JP3546605B2 - Manufacturing method of steel sheet for cans - Google Patents

Description

【００４３】
【表２】

【００４４】
【表３】

以上の方法で製造した冷延鋼帯の平坦度を測定するとともに、ぶりき原板の幅方向各位置における硬さ（ＨＲ３０Ｔ） ，ランクフォード値（ｒ値）およびその面内異方性Δｒを測定した。
なお、平坦度は冷延鋼帯の長さ方向の各位置から幅×１０００ｍｍ長の大板を切り出し、定盤上に静置し、耳伸び、中伸びなど、高さをトースカンを使って測定した。またｒ値は、
ｒ＝（ｒ_ｌ ＋２ｒ_Ｄ ＋ｒ_Ｃ ）／４により、Δｒは、
Δｒ＝（ｒ_ｌ −２ｒ_Ｄ ＋ｒ_Ｃ ）／２、または調質度ＤＲ材のように、伸びが小さく塑性歪み法で測定することが不可能な超硬質鋼板については、固有振動法（ＪＩＳ Ｇ３１３５、１９８６解説、参考２）にて測定した。
ただし、ｒ_ｌ 、ｒ_Ｄ 、ｒ_Ｃ は、それぞれ圧延方向、圧延方向に対し４５°の方向、圧延方向に対し９０°の方向のランクフォード値を表す。
これらの測定結果を表３、表４に示す。
【００４５】
上記ぶりき原板に，ハロゲンタイプの電気すずめっき工程にて各種のすずめっき後，リフロー処理（溶錫化処理），クロメート処理を連続して行い，ぶりきに仕上げた。
使用したＳｎめっき浴およびリフローおよびクロメート条件は下記の通りである。
・Ｓｎめっき
浴組成 塩化第１スズ ７５ｇ／ｌ
弗化ナトリウム ２５ｇ／ｌ
弗化水素カリウム ５０ｇ／ｌ
塩化ナトリウム ４５ｇ／ｌ
Ｓｎ^２＋ ３６ｇ／ｌ
Ｓｎ^４＋ １ｇ／ｌ
ｐＨ ２．７
浴温度 ６５℃
電流密度 ４８Ａ／ｄｍ^２
・リフロー条件
通電加熱 ２８０℃
・クロメート
液組成 無水クロム酸 １５ｇ／ｌ
硫酸 ０．１３ｇ／ｌ
液温度 ４０℃
電流密度 １０Ａ／ｄｍ^２
陰極電解処理
【００４６】
また、ティンフリー鋼板は電気めっきラインで，先ずＣｒＯ_３ ；１８０ｇ／ｌ，Ｈ_２ ＳＯ _４；０．８ｇ／ｌのクロメート液で金属Ｃｒ量５〜１２０ｍｇ／ｍ^２ のめっきを施した後，引き続きＣｒＯ_３ ；６０ｇ／ｌ，Ｈ_２ ＳＯ _４；０．２ｇ／ｌのクロメート液で酸化Ｃｒ（クロム換算量で１〜３０ｍｇ／ｍ^２）のめっきを行って仕上げた。
【００４７】
これらのめっき鋼板を用い，３ピース缶については曲げ加工を施して耐フルーティング性および高速溶接性のテストを行った。
フルーティング性の評価は、缶胴の成形に相当するように曲げ加工を施し，胴体に発生した折れが商品として見るに耐えない程度のものまたは設計通りの真円度が得られず偏平になったもの（×印で表示）と、そうでないもの（○印で表示）に判定した。
高速溶接性は、銅ワイヤー型電気抵抗加熱シーム溶接機でワイヤー速度６５ｍ／分，溶接圧力４０ｋｇ，周波数６００Ｈｚで溶接して，散り（スプラッシュ）の発生しない上限電流値とピール溶接強度（溶接部の一端に切り込みを入れ，溶接部を缶胴から引き剥がすピールテスト法により溶接部の全長が引きちぎれるものが強度が十分と判定）が得られる下限電流値の差を適正溶接電流範囲として評価し，５Ａ以上あれば高速溶接の工程化が可能と判定して，さらに，フランジ拡缶成形で溶接部の近傍から割れない，いわゆるＨＡＺ（ｈｅａｔ ａｆｆｅｃｔｅｄ ｚｏｎｅ）割れが発生しないことを確認して最終判定とした。
【００４８】
また、２ピース缶については，缶壁の傷付性を評価し，肉眼観察で傷が確認されないもの（○印で表示）と，傷が確認され，耐蝕性が悪くなると推定されるもの（×印で表示）に判定した。
これらのめっき条件、製缶結果を表５にまとめて示す。
【００４９】
【表４】

【００５０】
【表５】

【００５１】
以上の実施例から、本発明例はすべて、冷延鋼帯における耳伸び、中伸びも少なく平坦度が良好であること、調質後の幅方向の硬さが中央〜幅端５ｍｍの位置まで均一であり、ｒ値、Δｒも全幅にわたって一様で、しかも優れた値を示している。とくに、実施例において、幅中央部と幅端５ｍｍの位置のＦＤＴの差は、３５℃以上もあり、従来このような温度差を有しては冷延鋼帯の均一性は実現できなかったところ、本発明で達成しえた意義は大きい。
【００５２】
【発明の効果】
以上説明したように、本発明法によれば，低Ｃの鋼からなるシートバーの幅端部を加熱昇温して、圧延終了温度を全幅にわたってＡｒ_３変態点未満〜（Ａｒ_３変態点−１００℃）に維持して熱間圧延することにより、鋳片の再加熱を施さずとも、均一な材質の熱延鋼帯を製造でき，その結果、均一な材質を有し、プレス加工性、製缶性にも優れる缶用鋼板を製造することが可能になる。
また，本発明法によれば，さらに、シートバーの接合による連続熱間圧延、熱延後の冷却制御、熱延鋼板の薄厚化による冷延圧下率の低減などを行うことにより、熱延終了温度の低温化にもかかわらず，結晶粒径が大きく，ｒ値が大きい深絞り加工性に優れる缶用鋼板を製造することが可能になる。
以上の結果、合理的に再加熱を省略して熱間圧延を行い、缶用鋼板を製造できるようになるので、省エネルギー、生産性の向上に大きく寄与する。
【図面の簡単な説明】
【図１】従来の、再加熱を省略した熱間圧延法で圧延した熱延鋼帯における結晶粒組織およびＦＤＴの分布関係を示す図である。
【図２】熱延鋼帯幅方向の硬さ分布に及ぼすＦＤＴと結晶粒組織の影響を示す図である。
【図３】熱間圧延後部における熱延鋼帯幅方向の硬さ分布に及ぼす幅端部加熱、熱延後放冷時間の影響を示す図である。
【図４】熱間圧延後端部における熱延鋼帯幅方向の硬さ分布に及ぼす圧延方式（連続、単一）、幅端部加熱および熱延後空冷時間の影響を示す図である。
【図５】ｒ値に及ぼすＣ量，ＦＤＴおよび冷間圧延圧下率の影響を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a rational method for producing a steel sheet for cans, and in particular, to a two-piece can (SDC: Shallow-Draw Can Can) made by various tempering methods and all temper degrees T1 to T6 and DR8 to DR10. , DRDC: Drawn & Reddraw Can, DTRC: Drawn & Thin Drawn Can, DWIC: Drawing & Wall Ironing Can, three-piece cans made by joining the body (Side Seam Soldeed, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Sold, Used, Sold, Carved, and Solded) Can)), and after laminating a plain film on both front and back sides, or using a printed film for the outer surface of the can. , Can be made without any problem even after laminating a plain film on the back side. Also, the winding direction of the body plate at the time of canning of three-piece can does not matter in the rolling direction or the sheet width direction. The present invention relates to a method for economically producing a steel plate for cans having a uniform material.
[0002]
[Prior art]
The steel plate for cans is subjected to various platings such as Sn, Ni, and Cr, and then made into cans, and used for beverage cans, food cans, and the like. In particular, the production of beverage cans, which account for more than 95% of cans, has been increasing steadily, and today, it has become possible to consume 1 can / day of beverage cans per capita. Reasonably increasing the productivity of steel plates for cans, which have become mass consumer goods, is becoming increasingly important from the global environment as well.
What is notable in this steel sheet for cans is that it is extremely thin and requires a uniform material in the width direction as compared with other steel sheets.
[0003]
By the way, in order to manufacture the above-mentioned steel sheet for cans, a method which has been generally adopted in the past is to continuously melt molten steel of low-carbon steel or ultra-low-carbon steel whose components have been adjusted by a converter and vacuum degassing. After solidifying into a slab by the casting method, the surface defects of the slab are removed, reheated in a heating furnace, rolled into sheet bars by several rough rolling mills, and then finished to a thickness of several mm by a finishing rolling mill. After being formed into a hot-rolled steel strip, it was immediately cooled with water and wound up to finish a hot-rolled steel sheet, which was pickled, cold-rolled, annealed, temper-rolled, and then subjected to the above-mentioned various platings.
In the above manufacturing method, it can be said that 60% or more of the manufacturing cost and quality is controlled in the stage of manufacturing a hot-rolled steel strip from a continuously cast slab. Therefore, it has been strongly desired to establish a rational manufacturing method that satisfies both manufacturing cost and quality, particularly in this step.
From such a viewpoint, if it is possible to manufacture the continuous cast slab by a process of directly hot rolling without reheating, energy saving and a reduction in the process can be achieved, which is advantageous in terms of manufacturing cost.
[0004]
Now, there are problems to be solved in order to directly hot roll slabs, and some of them have been solved to a large extent by previous efforts.
First, the establishment of a defect-free slab manufacturing technique can be mentioned. That is, if the continuous cast slab is once cooled and the surface defects are carefully removed as in the prior art, the temperature of the slab is greatly reduced, and it is impossible to perform direct rolling without passing through a heating furnace. For this reason, defect-free slabs are indispensable. Refining in a bottom-blowing converter and high-purity steel by vacuum degassing, use of a large-capacity tundish / vertical-bending continuous casting machine, and suppression of fluctuations in the mold level in the mold The problem was solved by optimizing the discharge flow in the molten steel by optimizing the discharge shape of the immersion nozzle, controlling the flow of the molten steel in the mold by using an electromagnetic brake, and adopting a mold flux with excellent inclusion absorption capacity. Production is now possible.
[0005]
In addition, continuous casting and the establishment of technology for changing the width of hot-rolled steel strip also contributed greatly. That is, the conventional technology could not efficiently cope with various order widths of steel sheets, but in order to enable the development of large width reduction technology using slab sizing mills and slab width presses, and to enable different width rolling in finishing mills. The development of high-strength abrasion-resistant rolls, technology for preventing local abrasion of rolls, and the application of an online roll grinder to locally worn rolls have made it possible to solve the problem. Crown control was greatly improved by the use of cross rolls. The degree of freedom in finish rolling, the development of schedule-free rolling technology, and the dimensional accuracy of steel sheets were improved.
[0006]
Furthermore, in order to directly hot roll the slab, it is necessary to establish a technique for coping with a decrease in the slab temperature. If the slab temperature after continuous casting is low and hot rolling is performed without passing through a heating furnace, the same slab is stretched significantly at high slab temperatures, and hardly stretches at low temperatures. It was difficult to perform rolling in a straight line, exceeding the limit. In addition, the finish rolling end temperature (FDT) must be set to Ar to obtain a good r value.₃It is considered necessary to keep the temperature higher than the temperature (for example, Japanese Patent Application Laid-Open No. 4-333525), and it has been required to secure the temperature during hot rolling to a certain level or higher.
To cope with these, the continuous casting machine and the hot rolling mill are connected directly and short-circuited, and the temperature drop during transportation or rolling is minimized based on the equipment arrangement that keeps heat and insulates between them. To increase the thickness of the slab, to develop a high-speed casting technology, to adopt a water-cooling system that focuses water cooling on the center of the slab in the width direction, and to omit the cooling in the latter half of the casting process, The effective use of latent and sensible heat has led to the use of higher slab temperatures, as well as increased heating to the width-wise end (width end) where the slab temperature drops significantly. .
[Problems to be solved by the invention]
[0007]
However, even if these conventional techniques are applied, the temperature required for hot rolling to a steel sheet having a large thickness, such as a steel sheet for automobiles, can be ensured, but a hot steel sheet for a can having a small thickness can be obtained. It was difficult to secure the temperature required for rolling.
As described above, even if the technical development of facilities is advanced, if reheating is omitted, low-temperature rolling and low-temperature winding are inevitable as compared with the conventional reheating method. In addition, the temperature drop is remarkable at the width end of the hot-rolled steel strip, or furthermore, at the leading end and the rear end in the longitudinal direction of the steel strip, resulting in unevenness of the material in the steel strip and the resulting defective shape of the steel strip. Was inevitable.
[0008]
Accordingly, an object of the present invention is to provide a can steel plate having a uniform material in the width direction of the steel strip even if the reheating of the slab is omitted, in view of the above-mentioned problems of the prior art. It is to provide a manufacturing method.
Another object of the present invention is to provide a steel sheet for cans having uniform hardness, Rankford value (r value), and other materials from the position at the end of 5 mm in the width direction to the center even if reheating of the slab is omitted. It is to provide a manufacturing method.
Still another object of the present invention is to provide a steel strip having uniform hardness and Rankford value (r-value) in the width direction and the length direction of the steel strip even if reheating of the slab is omitted. Another object of the present invention is to provide a method for producing a steel sheet for cans having a can-making process characteristic and capable of being used for various can-making applications.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the inventors have directly connected a continuous casting machine and a hot rolling mill, and have used a short-circuited equipment line, and have used a hot-rolled steel strip for cans without reheating the slab. We studied the technology for manufacturing. In particular, focusing on sheet bar soaking temperature control, cooling control from immediately after the exit of the finishing mill to winding up, and the composition of steel, the results of a diligent study that returned to the origin of steel plate manufacturing technology for cans by direct rolling By properly controlling these conditions, it was found that the above problem could be solved, and the present invention was completed. That is, the gist configuration of the present invention is as follows.
[0010]
(1)The composition of the steel is C: 0.03wt %Less than, Si : 0.03wt %Less than, Mn : 0.05 ~ 0.30wt %, P: 0.02wt % Or less, S: 0.02wt %Less than, Al : 0.02 ~ 0.10wt %, N: 0.01wt % Or less, O: 0.005wt % Or less, with the balance being Fe And unavoidable impuritiesThe continuous cast slab is immediately hot-rolled without passing through a heating furnace, and the both ends of the sheet bar obtained by the rough rolling are heated and heated, so that the rolling end temperature is over the entire width of the steel strip. Ar_ThreeBelow the transformation point, (Ar_ThreeHot finish rolling so that the transformation point is -100 ° C) or moreAfter doing Ten Let cool for a second and continue 100 ° C / sec Cool at the above speed, 700 Winding below ℃And thereafter performing cold rolling, annealing and temper rolling.
(2) The continuous cast slab, in addition to the component composition, Nb : 0.10wt %Less than, Ti : 0.20wt % Or less and B: 0.005wt % Or any one or more selected from below. (1) 3. The method for producing a steel sheet for cans according to 1.).
[0011]
(3) After joining the sheet bar obtained by hot rough rolling with the preceding sheet bar, both ends are heated and heated.Or (2)3. The method for producing a steel sheet for cans according to 1.).
[0013]
(4) Production of a steel sheet for a can according to any one of the above (1) to (3), wherein the hot finish rolling is performed to a finished plate thickness of 2.0 mm or less and the cold rolling is performed to a rolling reduction of 90% or less. Method.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The inventors first use a conventionally known method, that is, a method in which a continuous casting machine and a hot rolling mill are simply directly connected in a straight line, and a method of performing hot rolling using a short-circuited equipment row and omitting reheating. The metal structure and material properties of the manufactured hot rolled steel strip were investigated.
At this time, the size of the cast slab is 260 mm thick × 1000 mm wide, and the hot cast slab after continuous casting is hot-rolled without reheating by large rolling and ultra-high-speed rolling (finish rolling finish temperature: Ar₃Above) to obtain a 2.0 mm 2 hot-rolled steel strip. FIG. 1 shows the results of investigating the crystal grain size distribution of the obtained hot-rolled steel strip with an optical microscope.
As shown in FIG. 1, it was found that the distribution of the crystal grain size was largely divided into three regions, and became uneven in both the width direction and the length direction. This phenomenon is different from the fact that, when manufactured by the conventional reheating method under the same conditions, the crystal grain size distribution becomes fine grains which are substantially uniform over the entire width and the entire length.
[0017]
Even if the hot-rolled steel sheet with the grain size distribution as shown in Fig. 1 is pickled and cold-rolled, the width direction end and length direction end of the steel strip having a large grain size are larger than the center. As a result, the elongation increases and the cold rolled steel strip has poor flatness.
And even if this cold-rolled steel strip is apparently flattened by temper rolling after continuous annealing, it is slit-cut into blank sheets in can units after printing in the can making process of three-piece cans. When this is done, the peripheral constraints are released, warping in the rolling direction or warping in the width direction of the sheet, making it a blank sheet with almost irregular flatness in one large sheet, making it difficult to make cans I understood.
In the two-piece can method, which is made by pressing, if the deep drawing is performed directly from a large coil, the above-mentioned problem does not occur. Since the can height is not uniform at the width direction end and the length direction end of the hot-rolled steel strip than at the center, the thickness distribution in the circumferential direction of the can body also becomes uneven. It turned out that it was not finished in a normal can. This was considered to be due to the deterioration of the in-plane anisotropy (Δr) of the r value.
[0018]
The present inventors have investigated and examined the cause of the above-described grain size distribution, particularly the relationship with the hot finish rolling end temperature (hereinafter, simply abbreviated as “FDT”). Thought so.
That is, FDT is Ar₃In the austenite (γ) single-phase region above the transformation point temperature, it has a hot-rolled structure immediately after the final stand exit side of the finishing mill, but after γ is recrystallized and further cooled, ferrite (γ) The transformation of α) occurs, resulting in fine grains. If the coiling temperature (CT) at the time of winding into a coil is high, the grain size increases by self-annealing, and the carbides also aggregate and coarsen. In addition, if it is wound at a low temperature, the particle size becomes fine and the carbide becomes fine.
On the other hand, if FDT is Ar₃In the (α + γ) two-phase region below the transformation point temperature, the portion of γ goes through the same process as above, but the portion of α simply becomes strain-annealing. That is, after hot working at a light reduction rate (approximately 10 to 20%) of the final stand, if winding is performed at a high temperature, annealing proceeds, and the crystal grain size becomes extremely large. Therefore, when the FDT is in the two-phase region, a mixed structure of grains in which γ has been transformed into α and grains in which α has been extremely coarsened by strain-annealing has a coarse structure as a whole. In addition, if the film is wound at a low temperature, the particle size becomes smaller corresponding to each temperature, but still, it basically becomes a coarse grain structure.
[0019]
For this reason, even if reheating is omitted, if the CT is the same, the center of the hot-rolled steel strip in the width and length directions is Ar₃The FDT above the temperature can be secured, and the crystal grain size becomes fine. However, the peripheral part of the hot-rolled steel strip was reduced in temperature by the temperature drop during hot rolling.₃The temperature becomes lower, resulting in a coarse-grained structure.
Also, FDT is Ar₃Even in the central part where the temperature can be maintained, a temperature gradient occurs due to the difference in temperature drop during hot rolling, and the self-annealing temperature after winding into a large coil can be maintained at a higher temperature in the central part. As a result, even in the central part, the outer peripheral part is Ar₃Since the temperature is just above the temperature, the crystal grain size becomes smaller. That is, the central portion is further divided into two regions, and the crystal grain structure band becomes three regions. In FIG. 1, the FDTs corresponding to these are shown together with the crystal grain structure.
[0020]
FIG. 2 shows that the FDT at the center of the plate width was changed to Ar₃Point (Ar₃: 900 ° C.) or more, and Ar₃The results obtained by examining the hardness and the crystal grain size in the width direction of the sheet, respectively, in the case of manufacturing as less than are shown.
From FIG. 2, it can be seen that the FDT, which has been conventionally used in common sense, is₃Even when hot rolling is performed under the conditions of not less than the point, the hardness at the width end from the width end to 40 to 50 mm is small, and the hardness at the position 5 mm from the width end becomes extremely small, and vice versa. In addition, it was found that the inside of the width end became fine grains and the hardness became large, and the hardness was uneven over a wide area of the width end.
As described above, in the conventional reheating omission method, the FDT is transferred to the width end by Ar₃Therefore, it is difficult to obtain a hot-rolled steel strip having a uniform material in the width direction. If this is cold-rolled as it is, the width edge is elongated, resulting in so-called “ear extension” failure, and the boundary between the center and the edge is extremely difficult to stretch, resulting in poor warpage after cold rolling. It is possible to become.
Even with such a manufacturing method, due to high strength and wide and ultra-thin, the edge of the width must be removed by trimming and the blank warpage must be removed by a large plate, and the product yield is low (economically). Worse).
In addition, a method of preventing the temperature decrease at the width end by heating with a sheet bar edge heater provided between the rough rolling mill and the finishing rolling mill can be considered, but the FDT at the width end is actually reduced by Ar.₃It was difficult to ensure the above because the load on the heater was large. In addition, the heating method using the sheet bar edge heater, as described above, uses Ar₃Since a small temperature change directly above causes a large change in the tissue, control for obtaining a uniform tissue in the width direction has not actually been realized.
[0021]
On the other hand, in FIG.₃On the other hand, when hot rolling is performed below the point, the hardness at the width end increases, but the uneven width is as small as about 20 mm, and the hardness is a mixture of fibrous structure and fine grains. The outermost part is large, but otherwise low. From these facts, the inventors considered that the recrystallization of the fibrous structure can be achieved with a relatively small temperature compensation, and the unevenness in hardness in the width direction is eliminated.
In other words, the inventors have proposed that FDT be replaced with Ar₃It is considered that it is technically impossible to secure a high temperature above the point, especially for an extremely thin steel plate for a can, and conversely, FDT is considered to be insane conventionally.₃It was thought that if hot rolling was performed at a low temperature region below the point, a hot rolled steel strip for cans having a uniform material could be produced economically with a small amount of heat supply.
[0022]
However, based on such an idea, the FDT is reduced to Ar by a reheating omission method (a method in which the slab after continuous casting is not reheated).₃When hot rolling is performed below the point to manufacture a steel sheet for cans, there are still other problems to be solved as listed below.
1) Ar₃As shown in FIG. 1, when the FDT is rolled at an FDT of less than 10 mm, the fibrous structure remains in a part of the width end of the hot-rolled steel strip, particularly in the range of several tens mm from the width end, and the crystal grain size is sufficiently large. Does not grow. When this steel strip is subjected to cold rolling, it becomes a cold-rolled steel strip having poor flatness.
2) As shown in Fig. 1, a part of the rear end in the longitudinal direction of the steel strip has the same structure as in 1) above, and cannot be used for steel plates for cans. . This amount reduces the yield by about 10%, which is more uneconomical than the energy saving effect by omitting reheating. It is considered that the reason for this is that the rear end of the rolling has a long waiting time in front of the hot finish rolling mill and a large temperature drop.
3) Ar₃When hot rolling is performed below the point, the crystal grain size becomes large as a whole, and becomes excessively large in some cases. In some cases, a rough surface phenomenon called orange peel during press working or breakage occurs in severe overhanging work. This phenomenon is a serious problem, especially for two-piece cans.
4) Ar₃If hot rolling is performed below the point, the r-value becomes poor, and it cannot be used for severe press working in a two-piece can.
[0023]
To solve these problems, the inventors have further studied and found that the following means are extremely effective in solving these problems.
{Circle around (1)} In order to compensate for the temperature drop at the width end, the sheet bar is heated and heated by an edge heater. The finishing temperature of the hot finish rolling is set to be Ar over the entire width of the steel strip (range from the center to a position 5 mm inside from the width end).₃Below the transformation point, (Ar₃(Transformation point-100 ° C) or more.
For this purpose, for example, the heating range of the sheet bar by the edge heater may be set to about 30 mm from the width end. The heating method may be any method such as induction heating.
By performing the heating / heating operation in this manner, the FDT has a substantially uniform distribution over the entire width from the center of the plate width to the position of 5 mm at the width end, and the crystal grains at the width end are slightly more than those at the center. Although small, there is almost no fibrous structure affecting flatness, and a substantially uniform hot-rolled steel strip in which the grain structure in this range exhibits a coarse-grained mixed-grain structure is obtained.
If the FDT becomes too low, the mixed grain structure of fibrous and fine grains as described above is difficult to be eliminated.₃(Transformation point −100 ° C.) or more.
FIG. 3 shows the effect of increasing the heating temperature of the end portion of the steel strip width by the sheet bar edge heater. Thus, it was found that when the width end was heated and heated, the hardness distribution in the steel strip width direction was improved, and the flatness of the cold-rolled steel sheet was also improved.
From these facts, by heating and heating both width end portions of the sheet bar obtained by the rough rolling, the rolling end temperature is increased over the entire width of the steel strip from the center in the width direction to the position of 5 mm in the width end.₃Below the transformation point, (Ar₃(Transformation point −100 ° C.) or higher, preferably (Ar₃It is necessary to perform hot finish rolling so that the transformation point becomes −70 ° C. or more.
[0024]
{Circle around (2)} The sheet bar is joined to the preceding sheet bar before the width end is heated and heated. Prior to this joining, the sheet bar is wound up in front of the finishing mill, and its leading and trailing ends are reversed to be joined to the preceding sheet bar.
FIG. 4 shows the effect of joining a sheet bar with a preceding sheet bar and performing continuous finish rolling on the hardness distribution in the width direction of the hot-rolled steel strip at the rear end of the hot rolling. As shown in FIG. 4, when the sheet bars are joined and subjected to continuous finish rolling (FIG. 4 (a)), the material in the width direction of the steel strip is smaller than the finish rolling in slab units (FIG. 4 (b)). It can be seen that is uniform. At that time, it was also found that it is effective to reverse the front and rear ends of the sheet bar finished by rough rolling as a method of preventing the temperature drop at the rear end in the longitudinal direction.
[0025]
To achieve continuity in the finishing mill, the sheet bar joining timing is adjusted, and the joining device itself joins the sheet bars within 20 seconds while moving according to the speed of the sheet bar. It is desirable to use a short-time bonding machine that heats and compresses the sheet by an electromagnetic induction method in order to prevent the temperature of the sheet bar from lowering. Further, the sheet bar before joining can be wound around a coil in order to secure the time for keeping the temperature of the sheet bar, equalizing the temperature, reversing the front and rear ends, and joining.
The rough rolling start temperature is desirably 1100 to 1200 ° C. Further, after finishing the hot finish rolling and taking up the coil, pickling, cold rolling (rolling rate is as described above), and recrystallization annealing (680 to 800 ° C.) are performed according to a conventional method. % To give a steel sheet for cans.
[0026]
{Circle around (3)} After completion of hot finishing rolling, gradually cool by cooling in the air for 2 to 10 seconds, cool at a rate of 100 ° C./sec or more, and wind at a temperature of 700 ° C. or less.
Rather than starting water cooling immediately after the finish rolling (immediately after the finish rolling mill exit side) as in the conventional method, the crystal grains at the width end are gradually cooled by being allowed to cool in the air for 2 to 10 seconds. It is possible to increase the size to some extent. After the crystal grains have been grown in this manner, the steel strip is strongly water-cooled from the upper and lower surfaces with a large amount of water, cooled at a rate of 100 ° C./sec or more, and wound up at a low temperature of 700 ° C. or less to perform self-annealing. When it is suppressed, a steel strip composed of uniform crystal grains can be obtained, and a steel sheet for cans having a good r value can be manufactured. 3 and 4, the influence of the cooling time can be confirmed.
Here, if the slow cooling time is less than 2 seconds, the crystal grain growth is insufficient, and if it exceeds 10 seconds, the α grain size becomes coarse, and the grains become coarse even after recrystallization annealing. This is not preferred because it is likely to cause cracks. Further, if the CT exceeds 700 ° C., the carbides become coarse even if water-cooled in a short time, the crystal grain size becomes large, and the descaling property in pickling deteriorates. . In order to obtain T1 hardness even when the recrystallized grain size becomes fine and becomes hard, it is preferable to wind the film at 400 ° C. or higher.
[0027]
{Circle over (4)} The finished plate thickness of the hot finish rolling is 2.0 mm or less, and the rolling reduction of the cold rolling is 90% or less.
The improvement of the r value is usually achieved by raising the CT temperature, but as described in (3) above, the Ar value is improved.₃If rolling is performed below the point, high temperature CT must be avoided. Therefore, it has been found that it is effective to reduce the cold rolling reduction to 90% or less as an alternative measure. However, if the rolling reduction is less than 50%, the recrystallized grain size becomes coarse and the skin becomes rough as described above. This is because the size of the grains reached by recrystallization becomes smaller as the working ratio becomes larger and the cold reduction ratio becomes higher. In particular, those having a low working ratio become too large, so that 50% or more should be secured. desirable. Conventionally, the hot-rolled finished plate thickness of a steel plate for cans is 2 mm or more, and the product plate thickness is thicker than thinner. For this reason, the rolling reduction of the cold rolling usually exceeds 90%, and a sufficient r value cannot be obtained.
However, the r-value can be improved if the cold reduction can be reduced, but there is a limit in producing a thin hot-rolled steel strip due to the mill power of the hot rolling mill. In the conventional method in which hot rolling is performed on a slab basis by a hot rolling mill, a steel strip having a small thickness is subjected to finish-rolling and then cooled with water while being accurately placed on a winding machine that is a few hundred meters ahead. In order to achieve this, it is necessary to impart a certain degree of rigidity to the hot-rolled steel strip, and there is a limit in the production of a hot-rolled steel strip having a small thickness (small rolling reduction). However, if it is joined to the preceding sheet bar in front of the finishing mill and continuous rolling is performed, a thin hot-rolled steel strip can be manufactured without such a concern.
[0028]
{Circle around (5)} The C content in the steel is set to 0.03 wt% or less.
Ar₃The point is dominated by the C content, and in the low carbon steel region, when the C content increases, the Ar₃The spot gets cold. In this case, the FDT is also Ar₃The temperature becomes low corresponding to the point, the amount of heat at the end is insufficient, and the crystal grain size does not increase, resulting in an uneven distribution of crystal grains. Therefore, in order to produce a hot-rolled steel strip having a uniform crystal grain distribution by the reheating elimination method, Ar₃High dot, low C component compositions are advantageous.
Also, lowering the C is advantageous for improving the r value. Ar₃FIG. 5 shows the results of an experiment conducted to improve the r value on the assumption that hot rolling is performed with an FDT below the point. From FIG. 5, it can be seen that when the C amount is reduced to 0.03 wt% or less, the r value is remarkably improved. According to FIG. 5, it is also effective to reduce the amount of Mn.
From these two viewpoints, the C content needs to be 0.03 wt% or less. Incidentally, the amount of C and Ar₃As a result of examining the relationship with the point, the C content was 900 ° C. at 0.01 wt%, 870 ° C. at 0.03 wt%, 840 ° C. at 0.06 wt%, and 800 ° C. at 0.09 wt%.
[0029]
Next, the component composition of steel suitable for the method of the present invention will be described, including the reasons for limitation.
As described above, C is an important element for controlling the recrystallization temperature and the recrystallization particle size and improving the press workability. FDT to Ar₃In order to increase the crystal grain size at the end of the hot-rolled steel strip which has been hot-rolled below the point, it is preferable to set the FDT temperature as high as possible.₃A steel with a low C composition, whose temperature is high, is preferred. In order to improve the press workability, it is important to reduce the C content, increase the crystal grain size, and increase the r value. Thus, the FDT is changed to Ar₃Despite performing hot rolling at less than the point, in order to produce a steel sheet for cans having a good r value, the C content needs to be less than 0.03 wt%.
[0030]
Si is an element that not only deteriorates the corrosion resistance of the tinplate but also makes the material extremely hard, so that it should be avoided to contain excessively. Therefore, it is important to reduce as much as possible at the steel making stage.₂In order to suppress the reduction of Al by the Al in the molten steel, consideration must be given to using a zircon refractory instead of the conventionally used chamotte refractory.
Specifically, if the Si content exceeds 0.03 wt%, the material becomes hard, and it becomes impossible to manufacture tinplates having temper degrees T1 to T3. Therefore, the Si content is limited to 0.03 wt% or less. There is a need.
[0031]
Mn needs to be added to prevent the occurrence of edge cracks in the hot-rolled coil due to S. Since this edge crack is directly controlled by S, it is not necessary to add Mn if the amount of S is small. However, since S is inevitably contained in steel, it is necessary to add Mn. There is. Further, as in the case of C, if the Mn is reduced, the r value can be improved. If the Mn content is less than 0.05 wt%, the occurrence of ear cracks cannot be prevented. On the other hand, if the Mn content exceeds 0.30 wt%, the crystal grain size becomes harder due to the refinement of the grain size and the solid solution strengthening, and the r value increases. Therefore, the content is in the range of 0.05 to 0.30 wt%.
[0032]
P is an element hardening the material and deteriorating the corrosion resistance of the tinplate, so its excessive inclusion is not preferred. Therefore, the content is set to 0.02 wt% or less.
[0033]
If S is excessively contained, S which has been dissolved in the high temperature γ region of hot rolling becomes supersaturated with a decrease in temperature, and precipitates as (Fe, Mn) S at the γ grain boundary to cause red hot embrittlement and heat. This may cause cracking of the rolled coil. Further, it becomes an S-based inclusion and causes a press defect. Therefore, the S content is limited to 0.02 wt% or less. In order to prevent the occurrence of edge cracks or press defects, it is particularly desirable that the Mn / S ratio be 8 or more.
[0034]
Al is an element necessary for the deoxidation of steel, and the higher the content, the higher the cleanliness of the steel. However, excessive addition suppresses the growth of the recrystallized grain size and economically. Since it is not preferable, the amount of Al added is set to 0.10 wt% or less. On the other hand, the lower limit of the amount of Al is essentially that there is no need to deoxidize with the amount of Al corresponding to the amount of dissolved oxygen in the molten steel and leave it as metallic Al in the steel. Tinplate is less clean. Furthermore, in order to obtain a soft tinsel, it is necessary to fix solid solution N with Al and reduce the remaining amount. Therefore, the Al content is in the range of 0.02 to 0.10 wt%.
[0035]
N is an element mixed from N in the air during the steel manufacturing process, and if it is dissolved in steel, a soft steel plate cannot be obtained. For this reason, it is necessary to minimize the incorporation of N from the air during the steelmaking process and to limit it to 0.01 wt% or less.
[0036]
O forms an oxide with Al, Mn in the steel or Ca, Na, F, etc. of the Si flux of the refractory, causing cracks during press working and deteriorating the corrosion resistance. There is. In particular, when the O content exceeds 0.005 wt%, these adverse effects become remarkable, so the content is limited to 0.005 wt% or less.
As a method for suppressing the amount of O, it is effective to take measures for strengthening deoxidation by vacuum degassing, adjusting the weir shape of the tundish, the shape of the nozzle, and the casting speed. Increasing the amount of Al in the steel in the course of these means is effective because flotation is promoted by clustering inclusions.
[0037]
In order to further improve the workability, it is effective to add B to Ti and Nb for work embrittlement resistance.
Nb is an element that forms carbides and nitrides and reduces the remaining amount of solid solution C and solid solution N. On the other hand, when a large amount is added, the recrystallization temperature rises due to the pinning effect of the crystal grain boundaries by the Nb-based precipitates, and the workability in the continuous annealing furnace is deteriorated and the steel strip structure is refined. . Therefore, the added amount of Nb is set to a range of 0.1 wt% or less. Note that a preferable addition amount is 0.001 wt% or more.
[0038]
Ti is an element that forms carbides and nitrides and reduces the remaining amounts of solid solution C and solid solution N. On the other hand, if it is added in a large amount, a sharp pointed precipitate is formed, which is confirmed by microscopic observation of the cross section of the steel sheet, thereby deteriorating corrosion resistance and causing scratches during press working. Therefore, the amount of Ti to be added is in the range of 0.20 wt% or less. Note that a preferable addition amount is 0.0001 wt% or more.
[0039]
B is an element having an effect of suppressing embrittlement cracking after press working, which is a concern when the solid solution C is reduced by adding a carbide forming element to ultra-low carbon steel. In this embrittlement cracking, P segregates at the grain boundary and becomes embrittled when the amount of solute C decreases. B plays the role of solid solution C at that time, or B itself increases the grain boundary strength to suppress embrittlement. B also forms carbides and nitrides and is therefore effective for softening. However, if added in an excessively large amount, B will segregate at the recrystallized grain boundaries during continuous annealing, delaying the recrystallization, so that it is added in an amount of 0.005 wt% or less. Note that a preferable addition amount is 0.0001 wt% or more.
[0040]
【Example】
Hereinafter, the present invention will be specifically described based on examples.
The continuous casting machine and the hot rolling mill are connected directly and short-circuited linearly, and a heat insulating cover with heat insulating material is provided inside each joint to provide thorough heat insulation and heat insulation. In the line, the implementation and comparison with the method of the present invention were performed.
Steel having the component composition shown in Table 1 was melted by a bottom-blowing converter, and C was cast to 0.03 wt%. Subsequently, the following measures were taken to prevent defects such as cooling and care for the slab. A vacuum degassing treatment was performed to adjust the C content and increase the cleanliness of the molten steel, and Al was added, followed by addition of a carbide forming element and a nitride forming element. These were cast using a vertical bending type continuous caster having a large capacity tundish, each of which is advantageous for producing high cleanliness steel. Here, in order to further promote the floating separation of inclusions for the purpose of further purification, a weir is provided in the tundish to integrate and float the inclusions, and to suppress fluctuations in the molten metal level in the mold. Therefore, a mold flux having a large viscosity (4 poise or more) and an excellent ability to absorb inclusions was used. In addition, in order to normalize the flow of molten steel in the mold and prevent the inclusions from being trapped in the solidified layer, a reverse immersion nozzle with an inverted Y-type 25 ° is used, and in order to prevent the molten steel flow from penetrating deeply, Utilized the brake. In this way, a slab having a thickness of 260 mm and a width of 1000 mm is cast at a high speed at a casting speed of 1.5 m / min or more, and then the center portion in the slab width direction is mainly water-cooled, and the rear end portion is water-cooled. Was omitted, and a defect-free high-temperature slab was obtained.
[0041]
These slabs were rolled by a mill equipped with an ultra-high-speed finishing mill capable of eliminating the reheating, having a large rigidity and capable of large reduction, a maximum rolling speed of 1680 mpm and a short heat radiation time. A sheet bar is manufactured by this rough rolling mill, and the front and rear ends of the sheet bar are reversed, and then the continuous pressure for joining with the preceding sheet bar is obtained.In the endA thinner hot rolled steel strip was used. In hot rolling, the presence or absence of an edge heater (if present, the width of the entire length of the sheet bar is heated and heated), the hot-rolling end temperature (FDT), and cooling conditions after hot-rolling is completed (with an elevated water tank The control valve was subdivided and a hot-run cooling system that can perform strong cooling slowly and rapidly was used), the winding temperature (self-annealing, 30 minutes or more), and the hot-rolled sheet thickness were changed. Then, it was immediately pickled, descaled, and rolled at various rolling reductions in a 6-stand tandem continuous cold rolling mill to obtain a cold-rolled steel strip. Next, the ultra-low carbon steel (C ≤ 0.01 wt%) was continuously annealed at 750 ° C and the low carbon steel (C; 0.01-0.03 wt%) at 680 ° C, and then the rolling reduction of temper rolling was changed. Then, tinplates of various temper degrees were finished. Table 2 shows the hot rolling conditions, and Table 3 shows the cold rolling and temper rolling conditions.
[0042]
[Table 1]

[0043]
[Table 2]

[0044]
[Table 3]

The flatness of the cold-rolled steel strip manufactured by the above method was measured, and the hardness (HR30T), Rankford value (r value), and its in-plane anisotropy Δr of the tinplate were measured at various positions in the width direction. did.
The flatness is measured by cutting a large plate of width x 1000 mm from each position in the length direction of the cold-rolled steel strip, leaving it on the platen, and measuring the height, such as ear extension and medium extension, using a toscan. did. The r value is
r = (r_l+ 2r_D+ R_C) / 4, Δr becomes
Δr = (r_l-2r_D+ R_C) / 2, or ultra-hard steel sheet that cannot be measured by the plastic strain method because of its small elongation, such as tempered DR material, is measured by the natural vibration method (JIS G3135, 1986 commentary, Reference 2). did.
Where r_l, R_D, R_CRepresents a Rankford value in a rolling direction, a direction at 45 ° to the rolling direction, and a direction at 90 ° to the rolling direction, respectively.
Tables 3 and 4 show these measurement results.
[0045]
The tinplate was tin-plated in a halogen-type electroplating step, followed by a reflow treatment (tin-tin treatment) and a chromate treatment, and the tinplate was finished.
The used Sn plating bath and reflow and chromate conditions are as follows.
・ Sn plating
Bath composition Stannous chloride 75g / l
Sodium fluoride 25g / l
Potassium hydrogen fluoride 50g / l
Sodium chloride 45g / l
Sn²⁺            36g / l
Sn⁴⁺              1g / l
pH 2.7
Bath temperature 65 ° C
Current density 48A / dm²
・ Reflow condition
Electric heating 280 ° C
・ Chromate
Liquid composition Chromic anhydride 15g / l
Sulfuric acid 0.13g / l
Liquid temperature 40 ℃
Current density 10A / dm²
Cathodic electrolytic treatment
[0046]
In addition, tin-free steel sheets are used in an electroplating line.₃180 g / l, H₂SO₄A Cr content of 5 g to 120 mg / m in a 0.8 g / l chromate solution²After plating, CrO₃; 60 g / l, H₂SO₄A 0.2 g / l chromate solution containing Cr oxide (1 to 30 mg / m in terms of chromium);²) Plating.
[0047]
Using these plated steel sheets, bending tests were performed on three-piece cans, and fluting resistance and high-speed weldability were tested.
The fluting property was evaluated by bending the can body so as to correspond to the forming of the can body, and bending the body so that it could not withstand the product as a product or the roundness as designed was not obtained. Were determined (indicated by x) and those not (indicated by そ う).
The high-speed weldability is determined by welding with a copper wire-type electric resistance heating seam welding machine at a wire speed of 65 m / min, a welding pressure of 40 kg, and a frequency of 600 Hz. An incision was made at one end, and the peeling test method of peeling off the weld from the can body was judged to be sufficient if the entire length of the weld was torn off.) If it is 5A or more, it is determined that the high-speed welding process can be performed, and furthermore, it is confirmed that there is no so-called HAZ (heat affected zone) crack that does not crack from the vicinity of the welded portion by flange expansion molding, and the final determination is made. did.
[0048]
For two-piece cans, the scratch resistance of the can wall was evaluated, and no damage was confirmed by visual observation (indicated by a circle), and a damage was confirmed and the corrosion resistance was estimated to be poor (×). (Indicated by a mark).
Table 5 summarizes these plating conditions and canning results.
[0049]
[Table 4]

[0050]
[Table 5]

[0051]
From the above examples, all of the examples of the present invention have a low elongation in the cold-rolled steel strip, a low flatness and a low middle elongation, and a hardness in the width direction after tempering from the center to the position at the width end of 5 mm. It is uniform, and the r value and Δr are also uniform over the entire width and show excellent values. In particular, in the examples, the difference between the FDT at the center of the width and the position of 5 mm at the end of the width was 35 ° C. or more, and the uniformity of the cold-rolled steel strip could not be realized with such a conventional temperature difference. However, the significance achieved by the present invention is significant.
[0052]
【The invention's effect】
As described above, according to the method of the present invention, the end of the width of the sheet bar made of low-C steel is heated to raise the rolling end temperature over the entire width.₃Below the transformation point-(Ar₃By performing hot rolling while maintaining the temperature at the (transformation point −100 ° C.), a hot-rolled steel strip having a uniform material can be manufactured without reheating the slab, and as a result, the hot-rolled steel strip has a uniform material, It becomes possible to manufacture steel plates for cans that are also excellent in workability and can-making properties.
According to the method of the present invention, furthermore, continuous hot rolling by joining sheet bars, cooling control after hot rolling, reduction of cold rolling reduction rate by thinning of hot rolled steel sheet, and the like are performed to complete hot rolling. Despite the lowering of the temperature, it becomes possible to produce a steel sheet for cans having a large crystal grain size and a large r value and excellent in deep drawing workability.
As a result, the steel sheet for cans can be manufactured by rationally omitting reheating and performing hot rolling, which greatly contributes to energy saving and improvement in productivity.
[Brief description of the drawings]
FIG. 1 is a diagram showing a crystal grain structure and a distribution relationship of FDT in a hot-rolled steel strip rolled by a conventional hot rolling method without reheating.
FIG. 2 is a diagram showing the effect of FDT and grain structure on hardness distribution in the width direction of a hot-rolled steel strip.
FIG. 3 is a view showing the influence of width edge heating and cooling time after hot rolling on hardness distribution in the width direction of a hot-rolled steel strip in the rear part of hot rolling.
FIG. 4 is a diagram showing the effects of the rolling method (continuous, single), width edge heating, and air cooling time after hot rolling on the hardness distribution in the width direction of the hot-rolled steel strip at the rear end of hot rolling.
FIG. 5 is a graph showing the influence of the amount of C, FDT and cold rolling reduction on the r value.

Claims (4)

The composition of steel is as follows : C: 0.03 wt % or less, Si : 0.03 wt % or less, Mn : 0.05 to 0.30 wt %, P: 0.02 wt % or less, S: 0.02 wt % or less, Al : 0.02 to 0.10 wt %, N: 0.01 wt % or less, O: 0.005 wt % or less, continuous cast slab consisting of Fe and unavoidable impurities is hot-rolled immediately without passing through a heating furnace, and obtained by rough rolling. by Atsushi Nobori both width ends of the sheet bar that is less than Ar ₃ transformation point rolling end temperature is over the entire width of the steel strip, (Ar ₃ transformation point -100 ° C.) hot finish rolling so that above After cooling, it is allowed to cool for 2 to 10 seconds, then cooled at a rate of 100 ° C / sec or more , wound up at a temperature of 700 ° C or less , and then subjected to cold rolling, annealing and temper rolling. Manufacturing method of canned steel sheet. The continuous cast slab, in addition to the component composition, Nb : 0.10wt %Less than, Ti : 0.20wt % Or less and B: 0.005wt %. The method for producing a steel sheet for a can according to claim 1, wherein the steel sheet contains one or more kinds selected from not more than%. The method for producing a steel sheet for a can according to claim 1 or 2 , wherein after joining the sheet bar obtained by the hot rough rolling with the preceding sheet bar, both ends are heated and heated. The method for producing a steel sheet for cans according to any one of claims 1 to 3, wherein hot finish rolling is performed to a finished plate thickness of 2.0 mm or less, and cold rolling is performed to a rolling reduction of 90% or less.

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