction at (Ar ₃ transformation point +100) ° C. or less being 50% or more, and the finish rolling finish temperature ranges from Ar ₃ transformation point to (Ar ₃ transformation point +50) ° C. It is preferable that Further, when performing finish rolling, if lubricated rolling is performed, it is possible to suppress the development of texture due to shear strain that is disadvantageous for high rigidity.

4-2) Winding temperature When winding the steel sheet after hot rolling, if the winding temperature falls below 500 ° C, Ti carbides do not precipitate, and it becomes impossible to develop a texture that improves rigidity. Therefore, the coiling temperature needs to be 500 ° C. or higher. On the other hand, when the coiling temperature exceeds 700 ° C., the scale grows and the yield is reduced, so the coiling temperature is preferably 700 ° C. or lower.

  The hot-rolled steel sheet after winding needs to be pickled before cold rolling in order to remove scale. In addition, what is necessary is just to perform pickling conditions on normal conditions.

4-3) Reduction ratio during cold rolling When cold rolling a hot-rolled steel sheet after pickling, it is effective to improve rigidity by optimizing the reduction ratio (111) [1-10] It can be rotated to (111) [-1-12] orientation and (113) [1-10] to (223) [1-10] orientation. In order to develop such an orientation, the rolling reduction needs to be 20 to 85%. On the other hand, when the rolling reduction is high, the rolling load increases and the operational cost increases, so the rolling reduction is preferably 60% or less, and more preferably 50% or less.

4-4) Rate of temperature increase during annealing If the rate of temperature increase during annealing is extremely slow, recrystallization of ferrite is promoted during temperature increase and the rigidity decreases, so the rate of temperature increase during annealing is from room temperature. It must be 1 ° C / s or higher on average up to 820 ° C. The heating rate is not particularly set as an upper limit, but in order to obtain a large heating rate, a rapid heating facility or the like is required and the manufacturing cost is increased. Therefore, the heating rate is preferably less than 30 ° C./s on average. .

4-5) Heating temperature during annealing If the heating temperature during annealing is less than 820 ° C, unrecrystallized remains after annealing, and the workability is remarkably reduced, so the heating temperature needs to be 820 ° C or higher. On the other hand, if the heating temperature exceeds 900 ° C., the development of the texture effective for improving the rigidity is hindered, so the heating temperature needs to be 900 ° C. or less.

4-6) Residence time during annealing heating Even if the heating temperature during annealing is within the range of the present invention, if the residence time is kept for a long time, the grain growth is excessive and the development of the texture effective in improving the rigidity is inhibited. Therefore, it is necessary to hold for a time v (s) that satisfies the above expression (3) in the temperature range of 820 to 900 ° C. Here, the equation (3) is an empirical equation for obtaining a residence time at which a predetermined texture can be obtained. In the temperature range of 820 to 900 ° C., it is only necessary to satisfy the residence time v (s), and the heat history in this temperature range does not need to be specified in particular and may be set according to the manufacturing equipment.

  Although the cooling after heating at the time of annealing is not particularly defined, it is preferable to cool at an average cooling rate of 3 ° C./s or more because a slow cooling rate causes a drop in strength due to grain growth. On the other hand, if the cooling rate is extremely high, the production cost is increased. Therefore, it is preferable to cool at a cooling rate of 50 ° C./s or less.

  In addition, after annealing, the shape can be corrected and the rigidity can be further improved by rotating the crystal by processing, so that temper rolling can be performed at an elongation of 0.3% or more.

  In carrying out the invention, steel having a chemical composition corresponding to the intended strength level is melted by a normal converter method, electric furnace method, or the like. The molten steel is hot-rolled after being cast into a slab, as it is, or once cooled and then reheated. At the time of annealing, an overaging treatment may be performed in the middle of cooling, or after cooling, the overaging treatment may be performed by reheating. In the case of producing a hot dip galvanized steel sheet, it can be plated by immersing in hot dip galvanized steel, or after immersing, reheating at 500 ° C. or higher can be performed for alloying treatment of the plating layer.

Steels A to J having the component compositions shown in Table 1 were melted and cast into slabs, and then the slabs were reheated to produce hot rolled steel sheets under the hot rolling conditions shown in Table 2. Here, the Ar ₃ transformation point in Table 1 is an empirical formula obtained by the inventors 900-200 × C ^0.5 + 40 × Si-30 × Mn + 40 × Al-10 × Cr + 30 × Mo-15 × Ni-20 × Cu + 10 × W (However, each element symbol represents the content of each element.) Thereafter, pickling, cold rolling at the rolling reduction shown in Table 2, and heating under the annealing conditions shown in Table 2, after cooling at an average cooling rate of 820 ℃ to 10 ℃ / s Steel plates 1 to 21 were produced. In addition, the steel sheet is aged at 350 ° C. for 150 s during cooling during annealing, or after galvanizing at 470 ° C. during cooling and reheated to 500 to 550 ° C. for alloying treatment. An alloyed hot dip galvanized steel sheet was produced.

Then, the plate thickness cross section of the steel plate was polished and then subjected to Nital corrosion, and the structure was observed with an optical microscope. Three 30 × 30 μm regions were image-processed, and the area ratio of the ferrite phase was measured. In addition, by the above-described method, the average ODF analysis strength f _{1 in} the (111) [1-10] to (111) [-1-12] orientations of the plate surface at a 1/4 plate thickness of the steel plate and (113) [ 1-10] ~ (223) [1-10] was measured average ODF analysis intensities f ₂ of the azimuth. Further, a 10 × 60 mm test piece with 0 °, 45 ° and 90 ° directions as the longitudinal direction with respect to the rolling direction was cut out, and a transverse vibration type resonance frequency measuring device was used, and the standard of American Society for Testing Materials (C1259 ), The Young's moduli E ₀ , E ₄₅ , E ₉₀ (GPa) in the 0 °, 45 ° and 90 ° directions with respect to the rolling direction are measured, and the average Young's modulus Eave [= (E ₀ + 2E ₄₅ + E ₉₀ ) / 4]. Furthermore, a tensile property value in the direction of 90 ° with respect to the rolling direction was obtained at a tensile speed of 1 mm / min using a JIS No. 5 tensile test piece.

The results are shown in Table 2 and FIGS. In the examples of the present invention, TS is 590 MPa or more, Young's modulus E _{90 in the} 90 ° direction with respect to the rolling direction is 230 GPa or more, and average Young's modulus Eave in the 0 °, 45 °, and 90 ° directions with respect to the rolling direction is It can be seen that it is a high-strength steel sheet having a rigidity of 215 GPa or more and excellent in rigidity.

Young's modulus E ₉₀ and average Young's modulus Eave and average ODF analysis strength f _{1 in the} (111) [1-10] to (111) [-1-12] orientation and (113) [1-10] to (223) FIG. 6 is a diagram showing a relationship with an average ODF analysis strength f ₂ in the [1-10] orientation.

Claims (6)

In mass%, C: 0.02 to 0.15%, Si: 0.3% or less, Mn: 1.0 to 3.5%, P: 0.05% or less, S: 0.01% or less, Al: 1.0% or less, N: 0.01% or less, Ti: Containing 0.1 to 1.0%, the content of C, N, S, Ti satisfies the following formula (1), the balance is composed of Fe and inevitable impurities, and has a ferrite single phase microstructure And the average ODF analysis strength f in the (111) [1-10] to (111) [-1-12] orientations of the plate surface at a quarter thickness of the steel plate is 5 or more, (113) [ 1-10] to (223) high-strength steel sheet with excellent rigidity characterized by an average ODF analysis strength f of 3 or more in the [1-10] orientation;
C- (12 / 47.9) × Ti _-1 ≦ 0 ... (1)
Here, [1-10] and [-1-12] represent directions of (1, -1,0) and (-1, -1,2), respectively, and Ti _-1 = Ti- (47.9 / 14) × N- (47.9 / 32.1) × S, and each element symbol in the formula represents the content (% by mass) of each element. Further, it contains at least one element selected from Nb: 0.005 to 0.2% and V: 0.01 to 1.0% by mass%, and instead of the above formula (1), C, N, S, Ti, Nb The high-strength thin steel sheet having excellent rigidity according to claim 1, wherein the V content satisfies the following formula (2):
C- (12 / 47.9) × Ti _-1- (12 / 92.9) × Nb- (12 / 50.9) × V ≦ 0 ... (2)
However, each element symbol in the formula represents the content (% by mass) of each element.   Furthermore, it is characterized by containing at least one element selected from Cr: 0.05-1.0%, Mo: 0.05-1.0%, Ni: 0.05-1.0%, B: 0.0005-0.0030% by mass%. The high-strength thin steel sheet having excellent rigidity according to claim 1 or 2.   4. The high-strength thin steel sheet having excellent rigidity according to any one of claims 1 to 3, further comprising Cu: 0.1 to 2.0% by mass.   5. The high-strength thin steel sheet having excellent rigidity according to any one of claims 1 to 4, further comprising W: 0.1 to 2.0% by mass%. A steel having the composition according to any one of claims 1 to 5 is cast, hot-rolled at a finish rolling finish temperature not lower than the Ar ₃ transformation point, and wound at a winding temperature of 500 ° C or higher. Then, pickling and cold rolling at a reduction rate in the range of 20 to 85%, followed by heating from room temperature to 820 ° C at an average rate of 1 ° C / s or higher when annealing. , A method for producing a high-strength thin steel sheet having excellent rigidity, characterized in that the residence time v (s) satisfies the following formula (3) in a temperature range of 820 to 900 ° C .;

Here, F (w) is the temperature (° C) at an arbitrary time w (s) within the time v (s) that the steel sheet stays in the temperature range of 820 to 900 ° C after it reaches 820 ° C. To express.

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