JPS61562A - Ferritic stainless steel for outer tube of double boiler tube - Google Patents

Abstract

PURPOSE:To obtain the titled ferritic stainless steel with corrosion resistance by adding specified percentages of C, Si, Mn and Cr to Fe. CONSTITUTION:The ferritic stainless steel consisting of, by weight, <=0.2% C, 1.5-4.5% Si, <=1.0% Mn, 10-25% Cr and the balance practically Fe or further, if necessary, contg. 0.03-0.2% N or 0.03-0.2% N and <=1.5% in total of one or more kinds among Nb, Ti and Zr is manufactured. The ferritic stainless steel for the outer tube of a double boiler tube having superior corrosion resistance in a low-oxygen reducing atmosphere and performance necessary for a boiler tube is obtd. at a low cost.

Description

【発明の詳細な説明】 〔産業上の利用分野〕 本発明は黒液回収ボイラ等低酸素および還元性の燃焼ガ
スに触れて使われるボイヲ二重管外管用の剛食性フェラ
イト系ステンレス鋼に関する。DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a rigid ferritic stainless steel for double outer tubes of boilers used in contact with low oxygen and reducing combustion gases such as black liquor recovery boilers.

〔従来技術〕[Prior art]

ボイラでは燃焼ガスが水管を加熱して蒸気を発生させる
。火力発電用ボイラ等では熱交換用水管の捷わシの燃焼
ガス雰囲気は、燃料の種類、運転条件、部位によって若
干異なるが、通常は酸化性雰囲気である。製紙工場等で
パルプ廃液中の薬剤を回収することを主目的とした黒液
回収ボイラでは、薬剤を回収する目的から蒸発管部は燃
焼雰囲気を還元性にする必要がある。In a boiler, combustion gases heat water pipes to generate steam. In boilers for thermal power generation, etc., the combustion gas atmosphere at the break of heat exchange water pipes varies slightly depending on the type of fuel, operating conditions, and location, but is usually an oxidizing atmosphere. In a black liquor recovery boiler whose main purpose is to recover chemicals from pulp waste liquid in a paper mill or the like, the combustion atmosphere in the evaporator tube section needs to be reduced in order to recover the chemicals.

これ等の炉に使われるボイラ管は堆積法および燃焼ガス
による腐食をうける。燃焼ガスが還元性雰囲気のときの
腐食は酸化性雰囲気での酸化主体の腐食とは異なる。す
なわち還元性雰囲気の屑食は硫化および浸炭が主体であ
シ、酸化性雰囲気下のように酸化スケールによる保護作
用が働かないので、その腐食は著るしくボイラ管を激し
く減肉式す。The boiler tubes used in these furnaces are subject to corrosion from the deposition process and the combustion gases. Corrosion when the combustion gas is in a reducing atmosphere is different from oxidizing-based corrosion in an oxidizing atmosphere. In other words, the corrosion of waste in a reducing atmosphere is mainly caused by sulfidation and carburization, and since the protective effect of oxide scale does not work as in an oxidizing atmosphere, the corrosion significantly reduces the thickness of the boiler tube.

ボイラ管として一般に要求でれる性質には、高温の使用
に耐えるための高温強度、取付加工時の曲げ加工性等が
あるが、さらに燃焼ガス腐食に対する耐食性がある。Properties generally required for boiler tubes include high-temperature strength to withstand high-temperature use, bendability during installation, and corrosion resistance against combustion gas corrosion.

〔解決しようとする問題点〕[Problem to be solved]

腐食環境に使われるボイラ管に二重管がある８一般にボ
イラ管には低炭素鋼、低合金鋼のものが以前よ！ｌｌあ
シ、燃焼ガスに耐える材料として５ＵＳ８０４（オーヌ
テナイト系１８−８ヌテンレヌ＆！１１）がある。従来
はポイフ用として、外管をＳＵＳ　８０４、内管を低炭
素鋼または低合金鋼とした二重管が使われて来た。この
二重管は酸化性の燃焼雰囲気のときは外管の耐酸化性と
内管の水および蒸気に対する耐熱、耐食性がよいので好
成績であった。またこの二重管は還元性燃焼ガスの雰囲
気に対して４　　　　　　　　も耐用するが高価である
欠点があった。それ故還元性雰囲気に削える安価な二重
管の外管材質の開発が望まれていた。Boiler tubes used in corrosive environments have double tubes 8 Generally, boiler tubes used to be made of low carbon steel or low alloy steel! As a material that can withstand combustion gas, there is 5US804 (aunutenitic 18-8 Nutenrenu&!11). Conventionally, double-walled tubes have been used for poufs, with the outer tube made of SUS 804 and the inner tube made of low carbon steel or low alloy steel. This double tube had good results in an oxidizing combustion atmosphere because the outer tube had good oxidation resistance and the inner tube had good heat resistance and corrosion resistance against water and steam. Furthermore, although this double-walled pipe can withstand up to 4 hours in the atmosphere of reducing combustion gas, it has the drawback of being expensive. Therefore, it has been desired to develop an inexpensive outer tube material for double tubes that can be cut in a reducing atmosphere.

かかる要望にこたえるため、本発明者は天険、研究の結
果還元性燃焼ガスに耐える二重管の外管材質としてフェ
ライト系ステンレス鋼が好適であることを見出した。従
来は、フェライト系ステンレス鋼は一般に耐酸化性はす
ぐれているが、高温強度が低いことから、特に高温強ｆ
ｆｋ必要としない耐熱部材として使用されていた。また
Ｓｌを添加し耐酸化性を改善したフェライト系ステンレ
ス鋼は主に耐勲、耐酸化部品（石油ヌトーブ、自動車排
ガス浄化装置）用として従来よシ公知である（特開昭５
８−２３２８号、特公昭５７−２２６７号、特公昭５９
−１７８３号）。In order to meet such demands, the inventor of the present invention conducted research and discovered that ferritic stainless steel is suitable as the material for the outer tube of a double tube that can withstand reducing combustion gas. Conventionally, ferritic stainless steels generally have excellent oxidation resistance, but because of their low high temperature strength,
It was used as a heat-resistant member that does not require fk. In addition, ferritic stainless steel with improved oxidation resistance by adding Sl has been known in the past for use mainly in resistant and oxidation-resistant parts (petroleum nutaubes, automobile exhaust gas purification equipment) (Japanese Patent Laid-Open No. 5
No. 8-2328, Special Publication No. 57-2267, Special Publication No. 1983
-1783).

しかし、これらはいずれも耐酸化性改善効果をあげるも
のであり、本発明の対象とする低酸素または還元性雰囲
気に使われる二重管外管用のものではない。すなわち、
本発明のフェライト系ステンレス鋼は低酸素で還元性の
雰囲気において腐食生成物として酸化スケールではな（
ＦｅＳを生ずるような環境で優秀な耐食性をもつ特性を
二重管の外管に利用するものである。この場合内管は通
常の低広素鋼捷たは低合金鋼等でよい。However, all of these are effective for improving oxidation resistance, and are not suitable for double-walled outer tubes used in low-oxygen or reducing atmospheres, which is the object of the present invention. That is,
The ferritic stainless steel of the present invention does not produce oxidized scale as a corrosion product in a low oxygen and reducing atmosphere.
The outer tube of the double tube utilizes its excellent corrosion resistance in environments that generate FeS. In this case, the inner tube may be made of ordinary low-element steel or low-alloy steel.

本発明はポイフ等で低酸素および還元性雰囲気下ですぐ
れた耐食性を有しかつボイラ管に要求される性能を有す
ると共に安価であることを特徴とするボイフ二重管外管
用フェライト系ヌテンレヌ鋼を提供するものである。The present invention provides a ferritic steel for use in boiler double tube outer tubes, which has excellent corrosion resistance in low oxygen and reducing atmospheres, has the performance required for boiler tubes, and is inexpensive. This is what we provide.

〔問題点を解決するための手段〕[Means for solving problems]

本発明は、Ｃ０９２％以下、５１１５〜４．５％、１血
１．０％以下、Ｃｒ１Ｏ〜２５％を含有し、でらに必要
に応じＮＯ，０８〜０．２％含有し、又は必要に応じＮ
　Ｏ，０３〜０．２％とＮＤ、Ｔｉ、Ｚｒの１種または
２種以上を合計量で１．５％以下含有し残部は笑質的に
鉄よりなるポイフ二重管外管用フェライト系ヌテンレヌ
鋼や要旨とする。The present invention contains CO92% or less, 5115 to 4.5%, 1 blood 1.0% or less, Cr1O to 25%, and optionally NO, 08 to 0.2%, or as necessary. Depending on N
A ferritic nutene for a poif double tube outer tube containing 0.03 to 0.2% and one or more of ND, Ti, and Zr in a total amount of 1.5% or less, and the remainder being iron. Steel and gist.

上記各成分の限定理由は次の通っである・Ｃ：耐食性の
点から特に限定する必要はない。しかし、二重管製造の
ための熱間加工性およびその後の冷間加工性の点で、Ｃ
が０．２％を越えると変形抵抗性が著るしく上昇するの
で０．２％以下に限定した。The reasons for limiting each of the above components are as follows: C: There is no need to specifically limit them from the viewpoint of corrosion resistance. However, in terms of hot workability and subsequent cold workability for double tube manufacturing, C
If it exceeds 0.2%, the deformation resistance increases significantly, so it is limited to 0.2% or less.

Ｓｉ　：　Ｓｉは耐食性の点できわめて有効な元素であ
り、１．５％以下ではその効果は少ない。１．５％を越
えると耐食性は改善されるが、４．５％を越えると熱間
加工性が低下するので４．５％を上限とした。Si: Si is an extremely effective element in terms of corrosion resistance, and its effect is small at 1.5% or less. If it exceeds 1.5%, corrosion resistance is improved, but if it exceeds 4.5%, hot workability deteriorates, so 4.5% is set as the upper limit.

Ｍｎ：脱酸効果があシ、清浄度を改善する効果があるこ
とから１％以下の鹿が添７Ｘｌをれる。１％を越えても
効果は改善されないので１％を上限とした。Mn: Less than 1% of deer consume 7Xl because it has a deoxidizing effect and improves cleanliness. Since the effect is not improved even if it exceeds 1%, 1% is set as the upper limit.

Ｃｒ　：　Ｃｒも耐食性の点で有効な元素で、耐食性改
善効果を示すＳｉ曾の下限を低める効果がある。Cr: Cr is also an effective element in terms of corrosion resistance, and has the effect of lowering the lower limit of Si so, which shows the effect of improving corrosion resistance.

このような顕著な効果を得るためには１０％以上のＣｒ
量が必要で、２５％を越えても顕著な効果はない。一方
熱間加工性の低下が顕著になることからＣｒ量の上限を
２５％とした。In order to obtain such a remarkable effect, 10% or more of Cr is required.
A large amount is necessary, and there is no noticeable effect even if it exceeds 25%. On the other hand, the upper limit of the Cr content was set to 25% since the deterioration of hot workability becomes significant.

Ｎ：Ｎを０．０３〜０．２％添加することにより、結晶
粒度の細粒化効果がちシ、曲げ加工後の表面肌荒れを防
止する効果がある。しかし０．２％を越えての添加は熱
間加工時の変形抵抗を著しく高めるから０．２％以下に
限定した。N: Adding 0.03 to 0.2% of N has the effect of reducing the crystal grain size and preventing surface roughness after bending. However, addition of more than 0.2% significantly increases deformation resistance during hot working, so it was limited to 0.2% or less.

Ｎ’ｌ）、　Ｔｉ、、Ｚｒ　：　Ｎ添加と複合すること
によシ、結晶粒剤粒化効果をよシ顕著となし、曲げ加工
の際の表面肌荒れを防止すると共に、酸洗の際の耐食性
改善の効果があることがらＮ’ｌ）、　Ｔｌ、ｚｒを１
種または２種以上を複合添加され得る、但し、これらの
合計量が１．５％を越えると熱間加工性の低下を大きく
することから上限を１．５％とした。N'l), Ti, Zr: By combining with N addition, it makes the crystal grain granulation effect more pronounced, prevents surface roughness during bending, and improves the roughness during pickling. Because it has the effect of improving corrosion resistance, N'l), Tl, and zr are set to 1.
A seed or a combination of two or more types may be added. However, if the total amount exceeds 1.5%, the hot workability will be greatly reduced, so the upper limit is set to 1.5%.

〔実施例〕〔Example〕

実施例１ 第１表に示す化学組成の鋼を溶製後、熱間および冷間圧
延して製作した６ｍ厚みの鋼板から機械加工により３Ｍ
厚みＸ１５Ｗ巾Ｘ１５Ｍ長さの試験片を切出した。Example 1 A 6m thick steel plate was produced by hot and cold rolling after melting steel with the chemical composition shown in Table 1.
A test piece having a thickness of 15W and a width of 15M and a length of 15M was cut out.

耐食性をしらべるため上記の試験片について次の腐食試
験を行った。腐食量として黒液回収ボイラで使用されて
いる実機スメルトを用い、試験雰囲気とシテＮ２オヨび
０．　Ｉ　ＸＨＪ　Ｓ　＋　１０％Ｈ２ガスからなる還
元雰囲気を使用した。腐食量の評価と４　　　　　　　
して脱スケール試験前後の重量減少（腐食減量ｍシ積）
を用いた。腐食結果を第２表に示す。In order to examine the corrosion resistance, the following corrosion test was conducted on the above test piece. As the amount of corrosion, actual smelt used in a black liquor recovery boiler was used, and the test atmosphere and shite N2 concentration were 0. A reducing atmosphere consisting of I XHJ S + 10% H2 gas was used. Evaluation of corrosion amount and 4
Weight loss before and after descaling test (corrosion loss m product)
was used. The corrosion results are shown in Table 2.

第　　　１　　　表 試験条件：脳食灰：笑機ヌメル）、　（Ｂ　０ｍ１ｒｙ
繍塗布）雰囲気ガス二Ｎ２又は０．１％ジ８０９＋１０
％ルＯ温度＝４００℃ 時間：２０ｈ 第２表の通り試験番号（１）〜（６）の発明鋼は試験番
号（７）（８）の比較鋼及び試験番号（９）〜αυの比
較鋼（市販鋼）に比べて還元雰囲気中の腐食減量は少な
くいずれも二重管外管として良好な耐食性が得られた。Table 1 Test conditions: Brain food ash: Shoki Numer), (B 0m1ry
Embroidery coating) Atmosphere gas 2N2 or 0.1% 809+10
% Le O temperature = 400℃ Time: 20h As shown in Table 2, the invention steels of test numbers (1) to (6) are the comparison steels of test numbers (7) and (8) and the comparative steels of test numbers (9) to αυ. Compared to (commercially available steel), the corrosion loss in a reducing atmosphere was small and good corrosion resistance was obtained in both cases as a double outer tube.

実施例２ 試験番号（２＋の発明鋼を用いて炭素鋼の二重管を試作
した。予め用意した内管用炭素鋼ビレットおよび外管用
試験番号（２）ビレットを製作し、所定の寸法に切削加
工によυ仕上げた後二重管用に組合せ、これを熱間押出
製管法にて製管し、さらに酸洗、焼鈍の後冷間抽伸およ
び仕上焼鈍し、最終製品として外管、内管の肉厚は１．
５Ｍ厚み、６履厚みで管外径は５０．１１１１であった
。Example 2 A carbon steel double pipe was prototyped using the invention steel of test number (2+). A carbon steel billet for the inner pipe prepared in advance and a test number (2) billet for the outer pipe were produced and cut to predetermined dimensions. After finishing, it is assembled into a double tube, which is then made into a tube using hot extrusion tube manufacturing method, and then pickled and annealed, followed by cold drawing and final annealing, and the final product is an outer tube and an inner tube. The wall thickness is 1.
The tube had a thickness of 5M and a thickness of 6 shoes, and the outer diameter of the tube was 50.1111.

製品のマクロおよびミクロ調査の結果密着性は良好であ
り、また２×Ｄ（管外径Ｄ）を曲げ半径とする曲げ加工
（管状試験片）の後の横断面および縦断面のマクロおよ
びミクロの金属組織調査の結果いずれもボイラ管として
良好な成績を得た。As a result of macro and micro inspection of the product, the adhesion was good, and the macro and micro cross-sectional and longitudinal cross-sections after bending (tubular specimen) using 2×D (tube outer diameter D) as the bending radius were found to be good. As a result of metallographic investigation, good results were obtained in all cases for use as boiler tubes.

〔発明の効果〕〔Effect of the invention〕

以上に説明したように本発明のフェライト系ヌデンレス
鋼はボイフ二重管外管に使用して還元性燃焼ガス腐食に
充分に耐えかつボイラ管として要求される性質を充足し
かつ安価であるのでその効果はきわめて大きい。As explained above, the ferritic slim steel of the present invention can be used for boiler double tube outer tubes, has sufficient resistance to reducing combustion gas corrosion, satisfies the properties required for boiler tubes, and is inexpensive. The effect is extremely large.

Claims (3)

【特許請求の範囲】[Claims] （１）Ｃ０．２％以下Ｓｉ１．５〜４．５％Ｍｎ１．０
％以下Ｃｒ１０〜２５％ を含有し残部は実質的に鉄よりなるボイラ二重管外管用
フェライト系ステンレス鋼。(1)C0.2% or lessSi1.5-4.5%Mn1.0
A ferritic stainless steel for boiler double outer tubes containing 10 to 25% of Cr and the remainder being substantially iron. （２）Ｃ０．２％以下Ｓｉ１．５〜４．５％Ｍｎ１．０
％以下Ｃｒ１０〜２５％ Ｎ０．０３〜０．２％ を含有し残部は実質的に鉄よりなるボイラ二重管外管用
フェライト系ステンレス鋼。(2)C0.2% or lessSi1.5-4.5%Mn1.0
A ferritic stainless steel for boiler double outer tubes containing 10 to 25% Cr and 0.03 to 0.2% N, the remainder being substantially iron. （３）Ｃ０．２％以下Ｓｉ１．５〜４．５％Ｍｎ１．０
％以下Ｃｒ１０〜２５％ Ｎ０．０３〜０．２％ を含有するほかＮｂ、Ｔｉ、Ｚｒの１種または２種以上
を合計量で１．５％以下含有し残部は実質的に鉄よりな
るボイラ二重管外管用フェライト系ステンレス鋼。(3)C0.2% or lessSi1.5-4.5%Mn1.0
% or less Cr10 to 25% N0.03 to 0.2%, and also contains one or more of Nb, Ti, and Zr in a total amount of 1.5% or less, and the balance is substantially iron. Ferritic stainless steel for double outer tube.