JP4620529B2 - Manufacturing method of high strength hot-rolled steel sheet - Google Patents
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本発明は、目標とする機械的特性になるようなフィードフォワード制御を行なう高強度熱延鋼板の製造方法に関するものである。本発明において高強度熱延鋼板とは、引張強さが５２０ＭＰａ以上の厚板あるいは熱延鋼板のことを言う。 The present invention relates to a method for manufacturing a high-strength hot-rolled steel sheet that performs feedforward control so as to achieve target mechanical characteristics. In the present invention, the high-strength hot-rolled steel sheet refers to a thick plate or a hot-rolled steel sheet having a tensile strength of 520 MPa or more.
高強度熱延鋼板の製造において、従来から、鋼の成分組成に応じて、目標とする機械的特性になるように、熱延の加熱条件、圧延条件、圧延後の冷却条件が制御されている。 In the production of high-strength hot-rolled steel sheets, conventionally, heating conditions for hot rolling, rolling conditions, and cooling conditions after rolling have been controlled so as to achieve target mechanical properties according to the composition of steel. .
しかしながら、析出強化型の元素として、Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有する高強度熱延鋼板において、これら元素の実際の鋳造後の実績値は、目標値に対して、どうしてもバラつきやすい。 However, in high-strength hot-rolled steel sheets containing one or more of Ti, Nb, V, and B as precipitation strengthening elements, the actual values after actual casting of these elements are the target values, It's easy to be loose.
このため、目標値に対して設定された熱延の標準条件（加熱条件、圧延条件、圧延後の冷却条件など）で製造した場合、実績値としての引張強さなどの機械的な特性が、目標とする機械的特性にならないような、ばらつきが生じる場合がある。特に、近年では、溶接性向上のために、Ｃ含有量を低減する代わりに、Ｔｉ、Ｎｂ、Ｖ、Ｂなどの析出強化型の元素を含有させて、Ｃ含有量低減に伴う強度低下を補うことが行なわれており、このような鋼では、前記機械的特性のばらつきの傾向が特に強い。 For this reason, when manufactured under standard hot rolling conditions set for the target value (heating conditions, rolling conditions, cooling conditions after rolling, etc.), mechanical properties such as tensile strength as actual values are Variations may occur that do not achieve the target mechanical properties. In particular, in recent years, in order to improve weldability, instead of reducing the C content, precipitation strengthening type elements such as Ti, Nb, V, and B are included to compensate for the strength reduction accompanying the C content reduction. In such steels, the tendency of variation in the mechanical properties is particularly strong.
これに対して、従来から、熱延鋼板の分野において、目標とする機械的特性に近づける、あるいは機械的な特性のばらつきを抑制することが提案されている。例えば、圧延前の鋼材成分の実績値、圧延後の鋼材サイズ、鋼材材質保証値から加熱、圧延、冷却の予定プロセス条件を求め、それぞれのプロセス条件を取り込み、予定プロセスを再計算修正すべく、材質予測を行なう材質予測方法が提案されている（特許文献１参照）。 On the other hand, conventionally, in the field of hot-rolled steel sheets, it has been proposed to approach the target mechanical characteristics or suppress variations in mechanical characteristics. For example, to obtain the expected process conditions of heating, rolling, and cooling from the actual value of the steel material component before rolling, the size of the steel material after rolling, and the guaranteed quality of the steel material, incorporate each process condition, and recalculate and correct the scheduled process. A material prediction method for performing material prediction has been proposed (see Patent Document 1).
更には、加熱炉内での加熱を経て、その後圧延を行う鋼材の製造方法において、前記加熱炉内にある個々の被加熱鋼材の鋼中成分における析出強化元素の固溶度Ｋｃを計算するとともに、予め該固溶度の到達目標値Ｋｏを設定しておいて、Ｋｃ≧Ｋｏを満たすことを条件として、前記被加熱鋼材を前記加熱炉から取り出して圧延する鋼材の製造方法が提案されている（特許文献２参照）。
析出強化型の元素として、Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有する高強度熱延鋼板では、熱間加工モデル、析出モデル、変態モデル、組織・材質モデルなどは複雑に絡み合う。このため、特許文献１の方法では、精度の良いモデルを作成することは非現実的であり、材質予測自体が難しく、材質を安定化させることはできない。 In high-strength hot-rolled steel sheets containing one or more of Ti, Nb, V, and B as precipitation-strengthening elements, the hot working model, precipitation model, transformation model, and structure / material model are intertwined in a complex manner. . For this reason, in the method of Patent Document 1, it is impractical to create a model with high accuracy, it is difficult to predict the material itself, and the material cannot be stabilized.
特許文献２の方法であっても、析出強化型の元素として、Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有する高強度熱延鋼板では、加熱炉における析出強化元素の固溶度Ｋｃを計算すること自体が難しい。加熱時の実際の昇温パターンの違いなども析出強化元素の固溶度Ｋｃに大きな影響を与えるからである。また、熱延した際の熱延鋼板における圧延後で組織変態前までのこれら元素の固溶量も、実際の熱延条件によって大きく変化する。このため、加熱時のＴｉ、Ｎｂ、Ｖ、Ｂの固溶度Ｋｃ自体の計算精度が低く、また、加熱時の固溶度Ｋｃだけでは、機械的特性を精度良く予測することができない。このため、特許文献２の方法のように、加熱時の固溶量だけを問題とする制御方法では、精度の良い材質予測が難しく、材質を安定化させることはできない。
Even in the method of
本発明は上記事情に鑑みてなされたものであって、その目的は、析出強化型の元素として、Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有する高強度熱延鋼板が目標とする機械的特性になるようにフィードフォワード制御できる高強度熱延鋼板の製造方法を提供することである。 The present invention has been made in view of the above circumstances, and its purpose is to provide a high-strength hot-rolled steel sheet containing one or more of Ti, Nb, V, and B as a precipitation strengthening type element. Another object of the present invention is to provide a method for producing a high-strength hot-rolled steel sheet that can be feedforward controlled so as to achieve mechanical properties.
この目的を達成するために、本発明の高強度熱延鋼板の製造方法の要旨は、 Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有し、鋼組織がベイナイトおよび／またはマルテンサイトからなり、変態前と変態後とでこれら元素の固溶量が略同じである高強度熱延鋼板の製造方法であって、Ｔｉ、Ｎｂ、Ｖ、Ｂから選択される元素の鋼中の実績成分値と、この鋼を予め定めた標準の条件で熱延した際の熱延鋼板における圧延後で組織変態前までのこれら選択された元素の固溶量との関係、および、これら選択された元素の固溶量と熱延鋼板の機械的特性との関係を、各々予め求めておき、実際の熱延鋼板の製造における鋼中のこれら選択された元素の実績成分値から、前記関係を用いて、前記標準の条件で熱延した際の熱延鋼板におけるこれら選択された元素の圧延後で組織変態前までの固溶量を求め、更に、これら選択された元素の圧延後で組織変態前までの固溶量から、前記関係を用いて、前記標準の条件で熱延した際の熱延鋼板の機械的特性を予測し、この予測した機械的特性が目標とする機械的特性になるような、これら選択された元素の圧延後で組織変態前までのあるべき固溶量を求めるとともに、この固溶量を実現するためのあるべき熱延条件を求め、このあるべき熱延条件になるように、実際の熱延条件をフィードフォワード制御することである。 In order to achieve this object, the gist of the method for producing a high-strength hot-rolled steel sheet of the present invention includes one or more of Ti, Nb, V, and B, and the steel structure is from bainite and / or martensite. A high strength hot-rolled steel sheet manufacturing method in which the solid solution amount of these elements is substantially the same before and after transformation, and the actual component in the steel of an element selected from Ti, Nb, V and B Value and the relationship between the solid solution amount of these selected elements after rolling and before structure transformation in the hot-rolled steel sheet when this steel is hot-rolled under predetermined standard conditions, and these selected elements The relationship between the solid solution amount and the mechanical properties of the hot-rolled steel sheet is determined in advance, and from the actual component values of these selected elements in the steel in the production of the actual hot-rolled steel sheet, These in the hot-rolled steel sheet when hot-rolled under the standard conditions The solid solution amount after rolling of the selected element and before structure transformation is obtained, and further, from the solid solution amount after rolling of the selected element and before structure transformation, the above conditions are used to determine the standard condition. Predict the mechanical properties of the hot-rolled steel sheet when it is hot-rolled, and the predicted mechanical properties will be the target mechanical properties, after the rolling of these selected elements and before the structural transformation In addition to determining the amount of solid solution to be solved, it is necessary to determine the desired hot rolling condition for realizing this solid solution amount, and to feedforward control the actual hot rolling condition so as to be the desired hot rolling condition.
本発明者らの知見によれば、Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有し、鋼組織がベイナイトおよび／またはマルテンサイトからなり、変態前と変態後とでこれら元素の固溶量が略同じである高強度熱延鋼板では、圧延後で変態前の、これら元素の固溶量が、熱延鋼板の機械的特性を支配する。 According to the knowledge of the present inventors, one or more of Ti, Nb, V and B are contained, the steel structure is composed of bainite and / or martensite, and these elements are solid before and after transformation. In a high-strength hot-rolled steel sheet having substantially the same amount of solution, the solid solution amount of these elements after rolling and before transformation dominates the mechanical properties of the hot-rolled steel sheet.
通常、熱延鋼板の組織や他の元素量も熱延鋼板の機械的特性を当然支配する。しかし、本発明者らの知見によれば、上記高強度熱延鋼板では、後述する図３や４の通り、熱延鋼板の組織や他の元素量などに依らずとも、含有するＴｉ、Ｎｂ、Ｖ、Ｂなどの固溶量のみによって、製造される熱延鋼板の機械的特性が予測できる。 Usually, the structure of the hot-rolled steel sheet and the amount of other elements naturally dominate the mechanical properties of the hot-rolled steel sheet. However, according to the knowledge of the present inventors, in the high-strength hot-rolled steel sheet, as shown in FIGS. 3 and 4 described later, Ti, Nb contained, regardless of the structure of the hot-rolled steel sheet and the amount of other elements. The mechanical properties of the hot-rolled steel sheet to be manufactured can be predicted only by the solid solution amount of V, B, and the like.
したがって、この現象を用いれば、圧延後で変態前の、含有するＴｉ、Ｎｂ、Ｖ、Ｂなどの元素の固溶量を把握できれば、熱延鋼板の組織モデルや他の元素量などを介さなくても、標準条件など一定熱延圧延条件下での熱延鋼板の機械的特性を予測できる。 Therefore, if this phenomenon is used, if the solid solution amount of elements such as Ti, Nb, V, and B contained after rolling and before transformation can be grasped, the structure model of the hot rolled steel sheet and the amount of other elements are not involved. However, it is possible to predict the mechanical properties of the hot-rolled steel sheet under constant hot-rolling conditions such as standard conditions.
そして、この予測した熱延鋼板の機械的特性（標準条件での熱延）が、目標とする機械的特性になるような、あるべき熱延条件を求めることができる。このため、これに基づいて、実際の熱延の加熱条件、圧延条件、圧延後の冷却条件を、あるべき熱延条件になるようにフィードフォワード制御することができる。 Then, it is possible to obtain a desired hot rolling condition such that the predicted mechanical characteristics (hot rolling under standard conditions) of the hot rolled steel sheet become the target mechanical characteristics. For this reason, on the basis of this, feed-forward control can be performed so that the actual hot rolling heating conditions, rolling conditions, and cooling conditions after rolling become the desired hot rolling conditions.
前記したように、析出強化型の元素として、Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有する高強度熱延鋼板では、熱間加工モデル、析出モデル、変態モデル、組織・材質モデルなどが複雑に絡み合う。しかし、だからと言って、これら考えられる因子を全て取り込んで、材質予測しようとすると、却って、前記特許文献１にのように、精度の良いモデルを作成することが難しくなる。前記した従来技術が、精度の良いモデルを作成できなかったのは、本発明のように、上記高強度熱延鋼板が、組織や他の元素量などに依らずとも、含有するＴｉ、Ｎｂ、Ｖ、Ｂなどの固溶量のみによって機械的特性が予測できることを知見し得なかったことによる。 As described above, in a high-strength hot-rolled steel sheet containing one or more of Ti, Nb, V, and B as a precipitation strengthening type element, a hot working model, a precipitation model, a transformation model, and a structure / material model are used. Etc. are intricately intertwined. However, it is difficult to create a highly accurate model as described in Patent Document 1 if it is attempted to predict the material by incorporating all of these possible factors. The reason why the above-described prior art has not been able to create an accurate model is that, as in the present invention, the high-strength hot-rolled steel sheet contains Ti, Nb, This is because it was not possible to find out that mechanical properties could be predicted only by the amount of solid solution such as V and B.
これに対して、本発明では、これら考えられる因子を全て取り込むのではなく、材質に最も相関する因子としては、基本的には、前記した通り、圧延後で変態前のＴｉ、Ｎｂ、Ｖ、Ｂの固溶量のみを選択する。これは、前記した通り、圧延後で変態前のＴｉ、Ｎｂ、Ｖ、Ｂの固溶量が、熱延鋼板の機械的特性を支配することを知見できた故である。したがって、例え、圧延後で変態前のＴｉ、Ｎｂ、Ｖ、Ｂの固溶量を熱延鋼板の機械的特性予測に使用したとしても、前記したように、他の考えられる因子を全て取り込んで、圧延後で変態前のＴｉ、Ｎｂ、Ｖ、Ｂの固溶量を考えられるそれらの因子の一つに過ぎなくした場合には、却って、前記特許文献１にのように、材質予測が難しくなる。 On the other hand, in the present invention, not all of these possible factors are taken in, but as the factors most correlated with the material, basically, as described above, Ti, Nb, V, after rolling and before transformation, Only the solid solution amount of B is selected. This is because, as described above, it was found that the solid solution amount of Ti, Nb, V, B after rolling and before transformation dominates the mechanical properties of the hot-rolled steel sheet. Therefore, even if the solid solution amount of Ti, Nb, V, B after rolling and before transformation is used for predicting the mechanical properties of the hot-rolled steel sheet, as described above, all other possible factors are incorporated. When the solid solution amount of Ti, Nb, V, B after rolling and before transformation is only one of those possible factors, it is difficult to predict the material as in Patent Document 1 above. Become.
（対象とする高強度熱延鋼板）
本発明では、その対象とする高強度熱延鋼板の前提として、Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有し、鋼組織がベイナイトおよび／またはマルテンサイトからなり、変態前と変態後とでこれら元素の固溶量が略同じである高強度熱延鋼板とする。
(Target high-strength hot-rolled steel sheet)
In the present invention, as a premise of the high-strength hot-rolled steel sheet as the object, it contains one or more of Ti, Nb, V, B, the steel structure is composed of bainite and / or martensite, and before transformation A high-strength hot-rolled steel sheet in which the solid solution amounts of these elements are substantially the same is used later.
これらの条件を満足する高強度熱延鋼板は、前記した通り、Ｔｉ、Ｎｂ、Ｖ、Ｂの固溶量が、熱延鋼板の機械的特性を支配し、熱延鋼板の組織や他の元素量などに依らずとも、含有するＴｉ、Ｎｂ、Ｖ、Ｂなどの固溶量のみによって、製造される熱延鋼板の機械的特性が予測できる。 As described above, the high-strength hot-rolled steel sheet that satisfies these conditions has a solid solution amount of Ti, Nb, V, and B that controls the mechanical properties of the hot-rolled steel sheet, and the structure of the hot-rolled steel sheet and other elements. Regardless of the amount or the like, the mechanical properties of the hot-rolled steel sheet to be produced can be predicted only by the solid solution amount of Ti, Nb, V, B, etc. contained.
本発明が対象とする、ベイナイトおよび／またはマルテンサイトからなる鋼組織の機械的特性のばらつきは、焼入れ性のばらつきにより生じる。この焼入れ性のばらつきは、固溶Ｔｉ、Ｎｂ、Ｖ、Ｂのばらつきが支配因子となっている。しかも、この固溶Ｔｉ、Ｎｂ、Ｖ、Ｂのばらつきによる機械的特性のばらつきは非常に大きい。 Variations in the mechanical properties of the steel structure consisting of bainite and / or martensite targeted by the present invention are caused by variations in hardenability. This variation in hardenability is governed by variations in solute Ti, Nb, V, and B. In addition, the variation in mechanical properties due to the variation in solid solution Ti, Nb, V, B is very large.
一方、フェライト、フェライト・パーライトからなる組織の機械的特性のばらつきは、フェライト粒径、パーライト分率などのばらつきにより生じる。このフェライト粒径、パーライト分率などのばらつきは、旧γ粒径、残留ひずみ、合金元素および微細析出物量などのばらつきに起因している。これらのばらつきは、非常に複雑ではあるが、そのばらつきの程度による機械的特性のばらつきは、逆に非常に小さい。 On the other hand, variations in the mechanical properties of the structure composed of ferrite and ferrite / pearlite are caused by variations in ferrite grain size, pearlite fraction, and the like. Variations in the ferrite particle size, pearlite fraction, and the like are caused by variations in the prior γ particle size, residual strain, alloy elements, and fine precipitate amounts. These variations are very complicated, but the variation in mechanical characteristics depending on the degree of the variation is very small.
これに対して、本発明が対象とする、ベイナイトおよび／またはマルテンサイトからなる鋼組織であれば、引張強さが５２０ＭＰａ以上で、前記した通り、引張強さなどの機械的な特性が大きくばらつき、本発明適用の必要性が高い。また、ベイナイトおよび／またはマルテンサイトは変態温度が６００℃以下と低いので、Ｔｉ、Ｎｂ、Ｖ、Ｂが析出しにくく、変態前と変態後とで、Ｔｉ、Ｎｂ、Ｖ、Ｂの固溶量が略同じである。このため、圧延後で変態前の、これら元素の固溶量から熱延鋼板の機械的特性を予測することができる。 On the other hand, in the case of a steel structure composed of bainite and / or martensite targeted by the present invention, the tensile strength is 520 MPa or more, and as described above, mechanical properties such as tensile strength vary greatly. Therefore, the necessity of applying the present invention is high. Moreover, since the transformation temperature of bainite and / or martensite is as low as 600 ° C. or less, Ti, Nb, V, and B are difficult to precipitate, and the solid solution amount of Ti, Nb, V, and B before and after transformation Are substantially the same. For this reason, the mechanical properties of the hot-rolled steel sheet can be predicted from the solid solution amounts of these elements after rolling and before transformation.
より具体的には、ベイナイトおよび／またはマルテンサイトが占積率で８０％以上の場合には、変態前と変態後とで、Ｔｉ、Ｎｂ、Ｖ、Ｂの固溶量が略同じである。また、引張強さが５２０ＭＰａ以上の高強度とするためにも、ベイナイトおよび／またはマルテンサイトが占積率で８０％以上必要である。 More specifically, when bainite and / or martensite is 80% or more in space factor, the solid solution amounts of Ti, Nb, V, and B are substantially the same before and after transformation. Further, in order to obtain a high strength with a tensile strength of 520 MPa or more, bainite and / or martensite needs to be 80% or more in space factor.
ベイナイトおよび／またはマルテンサイトの占積率は、鋼板の１／４の厚さ部分の光学顕微鏡観察（倍率４００倍）により組織観察したのち、画像解析によって、面積率として占積率を測定する。具体的には、まず、鋼板をナイタールで腐食して、前記光学顕微鏡で観察し、板厚約１／４の位置（ｔ／４位置）における板断面の圧延方向面を写真撮影する。そして、この写真のうち、ベイナイトおよびマルテンサイトと認められる組織をトレースし、市販の画像ソフト［汎用画像処理ソフト「Ｉｍａｇｅ−Ｐｒｏ Ｐｌｕｓ」（Ｍｅｄｉａ，Ｃｙｂｅｒｎｅｔｉｃｓ社製）］を用いて、各組織の面積率としての占積率を測定する。 The space factor of bainite and / or martensite is measured by optical microscope observation (magnification 400 times) of a 1/4 thickness portion of the steel sheet, and then the space factor is measured by image analysis. Specifically, first, the steel sheet is corroded with nital and observed with the optical microscope, and the rolling direction plane of the cross section of the plate at the position of about 1/4 thickness (t / 4 position) is photographed. In this photograph, the structure recognized as bainite and martensite is traced, and the area of each structure is obtained using commercially available image software [general-purpose image processing software “Image-Pro Plus” (Media, manufactured by Cybernetics)]. Measure the space factor as a rate.
本発明では、鋼組織において、上記ベイナイトおよび／またはマルテンサイトの占積率を満たせば、残部の組織に、ポリゴナルフェライトやパーライトなどの他の組織を含むものであって良い。 In the present invention, as long as the steel structure satisfies the bainite and / or martensite space factor, the remaining structure may include other structures such as polygonal ferrite and pearlite.
（熱延鋼板の製造方法）
本発明における高強度熱延鋼板の製造方法を、図１のフローチャートに基づき以下に説明する。
(Method for producing hot-rolled steel sheet)
A method for producing a high-strength hot-rolled steel sheet according to the present invention will be described below based on the flowchart of FIG.
図１において、先ず、転炉などの出鋼時における鋼中のＴｉ、Ｎｂ、Ｖ、Ｂから選択される元素の実績成分値と、これを予め定めた標準の熱延条件で熱延した（熱延後冷却した）鋼板のＴｉ、Ｎｂ、Ｖ、Ｂの固溶量、そして、この熱延鋼板の強度などの機械的な特性との関係を予め求める。この予め定める標準の熱延条件は、各熱延の温度条件などの、フィードフォワード制御における制御しろを考慮して（制御の余地があるように）、スラブ加熱温度、粗圧延開始温度、仕上圧延開始温度、仕上圧延終了温度、冷却速度などの、設定制御範囲における中庸値程度に定めるのが好ましい。 In FIG. 1, first, actual component values of elements selected from Ti, Nb, V, and B in steel at the time of steelmaking such as in a converter, and this were hot-rolled under predetermined standard hot-rolling conditions ( The relationship between the solid solution amount of Ti, Nb, V, B of the steel sheet (cooled after hot rolling) and mechanical properties such as the strength of the hot rolled steel sheet is obtained in advance. This standard hot rolling condition is determined in consideration of the control margin in feedforward control, such as the temperature condition of each hot rolling (so that there is room for control), slab heating temperature, rough rolling start temperature, finish rolling. It is preferable to determine the intermediate value within the set control range, such as the start temperature, finish rolling end temperature, and cooling rate.
この内、本発明において基本的なデータとなる、出鋼時における鋼中のＴｉ、Ｎｂ、Ｖ、Ｂの実績成分値は実測値から求める。 Among these, the actual component values of Ti, Nb, V, and B in the steel at the time of steel output, which are basic data in the present invention, are obtained from the actually measured values.
これに対して、熱延鋼板の圧延後で変態前のＴｉ、Ｎｂ、Ｖ、Ｂの固溶量、そして、この熱延鋼板の強度などの機械的な特性は、これまでの製造された熱延鋼板の実績値からの統計的な処理から算出しても、あるいは理論的に計算して算出しても良い。 On the other hand, the mechanical properties such as the solid solution amount of Ti, Nb, V and B after rolling of the hot-rolled steel sheet and before transformation, and the strength of the hot-rolled steel sheet are the same as the heat produced so far. You may calculate from the statistical process from the actual value of a rolled steel plate, or you may calculate by calculating theoretically.
ここで、本発明対象鋼板は、前記した通り、変態前と変態後とで、Ｔｉ、Ｎｂ、Ｖ、Ｂの固溶量が略同じであるので、前記標準の熱延条件で熱延した鋼板の（変態後の）Ｔｉ、Ｎｂ、Ｖ、Ｂの固溶量を、熱延後で組織変態前までのＴｉ、Ｎｂ、Ｖ、Ｂの固溶量と見なす。以下、特別に記載しない限り、熱延（圧延）後で組織変態前までのＴｉ、Ｎｂ、Ｖ、Ｂの固溶量を単に固溶量とも言う。 Here, as described above, the steel sheet subject to the present invention has the same amount of Ti, Nb, V, B as a solid solution before and after transformation as described above. The solid solution amount of Ti, Nb, V, and B (after transformation) is regarded as the solid solution amount of Ti, Nb, V, and B after hot rolling and before the structural transformation. Hereinafter, unless otherwise specified, the solid solution amounts of Ti, Nb, V, and B after hot rolling (rolling) and before structure transformation are also simply referred to as solid solution amounts.
鋼中にＴｉ、Ｎｂ、Ｖ、Ｂの内の一種しか含まない場合には、当然、この一種含まれる元素が選択される固溶量算出対象となる。これに対して、Ｔｉ、Ｎｂ、Ｖ、Ｂの内の二種以上を含有する場合には、その内の含有する一種の元素を選択して、熱延鋼板の圧延後で変態前の固溶量の算出対象としても良く、その内の含有する二種以上の元素を熱延鋼板の圧延後で変態前の固溶量の算出対象としても良い。 When only one of Ti, Nb, V, and B is contained in the steel, naturally, the element contained in the one kind is selected as a solid solution amount calculation target. On the other hand, when two or more of Ti, Nb, V, and B are contained, a kind of element contained therein is selected, and the solid solution before transformation after rolling of the hot-rolled steel sheet is selected. It is good also as a calculation object of quantity, and it is good also as a calculation object of the solid solution amount before the transformation after the rolling of a hot-rolled steel plate in the 2 or more types of element to contain.
また、これらＴｉ、Ｎｂ、Ｖ、Ｂに加えて、鋼板の基本的な成分であるＣ、Ｓｉ、Ｍｎや、他の合金元素であるＭｏ、Ｎｉ、Ｃｕ、Ｃｒなどの標準の熱延条件で熱延した（熱延後冷却した）鋼板の固溶量を求め、これら元素の固溶量をＴｉ、Ｎｂ、Ｖ、Ｂと同様に、後述する熱延鋼板の強度などの機械的特性の予測に用いても良い。しかし、本発明では、基本的に、Ｔｉ、Ｎｂ、Ｖ、Ｂの固溶量のみから、熱延鋼板の強度などの機械的特性の予測ができることが特徴であり、その他元素の固溶量を考慮する必要は基本的には無い。また、これら元素の数を増した場合、計算が複雑となり時間を要するなどの欠点も生じる。 In addition to these Ti, Nb, V, and B, standard hot rolling conditions such as C, Si, and Mn, which are basic components of steel sheets, and Mo, Ni, Cu, and Cr, which are other alloy elements, are used. The solid solution amount of the hot-rolled steel plate (cooled after hot rolling) is obtained, and the solid solution amount of these elements is predicted for mechanical properties such as the strength of the hot-rolled steel plate, which will be described later, in the same manner as Ti, Nb, V, and B. You may use for. However, the present invention is basically characterized in that the mechanical properties such as the strength of the hot-rolled steel sheet can be predicted from only the solid solution amounts of Ti, Nb, V, and B. There is basically no need to consider. Further, when the number of these elements is increased, the calculation becomes complicated and time is required.
以上の手順によって、鋼のＴｉ、Ｎｂ、Ｖ、Ｂの実績成分値と、この鋼を標準の熱延条件で熱延した鋼板の、熱延後で組織変態前までのＴｉ、Ｎｂ、Ｖ、Ｂの各固溶量と、この熱延鋼板の強度などの機械的な特性との関係を、後述する図３、４のように予め求めておく。 By the above procedure, the actual component values of Ti, Nb, V, and B of the steel, and Ti, Nb, V, and the steel sheet obtained by hot-rolling the steel under the standard hot-rolling conditions before hot-rolling and before structural transformation. The relationship between each solid solution amount of B and mechanical properties such as the strength of the hot-rolled steel sheet is obtained in advance as shown in FIGS.
実際の熱延鋼板の製造に際しては、熱延される鋼のこれら元素の実績成分値（出鋼時等）から、前記予め求めた関係を用いて、標準の条件で熱延した際の熱延鋼板におけるこれら元素の圧延後で組織変態前までの各固溶量を求める。 In the actual production of hot-rolled steel sheets, the hot-rolling at the time of hot-rolling under standard conditions from the actual component values of these elements of the steel to be hot-rolled (at the time of steel production, etc.) using the relationship previously determined. The respective solid solution amounts after rolling of these elements in the steel sheet and before the structural transformation are obtained.
更に、これら求めた元素の固溶量から、前記予め求めた関係を用いて、標準の条件で熱延した際の熱延鋼板の機械的特性を予測する。この際、〔ＴＳ＝ｆ（固溶Ｎｂ量、固溶Ｂ量、固溶Ｖ量、固溶Ｔｉ量）〕などの予測式を作成して、これを重回帰することによって、熱延鋼板のＴＳを予測しても良い。この場合、特に、熱延の仕上げ開始温度は、熱延鋼板への歪み蓄積量に大きく効くため、熱延鋼板の機械的特性に比較的大きな影響を与える。このため、熱延鋼板の機械的特性を予測する際には、上記予測式に、この熱延の仕上げ開始温度を入れて、〔ＴＳ＝ｆ（固溶Ｎｂ量、固溶Ｂ量、固溶Ｖ量、固溶Ｔｉ量、熱延の仕上げ開始温度）〕として考慮することが好ましい。 Further, from the obtained solid solution amounts of the elements, the mechanical properties of the hot-rolled steel sheet when hot-rolled under standard conditions are predicted using the previously obtained relationship. At this time, a prediction formula such as [TS = f (the amount of solute Nb, the amount of solute B, the amount of solute V, the amount of solute Ti)] is created, and this is subjected to multiple regression, thereby TS may be predicted. In this case, in particular, the finishing start temperature of hot rolling greatly affects the amount of strain accumulated in the hot rolled steel sheet, and thus has a relatively large influence on the mechanical properties of the hot rolled steel sheet. For this reason, when predicting the mechanical properties of the hot-rolled steel sheet, the hot rolling finishing start temperature is put into the prediction formula, and [TS = f (the amount of solute Nb, the amount of solute B, the amount of solute V amount, solute Ti amount, hot rolling finishing start temperature)] are preferable.
この熱延鋼板の予測した機械的特性が、目標とする機械的特性になるようであれば、標準の条件でそのまま熱延を行なう。目標とする機械的特性とは、主として引張強度、伸び、靱性などであり、具体的な鋼板用途からくる要求特性に応じて、これら目標とする機械的特性を選択する。 If the predicted mechanical characteristics of the hot-rolled steel sheet become the target mechanical characteristics, the hot-rolling is performed as it is under standard conditions. The target mechanical properties are mainly tensile strength, elongation, toughness, etc., and these target mechanical properties are selected according to the required properties coming from the specific steel sheet application.
これに対して、熱延鋼板の予測した機械的特性が、目標とする機械的特性にならないようであれば、熱延鋼板の予測した機械的特性が、目標とする機械的特性になるための、あるべき組織変態前までのＴｉ、Ｎｂ、Ｖ、Ｂの各固溶量と、それを得るための、あるべき熱延条件を、後述する加熱時、圧延時、冷却時のＴｉ、Ｎｂ、Ｖ、Ｂの各固溶析出モデルを用いて求める。 On the other hand, if the predicted mechanical characteristics of the hot-rolled steel sheet do not become the target mechanical characteristics, the predicted mechanical characteristics of the hot-rolled steel sheet become the target mechanical characteristics. The respective solid solution amounts of Ti, Nb, V, and B before the desired structural transformation and the desired hot rolling conditions for obtaining them are Ti, Nb, It calculates | requires using each solid solution precipitation model of V and B.
これらの一連の操作を、熱延鋼板の予測した機械的特性が、目標とする機械的特性になるようになるまで繰り返し行ってあるべき熱延条件を決定する。そして、このあるべき熱延条件に基づいて、実際の熱延の加熱条件、圧延条件、圧延後の冷却条件を、熱延工程のプロセスコンピューターへフィードフォワードし、前記した実際の熱延条件を、あるべき熱延条件になるように選択的に制御して、熱延板を製造する。 These series of operations are repeated until the predicted mechanical properties of the hot-rolled steel sheet become the target mechanical properties, and the hot-rolling conditions that should be repeated are determined. And based on the desired hot rolling conditions, the actual hot rolling heating conditions, rolling conditions, cooling conditions after rolling are fed forward to the process computer of the hot rolling process, and the actual hot rolling conditions described above are A hot-rolled sheet is manufactured by selectively controlling the hot-rolling conditions as desired.
ここで、本発明では、以上求めたＴｉ、Ｎｂ、Ｖ、Ｂの固溶量に基づいて、これから製造する熱延鋼板のこれら元素の固溶量を制御すべく、熱延プロセス条件を制御乃至操作する。したがって、熱延の加熱時、圧延時、圧延後の冷却時における、加熱温度、粗圧延温度、仕上げ圧延温度、冷却開始温度、冷却速度などの熱延条件と、Ｔｉ、Ｎｂ、Ｖ、Ｂの固溶量との相関を予め求めておくことが必要となる。即ち、加熱時、圧延時、冷却時のＴｉ、Ｎｂ、Ｖ、Ｂの各固溶析出モデルを予め各々作成しておく。 Here, in the present invention, based on the solid solution amounts of Ti, Nb, V, and B obtained above, the hot rolling process conditions are controlled or controlled so as to control the solid solution amounts of these elements in the hot rolled steel sheet to be manufactured. Manipulate. Therefore, the hot rolling conditions such as heating temperature, rough rolling temperature, finish rolling temperature, cooling start temperature, cooling rate, etc. during heating, rolling, and cooling after rolling, and Ti, Nb, V, B It is necessary to obtain a correlation with the solid solution amount in advance. That is, each solid solution precipitation model of Ti, Nb, V, and B during heating, rolling, and cooling is prepared in advance.
（固溶量算出）
ここで、Ｔｉ、Ｎｂ、Ｖ、Ｂの含有量実績値に基づく熱延鋼板の固溶量や、加熱時、圧延時、冷却時のＴｉ、Ｎｂ、Ｖ、Ｂの各固溶析出モデル作成の際に用いるＴｉ、Ｎｂ、Ｖ、Ｂの固溶量は、これまでの製造された熱延鋼板の実績値（測定値）からの統計的な処理から算出しても、あるいは理論的に計算して算出しても良い。
(Solution calculation)
Here, the solid solution amount of the hot rolled steel sheet based on the actual content values of Ti, Nb, V, and B, and the respective solid solution precipitation models of Ti, Nb, V, and B during heating, rolling, and cooling are prepared. The solid solution amount of Ti, Nb, V, and B used at the time can be calculated from statistical processing from the actual value (measured value) of the hot-rolled steel sheet manufactured so far, or calculated theoretically. May be calculated.
Ｔｉ、Ｎｂ、Ｖ、Ｂなどの固溶量の理論的計算式は何を使ってもよいが、例えば朝倉書店「機械材料学」６８頁〜７１頁（１９９９年３月１０日初版発行、著者：平川賢爾ら）に開示されているＮｂ、Ｔｉ、Ｖ、ＢなどのＣ、Ｎに対する溶解度積に関する計算式を用いてもよいし、熱力学モデルに基づく相平衡計算などによる独自の式を用いてもよい。 Any theoretical calculation formula for the amount of solid solution of Ti, Nb, V, B, etc. may be used. For example, Asakura Shoten "Mechanical Materials", pages 68-71 (published first edition on March 10, 1999, author) : Kenji Hirakawa et al.) May use formulas for solubility products for C and N such as Nb, Ti, V, B, etc., or use original formulas such as phase equilibrium calculations based on thermodynamic models May be.
（熱延鋼板製造ライン）
図２に、本発明が適用される熱延鋼板製造ラインの一例を、設備構成図で示す。製鋼工程１２からの出鋼に対し、連続鋳造工程（ＣＣ）１３または造塊工程１４でスラブが製造される。スラブは加熱炉２で加熱された後に、粗圧延機３、仕上圧延機４を通されて鋼板１に熱間圧延されて、次いで反りの矯正用のホットレベラ（ＨＬ）５を介して、冷却装置６によって変態組織とされ、所定厚の熱延鋼板を得る。
(Hot rolled steel sheet production line)
In FIG. 2, an example of a hot-rolled steel sheet production line to which the present invention is applied is shown in an equipment configuration diagram. A slab is manufactured in the continuous casting process (CC) 13 or the ingot-making
このような熱延鋼板製造ラインにおいて、製鋼工程１２、ＣＣ１３、造塊工程１４の各々に対しては製鋼・分塊プロセスコンピューター（以下、プロコンと言う）１５が、加熱炉２に対しては加熱プロコン７が、粗圧延機３、仕上圧延機４に対しては圧延プロコン８が、ＨＬ５、冷却装置６に対しては冷却プロコン９が、各々接続されている。
In such a hot-rolled steel sheet production line, a steelmaking / bundling process computer (hereinafter referred to as “procon”) 15 is heated for each of the
前記フローチャートにおける出鋼時における鋼中のＴｉ、Ｎｂ、Ｖ、Ｂの実績成分値は、製鋼・分塊プロセスコン１５から、中央制御室１０の上位コンピューターに送られ、予め求められた、標準の熱延条件で熱延した（熱延後冷却した）鋼板のＴｉ、Ｎｂ、Ｖ、Ｂの固溶量との関係から、この鋼を標準の熱延条件で熱延した熱延鋼板の強度などの機械的な特性が予測される。
The actual component values of Ti, Nb, V, and B in the steel at the time of steel production in the flowchart are sent from the steelmaking /
この熱延鋼板の予測した機械的特性が、目標とする機械的特性になるようであれば、標準の条件でそのまま熱延を行なうように、中央制御室１０の上位コンピューターから、加熱プロコン７、圧延プロコン８、冷却プロコン９に指示が送られ、が、標準の条件でそのまま、加熱、熱延、冷却される。
If the predicted mechanical properties of the hot-rolled steel sheet become the target mechanical properties, the
一方、熱延鋼板の予測した機械的特性が、目標とする機械的特性にならないようであれば、中央制御室１０の上位コンピューターでは、熱延鋼板の予測した機械的特性が、目標とする機械的特性になる、あるべき組織変態前までのＴｉ、Ｎｂ、Ｖ、Ｂの各固溶量と、それを得るための、あるべき熱延条件を、前記した加熱時、圧延時、冷却時のＴｉ、Ｎｂ、Ｖ、Ｂの各固溶析出モデルを用いて求める。
On the other hand, if the predicted mechanical characteristics of the hot-rolled steel sheet do not become the target mechanical characteristics, the host computer of the
そして、このあるべき熱延条件に基づいて、実際の熱延の加熱条件、圧延条件、圧延後の冷却条件を、中央制御室１０の上位コンピューターから、加熱プロコン７、圧延プロコン８、冷却プロコン９へフィードフォワードし、実際の熱延条件を、あるべき熱延条件になるように選択的に制御して、熱延板を製造する。
Then, based on the desired hot rolling conditions, the actual hot rolling heating conditions, rolling conditions, and cooling conditions after rolling are obtained from the upper computer of the
（化学成分組成）
次に、本発明が対象とする熱延鋼板の好ましい成分について以下に説明する。なお化学成分の単位はすべて質量％である。
本発明では、特に熱延鋼板の成分組成を限定しないが、前記した通り、本発明が対象とするのは、Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有し、鋼組織がベイナイトおよび／またはマルテンサイトからなり、変態前と変態後とでこれら元素の固溶量が略同じである高強度熱延鋼板である。このため、このような組織とし、また高強度を確保するための好ましい成分組成がある。
また、本発明が対象とする熱延鋼板は、溶接性向上のために、Ｃ含有量を低減する代わりに、Ｔｉ、Ｎｂ、Ｖ、Ｂなどの析出強化型の元素を含有させて、Ｃ含有量低減に伴う強度低下を補うタイプの鋼板が望ましい。このような鋼では、前記した通り、溶接性は改善されるように、機械的特性のばらつきの傾向が特に強く、本発明の必要性が高い。
(Chemical composition)
Next, preferable components of the hot-rolled steel sheet targeted by the present invention will be described below. All units of chemical components are mass%.
In the present invention, the component composition of the hot-rolled steel sheet is not particularly limited. However, as described above, the present invention is intended to contain one or more of Ti, Nb, V, and B, and the steel structure is bainite. It is a high-strength hot-rolled steel sheet comprising martensite and having substantially the same solid solution amount before and after transformation. For this reason, there exists a preferable component composition for setting it as such a structure and ensuring high intensity | strength.
In addition, the hot-rolled steel sheet targeted by the present invention contains precipitation strengthening elements such as Ti, Nb, V, and B instead of reducing the C content in order to improve weldability. A steel sheet of a type that compensates for the strength reduction accompanying the amount reduction is desirable. In such steel, as described above, the tendency of variation in mechanical properties is particularly strong so that the weldability is improved, and the necessity of the present invention is high.
これら熱延鋼板の、上記した組織と、強度などの特性を保障するための好ましい基本成分元素としては、Ｃ：０．０１〜０．１２％、Ｓｉ：０．０５〜１．０％、Ｍｎ：１．０〜３．０％を含有することが好ましい。 Preferred basic component elements for ensuring the above-described structure and strength of the hot-rolled steel sheet include C: 0.01 to 0.12%, Si: 0.05 to 1.0%, Mn : It is preferable to contain 1.0 to 3.0%.
（Ｃ：０．０１〜０．１２％）
Ｃは、鋼板の強度を確保する為に必須の元素である。Ｃの含有量が０．０１％未満では、引張強さが５２０ＭＰａ以上の強度が得られない。一方、Ｃを０．１２％を超えて含有させると、溶接性が低下する。また、粗大な塊状の第２相の生成が多くなり、破壊の起点が増す為、伸びおよび伸びフランジ性が低下する。したがって、Ｃ含有量は０．０１〜０．１２％の範囲とする。
(C: 0.01 to 0.12%)
C is an essential element for ensuring the strength of the steel sheet. If the C content is less than 0.01%, a tensile strength of 520 MPa or more cannot be obtained. On the other hand, when C is contained exceeding 0.12%, the weldability is lowered. Moreover, since the production | generation of a coarse massive 2nd phase increases and the origin of a fracture | rupture increases, elongation and stretch flangeability will fall. Therefore, the C content is in the range of 0.01 to 0.12%.
（Ｓｉ：０．０５〜１．０％）
Ｓｉは固溶強化元素としても有用である。このような効果を発揮させるためには０．０５％以上含有させる必要がある。一方、Ｓｉを１．０％を超えて含有させても、その効果は飽和し、却って、熱間脆性を起こして圧延中に割れやすくなる。したがって、Ｓｉ含有量は好ましくは０．０５〜１．０％の範囲とする。
(Si: 0.05-1.0%)
Si is also useful as a solid solution strengthening element. In order to exhibit such an effect, it is necessary to contain 0.05% or more. On the other hand, even if Si is contained in excess of 1.0%, the effect is saturated. On the other hand, hot brittleness is caused and cracking is likely to occur during rolling. Therefore, the Si content is preferably in the range of 0.05 to 1.0%.
（Ｍｎ：１．０〜３．０％）
Ｍｎの含有量が１．０％未満では、引張強さが５２０ＭＰａ以上の強度が得られない。一方、Ｍｎを３．０％を超えて含有させると、鋳片の割れなどの悪影響が生じる。したがって、Ｍｎ含有量は好ましくは１．０〜３．０％の範囲とする。
(Mn: 1.0-3.0%)
If the Mn content is less than 1.0%, a strength with a tensile strength of 520 MPa or more cannot be obtained. On the other hand, when Mn is contained exceeding 3.0%, adverse effects such as cracking of the slab occur. Therefore, the Mn content is preferably in the range of 1.0 to 3.0%.
（Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上）
Ｔｉ、Ｎｂ、Ｖ、Ｂの元素はいずれも、析出強化および組織微細化作用による高強度化効果を有している。この様な効果を有効に発揮させる為に、Ｔｉ：０．１％以下（０％を含まない）、Ｎｂ：０．１％以下（０％を含まない）、Ｖ：０．１％以下（０％を含まない）、Ｂ：０．０１％以下（０％を含まない）の一種または二種以上を含有させる。これらの元素含有量が各々上限を超えると炭化物が多く生成し、所望の強度や靱性などが得られない。
(One or more of Ti, Nb, V, B)
All elements of Ti, Nb, V, and B have an effect of increasing the strength by precipitation strengthening and microstructure refining action. In order to effectively exhibit such an effect, Ti: 0.1% or less (not including 0%), Nb: 0.1% or less (not including 0%), V: 0.1% or less ( 0% is not included), B: 0.01% or less (not including 0%), or two or more of them are included. When the content of these elements exceeds the upper limit, a large amount of carbide is generated, and desired strength and toughness cannot be obtained.
（その他の元素）
これらの元素の他に、更に、その他の元素を選択的に含有しても良い。
例えば、母材、溶接部の強度向上、あるいは焼き入れ性の向上や高強度の確保のために、Ｍｏ：１．５％以下（０％を含まない）、Ｃｒ：２．０％以下（０％を含まない）、Ｎｉ：２．０％以下（０％を含まない）、Ｃｕ：２．０％以下（０％を含まない）の一種または二種以上を含有しても良い。
また、脱酸およびミクロ組織の微細化による母材靭性向上のために、Ａｌ：０．２００％以下（０％を含まない）を含有しても良い。
また、粒内ベイナイトの生成を促進してＨＡＺ靭性を向上させるために、窒素（Ｎ2 ）：０．０１００％以下（０％を含まない）、酸素（Ｏ2 ）：０．００５０％以下（０％を含まない）を含有しても良い。
更に、組織を微細化して靱性を高めるために、Ｃａ：０．００７％以下（０％を含まず）、Ｍｇ：０．００７％以下（０％を含まず）、ＲＥＭ：０．０５％以下（０％を含まず）の一種または二種以上を含有しても良い。
一方、Ｐ、Ｓは不純物であり、Ｐ：０．０３０％以下、Ｓ：０．０１０％以下に止めるのがよい。
(Other elements)
In addition to these elements, other elements may be further selectively contained.
For example, Mo: 1.5% or less (not including 0%), Cr: 2.0% or less (0) in order to improve the strength of the base material and the welded portion, or improve hardenability and ensure high strength. %), Ni: 2.0% or less (not including 0%), Cu: 2.0% or less (not including 0%), or two or more thereof may be included.
Further, Al: 0.200% or less (excluding 0%) may be contained in order to improve the base material toughness by deoxidation and refinement of the microstructure.
Further, in order to promote the formation of intragranular bainite and improve the HAZ toughness, nitrogen (N 2 ): 0.0100% or less (excluding 0%), oxygen (O 2 ): 0.0050% or less ( 0% is not included).
Furthermore, in order to refine the structure and increase toughness, Ca: 0.007% or less (excluding 0%), Mg: 0.007% or less (not including 0%), REM: 0.05% or less You may contain 1 type, or 2 or more types (it does not contain 0%).
On the other hand, P and S are impurities, and it is preferable to stop P: 0.030% or less and S: 0.010% or less.
以下実施例に基づいて本発明を詳述する。ただし、下記実施例は本発明を制
限するものではなく、前・後記の趣旨を逸脱しない範囲で変更実施することは
全て本発明の技術範囲に包含される。
The present invention is described in detail below based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.
（固溶量と機械的な特性との関係）
Ｃ：０．０４％、Ｓｉ：０．２％、Ｍｎ：２．０％、Ｃｒ：０．６％、Ｔｉ：０．０１％、Ｎｂ：０．０２％、残部Ｆｅからなる化学成分組成を有する鋼において、Ｂ含有量を１０〜３５ｐｐｍの範囲で変化させ、固溶Ｂ量を５〜２０ｐｐｍの範囲で変化させた熱延鋼板の、変態後の固溶Ｂ量と熱延鋼板の強度と靱性との関係を図３に示す。
(Relationship between solid solution and mechanical properties)
A chemical composition comprising C: 0.04%, Si: 0.2%, Mn: 2.0%, Cr: 0.6%, Ti: 0.01%, Nb: 0.02%, and the balance Fe. In the steel having, in the hot rolled steel sheet in which the B content is changed in the range of 10 to 35 ppm and the solid solution B content is changed in the range of 5 to 20 ppm, the solid solution B amount after transformation and the strength of the hot rolled steel sheet The relationship with toughness is shown in FIG.
この固溶Ｂ量を変化させた熱延鋼板は、前記標準製造条件として、一定の共通条件で製造した。即ち、連続鋳造によって得られた、上記化学成分組成を有するスラブを１２００℃±２０℃で加熱し、粗圧延開始温度を１１００℃±２０℃、仕上圧延開始温度を１０００℃±２０℃、仕上圧延終了温度を９００℃±２０℃として、この温度から水冷により冷却し、３０ｍｍ厚の熱延鋼板（厚板）を得るものとした。そして、熱延鋼板のベイナイト占積率は８０％以上とした。 The hot-rolled steel sheet in which the amount of dissolved B was changed was manufactured under certain common conditions as the standard manufacturing conditions. That is, the slab having the above chemical composition obtained by continuous casting is heated at 1200 ° C. ± 20 ° C., the rough rolling start temperature is 1100 ° C. ± 20 ° C., the finish rolling start temperature is 1000 ° C. ± 20 ° C., and finish rolling. The end temperature was set to 900 ° C. ± 20 ° C., and cooling was performed from this temperature by water cooling to obtain a 30 mm thick hot-rolled steel plate (thick plate). And the bainite space factor of the hot-rolled steel sheet was 80% or more.
図３に示す通り、Ｂ含有量乃至固溶Ｂ量によって、同じ標準製造条件で製造された熱延鋼板であっても、大きく強度や靱性が異なることが分かる。また、Ｂ含有量乃至固溶Ｂ量が、熱延鋼板の強度や靱性の支配因子であることが分かる。 As shown in FIG. 3, it can be seen that even hot-rolled steel sheets manufactured under the same standard manufacturing conditions differ greatly in strength and toughness depending on the B content or the solute B content. Moreover, it turns out that B content thru | or solute B amount are the governing factors of the intensity | strength and toughness of a hot-rolled steel plate.
更に、上記化学成分組成を有する鋼において、Ｂ含有量や固溶Ｂ量とともに、Ｎｂ含有量や固溶Ｎｂ量を変化させた９鋼種について、前記標準製造条件として共通条件で熱延鋼板を製造した。そして、これら変態後の熱延鋼板の固溶Ｂ量と固溶Ｎｂ量とから引張強度の予測式〔ＴＳ＝ｆ（固溶Ｎｂ量、固溶Ｂ量）〕を作成した。 Furthermore, in the steel having the chemical composition described above, hot-rolled steel sheets are manufactured under common conditions as the standard production conditions for nine steel types in which the Nb content and the solute Nb content are changed together with the B content and the solute B content. did. And the prediction formula [TS = f (solid solution Nb amount, solid solution B amount)] of the tensile strength was created from the solid solution B amount and solid solution Nb amount of these hot-rolled steel sheets after transformation.
この引張強度の予測式と、同じく、この９鋼種の熱延鋼板の引張強度を実測した値と比較した結果を図４に示す。この図４において、縦軸の熱延鋼板の引張強度実測値と、変態後の熱延鋼板の固溶Ｂ量と固溶Ｎｂ量とからの引張強度の予測値式とは、非常に良く対応しており、変態後の固溶Ｂ量と固溶Ｎｂ量とから熱延鋼板の引張強度を十分予測できることが分かる。 FIG. 4 shows the prediction formula of this tensile strength and the result of comparing the tensile strength of the nine steel types of hot-rolled steel plate with the actually measured value. In FIG. 4, the measured value of the tensile strength of the hot-rolled steel sheet on the vertical axis corresponds to the predicted value formula of the tensile strength from the amount of solute B and the amount of solute Nb of the hot-rolled steel sheet after transformation. It can be seen that the tensile strength of the hot-rolled steel sheet can be sufficiently predicted from the solute B amount and the solute Nb amount after transformation.
以上の結果は、Ｂ単独、ＮｂとＢとの同時含有の場合について示したが、Ｖ単独、Ｔｉ単独、Ｎｂ単独の各含有場合や、Ｔｉ、Ｎｂ、Ｖ、Ｂの二種以上を同時に含有する場合でも同様の結果を示す。 Although the above results showed the case of containing B alone and Nb and B at the same time, each case of containing V alone, Ti alone and Nb alone, and simultaneously containing two or more of Ti, Nb, V and B Similar results are shown even when
（実際の操業での実施）
Ｃ：０．０４％、Ｓｉ：０．２％、Ｍｎ：２．０％、Ｃｒ：０．６％、Ｔｉ：０．０１％、Ｎｂ：０．０２％、Ｂ：２０ｐｐｍ、残部Ｆｅからなる目標成分組成とし、前記した標準製造条件とした、熱延鋼板におけるＮｂ、Ｂの固溶量を基準として、本発明フィードフォワード制御を行い、溶解２０チャージ分の熱延鋼板の強度ばらつきを調査した。これら熱延鋼板のベイナイト占積率は全て８０％以上とした。
(Implementation in actual operation)
C: 0.04%, Si: 0.2%, Mn: 2.0%, Cr: 0.6%, Ti: 0.01%, Nb: 0.02%, B: 20ppm, balance Fe Based on the solid solution amount of Nb and B in the hot-rolled steel sheet as the target component composition and the above-described standard production conditions, the feedforward control of the present invention was performed, and the strength variation of the hot-rolled steel sheet for 20 charges was investigated. . The bainite space factor of these hot rolled steel sheets was 80% or more.
溶解２０チャージ分の成分組成のばらつきは、最大で、Ｃ：±０．０１５％、Ｓｉ：±０．１％、Ｍｎ：±０．１％、Ｃｒ：±０．１％、Ｔｉ：±０．０５％、Ｎｂ：±０．００５％、Ｂ：±５ｐｐｍ、であった。 Variations in the component composition for 20 dissolved charges are C: ± 0.015%, Si: ± 0.1%, Mn: ± 0.1%, Cr: ± 0.1%, Ti: ± 0. 0.05%, Nb: ± 0.005%, B: ± 5 ppm.
先ず、固溶量を制御する元素としてＮｂ、Ｂを選択し、これらのばらつきを有する出鋼時における各チャージ鋼中のＮｂ、Ｂの各実績成分値から、これを上記標準の熱延条件で熱延した（熱延後冷却した）鋼板のＮｂ、Ｂの固溶量、そして、この熱延鋼板の強度などの機械的な特性との関係を、前記図４のように予め求めた。 First, Nb and B are selected as elements for controlling the amount of solid solution. From the actual component values of Nb and B in each charged steel at the time of steelmaking having these variations, this is the above-mentioned standard hot rolling condition. The relationship between the solid solution amounts of Nb and B of the hot-rolled steel plate (cooled after hot rolling) and mechanical properties such as the strength of the hot-rolled steel plate was obtained in advance as shown in FIG.
ここで、対象鋼板は、変態前と変態後とで、選択したＮｂ、Ｂの固溶量が略同じであるので、前記標準の熱延条件で熱延した鋼板の（変態後の）Ｎｂ、Ｂの固溶量を、熱延後で組織変態前までのＮｂ、Ｂの固溶量と見なした。 Here, since the target steel plate has the same amount of Nb and B as dissolved before and after transformation, the Nb (after transformation) of the steel plate hot-rolled under the standard hot-rolling conditions. The solid solution amount of B was regarded as the solid solution amount of Nb and B after hot rolling and before structure transformation.
そして、実際の各チャージの熱延鋼板の製造に際して、熱延される鋼のＮｂ、Ｂの実績成分値（出鋼時等）から、前記予め求めた関係を用いて、前記標準の条件で熱延した際の熱延鋼板におけるＮｂ、Ｂの組織変態前までの各固溶量を求めた。更に、これら求めたＮｂ、Ｂの固溶量から、前記予め求めた関係を用いて、前記標準の条件で熱延した際の、熱延の仕上げ開始温度を考慮した、熱延鋼板の引張強度の予測式〔ＴＳ＝ｆ（固溶Ｎｂ量、固溶Ｂ量、熱延の仕上げ開始温度）〕を作成し、これを重回帰して、前記標準の条件で熱延した際の熱延鋼板の引張強度を予測した。 Then, in the actual production of hot-rolled steel sheets for each charge, heat is produced under the standard conditions using the relationship obtained in advance from the actual component values of Nb and B of the hot-rolled steel (at the time of steel production, etc.). The amount of each solid solution until the structural transformation of Nb and B in the hot-rolled steel sheet when rolled was determined. Further, from the obtained solid solution amounts of Nb and B, the tensile strength of the hot-rolled steel sheet in consideration of the finishing start temperature of hot-rolled steel when hot-rolled under the standard conditions using the previously obtained relationship. The prediction formula [TS = f (the amount of solute Nb, the amount of solute B, the finishing start temperature of hot rolling)] is prepared, and this is subjected to multiple regression and hot rolled steel sheet when hot rolled under the above standard conditions The tensile strength of was predicted.
この熱延鋼板の予測した機械的特性が、目標とする機械的特性は、引張強度で、６２０〜６６０ＭＰａの範囲内とし、この範囲内になるようであれば、前記標準の条件でそのまま熱延を行なった。一方、熱延鋼板の予測した機械的特性がこの目標とする引張強度範囲内にならないようであれば、熱延鋼板の予測した機械的特性が、目標とする機械的特性になるような組織変態前までのあるべきＮｂ、Ｂの各固溶量を求めた。更に、このＮｂ、Ｂの各固溶量を得るための、スラブ加熱温度、粗圧延開始温度、仕上圧延開始温度、仕上圧延終了温度などのあるべき熱延条件を求めた。 The predicted mechanical properties of this hot-rolled steel sheet are the target mechanical properties of tensile strength within the range of 620 to 660 MPa. Was done. On the other hand, if the predicted mechanical properties of the hot-rolled steel sheet do not fall within the target tensile strength range, the structural transformation is such that the predicted mechanical properties of the hot-rolled steel sheet become the target mechanical characteristics. The respective solid solution amounts of Nb and B that should be before were obtained. Furthermore, the desired hot rolling conditions such as the slab heating temperature, the rough rolling start temperature, the finish rolling start temperature, and the finish rolling end temperature for obtaining the respective solid solution amounts of Nb and B were determined.
このあるべき熱延条件に基づいて、実際の熱延の加熱条件、圧延条件、圧延後の冷却条件を、熱延工程のプロセスコンピューターへフィードフォワードし、先の実際の熱延条件を、あるべき熱延条件になるように選択的に制御して、熱延板を製造した。 Based on the desired hot rolling conditions, the actual hot rolling heating conditions, rolling conditions, and cooling conditions after rolling are fed forward to the process computer of the hot rolling process, and the previous actual hot rolling conditions should be A hot-rolled sheet was manufactured by selectively controlling the hot-rolled condition.
本発明例による溶解２０チャージ分の引張強度のばらつきΔＴを図５の右側に示す。一方、図４の左側が、本発明のフィードフォワードを用いずに、前記鋼の成分組成の最大ばらつきを有しながら、共通する熱延標準条件で製造した際の、同じく溶解２０チャージ分の引張強度のばらつきΔＴである。 A variation ΔT in tensile strength for 20 charges in the example of the present invention is shown on the right side of FIG. On the other hand, the left side of FIG. 4 shows the same tensile strength for 20 charges when manufactured under the common hot rolling standard conditions while having the maximum variation in the composition of the steel without using the feed forward of the present invention. It is intensity variation ΔT.
図５から明らかな通り、本発明例によれば、引張強度のばらつきΔＴは、従来の１／４程度に抑制されていることが分かる。 As is apparent from FIG. 5, according to the example of the present invention, it can be seen that the variation ΔT in the tensile strength is suppressed to about ¼ of the conventional one.
以上説明したように、本発明によれば、析出強化型の元素として、Ｔｉ、Ｎｂ、Ｖ、Ｂの一種または二種以上を含有する高強度熱延鋼板が目標とする機械的特性になるような、熱延条件になるようにフィードフォワード制御できる高強度熱延鋼板の製造方法を提供できる。このため、本発明は、引張強度などの機械的な特性がばらつきやすい高強度熱延鋼板の製造方法に適用できる。 As described above, according to the present invention, high strength hot-rolled steel sheets containing one or more of Ti, Nb, V, and B as precipitation strengthening type elements have the targeted mechanical properties. Moreover, the manufacturing method of the high intensity | strength hot-rolled steel plate which can be feedforward controlled so that it may become a hot-rolling condition can be provided. For this reason, this invention is applicable to the manufacturing method of the high strength hot-rolled steel plate in which mechanical characteristics, such as tensile strength, are easy to vary.
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| JPH044911A (en) * | 1990-04-19 | 1992-01-09 | Nippon Steel Corp | Method for predicting the quality of steel material |
| JPH05271760A (en) * | 1992-03-23 | 1993-10-19 | Nippon Steel Corp | Manufacture of high strength and high toughness thick steel plate for structural use |
| JP2005060820A (en) * | 2003-07-31 | 2005-03-10 | Jfe Steel Kk | High strength steel sheet for line pipe excellent in anti-hic (hydrogen induced cracking) characteristic and its manufacturing method |
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| JPH044911A (en) * | 1990-04-19 | 1992-01-09 | Nippon Steel Corp | Method for predicting the quality of steel material |
| JPH05271760A (en) * | 1992-03-23 | 1993-10-19 | Nippon Steel Corp | Manufacture of high strength and high toughness thick steel plate for structural use |
| JP2005060820A (en) * | 2003-07-31 | 2005-03-10 | Jfe Steel Kk | High strength steel sheet for line pipe excellent in anti-hic (hydrogen induced cracking) characteristic and its manufacturing method |
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