JP2014214348A - Ferritic stainless steel excellent in oxidation resistance and high temperature creep strength - Google Patents
Ferritic stainless steel excellent in oxidation resistance and high temperature creep strength Download PDFInfo
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- JP2014214348A JP2014214348A JP2013092808A JP2013092808A JP2014214348A JP 2014214348 A JP2014214348 A JP 2014214348A JP 2013092808 A JP2013092808 A JP 2013092808A JP 2013092808 A JP2013092808 A JP 2013092808A JP 2014214348 A JP2014214348 A JP 2014214348A
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- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 13
- 230000003647 oxidation Effects 0.000 title abstract description 43
- 238000007254 oxidation reaction Methods 0.000 title abstract description 43
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 35
- 239000010959 steel Substances 0.000 claims abstract description 35
- 229910001068 laves phase Inorganic materials 0.000 claims abstract description 31
- 229910052758 niobium Inorganic materials 0.000 claims abstract description 16
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 6
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 5
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 4
- 239000012535 impurity Substances 0.000 claims abstract description 3
- 239000000463 material Substances 0.000 description 18
- 230000000052 comparative effect Effects 0.000 description 14
- 238000011156 evaluation Methods 0.000 description 10
- 230000000694 effects Effects 0.000 description 8
- 238000001556 precipitation Methods 0.000 description 8
- 238000005728 strengthening Methods 0.000 description 8
- 230000002159 abnormal effect Effects 0.000 description 6
- 230000015572 biosynthetic process Effects 0.000 description 6
- 230000007423 decrease Effects 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- 238000000034 method Methods 0.000 description 4
- 229910000859 α-Fe Inorganic materials 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 238000009628 steelmaking Methods 0.000 description 3
- 229910001566 austenite Inorganic materials 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 229910002796 Si–Al Inorganic materials 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 239000000567 combustion gas Substances 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 238000005242 forging Methods 0.000 description 1
- 229910052735 hafnium Inorganic materials 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
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- Organic Chemistry (AREA)
- Heat Treatment Of Steel (AREA)
Abstract
Description
本発明は、レキュペレータ（復熱装置）熱交換器や他の熱収支を高める熱交換器用などの高温かつ腐食性燃焼ガス環境下において、優れた耐酸化性を有するとともに高温クリープ特性に優れたフェライト系耐熱鋼に関する。 The present invention provides a ferrite having excellent oxidation resistance and excellent high-temperature creep characteristics in a high-temperature and corrosive combustion gas environment such as for a recuperator (recuperator) heat exchanger and other heat exchangers for increasing heat balance. Related to heat resistant steel.
従来のレキュペレータにおける熱交換器では、鋼材温度は最高で約７５０℃であり、当該温度域で耐えうる鋼材として、フェライト系耐熱鋼（Ｃｒ−Ｓｉ−Ａｌ鋼）として知られているＤＩＮ規格鋼種のＸ１０ＣｒＡｌ２４などが利用されている。しかし、熱効率のさらなる向上には使用環境温度の上昇例えば８００℃以上が必要とされるが、高温環境においては酸化や腐食による鋼材の減肉量が著しいため耐高温酸化性が要求されるとともに、高温ではクリープ強度が低下し鋼材が使用時に変形してしまうため、鋼材を長寿命化させ経済性を高めるために優れた高温クリープ強度が要求される。 In a heat exchanger in a conventional recuperator, the steel material temperature is about 750 ° C. at the maximum, and as a steel material that can endure in the temperature range, a DIN standard steel class known as ferritic heat resistant steel (Cr—Si—Al steel) is used. X10CrAl24 or the like is used. However, for further improvement in thermal efficiency, an increase in the use environment temperature, for example, 800 ° C. or higher is required, but in a high temperature environment, the reduction in the thickness of the steel material due to oxidation and corrosion is significant, and high temperature oxidation resistance is required. At high temperatures, the creep strength is reduced and the steel material is deformed during use. Therefore, an excellent high temperature creep strength is required for extending the life of the steel material and improving the economy.
これに対して、耐用温度の高い鋼材としてオーステナイト系ステンレス鋼やＮｉ基合金が有用であるが、これらはＮｉなどの合金元素量が多く経済性に優れない。一方で、フェライト系ステンレス鋼はＮｉなどの合金元素量が少ないことから経済性に優れており、ＨｆやＺｒなどのようなレアメタルを添加することによって、高温でのクリープ強度を改善する方法が提案されている（例えば、特許文献１参照）。しかし、この提案方法では６５０℃におけるクリープ強度を改善した例しか示されておらず、また一般的にこれらの炭化物や窒化物生成元素による強化は、析出が速いことからより高温での強化作用は小さく、現状のレキュペレータ用熱交換器の使用環境温度を上昇させることは出来ない。またレアメタルは希少価値が高いことから、経済性を悪化させる他、原料の安定供給性に課題がある。 On the other hand, austenitic stainless steel and Ni-based alloy are useful as steel materials having a high durability temperature, but these have a large amount of alloy elements such as Ni and are not economical. On the other hand, ferritic stainless steel is economical because it has a small amount of alloy elements such as Ni, and a method for improving the creep strength at high temperatures by adding rare metals such as Hf and Zr is proposed. (For example, refer to Patent Document 1). However, in this proposed method, only an example in which the creep strength at 650 ° C. is improved is shown, and in general, strengthening by these carbides and nitride-forming elements is due to rapid precipitation, so The operating temperature of the current recuperator heat exchanger is small and cannot be raised. In addition, since rare metals have high scarcity value, there are problems in terms of stable supply of raw materials in addition to deteriorating economic efficiency.
耐高温酸化性を向上させる方法として、例えば、特許文献２ではＣｕ添加などによる手法を示している。一般的に、温度の上昇により酸化量は著しく増加することが知られているが、特許文献２では１０００℃で連続酸化試験を行った結果について示されており、これを超える温度における鋼材の耐酸化性については示されていない。また、クリープ強度が低いことは鋼材が短寿命であることを意味するが、特許文献２では鋼材の早期破損による設備トラブルや鋼材の早期交換など、経済性を悪化させるクリープ強度の特性については言及されていない。 As a method for improving the high temperature oxidation resistance, for example, Patent Document 2 shows a method by adding Cu or the like. In general, it is known that the amount of oxidation significantly increases as the temperature rises. However, Patent Document 2 shows the results of a continuous oxidation test performed at 1000 ° C., and the acid resistance of steel at temperatures exceeding this is shown. There is no indication of its chemical properties. In addition, the low creep strength means that the steel material has a short life, but Patent Document 2 mentions the characteristics of creep strength that deteriorate the economy, such as equipment trouble due to early breakage of the steel material and early replacement of the steel material. It has not been.
以上のような背景から、本発明が解決しようとする課題は、鋼材到達温度が８００℃以上の領域における高温クリープ強度へ寄与する要因を示しクリープ強度を改善するとともに、耐高温酸化性においても既存のフェライト系ステンレスと同等以上の性能を有し、特に復熱装置であるレキュペレータ用途における熱交換器の熱効率向上および長寿命化への要求を満たす、経済性に優れたフェライト系ステンレス鋼を提供することである。 From the background as described above, the problem to be solved by the present invention is to improve the creep strength by showing the factors contributing to the high temperature creep strength in the region where the steel material reaching temperature is 800 ° C. or higher, and also in the high temperature oxidation resistance. A ferritic stainless steel with excellent economic performance that meets or exceeds the same performance as other ferritic stainless steels and meets the demands for improving the heat efficiency and extending the life of heat exchangers, especially in recuperator applications as recuperators. That is.
上述の課題を解決するためには、鋼材到達温度におけるクリープ強度を向上させる（Ｆｅ、Ｃｒ、Ｓｉ）2（Ｎｂ、Ｔｉ）からなる析出強化相であるＬａｖｅｓ相を、ＮｂおよびＴｉの複合添加することによって、ＮｂあるいはＴｉ単独添加での析出強化よりも、改善させ得ることを見出し、本発明の解決するための手段を得たものである。 In order to solve the above-mentioned problems, a Laves phase, which is a precipitation strengthening phase made of (Fe, Cr, Si) 2 (Nb, Ti), which improves the creep strength at the steel material arrival temperature, is added in a composite manner by Nb and Ti. Thus, the present inventors have found that it can be improved over precipitation strengthening by adding Nb or Ti alone, and have obtained means for solving the present invention.
本発明の課題を解決するための手段は、第１の手段では、質量％で、Ｃ：０．０４％以下、Ｓｉ：０．４０〜１．２０％、Ｍｎ：０．０１〜０．４０％、Ｃｒ：１５．００〜２２．００％、Ａｌ：０．６０〜１．４０％、Ｎ：０．０３％以下、Ｎｂ：０．１０〜０．９０％、Ｔｉ：０．１０〜０．９０％を含有し、かつ、前記の範囲において、（Ｓｉ＋Ａｌ）：１．００〜２．６０％、および、４（Ｃ＋Ｎ）≦（Ｔｉ＋Ｎｂ）≦１．６０％、の関係を満足し、残部がＦｅおよび不可避的不純物からなる鋼で、鋼中におけるＬａｖｅｓ相は０．２ｖｏｌ％以上であることを特徴とするフェライト系ステンレス鋼である。 Means for solving the problems of the present invention are, in the first means, mass%, C: 0.04% or less, Si: 0.40 to 1.20%, Mn: 0.01 to 0.40. %, Cr: 15.00 to 22.00%, Al: 0.60 to 1.40%, N: 0.03% or less, Nb: 0.10 to 0.90%, Ti: 0.10 to 0 .90%, and within the above range, (Si + Al): 1.00 to 2.60%, and 4 (C + N) ≦ (Ti + Nb) ≦ 1.60%, and the balance Is a ferritic stainless steel characterized in that the Laves phase in the steel is 0.2 vol% or more.
本発明の耐高温酸化性および高温クリープ強度に優れたフェライト系ステンレス鋼からなる鋼材は、鋼材の耐用温度域および鋼材寿命を増大させることができ、したがって、鋼材減肉量が大きくなる高温環境かつ酸化性雰囲気であるレキュペレータ用熱交換器に使用することができて、工業的に極めて優れた効果を奏するものである。 The steel material made of ferritic stainless steel having excellent high-temperature oxidation resistance and high-temperature creep strength according to the present invention can increase the serviceable temperature range and life of the steel material, and therefore, the high-temperature environment in which the steel material thinning amount is increased. It can be used in a heat exchanger for a recuperator that is an oxidizing atmosphere, and has an extremely excellent industrial effect.
本発明を実施するための形態について、表を参照して、以下に順次説明する。先ず、初めに、本発明によるフェライト系ステンレス鋼の化学成分の含有量の限定理由を各成分ごとに順次説明する。なお、含有量における％は質量％である。 DESCRIPTION OF EMBODIMENTS Embodiments for carrying out the present invention will be sequentially described below with reference to tables. First, the reasons for limiting the content of chemical components of the ferritic stainless steel according to the present invention will be sequentially described for each component. In addition,% in content is the mass%.
Ｃ：０．０４％以下、Ｎ：０．０３％以下
ＣおよびＮは、高温でのクリープ強度を向上させる元素であるが、それらの含有量が多い場合には、耐酸化性および靭性が低下する。したがって、本成分系においてはＣおよびＮは低いことが望ましく、そこで、Ｃは０．０４％以下、およびＮは０．０３％以下とする。
C: 0.04% or less, N: 0.03% or less C and N are elements that improve the creep strength at high temperatures, but when their content is large, the oxidation resistance and toughness are reduced. To do. Therefore, in this component system, it is desirable that C and N are low, so that C is 0.04% or less and N is 0.03% or less.
Ｓｉ：０．４０〜１．２０％
Ｓｉは、製鋼の際に脱酸材として用いられるとともに、製造および溶接の際の溶鋼の流動性を高め、さらに耐酸化性を高めるとともにクリープ強度を向上させるＬａｖｅｓ相の形成に必要な元素で、０．４０％以上が必要である。しかし、Ｓｉ含有量が多い場合、硬さが上昇して靭性の低下および加工性の低下を招くので、１．２０％以下とする。そこで、Ｓｉは０．４０〜１．２０％とする。
Si: 0.40 to 1.20%
Si is an element necessary for the formation of a Laves phase that is used as a deoxidizer during steelmaking, increases the fluidity of the molten steel during manufacturing and welding, further improves oxidation resistance and improves creep strength, 0.40% or more is necessary. However, when the Si content is high, the hardness increases, leading to a decrease in toughness and a decrease in workability, so the content is made 1.20% or less. Therefore, Si is set to 0.40 to 1.20%.
Ｍｎ：０．０１〜０．４０％
Ｍｎは、Ｓｉと同様に製鋼の際に脱酸材として用いられるとともに、耐酸化性および耐スケール剥離性を向上させる元素であり、このためには０．０１％以上が必要である。しかし、Ｍｎの含有量が多い場合、オーステナイト相が形成されて異常酸化の起点を招くとともに、オーステナイト相は熱膨張係数がフェライト相に比較して大きいため、寸法変化が生じるおそれがあるので、０．４０％以下とする。そこで、Ｍｎは０．０１〜０．４０％とする。
Mn: 0.01-0.40%
Mn is an element that is used as a deoxidizing material during steelmaking, as is the case with Si, and also improves oxidation resistance and scale peeling resistance. For this purpose, 0.01% or more is required. However, when the content of Mn is large, an austenite phase is formed and causes abnormal oxidation, and the austenite phase has a larger thermal expansion coefficient than the ferrite phase, so there is a possibility that a dimensional change may occur. 40% or less. Therefore, Mn is set to 0.01 to 0.40%.
Ｃｒ：１５．００〜２２．００％
Ｃｒは、フェライト系ステンレス鋼の基本成分の一つでフェライト相を安定させるとともに、高温用材料として重要視される耐酸化性の改善に重要な元素である。基本的な耐酸化性を満足するために、Ｃｒは１５．００％以上含有させ、より高い効果を望む場合は、さらに含有量を増加させる。しかし、Ｃｒは２２．００％を超えて含有させると、靭性および加工性が低下するので２２．００％以下とする。そこで、Ｃｒは１５．００〜２２．００％とする。
Cr: 15.00-22.00%
Cr is one of the basic components of ferritic stainless steel and stabilizes the ferrite phase, and is an element important for improving oxidation resistance, which is regarded as important as a high-temperature material. In order to satisfy basic oxidation resistance, Cr is contained in an amount of 15.00% or more. If a higher effect is desired, the content is further increased. However, if Cr is contained in excess of 22.00%, the toughness and workability deteriorate, so the content is made 22.00% or less. Therefore, Cr is made 15.00 to 22.00%.
Ａｌ：０．６０〜１．４０％
Ａｌは、脱酸能の高い元素であり、ＳｉおよびＭｎ同様に製鋼の際に脱酸材として用いられるとともに、高温酸化性環境下で表面に緻密な酸化皮膜を形成することで耐酸化性を向上させる元素である。Ａｌは酸化皮膜を形成させ、十分な耐酸化性向上の効果を得るために０．６０％以上が必要である。しかし、Ａは１．４０％より過剰になると鋼の靭性および加工性が低下するため、Ａｌの上限を１．４０％とした。そこで、Ａｌは０．６０〜１．４０％とする。
Al: 0.60 to 1.40%
Al is an element having a high deoxidizing ability, and is used as a deoxidizing material in steel making like Si and Mn, and has a high oxidation resistance by forming a dense oxide film on the surface in a high temperature oxidizing environment. It is an element to improve. Al needs to be 0.60% or more in order to form an oxide film and obtain a sufficient effect of improving oxidation resistance. However, if A exceeds 1.40%, the toughness and workability of the steel decrease, so the upper limit of Al is 1.40%. Therefore, Al is made 0.60 to 1.40%.
Ｎｂ：０．１０〜０．９０％、Ｔｉ：０．１０〜０．９０％
ＮｂおよびＴｉは、固溶強化により高温強度を向上させる元素で、ＮｂおよびＴｉの複合添加によるＬａｖｅｓ相の形成により、その効果はより向上される。ＮｂまたはＴｉの単独添加のみではＬａｖｅｓ相の析出が困難であり、十分な高温強度向上の効果が得られないため、ＮｂおよびＴｉの複合添加が必要である。しかし、ＮｂおよびＴｉは強力な炭窒化物の形成元素であるため、これら元素が炭窒化物の形成を助長すると、固溶強化およびＬａｖｅｓ相形成による高温強度の向上の効果が得られない。そこで、Ｎｂは０．１０％以上、Ｔｉは０．１０％以上とする。しかし添加量が多く０．９０％を超える場合、炭窒化物の量が多くなりマトリックス中の固溶強化に寄与するＣおよびＮの量が減り強度の低下が生じる、あるいは多量の炭窒化物が異常酸化の起点となり耐酸化性が劣化するため、ＮｂおよびＴｉの上限を０．９０％とした。
Nb: 0.10-0.90%, Ti: 0.10-0.90%
Nb and Ti are elements that improve the high-temperature strength by solid solution strengthening, and the effect is further improved by the formation of the Laves phase by the combined addition of Nb and Ti. Precipitation of the Laves phase is difficult only by adding Nb or Ti alone, and a sufficient effect of improving high-temperature strength cannot be obtained. Therefore, a combined addition of Nb and Ti is necessary. However, since Nb and Ti are strong carbonitride forming elements, if these elements promote the formation of carbonitrides, the effect of improving the high temperature strength due to solid solution strengthening and the formation of the Laves phase cannot be obtained. Therefore, Nb is 0.10% or more and Ti is 0.10% or more. However, if the amount added exceeds 0.90%, the amount of carbonitride increases and the amount of C and N contributing to solid solution strengthening in the matrix decreases, resulting in a decrease in strength, or a large amount of carbonitride. The upper limit of Nb and Ti is set to 0.90% because the oxidation resistance deteriorates as a starting point for abnormal oxidation.
（Ｓｉ＋Ａｌ）：１．００〜２．６０％
上記したような成分組成に加えて、鋼の表面に形成される酸化皮膜の構造を一層緻密なものにし、本発明の目的を達成する耐酸化性を得るためには、（Ｓｉ＋Ａｌ）は１．００〜２．６０％の関係を満足するように、これらの元素の含有量を限定する必要がある。
(Si + Al): 1.00 to 2.60%
In addition to the above component composition, in order to make the structure of the oxide film formed on the surface of steel more dense and to obtain oxidation resistance that achieves the object of the present invention, (Si + Al) is 1. It is necessary to limit the content of these elements so as to satisfy the relationship of 00 to 2.60%.
クリープ強度を向上させるためには（Ｆｅ、Ｃｒ、Ｓｉ）2（Ｎｂ、Ｔｉ）からなる析出強化相であるＬａｖｅｓ相の形成が有効であるが、Ｌａｖｅｓ相の形成元素であるＮｂおよびＴｉはいずれも強力な炭窒化物形成元素であるため、炭窒化物形成元素が促進されるとＬａｖｅｓ相量が低減し、クリープ強度を向上させるための十分な効果が得られない。したがってＣおよびＮ含有量に対して４（Ｃ＋Ｎ）≦（Ｔｉ＋Ｎｂ）からなる関係を満足するように、これらの元素の含有量を限定する必要がある。しかし、ＴｉおよびＮｂの含有量が多くなると、Ｌａｖｅｓ相量が多くなりクリープ強度の向上に対しては望ましいが、Ｌａｖｅｓ相形成元素であるＣｒは基地成分における耐酸化性およびフェライト安定化元素であるため、Ｌａｖｅｓ相量が多くなることはすなわち基地のＣｒ含有量が低下し、基地の耐酸化性の低下を招く。したがって、（Ｔｉ＋Ｎｂ）≦１．６０％からなる関係を満足させるように含有させることが必要である。 In order to improve the creep strength, formation of the Laves phase, which is a precipitation strengthening phase made of (Fe, Cr, Si) 2 (Nb, Ti), is effective, but Nb and Ti that are elements forming the Laves phase are Since it is a strong carbonitride-forming element, when the carbonitride-forming element is promoted, the amount of the Laves phase is reduced, and a sufficient effect for improving the creep strength cannot be obtained. Therefore, it is necessary to limit the contents of these elements so as to satisfy the relationship of 4 (C + N) ≦ (Ti + Nb) with respect to the C and N contents. However, when the Ti and Nb contents increase, the amount of the Laves phase increases, which is desirable for improving the creep strength. However, Cr, which is a Laves phase forming element, is an oxidation resistance and ferrite stabilizing element in the base component. Therefore, when the amount of the Laves phase is increased, that is, the Cr content of the base is lowered, and the oxidation resistance of the base is lowered. Therefore, it is necessary to contain it so as to satisfy the relationship of (Ti + Nb) ≦ 1.60%.
本発明者らは、フェライト系ステンレス鋼のＮｂおよびＴｉ複合添加におけるＬａｖｅｓ相量とクリープ強度の関係を検討した結果、上記のような成分組成において０．２ｖｏｌ％以上のＬａｖｅｓ相が形成され、クリープ強度の向上へ寄与することを見出した。したがって、良好なクリープ強度が得られるＬａｖｅｓ相の析出状態は、０．２ｖｏｌ％以上とする。 As a result of studying the relationship between the amount of the Laves phase and the creep strength in the Nb and Ti composite addition of ferritic stainless steel, the present inventors have formed a Laves phase of 0.2 vol% or more in the above component composition, and creep. It was found that it contributes to the improvement of strength. Therefore, the precipitation state of the Laves phase that provides good creep strength is 0.2 vol% or more.
以下、本発明について実施例によって具体的に説明する。下記の表１は、Ｎｏ．１〜７の発明鋼とＮｏ．８〜１７の比較鋼についての、Ｆｅおよび不可避的不純物を除く、化学成分の各成分量を示している。この表１のＮｏ．１〜７の発明鋼と、Ｎｏ．８〜１７の比較鋼について、真空溶解炉にて各１ｋｇを溶解し、この溶鋼を鋳造してインゴットとした。次いで、このインゴットを加熱温度１０００〜１１００℃で径１５ｍｍに鍛造および圧延し、１０００〜１１００℃で３０分間保持して水冷することで焼きなましを行って、各供試材を得た。 Hereinafter, the present invention will be specifically described with reference to examples. Table 1 below shows No. Inventive steels 1 to 7 and No. 1 The amount of each of the chemical components excluding Fe and inevitable impurities is shown for comparative steels 8-17. No. 1 in Table 1 No. 1-7 invention steels, About the comparative steels 8-17, 1 kg each was melt | dissolved in the vacuum melting furnace, this molten steel was cast, and it was set as the ingot. Next, this ingot was forged and rolled to a diameter of 15 mm at a heating temperature of 1000 to 1100 ° C., held at 1000 to 1100 ° C. for 30 minutes, and then annealed to obtain each specimen.
表１に示す鋼からなる供試材を用いて、以下に記載の試験方法で、各鋼の（１）耐高温酸化性、（２）クリープ温度、（３）Ｌａｖｅｓ相量の評価およびそれらの総合評価を行い、下記の表２に示している。 Using the test materials made of steel shown in Table 1, the following test methods were used to evaluate (1) high-temperature oxidation resistance, (2) creep temperature, (3) Laves phase amount of each steel and their Comprehensive evaluation was performed and shown in Table 2 below.
（１）耐高温酸化性の評価は、カンタル炉で大気雰囲気中において１１００℃にて１００時間保持し、質量増分を測定した。質量増分を酸化量とし、１ｃｍ2当り５．００ｍｇ以下の酸化量を表２の評価で○とした。 (1) Evaluation of high-temperature oxidation resistance was carried out in an air atmosphere in a cantal furnace at 1100 ° C. for 100 hours, and the mass increment was measured. The mass increment the oxidation amount, the following oxidation amount 1 cm 2 per 5.00mg was ○ in the evaluation of Table 2.
（２）クリープ強度の評価は、試験片の平行部が径６ｍｍであるクリープ試験片をＪＩＳ Ｚ２２７１の規格に基づき作製し、８５０℃にて９．０ＭＰａの引張応力を負荷させ、破断するまでの時間を測定した。破断時間が２００時間を超えるものを表２の評価で○とした。 (2) Creep strength was evaluated by preparing a creep test piece having a parallel part of the test piece having a diameter of 6 mm based on the standard of JIS Z2271, applying a tensile stress of 9.0 MPa at 850 ° C., and breaking. Time was measured. Those with a rupture time exceeding 200 hours were evaluated as “good” in Table 2.
（３）Ｌａｖｅｓ相量は、クリープ試験終了後の試験片を電子顕微鏡で写真を撮影し、その画像解析によりＬａｖｅｓ相の析出量を算出した値である。Ｌａｖｅｓ相量の評価は０．２％以上のものを表２の評価で○とした。 (3) The amount of the Laves phase is a value obtained by taking a photograph of the test piece after completion of the creep test with an electron microscope and calculating the amount of precipitation of the Laves phase by image analysis. For the evaluation of the amount of the Laves phase, a value of 0.2% or more was evaluated as ◯ in the evaluation of Table 2.
なお、比較例のＮｏ．１０は、表１における化学成分のＣｒ含有量が２２．００％を超えて２２．５０％であるので、溶解後のインゴットの鍛造および圧延時に割れが発生して試験片を作製することができなかったので、表２において各測定値および評価は記載していない。 The comparative example No. No. 10, since the Cr content of the chemical component in Table 1 exceeds 22.00% and is 22.50%, it is possible to produce a test piece by cracking during forging and rolling of the ingot after melting. Since there was not, each measured value and evaluation are not described in Table 2.
表２に、耐高温酸化性およびクリープ強度およびＬａｖｅｓ相量の評価が○である実施例と比較例、および耐高温酸化性またはクリープ強度またはＬａｖｅｓ相量の評価が×である比較例をそれぞれ示している。これらのうち、各比較例の×の評価となったものの項目にはアンダーラインを付して示している。 Table 2 shows examples and comparative examples in which the evaluation of high-temperature oxidation resistance and creep strength and the amount of the Laves phase is ○, and comparative examples in which the evaluation of high-temperature oxidation resistance or creep strength or the amount of the Laves phase is x, respectively. ing. Among these, items that are evaluated as x in each comparative example are shown with an underline.
比較例のＮｏ．８は本発明のＣｒの下限値を逸脱しており、Ｎｏ．９は本発明のＡｌの下限値を逸脱しており、Ｎｏ．１６は本発明のＳｉの下限値を逸脱しており、これらは、表２に示すように、酸化皮膜の形成が十分ではなく耐酸化性の効果が得られず、耐高温酸化性は×である。比較例のＮｏ．１４は本発明の（Ｔｉ＋Ｎｂ）の上限値を逸脱しており、表２に示すように、異常酸化により耐酸化性が劣化し、耐高温酸化性は×である。比較例のＮｏ．１１は本発明のＭｎの上限値を逸脱しており、異常酸化により耐酸化性が劣化しており、かつ、Ｎｂは本発明の下限値を逸脱しているので、表２に示すように、Ｌａｖｅｓ相量が少なく、十分なクリープ強度が得られず×である。比較例のＮｏ．１７はＣおよびＮの本発明の各上限値を逸脱しており、かつ（Ｔｉ＋Ｎｂ）の下限を逸脱しているので、ＣおよびＮの固定が十分ではなく、表２に示すように、異常酸化により耐酸化性が劣化し、耐高温酸化性が×である。比較例のＮｏ．１２は本発明のＴｉの下限値を逸脱しており、さらにＮは本発明の上限値を逸脱しているので、Ｌａｖｅｓ相量が少なく、十分なクリープ強度が得られず、表２に示すように、クリープ強度およびＬａｖｅｓ相量が×である。比較例のＮｏ．１３はＮｂの本発明の下限値を逸脱しており、かつＴｉの単独添加と略同じ状態となっているので、Ｌａｖｅｓ相量が少なく十分なクリープ強度が得られず、表２に示すように、Ｌａｖｅｓ相量およびクリープ強度が共に×である。比較例のＮｏ．１５はＴｉの本発明の下限値を逸脱しており、かつＮｂの単独添加と略同じ状態となっているので、Ｌａｖｅｓ相量が少なく、さらに十分なクリープ強度が得られず、表２に示すように、クリープ特性およびＬａｖｅｓ相量は共に×である。以上の理由から比較鋼のＮｏ．８〜１７の総合評価は×である。 Comparative Example No. No. 8 deviates from the lower limit of Cr of the present invention. No. 9 deviates from the lower limit of Al of the present invention. No. 16 deviates from the lower limit of Si of the present invention, and as shown in Table 2, the formation of an oxide film is not sufficient and the effect of oxidation resistance is not obtained, and the high temperature oxidation resistance is x. is there. Comparative Example No. No. 14 deviates from the upper limit of (Ti + Nb) of the present invention. As shown in Table 2, the oxidation resistance deteriorates due to abnormal oxidation, and the high temperature oxidation resistance is x. Comparative Example No. 11 deviates from the upper limit value of Mn of the present invention, oxidation resistance has deteriorated due to abnormal oxidation, and Nb deviates from the lower limit value of the present invention. The amount of the Laves phase is small and sufficient creep strength cannot be obtained. Comparative Example No. No. 17 deviates from the respective upper limits of the present invention for C and N, and deviates from the lower limit of (Ti + Nb), so C and N are not sufficiently fixed. As shown in Table 2, abnormal oxidation As a result, the oxidation resistance deteriorates and the high-temperature oxidation resistance is x. Comparative Example No. No. 12 deviates from the lower limit value of Ti of the present invention, and further N deviates from the upper limit value of the present invention, so that the amount of the Laves phase is small and sufficient creep strength cannot be obtained, as shown in Table 2. Further, the creep strength and the amount of the Laves phase are x. Comparative Example No. No. 13 deviates from the lower limit of the present invention for Nb, and is in the same state as Ti alone, so the amount of the Laves phase is small and sufficient creep strength cannot be obtained, as shown in Table 2. The Laves phase amount and the creep strength are both x. Comparative Example No. No. 15 deviates from the lower limit of the present invention of Ti, and is almost in the same state as the single addition of Nb. Therefore, the amount of the Laves phase is small, and a sufficient creep strength cannot be obtained. Thus, both the creep characteristics and the Laves phase amount are x. For the above reasons, the comparative steel No. The comprehensive evaluation of 8-17 is x.
一方、表１の本発明鋼のＮｏ．１〜７のフェライト系ステンレス鋼は、化学成分の最適化によって炭窒化物析出の影響が軽減されており、表２に見られるように、Ｌａｖｅｓ相による強化を得た良好なクリープ強度が得られ、クリープ強度の評価は○であり、さらに異常酸化を抑制した良好な耐酸化性を示し、酸化増量は１ｃｍ2当り４．７１ｍｇ以下であり、耐高温酸化性の評価は○であった。したがって、本発明鋼のＮｏ．１〜７は総合評価は○である。 On the other hand, no. In the 1-7 ferritic stainless steels, the influence of carbonitride precipitation is reduced by optimization of chemical components, and as shown in Table 2, good creep strength obtained by strengthening by the Laves phase is obtained. The creep strength was evaluated as “good”, and good oxidation resistance with abnormal oxidation suppressed was exhibited. The increase in oxidation was 4.71 mg or less per 1 cm 2 , and the high temperature oxidation resistance was evaluated as “good”. Accordingly, No. of the steel of the present invention. As for 1-7, comprehensive evaluation is (circle).
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| CN114364820A (en) * | 2019-08-05 | 2022-04-15 | 株式会社Posco | Ferritic stainless steel with improved high temperature creep resistance and method for manufacturing same |
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