JP2007291464A - High-strength steel material and its production method - Google Patents
High-strength steel material and its production method Download PDFInfo
- Publication number
- JP2007291464A JP2007291464A JP2006122205A JP2006122205A JP2007291464A JP 2007291464 A JP2007291464 A JP 2007291464A JP 2006122205 A JP2006122205 A JP 2006122205A JP 2006122205 A JP2006122205 A JP 2006122205A JP 2007291464 A JP2007291464 A JP 2007291464A
- Authority
- JP
- Japan
- Prior art keywords
- steel material
- less
- steel
- strength
- tempering
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Images
Landscapes
- Heat Treatment Of Steel (AREA)
Abstract
Description
本発明は、熱処理によって高強度化された降伏比の高い高強度鋼材及びその製造方法に関する。 The present invention relates to a high-strength steel material having a high yield ratio that has been strengthened by heat treatment and a method for producing the same.
乗用車、トラック等の輸送用機器について、軽量化や衝突安全性向上を達成するため、鋼材の高強度化が進められている。そのため近年ハイテンと称される種々の高強度鋼材が開発され、その適用は年々拡大している。しかし高強度鋼材は延性が乏しく、成形荷重の増加や寸法精度の低下等を生じる問題がある。 With regard to transportation equipment such as passenger cars and trucks, steel materials are being strengthened in order to achieve weight reduction and improved collision safety. Therefore, various high-strength steel materials called “HITEN” have been developed in recent years, and their application is expanding year by year. However, high-strength steel materials have poor ductility, and there is a problem that an increase in forming load and a decrease in dimensional accuracy occur.
そこで近年、特許文献１に開示される熱間プレス法のような熱間成形時またはそれに続いて行う後熱処理法の適用が拡大している。上記方法は、成形後の熱処理によって鋼材を高強度化するため、成形性の確保と高強度化とを両立できる。このような後熱処理は焼入れ処理である。 Therefore, in recent years, application of post-heat treatment methods performed during or subsequent to hot forming such as the hot press method disclosed in Patent Document 1 has been expanded. Since the above method increases the strength of the steel material by heat treatment after forming, it is possible to ensure both formability and increase the strength. Such post heat treatment is a quenching treatment.
一方、特許文献２には、そのような後熱処理法において強度と靱性とを両立できる焼入れ材を得る方法が記載されている。これは焼入れ前の加熱温度をＡｃ１点とＡｃ３点の中間の温度とし、焼入れ後のミクロ組織をフェライトとマルテンサイトの二相焼入れ組織とすることで、フルマルテンサイト組織よりも低強度、高靱性の鋼材を製造する方法である。
例えば、自動車用の構造材、例えばフレーム材のような骨格部材用としては、強度が高いことのみならず降伏比が高い材料が求められている。しかも、材料コストも含めて製造コストが安価であり、安定して製造・供給できることが必要である。 For example, for a structural material for automobiles, for example, a skeleton member such as a frame material, a material having a high yield ratio as well as a high strength is required. In addition, it is necessary that the manufacturing cost including the material cost is low and that it can be stably manufactured and supplied.
ここで、高強度化に関しては、特許文献１、２に開示された方法のように熱処理により高強度化を図る技術が開示されているが、高降伏比化に関する熱処理については未だ検討されていないのが実状である。 Here, regarding the increase in strength, a technique for increasing the strength by heat treatment, such as the methods disclosed in Patent Documents 1 and 2, has been disclosed, but the heat treatment for increasing the yield ratio has not yet been studied. This is the actual situation.
一方、今日のように材料開発が進展すると、例えば、自動車用材料においては同じ構造部材といっても部位によっては材料特性、特に強度が異なる材料を使用したいときがある。もちろん、それぞれ異なった材料でそのような部材を構成すればよく、その限りでは問題はないが、最近のような材料コスト低減の強い要求の下では、同一鋼種を用いて、いくつかの強度レベルの材料を作り分けることが重要となってきている。 On the other hand, when material development progresses like today, for example, in automobile materials, there are times when it is desired to use materials having different material characteristics, particularly strength, depending on the part even though they are the same structural members. Of course, it is only necessary to construct such a member with different materials, so long as there is no problem, but under the strong demand for material cost reduction as in recent years, the same steel grade is used and several strength levels are used. It has become important to make different materials.
もちろん、そのような各種強度レベルの材料の作り分けは製造方法によるものであるが、またそのような材料の作り分けを許容できる材質そのものを開発する必要がある。
したがって、本発明の一般的課題は、熱処理により得られる高い降伏比と高い強度とを併せ持つ鋼材と、そのような鋼材の簡便な製造方法を提供することである。
Of course, the creation of such materials of various strength levels depends on the manufacturing method, but it is also necessary to develop a material itself that allows the creation of such materials.
Therefore, a general problem of the present invention is to provide a steel material having both a high yield ratio and high strength obtained by heat treatment, and a simple method for producing such a steel material.
さらに、本発明の課題は、そのように高強度化された高い降伏比と高い強度とを併せ持つ高強度鋼材において、同一鋼種であっても製造条件を規定することで簡単に各種強度レベルの材料を高い降伏比を確保しつつ作り分けることのできる鋼種およびそのための製造方法を提供することである。 Furthermore, the object of the present invention is to provide a material with various strength levels by simply defining the manufacturing conditions even in the same steel type in a high strength steel material having both a high yield ratio and a high strength. Is to provide a steel type and a manufacturing method therefor that can be made separately while ensuring a high yield ratio.
かかる課題を解決すべく種々検討を重ねた結果、次のような知見を得た。
熱間成形後の焼入れなどの後熱処理法で製造した鋼材の強度は、鋼中のＣ含有量によって決定される。しかし、目的とする強度ごとに成分が異なる鋼材を調達するには多大なコストを要する。この問題を解決するため、同一成分で強度をつくり分ける技術が要請されている。
As a result of various studies to solve this problem, the following knowledge was obtained.
The strength of a steel material produced by a post heat treatment method such as quenching after hot forming is determined by the C content in the steel. However, enormous costs are required to procure steel materials having different components for each desired strength. In order to solve this problem, there is a demand for a technique for creating strength with the same component.
一方、前述の特許文献１、２にあっては、当該技術分野におけるコスト面からの要請により焼戻し処理については元来検討されておらず、いずれも焼入れままで使用される。特に、特許文献２に開示の方法では、マルテンサイトとフェライトもしくはパーライトとの量比によって所定強度を与えていることから、焼戻し処理は排除されている。そして、特許文献１、２に開示の方法で製造した鋼材は降伏比が低く、とりわけ特許文献２の開示する方法で製造した鋼材は降伏比が著しく低いため、高い降伏強度（ＹＳ）が求められるフレーム等の骨格部材には適さない。また、特許文献２の開示する方法において強度は焼入れ後のマルテンサイト体積率で決まるが、加熱温度のばらつきによってマルテンサイト体積率は大きく変動するため、強度ばらつきの抑制が困難である。 On the other hand, in the above-mentioned Patent Documents 1 and 2, tempering has not been originally studied due to cost requirements in the technical field, and both are used as-quenched. In particular, in the method disclosed in Patent Document 2, since the predetermined strength is given by the quantitative ratio between martensite and ferrite or pearlite, tempering treatment is eliminated. And since the steel materials manufactured by the method disclosed in Patent Documents 1 and 2 have a low yield ratio, and particularly the steel materials manufactured by the method disclosed in Patent Document 2 have a significantly low yield ratio, a high yield strength (YS) is required. It is not suitable for frame members such as frames. Further, in the method disclosed in Patent Document 2, the strength is determined by the martensite volume ratio after quenching. However, since the martensite volume ratio varies greatly due to variations in heating temperature, it is difficult to suppress variations in strength.
そこで、本発明者等は上記課題を解決するために、焼入れ後の焼戻しによって鋼材を低強度化するとともに高降伏比化し、所望の強度と高い降伏比の鋼材を製造する方法について検討した。その結果、次の知見を得た。 In order to solve the above-mentioned problems, the present inventors studied a method for producing a steel material having a desired strength and a high yield ratio by reducing the strength of the steel material by tempering after quenching and increasing the yield ratio. As a result, the following knowledge was obtained.
（１）焼入れ焼戻しによって低強度化を図ると、二相焼入れだけを行った場合に比べ、予想外にも、低い引張強度ＴＳでありながら高い降伏強度ＹＳを持つ、すなわち降伏比ＹＲが高い鋼材を得ることができる。 (1) Compared to the case where only two-phase quenching is performed by reducing the strength by quenching and tempering, the steel material unexpectedly has a high yield strength YS while having a low tensile strength TS, that is, a high yield ratio YR. Can be obtained.
（２）焼戻し後の機械特性は、下記式（１）で規定されるパラメータλによって概ね決定される。すなわち、パラメータλが同じならば焼戻温度や焼戻時間が異なっても略同一の機械特性が得られる。パラメータλが１１０００〜１６５００となる条件で焼戻し処理を施すと、降伏比ＹＲが９０％以上で引張強さＴＳが７００ＭＰａ以上の機械特性を有する鋼材が得られる。 (2) The mechanical characteristics after tempering are generally determined by the parameter λ defined by the following formula (1). That is, if the parameter λ is the same, substantially the same mechanical characteristics can be obtained even if the tempering temperature and the tempering time are different. When the tempering treatment is performed under the condition that the parameter λ is 11000 to 16500, a steel material having a mechanical property with a yield ratio YR of 90% or more and a tensile strength TS of 700 MPa or more is obtained.
λ＝Ｔ｛ｌｏｇ（ｔ）＋２０｝ （１）
ここで、式中のＴは焼戻温度（単位：Ｋ）、ｔは焼戻時間（単位：ｈ）を示す。
（３）パラメータλが１１０００〜１６５００となる条件で焼戻し処理を施した鋼材の引張強度ＴＳＱＴ（ＭＰａ）は下記式（５）により近似することができ、ＴＳＱＴに対して０.９×ＴＳＱＴ〜１.１×ＴＳＱＴの範囲の引張強度を有する鋼材が得られる。
λ = T {log (t) +20} (1)
Here, T in the formula represents a tempering temperature (unit: K), and t represents a tempering time (unit: h).
(3) The tensile strength TS QT (MPa) of the steel material tempered under the condition that the parameter λ is 11000-16500 can be approximated by the following formula (5), and 0.9 × TS with respect to TS QT . A steel material having a tensile strength in the range of QT to 1.1 × TS QT is obtained.
ＴＳＱＴ＝−０.１１×λ＋３７００×Ｃ＋１７６０ （５）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。
したがって、前記ＴＳＱＴと前記パラメータλとは下記式（２）を満足する。
TS QT = −0.11 × λ + 3700 × C + 1760 (5)
Here, C in a formula shows C content (unit: mass%) in steel.
Therefore, the TS QT and the parameter λ satisfy the following formula (2).
（３７００×Ｃ−１.１×ＴＳＱＴ＋１７６０）／０.１１≦λ≦（３７００×Ｃ−０.９×ＴＳＱＴ＋１７６０）／０.１１ （２）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）、ＴＳＱＴは高強度鋼材の引張強度（ＭＰａ）を示す。
(3700 × C-1.1 × TS QT + 1760) /1.11≦λ≦ (3700 × C−0.9 × TS QT + 1760) /1.11 (2)
Here, C in the formula indicates the C content (unit: mass%) in the steel, and TS QT indicates the tensile strength (MPa) of the high-strength steel material.
（４）一般に、高強度鋼材については目標引張強度下限ＴＳＱＴ ｍｉｎ（ＭＰａ）が設定されるから、上記式（５）とその誤差量より、パラメータλが下記式（３）を満足する条件で焼戻し処理を施すことにより、目標引張強度下限ＴＳＱＴ ｍｉｎ（ＭＰａ）以上の引張強度を有する鋼材を得ることができる。 (4) In general, since the target tensile strength lower limit TS QT min (MPa) is set for high-strength steel materials, from the above equation (5) and its error amount, the parameter λ satisfies the following equation (3). By performing a tempering treatment, a steel material having a tensile strength equal to or higher than the target tensile strength lower limit TS QT min (MPa) can be obtained.
λ≦（３７００×Ｃ−０.９×ＴＳＱＴ ｍｉｎ＋１７６０）／０.１１ （３）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。
（５）また、高強度鋼材について目標引張強度上限ＴＳＱＴ ｍａｘ（ＭＰａ）が設定される場合には、上記式（５）とその誤差量より、パラメータλが下記式（４）を満足する条件で焼戻し処理を施すことにより、目標引張強度上限ＴＳＱＴ ｍａｘ（ＭＰａ）以下の引張強度を有する鋼材を得ることができる。
λ ≦ (3700 × C−0.9 × TS QT min + 1760) /0.11 (3)
Here, C in a formula shows C content (unit: mass%) in steel.
(5) When the target tensile strength upper limit TS QT max (MPa) is set for a high-strength steel material, the condition that the parameter λ satisfies the following equation (4) from the above equation (5) and the error amount thereof. By tempering, a steel material having a tensile strength equal to or lower than the target tensile strength upper limit TS QT max (MPa) can be obtained.
λ≧（３７００×Ｃ−１.１×ＴＳＱＴ ｍｉｎ＋１７６０）／０.１１ （４）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。
本発明は上記の知見に基づいて完成されたものであり、その要旨は下記の通りである。
λ ≧ (3700 × C−1.1 × TS QT min + 1760) /0.11 (4)
Here, C in a formula shows C content (unit: mass%) in steel.
The present invention has been completed based on the above findings, and the gist thereof is as follows.
(1)質量％で、Ｃ：０.０５〜０.４５％、Ｓｉ：１.０％以下、Ｍｎ：０.２〜３.０％、Ｐ：０.１％以下、Ｓ：０.０２％以下、Ａｌ：０.２％以下、Ｎ：０.０１％以下を含有し、残部がＦｅおよび不純物からなる化学組成を有するとともに、降伏比ＹＲが９０％以上で引張強さＴＳが７００ＭＰａ以上１７００ＭＰａ以下の機械特性を有することを特徴とする高強度鋼材。 (1) By mass%, C: 0.05 to 0.45%, Si: 1.0% or less, Mn: 0.2 to 3.0%, P: 0.1% or less, S: 0.02 %, Al: 0.2% or less, N: 0.01% or less, with the balance being a chemical composition comprising Fe and impurities, with a yield ratio YR of 90% or more and a tensile strength TS of 700 MPa or more. A high-strength steel material having mechanical properties of 1700 MPa or less.
(2)前記化学組成が、Ｆｅの一部に代えて、Ｂ：０.０１％以下、Ｔｉ：０.１％以下およびＣｒ：１.０％以下からなる群から選ばれた１種または２種以上を含有することを特徴とする上記(1)に記載の高強度鋼材。 (2) The chemical composition is one or two selected from the group consisting of B: 0.01% or less, Ti: 0.1% or less, and Cr: 1.0% or less instead of a part of Fe The high-strength steel material according to (1) above, which contains more than seeds.
(3)前記化学組成が、Ｆｅの一部に代えて、Ｍｏ：１.０％以下、Ｗ：１.０％以下、Ｎｉ：１.０％以下、Ｎｂ：１.０％以下、Ｖ：１.０％以下およびＣｕ：１.０％以下からなる群から選ばれた１種または２種以上を含有することを特徴とする上記(1)または(2)に記載の高強度鋼材。 (3) When the chemical composition is replaced with a part of Fe, Mo: 1.0% or less, W: 1.0% or less, Ni: 1.0% or less, Nb: 1.0% or less, V: The high-strength steel material according to (1) or (2) above, which contains one or more selected from the group consisting of 1.0% or less and Cu: 1.0% or less.
(4)上記(1)〜(3)のいずれかに記載の化学組成を有する鋼材を、オーステナイト単相状態としたのちに、上部臨界冷却速度以上の冷却速度でＭｓ点以下の温度域まで冷却し、次いで下記式（１）で規定されるパラメータλが１１０００〜１６５００となる条件で焼戻し処理を施すことを特徴とする高強度鋼材の製造方法。
λ＝Ｔ｛ｌｏｇ（ｔ）＋２０｝ （１）
ここで、式中のＴは焼戻温度（単位：Ｋ）、ｔは焼戻時間（単位：ｈ）を示す。
(4) After the steel material having the chemical composition described in any one of (1) to (3) above is changed to an austenite single phase state, it is cooled to a temperature range below the Ms point at a cooling rate higher than the upper critical cooling rate. Then, a tempering process is performed under the condition that the parameter λ defined by the following formula (1) is 11000-16500.
λ = T {log (t) +20} (1)
Here, T in the formula represents a tempering temperature (unit: K), and t represents a tempering time (unit: h).
(5) 前記パラメータλが下記式（２）を満足することを特徴とする上記(4)に記載の高強度鋼材の製造方法。
（３７００×Ｃ−１.１×ＴＳＱＴ＋１７６０）／０.１１≦λ≦（３７００×Ｃ−０.９×ＴＳＱＴ＋１７６０）／０.１１ （２）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）、ＴＳＱＴは高強度鋼材の引張強度（ＭＰａ）を示す。
(5) The method for producing a high-strength steel material according to (4), wherein the parameter λ satisfies the following formula (2).
(3700 × C-1.1 × TS QT + 1760) /1.11≦λ≦ (3700 × C−0.9 × TS QT + 1760) /1.11 (2)
Here, C in the formula indicates the C content (unit: mass%) in the steel, and TS QT indicates the tensile strength (MPa) of the high-strength steel material.
(6)高強度鋼材の目標引張強度下限ＴＳＱＴ ｍｉｎ（ＭＰａ）に基づいて前記パラメータλが下記式（３）を満足する条件で焼戻し処理を施すことを特徴とする上記(4)に記載の高強度鋼材の製造方法。
λ≦（３７００×Ｃ−０.９×ＴＳＱＴ ｍｉｎ＋１７６０）／０.１１ （３）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。
(6) The tempering treatment is performed on the condition that the parameter λ satisfies the following expression (3) based on a target tensile strength lower limit TS QT min (MPa) of the high-strength steel material. Manufacturing method of high strength steel.
λ ≦ (3700 × C−0.9 × TS QT min + 1760) /0.11 (3)
Here, C in a formula shows C content (unit: mass%) in steel.
(7)高強度鋼材の目標引張強度上限ＴＳＱＴ ｍａｘ（ＭＰａ）に基づいて前記パラメータλが下記式（４）を満足する条件で焼戻し処理を施すことを特徴とする上記(4)または(6)に記載の高強度鋼材の製造方法。
λ≧（３７００×Ｃ−１.１×ＴＳＱＴ ｍａｘ＋１７６０）／０.１１ （４）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。
(7) The above-described (4) or (6), wherein the tempering treatment is performed on the condition that the parameter λ satisfies the following formula (4) based on the target tensile strength upper limit TS QT max (MPa) of the high-strength steel material. The manufacturing method of the high strength steel materials as described in).
λ ≧ (3700 × C−1.1 × TS QT max +1760) /0.11 (4)
Here, C in a formula shows C content (unit: mass%) in steel.
本発明によれば、熱処理により得られる高い降伏比と高い強度とを併せ持つ鋼材と、そのような鋼材の簡便な製造方法が提供される。さらに、そのように高強度化された高い降伏比と高い強度とを併せ持つ高強度鋼材において、同一鋼種であっても製造条件を規定することで簡単に各種強度レベルの材料を高い降伏比を確保しつつ作り分けることのできる鋼種およびそのための製造方法が提供される。 According to the present invention, a steel material having both a high yield ratio and high strength obtained by heat treatment, and a simple method for producing such a steel material are provided. Furthermore, in high-strength steel materials that have both high yield ratios and high strengths that have been strengthened in this way, it is easy to secure high yield ratios for materials of various strength levels by prescribing manufacturing conditions even for the same steel type. However, a steel type that can be produced separately and a manufacturing method therefor are provided.
本発明に使用する鋼材の成分、製造方法、及び熱処理条件の限定理由について詳述する。本明細書において鋼の化学組成を示す「％」は、いずれも「質量％」である。
（１）鋼の化学組成
Ｃ：Ｃは焼入れ後の鋼の強度を決定する重要な元素であり、Ｃ含有量が低すぎると焼入れ後に十分な強度が得られない。一方Ｃ含有量が高すぎると、焼入れ前の鋼材の延性が低下し焼入れ前の加工性が損なわれる。従ってＣ含有量を０.０５〜０.４５％とする。好ましくは０.０９〜０.２６％である。
The reasons for limiting the components of the steel used in the present invention, the production method, and the heat treatment conditions will be described in detail. In this specification, “%” indicating the chemical composition of steel is “mass%”.
(1) Chemical composition of steel C: C is an important element that determines the strength of steel after quenching. If the C content is too low, sufficient strength cannot be obtained after quenching. On the other hand, if the C content is too high, the ductility of the steel material before quenching decreases and the workability before quenching is impaired. Therefore, the C content is set to 0.05 to 0.45%. Preferably it is 0.09 to 0.26%.
Ｓｉ：Ｓｉは鋼の焼入れ性を高める元素であり、必要に応じて含有させることができる。ただし過剰な添加は化成処理性やめっき性が低下し、さらにＡ３点が上昇するため、含有量を１.０％以下とする。望ましくは０.１〜０.３％である。 Si: Si is an element that enhances the hardenability of steel, and can be contained as necessary. However excessive addition reduces the chemical conversion treatability and coating property, and is further three points A rises, the content of 1.0% or less. Desirably, the content is 0.1 to 0.3%.
Ｍｎ：Ｍｎは鋼の焼入れ性を確保するために重要な元素であり、０.２％以上含有させる。一方過剰な添加は焼入れ前の加工性を劣化させるだけでなく、炭化物が安定化し、焼入れ加熱時に溶け残りやすくなる。従ってＭｎの含有量を０.２〜３.０％とする。望ましくは０.７〜１.５％である。 Mn: Mn is an important element for securing the hardenability of steel, and is contained by 0.2% or more. On the other hand, excessive addition not only deteriorates the workability before quenching, but also stabilizes the carbide and tends to remain undissolved during quenching heating. Therefore, the Mn content is set to 0.2 to 3.0%. Preferably it is 0.7 to 1.5%.
Ｐ：Ｐは不可避不純物の一つであり、焼入れ前の鋼の加工性および焼入れ後の鋼の靱性を劣化させる。従って含有量は少ないほど好ましく、含有量を０.１％以下とする。望ましくは０.０３％以下である。 P: P is one of inevitable impurities, and deteriorates the workability of steel before quenching and the toughness of steel after quenching. Therefore, the smaller the content, the better. The content is 0.1% or less. Desirably, it is 0.03% or less.
Ｓ：Ｓも不可避不純物の一つであり、焼入れ前の鋼の加工性および焼入れ後の鋼の靱性を劣化させる。従って含有量は少ないほど望ましく、含有量を０.０２％以下とする。望ましくは０.０１％以下である。 S: S is one of the inevitable impurities, and deteriorates the workability of the steel before quenching and the toughness of the steel after quenching. Therefore, the smaller the content, the better, and the content is set to 0.02% or less. Desirably, it is 0.01% or less.
Ａｌ：Ａｌは製鋼工程で脱酸を目的として添加することができる。しかし過剰な添加は製造コストの上昇を招くとともに、Ａ３点も上昇して製造を困難にする。したがって含有量を０.２％以下とする。望ましくは０.００５〜０.１％である。 Al: Al can be added for the purpose of deoxidation in the steelmaking process. But excessive addition with causes an increase in manufacturing cost and A 3-point makes it difficult to manufacture to rise. Therefore, the content is made 0.2% or less. Preferably it is 0.005 to 0.1%.
Ｎ：Ｎは鋼中に不可避に含有される元素であり、焼入れ前の鋼の加工性を劣化させる。そのため含有量を０.０１％以下と定めた。望ましくは０.００５％以下である。
本発明においては上記元素に加えてさらに以下の元素を少なくとも１種含有させても良い。
N: N is an element inevitably contained in the steel, and deteriorates the workability of the steel before quenching. Therefore, the content is determined to be 0.01% or less. Desirably, it is 0.005% or less.
In the present invention, in addition to the above elements, at least one of the following elements may be contained.
Ｂ：Ｂは焼入れ性を向上させる作用を有するので適宜含有させることができる。しかしながら、過剰な含有は焼入れ処理前の鋼材の加工性を劣化させる。したがってＢ含有量を０.０１％以下とする。より好ましくは０.００４％以下である。上記作用による効果を確実に得るには、Ｂ含有量を０.０００２％以上とすることが好ましく、０.０００５％以上とすることがより好ましい。 B: Since B has the effect | action which improves hardenability, it can be contained suitably. However, excessive inclusion deteriorates the workability of the steel before quenching. Therefore, the B content is set to 0.01% or less. More preferably, it is 0.004% or less. In order to surely obtain the effect by the above action, the B content is preferably 0.0002% or more, and more preferably 0.0005% or more.
Ｔｉ：Ｔｉは焼入れ性を向上させる作用を有するので適宜含有させることができる。Ｔｉはそのような作用ばかりでなく、さらに鋼中の固溶Ｎを析出固定して焼入れ前の鋼材の成形性を向上させることができる。しかしながら過剰に含有するとＴｉＣの析出量が増し、焼入れ処理前の鋼材の加工性が低下するので、Ｔｉ含有量を０.１％以下とする。より好ましくは０.０４％以下である。上記作用による効果を確実に得るには、Ｔｉ含有量を０.００２％以上とすることが好ましく、０.０１％以上であることがより好ましい。
また、ＴｉはＢＮの析出を抑制し、Ｂの焼入れ性を高める作用を有するので、Ｔｉ≧４８／１１×Ｂ（ＴｉおよびＢは各元素の鋼中の含有量（質量％）を示す）となるようにＴｉとＢとを同時に含有させることが望ましい。
Ti: Ti has an effect of improving hardenability, and therefore can be appropriately contained. Ti not only has such an effect, but can also precipitate and fix solute N in the steel to improve the formability of the steel before quenching. However, if excessively contained, the amount of TiC precipitated increases and the workability of the steel before quenching decreases, so the Ti content is set to 0.1% or less. More preferably, it is 0.04% or less. In order to surely obtain the effect by the above action, the Ti content is preferably 0.002% or more, and more preferably 0.01% or more.
Further, since Ti has the effect of suppressing the precipitation of BN and enhancing the hardenability of B, Ti ≧ 48/11 × B (Ti and B indicate the content (mass%) of each element in the steel) and It is desirable to contain Ti and B at the same time.
Ｃｒ：Ｃｒは焼入れ性を向上させる作用を有するので適宜含有させることができる。しかしながら、過剰な含有は焼入れ前の鋼材の加工性を劣化させるので、Ｃｒ含有量を１.０％以下とする。好ましくは０.６％以下である。上記作用による効果を確実に得るにはＣｒ含有量を０.０２％以上とすることが好ましい。 Cr: Cr has a function of improving hardenability, and therefore can be appropriately contained. However, excessive content degrades the workability of the steel before quenching, so the Cr content is 1.0% or less. Preferably it is 0.6% or less. In order to surely obtain the effect by the above action, the Cr content is preferably 0.02% or more.
Ｍｏ、Ｗ、Ｎｉ、Ｎｂ、Ｖ、Ｃｕ：
これらの元素も焼入れ性を向上させる作用を有するので適宜含有させることができる。しかしながら過剰な含有は焼入れ前の鋼材の加工性を劣化させる。したがって各元素の含有量を１.０％以下と定めた。一方、上記作用による効果を確実に得るには、何れかの元素の含有量を０.０２％以上とすることが望ましい。より望ましくは、これらの元素の合計含有量を０.０５〜１.０％とすることである。
Mo, W, Ni, Nb, V, Cu:
Since these elements also have the effect of improving the hardenability, they can be appropriately contained. However, excessive inclusion deteriorates the workability of the steel before quenching. Therefore, the content of each element is determined to be 1.0% or less. On the other hand, in order to reliably obtain the effect by the above action, it is desirable that the content of any element is 0.02% or more. More desirably, the total content of these elements is set to 0.05 to 1.0%.
（２）鋼材の機械特性
降伏比ＹＲ：９０％以上、引張強さＴＳ：７００ＭＰａ以上１７００ＭＰａ以下
鋼材の降伏比が低いと高い降伏比が要求されるフレーム等の骨格部材への適用が制限される。したがって降伏比ＹＲは９０％以上とする。好ましくは９５％以上である。また、鋼材の引張強さが７００ＭＰａ未満では高強度鋼材としては強度が不十分である。したがって、引張強さを７００ＭＰａ以上とする。好ましくは、８５０ＭＰａ以上、さらに好ましくは１０００ＭＰａ以上である。一方、引張強さが高過ぎる場合には充分な靭性を確保することが困難となる。したがって、鋼材の引張強さを１７００ＭＰａ以下とする。好ましくは、１５００ＭＰａ以下、さらに好ましくは１３５０ＭＰａ以下である。
(2) Mechanical properties of steel materials Yield ratio YR: 90% or more, Tensile strength TS: 700 MPa or more and 1700 MPa or less If the yield ratio of steel materials is low, application to frame members such as frames that require a high yield ratio is restricted. . Therefore, the yield ratio YR is 90% or more. Preferably it is 95% or more. Further, if the tensile strength of the steel material is less than 700 MPa, the strength is insufficient as a high-strength steel material. Accordingly, the tensile strength is set to 700 MPa or more. Preferably, it is 850 MPa or more, more preferably 1000 MPa or more. On the other hand, if the tensile strength is too high, it is difficult to ensure sufficient toughness. Therefore, the tensile strength of the steel material is set to 1700 MPa or less. Preferably, it is 1500 MPa or less, more preferably 1350 MPa or less.
（３）鋼材の製造方法
本発明は、所定の化学組成を備える鋼材をオーステナイト単相状態とする熱処理を施すことにより目的とする強度を付与するものであるから、熱処理前の鋼材の製造方法は特に限定されることはなく常法で構わない。また、当該鋼材の形状は、板、帯、棒、パイプ等のいずれでも構わないし、これらにプレス成形等の加工を施したものであっても構わない。当該鋼材が鋼板もしくは鋼板を素材として加工が施された鋼材である場合には、当該鋼板は、熱間圧延ままの熱間圧延鋼板や酸洗等により脱スケール処理が施された熱間圧延鋼板であってもよく、熱間圧延鋼板に冷間圧延が施された冷間圧延鋼板であってもよい。また、鋼材の表面には、耐食性向上や熱処理におけるスケール形成の抑制を目的としてＺｎ系めっき、Ａｌ系めっき、耐酸化コーティング等が施されていても構わない。焼入れを施す鋼材が加工を施された鋼材である場合であって、加工前の素材の強度が高く加工が困難な場合には、当該素材に焼鈍を施して軟質化させてもよい。当該素材が鋼板の場合には箱焼鈍や連続焼鈍を適用することができる。
(3) Manufacturing method of steel material Since this invention provides the intensity | strength intended by giving the heat processing which makes the steel material provided with a predetermined | prescribed chemical composition the austenite single phase state, the manufacturing method of the steel material before heat processing is the following. There is no particular limitation and a conventional method may be used. Further, the shape of the steel material may be any of a plate, a band, a rod, a pipe, or the like, or may be obtained by processing such as press molding. When the steel material is a steel plate or a steel material processed by using a steel plate, the steel plate is a hot-rolled steel plate that has been hot-rolled or a hot-rolled steel plate that has been descaled by pickling or the like. It may be a cold rolled steel sheet obtained by cold rolling a hot rolled steel sheet. In addition, the surface of the steel material may be subjected to Zn-based plating, Al-based plating, oxidation-resistant coating, or the like for the purpose of improving corrosion resistance or suppressing scale formation during heat treatment. If the steel material to be quenched is a processed steel material, and the strength of the material before processing is high and processing is difficult, the material may be annealed to be softened. When the material is a steel plate, box annealing or continuous annealing can be applied.
（３）熱処理方法
上記の方法により製造した鋼材に焼入れ焼戻しの熱処理を施す。
焼入れ処理は、鋼材をオーステナイト単相状態としたのちに、上部臨界冷却速度以上の冷却速度でＭｓ点以下の温度域まで冷却して行う。
(3) Heat treatment method The steel material manufactured by said method is heat-treated by quenching and tempering.
The quenching treatment is performed by bringing the steel material into an austenite single phase state and then cooling it to a temperature range below the Ms point at a cooling rate equal to or higher than the upper critical cooling rate.
オーステナイト単相状態とする際に加熱する場合の加熱方法は炉加熱、高周波加熱、通電加熱等の公知の方法の何れであってもよい。また、鋼材が加工を施されたものである場合には、熱間プレス法のようにオーステナイト単相状態としたのちに素材に加工を施して鋼材としたのちに、オーステナイト単相状態を保持したまま加熱すること無しに焼入れ処理を施してもよい。また、オーステナイト単相状態とするのは必ずしも鋼材全体である必要はなく、鋼材の目的に応じて鋼材全体を焼入れたり部分的に焼入れたりすることができる。 The heating method for heating in the austenite single phase state may be any of known methods such as furnace heating, high-frequency heating, and electric heating. In addition, when the steel material is processed, the austenite single phase state was maintained after processing the material into a steel material after making the austenite single phase state as in the hot press method. Quenching may be performed without heating. The austenite single phase state does not necessarily need to be the entire steel material, and the entire steel material can be quenched or partially quenched depending on the purpose of the steel material.
オーステナイト単相状態としたのちに、上部臨界冷却速度以上の冷却速度でＭｓ点以下の温度域まで冷却するが、当該冷却速度が上部臨界冷却速度未満の場合には焼戻し処理後の鋼材について機械的特性のばらつきが生じる。従って１０℃／ｓ以上で冷却し、焼戻し後の鋼材の中心部のビッカース硬度Ｈｖを全厚で測定した引張強度ＴＳ（ＭＰａ）／４以上とするのが望ましい。一方、冷却速度が高過ぎると焼割れが生じる可能性があるので冷却速度は１０００℃／ｓ以下とすることが望ましい。十分な冷却速度が確保できれば水冷、油冷、ガス冷、あるいはプレス冷却等のいずれの方法で冷却しても構わない。 After the austenite single phase state, the steel is cooled to a temperature range below the Ms point at a cooling rate higher than the upper critical cooling rate. If the cooling rate is lower than the upper critical cooling rate, the steel material after tempering is mechanically Variations in characteristics occur. Therefore, it is desirable to cool at 10 ° C./s or more and to set the Vickers hardness Hv at the center of the steel material after tempering to a tensile strength TS (MPa) / 4 or more as measured by the total thickness. On the other hand, if the cooling rate is too high, there is a possibility that burning cracks may occur, so the cooling rate is preferably 1000 ° C./s or less. If a sufficient cooling rate can be ensured, the cooling may be performed by any method such as water cooling, oil cooling, gas cooling, or press cooling.
焼入処理後に焼戻処理を行うが、下記式（１）に表されるパラメータλが１１０００未満だと降伏比ＹＲを９０％以上とすることが困難となる。一方、パラメータλが１６５００超だと引張強度ＴＳを７００ＭＰａ以上とすることが困難となり、充分な鋼材の強度向上を図ることができない場合がある。したがって１１０００≦λ≦１６５００となる範囲で焼戻し処理を施す。なお降伏比ＹＲは高い方が望ましく、ＹＲが９５％以上となる条件で焼戻し処理を施すことが望ましい。また焼戻し後の強度が高すぎると靱性が低いため、焼戻し後の引張強度が１３５０ＭＰａ以下となる条件で焼戻し処理を施すことが望ましい。
λ＝Ｔ｛ｌｏｇ（ｔ）＋２０｝ （１）
ここで、式中のＴは焼戻温度（単位：Ｋ）、ｔは焼戻時間（単位：ｈ）を示す。
A tempering process is performed after the quenching process. If the parameter λ represented by the following formula (1) is less than 11000, it is difficult to set the yield ratio YR to 90% or more. On the other hand, if the parameter λ exceeds 16500, it will be difficult to make the tensile strength TS 700 MPa or more, and it may not be possible to sufficiently improve the strength of the steel material. Therefore, the tempering process is performed in the range of 11000 ≦ λ ≦ 16500. A higher yield ratio YR is desirable, and it is desirable to perform tempering under conditions where YR is 95% or more. Moreover, since the toughness is low when the strength after tempering is too high, it is desirable to perform the tempering treatment under the condition that the tensile strength after tempering is 1350 MPa or less.
λ = T {log (t) +20} (1)
Here, T in the formula represents a tempering temperature (unit: K), and t represents a tempering time (unit: h).
焼戻し処理における加熱方法は、焼入れと同じく、炉加熱、高周波加熱、通電加熱等のいずれの方法でも構わない。また鋼材全体を焼戻しても、部分的に焼戻しても構わない。
焼戻時間が短すぎると、パラメータλの制御が困難であり、かつ焼戻温度を高温とする必要があるため１秒間以上とすることが望ましい。一方焼戻時間が長すぎると焼戻処理に要するコストが嵩み、生産性が低下するため、１０００秒間以下とすることが望ましい。焼戻処理後の冷却方法は、水冷、油冷、ガス冷、あるいはプレス冷却等のいずれの方法で冷却しても構わない。冷却速度は特に規定しないが高いほうが望ましい。
The heating method in the tempering process may be any method such as furnace heating, high-frequency heating, and electric heating as in the case of quenching. Further, the entire steel material may be tempered or partially tempered.
If the tempering time is too short, it is difficult to control the parameter λ, and the tempering temperature needs to be high. On the other hand, if the tempering time is too long, the cost required for the tempering process increases and the productivity is lowered. As a cooling method after the tempering treatment, cooling may be performed by any method such as water cooling, oil cooling, gas cooling, or press cooling. Although the cooling rate is not particularly specified, a higher one is desirable.
このようにして得られた本発明にかかる鋼材の組織は、一般には焼戻しマルテンサイト組織であるが、化学組成によっては、また上記熱処理条件の範囲内でも一部ベイナイトが生じることがある。 The structure of the steel material according to the present invention thus obtained is generally a tempered martensite structure, but depending on the chemical composition, some bainite may be generated even within the range of the heat treatment conditions.
ここに、「焼戻し温度」は、鋼材の温度を計測する直接的方法により求めることが好ましいが、困難な場合には加熱媒体の温度を計測する間接的方法により求めてもよい。「焼戻し時間」は、上記方法によって計測される温度が目標温度に保持されている時間を言う。なお、焼戻し処理が連続的温度変化を伴う場合には、日本熱処理技術協会発行(2002年)雑誌「熱処理」42(3)P163に記載の方法でパラメータλを補正する。 Here, the “tempering temperature” is preferably obtained by a direct method of measuring the temperature of the steel material, but if difficult, it may be obtained by an indirect method of measuring the temperature of the heating medium. “Tempering time” refers to the time during which the temperature measured by the above method is maintained at the target temperature. In addition, the tempering process is to be accompanied by continuous temperature change corrects the parameter λ in accordance with the method described in Japanese heat treatment technology Association of issuance (2002) magazine "heat treatment" 42 (3) P163.
焼戻し処理後の鋼材の引張強度ＴＳＱＴ（ＭＰａ）は下記式（５）により近似することができ、パラメータλを１１０００〜１６５００となる条件で焼戻し処理を施すと、ＴＳＱＴに対して０.９×ＴＳＱＴ〜１.１×ＴＳＱＴの範囲の強度を持つ鋼材が得られる。
ＴＳＱＴ＝−０.１１×λ＋３７００×Ｃ＋１７６０ （５）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。
The tensile strength of the steel after tempering TS QT (MPa) can be approximated by the following equation (5), when subjected to a tempering treatment under the conditions to be from 11,000 to 16,500 parameters lambda, 0.9 against TS QT A steel material having a strength in the range of × TS QT to 1.1 × TS QT is obtained.
TS QT = −0.11 × λ + 3700 × C + 1760 (5)
Here, C in a formula shows C content (unit: mass%) in steel.
したがって、前記ＴＳＱＴと前記パラメータλとは下記式（２）を満足する。
（３７００×Ｃ−１.１×ＴＳＱＴ＋１７６０）／０.１１≦λ≦（３７００×Ｃ−０.９×ＴＳＱＴ＋１７６０）／０.１１ （２）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）、ＴＳＱＴは高強度鋼材の引張強度（ＭＰａ）を示す。
Therefore, the TS QT and the parameter λ satisfy the following formula (2).
(3700 × C-1.1 × TS QT + 1760) /1.11≦λ≦ (3700 × C−0.9 × TS QT + 1760) /1.11 (2)
Here, C in the formula indicates the C content (unit: mass%) in the steel, and TS QT indicates the tensile strength (MPa) of the high-strength steel material.
一般に、高強度鋼材については目標引張強度下限ＴＳＱＴ ｍｉｎ（ＭＰａ）が設定されるから、上記式（５）とその誤差量より、パラメータλが下記式（３）を満足する条件で焼戻し処理を施すことにより、目標引張強度下限ＴＳＱＴ ｍｉｎ（ＭＰａ）以上の引張強度を有する鋼材を得ることができる。
λ≦（３７００×Ｃ−０.９×ＴＳＱＴ ｍｉｎ＋１７６０）／０.１１ （３）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。
In general, since the target tensile strength lower limit TS QT min (MPa) is set for high-strength steel materials, the tempering treatment is performed under the condition that the parameter λ satisfies the following formula (3) from the above formula (5) and the error amount. By applying, a steel material having a tensile strength equal to or higher than the target tensile strength lower limit TS QT min (MPa) can be obtained.
λ ≦ (3700 × C−0.9 × TS QT min + 1760) /0.11 (3)
Here, C in a formula shows C content (unit: mass%) in steel.
また、高強度鋼材について目標引張強度上限ＴＳＱＴ ｍａｘ（ＭＰａ）が設定される場合には、上記式（５）とその誤差量より、パラメータλが下記式（４）を満足する条件で焼戻し処理を施すことにより、目標引張強度上限ＴＳＱＴ ｍａｘ（ＭＰａ）以下の引張強度を有する鋼材を得ることができる。
λ≧（３７００×Ｃ−１.１×ＴＳＱＴ ｍｉｎ＋１７６０）／０.１１ （４）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。
Further, when the target tensile strength upper limit TS QT max (MPa) is set for the high-strength steel material, the tempering process is performed under the condition that the parameter λ satisfies the following expression (4) from the above expression (5) and the error amount. By applying the above, it is possible to obtain a steel material having a tensile strength equal to or lower than the target tensile strength upper limit TS QT max (MPa).
λ ≧ (3700 × C−1.1 × TS QT min + 1760) /0.11 (4)
Here, C in a formula shows C content (unit: mass%) in steel.
表１の化学組成を有する鋼を溶製し、鍛造、熱間圧延して板厚２.６ｔの鋼材を作成した。この鋼材を加熱速度１００℃／ｓで９００℃のオーステナイト単相域まで昇温し、１０ｓ保持した後、水焼入れした。この鋼材を加熱温度５５０℃まで再び昇温し、１０ｓ保持した後、水冷することにより、式(1)のλ＝１４３５６に相当する焼戻し処理を行った。なお、このときの温度(K)、時間(t)は前述のようにして求めたものである。
熱処理前の鋼材、焼入れ後及び焼戻し後の鋼材をＪＩＳ５号引張試験片に加工し、引張速度３ｍｍ／ｍｉｎで引張試験を行った。
Steel having the chemical composition shown in Table 1 was melted, forged and hot-rolled to produce a steel material having a thickness of 2.6 t. The steel material was heated to an austenite single phase region of 900 ° C. at a heating rate of 100 ° C./s, held for 10 s, and then water quenched. The steel material was heated again to a heating temperature of 550 ° C., held for 10 s, and then water-cooled to perform a tempering treatment corresponding to λ = 14356 of formula (1). The temperature (K) and time (t) at this time are obtained as described above.
The steel material before heat treatment, the steel material after quenching and after tempering were processed into a JIS No. 5 tensile test piece, and a tensile test was performed at a tensile speed of 3 mm / min.
熱処理前の鋼材、焼入れ後、及び焼戻し後の鋼材の引張特性を表２に示す。 Table 2 shows the tensile properties of the steel before heat treatment, after quenching, and after tempering.
本発明の範囲よりＣ量及びＭｎ量が高い試番３と試番５は、熱処理前の降伏強度ＹＳが５００ＭＰａを超え、加工が困難である。
本発明の範囲よりＭｎ量が低い試番４は、焼入れ性が低く、焼入れ焼戻し後に十分な機械特性が得られない。
Sample No. 3 and No. 5 having a C amount and Mn amount higher than the range of the present invention have a yield strength YS before heat treatment exceeding 500 MPa, and are difficult to process.
Sample No. 4 having an Mn content lower than the range of the present invention has low hardenability and does not provide sufficient mechanical properties after quenching and tempering.
鋼材の化学成分が本発明の範囲内である試番２、及び試番６〜１６は、熱処理前の加工性は十分であり、焼戻し後にＹＲ：９０％以上、ＴＳ：７００ＭＰａ以上の機械的特性を持つ。 Sample Nos. 2 and 6 to 16 in which the chemical composition of the steel material is within the scope of the present invention have sufficient workability before heat treatment, and mechanical properties of YR: 90% or more and TS: 700 MPa or more after tempering. have.
Ｃ：０.２２％、Ｓｉ：０.２５％、Ｍｎ：１.２８％、Ｐ：０.００９％、Ｓ：０.００２％、Ａｌ：０.０４３％、Ｎ：０.００３％、Ｃｒ：０.１８％、Ｔｉ：０.０２１％、Ｂ：０.００１８％を含有する鋼を溶製し、鍛造、熱間圧延して板厚２.６ｔの鋼材を作成した。得られた鋼材を、表３に示す条件で二相焼入れまたは焼入れ焼戻しの熱処理を行った。得られた鋼材をＪＩＳ５号引張試験片に加工し、引張速度３ｍｍ／ｍｉｎで引張試験を行った。 C: 0.22%, Si: 0.25%, Mn: 1.28%, P: 0.009%, S: 0.002%, Al: 0.043%, N: 0.003%, Cr : Steel containing 0.18%, Ti: 0.021%, B: 0.0019% was melted and forged and hot-rolled to produce a steel material having a thickness of 2.6 t. The obtained steel was subjected to heat treatment of two-phase quenching or quenching and tempering under the conditions shown in Table 3. The obtained steel material was processed into a JIS No. 5 tensile test piece, and a tensile test was performed at a tensile speed of 3 mm / min.
図示結果から分かるように、比較例として示す二相焼入れ材は、引張強度ＴＳは高いが、降伏強度ＹＳが低く、ＹＲ９０％未満である。図１、図２参照。
As can be seen from the illustrated results, the two-phase hardened material shown as a comparative example has a high tensile strength TS but a low yield strength YS, which is less than 90% YR. See FIG. 1 and FIG.
一方、マルテンサイト単相域からの焼入れ材を、λが本発明で規定する１１０００≦λ≦１６５００の範囲内で焼戻すと、図１からも分かるように、本発明の範囲内の７００ＭＰａ以上の任意の目標引張強度の焼戻し材が得られ、しかも、図２からも分かるように、この範囲において特異的に降伏比ＹＲが９０％以上で引張強度ＴＳが７００ＭＰａ以上の機械的特性を持つ鋼材が得られる。しかし、λが本発明の範囲より小さい条件で焼戻すとＹＲが９０％未満であり、大きい条件で焼戻すとＴＳが７００ＭＰａ未満である。 On the other hand, when the tempered material from the martensite single phase region is tempered within the range of 11000 ≦ λ ≦ 16500 defined by the present invention, as can be seen from FIG. A tempered material having an arbitrary target tensile strength can be obtained, and, as can be seen from FIG. 2, a steel material having a mechanical property with a yield ratio YR of 90% or more and a tensile strength TS of 700 MPa or more specifically in this range. can get. However, if λ is tempered under a condition smaller than the range of the present invention, YR is less than 90%, and if tempered under a larger condition, TS is less than 700 MPa.
さらにλが本発明で規定する１１０００≦λ≦１６５００の範囲内で焼戻すと、焼戻し処理後の鋼材の引張強度は下記式（５）で表されるＴＳＱＴ（ＭＰａ）に対して０.９×ＴＳＱＴ〜１.１×ＴＳＱＴの範囲である。
ＴＳＱＴ＝−０.１１×λ＋３７００×Ｃ＋１７６０ （５）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。
Further, if λ is tempered within the range of 11000 ≦ λ ≦ 16500 defined in the present invention, the tensile strength of the steel material after the tempering treatment is 0.9 with respect to TS QT (MPa) represented by the following formula (5). × is in the range of TS QT ~1.1 × TS QT.
TS QT = −0.11 × λ + 3700 × C + 1760 (5)
Here, C in a formula shows C content (unit: mass%) in steel.
したがって、式(5)の関係を利用することで、目標の引張強度レベルであって、かつ90％以上の降伏比の鋼材が得られることが分かる。
なお、本例では、鋼の化学組成がCr、Ti、Bを含有するものであるが、実施例１の結果を参照すれば、鋼種２、６ないし７と、鋼種８以降が同じ傾向を示すことから、図１、図２の関係は鋼種２、６ないし７においても同様に成立し、目標強度レベルにおいていずれも９０％以上という高い降伏比を実現できることが分かる。
Therefore, it can be seen that a steel material having a target tensile strength level and a yield ratio of 90% or more can be obtained by utilizing the relationship of the formula (5).
In addition, in this example, although the chemical composition of steel contains Cr, Ti, and B, referring to the results of Example 1, steel types 2, 6 to 7, and steel types 8 and later show the same tendency. From the above, it can be seen that the relationship between FIG. 1 and FIG. 2 is similarly established for steel types 2, 6 to 7, and that a high yield ratio of 90% or more can be realized at the target strength level.
Claims (7)
λ＝Ｔ｛ｌｏｇ（ｔ）＋２０｝ （１）
ここで、式中のＴは焼戻温度（単位：Ｋ）、ｔは焼戻時間（単位：ｈ）を示す。 After the steel material having the chemical composition according to any one of claims 1 to 3 is made into an austenite single phase state, the steel material is cooled to a temperature range below the Ms point at a cooling rate equal to or higher than the upper critical cooling rate, and then the following formula ( A method for producing a high-strength steel material, characterized in that a tempering treatment is performed under the condition that the parameter λ defined in 1) is 11000-16500.
λ = T {log (t) +20} (1)
Here, T in the formula represents a tempering temperature (unit: K), and t represents a tempering time (unit: h).
（３７００×Ｃ−１.１×ＴＳＱＴ＋１７６０）／０.１１≦λ≦（３７００×Ｃ−０.９×ＴＳＱＴ＋１７６０）／０.１１ （２）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）、ＴＳＱＴは高強度鋼材の引張強度（ＭＰａ）を示す。 The method for producing a high-strength steel material according to claim 4, wherein the parameter λ satisfies the following formula (2).
(3700 × C-1.1 × TS QT + 1760) /1.11≦λ≦ (3700 × C−0.9 × TS QT + 1760) /1.11 (2)
Here, C in the formula indicates the C content (unit: mass%) in the steel, and TS QT indicates the tensile strength (MPa) of the high-strength steel material.
λ≦（３７００×Ｃ−０.９×ＴＳＱＴ ｍｉｎ＋１７６０）／０.１１ （３）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。 The tempering treatment is performed on the condition that the parameter λ satisfies the following formula (3) based on a target tensile strength lower limit TS QT min (MPa) of the high-strength steel material. Production method.
λ ≦ (3700 × C-0.9 × TS QT min +1760) /0.11 (3)
Here, C in a formula shows C content (unit: mass%) in steel.
λ≧（３７００×Ｃ−１.１×ＴＳＱＴ ｍａｘ＋１７６０）／０.１１ （４）
ここで、式中のＣは鋼中のＣ含有量（単位：質量％）を示す。 The high strength according to claim 4 or 6, wherein the tempering treatment is performed on the condition that the parameter λ satisfies the following formula (4) based on the target tensile strength upper limit TS QT max (MPa) of the high strength steel material. Steel manufacturing method.
λ ≧ (3700 × C−1.1 × TS QT max +1760) /0.11 (4)
Here, C in a formula shows C content (unit: mass%) in steel.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2006122205A JP4983082B2 (en) | 2006-04-26 | 2006-04-26 | High-strength steel and manufacturing method thereof |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2006122205A JP4983082B2 (en) | 2006-04-26 | 2006-04-26 | High-strength steel and manufacturing method thereof |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2007291464A true JP2007291464A (en) | 2007-11-08 |
| JP4983082B2 JP4983082B2 (en) | 2012-07-25 |
Family
ID=38762360
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2006122205A Active JP4983082B2 (en) | 2006-04-26 | 2006-04-26 | High-strength steel and manufacturing method thereof |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP4983082B2 (en) |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010248565A (en) * | 2009-04-15 | 2010-11-04 | Jfe Steel Corp | Ultrahigh-strength cold-rolled steel sheet superior in formability for extension flange, and method for manufacturing the same |
| JP4927236B1 (en) * | 2011-03-09 | 2012-05-09 | 新日本製鐵株式会社 | Steel sheet for hot stamping, manufacturing method thereof, and manufacturing method of high-strength parts |
| CN102877001A (en) * | 2012-10-29 | 2013-01-16 | 北京科技大学 | Low-carbon tempering-free all-bainite structure plastic mould steel and preparation method thereof |
| WO2014196645A1 (en) | 2013-06-07 | 2014-12-11 | 新日鐵住金株式会社 | Heat-treated steel material and method for producing same |
| KR101797316B1 (en) * | 2015-12-21 | 2017-11-14 | 주식회사 포스코 | Part for automobile having high strength and excellent durability and manufacturing method therefor |
| KR20170133495A (en) | 2015-04-08 | 2017-12-05 | 신닛테츠스미킨 카부시키카이샤 | Heat treated steel sheet member and method for manufacturing the same |
| KR20170134680A (en) | 2015-04-08 | 2017-12-06 | 신닛테츠스미킨 카부시키카이샤 | Steel sheet for heat treatment |
| JP2019529717A (en) * | 2016-07-08 | 2019-10-17 | 東北大学Ｎｏｒｔｈｅａｓｔｅｒｎ Ｕｎｉｖｅｒｓｉｔｙ | Hot stamp forming steel, hot stamp forming method, and hot stamp forming member |
| US11041225B2 (en) | 2015-04-08 | 2021-06-22 | Nippon Steel Corporation | Heat-treated steel sheet member and method for producing the same |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH06306460A (en) * | 1993-04-16 | 1994-11-01 | Nippon Steel Corp | Production of hot forged product with high fatigue strength |
| JPH0967645A (en) * | 1995-08-29 | 1997-03-11 | Kobe Steel Ltd | Thin steel sheet excellent in stretch-flanging property after shearing and sheet stock using the same thin steel sheet |
| JPH11131134A (en) * | 1997-10-30 | 1999-05-18 | Kobe Steel Ltd | Production of high strength formed part made of non-refining steel |
| JP2001123224A (en) * | 1999-10-27 | 2001-05-08 | Sumitomo Metal Ind Ltd | Method for producing high strength and high toughness non-heattreated parts |
| JP2001131680A (en) * | 1999-11-10 | 2001-05-15 | Sumitomo Metal Ind Ltd | High strength and high toughness non-heattreated cold formed parts and method for producing same |
| JP2005133181A (en) * | 2003-10-31 | 2005-05-26 | Sumitomo Metal Ind Ltd | High-strength cold-rolled steel sheet and manufacturing method therefor |
-
2006
- 2006-04-26 JP JP2006122205A patent/JP4983082B2/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH06306460A (en) * | 1993-04-16 | 1994-11-01 | Nippon Steel Corp | Production of hot forged product with high fatigue strength |
| JPH0967645A (en) * | 1995-08-29 | 1997-03-11 | Kobe Steel Ltd | Thin steel sheet excellent in stretch-flanging property after shearing and sheet stock using the same thin steel sheet |
| JPH11131134A (en) * | 1997-10-30 | 1999-05-18 | Kobe Steel Ltd | Production of high strength formed part made of non-refining steel |
| JP2001123224A (en) * | 1999-10-27 | 2001-05-08 | Sumitomo Metal Ind Ltd | Method for producing high strength and high toughness non-heattreated parts |
| JP2001131680A (en) * | 1999-11-10 | 2001-05-15 | Sumitomo Metal Ind Ltd | High strength and high toughness non-heattreated cold formed parts and method for producing same |
| JP2005133181A (en) * | 2003-10-31 | 2005-05-26 | Sumitomo Metal Ind Ltd | High-strength cold-rolled steel sheet and manufacturing method therefor |
Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010248565A (en) * | 2009-04-15 | 2010-11-04 | Jfe Steel Corp | Ultrahigh-strength cold-rolled steel sheet superior in formability for extension flange, and method for manufacturing the same |
| JP4927236B1 (en) * | 2011-03-09 | 2012-05-09 | 新日本製鐵株式会社 | Steel sheet for hot stamping, manufacturing method thereof, and manufacturing method of high-strength parts |
| KR101536703B1 (en) * | 2011-03-09 | 2015-07-14 | 신닛테츠스미킨 카부시키카이샤 | Steel sheets for hot stamping, method for manufacturing same, and method for manufacturing high-strength parts |
| CN102877001A (en) * | 2012-10-29 | 2013-01-16 | 北京科技大学 | Low-carbon tempering-free all-bainite structure plastic mould steel and preparation method thereof |
| WO2014196645A1 (en) | 2013-06-07 | 2014-12-11 | 新日鐵住金株式会社 | Heat-treated steel material and method for producing same |
| KR20160003263A (en) | 2013-06-07 | 2016-01-08 | 신닛테츠스미킨 카부시키카이샤 | Heat-treated steel material and method for producing same |
| US10435761B2 (en) | 2013-06-07 | 2019-10-08 | Nippon Steel Corporation | Heat-treated steel material and method of manufacturing the same |
| KR20170134680A (en) | 2015-04-08 | 2017-12-06 | 신닛테츠스미킨 카부시키카이샤 | Steel sheet for heat treatment |
| KR20170133495A (en) | 2015-04-08 | 2017-12-05 | 신닛테츠스미킨 카부시키카이샤 | Heat treated steel sheet member and method for manufacturing the same |
| US10563281B2 (en) | 2015-04-08 | 2020-02-18 | Nippon Steel Corporation | Heat-treated steel sheet member and method for producing the same |
| US10822680B2 (en) | 2015-04-08 | 2020-11-03 | Nippon Steel Corporation | Steel sheet for heat treatment |
| US11041225B2 (en) | 2015-04-08 | 2021-06-22 | Nippon Steel Corporation | Heat-treated steel sheet member and method for producing the same |
| KR101797316B1 (en) * | 2015-12-21 | 2017-11-14 | 주식회사 포스코 | Part for automobile having high strength and excellent durability and manufacturing method therefor |
| JP2019529717A (en) * | 2016-07-08 | 2019-10-17 | 東北大学Ｎｏｒｔｈｅａｓｔｅｒｎ Ｕｎｉｖｅｒｓｉｔｙ | Hot stamp forming steel, hot stamp forming method, and hot stamp forming member |
| JP2022023165A (en) * | 2016-07-08 | 2022-02-07 | 東北大学 | Steel material for hot stamp forming, hot stamp forming method, and hot stamp forming member |
| US11377703B2 (en) | 2016-07-08 | 2022-07-05 | Northeastern University | Steel material for hot stamping, hot stamping process and hot stamped component |
Also Published As
| Publication number | Publication date |
|---|---|
| JP4983082B2 (en) | 2012-07-25 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN110832098B (en) | Hot-rolled steel sheet and method for producing same | |
| EP3239339B1 (en) | Product formed from heat treatable steel having ultra high strength and excellent durability, and method for manufacturing same | |
| JP6341214B2 (en) | Hot-formed steel plate member, method for producing the same, and hot-formed steel plate | |
| JP6306711B2 (en) | Martensitic steel with delayed fracture resistance and manufacturing method | |
| JP4947176B2 (en) | Manufacturing method of ultra-high strength cold-rolled steel sheet | |
| KR101621639B1 (en) | Steel sheet, plated steel sheet, method for producing steel sheet, and method for producing plated steel sheet | |
| JP4983082B2 (en) | High-strength steel and manufacturing method thereof | |
| CN104513927B (en) | A kind of tensile strength 800MPa grade high-strength high-tenacity steel plate and its manufacture method | |
| WO2015102051A1 (en) | Hot-formed member and process for manufacturing same | |
| EP3653736B1 (en) | Hot-rolled steel strip and manufacturing method | |
| MXPA97008775A (en) | Process to produce steel pipe without seams of great strength having excellent resistance to the fissure by tensions by sulf | |
| JP6229736B2 (en) | Hot-formed member and method for producing the same | |
| WO2014061270A1 (en) | High-strength cold-rolled steel sheet and method for manufacturing same | |
| JP2007031733A (en) | STEEL HAVING EXCELLENT DELAYED FRACTURE RESISTANCE AND TENSILE STRENGTH IN CLASS OF >=1,600 MPa, AND METHOD FOR PRODUCING FORMING THEREOF | |
| EP2562272B1 (en) | Method for producing steel product or steel component having excellent mechanical properties, steel product produced by the method and use of steel pipe made of strain hardened steel | |
| WO2015004906A1 (en) | High-carbon hot-rolled steel sheet and production method for same | |
| CN107747039A (en) | A kind of high reaming performance cold-rolled biphase steel and preparation method thereof | |
| KR20240000646A (en) | Hot rolled steel sheet with high hole expansion ratio and manufacturing process thereof | |
| JP5857913B2 (en) | Hot-formed steel plate member, method for producing the same, and hot-formed steel plate | |
| KR102209555B1 (en) | Hot rolled and annealed steel sheet having low strength-deviation, formed member, and manufacturing method of therefor | |
| JP2005240135A (en) | Method for manufacturing wear-resistant steel having excellent bendability, and wear-resistant steel | |
| JP4265582B2 (en) | Hot-rolled steel sheet with excellent impact properties after quenching and method for producing the same | |
| JP5228963B2 (en) | Cold rolled steel sheet and method for producing the same | |
| JP5363867B2 (en) | High strength cold-rolled steel sheet with excellent elongation and stretch flangeability | |
| JP4265583B2 (en) | Cold-rolled steel sheet having excellent toughness after quenching and method for producing the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20080523 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20100728 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20110322 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20110517 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20120327 |
|
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20120409 |
|
| R150 | Certificate of patent or registration of utility model |
Ref document number: 4983082 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R150 Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150511 Year of fee payment: 3 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150511 Year of fee payment: 3 |
|
| S111 | Request for change of ownership or part of ownership |
Free format text: JAPANESE INTERMEDIATE CODE: R313111 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20150511 Year of fee payment: 3 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| S533 | Written request for registration of change of name |
Free format text: JAPANESE INTERMEDIATE CODE: R313533 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |