JP4728710B2 - Hot-rolled steel sheet having excellent workability and manufacturing method thereof - Google Patents
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本発明は加工性に優れる熱延鋼板およびその製造方法に関するものであり、特に加工性が劣る４４０ＭＰａ級超のグレードであっても優れた加工性を発現させるＣ断面に均一なミクロ組織を圧延方向にも持続的に有している加工性に優れる熱延鋼板およびそのような均一なミクロ組織を有する加工性に優れる熱延鋼板の製造方法に関する。
TECHNICAL FIELD The present invention relates to a hot-rolled steel sheet having excellent workability and a method for producing the same, and in particular, a uniform microstructure in a C cross section that exhibits excellent workability even in a grade exceeding 440 MPa class with poor workability. Furthermore , the present invention relates to a hot-rolled steel sheet having excellent workability that is continuously possessed and a method for producing a hot-rolled steel sheet having such a uniform microstructure and excellent workability.
自動車、家電、容器、産業機械、建材等の素材として広範囲に使用されている薄鋼板は、その製品形状を得るために様々な加工を受ける。この加工の際に発生する割れ、形状不良等の不具合は歩留まり落ちや手入れによる工程増等を引起し、生産性の低下を招くために好ましくない。従って、これら不具合の解消に対する需要家の要求は厳しく、改善のために素材面からの試みとして打抜き、曲げ、張出し、絞り、伸びフランジ等に代表される加工性の指標となる均一伸び、局部伸び、ランクフォード値等の向上がなされてきた。 Thin steel plates used extensively as materials for automobiles, home appliances, containers, industrial machines, building materials, etc. are subjected to various processing in order to obtain their product shapes. Problems such as cracks and shape defects that occur during this processing are not preferable because they cause a drop in yield and an increase in the number of processes due to care, leading to a decrease in productivity. Accordingly, the demands of customers for eliminating these defects are severe, and as an attempt from the material side for improvement, uniform elongation and local elongation, which are indexes of workability represented by punching, bending, overhanging, drawing, stretch flange, etc. The Rankford value has been improved.
一方、近年の地球温暖化問題を背景とした環境対策の必要性から自動車産業をはじめとする幅広い分野で温室効果ガス等削減のため更なる省エネルギー化が要求されている。例えば、自動車の燃費改善施策の一つとして車体軽量化を目的に自動車用鋼板の薄肉化すなわち高強度鋼板の適用が進められている。しかしながら、高強度鋼板の適用拡大に伴って生産現場では加工割れに加えて加工性の指標の１つである形状凍結性に係る「反り」、「ねじれ」等の形状不良が多発するようになりその対策に苦慮するようになった。これら「反り」、「ねじれ」等の形状不良対策としては、これまでの均一伸び、局部伸び、ランクフォード値等の加工性の指標の向上では十分ではなく、今までとは違ったまったく新しい対策が必要とされている。 On the other hand, due to the necessity of environmental measures against the background of the global warming problem in recent years, further energy saving is required in order to reduce greenhouse gases in a wide range of fields including the automobile industry. For example, as one of the measures for improving the fuel consumption of automobiles, thinning of steel sheets for automobiles, that is, application of high-strength steel sheets is being promoted for the purpose of reducing vehicle body weight. However, along with the expansion of the application of high-strength steel sheets, in addition to processing cracks, shape defects such as “warp” and “twist” related to shape freezing, which is one of the indexes of workability, frequently occur. I came to struggle with the countermeasures. As measures for shape defects such as “warp” and “twist”, improvement of workability indicators such as uniform elongation, local elongation, and Rankford value is not sufficient, and it is a completely new measure that is different from the past. Is needed.
形状不良を改善する技術としてスプリングバックや壁そりを低減するために板厚最表面における板面と平行な｛１００｝面の反射Ｘ線強度比が３．０以上で、鋼板の板厚中心層における板面と平行な｛１１１｝面の反射Ｘ線強度比が４．５以上である冷延鋼板が提案されている（例えば、特許文献１参照）。 In order to reduce springback and wall warpage as a technique to improve shape defects, the reflection X-ray intensity ratio of the {100} plane parallel to the plate surface at the plate thickness outermost surface is 3.0 or more, and the plate thickness center layer of the steel plate A cold-rolled steel sheet is proposed in which the reflected X-ray intensity ratio of the {111} plane parallel to the plate surface is 4.5 or more (see, for example, Patent Document 1).
しかしながら、当該技術はスプリングバックや壁そりを低減できるもの「ねじれ」については何ら言及していない。また、製品出荷単位であるコイルの平均値としてスプリングバックや壁そりを低減できるものの、コイル長手、幅方向の面全体として評価すると均質な材料特性が得られているとは限らず、そのためある頻度で割れ、形状不良等の不具合が発生する危険性がある。 However, the technology does not mention anything about “twist” that can reduce springback and wall warpage. In addition, although the springback and wall warpage can be reduced as the average value of the coil, which is the unit of product shipment, uniform material characteristics are not always obtained when evaluated as the entire surface in the longitudinal and width directions of the coil. There is a risk of problems such as cracks and shape defects.
一方、熱間圧延において仕上げ圧延直前または仕上げ圧延中に被圧延材を誘導加熱装置により加熱し、仕上圧延後０．１秒超〜１．０秒未満で一次冷却し、一次冷却後の鋼帯の幅方向および長手方向温度の最高値と最低値の差を６０℃以内とすることでコイル内の幅方向及び長手方向の引張強さの変動が平均値の±８％以内とする技術がある（例えば、特許文献２参照）。 On the other hand, in hot rolling, the material to be rolled is heated by an induction heating device immediately before or during finish rolling, and is subjected to primary cooling in a period of more than 0.1 seconds to less than 1.0 seconds after finish rolling, and a steel strip after primary cooling. There is a technology that makes the fluctuation of the tensile strength in the width direction and the longitudinal direction in the coil within ± 8% of the average value by making the difference between the maximum value and the minimum value of the temperature in the width direction and the longitudinal direction within 60 ° C. (For example, refer to Patent Document 2).
しかしながら、当該技術はコイル内の引張強さの変動を小さくするものの、材料の加工性に関わる「反り」、「ねじれ」等の形状不良そのものを改善する技術ではない。 However, although this technique reduces the fluctuation of the tensile strength in the coil, it is not a technique for improving shape defects such as “warping” and “twisting” related to the workability of the material.
また、ブレス成形性に優れ且つコイル内でのプレス成形性の変動が少ない冷延鋼板を製造するために、熱間圧延条件及びその後の冷却、巻取条件を最適化することが提案されていて、熱間圧延条件としては、仕上圧延機最終スタンドにおける材料温度が、粗バーの先端部から後端部に至るまで粗バー全体及び／又は幅方向エッジ部を誘導加熱装置で加熱することが開示されている（例えば、特許文献３参照）。 In addition, it has been proposed to optimize hot rolling conditions and subsequent cooling and winding conditions in order to produce cold-rolled steel sheets with excellent breath formability and small fluctuations in press formability in the coil. As the hot rolling conditions, it is disclosed that the material temperature in the final stand of the finish rolling mill heats the entire coarse bar and / or the edge in the width direction with an induction heating device from the leading end to the rear end of the coarse bar. (For example, see Patent Document 3).
しかし、これらの誘導加熱装置による加熱技術は、圧延方向や幅方向の温度分布を調整し、熱延鋼板の材質を均質化し、加工性を改善しようとするものであるが、この技術も板厚方向の温度分布を均一化する技術ではなく、材料の加工性に関わる「反り」、「ねじれ」等の形状不良そのものを改善する技術でもない。 However, the heating technology using these induction heating devices is intended to improve the workability by adjusting the temperature distribution in the rolling direction and width direction, homogenizing the material of the hot-rolled steel plate, It is not a technique for making the temperature distribution in the direction uniform, nor a technique for improving shape defects such as “warping” and “twisting” related to the workability of the material.
そこで、本発明は、加工性に優れる熱延鋼板およびその製造方法を提供する。すなわち、本発明は、加工性、特に形状凍結性に係る「反り」、「ねじれ」等の形状不良の大幅な改善効果を発現させるＣ断面に均一なミクロ組織を圧延方向にも持続的に有している熱延鋼板およびその熱延鋼板を安価に安定して製造できる方法を提供することを課題とするものである。
Therefore, the present invention provides a hot-rolled steel sheet excellent in workability and a method for producing the same. That is, the present invention continuously has a uniform microstructure in the rolling direction in the C cross section, which exhibits a significant improvement effect of shape defects such as “warping” and “twist” related to workability, particularly shape freezing. It is an object of the present invention to provide a hot- rolled steel sheet and a method for stably producing the hot-rolled steel sheet at a low cost.
本発明者らは、工業的規模で生産できる製造プロセスを念頭において加工性、特に形状凍結性に係る「反り」、「ねじれ」等の形状不良に係る加工性に優れる熱延鋼板を得るべく鋭意研究を重ねた。その結果、加工後の「反り」、「ねじれ」等の形状不良を解消するためには、圧延方向、幅方向および板厚方向の硬度、粒径、析出物の分布の不均一さを改善することが必要であり、そのためには、特に板厚方向の温度分布の調整が重要であることを見出して本発明を完成した。
The inventors have made eagerness to obtain a hot-rolled steel sheet excellent in workability related to shape defects such as “warping” and “twist” relating to workability, in particular shape freezing, in view of a manufacturing process that can be produced on an industrial scale. Repeated research. As a result, in order to eliminate shape defects such as “warp” and “twist” after processing, the hardness in the rolling direction, width direction and plate thickness direction, grain size, and uneven distribution of precipitates are improved. For this purpose, the present invention has been completed by finding that adjustment of the temperature distribution in the thickness direction is particularly important.
本発明の要旨とするところは以下の通りである。 The gist of the present invention is as follows.
（１） 質量％にて、
Ｃ ＝０．００１〜０．４％、
Ｓｉ＝０．００１〜５％、
Ｍｎ＝０．１〜５％、
Ｐ ≦０．１％、
Ｓ ≦０．０３％、
Ａｌ＝０．００１〜３％、
Ｎ ≦０．０１％、
を含有し残部がＦｅ及び不可避的不純物からなる化学組成の鋼板であって、その断面の硬度分布が標準偏差σ≦５であり、鋼板の断面のミクロ組織単位径分布が標準偏差σ≦２．５μｍであることを特徴とする加工性に優れる熱延鋼板。
(1) In mass%
C = 0.001 to 0.4%,
Si = 0.001-5%,
Mn = 0.1-5%,
P ≦ 0.1%,
S ≦ 0.03%,
Al = 0.001 to 3%,
N ≦ 0.01%,
In which the balance is Fe and inevitable impurities, and the hardness distribution of the cross section is standard deviation σ ≦ 5, and the microstructural unit diameter distribution of the cross section of the steel sheet is standard deviation σ ≦ 2. A hot-rolled steel sheet excellent in workability, characterized by being 5 μm.
（２） 鋼板が、さらに質量％にて、
Ｎｂ＝０．０１〜０．３％、
Ｔｉ＝０．０１〜０．３％、
Ｍｏ＝０．０５〜１％、
Ｖ ＝０．０２〜１％、
Ｃｒ＝０．０１〜１％、
Ｃｕ＝０．２〜１．２％、
の一種または二種以上を含有することを特徴とする上記（１）に記載の加工性に優れる熱延鋼板。
( 2 ) The steel sheet is further in mass%,
Nb = 0.01-0.3%,
Ti = 0.01-0.3%,
Mo = 0.05-1%,
V = 0.02 to 1%,
Cr = 0.01-1%,
Cu = 0.2-1.2%,
The hot-rolled steel sheet having excellent workability as described in (1) above, comprising one or more of the above .
（３） 鋼板が、析出物を含み且つ鋼板断面におけるその析出物径分布が標準偏差σ≦２ｎｍであることを特徴とする上記（２）に記載の加工性に優れる熱延鋼板。
( 3 ) The hot-rolled steel sheet having excellent workability as described in ( 2 ) above, wherein the steel sheet contains precipitates, and the precipitate diameter distribution in the cross section of the steel sheet has a standard deviation σ ≦ 2 nm.
（４） 鋼板が、さらに、質量％にて、
Ｃａ＝０．０００５〜０．００５％、
ＲＥＭ＝０．０００５〜０．０２％、
の一種または二種を含有することを特徴とする上記（１）ないし（３）のいずれか１項に記載の加工性に優れる熱延鋼板。
( 4 ) The steel plate is further in mass%,
Ca = 0.005 to 0.005%,
REM = 0.005-0.02%,
The hot-rolled steel sheet having excellent workability according to any one of the above (1) to ( 3 ), comprising one or two of the above.
（５） 鋼板が、さらに、質量％にて、
Ｂ ＝０．０００２〜０．００２％
を含有することを特徴とする上記（１）ないし（４）のいずれか１項に記載の加工性に優れる熱延鋼板。
( 5 ) The steel plate is further in mass%,
B = 0.0002 to 0.002%
The hot-rolled steel sheet having excellent workability according to any one of the above (1) to ( 4 ), comprising:
（６） 鋼板が、さらに質量％にて、
Ｎｉ＝０．１〜０．６％、
を含有することを特徴とする上記（１）ないし（５）のいずれか１項に記載の加工性に優れる熱延鋼板。
( 6 ) The steel sheet is further in mass%,
Ni = 0.1-0.6%,
The hot-rolled steel sheet having excellent workability according to any one of the above (1) to ( 5 ), comprising:
（７） 上記（１）、（２）、（４）、（５）、（６）のいずれか１項に記載の成分を有する熱延鋼板を得るための熱間圧延する際に、鋼板断面における仕上げ温度ＦＴが標準偏差σ≦７℃であり、ＦＴ〜ＦＴ＋２０℃での圧下率が２５％以上であることを特徴とする加工性に優れる熱延鋼板の製造方法。
(7) When hot rolling to obtain a hot-rolled steel sheet having the component according to any one of (1), ( 2), (4) , (5), and (6), finishing temperature FT is Ri standard deviation sigma ≦ 7 ° C. der method for producing a hot-rolled steel sheet excellent in workability rolling reduction in FT~FT + 20 ℃ is characterized in that at least 25% in.
本発明は、加工性、特に、加工性の１つの指標となる形状凍結性に優れる熱延鋼板およびその製造方法が提供でき、これらの鋼板を用いることにより厳しい加工精度が要求される部品でも容易に形状不良なしで成形できるだけでなく、安定した均質な材料特性を得ることができるという顕著な効果を奏するため、本発明は、工業的価値が高い発明であると言える。
INDUSTRIAL APPLICABILITY The present invention can provide a hot-rolled steel sheet excellent in workability, in particular, shape freezing property, which is one index of workability, and a method for manufacturing the hot-rolled steel sheet. Therefore, the present invention can be said to be an invention with high industrial value because it has a remarkable effect that it can be molded without defective shape and can obtain stable and homogeneous material characteristics.
以下に、本発明に至った基礎的研究結果について説明する。 Hereinafter, the basic research results that led to the present invention will be described.
本発明者らは、需要家での加工の際に発生する割れ、形状不良等の不具合、特に「反り」、「ねじれ」等の形状不良を解消するべく鋭意研究を重ねた結果、これら不具合の発生原因が介在物等の不純物であるものを除けば当該断面におけるミクロ組織、結晶粒径、析出物径等の統計的な不均一さに起因していることを突き止めた。さらに、コイル長手、幅方向の不均一さが改善されると強度、伸びといった一般的な材質変動は減少するが、面外の曲げ曲げ戻し加工により生ずる内部応力差により発生する「ねじれ」を解消するためには板厚方向を含めたコイルのＣ断面およびＬ断面での硬度、粒径、析出物分布の不均一を改善することが必要であると考えるに至った。即ち、特許文献１で開示があるように単に仕上げ圧延直前または仕上げ圧延中に被圧延材を加熱して最高値と最低値の差を小さくしたり、或は、被圧延材（粗バー）の幅方向及び圧延方向の温度を調整しただけでは、「反り」、「ねじれ」等の形状不良を解消することはできない。つまり、従来技術では幅方向及び圧延方向の温度を均一化するように誘導加熱装置で加熱している。しかし、このような加熱では被圧延材の表層部と中央部とでは温度差が生じていて、板厚方向の温度分布が均一化していない。このため、仕上圧延された鋼板の表層部と中央部とでは熱延鋼板の材質特性が異なり、熱延鋼板の加工によって「反り」、「ねじれ」等の形状不良が生じることを避けることができないものと考えられる。「反り」、「ねじれ」等の形状不良を解消するためには、特に板厚方向の温度制御が重要であり、板厚方向の温度制御により板厚方向の硬度、粒径、析出物分布の不均一さが改善された加工性に優れる薄鋼板が得られることを知見したのである。
The present inventors have conducted extensive research to eliminate defects such as cracks and shape defects, particularly “warping” and “twist” that occur during processing at the customer. Except for the cause of the occurrence of impurities such as inclusions, the inventors have found that this is due to statistical inhomogeneities such as microstructure, crystal grain size, and precipitate size in the cross section. In addition, the improvement of non-uniformity in the coil length and width direction reduces general material fluctuations such as strength and elongation, but eliminates the "twist" caused by the internal stress difference caused by out-of-plane bending and bending back processing. In order to achieve this, it has been considered that it is necessary to improve the hardness, particle size, and precipitate distribution non-uniformity in the C cross section and L cross section of the coil including the plate thickness direction. That is, as disclosed in
本発明者が実験により知見した熱延鋼板（薄鋼板）の各製造工程での温度等の製造条件とコイルのＣ断面およびＬ断面での硬度、ミクロ組織、結晶粒径、析出物径等の統計的分布と「反り」、「ねじれ」等の形状不良の関係について説明する。
Manufacturing conditions such as temperature in each manufacturing process of the hot-rolled steel sheet ( thin steel sheet ) discovered by the inventor through experiments, and hardness, microstructure, crystal grain size, precipitate diameter, etc. in the C and L sections of the coil The relationship between the statistical distribution and shape defects such as “warping” and “twist” will be described.
スラブ片を１２１９℃に再加熱し、仕上げ圧延温度の狙い温度を８５０℃として粗圧延後、得られた粗バー（板厚３０ｍｍ）を板厚３．２ｍｍまで仕上げ圧延を行いランナウトテーブルにて冷却した後に１００℃以下の温度で巻き取った。その際、粗圧延機と仕上げ圧延機の間に設置されたトランスバース型誘導加熱装置を用いて、粗バーの圧延方向、板幅方向、板厚方向に温度制御した水準と誘導加熱装置を用いない水準を設けて比較した。トランスバース型誘導加熱装置によって、粗バーの圧延方向、板幅方向の加熱は従来と同様に行なうことができ、また、板厚方向の温度のバラツキを小さくするため周波数の異なる加熱装置を複数配置して必要な厚み方向加熱パターンが得られるように各々の加熱量の配分を変更しして板厚方向の加熱温度パターンを操作することでその温度分布の均一化を行なった。図１および図２は、ある長手位置における仕上げ圧延機出側での温度のＣ断面温度分布例を示す図である。即ち、図１および図２は誘導加熱を行なわなかった場合と、誘導加熱により温度制御を行なった場合の夫々について、（ａ）は仕上げ圧延機出側での温度のＣ断面温度分布例を示し、（ｂ）はＡ−Ａ’位置での板幅方向の温度分布を示し、（ｃ）はＢ−Ｂ’位置での板厚方向の温度分布位置での板厚方向の温度分布を示す図である。誘導加熱を用いなかった場合は、図１（ｂ）に示すように、板幅方向の温度分布は両エッジ部の温度が低くなり、そして、図１（ｃ）に示すように、板厚方向の温度分布は中央部の温度が高い温度分布状態を示していた。これに対して、誘導加熱を用いて温度制御した場合には、図２（ｂ）および（ｃ）に示すように、圧延方向や板幅方向のみならず、板厚方向の温度のバラツキが小さくなり、温度分布が均一化していることがわかる。 The slab piece was reheated to 1219 ° C, the target temperature of the finish rolling temperature was set to 850 ° C, rough rolling was performed, and the resulting rough bar (thickness 30 mm) was finish-rolled to a thickness of 3.2 mm and cooled by a runout table. And then wound up at a temperature of 100 ° C. or lower. At that time, using a transverse type induction heating device installed between the rough rolling mill and the finish rolling mill, the level and the induction heating device temperature-controlled in the rolling direction, plate width direction and plate thickness direction of the rough bar are used. A comparison was made with no standard. The transverse type induction heating device can be used to heat the rough bar in the rolling direction and width direction as before, and multiple heating devices with different frequencies are provided to reduce temperature variations in the thickness direction. Then, the distribution of each heating amount was changed so that the necessary thickness direction heating pattern was obtained, and the temperature distribution was made uniform by operating the heating temperature pattern in the plate thickness direction. FIG. 1 and FIG. 2 are diagrams showing an example of C cross-section temperature distribution of the temperature at the delivery side of the finish rolling mill at a certain longitudinal position. That is, FIG. 1 and FIG. 2 show examples of the C cross-section temperature distribution of the temperature on the exit side of the finish rolling mill when the induction heating is not performed and when the temperature control is performed by induction heating. (B) shows the temperature distribution in the plate width direction at the AA ′ position, and (c) shows the temperature distribution in the plate thickness direction at the temperature distribution position in the plate thickness direction at the BB ′ position. It is. When induction heating is not used, as shown in FIG. 1 (b), the temperature distribution in the plate width direction has a lower temperature at both edges, and as shown in FIG. 1 (c), the thickness direction The temperature distribution of was a temperature distribution state in which the temperature in the central part was high. On the other hand, when temperature control is performed using induction heating, as shown in FIGS. 2B and 2C, temperature variation in the plate thickness direction as well as the rolling direction and the plate width direction is small. It can be seen that the temperature distribution is uniform.
このようにして得られた板厚３．２ｍｍでコイル長６００ｍの熱延コイルの長手方向のコイル圧延フロントから１００ｍごとに等間隔で７箇所切り板サンプルを採取し、Ｃ断面硬度測定、ミクロ組織観察等および「ねじれ」評価試験に供した。 Seven cut sheet samples were taken at equal intervals from the front coil rolling front of the hot rolled coil having a plate thickness of 3.2 mm and a coil length of 600 m obtained in this manner every 100 m, and C cross-section hardness measurement, microstructure It was used for observation etc. and "twist" evaluation test.
「ねじれ」評価試験では、図３に示すプレス形状品にて評価を行った。上記にて採取した切り板サンプルより、プレス成形品の長手方向が板幅方向と平行になるようにブランクを切り出し、プレス試験に供した後に「ねじれ」量を評価するために非接触型三次元形状測定器により成形パネル外面を測定し、金型ＣＡＤデータとの寸法誤差を評価した。 In the “twist” evaluation test, evaluation was performed using a press-shaped product shown in FIG. In order to evaluate the amount of "twist" after cutting a blank from the cut plate sample collected above so that the longitudinal direction of the press-molded product is parallel to the plate width direction and subjecting it to a press test, it is a non-contact type three-dimensional The outer surface of the molded panel was measured with a shape measuring instrument, and the dimensional error with the mold CAD data was evaluated.
また、プレス成形品左右のエッジより５ｍｍ内側の断面座標値から各断面のウエブ面の角度を算出し、その角度差をθｗとして「ねじれ」量の評価値と定義した。
Further, the angle of the web surface of each cross section was calculated from the cross-sectional coordinate
この角度差θｗが小さいほど「ねじれ」が少なくプレス品形状が良好であることを意味する。プレス品の組み付け精度等を考慮すると、組み付け後の形状不良を発生させないためにはθｗが０．５°以下が必要であると考えられる。 A smaller angle difference θw means less “twist” and better pressed product shape. Considering the assembly accuracy of the press product, it is considered that θw needs to be 0.5 ° or less in order not to cause a shape defect after assembly.
図４に硬度（Ｈｖ）の標準偏差σと角度差θｗの関係を示す。誘導加熱装置等を適用して鋼板の板厚方向をも含めて温度のバラツキを小さくすることで硬度（Ｈｖ）の標準偏差σが５以下となり、「ねじれ」量の評価値である角度差θｗはプレス品形状が良好な０．５以下となることが判明した。 FIG. 4 shows the relationship between the standard deviation σ of the hardness (Hv) and the angle difference θw. The standard deviation σ of hardness (Hv) is 5 or less by applying an induction heating device or the like to reduce the temperature variation including the thickness direction of the steel sheet, and the angle difference θw that is an evaluation value of the “twist” amount Was found to have a good press product shape of 0.5 or less.
そのメカニズムは明らかではないが、板厚方向に硬度の不均一が存在すると、曲げＲ部もしくは曲げ曲げ戻し加工を受ける縦壁部において板厚方向の各幅、長手位置で塑性変形の不均一が生じ、その結果内部応力にも不均一が発生し、板幅方向に長い加工品においては「ねじれ」が生じるものと推定される。従ってこの「ねじれ」に代表される形状不良を抑制するためには、その断面の硬度分布を標準偏差（○印の線）σ≦５にすることが必要なのである。これよりも大きくなると、板厚方向の各幅、長手位置で塑性変形の不均一が大きくなって「ねじれ」の許容限度を超えるために、急激に鋼板加工後の形状凍結性が劣化し、形状不良発生率が大きく悪化するためである。また、硬度分布の標準偏差σは小さいほうが好ましいが（理論的には０であることが好ましい）、現実の工業的操業では標準偏差σの下限を１程度とするのが現実的である。 Although the mechanism is not clear, if there is non-uniform hardness in the plate thickness direction, plastic deformation is not uniform at each width and longitudinal position in the plate thickness direction at the bending R portion or the vertical wall portion subjected to bending and bending back processing. As a result, the internal stress is also uneven, and it is presumed that “twist” occurs in a workpiece that is long in the plate width direction. Therefore, in order to suppress the shape defect typified by this “twist”, it is necessary to make the hardness distribution of the cross section a standard deviation (circled line) σ ≦ 5. If it is larger than this, the unevenness of plastic deformation at each width and longitudinal position in the plate thickness direction becomes large and exceeds the allowable limit of `` twist '', so the shape freezing property after steel plate processing deteriorates rapidly, and the shape This is because the defect occurrence rate greatly deteriorates. Further, the standard deviation σ of the hardness distribution is preferably small (theoretically, it is preferably 0), but it is practical that the lower limit of the standard deviation σ is about 1 in actual industrial operation.
硬度測定は上記コイル長手方向の各箇所サンプルから切り出し、幅方向Ｃ断面の幅のＤＳエッジ、１／４Ｗ、１／２Ｗ、３／４ＷおよびＷＳエッジの各位置より切出した試料をＣ断面に研磨し、ナイタール試薬を用いてエッチングし、表層、板厚の１／８ｔ、１／４ｔ、３／８ｔ、１／２ｔ、５／８ｔ、３／４ｔ、うら表層における硬度測定をＪＩＳ Ｚ ２２４４に記載の方法にて試験荷重を１〜５ｇｆとしてビッカース硬度をそれぞれ１０点以上測定した。なお、第二相として二種類以上のミクロ組織が存在する場合は各々の測定を行う。 Hardness measurement was cut out from each sample in the longitudinal direction of the coil, and the sample cut out from each position of the DS edge, 1 / 4W, 1 / 2W, 3 / 4W and WS edge of the width C cross section was polished to the C cross section. Etching with a Nital reagent, and the surface layer, 1 / 8t, 1 / 4t, 3 / 8t, 1 / 2t, 5 / 8t, 3 / 4t of the plate thickness, and the hardness measurement on the back surface are described in JIS Z 2244 The test load was 1 to 5 gf and the Vickers hardness was measured at 10 points or more. In addition, when two or more types of microstructures exist as the second phase, each measurement is performed.
さらに、鋼板の断面のミクロ組織単位径分布も前記「ねじれ」発生に影響を及ぼすと考えられるため、鋼板の断面のミクロ組織単位径分布を調査したところ、図３の（●印の線）で示したように、標準偏差σ≦２．５μｍでは、θｗがさらに小さくなりプレス品形状性がさらに向上する効果が認められた。
Furthermore, since the microstructural unit diameter distribution of the cross section of the steel sheet is considered to affect the occurrence of the “twist”, the microstructural unit diameter distribution of the cross section of the steel sheet was investigated. As shown, when the standard deviation σ ≦ 2.5 μm, the effect of further reducing θw and further improving the shape of the pressed product was recognized.
これはミクロ組織単位径分布が板厚方向にバラツキが小さくなることによってさらに内部応力が均一となるためであり、従ってミクロ組織単位径分布の標準偏差σ≦２．５μｍが好ましい範囲と考えられる。
This is because the microstructure unit size distribution becomes uniform more internal stresses by variation becomes smaller in the thickness direction, thus Miku b Organization standard deviation sigma ≦ 2.5 [mu] m of unit size distribution is preferably in the range and consider It is done.
ミクロ組織およびミクロ組織単位径分布の測定は、硬度を測定した同一サンプルより行う。ここでミクロ組織単位径分布（以下単に組織単位径分布と言うことがある）とは、ミクロ組織がフェライト単相もしくはフェライトと硬質第二相を含むミクロ組織の場合はフェライトと第二相の結晶粒径分布を指し、連続冷却変態組織（Ｚｗ）のように結晶粒界が光学顕微鏡観察で明確に識別できないような場合はパケット径分布を指す。前者のミクロ組織がフェライト単相もしくはフェライトと硬質第二相を含むミクロ組織の場合は上記のナイタール試薬を用いてエッチングし、そのまま光学顕微鏡を用い２００〜５００倍の倍率で観察されたおもて表層、板厚の１／８ｔ、１／４ｔ、３／８ｔ、１／２ｔ、５／８ｔ、３／４ｔ、うら表層における視野の写真にて行った。すなわち、ミクロ組織単位径（以下単に組織単位径と言うことがある）とは、この場合、フェライト結晶粒径および／または第二相粒径である。従って、結晶粒径の測定はＪＩＳ Ｇ ０５５２記載の切断法を用いた。
Microstructure and measurement of microstructural unit size distribution, intends the same sample by Rigyo of measuring the hardness. Here (sometimes hereinafter referred to simply organizational unit size distribution) Miku b Organization Unit size distribution and, if the microstructure is a microstructure including a ferrite single phase or ferrite and hard second phase ferrite and the second phase When the crystal grain boundary cannot be clearly identified by observation with an optical microscope as in the case of a continuous cooling transformation structure (Zw), it indicates the packet size distribution. When the former microstructure is a ferrite single phase or a microstructure containing ferrite and a hard second phase, etching is performed using the above-mentioned Nital reagent, and the surface is observed as it is at a magnification of 200 to 500 times using an optical microscope. The surface layer and the plate thickness were 1 / 8t, 1 / 4t, 3 / 8t, 1 / 2t, 5 / 8t, 3 / 4t, and a photograph of the visual field on the back surface layer. That is, the microstructure unit size (hereinafter referred to simply as organizational unit diameter), In this case, a ferrite grain diameter and / or the second phase particle size. Therefore, the crystal grain size was measured using the cutting method described in JIS G 0552.
一方、後者の連続冷却変態組織（Ｚｗ）のようにナイタール試薬を用いたエッチングでの光学顕微鏡観察では粒径が判別しにくい組織においては、ミクロ組織単位径分布とはパケット径分布のことである。 On the other hand, in the latter continuous cooling transformation structure (Zw), in the structure in which the particle diameter is difficult to discriminate by the optical microscope observation in the etching using the Nital reagent, the micro structure unit diameter distribution is the packet diameter distribution. .
パケットとは、γ→α変態を経る際にオーステナイト粒が多くの方位が異なる組織単位に分割された組織単位である。ナイタール試薬を用いたエッチングでの光学顕微鏡観察ではパケット境界が判別しにくいのでＥＢＳＰ−ＯＩＭを用いてパケット径分布を測定する。 A packet is a structural unit in which austenite grains are divided into many structural units having different orientations when undergoing the γ → α transformation. Packet boundary distribution is measured using EBSP-OIM because it is difficult to distinguish the packet boundary by optical microscope observation in etching using a Nital reagent.
ＥＢＳＰ−ＯＩＭ（Ｅｌｅｃｔｒｏｎ Ｂａｃｋ Ｓｃａｔｔｅｒ Ｄｉｆｆｒａｃｔｉｏｎ Ｐａｔｔｅｒｎ−Ｏｒｉｅｎｔａｔｉｏｎ Ｉｍａｇｅ Ｍｉｃｒｏｓｃｏｐｙ）法は走査型電子顕微鏡内で高傾斜した試料に電子線を照射し、後方散乱して形成された菊池パターンを高感度カメラで撮影し、コンピュータ画像処理する事により照射点の結晶方位を短時間で測定する装置およびソフトウエアで構成されている。ＥＢＳＰ法ではバルク試料表面の微細構造並びに結晶方位の定量的解析ができ、分析エリアはＳＥＭで観察できる領域で、ＳＥＭの分解能にもよるが、最小２０ｎｍの分解能で分析できる。 The EBSP-OIM (Electron Back Scatter Diffraction Pattern-Orientation Image Microscopy) method irradiates a highly inclined sample with an electron beam in a scanning electron microscope, and images the Kikuchi pattern formed by backscattering with a high sensitivity camera. It consists of a device and software that measure the crystal orientation of the irradiated spot in a short time by computer image processing. The EBSP method can quantitatively analyze the microstructure and crystal orientation of the surface of the bulk sample, and the analysis area is an area that can be observed with an SEM. Depending on the resolution of the SEM, analysis can be performed with a minimum resolution of 20 nm.
解析は数時間かけて、分析したい領域を等間隔のグリッド状に数万点マッピングして行う。多結晶材料では試料内の結晶方位分布や結晶粒の大きさを見ることができる。本発明おいては、その各パケットの方位差を１５°としてマッピングした画像よりパケット径分布を求める。また、粒内に存在している析出物径分布を測定するために三次元アトムプローブ法を用いた。測定条件は試料位置温度約７０Ｋ、プローブ全電圧１０〜１５ｋＶ、パルス比２５％である。各試料の粒界、粒内それぞれ三回測定してその平均値を代表値とした。測定値よりバックグラウンドノイズ等を除去する。 The analysis takes several hours and is performed by mapping tens of thousands of points to be analyzed in a grid at equal intervals. With polycrystalline materials, the crystal orientation distribution and crystal grain size in the sample can be seen. In the present invention, the packet diameter distribution is obtained from an image obtained by mapping the azimuth difference of each packet as 15 °. A three-dimensional atom probe method was used to measure the precipitate size distribution existing in the grains. The measurement conditions are a sample position temperature of about 70 K, a probe total voltage of 10 to 15 kV, and a pulse ratio of 25%. Each sample was measured three times at the grain boundary and within the grain, and the average value was taken as the representative value. Remove background noise from measured values.
また、Ｎｂ、Ｔｉ、Ｍｏ、Ｖ、Ｃｒ、Ｃｕ等の成分を含有し、ミクロ組織に析出物が含まれる場合には、析出物分布が板厚方向に均一であることが内部応力を均一にするために重要であると推定され、その析出物径分布が標準偏差σ≦２ｎｍであることが好ましい。これは、析出物が転位移動の障害となり、フランリード機構等の作用により転位増殖等による加工硬化が起こるが、析出物径分布が板厚方向に均一でないと加工硬化の不均一が板厚方向に生じ「ねじれ」の原因となるためと推測される。析出物径分布の標準偏差σは小さいほうが好ましいが（理論的には０であることが好ましい）、現実の工業的操業では標準偏差σの下限を１程度とするのが現実的である。この粒内に存在している析出物径分布を測定するために三次元アトムプローブ法を用いた。測定条件は試料位置温度約７０Ｋ、プローブ全電圧１０〜１５ｋＶ、パルス比２５％である。各試料の粒界、粒内それぞれ三回測定してその平均値を代表値とした。測定値よりバックグラウンドノイズ等を除去する。 In addition, when components such as Nb, Ti, Mo, V, Cr, and Cu are contained and precipitates are included in the microstructure, the distribution of precipitates is uniform in the thickness direction, and the internal stress is uniform. Therefore, it is preferable that the precipitate size distribution has a standard deviation σ ≦ 2 nm. This is because the precipitate becomes an obstacle to dislocation movement, and work hardening due to dislocation growth occurs due to the action of the furan lead mechanism, etc., but if the precipitate diameter distribution is not uniform in the plate thickness direction, non-uniform work hardening will occur in the plate thickness direction. This is presumed to be caused by “twist”. The standard deviation σ of the precipitate size distribution is preferably small (in theory, it is preferably 0), but in actual industrial operation, the lower limit of the standard deviation σ is practically about 1. A three-dimensional atom probe method was used to measure the precipitate size distribution present in the grains. The measurement conditions are a sample position temperature of about 70 K, a probe total voltage of 10 to 15 kV, and a pulse ratio of 25%. Each sample was measured three times at the grain boundary and within the grain, and the average value was taken as the representative value. Remove background noise from measured values.
以上のように、板厚方向、板幅方向および長手方向の硬度分布の標準偏差を小さくし、好ましくはミクロ組織単位径分布や析出物径分布が板厚方向に均一になれば、「ねじれ」に代表される形状不良が抑制できる鋼板が得られるが、熱間圧延に際して粗圧延機と仕上げ圧延機の間に設置された誘導加熱装置等を用いて板厚方向を含め温度のバラツキを小さくすることが好ましい態様である。 As described above, if the standard deviation of the hardness distribution in the plate thickness direction, the plate width direction and the longitudinal direction is reduced, and preferably the microstructure unit diameter distribution and the precipitate diameter distribution become uniform in the plate thickness direction, "twist" Steel sheets that can suppress shape defects typified by are obtained, but the temperature variation including the sheet thickness direction is reduced by using an induction heating device or the like installed between the roughing mill and the finishing mill during hot rolling. Is a preferred embodiment.
なお、上記のように本発明において「ねじれ」に代表される形状不良を抑制するためには、鋼板の硬度、好ましくはミクロ組織単位径分布や析出物分布が板厚方向に均一にすれば良く、必ずしもミクロ組織構成を限定する必要はない。通常の鋼が呈するフェライト、ベイナイト、パーライト、マルテンサイト、残留オーステナイト組織等において本発明範囲の断面の硬度分布が得られていれば、本発明の効果は得られる。ただし、特定のミクロ組織で構成されると、例えばフェライト相と硬質第二相を主にマルテンサイトとする複合組織等においては、張り出し性等を高めることができるし、例えば連続冷却変態組織等の均一なミクロ組織等においては、伸びフランジ性等を高めることができる。また、或る特定のサイズの析出物を含有させることにより、強度を向上させることもできる。 In addition, as described above, in order to suppress the shape defect typified by “twist” in the present invention, the hardness of the steel sheet, preferably the microstructure unit diameter distribution and precipitate distribution should be uniform in the sheet thickness direction. However, it is not always necessary to limit the microstructure. If the hardness distribution of the cross section within the range of the present invention is obtained in the ferrite, bainite, pearlite, martensite, retained austenite structure, etc. exhibited by ordinary steel, the effect of the present invention can be obtained. However, when it is composed of a specific microstructure, for example, in a composite structure mainly composed of a ferrite phase and a hard second phase and martensite, it is possible to improve the stretchability and the like, for example, a continuous cooling transformation structure, etc. In a uniform microstructure or the like, stretch flangeability and the like can be improved. In addition, the strength can be improved by including a precipitate having a specific size.
ここで連続冷却変態組織（Ｚｗ）とは日本鉄鋼協会基礎研究会ベイナイト調査研究部会／編；低炭素鋼のベイナイト組織と変態挙動に関する最近の研究−ベイナイト調査研究部会最終報告書−（１９９４年 日本鉄鋼協会）に記載されているように拡散的機構により生成するポリゴナルフェライトやパーライトを含むミクロ組織と無拡散でせん断的機構により生成するマルテンサイトの中間段階にある変態組織と定義されるミクロ組織である。すなわち、連続冷却変態組織（Ｚｗ）とは光学顕微鏡観察組織として上記参考文献１２５〜１２７項にあるようにそのミクロ組織は主にＢａｉｎｉｔｉｃ ｆｅｒｒｉｔｅ（α°B）、Ｇｒａｎｕｌａｒ ｂａｉｎｉｔｉｃ ｆｅｒｒｉｔｅ（αB）、Ｑｕａｓｉ−ｐｏｌｙｇｏｎａｌ ｆｅｒｒｉｔｅ（αq）から構成され、さらに少量の残留オーステナイト（γr）、Ｍａｒｔｅｎｓｉｔｅ−ａｕｓｔｅｎｉｔｅ（ＭＡ）を含むミクロ組織であると定義されている。 Here, the continuous cooling transformation structure (Zw) is the Japan Iron and Steel Institute Basic Research Group Bainite Research Group / Edit; Recent Research on Bainite Structure and Transformation Behavior of Low Carbon Steels-Final Report of Bainite Research Group (1994 Japan) The microstructure defined as the transformation structure in the intermediate stage between the microstructure containing polygonal ferrite and pearlite produced by the diffusion mechanism and the martensite produced by the non-diffusion shearing mechanism as described in It is. That is, the continuous cooling transformation structure (Zw) is an optical microscope observation structure as described in the above-mentioned References 125 to 127, and the microstructure is mainly Bainitic ferrite (α ° B ), Granular ferritic ferrite (α B ), Quasi. -Polygonal ferrite (α q ), which is further defined as a microstructure containing a small amount of retained austenite (γ r ) and Martensite-austenite (MA).
続いて、本発明の化学成分の限定理由について説明する。 Then, the reason for limitation of the chemical component of this invention is demonstrated.
Ｃ：強化元素として有効であり、０．００１％以上必要であるが、加工性、溶接性から０．４％未満が好ましい。 C: Effective as a strengthening element and needs to be 0.001% or more, but is preferably less than 0.4% in view of workability and weldability.
Ｓｉ、Ｍｎ：強化元素であり、Ｓｉは０．００１％以上、Ｍｎは０．１％以上必要である。但し、溶接性からはそれぞれ５％以下、５％以下がよい。但し、成形性の点からはＳｉが好ましく２．５％以下、焼き入れ性、化成処理性の点からはＭｎが好ましく３％以下が好ましい。 Si, Mn: Strengthening elements, Si is required to be 0.001% or more, and Mn is required to be 0.1% or more. However, in terms of weldability, 5% or less and 5% or less are preferable, respectively. However, Si is preferably 2.5% or less from the viewpoint of moldability, and Mn is preferably 3% or less from the viewpoint of hardenability and chemical conversion treatment.
Ｐは、不純物であり低いほど望ましく、０．１％超含有すると加工性や溶接性に悪影響を及ぼすので、０．１％以下とする。ただし、穴拡げ性や溶接性を考慮すると０．０２％以下が望ましい。 P is an impurity and is preferably as low as possible. If contained over 0.1%, the workability and weldability are adversely affected. However, considering hole expansibility and weldability, 0.02% or less is desirable.
Ｓは、熱間圧延時の割れを引き起こすばかりでなく、多すぎると穴拡げ性を劣化させるＡ系介在物を生成するので極力低減させるべきであるが、０．０３％以下ならば許容できる範囲である。ただし、ある程度の穴拡げ性を必要とする場合は０．０１％以下が、さらに高い穴拡げが要求される場合は、０．００３％以下が望ましい。 S not only causes cracking during hot rolling, but if it is too much, it generates A-based inclusions that degrade the hole expandability, so it should be reduced as much as possible. It is. However, 0.01% or less is desirable when a certain degree of hole expansion is required, and 0.003% or less is desirable when higher hole expansion is required.
Ａｌは、溶鋼脱酸のために０．００１％以上添加。加工性への悪影響が少ない強化元素なので３％まで添加可。 Al is added 0.001% or more for deoxidation of molten steel. Can be added up to 3% because it is a strengthening element that has little adverse effect on processability.
Ｎは、溶接性から０．０１％以下。但し、時効から０．００６％以下が望ましい。 N is 0.01% or less from the viewpoint of weldability. However, 0.006% or less is desirable from aging.
Ｎｂ、Ｔｉ、Ｍｏ、Ｖ、Ｃｒ，Ｃｕ：強度を付与するために一種または二種以上を添加してもよい。但し、それぞれ０．０１％、０．０１％、０．０５％、０．０２％、０．０１％、０．２％未満では効果が不十分であり、０．３％、０．３％、１％、１％、１％、１．２％を超えて添加すると効果が飽和する。 Nb, Ti, Mo, V, Cr, Cu: One or two or more of them may be added to impart strength. However, the effect is insufficient if less than 0.01%, 0.01%, 0.05%, 0.02%, 0.01%, 0.2% respectively, 0.3%, 0.3% Addition exceeding 1%, 1%, 1%, 1.2% will saturate the effect.
ＣａおよびＲＥＭは、破壊の起点となり、加工性を劣化させる非金属介在物の形態を変化させて無害化する元素である。ただし、０．０００５％未満添加してもその効果がなく、Ｃａならば０．００５％超、ＲＥＭならば０．０２％超添加してもその効果が飽和するのでＣａ＝０．０００５〜０．００５％、ＲＥＭ＝０．０００５〜０．０２％添加することが望ましい。 Ca and REM are elements that become destructive by changing the form of non-metallic inclusions that become the starting point of destruction and degrade workability. However, even if less than 0.0005% is added, there is no effect, and if Ca is more than 0.005%, and if REM is added more than 0.02%, the effect is saturated, so Ca = 0.005 to 0 It is desirable to add 0.005% and REM = 0.005 to 0.02%.
Ｂは、焼き入れ性を向上させる効果があるので必要に応じ添加する。ただし、０．０００２％未満ではその効果を得るために不十分であり、０．００２％超添加すると効果が飽和する。よって、Ｂの添加は、０．０００２％以上、０．００２％以下とする。 Since B has an effect of improving the hardenability, it is added as necessary. However, if it is less than 0.0002%, it is insufficient for obtaining the effect, and if it exceeds 0.002%, the effect is saturated. Therefore, the addition of B is set to 0.0002% or more and 0.002% or less.
Ｎｉ：強度を付与するためにＮｉの固溶強化元素として添加してもよい。ただし、それぞれ、０．１％未満ではその効果を得ることができない。また、０．６％を超え添加してもその効果は飽和する。 Ni: You may add as a solid solution strengthening element of Ni in order to provide intensity | strength. However, if less than 0.1%, the effect cannot be obtained. Moreover, the effect is saturated even if it adds exceeding 0.6%.
次に、本発明の製造方法の限定理由について、以下に詳細に述べる。 Next, the reasons for limiting the production method of the present invention will be described in detail below.
本発明は、鋳造後、熱間圧延後冷却ままもしくは熱間圧延後に熱延鋼板を冷間圧延さらに／または焼鈍すること、或るいは得られた熱延鋼板または冷延もしくは焼鈍後の鋼板に別途表面処理を施すことによっても得られる。 The present invention is to cold-roll and / or anneal a hot-rolled steel sheet after casting, after hot-rolling and after cooling or after hot-rolling, or to obtain a hot-rolled steel sheet or a steel sheet after cold-rolling or annealing. It can also be obtained by performing a surface treatment separately.
本発明において熱間圧延に先行する製造方法は特に限定するものではない。すなわち、高炉、転炉や電炉等による溶製に引き続き、各種の２次精練で目的の成分含有量になるように成分調整を行い、次いで通常の連続鋳造、インゴット法による鋳造の他、薄スラブ鋳造などの方法で鋳造すればよい。原料にはスクラップを使用しても構わない。連続鋳造よって得たスラブの場合には高温鋳片のまま熱間圧延機に直送してもよいし、室温まで冷却後に加熱炉にて再加熱した後に熱間圧延してもよい。 In the present invention, the production method preceding hot rolling is not particularly limited. In other words, following smelting with a blast furnace, converter, electric furnace, etc., the components are adjusted so that the desired component content is obtained by various secondary scouring, and then, in addition to normal continuous casting, casting by ingot method, thin slab What is necessary is just to cast by methods, such as casting. Scrap may be used as a raw material. In the case of a slab obtained by continuous casting, it may be directly sent to a hot rolling mill as it is a high-temperature slab, or may be hot-rolled after being reheated in a heating furnace after being cooled to room temperature.
スラブ再加熱温度については特に制限はないが、１４００℃以上であると、スケールオフ量が多量になり歩留まりが低下するので、再加熱温度は１４００℃未満が望ましい。また、１０００℃未満の加熱ではスケジュール上操業効率を著しく損なうため、スラブ再加熱温度は１０００℃以上が望ましい。さらには、１１００℃未満の加熱ではスケールオフ量が少なくスラブ表層の介在物をスケールと共に後のデスケーリングによって除去できなくなる可能性があるため、スラブ再加熱温度は１１００℃以上が望ましい。スラブ加熱時間については特に定めないが、Ｎｂ等の析出強化元素を添加している場合その炭窒化物の溶解を十分に進行させるためには当該温度に達してから３０分以上保持することが望ましい。ただし、鋳造後の鋳片を高温のまま直送して圧延する場合にこの限りではない。
本発明において、その「ねじれ」に代表される形状不良を抑制するという目的のために鋼板のミクロ組織構成を特に限定する必要はないので、スラブ再加熱に続く粗圧延および仕上げ圧延の条件は特に限定するものではない。ただし、仕上げ圧延終了温度をＡｒ3変態点温度以上とすることが望ましい。仕上げ圧延終了温度はＡｒ3変態点温度未満であると得られた製品コイルのミクロ組織に加工組織が残留し、伸びが劣化する恐れがある。
Although there is no restriction | limiting in particular about slab reheating temperature, Since a scale-off amount will become large and a yield will fall when it is 1400 degreeC or more, reheating temperature is desirable below 1400 degreeC. In addition, heating below 1000 ° C significantly impairs the operation efficiency in terms of schedule, so the slab reheating temperature is desirably 1000 ° C or higher. Furthermore, since the scale-off amount is small when heating at less than 1100 ° C., inclusions on the slab surface layer may not be removed together with the scale by subsequent descaling, and therefore, the slab reheating temperature is desirably 1100 ° C. or higher. The slab heating time is not particularly defined, but when a precipitation strengthening element such as Nb is added, it is desirable to keep it for 30 minutes or more after reaching the temperature in order to sufficiently dissolve the carbonitride. . However, this is not the case when the cast slab is directly fed and rolled at a high temperature.
In the present invention, it is not necessary to specifically limit the microstructure of the steel sheet for the purpose of suppressing shape defects typified by the “twist”, so the conditions of rough rolling and finish rolling following slab reheating are particularly It is not limited. However, it is desirable that the finish rolling end temperature is not less than the Ar 3 transformation point temperature. If the finish rolling end temperature is lower than the Ar 3 transformation point temperature, the processed structure remains in the microstructure of the product coil obtained, and the elongation may deteriorate.
ここでＡｒ3変態点温度とは、例えば以下の計算式により鋼成分との関係で簡易的に示される。すなわち
Ａｒ3＝９１０−３１０×％Ｃ＋２５×％Ｓｉ−８０×％Ｍｎ−１５×％Ｃｒ−２０×％Ｃｕ−８０×％Ｍｏ−５５×％Ｎｉ
Here, the Ar 3 transformation point temperature is simply shown in relation to the steel component by the following calculation formula, for example. That is, Ar 3 = 910-310 ×% C + 25 ×% Si-80 ×% Mn-15 ×% Cr-20 ×% Cu-80 ×% Mo-55 ×% Ni
さらに、より優れた形状凍結性を得るためには組織単位分布が標準偏差σ≦２．５μｍであることが必要であるが、そのためにγ→α変態時のα核生成を均一化する必要があり、核生成サイトとしての特定の温度域で均質なひずみの導入が望ましいので、その仕上げ圧延中において仕上げ圧延終了温度ＦＴ以上ＦＴ＋２０℃以下における合計圧下率２５％以上の圧延を行うことが好ましい。 Furthermore, in order to obtain a better shape freezing property, it is necessary that the tissue unit distribution has a standard deviation σ ≦ 2.5 μm. For this reason, it is necessary to uniformize α nucleation during γ → α transformation. In addition, since it is desirable to introduce a uniform strain in a specific temperature range as a nucleation site, it is preferable to perform rolling with a total rolling reduction of 25% or more at the finish rolling end temperature FT or higher and FT + 20 ° C. or lower during the finish rolling.
仕上げ圧延終了温度ＦＴの上限は特に設けないが、Ａｒ3変態点温度＋２００℃超を得るためには加熱炉温度または粗圧延終了から仕上げ圧延開始までの間または／および仕上げ圧延中での粗バーまたは圧延材の加熱は設備的に負荷が大きいので、その上限はＡｒ3変態点温度＋２００℃以下が望ましい。また、粗圧延と仕上げ圧延の間にシートバーを接合し、連続的に仕上げ圧延をしてもよい。その際に粗バーを一旦コイル状に巻き、必要に応じて保温機能を有するカバーに格納し、再度巻き戻してから接合を行ってもよい。 The upper limit of finish rolling finish temperature FT is not particularly set, but in order to obtain Ar 3 transformation point temperature + 200 ° C. or higher, the heating furnace temperature or rough bar during finish rolling and / or finish rolling starts. Alternatively, since the heating of the rolled material is heavy in terms of equipment, the upper limit is preferably Ar 3 transformation temperature + 200 ° C. or less. Moreover, a sheet bar may be joined between rough rolling and finish rolling, and finish rolling may be performed continuously. At that time, the coarse bar may be wound once in a coil shape, stored in a cover having a heat retaining function as necessary, and rewound again before joining.
なお、本発明においては特に仕上げ圧延終了温度を圧延方向、板幅方向、板厚方向において温度バラツキを小さく制御することが重要であり、温度バラツキとして標準偏差≦７℃にすることが必要である。そのためには、粗圧延機と仕上げ圧延機の間、もしくは仕上げ圧延機のスタンド間で圧延方向、板幅方向、板厚方向に温度制御できる加熱装置を設置することが好ましい。加熱装置の方式としては、ガス加熱、通電加熱、誘導加熱等の様々な加熱手段が考えられるが、圧延方向、板幅方向、板厚方向に温度のバラツキを小さく制御可能であれば手段は限定する必要はない。但し、工業的に温度の制御応答性が良い誘導加熱方式が好ましいが、誘導加熱方式でも板幅方向でシフト可能な複数のトランスバース型誘導加熱を設置すれば、板幅に応じて板幅方向の温度分布を任意にコントロールできるのでより好ましい。さらにトランスバース型誘導加熱と共に板幅全体加熱に優れるソレノイド型誘導加熱との組み合わせが最も好ましい。 In the present invention, it is particularly important to control the finish rolling end temperature so that the temperature variation is small in the rolling direction, the sheet width direction, and the sheet thickness direction, and it is necessary to make the standard deviation ≦ 7 ° C. as the temperature variation. . For this purpose, it is preferable to install a heating device capable of controlling the temperature in the rolling direction, the sheet width direction, and the sheet thickness direction between the roughing mill and the finishing mill or between the stands of the finishing mill. Various heating means such as gas heating, energization heating, induction heating, etc. can be considered as the heating device, but the means are limited as long as the temperature variation can be controlled to be small in the rolling direction, the sheet width direction, and the sheet thickness direction. do not have to. However, the induction heating method with good temperature control responsiveness industrially is preferable. However, if a plurality of transverse induction heating that can be shifted in the plate width direction is installed even in the induction heating method, the plate width direction depends on the plate width. This is more preferable because the temperature distribution can be controlled arbitrarily. Further, the combination with the solenoid type induction heating which is excellent in the whole plate width heating together with the transverse type induction heating is most preferable.
前記加熱装置を用いて温度制御する場合には、加熱装置による加熱量の制御が必要であるが、粗バー内部の温度は実測できないため、予め加熱炉に装入スラブ温度、スラブ在炉時間、加熱炉雰囲気温度、加熱炉抽出温度、さらにテーブルローラーの搬送時間等の実績データを用いて、粗バーが加熱装置に到着時の圧延方向、板幅方向、板厚方向の温度分布を推定して加熱装置による加熱量を制御すれば良い。
例えば、以下のように制御する。
When controlling the temperature using the heating device, it is necessary to control the amount of heating by the heating device, but the temperature inside the coarse bar cannot be measured, so the slab temperature charged in the heating furnace in advance, the slab in-furnace time, Estimate the temperature distribution in the rolling direction, plate width direction, and plate thickness direction when the coarse bar arrives at the heating device using actual data such as the furnace temperature, heating furnace extraction temperature, and table roller transport time. What is necessary is just to control the heating amount by a heating apparatus.
For example, the control is performed as follows.
誘導加熱装置（トランスバース型誘導加熱装置）の特性として、コイルに交流電流を通じると、その内側に鋼板磁場を生ずる。そして、この中に置かれている導電体には、電磁誘導作用により磁束と直角の円周方向にコイル電流と反対の向きの渦電流が起こり、そのジュール熱によって導電体は加熱される。渦電流はコイル内側の表面に最も強く発生し、内側に向かって指数関数的に低減する（この現象を表皮効果という）。したがって、周波数が小さいほど電流浸透深さが大きくなり、厚み方向に均一な加熱パターンが得られ、逆に、周波数が大きいほど電流浸透深さが小さくなり、厚み方向に表層をピークとした過加熱の小さな加熱パターンが得られることが知られている。よって、トランスバース型誘導加熱装置によって、粗バーの圧延方向、板幅方向の加熱は従来と同様に行なうことができ、また、板厚方向の加熱は、トランスバース型誘導加熱装置の周波数変更によって浸透深さを可変化して板厚方向の加熱温度パターンを操作することでその温度分布の均一化を行なうことができる。なお、この場合、周波数変更可変型の誘導加熱装置を用いることが好ましいが、コンデンサーの調整によって周波数変更を行ってもよい。また、周波数の異なるインダクターを複数配置して必要な厚み方向加熱パターンが得られるように夫々の加熱量の配分を変更してもよい。または、被加熱材とのエアーギャップを変更すると周波数が変動するためエアーギャップを変更して所望の周波数および加熱パターンを得てもよい。 As a characteristic of the induction heating device (transverse induction heating device), when an alternating current is passed through the coil, a steel plate magnetic field is generated inside the coil. Then, an eddy current in the direction opposite to the coil current is generated in the circumferential direction perpendicular to the magnetic flux by the electromagnetic induction action in the conductor placed therein, and the conductor is heated by the Joule heat. Eddy currents are generated most strongly on the inner surface of the coil and decrease exponentially toward the inner side (this phenomenon is called the skin effect). Therefore, the smaller the frequency, the greater the current penetration depth, and a uniform heating pattern is obtained in the thickness direction. Conversely, the greater the frequency, the smaller the current penetration depth, and the overheating with the surface layer peaking in the thickness direction. It is known that a small heating pattern can be obtained. Therefore, with the transverse induction heating device, the heating of the rough bars in the rolling direction and the plate width direction can be performed in the same manner as in the past, and the heating in the plate thickness direction can be performed by changing the frequency of the transverse induction heating device. By varying the penetration depth and operating the heating temperature pattern in the thickness direction, the temperature distribution can be made uniform. In this case, it is preferable to use a variable frequency induction heating apparatus, but the frequency may be changed by adjusting a condenser. Further, the distribution of the respective heating amounts may be changed so that a plurality of inductors having different frequencies are arranged to obtain a necessary thickness direction heating pattern. Alternatively, since the frequency varies when the air gap with the material to be heated is changed, the air gap may be changed to obtain a desired frequency and heating pattern.
本発明において、その「ねじれ」に代表される形状不良を抑制するという目的のために鋼板のミクロ組織構成を特に限定する必要はないので、仕上げ圧延を終了した後、巻取温度にて巻取るまでの冷却工程については特に定めないが、所望のミクロ組織構成（従来知られているような例えばフェライト+マルテンサイト）を得るために巻き取り温度制御や冷却熱履歴制御を行なう。但し、仕上げ圧延温度の温度バラツキを小さくすることにより達成できる鋼板の断面の硬さ分布や組織単位分布の均一性を維持するために巻き取り温度を±２０℃、冷却履歴変更温度を±２０℃とする必要がある。 In the present invention, there is no need to specifically limit the microstructure of the steel sheet for the purpose of suppressing the shape defect typified by the “twist”, so that the winding is performed at the winding temperature after finishing rolling. The cooling process up to is not particularly defined, but the coiling temperature control and the cooling heat history control are performed in order to obtain a desired microstructure (eg, ferrite + martensite as conventionally known). However, the coiling temperature is ± 20 ° C and the cooling history change temperature is ± 20 ° C in order to maintain the uniformity of the hardness distribution and structural unit distribution of the cross section of the steel sheet that can be achieved by reducing the temperature variation of the finish rolling temperature. It is necessary to.
冷却速度の上限は特に限定しないが、熱ひずみによる板そりが懸念されることから、３００℃／ｓ以下とすることが望ましい。さらに、あまりにもこの冷却速度が早いと冷却終了温度を制御できず、オーバーシュートして所定の巻取温度以下まで過冷却されてしまう可能性があるので、ここでの冷却速度は１５０℃／ｓ以下が望ましい。また、冷却速度の下限は特に定めないが、空冷であっても構わない。 The upper limit of the cooling rate is not particularly limited, but it is desirable that the cooling rate be 300 ° C./s or less because there is a concern about warpage due to thermal strain. Furthermore, if this cooling rate is too fast, the cooling end temperature cannot be controlled, and overcooling may cause overcooling to a predetermined coiling temperature or lower, so the cooling rate here is 150 ° C./s. The following is desirable. The lower limit of the cooling rate is not particularly defined, but air cooling may be used.
ただし、鋼板の強度を析出強化により担保するために析出強化元素を添加し、さらに「ねじれ」に代表される形状不良を抑制するためには、その析出物径分布が標準偏差σ≦２ｎｍであることが必要であるので巻取温度を５２５〜５７５℃とする。 However, in order to add a precipitation strengthening element in order to secure the strength of the steel sheet by precipitation strengthening, and to suppress shape defects typified by “twist”, the precipitate diameter distribution has a standard deviation σ ≦ 2 nm. Therefore, the coiling temperature is set to 525 to 575 ° C.
熱間圧延工程終了後は必要に応じて酸洗し、その後インラインまたはオフラインで圧下率１０％以下のスキンパスまたは圧下率４０％程度までの冷間圧延を施しても構わない。 After completion of the hot rolling process, pickling may be performed as necessary, and then a skin pass with a reduction rate of 10% or less or cold rolling to a reduction rate of about 40% may be performed inline or offline.
なお、鋼板形状の矯正や可動転位導入による延性の向上のためには０．１％以上２％以下のスキンパス圧延を施すことが望ましい。 In order to improve the ductility by correcting the shape of the steel sheet or introducing movable dislocations, it is desirable to perform skin pass rolling of 0.1% or more and 2% or less.
次に、冷延鋼板として最終製品にする場合であるが、「ねじれ」に代表される形状不良の抑制効果を得るためには、熱間圧延工程での仕上げ温度の標準偏差がσ≦７℃であることが必要である。これは、熱延鋼板での断面の硬度分布の標準偏差が小さいことで冷延後の硬度分布の標準偏差も改善され、結果として「ねじれ」に代表される形状不良の抑制が可能となるためである。また、さらに良好な形状凍結性を得るためには熱間圧延工程において仕上げ圧延温度〜仕上げ圧延温度＋２０℃の温度域で合計圧下率２５％以上の圧延を行うことで、冷延後でも断面の組織単位径分布の標準偏差が改善されるためである。 Next, in the case of making the final product as a cold-rolled steel sheet, in order to obtain the effect of suppressing the shape defect represented by “twist”, the standard deviation of the finishing temperature in the hot rolling process is σ ≦ 7 ° C. It is necessary to be. This is because the standard deviation of the hardness distribution after cold rolling is improved because the standard deviation of the hardness distribution of the cross section in the hot-rolled steel sheet is small, and as a result, it is possible to suppress shape defects typified by “twist”. It is. Moreover, in order to obtain a better shape freezing property, by performing rolling with a total rolling reduction of 25% or more in the temperature range of finish rolling temperature to finishing rolling temperature + 20 ° C. in the hot rolling process, the cross section of the cross-section can be obtained even after cold rolling. This is because the standard deviation of the tissue unit diameter distribution is improved.
また、仕上げ圧延終了温度（ＦＴ）はＡｒ3変態点温度未満で終了しても差し支えないが、その場合は、圧延前もしくは圧延中に析出したフェライトに強い加工組織が残留するため、続く巻取処理または加熱処理により回復、再結晶させることが望ましい。 Further, the finish rolling finish temperature (FT) may be finished at a temperature lower than the Ar 3 transformation point temperature, but in that case, a strong work structure remains in the ferrite precipitated before or during the rolling, and the subsequent winding is continued. It is desirable to recover and recrystallize by treatment or heat treatment.
酸洗後に冷間圧延を行う場合の条件は「ねじれ」に代表される形状不良を抑制するという目的のために特に限定する必要はない。ただし、続けて焼鈍を行う場合には回復再結晶を促進させるためにその合計圧下率は４０％以上が望ましい。 Conditions for cold rolling after pickling need not be particularly limited for the purpose of suppressing shape defects typified by “twist”. However, when the subsequent annealing is performed, the total rolling reduction is preferably 40% or more in order to promote recovery recrystallization.
冷間圧延された鋼板の熱処理は、連続焼鈍工程を前提としている。その焼鈍条件は「ねじれ」に代表される形状不良を抑制するという目的のために鋼板のミクロ組織構成を特に限定する必要はないので、特に限定する必要はなく回復温度以上で構わないが、回復温度未満の場合には加工組織が残留し成形性を著しく劣化させるので、熱処理の下限温度は回復温度以上が望ましい。さらに熱間圧延後、もしく冷間圧延後に得られた鋼板を焼鈍する場合に、前記熱間圧延での形状不良に優れた特性を損なわないようにするために、均熱帯の温度の標準偏差を１０℃以下にすることが好ましい。 The heat treatment of the cold-rolled steel sheet is based on a continuous annealing process. The annealing condition does not need to be specifically limited for the microstructure structure of the steel sheet for the purpose of suppressing shape defects typified by “twist”. If the temperature is lower than the temperature, the processed structure remains and the formability is remarkably deteriorated. Therefore, the lower limit temperature of the heat treatment is preferably not less than the recovery temperature. Furthermore, when annealing the steel sheet obtained after hot rolling or after cold rolling, in order not to impair the properties excellent in shape failure in the hot rolling, the standard deviation of the temperature of the soaking zone Is preferably 10 ° C. or lower.
また、この温度域での保持時間は、５秒未満では、伸び等に有害なセメンタイトが完全に再固溶するのに不十分であり、一方、１５０秒超の熱処理を行ってもその効果が飽和するばかりでなく生産性を低下させるので、保持時間は５〜１５０秒間とする。 In addition, if the holding time in this temperature range is less than 5 seconds, it is insufficient to completely re-dissolve cementite which is harmful to elongation and the like. The holding time is set to 5 to 150 seconds because it not only saturates but also reduces productivity.
その後の冷却条件については特に限定しないが、ミクロ組織を制御するために必要に応じて以下の冷却または任意温度での保持および冷却を行ってもよい。冷却工程の終了温度の下限については特に限定しないが、水冷もしくはミストで冷却する場合、コイルが長時間水濡れの状態にあると錆による外観不良が懸念されるため、５０℃以上が望ましい。 Subsequent cooling conditions are not particularly limited, but the following cooling or holding and cooling at an arbitrary temperature may be performed as necessary to control the microstructure. The lower limit of the end temperature of the cooling step is not particularly limited. However, when cooling with water or mist, if the coil is in a wet state for a long time, there is a concern about poor appearance due to rust.
熱延鋼板、冷延鋼板、焼鈍工程終了後の鋼板に表面処理を施しても良く、めっき種、樹脂皮膜種類、めっき方法、被覆方法を限定する必要はない。溶融亜鉛めっきの場合には、必要に応じて合金化処理してもよい。さらにその後、必要に応じてスキンパス圧延を実施する。 The hot-rolled steel sheet, cold-rolled steel sheet, and steel sheet after the annealing process may be subjected to surface treatment, and there is no need to limit the plating type, resin film type, plating method, and coating method. In the case of hot dip galvanizing, alloying treatment may be performed as necessary. Thereafter, skin pass rolling is performed as necessary.
以下に、実施例により本発明をさらに説明する。 The following examples further illustrate the present invention.
表１に示す化学成分を有する鋼種の鋼を溶製してスラブ片に鋳造した。鋳造スラブ片を粗圧延して薄鋼板に熱間圧延した。熱間圧延では、粗圧延機と仕上圧延機との間にトランスバース型誘導加熱装置を配置して粗バーを加熱して仕上圧延を実施した。なお、粗バーの両エッジ部を加熱するためにエッジヒータを用いた。粗バーの加熱は、仕上圧延機出側の鋼板の幅方向、圧延方向、板厚方向の温度分布が均一化するように行った。トランスバース型誘導加熱装置の加熱条件は、周波数の異なる加熱装置を複数配置して可能な範囲で必要な厚み方向加熱パターンが得られるように各々の加熱配分を変更した。 Steels having the chemical components shown in Table 1 were melted and cast into slab pieces. The cast slab piece was roughly rolled and hot rolled into a thin steel plate. In the hot rolling, a transverse type induction heating device was disposed between the rough rolling mill and the finish rolling mill, and the rough bar was heated to perform the finish rolling. An edge heater was used to heat both edge portions of the coarse bar. The coarse bar was heated so that the temperature distribution in the width direction, rolling direction, and thickness direction of the steel plate on the exit side of the finishing mill became uniform. Regarding the heating conditions of the transverse induction heating device, each heating distribution was changed so that a plurality of heating devices having different frequencies could be arranged to obtain a necessary thickness direction heating pattern within a possible range.
仕上圧延した後、ランアウトテ−ブル（ＲＯＴ）で冷却して巻き取ってコイルとした。コイルとした薄鋼板の一部に冷間圧延または冷間圧延と焼鈍を施した。 After finish-rolling, it was cooled by a run-out table (ROT) and wound to form a coil. Cold rolling or cold rolling and annealing were performed on a part of the thin steel sheet used as the coil.
仕上圧延後の冷却では冷却パターン（ＡおよびＢ）を選択して冷却を行なった。Ａパターンの冷却（ＣＲ１）は、水冷を行い、Ｂパターンの冷却（ＣＲ２）は、冷却履歴変更温度まで空冷を行い、その後水冷を行なった。Ａパターンの冷却では、ミクロ組織が連続冷却変態組織（Ｚｗ）となり、Ｂパターンの冷却では、ミクロ組織がフェライト（Ｆ）とマルテンサイト（Ｍ）組織となった。 For cooling after finish rolling, cooling was performed by selecting a cooling pattern (A and B). The cooling of pattern A (CR1) was water-cooled, and the cooling of pattern B (CR2) was air-cooled to the cooling history change temperature, and then water-cooled. In the cooling of the A pattern, the microstructure became a continuous cooling transformation structure (Zw), and in the cooling of the B pattern, the microstructure became a ferrite (F) and martensite (M) structure.
また、比較例として、誘導加熱を行わないで薄鋼板の製造を実施した。 In addition, as a comparative example, a thin steel plate was manufactured without performing induction heating.
熱間圧延の条件を表２に示す。得られた薄鋼板について、断面の硬度分布の標準偏差σ、組織単位径分布の標準偏差σおよび析出物径分布の標準偏差σを測定した。その結果を表３に、そして、薄鋼板の特性及び、得られた薄鋼板にプレス加工を施して、「反り」、「ねじれ」等の形状不良について調査した。その結果を表４に記載した。 Table 2 shows the hot rolling conditions. With respect to the obtained thin steel sheet, the standard deviation σ of the hardness distribution of the cross section, the standard deviation σ of the structure unit diameter distribution, and the standard deviation σ of the precipitate diameter distribution were measured. The results are shown in Table 3, and the characteristics of the thin steel sheet and the obtained thin steel sheet were subjected to press working to investigate shape defects such as “warping” and “twist”. The results are shown in Table 4.
表２から表４に示すように、均熱加熱装置により粗バーの加熱制御を行なって、仕上圧延機出側で圧延方向、板幅方向および板厚方向の温度差を均一化するようにして得られた薄鋼板の硬度分布の標準偏差σ（硬度偏差σ）が５以下の要件を満足する発明例（鋼番Ａ１、Ｂ、Ｃ１、Ｄ、Ｅ１〜Ｅ４）は、いずれも「ねじれ」、「反り」評価が良好（θｗ≦０．５：◎または○）であった。また、加熱制御をし、さらに仕上圧延温度偏差を７度以下、仕上圧延圧下率を２５％以下以上にと圧延条件を制御して、組織単位径分布の標準偏差σ（組織単位径偏差σ）を２．５μｍ以下とした発明例（鋼番Ａ１、Ｂ、Ｃ１、Ｄ）は、特に優れた「ねじれ」、「反り」評価（θｗ≦０．４：◎）となった。また、仕上圧延温度偏差を７度以下、仕上圧延後の巻取温度を制御して析出物径の制御を行なって析出物径分布の標準偏差σ（析出物径偏差σ）を２ｎｍ以下とした発明例（鋼番Ｅ１、Ｅ２）では、優れた「ねじれ」、「反り」評価（θｗ≦０．４：◎）となった。しかし、析出物径の制御を行なわなかった発明例（鋼番Ｅ３、Ｅ４）に於いても、良好な「ねじれ」、「反り」評価（０．４＜θｗ≦０．５：○）となった。
As shown in Table 2 to Table 4, the heating control of the coarse bar is performed by the soaking device, and the temperature difference in the rolling direction, the plate width direction and the plate thickness direction is made uniform on the exit side of the finishing mill. The invention examples (steel numbers A1, B, C1 , D, E1 to E4) satisfying the requirement that the standard deviation σ (hardness deviation σ) of the hardness distribution of the obtained thin steel sheet is 5 or less are all “twisted”, The “warp” evaluation was good (θw ≦ 0.5: ◎ or ○). In addition, by controlling the heating and controlling the rolling conditions such that the finish rolling temperature deviation is 7 degrees or less and the finish rolling reduction ratio is 25% or less, the standard deviation σ of the structure unit diameter distribution (structure unit diameter deviation σ) Inventive examples (steel numbers A1, B, C1 , and D) having a thickness of 2.5 μm or less exhibited particularly excellent “twist” and “warp” evaluations (θw ≦ 0.4: ◎). Also, the finish rolling temperature deviation is 7 degrees or less, the winding temperature after finish rolling is controlled to control the precipitate diameter, and the standard deviation σ (precipitate diameter deviation σ) of the precipitate diameter distribution is set to 2 nm or less. In the inventive examples (steel numbers E1 and E2), excellent “twist” and “warp” evaluations (θw ≦ 0.4: A) were obtained. However, even in the invention examples (steel numbers E3 and E4) in which the precipitate diameter was not controlled, good “twist” and “warp” evaluations (0.4 <θw ≦ 0.5: ○) became.
これに対して、加熱制御を行なわなかった比較例では、硬度分布の標準偏差σ（硬度偏差σ）が５超となっていて「ねじれ」、「反り」評価（０．５＜θｗ：×）が劣っていた。 On the other hand, in the comparative example in which the heating control was not performed, the standard deviation σ (hardness deviation σ) of the hardness distribution was more than 5, indicating “twist” and “warp” (0.5 <θw: ×). Was inferior.
さらに、記載は省略するが冷延鋼板や、熱延鋼板や冷延鋼板に亜鉛めっきした薄鋼板についても同様の結果が得られ、本発明の効果が検証された。 Furthermore, although description is abbreviate | omitted, the same result was obtained also about the cold-rolled steel plate, the hot-rolled steel plate, and the thin steel plate which carried out the galvanization of the cold-rolled steel plate, and the effect of this invention was verified.
Claims (7)
Ｃ ＝０．００１〜０．４％、
Ｓｉ＝０．００１〜５％、
Ｍｎ＝０．１〜５％、
Ｐ ≦０．１％、
Ｓ ≦０．０３％、
Ａｌ＝０．００１〜３％、
Ｎ ≦０．０１％、
を含有し残部がＦｅ及び不可避的不純物からなる化学組成の鋼板であって、その断面の硬度分布が標準偏差σ≦５であり、鋼板の断面のミクロ組織単位径分布が標準偏差σ≦２．５μｍであることを特徴とする加工性に優れる熱延鋼板。
In mass%
C = 0.001 to 0.4%,
Si = 0.001-5%,
Mn = 0.1-5%,
P ≦ 0.1%,
S ≦ 0.03%,
Al = 0.001 to 3%,
N ≦ 0.01%,
In which the balance is Fe and inevitable impurities, and the hardness distribution of the cross section is standard deviation σ ≦ 5, and the microstructural unit diameter distribution of the cross section of the steel sheet is standard deviation σ ≦ 2. A hot-rolled steel sheet excellent in workability, characterized by being 5 μm.
Ｎｂ＝０．０１〜０．３％、
Ｔｉ＝０．０１〜０．３％、
Ｍｏ＝０．０５〜１％、
Ｖ ＝０．０２〜１％、
Ｃｒ＝０．０１〜１％、
Ｃｕ＝０．２〜１．２％、
の一種または二種以上を含有することを特徴とする請求項１に記載の加工性に優れる熱延鋼板。 The steel sheet is further in mass%,
Nb = 0.01-0.3%,
Ti = 0.01-0.3%,
Mo = 0.05-1%,
V = 0.02 to 1%,
Cr = 0.01-1%,
Cu = 0.2-1.2%,
The hot-rolled steel sheet having excellent workability according to claim 1, comprising one or more of the following.
Ｃａ＝０．０００５〜０．００５％、
ＲＥＭ＝０．０００５〜０．０２％、
の一種または二種を含有することを特徴とする請求項１ないし請求項３のいずれか１項に記載の加工性に優れる熱延鋼板。 The steel sheet is further in mass%,
Ca = 0.005 to 0.005%,
REM = 0.005-0.02%,
Hot-rolled steel sheet having excellent workability according to any one of claims 1 to claim 3, characterized in that it contains the one or two.
Ｂ ＝０．０００２〜０．００２％
を含有することを特徴とする請求項１ないし請求項４のいずれか１項に記載の加工性に優れる熱延鋼板。 The steel sheet is further in mass%,
B = 0.0002 to 0.002%
The hot-rolled steel sheet having excellent workability according to any one of claims 1 to 4 , comprising:
Ｎｉ＝０．１〜０．６％、
を含有することを特徴とする請求項１ないし請求項５のいずれか１項に記載の加工性に優れる熱延鋼板。 The steel sheet is further in mass%,
Ni = 0.1-0.6%,
The hot-rolled steel sheet having excellent workability according to any one of claims 1 to 5 , characterized by comprising:
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| KR20200064511A (en) * | 2018-11-29 | 2020-06-08 | 주식회사 포스코 | High-strength steel sheet having excellent ductility and low-temperature toughness and method for manufacturing thereof |
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| JP2000119747A (en) * | 1998-10-14 | 2000-04-25 | Nkk Corp | Production of high tensile strength steel plate small in difference of material in plate thickness direction |
| JP4969742B2 (en) * | 2001-08-20 | 2012-07-04 | 株式会社神戸製鋼所 | Steel plate with good workability |
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| KR20200064511A (en) * | 2018-11-29 | 2020-06-08 | 주식회사 포스코 | High-strength steel sheet having excellent ductility and low-temperature toughness and method for manufacturing thereof |
| WO2020111856A3 (en) * | 2018-11-29 | 2020-08-13 | 주식회사 포스코 | High-strength steel sheet having excellent ductility and low-temperature toughness and method for manufacturing thereof |
| KR102164112B1 (en) | 2018-11-29 | 2020-10-12 | 주식회사 포스코 | High-strength steel sheet having excellent ductility and low-temperature toughness and method for manufacturing thereof |
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