JPS6227519A - Manufacture of ultrafine grain hot rolled high tensile steel plate - Google Patents

Abstract

PURPOSE:To manufacture easily and certainly the titled plate with a low cost, by rolling steel having a specified compsn. contg. C, Si, Mn, Al, N as main components, further deposited material forming element such as Nb under a suitable condition. CONSTITUTION:Steel contg. by weight 0.05-0.2% C, 0.01-1.0% Si, 0.3-2.0% Mn, 0.05-0.1% Al, 0.001-0.02% N as main components, further <= one kind among 0.005-0.1% Nb, 0.005-0.1% Zr, 0.01-0.2% V, 0.01-0.3% Ti, 0.005-0.1% Ta, 0.2-3.0% W, 0.1-1.5% Mo, 0.1-1.5% Cu, 0.1-1.5% Cr, 0.1-1.5% Ni as deposited material forming element is cast then or heated to high temp. where ppt. forming element enters into solid soln. and cooled, and subjected to the first step rolling at 850-950 deg.C by >=50% total draft. In <=10min thereafter, the second step rolling is carried out by >=65% total draft so that rolling finish temp. is regulated to 870 deg.C-Ar3 transformation point. Thereafter the plate is cooled to <=550 deg.C at >=20 deg.C/s rate.

Description

【発明の詳細な説明】 （産業上の利用分野） 本発明は延・靭性および加工性の高い熱延高張力鋼板の
製造法に関するものである。DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a hot-rolled high-strength steel plate with high elongation, toughness, and workability.

（従来の技術） 鋼材の加工性や使用特性を向上させるために結晶粒の微
細化は従来より広く研究され、種々の方法が考えられて
きたが、本発明者らは何ら特殊元素を含まず、また特に
熱処理も必要としない熱延ままの炭素鋼で従来以上の微
細結晶組織を得る方法を以前に発明した（特開昭５８−
１２３８２３）、この方法は熱延仕上圧延時の圧下率を
大とし、加工歪によりフェライト変態を誘起させるとい
う極めて斬新なものであったが、大圧下を工業的に実現
する方法が限られてしまう欠点があった。(Prior art) Grain refinement has been widely studied and various methods have been devised to improve the workability and usability characteristics of steel materials, but the present inventors have developed a method that does not contain any special elements. , also previously invented a method for obtaining a finer crystal structure than before in hot-rolled carbon steel that does not require any particular heat treatment (Japanese Patent Application Laid-Open No. 1983-1999).
123823), this method was extremely innovative in that it increases the rolling reduction during hot finish rolling and induces ferrite transformation through processing strain, but there are limits to how to industrially realize large rolling reductions. There were drawbacks.

そこで本発明者らはさらに検討を進めた結果、圧延前に
析出物を生成せしめておけば析出物が加工誘起変態の核
となり、通常の圧下率でも結晶粒は超微細化する知見を
得、低合金鋼スラブの低温加熱による超細粒化法（特願
昭５９−１７４１８８）を提案した。ところが、低温加
熱法は利点が多いものの万能ではなく、問題点として以
下の３点がある。As a result of further investigation, the present inventors found that if precipitates were formed before rolling, the precipitates would become the core of deformation-induced transformation, and the crystal grains would become ultra-fine even at a normal rolling reduction. We proposed a method for ultra-fine graining of low-alloy steel slabs by low-temperature heating (Japanese Patent Application No. 59-174188). However, although the low-temperature heating method has many advantages, it is not a panacea and has the following three problems.

■低温加熱が必須条件であるためにロフト構成上の制約
を受け、生産上書にスケジュールフリーとはならない。■Since low-temperature heating is an essential condition, there are restrictions on the loft configuration, and there is no schedule-free schedule for production overrides.

■析出物のサイズを適正なものとするために鋳造後の冷
却を管理する必要がある。■It is necessary to control cooling after casting to ensure that the size of the precipitates is appropriate.

■鋳造後変態する前に圧延される直送圧延やホットチャ
ージ等のプロセスには適さない。■It is not suitable for processes such as direct rolling and hot charging, which involve rolling after casting but before transformation.

（発明が解決しようとする問題点） 本発明は低合金鋼の高温加熱、直送圧延、ホー。(Problem to be solved by the invention) The present invention relates to high-temperature heating, direct rolling, and hoeing of low-alloy steel.

トチャージ等のスラブ処理プロセスであっても制御圧延
鋼以上の超細粒化を実現し、前記した３点の問題点を解
決するものである。Even in a slab treatment process such as to-charging, ultra-fine grains can be achieved that are greater than that of controlled rolled steel, and the three problems mentioned above can be solved.

（問題点を解決するための手段） 既に述べた如く本発明は析出物を加工誘起変態の核とし
て軽圧下でも微細粒を得る方法であるから、圧延時に析
出物が適正なサイズと分布で存在する事が重要である。(Means for Solving the Problems) As already mentioned, the present invention is a method for obtaining fine grains even under light rolling by using precipitates as nuclei for deformation-induced transformation. It is important to do so.

従来の制御圧延法は高温で固溶せしめた析出物形成元素
を圧延開始時にも固溶維持させる事から成立っており、
本発明に適用する事はできない。The conventional controlled rolling method is based on maintaining the precipitate-forming elements dissolved in solid solution at high temperatures even at the start of rolling.
It cannot be applied to the present invention.

一般に、鋼材の熱延仕上温度はＡｒ３変態点以上であり
、仕上圧延の開始温度はそれより１００℃程度高い、す
なわち約９００℃付近の温度において成る大きさの（後
述するが、０．０１！程度と思われる）析出物を生じせ
しめる事が問題点の解決となり、この温度域で析出可能
な元素はＮｂ、Ｖ、Ｔａ。Generally, the finishing temperature of hot rolling of steel is equal to or higher than the Ar3 transformation point, and the start temperature of finish rolling is about 100°C higher than that, that is, around 900°C (0.01! The solution to the problem is to form a precipitate, and the elements that can be precipitated in this temperature range are Nb, V, and Ta.

Ｔｉ、Ｗである。ＮｂやＴｉは制御圧延法でも用いられ
るが、これは接置度域での析出に時間がかかり、通常は
大部分が固溶しているからである。すなわち、高温で固
溶したＮｂやＴｉを含む鋼を単に１００℃付近に冷却せ
しめても十分な析出物は得られない。一方、本来析出す
べき温度で固溶している元素が加工歪によって析出促進
する事は良く知られた事実であり、圧延が二段に分けら
れる様なプロセス（例えば粗圧延と仕上圧延）ならば可
能性がある。この観点より本発明者らは高温加熱された
低合金鋼の粗圧延を従来より低温で行なうという研究を
行なった結果、期待通りに超細粒化現象が発現し、本発
明に至った。Ti and W. Nb and Ti are also used in the controlled rolling method, but this is because it takes time to precipitate in the contact region and most of them are usually in solid solution. That is, even if steel containing solid solution Nb and Ti at high temperature is simply cooled to around 100° C., sufficient precipitates cannot be obtained. On the other hand, it is a well-known fact that elements that are in solid solution at the temperature at which they should originally precipitate are accelerated by processing strain, and in processes where rolling is divided into two stages (e.g. rough rolling and finish rolling). There is a possibility that From this point of view, the present inventors conducted research on rough rolling low alloy steel heated to a high temperature at a lower temperature than before, and as a result, an ultra-fine grain phenomenon occurred as expected, leading to the present invention.

すなわち、本発明は、 重量２で Ｃ：　Ｑ、０５〜０．２％ Ｓ　ｉ　：　０．０１〜１．０％ Ｍｎ　：　０．３〜２．０！ Ａｌ　　：　　０．００５　〜０．１！Ｎ　　：　　０
．００１　〜０．０２％を主成分とし、他に析出物形成
元素であるＮｂ　：０．００５〜０．１＄、　Ｚ　ｒ　
　：　０．００５〜Ｏ，ｌ％、　Ｖ　：　０．０１〜Ｇ
、２％　、　Ｔ　ｉ　　：　Ｑ、Ｇｌ　〜０．３％、　
Ｔａ　　：　Ｏ，ＱＯ５〜０．１％。That is, in the present invention, C: Q, 05-0.2% Si: 0.01-1.0% Mn: 0.3-2.0! Al: 0.005 ~ 0.1! N: 0
．． 001 to 0.02% as the main component, and Nb as a precipitate forming element: 0.005 to 0.1$, Zr
: 0.005~O,l%, V: 0.01~G
, 2%, T i : Q, Gl ~0.3%,
Ta: O, QO5-0.1%.

Ｗ　：　０．２〜３．０＄、　Ｍｏ　　：　０．１〜１
．５％、　Ｃｕ　　：　０．１〜１．５＄、　Ｃｒ　　
：　０．１　　”１．５＄、　Ｎｉ　　：　０．１　〜
１．５＄（７）１種又は２種以上を含有する鋼を、析出
物形成元素が固溶している高温から冷却する過程におい
て８５０〜９５０℃の間で合計圧下率５０％以上の第一
段圧延を行ない、第一段圧延終了後１０分以内に圧延仕
上温度が８７０℃以下＾ｒ３変態点以上となる様に合計
圧下率６５ｚ以上の第二段圧延を行なうことを特徴とす
る超微細組織からなる熱延高張力鋼板の製造方法である
。W: 0.2~3.0$, Mo: 0.1~1
．． 5%, Cu: 0.1~1.5$, Cr
: 0.1" 1.5$, Ni: 0.1~
1.5$ (7) In the process of cooling steel containing one or more elements from a high temperature where precipitate-forming elements are solid solution, a total reduction rate of 50% or more is applied between 850 and 950°C. One-stage rolling is carried out, and a second-stage rolling is carried out at a total reduction rate of 65z or more so that the finishing temperature of the rolling becomes 870°C or lower and 3 transformation point or higher within 10 minutes after the completion of the first-stage rolling. This is a method for producing hot-rolled high-strength steel sheets having a microstructure.

上述の如く、本発明は第一段圧延を低温（〜９００°Ｃ
近辺）で行なうことにより、第−膜圧延時、およびそれ
に引続く第二段圧延までの移送時間中に微細な析出物を
得る第一段階と、それらの微細析出物を変態核とし第二
段圧延中に加工誘起変態を起させる事によって超微細結
晶粒を得る第二段階とから成る。第一段階は単に圧延素
材を低温加熱するだけでも達成させられるが、この場合
は加熱前のスラブ中に析出物形成元素が固溶しているか
または十分微細に析出している必要がある。すなわち、
低温加熱であっても析出物が適正なサイズを超えて成長
してしまっては、第二段階における超細粒化は達成され
ない。As mentioned above, the present invention performs the first rolling at a low temperature (~900°C).
The first step is to obtain fine precipitates during the first film rolling and the subsequent transfer time up to the second step rolling, and the second step is to use these fine precipitates as transformation nuclei. and a second step in which ultrafine grains are obtained by causing deformation-induced transformation during rolling. The first stage can be achieved by simply heating the rolled material at a low temperature, but in this case, the precipitate-forming elements must be in solid solution or sufficiently finely precipitated in the slab before heating. That is,
Even with low temperature heating, if the precipitates grow beyond an appropriate size, ultrafine grain formation in the second stage cannot be achieved.

それに対し析出物を加工により生成させる本発明では生
成温度が低温であることもあってサイズは小さい。本発
明における析出物の有効サイズに関しては、径が０．０
５ＬＬを超えると効果が発揮されない様であり、０．０
１ｐ以下である事が望ましい。In contrast, in the present invention in which precipitates are formed by processing, the size is small partly because the formation temperature is low. Regarding the effective size of precipitates in the present invention, the diameter is 0.0
It seems that the effect is not exerted when it exceeds 5LL, and 0.0
It is desirable that it be 1p or less.

この点より、粗大な析出物となり易い酸化物系の析出物
や介在物は使えない、また析出物が軟かく、加工によっ
て地鉄と同様に変形するものは効果がないと思われるの
で例えばＭｎＳ等は不適当であろう。From this point of view, oxide-based precipitates and inclusions that tend to form coarse precipitates cannot be used, and precipitates that are soft and deform in the same way as the base steel are considered ineffective, so for example MnS etc. would be inappropriate.

また、粗圧延によって生成した析出物が、仕上圧延開始
までに時間がかかり過ぎると成長してしまうために効果
が十分に発揮されないこともある０例えば、第１図は第
一段圧延の温度と、第二段圧延開始までの時間が鋼板の
結晶粒度におよぼす影響を示しているが、第一段圧延終
了後の経過時間が長くなるに従って粒径は大きくなる。In addition, if it takes too long for the start of finish rolling, the precipitates generated during rough rolling may grow and the effect may not be fully demonstrated. For example, Figure 1 shows the temperature and , which shows the influence of the time until the start of the second stage rolling on the grain size of the steel sheet, and the grain size increases as the time elapses after the end of the first stage rolling increases.

次に限定理由を説明する。Next, the reason for the limitation will be explained.

［成分］ Ｃ：Ｃは鋼材の組織、材質を左右する主成分であると共
に析出物としての炭化物を形成する必須元素であるが、
０．０５％未満では炭化物が十分に生成せずまた高強度
が得られない、　０．２％を超えると第二段加工による
変態が不十分となり、また溶接性や加工性が低下する。[Component] C: C is the main component that influences the structure and material quality of steel materials, and is an essential element that forms carbides as precipitates.
If it is less than 0.05%, carbides will not be sufficiently generated and high strength will not be obtained, and if it exceeds 0.2%, transformation in the second stage processing will be insufficient and weldability and workability will deteriorate.

そこで０．０５％〜０．２ｚに限定した。Therefore, it was limited to 0.05% to 0.2z.

Ｍｎ：Ｍｎは高強度化と組織微細化に有効で添加が望ま
しいが、その効果は０．３＄未満では現れず、また２ｚ
を超えると変態点が低下しすぎてフェライト変態が不十
分となる。そこで０．３Ｘ〜２＄に限定した。Mn: Mn is effective in increasing strength and refining the structure and is desirable to add, but its effect does not appear below 0.3$, and 2z
If it exceeds , the transformation point will drop too much and ferrite transformation will be insufficient. Therefore, it was limited to 0.3X to 2$.

Ｓｉ：Ｓｉはｏ、ｏｔｘ以上を添加すると鋼板の強度−
延性バランスを向上させるので添加が望ましいが、１％
を超えると溶接性を損なうことがあり、また変態点が上
昇して粗大フェライト混入の原因となる。そこで０．０
１〜１ｚに限定した。Si: When Si is added in an amount of o, otx or more, the strength of the steel plate -
It is desirable to add 1% as it improves the ductility balance.
Exceeding this may impair weldability and raise the transformation point, causing coarse ferrite to be mixed in. So 0.0
It was limited to 1 to 1z.

ＡＩ：Ａｌは製鋼時の脱酸剤として普通に用いられると
共に窒化物が結晶粒成長を抑制する。また、ＣｕやＮｉ
が存在する時は金属間化合物を形成し析出するが、効果
が見られるのは０．００５Ｘ以上添加された時である。AI: Al is commonly used as a deoxidizing agent during steel making, and nitrides inhibit grain growth. In addition, Cu and Ni
is present, an intermetallic compound is formed and precipitated, but the effect is seen when 0.005X or more is added.

　０．Ｈを超えると、変態挙動が変化し細粒が得難くな
り、粗大な介在物も増加する。　ソコテｏ、Ｏｏ５＄≦
Ａｌ　≦ｏ、１ｘニ限定シタ。0. When H is exceeded, the transformation behavior changes, making it difficult to obtain fine grains, and coarse inclusions also increase. Sokote o, Oo5$≦
Al ≦o, 1x Ni limited position.

Ｎ：Ｎは窒化物形成のための重要な元素であるが、０．
００１Ｘ未満では効果が不十分であり、０．０２２を超
えると伸びや加工性が劣化する。そこで０．００１＄≦
Ｎ　≦０．０２％　ニ限定シタ。N: N is an important element for nitride formation, but 0.
If it is less than 0.001X, the effect is insufficient, and if it exceeds 0.022, elongation and workability deteriorate. So 0.001$≦
N ≦0.02% Limited to 2.

析出物形成元素：析出物形成元素としてはオーステナイ
ト域の高温では固溶し、オーステナイト域の低温で析出
するものであって、析出物が微細かつ硬いものである必
要がある。添加量としては十分な析出物数が生成する量
を下限とし、上限はそれ以上添加するとかえって析出物
が粗大化して効果が減する量である。この観点より０．
００５＄≦Ｎｂ≦０．１％　、　０．ＯＩＸ　≦Ｔ　ｉ
　≦０．３％　、　０．００５％≦Ｔａ≦０．１＄　、
　０．００！Ｊ≦Ｚ　ｒ　≦０．１＄　、　０．０１＄
　≦Ｖ　≦０．２％　。Precipitate-forming element: The precipitate-forming element must be a solid solution at high temperatures in the austenite region and precipitate at low temperatures in the austenite region, and the precipitates must be fine and hard. The lower limit of the amount added is the amount that produces a sufficient number of precipitates, and the upper limit is the amount where adding more will cause the precipitates to become coarser and reduce the effect. From this point of view, 0.
005$≦Nb≦0.1%, 0. OIX ≦T i
≦0.3%, 0.005%≦Ta≦0.1$,
0.00! J≦Zr≦0.1$, 0.01$
≦V≦0.2%.

０．２％≦Ｗ≦３．０％、　０．１＄≦Ｍｏ　≦１．５
Ｌ　Ｏ，１１≦Ｃｕ≦１．５％、　０．１％≦Ｃｒ　≦
１．５＄、　０．１＄≦Ｎｉ　　＜１．５＄（７）様に
種類と添加量を限定する。これらの元素は一種だけでも
十分な効果が得られるが、二種以上の複合添加で効果を
高める。0.2%≦W≦3.0%, 0.1$≦Mo≦1.5
L O, 11≦Cu≦1.5%, 0.1%≦Cr≦
1.5$, 0.1$≦Ni <1.5$ (7) The type and amount added are limited. Although a sufficient effect can be obtained with just one type of these elements, the effect is enhanced by adding two or more types in combination.

［スラブプロセス］ スラブプロセスとしては第一段圧延前に析出元素は固溶
している必要があるので、１２００℃以上の高温加熱か
、あるいは鋳造後または分塊後高温のままでＡｒ３変態
点以上に保たれる直送圧延およびホットチャージ等が適
している。[Slab process] In the slab process, the precipitated elements must be in solid solution before the first rolling, so either high temperature heating of 1200°C or higher is required, or the Ar3 transformation point or higher is maintained at high temperature after casting or blooming. Direct rolling and hot charging, etc., which are maintained at a constant temperature, are suitable.

直送圧延の場合は第一段圧延を８５０℃以上で行なうた
めに、この温度よりスラブ温度が高い必要がある。ホッ
トチャージの場合はスラブ温度がＡｒ３変態点以下に低
下し、フェライト変態が始まるとそれと同時に析出も起
ってしまうから、圧延前に析出物を固溶させるには１２
００℃以上の高温加熱をしなければならない。従ってホ
７）チャージの特徴を生かし省エネルギー効果を高水準
に達成するには、スラブ温度がＡｒ３点より高温である
うちに再加熱する必要がある。この場合の再加熱温度は
オーステナイト域の温度であれば低くてよいが、第一段
圧延を８５０℃以上で行なうためにはそれより５０℃は
高い必要がある。そこでホットチャージの場合スラブ温
度がＡｒ３点以下に低下するまえに９００℃以上に再加
熱することとした。In the case of direct rolling, the first stage rolling is performed at 850° C. or higher, so the slab temperature needs to be higher than this temperature. In the case of hot charging, the slab temperature drops below the Ar3 transformation point, and when ferrite transformation begins, precipitation also occurs at the same time, so in order to dissolve the precipitates into solid solution before rolling, it is necessary to
It is necessary to heat the product to a high temperature of 00°C or higher. Therefore, e7) In order to achieve a high level of energy saving effect by taking advantage of the characteristics of the charge, it is necessary to reheat the slab while the temperature is higher than the Ar3 point. In this case, the reheating temperature may be low as long as it is in the austenite range, but in order to perform the first rolling at 850°C or higher, it needs to be higher by 50°C. Therefore, in the case of hot charging, it was decided to reheat the slab to 900° C. or higher before the slab temperature dropped below the Ar3 point.

尚、再加熱の方法は何でも良く、加熱炉への装入、誘導
加熱、バーナーの使用等が考えられる。Note that any method for reheating may be used, and possible methods include charging into a heating furnace, induction heating, and using a burner.

［第一段圧延］ 第一段圧延は本発明の中核となる技術であり、加工によ
って析出物を生成させる事を目的とする。従って圧延温
度の上限は析出物が十分に生成し始める温度である必要
があり、本発明では３５０℃である。圧延温度は９５０
℃より低温になる程、析出物は微細になるが、８５０℃
以下になると十分な量が析出しなくなる。そこで８５０
℃を下限とした。[First-stage rolling] First-stage rolling is a core technology of the present invention, and its purpose is to generate precipitates through processing. Therefore, the upper limit of the rolling temperature needs to be the temperature at which precipitates begin to sufficiently form, and in the present invention it is 350°C. Rolling temperature is 950
The precipitates become finer as the temperature decreases below 850℃.
If the amount is below, a sufficient amount will not be precipitated. So 850
The lower limit was ℃.

上記圧延段階で有効な析出物を得るにはある程度以上の
加工歪が必要であり、１パスの圧下率は大きい程効果的
であるが、該温度域では再結晶があまり進行しないので
歪の累積効果がある。すなわち、合計圧下率がある値以
上であれば１パスの圧下率に拘わらず有効であり、本発
明での値は５０％である。そこで合計圧下率を５０％以
上に限定した。In order to obtain effective precipitates in the above-mentioned rolling stage, a certain amount of processing strain is required, and the larger the rolling reduction rate in one pass, the more effective it is, but recrystallization does not progress much in this temperature range, so the accumulation of strain effective. That is, as long as the total rolling reduction is at least a certain value, it is effective regardless of the rolling reduction of one pass, and the value in the present invention is 50%. Therefore, the total rolling reduction rate was limited to 50% or more.

尚、第一段圧延に至る８５０℃を超えた高温域では、圧
延を行なってもオーステナイトが再結晶するのみで、該
圧延段階に有効な析出は起らないので特に限定する事は
無いが、例えば温度待ちの時間を減らすために圧延材の
厚みを薄くする圧延等は一向に差支えない。In addition, in the high temperature range exceeding 850°C leading to the first stage rolling, even if rolling is performed, austenite only recrystallizes and effective precipitation does not occur in the rolling stage, so there is no particular limitation. For example, there is no problem with rolling to reduce the thickness of the rolled material in order to reduce the waiting time for temperature.

［第二段圧延］ 第一段圧延によって生成した析出物はその後成長する。[Second rolling] The precipitates generated by the first rolling then grow.

従って第二段圧延を第一段圧延終了後限られた時間内に
開始しないと効果が薄れてしまう、第１図は第一段圧延
終了後から第二段圧延開始までの時間と得られた結晶粒
度の関係を示しており、１０分を超えると粒径が粗大化
する事が分る。そこで第二段圧延を第一段圧延終了から
１０分以内に行なう様に限定する。Therefore, if the second stage rolling is not started within a limited time after the end of the first stage rolling, the effect will be diminished. Figure 1 shows the time from the end of the first stage rolling to the start of the second stage rolling. It shows the relationship between crystal grain size, and it can be seen that the grain size becomes coarser when the time exceeds 10 minutes. Therefore, the second stage rolling is limited to be performed within 10 minutes from the end of the first stage rolling.

析出物を変態核とする本発明では第二段圧延開始前に圧
延により変態するフェライト粒の数は大略法まっている
。更にこの圧延が行なわれる温度域では加工歪の回復も
進行し難いので、圧延圧下率は合計圧下率である値以上
であれば良くその値は６５’Ｘである。In the present invention, which uses precipitates as transformation nuclei, the number of ferrite grains transformed by rolling before the start of second-stage rolling is approximately constant. Further, in the temperature range in which this rolling is performed, recovery of work strain is difficult to proceed, so the rolling reduction ratio may be at least a certain value of the total reduction ratio, and the value is 65'X.

尚、第一段圧延も第二段圧延も１パスの圧下率が大きい
時は合計圧下率が小さくとも同等以上の効果が得られる
が、実用上は非常に困難であるから技術的に容易な方で
圧延条件を限定する。In addition, when the rolling reduction in one pass is large in both the first and second rolling, the same or better effect can be obtained even if the total rolling reduction is small, but this is extremely difficult in practice, so it is not technically easy to do so. However, the rolling conditions are limited.

圧延仕上温度は８７０℃を超えると十分に変態が進行せ
ず、＾ｒ３変態点以下になると圧延によらない通常の変
態が起り粗大粒が混在する。従って第二段圧延の仕上温
度を８７０℃以下Ａｒ３変態以上に限定する。（第２図
参照） ［冷却］ 第二段圧延が終了した時点でフェライト変態は殆んど終
了しており、未変態オーステナイトが僅かに残っている
状態である。この時点での微細なフェライトは変態核と
なった析出物が成長を妨げるので冷速か遅くとも粗大化
する事は無い。そこで所望鋼材の強度が高くない時は特
に急冷する必要は無いし、低温に冷却する必要もない。If the rolling finish temperature exceeds 870°C, transformation will not proceed sufficiently, and if it is below the ^r3 transformation point, normal transformation that is not caused by rolling will occur and coarse grains will be mixed. Therefore, the finishing temperature of the second stage rolling is limited to 870° C. or lower and Ar3 transformation or higher. (See FIG. 2) [Cooling] When the second stage rolling is completed, ferrite transformation is almost completed, and a small amount of untransformed austenite remains. At this point, the fine ferrite does not become coarser even if it is cooled quickly or slowly because the precipitates that serve as transformation nuclei hinder the growth. Therefore, when the desired steel material does not have high strength, there is no particular need to rapidly cool it, and there is no need to cool it to a low temperature.

所望鋼材の強度が高い時は、僅かに残っているオーステ
ナイトを低温で変態させる事によって調整する事ができ
る。そのためには鋼板を２０℃／Ｓ以上で５５０℃以下
に冷却する事が必要で所望強度が高くなる程冷速は大き
く、冷却終了温度は低くなる。When the desired strength of the steel material is high, it can be adjusted by transforming the slight remaining austenite at low temperature. For this purpose, it is necessary to cool the steel plate to 550°C or less at a rate of 20°C/S or more, and the higher the desired strength, the faster the cooling rate and the lower the cooling end temperature.

次に本発明適用時の問題について述べる。Next, problems when applying the present invention will be described.

第一段圧延は既に述べた如く低温で行なう、従来の制御
圧延はこの段階で析出物を生成させないために、例えば
９５０℃以上の温度で圧延されるが、本発明による適当
な温度範囲は析出が促進される様な温度であって、例え
ばＮｂ鋼では析出Ｃ曲線のノーズ温度である８００℃と
も考えられる。As mentioned above, the first stage rolling is carried out at a low temperature. In conventional controlled rolling, rolling is carried out at a temperature of 950°C or higher, for example, in order to prevent the formation of precipitates at this stage, but the suitable temperature range according to the present invention is For example, in Nb steel, it is considered to be 800° C., which is the nose temperature of the precipitation C curve.

第一段圧延温度の最適値は析出物の種類によって変わる
。The optimum value for the first stage rolling temperature varies depending on the type of precipitates.

粗圧延を低温で行なうにはスラブが高温に再加熱された
場合は、長い待ち時間が必要となり生産上の問題はある
。これに対し、直送圧延はスラブのハンドリング間に起
る温度低下によって、圧延機ｉ１ｊ面にスラブが到着し
た時に適当な粗圧延温度となることが考えられ、本発明
には非常に適している。ホットチャージプロセスではス
ラブ温度が弔にＡｒ３変態点以上の時は直送圧延と同様
の事が言える。スラブ温度が一旦変態点以下になるホッ
トチャージでは１本発明を適用するならば炉温を高温と
する必要があるが、高温再加熱材と同様長い待ち時間を
要するので生産上は得策とは言えない。この場合はむし
ろ炉温を低温として既に生成している析出物を利用する
方が有利であろう。In order to carry out rough rolling at a low temperature, if the slab is reheated to a high temperature, a long waiting time is required, which poses a production problem. On the other hand, direct rolling is considered to be very suitable for the present invention because the temperature drop that occurs during handling of the slab brings the slab to an appropriate rough rolling temperature when it arrives at the rolling mill i1j surface. In the hot charge process, when the slab temperature is above the Ar3 transformation point, the same thing can be said as in direct rolling. In hot charging, where the slab temperature is once below the transformation point, if the present invention is applied, it is necessary to increase the furnace temperature, but as with high-temperature reheating material, a long waiting time is required, so it is not a good idea from a production standpoint. do not have. In this case, it would be more advantageous to lower the furnace temperature and utilize the precipitates that have already formed.

析出物が適当なサイズと分布を持てば、第二段圧延にお
いて特に大圧下圧延や低温圧延を必要としない。例えば
Ｎｂ鋼を圧延素材とした場合に粒度番号１３．５番以上
の微細粒が得られる範囲を第３図に示すが、広い温度範
囲と通常の圧下率で十分な細粒化効果が得られる。より
細粒を得ようとする時は圧下率の増加は有効であり、ま
た仕上温度も最適範囲に調整することでさらに効果が上
がる。仕上温度の最適範囲は圧下率によって異なり、圧
下率を大きくできない時は通常の変態が起る様な低温に
なると、粗大な加工フェライトが生ずるので変態点より
３０〜５０℃高目が良く、また圧下率が大きくフェライ
トを再結晶させられるならば最適温度は低下する。If the precipitates have an appropriate size and distribution, there is no need for particularly large reduction rolling or low temperature rolling in the second stage rolling. For example, Figure 3 shows the range in which fine grains with a grain size number of 13.5 or higher can be obtained when Nb steel is used as a rolled material, and a sufficient grain refining effect can be obtained within a wide temperature range and normal rolling reduction rate. . When trying to obtain finer grains, increasing the rolling reduction ratio is effective, and adjusting the finishing temperature to the optimum range will further improve the effect. The optimal range of finishing temperature varies depending on the rolling reduction rate, and if the rolling reduction rate cannot be increased, coarse processed ferrite will be formed at a low temperature at which normal transformation occurs. If the reduction rate is large and the ferrite can be recrystallized, the optimum temperature will decrease.

本発明は基本的には大圧下圧延やパス間時間の短い連続
熱延が向いているが、仕上圧延条件に対する要求が緩い
ので圧下率が大きくできない厚手材や、厚板圧延２条鋼
圧延等広く応用ができる技術である。The present invention is basically suitable for large reduction rolling and continuous hot rolling with a short inter-pass time, but it is widely used for thick materials such as thick plate rolling and double-strip steel rolling, where the requirements for finish rolling conditions are lenient and the reduction ratio cannot be increased. It is a technology that can be applied.

（実施例） 表１に示す成分で厚み２２０鳳層の鋼スラブを１２５０
℃に加熱し、１１００℃以上で９０ｍｍまで減厚した後
、出口温度８７０〜９３０℃で３０ｍｍ厚まで粗圧延し
、粗圧延終了３分後に最終パス圧下率２２％の圧下スケ
ジュールにより板厚２．８腸醋まで仕上圧延を行なった
。粗圧延および仕上圧延のパススケジュールは表２に示
しである。圧延後の冷却は冷速〜４０℃／Ｓで５５０℃
まで行なった。また比較のために従来の制御圧延および
１０５０℃の低温加熱圧延も行なったが、これらの場合
における粗圧延は９５０℃以上で２２０ｍｍから３０履
膳へ圧延するという条件で行なわれ、仕上圧延のパスス
ケジュールは表２と同一である。(Example) A steel slab with a thickness of 220 mm and a thickness of 1250 mm with the ingredients shown in Table 1.
℃, and after reducing the thickness to 90 mm at 1100℃ or higher, it was roughly rolled to a thickness of 30 mm at an exit temperature of 870 to 930℃, and 3 minutes after the completion of rough rolling, the plate thickness was reduced to 2.5 mm using a reduction schedule with a final pass reduction rate of 22%. Finish rolling was carried out to 8 mm. The pass schedule for rough rolling and finish rolling is shown in Table 2. Cooling after rolling is at a cooling rate of ~40°C/S to 550°C
I went up to For comparison, conventional controlled rolling and low-temperature hot rolling at 1050°C were also carried out, but in these cases the rough rolling was carried out at 950°C or higher, rolling from 220 mm to 30 mm, and the finish rolling pass was The schedule is the same as Table 2.

表１　試験材成分 ： 表　２　圧延パススケジュール 表３に各圧延材の結晶粒度番号と材質を示す。Table 1 Test material components : Table 2 Rolling pass schedule Table 3 shows the grain size number and material of each rolled material.

賦香■〜■は本発明に基づいたものであり、低い粗圧延
温度が特徴である。■〜■の中ではＦＴが８２０℃の■
が最も微細な結晶粒が得られ、粒度番号は１５．５番で
あって低温加熱法による賦香■よりも微細化している。Flavoring samples (1) to (2) are based on the present invention and are characterized by a low rough rolling temperature. Among ■～■, FT is 820℃■
The finest crystal grains were obtained, and the grain size number was 15.5, which was finer than that of the perfume-imparting method (2) produced by the low-temperature heating method.

　ＦＴの低い賦香■は加工によらない変態が一部始まる
ためにやや大きな加工フェライト粒が混在して伸びの低
下が見られるが、それでも平均粒径は従来の制御圧延法
による賦香■より小さい、賦香■は低温加熱により粗圧
延開始前に微細な析出物を形成させたもので本発明範囲
外であるが、仕上圧延以降の技術内容は本発明と一致し
、制御圧延材よりも細粒となっている。すなわち析出物
を利用した加工誘起（あるいは促進）変態の有利性が示
されている。賦香■はＮＢを含まない炭素鋼であって、
析出物が無ければ粗圧延温度を低くしてもあまり細粒化
効果は得られないことが明らかである。尚、賦香■〜■
および■の粗圧延のうち２２０■■から９０■層までは
高温で行なわれているのでオーステナイトの再結晶のみ
起り、析出とは無関係である。この厚み範囲も低温で圧
延されれば細粒化効果は更に高まろう。この点からも粗
圧延の前や途中で温度待ちをするよりも直送圧延がより
本発明に適していると言える。In case of rolling ■ with low FT, a portion of transformation that is not caused by processing begins, so slightly larger processed ferrite grains are mixed in, resulting in a decrease in elongation. The small, unscented material is one in which fine precipitates are formed before the start of rough rolling by low-temperature heating, and is outside the scope of the present invention, but the technical content after finish rolling is consistent with the present invention, and is better than the control-rolled material. It has fine grains. In other words, the advantage of deformation-induced (or accelerated) transformation using precipitates has been shown. The fragrance ■ is carbon steel that does not contain NB,
It is clear that if there are no precipitates, no significant grain refining effect can be obtained even if the rough rolling temperature is lowered. In addition, incense ■〜■
Of the rough rolling of (2) and (2), layers from 220 to 90 are carried out at high temperatures, so only austenite recrystallization occurs and is unrelated to precipitation. If this thickness range is also rolled at a low temperature, the grain refining effect will be further enhanced. From this point of view, it can be said that direct rolling is more suitable for the present invention than waiting for temperature before or during rough rolling.

以上を綜括するのが第４図であり、本発明が工業的に結
晶粒を微細化する方法として非常に優れている事が分る
。尚、同図中で０印の横に書かれた数字は実施例の賦香
を示し、説明図の太線部は析出物が生成する時期を示し
ている。FIG. 4 summarizes the above, and it can be seen that the present invention is extremely excellent as a method for industrially refining crystal grains. In addition, the number written next to the 0 mark in the figure indicates the incense of the example, and the thick line part in the explanatory figure indicates the time when precipitates are formed.

（発明の効果） 本発明により、高温スラブ加熱や直送圧延の場合でも通
常の仕上圧延スケジュールにより容易かつ確実にａ微細
結晶組織が得られ、高材質熱延ハイテンを低コストで製
造する事が可能となった。(Effects of the Invention) According to the present invention, even in the case of high-temperature slab heating or direct rolling, an a-microcrystalline structure can be easily and reliably obtained by a normal finish rolling schedule, and high-quality hot-rolled high-strength steel can be manufactured at low cost. It became.

【図面の簡単な説明】[Brief explanation of drawings]

８１図は本発明における圧延条件と鋼板の結晶粒度との
関係を示し、第２図は本発明の第二段圧延仕上温度と結
晶粒度との関係を示し、第３図は本発明における圧延条
件と鋼板の結晶粒度との関係を示し、第４図は本発明法
及び比較法と鋼板の結晶粒度との関係を示す。Figure 81 shows the relationship between the rolling conditions and the grain size of the steel sheet in the present invention, Figure 2 shows the relationship between the second-stage rolling finishing temperature and the grain size in the present invention, and Figure 3 shows the relationship between the rolling conditions in the present invention and the grain size. FIG. 4 shows the relationship between the method of the present invention and the comparative method and the grain size of the steel sheet.

Claims (5)

【特許請求の範囲】[Claims] （１）重量％で Ｃ：０．０５〜０．２％ Ｓｉ：０．０１〜１．０％ Ｍｎ：０．３〜２．０％ Ａｌ：０．００５〜０．１％ Ｎ：０．００１〜０．０２％ を主成分とし、他に析出物形成元素であるＮｂ：０．０
０５〜０．１％、Ｚｒ：０．００５〜０．１％、Ｖ：０
．０１〜０．２％、Ｔｉ：０．０１〜０．３％、Ｔａ：
０．００５〜０．１％、Ｗ：０．２〜３．０％、Ｍｏ：
０．１〜１．５％、Ｃｕ：０．１〜１．５％、Ｃｒ：０
．１〜１．５％、Ｎｉ：０．１〜１．５％の１種又は２
種以上を含有する鋼を、析出物形成元素が固溶している
高温から冷却する過程において８５０〜９５０℃の間で
合計圧下率５０％以上の第一段圧延を行ない、第一段圧
延終了後１０分以内に圧延仕上温度が８７０℃以下Ａｒ
＿３変態点以上となる様に合計圧下率６５％以上の第二
段圧延を行なうことを特徴とする超微細組織からなる熱
延高張力鋼板の製造方法。(1) C: 0.05-0.2% Si: 0.01-1.0% Mn: 0.3-2.0% Al: 0.005-0.1% N: 0. 001~0.02% as the main component, and Nb as a precipitate forming element: 0.0
05-0.1%, Zr: 0.005-0.1%, V: 0
．． 01-0.2%, Ti: 0.01-0.3%, Ta:
0.005-0.1%, W: 0.2-3.0%, Mo:
0.1-1.5%, Cu: 0.1-1.5%, Cr: 0
．． 1 to 1.5%, one or two of Ni: 0.1 to 1.5%
In the process of cooling the steel containing more than 100% precipitate-forming elements from a high temperature at which the precipitate-forming elements are dissolved, the first stage rolling is performed at a total reduction rate of 50% or more between 850 and 950°C, and the first stage rolling is completed. Within 10 minutes, the finishing temperature of rolling is 870℃ or less Ar
_3 A method for producing a hot-rolled high-strength steel sheet having an ultrafine structure, characterized by performing second rolling at a total reduction rate of 65% or more so as to achieve a transformation point of 3 or more. （２）鋼スラブを１２００℃以上の高温に加熱する特許
請求の範囲第１項記載の方法。(2) The method according to claim 1, wherein the steel slab is heated to a high temperature of 1200° C. or higher. （３）スラブを鋳造後８５０℃以下に温度が低下する以
前に圧延を開始する特許請求の範囲第１項記載の方法。(3) The method according to claim 1, wherein rolling is started before the temperature of the slab drops to 850° C. or lower after casting. （４）スラブを鋳造後Ａｒ＿３変態点以下に温度が低下
する前に９００℃以上に再加熱する特許請求の範囲第１
項記載の方法。(4) Claim 1 of reheating the slab to 900°C or higher after casting and before the temperature drops below the Ar_3 transformation point.
The method described in section. （５）第二段圧延完了後２０℃／Ｓ以上の冷速で５５０
℃以下に冷却する特許請求の範囲第１項記載の方法。(5) 550 at a cooling rate of 20°C/S or more after completion of second stage rolling
The method according to claim 1, wherein the method is cooled to a temperature below .degree.