JP5026327B2 - High-stiffness steel plate and method for manufacturing the same - Google Patents

Description

  The present invention relates to a high-rigidity steel plate used for automobiles and building materials, and a method for manufacturing the same.

In recent years, in order to cope with environmental problems, it has been desired to reduce the weight of automobiles for the purpose of suppressing carbon dioxide emission and reducing fuel consumption. In order to reduce the weight of automobiles, it is effective to increase the strength of steel, but reducing the plate thickness may reduce the rigidity of the member. Therefore, in a member that requires high rigidity, the plate thickness may not be reduced even if the strength of the steel material is increased, and it is difficult to reduce the weight.
As a means for reducing the weight of such a member that requires rigidity, it is effective to use an aluminum alloy plate having a specific gravity lower than that of steel. However, in addition to being expensive, aluminum alloy plates have disadvantages such as inferior workability compared to steel materials and difficulty in welding with steel plates, and application to automobile parts is limited. It has become. Therefore, as a material having the advantages of a steel plate and an aluminum alloy plate, a high Al-containing steel plate in which a large amount of aluminum is added to iron has been proposed (for example, Patent Documents 1 to 5).
Moreover, the technique which raises {110} <001> and raises the torsional rigidity of a steel plate is proposed (for example, patent document 6). However, the technique of Patent Document 6 limits the Al content, and it cannot be said that the effect of reducing the weight of the member is sufficient.

JP 2000-51001 Gazette Japanese Patent Laid-Open No. 2005-015909 JP 2005-273004 A JP 2006-176844 A JP2007-32168A JP 2006-257488 A

In members such as automobiles and building materials, the rolling direction of the steel sheet is often in the longitudinal direction. Conventionally, in order to increase the rigidity of a member, it has been considered effective to set the direction in which the Young's modulus of the steel material is high as the longitudinal direction of the member. Patent Document 5 proposes a steel sheet in which {001} <010> is developed and the shear elastic modulus in the direction perpendicular to the rolling direction and the rolling direction is increased.
However, as a result of the study by the present inventors, depending on the use and shape of the member, the Young's modulus can be increased not in the longitudinal direction of the member but obliquely with respect to the longitudinal direction, specifically in the range of 35 to 75 °. It was found that this is effective in improving the rigidity of the member. The present invention has been made in view of such circumstances, and a high-rigidity steel sheet having an increased Young's modulus in an oblique direction with respect to the rolling direction, rather than the rolling direction of the steel sheet and the width direction perpendicular thereto, and a method for producing the same The issue is to provide

This inventor earnestly examined about the method of raising the Young's modulus of the range of 35-75 degree direction with respect to the rolling direction of a steel plate instead of the rolling direction of a steel plate. As a result, in order to improve the Young's modulus in the range of 35 to 75 ° with respect to the rolling direction of the steel sheet, it is effective to increase the pole density of {110} <001> in the ¼ layer thickness. For this, the inventors have found that the addition of one or more of Bi, Pb, Sb, and Sn is effective by increasing the Al content.
Furthermore, by performing hot-rolled sheet annealing after lowering the finishing temperature and performing hot rolling, or by raising the finishing temperature of hot rolling and performing final annealing after cold rolling, The pole density of {110} <001> was successfully increased to 6 or more, and a steel sheet having a high Young's modulus in the direction of 30 to 75 ° with respect to the rolling direction could be obtained.
The present invention is configured based on such knowledge, and the gist thereof is as follows.

(1) By mass%, C: 0.0003 to 0.250%, Mn: 0.20% to 4.00%, Al: more than 1.50% to 10.00%, Si: 2. It is limited to 20% or less, P: 0.200% or less, S: 0.0500% or less, N: 0.0500% or less, and further by mass%, Bi: 0.001 to 0.300%, Pb: 0 .001 to 0.300%, Sb: 0.001 to 0.300%, Sn: 0.0005 to 0.300%, or one or more of them, the balance being made of Fe and inevitable impurities, A high-rigidity steel plate characterized in that the pole density of {110} <001> in the quarter-thick layer is 6 or more and the plate thickness is 0.5 mm or more.
(2) The high-rigidity steel sheet according to (1), wherein the Young's modulus in the direction of 55 ° with respect to the rolling direction is 235 GPa or more.
(3) Further, by mass%, one or two of Ti: 0.003-0.150%, Nb: 0.003-0.150%, V: 0.003-0.150% should be contained. The high-rigidity steel plate according to (1) or (2).
(4) Further, by mass%, Cr: 0.01 to 3.00%, Ni: 0.01 to 3.00%, Mo: 0.01 to 3.00%, Cu: 0.01 to 3.00 % Of 1 type or 2 types or more, The high-rigidity steel plate of any one of (1)-(3) characterized by the above-mentioned.
(5) The high-rigidity steel sheet according to any one of (1) to (4), further containing B: 0.0001 to 0.0060% by mass%.
(6) Further, by mass%, Ca: 0.001 to 0.010%, Mg: 0.0005 to 0.050%, Zr: 0.001 to 0.200%, REM: 0.001 to 0.050 % Of 1 type or 2 types or more, The high-rigidity steel plate of any one of (1)-(5) characterized by the above-mentioned.

(7) The method according to any one of (1) to (6), wherein the high-rigidity steel plate according to any one of (1) to (6) is manufactured. Is heated to a temperature of 1000 ° C. or higher, hot-rolled to a finish temperature of less than 800 ° C., and subjected to hot-rolled sheet annealing to a maximum temperature of 800 ° C. or higher without cold rolling. A method for producing a high-rigidity steel plate characterized by the above.
(8) A method for producing the high-rigidity steel plate according to any one of (1) to (6), wherein the component according to any one of (1) and (3) to (6) above Is heated to a temperature of 1000 ° C. or higher, the total reduction at 890 ° C. or lower is limited to less than 50%, hot rolling is performed to a finishing temperature of 800 ° C. or higher, and the reduction is 20 to 80%. A method for producing a high-rigidity steel sheet, characterized by performing cold rolling at a rate and subjecting to a final annealing at a maximum temperature of 850 ° C. or higher.

  According to the present invention, a high-rigidity steel plate having excellent formability can be obtained.

As a steel sheet having a high Young's modulus in the direction of 35 to 75 ° with respect to the rolling direction of the steel sheet, a grain-oriented electrical steel sheet is exemplified. However, since the electrical steel sheet has an extremely large amount of Si, it is poor in ductility and cannot be applied to uses that require formability, such as automobile parts.
Therefore, the present inventor has intensively studied to develop a new high-rigidity steel plate. As a result, when one or more of Bi, Pb, Sb, Sn is added to the steel sheet containing Al and the finishing temperature of hot rolling is lowered, the texture is the same as that of the grain-oriented electrical steel sheet. It has been found that a steel sheet can be obtained. That is, the pole density of {110} <001>, which is a crystal orientation effective for improving the Young's modulus in the direction of 35 to 75 ° with respect to the rolling direction, is 6 or more. Moreover, it turned out that it is necessary to raise finishing temperature, when performing cold rolling and final annealing after hot rolling.

Hereinafter, the present invention will be described in detail.
Al is an extremely important element for increasing the pole density of {110} <001> in the present invention. In order to increase the Young's modulus in the direction of 35 to 75 ° with respect to the rolling direction of the steel sheet, it is necessary to add more than 1.50% Al. Al is an effective element for reducing the specific gravity of the steel material, and it is preferable to add 2.00% or more. On the other hand, if the Al content exceeds 10.00%, precipitation of intermetallic compounds becomes remarkable, and hot workability and cold workability deteriorate, so 10.00% is made the upper limit. In order to suppress the decrease in ductility, the Al content is preferably 6.00% or less. A more preferable range of the Al addition amount is 2.50 to 4.50%. Further, when the Al content is less than 2.50%, in order to increase the pole density of {110} <001>,
(Al + Si) ≧ 2.50%
It is preferable to simultaneously add Si so as to satisfy the above.

  Bi, Pb, Sb, and Sn, when added simultaneously with Al, have a remarkable effect of increasing the pole density of {110} <001>, and are important in the present invention. In order to increase the Young's modulus in the direction of 35 to 75 ° with respect to the rolling direction of the steel sheet, Bi, Pb, and Sb each need to be added by 0.001% or more, and Sn by 0.0005% or more. In addition, Bi, Pb, Sb, and Sn all have their effects saturated even if over 0.300% is added. Therefore, in the present invention, Bi: 0.001 to 0.300%, Pb: 0.0010 to 0.300%, Sb: 0.0010 to 0.300%, Sn: 0.0005 to 0.30% It is necessary to add one or two or more. The preferable ranges of the addition amount of Bi, Pb, Sb and Sn are Bi: 0.010 to 0.150%, Pb: 0.010 to 0.150%, Sb: 0.020 to 0.150%, Sn: 0.050 to 0.150%.

  C is an element effective for improving the strength, and in order to obtain the effect, the lower limit of the content needs to be 0.0003% or more. On the other hand, if more than 0.250% of C is added, workability deteriorates, so the upper limit of the C amount is 0.250%. From the viewpoint of cold rollability and formability of the steel sheet, it is better that the amount of C is smaller, and it is preferably 0.100% or less. It is more preferable if it is 0.050% or less, and it is still more preferable if it is 0.020% or less.

Si is a deoxidizing element, but if over 2.20% is added, the hot workability decreases, so the upper limit of Si content is 2.20%. In addition, the upper limit of the Si amount is preferably 2.00% or less from the viewpoint of peelability of scale generated by hot rolling, and is preferably 0.80% or less from the viewpoint of chemical conversion treatment. On the other hand, in order to effectively perform deoxidation, 0.003% or more of Si is preferably added. Moreover, Si is an element useful for increasing the strength of the steel sheet by solid solution strengthening, and it is preferable to contain 0.005% or more.
Furthermore, when Si is contained at the same time as Al, the effect of increasing the extreme density of {110} <001> is exhibited. Therefore, when the amount of Al is particularly small, it is preferable to add so that the total amount of Al and Si is 2.50% or more.

  Mn is an element that forms MnS and suppresses grain boundary embrittlement due to solid solution S, and 0.20% or more is added. Further, Mn is an element effective for increasing the strength of the steel sheet, and addition of 0.50% or more is preferable. On the other hand, when Mn exceeding 4.00% is added, the ferrite becomes unstable, and the pole density of {110} <001> decreases. In order to increase the Young's modulus in the direction of 35 to 75 ° with respect to the rolling direction of the steel sheet, the amount of Mn added is preferably 3.00% or less. A more preferable range of the amount of Mn added is 0.55 to 2.60%.

  P is an impurity, and segregates at the crystal grain boundaries to lower the grain boundary strength, so the upper limit is made 0.200%. However, if P is reduced to less than 0.001%, the manufacturing cost increases. Further, since P is an element effective for strengthening, it is preferable to contain 0.005% or more of P in order to increase the strength. In order to suppress secondary work brittleness resistance and toughness deterioration due to P segregation, the upper limit is preferably made 0.080% or less. Furthermore, in order to suppress the deterioration of workability, it is preferable to make it 0.040% or less.

  In the present invention, S is an impurity element that deteriorates hot workability, and the upper limit is 0.0500%. Moreover, in order to suppress a reduction in toughness and improve cold workability, the upper limit of the amount of S is preferably set to 0.0150% or less. The lower limit of the amount of S is not limited, but if S is reduced to less than 0,0005%, the manufacturing cost increases.

  N is an impurity element, and when it exceeds 0.0500%, toughness deteriorates. In particular, since the steel sheet of the present invention has a high Al content and Al-based nitrides are likely to be coarsened, the preferable upper limit of the N content is 0.0150% or less, and more preferably 0.0040% or less. On the other hand, fine Al-based nitrides are effective in increasing the pole density of {110} <001>, and it is preferable to contain 0.0005% or more of N. In order to increase the Young's modulus in the direction of 35 to 75 ° with respect to the rolling direction of the steel sheet, when an Al-based nitride is used, a particularly preferable range of the N amount is 0.0010 to 0.0030%.

  Furthermore, in order to enhance strength, ductility, toughness and manufacturability, one or two of Ti, Nb, V, Cr, Ni, Mo, Cu, B, Ca, Mg, Zr, and REM depending on the required characteristics The above may be added.

  Ti, Nb, and V are elements that generate precipitates and contribute to strengthening, and it is preferable to add one or two or more of each in an amount of 0.003% or more. Moreover, since Ti, Nb, and V also have the effect of improving castability, the preferable lower limit of the addition amount is 0.012% or more, respectively. On the other hand, when Ti, Nb, and V are added in excess of 0.150%, the crystal grains may be refined and the workability may be reduced. Further, in order to prevent a decrease in Young's modulus in the direction of 35 to 75 ° with respect to the rolling direction of the steel sheet, it is more preferable that the upper limit of each of Ti, Nb, and V is 0.050%. Since Ti is an element that forms sulfide with S, it is preferably added so that Ti / S <1.

  Cr, Ni, Mo, and Cu are effective elements for improving ductility and toughness, and it is preferable to add one or more elements each in an amount of 0.01% or more. On the other hand, if adding more than 3.00% of Cr, Ni, Mo and Cu, respectively, ductility and toughness may be deteriorated, so the upper limit of the content of each element is preferably set to 3.00%. More preferable ranges of Cr, Ni, Mo, and Cu are 0.10% to 1.40%, respectively.

  B is an element that segregates at the grain boundary and improves the grain boundary bonding force. In order to suppress grain boundary segregation of P and S and increase grain boundary strength, 0.0001% or more of B is preferably added. Furthermore, in order to improve ductility, toughness, and hot workability, 0.0003% or more is preferably added. On the other hand, the effect is saturated even if B exceeding 0.0060% is added. Moreover, since coarse precipitates may be generated at the grain boundaries and the hot workability may deteriorate, the upper limit of the B content is preferably 0.0025% or less.

  Ca, Mg, Zr, and REM are all elements that control the form of sulfides and are effective in suppressing deterioration of hot workability and toughness, and it is preferable to add one or more of them. In order to obtain this effect, it is preferable to add 0.001% or more of Ca, 0.0005% or more of Mg, 0.001% or more of Zr, and 0.001% or more of REM. On the other hand, if Ca is added in excess of 0.010%, Mg is 0.050%, Zr is 0.200%, and REM exceeds 0.050%, toughness may deteriorate.

Next, the structure of the high-rigidity steel plate of the present invention will be described.
Since the high-rigidity steel sheet of the present invention contains more than 1.50% Al, ferrite becomes stable. When the total area ratio of the second phase of the structure other than ferrite, such as austenite, bainite, martensite, pearlite, carbide, and other compounds exceeds 20%, the {110} <001> pole in the ¼ layer thickness The density may decrease. Therefore, in the present invention, the area ratio of ferrite is preferably 80% or more. The area ratio of ferrite is preferably 90% or more, and more preferably 98% or more.

  The structure other than ferrite, that is, the balance is composed of one or more of austenite, bainite, martensite, pearlite, cementite, carbide, nitride, an intermetallic compound mainly composed of Al and Fe, and other compounds. . The area ratio of the ferrite and the remaining structure can be observed by an optical microscope or a scanning electron microscope, and can be measured by a point calculation method. In addition, carbides, nitrides, intermetallic compounds mainly composed of Al and Fe, and other compounds can be identified by a method of analyzing the amount of residue extracted by an electrolytic extraction method, X-ray diffraction, or the like.

  In addition, in this invention, the area ratio of a ferrite is 10 visual fields by the optical microscope or a scanning electron microscope about 1/4 part of the plate | board thickness in the plate | board thickness cross section (L cross section) parallel to the rolling direction of a steel plate. It is defined as the average value when observed.

  The average crystal grain size of ferrite is not particularly limited, but in order to increase the pole density of {110} <001> in the 1/4 layer thickness, it is preferable that the crystal grains are grown to 100 μm or more. When crystal grains having {110} <001> are grown, the pole density in the orientation becomes higher. Therefore, it is preferable that the average crystal grain size of ferrite is larger, specifically, 200 μm or more, further 500 μm or more. It is preferable.

  {110} <001> is an orientation that increases the Young's modulus in the direction of 35 to 75 ° with respect to the rolling direction. When the pole density of {110} <001> in the ¼ layer thickness is 6 or more, the Young's modulus in the 55 ° direction with respect to the rolling direction can be increased to 235 GPa or more. This is because when <110} <001> develops, <111> orientations accumulate in the direction of 35 to 75 ° with respect to the rolling direction. Therefore, the Young's modulus in the direction of 55 °, which is substantially the center in the direction of 35 to 75 °, can be reliably set to 235 GPa or more. The preferable lower limit of the pole density of {110} <001> in the 1/4 layer thickness is 8 or more, more preferably 10 or more.

  The pole density (X-ray random intensity ratio) of {110} <001> is based on a plurality of pole figures among {110}, {100}, {211}, {310} pole figures measured by X-ray diffraction. It can be obtained from the three-dimensional texture (ODF) calculated by the series expansion method. That is, in order to obtain the pole density of each crystal orientation, it is represented by the intensity of (110) [001] in the φ2 = 45 ° cross section of the three-dimensional texture.

  The sample for X-ray diffraction is manufactured as follows. The steel plate is polished to a predetermined position in the plate thickness direction by mechanical polishing or chemical polishing, and finished to a mirror surface by buffing, and then the distortion is removed by electrolytic polishing or chemical polishing, and at the same time, the 1/4 layer thickness is measured as the measurement surface. Adjust so that In addition, since it is difficult to accurately set a ¼ layer thickness as a measurement surface, samples are prepared so that the measurement surface is within a range of ± 5% of the plate thickness with these target layers as the center. do it.

  Further, when X-ray measurement is difficult, a statistically sufficient number of measurements are performed using an electron backscattering pattern (EBSP) or an electron channeling pattern (ECP). In addition, {hkl} <uvw> means that when an X-ray sample is collected by the above-described method, the crystal orientation perpendicular to the plate surface is <hkl> and the rolling direction is <uvw>.

  Further, the pole density of {111} <112> and {111} <110> in the 1/4 layer thickness, that is, (111) [1-21] and (111) [0] in the φ2 = 45 ° cross section of the ODF. −11] is an orientation that improves the average Young's modulus, and is preferably 1.5 or more. Furthermore, the pole density of {110} <110> is an orientation that increases the Young's modulus in the rolling direction, and is preferably 1.5 or more.

  On the other hand, the pole density of {001} <010>, that is, the pole density of (001) [0-10] in the ODF φ2 = 45 ° cross section is not particularly limited, but decreases the Young's modulus in the direction perpendicular to the rolling direction. Therefore, it is preferably less than 2.5, more preferably 2.0 or less.

  The above-mentioned limitation regarding the pole density is satisfied at least for a quarter-thickness layer, and in practice, it is preferable to hold not only the quarter-layer but also a wide range from the thickness-thickness surface layer to the central layer.

  The steel plate of the present invention has high rigidity, is mainly used for automobiles and building materials, and contributes to improving the rigidity of automobile members and buildings. Therefore, it is necessary to make the steel sheet thickness 0.5 mm or more. It is. The upper limit is not limited, but it is 8.0 mm or less at best from the viewpoint of use. Further, in hot rolling, it is difficult to make the plate thickness less than 0.5 mm, and it is difficult to accumulate {110} <001> when the rolling reduction ratio of cold rolling is increased. In addition, from the viewpoint of manufacturability, the thickness of the hot-rolled steel sheet not subjected to cold rolling is preferably 2.0 mm or more, and when a thinner thickness is required, it is manufactured by cold rolling and final annealing. It is preferable.

  When the pole density of {110} <001> in the ¼ layer thickness of the steel sheet is increased to 6 or more, the Young's modulus in the 55 ° direction (referred to as the 55 ° direction) with respect to the rolling direction can be set to 235 GPa or more. . The Young's modulus in the 55 ° direction is preferably 245 GPa or more, and more preferably 260 GPa or more in order to increase the rigidity of the member.

  {110} <001> is an orientation that increases the Young's modulus in the 55 ° direction but decreases the Young's modulus in the rolling direction. Therefore, when the Young's modulus in the 55 ° direction is 235 GPa or more, the Young's modulus in the rolling direction is relatively lowered and may be less than 210 GPa. Furthermore, when the Young's modulus in the 55 ° direction is increased to 245 GPa or more and 260 GPa or more, the Young's modulus in the rolling direction may decrease to less than 190 GPa or less than 170 GPa, respectively.

  The Young's modulus in the direction perpendicular to the rolling direction (referred to as the C direction) is not particularly limited. However, when the Young's modulus in the 55 ° direction is 235 GPa or more, the Young's modulus in the C direction is 180 GPa or more. The Young's modulus in the C direction increases to 190 GPa or more and 200 GPa or more as the Young's modulus in the 55 ° direction is improved to 245 GPa or more, and further to 260 GPa or more. In addition, Young's modulus becomes the maximum within the range of 45-65 degrees with respect to a rolling direction by in-plane anisotropy.

The Young's modulus is measured by a transverse resonance method at room temperature in accordance with JIS Z 2280. In other words, vibration is applied without fixing the sample, the frequency of the oscillator is gradually changed, the primary resonance frequency is measured, and the Young's modulus is calculated from the following equation.
E = 0.946 x (l / h) ³ x m / w x f ²
Here, E: dynamic Young's modulus [GPa], l: length of test piece [m], h: thickness of test piece [m], m: mass [kg], w: width of test piece [m] ], F: primary resonance frequency [s ⁻¹ ] of the transverse resonance method.

  The shear modulus G [GPa] is not particularly limited, but the shear modulus in the rolling direction and the direction perpendicular to the rolling direction is preferably 90 GPa or more, and more preferably 100 GPa. The shear modulus can be calculated according to the American Society for Testing and Materials (ASTM) standard (C1259) as described in Patent Documents 5 and 6.

  In addition, although it does not specifically limit about the tensile strength of a steel plate, Since toughness will fall if it is 1300 Mpa or more, it is preferable to set it as less than 1300 Mpa.

Next, the manufacturing method of the highly rigid steel plate of this invention is demonstrated.
The steel sheet of the present invention is manufactured by hot rolling a steel slab and annealing the obtained hot-rolled sheet, or after hot rolling and further cold rolling and final annealing. In the present invention, the production method preceding hot rolling is not particularly limited. In other words, following smelting with a blast furnace, converter, electric furnace, etc., the components are adjusted so that the desired component content is obtained by various secondary scouring, and then, in addition to normal continuous casting, casting by ingot method, thin slab What is necessary is just to cast by methods, such as casting. Scrap may be used as a raw material. In the case of a slab obtained by continuous casting, it may be directly sent to a hot rolling mill as it is a high-temperature slab, or may be hot-rolled after being reheated in a heating furnace after being cooled to room temperature.
In hot rolling, a sheet bar may be joined between rough rolling and finish rolling, and finish rolling may be performed continuously. At that time, the coarse bar may be wound once in a coil shape, stored in a cover having a heat retaining function as necessary, and rewound again before joining.

  If the heating temperature for hot rolling is less than 1000 ° C., the rolling load becomes excessive and the productivity may be impaired. The upper limit of the heating temperature is not particularly limited, but it is difficult to set the temperature above 1450 ° C., and the upper limit is substantially 1400 ° C. due to equipment limitations. In order to heat a steel piece uniformly, more than 1250 degreeC-1350 degreeC is a more preferable range.

  When hot-rolled sheet annealing is performed after hot rolling without performing cold rolling, the finishing temperature of hot rolling is lowered so that strain introduced by hot rolling does not disappear due to recovery or recrystallization. When the hot rolling finish temperature is less than 800 ° C. and hot rolled sheet annealing is performed without performing cold rolling, {110} <001> accumulates due to strain introduced by hot rolling, and the Young's modulus in the 55 ° direction Can be increased. When cold rolling is not performed, the finishing temperature is preferably less than 750 ° C. in order to reduce the finishing temperature of hot rolling and introduce strain. On the other hand, when rolling at less than 500 ° C., the rolling load becomes excessive and the productivity is impaired, so the lower limit of the finishing temperature is preferably 500 ° C. or more.

  If the rolling reduction at less than 800 ° C. is 30% or more, {110} <001> can be further developed. Moreover, since recrystallization will be accelerated | stimulated when the rolling reduction in less than 800 degreeC becomes excessive, it is preferable to set it as 80% or less. The rolling reduction at less than 800 ° C is more preferably 40 to 70%.

  When not performing cold rolling after hot rolling, the maximum temperature of hot-rolled sheet annealing is set to 800 ° C. or higher. By this hot-rolled sheet annealing, recrystallization using a strain introduced by hot rolling with a finishing temperature of less than 800 ° C. as a driving force, followed by grain growth, and {110} <001> developed into a texture It becomes possible to do. In order to promote grain growth and increase the pole density of {110} <001>, the maximum temperature of hot-rolled sheet annealing is preferably 850 ° C. or higher. Although the upper limit of the maximum temperature of hot-rolled sheet annealing is not limited, when performing continuous annealing, 1000 degrees C or less is preferable from a viewpoint of productivity.

  When cold rolling is performed after hot rolling and final annealing is performed, the finishing temperature is set to 800 ° C. or higher so that excessive strain is not introduced by hot rolling. If the finishing temperature is set to 800 ° C. or higher, recrystallization is not excessively promoted by the final annealing after cold rolling, so that the extreme density of {110} <001> can be increased. In order to suppress the generation of scale on the surface, the finishing temperature is preferably 1050 ° C. or lower. In addition, when the final annealing is performed by performing cold rolling after hot rolling, the upper limit of the hot rolling finishing temperature may be determined as appropriate depending on the heating temperature and the rolling schedule, and is not particularly limited.

Furthermore, in the present invention, in order to suppress the introduction of strain in hot rolling, the total reduction amount at 890 ° C. or lower is limited to less than 50%. Furthermore, the total amount of reduction at 890 ° C. or lower is preferably less than 40%. However, the finish rolling of the hot rolling is preferably 900 ° C. or higher in order to suppress the introduction of strain. Thus, when the finishing temperature is higher than 890 ° C., the total reduction amount at 890 ° C. or lower Is 0%. Note that the total amount of reduction at 890 ° C. or lower is the plate thickness t ₀ at 890 ° C., the plate thickness t ₁ after completion of hot rolling,
{(T ₀ −t ₁ ) / t ₀ } × 100 (%)
Is required.

  If the rolling reduction of the cold rolling is less than 20%, the introduction of strain is insufficient, and the pole density of {110} <001> decreases after annealing. On the other hand, when the rolling reduction of cold rolling exceeds 80%, the introduction of strain becomes excessive, recrystallization is promoted, and the final density of {110} <001> is lowered after the final annealing. In order to increase the pole density of {110} <001> and increase the Young's modulus in the 55 ° direction, the rolling reduction of cold rolling is more preferably 30 to 70%, and further preferably 35 to 65%. Note that the temperature of the steel sheet may rise during cold rolling, but this temperature is usually less than 100 ° C. and is less than 200 ° C. even when subjected to a large reduction.

  The heating temperature of the final annealing following the cold rolling is set to 850 ° C. or higher in order to promote grain growth and develop {110} <001>. In order to increase the pole density of {110} <001>, the heating temperature of the final annealing is preferably 900 ° C. or higher, and more preferably 950 ° C. or higher. Although the upper limit of the maximum temperature of final annealing is not limited, when performing continuous annealing, 1100 degrees C or less is preferable from a viewpoint of productivity.

  In the case of performing cold rolling, annealing before cold rolling may be performed before cold rolling, or one or more intermediate annealings may be performed during the cold rolling. This has the effect of reducing the cold rolling load and avoiding troubles such as cracks during cold rolling, as well as promoting the development of {110} <001> texture.

700-1200 degreeC is preferable and, as for the highest temperature of annealing before cold rolling and intermediate annealing, 800-1000 degreeC is more preferable. Further, from the economical viewpoint, it is preferable to perform the annealing before cold rolling and the intermediate annealing at a maximum temperature of 900 ° C. or less.
Moreover, you may perform the annealing before cold rolling which makes a maximum temperature 700-1200 degrees C or less before cold rolling. Thus, in addition to the effect of reducing the cold rolling load and avoiding troubles such as cracks during cold rolling, the development of {110} <001> can be promoted. The preferable range of the maximum temperature of annealing before cold rolling is 800-1000 degreeC.

  In addition, when performing annealing before cold rolling and intermediate annealing, let the rolling reduction of the cold rolling immediately before the last annealing be in the above-mentioned range, that is, 20 to 80%, preferably 30 to 70%.

  It is preferable to perform pickling after hot rolling both when hot-rolled sheet annealing is performed after hot rolling without performing cold rolling, and when cold rolling is performed after hot rolling and final annealing is performed. Moreover, although it does not specifically limit about the heating rate of hot-rolled sheet annealing and final annealing, In order to raise the extreme density of {110} <001> and to raise the Young's modulus of a 55 degree direction, between 500-800 degreeC. The average heating rate is preferably 100 ° C./h or less.

  Furthermore, you may give various plating to the surface of a steel plate. In addition to zinc-based plating, Al-based plating may be applied as necessary. In the case of hot dip plating, the steel sheet may be immersed in a predetermined plating bath on the assumption of cooling after the final annealing, and reheated as necessary to be alloyed. Alternatively, after annealing, after completion of cooling, the steel plate may be heated again and then immersed in a plating bath. Electroplating may be performed after the final annealing.

引張試験は、ＪＩＳ Ｚ ２２４１に準拠して行った。｛１１０｝＜００１＞の極密度は、板厚１／４が測定面になるように試験片を採取し、Ｘ線回折法によって測定した。ヤング率の測定は、ＪＩＳ Ｚ ２２８０に準拠した横共振法によって行った。
結果を表２に示す。

表２から明らかなように、本発明の成分を有する鋼を適切な条件で熱延、焼鈍した場合には、｛１１０｝＜００１＞の極密度が高くなり、圧延方向から斜めの方向、特に５５°方向のヤング率が高くなっている。
一方、鋼Ｎｏ．ＡはＢｉ、Ｐｂ、Ｓｎ、Ｓｎを含有せず、鋼Ｎｏ．ＤはＡｌ量の含有量が少ないため、｛１１０｝＜００１＞の極密度が低い。また、製造Ｎｏ．Ｂ−２およびＣ−５は熱間圧延の仕上温度が高く、製造Ｎｏ．Ｂ−１、Ｃ−４およびＪ−３は熱延板焼鈍の最高温度が低いため、｛１１０｝＜００１＞の極密度が低下している。 Steel having the composition shown in Table 1 was melted and cast into steel pieces. Among these, using steel A, B, C, D, J, hot rolling and subsequent annealing were performed under the conditions shown in Table 2. The obtained steel plate having a thickness of 3.0 mm was subjected to skin pass rolling with a reduction ratio of 0.5%, and then tensile properties in the direction perpendicular to the rolling direction (C direction), pole density of {110} <001>, and various The Young's modulus in the direction of was measured.

The tensile test was conducted in accordance with JIS Z 2241. The pole density of {110} <001> was measured by an X-ray diffraction method by collecting a test piece so that the plate thickness ¼ becomes a measurement surface. The Young's modulus was measured by a transverse resonance method based on JIS Z 2280.
The results are shown in Table 2.

As is apparent from Table 2, when the steel having the components of the present invention is hot-rolled and annealed under appropriate conditions, the pole density of {110} <001> increases, and the direction oblique from the rolling direction, particularly The Young's modulus in the 55 ° direction is high.
On the other hand, Steel No. A does not contain Bi, Pb, Sn, or Sn. Since D has a small content of Al, the extreme density of {110} <001> is low. In addition, production No. B-2 and C-5 have high hot rolling finishing temperatures. Since B-1, C-4 and J-3 have a low maximum temperature for hot-rolled sheet annealing, the pole density of {110} <001> is lowered.

表３から明らかなように、本発明の成分を有する鋼を適切な条件で熱延、焼鈍した場合には、｛１１０｝＜００１＞の極密度が高くなり、圧延方向から斜めの方向、特に５５°方向のヤング率が高くなっている。
一方、鋼Ｎｏ．Ａおよび鋼Ｎｏ．ＯはＢｉ、Ｐｂ、Ｓｎ、Ｓｎを含有せず、鋼Ｎｏ．ＤはＡｌ量が少なく、鋼Ｎｏ．ＭはＭｎ量が多いため、いずれも｛１１０｝＜００１＞の極密度が低下している。また、鋼Ｎｏ．ＨはＳｉ量が多く、冷間圧延時に割れが生じ、鋼Ｎｏ．ＮはＡｌ量が多く、熱間圧延にて割れが生じたため、以後の試験を中止した。
製造Ｎｏ．Ｅ−２は、熱間圧延の仕上温度が低く、８９０℃以下での総圧下量が大きいため、製造Ｎｏ．Ｇ−１はさらに最終焼鈍の最高温度も低いため、｛１１０｝＜００１＞の極密度が低下している。製造Ｎｏ．Ｂ−４は８９０℃以下での総圧下量が大きく、製造Ｎｏ．Ｋ−２はさらに冷間圧延の圧下率も小さいため、｛１１０｝＜００１＞の極密度が低下している。製造Ｎｏ．Ｂ−６、Ｄ−３およびＪ−５は、冷間圧延の圧下率が範囲外であるため、｛１１０｝＜００１＞の極密度が低下している。製造Ｎｏ．Ｃ−６およびＬ−３は、最終焼鈍の最高温度が低いため、｛１１０｝＜００１＞の極密度が低下している。 A steel slab having the composition shown in Table 1 was subjected to cold rolling and final annealing after hot rolling under the conditions shown in Table 3. Some steel plates were subsequently hot dip galvanized. At this time, the temperature of the hot dip galvanizing bath was set to 460 ° C. The heating temperature of the hot-rolled steel slab was 1230 ° C. The tensile properties in the direction perpendicular to the rolling direction of the obtained steel plate having a thickness of 1.2 mm, the pole density of {110} <001>, and the Young's modulus in various directions were measured in the same manner as in Example 1.
The results are shown in Table 3.

As is apparent from Table 3, when the steel having the components of the present invention is hot-rolled and annealed under appropriate conditions, the pole density of {110} <001> increases, and the direction oblique from the rolling direction, particularly The Young's modulus in the 55 ° direction is high.
On the other hand, Steel No. A and steel no. O does not contain Bi, Pb, Sn, or Sn. D has a small amount of Al. Since M has a large amount of Mn, the extreme density of {110} <001> is reduced in all cases. Steel No. H has a large amount of Si and cracks occur during cold rolling. Since N had a large amount of Al and cracked during hot rolling, the subsequent test was stopped.
Production No. Since E-2 has a low finishing temperature in hot rolling and a large total rolling amount at 890 ° C. or less, the production No. Since G-1 also has a lower final annealing maximum temperature, the pole density of {110} <001> is lowered. Production No. B-4 has a large total rolling amount at 890 ° C. or lower, and production No. Since K-2 also has a small cold rolling reduction, the extreme density of {110} <001> is lowered. Production No. In B-6, D-3 and J-5, the reduction ratio of the cold rolling is out of the range, so the extreme density of {110} <001> is lowered. Production No. In C-6 and L-3, since the maximum temperature of the final annealing is low, the extreme density of {110} <001> is lowered.

Claims (8)

% By mass
C: 0.0003 to 0.250%,
Mn: 0.20% to 4.00%,
Al: more than 1.50% to 10.00%
Containing
Si: 2.20% or less,
P: 0.200% or less,
S: 0.0500% or less,
N: It is limited to 0.0500% or less, and further in mass%,
Bi: 0.001 to 0.300%,
Pb: 0.001 to 0.300%,
Sb: 0.001 to 0.300%,
Sn: 0.0005 to 0.300%
1 or 2 or more, and the balance consists of Fe and inevitable impurities, the {110} <001> pole density in the ¼ layer thickness is 6 or more, and the plate thickness is 0.5 mm or more A high-rigidity steel sheet characterized by   The high-rigidity steel sheet according to claim 1, wherein the Young's modulus in the 55 ° direction with respect to the rolling direction is 235 GPa or more. In addition,
Ti: 0.003 to 0.150%,
Nb: 0.003 to 0.150%,
V: 0.003-0.150%
The high-rigidity steel plate according to claim 1 or 2, comprising one or two of the following. In addition,
Cr: 0.01 to 3.00%,
Ni: 0.01 to 3.00%,
Mo: 0.01 to 3.00%
Cu: 0.01 to 3.00%
The high-rigidity steel plate according to any one of claims 1 to 3, comprising one or more of the following. In addition,
B: 0.0001 to 0.0060%
The high-rigidity steel plate according to claim 1, comprising: In addition,
Ca: 0.001 to 0.010%,
Mg: 0.0005 to 0.050%,
Zr: 0.001 to 0.200%,
REM: 0.001 to 0.050%
The high-rigidity steel plate according to any one of claims 1 to 5, comprising one or more of the following.   A method for producing the high-rigidity steel plate according to any one of claims 1 to 6, wherein the steel slab having the component according to any one of claims 1 and 3 to 6 is heated to a temperature of 1000 ° C or higher. To produce a high-rigidity steel sheet characterized by performing hot rolling to a finish temperature of less than 800 ° C. and performing hot-rolled sheet annealing to a maximum temperature of 800 ° C. or higher without performing cold rolling. Method.   A method for producing the high-rigidity steel plate according to any one of claims 1 to 6, wherein the steel slab having the component according to any one of claims 1 and 3 to 6 is heated to a temperature of 1000 ° C or higher. The total rolling amount at 890 ° C. or lower is limited to less than 50%, hot rolling is performed with a finishing temperature of 800 ° C. or higher, cold rolling is performed at a rolling reduction rate of 20 to 80%, and the maximum temperature is reached. A method for producing a high-rigidity steel sheet, characterized by performing final annealing at a temperature of 850 ° C. or higher.