JPH0152465B2

JPH0152465B2 -

Info

Publication number: JPH0152465B2
Application number: JP55097568A
Authority: JP
Inventors: Yoshiatsu Sawaragi; Kunihiko Yoshikawa; Hiroshi Teranishi; Yasutaka Okada
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 1980-07-18
Filing date: 1980-07-18
Publication date: 1989-11-08
Also published as: JPS5723050A

Description

[Detailed description of the invention]

本発明は高温強度のすぐれた耐熱鋼に関する。化学工業用材料として従来使用されている
ASTM規格HK40（20Ni−25Cr鋼）は水素製造用
の改質炉管やエチレンプラントの分解炉管として
使用されているが、鋳造管であるので細径薄肉及
び長尺管の製造が難かしく、低延性、低靭性など
の問題がある。又長尺管が製造できないため、長
い配管を必要とするエチレンプラントの分解炉管
などには多数の鋳造管を溶接接合して使用してい
るのが現状であるが、高温、高圧のため溶接部か
ら浸炭が起るという問題もある。一方、鍛伸管材
料としてインコロイ800が使用されるが、高温強
度が必ずしも充分でない。従つて化学工業用機器
の安定化操業及び能率化を考慮すると小径長尺管
の製造可能な高温強度特性にすぐれている鍛伸管
材料の開発が強く望まれている。本発明は斯る要望に答えるべく、本発明者らが
鋭意研究した結果、完成したもので、前述のイン
コロイ800のような鍛伸管は細径薄肉、長尺管の
製造が可能で延性、靭性もHK40遠心鋳造管に比
較してすぐれていることに着目し、鍛伸管材料で
ありながら高温強度が従来のHK40及びインコロ
イ800よりも高くかつ加工性、溶接性などにおい
てすぐれた耐熱鋼を提供することを目的としたも
ので、高温強度改善に有効と考えられる粒界強化
元素と固溶強化元素を添加することを特徴とする
ものである。すなわち本発明はC0.10超〜0.30％、Si5％以
下、Mn10％以下、Cr23超〜35％、Ni23超〜50
％、Ti0.01〜1.5％、Al0.01〜0.6％を含み、
B0.001〜0.03％、Zr0.005〜0.05未満％の１種又は
２種を含有し、残部Fe及び不可避的不純物より
成るオーステナイトステンレス鋼か、又は上記成
分にさらにMo0.5〜3.0％を単独またはMo0.5〜
3.0％とW0.5〜6.0％とを複合（但しMo＋1/2
W0.5〜3.0％）して含有するオーステナイトステ
ンレス鋼であつて、高温強度の高い鍛伸管材料で
ある。次に本発明の成分組成を限定した理由を詳細に
説明する。Ｃ：Ｃは耐熱鋼として必要な引張強さ及びクリ
ーブ被断強度を向上させるのに有効な元素で、
0.10％を超える量が必要であるが、0.30％を超え
ると固溶化処理状態で未固溶の炭化物が残存し高
温強度に寄与しなくなる。 Si：Siは脱酸剤として必要であり、又耐酸化性
を高めるためにも有効な元素であるが、５％を超
えると溶接性が劣化し組織も不安定にするので５
％以下とした。 Mn：Mnは脱酸及び加工性改善のために添加
するものであり、さらにオーステナイト生成元素
であることからNiの一部をMnで置き換えること
もできるが、過剰添加すると耐熱特性が劣化する
ので10％以下にするのが望ましい。 Cr：Crは高温強度及び耐酸化性の改善にすぐ
れた効果を示すが、23％以下では耐酸化性が劣
り、また35％を超えると加工性が劣化し安定した
完全なオーステナイト相を得ることが困難となる
ので23超〜35％とした。 Ni：NiはCr量に応じて安定した完全オーステ
ナイト相を得るために必要な元素であり、23超〜
50％のNi量が必要である。 Ti，Al：Ti及びAlは極く微量の添加でも高温
強度及び延性、靭性の改善に大きく寄与するもの
であるが、いずれも0.01％未満ではその効果が得
られず、又はTiは1.5％を、またAlは0.6％を超え
ると加工性や溶接性が劣化する。Ｂ，Zr：Ｂ及びZrはいずれも粒界を強化し、
高温強度特性を改善するのに有効な元素である
が、B0.001％未満、Zr0.005％未満ではその効果
が得られず、又Ｂは0.03％を超えると、またZrは
0.05％以上となると溶接性が劣化するので、夫々
0.001〜0.03％、0.005〜0.05未満％とする。 Mo，Ｗ：Moはいずれも固溶強化元素として
高温強度向上に有効であるが、その効果を発揮さ
せるためには少くともMoを0.5％以上含有せしめ
ることが必要である。しかし過剰添加すると加工
性が劣化し、かつ組織を不安定にするので上限は
3.0％とするが、Ｗもまた固溶強化元素として高
温強度向上に有効であるので0.5〜6.0％の範囲内
で複合して含有せしめることができ、Mo＋1/2
Ｗで0.5〜3.0％に制限する必要がある。次に本発明の実施例を示す。下記第１表に供試材の化学成分を示す。従来鋼としてのHK40は遠心鋳造管であり、イ
ンコロイ800は鍛伸材である。No.１〜10鋼は比較
鋼、No.Ａ〜Ｐ鋼は本発明鋼であるが、これらはい
ずれも25Kg鋼塊を大気溶製して15mm厚に鍛造し、
さらに冷間圧延を行ない10mm厚の冷延鋼板とした
後1250℃×30分水冷の固溶化処理を施したもので
ある。これらの供試材について1000℃でのクリープ破
断試験を行ない、直線内挿法を用いて1000℃、
1000hrでのクリープ破断強度を求めた、その結果
を下記第２表に示す。比較鋼としてのNo.１〜10鋼についてみると、
Ti，Alを含有するNo.３〜10鋼のクリープ破断強
度はTi，Alを含有しないNo.１〜２鋼より高いが、
従来鋼のHK40より低強度である。これに対して
本発明鋼のNo.Ａ〜Ｇ鋼のようにさらにＢを単独添
加したもの、或はNo.Ｈ〜Ｉ鋼のようにZrを単独
添加したものでは破断強度が改善され、HK40よ
り高強度を示している。又No.Ｊ〜Ｍ鋼のようにＢ
とZrを複合添加させることにより強度は一層改
善することができる。さらに固溶強化元素として
有効なMo，Ｗを添加したNo.Ｎ〜Ｐ鋼においては
HK40に比較して25〜40％も破断強度が改善され
ているのが明らかである。又下記第３表には900℃、1000℃で1000hr時効
後の常温シヤルピー衝撃試験結果を示したが、こ
れにより本発明のＡ〜Ｐ鋼の時効後靭性はHK40
遠心鋳造管より著しくすぐれていることがわか
る。また、これら本発明鋼にNbを添加すると、
500時間以下の短時間クリープ破断強度は改善さ
れる効果が認められたが第２表の本発明鋼Ｆと比
較鋼９および本発明鋼10と比較鋼10との比較で明
らかなようにNbを添加した比較鋼はクリープ破
断強度の安定性に劣り、1000時間クリープ破断強
度はNbを含有しない本発明鋼より著しく低下し
ている。かつ第３表に示すように時効処理後の靭
性低下も大きいことがわかる。 The present invention relates to heat-resistant steel with excellent high-temperature strength. Traditionally used as a material for the chemical industry
ASTM standard HK40 (20Ni-25Cr steel) is used as reforming furnace tubes for hydrogen production and cracking furnace tubes in ethylene plants, but since it is a cast tube, it is difficult to manufacture small diameter thin walled and long tubes. There are problems such as low ductility and low toughness. In addition, since long pipes cannot be manufactured, many cast pipes are currently used by welding together for cracking furnace tubes in ethylene plants, etc., which require long pipes. There is also the problem that carburization occurs from some parts. On the other hand, Incoloy 800 is used as a forged pipe material, but its high temperature strength is not necessarily sufficient. Therefore, in consideration of the stable operation and efficiency of chemical industry equipment, there is a strong desire to develop a forged pipe material with excellent high-temperature strength properties that can be used to manufacture small-diameter long pipes. The present invention was completed as a result of intensive research by the present inventors in order to meet such demands.Forged and drawn tubes such as the above-mentioned Incoloy 800 can be manufactured into long tubes with small diameters and thin walls, and have excellent ductility and Focusing on its superior toughness compared to HK40 centrifugally cast pipe, we developed a heat-resistant steel that is a forged pipe material but has higher high-temperature strength than conventional HK40 and Incoloy 800, and has excellent workability and weldability. It is characterized by the addition of grain boundary strengthening elements and solid solution strengthening elements that are considered effective in improving high-temperature strength. That is, the present invention uses C0.10 to 0.30%, Si5% or less, Mn10% or less, Cr23 to 35%, Ni23 to 50%.
%, including Ti0.01~1.5%, Al0.01~0.6%,
Austenitic stainless steel containing one or two of B0.001~0.03%, Zr0.005~less than 0.05%, and the balance consisting of Fe and unavoidable impurities, or the above components and Mo0.5~3.0% alone. or Mo0.5~
Composite of 3.0% and W0.5~6.0% (however, Mo + 1/2
It is an austenitic stainless steel containing W0.5-3.0%) and is a forged and drawn pipe material with high high temperature strength. Next, the reason for limiting the component composition of the present invention will be explained in detail. C: C is an effective element for improving the tensile strength and cleave breaking strength necessary for heat-resistant steel.
An amount exceeding 0.10% is required, but if it exceeds 0.30%, undissolved carbides remain in the solution treatment state and do not contribute to high-temperature strength. Si: Si is necessary as a deoxidizing agent and is also an effective element for increasing oxidation resistance, but if it exceeds 5%, weldability deteriorates and the structure becomes unstable.
% or less. Mn: Mn is added to deoxidize and improve workability, and since it is an austenite-forming element, part of Ni can be replaced with Mn, but if added excessively, the heat resistance properties will deteriorate. It is desirable to keep it below %. Cr: Cr shows excellent effects in improving high temperature strength and oxidation resistance, but if it is less than 23%, oxidation resistance is poor, and if it exceeds 35%, workability deteriorates and it is difficult to obtain a stable complete austenite phase. Since this would be difficult, it was set at over 23 to 35%. Ni: Ni is an element necessary to obtain a stable complete austenite phase depending on the amount of Cr, and is more than 23~
50% Ni content is required. Ti, Al: Even when added in extremely small amounts, Ti and Al contribute significantly to improving high-temperature strength, ductility, and toughness. However, if they are less than 0.01%, the effect cannot be obtained, or if Ti is added at 1.5%. Also, if Al exceeds 0.6%, workability and weldability will deteriorate. B, Zr: Both B and Zr strengthen grain boundaries,
Although it is an effective element for improving high-temperature strength properties, the effect cannot be obtained if B is less than 0.001% and Zr is less than 0.005%, and if B exceeds 0.03%, and Zr
If it exceeds 0.05%, weldability deteriorates, so each
0.001-0.03%, 0.005-less than 0.05%. Mo, W: Both Mo are effective as solid solution strengthening elements in improving high-temperature strength, but in order to exhibit their effects, it is necessary to contain at least 0.5% Mo. However, excessive addition deteriorates workability and makes the structure unstable, so the upper limit is
3.0%, but since W is also effective as a solid solution strengthening element in improving high temperature strength, it can be contained in combination within the range of 0.5 to 6.0%, and Mo + 1/2
W must be limited to 0.5 to 3.0%. Next, examples of the present invention will be shown. Table 1 below shows the chemical components of the test materials. HK40, a conventional steel, is a centrifugally cast tube, and Incoloy 800 is a forged and drawn material. No. 1 to 10 steels are comparative steels, and No. A to P steels are inventive steels. Both of these are made by atmospheric melting of 25 kg steel ingots and forged to a thickness of 15 mm.
Further cold rolling was performed to obtain a cold rolled steel sheet with a thickness of 10 mm, which was then subjected to a solution treatment of water cooling at 1250°C for 30 minutes. A creep rupture test was conducted on these test materials at 1000°C using a linear interpolation method.
The creep rupture strength at 1000 hours was determined and the results are shown in Table 2 below. Looking at No. 1 to 10 steels as comparison steels,
The creep rupture strength of No. 3 to 10 steels containing Ti and Al is higher than that of No. 1 to 2 steels that do not contain Ti and Al, but
It has lower strength than the conventional steel HK40. On the other hand, in the steels of the present invention, such as No. A to G steels, in which B is added alone, or in the steels, such as No. H to I, in which Zr is added alone, the breaking strength is improved, and HK40 It shows higher strength. Also No. J~M steel like B
The strength can be further improved by adding Zr and Zr in combination. Furthermore, in No. NP to P steels containing Mo and W, which are effective solid solution strengthening elements,
It is clear that the breaking strength is improved by 25-40% compared to HK40. In addition, Table 3 below shows the results of a normal temperature Charpy impact test after aging at 900℃ and 1000℃ for 1000 hours.
It can be seen that this is significantly superior to centrifugally cast tubes. Furthermore, when Nb is added to these inventive steels,
Although the short-term creep rupture strength of 500 hours or less was recognized to be improved, as is clear from the comparisons between inventive steel F and comparative steel 9 and inventive steel 10 and comparative steel 10 in Table 2, Nb The comparative steel with added Nb has inferior stability in creep rupture strength, and the 1000 hour creep rupture strength is significantly lower than that of the invention steel that does not contain Nb. Moreover, as shown in Table 3, it can be seen that the toughness decreases significantly after aging treatment.

【表】【table】

【表】以上より明らかなように本発明によれば、従来
のHK40遠心鋳造管より高い高温強度が得られ、
延性、靭性も良好であり、かつ細経薄肉、長尺管
の製造が可能な耐熱鋼を提供することができる。[Table] As is clear from the above, according to the present invention, higher high temperature strength can be obtained than the conventional HK40 centrifugally cast pipe,
It is possible to provide a heat-resistant steel that has good ductility and toughness and can be manufactured into thin, thin-walled, long tubes.

Claims

[Claims] 1. More than 0.10 to 0.30% of C, 5% or less of Si, 10% or less of Mn,
Over Cr23~35%, Over Ni23~50%, Ti0.01~1.5%,
Contains Al0.01~0.6%, B0.001~0.03%, Zr0.005
- Contains less than 0.05% of one or two types, the remainder being Fe
A heat-resistant steel with excellent high-temperature strength and consisting of unavoidable impurities. 2 C over 0.10 ~ 0.30%, Si 5% or less, Mn 10% or less,
Over Cr23~35%, Over Ni23~50%, Ti0.01~1.5%,
Contains Al0.01~0.6%, B0.001~0.03%, Zr0.005
- Contains less than 0.05% of one or two types, and further
Mo0.5~3.0% alone or Mo0.5~30% and W0.5
A heat-resistant steel with excellent high-temperature strength, containing ~6.0% (Mo+1/2W0.5~3.0%), and the remainder consisting of Fe and unavoidable impurities.