JP2010229512A - Method for producing ferrite-pearlite type rolled non-heat treated steel material - Google Patents
Method for producing ferrite-pearlite type rolled non-heat treated steel material Download PDFInfo
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Abstract
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本発明は、圧延後に焼入れ焼戻し等の熱処理を行うことなしに、高い強度及び靭性を得ることができる、直接切削用のフェライト・パーライト型圧延非調質鋼材の製造方法に関する。 The present invention relates to a method for producing a ferritic pearlite rolled non-heat treated steel material for direct cutting, which can obtain high strength and toughness without performing heat treatment such as quenching and tempering after rolling.
従来、建築機械、産業機械および船舶の分野において、高強度かつ高靭性を要求される部品には、S45Cに代表される機械構造用炭素鋼材や、これにCr、Moを含有した機械構造用低合金鋼の焼入れ焼戻し処理材が用いられてきた。ところが、近年の省コスト化或いは、CO2排出量削減の観点から、焼入れ焼戻し処理を省略可能な非調質鋼の開発が積極的に進められてきた。 Conventionally, in the fields of construction machinery, industrial machinery and ships, parts that require high strength and high toughness include carbon steel materials for mechanical structures represented by S45C, and low mechanical structural materials containing Cr and Mo. Alloy steel quenching and tempering treatment materials have been used. However, the development of non-tempered steel that can omit the quenching and tempering treatment has been actively promoted from the viewpoint of cost reduction or CO 2 emission reduction in recent years.
代表的な非調質鋼としては、フェライト・パーライト型非調質鋼がある（例えば、非特許文献１参照）。これは、圧延後の冷却過程において、フェライト・パーライト変態とほぼ同時に析出する、Ｖ炭化物によりフェライトを強化して焼入れ焼戻し材並みの強度を得ているが、焼入れ焼戻し材に比べて靭性が低いという問題があった。 As a typical non-heat treated steel, there is a ferrite / pearlite non-heat treated steel (for example, see Non-Patent Document 1). This is because, in the cooling process after rolling, the ferrite and pearlite transformation precipitates almost simultaneously, strengthening the ferrite with V carbide to obtain the same strength as the quenched and tempered material, but the toughness is lower than the quenched and tempered material There was a problem.
そこで、フェライト・パーライト型非調質鋼材の勒性を改善する試みがなされた。例えば、勒性を改善する方法として、特許文献１には、オーステナイト再結晶域で圧延前の粗大なオーステナイト結晶粒に再結晶を起こさせる圧延（第１圧延）と、オーステナイト未再結晶域でオーステナイトに歪みを付与（第２圧延）し、その歪みによって結晶粒内での初析フェライトの発生を促して微細なフェライト・パーライト組織を得ることによって、低温靭性を改善している。 Therefore, an attempt was made to improve the fertility of the ferrite-pearlite type non-heat treated steel. For example, as a method for improving the fertility, Patent Document 1 discloses rolling (first rolling) in which coarse austenite crystal grains before rolling are recrystallized in the austenite recrystallization region, and austenite in the austenite non-recrystallized region. The low temperature toughness is improved by imparting a strain to the steel (second rolling) and promoting the generation of pro-eutectoid ferrite in the crystal grains by the strain to obtain a fine ferrite / pearlite structure.
しかし、特許文献１に記載の技術では、低温靭性は改善するものの、この靭性を改善するために実施する圧延により強度が低下するため、所期した量以上のＶを添加する必要があり、低合金化によるコスト削減を求める産業界の要求に必ずしも応えるものではなかった。 However, in the technique described in Patent Document 1, although the low-temperature toughness is improved, the strength is reduced by rolling performed to improve the toughness, so it is necessary to add more V than the expected amount. It did not always meet the demands of the industry for cost reduction by alloying.
そこで、本発明は、鋼材の合金成分を高めることなく、高い強度及び靭性を非調質の下で実現する方途について提供することを目的とする。 Then, an object of this invention is to provide the method of implement | achieving high intensity | strength and toughness under non-tempering, without raising the alloy component of steel materials.
さて、Ｖ析出型フェライト・パーライト非調質鋼の強度は、組織のフェライト分率、Ｖによるフェライトの析出強化量及びパーライトの強度、によって決まる。Ｖによる析出強化量を最大限にするためには、オーステナイト域でのＶの析出を極力低減し、フェライト・パーライト変態時に析出するＶ量を多くする必要がある。そのためには、オーステナイト域の圧延条件に配慮する必要がある。また、靭性を向上させるためには、一般的に細粒化やフェライト分率の向上が有効とされているが、これらの対策は同時に強度低下を招くことから、フェライト・パーライト変態に影響を及ぼす、圧延・冷却条件に配慮する必要がある。このように靭性と強度を両立するためには、析出制御及び組織制御の総合的な観点から圧延条件を検討する必要がある、との結論に到り、本発明を完成するに至った。 Now, the strength of the V precipitation type ferrite-pearlite non-heat treated steel is determined by the ferrite fraction of the structure, the precipitation strengthening amount of ferrite due to V, and the strength of pearlite. In order to maximize the precipitation strengthening amount due to V, it is necessary to reduce the precipitation of V in the austenite region as much as possible and to increase the amount of V precipitated during the ferrite-pearlite transformation. For that purpose, it is necessary to consider the rolling conditions in the austenite region. In order to improve toughness, it is generally effective to refine the grain size and increase the ferrite fraction. However, these measures simultaneously lead to a decrease in strength, which affects the ferrite-pearlite transformation. It is necessary to consider rolling and cooling conditions. Thus, in order to achieve both toughness and strength, it was concluded that it was necessary to examine the rolling conditions from the comprehensive viewpoints of precipitation control and structure control, and the present invention was completed.
本発明は、以上の知見に基いてなされたものであって、その要旨は次の通り
１．Ｃ：0.30〜0.55質量％、
Si：0.01〜1.2質量％、
Mn：1.8超〜2.5質量％、
Ｐ：0.040質量％以下、
Ｓ：0.040質量％以下、
Al：0.005〜0.06質量％及び
Ｖ：0.05〜0.20質量％
を含有し、残部Feおよび不可避的不純物からなる鋼素材に熱間圧延を施すに当り、下記（１）式で求められるＴ１℃以下の温度域での粗圧延の減面率を25％以下とし、その後下記（２）式で求められる（Ｔ２−200）〜Ｔ２℃の温度域で減面率25％以上の仕上げ圧延を施した後、550℃まで５℃／s未満の冷却速度で冷却することを特徴とするフェライト・パーライト型圧延非調質鋼材の製造方法。
記
Ｔ１（℃）＝−5440／（log[V] [C]−3.314）−173 …（1）
Ｔ２（℃）＝910−203[C]＋44.7[Si]−30[Mn]−20[Cu]−15.2[Ni]−11[Cr]＋31.5[Mo]＋104[V]+400[Ti]＋460[Al]＋700[P] …（2）
ここで、上の式中の［］表示は、その括弧内の成分の含有率（質量％）を意味している。
The present invention has been made on the basis of the above knowledge, and the gist thereof is as follows. C: 0.30 to 0.55 mass%,
Si: 0.01 to 1.2% by mass,
Mn: more than 1.8 to 2.5% by mass,
P: 0.040 mass% or less,
S: 0.040 mass% or less,
Al: 0.005 to 0.06 mass% and V: 0.05 to 0.20 mass%
When hot rolling a steel material containing the balance Fe and inevitable impurities, the area reduction rate of rough rolling in the temperature range of T1 ° C. or less determined by the following formula (1) is 25% or less. Then, after performing finish rolling with a reduction in area of 25% or more in the temperature range of (T2-200) to T2 ° C. obtained by the following equation (2), cooling to 550 ° C. at a cooling rate of less than 5 ° C./s. A method for producing a ferrite-pearlite-type rolled non-heat treated steel characterized by the above.
T1 (° C.) = − 5440 / (log [V] [C] −3.314) −173 (1)
T2 (° C.) = 910−203 [C] +44.7 [Si] −30 [Mn] −20 [Cu] −15.2 [Ni] −11 [Cr] +31.5 [Mo] +104 [V] +400 [ Ti] +460 [Al] +700 [P] (2)
Here, [] in the above formula means the content (mass%) of the component in the parentheses.
２．前記1において、前記鋼素材が、さらに
Cr：1.0質量％以下、
Cu：1.0質量％以下、
Ni：1.0質量％以下及び
Mo：1.0質量％以下
から選ばれる１種または２種以上を含有するフェライト・パーライト型圧延非調質鋼材の製造方法。
2. In 1, the steel material is further
Cr: 1.0% by mass or less,
Cu: 1.0 mass% or less,
Ni: 1.0% by mass or less
Mo: A method for producing a ferrite-pearlite rolled non-tempered steel material containing one or more selected from 1.0% by mass or less.
３．前記１または２において、前記鋼素材が、さらに
Ti：0.15質量％以下及び
Nb：0.15質量％以下
のいずれか１種または２種を含有するフェライト・パーライト型圧延非調質鋼材の製造方法。
3. In 1 or 2, the steel material is further
Ti: 0.15 mass% or less and
Nb: A method for producing a ferrite-pearlite rolled non-heat treated steel material containing any one or two of 0.15% by mass or less.
４．前記１、２または３において、前記鋼素材が、さらに
Pb：0.01〜0.40質量％、
Bi：0.01〜0.40質量％及び
Ca：0.0005〜0.0100質量％
から選ばれる１種または２種以上を含有するフェライト・パーライト型圧延非調質鋼材の製造方法。
4). In the above 1, 2 or 3, the steel material is further
Pb: 0.01-0.40 mass%,
Bi: 0.01-0.40 mass% and
Ca: 0.0005 to 0.0100 mass%
A method for producing a ferritic / pearlite-type rolled non-heat treated steel material containing one or more selected from:
本発明の製造方法を用いれば、高い強度及び靭性を有する圧延非調質鋼材を、該鋼材の合金成分を高めることなく、製造することが可能であり、本発明による産業上の効果は極めて顕著である。 By using the production method of the present invention, it is possible to produce a rolled non-tempered steel material having high strength and toughness without increasing the alloy components of the steel material, and the industrial effects of the present invention are extremely remarkable. It is.
以下、本発明を具体的に説明する。
まず、本発明における鋼素材について、その成分組成を詳しく説明する。
［成分組成］
Ｃ：0.30〜0.55質量％
Ｃは、強度を得るために必要な元素であり、そのためには0.30質量％以上は必要である。一方、多量に含有させると靭性が低下するため、上限を0.55質量％とした。好ましくは、0.35〜0.50質量％である。
The present invention will be specifically described below.
First, the component composition of the steel material in the present invention will be described in detail.
[Ingredient composition]
C: 0.30 to 0.55 mass%
C is an element necessary for obtaining strength, and for that purpose, 0.30% by mass or more is necessary. On the other hand, since the toughness decreases when a large amount is contained, the upper limit is set to 0.55% by mass. Preferably, it is 0.35-0.50 mass%.
Si：0.01〜1.2質量％
Siは、製鋼プロセスにおいて、脱酸剤および強度を調整するのに有効な元素である。これらの効果を得るには、0.01質量％以上が必要であり、一方1.2質量％を超えると靭性が損なわれるため、0.01〜1.2質量％の範囲とした。好ましくは、0.1〜1.0質量％である。
Si: 0.01-1.2% by mass
Si is an effective element for adjusting the deoxidizer and strength in the steelmaking process. In order to obtain these effects, 0.01% by mass or more is necessary. On the other hand, if it exceeds 1.2% by mass, the toughness is impaired. Preferably, it is 0.1-1.0 mass%.
Mn：1.8超〜2.5質量％
Mnは、パーライトラメラ間隔を制御し、強度と靭性を調整するために重要な元素であるが、その効果を得るためには1.8質量％を超えて含有させる必要があり、一方2.5質量％を超えると靭性が損なわれるため、1.8超〜2.5質量％の範囲とした。好ましくは、1.85〜2.2質量％である。
Mn: more than 1.8 to 2.5% by mass
Mn is an important element for controlling the pearlite lamella spacing and adjusting the strength and toughness, but in order to obtain its effect, it must be contained in excess of 1.8% by mass, whereas it exceeds 2.5% by mass. And the toughness is impaired, so the range is more than 1.8 to 2.5% by mass. Preferably, it is 1.85 to 2.2 mass%.
Ｐ：0.040質量％以下
Ｐは、勒性を劣化させる元素であり、極力低減することが好ましいが、0.040質量％までは許容される。
P: 0.040% by mass or less P is an element that deteriorates the inertia and is preferably reduced as much as possible, but is allowed up to 0.040% by mass.
Ｓ：0.040質量％以下
Ｓは、Ｐとともに靭性を劣化させる元素であり、やはり極力低減することが好ましいが、0.040質量％までは許容される。
S: 0.040% by mass or less S is an element that deteriorates toughness together with P, and is preferably reduced as much as possible, but is allowed to 0.040% by mass.
Al：0.005〜0.06質量％
Alは、脱酸剤として添加する元素であり、0.005質量％未満ではその効果が小さく、一方0.06質量％を超えて添加すると、靭性に影響を及ぼすためAlは0.005〜0.06質量％の範囲とした。好ましくは、0.01〜0.05質量％である。
Al: 0.005-0.06 mass%
Al is an element to be added as a deoxidizing agent, and its effect is small when it is less than 0.005% by mass. On the other hand, if it exceeds 0.06% by mass, it affects toughness, so Al is in the range of 0.005 to 0.06% by mass. . Preferably, it is 0.01-0.05 mass%.
Ｖ：0.05〜0.20質量％
Ｖは、Ｃと析出物を形成して強度の向上に寄与する元素である。その効果を得るためには0.05質量％以上が必要であるが、0.20質量％を超えて添加しても効果が飽和するため、0.05〜0.20質量％の範囲とした。好ましくは、0.06〜0.18質量％である。
V: 0.05-0.20 mass%
V is an element that forms precipitates with C and contributes to improvement in strength. In order to acquire the effect, 0.05 mass% or more is required, but even if it added exceeding 0.20 mass%, since an effect will be saturated, it was set as the range of 0.05-0.20 mass%. Preferably, it is 0.06-0.18 mass%.
本発明では、さらに以下の元素の１種または２種以上を添加することが可能である。
Cr：1.0質量％以下、Cu：1.0質量％以下、Ni：1.0質量％以下、Mo：1.0質量％以下
Cr、Cu、Ni及びMoは、固溶強化元素として強度調整に有効な元素である。必要に応じて、上記４種のいずれか１種または２種以上を、好ましくは0.2質量％以上で添加することが可能である。一方、いずれの元素も、1.0質量％を超えると靭性が低下するため、1.0質量％以下とすることが好ましい。
In the present invention, one or more of the following elements can be added.
Cr: 1.0 mass% or less, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Mo: 1.0 mass% or less
Cr, Cu, Ni and Mo are effective elements for strength adjustment as solid solution strengthening elements. As needed, it is possible to add any one or two or more of the above four types, preferably 0.2% by mass or more. On the other hand, if any element exceeds 1.0% by mass, the toughness decreases, and therefore, it is preferably 1.0% by mass or less.
また、本発明では、さらに以下の元素の１種または２種を添加することが可能である。
Ti：0.15質量％以下
Tiは、鋼中のＮをTiNとして固定し、結晶粒の粗大化を防止する効果を有するとともに、Ｖと同様にＣと析出物を形成するため、強度を得るのに有用な元素であるが、0.15質量％を超えて添加すると靭性が低下するため、0.15質量％以下とした。好ましくは、0.05〜0.12質量％である。
In the present invention, it is possible to further add one or two of the following elements.
Ti: 0.15 mass% or less
Ti is an element useful for obtaining strength because it fixes N in steel as TiN and has the effect of preventing coarsening of crystal grains and forms precipitates with C in the same manner as V. When added in excess of 0.15 mass%, the toughness decreases, so the content was made 0.15 mass% or less. Preferably, it is 0.05-0.12 mass%.
Nb：0.15質量％以下
Nbは、炭窒化物を形成することによって結晶粒の粗大化を防止する効果を有するとともに、ＶやTiと同様にＣと析出物を形成し、強度を得るために有用な元素であるが、0.15質量％を超えて添加すると靭性が低下するため、0.15質量％以下とした。好ましくは、0.05〜0.12質量％である。
Nb: 0.15 mass% or less
Nb has the effect of preventing coarsening of crystal grains by forming carbonitrides, and is a useful element for obtaining strength by forming precipitates with C in the same manner as V and Ti. If added in excess of 0.15% by mass, the toughness decreases, so the content was made 0.15% by mass or less. Preferably, it is 0.05-0.12 mass%.
さらに、本発明では、被削性を向上させるために、以下の元素を添加することが可能である。
Pb：0.01〜0.40質量％
Pbは、被削性を向上させる元素であり、その効果を得るためには、0.01質量％以上で添加することが好ましい。一方、0.40質量％を超えて添加すると、靭性を低下させるため、0.01〜0.40質量％の範囲とした。
Furthermore, in the present invention, the following elements can be added to improve machinability.
Pb: 0.01-0.40 mass%
Pb is an element that improves machinability. In order to obtain the effect, Pb is preferably added in an amount of 0.01% by mass or more. On the other hand, if added over 0.40% by mass, the toughness is lowered, so the range was 0.01 to 0.40% by mass.
Bi：0.01〜0.40質量％
Biは、被削性を向上させる元素である。その効果を得るためには、0.01質量％以上で添加させることが好ましい。一方、0.40質量％を超えて添加すると、靭性を著しく低下させるため、0.01〜0.40質量％の範囲とする。
Bi: 0.01-0.40 mass%
Bi is an element that improves machinability. In order to acquire the effect, it is preferable to add at 0.01 mass% or more. On the other hand, if added over 0.40% by mass, the toughness is remarkably reduced, so the range is 0.01 to 0.40% by mass.
Ca：0.0005〜0.0100質量％
Caは、被削性を向上させる元素である。その効果を得るためには、0.005質量％以上で添加させることが好ましい。一方、0.0100質量％を超えて添加しても効果が飽和するため、0.0005〜0.0100質量％の範囲とする。
Ca: 0.0005 to 0.0100 mass%
Ca is an element that improves machinability. In order to acquire the effect, it is preferable to add at 0.005 mass% or more. On the other hand, even if added over 0.0100 mass%, the effect is saturated, so the range is 0.0005 to 0.0100 mass%.
以上の成分組成を有する鋼は、例えばスラブや、ブルーム、ビレット等の鋼素材に成形され、その後、熱間圧延に供される。すなわち、鋼素材を、上記した（１）式で求められるＴ１℃以下の温度域での粗圧延の減面率を25％以下とし、その後上記した（２）式で求められる（Ｔ２−200）〜Ｔ２℃の温度域で減面率25％以上の仕上げ圧延を施した後、550℃まで５℃／s未満の冷却速度で冷却する。
次に、各工程の限定理由を詳しく述べる。
The steel having the above component composition is formed into a steel material such as slab, bloom, billet, etc., and then subjected to hot rolling. That is, the steel material is determined by the above-described equation (2) (T2-200), with the area reduction rate of rough rolling in the temperature range of T1 ° C. or less determined by the above equation (1) being 25% or less. After finishing rolling with a reduction in area of 25% or more in a temperature range of ˜T2 ° C., cooling to 550 ° C. at a cooling rate of less than 5 ° C./s.
Next, the reasons for limiting each process will be described in detail.
［Ｔ１℃以下温度域での粗圧延減面率：25％以下］
本発明が対象とするフェライト・パーライト型非調質鋼において、高い強度及び靭性を両立させるには、オーステナイト再結晶域圧延にて結晶粒を微細化することが重要であるが、Ｖの析出を考慮して最適圧延条件を検討する必要がある。ここに、Ｖの固溶温度は溶解度積から推定することが可能であり、この温度以上で圧延すれば、理論上Ｖは析出しない。しかし、実際の熱間圧延では、熱間加工歪みによる析出の促進によって、上記推定温度よりも高い温度でＶ炭化物が析出する。これを回避するためには、次式（１）で得られる温度Ｔ１℃以下の温度域での粗圧延減面率を25％以下に規制する必要がある。
Ｔ１（℃）＝−5440／（log[V] [C]−3.314）−173 …（１）
[Rough rolling reduction in T1 ° C or less temperature range: 25% or less]
In the ferrite-pearlite type non-heat treated steel targeted by the present invention, in order to achieve both high strength and toughness, it is important to refine crystal grains by austenite recrystallization zone rolling. It is necessary to consider the optimum rolling conditions in consideration. Here, the solid solution temperature of V can be estimated from the solubility product, and if it is rolled at a temperature higher than this temperature, V does not precipitate theoretically. However, in actual hot rolling, V carbide precipitates at a temperature higher than the estimated temperature by promoting precipitation due to hot working strain. In order to avoid this, it is necessary to regulate the rough rolling area reduction rate to 25% or less in the temperature range of temperature T1 ° C. or less obtained by the following equation (1).
T1 (° C.) = − 5440 / (log [V] [C] −3.314) −173 (1)
上記（１）式で求まるＴ１℃を超える温度では、温度が十分に高いため、圧延歪みの影響を受けてもＶ炭化物の析出が促進されることはない。一方、Ｔ１℃以下では、圧下量が減面率で25％を超えると、圧延歪みによってＶ炭化物の析出が促進されるため、析出強化に有効に作用するＶ量、すなわちフェライト・パーライト変態時に析出するＶ量を確保するためには、Ｔ１℃以下の粗圧延時の減面率を25％以下に制限する必要がある。
なお、Ｔ１℃以下での粗圧延は複数パスで行ってもよいが、ここでいう減面率は、Ｔ１℃以下で行う粗圧延の開始前の断面率Ｓ０と粗圧延後の断面積Ｓ１とから、
（Ｓ０−Ｓ１）／Ｓ０×100（％）
で求めることができる。
Since the temperature is sufficiently high at a temperature exceeding T1 ° C. obtained by the above equation (1), precipitation of V carbide is not promoted even under the influence of rolling distortion. On the other hand, at T1 ° C. or lower, when the reduction amount exceeds 25% in terms of the area reduction rate, precipitation of V carbide is promoted by rolling strain, so that the amount of V that effectively acts on precipitation strengthening, that is, precipitation during ferrite-pearlite transformation. In order to ensure the amount of V to perform, it is necessary to limit the area reduction rate at the time of rough rolling below T1 degreeC to 25% or less.
The rough rolling at T1 ° C. or lower may be performed in a plurality of passes, but the area reduction ratio here is the cross-sectional area S 0 before the start of rough rolling performed at T1 ° C. or lower and the cross-sectional area S after rough rolling. From 1 and
(S 0 −S 1 ) / S 0 × 100 (%)
Can be obtained.
［（Ｔ２−200）〜Ｔ２℃温度域での仕上げ圧延減面率：25％以上］
仕上げ圧延では、粗圧延で微細化したオーステナイトを未再結晶域でさらに微細化すると同時に、圧延歪みを用いてＶ炭化物の析出強化を促進させる必要がある。フェライト・パーライト鋼のミクロ組織は、旧オーステナイト粒界から生成した初析フェライトとパーライトとの混合組織である。特に、中炭素鋼においては、パーライト分率が高いため、旧オーステナイト粒径を細かくすることが靭性向上の上で重要となる。オーステナイト未再結晶域での圧延は、圧下されたオーステナイト粒が圧下方向と垂直な方向に伸長し、圧下方向の見掛けのオーステナイト粒径が小さくなるため、靭性向上には有効な手法である。この効果を発揮させるためには、次式で得られる温度Ｔ２につき、（Ｔ２−200）〜Ｔ２℃の温度域での仕上げ圧延の減面率を25％以上とすることが重要である。
Ｔ２（℃）＝910−203[C]＋44.7[Si]−30[Mn]−20[Cu]−15.2[Ni]−11[Cr]＋31.5[Mo]＋104[V]+400[Ti]＋460[Al]＋700[P] …（２）
[(T2-200) to T2 ° C finish rolling area reduction: 25% or more]
In finish rolling, it is necessary to further refine the austenite refined by rough rolling in the non-recrystallized region, and at the same time, promote precipitation strengthening of V carbide using rolling strain. The microstructure of ferrite and pearlite steel is a mixed structure of proeutectoid ferrite and pearlite formed from the prior austenite grain boundaries. In particular, since medium carbon steel has a high pearlite fraction, it is important to improve the toughness by reducing the prior austenite grain size. Rolling in the austenite non-recrystallized region is an effective technique for improving toughness because the austenite grains that have been drawn are elongated in the direction perpendicular to the reduction direction and the apparent austenite grain size in the reduction direction is reduced. In order to exert this effect, it is important that the area reduction rate of finish rolling in the temperature range of (T2-200) to T2 ° C. is 25% or more for the temperature T2 obtained by the following equation.
T2 (° C.) = 910−203 [C] +44.7 [Si] −30 [Mn] −20 [Cu] −15.2 [Ni] −11 [Cr] +31.5 [Mo] +104 [V] +400 [ Ti] +460 [Al] +700 [P] (2)
なぜなら、Ｔ２℃を超えると、未再結晶域圧延の効果を十分に生かすことができず、また圧延による減面率が25％未満では十分な微細化効果および析出促進効果が得られない。また、仕上げ圧延温度の下限を（Ｔ２−200）℃としたのは、低温圧延による圧延荷重の増加により、製造が困難となるためである。従って、仕上げ圧延の条件を、温度範囲（Ｔ２−200）〜Ｔ２℃で、減面率25％以上とした。
なお、仕上げ圧延についても、複数パスで行っても１パスで行ってもよく、ここでいう減面率も、仕上げ圧延開始前の断面積ｓ０と仕上げ圧延後の断面積ｓ１とから、
（ｓ０−ｓ１）／ｓ０×100（％）
で求めることができる。
This is because if it exceeds T2 ° C., the effect of non-recrystallized zone rolling cannot be fully utilized, and if the area reduction rate by rolling is less than 25%, sufficient refinement effect and precipitation promoting effect cannot be obtained. Moreover, the reason why the lower limit of the finish rolling temperature is set to (T2−200) ° C. is that manufacturing becomes difficult due to an increase in rolling load due to low temperature rolling. Therefore, the finish rolling conditions were a temperature range (T2-200) to T2 ° C. and a reduction in area of 25% or more.
Note that the finish rolling may be performed in a plurality of passes or in one pass, and the area reduction rate here is also determined from the cross-sectional area s 0 before the start of the finish rolling and the cross-sectional area s 1 after the finish rolling.
(S 0 −s 1 ) / s 0 × 100 (%)
Can be obtained.
［仕上げ圧延後550℃までの冷却速度：５℃／s未満］
さらに、（Ｔ２−200）〜Ｔ２℃の温度域で減面率25％以上の圧下量で仕上げ圧延を施すと、見掛けの結晶粒径が小さくなり、それと同時にフェライト分率が増加する。このフェライト分率の最適化を図るために、冷却制御が必要である。すなわち、本発明では、Mn量を1.8超〜2.5質量％とすることによって、パーライトラメラの微細化を図り高強度化している。ここで、仕上げ圧延後の冷却速度が５℃／ｓ以上の場合、フェライト分率が低くなり、また、一部ベイナイトが混入し、靭性が低下するが、冷却速度を５℃／ｓ未満に制御することにより、フェライト・パーライト組織となり、靭性を良好にできることが新たに判明した。
なお、下限は、特に設定する必要はないが、実用上は0.01℃／ｓ以上とすればよい。
[Cooling rate to 550 ° C after finish rolling: less than 5 ° C / s]
Further, when finish rolling is performed at a reduction amount of 25% or more in the temperature range of (T2-200) to T2 ° C., the apparent crystal grain size is reduced, and at the same time, the ferrite fraction is increased. Cooling control is necessary to optimize the ferrite fraction. That is, in the present invention, the Mn content is more than 1.8 to 2.5 mass%, so that the pearlite lamella is refined and the strength is increased. Here, when the cooling rate after finish rolling is 5 ° C./s or more, the ferrite fraction is low, and some bainite is mixed and the toughness is reduced, but the cooling rate is controlled to less than 5 ° C./s. As a result, it has been newly found that a ferrite-pearlite structure is obtained and the toughness can be improved.
The lower limit is not particularly required to be set, but it may be 0.01 ° C./s or more for practical use.
表１に示す成分組成の鋼を転炉で溶製し、湾曲型連続鋳造機によってブルーム（断面寸法300×400mm）を製造した。このブルームを1150℃に加熱した後、900〜1100℃の温度範囲で表１に示す減面率での粗圧延を行った後、種々の仕上げ圧延条件で丸棒に熱間圧延した。この圧延ままの棒鋼の表面から直径の1/4深さ部分より、JIS4号引張試験片およびJIS3号シャルピー衝撃試験片を切り出し、機械的特性を評価した。なお、シャルピー衝撃試験は、試験温度０℃で３本実施し、平均衝撃値で評価した。機械的特性の評価結果を表２に示す。 Steels having the component compositions shown in Table 1 were melted in a converter, and blooms (cross-sectional dimensions of 300 × 400 mm) were produced using a curved continuous casting machine. The bloom was heated to 1150 ° C., then subjected to rough rolling at a reduction in area shown in Table 1 in the temperature range of 900 to 1100 ° C., and then hot-rolled to a round bar under various finish rolling conditions. A JIS No. 4 tensile test piece and a JIS No. 3 Charpy impact test piece were cut out from a 1/4 depth portion from the surface of the rolled steel bar, and the mechanical properties were evaluated. Three Charpy impact tests were performed at a test temperature of 0 ° C., and the average impact value was evaluated. Table 2 shows the evaluation results of the mechanical properties.
表２に示す通り、No.１〜11は発明例であり、878MPa以上の引張強さと32Ｊ／cm２以上の優れた衝撃値が得られた。No.12は仕上げ圧延温度が高く、強度及び衝撃値ともに低い値であった。No.13は仕上げ圧延の圧下率が不足する場合の例であり、衝撃値が低い値であった。No.14は仕上げ圧延の圧下率が低く、また冷却速度が速いため、強度及び衝撃値ともに低い値であった。No.15は仕上げ温度が高く、靭性が低下した。No.16は、粗圧延の減面率が高く、また仕上げ圧延温度が高いため、衝撃値が低い値であった。No.17は粗圧延の減面率が高いため、衝撃値が低い値であった。 As shown in Table 2, Nos. 1 to 11 are invention examples, and a tensile strength of 878 MPa or more and an excellent impact value of 32 J / cm 2 or more were obtained. No. 12 had a high finish rolling temperature and a low strength and impact value. No. 13 is an example when the rolling reduction of finish rolling is insufficient, and the impact value is low. No. 14 had a low rolling reduction in finish rolling and a high cooling rate, so both strength and impact values were low. No. 15 had a high finishing temperature and decreased toughness. No. 16 had a low impact value due to a high area reduction in rough rolling and a high finish rolling temperature. No. 17 had a low impact value due to a high reduction in rough rolling.
Claims (4)
Si：0.01〜1.2質量％、
Mn：1.8超〜2.5質量％、
Ｐ：0.040質量％以下、
Ｓ：0.040質量％以下、
Al：0.005〜0.06質量％及び
Ｖ：0.05〜0.20質量％
を含有し、残部Feおよび不可避的不純物からなる鋼素材に熱間圧延を施すに当り、下記（１）式で求められるＴ１℃以下の温度域での粗圧延の減面率を25％以下とし、その後下記（２）式で求められる（Ｔ２−200）〜Ｔ２℃の温度域で減面率25％以上の仕上げ圧延を施した後、550℃まで５℃／s未満の冷却速度で冷却することを特徴とするフェライト・パーライト型圧延非調質鋼材の製造方法。
記
Ｔ１（℃）＝−5440／（log[V] [C]−3.314）−173 …（1）
Ｔ２（℃）＝910−203[C]＋44.7[Si]−30[Mn]−20[Cu]−15.2[Ni]−11[Cr]＋31.5[Mo]＋104[V]+400[Ti]＋460[Al]＋700[P] …（2） C: 0.30 to 0.55 mass%,
Si: 0.01 to 1.2% by mass,
Mn: more than 1.8 to 2.5% by mass,
P: 0.040 mass% or less,
S: 0.040 mass% or less,
Al: 0.005 to 0.06 mass% and V: 0.05 to 0.20 mass%
When hot rolling a steel material containing the balance Fe and inevitable impurities, the area reduction rate of rough rolling in the temperature range of T1 ° C. or less determined by the following formula (1) is 25% or less. Then, after performing finish rolling with a reduction in area of 25% or more in the temperature range of (T2-200) to T2 ° C. obtained by the following equation (2), it is cooled to 550 ° C. at a cooling rate of less than 5 ° C./s. A method for producing a ferrite-pearlite-type rolled non-heat treated steel characterized by the above.
T1 (° C.) = − 5440 / (log [V] [C] −3.314) −173 (1)
T2 (° C.) = 910−203 [C] +44.7 [Si] −30 [Mn] −20 [Cu] −15.2 [Ni] −11 [Cr] +31.5 [Mo] +104 [V] +400 [ Ti] +460 [Al] +700 [P] (2)
Cr：1.0質量％以下、
Cu：1.0質量％以下、
Ni：1.0質量％以下及び
Mo：1.0質量％以下
から選ばれる１種または２種以上を含有するフェライト・パーライト型圧延非調質鋼材の製造方法。 2. The steel material according to claim 1, further comprising:
Cr: 1.0% by mass or less,
Cu: 1.0 mass% or less,
Ni: 1.0% by mass or less
Mo: A method for producing a ferrite-pearlite rolled non-tempered steel material containing one or more selected from 1.0% by mass or less.
Ti：0.15質量％以下及び
Nb：0.15質量％以下
のいずれか１種または２種を含有するフェライト・パーライト型圧延非調質鋼材の製造方法。 The steel material according to claim 1 or 2, further comprising:
Ti: 0.15 mass% or less and
Nb: A method for producing a ferrite-pearlite rolled non-heat treated steel material containing any one or two of 0.15% by mass or less.
Pb：0.01〜0.40質量％、
Bi：0.01〜0.40質量％及び
Ca：0.0005〜0.0100質量％
から選ばれる１種または２種以上を含有するフェライト・パーライト型圧延非調質鋼材の製造方法。 The steel material according to claim 1, 2, or 3,
Pb: 0.01-0.40 mass%,
Bi: 0.01-0.40 mass% and
Ca: 0.0005 to 0.0100 mass%
A method for producing a ferritic / pearlite-type rolled non-heat treated steel material containing one or more selected from:
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| KR101795863B1 (en) | 2015-11-02 | 2017-11-09 | 주식회사 포스코 | Wire rod having excellent hot workability and machinability and method for manafacturing the same |
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| JPH0617126A (en) * | 1992-06-30 | 1994-01-25 | Aichi Steel Works Ltd | Production of non-heattreated bar steel excellent in toughness at low temperature |
| JP2009215576A (en) * | 2008-03-07 | 2009-09-24 | Jfe Steel Corp | Method for producing rolled non-heat treated steel material |
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| JPH0617126A (en) * | 1992-06-30 | 1994-01-25 | Aichi Steel Works Ltd | Production of non-heattreated bar steel excellent in toughness at low temperature |
| JP2009215576A (en) * | 2008-03-07 | 2009-09-24 | Jfe Steel Corp | Method for producing rolled non-heat treated steel material |
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| CN103517996A (en) * | 2011-05-12 | 2014-01-15 | 安赛乐米塔尔研究与发展有限责任公司 | Method for the production of martensitic steel having a very high yield point and sheet or part thus obtained |
| CN103517996B (en) * | 2011-05-12 | 2016-05-11 | 安赛乐米塔尔研究与发展有限责任公司 | Sheet material or the parts manufacturing the method for high elastic limit martensite steel and so obtain |
| US9963756B2 (en) | 2011-05-12 | 2018-05-08 | ArcelorMittal Investigación y Desarrollo, S.L. | Method for production of martensitic steel having a very high yield point and sheet or part thus obtained |
| KR101795863B1 (en) | 2015-11-02 | 2017-11-09 | 주식회사 포스코 | Wire rod having excellent hot workability and machinability and method for manafacturing the same |
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