JP5477089B2 - Manufacturing method of high strength and high toughness steel - Google Patents

Manufacturing method of high strength and high toughness steel Download PDF

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JP5477089B2
JP5477089B2 JP2010062444A JP2010062444A JP5477089B2 JP 5477089 B2 JP5477089 B2 JP 5477089B2 JP 2010062444 A JP2010062444 A JP 2010062444A JP 2010062444 A JP2010062444 A JP 2010062444A JP 5477089 B2 JP5477089 B2 JP 5477089B2
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JP2010248621A (en
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謙次 林
智之 横田
光浩 岡津
健次 大井
伸夫 鹿内
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Jfeスチール株式会社
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本発明は、靭性に優れた鋼材の製造方法に関し、特に、造船、海洋構造物、建設機械、建築、橋梁、タンク、鋼管、水圧鉄管などの溶接鋼構造物に利用する厚鋼板、形鋼、棒鋼など種々の形状の鋼の製造方法として好適なものに関する。   The present invention relates to a method for producing a steel material having excellent toughness, and in particular, a thick steel plate, a section steel, used for welded steel structures such as shipbuilding, marine structures, construction machinery, architecture, bridges, tanks, steel pipes, hydraulic iron pipes, The present invention relates to a method suitable for manufacturing steel of various shapes such as steel bars.

脆性破壊を起こす可能性のある大型の溶接構造物として使用される厚鋼板への要求性能は、高強度化に加え高い靭性や溶接性の確保などますます過酷化する傾向にある。鋼板の強度や板厚が増加すると、一般的に靭性は低下する傾向にあるので、厚鋼板の靭性の向上技術としては、これまで、特許文献1および特許文献2には制御圧延や制御冷却が記載され、さらには、特許文献3には直接焼入れ-焼戻し技術が記載されており、これらTMCP技術や圧延後に行うオンラインの熱処理技術の適用がなされてきた。   The required performance of thick steel plates used as large welded structures that may cause brittle fracture tends to become increasingly severe, such as ensuring high toughness and weldability in addition to increasing strength. Since the toughness generally tends to decrease as the strength and thickness of the steel sheet increase, as a technique for improving the toughness of the thick steel sheet, Patent Document 1 and Patent Document 2 include controlled rolling and controlled cooling. In addition, Patent Document 3 describes a direct quenching-tempering technique, and these TMCP techniques and on-line heat treatment techniques performed after rolling have been applied.

靭性の向上には、結晶粒の微細化が有効であることが従来から知られており、様々な検討がなされている。合金設計や圧延時の加熱温度や圧延温度などを工夫することによる細粒化も検討されているが、現状では、圧延−冷却で得られる厚鋼板のオーステナイト粒径は20〜30μm程度が限界であり、圧延後の再加熱焼入れなどで得られる結晶粒径に比べても大きく、圧延−冷却ままあるいは、圧延−冷却−焼戻しプロセスでの靭性の向上には限界がある。   It has been known that refinement of crystal grains is effective for improving toughness, and various studies have been made. Although refinement by designing the alloy design, the heating temperature at the time of rolling, the rolling temperature, etc. has been studied, at present, the austenite grain size of the thick steel plate obtained by rolling and cooling is limited to about 20 to 30 μm. Yes, it is larger than the crystal grain size obtained by reheating and quenching after rolling, and there is a limit to improving toughness in the rolling-cooling or rolling-cooling-tempering process.

特開昭57−134518号公報JP-A-57-134518 特開昭59−83722号公報JP 59-83722 A 特開昭63−223125号公報JP-A-63-223125

上述したように、これまでの厚板製造プロセスを用いた靭性向上には限界があり、更なる靭性の向上が望まれている。本発明は、再加熱焼入れを必要としない、圧延−加速冷却ままあるいは直接焼入れ−焼戻しプロセスにおいて、微細なオーステナイト粒径を得ることにより、靭性を大幅に向上させる製造方法を得ることを目的とする。   As described above, there is a limit to the improvement in toughness using the conventional plate manufacturing process, and further improvement in toughness is desired. An object of the present invention is to obtain a production method that greatly improves toughness by obtaining a fine austenite grain size in a rolling-accelerated cooling or direct quenching-tempering process that does not require reheating and quenching. .

本発明者等は、上記問題点を解決するため、オーステナイト粒径に及ぼす圧延時の加熱・冷却・圧下パターンに着目して鋭意検討を行った結果、高強度鋼において、初めにオーステナイト再結晶温度域圧延を、次にオーステナイト未再結晶温度域圧延を実施し、その後、オーステナイト再結晶温度域へ急速加熱することにより微細なオーステナイトが得られ、その後の圧延・冷却条件の組合せにより、優れた靭性が得られることを知見した。   In order to solve the above-mentioned problems, the present inventors conducted intensive studies focusing on the heating, cooling, and rolling patterns during rolling that affect the austenite grain size. Next, austenite non-recrystallization temperature range rolling is performed, then fine austenite is obtained by rapid heating to the austenite recrystallization temperature range, and excellent toughness is achieved by a combination of subsequent rolling and cooling conditions. It was found that can be obtained.

すなわち、適正条件下の圧延時の加熱温度とオーステナイト再結晶温度域圧延により初期オーステナイト粒径の粗大化を防止して均一なオーステナイト粒を得、その後の未再結晶温度域圧延の累積圧下率を確保し、フェライト変態を生じさせることなく、Ar変態点以上の温度から再結晶温度域に短時間で加熱することにより、微細な再結晶オーステナイトが得られること、さらにその後、微細なオーステナイト粒に対して未再結晶温度域圧延を行うことにより、組織のいっそうの微細化が図られ、加速冷却後、または直接焼入れ−焼戻し後に優れた強度および靭性が得られることを知見した。
本発明の要旨はつぎのとおりである。
That is, the heating temperature during rolling under appropriate conditions and austenite recrystallization temperature range rolling prevent coarsening of the initial austenite grain size to obtain uniform austenite grains, and the cumulative reduction ratio of subsequent non-recrystallization temperature range rolling The fine recrystallized austenite can be obtained by heating in a short time from the temperature above the Ar 3 transformation point to the recrystallization temperature range without causing ferrite transformation, and further to fine austenite grains. On the other hand, it has been found that by performing non-recrystallization temperature range rolling, the structure can be further refined and excellent strength and toughness can be obtained after accelerated cooling or directly after quenching and tempering.
The gist of the present invention is as follows.

第一の発明は、質量%で、C:0.01〜0.30%、Si:0.01〜0.80%、Mn:0.20〜2.50%、P:0.020%以下、S:0.0070%以下、sol.Al:0.003〜0.100%を含有し、残部がFeおよび不可避的不純物からなる組成を有する鋼素材を、1000℃以上に加熱し、オーステナイト再結晶温度域において圧延後、オーステナイト未再結晶温度域において累積圧下率40%以上の圧延を実施した後、Ar変態点以上の温度からオーステナイト再結晶温度域まで2℃/sec以上の昇温速度で加熱し、さらに、Ar変態点以上の温度から600℃以下に加速冷却する工程を有する高強度高靭性鋼の製造方法である。 1st invention is the mass%, C: 0.01-0.30%, Si: 0.01-0.80%, Mn: 0.20-2.50%, P: 0.020% or less , S: 0.0070% or less, sol. A steel material having a composition containing Al: 0.003 to 0.100%, the balance being Fe and inevitable impurities is heated to 1000 ° C. or more, rolled in the austenite recrystallization temperature range, and then austenite unrecrystallized. After rolling with a cumulative rolling reduction of 40% or more in the temperature range, the steel is heated from the temperature above the Ar 3 transformation point to the austenite recrystallization temperature range at a rate of 2 ° C./sec or more, and further above the Ar 3 transformation point. It is a manufacturing method of the high strength high toughness steel which has the process of accelerated cooling to 600 degrees C or less from the temperature of this.

第二の発明は、鋼組成に、更に、質量%で、Cu:0.01〜2.0%、Ni:0.01〜9.0%、Cr:0.01〜3.0%、Mo:0.01〜2.0%、Nb:0.003〜0.1%、V:0.003〜0.5%、Ti:0.005〜0.20%、B:0.0005〜0.0040%、Ca:0.0001〜0.0060%、Mg:0.0001〜0.0060%、REM:0.0001〜0.0200%のうちから選ばれた1種または2種以上を含有することを特徴とする第一の発明に記載の高強度高靭性鋼の製造方法である。   In the second invention, the steel composition is further, in mass%, Cu: 0.01 to 2.0%, Ni: 0.01 to 9.0%, Cr: 0.01 to 3.0%, Mo : 0.01-2.0%, Nb: 0.003-0.1%, V: 0.003-0.5%, Ti: 0.005-0.20%, B: 0.0005-0 .0040%, Ca: 0.0001 to 0.0060%, Mg: 0.0001 to 0.0060%, REM: One or more selected from 0.0001 to 0.0200% A method for producing a high-strength, high-toughness steel according to the first invention.

第三の発明は、600℃以下に加速冷却した後、さらに、Ac変態点以下の温度に焼戻す工程を有する第一または第二の発明に記載の高強度高靭性鋼の製造方法である。 The third invention is, after accelerated cooling to 600 ° C. or less, further, is the first or second method of producing a high strength and high toughness steel according to the invention has a step of tempering at a temperature of less than Ac 1 transformation point .

第四の発明は、質量%で、C:0.01〜0.30%、Si:0.01〜0.80%、Mn:0.20〜2.50%、P:0.020%以下、S:0.0070%以下、sol.Al:0.003〜0.100%を含有し、残部がFeおよび不可避的不純物からなる組成を有する鋼素材を、1000℃以上に加熱し、オーステナイト再結晶温度域において圧延後、オーステナイト未再結晶温度域において累積圧下率40%以上の圧延を実施した後、Ar変態点以上の温度からオーステナイト再結晶温度域まで2℃/sec以上の昇温速度で加熱し、さらに、オーステナイト未再結晶温度域において累積圧下率15%以上の圧延を行い、Ar変態点以上の温度から600℃以下に加速冷却する工程を有する高強度高靭性鋼の製造方法である。 4th invention is the mass%, C: 0.01-0.30%, Si: 0.01-0.80%, Mn: 0.20-2.50%, P: 0.020% or less , S: 0.0070% or less, sol. A steel material having a composition containing Al: 0.003 to 0.100%, the balance being Fe and inevitable impurities is heated to 1000 ° C. or more, rolled in the austenite recrystallization temperature range, and then austenite unrecrystallized. After rolling with a cumulative rolling reduction of 40% or more in the temperature range, the steel is heated from the temperature above the Ar 3 transformation point to the austenite recrystallization temperature range at a rate of 2 ° C./sec or more, and further the austenite non-recrystallization temperature It is a manufacturing method of high-strength and high-toughness steel which has the process of rolling at a cumulative reduction of 15% or more in the region and accelerating cooling from a temperature not lower than the Ar 3 transformation point to 600 ° C. or lower.

第五の発明は、鋼組成に、更に、質量%で、Cu:0.01〜2.0%、Ni:0.01〜9.0%、Cr:0.01〜3.0%、Mo:0.01〜2.0%、Nb:0.003〜0.1%、V:0.003〜0.5%、Ti:0.005〜0.20%、B:0.0005〜0.0040%、Ca:0.0001〜0.0060%、Mg:0.0001〜0.0060%、REM:0.0001〜0.0200%のうちから選ばれた1種または2種以上を含有することを特徴とする第四の発明に記載の高強度高靭性鋼の製造方法である。   According to a fifth aspect of the present invention, the steel composition further includes, in mass%, Cu: 0.01 to 2.0%, Ni: 0.01 to 9.0%, Cr: 0.01 to 3.0%, Mo : 0.01-2.0%, Nb: 0.003-0.1%, V: 0.003-0.5%, Ti: 0.005-0.20%, B: 0.0005-0 .0040%, Ca: 0.0001 to 0.0060%, Mg: 0.0001 to 0.0060%, REM: One or more selected from 0.0001 to 0.0200% A method for producing high-strength and high-toughness steel according to the fourth invention.

第六の発明は、600℃以下に加速冷却した後、さらに、Ac変態点以下の温度に焼戻す工程を有する第四または第五の発明に記載の高強度高靭性鋼の製造方法である。 A sixth invention is a method for producing a high-strength and high-toughness steel according to the fourth or fifth invention, further comprising a step of accelerating and cooling to 600 ° C. or lower and further tempering to a temperature not higher than Ac 1 transformation point. .

第七の発明は、前記累積圧下率40%以上のオーステナイト未再結晶温度域圧延を行う前のオーステナイト再結晶温度域圧延中または同オーステナイト再結晶温度域圧延後に水冷を実施し、オーステナイト未再結晶温度域まで空冷よりも速い速度で冷却する工程を有する第一乃至第六の発明のいずれかに記載の高強度高靭性鋼の製造方法である。   In the seventh invention, the austenite recrystallization temperature range rolling before or after the austenite recrystallization temperature range rolling with the cumulative rolling reduction of 40% or more is performed, or after the austenite recrystallization temperature range rolling, water cooling is performed, It is a manufacturing method of the high strength high toughness steel in any one of the 1st thru | or 6th invention which has the process cooled at a faster speed than air cooling to a temperature range.

第八の発明は、前記オーステナイト未再結晶温度域において累積圧下率40%以上の圧延を実施した後のオーステナイト再結晶温度域への加熱後に、15μm以下の平均オーステナイト粒径を有することを特徴とする第一乃至第七の発明のいずれかに記載の高強度高靭性鋼の製造方法である。   The eighth invention is characterized by having an average austenite grain size of 15 μm or less after heating to the austenite recrystallization temperature range after rolling at a cumulative reduction of 40% or more in the austenite non-recrystallization temperature range. A method for producing a high-strength, high-toughness steel according to any one of the first to seventh inventions.

本発明によれば、再結晶域圧延と累積圧下率40%以上の未再結晶域圧延の後に、再結晶温度域への急速加熱を行うプロセスを有することにより、急速加熱ままで15μm以下のオーステナイト粒径が得られ、本プロセスを適用しない場合と比較して、破面遷移温度を指標として約20℃〜60℃の靭性向上が認められ、強度−靭性バランスが向上し、産業上極めて有用である。   According to the present invention, by having a process of rapid heating to the recrystallization temperature range after recrystallization zone rolling and non-recrystallization zone rolling with a cumulative reduction ratio of 40% or more, austenite of 15 μm or less is maintained while rapidly heating. Compared to the case where the particle size is obtained and this process is not applied, an improvement in toughness of about 20 ° C. to 60 ° C. is recognized using the fracture surface transition temperature as an index, and the strength-toughness balance is improved, which is extremely useful industrially. is there.

以下、本発明を詳細に説明する。   Hereinafter, the present invention will be described in detail.

1.成分組成について
成分組成における%は全て質量%とする。
1. About component composition All% in a component composition shall be the mass%.

C:0.01〜0.30%
Cは鋼板の強度を確保するため、少なくとも0.01%の添加が必要であり0.30%を超えて添加すると、著しく溶接性を低下させ、また母材靱性を低下させるため、C量は、0.01〜0.30%の範囲とする。
C: 0.01 to 0.30%
In order to ensure the strength of the steel sheet, C needs to be added at least 0.01%. If added over 0.30%, the weldability is remarkably lowered, and the base material toughness is also lowered. , 0.01 to 0.30% of range.

Si:0.01〜0.80%
Siは脱酸に必要な元素であるが、0.01%未満ではその効果は少なく、0.80%を超えて添加すると溶接性および母材靭性を著しく低下させるため、Si量は0.01〜0.80%の範囲とする。
Si: 0.01-0.80%
Si is an element necessary for deoxidation, but its effect is small if it is less than 0.01%, and if added over 0.80%, the weldability and the base metal toughness are remarkably lowered. It is made into the range of -0.80%.

Mn:0.20〜2.50%
MnはCと同様に鋼板の強度を確保するために必要であるが、過剰に添加すると溶接性を損なう問題があるため、Mn量は0.20〜2.50%の範囲とする。
Mn: 0.20 to 2.50%
Mn is necessary for securing the strength of the steel sheet in the same manner as C. However, if excessively added, there is a problem that the weldability is impaired, so the amount of Mn is set in the range of 0.20 to 2.50%.

P:0.020%以下、S:0.0070%以下
P、Sは不純物として鋼中に不可避的に含有される元素であり、鋼母材や、溶接熱影響部の靭性を劣化させるため、経済性を考慮して可能な範囲で低減することが好ましく、P量、S量はそれぞれ0.020%以下、0.0070%以下とする。
P: 0.020% or less, S: 0.0070% or less P and S are elements inevitably contained in the steel as impurities, and deteriorate the toughness of the steel base material and the weld heat affected zone. It is preferable to reduce as much as possible in consideration of economy, and the P amount and S amount are 0.020% or less and 0.0070% or less, respectively.

sol.Al:0.003〜0.100%
Alは脱酸元素であり、sol.Al量が0.003%未満ではその効果は十分ではなく、過剰に添加すると靭性の劣化をもたらすため、sol.Al量は0.003〜0.100%の範囲とする。
sol. Al: 0.003 to 0.100%
Al is a deoxidizing element. If the amount of Al is less than 0.003%, the effect is not sufficient, and if added excessively, the toughness is deteriorated. The Al content is in the range of 0.003 to 0.100%.

本発明の基本成分組成は以上であるが、更に所望の特性を向上させる場合は、Cu、Ni、Cr、Mo、Nb、V、Ti、B、Ca、Mg、REMの1種または2種以上を選択元素として添加することができる。   The basic component composition of the present invention is as described above, but when further improving desired characteristics, one or more of Cu, Ni, Cr, Mo, Nb, V, Ti, B, Ca, Mg, and REM are used. Can be added as a selective element.

Cu:0.01〜2.0%
Cuは強度を増加させるために添加することができる元素で0.01%以上添加するとその効果を発揮し、2.0%を超えて添加すると、熱間脆性により鋼板表面の性状を劣化するため、添加する場合、その量は0.01〜2.0%の範囲とする。
Cu: 0.01 to 2.0%
Cu is an element that can be added to increase the strength. When added over 0.01%, its effect is exhibited. When added over 2.0%, the surface properties of the steel sheet deteriorate due to hot brittleness. When added, the amount is in the range of 0.01 to 2.0%.

Ni:0.01〜9.0%
Niは母材の強度を増加させつつ靭性も向上させることが可能な元素である。0.01%以上の添加で効果を発揮し、9.0%超えでは効果が飽和し経済的に不利であるので、Niを添加する場合は、その量は0.01〜9.0%の範囲とする。
Ni: 0.01-9.0%
Ni is an element that can improve the toughness while increasing the strength of the base material. The effect is exhibited by addition of 0.01% or more, and if it exceeds 9.0%, the effect is saturated and economically disadvantageous. Therefore, when Ni is added, the amount is 0.01 to 9.0%. Range.

Cr:0.01〜3.0%
Crは強度を増加するのに有効であり、0.01%以上添加するとその効果を発揮し、3.0%を超えて添加すると、靭性を劣化させるため、Crを添加する場合、その量は0.01〜3.0%の範囲とする。
Cr: 0.01 to 3.0%
Cr is effective for increasing the strength, and when 0.01% or more is added, the effect is exhibited, and when adding over 3.0%, the toughness is deteriorated. The range is 0.01 to 3.0%.

Mo:0.01〜2.0%
Moは強度を増加するのに有効であり、0.01%以上添加するとその効果を発揮し、2.0%を超えて添加すると、著しく靭性を劣化させるとともに経済性を損なうため、Moを添加する場合、その量は0.01〜2.0%の範囲とする。
Mo: 0.01 to 2.0%
Mo is effective in increasing the strength, and when 0.01% or more is added, the effect is exerted, and when adding over 2.0%, the toughness is remarkably deteriorated and the economy is impaired, so Mo is added. If so, the amount is in the range of 0.01 to 2.0%.

Nb:0.003〜0.1%、V:0.003〜0.5%
Nb、Vは母材の強度と靭性を向上させる元素であり、いずれも0.003%以上の添加で効果を発揮する。またそれぞれ0.1%、0.5%を超えるとかえって靭性の低下を招くおそれがある。従って、これらの元素を添加する場合、Nb量は0.003〜0.1%の範囲、V量は0.003〜0.5%の範囲とする。
Nb: 0.003-0.1%, V: 0.003-0.5%
Nb and V are elements that improve the strength and toughness of the base material, and both exhibit an effect when added in an amount of 0.003% or more. On the other hand, if it exceeds 0.1% and 0.5%, respectively, the toughness may be lowered. Therefore, when these elements are added, the Nb content is in the range of 0.003 to 0.1%, and the V content is in the range of 0.003 to 0.5%.

Ti:0.005〜0.20%
Tiは母材の靭性確保や溶接熱影響部での靭性確保に効果があるので添加することができ、この効果は、0.005%以上の含有で生じる。しかし0.20%を超えて添加すると靭性が劣化するため添加する場合には、0.005〜0.20%の範囲とする。
Ti: 0.005 to 0.20%
Ti is effective in ensuring the toughness of the base metal and ensuring the toughness in the weld heat affected zone, and can be added. This effect is produced when the content is 0.005% or more. However, if added over 0.20%, the toughness deteriorates, so when added, the content is made 0.005 to 0.20%.

B:0.0005〜0.0040%
Bは鋼の焼入れ性を向上させる元素であり、この効果によって強度を増加させることができる。この効果は0.0005%以上の添加で顕著になり、0.0040%を超えて添加しても効果は飽和するため、Bを添加する場合、その量は0.0005〜0.0040%の範囲とする。
B: 0.0005 to 0.0040%
B is an element that improves the hardenability of steel, and the strength can be increased by this effect. This effect becomes significant when 0.0005% or more is added, and even if added over 0.0040%, the effect is saturated. Therefore, when B is added, the amount is 0.0005 to 0.0040%. Range.

Ca:0.0001〜0.0060%、Mg:0.0001〜0.0060%、REM:0.0001〜0.0200%
Ca、Mg、REMは鋼中のSを固定して鋼板の靭性を向上させる働きがあり、0.0001%以上の添加で効果がある。しかし、それぞれ0.0060%、0.0060%、0.0200%を超えて添加すると鋼中の介在物量が増加し靭性をかえって劣化させる。従って、これらの元素を添加する場合、Ca量は0.0001〜0.0060%、Mg量は0.0001〜0.0060%、REM量は0.0001〜0.0200%の範囲とする。
なお、上記した成分以外の残部は、Feおよび不可避的不純物からなる。
Ca: 0.0001 to 0.0060%, Mg: 0.0001 to 0.0060%, REM: 0.0001 to 0.0200%
Ca, Mg, and REM have a function of fixing S in steel and improving the toughness of the steel sheet, and are effective when added in an amount of 0.0001% or more. However, if added over 0.0060%, 0.0060%, and 0.0200%, respectively, the amount of inclusions in the steel increases and the toughness is changed and deteriorated. Therefore, when these elements are added, the Ca content is in the range of 0.0001 to 0.0060%, the Mg content is in the range of 0.0001 to 0.0060%, and the REM content is in the range of 0.0001 to 0.0200%.
The balance other than the above components is composed of Fe and inevitable impurities.

2.製造条件について
上記した組成を有する鋼を、転炉、電気炉等の溶製手段で常法により溶製し、連続鋳造法または造塊〜分塊法等で常法によりスラブ等の鋼素材とすることが好ましい。なお、溶製方法、鋳造法については上記した方法に限定されるものではない。その後、性能所望の形状に圧延し、圧延中または圧延後に、冷却および加熱を行う。
2. Manufacturing conditions Steel having the above-described composition is melted by a conventional method using a melting means such as a converter or an electric furnace, and a steel material such as a slab is formed by a conventional method such as a continuous casting method or an ingot-bundling method. It is preferable to do. The melting method and the casting method are not limited to the methods described above. Thereafter, the product is rolled into a desired shape, and cooled and heated during or after rolling.

(1)加熱温度
鋳造後、鋼片温度が室温まで低下してからあるいは高温の状態で、鋼片を加熱炉に挿入して鋼片加熱温度は1000℃以上とする。鋼片加熱温度は、靭性確保の観点からはより低温が好ましいが、1000℃未満では鋼片厚中央の未厚着ザクが残存して、板厚1/2部性能を劣化させる可能性があることと、Nb,Vなどを添加した場合には十分に固溶しないため、1000℃以上とする。また、過度の高温に加熱すると初期オーステナイト粒が粗大化し、靭性が劣化するので、通常、鋼片加熱温度は1300℃以下とするが、より好ましくは1150℃以下である。
(1) Heating temperature After casting, after the steel slab temperature has dropped to room temperature or in a high temperature state, the steel slab is inserted into a heating furnace so that the steel slab heating temperature is 1000 ° C. or higher. The slab heating temperature is preferably lower from the viewpoint of securing toughness, but if it is less than 1000 ° C, unthickened zaku in the center of the slab thickness may remain, which may deteriorate the plate thickness 1/2 part performance. When Nb, V or the like is added, the solid solution is not sufficiently dissolved. Further, when heated to an excessively high temperature, the initial austenite grains become coarse and the toughness deteriorates. Therefore, the steel slab heating temperature is usually 1300 ° C. or lower, more preferably 1150 ° C. or lower.

(2)1次圧延
1次圧延は、鋼片等の鋼素材を、所望の形状とするために行い、オーステナイト再結晶温度域で1パス以上の圧下を行い、引き続き、オーステナイト未再結晶温度域で累積圧下率40%以上の圧延を行う。オーステナイト再結晶温度域圧延は加熱時のオーステナイト粒をある程度まで均一微細化するのに必要であり、1パス以上、好ましくは累積圧下率が20%以上の圧延を行う。その後のオーステナイト未再結晶温度域圧延は、圧下率が小さいと、その後急速加熱後のミクロ組織微細化効果が発揮できないため、累積圧下率40%以上を確保する。また、圧下率は高い方が好ましいが、工業的には80%程度が上限となる。
(2) Primary rolling Primary rolling is performed to make a steel material such as a steel slab into a desired shape, and a reduction of one pass or more is performed in the austenite recrystallization temperature range, followed by the austenite non-recrystallization temperature range. Then, rolling is performed at a cumulative rolling reduction of 40% or more. The austenite recrystallization temperature range rolling is necessary to uniformly refine the austenite grains during heating to a certain degree, and performs rolling at one pass or more, preferably at a cumulative reduction of 20% or more. In the subsequent austenite non-recrystallization temperature range rolling, if the rolling reduction is small, the effect of refining the microstructure after rapid heating cannot be exhibited thereafter, so a cumulative rolling reduction of 40% or more is ensured. Moreover, although the one where a rolling reduction is higher is preferable, about 80% becomes an upper limit industrially.

また、オーステナイト再結晶温度域圧延の後、オーステナイト未再結晶温度域圧延を開始するまでの間は、空冷で待ってもよいが、オーステナイト再結晶温度域圧延中あるいは同オーステナイト再結晶温度域圧延後に水冷により冷却を行い、オーステナイト未再結晶温度域圧延までの時間を空冷よりも短縮する方が効率的にも好ましく、また、空冷の場合に比べて水冷による冷却の方が再結晶オーステナイトの成長を抑制する効果があり、組織の微細化に対して、より有効である。   In addition, after the austenite recrystallization temperature range rolling, you may wait by air cooling until the start of the austenite non-recrystallization temperature range rolling, but during the austenite recrystallization temperature range rolling or after the austenite recrystallization temperature range rolling It is more efficient to cool by water cooling and shorten the time until rolling to the austenite non-recrystallization temperature range than air cooling, and cooling by water cooling increases the growth of recrystallized austenite compared to air cooling. There is an effect to suppress, and it is more effective for miniaturization of the structure.

(3)1次圧延後の急速加熱
オーステナイト未再結晶温度域圧延の後、温度がAr変態点を下回ることのない温度域から、オーステナイト再結晶温度域までを2℃/sec以上の昇温速度で加熱する。加熱方法は特に限定しないが、高周波誘導加熱が好ましい。
(3) Rapid heating after primary rolling After the austenite non-recrystallization temperature range rolling, the temperature rise from the temperature range where the temperature does not fall below the Ar 3 transformation point to the austenite recrystallization temperature range of 2 ° C./sec or more. Heat at speed. The heating method is not particularly limited, but high frequency induction heating is preferable.

加熱開始温度がAr変態点を下回れば、フェライト変態が起こり、再加熱時に逆変態によりオーステナイトは微細化されるが、その後の加熱時の加熱温度代が大きくなり効率および経済性を損なうとともに、Nb炭化物などの析出・粗大化が促進され、混粒組織となりやすく靭性低下の原因となるので、Ar変態点以上の温度から昇温を開始するのが良い。この場合の最高加熱温度はオーステナイト再結晶温度域内であることが必要であり、(オーステナイト再結晶温度の下限+100℃)以下の低温が好ましい。必要以上に温度を上げるとオーステナイト粒の成長が起こり、オーステナイトの微細化効果が得られないためである。 If the heating start temperature is lower than the Ar 3 transformation point, ferrite transformation occurs, and austenite is refined by reverse transformation at the time of reheating, but the heating temperature cost at the time of subsequent heating is increased and the efficiency and economy are impaired. Precipitation and coarsening of Nb carbide and the like are promoted and a mixed grain structure is likely to be caused, resulting in a decrease in toughness. Therefore, it is preferable to start the temperature rise from a temperature equal to or higher than the Ar 3 transformation point. In this case, the maximum heating temperature needs to be within the austenite recrystallization temperature range, and a low temperature of (lower limit of austenite recrystallization temperature + 100 ° C.) or less is preferable. This is because if the temperature is raised more than necessary, austenite grains grow and the effect of refining austenite cannot be obtained.

また、昇温速度は、2℃/sec以下では、再結晶の前に加工組織の回復や、NbやTiなどの炭化物の加工誘起析出が起こり、靭性を劣化させるため、2℃/sec以上とする。加熱後の保持は行ってもよいが、再結晶が完了するとその後に粒成長が起こるため、必要以上の保持は行うべきではなく、短時間が好ましい。   In addition, when the rate of temperature rise is 2 ° C./sec or less, recovery of the processed structure or processing-induced precipitation of carbides such as Nb and Ti occurs before recrystallization, and the toughness is deteriorated. To do. Although holding after heating may be performed, since grain growth occurs after completion of recrystallization, holding more than necessary should not be performed, and a short time is preferable.

以上説明したように、初期オーステナイト粒径を制御した上でオーステナイト未再結晶温度域圧延の累積圧延率を確保し、オーステナイト再結晶温度域に急速に加熱することにより、オーステナイトの微細化が達成される。条件を整えることにより、結晶粒径が15μm以下や10μm以下のオーステナイト粒が得られる。   As explained above, by controlling the initial austenite grain size, ensuring the cumulative rolling rate of the austenite non-recrystallization temperature range rolling, and rapidly heating to the austenite recrystallization temperature range, the austenite refinement can be achieved. The By adjusting the conditions, austenite grains having a crystal grain size of 15 μm or less or 10 μm or less are obtained.

なお、前記オーステナイト再結晶温度域に加熱時のオーステナイト粒の形態は、その後の圧延・冷却・熱処理後、オーステナイト粒界を優先的に腐食する腐食液で腐食して、金属組織を観察することにより、旧オーステナイト粒界として観察することができる。よって、この組織観察結果から線分法や画像処理などの方法により求められる、旧オーステナイト粒の円相当径を以って、前記加熱時のオーステナイト粒径を把握することができる。   The form of austenite grains during heating in the austenite recrystallization temperature range is corroded with a corrosive liquid that preferentially corrodes austenite grain boundaries after subsequent rolling, cooling, and heat treatment, and the metal structure is observed. It can be observed as a prior austenite grain boundary. Therefore, the austenite grain size at the time of the heating can be grasped from the circle observation equivalent diameter of the prior austenite grains obtained by a method such as line segmentation or image processing.

(4)2次圧延
急速加熱後は、ミクロ組織のいっそうの微細化やオースフォーム効果を得ることを目的として、さらに圧延を行うことができる。その場合はオーステナイト未再結晶温度域で行い、その効果を発揮するにはこの温度域において15%以上の累積圧下率が必要である。
(4) Secondary rolling After rapid heating, further rolling can be performed for the purpose of obtaining a finer microstructure and an ausfoam effect. In that case, it is carried out in the austenite non-recrystallization temperature range, and in order to exert its effect, a cumulative reduction ratio of 15% or more is necessary in this temperature range.

(5)加速冷却
加速冷却は、オーステナイト再結晶温度域に急速加熱した鋼板あるいは、その後累積圧下率15%以上のオーステナイト未再結晶温度域圧延を行った鋼板に対して行い、Ar変態点以上の温度から600℃以下の温度まで行う。Ar変態点未満の温度から行った場合には一部フェライトが生成するため、所定の強度が得られない。また、600℃以上で冷却を停止した場合も同様である。冷却速度は、空冷以上の冷却速度が必要であり、10℃/secの強冷却が好ましい。冷却方法は特に限定しないが、水冷による冷却が好ましい。
(5) Accelerated cooling Accelerated cooling is performed on a steel sheet rapidly heated to the austenite recrystallization temperature range or a steel sheet subjected to austenite non-recrystallization temperature range rolling with a cumulative rolling reduction of 15% or more, and the Ar 3 transformation point or higher. To a temperature of 600 ° C. or lower. When it is carried out from a temperature lower than the Ar 3 transformation point, a part of ferrite is generated, and thus a predetermined strength cannot be obtained. The same applies when cooling is stopped at 600 ° C. or higher. The cooling rate requires a cooling rate higher than that of air cooling, and strong cooling of 10 ° C./sec is preferable. The cooling method is not particularly limited, but cooling by water cooling is preferable.

(6)焼戻し
加速冷却後、必要に応じ、焼戻しを行う。焼戻しは、主として、加速冷却により焼入れを行った鋼材に対して、強度・靭性バランスの適正化、残留応力の軽減などの目的で行われ、実施する場合はAc変態点以下の温度で行う。昇温速度、保持時間は特に限定しないが、圧延ライン上の高周波誘導加熱装置などの急速加熱装置で実施することが、靭性および効率の点で好ましい。
(6) Tempering After accelerated cooling, tempering is performed as necessary. Tempering is carried out mainly for the purpose of optimizing the balance between strength and toughness, reducing residual stress, etc., on steel materials that have been quenched by accelerated cooling, and when carried out at a temperature not higher than the Ac 1 transformation point. The heating rate and the holding time are not particularly limited, but it is preferable in terms of toughness and efficiency to carry out with a rapid heating apparatus such as a high-frequency induction heating apparatus on the rolling line.

なお、焼入れ焼戻しプロセスによらず、加速冷却ままの状態で製品となるいわゆる非調質鋼の場合には、通常、焼戻しを実施しない。   In addition, tempering is not normally performed in the case of what is called non-tempered steel which becomes a product in the state of accelerated cooling irrespective of a quenching tempering process.

ここで、本発明における鋼材温度は、鋼材の表面と中心部の平均温度を示している。Ar、Ac変態点は鋼成分によって異なる。Ar、Ac変態点は下式によって求めることができる。但し、各式において、各元素記号は各元素の含有量(質量%)を示す。
Ar=910−273C−74Mn−56Ni−16Cr−9Mo−5Cu
Ac=751−26.6C+17.6Si−11.6Mn−169Al−23Cu−23Ni+24.1Cr+22.5Mo+233Nb−39.7V−5.7Ti−895B
一方、オーステナイト再結晶温度域の下限温度は、鋼組成のほか、結晶粒径や加工履歴や歪量などの影響を受けるが、概ね800〜950℃の範囲にある。事前に予備試験をして調査することにより、前記下限温度を推測することができる。
Here, the steel material temperature in this invention has shown the average temperature of the surface and center part of steel materials. The Ar 3 and Ac 1 transformation points vary depending on the steel components. The Ar 3 and Ac 1 transformation points can be obtained by the following equation. However, in each formula, each element symbol indicates the content (% by mass) of each element.
Ar 3 = 910-273C-74Mn-56Ni-16Cr-9Mo-5Cu
Ac 1 = 751-26.6C + 17.6Si-11.6Mn -169Al-23Cu-23Ni + 24.1Cr + 22.5Mo + 233Nb-39.7V-5.7Ti-895B
On the other hand, the lower limit temperature of the austenite recrystallization temperature region is affected by the crystal grain size, processing history, strain amount, etc. in addition to the steel composition, but is generally in the range of 800 to 950 ° C. By conducting a preliminary test and investigating in advance, the lower limit temperature can be estimated.

本発明は厚鋼板、形鋼、棒鋼など種々の形状の鋼製品に適用可能である。本発明で「厚鋼板」とは、板厚6mm以上の鋼板を指すものとする。   The present invention is applicable to steel products having various shapes such as thick steel plates, section steels, and steel bars. In the present invention, the “thick steel plate” refers to a steel plate having a thickness of 6 mm or more.

表1に示す組成の鋼を転炉で溶製し、連続鋳造法で250mm厚のスラブ(鋼素材)とし、表2および表3に示す熱間圧延条件により10〜40mm厚の鋼板を作製した。表1において、鋼種Zの供試鋼は成分組成のいずれかが本発明の範囲外となっている。   Steel with the composition shown in Table 1 was melted in a converter, and a slab (steel material) having a thickness of 250 mm was formed by a continuous casting method, and a steel plate having a thickness of 10 to 40 mm was produced according to the hot rolling conditions shown in Tables 2 and 3. . In Table 1, one of the component compositions of the test steel of steel type Z is outside the scope of the present invention.

得られた厚鋼板について、板厚方向1/4の位置から平行部直径6mmφの引張試験片を採取して、JIS Z 2241(1998)の規定に準拠して引張試験を実施し、引張強さTSおよび0.2%耐力YSを求めた。   About the obtained thick steel plate, a tensile test piece having a parallel part diameter of 6 mmφ is taken from a position of ¼ in the plate thickness direction, and a tensile test is performed in accordance with the provisions of JIS Z 2241 (1998). TS and 0.2% yield strength YS were determined.

また、板厚方向1/4の位置からJIS Z 2202(1998)の規定に準拠して、Vノッチ標準寸法のシャルピー衝撃試験片を採取して、JIS Z 2242(1998)の規定に準拠して衝撃試験を実施し、破面遷移温度vTrsを求めた。   In addition, a Charpy impact test piece having a V-notch standard dimension was taken from a position in the thickness direction 1/4 in accordance with JIS Z 2202 (1998), and in accordance with JIS Z 2242 (1998). An impact test was performed to determine the fracture surface transition temperature vTrs.

更に、板厚方向1/4の位置から組織観察用試験片を採取し、オーステナイト粒界を優先的に腐食する腐食液で腐食後、光学顕微鏡により平均旧オ−ステナイト粒径(円相当径)を線分法にて測定した。これは、高温時のオーステナイトの粒界に相当する部分を腐食により現出するものであるが、観察時にはベイナイトやマルテンサイトなど、他の相に変態した後の状態なので、観察時に現存する組織と区別するために「旧オーステナイト(粒径)」などと称するものである。   Further, a specimen for observing the structure is taken from a position of 1/4 in the plate thickness direction, and after corroding with a corrosive solution preferentially corroding the austenite grain boundary, the average prior austenite grain size (equivalent circle diameter) is measured by an optical microscope. Was measured by the line segment method. This is because the part corresponding to the grain boundary of austenite at high temperature appears due to corrosion, but at the time of observation it is a state after transformation into other phases such as bainite and martensite, In order to distinguish, it is called “old austenite (particle size)”.

表4および表5に試験結果を示す。   Tables 4 and 5 show the test results.

ここでは、引張強度950MPa以上で、シャルピー衝撃試験における脆性破面遷移温度(vTrs)が−40℃以下、旧オーステナイト粒径は15μm以下を発明例とした。   In this example, the tensile strength was 950 MPa or more, the brittle fracture surface transition temperature (vTrs) in the Charpy impact test was −40 ° C. or less, and the prior austenite grain size was 15 μm or less.

成分組成、製造条件の規定のいずれかが本発明範囲外となった鋼板No.4、5、9、10、14、30は、本発明例鋼板No.1〜3、6〜8、No.11〜13、No.15〜28と比較して靱性が劣っている。なお、鋼板No.5は、1次圧延終了温度がオーステナイト未再結晶温度域内の比較的高温域であったため、オーステナイト未再結晶温度域での圧延の累積圧下率が本発明の範囲よりも小さくなり、かつ、再加熱がない条件であったので、靱性が低下した例である。   Steel plate No. in which either the composition of the components or the provisions of the manufacturing conditions are out of the scope of the present invention. 4, 5, 9, 10, 14, 30 are examples of the present invention steel plate Nos. 1-3, 6-8, no. Compared with 11-13 and No.15-28, toughness is inferior. In addition, steel plate No. No. 5, since the primary rolling end temperature was a relatively high temperature range within the austenite non-recrystallization temperature range, the cumulative reduction ratio of rolling in the austenite non-recrystallization temperature range was smaller than the range of the present invention, and This is an example in which the toughness was lowered because there was no heating.

Claims (8)

質量%で、C:0.01〜0.30%、Si:0.01〜0.80%、Mn:0.20〜2.50%、P:0.020%以下、S:0.0070%以下、sol.Al:0.003〜0.100%を含有し、残部がFeおよび不可避的不純物からなる組成を有する鋼素材を、1000℃以上に加熱し、オーステナイト再結晶温度域において圧延後、オーステナイト未再結晶温度域において累積圧下率40%以上の圧延を実施した後、Ar変態点以上の温度からオーステナイト再結晶温度域まで2℃/sec以上の昇温速度で加熱し、さらに、Ar変態点以上の温度から600℃以下に加速冷却して旧オーステナイト粒径を15μm以下、シャルピー衝撃試験における脆性破面遷移温度(vTrs)を−40℃以下とすることを特徴とする高強度高靭性鋼の製造方法。 In mass%, C: 0.01 to 0.30%, Si: 0.01 to 0.80%, Mn: 0.20 to 2.50%, P: 0.020% or less, S: 0.0070 % Or less, sol. A steel material having a composition containing Al: 0.003 to 0.100%, the balance being Fe and inevitable impurities is heated to 1000 ° C. or more, rolled in the austenite recrystallization temperature range, and then austenite unrecrystallized. After rolling with a cumulative rolling reduction of 40% or more in the temperature range, the steel is heated from the temperature above the Ar 3 transformation point to the austenite recrystallization temperature range at a rate of temperature rise of 2 ° C./sec or more, and further above the Ar 3 transformation point. Of high-strength and high-toughness steel characterized in that the prior austenite grain size is 15 μm or less and the brittle fracture surface transition temperature (vTrs) in the Charpy impact test is −40 ° C. or less by accelerated cooling from 600 ° C. to 600 ° C. or less. Method. 鋼組成に、更に、質量%で、Cu:0.01〜2.0%、Ni:0.01〜9.0%、Cr:0.01〜3.0%、Mo:0.01〜2.0%、Nb:0.003〜0.1%、V:0.003〜0.5%、Ti:0.005〜0.20%、B:0.0005〜0.0040%、Ca:0.0001〜0.0060%、Mg:0.0001〜0.0060%、REM:0.0001〜0.0200%のうちから選ばれた1種または2種以上を含有することを特徴とする請求項1に記載の高強度高靭性鋼の製造方法。   In addition to the steel composition, in mass%, Cu: 0.01 to 2.0%, Ni: 0.01 to 9.0%, Cr: 0.01 to 3.0%, Mo: 0.01 to 2 0.0%, Nb: 0.003-0.1%, V: 0.003-0.5%, Ti: 0.005-0.20%, B: 0.0005-0.0040%, Ca: It contains one or more selected from 0.0001 to 0.0060%, Mg: 0.0001 to 0.0060%, and REM: 0.0001 to 0.0200%. The manufacturing method of the high strength high toughness steel of Claim 1. 600℃以下に加速冷却した後、さらに、Ac変態点以下の温度に焼戻すことを特徴とする請求項1または2に記載の高強度高靭性鋼の製造方法。 The method for producing high-strength and high-toughness steel according to claim 1 or 2, further comprising tempering to a temperature not higher than the Ac 1 transformation point after accelerated cooling to 600 ° C or lower. 質量%で、C:0.01〜0.30%、Si:0.01〜0.80%、Mn:0.20〜2.50%、P:0.020%以下、S:0.0070%以下、sol.Al:0.003〜0.100%を含有し、残部がFeおよび不可避的不純物からなる組成を有する鋼素材を、1000℃以上に加熱し、オーステナイト再結晶温度域において圧延後、オーステナイト未再結晶温度域において累積圧下率40%以上の圧延を実施した後、Ar変態点以上の温度からオーステナイト再結晶温度域まで2℃/sec以上の昇温速度で加熱し、さらに、オーステナイト未再結晶温度域において累積圧下率15%以上の圧延を行い、Ar変態点以上の温度から600℃以下に加速冷却して旧オーステナイト粒径を15μm以下、シャルピー衝撃試験における脆性破面遷移温度(vTrs)を−40℃以下とすることを特徴とする高強度高靭性鋼の製造方法。 In mass%, C: 0.01 to 0.30%, Si: 0.01 to 0.80%, Mn: 0.20 to 2.50%, P: 0.020% or less, S: 0.0070 % Or less, sol. A steel material having a composition containing Al: 0.003 to 0.100%, the balance being Fe and inevitable impurities is heated to 1000 ° C. or more, rolled in the austenite recrystallization temperature range, and then austenite unrecrystallized. After rolling with a cumulative rolling reduction of 40% or more in the temperature range, the steel is heated from the temperature above the Ar 3 transformation point to the austenite recrystallization temperature range at a temperature increase rate of 2 ° C./sec or more, and further, the austenite non-recrystallization temperature Rolling at a cumulative rolling reduction of 15% or more in the region, accelerated cooling from a temperature above the Ar 3 transformation point to 600 ° C. or less to reduce the prior austenite grain size to 15 μm or less, and the brittle fracture surface transition temperature (vTrs) in the Charpy impact test. A method for producing a high-strength, high-toughness steel, characterized by being -40 ° C or lower . 鋼組成に、更に、質量%で、Cu:0.01〜2.0%、Ni:0.01〜9.0%、Cr:0.01〜3.0%、Mo:0.01〜2.0%、Nb:0.003〜0.1%、V:0.003〜0.5%、Ti:0.005〜0.20%、B:0.0005〜0.0040%、Ca:0.0001〜0.0060%、Mg:0.0001〜0.0060%、REM:0.0001〜0.0200%のうちから選ばれた1種または2種以上を含有することを特徴とする請求項4に記載の高強度高靭性鋼の製造方法。   In addition to the steel composition, in mass%, Cu: 0.01 to 2.0%, Ni: 0.01 to 9.0%, Cr: 0.01 to 3.0%, Mo: 0.01 to 2 0.0%, Nb: 0.003-0.1%, V: 0.003-0.5%, Ti: 0.005-0.20%, B: 0.0005-0.0040%, Ca: It contains one or more selected from 0.0001 to 0.0060%, Mg: 0.0001 to 0.0060%, and REM: 0.0001 to 0.0200%. The manufacturing method of the high strength high toughness steel of Claim 4. 600℃以下に加速冷却した後、さらに、Ac変態点以下の温度に焼戻すことを特徴とする請求項4または5に記載の高強度高靭性鋼の製造方法。 After accelerated cooling to 600 ° C. or less, further, the method of producing a high strength and high toughness steel according to claim 4 or 5, wherein the tempering Succoth to a temperature below Ac 1 transformation point. 前記累積圧下率40%以上のオーステナイト未再結晶温度域圧延を行う前のオーステナイト再結晶温度域圧延中または同オーステナイト再結晶温度域圧延後に水冷を実施し、オーステナイト未再結晶温度域まで空冷よりも速い速度で冷却することを特徴とする請求項1乃至6のいずれかに記載の高強度高靭性鋼の製造方法。 The austenite recrystallization temperature range rolling before or after the austenite recrystallization temperature range rolling with the cumulative reduction rate of 40% or more is performed after the austenite recrystallization temperature range rolling or after the austenite recrystallization temperature range rolling. The method for producing high-strength and high-toughness steel according to any one of claims 1 to 6, wherein cooling is performed at a high speed. 前記オーステナイト未再結晶温度域において累積圧下率40%以上の圧延を実施した後のオーステナイト再結晶温度域への加熱後に、15μm以下の平均オーステナイト粒径を有することを特徴とする請求項1乃至7のいずれかに記載の高強度高靭性鋼の製造方法。   The average austenite grain size of 15 µm or less after heating to the austenite recrystallization temperature range after rolling at a cumulative reduction rate of 40% or more in the austenite non-recrystallization temperature range. The manufacturing method of the high strength high toughness steel in any one of.
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