JPH08209239A - Production of thick steel for low temperature use having brittle fracture propagation stop characteristic at lower than-50×c - Google Patents
Production of thick steel for low temperature use having brittle fracture propagation stop characteristic at lower than-50×cInfo
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- JPH08209239A JPH08209239A JP1514395A JP1514395A JPH08209239A JP H08209239 A JPH08209239 A JP H08209239A JP 1514395 A JP1514395 A JP 1514395A JP 1514395 A JP1514395 A JP 1514395A JP H08209239 A JPH08209239 A JP H08209239A
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- toughness
- crack propagation
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Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は、脆性亀裂伝播停止特性
に優れた低温用鋼の製造方法に関し、さらに詳しくは、
ＬＰＧタンク等の構造物の安全を確保するために使用す
る−50℃以下の脆性亀裂伝播停止特性を有する低温用厚
鋼材の製造方法に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a low temperature steel having an excellent brittle crack propagation arresting property.
The present invention relates to a method for manufacturing a low temperature thick steel material having a brittle crack propagation arresting characteristic of -50 ° C. or lower, which is used for ensuring the safety of a structure such as an LPG tank.
【０００２】[0002]
【従来の技術】ＬＰＧタンク、氷海域海洋構造物等に使
用される鋼には脆性破壊に対する安全性を確保するた
め、低温環境下で優れた耐脆性破壊特性とともに脆性亀
裂伝播停止特性が要求される。例えば、−46℃の液化ガ
ス貯蔵タンク用鋼材の脆性亀裂伝播停止特性は−50℃に
おける破壊靱性値（Ｋca）が3923N/mm3/2 以上であるこ
とが要求されている。2. Description of the Related Art Steels used for LPG tanks, offshore structures in ice and sea, etc. are required to have excellent brittle fracture resistance as well as brittle crack propagation stopping characteristics in a low temperature environment in order to ensure safety against brittle fracture. It For example, the brittle crack propagation stopping property of a steel material for a liquefied gas storage tank at −46 ° C. is required to have a fracture toughness value (Kca) at −50 ° C. of 3923 N / mm 3/2 or more.
【０００３】従来、490N/mm2級低温用鋼はその要求レベ
ルに応じて、焼ならしまたは焼入れ焼戻し等の熱処理を
行って製造されているが、いずれも脆性亀裂伝播停止特
性の要求レベルへの対応が困難になってきた。このた
め、最近では製造技術の進歩が著しい制御圧延および制
御冷却により鋼の組織をアシキュラフェライト化するこ
とで優れた脆性亀裂伝播停止特性を有する鋼が開発され
ている。Conventionally, 490 N / mm 2 class low temperature steel has been manufactured by performing heat treatment such as normalizing or quenching and tempering according to the required level. It has become difficult to deal with. For this reason, recently, steels having excellent brittle crack propagation arresting properties have been developed by converting the structure of the steels to acicular ferrite by controlled rolling and controlled cooling, for which the manufacturing technology has made remarkable progress.
【０００４】[0004]
【発明が解決しようとする課題】しかし、制御圧延によ
る方法では、板厚が薄い物には有効であるが、板厚が25
mm以上と厚くなると要求特性を満足できなくなる。この
ため、高価なNiやMo等の合金成分を多量に添加し靱性を
向上させる必要がある。一方、制御冷却方法を用いて脆
性亀裂伝播停止特性を向上させた鋼の製造方法の例が、
特開昭62-77419号公報および特開平2-217416号公報に開
示してある。前者はフェライトの層状化によりセパレー
ションを多発し、脆性亀裂伝播停止特性を向上させたも
のである。この方法では、靱性の異方性が発生し、さら
にシャルピー衝撃試験における吸収エネルギーが低下し
十分な靱性が期待できない。また、後者はダイレクトロ
ーリング（直送圧延）およびホットチャージローリング
（温間装入圧延）材を用い、未再結晶温度域圧延と制御
冷却により脆性亀裂伝播停止特性を向上させるものであ
る。この方法では、圧延前の初期オーステナイト粒が粗
大であり、高い靱性が得にくく、脆性亀裂伝播停止特性
の大きな改善が望めない。However, the method by controlled rolling is effective for a product having a small plate thickness, but the plate thickness is 25
If the thickness becomes thicker than mm, the required characteristics cannot be satisfied. Therefore, it is necessary to add a large amount of expensive alloy components such as Ni and Mo to improve the toughness. On the other hand, an example of a method for manufacturing steel with improved brittle crack propagation arresting properties using a controlled cooling method,
It is disclosed in JP-A-62-77419 and JP-A-2-217416. The former is the one in which the layering of ferrite frequently causes separation and improves the brittle crack propagation arresting property. In this method, anisotropy of toughness occurs, and further, absorbed energy in the Charpy impact test decreases, and sufficient toughness cannot be expected. The latter uses direct rolling (direct feed rolling) and hot charge rolling (warm charging rolling), and improves the brittle crack propagation stopping property by rolling in a non-recrystallization temperature region and controlled cooling. In this method, the initial austenite grains before rolling are coarse, it is difficult to obtain high toughness, and it is not possible to expect a great improvement in the brittle crack propagation arresting property.
【０００５】本発明は、上記の問題点を解決するために
なされたもので、高価な合金元素を多量に必要とせず、
化学成分の調整、鋼片の低温加熱、制御圧延および直接
焼入れ−焼戻し処理を行うとともに、焼戻し処理後に軽
圧下を行うことによる−50℃以下の脆性亀裂伝播停止特
性を有する低温用厚鋼材の製造方法を提供することを目
的とする。The present invention has been made to solve the above problems, and does not require a large amount of expensive alloying elements,
Manufacture of low temperature thick steel products with brittle crack propagation arresting characteristics of -50 ° C or less by adjusting chemical composition, low temperature heating of steel slabs, controlled rolling and direct quenching-tempering, and light reduction after tempering. The purpose is to provide a method.
【０００６】[0006]
【課題を解決するための手段】本発明の要旨は、(1) 質
量％で、C:0.03〜0.10％、 Si:0.03〜0.60％、 Mn:0.70
〜2.0 ％、 Al:0.01〜0.08％、Ti:0.005〜0.03％、 N:
0.002〜0.007 ％を含有し、残部がFeおよび不可避的不
純物からなる鋼片を、 950〜1150℃の温度に加熱し、未
再結晶温度域で累積圧下率50％以上の圧下を行い、その
後Ａr3点〜Ａr3点＋50℃の温度から、20℃/s以上の冷却
速度で 150℃以下の温度まで直接焼き入れした後、 500
℃〜Ａc1点の温度で焼戻しする−50℃以下の脆性亀裂伝
播停止特性を有する低温用厚鋼材の製造方法である。Means for Solving the Problems The gist of the present invention is (1) in mass%, C: 0.03 to 0.10%, Si: 0.03 to 0.60%, Mn: 0.70
~ 2.0%, Al: 0.01 ~ 0.08%, Ti: 0.005 ~ 0.03%, N:
A steel slab containing 0.002 to 0.007% with the balance Fe and unavoidable impurities is heated to a temperature of 950 to 1150 ° C and subjected to a cumulative reduction of 50% or more in the unrecrystallized temperature range, and then Ar. 500 points after directly quenching from the temperature of 3 points to Ar 3 points + 50 ° C to a temperature of 150 ° C or less at a cooling rate of 20 ° C / s or more.
A method for producing a thick steel material for low temperature having a brittle crack propagation stopping characteristic of -50 ° C or less, which is tempered at a temperature of ℃ to Ac 1 point.
【０００７】(2) さらに化学成分として、質量％で、 N
b:0.01〜0.05％、Ni:1.0％以下、 B:0.003％以下、 Ca:
0.0005〜0.005 ％、REM:0.0005〜0.001 ％の内から選ん
だ１種または２種以上を含有する上記(1) の−50℃以下
の脆性亀裂伝播停止特性を有する低温用厚鋼材の製造方
法である。(2) Further, as a chemical component, in mass%, N
b: 0.01-0.05%, Ni: 1.0% or less, B: 0.003% or less, Ca:
The method for producing a thick steel material for low temperature having a brittle crack propagation arresting property of -50 ° C or lower according to (1) above, which contains one or more selected from 0.0005 to 0.005% and REM: 0.0005 to 0.001%. is there.
【０００８】(3) 焼戻し後、 500℃以下の温度で累積圧
下率 1〜5 ％の圧下を行う上記(1)または(2) の−50℃
以下の脆性亀裂伝播停止特性を有する低温用厚鋼材の製
造方法である。(3) After tempering, a cumulative rolling reduction of 1 to 5% is carried out at a temperature of 500 ° C. or lower, and -50 ° C. in the above (1) or (2).
The method for producing a low temperature thick steel material having the following brittle crack propagation stopping properties is as follows.
【０００９】[0009]
【作用】以下に、本発明の製造条件の限定理由について
説明する。本発明者らは鋼片の加熱温度範囲を限定する
ために、次のような実験を行った。すなわち、0.009%C-
0.26%Si-1.31%Mn-0.013%Ti鋼を 950〜1250℃の温度に加
熱し、未再結晶温度域で累積圧下率60％の圧下を行い板
厚30mmに仕上げ、その後 790℃の温度から、30℃/sの冷
却速度で 150℃以下の温度まで直接焼入れした後、600
℃の温度で焼戻しした鋼板について、破壊靱性値を求め
た。その結果を図１に示す。The reason for limiting the manufacturing conditions of the present invention will be described below. The present inventors conducted the following experiment in order to limit the heating temperature range of the steel slab. That is, 0.009% C-
0.26% Si-1.31% Mn-0.013% Ti steel is heated to a temperature of 950 to 1250 ° C, and a cumulative reduction of 60% is performed in the unrecrystallized temperature range to finish the plate thickness to 30mm, and then from 790 ° C. Direct quenching at a cooling rate of 30 ℃ / s to a temperature below 150 ℃, then 600
A fracture toughness value was obtained for the steel sheet tempered at a temperature of ° C. The result is shown in FIG.
【００１０】図１に示すように、鋼片の加熱温度が 950
〜1150℃の範囲では−50℃以下で破壊靱性値（Ｋca）が
3923N/mm3/2 を満足しているが、加熱温度が1250℃と高
くなると破壊靱性値（Ｋca）が3923N/mm3/2 を満足する
温度が上昇する。これは加熱温度が1150℃を超えると加
熱時のオーステナイト粒が大きくなり、その後の圧延で
も細粒化することができず鋼の脆性亀裂伝播停止特性が
低下するためである。一方、圧延時の温度低下のため 9
50℃未満の加熱温度では圧延完了後の直接焼入れに必要
な温度確保が困難であり、所定の強度および靱性が得ら
れない。したがって、鋼片の加熱温度は 950〜1150℃の
範囲に限定する。As shown in FIG. 1, the heating temperature of the billet is 950.
Fracture toughness value (Kca) is below -50 ℃ in the range of up to 1150 ℃.
Although it satisfies 3923 N / mm 3/2 , when the heating temperature rises to 1250 ° C, the temperature at which the fracture toughness value (Kca) satisfies 3923 N / mm 3/2 rises. This is because if the heating temperature exceeds 1150 ° C., the austenite grains during heating become large, and the grains cannot be refined even in the subsequent rolling, and the brittle crack propagation arresting property of the steel deteriorates. On the other hand, due to the temperature drop during rolling, 9
If the heating temperature is less than 50 ° C, it is difficult to secure the temperature required for direct quenching after the completion of rolling, and the desired strength and toughness cannot be obtained. Therefore, the heating temperature of the billet is limited to the range of 950 to 1150 ° C.
【００１１】未再結晶温度域において、累積圧下率50％
以上の圧下を行う理由は、オーステナイト粒の微細化を
図るためであり、圧下率が50％未満では直接焼入れ後の
組織に粗大ベイナイト＋マルテンサイトが混入して靱性
が低下するからである。Cumulative reduction of 50% in the non-recrystallization temperature range
The reason for carrying out the above-mentioned reduction is for the purpose of refining the austenite grains, and if the reduction ratio is less than 50%, coarse bainite + martensite is mixed in the structure after direct quenching, and the toughness is reduced.
【００１２】本発明者らは直接焼入れにおける冷却開始
温度を限定するために、次のような実験を行った。すな
わち、0.009%C-0.26%Si-1.31%Mn-0.013%Ti鋼を1050℃の
温度に加熱し、未再結晶温度域で累積圧下率60％の圧下
を行い板厚30mmに仕上げ、その後 750〜850 ℃の温度か
ら、30℃/sの冷却速度で 150℃以下の温度まで直接焼入
れした後、 600℃の温度で焼戻しした鋼板について、破
壊靱性値を求めた。その結果を図２に示す。The present inventors conducted the following experiment in order to limit the cooling start temperature in direct quenching. That is, 0.009% C-0.26% Si-1.31% Mn-0.013% Ti steel is heated to a temperature of 1050 ° C, and a cumulative reduction of 60% is performed in the unrecrystallized temperature range to finish the plate to a thickness of 30 mm and then 750 Fracture toughness values were determined for steel sheets that were directly quenched from a temperature of ~ 850 ° C to a temperature of 150 ° C or less at a cooling rate of 30 ° C / s and then tempered at a temperature of 600 ° C. The result is shown in FIG.
【００１３】図２に示すように、破壊靱性値（Ｋca）が
3923N/mm3/2 を満足する温度をより低温にする冷却開始
温度は、鋼ごとに決まる。すなわち、冷却開始温度がＡ
r3点以上では微細なオーステナイトから微細なフェライ
ト＋ベイナイトが生成し靱性が向上するため、目標とす
る破壊靱性値（Ｋca）が3923N/mm3/2 を満足する脆性亀
裂伝播停止温度として−50℃以下が得られている。一
方、冷却開始温度がＡr3点未満では、オーステナイトか
ら初析フェライト＋上部ベイナイトが生成し、十分な強
度、靱性を得ることが困難となる。As shown in FIG. 2, the fracture toughness value (Kca) is
The cooling start temperature for lowering the temperature satisfying 3923 N / mm 3/2 is determined for each steel. That is, the cooling start temperature is A
Since the r 3 points or more to improve the toughness generates fine ferrite + bainite from fine austenite, -50 fracture toughness value of a target (Kca) as a brittle crack propagation stop temperature which satisfies 3923N / mm 3/2 The temperature is below ℃. On the other hand, when the cooling start temperature is less than Ar 3 point, proeutectoid ferrite + upper bainite is generated from austenite, and it becomes difficult to obtain sufficient strength and toughness.
【００１４】一方、冷却開始温度が高くなりＡr3点＋50
℃を超えると破壊靱性値（Ｋca）が3923N/mm3/2 を満足
する温度が上昇し、−50℃を満足できなくなる。これは
粗大ベイナイトが生成し靱性が低下したものである。し
たがって、直接焼入れにおける冷却開始温度はＡr3点〜
Ａr3点＋50℃の温度範囲に限定する。On the other hand, the cooling start temperature becomes high and Ar 3 points +50
If the temperature exceeds ℃, the temperature at which the fracture toughness value (Kca) satisfies 3923 N / mm 3/2 rises and it becomes impossible to satisfy -50 ℃. This is due to the formation of coarse bainite and the decrease in toughness. Therefore, the cooling start temperature in direct quenching is from Ar 3 point to
Limited to the temperature range of Ar 3 points + 50 ° C.
【００１５】また、本発明者らは直接焼入れにおける冷
却速度を限定するために、次のような実験を行った。す
なわち、0.009%C-0.26%Si-1.31%Mn-0.013%Ti鋼を1050℃
の温度に加熱し、未再結晶温度域で累積圧下率60％の圧
下を行い板厚30mmに仕上げ、その後 790℃の温度から、
10〜30℃/sの冷却速度で 150℃以下の温度まで直接焼入
れした後、 600℃の温度で焼戻しした鋼板について、破
壊靱性値を求めた。その結果を図３に示す。Further, the present inventors conducted the following experiment in order to limit the cooling rate in direct quenching. That is, 0.009% C-0.26% Si-1.31% Mn-0.013% Ti steel at 1050 ℃
It is heated to the temperature of, and the cumulative reduction is 60% in the non-recrystallization temperature range to finish the plate thickness to 30 mm, and then from the temperature of 790 ℃,
Fracture toughness values were obtained for steel sheets that were directly quenched at a cooling rate of 10 to 30 ° C / s to a temperature of 150 ° C or less and then tempered at a temperature of 600 ° C. The result is shown in FIG.
【００１６】図３に示すように、冷却速度が速くなると
破壊靱性値（Ｋca）が3923N/mm3/2を満足する温度は低
くなり、冷却速度が20℃/s以上では−50℃を満足でき
る。したがって、直接焼入れにおける冷却速度は20℃/s
以上で、 150℃以下の温度まで冷却する。また、圧延完
了後直接焼入れを行う理由は、高価な強化元素を多量に
使用せずに板厚25mm以上の比較的厚物材の強度を確保す
るためである。As shown in FIG. 3, when the cooling rate is high, the temperature at which the fracture toughness value (Kca) satisfies 3923 N / mm 3/2 is low, and when the cooling rate is 20 ° C./s or more, -50 ° C. is satisfied. it can. Therefore, the cooling rate in direct quenching is 20 ℃ / s
Above, it cools to the temperature below 150 ℃. Further, the reason for directly quenching after completion of rolling is to secure the strength of a relatively thick material having a plate thickness of 25 mm or more without using a large amount of expensive strengthening elements.
【００１７】直接焼入れ後、 500℃〜Ａc1点の温度で焼
戻しする理由は、直接焼入れにより硬く、脆くなった鋼
を目標の強度、靱性に調整する目的の外に、直接焼入れ
にかかわらず制御冷却された場合、鋼は冷却時の熱応力
差に起因し、鋼の表面側に圧縮応力、中心部に引張応力
等の残留応力が発生する。その大きさは、時に降伏応力
近くにもなる。これらの大きな残留応力が鋼中に存在す
ると、特に、引張応力は脆性亀裂の伝播を促進させるた
め、これを除く必要から焼戻しを行う。焼戻し温度が 5
00℃未満ではその効果が得られず、また、Ａc1点を超え
ると強度低下が大きくなる。したがって、直接焼入れ後
の焼戻し温度は 500℃〜Ａc1点の温度範囲に限定する。After direct quenching, the reason for tempering at a temperature of 500 ° C. to Ac 1 point is that the steel hardened and brittle by direct quenching is controlled in addition to the purpose of adjusting it to the target strength and toughness, regardless of direct quenching. When cooled, a residual stress such as a compressive stress is generated on the surface side of the steel and a residual stress such as a tensile stress is generated at the center of the steel due to the difference in thermal stress during cooling. Its magnitude is sometimes close to the yield stress. When these large residual stresses are present in the steel, in particular, tensile stress promotes the propagation of brittle cracks, and therefore tempering is performed because it is necessary to remove this. Tempering temperature 5
If it is less than 00 ° C, the effect cannot be obtained, and if it exceeds the Ac 1 point, the strength is greatly reduced. Therefore, the tempering temperature after direct quenching is limited to the temperature range of 500 ° C to the Ac 1 point.
【００１８】さらに、脆性亀裂伝播停止特性を向上させ
る手段として、上記に加え、焼戻しを行った後、 500℃
以下の温度で累積圧下率 1〜5 ％の圧下を行う。これは
鋼の表面に圧延歪みを与え、表層部のフェライト粒を層
状化することによる脆性亀裂の伝播抑止効果を利用し、
脆性亀裂伝播停止特性を改善するものである。その効果
を十分得るためには累積圧下率が 1％以上必要であり、
また、 5％を超えると加工硬化が著しく逆に表面部の靱
性が低下する。一方、圧下温度を 500℃以下とした理由
は、焼戻し時の温度を利用して圧下が可能であり、再加
熱を必要としないためである。したがって、焼戻し後の
圧下は500 ℃以下の温度で累積圧下率 1〜5 ％とする。Furthermore, as a means for improving the brittle crack propagation stopping property, after tempering is performed in addition to the above, 500 ° C.
Roll down at a cumulative rolling reduction of 1 to 5% at the following temperatures. This gives rolling strain to the surface of the steel and utilizes the effect of suppressing the propagation of brittle cracks by layering the ferrite grains in the surface layer,
It is intended to improve the brittle crack propagation arresting property. In order to obtain the effect sufficiently, the cumulative rolling reduction must be 1% or more,
On the other hand, if it exceeds 5%, work hardening is remarkable, and conversely, the toughness of the surface portion decreases. On the other hand, the reason why the reduction temperature is set to 500 ° C. or lower is that the reduction can be performed by utilizing the temperature at the time of tempering and reheating is not required. Therefore, the reduction after tempering shall be a cumulative reduction of 1 to 5% at a temperature of 500 ° C or less.
【００１９】次に、本発明における化学成分の限定理由
について説明する。C は、鋼板の強度確保のために必要
な元素であるが、含有量が0.03％未満では強度の確保が
困難となるとともに、溶接熱影響部の軟化が大きくな
る。また、含有量が0.10％を超えると母材の靱性が劣化
する。したがって、C 含有量は0.03〜0.10％の範囲とす
る。Next, the reasons for limiting the chemical components in the present invention will be explained. C is an element necessary for securing the strength of the steel sheet, but if the content is less than 0.03%, it becomes difficult to secure the strength and the softening of the weld heat affected zone becomes large. Further, if the content exceeds 0.10%, the toughness of the base material deteriorates. Therefore, the C content is in the range of 0.03 to 0.10%.
【００２０】Siは、鋼の脱酸に必要な元素であり、その
ためには0.03％以上の含有量が必要である。また、0.60
％を超えて多量に含有すると母材および溶接熱影響部の
靱性が低下する。したがって、Si含有量は0.03〜0.60％
の範囲とする。Si is an element necessary for deoxidizing steel, and for this purpose, its content must be 0.03% or more. Also, 0.60
%, The toughness of the base material and the weld heat affected zone deteriorates. Therefore, the Si content is 0.03-0.60%
Range.
【００２１】Mnは、鋼板の強度および靱性を確保のため
に必要な元素であるが、含有量が0.70％未満ではこのよ
うな効果は少なく、また、 2.0％を超えて含有すると溶
接熱影響部の靱性が低下する。したがって、Mn含有量は
0.70〜2.0 ％の範囲とする。Mn is an element necessary to secure the strength and toughness of the steel sheet, but if the content is less than 0.70%, such an effect is small, and if it exceeds 2.0%, the weld heat affected zone is present. Toughness is reduced. Therefore, the Mn content is
The range is 0.70 to 2.0%.
【００２２】Alは、鋼の脱酸に必要な元素であり、その
ためには0.01％以上の含有量が必要である。また、0.08
％を超えて含有すると溶接金属および溶接熱影響部の靱
性が低下する。したがって、Al含有量は0.01〜0.08％の
範囲とする。Al is an element necessary for deoxidizing steel, and for this purpose, its content must be 0.01% or more. Also, 0.08
%, The toughness of the weld metal and the heat-affected zone of the weld decreases. Therefore, the Al content is set to the range of 0.01 to 0.08%.
【００２３】Tiは、N と結合してTiN を形成し鋼中に微
細に分散し、オーステナイト粒の粗大化防止とフェライ
ト結晶粒の微細化に寄与するため、母材の低温靱性およ
び溶接熱影響部の靱性を改善するのに有効な元素であ
る。含有量が 0.005％未満ではこの効果が小さく、ま
た、0.03％を超えて含有すると母材の低温靱性および溶
接熱影響部の靱性が低下する。したがって、Ti含有量は
0.005〜0.03％の範囲とする。Ti combines with N to form TiN, which is finely dispersed in the steel and contributes to preventing coarsening of austenite grains and refining of ferrite crystal grains. It is an element effective in improving the toughness of the part. If the content is less than 0.005%, this effect is small, and if the content exceeds 0.03%, the low temperature toughness of the base metal and the toughness of the weld heat affected zone are deteriorated. Therefore, the Ti content is
The range is 0.005 to 0.03%.
【００２４】N は、Tiと結合して上記TiN の靱性向上効
果を発揮させる上で重要な元素であり、少なくとも 0.0
02％以上の添加が必要である。しかし、過度の添加は固
溶Nの増加になりフェライト地の脆化を生じるため、上
限を 0.007％に抑える必要がある。したがって、N 含有
量は 0.002〜0.007 ％の範囲とする。[0024] N is an important element in combining with Ti to exert the toughness improving effect of TiN, and is at least 0.0
It is necessary to add more than 02%. However, excessive addition causes an increase in solute N and causes embrittlement of the ferrite material, so the upper limit must be suppressed to 0.007%. Therefore, the N content should be in the range of 0.002 to 0.007%.
【００２５】本発明では、上記の化学成分以外に強度向
上あるいは靱性向上のためにNb、Ni、 B、Ca、REM の内
から選んだ１種または２種以上を含有させることができ
る。In the present invention, one or more selected from Nb, Ni, B, Ca and REM may be contained in addition to the above chemical components in order to improve strength or toughness.
【００２６】Nbは、オーステナイトの再結晶を抑制し、
圧延でのオーステナイト粒の細粒化を促進させる。この
効果を発揮させるためには、0.01％以上の含有量が必要
である。一方、0.05％を超えて多量に含有すると溶接熱
影響部の靱性が低下する。したがって、Nb含有量は0.01
〜0.05％の範囲とする。Nb suppresses recrystallization of austenite,
It promotes the refinement of austenite grains during rolling. In order to exert this effect, the content of 0.01% or more is required. On the other hand, if it is contained in a large amount exceeding 0.05%, the toughness of the heat-affected zone of the welding is reduced. Therefore, the Nb content is 0.01
The range is ~ 0.05%.
【００２７】Niは、溶接熱影響部の靱性に悪影響を与え
ることが少なく、鋼の強度および靱性を向上させる元素
であるが、高価であるため製造コストアップを抑える意
味で、目的を達成するに必要な含有量として 1.0％以下
が望ましい。したがって、Ni含有量は 1.0％以下とす
る。Ni is an element that does not adversely affect the toughness of the heat-affected zone of welding and improves the strength and toughness of steel. However, since it is expensive, it is necessary to achieve the purpose in the sense of suppressing an increase in manufacturing cost. The required content is 1.0% or less. Therefore, the Ni content should be 1.0% or less.
【００２８】B は、鋼の焼入れ性を上昇させるために含
有させる元素であるが、含有量が0.003 ％を超えると溶
接熱影響部の靱性が低下する。したがって、B 含有量は
0.003％以下とする。B is an element to be contained in order to increase the hardenability of steel, but if the content exceeds 0.003%, the toughness of the weld heat affected zone decreases. Therefore, the B content is
It should be 0.003% or less.
【００２９】Caは、MnS の形態制御を行い鋼の圧延方向
に対する直角方向の靱性向上のために含有させる元素で
ある。含有量が0.0005％未満ではその効果が少なく、ま
た、0.005％を超えて含有させると鋼中の非金属介在物
が増加し、内部欠陥の原因となる。したがって、Ca含有
量は0.0005〜0.005 ％の範囲とする。Ca is an element contained for controlling the morphology of MnS and improving the toughness in the direction perpendicular to the rolling direction of steel. If the content is less than 0.0005%, the effect is small, and if the content exceeds 0.005%, the amount of nonmetallic inclusions in the steel increases, causing internal defects. Therefore, the Ca content should be in the range of 0.0005 to 0.005%.
【００３０】REM は、Caと同様の効果を付与する元素で
ある。含有量が0.0005％未満ではその効果が少なく、ま
た、 0.001％を超えて含有させると鋼中の非金属介在物
が増加し、内部欠陥の原因となる。したがって、REM 含
有量は0.0005〜0.001 ％の範囲とする。REM is an element that imparts the same effect as Ca. If the content is less than 0.0005%, the effect is small, and if the content exceeds 0.001%, the nonmetallic inclusions in the steel increase, causing internal defects. Therefore, the REM content should be in the range of 0.0005 to 0.001%.
【００３１】なお、Ａr3点およびＡc1点は下記式で求め
た値を使用する。Ａr3=910-310C-80Mn-20Cr-55Ni-80Mo+
0.35(t-8) ここでt は板厚(mm)。 Ａc1=723-14Mn+22Si-14.4Ni+23.3CrThe values obtained by the following equations are used for the Ar 3 point and the Ac 1 point. Ar 3 = 910-310C-80Mn-20Cr-55Ni-80Mo +
0.35 (t-8) where t is plate thickness (mm). Ac 1 = 723-14Mn + 22Si-14.4Ni + 23.3Cr
【００３２】[0032]
【実施例】以下に、本発明の実施例について説明する。 実施例１ 供試鋼は表１に示す化学成分を有する鋼片を表２に示す
製造条件で、板厚30〜40mmの鋼板に仕上げたものであ
る。これらの鋼板について、引張特性、衝撃特性および
脆性亀裂伝播停止特性を調査した。その結果を表２に併
記した。EXAMPLES Examples of the present invention will be described below. Example 1 The test steel is a steel plate having a chemical composition shown in Table 1 and finished into a steel plate having a thickness of 30 to 40 mm under the manufacturing conditions shown in Table 2. The tensile properties, impact properties and brittle crack propagation arrest properties of these steel sheets were investigated. The results are also shown in Table 2.
【００３３】[0033]
【表１】 [Table 1]
【００３４】[0034]
【表２】 [Table 2]
【００３５】表２から明らかなように、本発明法による
鋼Ａ、B1、Ｇ、Ｈ、Ｉ、Ｊは化学成分、製造条件とも本
発明の限定範囲内であるため、強度、靱性（vTrs）およ
び脆性亀裂伝播停止特性とも良好な値を示しているが、
特に脆性亀裂伝播停止特性は−50℃で3923N/mm3/2 以上
の破壊靱性値（Ｋca）を示している。一方、比較例であ
る鋼Ｃ、Ｄ、Ｅ、Ｆは、製造条件は本発明の限定範囲内
であるが、化学成分が本発明の限定範囲から外れている
ため、破壊靱性値が低く、−50℃以下の脆性亀裂伝播停
止温度を確保することができない。As is clear from Table 2, the steels A, B1, G, H, I and J obtained by the method of the present invention have the chemical composition and the manufacturing conditions within the limits of the present invention, so that the strength and toughness (vTrs) are obtained. And the brittle crack propagation arresting properties also show good values,
Particularly, the brittle crack propagation stopping property shows a fracture toughness value (Kca) of 3923 N / mm 3/2 or more at -50 ° C. On the other hand, steels C, D, E, and F, which are comparative examples, have manufacturing conditions within the limited range of the present invention, but have low fracture toughness values because their chemical components are out of the limited range of the present invention. A brittle crack propagation stop temperature of 50 ° C or less cannot be secured.
【００３６】実施例２ 供試鋼は表１に示す鋼Ｂの鋼片を表３に示す製造条件
で、板厚35の鋼板に仕上げたものである。これらの鋼板
について、引張特性、衝撃特性および脆性亀裂伝播停止
特性を調査した。その結果を表３に併記した。Example 2 The test steel is a steel piece of steel B shown in Table 1 and finished into a steel sheet having a thickness of 35 under the production conditions shown in Table 3. The tensile properties, impact properties and brittle crack propagation arrest properties of these steel sheets were investigated. The results are shown in Table 3.
【００３７】表３に示すように、本発明の製造方法で製
造した本発明例の鋼B1は良好な強度、靱性（vTrs）およ
びＫca値が得られているが、加熱温度が高く本発明の製
造条件から外れている鋼B2は、結晶粒が大きく靱性およ
びＫca値が低下している。また、未再結晶温度域の圧下
率が小さい鋼B3は、粗大ベイナイトの混入により靱性お
よびＫca値が低下している。直接焼入れで冷却開始温度
が低い鋼B4は、引張強度が低い。逆に、直接焼入れで冷
却開始温度が高い鋼B5は、粗大ベイナイトの生成により
靱性およびＫca値が低下している。圧延完了後の直接焼
入れで冷却速度が遅い鋼B6は、強度が低い。また、直接
焼入れ後の焼戻し温度の高い鋼B7は、強度が低くなって
いる。As shown in Table 3, although the steel B1 of the present invention produced by the production method of the present invention has good strength, toughness (vTrs) and Kca value, the heating temperature is high and the steel of the present invention is high. Steel B2, which is out of the manufacturing conditions, has large crystal grains and has low toughness and Kca value. Further, in steel B3 having a small rolling reduction in the non-recrystallization temperature region, the toughness and Kca value are lowered due to the inclusion of coarse bainite. Steel B4, which has a low cooling start temperature by direct quenching, has low tensile strength. On the contrary, in steel B5 having a high cooling start temperature by direct quenching, the toughness and Kca value are lowered due to the formation of coarse bainite. Steel B6, which has a low cooling rate by direct quenching after completion of rolling, has low strength. Steel B7, which has a high tempering temperature after direct quenching, has low strength.
【００３８】焼戻し後に圧下を行った本発明例の鋼B8と
比較例の鋼B9を比較すると、本発明例の鋼B8はＫca値が
より改善されて高い値が得られているが、累積圧下率が
高い比較例の鋼B9は表面の加工硬化が大きく、靱性およ
びＫca値が低下している。Comparing the steel B8 of the present invention example subjected to reduction after tempering with the steel B9 of the comparative example, the steel B8 of the present invention example has an improved Kca value and a high value, but the cumulative reduction The steel B9 of the comparative example having a high ratio has a large work hardening on the surface, and the toughness and Kca value are lowered.
【００３９】[0039]
【表３】 [Table 3]
【００４０】[0040]
【発明の効果】以上述べたところから明らかなように、
本発明によれば−50℃以下の脆性亀裂伝播停止特性を有
する低温用厚鋼材の製造が可能となり、本発明法による
鋼材を使用することによってＬＰＧタンク等の構造物の
安全をより高めることができる。As is apparent from the above description,
INDUSTRIAL APPLICABILITY According to the present invention, it is possible to manufacture a low temperature thick steel material having a brittle crack propagation arresting property of -50 ° C or less, and by using the steel material according to the present invention, it is possible to further enhance the safety of a structure such as an LPG tank. it can.
【図面の簡単な説明】[Brief description of drawings]
【図１】鋼片加熱温度とＫca=3923N/mm3/2を示す温度と
の関係を示す図である。FIG. 1 is a diagram showing a relationship between a billet heating temperature and a temperature at which Kca = 3923 N / mm 3/2 .
【図２】直接焼入れにおける冷却開始温度とＫca=3923N
/mm3/2を示す温度との関係を示す図である。[Fig.2] Cooling start temperature and Kca = 3923N in direct quenching
It is a figure which shows the relationship with the temperature which shows / mm <3/2 >.
【図３】直接焼入れにおける冷却速度とＫca=3923N/mm
3/2を示す温度との関係を示す図である。[Fig. 3] Cooling rate in direct hardening and Kca = 3923N / mm
It is a figure which shows the relationship with the temperature which shows 3/2 .
Claims (3)
0.60％、 Mn:0.70〜2.0 ％、 Al:0.01〜0.08％、Ti:0.0
05〜0.03％、 N:0.002〜0.007 ％を含有し、残部がFeお
よび不可避的不純物からなる鋼片を、 950〜1150℃の温
度に加熱し、未再結晶温度域で累積圧下率50％以上の圧
下を行い、その後Ａr3点〜Ａr3点＋50℃の温度から、20
℃/s以上の冷却速度で 150℃以下の温度まで直接焼き入
れした後、 500℃〜Ａc1点の温度で焼戻しすることを特
徴とする−50℃以下の脆性亀裂伝播停止特性を有する低
温用厚鋼材の製造方法。1. In mass%, C: 0.03 to 0.10%, Si: 0.03 to
0.60%, Mn: 0.70 to 2.0%, Al: 0.01 to 0.08%, Ti: 0.0
A steel slab containing 05 to 0.03% and N: 0.002 to 0.007%, the balance of which is Fe and unavoidable impurities is heated to a temperature of 950 to 1150 ° C, and the cumulative rolling reduction is 50% or more in the non-recrystallization temperature range. Is carried out, and then from the temperature of Ar 3 points to Ar 3 points + 50 ° C, 20
Direct quenching at a cooling rate of ℃ / s or more to a temperature of 150 ℃ or less, followed by tempering at a temperature of 500 ℃ ~ Ac 1 point for low temperature with -50 ℃ or less brittle crack propagation stopping characteristics Manufacturing method of thick steel.
0.01〜0.05％、Ni:1.0％以下、 B:0.003％以下、 Ca:0.
0005〜0.005 ％、REM:0.0005〜0.001 ％の内から選んだ
１種または２種以上を含有する請求項１記載の−50℃以
下の脆性亀裂伝播停止特性を有する低温用厚鋼材の製造
方法。2. Further, as a chemical component, in mass%, Nb:
0.01-0.05%, Ni: 1.0% or less, B: 0.003% or less, Ca: 0.
The method for producing a thick steel material for low temperature having -50 ° C or less brittle crack propagation arresting property according to claim 1, which contains one or more selected from the group consisting of 0005 to 0.005% and REM: 0.0005 to 0.001%.
率 1〜5 ％の圧下を行う請求項１または２記載の−50℃
以下の脆性亀裂伝播停止特性を有する低温用厚鋼材の製
造方法。3. The tempering process after tempering is carried out at a temperature of 500 ° C. or lower at a cumulative rolling reduction of 1 to 5% at −50 ° C.
A method for manufacturing a thick steel material for low temperature having the following brittle crack propagation stopping characteristics.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1514395A JPH08209239A (en) | 1995-02-01 | 1995-02-01 | Production of thick steel for low temperature use having brittle fracture propagation stop characteristic at lower than-50×c |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP1514395A JPH08209239A (en) | 1995-02-01 | 1995-02-01 | Production of thick steel for low temperature use having brittle fracture propagation stop characteristic at lower than-50×c |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH08209239A true JPH08209239A (en) | 1996-08-13 |
Family
ID=11880597
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP1514395A Pending JPH08209239A (en) | 1995-02-01 | 1995-02-01 | Production of thick steel for low temperature use having brittle fracture propagation stop characteristic at lower than-50×c |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH08209239A (en) |
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