JP6984319B2 - Nickel-containing steel sheet for low temperature with excellent toughness and its manufacturing method - Google Patents
Nickel-containing steel sheet for low temperature with excellent toughness and its manufacturing method Download PDFInfo
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本発明は、靭性に優れた低温用ニッケル含有鋼板およびその製法に関するものである。この製法で製造した鋼板は、造船、橋梁、建築、海洋構造物、圧力容器、タンク、ラインパイプなどの溶接構造物一般に用いることができるが、特に−１３０℃程度の低温での破壊靱性が要求される低温タンクでの使用において有効である。 The present invention relates to a nickel-containing steel sheet for low temperature having excellent toughness and a method for producing the same. Steel sheets manufactured by this method can be used for general welded structures such as shipbuilding, bridges, construction, marine structures, pressure vessels, tanks, and line pipes, but fracture toughness at a low temperature of about -130 ° C is particularly required. It is effective for use in low temperature tanks.
エタン、エチレンなどの取引の広がりとともに、液化エタン、液化エチレンなどの船舶による長距離輸送が求められている。液化エタン、液化エチレンを積載するタンクの材料として、オーステナイト系ステンレス鋼のほかに、３．５％Ｎｉ鋼などのフェライト系低温用鋼も使用可能と考えられる。しかしながら、フェライト系低温用ニッケル鋼は、歪時効による靭性低下がみられることから、この克服が実用化への鍵となる。たとえば６％のひずみ付与後に２００℃で１ｈｒの熱処理を行った材料の−１３０℃のシャルピー衝撃吸収エネルギーの最低値が１５０Ｊ以上であることが望ましい。現在の水準では、これを達成することは必ずしも容易ではない。 With the expansion of transactions such as ethane and ethylene, long-distance transportation of liquefied ethane and liquefied ethylene by ship is required. In addition to austenitic stainless steel, ferritic low-temperature steel such as 3.5% Ni steel can be used as a material for tanks for loading liquefied ethane and liquefied ethylene. However, ferrite-based low-temperature nickel steel has a decrease in toughness due to strain aging, and overcoming this is the key to practical use. For example, it is desirable that the minimum value of the Charpy impact absorption energy at −130 ° C. of a material that has been heat-treated at 200 ° C. for 1 hr after applying a strain of 6% is 150 J or more. At current levels, achieving this is not always easy.
フェライト系低温用ニッケル鋼の−１３０℃でのシャルピー衝撃吸収エネルギーに、ごく低い確率で発生する低値には、介在物が関わっていることがある。連続鋳造で製造される鋼スラブには、数μｍの介在物が浮上分離せずに残存しているが、通常の清浄度であれば、そのような独立した介在物が−１３０℃でのシャルピー衝撃吸収エネルギーに与える影響は軽微である。しかしながら、数μｍの介在物が凝集合体したクラスターを形成した場合、６％のひずみ付与後に２００℃で１ｈｒの熱処理を行った材料の−１９６℃のシャルピー衝撃吸収エネルギーが１５０Ｊ以下に低下することがある。介在物の主たるものは、アルミナ（Ａｌ2Ｏ3）である。アルミナクラスターは、製鋼工程において一般的に生じうる事象であり、本質的な改善は困難である。 Inclusions may be involved in the low value of the Charpy impact absorption energy of ferrite-based low-temperature nickel steel at −130 ° C., which occurs with a very low probability. In steel slabs manufactured by continuous casting, inclusions of several μm remain without floating separation, but at normal cleanliness, such independent inclusions are Charpy at -130 ° C. The effect on shock absorption energy is minor. However, when a cluster of several μm inclusions is aggregated and coalesced, the Charpy impact absorption energy at -196 ° C. of the material heat-treated at 200 ° C. for 1 hr after applying a strain of 6% may decrease to 150 J or less. be. The main inclusion is alumina (Al 2 O 3 ). Alumina clusters are a common event in the steelmaking process and are difficult to improve in essence.
介在物、たとえばＭｎＳなどの伸長介在物による害悪を軽減する方法として、クロス圧延がある。クロス圧延とは、鋼板の形状を作りこむ熱間圧延において、普通は鋼板の長手方向にのみ実施する圧延のうち、一部の圧下を鋼板の幅方向に実施するものであり、介在物がＭｎＳの場合は鋼板長手方向のＭｎＳの伸長が抑制されることから、試験片の長手方向が圧延幅方向と平行になるような試験片を用いたシャルピー試験において、シャルピー衝撃吸収エネルギーが改善する。 There is cross rolling as a method of reducing the harm caused by inclusions, for example, extension inclusions such as MnS. Cross-rolling is hot rolling that creates the shape of a steel sheet. Of the rolling that is normally performed only in the longitudinal direction of the steel sheet, some rolling is performed in the width direction of the steel sheet, and the inclusions are MnS. In the case of, since the elongation of MnS in the longitudinal direction of the steel sheet is suppressed, the Charpy impact absorption energy is improved in the Charpy test using the test piece so that the longitudinal direction of the test piece is parallel to the rolling width direction.
たとえば、特許文献１、特許文献２では、クロス圧延を実施する際の幅方向圧延を未再結晶温度域で行うことで、曲げ加工性や低温靭性を改善している。しかしながら、未再結晶温度域での幅方向圧延を行った場合、圧下前のオーステナイト粒径が大きいまま未再結晶域圧延を行うこととなり、却って靭性が低下することが多く、この方法では前記の目的を達成できない。また、特許文献３には、クロス圧延を実施する際の幅方向圧延と長手方向圧延の圧下比率を規定することで等方性の高い鋼板としている。介在物の制御に関しては、この方法が有効であるものの、圧下比率の規定のみでは、シャルピー衝撃吸収エネルギーに最も影響する因子である有効結晶粒径を小さくできないため、この方法では前記の目的を達成できない。
つまり、現在の技術では、靭性に優れた低温用ニッケル含有鋼板を提供することはできない。
For example, in Patent Document 1 and Patent Document 2, bending workability and low-temperature toughness are improved by performing widthwise rolling in the unrecrystallized temperature range when performing cross rolling. However, when rolling in the width direction in the unrecrystallized temperature range, rolling in the unrecrystallized region is performed while the austenite grain size before rolling is large, and the toughness is often lowered. I can't achieve my purpose. Further, Patent Document 3 defines a rolling reduction ratio between widthwise rolling and longitudinal rolling when cross-rolling is performed, so that a steel sheet having high isotropic properties is obtained. Although this method is effective for controlling inclusions, the above-mentioned purpose is achieved by this method because the effective crystal grain size, which is the factor most influencing the Charpy impact absorption energy, cannot be reduced only by specifying the reduction ratio. Can not.
That is, the current technology cannot provide a nickel-containing steel sheet for low temperature with excellent toughness.
本発明は、靭性に優れた低温用ニッケル含有鋼板およびその製造方法を提供することである。 The present invention is to provide a nickel-containing steel sheet for low temperature having excellent toughness and a method for producing the same.
本発明は、靭性に優れた低温用ニッケル含有鋼板およびその製造方法を提供するものであり、その要旨とするところは以下の通りである。
（１）鋼が、質量％で、Ｃ：０．０２％以上０．１２％以下、Ｓｉ：０．０２％以上０．３５％以下、Ｍｎ：０．１０％以上１．５０％以下、Ｐ：０．００１０％以上０．０１００％以下、Ｓ：０．０００１％以上０．００３５％以下、Ｎｉ：２．７％以上５．０％以下、Ａｌ：０．００２％以上０．０９０％以下、Ｎ：０．０００１％以上０．００７０％以下、Ｔ−Ｏ：０．０００１％以上０．００３０％以下を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成であり、旧オーステナイト粒径が２０μm以下であり、有効結晶粒径が１２μm以下であり、引張強さが４５０ＭＰａ以上６９０ＭＰａ以下であることを特徴とする，靭性に優れた低温用ニッケル含有鋼板。
The present invention provides a nickel-containing steel sheet for low temperature having excellent toughness and a method for producing the same, and the gist thereof is as follows.
(1) Steel is by mass%, C: 0.02% or more and 0.12% or less, Si: 0.02% or more and 0.35% or less, Mn: 0.10% or more and 1.50% or less, P. : 0.0010% or more and 0.0100% or less, S: 0.0001% or more and 0.0035% or less, Ni: 2.7% or more and 5.0% or less, Al: 0.002% or more and 0.090% or less , N: 0.0001% or more 0.0070% or less, T-O: containing 0.0001% or more 0.0030% or less, the balance being a steel composition consisting of Fe and unavoidable impurities, the prior austenite grain size There are at 20μm or less, effective grain size is not less 12μm or less, a tensile strength is equal to or less than 690MPa or more 450 MPa, low-temperature nickel-containing steel sheet excellent in toughness.
（２）さらに質量％で、Ｃｕ：０．０１％以上２．００％以下、Ｃｒ：０．０１％以上５．００％以下、Ｍｏ：０．０１％以上１．００％以下、Ｂ：０．０００２％以上０．０５００％以下、Ｎｂ：０．００１％以上０．０５０％以下、Ｔｉ：０．００１％以上０．０５０％以下、Ｖ：０．００１％以上０．０５０％以下、Ｃａ：０．０００３％以上０．０３００％以下、Ｍｇ：０．０００３％以上０．０３００％以下、ＲＥＭ：０．０００３％以上０．０３００％以下のいずれか１種以上を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成であることを特徴とする、前記（１）に記載の靭性に優れた低温用ニッケル含有鋼板。 (2) Further, in terms of mass%, Cu: 0.01% or more and 2.00% or less, Cr: 0.01% or more and 5.00% or less, Mo: 0.01% or more and 1.00% or less, B: 0 .0002% or more and 0.0500% or less, Nb: 0.001% or more and 0.050% or less, Ti: 0.001% or more and 0.050% or less, V: 0.001% or more and 0.050% or less, Ca : 0.0003% or more and 0.0300% or less, Mg: 0.0003% or more and 0.0300% or less, REM: 0.0003% or more and 0.0300% or less, and the balance is Fe. The low temperature nickel-containing steel plate having excellent toughness according to (1) above, which has a steel composition composed of unavoidable impurities.
（３）質量％で、Ｃ：０．０２％以上０．１２％以下、Ｓｉ：０．０２％以上０．３５％以下、Ｍｎ：０．１０％以上１．５０％以下、Ｐ：０．００１０％以上０．０１００％以下、Ｓ：０．０００１％以上０．００３５％以下、Ｎｉ：２．７％以上５．０％以下、Ａｌ：０．００２％以上０．０９０％以下、Ｎ：０．０００１％以上０．００７０％以下、Ｔ−Ｏ：０．０００１％以上０．００３０％以下を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成である鋳片あるいは鋼片を、８５０℃以上１３００℃以下に加熱し、仕上げ１パス前温度が６００℃以上８５０℃以下の熱間圧延を行い、空冷したのち、焼入れを行う際の加熱中において、６００℃以上７５０℃以下の温度範囲の昇温速度を０．３℃/s以上とし、焼入れは最高加熱温度を８００℃以上９４０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とし、さらに焼戻しは最高加熱温度を５００℃以上６６０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とすることにより、旧オーステナイト円相当粒径が２０μｍ以下であり、有効結晶粒径が１２μｍ以下である鋼板を得ることを特徴とする、靭性に優れた低温用ニッケル含有鋼板の製造方法。 (3) In terms of mass%, C: 0.02% or more and 0.12% or less, Si: 0.02% or more and 0.35% or less, Mn: 0.10% or more and 1.50% or less, P: 0. 0010% or more and 0.0100% or less, S: 0.0001% or more and 0.0035% or less, Ni: 2.7% or more and 5.0% or less, Al: 0.002% or more and 0.090% or less, N: 850 slabs or steel pieces having a steel composition containing 0.0001% or more and 0.0070% or less, TO: 0.0001% or more and 0.0030% or less, and the balance being Fe and unavoidable impurities. The temperature range is 600 ° C or higher and 750 ° C or lower during heating during heating after heating to 1300 ° C or lower, hot rolling with a temperature of 600 ° C or higher and 850 ° C or lower before finishing, air cooling, and quenching. The temperature rise rate is 0.3 ° C / s or more, the maximum heating temperature is heated to a temperature range of 800 ° C or more and 940 ° C or less, the holding time is 5 minutes or more and 100 minutes or less, and the tempering is the maximum heating temperature. Is heated to a temperature range of 500 ° C. or higher and 660 ° C. or lower, and the holding time is set to 5 minutes or longer and 100 minutes or lower. A method for producing a low-temperature nickel-containing steel plate having excellent toughness, which is characterized by obtaining.
（４）質量％で、Ｃ：０．０２％以上０．１２％以下、Ｓｉ：０．０２％以上０．３５％以下、Ｍｎ：０．１０％以上１．５０％以下、Ｐ：０．００１０％以上０．０１００％以下、Ｓ：０．０００１％以上０．００３５％以下、Ｎｉ：２．７％以上５．０％以下、Ａｌ：０．００２％以上０．０９０％以下、Ｎ：０．０００１％以上０．００７０％以下、Ｔ−Ｏ：０．０００１％以上０．００３０％以下を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成である鋳片あるいは鋼片を、８５０℃以上１３００℃以下に加熱し、仕上げ１パス前温度が６００℃以上９００℃以下の熱間圧延を行い、冷却速度２００℃/s以下で水冷したのち、焼入れを行う際の加熱中において、６００℃以上７５０℃以下の温度範囲の昇温速度を０．３℃/s以上とし、焼入れは最高加熱温度を８００℃以上９４０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とし、さらに最高加熱温度を５００℃以上６６０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とすることにより、旧オーステナイト円相当粒径が２０μｍ以下であり、有効結晶粒径が１２μｍ以下である鋼板を得ることを特徴とする、靭性に優れた低温用ニッケル含有鋼板の製造方法。 (4) In terms of mass%, C: 0.02% or more and 0.12% or less, Si: 0.02% or more and 0.35% or less, Mn: 0.10% or more and 1.50% or less, P: 0. 0010% or more and 0.0100% or less, S: 0.0001% or more and 0.0035% or less, Ni: 2.7% or more and 5.0% or less, Al: 0.002% or more and 0.090% or less, N: 850 pieces of slabs or steel pieces having a steel composition containing 0.0001% or more and 0.0070% or less, TO: 0.0001% or more and 0.0030% or less, and the balance being Fe and unavoidable impurities. After heating to 1300 ° C or lower, hot rolling with a temperature of 600 ° C or higher and 900 ° C or lower before finishing 1 pass, water cooling at a cooling rate of 200 ° C / s or lower, and then heating during quenching, 600 The temperature rise rate in the temperature range of ° C. or higher and 750 ° C. or lower is set to 0.3 ° C./s or higher, and in quenching, the maximum heating temperature is heated to the temperature range of 800 ° C. or higher and 940 ° C. or lower, and the holding time is 5 minutes or longer and 100 minutes or lower. Further, by heating the maximum heating temperature to a temperature range of 500 ° C. or higher and 660 ° C. or lower and setting the holding time to 5 minutes or longer and 100 minutes or lower, the particle size equivalent to the old austenite circle is 20 μm or less and the effective crystal grain size. A method for producing a low-temperature nickel-containing steel sheet having excellent toughness, which comprises obtaining a steel sheet having a thickness of 12 μm or less.
（５）質量％で、Ｃ：０．０２％以上０．１２％以下、Ｓｉ：０．０２％以上０．３５％以下、Ｍｎ：０．１０％以上１．５０％以下、Ｐ：０．００１０％以上０．０１００％以下、Ｓ：０．０００１％以上０．００３５％以下、Ｎｉ：２．７％以上５．０％以下、Ａｌ：０．００２％以上０．０９０％以下、Ｎ：０．０００１％以上０．００７０％以下、Ｔ−Ｏ：０．０００１％以上０．００３０％以下を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成である鋳片あるいは鋼片を、８５０℃以上１３００℃以下に加熱し、仕上げ１パス前温度が６００℃以上９００℃以下の熱間圧延を行い、水冷停止温度を１５０℃以上５５０℃以下とする水冷を行ったのち、焼入れを行う際の加熱中において、６００℃以上７５０℃以下の温度範囲の昇温速度を０．３℃/s以上とし、焼入れは最高加熱温度を８００℃以上９４０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とし、さらに焼戻しは最高加熱温度を５００℃以上６６０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とすることにより、旧オーステナイト円相当粒径が２０μｍ以下であり、有効結晶粒径が１２μｍ以下である鋼板を得ることを特徴とする、靭性に優れた低温用ニッケル含有鋼板の製造方法。 (5) In terms of mass%, C: 0.02% or more and 0.12% or less, Si: 0.02% or more and 0.35% or less, Mn: 0.10% or more and 1.50% or less, P: 0. 0010% or more and 0.0100% or less, S: 0.0001% or more and 0.0035% or less, Ni: 2.7% or more and 5.0% or less, Al: 0.002% or more and 0.090% or less, N: 850 slabs or steel pieces having a steel composition containing 0.0001% or more and 0.0070% or less, TO: 0.0001% or more and 0.0030% or less, and the balance being Fe and unavoidable impurities. When heating to 1300 ° C or higher, hot rolling with a temperature of 600 ° C or higher and 900 ° C or lower before finishing 1 pass, water cooling to a water cooling stop temperature of 150 ° C or higher and 550 ° C or lower, and then quenching. During heating, the temperature rise rate in the temperature range of 600 ° C or higher and 750 ° C or lower is set to 0.3 ° C / s or higher, and in quenching, the maximum heating temperature is heated to the temperature range of 800 ° C or higher and 940 ° C or lower, and the holding time is set. By setting the temperature to 5 minutes or more and 100 minutes or less, further heating the maximum heating temperature to a temperature range of 500 ° C or more and 660 ° C or less, and setting the holding time to 5 minutes or more and 100 minutes or less, the particle size equivalent to the old austenite circle is 20 μm. A method for producing a low-temperature nickel-containing steel sheet having excellent toughness , which comprises the following and obtains a steel sheet having an effective crystal grain size of 12 μm or less.
（６）焼き入れと焼き戻しの間に、加熱温度範囲が７２０℃以上８２０℃以下、保持時間が５分以上１００分以下の中間熱処理を行うことを特徴とする、前記（３）乃至（５）に記載の靭性に優れた低温用ニッケル含有鋼板の製造方法。 (6) The above-mentioned (3) to (5) are characterized in that an intermediate heat treatment having a heating temperature range of 720 ° C. or higher and 820 ° C. or lower and a holding time of 5 minutes or longer and 100 minutes or shorter is performed between quenching and tempering. ). The method for producing a nickel-containing steel sheet for low temperature having excellent toughness.
（７）さらに質量％で、Ｃｕ：０．０１％以上２．００％以下、Ｃｒ：０．０１％以上５．００％以下、Ｍｏ：０．０１％以上１．００％以下、Ｂ：０．０００２％以上０．０５００％以下、Ｎｂ：０．００１％以上０．０５０％以下、Ｔｉ：０．００１％以上０．０５０％以下、Ｖ：０．００１％以上０．０５０％以下、Ｃａ：０．０００３％以上０．０３００％以下、Ｍｇ：０．０００３％以上０．０３００％以下、ＲＥＭ：０．０００３％以上０．０３００％以下のいずれか１種以上を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成であることを特徴とする前記（３）乃至（６）に記載の靭性に優れた低温用ニッケル含有鋼板の製造方法。 (7) Further, in terms of mass%, Cu: 0.01% or more and 2.00% or less, Cr: 0.01% or more and 5.00% or less, Mo: 0.01% or more and 1.00% or less, B: 0 .0002% or more and 0.0500% or less, Nb: 0.001% or more and 0.050% or less, Ti: 0.001% or more and 0.050% or less, V: 0.001% or more and 0.050% or less, Ca : 0.0003% or more and 0.0300% or less, Mg: 0.0003% or more and 0.0300% or less, REM: 0.0003% or more and 0.0300% or less, and the balance is Fe. The method for producing a low temperature nickel-containing steel sheet having excellent toughness according to the above (3) to (6), which has a steel composition composed of unavoidable impurities.
本発明によれば、不可避的にアルミナクラスターが存在する場合でも、厚板工程の製造方法の工夫により、優れた靭性の低温用ニッケル含有鋼板およびその製造方法を提供することが可能となり、産業上の価値の高い発明であるといえる。 According to the present invention, even when alumina clusters are inevitably present, it is possible to provide a nickel-containing steel sheet for low temperature with excellent toughness and a manufacturing method thereof by devising a manufacturing method in the thick plate process, which is industrially possible. It can be said that this is a highly valuable invention.
本発明を詳細に説明する。発明者は、低温用ニッケル含有鋼板のうち、Ｎｉ含有量が２．７％以上５．０％以下の鋼板において、製鋼工程ではなく熱間圧延以降の工程でアルミナクラスターに起因する靭性低下を回避、もしくはリカバリーできないか鋭意検討した。その結果、適正な熱間圧延の後、焼入れの昇温時に６００℃以上７５０℃以下の昇温速度をわずかに高めることで、焼入れ加熱段階のオーステナイトが大幅に微細化することを知見した。焼入れ加熱時の旧オーステナイト粒径の微細化は、最終的な組織、すなわち焼戻しベイナイトを主体とする組織の微細化に繋がることから、靭性を大幅に改善することができる。 The present invention will be described in detail. The inventor avoids the decrease in toughness caused by alumina clusters in the steel sheet containing nickel for low temperature and having a Ni content of 2.7% or more and 5.0% or less in the process after hot rolling instead of the steelmaking process. Or, I eagerly examined whether it could be recovered. As a result, it was found that after proper hot rolling, the austenite in the quenching heating stage is significantly refined by slightly increasing the heating rate of 600 ° C. or higher and 750 ° C. or lower when the temperature of the quenching is raised. Since the miniaturization of the old austenite particle size during quenching and heating leads to the miniaturization of the final structure, that is, the structure mainly composed of tempered bainite, the toughness can be significantly improved.
本発明において、焼入れ前の旧オーステナイト粒径を大幅に微細化するためには、２つの製造方法の組み合わせが重要である。第１点目は、焼入れ前に実施される熱間圧延の条件を適正に制御することであり、第２点目は、圧延後の焼入れの際の昇温条件を適正に制御することである。
最初に第１点目の方法、すなわち、焼入れ前に実施される熱間圧延の条件について説明する。尚、熱間圧延の条件は、熱間圧延後空冷する場合と、熱間圧延後水冷する場合で異なる。
In the present invention, the combination of the two production methods is important in order to significantly reduce the particle size of the old austenite before quenching. The first point is to properly control the conditions of hot rolling performed before quenching, and the second point is to appropriately control the temperature rising conditions during quenching after quenching. ..
First, the first method, that is, the conditions for hot rolling performed before quenching will be described. The conditions for hot rolling differ between the case of hot rolling and then air cooling and the case of hot rolling and then water cooling.
（１）熱間圧延後空冷する場合；
最初に、熱間圧延後空冷する場合について説明する。Ｎｉを２．７％以上５．０％以下含有する鋳片あるいは鋼片を、加熱温度を８５０℃以上１３００℃以下とした加熱を行った後、熱間圧延を行い、以後空冷する。熱間圧延は、圧下比４以上で行い、仕上げ１パス前温度を６００℃以上８５０℃以下とする。ここで、圧下比とは、圧延前の鋼片の厚さを、圧延後の鋼板の厚さで除した値である。また、仕上げ１パス前温度とは、圧延の最終１パスを行う直前たとえば５秒以内に測定された、鋼板表面の温度を指す。図１には、圧延後空冷する場合において、圧下比と仕上げ１パス前温度を種々変えた実験を行い、熱処理後の鋼板を用いて推定した、焼入れ加熱時の旧オーステナイト粒径と仕上げ１パス前温度の関係を示す。仕上げ１パス前温度が８５０℃超の場合、空冷で常温まで冷却された時点での組織が粗大であるため、焼入れ加熱時の旧オーステナイト粒径が大きくなる。また、仕上げ１パス前温度が６００℃未満では、変形抵抗が大きいため熱間圧延を実施できない。さらに、圧下比が４未満の際には、空冷後の組織が粗大になるため、焼入れ加熱時の旧オーステナイト粒径が大きくなる。なお、ここで旧オーステナイト円相当粒径とは、熱処理後、最終製品の鋼板の板厚中央部から採取した光学顕微鏡試料について、長手方向と厚さ方向がなす面に平行な面を研磨し、さらにピクリン酸等の腐食液により旧オーステナイト粒界を現出したのち、ＪＩＳＧ０５５１に記載の方法で測定した粒度番号から算出した円相当直径をいう。
(1) When air-cooled after hot rolling;
First, a case of air cooling after hot rolling will be described. A slab or steel slab containing 2.7% or more and 5.0% or less of Ni is heated at a heating temperature of 850 ° C. or higher and 1300 ° C. or lower, then hot-rolled, and then air-cooled. Hot rolling is performed at a rolling reduction ratio of 4 or more, and the temperature before finishing 1 pass is set to 600 ° C. or higher and 850 ° C. or lower. Here, the rolling ratio is a value obtained by dividing the thickness of the steel piece before rolling by the thickness of the steel plate after rolling. The temperature before finishing 1 pass refers to the temperature of the surface of the steel sheet measured immediately before the final 1 pass of rolling, for example, within 5 seconds. In FIG. 1, an experiment was conducted in which the rolling reduction ratio and the temperature before finishing 1 pass were variously changed in the case of air cooling after rolling, and the old austenite grain size and the finishing 1 pass at the time of quenching and heating were estimated using the steel plate after heat treatment. The relationship between the pre-temperature is shown. When the temperature one pass before finishing is more than 850 ° C., the structure at the time of cooling to room temperature by air cooling is coarse, so that the particle size of the old austenite at the time of quenching and heating becomes large. Further, if the temperature one pass before finishing is less than 600 ° C., hot rolling cannot be performed because the deformation resistance is large. Further, when the reduction ratio is less than 4, the structure after air cooling becomes coarse, so that the grain size of the old austenite at the time of quenching and heating becomes large. Here, the particle size equivalent to the old austenite circle is defined by polishing the surface parallel to the plane formed by the longitudinal direction and the thickness direction of the optical microscope sample collected from the center of the plate thickness of the final product steel plate after heat treatment. Further, it refers to a circle-equivalent diameter calculated from a particle size number measured by the method described in JISG0551 after the old austenite grain boundaries are exposed by a corrosive solution such as picric acid.
（２）熱間圧延後水冷する場合；
次に、熱間圧延後水冷する場合について説明する。Ｎｉを２．７％以上５．０％以下含有する鋳片あるいは鋼片を、加熱温度を８５０℃以上１３００℃以下とした加熱を行った後、熱間圧延を行い、以後水冷する。熱間圧延は、圧下比４以上で行い、仕上げ１パス前温度を６００℃以上９００℃以下とする。熱間圧延後、水冷の場合は、変態温度の低温化により、空冷よりも仕上げ１パス前温度上限が５０℃高温で同様の微細化効果が得られる。図２には、熱間圧延後水冷する場合において、圧下比と仕上げ１パス前温度を種々変えた実験を行い、熱処理後の鋼板を用いて推定した、焼入れ加熱時の旧オーステナイト粒径と仕上げ１パス前温度の関係を示す。仕上げ１パス前温度が９００℃超の場合、水冷で常温まで冷却された時点での組織が粗大であるため、焼入れ加熱時の旧オーステナイト粒径が大きくなる。また、仕上げ１パス前温度が６００℃未満では、変形抵抗が大きいため熱間圧延を実施できない。さらに、圧下比が４未満の際には、水冷後の組織が粗大になるため、焼入れ加熱時の旧オーステナイト粒径が大きくなる。
(2) When water-cooled after hot rolling;
Next, a case of hot rolling and then water cooling will be described. A slab or steel slab containing 2.7% or more and 5.0% or less of Ni is heated at a heating temperature of 850 ° C. or higher and 1300 ° C. or lower, then hot-rolled, and then water-cooled. Hot rolling is performed at a rolling reduction ratio of 4 or more, and the temperature before finishing 1 pass is set to 600 ° C. or higher and 900 ° C. or lower. In the case of water cooling after hot rolling, the same miniaturization effect can be obtained when the upper limit of the temperature one pass before finishing is 50 ° C. higher than that of air cooling by lowering the transformation temperature. In FIG. 2, an experiment was conducted in which the rolling reduction ratio and the temperature before finishing 1 pass were variously changed in the case of water cooling after hot rolling, and the old austenite grain size and finishing at the time of quenching heating were estimated using the steel plate after heat treatment. The relationship of the temperature before one pass is shown. When the temperature one pass before finishing is more than 900 ° C., the structure at the time of cooling to room temperature by water cooling is coarse, so that the grain size of the old austenite at the time of quenching and heating becomes large. Further, if the temperature one pass before finishing is less than 600 ° C., hot rolling cannot be performed because the deformation resistance is large. Further, when the reduction ratio is less than 4, the structure after water cooling becomes coarse, so that the grain size of the old austenite at the time of quenching and heating becomes large.
焼入れの際の昇温速度；
次に、第２点目の方法、すなわち、焼入れの際の加熱中の昇温速度について説明する。
焼入れの際の加熱中の昇温速度のうち、６００℃以上７５０℃以下の平均昇温速度を０．３℃/s以上とすることで、焼入れ前の旧オーステナイト粒径を大幅に微細化することができる。ここで、平均昇温速度とは、この場合、６００℃と７５０℃との間の温度差１５０℃を、この間の昇温に要した時間で除した値である。図３には、焼入れの昇温速度を種々変えた実験を行い、熱処理後の鋼板を用いて推定した、焼入れ加熱時の旧オーステナイト粒径と６００℃以上７５０℃以下の平均昇温速度の関係を示す。焼入れ時の昇温速度が０．３℃/s以上の場合、焼入れの加熱時の旧オーステナイト粒径が小さくなる。
Temperature rise rate during quenching;
Next, the second method, that is, the rate of temperature rise during heating during quenching will be described.
Of the heating rates during heating during quenching, by setting the average heating rate of 600 ° C or higher and 750 ° C or lower to 0.3 ° C / s or higher, the particle size of the old austenite before quenching is significantly reduced. be able to. Here, the average temperature rise rate is, in this case, a value obtained by dividing the temperature difference of 150 ° C. between 600 ° C. and 750 ° C. by the time required for temperature rise during this period. FIG. 3 shows the relationship between the old austenite grain size at the time of quenching and heating and the average heating rate of 600 ° C. or higher and 750 ° C. or lower, which was estimated by performing experiments in which the heating rate of quenching was variously changed and using a steel plate after heat treatment. Is shown. When the heating rate at the time of quenching is 0.3 ° C./s or more, the particle size of the old austenite at the time of heating the quenching becomes small.
ここで、昇温速度を高める温度区間を明らかにするために、２００℃以上焼入れ加熱温度以下の昇温速度を０．１℃/sとした標準的な昇温を行った際の焼入れ加熱時の旧オーステナイト粒径を、特定の温度範囲のみ昇温速度を２℃/sに高め、その他の温度範囲の昇温速度は０．１℃/sとした３つの条件、すなわち２００℃以上６００℃未満のみを２℃/sとした条件、６００℃以上７５０℃以下のみを２℃/sとした条件、７５０℃超焼入れ加熱温度以下のみを２℃/sとした条件での昇温時の焼入れ加熱時の旧オーステナイト粒径と比較した。その結果、表１に示すように、６００℃以上７５０℃以下のみを２℃/sとして、その他の温度区間は０．１℃/sとした条件のみで、著しい焼入れ加熱時の旧オーステナイト粒径の微細化がみられた。このことから、昇温速度の増大によって焼入れ加熱時の旧オーステナイト粒径の微細化をはかる場合、６００℃以上７５０℃以下の昇温速度を高めることが必要である。 Here, in order to clarify the temperature section in which the temperature rise rate is increased, during quenching heating when the standard temperature rise is performed with the temperature rise rate of 200 ° C. or higher and the quenching heating temperature or lower set to 0.1 ° C./s. The old austenite particle size was increased to 2 ° C / s only in a specific temperature range, and the temperature rise rate in other temperature ranges was 0.1 ° C / s, that is, 200 ° C or higher and 600 ° C. Quenching at the time of temperature rise under the condition that only less than 2 ° C / s, only 600 ° C or more and 750 ° C or less is 2 ° C / s, and only 750 ° C or more quenching heating temperature is 2 ° C / s. It was compared with the old austenite particle size at the time of heating. As a result, as shown in Table 1, the old austenite grain size at the time of remarkable quenching and heating was set only under the condition that only the temperature of 600 ° C. or higher and 750 ° C. or lower was set to 2 ° C./s and the other temperature sections were set to 0.1 ° C./s. Was seen to be finer. For this reason, it is necessary to increase the heating rate of 600 ° C. or higher and 750 ° C. or lower in order to reduce the particle size of the old austenite during quenching and heating by increasing the heating rate.
有効結晶粒径の微細化により、ひずみ時効後の靭性が向上する。図４には、ひずみ時効後の靭性と、有効結晶粒径の関係を示す。本発明の鋼板においては、高い安全性の観点から、６％のひずみを付与した後に２００℃で１時間熱処理をした後に試験片を採取して行った試験温度−１３０℃のシャルピー試験の吸収エネルギーが仕様上求められることが多く、その値は最大１５０Ｊであることから、１５０Ｊ以上を合格とした。この場合、有効結晶粒径は１２μｍ以下であることが必要である。焼入れ時の旧オーステナイト粒径が微細化すると、最終的な組織も微細化する。図５には、焼入れ、焼戻し後の有効結晶粒径と、焼入れ、焼戻し後の鋼板を用いて推定した、焼入れ加熱時の旧オーステナイト粒径の関係を示す。なお、ここで、有効結晶粒径とは、熱処理をすべて終了した鋼板の板厚中央部から採取した試料について、機械研磨およびひずみ除去のための化学研磨あるいは電解研磨、あるいはコロイダルシリカ等による研磨を行ったのち、ＥＢＳＤ（Ｅｌｅｃｔｒｏｎ
Ｂａｃｋｓｃａｔｔｅｒ Ｄｉｆｆｒａｃｔｉｏｎ Ｐａｔｔｅｒｎ）により測定したデータから、方位差１５°以上の界面を粒界と定義して算出した円相当直径である。
By refining the effective crystal grain size, the toughness after strain aging is improved. FIG. 4 shows the relationship between the toughness after strain aging and the effective crystal grain size. In the steel sheet of the present invention, from the viewpoint of high safety, the absorbed energy of the Charpy test at a test temperature of −130 ° C., which was performed by applying a strain of 6%, heat-treating at 200 ° C. for 1 hour, and then collecting a test piece. Is often required in terms of specifications, and the maximum value is 150J, so 150J or more was accepted. In this case, the effective crystal grain size needs to be 12 μm or less. As the grain size of the old austenite during quenching becomes finer, the final structure also becomes finer. FIG. 5 shows the relationship between the effective crystal grain size after quenching and tempering and the old austenite grain size during quenching and heating estimated using the steel sheet after quenching and tempering. Here, the effective crystal grain size is defined as the chemical polishing or electrolytic polishing for mechanical polishing and strain removal, or polishing with colloidal silica or the like for a sample collected from the central portion of the plate thickness of a steel plate that has been completely heat-treated. After going, EBSD (Electron)
It is a circle-equivalent diameter calculated by defining an interface having an azimuth difference of 15 ° or more as a grain boundary from data measured by Backscatter Diffraction Pattern).
前述の図４のように、試験温度−１３０℃のシャルピー試験の吸収エネルギーが１５０Ｊを達成するために必要な有効結晶粒径は最大１２μｍであることから、図５では有効結晶粒径１２μｍ以下を合格とした。この場合、旧オーステナイト粒径は２０μｍ以下であることが必要である。 As shown in FIG. 4, the effective crystal particle size required to achieve the absorption energy of 150 J in the Charpy test at the test temperature of −130 ° C. is a maximum of 12 μm. Therefore, in FIG. 5, the effective crystal particle size is 12 μm or less. I passed it. In this case, the particle size of the old austenite needs to be 20 μm or less.
以下に鋼板の合金元素の範囲を規定する。
Ｃは、強度確保に必須の元素であるため、その添加量を０．０２０％以上とする。しかし、一方でＣ量の増大は靱性低下を招くため、その上限を０．１２０％とする。
The range of alloying elements of steel sheets is specified below.
Since C is an element essential for ensuring strength, the amount added thereof should be 0.020% or more. However, on the other hand, an increase in the amount of C causes a decrease in toughness, so the upper limit is set to 0.120%.
Ｓｉは、強度確保に必須の元素であるため、その添加量を０．０２％以上とする。しかし、一方で０．３５％超のＳｉ添加は靭性や溶接性の低下を招くためその上限を０．３５％とする。 Since Si is an element essential for ensuring strength, the amount of Si added should be 0.02% or more. However, on the other hand, the addition of Si exceeding 0.35% causes deterioration of toughness and weldability, so the upper limit is set to 0.35%.
Ｍｎは、強度増大に有効な元素であり、最低でも０．１０％以上の添加が必要となるが、逆に１．５０％を超えて添加すると焼戻し脆化感受性が高くなって靭性が低下する。よって、Ｍｎの添加量を０．１０％以上１．５０％以下と規定する。 Mn is an element effective for increasing strength, and it is necessary to add at least 0.10% or more, but conversely, if it is added in excess of 1.50%, tempering embrittlement sensitivity increases and toughness decreases. .. Therefore, the amount of Mn added is defined as 0.10% or more and 1.50% or less.
Ｐは、０．００１０％未満とするには精錬負荷の増大により生産性が大幅に低下し、好ましくない。また０．０１００％を超えると焼戻し脆化により靭性が低下する。よって、Ｐの添加量を０．００１０％以上０．０１００％以下と規定する。 If P is less than 0.0010%, the productivity is significantly reduced due to an increase in the refining load, which is not preferable. If it exceeds 0.0100%, the toughness decreases due to temper embrittlement. Therefore, the amount of P added is defined as 0.0010% or more and 0.0100% or less.
Ｓは、０．０００１％未満では精錬負荷の増大により生産性が大幅に低下し、好ましくない。また０．００３５％を超えると靱性が低下する。よって、Ｓの添加量を０．０００１％以上０．００３５％以下と規定する。 If S is less than 0.0001%, the productivity is significantly reduced due to an increase in the refining load, which is not preferable. If it exceeds 0.0035%, the toughness decreases. Therefore, the amount of S added is defined as 0.0001% or more and 0.0035% or less.
Ｎｉは、下限については靭性確保のため、最低でも２．７％以上の添加が必要となる。また、５．０％超では製造コストが大幅に増大する。よって、Ｎｉの添加量を２．７％以上５．０％以下と規定する。 Ni needs to be added at least 2.7% or more to ensure toughness at the lower limit. Moreover, if it exceeds 5.0%, the manufacturing cost will increase significantly. Therefore, the amount of Ni added is specified to be 2.7% or more and 5.0% or less.
Ａｌは、脱酸に有効な元素であり、最低でも０．００２％以上の添加が必要となるが、逆に０．０９０％を超えて添加すると溶鋼再酸化を通じたアルミナクラスター形成を通じて靭性が低下する。よって、Ａｌの添加量を０．００２％以上０．０９０％以下と規定する。 Al is an element effective for deoxidation, and it is necessary to add at least 0.002% or more, but conversely, if it is added in excess of 0.090%, the toughness decreases through the formation of alumina clusters through the reoxidation of molten steel. do. Therefore, the amount of Al added is defined as 0.002% or more and 0.090% or less.
Ｎは、下限については特に規定はないものの、０．０００１％未満では精錬負荷の増大によって生産性が低下するため０．０００１％以上が好ましい。し、また０．００７０％を超える添加では靭性が低下するため上限は０．００７０％とする。よって、Ｎの添加量を０．０００１％以上０．００７０％以下と規定する。 Although the lower limit of N is not particularly specified, if it is less than 0.0001%, the productivity decreases due to an increase in the refining load, so 0.0001% or more is preferable. However, if the addition exceeds 0.0070%, the toughness decreases, so the upper limit is 0.0070%. Therefore, the amount of N added is defined as 0.0001% or more and 0.0070% or less.
Ｔ−Ｏは、下限については特に規定はないものの、０．０００１％未満では精錬負荷の増大によって生産性が低下するため０．０００１％以上が好ましい。０．００３０％を超えて添加するとアルミナクラスター形成を通じて靭性が低下するため上限は０．００３０％とする。よって、Ｔ−Ｏの添加量を０．０００１％以上０．００３０％以下とする。 Although the lower limit of TO is not particularly specified, if it is less than 0.0001%, the productivity decreases due to an increase in the refining load, so 0.0001% or more is preferable. If it is added in excess of 0.0030%, the toughness decreases through the formation of alumina clusters, so the upper limit is 0.0030%. Therefore, the amount of TO added is set to 0.0001% or more and 0.0030% or less.
なお、本発明では、さらに以下の元素を添加することができる。
Ｃｕは、強度確保のため、最低でも０．０１％以上の添加が必要となるが、２．００％を超えると靭性が低下する。よって、Ｃｕの添加量を０．０１％以上２．００％以下と規定する。
In the present invention, the following elements can be further added.
Cu needs to be added at least 0.01% or more in order to secure the strength, but if it exceeds 2.00%, the toughness decreases. Therefore, the amount of Cu added is defined as 0.01% or more and 2.00% or less.
Ｃｒは、焼入性の確保に有効な元素であり、最低でも０．０１％以上の添加が必要となるが、逆に５．００％を超えて添加すると靭性と溶接性が低下する。よって、Ｃｒの添加量を０．０１％以上５．００％以下と規定する。 Cr is an element effective for ensuring hardenability, and it is necessary to add at least 0.01% or more, but conversely, if it is added in excess of 5.00%, toughness and weldability deteriorate. Therefore, the amount of Cr added is defined as 0.01% or more and 5.00% or less.
Ｍｏは、焼戻し脆化の軽減に有効な元素であり、最低でも０．０１％の添加が必要となるが、逆に１．００％を超えて添加すると靭性と溶接性が低下する。よって、Ｍｏの添加量を０．０１％以上１．００％以下と規定する。 Mo is an element effective in reducing tempering embrittlement, and it is necessary to add at least 0.01%, but conversely, if it is added in excess of 1.00%, toughness and weldability are lowered. Therefore, the amount of Mo added is defined as 0.01% or more and 1.00% or less.
Ｂは、焼入性の向上に有効な元素である。０．０００２％未満ではその効果が小さく、０．０５００％を超える添加では靭性が低下する。よって、Ｂの添加量を０．０００２％以上０．０５００％以下と規定する。 B is an element effective for improving hardenability. If it is less than 0.0002%, the effect is small, and if it is added more than 0.0500%, the toughness is lowered. Therefore, the amount of B added is defined as 0.0002% or more and 0.0500% or less.
Ｎｂは強度確保に有効な元素である。０．００１％未満の添加では効果が小さく、０．０５０％超の添加では靱性の低下を招く。よって、Ｎｂの添加量を０．００１％以上０．０５０％以下と規定する。 Nb is an element effective for ensuring strength. Additions of less than 0.001% have a small effect, and additions of more than 0.050% result in a decrease in toughness. Therefore, the amount of Nb added is defined as 0.001% or more and 0.050% or less.
Ｔｉは、強度確保に有効な元素である。０．００１％未満の添加では効果が小さく、０．０５０％超の添加では靭性の低下を招く。よって、Ｔｉの添加量を０．００１％以上０．０５０％以下と規定する。 Ti is an element effective for ensuring strength. Additions of less than 0.001% have a small effect, and additions of more than 0.050% result in a decrease in toughness. Therefore, the amount of Ti added is defined as 0.001% or more and 0.050% or less.
Ｖは、強度確保に有効な元素である。０．００１％未満の添加では効果が小さく、０．０５０％超の添加では靱性の低下を招く。よって、Ｖの添加量を０．００１％以上０．０５０％以下と規定する。 V is an element effective for ensuring strength. Additions of less than 0.001% have a small effect, and additions of more than 0.050% result in a decrease in toughness. Therefore, the amount of V added is defined as 0.001% or more and 0.050% or less.
Ｃａは、ノズル閉塞防止に有効な元素である。０．０００３％未満の添加ではその効果が小さく、０．０３００％超の添加では靭性の低下を招く。よって、Ｃａの添加量を０．０００３％以上０．０３００％以下と規定する。 Ca is an element effective in preventing nozzle blockage. Additions of less than 0.0003% have a small effect, and additions of more than 0.0300% result in a decrease in toughness. Therefore, the amount of Ca added is defined as 0.0003% or more and 0.0300% or less.
Ｍｇは、靱性向上に有効な元素である。０．０００３％未満の添加ではその効果が小さく、０．０３００％超の添加では靭性の低下を招く。よって、Ｍｇの添加量を０．０００３％以上０．０３００％以下と規定する。 Mg is an element effective for improving toughness. Additions of less than 0.0003% have a small effect, and additions of more than 0.0300% result in a decrease in toughness. Therefore, the amount of Mg added is specified to be 0.0003% or more and 0.0300% or less.
ＲＥＭは、靱性向上に有効な元素である。０．０００３％未満の添加ではその効果が小さく、０．０３００％超の添加では靭性の低下を招く。よって、ＲＥＭの添加量を０．０００３％以上０．０３００％以下と規定する。 REM is an element effective for improving toughness. Additions of less than 0.0003% have a small effect, and additions of more than 0.0300% result in a decrease in toughness. Therefore, the amount of REM added is specified to be 0.0003% or more and 0.0300% or less.
なお、鋼板および溶接材料を製造する上で、添加合金を含めた使用原料または溶製中に炉材等から溶出する不可避的不純物として混入しうる、Ｚｎ、Ｓｎ、Ｓｂ等も０．００２％未満の混入であれば何ら本発明の効果を損なうものではない。 In manufacturing steel sheets and welding materials, Zn, Sn, Sb, etc., which can be mixed as unavoidable impurities eluted from the furnace material, etc. during the raw materials used including additive alloys or melting, are also less than 0.002%. If it is mixed with the above, the effect of the present invention is not impaired.
次に本発明の鋼板の製造方法について記載する。
鋼板は、連続鋳造で製造されたスラブを前記の方法で熱間圧延する方法で製造されるが、前記以外に、一般的にベイナイトを主体とする組織を微細化するために実施する下記の条件も必要になる。鋼片の加熱温度は、１３００℃以上ではオーステナイトの粒成長により変態後のベイナイトを主体とする組織が粗大化すること、８５０℃未満では熱間圧延が困難になることから、８５０℃以上１３００℃以下とする。
熱間圧延は、前述図１、図２での説明のように、圧下比４以上で行い、仕上げ１パス前温度を、その後の冷却が空冷の場合は６００℃以上８５０℃以下、水冷の場合は６００℃以上９００℃以下とする。
Next, the method for manufacturing the steel sheet of the present invention will be described.
The steel sheet is manufactured by a method of hot rolling a slab manufactured by continuous casting by the above-mentioned method, but in addition to the above, the following conditions generally carried out for miniaturizing a structure mainly composed of bainite. Is also needed. When the heating temperature of the steel pieces is 1300 ° C or higher, the structure mainly composed of bainite after transformation becomes coarse due to the grain growth of austenite, and when the temperature is lower than 850 ° C, hot rolling becomes difficult. Therefore, the heating temperature is 850 ° C or higher and 1300 ° C. It shall be as follows.
Hot rolling is performed at a reduction ratio of 4 or more as described in FIGS. 1 and 2 above, and the temperature before finishing 1 pass is set to 600 ° C or higher and 850 ° C or lower when the subsequent cooling is air cooling, and when water cooling. Is 600 ° C. or higher and 900 ° C. or lower.
熱間圧延後に水冷を行う場合、水冷時の冷却速度を２００℃/s超とすることは設備コストが高くなることから、水冷時の冷却速度は２００℃/s以下とすることが好ましい。なお、圧延後に水冷を実施する場合、常温まで水冷することのほかに、水冷を途中停止することができる。水冷停止温度が１５０℃未満では、温度が不均一になり材質がばらつくこと、水冷停止温度が５５０℃超では、組織が粗大化することから、水冷停止温度を１５０℃以上５５０℃以下とすることも好ましい。 When water cooling is performed after hot rolling, it is preferable that the cooling rate during water cooling is 200 ° C / s or less because the equipment cost increases if the cooling rate during water cooling exceeds 200 ° C / s. When water cooling is performed after rolling, water cooling can be stopped halfway in addition to water cooling to room temperature. If the water cooling stop temperature is less than 150 ° C, the temperature becomes non-uniform and the material varies, and if the water cooling stop temperature exceeds 550 ° C, the structure becomes coarse. Therefore, the water cooling stop temperature should be 150 ° C or higher and 550 ° C or lower. Is also preferable.
圧延後は、焼入れを行う。焼入れ時の６００℃以上７５０℃以下の昇温速度は、前述図３での説明のように、０．３℃/s以上とする。焼入れ時の最高加熱温度は、８００℃未満では未変態組織が残存して靭性が低下し、９４０℃超では焼入れ加熱時の旧オーステナイトが粗大化して靭性が低下する。よって、焼入れ時の最高加熱温度を８００℃以上９４０℃以下とする。
焼入れ加熱時の保持時間は、５分以下では材質が不均一になり、１００分以上では組織が粗大化して靭性が低下する。よって、焼入れ加熱時の保持時間を５分以上１００分以下とする。
After rolling, quenching is performed. The rate of temperature rise of 600 ° C. or higher and 750 ° C. or lower during quenching is 0.3 ° C./s or higher as described in FIG. If the maximum heating temperature during quenching is less than 800 ° C., untransformed structure remains and the toughness decreases, and if it exceeds 940 ° C., the old austenite during quenching heating becomes coarse and the toughness decreases. Therefore, the maximum heating temperature at the time of quenching is set to 800 ° C. or higher and 940 ° C. or lower.
When the holding time during quenching and heating is 5 minutes or less, the material becomes non-uniform, and when it is 100 minutes or more, the structure becomes coarse and the toughness decreases. Therefore, the holding time during quenching and heating is set to 5 minutes or more and 100 minutes or less.
なお、必要に応じて、焼入れと焼戻しの間に、中間熱処理を行うことができる。中間熱処理の加熱温度が７２０℃未満の場合、靭性低下し、８２０℃超では、中間熱処理によるオーステナイト安定化による靭性改善効果が殆ど得られないことから、中間熱処理の加熱温度を７２０℃以上８２０℃以下とすることが好ましい。 If necessary, an intermediate heat treatment can be performed between quenching and tempering. When the heating temperature of the intermediate heat treatment is less than 720 ° C, the toughness decreases, and when it exceeds 820 ° C, the effect of improving the toughness by stabilizing austenite by the intermediate heat treatment is hardly obtained. Therefore, the heating temperature of the intermediate heat treatment is 720 ° C or higher and 820 ° C. The following is preferable.
中間熱処理の保持時間は、５分未満では逆変態がほとんど進まずに焼入れ加熱時の旧オーステナイト安定化による靭性改善効果がほとんど得られず、１００分超では逆に焼入れ加熱時の旧オーステナイト分率が高くなり不安定化して靭性低下することから、中間熱処理の保持時間を５分以上１００分以下とする。 If the retention time of the intermediate heat treatment is less than 5 minutes, the reverse transformation hardly progresses, and the effect of improving the toughness by stabilizing the old austenite during quenching and heating is hardly obtained. The retention time of the intermediate heat treatment is set to 5 minutes or more and 100 minutes or less because the toughness is lowered due to destabilization.
焼戻しは、５００℃未満では、焼戻し脆化により靭性が低下し、６６０℃超では靭性が低下することから、５００℃以上６６０℃以下で実施するのが望ましい。また、焼戻しの保持時間は、５分未満では十分な効果が得られる靭性が低下し、１００分以上では生産性が低下することから、５分以上１００分以下とするのが望ましい。
なお、本発明の鋼の引張強さは、当該の分野で求められる引張強さ４５０ＭＰａ以上６９０ＭＰａ以下の範囲とする。
It is desirable to carry out tempering at 500 ° C. or higher and 660 ° C. or lower because the toughness decreases due to tempering embrittlement below 500 ° C. and the toughness decreases above 660 ° C. Further, the tempering holding time is preferably 5 minutes or more and 100 minutes or less because the toughness at which a sufficient effect can be obtained decreases when the tempering time is less than 5 minutes and the productivity decreases when the tempering time is 100 minutes or more.
The tensile strength of the steel of the present invention is in the range of 450 MPa or more and 690 MPa or less of the tensile strength required in the art.
種々の化学成分、製造条件で製造した板厚１３、４３ｍｍの鋼板について、引張試験およびシャルピー衝撃試験を実施した。鋼板の化学成分、焼入れ加熱時の旧オーステナイト粒径、有効結晶粒径、板厚を表２−１に、熱間圧延条件、熱処理条件、機械的特性の評価結果を表２−２に示す。焼入れ、中間熱処理、焼戻しの最高加熱温度における保持時間は、板厚１３ｍｍでは２０分、板厚４３ｍｍでは４０分とした。 Tensile tests and Charpy impact tests were carried out on steel sheets having a thickness of 13,43 mm manufactured under various chemical components and manufacturing conditions. Table 2-1 shows the chemical composition of the steel sheet, the old austenite grain size during quenching and heating, the effective crystal grain size, and the plate thickness, and Table 2-2 shows the evaluation results of hot rolling conditions, heat treatment conditions, and mechanical properties. The holding time at the maximum heating temperature for quenching, intermediate heat treatment, and tempering was 20 minutes for a plate thickness of 13 mm and 40 minutes for a plate thickness of 43 mm.
引張試験はＪＩＳ Ｚ ２２４１に記載の金属材料引張試験方法に基づいて行った。試験片は、板厚の１／４だけ鋼板表面から内部に入った部位において、試験片の長手方向が圧延方向と垂直になるように採取した。常温で２本の試験を行った。常温で２本の試験を行い，引張強さの平均値が４５０ＭＰａ以上６９０ＭＰａ以下を合格とした。 The tensile test was performed based on the metal material tensile test method described in JIS Z 2241. The test piece was collected so that the longitudinal direction of the test piece was perpendicular to the rolling direction at a portion that entered the inside from the surface of the steel sheet by 1/4 of the plate thickness. Two tests were performed at room temperature. Two tests were conducted at room temperature, and the average tensile strength was 450 MPa or more and 690 MPa or less.
シャルピー衝撃試験は、予め６％のひずみを常温で付与した後、２００℃で１ｈｒの熱処理を行った鋼板から、２ｍｍＶノッチ試験片のフルサイズ試験片を、板厚の１／４だけ鋼板表面から内部に入った部位において、試験片の長手方向が圧延方向と垂直になるように、またノッチの前縁を結ぶ線が板厚方向に平行になるように採取した。試験温度−１３０℃で３本の試験を行い、３本の平均値が１５０J以上を合格とした。 In the Charpy impact test, a full-size test piece of a 2 mm V notch test piece was applied from the surface of the steel sheet by applying a strain of 6% at room temperature in advance and then heat-treated at 200 ° C. for 1 hr. At the inside, the test piece was sampled so that the longitudinal direction of the test piece was perpendicular to the rolling direction and the line connecting the front edges of the notches was parallel to the plate thickness direction. Three tests were conducted at a test temperature of −130 ° C., and the average value of the three was 150 J or more.
実施例１〜３０に示すように、本発明に規定した成分および製造方法で鋼板を製造することにより、優れた引張強度および靭性の鋼板が得られた。
以上の実施例から、本発明により製造された鋼材である発明例実施例１〜３０の鋼板は、引張強度および靭性に優れた鋼板鋼材であることは明白である。
As shown in Examples 1 to 30, a steel sheet having excellent tensile strength and toughness was obtained by manufacturing the steel sheet by the components and the manufacturing method specified in the present invention.
From the above examples, it is clear that the steel sheets of Invention Examples Examples 1 to 30, which are the steel materials manufactured by the present invention, are steel sheets having excellent tensile strength and toughness.
Claims (7)
Ｃ ：０．０２％以上０．１２％以下、
Ｓｉ：０．０２％以上０．３５％以下、
Ｍｎ：０．１０％以上１．５０％以下、
Ｐ：０．００１０％以上０．０１００％以下、
Ｓ：０．０００１％以上０．００３５％以下、
Ｎｉ：２．７％以上５．０％以下、
Ａｌ：０．００２％以上０．０９０％以下、
Ｎ：０．０００１％以上０．００７０％以下、
Ｔ−Ｏ：０．０００１％以上０．００３０％以下を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成であり、旧オーステナイト粒径が２０μm以下であり、有効結晶粒径が１２μm以下であり、引張強さが４５０ＭＰａ以上６９０ＭＰａ以下であることを特徴とする，靭性に優れた低温用ニッケル含有鋼板。 Steel is by mass%,
C: 0.02% or more and 0.12% or less,
Si: 0.02% or more and 0.35% or less,
Mn: 0.10% or more and 1.50% or less,
P: 0.0010% or more and 0.0100% or less,
S: 0.0001% or more and 0.0035% or less,
Ni: 2.7% or more and 5.0% or less,
Al: 0.002% or more and 0.090% or less,
N: 0.0001% or more and 0.0070% or less,
T-O: containing 0.0001% or more 0.0030% or less, the balance Ri steel composition der of Fe and inevitable impurities, old austenite grain size Ri der less 20 [mu] m, the crystal grain size is effective A nickel-containing steel sheet for low temperature having excellent toughness, characterized by having a tensile strength of 450 MPa or more and 690 MPa or less, which is 12 μm or less.
Ｃｕ：０．０１％以上２．００％以下、
Ｃｒ：０．０１％以上５．００％以下、
Ｍｏ：０．０１％以上１．００％以下、
Ｂ：０．０００２％以上０．０５００％以下、
Ｎｂ：０．００１％以上０．０５０％以下、
Ｔｉ：０．００１％以上０．０５０％以下、
Ｖ：０．００１％以上０．０５０％以下、
Ｃａ：０．０００３％以上０．０３００％以下、
Ｍｇ：０．０００３％以上０．０３００％以下、
ＲＥＭ：０．０００３％以上０．０３００％以下のいずれか１種以上を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成であることを特徴とする、請求項１に記載の靭性に優れた低温用ニッケル含有鋼板。 In addition, by mass%,
Cu: 0.01% or more and 2.00% or less,
Cr: 0.01% or more and 5.00% or less,
Mo: 0.01% or more and 1.00% or less,
B: 0.0002% or more and 0.0500% or less,
Nb: 0.001% or more and 0.050% or less,
Ti: 0.001% or more and 0.050% or less,
V: 0.001% or more and 0.050% or less,
Ca: 0.0003% or more and 0.0300% or less,
Mg: 0.0003% or more and 0.0300% or less,
REM: The toughness according to claim 1, wherein the steel composition contains any one or more of 0.0003% or more and 0.0300% or less, and the balance is composed of Fe and unavoidable impurities. Nickel-containing steel sheet for low temperature.
Ｃ ：０．０２％以上０．１２％以下、
Ｓｉ：０．０２％以上０．３５％以下、
Ｍｎ：０．１０％以上１．５０％以下、
Ｐ：０．００１０％以上０．０１００％以下、
Ｓ：０．０００１％以上０．００３５％以下、
Ｎｉ：２．７％以上５．０％以下、
Ａｌ：０．００２％以上０．０９０％以下、
Ｎ：０．０００１％以上０．００７０％以下、
Ｔ−Ｏ：０．０００１％以上０．００３０％以下を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成である鋳片あるいは鋼片を、８５０℃以上１３００℃以下に加熱し、仕上げ１パス前温度が６００℃以上８５０℃以下の熱間圧延を行い、空冷したのち、焼入れを行う際の加熱中において、６００℃以上７５０℃以下の温度範囲の昇温速度を０．３℃/s以上とし、焼入れは最高加熱温度を８００℃以上９４０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とし、さらに焼戻しは最高加熱温度を５００℃以上６６０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とすることにより、旧オーステナイト円相当粒径が２０μｍ以下であり、有効結晶粒径が１２μｍ以下である鋼板を得ることを特徴とする、靭性に優れた低温用ニッケル含有鋼板の製造方法。 By mass%,
C: 0.02% or more and 0.12% or less,
Si: 0.02% or more and 0.35% or less,
Mn: 0.10% or more and 1.50% or less,
P: 0.0010% or more and 0.0100% or less,
S: 0.0001% or more and 0.0035% or less,
Ni: 2.7% or more and 5.0% or less,
Al: 0.002% or more and 0.090% or less,
N: 0.0001% or more and 0.0070% or less,
TO: A slab or steel slab containing 0.0001% or more and 0.0030% or less and having a steel composition in which the balance is Fe and unavoidable impurities is heated to 850 ° C. or higher and 1300 ° C. or lower to finish 1. During hot rolling with a pre-pass temperature of 600 ° C or higher and 850 ° C or lower, air cooling, and then heating during quenching, the temperature rise rate in the temperature range of 600 ° C or higher and 750 ° C or lower is 0.3 ° C / s. As described above, quenching heats the maximum heating temperature to a temperature range of 800 ° C. or higher and 940 ° C. or lower, holding time is 5 minutes or more and 100 minutes or less, and tempering sets the maximum heating temperature to a temperature range of 500 ° C. or higher and 660 ° C. or lower. By heating and setting the holding time to 5 minutes or more and 100 minutes or less, a steel plate having an old austenite circle equivalent particle size of 20 μm or less and an effective crystal particle size of 12 μm or less can be obtained , and has excellent toughness. A method for manufacturing a steel plate containing nickel for low temperature.
Ｃ ：０．０２％以上０．１２％以下、
Ｓｉ：０．０２％以上０．３５％以下、
Ｍｎ：０．１０％以上１．５０％以下、
Ｐ：０．００１０％以上０．０１００％以下、
Ｓ：０．０００１％以上０．００３５％以下、
Ｎｉ：２．７％以上５．０％以下、
Ａｌ：０．００２％以上０．０９０％以下、
Ｎ：０．０００１％以上０．００７０％以下、
Ｔ−Ｏ：０．０００１％以上０．００３０％以下を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成である鋳片あるいは鋼片を、８５０℃以上１３００℃以下に加熱し、仕上げ１パス前温度が６００℃以上９００℃以下の熱間圧延を行い、冷却速度２００℃/s以下で水冷したのち、焼入れを行う際の加熱中において、６００℃以上７５０℃以下の温度範囲の昇温速度を０．３℃/s以上とし、焼入れは最高加熱温度を８００℃以上９４０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とし、さらに焼戻しは最高加熱温度を５００℃以上６６０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とすることにより、旧オーステナイト円相当粒径が２０μｍ以下であり、有効結晶粒径が１２μｍ以下である鋼板を得ることを特徴とする、靭性に優れた低温用ニッケル含有鋼板の製造方法。 By mass%,
C: 0.02% or more and 0.12% or less,
Si: 0.02% or more and 0.35% or less,
Mn: 0.10% or more and 1.50% or less,
P: 0.0010% or more and 0.0100% or less,
S: 0.0001% or more and 0.0035% or less,
Ni: 2.7% or more and 5.0% or less,
Al: 0.002% or more and 0.090% or less,
N: 0.0001% or more and 0.0070% or less,
TO: A slab or steel slab containing 0.0001% or more and 0.0030% or less and having a steel composition in which the balance is Fe and unavoidable impurities is heated to 850 ° C. or higher and 1300 ° C. or lower to finish 1. After hot rolling with a pre-pass temperature of 600 ° C or higher and 900 ° C or lower, water cooling at a cooling rate of 200 ° C / s or lower, the temperature rises in the temperature range of 600 ° C or higher and 750 ° C or lower during heating during tempering. The speed is 0.3 ° C / s or more, the maximum heating temperature is 800 ° C or more and 940 ° C or less for quenching, the holding time is 5 minutes or more and 100 minutes or less, and the maximum heating temperature is 500 ° C for tempering. By heating to a temperature range of 660 ° C. or lower and setting the holding time to 5 minutes or more and 100 minutes or less, a steel sheet having an old austenite circle-equivalent particle size of 20 μm or less and an effective crystal grain size of 12 μm or less can be obtained. A method for manufacturing a low-temperature nickel-containing steel plate having excellent toughness.
Ｃ ：０．０２％以上０．１２％以下、
Ｓｉ：０．０２％以上０．３５％以下、
Ｍｎ：０．１０％以上１．５０％以下、
Ｐ：０．００１０％以上０．０１００％以下、
Ｓ：０．０００１％以上０．００３５％以下、
Ｎｉ：２．７％以上５．０％以下、
Ａｌ：０．００２％以上０．０９０％以下、
Ｎ：０．０００１％以上０．００７０％以下、
Ｔ−Ｏ：０．０００１％以上０．００３０％以下を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成である鋳片あるいは鋼片を、８５０℃以上１３００℃以下に加熱し、仕上げ１パス前温度が６００℃以上９００℃以下の熱間圧延を行い、水冷停止温度を１５０℃以上５５０℃以下とする水冷を行ったのち、焼入れを行う際の加熱中において、６００℃以上７５０℃以下の温度範囲の昇温速度を０．３℃/s以上とし、焼入れは最高加熱温度を８００℃以上９４０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とし、さらに焼戻しは最高加熱温度を５００℃以上６６０℃以下の温度範囲まで加熱し、保持時間を５分以上１００分以下とすることにより、旧オーステナイト円相当粒径が２０μｍ以下であり、有効結晶粒径が１２μｍ以下である鋼板を得ることを特徴とする、靭性に優れた低温用ニッケル含有鋼板の製造方法。 By mass%,
C: 0.02% or more and 0.12% or less,
Si: 0.02% or more and 0.35% or less,
Mn: 0.10% or more and 1.50% or less,
P: 0.0010% or more and 0.0100% or less,
S: 0.0001% or more and 0.0035% or less,
Ni: 2.7% or more and 5.0% or less,
Al: 0.002% or more and 0.090% or less,
N: 0.0001% or more and 0.0070% or less,
TO: A slab or steel slab containing 0.0001% or more and 0.0030% or less and having a steel composition in which the balance is Fe and unavoidable impurities is heated to 850 ° C. or higher and 1300 ° C. or lower to finish 1. After hot rolling with a pre-pass temperature of 600 ° C or more and 900 ° C or less, water cooling with a water cooling stop temperature of 150 ° C or more and 550 ° C or less, and then during heating during tempering, 600 ° C or more and 750 ° C or less. The temperature rise rate in the temperature range of is 0.3 ° C / s or more, the maximum heating temperature is heated to the temperature range of 800 ° C or more and 940 ° C or less, the holding time is set to 5 minutes or more and 100 minutes or less, and the tempering is further performed. By heating the maximum heating temperature to a temperature range of 500 ° C. or higher and 660 ° C. or lower and setting the holding time to 5 minutes or longer and 100 minutes or lower, the particle size equivalent to the old austenite circle is 20 μm or less and the effective crystal grain size is 12 μm or less. A method for producing a low-temperature nickel-containing steel plate having excellent toughness, which comprises obtaining a steel plate.
Ｃｕ：０．０１％以上２．００％以下、
Ｃｒ：０．０１％以上５．００％以下、
Ｍｏ：０．０１％以上１．００％以下、
Ｂ：０．０００２％以上０．０５００％以下、
Ｎｂ：０．００１％以上０．０５０％以下、
Ｔｉ：０．００１％以上０．０５０％以下、
Ｖ：０．００１％以上０．０５０％以下、
Ｃａ：０．０００３％以上０．０３００％以下、
Ｍｇ：０．０００３％以上０．０３００％以下、
ＲＥＭ：０．０００３％以上０．０３００％以下のいずれか１種以上を含有し、残部がＦｅ及び不可避的不純物からなる鋼組成であることを特徴とする請求項３乃至６に記載の靭性に優れた低温用ニッケル含有鋼板の製造方法。 In addition, by mass%,
Cu: 0.01% or more and 2.00% or less,
Cr: 0.01% or more and 5.00% or less,
Mo: 0.01% or more and 1.00% or less,
B: 0.0002% or more and 0.0500% or less,
Nb: 0.001% or more and 0.050% or less,
Ti: 0.001% or more and 0.050% or less,
V: 0.001% or more and 0.050% or less,
Ca: 0.0003% or more and 0.0300% or less,
Mg: 0.0003% or more and 0.0300% or less,
REM: The toughness according to claim 3 to 6, wherein the steel composition contains at least one of 0.0003% or more and 0.0300% or less, and the balance is Fe and unavoidable impurities. An excellent method for manufacturing nickel-containing steel sheets for low temperatures.
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