JPS61183449A - Austenitic steel having resistance to corrosion at high temperature under stuck caso4 - Google Patents

Abstract

PURPOSE:To obtain an austenitic steel having superior resistance to corrosion at high temp. under stuck CaSO4 and usable as a material for a steel pipe for the high temp. part of a fluidized bed boiler by adding >=20wt% Cr and a specified amount of one or more among Y, REM, Mg and Ca. CONSTITUTION:The composition of an austenitic steel is composed of, by weight, <=0.2% C, 1-2% Si, <=2% Mn, 20-44% Cr, 18-28% Ni, <0.1% in total of one or more among Y, REM, Mg and Ca, and the balance Fe with inevitable impurities. The composition may further contain 0.03-0.4% N and one or more among 0.05-1.5% each of Ti, Nb and Zr.

Description

【発明の詳細な説明】 （利用分野］ 本発明は耐ＣａＳＯ、付着高温腐食性オーステナイト鋼
、特に流動床ボイラーの高温部用鋼管に用いられるａａ
ｓｏ、付着下の高温腐食に対する抵抗性のすぐれたオー
ステナイト鋼に関する。Detailed Description of the Invention (Field of Application) The present invention is an austenitic steel that is resistant to CaSO, has high temperature corrosion properties, and is particularly suitable for use in steel pipes for high-temperature sections of fluidized bed boilers.
so, relates to an austenitic steel with excellent resistance to hot corrosion under deposition.

（発明の背景及び従来技術） 近年、石炭燃焼ボイラーの新しい方式として流動床ボイ
ラーが注目されている。流動床ボイラーは低品位燃料が
使用でき、流動層内の伝熱効率が高く炉内脱硫ができる
などの幾多の特徴を有し、小型産業用として世界各地で
使用されつ＼あり、近年では先進国でこのボイラーの事
集用としての開発が進められている。(Background of the Invention and Prior Art) In recent years, fluidized bed boilers have attracted attention as a new type of coal-fired boiler. Fluidized bed boilers have many features such as being able to use low-grade fuel, have high heat transfer efficiency in the fluidized bed, and can perform desulfurization in the furnace. The development of this boiler for use in collections is progressing.

流動床ボイラーでは前述の通り炉内脱硫の可能なことが
特徴の一つであるが、脱硫目的のためには石灰石やドロ
マイトが媒体として用いられる。石灰石（Ｃａ、ＯＯｓ
　）は熱分解しＯａＯとなり石炭燃焼の結果生ずる硫黄
分全下記の反応で吸収するので、石灰石全土な流動媒体
とすることにより炉より発生する硫黄分を低く抑えるこ
とができる。As mentioned above, one of the characteristics of a fluidized bed boiler is that it is capable of in-furnace desulfurization, and for the purpose of desulfurization, limestone or dolomite is used as a medium. Limestone (Ca, OOs
) thermally decomposes into OaO and absorbs all of the sulfur content produced as a result of coal combustion through the following reaction, so by using limestone as a fluid medium, the sulfur content generated from the furnace can be kept low.

ＯａＯ＋　　Ｂｏｚ　＋　　／２０２　　→０ａＳＯ４
しかし、反面この結果生成する０ａＳＯ４は流動床内伝
熱管の特に高温表面に付着し、管材として用いられる鋼
材の腐食の原因ともなることが判明してきている。これ
によって生ずる高温腐食は場合によっては厳しいもので
おり、殊に温度が５５０℃以上の高温部材では長期使用
寿命の観点からこの腐食に対する耐食性を配慮した材料
を用いなければならない。OaO+ Boz + /202 →0aSO4
However, on the other hand, it has been found that the OaSO4 produced as a result of this adheres to the particularly high-temperature surface of the heat exchanger tube in the fluidized bed and causes corrosion of the steel material used as the tube material. The high-temperature corrosion caused by this is severe in some cases, and in particular for high-temperature members at temperatures of 550° C. or higher, materials must be used that are resistant to this corrosion from the viewpoint of long service life.

一方、Ｃれまでの小型産業用ボイラーでは地域暖房など
の用途が多くあまり高温の蒸気発生には用いられていな
かった為に問題にならなかったが今後事業用として用い
られる場合には高温蒸気の発生が必要でメク、場合によ
っては６００〜６５０℃の蒸気発生に用いられる。流動
床ボイラーでは熱伝達が良好なため、伝熱管内の温度勾
配が大きく、約１００℃位の内外温麦 度差がつくと謂われておシ、管長面温度は７００〜７５
０℃にも及ぶものである。On the other hand, up until now, small industrial boilers were used for district heating and other purposes and were not used to generate very high-temperature steam, so this did not pose a problem. It is necessary to generate steam, and in some cases, it is used to generate steam at a temperature of 600 to 650°C. Because heat transfer is good in a fluidized bed boiler, there is a large temperature gradient inside the heat exchanger tubes, and it is said that there is a temperature difference between the inside and outside of about 100℃, and the temperature on the long side of the tubes is 700 to 75℃.
The temperature reaches as high as 0°C.

従って、今後の特に事業用流動床ボイラーでは高温部に
用いられる管で、Ｃａ５Ｏ，が付着し高温のため腐食が
進行することが予想されるので、このような高温腐食に
対し耐食性の良好な材料が必要とされてきている。Therefore, in the future, especially in commercial fluidized bed boilers, it is expected that the tubes used in the high-temperature section will have Ca5O attached and corrosion will progress due to the high temperature, so materials with good corrosion resistance against such high-temperature corrosion are needed. is becoming necessary.

従来、オーステナイトステンレス鋼としては本発明鋼と
成分的に重複する合金鋼が多く知られているけれども、
流動床ボイラーに用いられてＣａＳＯ４付着に基く高温
腐食に耐える効果を発揮した例は知られていない。Conventionally, as austenitic stainless steel, there are many alloy steels that are chemically overlapping with the steel of the present invention.
There is no known example in which it has been used in a fluidized bed boiler to exhibit the effect of resisting high-temperature corrosion based on CaSO4 adhesion.

従って、本発明は流動床ボイラーの高温部に適した管材
及び支持具などの構造部材用に０ａＳＯ４付着下の高温
腐食に対する抵抗性の大きな新しい鋼材を提供すること
全目的とするものである。It is therefore an object of the present invention to provide a new steel material with increased resistance to hot corrosion under OaSO4 deposits for structural members such as tubing and supports suitable for the high temperature sections of fluidized bed boilers.

（発明の構成） ＯａＳＯ４付着による高温腐食の機構は未だ充分に解明
されておらず、高ニッケル合金は抵抗性を示さず、僅カ
ＶｃＢＵＢ　５１０８．　　ＳＵＢ　５４７などのオー
ステナイト系ステンレス鋼が温度によっては相対的に耐
食性であるとの報告かめるのみであり、ＣａＳＯ４に各
種組成のオーステナイトステンレス鋼に付着させ、これ
に関し腐食試験を行なうことでその耐食性を調べた処、
腐食現象としては表面には酸化物が生成するが（場合に
よってはｃａｃｒ２ｏ４などの複酸化物が生成される）
、下地の合金内には硫化物が離散的に生ずる内部硫化層
を生じ、この内部硫化層は内部侵食を受けると非健全な
肉厚部分となシ、又異常酸化の原因ともなることからこ
の内部硫化層の生成を抑制することが重要であることが
判明した。(Structure of the Invention) The mechanism of high-temperature corrosion due to OaSO4 adhesion has not yet been fully elucidated, and high nickel alloys do not exhibit resistance and have only a small VcBUB 5108. There are only a few reports that austenitic stainless steels such as SUB 547 are relatively corrosion resistant depending on the temperature, but the corrosion resistance was investigated by attaching CaSO4 to austenitic stainless steels of various compositions and conducting corrosion tests on them. Where,
As a corrosion phenomenon, oxides are generated on the surface (in some cases, complex oxides such as cacr2o4 are generated).
In the underlying alloy, an internal sulfide layer is created in which sulfides are generated discretely, and when this internal sulfide layer undergoes internal erosion, it becomes an unhealthy thick part and can also cause abnormal oxidation. It was found that it is important to suppress the formation of an internal sulfide layer.

本発明者らはこのような現象に鑑み各種合金元素の効果
を調べる中からＹ、ＲＥＭ、ＯａＭｇ　がこの内部硫化
層の生＃：を抑制するのに効果かあシ、さらにＣａＳＯ
４付着下で生ずるＣａＳＯ４とスケールとの固相反応及
び内部硫化という大気酸化とは著しく異なる現象にはｃ
ｒが２０％以上で有　　　効になることを知見した。In view of this phenomenon, the present inventors investigated the effects of various alloying elements and found that Y, REM, and OaMg were effective in suppressing the formation of this internal sulfide layer, and CaSO
C
We found that it becomes effective when r is 20% or more.

本発明はこのような知見に基いて完成したもので、重量
でＣ≦α２０％、　Ｓｉα１へ２．０％。The present invention was completed based on such knowledge, and C≦α20% by weight, and 2.0% to Siα1.

Ｍｎ　　≦２．０％、　Ｇｒ２　（１〜２４　％、　Ｎ
ｉ１Ｂ−２８％（ただしＮ′に添加する場合は１２〜２
８％）及びＹ　、　　ＲＫＭ　、　Ｃａ　、　Ｍｇの１
株又は２種以上を合計で０．１％以下を含有し、さらに
必要に応じＮ［ＩＱ５〜（１４０％、Ｔ１．Ｎｂ、Ｚｒ
各α０５−ｊ、５チの１種又は２株以上を含有し、残部
はＦａ及び不可避的不純物よ構成る０ａＳＯ，付着下の
高温腐食に対する抵抗性のすぐれたオーステナイト鋼に
関するものである。Mn ≦2.0%, Gr2 (1~24%, N
i1B-28% (However, when added to N', 12-2
8%) and 1 of Y, RKM, Ca, Mg
strain or two or more types in a total of 0.1% or less, and if necessary, N
The steel contains one or more strains of α05-j and α05-j, and the remainder consists of Fa and unavoidable impurities such as OaSO, which is an austenitic steel with excellent resistance to high-temperature corrosion under adhesion.

本発明鋼は流動床ボイラーにおいて流動層内伝熱管に対
する材質として適切であるばかシでなく場合によっては
層内支持具は勿論、低コスト高強度の母管の外に二重管
として用いることもできるものである。The steel of the present invention is not only suitable as a material for heat exchanger tubes in the fluidized bed in fluidized bed boilers, but in some cases it can also be used not only as an intralayer support but also as a double tube in addition to a low cost and high strength main tube. It is possible.

次に本発明鋼における各種合金元素の含有量の限定理由
について述べる。Next, the reason for limiting the content of various alloying elements in the steel of the present invention will be described.

Ｃ；鋼の高温強度を確保するために有効な元素る。しか
し二重管の外管材のようＫ特に強度を必要としない場合
やＮで強化を計る場合は別として通常１０５％以上の添
加は高温強度確保上必要である。C: An element effective for ensuring high-temperature strength of steel. However, except in cases where K does not particularly require strength, such as the outer tube material of a double pipe, or where reinforcement is to be achieved with N, it is usually necessary to add 105% or more of K to ensure high-temperature strength.

Ｓｉ；鋼の脱酸全目的に［１１％以上添加するが同時に
耐食性全槽す効果もある。しかし本発明鋼では溶接性、
組織安定性を考慮し２．０％全最大とする。Si: Added in an amount of 11% or more for the purpose of deoxidizing steel, but also has the effect of improving corrosion resistance. However, the steel of the present invention has poor weldability.
Considering tissue stability, the total maximum is set at 2.0%.

Ｍｎ；脱酸、脱硫の目的で加えられ、鋼の熱間加工性を
向上するのに有用であり、又ＣａＳＯ４に起因する内部
硫化を軽減する効果を有するため多いほど好ましいけれ
ども、あまシ多量になると高温強度を害ない、かつ相安
定性に悪影響を与えるので本発明鋼では２．０％全上限
とする。Mn: It is added for the purpose of deoxidation and desulfurization, and is useful for improving the hot workability of steel. It also has the effect of reducing internal sulfidation caused by CaSO4, so it is preferable to use a large amount. Since this does not impair high-temperature strength and has an adverse effect on phase stability, the total upper limit is set at 2.0% in the steel of the present invention.

Ｃｒ：　０ａＳＯ４付着下の腐食軽減に基本的に重要な
元素であシ、その目的には最低２０％を必要とする。Ｃ
ｒは増大とともに耐食性向上効果を有するが、２４％以
上ではその効果が飽和傾向になるとともにオーステナイ
ト単相維持に要するＮｉ量が増大しかえって害が生ずる
。Cr: A fundamentally important element for reducing corrosion under 0aSO4 deposition, and requires a minimum content of 20% for that purpose. C
As r increases, it has the effect of improving corrosion resistance, but if it exceeds 24%, this effect tends to be saturated and the amount of Ni required to maintain the austenite single phase increases, which is even more harmful.

Ｎ１；オーステナイト相全維持するために必要な元素で
、Ｎ無添加鋼では１８％以上、Ｎ添加鋼では１２％以上
必要である。しかしＮｉは多すぎるとＣａＳＯ４による
腐食が急増するためＮ１は２８％を上限とする。N1: An element necessary to maintain the entire austenite phase, and is necessary in an amount of 18% or more in N-free steel and 12% or more in N-added steel. However, if too much Ni is added, corrosion due to CaSO4 will rapidly increase, so the upper limit of N1 is set at 28%.

Ｙ　、　ＲＦｉＭ　、　（４、ＭｇＳ本発明の特徴音な
す添加元素でｃｒ２ｏ３の皮膜生成を助長し、特にｃｒ
、ｏ３中に固溶したＦｅの量を減少しＣｒ　　濃度を高
める効果がア）、これがＣｒ２　ｏ３皮膜中を内部拡散
するＳの侵入を低減する。また一部Ｇｒ２　ｏ３−合金
界面に到着したＳはこれら元素によりトラップされるた
め内部硫化を軽減する効果を有する。この効果はＣｒが
２０％以上ではじめて顕著に現われるが、ｃＬ１％を超
えるとその効果の増大がなくなシ、又清浄度も害する。Y, RFiM, (4, MgS The characteristic sound of the present invention is an additive element that promotes the formation of a film of cr2o3, especially cr
, the effect of reducing the amount of solid-dissolved Fe in O3 and increasing the Cr concentration is a), which reduces the intrusion of S that diffuses internally into the Cr2 O3 film. In addition, some of the S that has arrived at the Gr2O3-alloy interface is trapped by these elements, which has the effect of reducing internal sulfidation. This effect becomes noticeable only when Cr is 20% or more, but if cL exceeds 1%, the effect does not increase and the cleanliness is also impaired.

Ｎ：鋼のオーステナイト化全助け、相安定性保持に有効
であり、又鋼の強度向上にも有効な元素であるが、Ｎは
溶解法によって異なるけれども通’ｉ［ｌｏ　１〜ａ、
０２％程度は含まれる。然し上記の効果全発揮せしめる
ためには００３％以上添加する必要が”　Ｄ　％　ｃＬ
’％以上では鋼の固溶限を超え窒化物の析出によシ延性
及び靭性に悪影響を与える。望ましくは１１〜［ｌＬ５
％であるが、ＮはＭｌ）と複合添加される場合にはさら
に強度向上効果を有し、特に高温長時間クリープ願な 強度の向上に有効１喰る。N: It is an element that is effective in helping the austenitization of steel, maintaining phase stability, and improving the strength of steel.
Approximately 0.2% is included. However, in order to fully exhibit the above effects, it is necessary to add 0.03% or more.
If it exceeds the solid solubility limit of the steel, precipitation of nitrides will adversely affect the ductility and toughness. Desirably 11~[lL5
%, but when N is added in combination with Ml), it has a further strength-improving effect, and is particularly effective in improving strength in high-temperature, long-term creep applications.

Ｎｂ；炭窒化物の析出により鋼の高温強度の向上に有効
で００５％以上添加した場合に効果全発揮し、殊ＫＮと
複合添加する場合にその効果は大となる。しかし、あま
シ多量になると析出物も粗大なものが多くなり強度向上
に効果がなくなるとともに溶接性に害を生ずるので１，
５％を上限とする。Nb: Effective in improving the high-temperature strength of steel through the precipitation of carbonitrides, and is fully effective when added in an amount of 0.05% or more, especially when added in combination with KN. However, if the amount of sludge increases, the number of coarse precipitates increases, making it ineffective in improving strength and harming weldability.1.
The upper limit is 5%.

Ｔｉ　、　Ｚｒ：Ｎｂと同様、窒炭化物析出により鋼の
強度向上に有効で、１）、添加に伴い効果を有するがあ
まり多量では鋼の清浄度全書するので１．５−以下に限
定する。望ましくはα０５〜１１５％であるが、またＮ
ｂと複合添加する場合も合計で１．５チとするのが望ま
しい。Ti, Zr: Like Nb, it is effective in improving the strength of steel through the precipitation of nitrides. 1) It has an effect as it is added, but too large a quantity will affect the cleanliness of the steel, so it should be limited to 1.5- or less. Desirably α is 05 to 115%, but N
Even when added in combination with b, it is desirable that the total amount is 1.5 h.

この他、ＭＯ、Ｗ　、　Ｖ　の３％以下、Ｃｊｕの７％
以害を生じない。なお、Ｙ　、　ＲＩＭ　、　Ｃａ　、
　Ｍｇなどの添加にはＡｔによる事前脱酸が必要であシ
、その場合通常ｌ１０１％程度は少くとも含有する。In addition, 3% or less of MO, W, V, 7% of Cju
No further harm will be caused. In addition, Y, RIM, Ca,
Addition of Mg, etc. requires prior deoxidation with At, and in that case, the content is usually at least about 101%.

また、Ｐは溶接性の点からＣ１０２％以下と少ないこと
が望ましく、８も鋼塊割れ防止、熱間加工性の改善のた
めα００５％以下と少ないことが望ましい。Further, P is desirably as low as C102% or less from the viewpoint of weldability, and 8 is desirably as low as α005% or less in order to prevent steel ingot cracking and improve hot workability.

実施例 下表に示す成分の合金＠を供試材として用いた。これら
の鋼は真空溶解にて１７ゆのインゴットとなし熱間鍛造
、熱間圧延の後、溶体化処理、冷間圧延、溶体化処理の
工程を経て５ｆｆｉＩ＋厚さに仕上げた試験材よシ試験
片全調裂し下記の試験に供した。Example An alloy @ having the components shown in the table below was used as a test material. These steels were made into 17 mm ingots by vacuum melting, and after hot forging, hot rolling, solution treatment, cold rolling, and solution treatment, the test materials were finished to a thickness of 5ffiI+. One piece was completely cracked and subjected to the following test.

流動床ボイラーではＣ！ａｓｏ４が高温部材表面に極め
て緻密に密着生成するので、その状況を模擬するため各
＆供試鋼の試験片ｆ　ＣａＳＯ４粉末中に埋没する方法
で行なった。即ち試験片（形状；　２．５　（ｔ）　Ｘ
　１０　（ｗ）　Ｘ　５０　（１）瓢、表面仕上：＋５
２０番エメリーペーパー）１−１３１０鋼で作成した円
筒容器（５０φ（より）Ｘ２５０（ｈ）１−＝）内にま
ず０ａＳ０４に少量装入し、これに上記試験片全挿入し
、さらにそれをカバーするようにＣａＳＯ４を装入し、
これを繰返して容器一杯となしネジ蓋を閉め込み、容器
全体音電気炉内にて７００℃及び８００℃で５００時間
加熱した。C in a fluidized bed boiler! Since aso4 forms in extremely close contact with the surface of a high-temperature member, in order to simulate this situation, a method was used in which the test piece f of each sample steel was buried in CaSO4 powder. That is, the test piece (shape; 2.5 (t)
10 (w) X 50 (1) Gourd, surface finish: +5
First, a small amount of 0aS04 was charged into a cylindrical container (50φ (more) Charge CaSO4 so that
This process was repeated until the container was full, and the screw cap was closed, and the entire container was heated at 700° C. and 800° C. for 500 hours in a sonic electric furnace.

試験後は腐食減量から表面スケーリングによる減肉を測
定するとともに断面の光学顕微鏡観察を行ない、内部硫
化深さを測定し、合計のｔ’を腐食侵食量として求め評
価基準とした。After the test, the thickness reduction due to surface scaling was measured from the corrosion weight loss, the cross section was observed with an optical microscope, the internal sulfidation depth was measured, and the total t' was determined as the amount of corrosion erosion and was used as the evaluation standard.

結果を下表に併記するが、これよりＹ、ＲＩＭ。The results are also listed in the table below, but from this Y, RIM.

ｃａ　、　Ｍｇ　　の添加効果は明らかで本発明鋼の耐
食性改善効果の著しいことがわかる。The effects of adding ca and Mg are clear, and it can be seen that the corrosion resistance of the steel of the present invention is significantly improved.

Claims (4)

【特許請求の範囲】[Claims] （１）重量で、Ｃ≦０．２０％、Ｓｉ０．１〜２．０％
、Ｍｎ≦２．０％、Ｃｒ２０〜２４％、Ｎｉ１８〜２８
％及びＹ、ＲＥＭ、Ｍｇ、Ｃａの１種又は２種以上を合
計で０．１％以下含有し、残部は実質的にＦｅより成る
ことを特徴とするＣａＳＯ＿４付着下の高温腐食に対す
る抵抗性のすぐれたオーステナイト鋼。(1) By weight, C≦0.20%, Si0.1-2.0%
, Mn≦2.0%, Cr20-24%, Ni18-28
% and one or more of Y, REM, Mg, and Ca in a total of 0.1% or less, with the remainder consisting essentially of Fe. Superior austenitic steel. （２）重量で、Ｃ≦０．２０％、Ｓｉ０．１〜２．０％
、Ｍｎ≦２．０％、Ｃｒ２０〜２４％、Ｎｉ１８〜２８
％（ただしＮを添加する場合１２〜２８％）及びＹ、Ｒ
ＥＭ、Ｍｇ、Ｃａの１種又は２種以上を合計で０．１％
以下、並びにＮ０．０３〜０．４０％、Ｔｉ、Ｎｂ、Ｚ
ｒ各０．０５〜１．５％の１種又は２種以上を含有し、
残部は実質的にＦｅより成ることを特徴とするＣａＳＯ
＿４付着下の高温腐食に対する抵抗性のすぐれたオース
テナイト鋼。(2) By weight, C≦0.20%, Si0.1-2.0%
, Mn≦2.0%, Cr20-24%, Ni18-28
% (12 to 28% if N is added) and Y, R
0.1% in total of one or more of EM, Mg, and Ca
The following, and N0.03-0.40%, Ti, Nb, Z
r Containing 0.05 to 1.5% of one or more types,
CaSO characterized in that the remainder consists essentially of Fe.
_4 Austenitic steel with excellent resistance to high temperature corrosion under adhesion. （３）Ｍｏ、Ｗ、Ｖ各≦３％、Ｃｕ≦７％、Ａｌ≦０．
５％、Ｂ≦０．０１％の１種又は２種以上を含有する特
許請求の範囲第（１）及び（２）項の何れか１項記載の
オーステナイト鋼。(3) Mo, W, V each ≦3%, Cu≦7%, Al≦0.
5%, and one or more types of B≦0.01%. （４）Ｐ、ＳはＰ≦０．０２％、Ｓ≦０．００５％含有
する特許請求の範囲第（１）乃至（３）項の何れか１項
記載のオーステナイト鋼。(4) The austenitic steel according to any one of claims (1) to (3), wherein P and S are contained in an amount of P≦0.02% and S≦0.005%.