JP6582892B2 - Hot rolling method for steel - Google Patents
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Description
本発明は、鋼材の熱間圧延方法に関し、特に、造船、建築、自動車、産業用機械などに使用する鋼板の熱間圧延方法に関するものである。 The present invention relates to a hot rolling method for steel materials, and more particularly to a hot rolling method for steel plates used in shipbuilding, construction, automobiles, industrial machines and the like.
熱間圧延ラインでは、冷間値である製品の板厚から圧延時の温度における熱間の狙い厚を設定する。ここで、製品とは冷却後に冷間圧延を行う場合には、熱延鋼板としての厚みを指すこととする。 In the hot rolling line, the hot target thickness at the temperature at the time of rolling is set from the plate thickness of the product, which is a cold value. Here, the product refers to the thickness of the hot-rolled steel sheet when cold rolling is performed after cooling.
一般的に熱間状態での鋼材の密度は、冷間状態のそれよりも低いため、この密度変化を考慮し、熱間では製品厚よりも厚めに圧延狙い厚を設定するのが通常である。 In general, the density of steel in the hot state is lower than that in the cold state, so it is normal to set the target rolling thickness to be thicker than the product thickness in consideration of this density change. .
熱間圧延ラインにおいて、圧延前に所望の板厚を得るためにパススケジュールを決定する。例えば、特許文献１には、パススケジュール決定の際に温度を考慮することで材質を安定化させることが、また特許文献２には、パススケジュール決定の際に圧延時間を最短にすることで生産量を増大させることが示されており、また特許文献３には、パススケジュール決定の際に平坦度を最適化する手法が示されている。 In the hot rolling line, a pass schedule is determined to obtain a desired thickness before rolling. For example, in Patent Document 1, it is possible to stabilize the material by considering the temperature when determining the pass schedule, and in Patent Document 2, it is produced by minimizing the rolling time when determining the pass schedule. It is shown that the amount is increased, and Patent Document 3 discloses a technique for optimizing the flatness when determining the path schedule.
このようにパススケジュールを設定する際に、種々の要素を考慮する必要があるが、所望の冷間板厚を得るための仕上げ圧延温度における最適な熱間板厚値を算出する方法に関する研究は余りなされてこなかった。 When setting the pass schedule in this way, it is necessary to consider various factors, but research on the method of calculating the optimum hot plate thickness value at the finish rolling temperature to obtain the desired cold plate thickness is Not too much has been done.
そこで発明者らは鋭意検討した結果、冷間状態での所望の板厚（以下製品厚と呼ぶ）から熱間における圧延狙い厚を算出する際に、最終パス圧延後の背応力と合金の偏析分布に由来するバンド組織とを考慮することで、高精度に製品厚を作り込むことが可能であることを見出した。 Accordingly, as a result of intensive studies, the inventors have calculated the back stress after the final pass rolling and segregation of the alloy when calculating the hot rolling target thickness from the desired sheet thickness in the cold state (hereinafter referred to as product thickness). It was found that the product thickness can be made with high accuracy by considering the band structure derived from the distribution.
ここで、背応力とは、材料を塑性変形させた際に導入される仮想的な応力であり、移動硬化現象を考えた際の降伏曲面の中心部の移動を表す２階のテンソルである。すなわち、背応力が導入されていると、ある方向には塑性変形しやすいが、ある方向には塑性変形しにくいといった異方性を表現できるようになる。この背応力を模式的に示したものが図１である。 Here, the back stress is a virtual stress introduced when the material is plastically deformed, and is a second-order tensor that represents the movement of the center portion of the yield surface when considering the kinematic hardening phenomenon. That is, when a back stress is introduced, it is possible to express anisotropy such that plastic deformation tends to occur in a certain direction but plastic deformation hardly occurs in a certain direction. FIG. 1 schematically shows the back stress.
また、バンド組織とは、鋳造時に発生する合金成分の偏析を起因とする層状の不均質組織であって、鋳造・圧延を経た材料に特徴的に表れる。この組織は高温（１３００℃以上）で長時間（３日程度）保持することによって回避することが可能であるが、通常はコスト増などの影響を考慮し、バンド組織が維持されたまま圧延ラインに送られる。 The band structure is a layered heterogeneous structure caused by segregation of alloy components generated during casting, and is characteristically expressed in a material that has undergone casting and rolling. This structure can be avoided by holding it at a high temperature (1300 ° C or higher) for a long time (about 3 days). Usually, the rolling line is maintained while keeping the band structure in consideration of the effects of cost increase. Sent to.
本発明は、上記実情に鑑み、背応力とバンド組織が変態ひずみや熱ひずみに与える影響を考慮した鋼材の熱間圧延方法を提供する。 In view of the above circumstances, the present invention provides a method for hot rolling a steel material in consideration of the influence of back stress and band structure on transformation strain and thermal strain.
本発明者らは、最終パスの圧延狙い厚計算を行うにあたり、圧延最終パス終了までの凝固プロセスや圧延・加工プロセスが変態ひずみや熱ひずみに与える影響を検討した。
その過程で、圧延プロセスによって導入される背応力と、凝固プロセスおよび圧延プロセスで形成されるバンド組織に着目した。
その結果、背応力の影響で変態ひずみと熱ひずみが大きく変化し、また、バンド組織によっても変態ひずみが大きく変化する現象を見出した。
The inventors examined the influence of the solidification process and rolling / working process up to the end of the final rolling pass on the transformation strain and thermal strain when calculating the thickness of the final pass for rolling.
In the process, we focused on the back stress introduced by the rolling process and the band structure formed by the solidification process and rolling process.
As a result, we found a phenomenon in which transformation strain and thermal strain change greatly due to the influence of back stress, and transformation strain changes greatly depending on the band structure.
本発明は、以上のような検討結果を踏まえて、圧延最終パスにおける狙い厚を求める際に、熱間値と冷間値との換算に、背応力とバンド組織の影響を考慮した密度モデルを用いることで、製品厚の精度を大幅に向上させることを可能にしたもので、その要旨とするところは以下の通りである。 Based on the above examination results, the present invention provides a density model that takes into account the effects of back stress and band structure when converting the hot and cold values when determining the target thickness in the final rolling pass. By using it, it is possible to greatly improve the accuracy of the product thickness, and the gist thereof is as follows.
（１）鋼材の熱間圧延における最終圧延パスの圧延狙い厚設定方法において、冷間における製品厚から、鋳造の履歴と加工の履歴を考慮した変態ひずみおよび熱ひずみを用いて圧延狙い厚を設定することを特徴とする鋼材の熱間圧延方法。 (1) In the method of setting the target rolling thickness of the final rolling pass in the hot rolling of steel, the rolling target thickness is set using the transformation strain and thermal strain considering the casting history and processing history from the cold product thickness. A method for hot rolling steel.
（２）（１）に記載の鋼材の熱間圧延方法において、背応力と変態ひずみおよび熱ひずみの関係、並びに、バンド組織と変態ひずみとの関係を鋼種毎に事前に求めておき、この関係を用いて冷間の製品厚から熱間における圧延狙い厚を設定する鋼材の熱間圧延方法。 (2) In the hot rolling method for steel materials described in (1), the relationship between the back stress, transformation strain, and thermal strain, and the relationship between the band structure and transformation strain are determined in advance for each steel type. A hot rolling method for steel, in which the hot rolling target thickness is set from the cold product thickness.
本発明によれば、高精度な板厚作り込みが可能な圧延狙い厚設定を可能とした鋼材の熱間圧延方法を供することが出来る。 ADVANTAGE OF THE INVENTION According to this invention, the hot rolling method of the steel materials which enabled the thickness setting aiming at the rolling which can make a plate thickness with high precision can be provided.
最初に、本発明の鋼材の熱間圧延方法の基本的な構成について説明する。
本発明者らは、圧延ラストパスにおける狙い厚設定方法について検討を重ね、製品厚からラストパス時の温度における熱間厚みを算出する際、高精度に変態ひずみや熱ひずみを予測する必要があることに着目し、変態ひずみや熱ひずみが、圧延中の材料の鋳造条件や圧延条件によって大きく変化することを見出した。
Initially, the basic structure of the hot rolling method of the steel material of this invention is demonstrated.
The present inventors have repeatedly studied the target thickness setting method in the rolling last pass, and when calculating the hot thickness at the temperature during the last pass from the product thickness, it is necessary to predict transformation strain and thermal strain with high accuracy. Paying attention, we found that transformation strain and thermal strain change greatly depending on the casting conditions and rolling conditions of the material being rolled.
従来から予加工によって変態開始温度が変化したり、転位密度による自由エネルギー状態が変化したり、変態モードが変化したりする現象については多くの研究がなされてきたが、これが背応力と結び付けられ、さらに圧延という加工モードによっても変態ひずみや熱応力にも大きな差が生じる現象については知られてこなかった。 Many studies have been conducted on the phenomenon that the transformation start temperature changes due to pre-processing, the free energy state due to the dislocation density, and the transformation mode changes, but this has been linked to the back stress, Furthermore, it has not been known about a phenomenon in which a large difference in transformation strain or thermal stress occurs depending on the processing mode of rolling.
また、バンド組織と異方性の変態膨張に関する研究はあるものの、それが鋳造や圧延条件によってどのように変化し、最終的に変態ひずみに影響を与えるか否かの研究はなされてこなかった。そこで、発明者らは種々の鋳造条件や圧延条件および冷却条件で実験を行い、これらの影響を考察した。 Although there are studies on the band structure and anisotropic transformation expansion, no studies have been made on how this changes depending on the casting and rolling conditions and ultimately affects the transformation strain. Therefore, the inventors conducted experiments under various casting conditions, rolling conditions, and cooling conditions, and considered these effects.
まず、鋳造条件および圧延条件によってバンド組織がどのような影響を受けるかを調査する。 First, it will be investigated how the band structure is affected by casting conditions and rolling conditions.
一般に、バンド組織は鋳造時に凝固組織であるデンドライト樹枝間に生じる凝固偏析が圧延後にバンド状に残存する現象であるが、この凝固偏析は、鋳造時の冷却速度との関連性が深い。また、この凝固偏析は圧延によって変形するため、鋳造条件（特に冷却速度）と圧延条件（特に圧下率）によって整理する。 In general, the band structure is a phenomenon in which solidification segregation that occurs between dendritic dendritic branches, which is a solidified structure during casting, remains in a band shape after rolling. This solidification segregation is closely related to the cooling rate during casting. Further, since this solidification segregation is deformed by rolling, the solidification segregation is arranged according to casting conditions (particularly cooling rate) and rolling conditions (particularly rolling reduction).
ここで、凝固偏析はソーキングと呼ばれる高温での熱処理によって均一拡散させることが可能である。そこで、圧延によって得られた材料を９５０℃に加熱し、９００℃で圧下を加えた場合と、１３００℃に加熱し（ソーキング処理）、９００℃に圧下を加えた場合について以下に示す。 Here, solidification segregation can be uniformly diffused by heat treatment at high temperature called soaking. Therefore, the case where the material obtained by rolling is heated to 950 ° C. and the reduction is applied at 900 ° C., the case where the material is heated to 1300 ° C. (soaking treatment), and the reduction is applied to 900 ° C. will be described below.
図２は引張り強度が６００ＭＰａである厚鋼板を（ａ）９５０℃まで加熱し９００℃で圧延した場合と、（ｂ）１３００℃まで加熱し９００℃で圧延した場合の、板幅方向に垂直な面におけるミクロ組織を示している。組織撮影には、３％ナイタール腐食液を用いて腐食させ、２００倍の光学顕微鏡を利用した。本結果から明らかなように、９５０℃加熱の場合にはバンド組織が残存しているが、１３００℃加熱ではバンド組織が消失し、均一な組織となっていることが分かる。これは、高温下における拡散で合金元素が均一化したためである。 FIG. 2 shows a case where a thick steel plate having a tensile strength of 600 MPa is (a) heated to 950 ° C. and rolled at 900 ° C., and (b) perpendicular to the sheet width direction when heated to 1300 ° C. and rolled at 900 ° C. The microstructure in the plane is shown. For tissue imaging, a 200% optical microscope was used, which was corroded with 3% nital etchant. As is clear from this result, the band structure remains in the case of heating at 950 ° C., but the band structure disappears in the case of heating at 1300 ° C., and a uniform structure is obtained. This is because the alloy elements are made uniform by diffusion under high temperature.
次に、本鋼板を９００℃で圧延した後、冷却時の板厚方向のひずみ変化を測定した。ひずみ変化の測定には、レーザ式変位計を用いた。このひずみ測定結果と温度との関係を図３に示す。ただし、図３は全ひずみ量から熱ひずみを除去し、変態ひずみのみを示している。 Next, after rolling this steel plate at 900 ° C., the strain change in the thickness direction during cooling was measured. A laser displacement meter was used to measure the strain change. The relationship between this strain measurement result and temperature is shown in FIG. However, FIG. 3 shows only the transformation strain by removing the thermal strain from the total strain amount.
図３からは、圧下量に従って変態ひずみが増大していることが分かる。これは、圧下によって材料に背応力が導入されたために、相変態で微視的な塑性変形が生じる際、異方性をもった変形を生じるために発生する現象である。 FIG. 3 shows that the transformation strain increases according to the amount of reduction. This is a phenomenon that occurs because a deformation having anisotropy occurs when a microscopic plastic deformation occurs in the phase transformation because a back stress is introduced into the material by the reduction.
ここで、圧延によって導入された背応力は、圧延中または圧延後の回復や再結晶などの影響で時間とともに減少する。そこで、成分・温度に応じた回復や再結晶などを考慮し、背応力の変化を考慮する。この減少量の演算方法の限定はしないが、成分系や温度履歴などに応じた式を用いることが好ましい。特に、Ｍｉｃｒｏａｌｌｏｙと呼ばれる、ＮｂやＴｉなどの合金成分に受ける影響は大きいので、これらの影響を考慮することがより好ましい。また、累積圧下の効果も背応力として導入することができる。ここで、背応力は通常２階のテンソルで表わされるが、圧延による背応力の導入を近似的に圧縮成分のみを考慮することで、背応力のスカラーとして取り扱っても精度上大きな影響は無い。圧縮の背応力が進展すると、見かけの板厚方向変態ひずみは大きくなる。ここで、本材料の変態はフェライト・パーライト変態であったが、基本的にベイナイトやマルテンサイトなどの相においても背応力が変態ひずみに同様の影響を与えることが分かった。 Here, the back stress introduced by rolling decreases with time under the influence of recovery or recrystallization during or after rolling. Therefore, considering the recovery and recrystallization depending on the component and temperature, changes in back stress are considered. Although there is no limitation on the calculation method of the decrease amount, it is preferable to use an equation according to the component system, the temperature history, or the like. In particular, the influence of alloy components such as Nb and Ti called microalloy is large, and it is more preferable to consider these influences. The effect of cumulative reduction can also be introduced as back stress. Here, the back stress is usually expressed by a tensor on the second floor. However, the introduction of the back stress by rolling is only considered as a scalar of the back stress by considering only the compression component, so that there is no great influence on accuracy. As the compression back stress develops, the apparent thickness-direction transformation strain increases. Here, the transformation of this material was the ferrite-pearlite transformation, but it was found that the back stress basically has the same effect on the transformation strain in phases such as bainite and martensite.
次に、熱ひずみについて述べる。熱ひずみは温度に関して線形で与えられるとしてよいが、相変態前後で大きく変わる。成分にもよるが、鋼の場合にはオーステナイト相では２．２×１０-5［Ｋ-1］程度、フェライト・パーライト相では１．５×１０-5［Ｋ-1］程度の値を取ることが知られている。 Next, thermal strain will be described. The thermal strain may be given linearly with respect to temperature, but varies greatly before and after the phase transformation. Depending on the components, in the case of steel, the austenite phase takes a value of about 2.2 × 10 −5 [K −1 ], and the ferrite-pearlite phase takes a value of about 1.5 × 10 −5 [K −1 ]. It is known.
一方で発明者らは、変形による熱ひずみへの影響を考察した。上記と同様の試験結果から、加工後のオーステナイト域、フェライト域それぞれでの線膨張係数を表１に示す。表１の結果からオーステナイト域の線膨張係数は加工の影響を殆ど受けないが、フェライト域の線膨張係数は圧下率と共に上昇する傾向が分かった。この原因は、加工と変態による集合組織形成と関係があると考えられる。 On the other hand, the inventors considered the influence of deformation on thermal strain. From the test results similar to the above, Table 1 shows the linear expansion coefficients in the austenite region and the ferrite region after processing. From the results in Table 1, it was found that the linear expansion coefficient in the austenite region is hardly affected by the processing, but the linear expansion coefficient in the ferrite region tends to increase with the rolling reduction. This cause is considered to be related to texture formation by processing and transformation.
本発明者らは、以上のような検討過程を経て本発明に至ったものであり、以下、本発明で規定する要件や好ましい要件について順次説明する。 The inventors of the present invention have reached the present invention through the above examination process, and the requirements and preferable requirements defined in the present invention will be sequentially described below.
まず、熱間圧延時のパススケジュール設定方法について述べる。
パススケジュールは、初期厚（通常スラブ厚）から製品厚（の熱間値）までのパス数、板厚、パス間時間、圧延温度、デスケーリングの可否、幅出し圧延がある場合はターンの有無、板形状、反り等を考慮して作り上げる圧延スケジュールである。
First, a method for setting a pass schedule during hot rolling will be described.
The pass schedule includes the number of passes from the initial thickness (usually slab thickness) to the product thickness (hot value), sheet thickness, time between passes, rolling temperature, descalability, and whether or not there is turn when there is tenter rolling. This is a rolling schedule that takes into account the plate shape and warpage.
この圧延スケジュールにおいて、ラストパスでの出側板厚は、必ず製品の熱間厚みとなるべきであり、この値は製品の冷間厚みからラストパス圧延温度を元に算出されるものである。 In this rolling schedule, the exit side plate thickness in the last pass should always be the hot thickness of the product, and this value is calculated based on the last pass rolling temperature from the cold thickness of the product.
これまで、板厚の冷間値から熱間値を算出する際には、鋼種と温度の依存性のみを考慮するだけで、鋳造条件、圧延条件などの影響を考慮していなかったが、本発明によれば、バンド組織（偏析組織）や背応力によって変態ひずみや熱ひずみが異方性を持つため、上記従来の算出方法では不十分である。すなわち、ベースとなる鋼種と温度に依存する密度式または密度データに加えて、鋳造条件や圧延条件に代表されるプロセス条件に応じた異方性の影響による補正を行う必要がある。 Until now, when calculating the hot value from the cold value of the plate thickness, only the dependence on the steel type and temperature was considered, but the influence of casting conditions, rolling conditions, etc. was not considered. According to the invention, since the transformation strain and the thermal strain have anisotropy due to the band structure (segregation structure) and the back stress, the above conventional calculation method is insufficient. That is, in addition to the density formula or density data depending on the base steel type and temperature, it is necessary to perform correction by the influence of anisotropy according to the process conditions represented by casting conditions and rolling conditions.
圧延対象となる熱間材料の密度は、対象材料の温度と結晶構造などによって変化する。例えば、鋼材の場合は、熱間ではオーステナイト相であり、冷間ではフェライト・パーライトなどの相となり、結晶構造によって、また温度や合金成分によって密度が変化する。
これらの影響を考慮した密度式が提案されており（非特許文献１および非特許文献２）、鉄鋼材料についてはこれらの値を用いることが出来るが、好ましくは事前に各温度域で鋼種毎に密度を測定しておく。
The density of the hot material to be rolled varies depending on the temperature and crystal structure of the target material. For example, in the case of a steel material, it is an austenite phase in the hot state, and becomes a phase such as ferrite and pearlite in the cold state, and the density changes depending on the crystal structure, temperature, and alloy components.
Density equations that take these effects into consideration have been proposed (Non-patent Document 1 and Non-Patent Document 2), and these values can be used for steel materials, but preferably for each steel type in each temperature range in advance. Measure the density.
一方で、本発明によれば、バンド組織（偏析組織）や背応力によって変態ひずみや熱ひずみが異方性を持つため、上記の密度式または密度データでは不十分である。すなわち、ベースとなる密度式または密度データに加えて、鋳造条件や圧延条件に代表されるプロセス条件に応じた異方性の影響による補正を行う。 On the other hand, according to the present invention, since the transformation strain and thermal strain have anisotropy due to the band structure (segregation structure) and back stress, the above density formula or density data is insufficient. That is, in addition to the density formula or density data as a base, correction is performed by the influence of anisotropy according to process conditions represented by casting conditions and rolling conditions.
本補正には、鋼種毎に圧延による背応力の影響や、鋳造・圧延によるバンド組織の影響を事前に実験や数値計算手法を通じて求めておく。好ましくは合金成分の影響を考慮した統一的な補正式を作成する。 For this correction, the influence of the back stress due to rolling and the influence of the band structure due to casting / rolling are obtained in advance through experiments and numerical calculation methods for each steel type. Preferably, a unified correction formula is created in consideration of the influence of alloy components.
本密度式を用いて冷間における板厚測定データを用いて熱間値を算出することが可能となる。 It is possible to calculate the hot value using the plate thickness measurement data in the cold using this density formula.
次に、実際のパススケジュール計算時に圧延狙い厚を算出する方法について、厚鋼板の熱間圧延ラインを例に述べる。 Next, a method for calculating the rolling target thickness at the time of actual pass schedule calculation will be described taking a hot rolling line for thick steel plates as an example.
圧延パススケジュールは、上記で述べた通り、種々の条件を元に算出されるものである。ここで、ラストパスの狙い厚は製品厚から冷間値を熱間値へ補正することで得られる。 As described above, the rolling pass schedule is calculated based on various conditions. Here, the target thickness of the last path is obtained by correcting the cold value from the product thickness to the hot value.
このとき、プロセスコンピュータ（レベル２）において、次圧延材の鋼種や製品厚、圧延指定温度等を上位のビジネスコンピュータ（レベル３）から入力する。次に、製品厚から圧延ラストパスの出側厚（圧延狙い厚）を求める方法について述べる。 At this time, in the process computer (level 2), the steel type, product thickness, designated rolling temperature, etc. of the next rolled material are input from the upper business computer (level 3). Next, a method for obtaining the exit side thickness (rolling target thickness) of the rolling last pass from the product thickness will be described.
ラストパス出側での背応力は、加熱炉出側の状態を０とし、その後の圧延による背応力進展、回復や再結晶による背応力減少を逐次演算する。また、バンド組織予測は連続鋳造時の冷却条件と成分系および加工履歴から計算する。ここで、背応力およびバンド組織予測方法について限定はしないが、例えば背応力の発展式として以下の式を用いることができる。 The back stress at the exit side of the last path is calculated by sequentially calculating the back stress progression by rolling and the reduction of back stress by recovery and recrystallization, with the state at the exit side of the heating furnace being zero. The band structure prediction is calculated from the cooling conditions, the component system and the machining history during continuous casting. Here, although the back stress and the band structure prediction method are not limited, for example, the following formula can be used as a development formula of the back stress.
ここで、通常パススケジュール計算は仕上げ圧延開始時に行われる。一方で、パススケジュール計算の後、仕上げ圧延が開始されると、温度や板厚の値において、実績とスケジュール間の誤差が発生するため、適応制御と呼ばれる各パスにおける修正計算においても、上記の背応力予測およびバンド組織予測を行うことが望ましい。 Here, the normal pass schedule calculation is performed at the start of finish rolling. On the other hand, when finishing rolling is started after the pass schedule calculation, an error between the actual results and the schedule occurs in the values of temperature and sheet thickness. Therefore, even in the correction calculation in each pass called adaptive control, the above-mentioned It is desirable to perform back stress prediction and band structure prediction.
次に変態開始温度について述べる。
変態開始温度は背応力の方向によらず、加工ひずみの導入に応じて高温側に推移する。これは、加工による転位密度の上昇が自由エネルギーの上昇をもたらし、変態を促進させるためである。
Next, the transformation start temperature will be described.
The transformation start temperature does not depend on the direction of the back stress and changes to the high temperature side according to the introduction of processing strain. This is because an increase in dislocation density due to processing brings about an increase in free energy and promotes transformation.
加工による変態開始温度の上昇も、図３に示す実験結果から判断することが可能である。ここで、変態開始温度の上昇は転位密度の上昇が起因となっているため、回復や再結晶の影響で転位密度が低下する影響を考慮することが好ましい。 The rise in transformation start temperature due to processing can also be determined from the experimental results shown in FIG. Here, since the increase in the transformation start temperature is caused by the increase in the dislocation density, it is preferable to consider the influence of the decrease in the dislocation density due to the effects of recovery and recrystallization.
次に熱ひずみについて述べる。
加工履歴によって熱ひずみも影響を受けるため、熱ひずみへの影響も事前に把握しておく必要がある。前掲の表１に熱ひずみの値（線膨張係数）の変化を圧下率毎に整理したものを示す。表１からは、加工(圧下)によってフェライト域の線膨張係数が大きくなっていることが分かる。
Next, thermal strain will be described.
Since the thermal strain is also affected by the machining history, it is necessary to grasp the influence on the thermal strain in advance. Table 1 above shows the changes in thermal strain values (linear expansion coefficient) arranged for each rolling reduction. From Table 1, it can be seen that the linear expansion coefficient in the ferrite region is increased by processing (rolling).
次に、本発明の実施例について説明するが、実施例での条件は、本発明の実施可能性及び効果を確認するために採用した一条件例であり、本発明は、この一条件例に限定されるものではない。本発明は、本発明の要旨を逸脱せず、本発明の目的を達成する限りにおいて、種々の条件を採用し得るものである。 Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.
（実施例）
質量％で、Ｃ：０．１％、Ｍｎ：１．２％、Ｓｉ：１．０％、Ａｌ：０．０３％、Ｎ：０．００４％、Ｐ：０．００１％、Ｓ：０．００１％、Ｔｉ：０．０％、Ｎｂ：０．０％、Ｃｒ：０．０％、Ｃｕ：０．１％、Ｎｉ：０．０％、Ｂ：０．０％、Ｍｏ：０．０％、Ｗ：０．０％、及び、Ｖ：０．０％を含有する連続鋳造機で鋳造した厚み２５０ｍｍの鋼片を複数枚用意した。
(Example)
By mass%, C: 0.1%, Mn: 1.2%, Si: 1.0%, Al: 0.03%, N: 0.004%, P: 0.001%, S: 0.00. 001%, Ti: 0.0%, Nb: 0.0%, Cr: 0.0%, Cu: 0.1%, Ni: 0.0%, B: 0.0%, Mo: 0.0 A plurality of steel pieces having a thickness of 250 mm casted by a continuous casting machine containing%, W: 0.0%, and V: 0.0% were prepared.
この鋼片の一部を板厚１０ｍｍとなるまで圧延し、常温まで自然放冷して冷却後にミクロ組織撮影用のサンプルを切り出し、３％ナイタール液で腐食させ、２００倍の光学顕微鏡撮影を行い、バンド組織を観察した（図２）。この結果から、バンド幅は約４０〜５０μｍ程度であり、ほぼ式(3)を満たすことが分かる。 A part of this steel slab is rolled to a plate thickness of 10 mm, allowed to cool to room temperature, cooled, and a sample for microstructural imaging is cut out, corroded with 3% nital solution, and 200 times optical microscope imaging is performed. The band tissue was observed (FIG. 2). From this result, it can be seen that the bandwidth is about 40 to 50 μm and substantially satisfies the expression (3).
次にこの鋼片から、圧縮試験片サンプルを切り出した。この圧縮試験片を誘導加熱装置を用いて９５０℃まで１０℃／sで加熱し、５分保持後、空冷を行って、長さ測定結果から変態開始温度を測定する。このとき、変態開始温度は約７８０℃であった。 Next, a compression test piece sample was cut out from the steel piece. This compression test piece is heated to 950 ° C. at 10 ° C./s using an induction heating device, held for 5 minutes, air-cooled, and the transformation start temperature is measured from the length measurement result. At this time, the transformation start temperature was about 780 ° C.
同様に切り出した圧縮試験片を、９５０℃まで１０℃／sで加熱し、５分保持後、７８０℃となる５ｓ前に１０％、２０％および３０％の圧縮ひずみを０．２ｓで加え、その後０．２ｓで除荷し、無負荷状態での変態ひずみ量を測定した（図３（ａ））。 Similarly, the cut compression test piece was heated to 950 ° C. at 10 ° C./s, held for 5 minutes, and then 10%, 20% and 30% compression strains were added at 0.2 s before 5 s to 780 ° C., Thereafter, the load was unloaded at 0.2 s, and the amount of transformation strain in an unloaded state was measured (FIG. 3 (a)).
次にこの鋼片から、上記同様圧縮試験片サンプルを切り出した。この圧縮試験片を誘導加熱装置を用いて１３００℃まで１０℃／sで加熱し、５分保持後、空冷を行って、長さ測定結果から変態開始温度を測定する。このとき、変態開始温度は９５０℃加熱時と同様に約７８０℃であった。 Next, a sample of a compression test piece was cut out from the steel piece as described above. The compression test piece is heated to 1300 ° C. at 10 ° C./s using an induction heating device, held for 5 minutes, air-cooled, and the transformation start temperature is measured from the length measurement result. At this time, the transformation start temperature was about 780 ° C. as in the case of heating at 950 ° C.
同様に切り出した圧縮試験片を、１３００℃まで１０℃／sで加熱し、５分保持後、７８０℃となる５ｓ前に１０％、２０％および３０％の圧縮ひずみを０．２ｓで加え、その後０．２ｓで除荷し、無負荷状態での変態ひずみ量を測定した（図３（ｂ））。 Similarly, the cut compression test piece was heated to 1300 ° C. at 10 ° C./s, held for 5 minutes, and then 10%, 20% and 30% compression strains were added in 0.2 s before 5 s to be 780 ° C., Thereafter, the load was unloaded at 0.2 s, and the transformation strain amount in an unloaded state was measured (FIG. 3B).
以上の結果から、圧下による変態開始温度への影響は以下のように得られる。 From the above results, the influence on the transformation start temperature due to the reduction is obtained as follows.
次に、これらの鋼片を加熱炉で１２００℃に加熱後、熱間圧延機において９ｍｍとなるまで圧延し、冷却床で９００℃から常温まで冷却した。 Next, these steel pieces were heated to 1200 ° C. in a heating furnace, then rolled to 9 mm in a hot rolling mill, and cooled from 900 ° C. to room temperature in a cooling bed.
常温まで冷却された板は、検査ラインに設置されているレーザ板厚計を用いて冷間での板厚を測定した。レーザ板厚計はＴＯＳＨＩＢＡ製のＴＯＳＧＡＧＥ−ＬＤを用いた。 The plate cooled to room temperature was measured for cold plate thickness using a laser plate thickness meter installed in the inspection line. The laser thickness gauge used was TOSHIBA-TOSAGE-LD.
従来の方法による変態ひずみおよび熱ひずみと、本発明によるそれらとの比較を図４に示す。 FIG. 4 shows a comparison between transformation strain and thermal strain according to the conventional method and those according to the present invention.
以上で得られたひずみデータ（変態ひずみおよび熱ひずみ）を使用し、同鋼種を４０本圧延し、板厚の作り込み精度比較を行った。この結果を図５に示す。本結果より、板厚の誤差平均値が−０．０９ｍｍから０．００２ｍｍに改善、板厚の誤差率の標準偏差が０．００８から０．００１２に改善した。 Using the strain data (transformation strain and thermal strain) obtained above, 40 steel grades were rolled, and the thickness accuracy was compared. The result is shown in FIG. From this result, the plate thickness error average value was improved from -0.09 mm to 0.002 mm, and the plate thickness error rate standard deviation was improved from 0.008 to 0.0012.
本発明によれば、鋼材の熱間圧延方法において、製品の板厚作り込み精度を向上させる圧延狙い厚設定方法を提供し、製品の品質の最も重要な一つである厚みの精度が向上する。よって、本発明は、産業上の利用可能性が高いものである。 According to the present invention, in the hot rolling method for steel materials, a thickness setting method for rolling aiming to improve the thickness accuracy of the product is provided, and the thickness accuracy, which is one of the most important product quality, is improved. . Therefore, the present invention has high industrial applicability.
Claims (2)
下記式（１）で表される、最終パス圧延後の背応力が変態ひずみに与える影響及びバンド組織が変態ひずみに与える影響ε ｔ 、及び下記式（２）で表される、最終パス圧延後の背応力が熱ひずみに与える影響ε th を、鋼種毎に事前に求めておき、
前記ε ｔ 及びε th の影響を考慮して、鋼材の熱間圧延における最終圧延パス後の板厚の冷間値から、鋼材の熱間圧延における最終圧延パス後の板厚の熱間値を設定することを特徴とする鋼材の熱間圧延方法。
Ｔは温度、Ｔ 0 は基準となる温度、
||ａ ij ||は、
Ｈ’は変態温度における材料の加工硬化係数（ＭＰａ）、
λは、鋼材の熱間圧延における最終圧延パス後の板厚の熱間値をＨ、鋼材の熱間圧延における最終圧延パス後の板厚の冷間値をｈとしたとき、λ＝８００×ｈ／Ｈ（μｍ）で表されるバンド幅である。 In the thickness setting method for rolling aim of the final rolling pass in hot rolling of steel materials,
The effect of back stress after the final pass rolling on the transformation strain and the effect of the band structure on the transformation strain ε t represented by the following formula (1), and after the final pass rolling represented by the following formula (2) The effect of the back stress on the thermal strain ε th is obtained in advance for each steel type,
In consideration of the influence of ε t and ε th , the hot value of the plate thickness after the final rolling pass in the hot rolling of the steel material is determined from the cold value of the plate thickness after the final rolling pass in the hot rolling of the steel product. A hot rolling method for steel, characterized by comprising:
T is the temperature, T 0 is the reference temperature,
|| a ij ||
H ′ is the work hardening coefficient (MPa) of the material at the transformation temperature,
λ is λ = 800 ×, where H is the hot value of the plate thickness after the final rolling pass in hot rolling of steel, and h is the cold value of the plate thickness after the final rolling pass in hot rolling of steel. It is a bandwidth represented by h / H (μm).
n、m、D１及びD２は材料定数、ｔは経過時間、Ｒは気体定数、Ｔは絶対温度である。n, m, D1 and D2 are material constants, t is an elapsed time, R is a gas constant, and T is an absolute temperature.
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