JP2000063955A - Production of thin dual-phase hot rolled steel strip - Google Patents
Production of thin dual-phase hot rolled steel stripInfo
- Publication number
- JP2000063955A JP2000063955A JP10227886A JP22788698A JP2000063955A JP 2000063955 A JP2000063955 A JP 2000063955A JP 10227886 A JP10227886 A JP 10227886A JP 22788698 A JP22788698 A JP 22788698A JP 2000063955 A JP2000063955 A JP 2000063955A
- Authority
- JP
- Japan
- Prior art keywords
- steel strip
- thin
- range
- temperature
- less
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
Landscapes
- Metal Rolling (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
【0001】[0001]
【発明の属する技術分野】本発明は、フェライト+マル
テンサイトからなる板厚が3.2mm以下の薄物2相組
織熱延鋼帯の製造方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin two-phase hot-rolled steel strip composed of ferrite and martensite and having a plate thickness of 3.2 mm or less.
【0002】[0002]
【従来の技術】近年、自動車用の構造部材には、省エネ
ルギーのための軽量化や安全性向上のための高強度化が
要請されて、高張力鋼板の適用される機会が増加してい
る。なかでも、成形性の要求される部材には、低降伏比
で強度ー延性バランスに優れたフェライト+マルテンサ
イトからなる2相組織熱延鋼板が使用される場合が多
い。ところが、コイル間、もしくはコイル内で材質のば
らつきが生じると、プレス成形の際、われを発生した
り、スプリングバック量が異なったりするため、材質の
ばらつきの小さい鋼板が求められている。2. Description of the Related Art In recent years, structural members for automobiles have been required to be lighter for energy saving and to have higher strength to improve safety, and the opportunities for applying high-tensile steel sheets have been increasing. Among them, a hot-rolled steel sheet having a two-phase structure composed of ferrite and martensite, which has a low yield ratio and an excellent strength-ductility balance, is often used for members requiring formability. However, if there is variation in the material between the coils or within the coil, cracks will occur during press forming and the springback amount will differ, so there is a demand for a steel sheet with less variation in the material.
【0003】この2相組織熱延鋼板の製造方法として
は、熱延後の鋼帯を連続焼鈍設備などを用いて熱処理す
る方法もあるが、コスト的に有利な熱延ままで製造する
方が望ましく、特開昭61ー79730号公報、特開平
4ー235219号公報、特開平4ー289126号公
報、特開平9ー67641号公報などには、そのための
方法が開示されている。いずれの方法においても、適正
なフェライト+マルテンサイトの2相組織を得るには、
仕上温度をAr3変態点直上にするとともに仕上圧延後
の冷却条件を厳密にコントロールする必要がある。As a method for producing this hot rolled steel sheet having a two-phase structure, there is a method in which a steel strip after hot rolling is heat-treated using a continuous annealing equipment or the like, but it is more cost-effective to produce the hot rolled steel sheet as it is. Desirably, Japanese Patent Laid-Open No. 61-79730, Japanese Patent Laid-Open No. 4-235219, Japanese Patent Laid-Open No. 4-289126, Japanese Patent Laid-Open No. 9-67641 disclose methods therefor. In any method, in order to obtain a proper two-phase structure of ferrite + martensite,
It is necessary to keep the finishing temperature just above the Ar 3 transformation point and strictly control the cooling conditions after finish rolling.
【0004】熱延鋼帯の仕上温度をAr3点直上にコント
ロールするために、粗バーを加熱するという技術は、例
えば、特開平9−225517号公報に開示されてい
る。しかし、熱延ままで製造するタイプの2相組織鋼板
は、熱延条件で変態組織を制御するため、仕上圧延温度
に加えて、冷却条件を一般鋼に比べて厳しく制御する必
要がある。すなわち、ランナウト冷却、とりわけ中間保
持条件がばらつくとフェライト相とマルテンサイト相と
の比が変化し、材質上ばらつきが大きくなる。このよう
に、仕上温度の均一化のみでは均一な材質が得られな
い。A technique of heating a rough bar in order to control the finishing temperature of the hot-rolled steel strip just above the Ar 3 point is disclosed in, for example, Japanese Patent Laid-Open No. 9-225517. However, in a two-phase steel sheet of the type that is manufactured by hot rolling as it is, since the transformation structure is controlled under hot rolling conditions, it is necessary to control the cooling conditions in addition to the finish rolling temperature more strictly than general steel. That is, if the runout cooling, especially the intermediate holding condition, varies, the ratio of the ferrite phase to the martensite phase changes, and the variation in the material becomes large. As described above, a uniform material cannot be obtained only by uniformizing the finishing temperature.
【0005】[0005]
【発明が解決しようとする課題】材質上のばらつきにつ
いては、前述のように仕上温度と中間保持条件の制御が
必要である。このうち、ランナウト冷却、とりわけ中間
保持時間を出来るだけ一定にし、適正なフェライト相と
マルテンサイト相との比を確保する点からは、一定速度
で圧延することが好ましい。Regarding variations in materials, it is necessary to control the finishing temperature and the intermediate holding conditions as described above. Among them, rolling is preferable at a constant speed in order to keep the runout cooling, especially the intermediate holding time as constant as possible and to secure an appropriate ratio of the ferrite phase and the martensite phase.
【0006】ところが、板厚が薄い、とりわけ3.2m
m以下の薄い熱延鋼帯を一定圧延速度で製造すると、鋼
帯端部においては圧延中の温度低下が著しく、鋼帯全体
を加工性にとって必要なAr3変態点以上での仕上圧延
ができなくなったり、Ar3変態点以上で仕上圧延がで
きても仕上圧延温度にばらつきが生じたりして、鋼帯全
体にわたって均一な特性が得られなくなる。However, the plate thickness is thin, especially 3.2 m.
When a thin hot-rolled steel strip having a thickness of m or less is manufactured at a constant rolling speed, the temperature drop during rolling is remarkable at the edges of the steel strip, and the entire steel strip can be finished rolled at the Ar 3 transformation point or higher required for workability. Or even if finish rolling can be performed at the Ar 3 transformation point or higher, variations in finish rolling temperature occur, and uniform properties cannot be obtained over the entire steel strip.
【0007】一方、仕上温度の均一化に重点を置き、加
速圧延(ズーミング)により、仕上げ圧延温度を一定に
しようという技術はある。該方法は、鋼帯の後端部の温
度低下を抑えることを目的として、圧延中の速度を上げ
る技術である。しかし、該方法でも、板厚が薄い場合仕
上温度の制御は難しく、また、仕上温度を均一化しよう
とすると、板厚が薄い故、圧延速度を例えば500から
800mpmというように、大きく変化させることが必
要である。そのため、仕上げから巻取にいたる冷却、保
持条件がコイル長手方向で異なる、とりわけ中間保持時
間は圧延速度に依存し、前記の例では位置により1.6
倍異なるように、コイル長手方向で大きく異なることと
なり、材質の均一性は得られない。[0007] On the other hand, there is a technique that focuses on equalizing the finishing temperature and makes the finish rolling temperature constant by accelerated rolling (zooming). The method is a technique for increasing the speed during rolling for the purpose of suppressing the temperature decrease at the rear end of the steel strip. However, even with this method, it is difficult to control the finishing temperature when the sheet thickness is thin, and when trying to make the finishing temperature uniform, the sheet thickness is thin, and therefore the rolling speed must be changed greatly, for example, from 500 to 800 mpm. is necessary. Therefore, the cooling and holding conditions from finishing to winding are different in the coil longitudinal direction. Especially, the intermediate holding time depends on the rolling speed, and in the above example, 1.6 depending on the position.
As it is twice as large, it is largely different in the longitudinal direction of the coil, and the uniformity of the material cannot be obtained.
【0008】本発明はこのような課題を解決するために
なされたもので、鋼帯全体にわたって均一な特性の得ら
れる薄物2相組織熱延鋼帯の製造方法を提供することを
目的とする。The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for manufacturing a thin-duplex hot-rolled steel strip having uniform properties over the entire steel strip.
【0009】[0009]
【課題を解決するための手段】上記課題は、wt%で、
C:0.03〜0.15%、Si:0.3〜2.5%、
Mn:0.5〜2.5%、P:0.07%以下、S:
0.02%以下、sol.Al:0.005〜0.08
%、N:0.008%以下を含む鋼の粗バーまたは薄ス
ラブを製造する工程と、前記粗バーまたは薄スラブを加
熱することにより、一定圧延速度で、鋼帯内の仕上温度
をAr3変態点〜(Ar3変態点+50℃)の範囲内に納
めて仕上圧延する工程と、前記仕上圧延後の鋼帯を20
℃/s以上の冷却速度で600〜780℃の温度範囲に
冷却し、前記温度範囲で3秒以上保持する工程と、前記
温度範囲で保持後の鋼帯を20℃/s以上の冷却速度で
冷却し、250℃以下の温度で巻取る工程と、を有して
なる薄物2相組織熱延鋼帯の製造方法により解決され
る。[Means for Solving the Problems] The above problems are in wt%,
C: 0.03 to 0.15%, Si: 0.3 to 2.5%,
Mn: 0.5 to 2.5%, P: 0.07% or less, S:
0.02% or less, sol. Al: 0.005-0.08
%, N: 0.008% or less, and a step of producing a steel rough bar or thin slab, and heating the rough bar or thin slab to achieve a finishing temperature in the steel strip of Ar 3 at a constant rolling speed. A step of finishing rolling within the range of transformation point to (Ar 3 transformation point + 50 ° C.), and the steel strip after the finishing rolling is 20 times.
A step of cooling to a temperature range of 600 to 780 ° C. at a cooling rate of ℃ / s or more and holding the temperature range for 3 seconds or more; and a steel strip after being held in the temperature range at a cooling rate of 20 ° C./s or more. It is solved by a method for producing a thin thin two-phase structure hot rolled steel strip, which comprises a step of cooling and winding at a temperature of 250 ° C. or less.
【0010】以下に、成分および製造条件の限定理由に
ついて説明する。
C:0.15wt%を超えると硬質・低延性となり、
0.03wt%未満では所定の強度を得るためには多量
の合金元素の添加が必要になりコスト高となる。The reasons for limiting the components and manufacturing conditions will be described below. C: When it exceeds 0.15 wt%, it becomes hard and has low ductility,
If it is less than 0.03 wt%, it is necessary to add a large amount of alloying elements in order to obtain a predetermined strength, resulting in high cost.
【0011】Si:目標強度レベルに応じて適宜添加す
る必要があるが、2.5wt%を超えると溶接性が劣化
し、0.3wt%未満ではフェライト+マルテンサイト
の2相組織が得られない。Si: It is necessary to appropriately add Si depending on the target strength level, but if it exceeds 2.5 wt%, the weldability deteriorates, and if it is less than 0.3 wt%, a two-phase structure of ferrite + martensite cannot be obtained. .
【0012】Mn:Si同様、目標強度レベルに応じて
適量添加する必要があるが、2.5wt%を超えると溶
接性が劣化し、0.5wt%未満ではフェライト+マル
テンサイトの2相組織が得られない。Similar to Mn: Si, it is necessary to add an appropriate amount depending on the target strength level, but if it exceeds 2.5 wt%, the weldability deteriorates, and if it is less than 0.5 wt%, a two-phase structure of ferrite + martensite occurs. I can't get it.
【0013】P:Pは高強度化、耐食性向上のため、適
宜添加するが、0.07wt%を超えると低延性・低靭
性となるため、0.07wt%以下とした。意図的に添
加しない場合、偏析防止のため、好ましい範囲は、0.
015wt%以下である。P: P is added as appropriate in order to increase the strength and improve the corrosion resistance, but if it exceeds 0.07 wt%, it has low ductility and low toughness, so it was made 0.07 wt% or less. When not intentionally added, the preferable range is 0.
It is 015 wt% or less.
【0014】S:0.02wt%を超えると低延性・低
靭性となるため、0.02wt%以下とした。好ましい
範囲は、0.005wt%以下である。S: If it exceeds 0.02 wt%, low ductility and low toughness will result, so the content was made 0.02 wt% or less. A preferred range is 0.005 wt% or less.
【0015】sol.Al:鋼の脱酸を安定して行うた
めに0.005wt%以上必要であるが、0.08wt
%を超えるとその効果は飽和し、コスト高になるため、
0.08wt%以下とした。好ましい範囲は、0.01
〜0.05wt%である。Sol. Al: 0.005 wt% or more is necessary for stable deoxidation of steel, but 0.08 wt
If it exceeds%, the effect will be saturated and the cost will increase, so
It was made 0.08 wt% or less. The preferred range is 0.01
~ 0.05 wt%.
【0016】N:0.008wt%を超えると低延性・
低靭性となるため0.008wt%以下とした。好まし
い範囲は、0.005wt%以下である。N: When it exceeds 0.008 wt%, low ductility
Since it has low toughness, it is set to 0.008 wt% or less. A preferred range is 0.005 wt% or less.
【0017】その他の元素については、本発明を妨げな
い範囲で含有することができる。例えば、伸びフランジ
性改善のためにCaを0.006wt%以下、REM:
0.1wt%以下、焼入性改善などのためにCrを0.
8wt%以下、B:0.01wt%以下、Ni:0.5
wt%以下、W:0.5wt%以下、Mo:0.7wt
%以下の範囲内で添加できる。また、析出強化、もしく
は溶接部のHAZ軟化防止などを目的として、Nb:0.
06wt%以下、Ti:0.15wt%以下、V:0.
1wt%以下、Zr:0.1wt%以下添加しても良
く、耐食性向上などのため、Sn:0.1wt%以下、
Cu:0.5wt%以下の範囲内で適宜添加しても本発
明の効果が妨げられることはない。Other elements can be contained within the range not hindering the present invention. For example, in order to improve stretch flangeability, Ca is 0.006 wt% or less, REM:
0.1 wt% or less, Cr for the hardenability improvement etc. 0.
8 wt% or less, B: 0.01 wt% or less, Ni: 0.5
wt% or less, W: 0.5 wt% or less, Mo: 0.7 wt
It can be added within the range of less than%. Further, for the purpose of precipitation strengthening or prevention of HAZ softening of the welded portion, Nb: 0.
06 wt% or less, Ti: 0.15 wt% or less, V: 0.
1 wt% or less, Zr: 0.1 wt% or less may be added, Sn: 0.1 wt% or less, for improving corrosion resistance,
Cu: Even if added appropriately within the range of 0.5 wt% or less, the effect of the present invention is not hindered.
【0018】こうした成分を含有する鋼を仕上圧延する
に際しては、鋼を溶製後粗バーあるいは粗バー相当の厚
みの薄スラブを製造する必要がある。その製法は特に限
定しないが、通常は、鋼を溶製後、連続鋳造あるいは造
塊ー分解圧延によりスラブとなし、そのまま直接あるい
は加熱炉で再加熱して粗圧延することにより粗バーを、
また、溶製後、連続鋳造により粗 バー相当の厚みを有
する薄スラブを製造する。When the steel containing such components is finish-rolled, it is necessary to produce a rough bar or a thin slab having a thickness corresponding to the rough bar after the steel is melted. The production method is not particularly limited, but usually, after smelting steel, it is made into a slab by continuous casting or ingot-decomposition rolling, and a rough bar is directly or directly reheated in a heating furnace to be rough rolled,
After the melting, a thin slab having a thickness corresponding to the coarse bar is manufactured by continuous casting.
【0019】スラブの再加熱を行う場合は、スケール欠
陥の発生防止や仕上圧延前のオーステナイト粒の微細化
を図る上で、1250℃以下の低温加熱が好ましい。When the slab is reheated, low temperature heating at 1250 ° C. or lower is preferable in order to prevent scale defects from occurring and to refine the austenite grains before finish rolling.
【0020】前述したように、板厚の薄い熱延鋼帯を一
定圧延速度で製造すると、鋼帯端部においては圧延中の
温度低下が著しくなり、仕上温度が確保できなくなるこ
とから、鋼帯全体にわたって均一な特性が得られない。
そこで、本発明者等が鋼帯全体にわたって均一な特性の
得られる条件を検討したところ、鋼帯全体にわたって均
一な特性の得るためには、一定圧延速度で、かつ鋼帯内
の仕上温度をAr3変態点〜(Ar3変態点+50℃)の
範囲内に納めて仕上圧延を行うことが必要であり、その
手段として粗バーや薄スラブを仕上圧延前に加熱するこ
とが有効であることが明らかになった。As described above, when a hot-rolled steel strip having a thin plate thickness is manufactured at a constant rolling speed, the temperature of the steel strip at the end thereof is remarkably lowered during rolling, and the finishing temperature cannot be secured. Uniform characteristics cannot be obtained throughout.
Therefore, the inventors of the present invention examined conditions under which uniform properties can be obtained over the entire steel strip. In order to obtain uniform properties over the entire steel strip, the finishing temperature in the steel strip was kept constant at a constant rolling speed in order to obtain uniform properties. It is necessary to carry out finish rolling within a range of 3 transformation points to (Ar 3 transformation point + 50 ° C), and as a means for that, it is effective to heat a rough bar or thin slab before finish rolling. It was revealed.
【0021】仕上圧延速度を一定にしながら仕上温度を
確保する方法としては、例えば、粗バーを仕上圧延に先
立ち、巻き取るという方法も考えられる。しかし、薄物
の鋼帯のように、端部の温度低下が著しい鋼帯では、一
定の圧延速度でしかも上記のような狭い範囲に仕上温度
を制御することは難しい。As a method of securing the finishing temperature while keeping the finishing rolling speed constant, for example, a method of winding the rough bar prior to the finishing rolling can be considered. However, it is difficult to control the finishing temperature at a constant rolling speed and in the narrow range as described above in a steel strip such as a thin steel strip in which the temperature drop at the end is remarkable.
【0022】また、該方法は積極的に温度を上げる技術
ではないため、スラブ加熱温度が低すぎるときなどでは
所定の仕上温度を確保することが出来ない。また、コイ
ルに巻きとっても加熱を行わないとコイルの先端、後端
部では温度低下が起こり、長手方向全般にわたり均一な
仕上温度を得ることは難しい。その点、粗バーもしくは
薄スラブを加熱する方法では、粗バーもしくは薄スラブ
の長手方向の温度分布に応じて加熱条件を変化させるこ
とが可能であり、鋼帯の仕上温度の均一化が容易であ
る。Further, since the method is not a technique for positively raising the temperature, it is impossible to secure a predetermined finishing temperature when the slab heating temperature is too low. Further, even if wound around the coil, unless heating is performed, the temperature lowers at the front end and the rear end of the coil, and it is difficult to obtain a uniform finishing temperature in the entire longitudinal direction. In that respect, in the method of heating the rough bar or the thin slab, it is possible to change the heating conditions according to the temperature distribution in the longitudinal direction of the rough bar or the thin slab, and it is easy to make the finishing temperature of the steel strip uniform. is there.
【0023】なお、本発明において粗バーまたは薄スラ
ブを加熱することが重要であって、粗バーまたは薄スラ
ブをコイルに巻取った後コイルままで加熱することも可
能であり、コイルに巻取る前、あるいは一旦コイルに巻
いてから巻きほぐした後、加熱することも可能であり、
いずれの場合も粗バーまたは薄スラブの加熱による仕上
温度の均一化の効果は妨げられない。なお、粗バーもし
くは薄スラブを長手方向に加熱することに加えて、必要
に応じてエッジヒーターを併用することについては、本
発明を妨げることはない。In the present invention, it is important to heat the rough bar or thin slab, and it is also possible to wind the rough bar or thin slab into a coil and then heat the coil as it is, or to wind the coil into a coil. It is also possible to heat before, or after coiling and then unwinding,
In either case, the effect of uniformizing the finishing temperature by heating the coarse bar or thin slab is not impeded. In addition to heating the rough bar or the thin slab in the longitudinal direction, optionally using an edge heater together does not hinder the present invention.
【0024】前述のごとく圧延速度を一定にすることが
重要であるが、圧延速度が300mpm未満では生産性
が著しく低下したりするため、300mpm以上が好ま
しい。一方、圧延速度が速すぎると、圧延中の温度、板
厚制御や圧延後の冷却条件、特に中間保持温度の制御が
困難になり、長手方向、および幅方向での材質均一性が
得にくいため、850mpm以下が好ましい。As mentioned above, it is important to keep the rolling speed constant. However, if the rolling speed is less than 300 mpm, the productivity is remarkably reduced, so 300 mpm or more is preferable. On the other hand, if the rolling speed is too fast, it becomes difficult to control the temperature during rolling, the plate thickness control and the cooling conditions after rolling, especially the intermediate holding temperature, and it is difficult to obtain material uniformity in the longitudinal direction and the width direction. , 850 mpm or less is preferable.
【0025】また、圧延速度が450mpmを超えると
鋼帯後端部の温度低下量が大きくなり、温度補償のた
め、粗バーもしくは薄スラブ加熱温度を大きくせねばな
らず、コストが大きくなるため、450mpm以下がさ
らに好ましい。なお、本発明で述べる一定圧延速度に関
しては、目標の中間保持時間に応じて変化するが、許容
差として100mpm以下程度までは本発明を損なわな
い。Further, when the rolling speed exceeds 450 mpm, the amount of temperature decrease at the rear end of the steel strip becomes large, and the temperature of the rough bar or thin slab must be increased for temperature compensation, resulting in an increase in cost. It is more preferably 450 mpm or less. The constant rolling speed described in the present invention changes according to the target intermediate holding time, but the present invention is not impaired up to a tolerance of about 100 mpm or less.
【0026】仕上温度がAr3変態点未満では、加工性
が著しく劣化するとともに、鋼帯全体にわたって均一な
特性が得られなくなる。また、(Ar3変態点+50
℃)を超えると、加工ひずみが解放されるとともにオー
ステナイト粒が大きくなりフェライトの核生成サイトが
少なくなることから、鋼帯全体にわたって均一な特性が
得られ難くなるとともに、降伏強度が上昇する。このよ
うに、鋼帯全体にわたって仕上温度をAr3変態点〜
(Ar3変態点+50℃)に制御し、併せて中間保持条件
を一定にすることにより、鋼帯全体にわたって材質を均
一化することができる。その値は、引張強度のばらつき
で50MPa、さらには30MPa以下である。If the finishing temperature is less than the Ar 3 transformation point, the workability is significantly deteriorated and uniform properties cannot be obtained over the entire steel strip. Also, (Ar 3 transformation point +50
(° C), the processing strain is released and the austenite grains become large and the ferrite nucleation sites decrease, so that it becomes difficult to obtain uniform properties over the entire steel strip and the yield strength increases. As described above, the finishing temperature is set to the Ar 3 transformation point over the entire steel strip.
By controlling the temperature to (Ar 3 transformation point + 50 ° C.) and keeping the intermediate holding condition constant, the material can be made uniform over the entire steel strip. The value is 50 MPa, further 30 MPa or less due to variations in tensile strength.
【0027】なお、粗バーや薄スラブの加熱温度は、粗
バーや薄スラブの加熱前の温度や鋼の変態点、圧延速度
などに応じて適宜決められる。粗バーや薄スラブは、通
常、位置により温度が異なるため、温度分布に応じて粗
バーや薄スラブの加熱条件を変えるのが好ましい。The heating temperature of the rough bar or thin slab is appropriately determined according to the temperature of the rough bar or thin slab before heating, the transformation point of steel, the rolling speed, and the like. Since the temperature of the coarse bar or the thin slab usually differs depending on the position, it is preferable to change the heating conditions of the coarse bar or the thin slab according to the temperature distribution.
【0028】仕上圧延後は、微細なフェライト粒を強度
に応じて適正量析出させるために、20℃/s以上の冷
却速度で600〜780℃の温度範囲に冷却し、この温
度範囲で3秒以上保持する必要がある。なぜなら、この
範囲をはずれると2相組織鋼として必要な低降伏比(Y
Rで70%以下程度)、および高延性が得られないから
である。なお、この範囲内であれば均一な材質が得られ
るわけではなく、鋼帯内での冷却条件を所定の材質に応
じて前記範囲内で可能な限り均一化させなければならな
い。特に中間保持時間のばらつきを小さくすることは、
フェライト相とマルテンサイト相の比を制御する上で、
重要である。After the finish rolling, in order to precipitate an appropriate amount of fine ferrite grains according to the strength, it is cooled to a temperature range of 600 to 780 ° C. at a cooling rate of 20 ° C./s or more, and this temperature range is used for 3 seconds. It is necessary to hold more than this. Because, if it is out of this range, the low yield ratio (Y
R is about 70% or less) and high ductility cannot be obtained. It should be noted that a uniform material cannot be obtained within this range, and the cooling conditions in the steel strip must be made as uniform as possible within the above range according to the predetermined material. Especially, to reduce the variation of the intermediate holding time,
In controlling the ratio of ferrite phase and martensite phase,
is important.
【0029】また、600〜780℃の温度範囲で保持
したときの未変態のオーステナイト相を安定してマルテ
ンサイト相に変態させるために、保持後は20℃/s以
上の冷却速度で冷却し、250℃以下の温度で巻取る必
要がある。Further, in order to stably transform the untransformed austenite phase into the martensite phase when kept in the temperature range of 600 to 780 ° C., after the holding, it is cooled at a cooling rate of 20 ° C./s or more, It is necessary to wind at a temperature of 250 ° C or lower.
【0030】鋼帯内の仕上温度をAr3変態点〜(Ar3
変態点+30℃)の範囲内に納めて仕上圧延すれば、鋼
帯全体にわたってより均一な特性が得られる。The finishing temperature in the steel strip is set to the Ar 3 transformation point to (Ar 3
If the temperature is set within the range of the transformation point + 30 ° C) and finish rolling is performed, more uniform properties can be obtained over the entire steel strip.
【0031】粗バーまたは薄スラブの加熱を、粗バーま
たは薄スラブを搬送しながらその幅方向全体を加熱でき
る粗バー加熱装置により行えば、生産性を損なうことな
く温度の均一化が可能になる。If the rough bar or the thin slab is heated by a rough bar heating device capable of heating the rough bar or the thin slab in its entire width direction, the temperature can be made uniform without impairing the productivity. .
【0032】粗バーまたは薄スラブの加熱を誘導加熱コ
イルを用いて行えば、加熱を迅速に行えるので、より生
産性をアップできる。When the rough bar or the thin slab is heated by using the induction heating coil, the heating can be performed quickly, so that the productivity can be further improved.
【0033】[0033]
【実施例】表1に示す成分を有する鋼a〜eを溶製し、
連続鋳造により厚さ約250mmのスラブを製造し、1
210℃に加熱後、粗圧延機により厚さ約30mmの粗
バーに圧延した。そして、表2に示す条件で、この粗バ
ーを加熱ー仕上圧延ー冷却を順次行い、室温で巻取って
板幅800mm、強度レベル550〜800MPaの2
相組織熱延鋼帯1〜20を作製した。なお、粗バー加熱
は、誘導コイルタイプの加熱手段を備え、このコイル中
に粗バーを通過させながら加熱する粗バー加熱装置を用
いて行った。EXAMPLES Steels a to e having the components shown in Table 1 were melted,
Approximately 250mm thick slab is manufactured by continuous casting, and
After heating to 210 ° C., it was rolled into a rough bar having a thickness of about 30 mm by a rough rolling machine. Then, under the conditions shown in Table 2, the rough bar is sequentially heated, finished rolled, and cooled, and wound at room temperature to obtain a plate width of 800 mm and a strength level of 550 to 800 MPa.
Phase-structure hot-rolled steel strips 1 to 20 were produced. The rough bar heating was carried out by using a rough bar heating device equipped with an induction coil type heating means and heating while passing the rough bar through the coil.
【0034】そして、作製した鋼帯1〜20の長手方向
先端部(T)、中央部(M)、後端部(B)の幅中央部
よりJIS5号試験片(圧延直角方向)を2本採取し引
張強度TSの平均値を求め、鋼帯の強度のバラツキΔT
Sを、T、M、Bにおける強度の最大値と最小値の差で
評価した。Then, two JIS No. 5 test pieces (in the direction perpendicular to the rolling direction) were formed from the widthwise central portions of the manufactured steel strips 1 to 20 in the longitudinal direction (T), the central portion (M), and the rear end portion (B). The average value of the tensile strength TS is obtained and the variation of the strength of the steel strip ΔT
S was evaluated by the difference between the maximum value and the minimum value of the strength in T, M and B.
【0035】結果を表2、表3、表4に示す。また、各
々の鋼板のB部での降伏強度、引張強度、伸び値を表5
に示す。The results are shown in Tables 2, 3 and 4. Table 5 shows the yield strength, tensile strength, and elongation value of the B part of each steel sheet.
Shown in.
【0036】本発明例である鋼帯No.3、4、7、
8、11、12、15、16、19、20は、いずれも
ΔTSが50MPa以下で、長手方向にわたって均一な
特性が得られる。特に、仕上温度をAr3変態点〜(A
r3変態点+30℃)の範囲内にしたり、圧延速度を30
0〜450mpmの範囲内にすると、ΔTSが30MP
a以下となり、より均一性に優れる。Steel strip No. which is an example of the present invention. 3, 4, 7,
All of 8, 11, 12, 15, 16, 19, and 20 have ΔTS of 50 MPa or less, and uniform characteristics can be obtained in the longitudinal direction. Particularly, the finishing temperature is set to the Ar 3 transformation point to (A
or in the range of r 3 transformation point + 30 ° C.), the rolling speed 30
Within the range of 0-450 mpm, ΔTS is 30MP
It becomes a or less and is more excellent in uniformity.
【0037】一方、加速圧延を行わない従来例である鋼
帯No.1、5、9、13、17は、仕上温度の制御が
十分に制御できず、ΔTSが大きくなり、長手方向にわ
たる均一性に劣る。また、加速圧延を行った従来例であ
る鋼帯No.2、6、10、14、18は、従来例に比
べて仕上温度の制御性が向上したが、冷却、保持条件、
特に保持時間がT、M、Bにより異なり、均一性に劣
る。On the other hand, steel strip No. which is a conventional example in which accelerated rolling is not performed. In Nos. 1, 5, 9, 13, and 17, the finishing temperature cannot be controlled sufficiently, ΔTS becomes large, and the uniformity in the longitudinal direction is poor. In addition, steel strip No. which is a conventional example subjected to accelerated rolling. Nos. 2, 6, 10, 14, and 18 have improved controllability of finishing temperature as compared with the conventional example, but cooling, holding conditions,
In particular, the holding time varies depending on T, M, and B, and the uniformity is poor.
【0038】[0038]
【表1】 [Table 1]
【0039】[0039]
【表2】 [Table 2]
【0040】[0040]
【表3】 [Table 3]
【0041】[0041]
【表4】 [Table 4]
【0042】[0042]
【表5】 [Table 5]
【0043】[0043]
【発明の効果】本発明は以上説明したように構成されて
いるので、鋼帯全体にわたって均一な特性の得られる薄
物2相組織熱延鋼帯の製造方法を提供できる。EFFECTS OF THE INVENTION Since the present invention is constructed as described above, it is possible to provide a method for producing a thin two-phase hot-rolled steel strip having uniform properties over the entire steel strip.
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 FI テーマコート゛(参考) C21D 9/00 101 C21D 9/00 101N // C22C 38/00 301 C22C 38/00 301W 38/06 38/06 (72)発明者 冨田 邦和 東京都千代田区丸の内一丁目1番2号 日 本鋼管株式会社内 (72)発明者 正木 潤 東京都千代田区丸の内一丁目1番2号 日 本鋼管株式会社内 Fターム(参考) 4E002 AA07 AB01 AD04 BC02 BC07 BD07 BD08 4K037 EA01 EA05 EA06 EA15 EA16 EA18 EA23 EA25 EA27 EA28 EB06 EB09 FB07 FC07 FD03 FD04 FD08 FE01 ─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. 7 Identification code FI theme code (reference) C21D 9/00 101 C21D 9/00 101N // C22C 38/00 301 C22C 38/00 301W 38/06 38 / 06 (72) Inventor Kunikazu Tomita Marunouchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Jun Masaki Marunouchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo F Nippon Steel Pipe Co., Ltd. F Term (reference) 4E002 AA07 AB01 AD04 BC02 BC07 BD07 BD08 4K037 EA01 EA05 EA06 EA15 EA16 EA18 EA23 EA25 EA27 EA28 EB06 EB09 FB07 FC07 FD03 FD04 FD08 FE01
Claims (6)
Si:0.3〜2.5%、Mn:0.5〜2.5%、
P:0.07%以下、S:0.02%以下、sol.A
l:0.005〜0.08%、N:0.008%以下を
含む鋼の粗バーまたは薄スラブを製造する工程と、前記
粗バーまたは薄スラブを加熱することにより、一定圧延
速度で、鋼帯内の仕上温度をAr3変態点〜(Ar3変態
点+50℃)の範囲内に納めて仕上圧延する工程と、前
記仕上圧延後の鋼帯を20℃/s以上の冷却速度で60
0〜780℃の温度範囲に冷却し、前記温度範囲で3秒
以上保持する工程と、前記温度範囲で保持後の鋼帯を2
0℃/s以上の冷却速度で冷却し、250℃以下の温度
で巻取る工程と、を有してなる薄物2相組織熱延鋼帯の
製造方法。1. C: 0.03 to 0.15% by weight,
Si: 0.3 to 2.5%, Mn: 0.5 to 2.5%,
P: 0.07% or less, S: 0.02% or less, sol. A
l: 0.005 to 0.08%, N: 0.008% or less of the step of manufacturing a steel rough bar or thin slab containing steel, by heating the rough bar or thin slab, at a constant rolling speed, A step of finishing rolling in which the finishing temperature in the steel strip is within the range of Ar 3 transformation point to (Ar 3 transformation point + 50 ° C.), and the steel strip after the finishing rolling is cooled at 20 ° C./s or more at a cooling rate of 60.
A step of cooling to a temperature range of 0 to 780 ° C. and holding the temperature range for 3 seconds or more;
A method for producing a thin hot-rolled steel strip having a two-phase structure, comprising a step of cooling at a cooling rate of 0 ° C./s or more and winding at a temperature of 250 ° C. or less.
r3変態点+30℃)の範囲内に納めて仕上圧延する請
求項1に記載の薄物2相組織熱延鋼帯の製造方法。2. The finishing temperature in the steel strip is set to the Ar 3 transformation point to (A
The method for producing a thin strip two-phase hot-rolled steel strip according to claim 1, wherein the sheet is placed within a range of (r 3 transformation point + 30 ° C) and finish-rolled.
延速度で仕上圧延を行う請求項1または請求項2に記載
の薄物2相組織熱延鋼帯の製造方法。3. The method for producing a thin strip two-phase hot-rolled steel strip according to claim 1, wherein the finish rolling is performed at a constant rolling speed within a range of 300 to 850 mpm.
延速度で仕上圧延を行う請求項1から請求項3のいずれ
か1項に記載の薄物2相組織熱延鋼帯の製造方法。4. The method for producing a thin strip two-phase hot-rolled steel strip according to any one of claims 1 to 3, wherein the finish rolling is performed at a constant rolling speed within a range of 300 to 450 mpm.
または薄スラブを搬送しながらその幅方向全体を加熱で
きる装置により行う請求項1から請求項4のいずれか1
項に記載の薄物2相組織熱延鋼帯の製造方法。5. The heating of the rough bar or the thin slab is performed by a device capable of heating the entire width direction of the rough bar or the thin slab while conveying the rough bar or the thin slab.
Item 2. A method of manufacturing a thin hot-rolled steel strip having a two-phase structure.
コイルを用いて行う請求項1から請求項5のいずれか1
項に記載の薄物2相組織熱延鋼帯の製造方法。6. The method according to claim 1, wherein the rough bar or the thin slab is heated by using an induction heating coil.
Item 2. A method of manufacturing a thin hot-rolled steel strip having a two-phase structure.
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