JPH09209076A - High strength hot rolled steel plate of (400 to 800)n/mm2 class excellent in workability and its production - Google Patents
High strength hot rolled steel plate of (400 to 800)n/mm2 class excellent in workability and its productionInfo
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- JPH09209076A JPH09209076A JP1995096A JP1995096A JPH09209076A JP H09209076 A JPH09209076 A JP H09209076A JP 1995096 A JP1995096 A JP 1995096A JP 1995096 A JP1995096 A JP 1995096A JP H09209076 A JPH09209076 A JP H09209076A
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、加工性に優れた４
００〜８００Ｎ／mm2 級高強度熱延鋼板及びの製造方法
に関わり、その用途は、自動車、家電、建材等である。TECHNICAL FIELD OF THE INVENTION The present invention relates to
The present invention relates to a high-strength hot-rolled steel sheet of 0 to 800 N / mm 2 grade and a manufacturing method thereof, and its applications are automobiles, home appliances, building materials and the like.
【０００２】[0002]
【従来の技術】近年、自動車、建築等多くの産業分野
で、部材の軽量化の要望が高まっており、それに対応す
るために高強度鋼板が用いられる場合が増えている。そ
して、これらの鋼板が用いられる用途においては、しば
しば高い加工性、特に穴拡げ性が要求される。2. Description of the Related Art In recent years, in many industrial fields such as automobiles and construction, there is an increasing demand for weight reduction of members, and in order to meet the demand, high strength steel sheets are increasingly used. In applications where these steel sheets are used, high workability, especially hole expandability, is often required.
【０００３】従来から、このような高強度熱延鋼板とし
ては、フェライト（Ｆ）＋マルテンサイト（Ｍ）また
は、フェライト（Ｆ）＋ベイナイト（Ｂ）の複合組織に
よる組織強化型の鋼板が多く使われている。しかし、Ｆ
＋Ｍの複合組織鋼では、高い強度は得られるものの穴拡
げ性が劣るという問題がある。また、Ｆ＋Ｂ鋼では、特
開昭５７−１０１６４９号公報に示されているように、
穴拡げ性には優れているものの、穴拡げ性を確保したま
まで７００Ｎ／mm2 以上の強度を得ることは困難であっ
た。Conventionally, as such a high-strength hot-rolled steel sheet, a structure strengthening steel sheet having a composite structure of ferrite (F) + martensite (M) or ferrite (F) + bainite (B) is often used. It is being appreciated. But F
In the + M composite structure steel, there is a problem that the hole expandability is inferior although the high strength is obtained. Further, in the case of F + B steel, as disclosed in JP-A-57-101649,
Although it has excellent hole expansibility, it was difficult to obtain a strength of 700 N / mm 2 or more while ensuring the hole expansibility.
【０００４】その他、組織の大部分をフェライトにし、
かつＴｉＣ析出強化を利用することで７００Ｎ／mm2 以
上の強度を確保し、同時に穴拡げ性も確保するものとし
て、特開平６−２００３５１号公報で開示された発明が
ある。しかし、この発明の鋼板は、０．５％以上のＭｎ
による固溶強化が必須であり、本発明のように広い強度
範囲を作り分ける技術でもない。In addition, most of the structure is made of ferrite,
In addition, there is an invention disclosed in Japanese Patent Laid-Open No. 6-200351 that secures a strength of 700 N / mm 2 or more by utilizing TiC precipitation strengthening and at the same time secures hole expandability. However, the steel sheet of the present invention has a Mn of 0.5% or more.
Solid solution strengthening is essential, and it is not a technique for creating a wide strength range as in the present invention.
【０００５】一般に、固溶強化は、高価な合金元素を要
するため、コスト的には不利な強化機構であるとされて
いる。特公昭５６−９２２３号公報で開示された発明で
は、低Ｍｎでも高強度が得られるが、これは、ＴｉｍＢ
ｎによる析出強化を活用するもので、高価なＢ添加が必
須である。また、本発明のように広い強度範囲を作り分
ける技術でもない。Generally, solid solution strengthening requires an expensive alloying element, and is therefore considered to be a costly disadvantageous strengthening mechanism. In the invention disclosed in Japanese Patent Publication No. 56-9223, high strength can be obtained even with low Mn.
Since the precipitation strengthening by n is utilized, expensive B addition is essential. In addition, it is not a technique for creating a wide range of strength as in the present invention.
【０００６】６００〜８００Ｎ／mm2 級の強度範囲にお
いて穴拡げ性を確保する技術とては、特開平６−１７２
９２４号公報の発明がある。これは、ベイネティックフ
ェライトによる組織強化鋼であり、フェライト中のＴｉ
Ｃ析出による強化が主である本発明鋼とはその強化機構
が全く異なる。また、低Ｍｎ化による効果を狙ったもの
でもない。As a technique for ensuring hole expandability in the strength range of 600 to 800 N / mm 2 class, Japanese Patent Laid-Open No. 6-172 is known.
There is an invention of Japanese Patent No. 924. This is a structurally strengthened steel with bainitic ferrite.
The strengthening mechanism is completely different from the steel of the present invention, which is mainly strengthened by C precipitation. In addition, the effect of reducing the Mn content is not intended.
【０００７】[0007]
【発明が解決しようとする課題】本発明は、高価な合金
元素を用いることなく、６００〜８００Ｎ／mm2 という
広い強度範囲にわたって加工性、特に穴拡げ性に優れる
高強度熱延鋼板とその製造方法を提供することを目的と
するものである。DISCLOSURE OF THE INVENTION The present invention provides a high-strength hot-rolled steel sheet which is excellent in workability, particularly hole expandability, over a wide strength range of 600 to 800 N / mm 2 without using an expensive alloy element, and its production. It is intended to provide a method.
【０００８】[0008]
【課題を解決するための手段】上記課題を解決するため
に、本発明者等は鋭意検討を行った。その結果、オース
テナイトフォーマーであるＭｎを低減しα域を広げるこ
とによって、熱延終了から巻取前までの冷却中のＴｉＣ
の析出が促進されて、鋼板強度がＴｉＣの析出強化によ
り確保されるとともに、セメンタイトの生成量が減少す
ることから鋼板の穴拡げ性が著しく向上することを見出
した。Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively studied. As a result, by reducing Mn, which is an austenite former, and widening the α region, TiC during cooling from the end of hot rolling to before winding.
It was found that the steel sheet strength is secured by the precipitation strengthening of TiC, and the amount of cementite produced is reduced, so that the hole expandability of the steel sheet is significantly improved.
【０００９】また、熱延終了から巻取前までの冷却速度
が大きくなるにつれて、ＴｉＣの微細化が促進され、Ｔ
ｉＣの強化への寄与が極めて大きくなることを見出し
た。さらに、粗圧延後に曲げ戻し加工を加えることによ
って、材質の長手、幅方向の均質化が促され、コイル内
の材質のばらつきが低減されることを見出した。Further, as the cooling rate from the end of hot rolling to the time before winding increases, the refinement of TiC is promoted and T
It has been found that the contribution to the strengthening of iC is extremely large. Furthermore, it has been found that by performing bending back processing after rough rolling, homogenization of the material in the longitudinal and width directions is promoted, and variation in the material in the coil is reduced.
【００１０】本発明は、このＴｉＣの析出強化を活用す
ることによって、低コストでかつ加工性に優れた高強度
鋼板を広い強度範囲において容易に作り分ける技術を確
立したものであり、その要旨とするところは下記の通り
である。The present invention establishes a technique for easily producing high-strength steel sheets at low cost and excellent in workability in a wide strength range by utilizing the precipitation strengthening of TiC. The place to do is as follows.
【００１１】（１） 重量％で、Ｃ：０．０５〜０．２
％、Ｍｎ：０．０１％以上、０．５％未満、Ｓｉ：０．
０１〜０．５％、Ａｌ：０．００５〜０．１％、Ｐ：
０．０５％以下、Ｓ：０．０１％以下、Ｎ：０．００７
％以下、Ｔｉ：０．０５〜０．３％を含有し、残部は鉄
および不可避的不純物よりなり、さらに、全Ｃ量のうち
セメンタイトとして析出しているＣの割合〔Ｍ＝（Ｃ％
as セメンタイト）／（全Ｃ％）〕が０．０３以下であ
ることを特徴とする加工性に優れた４００〜８００Ｎ／
mm2 級高強度熱延鋼板。(1) C: 0.05 to 0.2 in% by weight
%, Mn: 0.01% or more and less than 0.5%, Si: 0.
01-0.5%, Al: 0.005-0.1%, P:
0.05% or less, S: 0.01% or less, N: 0.007
% Or less, Ti: 0.05 to 0.3%, the balance consisting of iron and unavoidable impurities, and the proportion of C precipitated as cementite in the total amount of C [M = (C%
as cementite) / (total C%)] is 0.03 or less, which is excellent in workability and is 400 to 800 N /
mm 2 grade high strength hot rolled steel sheet.
【００１２】（２） 重量％で、Ｃ：０．０５〜０．２
％、Ｍｎ：０．０１％以上、０．５％未満、Ｓｉ：０．
０１〜０．５％、Ａｌ：０．００５〜０．１％、Ｐ：
０．０５％以下、Ｓ：０．０１％以下、Ｎ：０．００７
％以下、Ｔｉ：０．０５〜０．３％を含有し、残部は鉄
および不可避的不純物よりなる鋼を、加熱温度：１２０
０〜１３５０℃で加熱し、粗圧延後、仕上げ温度がＡｒ
3 以上の熱間圧延を施し、引き続き１〜６０℃／ｓの範
囲内の冷却速度で、かつ所望の引張強さに応じて下記
(1)式から求まる冷却速度に対して±５℃／ｓの範囲内
の冷却速度で、仕上げ温度から６００〜７５０℃まで冷
却し、その後、巻取温度：室温〜７５０℃で巻き取り、
全Ｃ量のうちセメンタイトとして析出しているＣの割合
〔Ｍ＝（Ｃ％ as セメンタイト）／（全Ｃ％）〕が０．
０３以下であることを特徴とする加工性に優れた４００
〜８００Ｎ／mm2 級高強度熱延鋼板の製造方法。 ＣＲ＝−200 ×（ 0.5×Ｃ％＋ 2.5×Ｔｉ％）＋ＴＳ/3 − 85 ……（１） ＣＲ：冷却速度（℃／ｓ）、Ｃ％：Ｃ濃度、Ｔｉ％：Ｔ
ｉ濃度、 ＴＳ：所望する引張強度（Ｎ／mm2 ）(2) C: 0.05 to 0.2 by weight%
%, Mn: 0.01% or more and less than 0.5%, Si: 0.
01-0.5%, Al: 0.005-0.1%, P:
0.05% or less, S: 0.01% or less, N: 0.007
% Or less, Ti: 0.05 to 0.3%, with the balance being steel consisting of iron and inevitable impurities. Heating temperature: 120
After heating at 0 ~ 1350 ℃ and rough rolling, finish temperature is Ar
3 or more hot rolling is performed, and subsequently, at the cooling rate within the range of 1 to 60 ° C./s, and according to the desired tensile strength,
Cooling is performed from the finishing temperature to 600 to 750 ° C. at a cooling rate within a range of ± 5 ° C./s with respect to the cooling rate obtained from the formula (1), and then winding temperature: room temperature to 750 ° C.
The ratio of C precipitated as cementite in the total amount of C [M = (C% as cementite) / (total C%)] is 0.
400 excellent in workability characterized by being 03 or less
~ 800 N / mm 2 High-strength hot-rolled steel sheet manufacturing method. CR = -200 x (0.5 x C% + 2.5 x Ti%) + TS / 3-85 (1) CR: Cooling rate (° C / s), C%: C concentration, Ti%: T
i concentration, TS: desired tensile strength (N / mm 2 )
【００１３】（３） 粗圧延後、粗バーをコイル状に巻
き取り、巻き戻し、その後、仕上圧延に供することを特
徴とする上記（２）記載の加工性に優れた４００〜８０
０Ｎ／mm2 級高強度熱延鋼板の製造方法。 （４） 仕上圧延前に、先行材の後端部と後行材の先端
部を接合して、仕上圧延に供することを特徴とする上記
（２）または（３）記載の加工性に優れた４００〜８０
０Ｎ／mm2 級高強度熱延鋼板の製造方法。(3) After rough rolling, the rough bar is wound into a coil shape, rewound, and then subjected to finish rolling, which is 400 to 80 excellent in workability according to the above (2).
0N / mm 2 class high strength hot rolled steel sheet manufacturing method. (4) The workability according to (2) or (3) above is excellent in that the rear end portion of the preceding material and the front end portion of the following material are joined to each other before the finish rolling and subjected to the finish rolling. 400-80
0N / mm 2 class high strength hot rolled steel sheet manufacturing method.
【００１４】本発明における鋼板及びその製造方法は、
Ｃ、Ｔｉ量、熱延条件を限定することによって、Ｍｎな
どの高価な合金元素を添加することなく、加工性に優れ
た高強度熱延鋼板を広い強度範囲に亘って提供するもの
である。以下にその限定理由を述べる。The steel sheet and the manufacturing method thereof according to the present invention are
By limiting the amounts of C, Ti, and hot rolling conditions, a high-strength hot-rolled steel sheet excellent in workability is provided over a wide strength range without adding expensive alloying elements such as Mn. The reasons for the limitation will be described below.
【００１５】まず、化学成分について、その限定理由を
説明する。Ｃは、本発明において最も重要な元素の一つ
である。その量が０．０５％以上の範囲では、Ｃ量が増
加するのに伴いＴｉＣ析出量が増加し強度が高くなる。
しかし、その量が０．２％を超えるとその効果は飽和
し、成形性も低下する。したがって、Ｃ添加量の範囲と
しては、０．０５〜０．２％とする。強度と成形性のバ
ランスの観点から、０．１〜０．１５％とするのが好ま
しい。First, the reasons for limiting the chemical components will be described. C is one of the most important elements in the present invention. When the amount is 0.05% or more, the TiC precipitation amount increases and the strength increases as the C amount increases.
However, if the amount exceeds 0.2%, the effect is saturated, and the moldability also decreases. Therefore, the range of the amount of C added is set to 0.05 to 0.2%. From the viewpoint of the balance between strength and moldability, it is preferably 0.1 to 0.15%.
【００１６】Ｓｉは、脱酸のために０．０１％以上添加
する。しかし、その添加量が０．５％を超えると溶接性
が劣化する。したがって、Ｓｉ添加量は０．０１〜０．
５％とする。この観点から、更に０．１〜０．３％とす
るのが好ましい。Si is added in an amount of 0.01% or more for deoxidation. However, if the amount added exceeds 0.5%, the weldability deteriorates. Therefore, the amount of Si added is 0.01 to 0.1.
5%. From this point of view, it is more preferably 0.1 to 0.3%.
【００１７】Ｍｎは、ＭｎＳを生成し固溶Ｓによる熱間
割れを防止するため、０．０１％以上添加する。しか
し、０．５％以上添加すると、α域が狭くなりＴｉＣの
析出が抑制される。また、粗大なＭｎＳによって穴拡げ
性が低下する。したがって、Ｍｎ添加量の範囲としては
０．０１〜０．５％未満とする。強度と成形性（穴拡げ
性）のバランスの観点から、０．０１〜０．３％とする
のが好ましい。Mn is added in an amount of 0.01% or more in order to form MnS and prevent hot cracking due to solid solution S. However, if it is added in an amount of 0.5% or more, the α region becomes narrow and the precipitation of TiC is suppressed. Further, coarse MnS reduces the hole expansibility. Therefore, the range of the amount of Mn added is 0.01 to less than 0.5%. From the viewpoint of the balance between strength and formability (hole expandability), it is preferably 0.01 to 0.3%.
【００１８】Ｐは、安価な固溶強化元素であるが、０．
０５％超では熱間あるいは冷間加工時の割れの原因とな
る。そこで、Ｐの含有量は０．０５％以下とする。さら
に、厳しい加工性を要求される場合は、０．０３％以下
とするのが好ましい。P is an inexpensive solid solution strengthening element.
If it exceeds 05%, it may cause cracking during hot or cold working. Therefore, the content of P is set to 0.05% or less. Furthermore, when severe workability is required, it is preferably 0.03% or less.
【００１９】Ｓ量は、０．０１％超ではγ域でのＴｉ4
Ｃ2 Ｓ2 の析出量が増加するためＴｉＣの析出量が低下
し、強度を確保できない。また、固溶Ｓとして残存した
場合は熱間割れの原因となる。このため、Ｓ量は０．０
１％以下とする。特に、Ｔｉ4 Ｃ2 Ｓ2 生成抑制の観点
からは、Ｓ量は０．００５％以下が望ましく、更に、
０．００３％以下とすることで、Ｔｉ4 Ｃ2 Ｓ2 の生成
が更に抑制されて好ましい条件である。If the amount of S exceeds 0.01%, Ti 4 in the γ region
Since the precipitation amount of C 2 S 2 increases, the precipitation amount of TiC decreases, and the strength cannot be secured. Further, if it remains as solid solution S, it causes hot cracking. Therefore, the amount of S is 0.0
1% or less. Particularly, from the viewpoint of suppressing Ti 4 C 2 S 2 production, the S content is preferably 0.005% or less, and further,
The content of 0.003% or less is a preferable condition because the production of Ti 4 C 2 S 2 is further suppressed.
【００２０】Ａｌは、脱酸剤として少なくとも０．００
５％を添加することが必要である。しかし、０．１％を
超えるとコストアップとなるばかりか介在物の増加を招
き、加工性を劣化させる。そこで、Ａｌ添加量の範囲と
しては０．００５〜０．１％とする。Al is used as a deoxidizer in at least 0.00
It is necessary to add 5%. However, when it exceeds 0.1%, not only the cost is increased but also the number of inclusions is increased, and the workability is deteriorated. Therefore, the range of the amount of Al added is 0.005 to 0.1%.
【００２１】Ｎは、窒化物の増加に伴い延性の劣化を招
くので、少ないほど望ましい。したがって、０．００７
％以下とする。より厳しい加工性が必要な場合は、０．
００３％以下とするのが好ましい。Since N causes deterioration of ductility as the amount of nitride increases, it is preferable that N is small. Therefore, 0.007
% Or less. If stricter workability is required, 0.
It is preferably 003% or less.
【００２２】Ｔｉは、本発明において最も重要な元素で
ある。その量が０．０５％以上では、Ｔｉの増加に伴い
ＴｉＣの析出量が増加し、かつＲＯＴ冷却速度の上昇に
伴い析出するＴｉＣが微細になり、強度が高くなる。そ
こで、強度レベルに応じて添加する。ただし、その量が
０．３％を超えると、これらの効果は飽和する。したが
って、Ｔｉ添加量の範囲は０．０５〜０．３％とする。[0022] Ti is the most important element in the present invention. When the amount is 0.05% or more, the amount of TiC precipitated increases with the increase of Ti, and the TiC precipitated with the increase of the ROT cooling rate becomes finer and the strength increases. Therefore, it is added according to the strength level. However, when the amount exceeds 0.3%, these effects are saturated. Therefore, the range of the added amount of Ti is set to 0.05 to 0.3%.
【００２３】また、加工性、特に穴拡げ性を確保するた
めには、全Ｃ量のうちセメンタイトとして析出するＣ量
の割合〔Ｍ＝（Ｃ％ as セメンタイト）／（全Ｃ％）〕
が０．０３以下でなければならない。更に厳しい加工性
（穴広げ性）が求められる場合には、Ｍ≦０．０１とす
るのが好ましい。In order to secure workability, particularly hole expandability, the ratio of the amount of C precipitated as cementite in the total amount of C [M = (C% as cementite) / (total C%)]
Must be 0.03 or less. When stricter workability (hole expandability) is required, it is preferable that M ≦ 0.01.
【００２４】この（Ｃ％ as セメンタイト）は、以下の
ようにして求められる。すなわち、非水溶媒によって抽
出した残渣を化学分析に供し、Ｆｅ量（＝Ｆ（ｇ）とす
る）を測定する。このときサンプル全体の抽出量をＺ
（ｇ）とすると、（Ｃ％ as セメンタイト）＝Ｆ／Ｚ×
１２／１６８×１００（％）となる。This (C% as cementite) is determined as follows. That is, the residue extracted with the non-aqueous solvent is subjected to chemical analysis, and the amount of Fe (= F (g)) is measured. At this time, the extraction amount of the entire sample is Z
If (g), then (C% as cementite) = F / Z x
It becomes 12/168 x 100 (%).
【００２５】上記成分を得るための原料は特に限定しな
いが、鉄鉱石を原料として高炉−転炉により成分を調製
する方法以外に、スクラップを原料として電炉で溶製し
てもよい。スクラップを原料の全部または一部として使
用する際には、Ｃｕ、Ｃｒ、Ｎｉ、Ｓｎ、Ｓｂ、Ｚｎ、
Ｐｂ、Ｍｏ等の元素を、合計で１％未満含有してもよ
い。The raw materials for obtaining the above components are not particularly limited, but scraps may be melted in an electric furnace in addition to the method of preparing the components by a blast furnace-converter using iron ore as a raw material. When scrap is used as all or part of the raw material, Cu, Cr, Ni, Sn, Sb, Zn,
The total amount of elements such as Pb and Mo may be less than 1%.
【００２６】次に、製造プロセスに関する限定理由を述
べる。熱間圧延に供するスラブは、特に限定するもので
はない。すなわち、連続鋳造スラブや薄スラブキャスタ
ーで製造したものなどであれば良い。また、鋳造後に直
ちに熱間圧延を行う、連続鋳造−直接圧延（ＣＣ−Ｄ
Ｒ）のようなプロセスにも適合する。粗圧延の後にコイ
ルボックスでの巻取、巻戻し処理を行ったり、更にその
後、先行の粗バーの後端と後行の粗バーの先端を接合し
仕上圧延を行う連続熱延のようなプロセスを行うと、材
質が均一化し歩留まりも向上する。Next, the reasons for limitation regarding the manufacturing process will be described. The slab used for hot rolling is not particularly limited. That is, it may be a continuous cast slab or a thin slab caster. In addition, continuous casting-direct rolling (CC-D
Also applicable to processes like R). A process such as continuous hot rolling in which coiling is performed in a coil box and then rewinding is performed after rough rolling, and then the trailing end of the preceding rough bar and the leading end of the following rough bar are joined and finish rolling is performed. By carrying out, the material is made uniform and the yield is improved.
【００２７】熱間圧延における加熱温度は、熱延前に生
成されているＴｉＣを再固溶させ、過飽和Ｔｉをできる
だけ多くするために、１２００℃以上とすることが必須
である。しかし、１３５０℃を超えるとその効果は飽和
するだけでコストがかかるので、加熱温度は１３５０℃
以下とする。ＴｉＣの再固溶の効果と製造コストのバラ
ンスの観点から、１３００℃未満とするのが好ましい。
仕上圧延における熱延終了温度は、プレス成形性を確保
するためにＡｒ3 変態点以上とする必要がある。It is essential that the heating temperature in hot rolling is 1200 ° C. or higher in order to re-dissolve TiC formed before hot rolling and increase the supersaturated Ti as much as possible. However, if the temperature exceeds 1350 ° C, the effect will be saturated and the cost will increase, so the heating temperature is 1350 ° C.
The following is assumed. From the viewpoint of the balance between the effect of re-dissolving TiC and the manufacturing cost, the temperature is preferably lower than 1300 ° C.
The hot rolling end temperature in finish rolling needs to be the Ar 3 transformation point or higher in order to ensure press formability.
【００２８】粗圧延終了後には、粗バーを一旦コイル状
に巻き取ってもよい。このとき、１０００℃以下での加
熱保持を行っても良いし、コイルボックスのような物の
中で恒温保持しても良い。大気中での保持でも良い。表
面性状の観点からは、不活性ガス雰囲気での保持を行う
のが好ましい。このコイルを巻き戻した後に、そのま
ま、Ａｒ3 以上の仕上げ温度で仕上げ圧延を行っても良
いし、先行の粗バーの後端と後行の粗バーの先端を接合
して連続的に仕上げ熱延を行っても構わない。After the rough rolling is finished, the rough bar may be once wound into a coil. At this time, heating and holding at 1000 ° C. or lower may be performed, or constant temperature holding may be performed in an object such as a coil box. It may be held in the atmosphere. From the viewpoint of surface properties, it is preferable to hold in an inert gas atmosphere. After rewinding this coil, finish rolling may be performed as it is at a finishing temperature of Ar 3 or higher. Alternatively, the trailing end of the preceding rough bar and the leading end of the following rough bar may be joined to continuously finish the heat treatment. You may postpone it.
【００２９】粗圧延終了後に、粗バーを一旦コイル状に
巻き取ることなく、先行の粗バーの後端と後行の粗バー
の先端を接合して連続的に仕上げ熱延を行っても構わな
い。このような工程によって材質が均一化し、端部切り
落としの必要が無くなり歩留まりが向上する。また、熱
延板の板厚精度も著しく向上する。After the rough rolling is finished, the rear end of the preceding rough bar and the leading end of the following rough bar may be joined to each other and the finish hot rolling may be continuously performed without temporarily winding the rough bar into a coil. Absent. By such a process, the material is made uniform, and it is not necessary to cut off the end portion, and the yield is improved. Further, the plate thickness accuracy of the hot rolled plate is significantly improved.
【００３０】仕上げ圧延後の冷却速度は、ＴｉＣの析出
量とベイナイト量を変えて強度を作り分けるために、１
〜６０℃／ｓの範囲で、かつ、所望の引張強さに応じ
て、引張強さと化学成分とから（１）式で求まる平均冷
却速度ＣＲに対して±５℃の範囲とする。冷却速度を１
℃／ｓ未満にすることは設備上困難であり、かつ、格段
の効果も得られないことから、冷却速度は１℃／ｓ以上
とする。The cooling rate after finish rolling is 1 in order to change the precipitation amount of TiC and the amount of bainite to make strength different.
-60 ° C / s, and within a range of ± 5 ° C with respect to the average cooling rate CR obtained by the formula (1) from the tensile strength and the chemical composition according to the desired tensile strength. Cooling rate 1
The cooling rate is set to 1 ° C./s or more because it is difficult to set the temperature to less than ° C./s in terms of equipment and no remarkable effect can be obtained.
【００３１】一方、６０℃／ｓ超の冷却速度を安定に確
保することは難しく、強度のばらつきの原因となること
から、冷却速度の上限は６０℃／ｓとする。また、
（１）式で求まる平均冷却速度ＣＲに対して±５℃の範
囲を超える冷却速度では、狙いとする引張強度を得られ
ないため、仕上げ圧延後の冷却速度は、ＣＲ±５℃とす
る。On the other hand, it is difficult to stably secure a cooling rate of more than 60 ° C./s, which causes variations in strength. Therefore, the upper limit of the cooling rate is 60 ° C./s. Also,
At the cooling rate exceeding the range of ± 5 ° C with respect to the average cooling rate CR obtained by the equation (1), the target tensile strength cannot be obtained, so the cooling rate after finish rolling is CR ± 5 ° C.
【００３２】強度に寄与するＴｉ、Ｃ量、引張強度と冷
却速度の関係は以下のようにして調べた。０．０８％Ｃ
−０．３％Ｍｎ−０．００２％Ｎ鋼をベ−スに、Ｔｉ含
有量を変化させた鋼片を、１２５０℃に加熱後、仕上げ
温度９０８℃で、板厚４mmに仕上げ、その後、種々の冷
却速度で冷却した時の冷却速度、Ｔｉ量と引張強度ＴＳ
との関係を図１に示す。The relationship between the amounts of Ti and C that contribute to the strength, the tensile strength and the cooling rate was examined as follows. 0.08% C
-0.3% Mn-0.002% N steel was used as a base, and a steel slab having a changed Ti content was heated to 1250 ° C., and then finished at a finishing temperature of 908 ° C. to a plate thickness of 4 mm, and then, Cooling rate, Ti content and tensile strength TS when cooled at various cooling rates
1 is shown in FIG.
【００３３】同じ熱延条件で、０．３％Ｍｎ−０．１２
％Ｔｉ−０．００２％Ｎ鋼をベ−スに、Ｃ含有量を変化
させた鋼片について、同様の調査を行った結果を図２に
示す。これより、Ｔｉ、Ｃ量の増加に比例して引張強度
（ＴＳ）が上昇することが分かる。また図３には、図１
と図２のデータを冷却速度とＴＳの関係に整理し直した
結果を示す。これより、ＲＯＴ冷却速度に比例してＴＳ
が上昇していることが分かる。Under the same hot rolling conditions, 0.3% Mn-0.12
FIG. 2 shows the results of a similar investigation performed on steel slabs in which the C content was changed with the base of% Ti-0.002% N steel. From this, it can be seen that the tensile strength (TS) increases in proportion to the increase in the Ti and C amounts. In addition, in FIG.
2 shows the result of rearranging the data of FIG. 2 into the relationship between the cooling rate and TS. Therefore, TS is proportional to the ROT cooling rate.
You can see that is rising.
【００３４】以上の関係を式にまとめると、下記の様に
なる。 ＣＲ＝−200 ×（ 0.5×Ｃ％＋ 2.5×Ｔｉ％）＋ＴＳ/3 − 85 ……（１） ＣＲ：冷却速度（℃／ｓ）、Ｃ％：Ｃ濃度、Ｔｉ％：Ｔ
ｉ濃度、 ＴＳ：引張強度（Ｎ／mm2 ）The above relationships are summarized in the following equation. CR = -200 x (0.5 x C% + 2.5 x Ti%) + TS / 3-85 (1) CR: Cooling rate (° C / s), C%: C concentration, Ti%: T
i concentration, TS: Tensile strength (N / mm 2 )
【００３５】冷却停止温度は、６００〜７５０℃とす
る。冷却停止温度を６００℃未満とすることは、特段の
効果が期待できない上に強度のばらつきの原因となるこ
とから、冷却停止温度の下限は６００℃とする。一方、
冷却停止温度を７５０℃超にすると、冷却中に析出する
ＴｉＣの量が減少し強度が低下するため、冷却停止温度
の上限は７５０℃とする。The cooling stop temperature is 600 to 750.degree. If the cooling stop temperature is less than 600 ° C., no particular effect can be expected and the strength may vary, so the lower limit of the cooling stop temperature is set to 600 ° C. on the other hand,
If the cooling stop temperature exceeds 750 ° C, the amount of TiC precipitated during cooling decreases and the strength decreases, so the upper limit of the cooling stop temperature is 750 ° C.
【００３６】巻取温度は、室温〜７５０℃の範囲とす
る。巻取温度を７５０℃超にすることは、強化に寄与し
ている微細ＴｉＣの粗大化を促し、強度の低下の原因と
なる。また、高温巻取のための設備と酸洗コストの観点
からも望ましくない。そこで、巻取温度の上限は７５０
℃とする。優れた表面性状が要求される場合は、表面ス
ケールの発生を抑制するために、巻取温度を７００℃以
下にするのが好ましい。The coiling temperature is in the range of room temperature to 750 ° C. When the coiling temperature is higher than 750 ° C., the fine TiC that contributes to the strengthening is promoted to become coarse, which causes a decrease in strength. It is also not desirable from the viewpoint of equipment for high-temperature winding and pickling cost. Therefore, the upper limit of the winding temperature is 750.
° C. When excellent surface properties are required, the winding temperature is preferably 700 ° C. or lower in order to suppress the generation of surface scale.
【００３７】更に厳しい表面性状の要求を満たすために
は、６００℃以下とするのが更に好ましい。本発明にお
いては、強化に寄与しているＴｉＣが粗大化して、強度
が低下してしまう温度領域未満の７５０℃以下の温度で
あれば基本的にはどの温度で巻き取っても良いが、室温
未満で巻き取ることは、過剰な設備が必要となるばかり
でなく、特段の効果もないため、巻取温度の下限は室温
とする。In order to meet more stringent surface quality requirements, the temperature is preferably 600 ° C. or lower. In the present invention, basically, any temperature may be used as long as the temperature is 750 ° C. or lower, which is lower than the temperature range in which TiC contributing to strengthening is coarsened and the strength is reduced. The lower limit of the coiling temperature is room temperature because the coiling at a temperature lower than that requires not only excessive equipment but also no particular effect.
【００３８】[0038]
（実施例１）表１に示す化学成分を有する低炭素鋼を転
炉にて出鋼し、連続鋳造機にてスラブとした後、１２５
０℃に加熱し、仕上げ温度９０３℃、板厚２mmとなるよ
うな熱間圧延を行った。表２に示すような種々のＲＯＴ
冷却速度（ランアウトテーブル (run out table)での平
均冷却速度）で６５０℃まで冷却した後、６２０℃でコ
イルに巻き取った。(Example 1) Low carbon steel having the chemical composition shown in Table 1 was tapped in a converter and made into a slab by a continuous casting machine.
It was heated to 0 ° C. and hot-rolled so that the finishing temperature was 903 ° C. and the plate thickness was 2 mm. Various ROTs as shown in Table 2
After cooling to 650 ° C. at a cooling rate (average cooling rate on a run out table), the coil was wound at 620 ° C.
【００３９】[0039]
【表１】 [Table 1]
【００４０】このようにして得られた熱延鋼板につい
て、圧延方向の引張試験片（ＪＩＳ Z2201 記載の５号
試験片）を加工し、ＪＩＳ Z 2241 記載の試験方法に従
って引張試験を行った。また、穴拡げ試験は１辺１００
mmの試験片の中央に径１０mmの打ち抜き穴を加工し、そ
の初期穴を頂角６０°の円錐ポンチにて押し広げ、割れ
が鋼板を貫通した時点での穴径ｄの初期穴径１０mmに対
する穴拡げ率λ（次式）で評価した。 λ＝｛（ｄ−１０）／１０｝×１００（％）With respect to the hot-rolled steel sheet thus obtained, a tensile test piece in the rolling direction (No. 5 test piece described in JIS Z2201) was processed, and a tensile test was performed according to the test method described in JIS Z 2241. The hole expansion test is 100 per side.
A 10 mm diameter punched hole was machined in the center of a mm test piece, and the initial hole was expanded by a conical punch with an apex angle of 60 °, and the initial hole diameter d was 10 mm when the crack penetrated the steel plate. The hole expansion rate λ (the following formula) was used for evaluation. λ = {(d-10) / 10} × 100 (%)
【００４１】以上の試験結果を表２に示す。表２から明
らかなように、Ｍｎ量が低く、Ｃ、Ｔｉ量が適正な鋼
は、上記製造条件で、かつ、狙いの引張強度ＴＳに対し
て、（１）式ＣＲ＝−200 ×（ 0.5×Ｃ％＋ 2.5×Ｔｉ
％）＋ＴＳ/3− 85 で計算されるＲＯＴ冷却速度の±５
℃以内に実測のＲＯＴ冷却速度を確保できているため、
セメンタイトの生成量も少なく（Ｍ≦０．０３）、穴拡
げ性にも優れていることが分かる。Table 2 shows the above test results. As is clear from Table 2, steel having a low Mn content and an appropriate C and Ti content is obtained under the above manufacturing conditions and with respect to the target tensile strength TS, by the formula (1) CR = −200 × (0.5 X C% + 2.5 x Ti
%) + TS / 3−85 of ROT cooling rate ± 5
Because the measured ROT cooling rate can be secured within ℃,
It can be seen that the amount of cementite produced is small (M ≦ 0.03) and the hole expandability is excellent.
【００４２】[0042]
【表２】 [Table 2]
【００４３】[0043]
【表３】 [Table 3]
【００４４】（実施例２）表１に示した鋼種ＣとＩにつ
いて、連続鋳造によって製造したスラブを、表３に示し
た種々の温度で１時間加熱し、仕上温度９００℃、板厚
５mmとなるような熱間圧延を行った後、鋼Ｃは２５±２
℃／ｓ（希望強度５５０Ｎ／mm2 ）、鋼Ｉは２０±３℃
／ｓ（希望強度７５０Ｎ／mm2 ）のＲＯＴ冷却速度で６
８０℃まで冷却した後に、６００℃でコイルに巻き取っ
た。(Example 2) For steel types C and I shown in Table 1, slabs produced by continuous casting were heated at various temperatures shown in Table 3 for 1 hour to obtain a finishing temperature of 900 ° C and a plate thickness of 5 mm. Steel C is 25 ± 2 after hot rolling
℃ / s (desired strength 550N / mm 2 ), Steel I is 20 ± 3 ℃
/ S (desired strength 750 N / mm 2 ) at a ROT cooling rate of 6
After cooling to 80 ° C, it was wound into a coil at 600 ° C.
【００４５】このようにして得られた熱延鋼板につい
て、実施例１と同様にＪＩＳ５号による圧延方向の引張
試験、穴拡げ試験を行った。その結果を表３に示す。こ
れより、加熱温度が１２００〜１３５０℃の範囲内で
は、狙いの強度±２０Ｎ／mm2 内の強度が得られている
が、加熱温度が１２００℃未満になると、強度が狙いの
強度に比べて著しく低下し、穴拡げ性も劣ることが分か
る。The hot-rolled steel sheet thus obtained was subjected to a tensile test in the rolling direction and a hole expansion test according to JIS 5 in the same manner as in Example 1. Table 3 shows the results. From this, when the heating temperature is in the range of 1200 to 1350 ° C., the target strength of ± 20 N / mm 2 is obtained, but when the heating temperature is less than 1200 ° C., the strength is lower than the target strength. It can be seen that it is remarkably lowered and the hole expandability is also poor.
【００４６】[0046]
【表４】 [Table 4]
【００４７】（実施例３）表１に示した鋼種Ｂ、Ｄ、
Ｈ、Ｎのスラブを用いて、製造条件の比較のために次の
ような試作を行った。すなわち、その製造条件は、１
２５０℃で加熱し、粗圧延終了後コイル状に巻き取り直
ちに巻き戻した後に、仕上げ温度９００℃、板厚３mmと
なるような仕上圧延を行い、表４に示したＲＯＴ冷却速
度で７００℃まで冷却した後コイルに巻き取った場合
と、１２５０度で加熱し、粗圧延終了後巻き取り巻き
戻しの工程を経ることなく、仕上温度９１０℃、板厚４
mmとなるような熱間圧延を行った後、表４に示したＲＯ
Ｔ冷却速度で６３０℃まで冷却した後４６０℃でコイル
に巻き取った場合である。それぞれの熱延板について、
長手方向先端から１０ｍ、中央部、後端から１０ｍの各
位置から試験片を採取し、実施例１と同じ試験を行った
結果を表４に示す。(Example 3) Steel types B, D, and
Using H and N slabs, the following prototypes were made for comparison of manufacturing conditions. That is, the manufacturing condition is 1
After heating at 250 ℃, after the rough rolling is finished, it is wound into a coil and immediately rewound, and then finish rolling is performed at a finishing temperature of 900 ℃ and a plate thickness of 3 mm, and at the ROT cooling rate shown in Table 4, up to 700 ℃. After cooling, the coil is wound into a coil and heated at 1250 ° C., and after finishing rough rolling, the finishing temperature is 910 ° C. and the plate thickness is 4 without undergoing the step of winding and rewinding.
After hot rolling such that
This is a case where the material was cooled to 630 ° C. at the T cooling rate and then wound around a coil at 460 ° C. For each hot rolled sheet,
Table 4 shows the results of the same test as in Example 1, in which test pieces were sampled from positions of 10 m from the front end in the longitudinal direction, 10 m from the center, and 10 m from the rear end.
【００４８】[0048]
【表５】 [Table 5]
【００４９】これより、本発明例では、粗圧延後の巻き
取り巻き戻し工程の有無に関わらず、コイル全長で狙い
の強度±２０Ｎ／mm2 が確保されているが、巻き取り巻
き戻し工程を加えた場合の方が、コイル材質の均一性に
より優れているのが分かる。From this, in the present invention example, the target strength of ± 20 N / mm 2 is secured over the entire length of the coil regardless of the presence or absence of the winding and rewinding step after rough rolling, but the winding and rewinding step was added. It can be seen that the case is superior to the uniformity of the coil material.
【００５０】[0050]
【発明の効果】本発明によれば、Ｃ、Ｔｉ量、熱延条件
を限定することによって、Ｍｎなどの高価な合金元素を
添加することなく、４００〜８００Ｎ／mm2 という広い
強度範囲にわたって、加工性に優れた高強度熱延鋼板及
びその製造方法を容易に提供することが可能である。According to the present invention, by limiting the amounts of C, Ti, and hot rolling conditions, without adding expensive alloying elements such as Mn, a wide strength range of 400 to 800 N / mm 2 can be achieved. It is possible to easily provide a high-strength hot-rolled steel sheet excellent in workability and a manufacturing method thereof.
【図面の簡単な説明】[Brief description of drawings]
【図１】引張強度ＴＳとＴｉ添加量、ＲＯＴ冷却速度の
関係を示す図表である。FIG. 1 is a table showing the relationship between tensile strength TS, Ti addition amount, and ROT cooling rate.
【図２】引張強度ＴＳとＣ添加量、ＲＯＴ冷却速度の関
係を示す図表である。FIG. 2 is a chart showing the relationship between the tensile strength TS, the amount of C added, and the ROT cooling rate.
【図３】引張強度ＴＳとＲＯＴ冷却速度の関係を示す図
表である。FIG. 3 is a table showing the relationship between tensile strength TS and ROT cooling rate.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 小山 一夫 富津市新富20−１ 新日本製鐵株式会社技 術開発本部内 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Koyama 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technical Development Division
Claims (4)
らに、全Ｃ量のうちセメンタイトとして析出しているＣ
の割合〔Ｍ＝（Ｃ％ as セメンタイト）／（全Ｃ％）〕
が０．０３以下であることを特徴とする加工性に優れた
４００〜８００Ｎ／mm2 級高強度熱延鋼板。1. By weight%, C: 0.05 to 0.2%, Mn: 0.01% or more and less than 0.5%, Si: 0.01 to 0.5%, Al: 0.005 -0.1%, P: 0.05% or less, S: 0.01% or less, N: 0.007% or less, Ti: 0.05-0.3%, and the balance is iron and unavoidable. C which is composed of impurities and which is precipitated as cementite in the total amount of C
Ratio [M = (C% as cementite) / (total C%)]
Is 0.03 or less, and is a 400-800 N / mm 2 class high strength hot rolled steel sheet excellent in workability.
を、加熱温度：１２００〜１３５０℃で加熱し、粗圧延
後、仕上げ温度がＡｒ3 以上の熱間圧延を施し、引き続
き１〜６０℃／ｓの範囲内の冷却速度で、かつ所望の引
張強さに応じて下記（１）式から求まる冷却速度に対し
て±５℃／ｓの範囲内の冷却速度で、仕上げ温度から６
００〜７５０℃まで冷却し、その後、巻取温度：室温〜
７５０℃で巻き取り、全Ｃ量のうちセメンタイトとして
析出しているＣの割合〔Ｍ＝（Ｃ％ as セメンタイト）
／（全Ｃ％）〕が０．０３以下であることを特徴とする
加工性に優れた４００〜８００Ｎ／mm2 級高強度熱延鋼
板の製造方法。 ＣＲ＝−200 × ( 0.5×Ｃ％＋ 2.5×Ｔｉ％）＋ＴＳ/3 − 85 ……（１） ＣＲ：冷却速度（℃／ｓ）、Ｃ％：Ｃ濃度、Ｔｉ％：Ｔ
ｉ濃度、 ＴＳ：所望する引張強度（Ｎ／mm2 ）2. By weight%, C: 0.05 to 0.2%, Mn: 0.01% or more and less than 0.5%, Si: 0.01 to 0.5%, Al: 0.005 -0.1%, P: 0.05% or less, S: 0.01% or less, N: 0.007% or less, Ti: 0.05-0.3%, and the balance is iron and unavoidable. Steel made of impurities is heated at a heating temperature of 1200 to 1350 ° C., rough rolling is performed, and then hot rolling is performed at a finishing temperature of Ar 3 or more, and subsequently at a cooling rate in the range of 1 to 60 ° C./s, and Depending on the desired tensile strength, at a cooling rate within the range of ± 5 ° C / s with respect to the cooling rate obtained from the formula (1) below, the finishing temperature is 6
After cooling to 00 to 750 ° C., the coiling temperature: room temperature to
Winding at 750 ° C, the proportion of C precipitated as cementite in the total amount of C [M = (C% as cementite)
/ (Total C%)] is 0.03 or less, a method for producing a 400-800 N / mm 2 class high-strength hot-rolled steel sheet with excellent workability. CR = -200 x (0.5 x C% + 2.5 x Ti%) + TS / 3-85 (1) CR: Cooling rate (° C / s), C%: C concentration, Ti%: T
i concentration, TS: desired tensile strength (N / mm 2 )
り、巻き戻し、その後、仕上圧延に供することを特徴と
する請求項２記載の加工性に優れた４００〜８００Ｎ／
mm2 級高強度熱延鋼板の製造方法。3. After rough rolling, the rough bar is wound into a coil shape, rewound, and then subjected to finish rolling, which is 400 to 800 N / which has excellent workability according to claim 2.
mm 2 High-strength hot-rolled steel sheet manufacturing method.
の先端部を接合して、仕上圧延に供することを特徴とす
る請求項２または３記載の加工性に優れた４００〜８０
０Ｎ／mm2 級高強度熱延鋼板の製造方法。4. The workability-improving 400 according to claim 2 or 3, wherein the trailing end portion of the preceding material and the leading end portion of the following material are joined to each other before the finishing rolling and subjected to the finishing rolling. ~ 80
0N / mm 2 class high strength hot rolled steel sheet manufacturing method.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP01995096A JP3425288B2 (en) | 1996-02-06 | 1996-02-06 | 400-800N / mm2 class high-strength hot-rolled steel sheet excellent in workability and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP01995096A JP3425288B2 (en) | 1996-02-06 | 1996-02-06 | 400-800N / mm2 class high-strength hot-rolled steel sheet excellent in workability and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH09209076A true JPH09209076A (en) | 1997-08-12 |
| JP3425288B2 JP3425288B2 (en) | 2003-07-14 |
Family
ID=12013491
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP01995096A Expired - Fee Related JP3425288B2 (en) | 1996-02-06 | 1996-02-06 | 400-800N / mm2 class high-strength hot-rolled steel sheet excellent in workability and method for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3425288B2 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2014119260A1 (en) | 2013-01-31 | 2014-08-07 | Ｊｆｅスチール株式会社 | High-strength hot-rolled steel sheet and production method thereof |
| WO2014119259A1 (en) | 2013-01-31 | 2014-08-07 | Ｊｆｅスチール株式会社 | High-strength hot-rolled steel sheet and manufacturing process therefor |
| US10301698B2 (en) | 2012-01-31 | 2019-05-28 | Jfe Steel Corporation | Hot-rolled steel sheet for generator rim and method for manufacturing the same |
-
1996
- 1996-02-06 JP JP01995096A patent/JP3425288B2/en not_active Expired - Fee Related
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10301698B2 (en) | 2012-01-31 | 2019-05-28 | Jfe Steel Corporation | Hot-rolled steel sheet for generator rim and method for manufacturing the same |
| WO2014119260A1 (en) | 2013-01-31 | 2014-08-07 | Ｊｆｅスチール株式会社 | High-strength hot-rolled steel sheet and production method thereof |
| WO2014119259A1 (en) | 2013-01-31 | 2014-08-07 | Ｊｆｅスチール株式会社 | High-strength hot-rolled steel sheet and manufacturing process therefor |
Also Published As
| Publication number | Publication date |
|---|---|
| JP3425288B2 (en) | 2003-07-14 |
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