WO2011087107A1 - Cold-rolled steel plate and method for producing same - Google Patents
Cold-rolled steel plate and method for producing same Download PDFInfo
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- WO2011087107A1 WO2011087107A1 PCT/JP2011/050586 JP2011050586W WO2011087107A1 WO 2011087107 A1 WO2011087107 A1 WO 2011087107A1 JP 2011050586 W JP2011050586 W JP 2011050586W WO 2011087107 A1 WO2011087107 A1 WO 2011087107A1
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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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- 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
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0236—Cold rolling
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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
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0273—Final recrystallisation annealing
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
Definitions
- the present invention relates to a cold-rolled steel sheet excellent in formability, shape freezing property, and actual machine manufacturing stability, which is optimal as a member of a large flat plate-like component such as a backlight chassis of a large-sized liquid crystal television and a manufacturing method thereof.
- Thin flat panel TVs and office automation equipment use a large number of flat-shaped parts formed by processing mainly bending and stretching.
- the members (materials) used for these parts often require flatness in addition to the degree of processing into the part shape from the viewpoints of product design and thickness reduction.
- flatness tends to deteriorate when bending / extrusion molding is performed on a flat plate surface of a member (material).
- Such deterioration of flatness is a phenomenon that occurs due to poor shape freezing property of the member (material) when the member (material) is press-molded. Shape freezing property is required.
- ridge warpage that occurs during bending is well known.
- Patent Document 1 discloses a technique for developing a cold-rolled steel sheet having a yield strength of 150 MPa and an r value of 0.67 in the rolling direction (a direction perpendicular to the rolling direction of 1.45).
- Patent Document 2 discloses a ferritic thin steel sheet for automobiles having a good shape freezing property in which the ratio of ⁇ 100 ⁇ plane and ⁇ 111 ⁇ plane parallel to the plate surface is 1.0 or more.
- Patent Document 3 in order to obtain a ferritic steel sheet having excellent shape freezing property, the strength of ⁇ 100 ⁇ ⁇ 011> to ⁇ 223 ⁇ ⁇ 110> orientation group and ⁇ 112 ⁇ ⁇ 110>, ⁇ 554 ⁇ ⁇ 225>, ⁇ 111 ⁇ ⁇ 112>, ⁇ 111 ⁇ ⁇ 110>, controlling the strength of each direction, at least one of the r value in the rolling direction and the r value in the direction perpendicular to the rolling direction is 0.7. The following is disclosed.
- Patent Documents 1 to 3 disclose a case where the cold rolling rate of the cold rolled steel sheet is low, specifically, the case where the r value is lowered to 40%, but the extremely low cold rolling of about 40% is disclosed.
- the plate shape deteriorates and the flatness of the final product deteriorates.
- manufacture of the thin steel plate about 1.0 mm or less becomes difficult.
- ultra-low carbon steel which is easy to obtain high ductility and is less prone to stretcher strain that causes forming breakage and wrinkling during press molding.
- extremely low carbon steel sheets such as Ti-based IF steels need to have a low r value because recrystallized grains that are advantageous for increasing the r value easily grow in the annealing process.
- annealing is performed at a low temperature at which recrystallization is difficult but grain growth is difficult, and for this purpose, it is necessary to control the annealing conditions under conditions where the soaking temperature exhibits a variation of only a few degrees Celsius. .
- An object of the present invention is to provide a cold-rolled steel sheet having excellent shape freezing property and excellent actual machine manufacturing stability, and a method for manufacturing the same.
- the r value is controlled while maintaining high ductility in the annealed sheet after cold rolling. is important. That is, by increasing the average elongation, it is possible to ensure the shape required for the part while ensuring the workability during drawing and overhanging. Furthermore, by reducing the r value in the three directions of the rolling direction, the direction perpendicular to the rolling direction, and the rolling 45 ° direction, and setting the average r value within a range that defines the average r value, the longitudinal direction becomes the rolling 45 ° direction.
- a method for producing a cold-rolled steel sheet is characterized in that annealing is performed for 30 to 200 seconds at a soaking temperature of (820 + Nb / 15 + B-CR) to 860 ° C., and then cooled.
- the cold-rolled steel sheet targeted by the present invention includes a steel sheet obtained by subjecting the cold-rolled steel sheet to surface treatment such as electrogalvanizing or hot dip galvanizing. Further, it includes a steel plate having a film formed thereon by chemical conversion treatment or the like.
- the steel sheet of the present invention can be widely used as a general member for home appliances that bends, projects, and slightly draws flat surfaces such as a large-screen TV backlight chassis, refrigerator panel, and air conditioner outdoor unit.
- the backlight chassis about 650x500 mm (32V type) or more can be manufactured, for example with the steel plate of plate
- a cold-rolled steel sheet having excellent formability and shape freezing property that can be drawn, bent, and stretched is obtained.
- the cold-rolled steel plate excellent in formability and shape freezing property can be stably manufactured with an actual machine, without controlling the soaking temperature at the time of annealing pinpoint.
- a flat plate shape required for a large component can be secured, and a member such as a backlight chassis of a large liquid crystal television can be manufactured.
- C 0.0010 to 0.0030% Since C has an effect of reducing the r value, it is desirable to add a large amount from the viewpoint of lowering the r value, and it is 0.0010% or more. However, excessive addition leads to stretcher strain that causes wrinkles during press molding, and at the same time, the steel sheet becomes stronger due to solid solution strengthening and dispersion strengthening due to the formation of carbides, and the elongation decreases. Therefore, C is 0.0010% or more and 0.0030% or less.
- Si 0.05% or less Si is an element having a high solid solution strengthening ability, increases the yield strength, and greatly reduces the elongation. Therefore, it is made 0.05% or less.
- Mn 0.1 to 0.3%
- Mn is an element that forms a sulfide and improves hot brittleness. In order to obtain this effect, addition of 0.1% or more is necessary. On the other hand, the upper limit is made 0.3% in order to increase yield strength and deteriorate ductility because it is an element with high solid solution strengthening ability.
- P 0.05% or less
- P is a solid solution strengthening element, which increases yield strength and degrades ductility. Therefore, it is made 0.05% or less.
- S 0.02% or less S forms sulfides at the stage of hot rolling and causes deterioration of ductility. Therefore, it is made 0.02% or less.
- Al 0.02 to 0.10%
- Al has a strong affinity with N, and has an effect of reducing the amount of solute N during the cold rolling process and suppressing age hardening.
- the precipitated AlN has a high tendency to precipitate finely and suppresses the grain growth in the annealing process.
- addition of 0.02% or more is necessary.
- excessive addition leads to an increase in production cost, and during hot rolling, the temperature at which austenite is transformed into ferrite is raised, so that it is difficult to finish rolling in the austenite region. Therefore, Al needs to be 0.10% or less.
- N 0.005% or less When N is contained in a large amount, it dissolves in steel and causes stretcher strain. Therefore, it is made 0.005% or less.
- Nb 0.010 to 0.030% Nb fixes solute C as a precipitate and suppresses stretcher strain. Furthermore, NbC, which is a precipitate, tends to precipitate finely and suppress grain growth during annealing. In order to obtain these effects, it is necessary to add 0.010% or more. However, when excessively added, the recrystallization temperature is excessively increased. In addition, the cost increases. Therefore, the upper limit is made 0.030%.
- B 0.0010 ⁇ B ⁇ 11 / 14 ⁇ N ⁇ 0.0050% (in the case of adding Ti, 0.0015 ⁇ B ⁇ 11 ⁇ (
- B is an element that is an important requirement in the present invention.
- B suppresses the grain growth of ferrite in the annealing process after cold rolling, and controls the r value even at a high soaking temperature. It is possible to do.
- solute B is present in an amount of 0.0010% or more after BN is precipitated at a high temperature during hot rolling.
- the present invention can contain Ti in the range of 0.005% to 0.020% for the following purpose.
- Ti has a strong affinity with N and forms precipitates at high temperatures, and has the effect of suppressing solid solution strengthening of solid solution N and dispersion strengthening due to fine precipitation of AlN.
- it can also be added when it is desired to particularly improve the elongation. In order to exhibit these effects, it is desirable to add 0.005% or more.
- excessive addition not only promotes precipitation of TiC and reduces the effect of suppressing grain growth during annealing with NbC, but also causes an increase in manufacturing cost. Therefore, the upper limit in the case of addition is 0.020%.
- the upper limit in the case of addition is 0.020%.
- the other components are composed of iron and inevitable impurities.
- Inevitable impurities include, for example, 0.05% or less of Cu and Cr that are easily mixed from scrap, and 0.01% or less of Sn, Mo, W, V, Ni, and the like.
- the steel sheet of the present invention has an average elongation of 42% or more determined by the following formula (a).
- Elongation has a good correlation with moldability, and the larger the elongation, for example, the higher the stretch molding. Therefore, the larger the required elongation, the better, and by increasing the average elongation to 42% or more, drawing and overhanging can be performed, and the shape required for the parts can be ensured.
- the average total elongation can be measured and determined by the following method. A JIS No. 5 tensile test piece is cut out from the rolling direction, the 45 ° direction of rolling, and the direction perpendicular to the rolling direction, and a tensile test based on JIS Z 2241 is performed.
- the steel sheet of the present invention has an average r value of 1.2 to 1 determined by the following formula (b) .6.
- the r value correlates with the warpage that occurs after bending or stretch forming. In bending, the r value in the bending direction is increased, so that saddle-shaped warpage occurs remarkably along the bending line.
- the use of a high r-value material makes the material inflow from the flange portion around the overhang portion remarkable, and residual stress and distortion occur in the flange portion. Therefore, for the purpose of improving the shape freezing property after press molding by lowering the r value, the average r value is set to 1.6 or less in the present invention. On the other hand, excessively low r value extremely reduces the elongation, so the lower limit of the average r value is 1.2.
- the average r value can be measured and determined by the following method.
- a JIS No. 5 tensile test piece is cut out from the rolling direction, the 45 ° direction of rolling, and the direction perpendicular to the rolling direction, and a plastic strain ratio test based on JIS Z 2254 is performed at a pre-strain of 15%. And it calculates
- a backlight chassis used in a thin liquid crystal television has a longitudinal direction of rolling 45
- r L r value in the rolling direction
- r D r value in the 45 ° direction of rolling
- r C r value in the direction perpendicular to the rolling direction
- a backlight chassis used in a thin liquid crystal television has a longitudinal direction of rolling 45
- the warpage of the ridge line generated in the longitudinal direction of the bead and the warpage of the backlight chassis caused by the material inflow of the flange portion in the vicinity of the bulged portion are in the direction of 45 ° rolling.
- the r value of is high, it becomes large.
- the r value in the three directions of the rolling direction, the direction perpendicular to the rolling direction, and the direction of rolling 45 ° In addition to the average r value of 1.2 to 1.6, It is preferable that the maximum r value among the three directions of the direction and the rolling 45 ° direction is less than 2.0.
- the manufacturing method of the cold rolled steel sheet of this invention is demonstrated.
- the steel slab having the above composition is heated at a heating temperature of 1150 ° C. or higher, then hot-rolled to finish the finish rolling at a finishing temperature of 880 ° C. or higher, and wound at 700 ° C. or lower.
- Heating temperature A steel material with components adjusted to 1150 ° C or higher is heated to 1150 ° C or higher to form precipitates.
- N and C remain undissolved, and during the winding process or annealing, carbide and nitride do not precipitate finely and the grain growth suppression effect during annealing is sufficient. Is not demonstrated. Therefore, the higher the heating temperature, the better, and it is 1150 ° C. or higher, desirably 1200 ° C. or higher.
- heating is performed excessively, a thick oxide scale is generated on the steel surface, and the cost of pickling treatment is increased.
- Finishing temperature 880 ° C. or higher followed by hot rolling.
- the finish temperature is set to 880 ° C. or higher, and finish rolling is performed in an austenite single phase.
- finishing temperature becomes too high, the oxide scale becomes thick and the cost of pickling treatment increases, so it is preferable to set the finishing temperature to 950 ° C. or lower. It is preferable to perform water cooling after finish rolling. It is known to reduce the r value by dissolving C and N before cold rolling, in order to suppress the precipitation of C and N, and to refine the precipitated carbides and nitrides, the grains during annealing In order to suppress growth, the cooling is preferably performed.
- Winding temperature 700 ° C. or lower
- the hot rolled coil is wound at 700 ° C. or lower.
- the coiling temperature exceeds 700 ° C.
- Al, Nb, and Ti form carbides and nitrides at high temperatures, which is not preferable from the viewpoint of securing solid solution C and solid solution N before cold rolling, which affects the r value reduction.
- Rolling ratio during cold rolling (CR) 55-80%
- the hot-rolled sheet is pickled by a normal method.
- cold rolling with a rolling reduction (CR) of 55% or more and 80% or less is performed to form a desired plate thickness.
- the rolling reduction (CR) is less than 55%, the structure is mixed and the ductility is extremely reduced.
- the rolling reduction (CR) is higher than 80%, it is easy to form a texture that is disadvantageous for reducing the r value after annealing.
- Soaking temperature (820 + Nb / 15 + B-CR) to 860 ° C., holding time: 30 to 200 sec
- the soaking temperature is in the range of (820 + Nb / 15 + B-CR) to 860 ° C., depending on the rolling reduction CR (%), the Nb amount (mass ppm), and the B amount (mass ppm). Hold for 30-200 s. Thereafter, cooling is performed.
- the strain introduced by cold rolling is eliminated by recrystallization, and the steel sheet is softened.
- the temperature at which the recrystallization is completed becomes lower as the rolling reduction (CR) is higher and the amount of additive elements, particularly Nb and B, is smaller. Therefore, the soaking temperature needs to be not less than (820 + Nb / 15 + B-CR) in order to prevent a decrease in elongation due to remaining unrecrystallized structure. The reason for limiting the soaking temperature will be described later.
- the recrystallization temperature is excessively increased, the manufacturing cost is increased, and the ferrite is transformed into austenite. Along with this, the elongation decreases. Therefore, the soaking temperature needs to be 860 ° C.
- the holding time needs to be 30 sec or more and 200 sec or less.
- the cooling after soaking is preferably performed at a rate of 3 ° C./sec or more in order to prevent the r value from being increased by excessive grain growth.
- the reason why the soaking temperature during annealing is set to (820 + Nb / 15 + B-CR) or higher will be specifically described.
- the recrystallization temperature is correlated with the rolling reduction (CR), the added Nb amount, and the B amount.
- the rolling reduction (CR) shows the relationship between the rolling reduction (CR) and the soaking temperature and performance, and the relationship between Nb [mass ppm] / 15 + B [mass ppm] and the soaking temperature and performance, respectively.
- the chemical composition of the test material in FIG. 1 is Nb: 150 ppm, B: 30 ppm, and in FIG. 2, the rolling reduction (CR) is 70%. Except for the soaking temperature at the time of annealing, all are the characteristic values of the annealed plate prepared within the scope of the present invention. Further, in each figure, when the average elongation is 42% or more and the average r value is 1.2 to 1.6, ⁇ is indicated, and otherwise x is indicated.
- a cold-rolled steel sheet having excellent formability and shape freezing property has been manufactured. From the above, the soaking temperature during annealing is set to (820 + Nb / 15 + B-CR) or higher.
- a melting method can be appropriately applied, such as a normal converter method or an electric furnace method.
- the melted steel is cast into a slab and then directly or cooled and heated at the above-mentioned heating temperature and subjected to hot rolling.
- hot rolling after finishing at the above-described finishing temperature, winding is performed at the above-described winding temperature.
- the cooling rate from finish rolling to winding is not particularly limited, but a cooling rate higher than air cooling is sufficient. Moreover, you may perform rapid cooling of 100 degrees C / s or more as needed. Then, after the usual pickling, the above-mentioned cold rolling is performed.
- annealing heating-uniform heat treatment-cooling
- plating with hot dip zinc may be performed at around 480 ° C.
- the plating may be alloyed by reheating to 500 ° C. or higher.
- a heat history such as holding during cooling may be taken.
- temper rolling and leveling may be performed at an elongation of up to 2%.
- electrogalvanization or the like may be performed.
- a film may be formed on the cold-rolled steel plate or the plated steel plate by chemical conversion treatment or the like. As described above, the cold-rolled steel sheet of the present invention is manufactured.
- the thickness of the hot-rolled sheet was 2.0 to 3.5 mm. Next, it was pickled before the cold rolling step and rolled at room temperature until the plate thickness became 0.6 to 1.0 mm. Subsequently, as an annealing step, the steel sheet was heated to a soaking temperature at a heating rate of 20 ° C./sec, held at the soaking temperature for 30 to 200 sec, and then cooled to room temperature at a cooling rate of 20 ° C./sec.
- CR, AT, and ATO shown in Tables 2 and 3 represent the cold rolling reduction ratio, the soaking temperature, and (820 + Nb / 15 + B-CR), respectively. After annealing, temper rolling with an elongation of 1.0% was performed to obtain a test material.
- the average elongation (El m ) and average r value (r m ) of the obtained specimens were investigated.
- the average elongation (El m ) and the average r value (r m ) are measured according to JIS No. 5 from the rolling direction (L direction), the 45 ° direction (D direction), and the perpendicular direction (C direction) of the specimen.
- Each tensile test piece was cut out, the elongation was measured by a tensile test according to JIS Z 2241, and the r value was measured at a pre-strain of 15% according to JIS Z 2254 as described above.
- the average elongation is 42% or more
- the average r value is 1.2 to 1.6, which is excellent in moldability and shape freezing property.
- the r value is 1.2 to 1.6 and the elongation is 42% or more.
- the soaking temperature range showing the value is from 800 ° C. to 850 ° C., whereas in the comparative example, the component system with a small amount of dissolved B, the r value is 1.2 to 1.6 and the elongation is 42% or more. No soaking temperature was observed.
- FIG. 3 is a diagram showing the influence of the soaking temperature during annealing on the average r value.
- the average r value is 1.2 to 1.6 even in a region where the soaking temperature during annealing is high.
- FIG. 4 is a diagram showing the relationship between AT-ATO, which is an indicator of whether the soaking temperature during annealing is appropriate, and the average r value. When AT-ATO is negative, the soaking temperature is not appropriate and recrystallization is not sufficiently performed.
- FIG. 5 is a diagram showing the relationship between AT-ATO, which is an indicator of whether the soaking temperature at the time of annealing is appropriate, and average elongation.
- AT-ATO is negative, the soaking temperature is not appropriate, and as a result of insufficient recrystallization, the average elongation is less than 42%.
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Abstract
Description
また、平坦度を悪化させる要因として、曲げ加工時に生じる稜線反りが良く知られている。その中の一つである曲げ端部に発生する反りは、材料のr値を低くすることによって低減されるといわれており、従来から、材料に低r値、低降伏強度を付与する技術が確立されている。
例えば、特許文献1には、降伏強度150MPa、圧延方向のr値0.67(圧延直角方向1.45)をもつ冷延鋼板を開発する技術が開示されている。
特許文献2には、板面に平行な{100}面と{111}面の比が1.0以上である形状凍結性に優れた自動車用フェライト系薄鋼板が開示されている。
特許文献3には、形状凍結性に優れたフェライト系薄鋼板を得るために、{100}<011>~{223}<110>方位群の強度と{112}<110>、{554}<225>、{111}<112>、{111}<110>の各方位の強度を制御すること、圧延方向のr値および圧延方向と直角方向のr値のうち、少なくとも一つを0.7以下にすることが開示されている。 Thin flat panel TVs and office automation equipment use a large number of flat-shaped parts formed by processing mainly bending and stretching. The members (materials) used for these parts often require flatness in addition to the degree of processing into the part shape from the viewpoints of product design and thickness reduction. However, flatness tends to deteriorate when bending / extrusion molding is performed on a flat plate surface of a member (material). Such deterioration of flatness is a phenomenon that occurs due to poor shape freezing property of the member (material) when the member (material) is press-molded. Shape freezing property is required.
Further, as a factor that deteriorates the flatness, ridge warpage that occurs during bending is well known. It is said that the warp that occurs at the bending end, which is one of them, is reduced by lowering the r value of the material. Conventionally, there is a technique for imparting a low r value and low yield strength to the material. Has been established.
For example,
Patent Document 2 discloses a ferritic thin steel sheet for automobiles having a good shape freezing property in which the ratio of {100} plane and {111} plane parallel to the plate surface is 1.0 or more.
In Patent Document 3, in order to obtain a ferritic steel sheet having excellent shape freezing property, the strength of {100} <011> to {223} <110> orientation group and {112} <110>, {554} <225>, {111} <112>, {111} <110>, controlling the strength of each direction, at least one of the r value in the rolling direction and the r value in the direction perpendicular to the rolling direction is 0.7. The following is disclosed.
また、特許文献1~3には、冷延鋼板については冷延率を低く、具体的には40%としてr値を低くした場合が開示されているが、40%程度の極度に低い冷延率で圧延すると、板形状が悪くなり、最終商品の平坦度が劣化するという問題がある。また、このような低冷延率は形状凍結性を向上させるものの、1.0mm程度以下の薄鋼板の製造を困難にする。 However, in the techniques described in
焼鈍工程における均熱温度範囲を圧下率とNb量およびB量に応じて設けることで、均熱温度をピンポイントで制御することなく安定的に製造することが可能となる。
本発明は、以上の知見に基づいてなされたものであり、その要旨は以下のとおりである。
(1)質量%で、C:0.0010~0.0030%、Si:0.05%以下、Mn:0.1~0.3%、P:0.05%以下、S:0.02%以下、Al:0.02~0.10%、N:0.005%以下、Nb:0.010~0.030%、B:0.0010≦B−11/14×N≦0.0050%で、残部が鉄および不可避不純物である組成を有し、下記(a)式で示す平均の伸び(Elm)が42%以上であり、下記(b)式で示す平均のr値(rm)が1.2~1.6であることを特徴とする冷延鋼板。
平均の伸び Elm=(ElL+2ElD+ElC)/4 ・・・(a)
平均のr値 rm=(rL+2rD+rC)/4 ・・・(b)
ここで、ElL:圧延方向の伸び、ElD:圧延45°方向の伸び、ElC:圧延直角方向の伸び、rL:圧延方向のr値、rD:圧延45°方向のr値、rC:圧延直角方向のr値
(2)前記(1)において、さらに、質量%で、Ti:0.005%~0.020%を含有し、上記B:0.0010≦B−11/14×N≦0.0050%に代えて、B:0.0015<B−11×(|N/14−Ti/48|+(N/14−Ti/48))/2≦0.0050%であることを特徴とする冷延鋼板。
(3)前記(1)または前記(2)に記載の組成からなる鋼スラブを、1150℃以上の加熱温度で加熱した後、880℃以上の仕上げ温度で仕上げ圧延を終了する熱間圧延を行い、700℃以下で巻取り、酸洗を施し、55~80%の圧下率で冷間圧延を行った後、該圧下率CR(%)、Nb量(質量ppm)及びB量(質量ppm)に応じて、(820+Nb/15+B−CR)~860℃の均熱温度で30~200sec間保持する焼鈍を行い、次いで、冷却することを特徴とする冷延鋼板の製造方法。 Inventors repeated earnest research investigation in order to solve the said subject. As a result, the following points were found. First, in order to achieve both workability in which warpage does not occur even when complicated processing is performed and high shape freezing property, the r value is controlled while maintaining high ductility in the annealed sheet after cold rolling. is important. That is, by increasing the average elongation, it is possible to ensure the shape required for the part while ensuring the workability during drawing and overhanging. Furthermore, by reducing the r value in the three directions of the rolling direction, the direction perpendicular to the rolling direction, and the rolling 45 ° direction, and setting the average r value within a range that defines the average r value, the longitudinal direction becomes the rolling 45 ° direction. In addition, even when elongated bead-shaped overhang molding is performed, warpage is prevented, and the occurrence of springback and warpage after processing is suppressed, and the shape freezing property can be secured.
By providing the soaking temperature range in the annealing process in accordance with the rolling reduction, the Nb amount, and the B amount, it is possible to stably manufacture the soaking temperature without pinpoint control.
This invention is made | formed based on the above knowledge, The summary is as follows.
(1) By mass%, C: 0.0010 to 0.0030%, Si: 0.05% or less, Mn: 0.1 to 0.3%, P: 0.05% or less, S: 0.02 %: Al: 0.02-0.10%, N: 0.005% or less, Nb: 0.010-0.030%, B: 0.0010 ≦ B-11 / 14 × N ≦ 0.0050 %, The balance being iron and inevitable impurities, the average elongation (El m ) represented by the following formula (a) is 42% or more, and the average r value (r) represented by the following formula (b) A cold rolled steel sheet, wherein m ) is 1.2 to 1.6.
The average elongation El m = (El L + 2El D + El C) / 4 ··· (a)
Average r value r m = (r L + 2r D + r C ) / 4 (b)
Here, El L : Elongation in the rolling direction, El D : Elongation in the rolling 45 ° direction, El C : Elongation in the direction perpendicular to the rolling, r L : R value in the rolling direction, r D : R value in the rolling 45 ° direction, r C : r value in the direction perpendicular to the rolling (2) In the above (1), the content of Ti is 0.005% to 0.020%, and B: 0.0010 ≦ B-11 / Instead of 14 × N ≦ 0.0050%, B: 0.0015 <B-11 × (| N / 14−Ti / 48 | + (N / 14−Ti / 48)) / 2 ≦ 0.0050% A cold-rolled steel sheet characterized by
(3) After the steel slab having the composition described in (1) or (2) is heated at a heating temperature of 1150 ° C. or higher, hot rolling is performed to finish finish rolling at a finishing temperature of 880 ° C. or higher. After rolling at 700 ° C. or less, pickling, and cold rolling at a rolling reduction of 55 to 80%, the rolling reduction CR (%), Nb content (mass ppm), and B content (mass ppm) Accordingly, a method for producing a cold-rolled steel sheet is characterized in that annealing is performed for 30 to 200 seconds at a soaking temperature of (820 + Nb / 15 + B-CR) to 860 ° C., and then cooled.
Cは、r値を低減する効果があるため、低r値化の観点からは、多く添加することが望ましく、0.0010%以上とする。しかし、過度の添加は、プレス成形時のシワ発生原因となるストレッチャーストレインをもたらすと同時に、固溶強化、炭化物の形成による分散強化によって鋼板が高強度化し、伸びが低下する。したがって、Cは0.0010%以上0.0030%以下とする。 C: 0.0010 to 0.0030%
Since C has an effect of reducing the r value, it is desirable to add a large amount from the viewpoint of lowering the r value, and it is 0.0010% or more. However, excessive addition leads to stretcher strain that causes wrinkles during press molding, and at the same time, the steel sheet becomes stronger due to solid solution strengthening and dispersion strengthening due to the formation of carbides, and the elongation decreases. Therefore, C is 0.0010% or more and 0.0030% or less.
Siは、固溶強化能が高い元素であり、降伏強度を高くし、伸びを大きく低減する。そのため、0.05%以下とする。 Si: 0.05% or less Si is an element having a high solid solution strengthening ability, increases the yield strength, and greatly reduces the elongation. Therefore, it is made 0.05% or less.
Mnは硫化物を形成して熱間脆性を改善する元素である。この効果を得るためには、0.1%以上の添加が必要である。一方、固溶強化能の高い元素であり降伏強度を高め延性を劣化させるため、上限は0.3%とする。 Mn: 0.1 to 0.3%
Mn is an element that forms a sulfide and improves hot brittleness. In order to obtain this effect, addition of 0.1% or more is necessary. On the other hand, the upper limit is made 0.3% in order to increase yield strength and deteriorate ductility because it is an element with high solid solution strengthening ability.
Pは固溶強化元素であり降伏強度を高くし、延性を劣化させる。そのため、0.05%以下とする。 P: 0.05% or less P is a solid solution strengthening element, which increases yield strength and degrades ductility. Therefore, it is made 0.05% or less.
Sは、熱延板の段階で硫化物を形成し、延性を劣化させる原因となる。そのため、0.02%以下とする。 S: 0.02% or less S forms sulfides at the stage of hot rolling and causes deterioration of ductility. Therefore, it is made 0.02% or less.
Alは、Nとの親和力が強く、冷延工程時の固溶N量を低減させ、時効硬化を抑制する効果がある。また、析出するAlNは微細に析出する傾向が高く、焼鈍工程における粒成長を抑制する。これらの効果を得るためには、0.02%以上の添加が必要である。しかし、過度の添加は、製造コストの上昇を招き、熱間圧延時、オーステナイトからフェライトに変態する温度を上昇させるため、オーステナイト域で圧延を終了させるのが困難になる。したがって、Alは0.10%以下とする必要がある。 Al: 0.02 to 0.10%
Al has a strong affinity with N, and has an effect of reducing the amount of solute N during the cold rolling process and suppressing age hardening. Moreover, the precipitated AlN has a high tendency to precipitate finely and suppresses the grain growth in the annealing process. In order to obtain these effects, addition of 0.02% or more is necessary. However, excessive addition leads to an increase in production cost, and during hot rolling, the temperature at which austenite is transformed into ferrite is raised, so that it is difficult to finish rolling in the austenite region. Therefore, Al needs to be 0.10% or less.
Nは多量に含有すると、鋼中に固溶し、ストレッチャーストレインの原因となる。そのため、0.005%以下とする。 N: 0.005% or less When N is contained in a large amount, it dissolves in steel and causes stretcher strain. Therefore, it is made 0.005% or less.
Nbは、固溶Cを析出物として固定して、ストレッチャーストレインを抑制させる。さらに析出物であるNbCは微細に析出して焼鈍時の粒成長を抑制する傾向がある。これらの効果を得るためには、0.010%以上添加する必要がある。しかし、過度に添加した場合には、再結晶温度を過度に上昇させる。また、コスト増を招く。よって、上限を0.030%とする。 Nb: 0.010 to 0.030%
Nb fixes solute C as a precipitate and suppresses stretcher strain. Furthermore, NbC, which is a precipitate, tends to precipitate finely and suppress grain growth during annealing. In order to obtain these effects, it is necessary to add 0.010% or more. However, when excessively added, the recrystallization temperature is excessively increased. In addition, the cost increases. Therefore, the upper limit is made 0.030%.
Bは、本発明において重要な要件となる元素であり、鋼中に固溶Bとして存在させることで冷延後の焼鈍過程でフェライトの粒成長を抑制し、高い均熱温度でもr値を制御することを可能とする。このような効果を得るためには、熱間圧延時に高温でBNが析出した後に、固溶Bが0.0010%以上存在する必要がある。しかし、過度の添加は、Cとの析出物を形成して、伸びを低減させる。以上の理由により0.0010≦B−11/14×N≦0.0050%とする。好ましくは0.0015<B−11/14×N≦0.0050%である。
さらにTiを添加する場合、NbCに比して粗大なTiCが析出し、焼鈍時の粒成長性が向上するため、粒成長抑制効果のある固溶B量は0.0015%超えにする必要がある。しかし、過度の添加は、Cとの析出物を形成して、伸びを低減させる。これらの理由により、上記B:0.0010≦B−11/14×N≦0.0050%の関係式に代えて、0.0015%<B−11×(|N/14−Ti/48|+(N/14−Ti/48))/2≦0.0050%とする。好ましくは0.0020%≦B−11×(|N/14−Ti/48|+(N/14−Ti/48))/2≦0.0050%とする。 B: 0.0010 ≦ B−11 / 14 × N ≦ 0.0050% (in the case of adding Ti, 0.0015 <B−11 × (| N / 14−Ti / 48 | + (N / 14− Ti / 48)) / 2 ≦ 0.0050%)
B is an element that is an important requirement in the present invention. By making it exist as solid solution B in steel, B suppresses the grain growth of ferrite in the annealing process after cold rolling, and controls the r value even at a high soaking temperature. It is possible to do. In order to obtain such an effect, it is necessary that solute B is present in an amount of 0.0010% or more after BN is precipitated at a high temperature during hot rolling. However, excessive addition forms precipitates with C and reduces elongation. For the above reason, 0.0010 ≦ B−11 / 14 × N ≦ 0.0050%. Preferably 0.0015 <B-11 / 14 × N ≦ 0.0050%.
Further, when Ti is added, coarse TiC is precipitated as compared with NbC, and the grain growth property during annealing is improved. Therefore, the amount of solute B having an effect of suppressing grain growth needs to exceed 0.0015%. is there. However, excessive addition forms precipitates with C and reduces elongation. For these reasons, instead of the relational expression B: 0.0010 ≦ B-11 / 14 × N ≦ 0.0050%, 0.0015% <B-11 × (| N / 14−Ti / 48 | + (N / 14-Ti / 48)) / 2≤0.0050%. Preferably, 0.0020% ≦ B-11 × (| N / 14−Ti / 48 | + (N / 14−Ti / 48)) / 2 ≦ 0.0050%.
Tiは、Nとの親和力が強く、高温で析出物を形成して、固溶Nの固溶強化や、AlNの微細析出による分散強化を抑制する効果がある。また、伸びを特に向上させたい場合に添加することもできる。これらの効果を発揮するためには、0.005%以上添加することが望ましい。しかし、過度の添加は、TiCの析出を促進させて、NbCによる焼鈍時の粒成長の抑制効果を低減するだけでなく、製造コストの上昇を招くため、添加する場合の上限は0.020%とする。 In addition to the above elements, the present invention can contain Ti in the range of 0.005% to 0.020% for the following purpose.
Ti has a strong affinity with N and forms precipitates at high temperatures, and has the effect of suppressing solid solution strengthening of solid solution N and dispersion strengthening due to fine precipitation of AlN. Moreover, it can also be added when it is desired to particularly improve the elongation. In order to exhibit these effects, it is desirable to add 0.005% or more. However, excessive addition not only promotes precipitation of TiC and reduces the effect of suppressing grain growth during annealing with NbC, but also causes an increase in manufacturing cost. Therefore, the upper limit in the case of addition is 0.020%. And
なお、平均の全伸びは以下の方法により測定し求めることができる。圧延方向、圧延45°方向および圧延直角方向からJIS5号引張試験片をそれぞれ切り出し、JIS Z 2241に準拠した引張試験を行う。そして、下記(a)式により求める。
平均の伸び Elm=(ElL+2ElD+ElC)/4 ・・・(a)
ここで、ElL:圧延方向の伸び
ElD:圧延45°方向の伸び
ElC:圧延直角方向の伸び
本発明の鋼板は、下記(b)式により求める平均のr値が1.2~1.6とする。r値は、曲げ成形、張出し成形後に生じる反りと相関がある。曲げ成形では、曲げ方向のr値が高くなることで、曲げ線に沿って鞍型の反りが顕著に発生する。また、張出し成形においては、高r値材の使用により、張出し部周辺のフランジ部からの材料流入が顕著になり、フランジ部に残留応力とゆがみが発生する。したがって、低r値化によってプレス成形後の形状凍結性を向上させることを目的として、本発明では平均のr値を1.6以下とする。一方で、過度な低r値化は、極度に伸びを低減させるので、平均のr値の下限は1.2とする。 The steel sheet of the present invention has an average elongation of 42% or more determined by the following formula (a). Elongation has a good correlation with moldability, and the larger the elongation, for example, the higher the stretch molding. Therefore, the larger the required elongation, the better, and by increasing the average elongation to 42% or more, drawing and overhanging can be performed, and the shape required for the parts can be ensured.
The average total elongation can be measured and determined by the following method. A JIS No. 5 tensile test piece is cut out from the rolling direction, the 45 ° direction of rolling, and the direction perpendicular to the rolling direction, and a tensile test based on JIS Z 2241 is performed. And it calculates | requires by the following (a) formula.
The average elongation El m = (El L + 2El D + El C) / 4 ··· (a)
Here, El L : Elongation in the rolling direction El D : Elongation in the rolling 45 ° direction El C : Elongation in the direction perpendicular to the rolling The steel sheet of the present invention has an average r value of 1.2 to 1 determined by the following formula (b) .6. The r value correlates with the warpage that occurs after bending or stretch forming. In bending, the r value in the bending direction is increased, so that saddle-shaped warpage occurs remarkably along the bending line. Further, in the overhang forming, the use of a high r-value material makes the material inflow from the flange portion around the overhang portion remarkable, and residual stress and distortion occur in the flange portion. Therefore, for the purpose of improving the shape freezing property after press molding by lowering the r value, the average r value is set to 1.6 or less in the present invention. On the other hand, excessively low r value extremely reduces the elongation, so the lower limit of the average r value is 1.2.
平均のr値 rm=(rL+2rD+rC)/4 ・・・(b)
ここで、rL:圧延方向のr値
rD:圧延45°方向のr値
rC:圧延直角方向のr値
また、例えば、薄型液晶テレビに使われるバックライトシャーシに、長手方向が圧延45°方向となるような、細長いビード形状の張出し成形が施される場合、ビード長手方向に生じる稜線反り、および張出し部近傍のフランジ部分の材料流入によって生じるバックライトシャーシの反りは、圧延45°方向のr値が高いと大きくなる。ゆえに、圧延方向、圧延直角方向、および圧延45°方向の3方向のr値の低減が重要であり、平均のr値が1.2~1.6に加え、好ましくは、圧延方向、圧延直角方向、および圧延45°方向の3方向のうちの最大r値は2.0未満であることが好ましい。 The average r value can be measured and determined by the following method. A JIS No. 5 tensile test piece is cut out from the rolling direction, the 45 ° direction of rolling, and the direction perpendicular to the rolling direction, and a plastic strain ratio test based on JIS Z 2254 is performed at a pre-strain of 15%. And it calculates | requires by the following (b) formula.
Average r value r m = (r L + 2r D + r C ) / 4 (b)
Here, r L : r value in the rolling direction r D : r value in the 45 ° direction of rolling r C : r value in the direction perpendicular to the rolling direction Further, for example, a backlight chassis used in a thin liquid crystal television has a longitudinal direction of rolling 45 When an elongated bead-shaped bulge forming is performed, the warpage of the ridge line generated in the longitudinal direction of the bead and the warpage of the backlight chassis caused by the material inflow of the flange portion in the vicinity of the bulged portion are in the direction of 45 ° rolling. When the r value of is high, it becomes large. Therefore, it is important to reduce the r value in the three directions of the rolling direction, the direction perpendicular to the rolling direction, and the direction of rolling 45 °. In addition to the average r value of 1.2 to 1.6, It is preferable that the maximum r value among the three directions of the direction and the rolling 45 ° direction is less than 2.0.
本発明においては、上記の組成を有する鋼スラブを、1150℃以上の加熱温度で加熱した後、880℃以上の仕上げ温度で仕上げ圧延を終了する熱間圧延を行い、700℃以下で巻取り、酸洗を施し、その後、55~80%の圧下率で冷間圧延を行った後、該圧下率CR(%)、Nb量(質量ppm)及びB量(質量ppm)に応じて、(820+Nb/15+B−CR)~860℃の均熱温度で30~200sec間保持する焼鈍を行い、次いで、冷却することで、高い伸び、低いr値を得ることができる。 Next, the manufacturing method of the cold rolled steel sheet of this invention is demonstrated.
In the present invention, the steel slab having the above composition is heated at a heating temperature of 1150 ° C. or higher, then hot-rolled to finish the finish rolling at a finishing temperature of 880 ° C. or higher, and wound at 700 ° C. or lower. After pickling and then cold rolling at a rolling reduction of 55 to 80%, (820 + Nb) according to the rolling reduction CR (%), Nb amount (mass ppm) and B amount (mass ppm) / 15 + B-CR)-Annealing is carried out at a soaking temperature of 860 ° C for 30 to 200 seconds, followed by cooling to obtain a high elongation and a low r value.
成分を調整した鋼素材を1150℃以上まで加熱し析出物を溶体化する。1150℃未満の加熱では、NやCが未固溶のままで残存してしまい、巻取り処理時、あるいは焼鈍時に、炭化物、窒化物が微細析出せずに焼鈍時の粒成長抑制効果が十分に発揮されない。従って、加熱温度は高いほど良く、1150℃以上、望ましくは1200℃以上である。しかし、過度に加熱を行うと、厚い酸化スケールが鋼表面に生成し酸洗処理のコストが増大するため、1300℃以下が好ましい。 Heating temperature: A steel material with components adjusted to 1150 ° C or higher is heated to 1150 ° C or higher to form precipitates. When heating at less than 1150 ° C., N and C remain undissolved, and during the winding process or annealing, carbide and nitride do not precipitate finely and the grain growth suppression effect during annealing is sufficient. Is not demonstrated. Therefore, the higher the heating temperature, the better, and it is 1150 ° C. or higher, desirably 1200 ° C. or higher. However, if heating is performed excessively, a thick oxide scale is generated on the steel surface, and the cost of pickling treatment is increased.
続いて熱間圧延を行う。仕上げ圧延時の、最終圧延スタンドにおいては、オーステナイト域単相で圧延を行う必要がある。オーステナイトとフェライトの二相域で圧延した場合、変態に伴って圧延荷重は大きく変化するため、圧延スタンドでの荷重制御が困難になって、板の破断を招く可能性がある。また、フェライト域単相での圧延は、未再結晶の残存を促進させて、続く冷間圧延での圧延荷重を過度に高くすることで製造コストの上昇を招く可能性がある。以上から、仕上げ温度を880℃以上とし、オーステナイト域単相で仕上げ圧延を行うこととする。なお、仕上げ温度は高くなりすぎると酸化スケールが厚くなり酸洗処理のコストが増大するため、950℃以下とすることが好ましい。
仕上げ圧延後は、水冷却を行うのが好ましい。冷延前にC、Nを固溶させるとr値を低減することが知られている、C、Nの析出を抑制するため、また、析出炭化物、窒化物を微細化して、焼鈍時の粒成長を抑制するため、上記冷却を行うことが好ましい。 Finishing temperature: 880 ° C. or higher followed by hot rolling. In the final rolling stand at the time of finish rolling, it is necessary to perform rolling in an austenite region single phase. When rolling in the two-phase region of austenite and ferrite, the rolling load changes greatly with the transformation, so that it becomes difficult to control the load at the rolling stand, and the plate may be broken. In addition, rolling in a ferrite region single phase promotes the remaining of non-recrystallization and may increase the manufacturing cost by excessively increasing the rolling load in the subsequent cold rolling. From the above, the finish temperature is set to 880 ° C. or higher, and finish rolling is performed in an austenite single phase. If the finishing temperature becomes too high, the oxide scale becomes thick and the cost of pickling treatment increases, so it is preferable to set the finishing temperature to 950 ° C. or lower.
It is preferable to perform water cooling after finish rolling. It is known to reduce the r value by dissolving C and N before cold rolling, in order to suppress the precipitation of C and N, and to refine the precipitated carbides and nitrides, the grains during annealing In order to suppress growth, the cooling is preferably performed.
熱間圧延の最終工程として、熱延コイルに700℃以下で巻取りを行う。巻取り温度が700℃を超えると、Al、Nb、Tiが高温で炭化物、窒化物を形成し、r値低減に影響する冷延前の固溶C、固溶N確保の点から好ましくない。なお、巻取り温度が低くなりすぎるとコイルの巻き形状が悪くなるため、400℃以上とすることが好ましい。 Winding temperature: 700 ° C. or lower As the final step of hot rolling, the hot rolled coil is wound at 700 ° C. or lower. When the coiling temperature exceeds 700 ° C., Al, Nb, and Ti form carbides and nitrides at high temperatures, which is not preferable from the viewpoint of securing solid solution C and solid solution N before cold rolling, which affects the r value reduction. In addition, since the winding shape of a coil will worsen if winding temperature becomes low too much, it is preferable to set it as 400 degreeC or more.
熱延板を通常の方法にて酸洗する。次いで、圧下率(CR)が55%以上80%以下の冷間圧延を行って所望の板厚に成形する。圧下率(CR)が55%未満では、組織が混粒となって延性が極度に低下する。一方、圧下率(CR)が80%より高くなると、焼鈍後にr値低減に不利な集合組織が形成しやすくなる。 Rolling ratio during cold rolling (CR): 55-80%
The hot-rolled sheet is pickled by a normal method. Next, cold rolling with a rolling reduction (CR) of 55% or more and 80% or less is performed to form a desired plate thickness. When the rolling reduction (CR) is less than 55%, the structure is mixed and the ductility is extremely reduced. On the other hand, when the rolling reduction (CR) is higher than 80%, it is easy to form a texture that is disadvantageous for reducing the r value after annealing.
次に、焼鈍工程として、均熱温度を、圧下率CR(%)とNb量(質量ppm)、B量(質量ppm)に応じて、(820+Nb/15+B−CR)~860℃の範囲で、30~200s間保持する。その後、冷却を行う。 Soaking temperature: (820 + Nb / 15 + B-CR) to 860 ° C., holding time: 30 to 200 sec
Next, as an annealing step, the soaking temperature is in the range of (820 + Nb / 15 + B-CR) to 860 ° C., depending on the rolling reduction CR (%), the Nb amount (mass ppm), and the B amount (mass ppm). Hold for 30-200 s. Thereafter, cooling is performed.
また、均熱保持時間は、短すぎると未再結晶組織が残存し、長すぎると粒成長が過度に進行してr値が高くなる。したがって、保持時間は30sec以上200sec以下とする必要がある。また、均熱後の冷却は、過度の粒成長によってr値が高くなることを防ぐため、3℃/sec以上の速度で冷却するのが好ましい。
ここで、焼鈍時の均熱温度を(820+Nb/15+B−CR)以上とした理由について具体的に説明する。一般的に、圧下率を高くすると、再結晶の駆動力が高まって、焼鈍時に再結晶が完了する温度(以下、再結晶温度と称す)は、低温側に移る。一方、添加Nb、B量を多くすると、再結晶が著しく抑制され、再結晶温度は高温側に移る。本発明者らの実験によれば、再結晶温度は、圧下率(CR)、添加Nb量、B量と相関関係がある。図1、図2は、それぞれ圧下率(CR)と均熱温度および性能との関係を、Nb[質量ppm]/15+B[質量ppm]と均熱温度および性能との関係を示したものである。ここで、図1において供試材の化学組成は、Nb:150ppm、B:30ppmであり、図2において圧下率(CR)は70%である。焼鈍時の均熱温度を除き、すべて本発明の範囲内で作成した焼鈍板の特性値である。また、各図中、平均の伸びが42%以上かつ平均のr値が1.2~1.6となる場合には○を、ならない場合には×とした。各図中の直線は、均熱温度=(820+Nb/15+B−CR)[℃]となる直線であり、○と×を分断する良い境界線であることがわかる。図1および図2より、焼鈍時の均熱温度が(820+Nb/15+B−CR)[℃]以上においては、平均の伸びが42%以上かつ平均のr値が1.2~1.6である、成形性と形状凍結性に優れた冷延鋼板が製造できている。以上より、焼鈍時の均熱温度を(820+Nb/15+B−CR)以上とする。 In the annealing step, the strain introduced by cold rolling is eliminated by recrystallization, and the steel sheet is softened. The temperature at which the recrystallization is completed becomes lower as the rolling reduction (CR) is higher and the amount of additive elements, particularly Nb and B, is smaller. Therefore, the soaking temperature needs to be not less than (820 + Nb / 15 + B-CR) in order to prevent a decrease in elongation due to remaining unrecrystallized structure. The reason for limiting the soaking temperature will be described later. On the other hand, when the recrystallization temperature is excessively increased, the manufacturing cost is increased, and the ferrite is transformed into austenite. Along with this, the elongation decreases. Therefore, the soaking temperature needs to be 860 ° C. or lower.
If the soaking time is too short, an unrecrystallized structure remains, and if it is too long, grain growth proceeds excessively and the r value increases. Therefore, the holding time needs to be 30 sec or more and 200 sec or less. Further, the cooling after soaking is preferably performed at a rate of 3 ° C./sec or more in order to prevent the r value from being increased by excessive grain growth.
Here, the reason why the soaking temperature during annealing is set to (820 + Nb / 15 + B-CR) or higher will be specifically described. Generally, when the rolling reduction is increased, the driving force for recrystallization increases, and the temperature at which recrystallization is completed during annealing (hereinafter referred to as the recrystallization temperature) shifts to the low temperature side. On the other hand, when the amount of added Nb and B is increased, recrystallization is remarkably suppressed, and the recrystallization temperature is shifted to the high temperature side. According to the experiments by the present inventors, the recrystallization temperature is correlated with the rolling reduction (CR), the added Nb amount, and the B amount. FIG. 1 and FIG. 2 show the relationship between the rolling reduction (CR) and the soaking temperature and performance, and the relationship between Nb [mass ppm] / 15 + B [mass ppm] and the soaking temperature and performance, respectively. . Here, the chemical composition of the test material in FIG. 1 is Nb: 150 ppm, B: 30 ppm, and in FIG. 2, the rolling reduction (CR) is 70%. Except for the soaking temperature at the time of annealing, all are the characteristic values of the annealed plate prepared within the scope of the present invention. Further, in each figure, when the average elongation is 42% or more and the average r value is 1.2 to 1.6, ◯ is indicated, and otherwise x is indicated. The straight line in each figure is a straight line where the soaking temperature = (820 + Nb / 15 + B−CR) [° C.], and it can be seen that this is a good boundary line for dividing the circle and the cross. 1 and 2, when the soaking temperature during annealing is (820 + Nb / 15 + B-CR) [° C.] or more, the average elongation is 42% or more and the average r value is 1.2 to 1.6. A cold-rolled steel sheet having excellent formability and shape freezing property has been manufactured. From the above, the soaking temperature during annealing is set to (820 + Nb / 15 + B-CR) or higher.
図3は焼鈍時の均熱温度が平均r値におよぼす影響を示す図である。固溶B量が多い本発明例では、焼鈍時の均熱温度が高い領域でも平均r値が1.2~1.6となっている。
図4は、焼鈍時の均熱温度が適正であるかの指標であるAT−ATOと平均のr値との関係を示す図である。AT−ATOが負の時、均熱温度が適正でなく、再結晶が十分行われない結果、平均r値が1.2未満となっている。
図5は、焼鈍時の均熱温度が適正であるかの指標であるAT−ATOと平均の伸びとの関係を示す図である。AT−ATOが負の時、均熱温度が適正でなく、再結晶が十分行われない結果、平均の伸びが42%未満となっている。 In the example of the present invention, the average elongation is 42% or more, and the average r value is 1.2 to 1.6, which is excellent in moldability and shape freezing property. Further, as can be seen from the manufacturing conditions and mechanical properties of symbols 32 to 35 in Table 2 and 41 to 44 in Table 3, in the present invention example, the r value is 1.2 to 1.6 and the elongation is 42% or more. The soaking temperature range showing the value is from 800 ° C. to 850 ° C., whereas in the comparative example, the component system with a small amount of dissolved B, the r value is 1.2 to 1.6 and the elongation is 42% or more. No soaking temperature was observed. From this, in the example of this invention, even if it annealed at high temperature, it was confirmed that low r value and high elongation are obtained and it has the outstanding real machine manufacture stability.
FIG. 3 is a diagram showing the influence of the soaking temperature during annealing on the average r value. In the present invention example having a large amount of dissolved B, the average r value is 1.2 to 1.6 even in a region where the soaking temperature during annealing is high.
FIG. 4 is a diagram showing the relationship between AT-ATO, which is an indicator of whether the soaking temperature during annealing is appropriate, and the average r value. When AT-ATO is negative, the soaking temperature is not appropriate and recrystallization is not sufficiently performed. As a result, the average r value is less than 1.2.
FIG. 5 is a diagram showing the relationship between AT-ATO, which is an indicator of whether the soaking temperature at the time of annealing is appropriate, and average elongation. When AT-ATO is negative, the soaking temperature is not appropriate, and as a result of insufficient recrystallization, the average elongation is less than 42%.
Claims (3)
- 質量%で、C:0.0010~0.0030%、Si:0.05%以下、Mn:0.1~0.3%、P:0.05%以下、S:0.02%以下、Al:0.02~0.10%、N:0.005%以下、Nb:0.010~0.030%、B:0.0010≦B−11/14×N≦0.0050%で、残部が鉄および不可避不純物である組成を有し、下記(a)式で示す平均の伸び(Elm)が42%以上であり、下記(b)式で示す平均のr値(rm)が1.2~1.6であることを特徴とする冷延鋼板。
平均の伸び Elm=(ElL+2ElD+ElC)/4 ・・・(a)
平均のr値 rm=(rL+2rD+rC)/4 ・・・(b)
ここで、ElL:圧延方向の伸び
ElD:圧延45°方向の伸び
ElC:圧延直角方向の伸び
rL:圧延方向のr値
rD:圧延45°方向のr値
rC:圧延直角方向のr値 In mass%, C: 0.0010 to 0.0030%, Si: 0.05% or less, Mn: 0.1 to 0.3%, P: 0.05% or less, S: 0.02% or less, Al: 0.02 to 0.10%, N: 0.005% or less, Nb: 0.010 to 0.030%, B: 0.0010 ≦ B-11 / 14 × N ≦ 0.0050%, The balance is iron and inevitable impurities, the average elongation (El m ) shown by the following formula (a) is 42% or more, and the average r value (r m ) shown by the following formula (b) is A cold-rolled steel sheet having a thickness of 1.2 to 1.6.
The average elongation El m = (El L + 2El D + El C) / 4 ··· (a)
Average r value r m = (r L + 2r D + r C ) / 4 (b)
Here, El L : Elongation in the rolling direction El D : Elongation in the 45 ° direction of rolling El C : Elongation in the direction perpendicular to the rolling r L : R value in the rolling direction r D : R value in the 45 ° direction of rolling r C : Right angle in the rolling direction R value of direction - さらに、質量%で、Ti:0.005%~0.020%を含有し、上記B:0.0010≦B−11/14×N≦0.0050%に代えて、B:0.0015<B−11×(|N/14−Ti/48|+(N/14−Ti/48))/2≦0.0050%であることを特徴とする請求項1に記載の冷延鋼板。 Furthermore, Ti: 0.005% to 0.020% in mass%, and instead of B: 0.0010 ≦ B-11 / 14 × N ≦ 0.0050%, B: 0.0015 < The cold rolled steel sheet according to claim 1, wherein B-11 × (| N / 14−Ti / 48 | + (N / 14−Ti / 48)) / 2 ≦ 0.0050%.
- 請求項1または請求項2に記載の組成からなる鋼スラブを、1150℃以上の加熱温度で加熱した後、880℃以上の仕上げ温度で仕上げ圧延を終了する熱間圧延を行い、700℃以下で巻取り、酸洗を施し、55~80%の圧下率で冷間圧延を行った後、該圧下率CR(%)、Nb量(質量ppm)及びB量(質量ppm)に応じて、(820+Nb/15+B−CR)~860℃の均熱温度で30~200sec間保持する焼鈍を行い、次いで、冷却することを特徴とする冷延鋼板の製造方法。 After the steel slab having the composition according to claim 1 or 2 is heated at a heating temperature of 1150 ° C or higher, hot rolling is performed to finish finish rolling at a finishing temperature of 880 ° C or higher. Winding and pickling, and after cold rolling at a rolling reduction of 55 to 80%, according to the rolling reduction CR (%), Nb amount (mass ppm) and B amount (mass ppm), ( 820 + Nb / 15 + B-CR) A method for producing a cold-rolled steel sheet, comprising annealing at a soaking temperature of 860 ° C. for 30 to 200 seconds and then cooling.
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EP4079903A4 (en) * | 2019-12-19 | 2023-02-22 | Posco | Cold-rolled steel sheet having excellent thermal-resistance and moldability, and method for manufacturing same |
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JPH02156023A (en) * | 1988-12-09 | 1990-06-15 | Sumitomo Metal Ind Ltd | Manufacture of cold rolled steel sheet having good formability |
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