JPH0874000A - Stainless steel used at high temperature and in high concentration sulfuric acid, excellent in intergranular corrosion resistance and ductility, and its production - Google Patents
Stainless steel used at high temperature and in high concentration sulfuric acid, excellent in intergranular corrosion resistance and ductility, and its productionInfo
- Publication number
- JPH0874000A JPH0874000A JP20561994A JP20561994A JPH0874000A JP H0874000 A JPH0874000 A JP H0874000A JP 20561994 A JP20561994 A JP 20561994A JP 20561994 A JP20561994 A JP 20561994A JP H0874000 A JPH0874000 A JP H0874000A
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- sulfuric acid
- corrosion resistance
- stainless steel
- content
- ductility
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Abstract
Description
【0001】[0001]
【産業上の利用分野】この発明は、硫酸製造プラントの
乾燥塔、吸収塔等の大型装置材料として利用できる、溶
接熱影響部の高温高濃度硫酸中における耐粒界腐食性、
ならびに延性に優れた高Si含有ステンレス鋼及びその
製造方法に関するものである。BACKGROUND OF THE INVENTION The present invention relates to intergranular corrosion resistance of welding heat-affected zone in high-temperature, high-concentration sulfuric acid, which can be used as a large-scale material for drying towers, absorption towers, etc. of sulfuric acid production plants.
The present invention also relates to a high Si-containing stainless steel having excellent ductility and a method for manufacturing the same.
【0002】[0002]
【従来の技術】接触式硫酸製造法で重要となる吸収、乾
燥、冷却工程において、装置材料は一般的に、濃度95
〜99%、温度65〜120℃の硫酸環境に曝される。
中でも吸収塔、乾燥塔本体には、従来、耐酸レンガを内
張りした炭素鋼板が使用されているが、長時間使用する
とレンガの目地より硫酸が浸透し、外側の炭素鋼が腐食
される問題がある。2. Description of the Related Art In the absorption, drying and cooling steps which are important in the catalytic sulfuric acid production method, the equipment material generally has a concentration of 95%.
Exposed to sulfuric acid environment of ~ 99%, temperature 65-120 ° C.
Among them, the absorption tower, the main body of the drying tower is conventionally used carbon steel sheet lined with acid-resistant brick, but when used for a long time sulfuric acid penetrates from the joints of the brick, and there is a problem that the outer carbon steel is corroded. .
【0003】上記のような大型の溶接構造材料には、ス
テンレス鋼や高Ni合金の適用が望ましいが、SUS3
16L等の汎用ステンレスでは上記環境に耐えず、ま
た、UNS N10276等の高Ni合金でも100℃
以上の温度では使用できない。従って、このような腐食
環境での使用を目的としたステンレス鋼として、特開昭
52−4418号公報ではSi含有量を高めたステンレ
ス鋼が開示されている。It is desirable to use stainless steel or a high Ni alloy as the large-scale welded structural material as described above.
General-purpose stainless steel such as 16L does not withstand the above environment, and even high Ni alloys such as UNS N10276 have a temperature of 100 ° C.
It cannot be used at higher temperatures. Therefore, as a stainless steel intended for use in such a corrosive environment, Japanese Patent Application Laid-Open No. 54-2418 discloses a stainless steel having a high Si content.
【0004】しかし、乾燥塔の操業環境は一般に濃度9
5%、温度65℃程度の硫酸中であるが、部位によって
は100℃程度まで温度が上昇することもある。また、
98%硫酸環境である吸収塔は、現状100〜120℃
で操業されているが、温度を上げることにより操業効率
の向上を図ることが可能となるため、150℃以上での
使用に耐える材料が必要とされている。However, the operating environment of the drying tower is generally 9
Although it is in 5% sulfuric acid at a temperature of about 65 ° C, the temperature may rise up to about 100 ° C depending on the site. Also,
The absorption tower which is a 98% sulfuric acid environment is currently 100-120 ° C.
However, since it is possible to improve the operation efficiency by increasing the temperature, a material that can be used at 150 ° C or higher is required.
【0005】このため、発明者の一部らは98%硫酸中
において220℃まで良好な耐食性が得られるステンレ
ス鋼として、Pd、あるいはWを添加した高Si含有ス
テンレス鋼を特開平5−78790号公報及び特開平5
−156410号公報において開示した。For this reason, some of the inventors of the present invention have disclosed a high Si content stainless steel containing Pd or W as a stainless steel having good corrosion resistance up to 220 ° C. in 98% sulfuric acid. Publication and JP-A-5
-156410.
【0006】また、高Si含有ステンレス鋼は脆化相が
生成しやすく熱間加工性に劣るため、鋼板などの製造が
困難であった。しかし、発明者の一部らは特開平6−9
3388号公報において、Cr,Mo,Si及びNi含
有量、ならびに熱間加工前の均熱温度を適正化する方法
により熱間加工での製造を容易とした。Further, since the high Si content stainless steel is apt to form an embrittlement phase and is inferior in hot workability, it is difficult to manufacture a steel sheet or the like. However, some of the inventors of the present invention disclosed in Japanese Patent Laid-Open No. 6-9
In Japanese Patent No. 3388, manufacturing by hot working was facilitated by a method of optimizing Cr, Mo, Si and Ni contents, and a soaking temperature before hot working.
【0007】[0007]
【発明が解決しようとする課題】しかし、上記従来技術
による高Si含有オーステナイト系ステンレス鋼は、い
ずれも溶接により熱影響部(以下、HAZと呼ぶ)の結
晶粒界に硬質の金属間化合物が析出し、高温高濃度硫酸
中において粒界腐食を生じるとともに、曲げ加工性も劣
化する場合がある。この場合、HAZ特性の改善を目的
とした溶接後熱処理が必要となるが、乾燥塔、吸収塔本
体等の大型の溶接構造物では溶接後熱処理が困難である
ため適用上問題がある。However, in any of the above-mentioned conventional high Si-containing austenitic stainless steels, a hard intermetallic compound is precipitated at the grain boundaries of the heat-affected zone (hereinafter referred to as HAZ) by welding. However, intergranular corrosion may occur in high-temperature, high-concentration sulfuric acid, and bending workability may deteriorate. In this case, a post-weld heat treatment is required for the purpose of improving the HAZ characteristics, but there is a problem in application because the post-weld heat treatment is difficult for a large welded structure such as a drying tower or an absorption tower main body.
【0008】この発明は上記のような従来技術における
問題を解決するためになされたもので、高Si含有ステ
ンレス鋼の成分範囲及び製造条件を規定することによ
り、95%硫酸中においては65℃以上、98%硫酸中
では150℃以上の環境で使用する溶接構造材料として
HAZの耐粒界腐食性、延性に優れたステンレス鋼を熱
間圧延や熱間押出等により容易に得ることを目的とす
る。The present invention has been made to solve the problems in the prior art as described above, and by defining the composition range and manufacturing conditions of stainless steel with a high Si content, 65 ° C. or more in 95% sulfuric acid. The objective is to easily obtain HAZ stainless steel having excellent intergranular corrosion resistance and ductility by hot rolling or hot extrusion as a welded structural material used in an environment of 150% or higher in 98% sulfuric acid. .
【0009】[0009]
【課題を解決するための手段】上記課題は、以下に述べ
る成分限定、製造条件により解決される。The above-mentioned problems can be solved by the following component limitation and manufacturing conditions.
【0010】第1発明は、重量%で、C:0.08%以
下、Si:4.5〜7.0%、Mn:2.0%以下、N
i:8〜30%、Cr:10〜20%とFeからなり、
且つ(1)式を満たすことを特徴とする溶接熱影響部の
耐粒界腐食性、延性に優れた高温高濃度硫酸用ステンレ
ス鋼である。The first aspect of the present invention is, by weight%, C: 0.08% or less, Si: 4.5 to 7.0%, Mn: 2.0% or less, N.
i: 8 to 30%, Cr: 10 to 20% and Fe,
Further, it is a stainless steel for high-temperature high-concentration sulfuric acid excellent in intergranular corrosion resistance and ductility of a heat-affected zone of welding, which satisfies the formula (1).
【0011】 −7≦3.2 ×Cr(%)+7.7 ×Si(%)−2.7 ×Ni(%) −55×C(%)−48.7<13 …(1) 第2発明は、重量%で、C:0.08%以下、Si:
4.5〜7.0%、Mn:2.0%以下、Ni:8〜3
0%、Cr:10〜20%を含有し、さらに、Cu:
0.5〜3.0%、Mo:0.2〜2.0%、Pd:
0.005〜1.0%のいずれか1種以上を含み、且つ
(2)式を満たすことを特徴とする溶接熱影響部の耐粒
界腐食性、延性に優れた高温高濃度硫酸用ステンレス鋼
である。−7 ≦ 3.2 × Cr (%) + 7.7 × Si (%) − 2.7 × Ni (%) −55 × C (%) − 48.7 <13 (1) The second invention is in terms of weight%. , C: 0.08% or less, Si:
4.5-7.0%, Mn: 2.0% or less, Ni: 8-3
0%, Cr: 10 to 20%, and further Cu:
0.5-3.0%, Mo: 0.2-2.0%, Pd:
A stainless steel for high-temperature high-concentration sulfuric acid excellent in intergranular corrosion resistance and ductility of a heat-affected zone of welding, characterized by containing at least one of 0.005 to 1.0% and satisfying the expression (2). It is steel.
【0012】 −7≦3.2 ×Cr(%)+3.6 ×Mo(%)+7.7 ×Si(%) −2.7 ×Ni(%)−1.0 ×Cu(%)−55×C(%)−48.7<13 …(2) 第3発明は、第1または第2発明のいずれかの成分を有
する鋼塊を、(3)式を満足する温度域T(℃)に均熱
後、熱間加工することを特徴とする溶接熱影響部の耐粒
界腐食性、延性に優れた高温高濃度硫酸用ステンレス鋼
の製造方法である。−7 ≦ 3.2 × Cr (%) + 3.6 × Mo (%) + 7.7 × Si (%) −2.7 × Ni (%) − 1.0 × Cu (%) −55 × C (%) − 48.7 <13 (2) In the third invention, the steel ingot having the component of the first or second invention is soaked in a temperature range T (° C) satisfying the expression (3), and then hot working. The method for producing a stainless steel for high-temperature high-concentration sulfuric acid excellent in intergranular corrosion resistance and ductility of a heat-affected zone of welding.
【0013】 T<1470−35×Si(%)−5×Ni(%) …(3)T <1470-35 × Si (%) − 5 × Ni (%) (3)
【0014】[0014]
【作用】以下に、この発明のステンレス鋼の成分限定理
由を述べる。The reason for limiting the components of the stainless steel of the present invention will be described below.
【0015】Cは含有量が多くなると炭化物を形成し、
耐食性を劣化させるため、その上限値は0.08%とす
る。When the content of C becomes large, it forms carbides,
The upper limit is 0.08% to deteriorate the corrosion resistance.
【0016】Siは高温、高濃度硫酸中での耐食性を著
しく向上させる成分であるが、上記環境で良好な耐食性
を得るには、4.5%以上含有する必要がある。また、
7.0%を超えて添加すると、以下に述べるδc を適正
化してもHAZの粒界に金属間化合物が多量に生成し、
延性が低下する。従って、Si含有量は4.5〜7.0
%とする。Si is a component that remarkably improves the corrosion resistance in high temperature and high concentration sulfuric acid, but in order to obtain good corrosion resistance in the above environment, it is necessary to contain Si by 4.5% or more. Also,
If added in excess of 7.0%, a large amount of intermetallic compounds will be generated at the HAZ grain boundaries even if δc described below is optimized.
Ductility decreases. Therefore, the Si content is 4.5 to 7.0.
%.
【0017】Mnは脱酸作用を有する成分であり、オー
ステナイト生成元素でもある。しかし、その含有量が
2.0%を超えると耐食性が劣化する。従って、Mn含
有量の上限値は2.0%とする。Mn is a component having a deoxidizing action and is also an austenite forming element. However, if the content exceeds 2.0%, the corrosion resistance deteriorates. Therefore, the upper limit of the Mn content is 2.0%.
【0018】Niはオーステナイト組織を得るのに必須
の成分であり、含有量が8%未満ではδフェライトやマ
ルテンサイト相が多くなり、延性が低下する。また、C
r,Mo及びSi含有量の増加にともないNi含有量も
多くする必要があり、詳細は後述する。ただし、その含
有量を多くするとコスト高になるばかりでなく、後述す
る部分溶融温度が低下し、熱間加工が可能な温度範囲が
狭くなり鋼板等の製造が不可能となる。従って、その上
限値は30%とする。Ni is an essential component for obtaining an austenite structure, and if the content is less than 8%, δ ferrite and martensite phase increase and the ductility decreases. Also, C
It is necessary to increase the Ni content as the r, Mo and Si contents increase, and the details will be described later. However, if the content thereof is increased, not only the cost becomes high, but also the partial melting temperature described later is lowered, the temperature range in which hot working is possible becomes narrow, and it becomes impossible to manufacture a steel sheet or the like. Therefore, the upper limit value is 30%.
【0019】Crはステンレス鋼の一般的な耐食性に対
して最も重要な元素であり、高Si含有ステンレス鋼に
おいては、その含有量を10%以上とする必要がある。
一方、高温高濃度硫酸中での耐食性もCr含有量の増加
にともない向上するが、20%を超えると耐食性に及ぼ
す効果は飽和する。また、Cr含有量が多くなると脆化
相の析出も促進される。従って、Cr含有量は10〜2
0%とする。Cr is the most important element for the general corrosion resistance of stainless steel, and in high Si content stainless steel, its content must be 10% or more.
On the other hand, the corrosion resistance in high-temperature high-concentration sulfuric acid also improves as the Cr content increases, but if it exceeds 20%, the effect on the corrosion resistance becomes saturated. Further, when the Cr content increases, precipitation of the embrittlement phase is promoted. Therefore, the Cr content is 10 to 2
0%
【0020】Cuは高濃度硫酸中での耐食性向上に有効
な成分であり、その効果は温度が高くなるほど顕著とな
ることを発明者らは見出した。しかし、その含有量が
0.5%未満では耐食性に及ぼす効果が発揮されない。
また、3.0%を超えて添加しても耐食性に及ぼす効果
は飽和するので、Cu含有量は0.5〜3.0%とす
る。The inventors have found that Cu is an effective component for improving the corrosion resistance in high-concentration sulfuric acid, and the effect becomes more remarkable as the temperature rises. However, if the content is less than 0.5%, the effect on the corrosion resistance is not exhibited.
Further, even if added over 3.0%, the effect on the corrosion resistance is saturated, so the Cu content is made 0.5 to 3.0%.
【0021】Moは同じく高濃度硫酸中での耐食性向上
に有効な成分であり、その効果は温度が高くなるほど顕
著となることを発明者らは見出した。しかし、その含有
量が0.2%未満では耐食性に及ぼす効果が発揮されな
い。また、2.0%を超えて添加しても耐食性に及ぼす
効果は飽和し、かつ含有量の増加にともない変形抵抗の
増加や脆化相の形成が促進されるので、上限値は2.0
%とする。The inventors have found that Mo is also a component effective for improving the corrosion resistance in high-concentration sulfuric acid, and the effect becomes more remarkable as the temperature rises. However, if the content is less than 0.2%, the effect on the corrosion resistance is not exhibited. Further, even if added over 2.0%, the effect on the corrosion resistance is saturated, and the increase of the content promotes the increase of the deformation resistance and the formation of the brittle phase, so the upper limit is 2.0.
%.
【0022】Pdは同じく高濃度硫酸中での耐食性向上
に有効な成分であり、その効果は温度が高くなるほど顕
著となることを発明者らは見出した。しかし、その含有
量が0.005%未満ではその効果が発揮されず、ま
た、1.0%を超えて添加しても耐食性に及ぼす効果は
飽和し、コスト高となる。従って、Pd含有量は0.0
05〜1.0%とする。The present inventors have found that Pd is also a component effective in improving corrosion resistance in high-concentration sulfuric acid, and its effect becomes more remarkable as the temperature rises. However, if its content is less than 0.005%, its effect is not exhibited, and if it is added in excess of 1.0%, the effect on corrosion resistance is saturated and the cost becomes high. Therefore, the Pd content is 0.0
05 to 1.0%.
【0023】また、本発明者らはHAZ粒界における金
属間化合物を詳細に検討した結果、この金属間化合物は
溶接熱影響により粒界が溶融して生成した低融点のNi
−Si系化合物であり、δフェライトを含む鋼種では全
く生成しないことを見出した。そこで、δフェライトの
生成傾向と成分との関係を調査した結果、δフェライト
生成傾向は(4)式を表せるδc の値によく対応し、こ
の値が−7未満になるとHAZ粒界の金属間化合物が顕
著となり、高温高濃度硫酸中で粒界腐食を生じるととも
に、曲げ加工時に割れが発生することを見出した。一
方、δフェライト自体も熱間加工時に金属間化合物に変
態し易いため、δc の値が13以上になると鋼板等の製
造時に割れが発生する。従って、各成分の含有量は上記
の限定に加えて、(2)式を満たす範囲とする。なお、
Cu及びMoを含まない鋼では(1)式を満たす範囲で
よい。Further, as a result of detailed examination of the intermetallic compound in the HAZ grain boundary, the present inventors have found that this intermetallic compound has a low melting point Ni produced by melting of the grain boundary under the influence of welding heat.
It was found that it is a -Si compound and is not generated at all in steel types containing δ ferrite. Therefore, as a result of investigating the relationship between the formation tendency of δ-ferrite and the composition, the δ-ferrite formation tendency corresponds well to the value of δc that can express the equation (4). It was found that the compound becomes remarkable, intergranular corrosion occurs in high temperature and high concentration sulfuric acid, and cracks occur during bending. On the other hand, δ-ferrite itself is also likely to transform into an intermetallic compound during hot working, so if the value of δc becomes 13 or more, cracks will occur during the production of steel sheets and the like. Therefore, the content of each component is in the range satisfying the formula (2) in addition to the above-mentioned limitations. In addition,
In the case of steel containing neither Cu nor Mo, the range may satisfy the formula (1).
【0024】 δc =3.2 ×Cr(%)+3.6 ×Mo(%)+7.7 ×Si(%) −2.7 ×Ni(%)−1.0 ×Cu(%)−55×C(%)−48.7 …(4) −7≦3.2 ×Cr(%)+3.6 ×Mo(%)+7.7 ×Si(%) −2.7 ×Ni(%)−1.0 ×Cu(%)−55×C(%)−48.7<13 …(2) −7 ≦3.2 ×Cr(%)+7.7 ×Si(%)−2.7 ×Ni(%) −55×C(%)−48.7<13 ……(1) 次に、製造条件の限定理由を述べると、この鋼は鋼塊の
均熱温度が高すぎると粒界が部分溶融を起こし、熱間加
工中に割れを生じる。この原因も先に述べたNi−Si
系低融点化合物の形成によるものであり、本発明者ら
は、部分溶融する最低温度が(5)式で表せるTm
(℃)となることを見出した。従って、鋼塊に対する熱
間加工前の均熱条件は、(3)式を満足する温度域T
(℃)とする。Δc = 3.2 × Cr (%) + 3.6 × Mo (%) + 7.7 × Si (%)-2.7 × Ni (%)-1.0 × Cu (%)-55 × C (%)-48.7 (4) -7 ≤ 3.2 x Cr (%) + 3.6 x Mo (%) + 7.7 x Si (%) -2.7 x Ni (%) -1.0 x Cu (%) -55 x C (%) −48.7 <13 (2) −7 ≦ 3.2 × Cr (%) + 7.7 × Si (%) −2.7 × Ni (%) −55 × C (%) −48.7 <13 (1) Next For the reasons for limiting the manufacturing conditions, if the soaking temperature of the steel ingot is too high, this steel causes partial melting of grain boundaries and cracking during hot working. This cause is also caused by the Ni-Si described above.
This is due to the formation of the low melting point compound of the system, and the present inventors have found that the minimum temperature for partial melting is Tm which can be expressed by the formula (5).
It was found that the temperature was (° C). Therefore, the soaking condition before hot working of the steel ingot is the temperature range T satisfying the expression (3).
(° C).
【0025】 Tm =1470−35×Si(%)−5×Ni(%) …(5) T<1470−35×Si(%)−5×Ni(%) …(3)Tm = 1470-35 × Si (%)-5 × Ni (%) (5) T <1470-35 × Si (%)-5 × Ni (%) (3)
【0026】[0026]
【実施例】本発明によるものの具体的な実施例について
説明すると、以下の如くである。EXAMPLES Specific examples of the present invention will be described below.
【0027】実施例1 表1に示す化学成分の150kgインゴットに対して、
1050℃で5時間の均熱処理を行い、熱間引張サンプ
ルを採取した。さらに、残りのインゴットを1050℃
加熱、800℃仕上の熱間圧延により12mmt の鋼板
を製造した。この鋼板に対し1050℃の固溶化熱処理
を施し、腐食試験サンプル(3t ×40w ×40l )を
採取した。また、鋼20〜24では孔食電位測定(JI
S G0577)用サンプルも採取した。なお、硫酸腐
食試験は95%,65℃及び100℃硫酸中、ならびに
98%,150℃及び220℃硫酸中に240hr浸漬
後、腐食速度を測定した。Example 1 For a 150 kg ingot of the chemical composition shown in Table 1,
Soaking was carried out at 1050 ° C. for 5 hours to collect hot tensile samples. Furthermore, the remaining ingot is heated to 1050 ° C.
A steel plate of 12 mm t was manufactured by heating and hot rolling at 800 ° C. This steel sheet was subjected to solution heat treatment at 1050 ° C., and a corrosion test sample (3 t × 40 w × 40 l ) was taken. For steels 20 to 24, pitting potential measurement (JI
A sample for S G0577) was also collected. In the sulfuric acid corrosion test, the corrosion rate was measured after immersion in 95%, 65 ° C. and 100 ° C. sulfuric acid and 98%, 150 ° C. and 220 ° C. sulfuric acid for 240 hours.
【0028】95%,65℃及び98%,150℃硫酸
中での耐食性とSi含有量との関係を図1及び図2に示
す。なお、図中の○印はCu,Mo及びPdのいずれも
含有していない鋼(以下、Cu,Mo,Pd無添加と呼
ぶ)、●印はCu,Mo及びPdのいずれか1種以上を
第2発明の下限値以上含有した鋼(以下、Cu,Mo,
Pd添加と呼ぶ)である。図1及び図2によれば本環境
ではCu,Mo,Pdといった合金成分の添加の有無に
よらず、4.5%以上のSi含有により腐食速度が著し
く低下することがわかる。The relationship between the corrosion resistance in 95%, 65 ° C. and 98%, 150 ° C. sulfuric acid and the Si content is shown in FIGS. 1 and 2. In the figure, the circles indicate steel containing neither Cu, Mo, nor Pd (hereinafter referred to as Cu, Mo, Pd-free), and the ● symbols indicate one or more of Cu, Mo, and Pd. Steel containing more than the lower limit of the second invention (hereinafter, Cu, Mo,
It is called Pd addition). From FIGS. 1 and 2, it can be seen that in this environment, the corrosion rate is remarkably reduced by the Si content of 4.5% or more regardless of the addition of alloy components such as Cu, Mo and Pd.
【0029】95%,100℃硫酸中での耐食性及び
3.5%NaCl中での孔食電位とCr含有量との関係
を図3に示す。図3によればCr含有量が10%未満に
なると孔食電位は著しく低下し、SUS304より耐孔
食性に劣ることがわかる。また、95%,100℃硫酸
中での耐食性はCr含有量の増加にともない向上する
が、20%を超えると腐食速度は一定になることが理解
される。The relationship between the corrosion resistance in 95%, 100 ° C. sulfuric acid and the pitting potential in 3.5% NaCl and the Cr content is shown in FIG. According to FIG. 3, it can be seen that when the Cr content is less than 10%, the pitting potential is remarkably lowered, and the pitting corrosion resistance is inferior to that of SUS304. Further, it is understood that the corrosion resistance in 95% sulfuric acid at 100 ° C. is improved with the increase of the Cr content, but if it exceeds 20%, the corrosion rate becomes constant.
【0030】98%,220℃及び95%,100℃硫
酸中での耐食性とCu含有量及びMo含有量との関係を
図4及び図5に各々示すが、これら図4及び図5によれ
ばCuを0.5%以上、あるいはMoを0.2%以上添
加すると、98%,220℃及び95%,100℃硫酸
中での腐食速度は著しく低下する。しかし、その含有量
がCuでは3%、Moでは2%を超えると腐食速度は一
定になることがわかる。The relationship between the corrosion resistance and the Cu content and Mo content in 98%, 220 ° C. and 95%, 100 ° C. sulfuric acid is shown in FIGS. 4 and 5, respectively. When Cu is added by 0.5% or more or Mo is added by 0.2% or more, the corrosion rate in 98%, 220 ° C. and 95%, 100 ° C. sulfuric acid is remarkably reduced. However, it can be seen that the corrosion rate becomes constant when the content of Cu exceeds 3% and the content of Mo exceeds 2%.
【0031】98%,220℃及び95%,100℃硫
酸中での耐食性とPd含有量との関係を図6に示す。図
6によれば98%,220℃及び95%,100℃硫酸
中での腐食性は、0.005%以上のPd添加により向
上することがわかる。しかし、その含有量が1.0%を
超えると腐食速度は一定になる。The relationship between the corrosion resistance in 98%, 220 ° C. and 95%, 100 ° C. sulfuric acid and the Pd content is shown in FIG. According to FIG. 6, the corrosiveness in 98%, 220 ° C. and 95%, 100 ° C. sulfuric acid is improved by adding 0.005% or more of Pd. However, if the content exceeds 1.0%, the corrosion rate becomes constant.
【0032】インゴットの熱間引張試験により、部分溶
融して絞りが0%になる最低温度とNi及びSi含有量
との関係を図7に示す。すなわち、この図7によれば部
分溶融する最低温度は(5)式の値Tm (℃)で表せる
ことがわかる。FIG. 7 shows the relationship between the minimum temperature at which the ingot is partially melted and the drawing becomes 0% by the hot tensile test of the ingot and the Ni and Si contents. That is, according to FIG. 7, it can be seen that the minimum temperature for partial melting can be represented by the value Tm (° C.) of the equation (5).
【0033】 Tm =1470−35×Si(%)−5×Ni(%) …(5) 実施例2 表2に示す化学成分の150kgインゴットを、表3に
示す加熱温度で1hr均熱後、800℃仕上の熱間圧延
により20mmt の鋼板となした。この鋼板に1100
℃の固溶化熱処理を施した後、ノンフィラーのTIG溶
接を180A×12V×75mm/minの条件で並列
に数パス行い、溶接ビードをなした。溶接ビードのすぐ
横からHAZを含む腐食試験サンプル(2t ×15w ×
50l )を採取するとともに、ビードと直角方向に曲げ
試験片(全厚,40w )を採取した。なお、熱間圧延時
の割れの有無は目視観察し、割れが発生した鋼板は割れ
の無い部位からTIG溶接用サンプルを採取した。ま
た、硫酸腐食試験は実施例1と同一の方法で行い、HA
Zの粒界腐食の有無はミクロ観察により確認した。一
方、曲げ試験は溶接ビードを表側とし、R=2tの表曲
げを行い、HAZ粒界の割れの有無を目視とミクロ観察
により確認した。Tm = 1470-35 × Si (%)-5 × Ni (%) (5) Example 2 A 150 kg ingot of the chemical components shown in Table 2 was soaked at the heating temperature shown in Table 3 for 1 hr, A steel plate of 20 mm t was obtained by hot rolling at 800 ° C. 1100 on this steel plate
After the solution heat treatment at 0 ° C., non-filler TIG welding was performed in parallel for several passes under the condition of 180 A × 12 V × 75 mm / min to form a welding bead. Corrosion test sample (2 t x 15 w x containing HAZ from the side of the weld bead)
50 l ) and a bending test piece (total thickness, 40 w ) were collected in the direction perpendicular to the beads. It should be noted that the presence or absence of cracks during hot rolling was visually observed, and for the steel plates in which cracks occurred, samples for TIG welding were taken from the sites without cracks. The sulfuric acid corrosion test was conducted in the same manner as in Example 1, and HA
The presence or absence of intergranular corrosion of Z was confirmed by microscopic observation. On the other hand, in the bending test, with the weld bead on the front side, surface bending was performed at R = 2t, and the presence or absence of cracks at the HAZ grain boundary was confirmed by visual observation and micro observation.
【0034】上記サンプルの高温高濃度硫酸中での腐食
速度とHAZの粒界腐食の有無、及び熱間圧延時とHA
Z粒界の割れの有無を表3に併せて示す。表3によれ
ば、本発明法で製造した高Si含有ステンレス鋼は熱間
圧延時の割れの発生もなく、95%,65℃以上の硫
酸、98%,150℃以上の硫酸中で良好な耐食性を有
し、特にHAZの耐粒界腐食性、及び延性にも優れてい
ることがわかる。一方、(4)式で表せるδc の値が−
7未満の鋼ではHAZの耐粒界腐食性、延性に劣り、ま
た、δc の値が13以上の鋼や熱間圧延前の均熱温度を
Tm 以上にした場合は、圧延時に割れが発生することが
理解される。Corrosion rate of the above sample in high temperature and high concentration sulfuric acid and presence / absence of intergranular corrosion of HAZ, and during hot rolling and HA
Table 3 also shows the presence or absence of cracks at the Z grain boundaries. According to Table 3, the high Si-containing stainless steel produced by the method of the present invention is free from cracking during hot rolling, and is excellent in sulfuric acid at 95%, 65 ° C or higher and sulfuric acid at 98%, 150 ° C or higher. It can be seen that it has corrosion resistance, and particularly HAZ is also excellent in intergranular corrosion resistance and ductility. On the other hand, the value of δc that can be expressed by equation (4) is −
Steels less than 7 are inferior in HAZ intergranular corrosion resistance and ductility, and cracks occur during rolling when steels having a δc value of 13 or more and a soaking temperature before hot rolling are set to Tm or more. Be understood.
【0035】 δc =3.2 ×Cr(%)+3.6 ×Mo(%)+7.7 ×Si(%) −2.7 ×Ni(%)−1.0 ×Cu(%)−55×C(%)−48.7 …(4)Δc = 3.2 × Cr (%) + 3.6 × Mo (%) + 7.7 × Si (%)-2.7 × Ni (%)-1.0 × Cu (%)-55 × C (%)-48.7 … (4)
【0036】[0036]
【発明の効果】以上のように、この発明によれば、95
%硫酸中においては65〜100℃、98%硫酸中では
150〜220℃の環境で良好な耐食性を有し、特に、
溶接構造用材料として重要な溶接熱影響部の耐粒界腐食
性、及び延性に優れた高Si含有ステンレス鋼を熱間圧
延や熱間押出等により容易に得られる効果がある。従っ
て、硫酸製造プラントの乾燥塔、吸収塔本体等に利用で
きるステンレス鋼の提供が可能となる。As described above, according to the present invention, 95
It has good corrosion resistance in the environment of 65 to 100 ° C. in% sulfuric acid and 150 to 220 ° C. in 98% sulfuric acid.
There is an effect that a high Si content stainless steel excellent in intergranular corrosion resistance and ductility of a heat-affected zone, which is important as a material for a welded structure, can be easily obtained by hot rolling, hot extrusion, or the like. Therefore, it becomes possible to provide stainless steel that can be used for a drying tower, an absorption tower body, etc. of a sulfuric acid production plant.
【0037】[0037]
【表1】 [Table 1]
【表2】 [Table 2]
【表3】 [Table 3]
【図1】本発明の実施例1による鋼の95%,65℃硫
酸中での耐食性とSi含有量との関係を示す図。FIG. 1 is a graph showing the relationship between the corrosion resistance of steel according to Example 1 of the present invention in 95%, 65 ° C. sulfuric acid and the Si content.
【図2】実施例1による鋼の98%,150℃硫酸中で
の耐食性とSi含有量との関係を示す図。FIG. 2 is a graph showing the relationship between the corrosion resistance of steel according to Example 1 in 98% sulfuric acid at 150 ° C. and the Si content.
【図3】同じく実施例1による鋼の95%,100℃硫
酸中での耐食性及び3.5%NaCl中での孔食電位と
Cr含有量との関係を示す図。FIG. 3 is a graph showing the relationship between the corrosion resistance of 95% steel at 100 ° C. in sulfuric acid and the pitting potential in 3.5% NaCl and the Cr content of the steel according to Example 1.
【図4】実施例1による鋼の98%,220℃及び95
%,100℃硫酸中での耐食性とCu含有量との関係を
示す図。FIG. 4 98% of steel according to Example 1, 220 ° C. and 95
%, A graph showing the relationship between the corrosion resistance in 100 ° C. sulfuric acid and the Cu content.
【図5】実施例1による鋼の98%,220℃及び95
%,100℃硫酸中での耐食性とMo含有量との関係を
示す図。5: 98% of steel according to Example 1, 220 ° C. and 95
%, A diagram showing the relationship between corrosion resistance in 100 ° C. sulfuric acid and Mo content.
【図6】実施例1による鋼の98%,220℃及び95
%,100℃硫酸中での耐食性とPd含有量との関係を
示す図。FIG. 6 98% of steel according to Example 1, 220 ° C. and 95
%, A graph showing the relationship between the corrosion resistance in 100 ° C. sulfuric acid and the Pd content.
【図7】実施例1による鋼の部分溶融する最低温度とN
i及びSi含有量との関係を示す図。FIG. 7: Minimum temperature and N for partial melting of steel according to Example 1
The figure which shows the relationship with i and Si content.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 小林 泰男 東京都千代田区丸の内一丁目1番2号 日 本鋼管株式会社内 (72)発明者 江原 隆一郎 広島県広島市西区観音新町四丁目6番22号 三菱重工業株式会社広島研究所内 (72)発明者 中本 英雄 広島県広島市西区観音新町四丁目6番22号 三菱重工業株式会社広島研究所内 (72)発明者 山田 義和 広島県広島市西区観音新町四丁目6番22号 三菱重工業株式会社広島研究所内 (72)発明者 長野 肇 東京都千代田区丸の内二丁目5番1号 三 菱重工業株式会社内 (72)発明者 中村 誠 東京都千代田区丸の内二丁目5番1号 三 菱重工業株式会社内 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Kobayashi 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Ryuichiro Ehara 4-22, Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima No. Mitsubishi Heavy Industries, Ltd. Hiroshima Research Institute (72) Inventor Hideo Nakamoto 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Yoshikazu Yamada Kannon Shinmachi, Nishi-ku, Hiroshima Prefecture 4-6-22 Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Hajime Nagano 2-5-1-5 Marunouchi, Chiyoda-ku, Tokyo Sanryo Heavy Industries Co., Ltd. (72) Makoto Nakamura 2 Marunouchi, Chiyoda-ku, Tokyo 5th-1th Sanryo Heavy Industries Co., Ltd.
Claims (3)
下、Si:4.5〜7.0%、Mn:2.0%以下、N
i:8〜30%、Cr:10〜20%とFeからなり、
且つ(1)式を満たすことを特徴とする溶接熱影響部の
耐粒界腐食性及び延性に優れた高温高濃度硫酸用ステン
レス鋼。 −7 ≦3.2 ×Cr(%)+7.7 ×Si(%)−2.7 ×Ni(%) −55×C(%)−48.7<13 ……(1)1. By weight%, substantially C: 0.08% or less, Si: 4.5 to 7.0%, Mn: 2.0% or less, N
i: 8 to 30%, Cr: 10 to 20% and Fe,
Further, a stainless steel for high-temperature high-concentration sulfuric acid which is excellent in intergranular corrosion resistance and ductility of a heat-affected zone of welding, which satisfies the formula (1). −7 ≦ 3.2 × Cr (%) + 7.7 × Si (%) −2.7 × Ni (%) −55 × C (%) − 48.7 <13 …… (1)
下、Si:4.5〜7.0%、Mn:2.0%以下、N
i:8〜30%、Cr:10〜20%とFeからなり、
さらに、Cu:0.5〜3.0%、Mo:0.2〜2.
0%及びPd:0.005〜1.0%の群から選択され
た1種又は2種以上を含み、且つ(2)式を満たすこと
を特徴とする溶接熱影響部の耐粒界腐食性及び延性に優
れた高温高濃度硫酸用ステンレス鋼。 −7≦3.2 ×Cr(%)+3.6 ×Mo(%)+7.7 ×Si(%) −2.7 ×Ni(%)−1.0 ×Cu(%)−55×C(%)−48.7<13 ……(2)2. By weight%, substantially C: 0.08% or less, Si: 4.5 to 7.0%, Mn: 2.0% or less, N
i: 8 to 30%, Cr: 10 to 20% and Fe,
Further, Cu: 0.5 to 3.0%, Mo: 0.2 to 2.
0% and Pd: 0.005 to 1.0%, one or more selected from the group, and satisfying the expression (2), the intergranular corrosion resistance of the weld heat affected zone. And high-temperature, high-concentration sulfuric acid stainless steel with excellent ductility. −7 ≦ 3.2 × Cr (%) + 3.6 × Mo (%) + 7.7 × Si (%) −2.7 × Ni (%) −1.0 × Cu (%) −55 × C (%) − 48.7 <13 …… (2)
成分を有する鋼塊を、(3)式を満足する温度域T
(℃)に均熱後、熱間加工することを特徴とする溶接熱
影響部の耐粒界腐食及び延性に優れた高温高濃度硫酸用
ステンレス鋼の製造方法。 T<1470−35×Si(%)−5×Ni(%) ……(3)3. A steel ingot having the composition according to claim 1 or 2 is used in a temperature range T satisfying the expression (3).
A method for producing a stainless steel for high-temperature high-concentration sulfuric acid, which is excellent in intergranular corrosion resistance and ductility of a heat-affected zone of a weld, characterized by hot working after soaking at (° C). T <1470-35 x Si (%)-5 x Ni (%) (3)
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1141432A1 (en) * | 1998-12-17 | 2001-10-10 | Ati Properties, Inc. | Corrosion resistant austenitic stainless steel |
-
1994
- 1994-08-30 JP JP20561994A patent/JPH0874000A/en active Pending
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1141432A1 (en) * | 1998-12-17 | 2001-10-10 | Ati Properties, Inc. | Corrosion resistant austenitic stainless steel |
EP1141432A4 (en) * | 1998-12-17 | 2002-06-05 | Ati Properties Inc | Corrosion resistant austenitic stainless steel |
JP2007284799A (en) * | 1998-12-17 | 2007-11-01 | Ati Properties Inc | Corrosion-resistant austenitic stainless steel |
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