JP2012112025A - Ferritic stainless steel sheet for part of urea scr system and method for production thereof - Google Patents
Ferritic stainless steel sheet for part of urea scr system and method for production thereof Download PDFInfo
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- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 title claims abstract description 137
- 239000004202 carbamide Substances 0.000 title claims abstract description 137
- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 52
- 238000004519 manufacturing process Methods 0.000 title claims description 18
- 230000003647 oxidation Effects 0.000 claims abstract description 111
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 111
- 229910052804 chromium Inorganic materials 0.000 claims abstract description 31
- 229910052719 titanium Inorganic materials 0.000 claims abstract description 28
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 25
- 229910052742 iron Inorganic materials 0.000 claims abstract description 18
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 18
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 18
- 239000012535 impurity Substances 0.000 claims abstract description 4
- 239000000203 mixture Substances 0.000 claims description 33
- 238000005554 pickling Methods 0.000 claims description 30
- 238000000034 method Methods 0.000 claims description 26
- 239000010960 cold rolled steel Substances 0.000 claims description 15
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 11
- 229910017604 nitric acid Inorganic materials 0.000 claims description 11
- 229910052750 molybdenum Inorganic materials 0.000 claims description 7
- 229910052757 nitrogen Inorganic materials 0.000 claims description 7
- 229910052759 nickel Inorganic materials 0.000 claims description 6
- 238000012545 processing Methods 0.000 claims description 6
- 229910052799 carbon Inorganic materials 0.000 claims description 4
- 229910052802 copper Inorganic materials 0.000 claims description 3
- 235000021110 pickles Nutrition 0.000 claims description 3
- 229910052718 tin Inorganic materials 0.000 claims description 2
- 229910052720 vanadium Inorganic materials 0.000 claims description 2
- 238000010531 catalytic reduction reaction Methods 0.000 abstract description 2
- 238000012360 testing method Methods 0.000 description 47
- 229910000831 Steel Inorganic materials 0.000 description 45
- 239000010959 steel Substances 0.000 description 45
- 230000007797 corrosion Effects 0.000 description 29
- 238000005260 corrosion Methods 0.000 description 29
- 239000000463 material Substances 0.000 description 23
- 241000219307 Atriplex rosea Species 0.000 description 21
- 239000007789 gas Substances 0.000 description 18
- WTHDKMILWLGDKL-UHFFFAOYSA-N urea;hydrate Chemical compound O.NC(N)=O WTHDKMILWLGDKL-UHFFFAOYSA-N 0.000 description 17
- 229910045601 alloy Inorganic materials 0.000 description 10
- 239000000956 alloy Substances 0.000 description 10
- 239000000243 solution Substances 0.000 description 10
- 238000002485 combustion reaction Methods 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 8
- 239000010410 layer Substances 0.000 description 7
- 238000005096 rolling process Methods 0.000 description 7
- 239000010935 stainless steel Substances 0.000 description 7
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 6
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 6
- 238000000137 annealing Methods 0.000 description 6
- 238000005097 cold rolling Methods 0.000 description 6
- 238000006722 reduction reaction Methods 0.000 description 6
- 239000007864 aqueous solution Substances 0.000 description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 238000007598 dipping method Methods 0.000 description 4
- 238000009826 distribution Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 230000001681 protective effect Effects 0.000 description 4
- 238000007670 refining Methods 0.000 description 4
- 239000002344 surface layer Substances 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 229910021529 ammonia Inorganic materials 0.000 description 3
- 239000012141 concentrate Substances 0.000 description 3
- 239000000470 constituent Substances 0.000 description 3
- 150000003839 salts Chemical class 0.000 description 3
- 229910052721 tungsten Inorganic materials 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 230000002159 abnormal effect Effects 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229910052786 argon Inorganic materials 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 2
- 239000003054 catalyst Substances 0.000 description 2
- 238000010828 elution Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 238000007654 immersion Methods 0.000 description 2
- 238000011835 investigation Methods 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 239000007788 liquid Substances 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 230000002829 reductive effect Effects 0.000 description 2
- 229910002089 NOx Inorganic materials 0.000 description 1
- 241001274216 Naso Species 0.000 description 1
- 230000037396 body weight Effects 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 230000002860 competitive effect Effects 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 229910001039 duplex stainless steel Inorganic materials 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000004299 exfoliation Methods 0.000 description 1
- 239000000945 filler Substances 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 238000002161 passivation Methods 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 238000010792 warming Methods 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
Abstract
Description
本発明は、尿素水を用いて排ガス中のＮＯｘを低減する装置、特に自動車排気ガス処理システムにおける自動車尿素ＳＣＲ（Ｓｅｌｅｃｔｉｖｅ Ｃａｔａｌｙｔｉｃ Ｒｅｄｕｃｔｉｏｎ）システムなどに使用される機器類に使用される材料として好適な尿素ＳＣＲシステム部品用フェライト系ステンレス鋼板に関するものである。 INDUSTRIAL APPLICABILITY The present invention is a urea suitable as a material used in equipment for reducing NOx in exhaust gas using urea water, in particular, equipment used in an automobile urea SCR (Selective Catalytic Reduction) system in an automobile exhaust gas treatment system. The present invention relates to a ferritic stainless steel sheet for SCR system components.
地球温暖化などの環境問題に対する対策において、主に輸送機器から排出される排気ガス規制が強化されており、炭酸ガス排出抑制の取り組みが進められている。自動車においては、燃料面からの取り組みに加え、車体軽量化や排気熱を再利用して燃費向上を図る方法、ＥＧＲ（Ｅｘｈａｕｓｔ Ｇａｓ Ｒｅｃｉｒｃｕｌａｔｉｏｎ）、ＤＰＦ（Ｄｉｅｓｅｌ Ｐａｒｔｉｃｕｌａｔｅ Ｆｉｌｔｅｒ）および尿素ＳＣＲと呼ばれる排ガス処理装置を搭載する対策が採られている。 In measures against environmental issues such as global warming, regulations on exhaust gas emitted mainly from transportation equipment have been strengthened, and efforts to reduce carbon dioxide emissions are being promoted. In automobiles, in addition to efforts from the fuel side, exhaust gas treatment devices called EGR (Exhaust Gas Recirculation), DPF (Diesel Particulate Filter), and urea SCR, in addition to efforts from the fuel side, reduce body weight and recycle exhaust heat. Measures to install are taken.
この中で、尿素ＳＣＲシステムは、エンジンから放出された高温の排気ガスがエキゾーストマニホールドや触媒コンバータを通り、マフラーから大気に放出される一連の排気システムの中に搭載される浄化装置である。尿素ＳＣＲシステムでは、５００℃程度の高温の排気ガスに尿素を吹き付けて、熱および水分により分解してアンモニアを生成し、アンモニアとＮＯｘとを触媒上で選択還元して無害な窒素に分解する。ＮＯｘ低減を目的とした処理システムは比較的取り扱いが容易であるため、自動車のみならず定置型のＮＯｘ処理システムへの適用も検討されている。 Among these, the urea SCR system is a purification device mounted in a series of exhaust systems in which high-temperature exhaust gas discharged from an engine passes through an exhaust manifold and a catalytic converter and is discharged from the muffler to the atmosphere. In the urea SCR system, urea is sprayed on high-temperature exhaust gas of about 500 ° C., decomposed by heat and moisture to generate ammonia, and ammonia and NOx are selectively reduced on the catalyst and decomposed into harmless nitrogen. Since the treatment system for the purpose of reducing NOx is relatively easy to handle, application to a stationary NOx treatment system as well as an automobile has been studied.
尿素ＳＣＲシステムでは、尿素水を貯蔵して、排気ガスへの噴射を行なうため、構成する材料においては優れた耐食性が要求される。また、尿素ＳＣＲシステム内に上記の様に高温の排気ガスが通るため、優れた耐酸化性も必要となる。なお、尿素ＳＣＲシステムにおいては、通常の大気中での酸化に対する耐酸化性とは異なり、尿素水が吹きつけられた水蒸気雰囲気での耐酸化性が必要となる。
即ち、尿素ＳＣＲシステムの尿素水を貯蔵する部位では、尿素水中での耐食性（以後、耐尿素性と記す。）が求められ、高温の排気ガスが通る部位では、耐酸化性が求められる。
In the urea SCR system, urea water is stored and injected into the exhaust gas, so that excellent corrosion resistance is required for the constituent materials. In addition, since high-temperature exhaust gas passes through the urea SCR system as described above, excellent oxidation resistance is also required. In addition, in the urea SCR system, unlike the oxidation resistance against oxidation in normal air, the oxidation resistance in a steam atmosphere in which urea water is blown is required.
That is, corrosion resistance in urea water (hereinafter referred to as urea resistance) is required at a portion where urea water of the urea SCR system is stored, and oxidation resistance is required at a portion through which high-temperature exhaust gas passes.
特許文献１には、内燃機関の排気ガスシステムに尿素混合物を配給する装置に関して開示されている。ここでは、構成する金属シートとしてフェライト系ステンレス鋼の使用が示されている。
特許文献２には、尿素水中での耐食性に優れたフェライト系ステンレス鋼として、各成分元素に加えて添加Ｃｒ、Ｓｉ、Ｍｎ、Ｔｉ、Ｎｂ量による関係式を満足する鋼が開示されている。ここでは、鋼成分による有効Ｃｒ量を所定の量以上にすることで尿素水溶液中環境における耐食性、金属溶出量が調べられている。
特許文献３には、尿素製造プラント用２相ステンレス鋼として、Ｃｒ，Ｎｉ，Ｍｏ，Ｗが多量に含まれる鋼が開示されており、腐食による減肉が小さい材料が必要とされている。
Patent Document 1 discloses an apparatus for distributing a urea mixture to an exhaust gas system of an internal combustion engine. Here, the use of ferritic stainless steel is shown as the metal sheet to be constructed.
Patent Document 2 discloses a steel that satisfies the relational expression based on the amount of added Cr, Si, Mn, Ti, and Nb in addition to each component element, as a ferritic stainless steel having excellent corrosion resistance in urea water. Here, the corrosion resistance in the environment in urea aqueous solution and the metal elution amount are investigated by making the effective Cr amount by a steel component more than predetermined amount.
Patent Document 3 discloses a steel containing a large amount of Cr, Ni, Mo, and W as a duplex stainless steel for a urea production plant, and a material that is small in thickness due to corrosion is required.
上記の様に、尿素ＳＣＲシステムに用いられる材料としては、これまで尿素環境における耐食性、即ち耐尿素性が重要とされてきた。しかしながら、主にディーゼルエンジンを主とする内燃機関において用いられる尿素ＳＣＲシステムにおいては、耐食性以外に水蒸気雰囲気における耐酸化性も重要となる場合があった。即ち、尿素ＳＣＲシステムにおいて高温の排気ガスに尿素水を吹き付けた場合、構成する材料は水蒸気雰囲気で酸化される。 As described above, as a material used in the urea SCR system, corrosion resistance in a urea environment, that is, urea resistance has been regarded as important so far. However, in a urea SCR system used mainly in an internal combustion engine mainly including a diesel engine, oxidation resistance in a water vapor atmosphere may be important in addition to corrosion resistance. That is, when urea water is sprayed on high-temperature exhaust gas in the urea SCR system, the constituent materials are oxidized in a water vapor atmosphere.
上記の様なフェライト系ステンレス鋼の場合、大気中で５００℃程度の雰囲気で長時間加熱されても、Ｃｒを主体とする緻密な保護性皮膜が生成し、酸化増量は殆ど生じず、酸化皮膜の剥離も生じない。
しかしながら、上記のフェライト系ステンレス鋼であっても、水蒸気雰囲気では酸化が加速されるとともに酸化皮膜の剥離が生じる。このため、上記のフェライト系ステンレス鋼を尿素ＳＣＲシステムの材料として用いた場合、尿素ＳＣＲシステムにおける触媒を損傷させる場合があった。更に、尿素ＳＣＲシステムの材料として用いたフェライト系ステンレス鋼が耐尿素性に劣るものであった場合、そのような酸化皮膜の剥離は加速され、尿素による腐食が進行することになる。
In the case of ferritic stainless steel as described above, a dense protective film mainly composed of Cr is generated even when heated in the atmosphere at a temperature of about 500 ° C. for a long time. No peeling occurs.
However, even in the above-described ferritic stainless steel, the oxidation is accelerated and the oxide film is peeled off in a steam atmosphere. For this reason, when the above ferritic stainless steel is used as a material for the urea SCR system, the catalyst in the urea SCR system may be damaged. Furthermore, when the ferritic stainless steel used as the material for the urea SCR system is inferior in urea resistance, such peeling of the oxide film is accelerated and corrosion by urea proceeds.
一方、高温疲労強度、高温耐酸化性、耐水蒸気酸化性に対する特性を改善したフェライト系ステンレス鋼が特許文献４〜特許文献７に開示されている。
しかしながら、特許文献４では、Ｍｏ，Ｗが多く含まれており、合金コストが増加する。また、特許文献５には、Ｓｉ含有量を下げて加工性を向上させるフェライト系ステンレスが開示されているが、Ｍｏを多く含み、かつ、Ｓｉ含有量低下のため不動態皮膜の不安定性が懸念される。
On the other hand, Patent Literature 4 to Patent Literature 7 disclose ferritic stainless steels having improved properties against high temperature fatigue strength, high temperature oxidation resistance, and steam oxidation resistance.
However, Patent Document 4 contains a large amount of Mo and W, which increases the alloy cost. Patent Document 5 discloses ferritic stainless steel that lowers the Si content and improves processability, but contains a large amount of Mo, and there is a concern about the instability of the passive film due to a decrease in the Si content. Is done.
また、特許文献６には、限定された雰囲気中で７００℃〜１２００℃の高温で加熱処理することで、高温雰囲気化でのＣｒの蒸発を抑止し、耐酸化性の低下を抑制する技術が開示されている。しかし、高温プロセスの採用により、エネルギーコストの上昇が懸念される。
更に、特許文献４〜特許文献７の鋼においては、当然ながら、耐尿素性に対する検討は行われていず、尿素ＳＣＲシステムに用いられるための条件は満足されていなかった。更に、Ｃｒ，Ｎｉ，Ｍｏ，Ｗが多量に含まれる鋼では、合金コストが著しく増加し、コスト面の課題があった。
Patent Document 6 discloses a technique for suppressing Cr evaporation in a high temperature atmosphere and suppressing deterioration in oxidation resistance by heat treatment at a high temperature of 700 ° C. to 1200 ° C. in a limited atmosphere. It is disclosed. However, there is a concern that the energy cost will increase due to the adoption of the high temperature process.
Further, in the steels of Patent Documents 4 to 7, the urea resistance has not been studied as a matter of course, and the conditions for use in the urea SCR system have not been satisfied. Furthermore, in steel containing a large amount of Cr, Ni, Mo, and W, the alloy cost is remarkably increased and there is a problem of cost.
また、特許文献８には、耐食性向上によってＳＵＳ４３０などＳｉ含有ステンレス鋼において、不動態皮膜中のＣｒ濃度の、Ｆｅ濃度に対する比を２以上にすることで、不動態皮膜をＣｒ酸化物主体の組成にすることで耐食性を上げ、接触抵抗の上昇を抑える技術が開示されている。しかし、特許文献８は、技術目的が電子部品等の接点部分の接触電気抵抗の低下であるため、表面Ｃｒ濃度と耐酸化性や耐尿素性等は不明である。該開示技術は、一般的な材料なので尿素ＳＣＲ等の材料としての充分な特性を得ることは困難であると推定される。 Further, Patent Document 8 discloses that the composition of the passive oxide film is mainly composed of Cr oxide by increasing the ratio of Cr concentration in the passive film to Fe concentration in Si-containing stainless steel such as SUS430 by improving corrosion resistance. Thus, a technique for improving corrosion resistance and suppressing an increase in contact resistance is disclosed. However, since the technical purpose of Patent Document 8 is to reduce the contact electrical resistance of the contact portion of an electronic component or the like, the surface Cr concentration, oxidation resistance, urea resistance, and the like are unknown. Since the disclosed technology is a general material, it is estimated that it is difficult to obtain sufficient characteristics as a material such as urea SCR.
さらに、非特許文献１〜３には、Ｔｉ、Ｓｉ、Ｍｎ、Ｍｏ等を含有するフェライト系ステンレス鋼を機械研磨し、長時間大気放置することによって表面層におけるＣｒ濃度がＦｅ濃度より高くなり、緻密なＣｒ酸化膜が生成され、高温酸化耐性が向上することが開示されている。しかしながら、これら非特許文献において開示されている技術は、表面のＣｒ濃化及び添加Ｍｏの高温耐酸化性に対する有効性であり、耐尿素性に関する調査は行っていない。
従って、高温耐酸化性を持つフェライト系ステンレス材においては、耐尿素性が不明であり、尿素ＳＣＲ等の材料としての充分な特性を得ることは困難であると推定される。
Further, in Non-Patent Documents 1 to 3, the ferritic stainless steel containing Ti, Si, Mn, Mo, etc. is mechanically polished, and the Cr concentration in the surface layer becomes higher than the Fe concentration by leaving it in the atmosphere for a long time. It is disclosed that a dense Cr oxide film is generated and high-temperature oxidation resistance is improved. However, the techniques disclosed in these non-patent documents are the effectiveness of Cr concentration on the surface and the high-temperature oxidation resistance of added Mo, and no investigation on urea resistance has been conducted.
Therefore, in a ferritic stainless material having high temperature oxidation resistance, urea resistance is unknown, and it is estimated that it is difficult to obtain sufficient characteristics as a material such as urea SCR.
また、特許文献９には、硝酸とふっ酸の混合溶液でフェライト系ステンレス熱延鋼板を酸洗し、表面のＣｒ濃度のＦｅ濃度に対する比を調整し、冷間圧延後の表面光沢を均一にする技術が開示されている。しかし、特許文献９では、耐酸化性及び耐尿素性については検討されていない。 In Patent Document 9, ferritic stainless steel hot rolled steel sheet is pickled with a mixed solution of nitric acid and hydrofluoric acid, the ratio of surface Cr concentration to Fe concentration is adjusted, and the surface gloss after cold rolling is made uniform. Techniques to do this are disclosed. However, Patent Document 9 does not discuss oxidation resistance and urea resistance.
更に、特許文献１０，特許文献１１には、硝酸、ふっ酸等を用いた処理によりフェライト系ステンレスの表面性状を調整したりスケールを除去したりする技術が開示されている。しかし、特許文献１０および特許文献１１では、表面のＣｒやＦｅ濃度と耐酸化性及び耐尿素性に関する調査は行われていない。 Further, Patent Documents 10 and 11 disclose techniques for adjusting the surface properties of ferritic stainless steel and removing scales by treatment using nitric acid, hydrofluoric acid, or the like. However, in Patent Document 10 and Patent Document 11, investigations regarding the Cr and Fe concentration, oxidation resistance, and urea resistance on the surface are not conducted.
また、特許文献１２には、内燃機関における水／尿素混合物を配給する装置が開示されており、装置に用いられる金属シートに、熱伝達率の高いフェライト系ステンレスを用いる技術が開示されている。しかしながら、これは、局所的な温度低下を防ぐための技術開示であり、一般的なフェライト系ステンレスに言及しているのみであり、その組成について規定しておらず、耐高温酸化性及び耐尿素性については検討されていない。即ち、尿素ＳＣＲシステム用部品としての特性を得ることは困難であると推定される。 Patent Document 12 discloses a device that distributes a water / urea mixture in an internal combustion engine, and discloses a technique that uses a ferritic stainless steel having a high heat transfer coefficient for a metal sheet used in the device. However, this is a technical disclosure for preventing local temperature drop, and only mentions general ferritic stainless steel, its composition is not specified, and high temperature oxidation resistance and urea resistance Sex has not been studied. That is, it is estimated that it is difficult to obtain characteristics as a component for a urea SCR system.
また、特許文献１３には、内燃機関において尿素水を効率よくアンモニアに分解する脱硝装置が開示されているが、分解反応を起こすため充填物材料としてステンレスが開示されている。しかしながら、排気ガスや尿素水に接する配管等の金属部品の耐高温酸化性及び耐尿素性については言及されていない。即ち、液状あるいは、気体状の尿素混合物に、低温から高温まで種々の温度で接する部分からなる内燃機関用の尿素ＳＣＲシステム部品において、その耐食性、即ち、耐高温酸化性と耐尿素性に優れた低コストの部品の開示は無かった。 Patent Document 13 discloses a denitration device that efficiently decomposes urea water into ammonia in an internal combustion engine. However, stainless steel is disclosed as a filler material for causing a decomposition reaction. However, there is no mention of high-temperature oxidation resistance and urea resistance of metal parts such as pipes in contact with exhaust gas and urea water. That is, in urea SCR system parts for internal combustion engines consisting of portions that come into contact with a liquid or gaseous urea mixture at various temperatures from low to high temperatures, they have excellent corrosion resistance, that is, high temperature oxidation resistance and urea resistance. There was no disclosure of low-cost parts.
尿素ＳＣＲシステムで使用されるステンレス鋼板においては、高濃度の尿素環境においてステンレス鋼の構成元素であるＦｅ，Ｃｒ、Ｎｉなどの元素の溶出を抑制する必要があり、優れた耐食性が要求される。更に、尿素ＳＣＲシステムで使用されるステンレス鋼板においては、水蒸気雰囲気下において高温の排気ガス雰囲気に曝されるため、優れた耐酸化性が要求される。 The stainless steel plate used in the urea SCR system needs to suppress elution of elements such as Fe, Cr and Ni, which are constituent elements of stainless steel, in a high concentration urea environment, and requires excellent corrosion resistance. Furthermore, since the stainless steel plate used in the urea SCR system is exposed to a high-temperature exhaust gas atmosphere in a water vapor atmosphere, excellent oxidation resistance is required.
しかし、尿素ＳＣＲシステムを構成する材料には、これまで耐尿素性の観点から好適な材料が開示されてきたが、耐酸化性の観点から不十分である。一方、耐酸化性が好適な材料は、尿素ＳＣＲシステムを構成する材料としては耐尿素性の観点から不十分であり、不適切であった。即ち、耐酸化性及び耐尿素性を同時に満たす低コストでかつ信頼性の高い尿素ＳＣＲ用フェライト系ステンレス鋼板が要望されていた。 However, materials suitable for the urea SCR system have been disclosed so far from the viewpoint of urea resistance, but are insufficient from the viewpoint of oxidation resistance. On the other hand, a material suitable for oxidation resistance is insufficient and inappropriate as a material constituting the urea SCR system from the viewpoint of urea resistance. That is, a low-cost and highly reliable ferritic stainless steel sheet for urea SCR that simultaneously satisfies oxidation resistance and urea resistance has been demanded.
本発明は、主にディーゼルエンジンを主体とする内燃機関において尿素水を用いて排気ガス中のＮＯｘを低減する装置、特に自動車尿素ＳＣＲシステムなどの機器類に使用されるタンクや配管などの材料として好適に用いられ、排気ガスと尿素水に曝される環境下で優れた耐酸化性及び耐尿素性を有するフェライト系ステンレス鋼板及びそれを用いて製造される尿素ＳＣＲシステム部品を提供することを目的とする。 The present invention is an apparatus for reducing NOx in exhaust gas using urea water in an internal combustion engine mainly composed of a diesel engine, particularly as a material for tanks and piping used in equipment such as an automobile urea SCR system. An object of the present invention is to provide a ferritic stainless steel plate which is suitably used and has excellent oxidation resistance and urea resistance in an environment exposed to exhaust gas and urea water, and a urea SCR system component manufactured using the same. And
本発明者らは、前記の課題を解決すべく鋭意検討した結果、５００℃程度の高温環境下で尿素水が吹きつけられる高温水蒸気環境下で、優れた耐酸化性を発現させるためには、鋼成分のみならず表面の不動態皮膜中の濃度分布が極めて重要であることを知見した。 As a result of intensive studies to solve the above-mentioned problems, the present inventors have expressed high oxidation resistance in a high-temperature steam environment in which urea water is sprayed in a high-temperature environment of about 500 ° C. It was found that the concentration distribution in the passive film on the surface as well as the steel components was extremely important.
従来、酸洗等によるフェライト系ステンレス鋼板の不動態皮膜中の元素濃度の調整方法や、不動態皮膜中の元素濃度と耐酸化性及び耐尿素性の関係についての詳細な技術は開示されておらず、不動態皮膜中の元素濃度を調整することで耐水蒸気酸化性と耐尿素性を同時に満足する技術は無かった。 Conventionally, a method for adjusting the element concentration in the passive film of a ferritic stainless steel sheet by pickling or the like, and a detailed technique regarding the relationship between the element concentration in the passive film and oxidation resistance and urea resistance have not been disclosed. First, there was no technology that satisfied both steam oxidation resistance and urea resistance simultaneously by adjusting the element concentration in the passive film.
なお、鋼表面にＣｒを濃化させることで耐食性を向上させることは、従来から知見されている。しかし、鋼表面にＣｒを濃化したフェライト系ステンレス鋼板であっても、尿素ＳＣＲシステムに用いる場合の様な５００℃程度の高温の水蒸気環境下においては、腐食することが無くても、酸化スケールが剥離したり、極端には異常酸化を起こしたりする恐れがあった。 It has been conventionally known that corrosion resistance is improved by concentrating Cr on the steel surface. However, even if it is a ferritic stainless steel plate with Cr enriched on the steel surface, it does not corrode in a high temperature steam environment of about 500 ° C. as used in a urea SCR system. May peel off or extremely abnormal oxidation may occur.
本発明者らは、１０％以上Ｃｒを含有するフェライト系ステンレス鋼において、表面不動態皮膜中に濃化する元素としてＣｒ以外のＴｉ，Ａｌの濃化度を制御することによって、健全な不動態皮膜を形成させ、良好な酸化特性が得られ、同時に良好な耐尿素性も得られることを見出した。
上記課題を解決する本発明の要旨は、以下のとおりである。
In the ferritic stainless steel containing 10% or more of Cr, the present inventors control the concentration of Ti and Al other than Cr as elements to be concentrated in the surface passivation film, thereby providing a healthy passive state. It was found that a film was formed, good oxidation characteristics were obtained, and good urea resistance was obtained at the same time.
The gist of the present invention for solving the above problems is as follows.
（１）質量％にて、Ｃ：０．０１０％以下、Ｎ：０．０２０％以下、Ｓｉ：０．５％以下、Ｍｎ：０．５％以下、Ｃｒ：１０．０〜２０．０％、Ｔｉ：０．０５〜０．３０％、Ｍｏ：１．５％以下、Ａｌ：０．０３〜０．５％を含有し、残部がＦｅおよび不可避的不純物からなるとともに、表面から２０ｎｍ以内におけるＣｒ、Ｓｉ、Ａｌ，Ｔｉ、ＭｎおよびＦｅの濃度によって構成される濃度比の最大値が以下の式に示す関係を有し、耐高温酸化性および耐尿素性に優れることを特徴とする尿素ＳＣＲシステム部品用フェライト系ステンレス鋼板。
（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ+Ｓｉ+Ｍｎ）＞０．３５
上記式において、Ｃｒ、Ｔｉ、Ａｌ、Ｆｅ、Ｓｉ、Ｍｎは、それぞれ、Ｃｒ、Ｔｉ、Ａｌ、Ｆｅ、Ｓｉ、Ｍｎの含有量［質量％］である。
(1) In mass%, C: 0.010% or less, N: 0.020% or less, Si: 0.5% or less, Mn: 0.5% or less, Cr: 10.0-20.0% Ti: 0.05 to 0.30%, Mo: 1.5% or less, Al: 0.03 to 0.5%, the balance is made of Fe and inevitable impurities, and within 20 nm from the surface Urea SCR characterized in that the maximum value of the concentration ratio constituted by the concentrations of Cr, Si, Al, Ti, Mn and Fe has the relationship shown in the following formula and is excellent in high temperature oxidation resistance and urea resistance Ferritic stainless steel sheet for system parts.
(Cr + Ti + Al) / (Fe + Si + Mn)> 0.35
In the above formula, Cr, Ti, Al, Fe, Si, and Mn are the contents [% by mass] of Cr, Ti, Al, Fe, Si, and Mn, respectively.
（２）質量％にて、Ｎｂ：０．５％以下、Ｃｕ：１．５％以下、Ｎｉ：３％以下、Ｖ：１％以下、Ｓｎ：０．５％以下、Ｂ：０．００２０％以下の１種以上を含有し、耐高温酸化性および耐尿素性に優れることを特徴とする（１）記載の尿素ＳＣＲシステム部品用フェライト系ステンレス鋼板。 (2) In mass%, Nb: 0.5% or less, Cu: 1.5% or less, Ni: 3% or less, V: 1% or less, Sn: 0.5% or less, B: 0.0020% The ferritic stainless steel sheet for urea SCR system components according to (1), which contains one or more of the following and is excellent in high-temperature oxidation resistance and urea resistance.
（３）（１）または（２）記載の尿素ＳＣＲシステム部品用フェライト系ステンレス鋼板を製造する方法であって、請求項１または２記載の組成を有するステンレス冷延鋼板を、硝酸濃度が５０〜２００ｇ／Ｌで温度が５０〜８０℃の溶液に４秒以上浸漬して酸洗する工程を含むことを特徴とする尿素ＳＣＲシステム部品用フェライト系ステンレス鋼板の製造方法。 (3) A method for producing a ferritic stainless steel sheet for urea SCR system components according to (1) or (2), wherein the stainless cold-rolled steel sheet having the composition according to claim 1 or 2 has a nitric acid concentration of 50 to 50. A method for producing a ferritic stainless steel sheet for urea SCR system parts, comprising a step of dipping in a solution having a temperature of 50 to 80 ° C. at 200 g / L for 4 seconds or more and pickling.
（４）（１）または（２）記載の尿素ＳＣＲシステム部品用フェライト系ステンレス鋼板からなることを特徴とする尿素ＳＣＲシステム部品。
（５）（１）または（２）記載の組成を有するステンレス冷延鋼板を部品形状に加工して尿素ＳＣＲシステム部材とする工程と、前記尿素ＳＣＲシステム部材を、硝酸濃度が５０〜２００ｇ／Ｌで温度が５０〜８０℃の溶液に４秒以上浸漬して酸洗して尿素ＳＣＲシステム部品とする工程とを含むことを特徴とする尿素ＳＣＲシステム部品の製造方法。
(4) A urea SCR system component comprising the ferritic stainless steel sheet for urea SCR system component according to (1) or (2).
(5) A step of processing a stainless cold-rolled steel sheet having the composition described in (1) or (2) into a component shape to form a urea SCR system member, and the urea SCR system member having a nitric acid concentration of 50 to 200 g / L And a step of dipping in a solution having a temperature of 50 to 80 ° C. for 4 seconds or more and pickling to form a urea SCR system component.
本発明によれば、排気ガスと尿素水に曝される環境において優れた酸化特性を有するフェライト系ステンレス鋼を比較的低コストで提供できるので、主にディーゼルエンジンを主体とする内燃機関において尿素水を用いて排気ガス中のＮＯｘを低減する装置、特に自動車尿素ＳＣＲシステムなどに使用される機器類に好適な材料を提供できる。本発明の尿素ＳＣＲシステム部品用フェライト系ステンレス鋼板を、タンク、パイプ、プレート、棒、スプリング等の尿素ＳＣＲシステム部品の材料として用いることで、尿素ＳＣＲシステムの簡素化、低コスト化に資することができる。 According to the present invention, since ferritic stainless steel having excellent oxidation characteristics in an environment exposed to exhaust gas and urea water can be provided at a relatively low cost, urea water is mainly used in internal combustion engines mainly including diesel engines. Can be used to provide a material suitable for devices used in an apparatus for reducing NOx in exhaust gas, particularly in an automobile urea SCR system. Using the ferritic stainless steel sheet for urea SCR system parts of the present invention as a material for urea SCR system parts such as tanks, pipes, plates, bars, springs, etc., can contribute to simplification and cost reduction of the urea SCR system. it can.
以下に、本発明で規定される尿素ＳＣＲに使用される耐酸化性に優れたフェライト系ステンレス鋼の化学成分、表面皮膜組成および製造方法について説明する。 The chemical components, surface film composition and manufacturing method of ferritic stainless steel excellent in oxidation resistance used for the urea SCR defined in the present invention will be described below.
Ｃは鋼板の成形性と耐食性を劣化させるため、その含有量は低く抑える必要があり、その含有量は０．０１０％以下とした。Ｃ含有量の過度の低減は精錬コストが増加するため、耐酸化性も考慮すると、０．００２〜０．００９％が望ましい。 Since C deteriorates the formability and corrosion resistance of the steel sheet, its content needs to be kept low, and its content is set to 0.010% or less. Excessive reduction of the C content increases the refining cost, so 0.002 to 0.009% is desirable considering oxidation resistance.
ＮはＣと同様、成形性と耐食性を劣化させるため、その含有量は少ないほど良く、０．０２０％以下とした。更に、Ｎ含有量の過度の低減は精錬コストが増加するため、耐酸化性も考慮すると、０．００２〜０．０１５％が望ましい。 N, like C, deteriorates moldability and corrosion resistance, so the smaller the content, the better. Furthermore, excessive reduction of the N content increases the refining cost, so 0.002 to 0.015% is desirable considering oxidation resistance.
Ｓｉは、脱酸剤としても有用であるとともに、耐食性、高温強度および耐酸化性に対して有効な元素である。一方、Ｓｉは、加工性を劣化させる他、Ｔｉとの複合添加の場合、長時間の酸化においてＴｉ酸化物とＳｉ酸化物の競合酸化によりスケール剥離が生じるため、０．５％以下とした。Ｓｉ含有量の過度な低減は精錬コストが増加するため、下限は０．０１％が望ましい。更に、耐酸化性も考慮するとＳｉ含有量は０．０１〜０．１％が望ましい。 Si is an element that is useful as a deoxidizer and is effective for corrosion resistance, high-temperature strength, and oxidation resistance. On the other hand, Si deteriorates workability and, in the case of complex addition with Ti, scale peeling occurs due to competitive oxidation of Ti oxide and Si oxide in long-term oxidation, so the content was made 0.5% or less. Since excessive reduction of the Si content increases the refining cost, the lower limit is desirably 0.01%. Furthermore, considering oxidation resistance, the Si content is preferably 0.01 to 0.1%.
Ｍｎは、脱酸剤として添加される元素であるが、過剰に添加すると耐食性や耐酸化性が劣化する。特に、尿素ＳＣＲ用の場合、スケールの外層側にＭｎ酸化物が生成し、赤スケールが発生し易くなるため、Ｍｎ含有量を０．５％以下とした。更に、Ｍｎ含有量は、スケール剥離性を考慮すると０．１％以下が望ましい。 Mn is an element added as a deoxidizer, but if added excessively, corrosion resistance and oxidation resistance deteriorate. In particular, in the case of urea SCR, Mn oxide is generated on the outer layer side of the scale, and red scale is easily generated. Therefore, the Mn content is set to 0.5% or less. Furthermore, the Mn content is preferably 0.1% or less in consideration of scale peelability.
Ｃｒは、本願発明において、耐酸化性のために必須な元素で、高温でかつ尿素水が塗布される水蒸気環境において、良好な耐酸化性を確保するための元素である。製品の不動態皮膜中にＣｒを濃化させ、尿素ＳＣＲに使用した際に保護性の緻密な酸化スケールを形成させるためには、少なくとも１０．０％以上Ｃｒを含有させることが必要であるため、下限を１０．０％とした。一方、過度な添加は加工性を劣化させるため、Ｃｒ含有量の上限は２０．０％とした。また、尿素水環境における耐食性や溶接性も考慮すると、Ｃｒ含有量は１４〜１８％が望ましい。 Cr is an element essential for oxidation resistance in the present invention, and is an element for ensuring good oxidation resistance in a steam environment where urea water is applied at a high temperature. In order to concentrate Cr in the passive film of the product and form a protective dense oxide scale when used for urea SCR, it is necessary to contain at least 10.0% Cr or more. The lower limit was made 10.0%. On the other hand, since excessive addition deteriorates workability, the upper limit of the Cr content is set to 20.0%. In consideration of corrosion resistance and weldability in a urea water environment, the Cr content is preferably 14 to 18%.
Ｔｉは、Ｃ，Ｎ，Ｓと結合して耐食性、耐粒界腐食性、常温延性や深絞り性を向上させる元素である。この作用に加えて、本発明では、不動態皮膜の内層側および不動態皮膜と母地との界面にＴｉを酸化物で濃化させ、耐酸化性特にスケール剥離性を向上させる。この効果は０．０５％以上のＴｉを含有させることにより発現するため、Ｔｉ含有量の下限を０．０５％とした。また、一方、Ｔｉを０．３０％超で含有させると加工性が著しく劣化するため、Ｔｉ含有量の上限を０．３０％とした。更に、耐酸化性や製造性を考慮すると、Ｔｉ含有量は０．０７〜０．２％が望ましい。 Ti is an element that combines with C, N, and S to improve corrosion resistance, intergranular corrosion resistance, room temperature ductility and deep drawability. In addition to this function, in the present invention, Ti is concentrated with an oxide on the inner layer side of the passive film and the interface between the passive film and the base material, thereby improving the oxidation resistance, particularly the scale peelability. Since this effect is manifested by containing 0.05% or more of Ti, the lower limit of the Ti content is set to 0.05%. On the other hand, if the Ti content exceeds 0.30%, the workability is remarkably deteriorated, so the upper limit of the Ti content is set to 0.30%. Furthermore, considering oxidation resistance and manufacturability, the Ti content is preferably 0.07 to 0.2%.
Ｍｏは、耐食性を向上させる元素であるが、過剰な添加は加工性と耐酸化性を劣化させるとともに、合金コストアップにつながる。よって、Ｍｏ含有量は１．５％以下とした。更に、製造性、スケール密着性および合金コストを考慮すると、Ｍｏ含有量は０．３〜０．６％であることが望ましい。 Mo is an element that improves corrosion resistance. However, excessive addition deteriorates workability and oxidation resistance, and leads to an increase in alloy cost. Therefore, the Mo content is set to 1.5% or less. Furthermore, in consideration of manufacturability, scale adhesion, and alloy cost, the Mo content is preferably 0.3 to 0.6%.
Ａｌは、脱酸元素として添加される他、鋼表層に濃化させることによって耐尿素性を向上させる元素であることが分かった。更に、Ａｌは、耐酸化性を向上させる元素である。本願発明では、Ａｌを不動態皮膜の内層側および不動態皮膜と母地との界面に酸化物として濃化させて、耐尿素性および水蒸気雰囲気における耐酸化性を向上させるため、Ａｌ含有量を０．０３％以上とする。一方、過度な添加は加工性を劣化させるため、Ａｌ含有量の上限は０．５％とした。更に、製造性や溶接性の観点から、Ａｌ含有量は０．０５〜０．１５％が望ましい。 In addition to being added as a deoxidizing element, Al was found to be an element that improves urea resistance by concentrating on the steel surface layer. Furthermore, Al is an element that improves oxidation resistance. In the present invention, Al is concentrated as an oxide on the inner layer side of the passive film and at the interface between the passive film and the base material to improve urea resistance and oxidation resistance in a water vapor atmosphere. 0.03% or more. On the other hand, since excessive addition deteriorates workability, the upper limit of the Al content is set to 0.5%. Furthermore, from the viewpoint of manufacturability and weldability, the Al content is desirably 0.05 to 0.15%.
Ｎｂは、耐粒界腐食性や高温強度を向上させる元素であり、必要に応じて添加することが出来る。Ｎｂ含有量が０．５％超になると加工性が著しく劣化するため、上限は０．５％とする。更に、製造性、耐酸化性、合金コストを考慮すると、Ｎｂ含有量は０．００５〜０．３％が望ましい。 Nb is an element that improves intergranular corrosion resistance and high-temperature strength, and can be added as necessary. If the Nb content exceeds 0.5%, the workability deteriorates remarkably, so the upper limit is made 0.5%. Furthermore, considering the manufacturability, oxidation resistance, and alloy cost, the Nb content is preferably 0.005 to 0.3%.
Ｃｕは、耐錆性や高温強度を向上させる元素であり、必要に応じて添加することが出来る。Ｃｕ含有量が１．５％超になると延性が著しく劣化するため、上限は１．５％とする。更に、製造性や耐酸化性を考慮すると、Ｃｕ含有量は０．３〜１．２％が望ましい。 Cu is an element that improves rust resistance and high-temperature strength, and can be added as necessary. If the Cu content exceeds 1.5%, the ductility deteriorates remarkably, so the upper limit is made 1.5%. Furthermore, considering the manufacturability and oxidation resistance, the Cu content is preferably 0.3 to 1.2%.
Ｎｉは、耐錆性を向上させる元素であり、必要に応じて添加することが出来る。Ｎｉ含有量が３％超になるとオーステナイト相が生成し、耐酸化性が劣化する他、加工性が著しく劣化するため、上限は３％とする。更に、製造性、耐酸化性、合金コストを考慮すると、Ｎｉ含有量は０．５〜２％が望ましい。 Ni is an element that improves rust resistance, and can be added as necessary. When the Ni content exceeds 3%, an austenite phase is generated, oxidation resistance is deteriorated, and workability is remarkably deteriorated, so the upper limit is made 3%. Furthermore, considering the manufacturability, oxidation resistance, and alloy cost, the Ni content is desirably 0.5 to 2%.
Ｖは、耐食性を向上させる元素であるため、必要に応じて添加することが出来る。Ｖ含有量が１％超になると耐食性と加工性が著しく劣化するため、上限は１％とする。更に、製造性、耐酸化性、合金コストを考慮すると、Ｖ含有量は０．１〜０．５％が望ましい。 V is an element that improves the corrosion resistance and can be added as necessary. If the V content exceeds 1%, the corrosion resistance and workability deteriorate significantly, so the upper limit is made 1%. Furthermore, considering the manufacturability, oxidation resistance, and alloy cost, the V content is preferably 0.1 to 0.5%.
Ｓｎは、耐食性や高温強度を向上させる元素であるため必要に応じて添加することが出来る。Ｓｎ含有量が０．５％超になると製造性が著しく劣化するため、上限は０．５％とする。更に、加工性、耐酸化性、合金コストを考慮すると、Ｓｎ含有量は０．１〜０．３％が望ましい。 Sn is an element that improves corrosion resistance and high-temperature strength, and can be added as necessary. If the Sn content exceeds 0.5%, the productivity is remarkably deteriorated, so the upper limit is made 0.5%. Furthermore, in consideration of workability, oxidation resistance, and alloy cost, the Sn content is preferably 0.1 to 0.3%.
Ｂは、部品成形時の２次加工性を向上させる元素であり、必要に応じて添加することが出来る。Ｂ含有量が０．００２０％超になると製造性や耐粒界腐食性が著しく劣化するため、上限は０．００２０％とする。更に、加工性、耐酸化性、合金コストを考慮すると、Ｂ含有量は０．０００３〜０．００１０％が望ましい。 B is an element that improves the secondary workability at the time of component molding, and can be added as necessary. If the B content exceeds 0.0020%, the manufacturability and intergranular corrosion resistance deteriorate significantly, so the upper limit is made 0.0020%. Furthermore, considering the workability, oxidation resistance, and alloy cost, the B content is preferably 0.0003 to 0.0010%.
鋼組成は上記の様に限定されるが、本発明者らは鋼組成に加えて鋼板表面の不動態皮膜組成が水蒸気雰囲気における耐酸化性に大きく影響することを見出した。更に、該不動態皮膜が耐尿素性に影響することも見出した。 Although the steel composition is limited as described above, the present inventors have found that the passive film composition on the steel sheet surface in addition to the steel composition greatly affects the oxidation resistance in a water vapor atmosphere. Furthermore, it has also been found that the passive film affects urea resistance.
本発明において、鋼板の耐酸化性は、酸化に伴う酸化増量に加えて赤スケールと呼ばれるスケールが生じるか否かで判断する。図１は、酸化試験後の試験片を示した外観写真であり、図１（ａ）は赤スケールの発生した試験片の一例を示し、図１（ｂ）は赤スケールの発生しなかった試験片の一例を示している。
図１（ａ）に示す赤スケールは、鋼板が水蒸気雰囲気の５００℃程度の温度域で連続酸化された場合に酸化増量が増えて生じた厚い酸化スケールである。赤スケールの剥離（図１（ａ）に示す例においては、試験片の下部約１／３は、スケールが剥離している。）は、尿素ＳＣＲシステムにおけるＮＯｘ還元性能を劣化させる場合がある。
In the present invention, the oxidation resistance of the steel sheet is determined by whether or not a scale called a red scale occurs in addition to the increase in oxidation accompanying oxidation. FIG. 1 is an appearance photograph showing a test piece after an oxidation test, FIG. 1 (a) shows an example of a test piece with red scale, and FIG. 1 (b) shows a test with no red scale. An example of a piece is shown.
The red scale shown in FIG. 1 (a) is a thick oxide scale produced by increasing the amount of oxidation when the steel sheet is continuously oxidized in a temperature range of about 500 ° C. in a steam atmosphere. The peeling of the red scale (in the example shown in FIG. 1 (a), the scale is peeled off at about 1/3 of the test piece) may degrade the NOx reduction performance in the urea SCR system.
尿素ＳＣＲ用フェライト系ステンレス鋼板は、鋳造−熱延−酸洗−冷延−焼鈍−酸洗工程を経て製品となる。本発明者らは鋼成分に加えて、冷延鋼板を酸洗する最終酸洗条件による不動態皮膜組成と下記酸化試験における酸化増量および赤スケール発生有無、耐尿素性を詳細に検討した。 The ferritic stainless steel sheet for urea SCR becomes a product through a casting-hot rolling-pickling-cold rolling-annealing-pickling process. In addition to the steel components, the present inventors examined in detail the composition of the passive film under the final pickling conditions for pickling cold-rolled steel sheets, the amount of oxidation increase, the presence / absence of red scale, and urea resistance in the following oxidation test.
酸化試験は、１０％のＯ２を含むアルゴンに加湿処理して２０％水蒸気雰囲気とし、５００℃で１００時間連続して行なった。酸化試験の試験片には、縦２０ｍｍ横２０ｍｍの大きさで、表面および裏面が最終酸洗ままであり、端面を＃４００研磨処理したものを用いた。
酸化試験の試験片を作成する際には、１７．５％Ｃｒ−１．１％Ｍｏ−０．２％Ｔｉ−０．０５％Ｓｉ−０．１２％Ｍｎ−０．０７％Ａｌ−０．００４％Ｃ−０．０１４％Ｎの組成を有する冷延・焼鈍板と、１７．２％Ｃｒ−０．５％Ｍｏ−０．１７％Ｔｉ−０．０９％Ｓｉ−０．０７％Ｍｎ−０．０９％Ａｌ−０．００２％Ｃ−０．０００９％Ｎの組成を有する冷延・焼鈍板とを、種々の酸洗法にて酸洗処理した鋼板を用いた。また、酸化試験の試験片に酸化試験を行う前に不動態皮膜中の組成を分析した。
The oxidation test was performed by continuously humidifying argon containing 10% O 2 to form a 20% steam atmosphere at 500 ° C. for 100 hours. As the test piece for the oxidation test, a test piece having a size of 20 mm in length and 20 mm in width, with the front and back surfaces being subjected to final pickling, and having an end surface subjected to # 400 polishing treatment was used.
When preparing a test piece for an oxidation test, 17.5% Cr-1.1% Mo-0.2% Ti-0.05% Si-0.12% Mn-0.07% Al-0. A cold-rolled / annealed plate having a composition of 004% C-0.014% N, 17.2% Cr-0.5% Mo-0.17% Ti-0.09% Si-0.07% Mn- A steel sheet obtained by pickling a cold-rolled / annealed sheet having a composition of 0.09% Al-0.002% C-0.0009% N by various pickling methods was used. In addition, the composition in the passive film was analyzed before the oxidation test piece was subjected to the oxidation test.
本発明においては、不動態皮膜中の組成として、表面から深さ２０ｎｍまでの各元素濃度分布を測定して得られた、表面から２０ｎｍ以内における各元素濃度によって構成される濃度比の最大値を用いた。表面から２０ｎｍ以内における各元素濃度によって構成される濃度比の最大値を測定すれば、不動態皮膜の濃度測定は十分なされる。なぜなら、耐酸化性へ影響を及ぼす不動態皮膜はこの範囲の部位内にあるからである。各元素濃度分布の測定には、グロー放電発光分光分析装置（株式会社リガク製、ＧＤＡ７５０）を用いた。 In the present invention, as the composition in the passive film, the maximum value of the concentration ratio constituted by the concentration of each element within 20 nm from the surface, obtained by measuring the concentration distribution of each element from the surface to a depth of 20 nm. Using. If the maximum value of the concentration ratio constituted by the concentration of each element within 20 nm from the surface is measured, the concentration measurement of the passive film is sufficient. This is because the passive film that affects the oxidation resistance is within this range. A glow discharge emission spectroscopic analyzer (manufactured by Rigaku Corporation, GDA750) was used to measure the concentration distribution of each element.
酸化試験の結果を図１および図２に示す。図２は、試験片の表面から２０ｎｍ以内におけるＣｒ、Ｓｉ、Ａｌ，Ｔｉ、ＭｎおよびＦｅの濃度によって構成される濃度比の最大値における（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ＋Ｓｉ＋Ｍｎ）の数値と、酸化試験後の試験片の酸化増量および赤スケール発生有無との関係を示すグラフである。なお、図２に示す（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ＋Ｓｉ＋Ｍｎ）において、Ｃｒ、Ｔｉ、Ａｌ、Ｆｅ、Ｓｉ、Ｍｎは、それぞれ、Ｃｒ、Ｔｉ、Ａｌ、Ｆｅ、Ｓｉ、Ｍｎの含有量［質量％］である。また、図２に示す△は赤スケール無を示し、▲は赤スケール発生を示す。また、図１は、図２に酸化試験の結果を記載した複数の試験片のうちの一部の試験片の写真である。 The results of the oxidation test are shown in FIG. 1 and FIG. FIG. 2 shows the value of (Cr + Ti + Al) / (Fe + Si + Mn) at the maximum value of the concentration ratio constituted by the concentrations of Cr, Si, Al, Ti, Mn and Fe within 20 nm from the surface of the test piece, and after the oxidation test It is a graph which shows the relationship between the oxidation increase of a test piece, and the presence or absence of red scale generation | occurrence | production. In addition, in (Cr + Ti + Al) / (Fe + Si + Mn) shown in FIG. 2, Cr, Ti, Al, Fe, Si, and Mn are the contents [mass%] of Cr, Ti, Al, Fe, Si, and Mn, respectively. . Further, Δ shown in FIG. 2 indicates no red scale, and ▲ indicates the occurrence of red scale. FIG. 1 is a photograph of some test pieces among the plurality of test pieces whose results of the oxidation test are shown in FIG.
図１および図２に示す様に、鋼板の不動態皮膜中の（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ+Ｓｉ+Ｍｎ）の数値は、酸化試験後の酸化増量および赤スケール発生有無に大きく影響する。図１および図２に示すように、鋼板の不動態皮膜中にＣｒ、ＴｉおよびＡｌを濃化させ、（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ＋Ｓｉ＋Ｍｎ）の数値を０．３５以上にした場合、酸化増量が抑制され、赤スケールが生じない（図１（ｂ）参照）。（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ＋Ｓｉ＋Ｍｎ）の数値が０．３５以上になると、Ｃｒ、Ｔｉ、Ａｌの保護性皮膜が生成し、水蒸気雰囲気で生成しやすく、保護性が小さいＦｅの酸化物（例えば、Ｆｅ２Ｏ３，Ｆｅ３Ｏ４）の生成が抑制されて、酸化増量が少なくなるとともに赤スケールが生成しなくなると推察される。 As shown in FIG. 1 and FIG. 2, the numerical value of (Cr + Ti + Al) / (Fe + Si + Mn) in the passive film of the steel sheet greatly influences the increase in oxidation after the oxidation test and the occurrence of red scale. As shown in FIG. 1 and FIG. 2, when Cr, Ti and Al are concentrated in the passive film of the steel sheet and the value of (Cr + Ti + Al) / (Fe + Si + Mn) is 0.35 or more, the increase in oxidation is suppressed. Red scale does not occur (see FIG. 1B). When the value of (Cr + Ti + Al) / (Fe + Si + Mn) is 0.35 or more, a protective film of Cr, Ti, and Al is generated, which is easily generated in a water vapor atmosphere and has a low protective property (for example, Fe 2 It is presumed that the production of O 3 , Fe 3 O 4 ) is suppressed, the oxidation increase is reduced, and the red scale is not produced.
また、尿素ＳＣＲシステムにおいて、高濃度尿素に接する部分では当然ながら、耐尿素性が必要となる。
耐尿素性試験は、次のように行った。即ち、酸化試験において用いた試験片と同様の試験片を６０℃、３０％の尿素水溶液（尿素には、特級試薬を使用した。比液量は３．６ｍｌ・ｃｍ−２とした。）に１４４時間浸漬し、浸漬前後の試験片の重量変化より、腐食速度を求め、ＩＣＰＳを用いて尿素水溶液中のＦｅ，Ｃｒ，Ｎｉ，Ｃｕの分析を行った。耐尿素性試験における腐食速度および尿素水溶液の分析結果が以下の条件（１）（２）をすべて満足した場合に耐尿素性を良好（○）と判断した。
Further, in the urea SCR system, naturally, the urea resistance is required at the portion in contact with the high concentration urea.
The urea resistance test was performed as follows. That is, a test piece similar to the test piece used in the oxidation test was prepared at 60 ° C. and a 30% urea aqueous solution (a special grade reagent was used for urea. The specific liquid amount was 3.6 ml · cm −2 ). It was immersed for 144 hours, the corrosion rate was determined from the change in weight of the test piece before and after immersion, and Fe, Cr, Ni, and Cu in the urea aqueous solution were analyzed using ICPS. When the corrosion rate in the urea resistance test and the analysis result of the urea aqueous solution satisfied all of the following conditions (1) and (2), the urea resistance was judged as good (◯).
（１）腐食速度が０．００１ｇ・ｍ−２・ｈ−１以下であること。
（２）Ｆｅ＜０．５，Ｃｒ＜０．２、Ｎｉ＜０．２，Ｃｕ＜０．２（以上、ｍｇ／ｋｇ）であること。
尚、上記条件（２）は、ＪＩＳ Ｋ２２４７−１による「ディーゼル機関ＮＯｘ還元添加材−ＡＵＳ３２−第一部：性状」（自動車規格ＪＡＳO Ｅ５０２も同様の規格）において規定された不純物規格のうちのステンレスに関連した元素を抽出したものである。
(1) The corrosion rate is 0.001 g · m−2 · h−1 or less.
(2) Fe <0.5, Cr <0.2, Ni <0.2, Cu <0.2 (more than mg / kg).
The above condition (2) is the stainless steel of the impurity standards defined in “Diesel Engine NOx Reduction Additive-AUS32-Part 1: Properties” (similar standard for automobile standard JASO E502) according to JIS K2247-1. Extracted elements related to.
酸化試験および耐尿素性試験の結果より、鋼板の不動態被膜中の（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ+Ｓｉ+Ｍｎ）の数値が０．３５より大きく、かつ必要なＡｌ量が存在した場合、高温酸化性と耐尿素性の両方を満足できることが分かった。以上の知見より、高温水蒸気雰囲気中で尿素水に曝される環境下で優れた耐酸化性および耐尿素性を有するフェライト系ステンレス鋼板を提供可能となる。 From the results of the oxidation test and the urea resistance test, when the value of (Cr + Ti + Al) / (Fe + Si + Mn) in the passive film of the steel sheet is larger than 0.35 and the necessary amount of Al is present, high temperature oxidation It was found that both the resistance and the urea resistance can be satisfied. From the above knowledge, it becomes possible to provide a ferritic stainless steel sheet having excellent oxidation resistance and urea resistance in an environment exposed to urea water in a high-temperature steam atmosphere.
次に製造方法について説明する。
本発明の鋼板の製造方法は、製鋼−熱間圧延−酸洗−冷間圧延−焼鈍・酸洗の各工程よりなる。製鋼においては、前記必須成分および必要に応じて添加される成分を含有する組成を有する鋼を、転炉溶製し続いて２次精錬を行う方法が好適である。溶製した溶鋼は、公知の鋳造方法（連続鋳造）に従ってスラブとする。スラブは、所定の温度に加熱され、所定の板厚に連続圧延で熱間圧延される。
熱間圧延された熱延鋼板は、必要に応じて酸洗される。また、熱延後の熱延板焼鈍は、生産性や材質を考慮して付与しても省略しても構わない。
Next, a manufacturing method will be described.
The manufacturing method of the steel plate of this invention consists of each process of steelmaking-hot rolling-pickling-cold rolling-annealing and pickling. In steelmaking, a method in which secondary refining is performed after steel having a composition containing the essential components and components added as necessary is subjected to furnace melting. The molten steel is made into a slab according to a known casting method (continuous casting). The slab is heated to a predetermined temperature and hot-rolled to a predetermined plate thickness by continuous rolling.
The hot-rolled hot-rolled steel sheet is pickled as necessary. Moreover, the hot-rolled sheet annealing after hot rolling may be applied or omitted in consideration of productivity and material.
冷間圧延条件について、ステンレス鋼板の冷間圧延は、通常ロール径が５０〜１００ｍｍ程度のゼンジミア圧延機でリバース圧延されるか、ロール径が４００ｍｍ以上のタンデム式圧延機で一方向圧延されるかである。本発明ではいずれの冷間圧延方法を採用しても構わない。なお、タンデム式圧延はゼンジミア圧延に比べて生産性おいても優れている。また、加工性の指標であるｒ値を高くするために、ロール径が４００ｍｍ以上のタンデム式圧延機で冷間圧延を施すことが好ましい。冷間圧延された冷延鋼板は、所定の条件で焼鈍される。 Regarding cold rolling conditions, is cold rolling of stainless steel sheet usually reverse rolled with a Sendzimir rolling mill with a roll diameter of about 50 to 100 mm or unidirectionally rolled with a tandem rolling mill with a roll diameter of 400 mm or more? It is. In the present invention, any cold rolling method may be adopted. Tandem rolling is also superior in productivity compared to Sendzimir rolling. In order to increase the r value, which is an index of workability, it is preferable to perform cold rolling with a tandem rolling mill having a roll diameter of 400 mm or more. The cold-rolled cold-rolled steel sheet is annealed under predetermined conditions.
本発明では、焼鈍した後の冷延鋼板を酸洗する最終酸洗処理により所定の不動態皮膜組成を得る。フェライト系ステンレス鋼の酸洗条件としては、種々の酸洗方法がある。本発明者らは、Ｆｅ、Ｓｉ、Ｍｎを積極的に溶解してＣｒ、Ｔｉ、Ａｌを表面に濃化させることが重要であることを見出した。前記特許文献８〜１１においては、フェライト系ステンレスの酸洗に関する技術が開示されている。しかしながら、特許文献８〜１１には本願に記載される、Ａｌを０．０３〜０．５質量％、且つＴｉを０．０５〜０．３０質量％含有するフェライト系ステンレス鋼板は開示されていない。すなわち、耐高温酸化性及び耐尿素性を向上させる目的で、Ｃｒ、Ｔｉ、Ａｌを表面に濃化させるために酸洗を行う技術は開示されていなかったのである。本発明者らは、このようなＡｌ及びＴｉ組成を有するフェライト系ステンレス冷延鋼板を、硝酸濃度が５０〜２００ｇ／Ｌで温度が５０〜８０℃の溶液に４秒以上浸漬して酸洗することでＣｒ，Ｔｉ，Ａｌが表面に濃化し、表面２０ｎｍ以内における濃度比（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ＋Ｓｉ＋Ｍｎ）が０．３５を超えることを見出した。更に、酸洗後に得られたフェライト系ステンレス鋼板及びそれを加工して製造されたタンク、パイプ、プレート、棒、スプリング等の内燃機関の尿素ＳＣＲシステム用部品が、耐高温酸化性と耐尿素性の両方を同時に満足することを見出した。 In this invention, a predetermined passive film composition is obtained by the final pickling process which pickles the cold-rolled steel plate after annealing. As pickling conditions for ferritic stainless steel, there are various pickling methods. The present inventors have found that it is important to actively dissolve Fe, Si, and Mn to concentrate Cr, Ti, and Al on the surface. In the said patent documents 8-11, the technique regarding the pickling of ferritic stainless steel is disclosed. However, Patent Documents 8 to 11 do not disclose a ferritic stainless steel sheet containing 0.03 to 0.5% by mass of Al and 0.05 to 0.30% by mass of Ti described in the present application. . That is, for the purpose of improving high-temperature oxidation resistance and urea resistance, a technique for pickling to concentrate Cr, Ti, and Al on the surface has not been disclosed. The present inventors pickle a ferritic stainless steel cold-rolled steel sheet having such an Al and Ti composition by immersing it in a solution having a nitric acid concentration of 50 to 200 g / L and a temperature of 50 to 80 ° C. for 4 seconds or more. As a result, it was found that Cr, Ti, Al was concentrated on the surface, and the concentration ratio (Cr + Ti + Al) / (Fe + Si + Mn) within 20 nm of the surface exceeded 0.35. In addition, ferritic stainless steel sheets obtained after pickling and parts for internal combustion engine urea SCR systems such as tanks, pipes, plates, rods, springs, etc. manufactured by processing them are resistant to high-temperature oxidation and urea. It was found that both were satisfied at the same time.
硝酸濃度が５０ｇ／Ｌに満たないと、酸洗による不動態皮膜の形成効果が充分に得られず、更にスケール残りが問題となる。また、硝酸濃度が２００ｇ／Ｌを超えると不動態皮膜の形成効果は飽和し、酸洗液コストが上昇してしまう。従って硝酸濃度は５０〜２００ｇ／Ｌとした。
また、溶液温度が５０℃に満たないと、鋼板表面の反応が不十分となり、目的とする不動態皮膜組成比を得ることが困難となる。更に、溶液温度が８０℃を超えるとＮＯｘの発生が問題となる。従って溶液温度は５０〜８０℃とした。
If the nitric acid concentration is less than 50 g / L, the effect of forming a passive film by pickling cannot be obtained sufficiently, and the remaining scale becomes a problem. On the other hand, if the nitric acid concentration exceeds 200 g / L, the effect of forming a passive film is saturated, and the cost of pickling solution increases. Therefore, the nitric acid concentration was 50 to 200 g / L.
On the other hand, when the solution temperature is less than 50 ° C., the reaction on the steel sheet surface becomes insufficient, and it becomes difficult to obtain the desired passive film composition ratio. Furthermore, when the solution temperature exceeds 80 ° C., generation of NOx becomes a problem. Therefore, the solution temperature was 50-80 ° C.
更に、浸漬時間は、あまり短いと不動態皮膜の組成比の調整が困難となり、スケール残りも問題となる。従って４秒以上とした。浸漬時間に上限は設けていないが、生産性に及ぼす影響を考えると１００秒とするのが好ましい。更に好ましくは７０秒である。 Furthermore, if the immersion time is too short, it is difficult to adjust the composition ratio of the passive film, and the remaining scale is also a problem. Therefore, it was set to 4 seconds or more. Although there is no upper limit for the dipping time, it is preferably set to 100 seconds in view of the effect on productivity. More preferably, it is 70 seconds.
酸洗に用いる溶液には、弗酸を含有しても良く、酸洗において電解処理を施しても構わない。また、この酸洗の前処理として、ＮａＯＨ＋ＮａＮＯ３の溶融塩によるソルトバス法、ＮａＳＯ４、Ｈ２ＳＯ４、ＮａＮＯ３、Ｎａ２ＳｉＦ６などの溶液中で予備脱スケール処理する電解酸洗法を用いても良いが、デスケール処理性やＣｒ、Ｔｉ，Ａｌを不動態皮膜中に濃化させる観点から、ソルト処理を施すことが望ましい。 The solution used for pickling may contain hydrofluoric acid and may be subjected to electrolytic treatment in pickling. Further, as a pretreatment for the pickling, a salt bath method using a molten salt of NaOH + NaNO 3 , an electrolytic pickling method in which a preliminary descaling process is performed in a solution of NaSO 4 , H 2 SO 4 , NaNO 3 , Na 2 SiF 6, etc. Although it may be used, it is desirable to perform a salt treatment from the viewpoint of descalability and concentration of Cr, Ti, Al in the passive film.
他工程の製造方法については特に規定しないが、熱延条件、熱延板厚、冷延鋼板の焼鈍温度、雰囲気などは適宜選択すれば良い。また、冷延・焼鈍後に調質圧延やテンションレベラーを付与しても構わない。更に、製品板厚についても、要求部材厚に応じて選択すれば良い。 The manufacturing method in other steps is not particularly defined, but the hot rolling conditions, the hot rolled sheet thickness, the annealing temperature of the cold rolled steel sheet, the atmosphere, etc. may be appropriately selected. Further, temper rolling or tension leveler may be applied after cold rolling and annealing. Further, the product plate thickness may be selected according to the required member thickness.
なお、上述した実施形態においては、上述した所定の組成を有するステンレス冷延鋼板を、硝酸濃度が５０〜２００ｇ／Ｌで温度が５０〜８０℃の溶液に４秒以上浸漬して酸洗することにより、尿素ＳＣＲシステム部品用フェライト系ステンレス鋼板を製造する方法や、尿素ＳＣＲシステム部品用フェライト系ステンレス鋼板からなる尿素ＳＣＲシステム部品を例に挙げて説明したが、本発明は本実施形態に限定されるものではない。
例えば、本発明の尿素ＳＣＲシステム部品の製造方法は、酸洗前または酸洗後の上述した所定の組成を有するステンレス冷延鋼板を、部品形状に加工して尿素ＳＣＲシステム部材とし、その後、尿素ＳＣＲシステム部材を上記条件で酸洗して尿素ＳＣＲシステム部品とする方法であってもよい。この場合であっても、優れた耐酸化性及び耐尿素性を有する尿素ＳＣＲシステム部品が得られる。このような製造方法は、対象とする部品が強加工を必要とするものであって、ステンレス冷延鋼板として、酸洗により表層に不動態被膜が形成されている本発明のステンレス冷延鋼板を用いたとしても、部品形状に加工することによって不動態被膜が損傷を受けることが懸念され、そのために耐酸化性および耐尿素性が低下する懸念がある場合に、特に有効な方法である。
In the above-described embodiment, the stainless cold-rolled steel sheet having the above-mentioned predetermined composition is pickled by dipping in a solution having a nitric acid concentration of 50 to 200 g / L and a temperature of 50 to 80 ° C. for 4 seconds or more. The method for producing a ferritic stainless steel sheet for urea SCR system parts and the urea SCR system part made of ferritic stainless steel sheets for urea SCR system parts have been described as examples. However, the present invention is limited to this embodiment. It is not something.
For example, the urea SCR system component manufacturing method of the present invention is a urea SCR system member obtained by processing a stainless cold-rolled steel sheet having the above-described predetermined composition before or after pickling into a component shape. A method may be used in which the SCR system member is pickled under the above conditions to form a urea SCR system component. Even in this case, a urea SCR system component having excellent oxidation resistance and urea resistance can be obtained. Such a manufacturing method requires that the target part requires strong processing, and the stainless cold-rolled steel sheet of the present invention in which a passive film is formed on the surface layer by pickling as a stainless cold-rolled steel sheet. Even if it is used, it is a particularly effective method when there is a concern that the passive film is damaged by processing into a part shape, and there is a concern that the oxidation resistance and urea resistance may be lowered.
表１および表２に示す成分組成の鋼を溶製してスラブに鋳造し、スラブを熱間圧延後、熱延コイルを酸洗し、冷間圧延を行うことにより１．２ｍｍ厚の冷延鋼板とした。その後、焼鈍・酸洗を施して製品板とした。冷延鋼板の焼鈍温度は、８５０〜９５０℃とし、表３および表４に示す酸洗条件で酸洗、または酸洗および電解処理を行った。 A steel having the composition shown in Table 1 and Table 2 is melted and cast into a slab. After the slab is hot-rolled, the hot-rolled coil is pickled and cold-rolled to obtain a 1.2 mm thick cold-rolled steel. A steel plate was used. Then, it annealed and pickled and made the product board. The annealing temperature of the cold-rolled steel sheet was 850 to 950 ° C., and pickling or pickling and electrolytic treatment were performed under the pickling conditions shown in Tables 3 and 4.
製品板の表面から深さ２０ｎｍまでの各元素濃度分布を、グロー放電発光分光分析装置（株式会社リガク製、ＧＤＡ７５０）を用いて測定し、表面から２０ｎｍ以内における各元素濃度によって構成される濃度比の最大値における（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ＋Ｓｉ＋Ｍｎ）の数値（不動態皮膜組成比（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ+Ｓｉ+Ｍｎ））を算出した。その結果を表３および表４に示す。 Each element concentration distribution from the surface of the product plate to a depth of 20 nm is measured using a glow discharge emission spectroscopic analyzer (manufactured by Rigaku Corporation, GDA750), and the concentration ratio constituted by the concentration of each element within 20 nm from the surface. The numerical value of (Cr + Ti + Al) / (Fe + Si + Mn) (passive film composition ratio (Cr + Ti + Al) / (Fe + Si + Mn)) was calculated. The results are shown in Tables 3 and 4.
このようにして得られた製品板から、前記の酸化試験と同様にして酸化試験の試験片を採取し、前記の酸化試験即ち、１０％のＯ２を含むアルゴンに加湿処理して２０％水蒸気雰囲気とし、５００℃で１００時間連続して行う酸化試験を行ない、赤スケール発生有無を目視観察した。赤スケールの発生が見られたものを×とし、赤スケールの発生が見られなかったものを〇と評価した。 From the product plate thus obtained, a test piece of the oxidation test was collected in the same manner as in the oxidation test, and was humidified in the oxidation test, that is, argon containing 10% O 2 to obtain 20% water vapor. An oxidation test was conducted for 100 hours at 500 ° C. in an atmosphere, and the presence or absence of red scale was visually observed. The case where red scale was observed was evaluated as x, and the case where red scale was not observed was evaluated as ◯.
また、このようにして得られた製品板から、酸化試験において用いた試験片と同様の試験片を採取し、前記の耐尿素性試験と同様にして耐尿素性試験を行い、腐食速度および尿素水溶液の分析結果が上記の条件（１）（２）をすべて満足した場合、耐尿素性（○）とし、それ以外を（×）と判断した。 In addition, from the product plate thus obtained, a test piece similar to the test piece used in the oxidation test is collected, and the urea resistance test is performed in the same manner as the urea resistance test described above. When the analysis result of the aqueous solution satisfied all of the above conditions (1) and (2), it was judged as urea resistance (O), and the others were judged as (x).
表３および表４から明らかなように、本発明で規定する成分組成および不動態皮膜組成比を有し、酸洗条件が本発明の範囲内であるＮｏ．１〜Ｎｏ．１３の鋼は、いずれも赤スケールの発生が無く、良好な酸化特性を示し、耐尿素性も〇となった。
これに対し、本発明の比較例であるＮｏ．１４〜Ｎｏ．２９では、不動態皮膜組成比が低くなり、耐酸化性および耐尿素性が×となった。また、比較例であるＮｏ．３０では、耐尿素性が×となった。
As is apparent from Tables 3 and 4, No. 1 has the component composition and passive film composition ratio defined in the present invention, and the pickling conditions are within the scope of the present invention. 1-No. All the 13 steels had no red scale, showed good oxidation characteristics, and exhibited urea resistance.
In contrast, No. 1 which is a comparative example of the present invention. 14-No. In No. 29, the passive film composition ratio was low, and the oxidation resistance and urea resistance were x. Moreover, No. which is a comparative example. In 30, the urea resistance was x.
比較例のＮｏ．１４、１５の鋼は、それぞれＣとＮが上限外れで、不動態皮膜への特にＣｒ濃化を阻害した結果、耐酸化性が劣る。Ｎｏ．１６の鋼は、Ｓｉが上限外れで、不動態皮膜組成比が低くなり、スケール剥離が生じ易くなる。Ｎｏ．１７の鋼は、Ｍｎが上限外れで、Ｍｎの酸化物が厚く発達することでスケール剥離が生じ易くなる。 Comparative Example No. In the steels of Nos. 14 and 15, C and N are out of the upper limit, respectively, and the oxidation resistance is inferior as a result of inhibiting especially the Cr concentration in the passive film. No. In Steel No. 16, Si is off the upper limit, the passive film composition ratio is low, and scale peeling is likely to occur. No. In Steel No. 17, Mn is off the upper limit, and the exfoliation of the scale is likely to occur due to the thick development of the Mn oxide.
Ｎｏ．１８の鋼はＣｒが下限外れで、該環境では異常酸化が生じる。Ｎｏ．１９の鋼はＴｉ添加量が少なく、酸化スケール内層のＴｉ酸化物が生成しないため、耐酸化性が劣化する。Ｎｏ．２０の鋼はＭｏが上限外れで、コスト高になるとともに不動態皮膜中のＣｒ等の元素濃化が抑制されて耐酸化性が悪くなる。Ｎｏ．２１の鋼はＡｌが少なく、酸化スケール内層のＡｌ酸化物が生成しないため、スケール剥離し易く耐酸化性が劣化する。 No. In No. 18 steel, Cr is off the lower limit, and abnormal oxidation occurs in this environment. No. Steel No. 19 has a small Ti addition amount, and the Ti oxide in the oxide scale inner layer is not generated, so that the oxidation resistance deteriorates. No. In the steel No. 20, Mo is off the upper limit, the cost is increased, and concentration of elements such as Cr in the passive film is suppressed, so that the oxidation resistance is deteriorated. No. Steel No. 21 is low in Al and does not produce Al oxide in the oxide scale inner layer, so that the scale is easily peeled off and the oxidation resistance deteriorates.
Ｎｏ．２２の鋼はＮｂが上限外れでコスト高になり加工性が劣化するとともに表層にＮｂの濃化層が生じてＣｒ，Ｔｉ，Ａｌの拡散および濃化が抑制される。Ｎｏ．２３の鋼はＣｕが上限外れで加工性が劣化するとともに、酸化スケールの最表層にＣｕ酸化物が発達して耐酸化性が劣化する。Ｎｏ．２４の鋼は、Ｎｉが上限外れで、コスト高になるとともに、オーステナイト相が生成しスケール剥離性が劣化する。Ｎｏ．２５はＶが上限外れで、コスト高になるとともに不動態皮膜中のＣｒ等の元素濃化が抑制されて耐酸化性が悪くなる。 No. Steel No. 22 is costly when Nb is off the upper limit and the workability is deteriorated, and a concentrated layer of Nb is formed on the surface layer to suppress the diffusion and concentration of Cr, Ti, Al. No. In Steel No. 23, Cu is off the upper limit and the workability deteriorates, and the Cu oxide develops on the outermost layer of the oxide scale to deteriorate the oxidation resistance. No. In the steel No. 24, Ni is off the upper limit and the cost is increased, and an austenite phase is generated and scale peelability is deteriorated. No. In No. 25, V is outside the upper limit, which increases the cost and suppresses concentration of elements such as Cr in the passive film, resulting in poor oxidation resistance.
Ｎｏ．２６の鋼はＳｎが上限外れで、コスト高や製造性が著しく劣化する他、長時間連続酸化で表層粒界にＳｎが粒界酸化してスケール剥離を伴う。Ｎｏ．２７の鋼はＢが上限外れで加工性が劣化する他、粒界にＣｒ炭窒化物が生成し耐酸化特性を劣化させる。 No. In Steel No. 26, Sn is off the upper limit, the cost and productivity are remarkably deteriorated, and Sn is grain boundary oxidized at the surface grain boundary by continuous oxidation for a long period of time, resulting in scale peeling. No. In Steel No. 27, B is off the upper limit and the workability deteriorates, and Cr carbonitrides are formed at the grain boundaries to deteriorate the oxidation resistance.
Ｎｏ．２８と２９の鋼は、鋼成分は本発明範囲内であるが、酸洗条件が外れており、製品表面の不動態皮膜組成比が低くなって、赤スケールが発生する。
Ｎｏ．３０の鋼は、Ａｌをほとんど含まないが、Ｔｉ及びＣｒ含有量が高いため、不動態組成皮膜比（Ｃｒ＋Ａｌ＋Ｔｉ）／（Ｆｅ＋Ｓｉ＋Ｍｎ）の数値が本発明を満たす。従って耐酸化特性は良好だが、Ａｌが欠乏しているため、耐尿素性において劣る。
No. Steels Nos. 28 and 29 are within the scope of the present invention, but the pickling condition is removed, the passive film composition ratio on the product surface is lowered, and red scale is generated.
No. Steel No. 30 contains almost no Al, but has a high Ti and Cr content, so the value of passive composition film ratio (Cr + Al + Ti) / (Fe + Si + Mn) satisfies the present invention. Therefore, although the oxidation resistance is good, the lack of Al is inferior in urea resistance.
本発明例において良好な耐酸化性及び耐尿素性を示した鋼板（製品板）は、尿素ＳＣＲシステム用のタンク,パイプ、プレート、棒、スプリング等の部品に簡便に加工することが可能であり、そのような部品及びそれを用いて製造した尿素ＳＣＲシステムは、耐酸化性及び耐尿素性に優れ、良好な性能を示すものである。
また、劣勢な特性を示した比較例の鋼板（製品板）を用いて製造した部品及びそれを用いて製造した尿素ＳＣＲシステムは、耐酸化性及び耐尿素性において劣勢である。
Steel plates (product plates) showing good oxidation resistance and urea resistance in the examples of the present invention can be easily processed into parts such as tanks, pipes, plates, bars and springs for urea SCR systems. Such a component and a urea SCR system manufactured using the same are excellent in oxidation resistance and urea resistance and exhibit good performance.
Moreover, the parts manufactured using the steel plate (product plate) of the comparative example which showed inferior characteristics and the urea SCR system manufactured using the same are inferior in oxidation resistance and urea resistance.
以上の説明から明らかなように、本発明によれば高価な合金元素を多量に添加せずとも尿素ＳＣＲシステムに好適で耐酸化特性に優れたフェライト系ステンレス鋼板を提供することが出来、特にディーゼル自動車の尿素ＳＣＲシステムに適用することにより、優れた尿素ＳＣＲシステム用部品を製造することができる。この部品を用いて尿素ＳＣＲシステムを製造することにより環境対策に大きく寄与することが可能となる。 As is apparent from the above description, according to the present invention, it is possible to provide a ferritic stainless steel sheet that is suitable for the urea SCR system and has excellent oxidation resistance without adding a large amount of expensive alloy elements. By applying it to a urea SCR system for automobiles, an excellent urea SCR system component can be manufactured. Manufacturing a urea SCR system using this component can greatly contribute to environmental measures.
Claims (5)
（Ｃｒ＋Ｔｉ＋Ａｌ）／（Ｆｅ+Ｓｉ+Ｍｎ）＞０．３５
上記式において、Ｃｒ、Ｔｉ、Ａｌ、Ｆｅ、Ｓｉ、Ｍｎは、それぞれ、Ｃｒ、Ｔｉ、Ａｌ、Ｆｅ、Ｓｉ、Ｍｎの含有量［質量％］である。 In mass%, C: 0.010% or less, N: 0.020% or less, Si: 0.5% or less, Mn: 0.5% or less, Cr: 10.0-20.0%, Ti: 0.05 to 0.30%, Mo: 1.5% or less, Al: 0.03 to 0.5%, the balance being Fe and inevitable impurities, and Cr, Si within 20 nm from the surface For urea SCR system parts characterized in that the maximum value of the concentration ratio constituted by the concentrations of Al, Ti, Mn and Fe has the relationship shown in the following formula and is excellent in high-temperature oxidation resistance and urea resistance Ferritic stainless steel sheet.
(Cr + Ti + Al) / (Fe + Si + Mn)> 0.35
In the above formula, Cr, Ti, Al, Fe, Si, and Mn are the contents [% by mass] of Cr, Ti, Al, Fe, Si, and Mn, respectively.
前記尿素ＳＣＲシステム部材を、硝酸濃度が５０〜２００ｇ／Ｌで温度が５０〜８０℃の溶液に４秒以上浸漬して酸洗して尿素ＳＣＲシステム部品とする工程とを含むことを特徴とする尿素ＳＣＲシステム部品の製造方法。
Processing a stainless cold-rolled steel sheet having the composition according to claim 1 or 2 into a component shape to form a urea SCR system member;
A step of immersing the urea SCR system member in a solution having a nitric acid concentration of 50 to 200 g / L and a temperature of 50 to 80 ° C. for 4 seconds or more to pickle and form a urea SCR system component. Urea SCR system component manufacturing method.
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