JP5170212B2 - Method for producing high-tensile steel with high yield point - Google Patents

Method for producing high-tensile steel with high yield point Download PDF

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JP5170212B2
JP5170212B2 JP2010249620A JP2010249620A JP5170212B2 JP 5170212 B2 JP5170212 B2 JP 5170212B2 JP 2010249620 A JP2010249620 A JP 2010249620A JP 2010249620 A JP2010249620 A JP 2010249620A JP 5170212 B2 JP5170212 B2 JP 5170212B2
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照輝 貞末
伸一 鈴木
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Jfeスチール株式会社
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本発明は、高い降伏点を有する高張力鋼材の製造方法に関し、詳しくは、橋梁、建築物、建産機等に代表されるような溶接構造物の主要部材を対象とした降伏強度が450MPa以上の優れた靭性および溶接性を有する高張力鋼材の製造方法に関する。   The present invention relates to a method for producing a high-strength steel material having a high yield point. Specifically, the yield strength for a main member of a welded structure such as a bridge, a building, or a construction machine is 450 MPa or more. The present invention relates to a method for producing a high-tensile steel material having excellent toughness and weldability.
橋梁、建築物、建産機等に代表される溶接構造物は近年、大型化、高度化の方向にある。これに伴い、このような構造物の主要鋼材には高張力鋼が適用される事例が多くなってきている。高張力鋼材の使用による鋼材重量の低減、薄肉化、さらにこれらに伴う溶接の省力化が狙いである。   In recent years, welded structures represented by bridges, buildings, industrial machinery, etc. have been increasing in size and sophistication. Along with this, there are an increasing number of cases in which high-strength steel is applied to the main steel materials of such structures. The aim is to reduce the weight of steel materials by using high-tensile steel materials, to reduce the thickness, and to save labor in welding.
従来、このような高張力鋼材の中でも450MPa以上の高降伏点を有する鋼材は、焼入れ・焼戻し処理する方法や種々の合金元素を添加する方法により製造されてきた。しかし、前者の処理方法は製造コストが増大すること、後者の方法は合金元素添加によるコスト増大に加えて靭性および溶接性が悪くなること、という問題がある。   Conventionally, steel materials having a high yield point of 450 MPa or higher among such high-tensile steel materials have been manufactured by a method of quenching / tempering or a method of adding various alloy elements. However, the former treatment method has a problem that the manufacturing cost is increased, and the latter method has a problem that the toughness and weldability are deteriorated in addition to the cost increase due to the addition of the alloy element.
このような問題を解決するために熱間圧延後の鋼材への加速冷却の適用が試みられている。特許文献1には圧延後さらにAr3点-30℃からAr3点-150℃の温度域でレベラー掛けまたは軽圧下処理を施すことでNb、Vの析出を促進しつつ、その後の加速冷却にて高降伏点鋼を得る手法が開示されている。また、特許文献2には圧延後、Ar3点-70℃からAr3点-150℃の温度範囲で2分間以上保持する間にNb、Vを析出させ、その後に加速冷却することで高降伏点鋼板を得る手法が開示されている。これらの技術に共通する問題点は圧延後に特殊な工程を必要とし作業が煩雑となることにある。また、特許文献3には降伏強度46kgf/mm2(451MPa)以上を得るために、Cu、Ni、Ti、REMを含有する鋼を圧延後、引き続き350〜500℃の温度域まで加速冷却する手法が開示されている。しかし、この場合でも高価な合金元素を添加する必要があるためコスト増大を招くという問題がある。 In order to solve such a problem, application of accelerated cooling to a steel material after hot rolling has been attempted. Nb by Patent Document 1 for performing leveler hanging or soft reduction treatment in a temperature range of Ar 3 point -150 ° C. from more Ar 3 point -30 ° C. After rolling, while facilitating the precipitation of V, and subsequent accelerated cooling Thus, a technique for obtaining high yield point steel is disclosed. Patent Document 2 discloses that after rolling, Nb and V are precipitated while being held for 2 minutes or more in the temperature range of Ar 3 point -70 ° C to Ar 3 point -150 ° C, and then accelerated cooling to achieve high yield. A technique for obtaining a point steel sheet is disclosed. A problem common to these techniques is that a special process is required after rolling, and the work becomes complicated. Patent Document 3 discloses a technique in which steel containing Cu, Ni, Ti, and REM is rolled and subsequently accelerated to a temperature range of 350 to 500 ° C. in order to obtain a yield strength of 46 kgf / mm 2 (451 MPa) or more. Is disclosed. However, even in this case, it is necessary to add an expensive alloy element, which causes a problem of increasing the cost.
上記のように、従来提案された加速冷却を用いた手法においては、所望特性を得るための製造工程が複雑であったり、或いは素材鋼として特殊な成分系のものを必要とするなど、実用的な手段とは言えなかった。   As described above, in the conventionally proposed method using accelerated cooling, the manufacturing process for obtaining desired characteristics is complicated, or a special component system is required as the material steel. It could not be said that it was a safe means.
特開昭62−89814号公報JP-A-62-89814 特開平4−221015号公報JP-A-4-221015 特開昭63−161119号公報JP 63-161119 A
本発明は、上記の問題点を解決するためになされたものであって、特殊な工程や多量の合金元素の添加を必要とせずに、優れた靭性および溶接性を有し、かつ450MPa以上の高い降伏点を有する高張力鋼材の製造方法を提供することを目的とする。   The present invention has been made to solve the above-described problems, and has excellent toughness and weldability without requiring a special process or addition of a large amount of alloying elements, and has a capacity of 450 MPa or more. It aims at providing the manufacturing method of the high strength steel materials which have a high yield point.
本発明者らは、450MPa以上の高降伏点を有し、かつ、靭性および溶接性に優れた鋼材の製造方法について鋭意研究を行った。その結果、VとNbを複合添加することによりマトリクスの強化と析出強化とを効果的に活用することで、加速冷却時において広範囲の停止温度でも安定的に高降伏点が得られるとの知見を得た。また、上記鋼材の成分を特定の範囲とすることにより、優れた靭性および溶接性を併せ持たせることができるとの知見を得た。   The inventors of the present invention have intensively studied a method for producing a steel material having a high yield point of 450 MPa or more and excellent in toughness and weldability. As a result, it has been found that by effectively using matrix strengthening and precipitation strengthening by the combined addition of V and Nb, a high yield point can be obtained stably even at a wide range of stop temperatures during accelerated cooling. Obtained. Moreover, the knowledge that the outstanding toughness and weldability could be made to have was acquired by making the component of the said steel materials into a specific range.
本発明はこのような知見に基づいてなされたものであって、質量%でC:0.05〜0.15%、Si:0.10〜0.50%、Mn:0.5〜2.0%、P:0.05%以下、S:0.02%以下、Nb:0.001〜0.10%、V:0.001〜0.10%、を含有し、かつ、Cu:1%以下、Ni:2%以下、Cr:1%以下、Mo:1%以下、Ti:0.1%以下、B:0.005%以下、のうち、いずれか一種または二種以上を含有し、残部Fe及び不可避不純物からなり、かつPCM≦0.25%である鋼を加熱後、熱間圧延し、直ちにAr3点以上の温度域から5℃/s以上の冷却速度で350〜650℃の温度域まで冷却することを特徴とする450MPa以上の高い降伏点を有する高張力鋼材の製造方法である。
但し、PCMは溶接割れ感受性指数であり、以下の(1)式で与えられる。(1)式中の元素記号は鋼材中の各成分元素の含有率(質量%)である。
CM=C+Si/30+(Mn+Cu+Cr)/20+Mo/15+Ni/60+V/10+5B…(1)
また、上記において前記熱間圧延後の鋼を、板厚40mm未満の場合は25℃/s以上、板厚40mm以上、60mm未満の場合は10℃/s以上、板厚60mm以上の場合は5℃/s以上の冷却速度で冷却する高張力鋼材の製造方法を用いることもできる。
The present invention has been made on the basis of such findings. In mass%, C: 0.05 to 0.15%, Si: 0.10 to 0.50%, Mn: 0.5 to 2.0%, P: 0.05% or less, S: 0.02 %: Nb: 0.001 to 0.10%, V: 0.001 to 0.10%, Cu: 1% or less, Ni: 2% or less, Cr: 1% or less, Mo: 1% or less, Ti: 0.1 % or less, B: 0.005% or less, of, containing more than one kind or two or, and the balance Fe and unavoidable impurities, and after heating the steel is P CM ≦ 0.25%, hot rolled, immediately A method for producing a high-tensile steel material having a high yield point of 450 MPa or more, characterized by cooling from a temperature range of Ar 3 points or more to a temperature range of 350 to 650 ° C. at a cooling rate of 5 ° C./s or more.
However, P CM is weld crack sensitivity index is given by the following equation (1). The element symbol in the formula (1) is the content (mass%) of each component element in the steel material.
P CM = C + Si / 30 + (Mn + Cu + Cr) / 20 + Mo / 15 + Ni / 60 + V / 10 + 5B (1)
In the above, the steel after hot rolling is 25 ° C / s or more when the plate thickness is less than 40mm, 10 ° C / s or more when the plate thickness is 40mm or more, less than 60mm, and 5 when the plate thickness is 60mm or more. It is also possible to use a method for producing a high-tensile steel material that is cooled at a cooling rate of ° C / s or more.
本発明を用いると、特殊な工程や多量の合金元素の添加を必要とせずに、優れた靭性と溶接性を兼ね備えた、450MPa以上の高い降伏点を有する高張力鋼材を製造することができる。従って、橋梁、建築物、建産機等に代表されるような溶接構造物の主要部材に対して十分な特性を有する鋼材を安価に提供することができる。   By using the present invention, it is possible to produce a high-tensile steel material having a high yield point of 450 MPa or more and having excellent toughness and weldability without requiring a special process or adding a large amount of alloy elements. Therefore, it is possible to provide a steel material having sufficient characteristics for the main members of a welded structure represented by a bridge, a building, a construction machine, and the like at a low cost.
本発明の実施例1に係る強度に及ぼす冷却停止温度の影響を示す図である。It is a figure which shows the influence of the cooling stop temperature which acts on the intensity | strength which concerns on Example 1 of this invention.
本発明者らは鋼材の高降伏点化のためには、NbおよびV添加によるマトリクスの強化および析出強化が必要と考え、これを加速冷却により最大限に発揮させることを目的として研究を行い、本発明を完成した。   The present inventors consider that it is necessary to strengthen the matrix by Nb and V addition and precipitation strengthening to increase the yield point of the steel material, and conduct research for the purpose of maximizing this by accelerated cooling, The present invention has been completed.
本発明の鋼の成分および製造条件の限定理由を詳細に説明する。まず、化学成分の限定理由について説明する。   The reasons for limiting the components and production conditions of the steel of the present invention will be described in detail. First, the reasons for limiting chemical components will be described.
C:0.05〜0.15%;
Cは強度確保のために0.03%以上の添加が必要である。しかし、0.15%を越える添加は溶接性を阻害する。本発明では、0.05%以上0.15%以下に限定する。
C: 0.05-0.15%;
C needs to be added in an amount of 0.03% or more to ensure strength. However, addition exceeding 0.15% inhibits weldability. In the present invention, it is limited to 0.05% or more and 0.15% or less.
Si:0.10〜0.50%;
Siは脱酸剤として有効であるとともに高強度化のためには0.10%以上必要であるが、0.50%を越えて添加すると溶接性、靭性を劣化させる。したがって0.10%以上0.50%以下に限定する。
Si: 0.10 to 0.50%;
Si is effective as a deoxidizer and needs to be 0.10% or more for increasing the strength, but if added over 0.50%, weldability and toughness are deteriorated. Therefore, it is limited to 0.10% or more and 0.50% or less.
Mn:0.5〜2.0%;
Mnは安価に焼入れ性を増加させ、強度を高めるだけでなく、靭性向上にも寄与する。この観点から0.5%以上必要であるが、2.0%を越えると溶接性の劣化に繋がる。したがって0.5%以上2.0%以下に限定する。
Mn: 0.5-2.0%;
Mn inexpensively increases hardenability and increases strength, but also contributes to improved toughness. From this viewpoint, 0.5% or more is necessary, but if it exceeds 2.0%, it leads to deterioration of weldability. Therefore, it is limited to 0.5% or more and 2.0% or less.
P:0.05%以下;
Pは鋼の靭性を劣化させるため、その含有量はできるだけ低いことが望ましい。このため上限を0.05%とした。好ましくは0.03%以下とする。
P: 0.05% or less;
Since P deteriorates the toughness of steel, its content is desirably as low as possible. For this reason, the upper limit was made 0.05%. Preferably it is 0.03% or less.
S:0.02%以下;
Sは多量に添加すると鋼の靭性を低下させるため極力低減するのが望ましい。このため、上限を0.02%とした。好ましくは0.01%以下とする。
S: 0.02% or less;
If S is added in a large amount, the toughness of the steel is lowered, so it is desirable to reduce it as much as possible. For this reason, the upper limit was made 0.02%. Preferably it is 0.01% or less.
Nb:0.001〜0.10%;
Nbは本発明において非常に重要な元素であり、マトリクスの強化ならびに析出強化を通じて高降伏点化をもたらす働きを有する。この効果を発揮させるには0.001%以上の添加が必要であるが、0.10%を越えて添加すると靭性が劣化する。したがって0.001%以上0.10%以下に限定する。
Nb: 0.001 to 0.10%;
Nb is a very important element in the present invention, and has a function of increasing the yield point through matrix strengthening and precipitation strengthening. In order to exert this effect, 0.001% or more must be added, but if added over 0.10%, the toughness deteriorates. Therefore, it is limited to 0.001% or more and 0.10% or less.
V:0.001〜0.10%;
VもNbと同様、本発明において重要な働きをなす元素であり、マトリクスの強化及び析出強化による高降伏点化をもたらす。このため0.001%以上の添加が必要となるが、0.10%を越える添加は溶接性および靭性の低下を招く。したがって0.001%以上0.10%以下に限定する。
V: 0.001 to 0.10%;
V, like Nb, is an element that plays an important role in the present invention, and brings about a high yield point due to matrix strengthening and precipitation strengthening. For this reason, addition of 0.001% or more is necessary, but addition exceeding 0.10% causes a decrease in weldability and toughness. Therefore, it is limited to 0.001% or more and 0.10% or less.
Cu:1%以下;
Cuは固溶による強度上昇効果をもたらすとともに耐候性確保のため必要により添加される。しかし、その含有量が1%を超えると溶接性を損なうとともに鋼材製造時に疵が生じやすくなる。したがってその上限を1%とする。好ましくは0.5%以下とする。
Cu: 1% or less;
Cu brings about an effect of increasing strength due to solid solution and is added if necessary to ensure weather resistance. However, if its content exceeds 1%, weldability is impaired and flaws are likely to occur during the manufacture of steel materials. Therefore, the upper limit is set to 1%. Preferably it is 0.5% or less.
Ni:2%以下;
Niは低温靭性を向上させるとともにCuを添加した場合に生ずる熱間脆性の改善に有効であるために必要に応じて添加される。しかし、その添加量が2%を超えると溶接性を阻害する上、コスト上昇に繋がる。したがってその上限を2%とする。好ましくは1%以下とする。
Ni: 2% or less;
Ni is added as necessary because it is effective in improving the low temperature toughness and improving hot brittleness that occurs when Cu is added. However, if the added amount exceeds 2%, weldability is hindered and the cost increases. Therefore, the upper limit is 2%. Preferably it is 1% or less.
Cr:1%以下;
Crは耐候性や強度の観点から必要に応じて添加されるが、その含有量が1%を超えると溶接性および靭性を損なう。したがって上限を1%とする。好ましくは0.5%以下とする。
Cr: 1% or less;
Cr is added as necessary from the viewpoint of weather resistance and strength, but if its content exceeds 1%, weldability and toughness are impaired. Therefore, the upper limit is 1%. Preferably it is 0.5% or less.
Mo:1%以下;
Moは強度上昇のために必要に応じて添加されるが、1%を超えると溶接性および靭性の劣化が生じる。したがってその上限を1%とする。好ましくは0.5%以下とする。
Mo: 1% or less;
Mo is added as necessary to increase the strength, but if it exceeds 1%, weldability and toughness deteriorate. Therefore, the upper limit is set to 1%. Preferably it is 0.5% or less.
Ti:0.1%以下;
Tiは強度上昇と溶接部靭性の改善のために必要に応じて添加される。しかし、その含有量が0.1%を超えるとコスト上昇を招く傾向にある。したがって上限を0.1%とする。好ましくは0.05%以下とする。
Ti: 0.1% or less;
Ti is added as necessary to increase strength and improve weld toughness. However, if the content exceeds 0.1%, the cost tends to increase. Therefore, the upper limit is set to 0.1%. Preferably it is 0.05% or less.
B:0.005%以下;
Bは焼入れ性を高め強度上昇に寄与するため必要に応じて添加される。しかし、0.005%を超えて添加すると溶接性を害する。したがって上限を0.005%とする。好ましくは0.003%以下とする。
B: 0.005% or less;
B is added as necessary to increase the hardenability and contribute to the increase in strength. However, if added over 0.005%, the weldability is impaired. Therefore, the upper limit is made 0.005%. Preferably it is 0.003% or less.
PCM≦0.25%
本発明においては溶接性の向上も目的としている。このためPCMで表される溶接割れ感受性指数を0.25%以下とし、低温割れの抑制を図るものである。好ましくはPCM≦0.22%とする。
P CM ≤0.25%
Another object of the present invention is to improve weldability. Therefore the weld cracking sensitivity index represented by P CM and 0.25% or less, is intended to achieve inhibition of cold cracking. Preferably, P CM ≦ 0.22%.
本発明の鋼の成分の残部は実質的にFeである。残部が実質的にFeであるとは、本発明の作用効果を無くさない限り、不可避不純物をはじめ、他の微量元素を含有するものが本発明の範囲に含まれ得ることを意味する。   The balance of the components of the steel of the present invention is substantially Fe. That the balance is substantially Fe means that an element containing other trace elements including inevitable impurities can be included in the scope of the present invention unless the effects of the present invention are lost.
次に製造条件についての限定理由を述べる。   Next, the reasons for limiting the manufacturing conditions will be described.
本発明による製造方法は上記組成を有する鋼を加熱する工程と、その後に熱間圧延する工程と、この鋼材を直ちにAr3点以上の温度域から5℃/s以上の冷却速度で350〜650℃の温度域まで冷却する工程とを備える。なお、上記温度および冷却速度は鋼板表面から板厚中央部にかけての平均温度および平均冷却速度とする。 The production method according to the present invention comprises a step of heating a steel having the above composition, a step of hot rolling thereafter, and the steel material is immediately cooled at a cooling rate of 5 ° C./s or more from a temperature range of Ar 3 or higher. And a step of cooling to a temperature range of ° C. The above temperature and cooling rate are the average temperature and average cooling rate from the steel plate surface to the center of the plate thickness.
上記の圧延前の鋼の加熱温度としては特に制限は設けないが、950〜1300℃にすることが望ましい。上記加熱温度を950℃未満にするとNbおよびVの固溶が不十分となる。また、1300℃を超える温度にすると鋼の結晶粒が粗大化するので靭性の確保が困難となる。   The heating temperature of the steel before rolling is not particularly limited, but is preferably 950 to 1300 ° C. When the heating temperature is less than 950 ° C., the solid solution of Nb and V becomes insufficient. Further, if the temperature exceeds 1300 ° C., the crystal grains of the steel become coarse and it becomes difficult to ensure toughness.
上記加熱後の鋼の熱間圧延に際しては特に制限は設けない。但し、オーステナイト再結晶域圧延あるいはオーステナイト未再結晶域圧延のどちらであっても、その仕上温度が後述するAr3点を超える温度域とする必要がある。 There are no particular restrictions on the hot rolling of the steel after heating. However, in either austenite recrystallization zone rolling or austenite non-recrystallization zone rolling, the finishing temperature needs to be a temperature range exceeding the Ar 3 point described later.
上記圧延後の鋼材の冷却に際しては、熱間圧延後直ちにAr3点以上の温度域から5℃/s以上の冷却速度で350〜650℃の温度域まで冷却する。Ar3点は例えば以下の(2)式のような関係式により鋼材の成分組成に基づいて導くことが出来る。(2)式中の元素記号は鋼材中の各成分元素の含有率(質量%)である。 When cooling the steel material after rolling, the steel material is immediately cooled to a temperature range of 350 to 650 ° C. at a cooling rate of 5 ° C./s or more from a temperature range of 3 or more points at Ar. The Ar 3 point can be derived on the basis of the component composition of the steel material by a relational expression such as the following expression (2). The element symbol in the formula (2) is the content (mass%) of each component element in the steel material.
上記冷却開始温度をAr3点以上とするのは冷却開始時点までにフェライトの生成が生じないようにするためである。冷却開始時点までにフェライトが生じた場合には降伏点の低下が著しい。 The reason why the cooling start temperature is set to the Ar 3 point or higher is to prevent generation of ferrite before the cooling start time. When ferrite is generated before the start of cooling, the yield point is remarkably lowered.
冷却速度を5℃/s以上とするのは金属組織をベイナイト主体、あるいはベイナイトとマルテンサイト主体の混合組織とし、鋼材の強度上昇を図るためである。   The reason why the cooling rate is 5 ° C./s or more is to increase the strength of the steel material by making the metal structure a bainite-based or mixed structure of bainite and martensite.
冷却停止温度を350〜650℃とするのは、この温度域でNbとVの複合添加によるマトリクスの強化と析出強化をバランスさせて鋼材の降伏強度を高めることが出来るためである。   The reason why the cooling stop temperature is set to 350 to 650 ° C. is that the yield strength of the steel material can be increased by balancing the strengthening of the matrix and the precipitation strengthening by the combined addition of Nb and V in this temperature range.
Ar3(℃)=910-310C-80Mn-20Cu-15Cr-55Ni-80Mo…(2) Ar 3 (° C.) = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo (2)
NbとVの複合添加の効果を調べるため、組成をC:0.10%、Si:0.30%、Mn1.45%、P:0.010%、S:0.003%とした鋼(鋼a)、鋼aに0.04%のVを単独添加した鋼(鋼b)、さらに鋼aに0.04%のVと0.02%のNbとを複合添加した鋼(鋼c)を用意した。これらの鋼を1100℃に加熱して板厚30mmの鋼板に圧延し、その後、直ちにAr3点以上の温度域から冷却し、冷却停止温度を変化させた。これらの鋼板について板厚の4分の1の位置で圧延方向に直角方向に採取したJIS Z 2201の4号試験片により引張試験を行って強度(降伏強度:YS、引張強度:TS)を評価した。結果を図1に示す。 In order to investigate the effect of the combined addition of Nb and V, steel (steel a) with a composition of C: 0.10%, Si: 0.30%, Mn 1.45%, P: 0.010%, S: 0.003%, 0.04% for steel a % Steel (steel b), and steel a (0.04% V and 0.02% Nb) added to steel a (steel c) were prepared. These steels were heated to 1100 ° C. and rolled into a steel plate with a thickness of 30 mm, and then immediately cooled from the temperature range of Ar 3 or higher to change the cooling stop temperature. These steel sheets were subjected to a tensile test using a JIS Z 2201 No. 4 specimen taken at a position perpendicular to the rolling direction at a quarter of the sheet thickness to evaluate the strength (yield strength: YS, tensile strength: TS). did. The results are shown in Figure 1.
図1において横軸は冷却停止温度、縦軸は降伏強度、引張強度を示している。   In FIG. 1, the horizontal axis indicates the cooling stop temperature, and the vertical axis indicates the yield strength and tensile strength.
まず、鋼aの降伏強度に及ぼす冷却停止温度の影響に注目する。この場合、降伏強度は、いずれの停止温度においても450MPaを上回ることは出来ない。次に、鋼bで示すV単独添加の降伏強度に注目すると冷却停止温度450℃〜550℃において450MPa以上の降伏強度を有しているがその温度幅は100℃であり安定的に高降伏点鋼材が製造可能とは言い難い。次に、鋼cに示すさらにNbを添加したNb+V複合添加に注目した場合、450MPa以上の高降伏点が確保できる冷却停止温度は350〜650℃までと大幅に広がっている。   First, attention is paid to the influence of the cooling stop temperature on the yield strength of steel a. In this case, the yield strength cannot exceed 450 MPa at any stop temperature. Next, paying attention to the yield strength of single addition of V shown in steel b, it has a yield strength of 450 MPa or more at a cooling stop temperature of 450 ° C. to 550 ° C., but its temperature range is 100 ° C., and it has a stable high yield point. It is hard to say that steel can be manufactured. Next, when attention is paid to the Nb + V composite addition in which Nb is further added to the steel c, the cooling stop temperature at which a high yield point of 450 MPa or more can be secured is greatly expanded to 350 to 650 ° C.
以上の結果より、Nb+Vの複合添加により高降伏点化が達成できる冷却停止温度が広がり、安定的に高降伏点鋼材が製造可能であることがわかった。これは、低い冷却停止温度範囲(例えば350〜450℃)においては、NbとVの複合添加によるマトリクス強化が主として作用し、高降伏点化が達成され、高い冷却停止温度範囲(例えば450〜650℃)においては、NbおよびVの析出強化機構により、高降伏点が得られたものと考えられる。   From the above results, it was found that the cooling stop temperature at which a high yield point can be achieved by the combined addition of Nb + V is widened, and a steel with a high yield point can be produced stably. This is because, in a low cooling stop temperature range (for example, 350 to 450 ° C.), matrix strengthening due to the combined addition of Nb and V mainly acts to achieve a high yield point, and a high cooling stop temperature range (for example, 450 to 650). (° C.), it is considered that a high yield point was obtained by the precipitation strengthening mechanism of Nb and V.
表1に示す組成を有する鋼を溶製して得られた鋼片を、表2に示す条件に基づいて加熱・圧延・冷却して、板厚20〜100mmの鋼板を製造し、強度・靭性・溶接性を測定した。   Steel pieces obtained by melting steel having the composition shown in Table 1 are heated / rolled / cooled based on the conditions shown in Table 2 to produce steel plates with a thickness of 20 to 100 mm. -Weldability was measured.
強度(降伏強度:YS、引張強度:TS)は板厚の4分の1の位置で圧延方向に直角方向に採取したJIS Z 2201の4号試験片により評価した。   The strength (yield strength: YS, tensile strength: TS) was evaluated by a No. 4 test piece of JIS Z 2201, which was taken in a direction perpendicular to the rolling direction at a position of a quarter of the plate thickness.
靭性は板厚の4分の1の位置で圧延方向と平行方向に採取したJIS Z 2202のVノッチ試験片により評価した。この場合、破面遷移温度で-30℃以下を合格とした。   Toughness was evaluated by a JIS Z 2202 V-notch specimen taken in a direction parallel to the rolling direction at a position of a quarter of the plate thickness. In this case, a fracture surface transition temperature of −30 ° C. or lower was regarded as acceptable.
溶接性(y割れ)はJIS Z 3158に準拠し、雰囲気20℃-60%、予熱温度25℃としたy形溶接割れ試験において割れの生じないものを合格とした。   The weldability (y-crack) conformed to JIS Z 3158, and passed the y-type weld crack test in which the atmosphere was 20 ° C.-60% and the preheating temperature was 25 ° C. and no crack occurred.
得られた結果を表2に併せて示す。   The obtained results are also shown in Table 2.
本発明に規定の成分および製造方法を採用した本発明例1〜9の鋼板は、いずれもYSは450MPa以上であり、破面遷移温度は-30℃以下、y形溶接割れ試験での割れは認められなかった。このように、本発明方法を用いると高降伏点化が達成され、かつ、靭性および溶接性にも優れた鋼材を製造することができた。   The steel sheets of Invention Examples 1 to 9 adopting the components and production methods defined in the present invention all have a YS of 450 MPa or more, a fracture surface transition temperature of −30 ° C. or less, and cracks in the y-type weld crack test. I was not able to admit. As described above, when the method of the present invention was used, a steel material having a high yield point and excellent in toughness and weldability could be produced.
これに対し、VとNbの添加を行わなかった比較例1の鋼板、Vのみ添加しNbを添加しなかった比較例2の鋼板は、いずれも本発明の製造条件を適用しても析出強化が発揮されず、高降伏点化が達成されなかった。   On the other hand, both the steel plate of Comparative Example 1 in which V and Nb were not added and the steel plate of Comparative Example 2 in which only V was added and Nb was not added were precipitation strengthened even when the production conditions of the present invention were applied. Was not achieved, and a high yield point was not achieved.
C、Si、Mnを本発明の下限に満たない添加量とした比較例3の鋼板は、本発明の製造条件を適用しても、マトリクスの強化と析出強化とのバランスが適性ではないために高降伏点化が達成されなかった。   The steel plate of Comparative Example 3 in which C, Si, and Mn are added in amounts not less than the lower limit of the present invention is not suitable for the balance between matrix strengthening and precipitation strengthening even when the production conditions of the present invention are applied. A high yield point was not achieved.
C、Si、Mnを本発明の上限を超える添加量とし、かつ、PCMが0.25%を超えた比較例4の鋼板は、本発明の製造条件を適用しても、靭性が劣化し、かつ、溶接性も劣っていた。 And C, Si, and the addition amount exceeds the upper limit of the present invention the Mn, and the steel plate of Comparative Example 4 P CM exceeds 0.25%, even by applying the manufacturing conditions of the present invention, the toughness is degraded, and The weldability was also poor.
P、Sを本発明の上限を超える添加量とした比較例5の鋼板、ならびにV、Nbを本発明の上限を超える添加量とした比較例6の鋼板は、本発明の製造条件を適用しても、靭性が劣っていた。   The steel sheet of Comparative Example 5 in which P and S were added in amounts exceeding the upper limit of the present invention, and the steel sheet of Comparative Example 6 in which V and Nb were added in amounts exceeding the upper limit of the present invention were applied with the production conditions of the present invention. Even toughness was inferior.
冷却停止温度を本発明の下限に満たない温度とした比較例7の鋼板、ならびに本発明の上限を超える温度とした比較例8の鋼板は、ともにマトリクスと析出強化のバランスが適性ではなく高降伏点化が達成されなかった。   The steel plate of Comparative Example 7 in which the cooling stop temperature is less than the lower limit of the present invention, and the steel plate of Comparative Example 8 in which the temperature exceeds the upper limit of the present invention are both high in yield because the balance between matrix and precipitation strengthening is not appropriate. Pointing was not achieved.
冷却開始温度がAr3点よりも低く、かつ、冷却速度が5℃/sに満たない比較例9の鋼板はフェライトが多量に生成したために高降伏点化が達成されなかった。 The steel sheet of Comparative Example 9 having a cooling start temperature lower than the Ar 3 point and a cooling rate of less than 5 ° C./s did not achieve a high yield point because a large amount of ferrite was generated.

Claims (1)

  1. 質量%で
    C:0.05〜0.15%、
    Si:0.10〜0.50%、
    Mn:0.5〜2.0%、
    P:0.05%以下、
    S:0.02%以下、
    Nb:0.001〜0.10%、
    V:0.001〜0.10%、
    を含有し、かつ、
    Cu:1%以下、
    Ni:2%以下、
    Cr:1%以下、
    Mo:1%以下、
    Ti:0.1%以下、
    B:0.005%以下、
    のうち、いずれか一種または二種以上を含有し、残部Fe及び不可避不純物からなり、かつ下記(1)式に示すPCM≦0.25%である鋼を加熱後、熱間圧延し、直ちにAr3点以上の温度域から5℃/s以上の冷却速度で350〜650℃の温度域まで冷却することを特徴とする450MPa以上の高い降伏点を有する高張力鋼材の製造方法。
    但し、PCM=C+Si/30+(Mn+Cu+Cr)/20+Mo/15+Ni/60+V/10+5B…(1)
    (1)式に示す元素記号は各元素の質量%を表す。
    C: 0.05 to 0.15% by mass%
    Si: 0.10 to 0.50%,
    Mn: 0.5 to 2.0%
    P: 0.05% or less,
    S: 0.02% or less,
    Nb: 0.001 to 0.10%,
    V: 0.001 to 0.10%,
    Containing, and
    Cu: 1% or less,
    Ni: 2% or less,
    Cr: 1% or less,
    Mo: 1% or less,
    Ti: 0.1% or less,
    B: 0.005% or less,
    Of, containing more than one kind or two or, and the balance Fe and unavoidable impurities, and after heating the steel is P CM ≦ 0.25% shown in the following equation (1), hot-rolled, immediately Ar 3 A method for producing a high-tensile steel material having a high yield point of 450 MPa or more, characterized by cooling from a temperature range of more than a point to a temperature range of 350 to 650 ° C. at a cooling rate of 5 ° C./s or more.
    However, P CM = C + Si / 30 + (Mn + Cu + Cr) / 20 + Mo / 15 + Ni / 60 + V / 10 + 5B (1)
    The element symbol shown in the formula (1) represents mass% of each element.
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