JP4308689B2 - High-strength steel with good workability and method for producing the same - Google Patents
High-strength steel with good workability and method for producing the same Download PDFInfo
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この発明は、加工性の良好な高強度鋼およびその製造方法、特に、建築材料あるいは自動車の構造用部品や補強部材などに適用される、加工性の良好な高強度鋼およびその製造方法に関するものである。 The present invention relates to a high-strength steel having good workability and a method for producing the same , and more particularly to a high-strength steel having good workability and a method for producing the same that are applied to building materials or structural parts and reinforcing members of automobiles. It is.
建築物の耐震性能向上あるいは自動車に対する軽量化や衝突安全性のニーズの高まりを背景として、引張強度７８０ＭＰａを超える超高強度鋼板の適用が拡大している。このような社会ニーズを背景として、加工性に優れた超高強度鋼板に関する発明が数多く開示されている。 The application of ultra-high-strength steel sheets with a tensile strength exceeding 780 MPa is expanding against the background of the improvement in the earthquake resistance performance of buildings and the growing needs for weight reduction and collision safety for automobiles. Many inventions related to ultra-high strength steel sheets with excellent workability have been disclosed against the background of such social needs.
一方、近年、自動車産業を含めて鉄鋼材料では、リサイクル事業が本格化しており、除去不可能なＣｕやＳｎといったトランプエレメントを逆に有効活用することもニーズとして高まってきている。特にＣｕについては、比較的多量のＣｕを固溶させられ、析出強化鋼の成分設計に活用し得ることから、Ｃｕ添加高強度鋼に関しては、これまで、多くの発明が開示されている。特許文献１および特許文献２にＣｕ添加高強度鋼が開示されている。
On the other hand, in recent years, in the steel materials including the automobile industry, the recycling business has become full-scale, and the need to effectively use the trump elements such as Cu and Sn that cannot be removed is increasing as a need. In particular, with regard to Cu, since a relatively large amount of Cu can be dissolved, and can be used for designing the components of precipitation-strengthened steel, many inventions have been disclosed regarding Cu-added high-strength steel. Patent Document 1 and
しかしながら、特許文献１および特許文献２に開示されているＣｕ添加高強度鋼は、Ｃｕ添加量を高々２％、大半は１．５％程度までを検討の上限としたもので、強度レベルの面でも５９０ＭＰａクラスのものが中心である。すなわち、これまでのＣｕ添加高強度鋼は、Ｃｕの本来有する高強度鋼への適用の最大限化を必ずしも明確にしたものではない。
However, the Cu-added high-strength steels disclosed in Patent Document 1 and
この発明は、上記先行技術の実態を鑑み、高強度鋼へのＣｕ適用の最大限化について鋭意検討し、近年各分野にて需要の高まる加工性の良好な高強度鋼板を得ることを課題とする。 In view of the actual state of the prior art described above, the present invention has been intensively studied to maximize the application of Cu to high-strength steel, and it is an object to obtain a high-strength steel sheet with good workability that has recently increased in demand in each field. To do.
本発明者らは、上述したように、高強度鋼の加工性へのＣｕ適用の最大限化について、Ｃｕ添加量、Ｃｕ粒子析出母相の影響、析出温度と時間との影響およびこれらの機械的性質に及ぼす影響について鋭意検討した。この結果、下記（１）から（４）の知見を得た。 As described above, the inventors of the present invention have made it possible to maximize the application of Cu to the workability of high-strength steel, the amount of Cu added, the influence of the Cu particle precipitation matrix, the influence of precipitation temperature and time, and these machines. The effects on the physical properties were investigated. As a result, the following findings (1) to (4) were obtained.
（１）Ｃｕの析出速度、分布形態を制御するには、析出母相の転位密度制御が重要で、転位密度を上昇させることで、より速く、より均一微細にＣｕを鋼中に分散することができる。特に、鋼の高温からの急冷相変態であるマルテンサイト変態を活用することで、均一な高転位密度の導入が可能であり、これを母相とすることで、理想的なＣｕの分散状態が得られる。 (1) In order to control the precipitation rate and distribution form of Cu, it is important to control the dislocation density of the precipitation matrix phase. By increasing the dislocation density, Cu can be dispersed more uniformly and finely in the steel. Can do. In particular, it is possible to introduce a uniform high dislocation density by utilizing the martensite transformation, which is a rapid cooling phase transformation from a high temperature of steel. By using this as a parent phase, an ideal Cu dispersion state can be obtained. can get.
（２）母相を制御する鋼成分の中では、特に焼入れ性を高めるＭｎとマルテンサイトの転位密度を高めるＣの影響が大きい。特にＣについては、ある下限値以下になるとＣｕの均一微細な析出分散が不十分となる。 (2) Among the steel components that control the matrix, the influence of Mn, which increases hardenability, and C, which increases the dislocation density of martensite, is particularly large. In particular, for C, when it is below a certain lower limit value, the uniform fine dispersion of Cu becomes insufficient.
（３）上述の知見より、マルテンサイト組織を母相に、特定温度にてＣｕ時効処理を施すことで、鋼中に軟質なＣｕ粒子が均一微細に分散し、かつ、同時に母相は適度に焼戻されて加工性の回復した焼戻しマルテンサイトとなり、高強度ながら延性が極めて良好な材質を得られる。ただし、適正な時効時間を過ぎて時効すると、Ｃｕ粒子の粗大化とマトリクスの過剰回復による強度の低下が著しく、良好な強度−延性バランスが保たれなくなるので、時効温度と時間については、Ｃｕ添加量に応じて精密な制御が必要である。 (3) From the above knowledge, by performing Cu aging treatment at a specific temperature with a martensite structure as a parent phase, soft Cu particles are uniformly and finely dispersed in the steel, and at the same time, the parent phase is moderately It becomes tempered martensite that has been tempered to recover its workability, and a material having high strength and extremely good ductility can be obtained. However, if the aging is performed after an appropriate aging time, the strength is significantly reduced due to the coarsening of the Cu particles and the excessive recovery of the matrix, so that a good strength-ductility balance cannot be maintained. Precise control is necessary according to the amount.
（４）また、上記のような延性向上効果は、Ｃｕ添加量に強く依存し、Ｃｕ添加量の増大にともない材料の強度−延性バランスは向上する。その効果は２％を超えて顕著となる。なお、析出Ｃｕ粒子の粒径は小さすぎても、粗大化しすぎても析出強化能が不十分となるため、粒径は１〜１００ｎｍが適正値である。 (4) The effect of improving ductility as described above depends strongly on the amount of Cu added, and the strength-ductility balance of the material improves as the amount of Cu added increases. The effect becomes remarkable exceeding 2%. In addition, since the precipitation strengthening ability will become inadequate even if the particle size of precipitation Cu particle | grains is too small or it coarsens too much, 1-100 nm is an appropriate value for a particle size.
この発明は、上述した知見に基づきなされたものであって、下記を特徴とするものである。 The present invention has been made on the basis of the above-described knowledge, and is characterized by the following.
請求項１記載の発明は、質量％で、Ｃ：０．０６〜０．３％、Ｓｉ：２％以下、Ｍｎ：１〜３％、Ｃｕ：２〜５％、Ｐ：０．０８％以下、Ｓ：０．０１％以下、sol.Ａｌ:０．１％以下、Ｎ：０．００７％以下を含有し、残部：Ｆｅおよび不可避的不純物からなる鋼で、その金属組織が焼戻しマルテンサイトまたは焼戻しマルテンサイトおよびフェライトからなる組織であって、該組織中に粒径１〜１００ｎｍの微細析出Ｃｕ粒子が分散していることを特徴とする、引張強度が１０００ＭＰａ超の加工性の良好な高強度鋼である。
Invention of Claim 1 is mass%, C: 0.06-0.3%, Si: 2% or less, Mn: 1-3%, Cu: 2-5%, P: 0.08% or less , S: 0.01% or less, sol.Al: 0.1% or less, N: 0.007% or less , balance: steel made of Fe and inevitable impurities , the metal structure of which is tempered martensite or A structure composed of tempered martensite and ferrite , wherein fine precipitated Cu particles having a particle size of 1 to 100 nm are dispersed in the structure, and has a high tensile strength of over 1000 MPa and good workability It is steel.
請求項２記載の発明は、請求項１に記載の成分を有する鋼を、Ａｒ3変態点以上にて仕上げ圧延後、３０℃／sec以上の冷却速度で３００℃以下まで冷却し、その後、４００〜７００℃で下記（１）式によって定まる時間（ｔ(A)min）、時効処理し、かくして、金属組織が焼戻しマルテンサイトを主体とする組織であって、該組織中に粒径１〜１００ｎｍの微細析出Ｃｕ粒子が分散していることに特徴を有するものである。
The invention described in
{(631-14.5×Cu)-T}/(8.7×Cu+76.9)≦ln(t(A))≦{(705-7×Cu)-T}/(1.1×Cu+35.5)
---（１）
但し、（１）式において、Ｃｕ：Ｃｕ添加量（質量％）、ｔ(A)：時効時間（min）、Ｔ：時効温度（℃）である。
{(631-14.5 × Cu) -T} / (8.7 × Cu + 76.9) ≦ ln (t (A)) ≦ {(705-7 × Cu) -T} / (1.1 × Cu + 35.5)
--- (1)
In the formula (1), Cu: Cu addition amount (mass%), t (A): aging time (min), and T: aging temperature (° C.).
請求項３記載の発明は、請求項１に記載の成分を有する鋼を、Ａｒ3変態点以上にて仕上げ圧延後、酸洗、あるいはさらに３０％以上の冷圧率で冷間圧延し、８００℃以上に均熱後３０℃／sec以上の冷却速度で３００℃以下まで冷却し、その後、４００〜７００℃で下記式によって定まる時間（ｔ(A)min）、時効処理し、かくして、金属組織が焼戻しマルテンサイトを主体とする組織であって、該組織中に粒径１〜１００ｎｍの微細析出Ｃｕ粒子が分散していることに特徴を有するものである。 The invention described in claim 3 is a steel having the components described in claim 1 after finish rolling at an Ar 3 transformation point or higher, pickling, or cold rolling at a cold pressure ratio of 30% or higher, and 800 After soaking to above ℃, it is cooled to below 300 ℃ at a cooling rate of at least 30 ℃ / sec. Is a structure mainly composed of tempered martensite, and is characterized in that fine precipitated Cu particles having a particle diameter of 1 to 100 nm are dispersed in the structure.
{(631-14.5×Cu)-T}/(8.7×Cu+76.9)≦ln(t(A))≦{(705-7×Cu)-T}/(1.1×Cu+35.5) ---（１）
但し、（１）式において、Ｃｕ：Ｃｕ添加量（質量％）、ｔ(A)：時効時間（min）、Ｔ：時効温度（℃）である。
{(631-14.5 × Cu) -T} / (8.7 × Cu + 76.9) ≦ ln (t (A)) ≦ {(705-7 × Cu) -T} / (1.1 × Cu + 35.5) --- (1)
In the formula (1), Cu: Cu addition amount (mass%), t (A): aging time (min), and T: aging temperature (° C.).
この発明によれば、建築材料あるいは自動車の構造用部品や補強部材などへの高強度鋼の適用範囲を飛躍的に増大させることができ、建築物の耐震性向上や、自動車の軽量化への貢献による省エネルギー化を図ることができる。 According to the present invention, the range of application of high-strength steel to building materials or structural parts and reinforcing members of automobiles can be dramatically increased, improving the earthquake resistance of buildings and reducing the weight of automobiles. Energy savings can be achieved through contributions.
この発明における成分限定理由について述べる。なお、各成分添加量の％は、何れも質量％である。 The reason for component limitation in this invention will be described. In addition, all% of each component addition amount is the mass%.
（Ｃ：０．０６〜０．３％）
上述した通り、Ｃは、マルテンサイト変態時に鋼中に高密度の転位を導入する上で、必須の元素である。すなわち、下限は、時効過程において析出Ｃｕ粒子を均一に分散させるために最低限必要なＣ量であり、上限は、これ以上添加しても効果が飽和するために規定する。
(C: 0.06-0.3%)
As described above, C is an essential element for introducing high-density dislocations in steel during martensitic transformation. That is, the lower limit is the minimum amount of C necessary to uniformly disperse the precipitated Cu particles in the aging process, and the upper limit is specified so that the effect is saturated even if added more than this.
（Ｓｉ：２％以下）
Ｓｉは、過剰に添加すると、鋼の靭性を劣化させるため上限を２％に規定する。
(Si: 2% or less)
If Si is added excessively, the upper limit is defined as 2% in order to deteriorate the toughness of the steel.
（Ｍｎ：１〜３％）
Ｍｎは、鋼の焼入れ性を確保してマルテンサイト組織を得るために必須の元素である。すなわち、下限は、マルテンサイト組織を得るための最低限量として、また、上限は、これ以上添加しても効果が飽和するために規定する。
(Mn: 1-3%)
Mn is an essential element for securing the hardenability of steel and obtaining a martensite structure. That is, the lower limit is defined as a minimum amount for obtaining a martensite structure, and the upper limit is defined so that the effect is saturated even if added more than this.
（Ｃｕ：２〜５％）
Ｃｕは、この発明において極めて重要な添加元素である。上述した通り、Ｃｕ添加量が２％未満であると、析出するＣｕ量が不十分となり、所望の効果が得られなくなるため、また、５％を超えて添加しても効果が飽和するため、これを上限とする。
(Cu: 2 to 5%)
Cu is an extremely important additive element in the present invention. As described above, if the amount of Cu added is less than 2%, the amount of precipitated Cu becomes insufficient, and the desired effect cannot be obtained, and even if added over 5%, the effect is saturated. This is the upper limit.
Ｐ、Ｓは、特に規定していないが、何れも含有量が高くなると、鋼の靭性や加工性が劣化して好ましくないので、それぞれ０．０８％以下、０．０１％以下であることが望ましい。 P and S are not particularly defined, but if the content of both is high, the toughness and workability of the steel deteriorate, which is not preferable. Therefore, it is 0.08% or less and 0.01% or less, respectively. desirable.
また、sol.ＡｌとＮとは、通常の鋼に含有される量であれば、この発明の効果を損なわず、それぞれ０．１％以下、０．００７％以下であれば良い。 Moreover, sol.Al and N may be 0.1% or less and 0.007% or less, respectively, as long as they are contained in ordinary steel, without impairing the effects of the present invention.
上記成分組成以外の残部は、実質的にＦｅおよび不可避的不純物とする。なお、この発明の作用効果を害さない範囲で、微量元素を含有することは許される。 The balance other than the above component composition is substantially Fe and inevitable impurities. It should be noted that it is allowed to contain a trace element as long as the effects of the present invention are not impaired.
この発明の効果を得るには、上記のごとく鋼成分を限定した上で、前述したように組織を焼戻しマルテンサイトを主体とする組織として、均一微細にＣｕ分子を分散させる必要がある。焼戻しマルテンサイトを主体とする組織とは、焼戻しマルテンサイトの体積率が７０％以上で、残部フェライト組織から成る組織である。焼戻しマルテンサイトの体積率が７０％未満では、Ｃｕ粒子の析出が焼戻しマルテンサイトの分布に対応して不均一となり、加工性が劣化する。また、Ｃｕ粒子径については、小さすぎても粗大化しすぎても強化能が低下して、強度−延性バランスは劣化する。このため、Ｃｕ粒子径は、１〜１００ｎｍの範囲内とする。 In order to obtain the effect of the present invention, it is necessary to uniformly disperse Cu molecules as a structure mainly composed of tempered martensite as described above after limiting the steel components as described above. The structure mainly composed of tempered martensite is a structure having a volume ratio of tempered martensite of 70% or more and composed of the remaining ferrite structure. If the volume ratio of tempered martensite is less than 70%, the precipitation of Cu particles becomes non-uniform corresponding to the distribution of tempered martensite, and workability deteriorates. Further, regarding the Cu particle diameter, if it is too small or too coarse, the strengthening ability is lowered and the strength-ductility balance is deteriorated. For this reason, Cu particle diameter shall be in the range of 1-100 nm.
次に、この発明の鋼板の製造法に関して説明する。 Next, the manufacturing method of the steel plate of this invention is demonstrated.
まず、鋳造後、熱間圧延を行う。加熱温度は、以降の圧延に支障をきたさなければ特段不都合は生じなく、１１００〜１３００℃の範囲内であれば良い。続く仕上げ熱間圧延では、仕上げ温度がＡｒ3変態点未満であると、組織の不均一が助長されて加工性に悪影響を及ぼすので、下限をＡｒ3変態点とする。仕上げ圧延後は、冷却を行うが、熱間圧延後にマルテンサイト組織を得る場合には、熱延終了後の冷却速度を３０℃／sec 以上として、３００℃以下まで冷却する必要がある。冷却速度が３０℃／sec 未満であったり、冷却停止温度が３００℃を超えると、マルテンサイト組織が十分得られなくなり、この発明の効果が得られなくなる。 First, hot rolling is performed after casting. The heating temperature is not particularly inconvenient as long as it does not hinder subsequent rolling, and may be in the range of 1100 to 1300 ° C. In the subsequent finish hot rolling, if the finishing temperature is lower than the Ar 3 transformation point, the non-uniformity of the structure is promoted and the workability is adversely affected, so the lower limit is made the Ar 3 transformation point. Although cooling is performed after finish rolling, when a martensite structure is obtained after hot rolling, it is necessary to cool to 300 ° C. or less by setting the cooling rate after hot rolling to 30 ° C./sec or more. If the cooling rate is less than 30 ° C./sec or the cooling stop temperature exceeds 300 ° C., a martensite structure cannot be obtained sufficiently, and the effects of the present invention cannot be obtained.
熱間圧延時にマルテンサイト組織を得ずに、その後、酸洗あるいは冷間圧延を経た後、焼入れ−時効処理を行う場合には、熱延後の熱履歴は特に制限は必要ない。 In the case of performing quenching-aging treatment after pickling or cold rolling without obtaining a martensite structure during hot rolling, the heat history after hot rolling is not particularly limited.
熱間圧延後に酸洗あるいは冷間圧延を経た後、焼入れ−時効処理を行う場合には、まず、マルテンサイト組織を得るため、８００℃以上に均熱後、３０℃／sec以上の冷却速度で３００℃以下まで冷却する。冷却速度の下限は、これ以下ではマルテンサイト組織を得られないため規定する。均熱後の急速冷却は、均熱後に直ちに行ってもよいが、パーライトが析出しない範囲で急冷開始温度を下げても良い。この場合、急冷開始温度は６００℃を下回らないことが必要である。 In the case of performing quenching and aging treatment after pickling or cold rolling after hot rolling, first, in order to obtain a martensite structure, after soaking to 800 ° C or higher, at a cooling rate of 30 ° C / sec or higher. Cool to below 300 ° C. The lower limit of the cooling rate is specified because a martensite structure cannot be obtained below this. The rapid cooling after soaking may be performed immediately after soaking, but the rapid cooling start temperature may be lowered within a range where pearlite does not precipitate. In this case, it is necessary that the rapid cooling start temperature does not fall below 600 ° C.
なお、熱間圧延時あるいはその後の熱処理によりマルテンサイトを得る場合の冷却速度については３０℃／sec以上と規定したが、好ましくは１００℃／sec以上として、より均一なマルテンサイト組織を得ることが望ましい。 The cooling rate when martensite is obtained during hot rolling or subsequent heat treatment is defined as 30 ° C./sec or more, but preferably 100 ° C./sec or more to obtain a more uniform martensite structure. desirable.
上記のように熱間圧延後、あるいはさらに酸洗・冷圧後、マルテンサイト組織を得た後、Ｃｕ粒子を均一微細に分散させるとともにマルテンサイト組織を適度に焼戻すため、所定の温度と時間で時効処理を行う。冷間圧延率は３０％以上として、組織の不均一が生じないようにする必要がある。時効温度は４００〜７００℃とするが、これは４００℃未満ではＣｕ粒子の析出およびマルテンサイトの焼戻しが不十分となり、良好な強度−延性バランスが得られなくなり、また、７００℃を超えて時効すると、析出するＣｕ粒子が極端に粗大化するとともに、マルテンサイト組織も過剰に焼戻されて強度低下が著しくなるためである。 After hot rolling as described above, or after further pickling / cold pressing, a martensite structure is obtained, and then the Cu particles are uniformly and finely dispersed and the martensite structure is appropriately tempered in order to obtain a predetermined temperature and time. The aging process is performed. The cold rolling rate should be 30% or more so as not to cause uneven structure. The aging temperature is set to 400 to 700 ° C. However, when the temperature is less than 400 ° C., the precipitation of Cu particles and the tempering of martensite become insufficient, and a good strength-ductility balance cannot be obtained. Then, the precipitated Cu particles become extremely coarse, and the martensite structure is excessively tempered, resulting in a significant decrease in strength.
時効時間については、Ｃｕ添加量と時効温度とによって、最適なＣｕ粒子分散形態を得るための条件が異なってくるため、仔細な制御が必要になる。この条件は、種々Ｃｕ添加量の異なる鋼を時効時間毎に特性を仔細に調査することで明らかとすることができた。 As for the aging time, since the conditions for obtaining the optimum Cu particle dispersion form vary depending on the amount of Cu added and the aging temperature, fine control is required. This condition could be clarified by investigating the characteristics of various steels with different amounts of Cu added for each aging time.
具体的には、下記（１）式にて最適時効時間が与えられる。 Specifically, the optimum aging time is given by the following equation (1).
{(631-14.5×Cu)-T}/(8.7×Cu+76.9)≦ln(t(A))≦{(705-7×Cu)-T}/(1.1×Cu+35.5)
---（１）
但し、上記（１）式において、
Ｃｕ：Ｃｕ添加量（質量％）、
ｔ(A)：時効時間（min）、
Ｔ：時効温度（℃）
である。
{(631-14.5 × Cu) -T} / (8.7 × Cu + 76.9) ≦ ln (t (A)) ≦ {(705-7 × Cu) -T} / (1.1 × Cu + 35.5)
--- (1)
However, in the above equation (1),
Cu: Cu addition amount (mass%),
t (A): Aging time (min),
T: Aging temperature (° C)
It is.
上記（１）式によれば、Ｃｕ添加量が多くなるほど、また、時効温度が高くなるほど、最適時効時間は短時間側に移行する。これは、Ｃｕ添加量が多くても、また時効温度が高くても、Ｃｕ粒子の析出する速度が大きくなり、粗大化も速く進行するため、これらの条件に応じて時効処理を制御する必要があるためである。 According to the above formula (1), the optimum aging time shifts to the short time side as the Cu addition amount increases and the aging temperature increases. This is because even if the amount of Cu added is large or the aging temperature is high, the rate of precipitation of Cu particles increases and the coarsening progresses rapidly, so it is necessary to control the aging treatment according to these conditions. Because there is.
その他、特に言及していないが、造塊あるいは連続鋳造によるスラブ製造法や、熱延での粗熱延バー接続による連続熱延、また、熱間圧延過程でのインダクションヒーターを利用した２００℃以内の昇温などは、この発明の効果に対して影響を及ぼさない。 Other than that, although not specifically mentioned, within 200 ° C using slab manufacturing method by ingot casting or continuous casting, continuous hot rolling by rough hot-rolling bar connection in hot rolling, and induction heater in hot rolling process The temperature rise or the like does not affect the effect of the present invention.
以下に、この発明を実施例によりさらに説明する。 Hereinafter, the present invention will be further described with reference to examples.
まず、表１に成分を示す本発明成分鋼Ａ〜Ｍと比較成分鋼ａ〜ｈとを準備し、１１００℃で加熱した後、仕上げ温度８７０℃で熱延を行った。続いて、表２に示す条件で一部は熱延終了後、一部は酸洗あるいは冷間圧延して種々の条件で時効処理を行った。また、これらの鋼材より圧延直角方向にＪＩＳ５号試験片を採取して、引張試験を行った結果、組織観察結果、および析出Ｃｕ粒子の粒径測定結果を合わせて表２に示す。図１には、強度−延性バランスの指標であるＴＳ×Ｅｌ値に及ぼすＣｕ添加量の影響を示す。 First, the present invention component steels A to M and comparative component steels a to h whose components are shown in Table 1 were prepared, heated at 1100 ° C., and then hot-rolled at a finishing temperature of 870 ° C. Subsequently, some of the conditions shown in Table 2 were subjected to aging treatment under various conditions after completion of hot rolling and partly pickling or cold rolling. Further, JIS No. 5 test pieces were collected from these steel materials in the direction perpendicular to the rolling direction, the results of the tensile test, the structure observation results, and the particle size measurement results of the precipitated Cu particles are shown together in Table 2. FIG. 1 shows the effect of the amount of Cu added on the TS × El value, which is an index of the strength-ductility balance.
表２および図１から明らかなように、鋼成分と組織および析出Ｃｕ粒子径とを本発明範囲内に制御することにより、引張強度が１０００ＭＰａを超える超高強度とともにＴＳ×Ｅｌ値で１８０００を超える良好な加工性を有する鋼材が得られていることがわかる。これに対して、成分が本発明範囲外の鋼や、成分が範囲内にあるものの製造条件が本発明範囲外である鋼の場合、ＴＳ×Ｅｌ値は１７０００を下回っていることがわかる。 As is apparent from Table 2 and FIG. 1, by controlling the steel component, the structure, and the precipitated Cu particle diameter within the range of the present invention, the tensile strength exceeds 18000 in TS × El value together with ultrahigh strength exceeding 1000 MPa. It turns out that the steel material which has favorable workability is obtained. On the other hand, when the steel is out of the scope of the present invention and the steel is in the range of manufacturing conditions but out of the scope of the present invention, the TS × El value is less than 17,000.
Claims (3)
Ｃ ：０．０６〜０．３％、
Ｓｉ：２％以下、
Ｍｎ：１〜３％、
Ｃｕ：２〜５％、
Ｐ ：０．０８％以下、
Ｓ ：０．０１％以下、
sol.Ａｌ:０．１％以下、
Ｎ ：０．００７％以下
を含有し、
残部：Ｆｅおよび不可避的不純物
からなる鋼で、その金属組織が焼戻しマルテンサイトまたは焼戻しマルテンサイトおよびフェライトからなる組織であって、該組織中に粒径１〜１００ｎｍの微細析出Ｃｕ粒子が分散していることを特徴とする、引張強度が１０００ＭＰａ超の加工性の良好な高強度鋼。 % By mass
C: 0.06-0.3%,
Si: 2% or less,
Mn: 1-3%
Cu: 2 to 5%,
P: 0.08% or less,
S: 0.01% or less,
sol.Al: 0.1% or less,
N: 0.007% or less ,
Remainder: Steel composed of Fe and unavoidable impurities , the metal structure of which is tempered martensite or tempered martensite and ferrite , and finely precipitated Cu particles having a particle size of 1 to 100 nm in the structure Is a high-strength steel with good workability having a tensile strength of over 1000 MPa , characterized by being dispersed.
{(631-14.5×Cu)-T}/(8.7×Cu+76.9)≦ln(t(A))≦{(705-7×Cu)-T}/(1.1×Cu+35.5)
---（１）
但し、上記（１）式において、
Ｃｕ：Ｃｕ添加量（質量％）、
ｔ(A)：時効時間（min）、
Ｔ：時効温度（℃）
である。 The steel having the component according to claim 1 is finish-rolled at an Ar 3 transformation point or higher, then cooled to 300 ° C. or lower at a cooling rate of 30 ° C./sec or higher, and then at 400 to 700 ° C. (1) A method for producing high-strength steel with good workability, characterized by performing an aging treatment for a time determined by an equation (t (A) min).
{(631-14.5 × Cu) -T} / (8.7 × Cu + 76.9) ≦ ln (t (A)) ≦ {(705-7 × Cu) -T} / (1.1 × Cu + 35.5)
--- (1)
However, in the above equation (1),
Cu: Cu addition amount (mass%),
t (A): Aging time (min),
T: Aging temperature (° C)
It is.
{(631-14.5×Cu)-T}/(8.7×Cu+76.9)≦ln(t(A))≦{(705-7×Cu)-T}/(1.1×Cu+35.5)
---（１）
但し、上記（１）式において、
Ｃｕ：Ｃｕ添加量（質量％）、
ｔ(A)：時効時間（min）、
Ｔ：時効温度（℃）
である。 The steel having the component according to claim 1 is finish-rolled at an Ar 3 transformation point or higher, pickled, or further cold-rolled at a cold pressure ratio of 30% or higher, soaked to 800 ° C. or higher, and 30 It is cooled to 300 ° C. or less at a cooling rate of at least ° C./sec, and then subjected to aging treatment at 400 to 700 ° C. for a time (t (A) min) determined by the following formula (1). Manufacturing method of good high strength steel.
{(631-14.5 × Cu) -T} / (8.7 × Cu + 76.9) ≦ ln (t (A)) ≦ {(705-7 × Cu) -T} / (1.1 × Cu + 35.5)
--- (1)
However, in the above equation (1),
Cu: Cu addition amount (mass%),
t (A): Aging time (min),
T: Aging temperature (° C)
It is.
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