JP6105167B2 - Pickling method of high chromium ferritic stainless cold rolled steel sheet - Google Patents
Pickling method of high chromium ferritic stainless cold rolled steel sheet Download PDFInfo
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- 238000005554 pickling Methods 0.000 title claims description 188
- 239000011651 chromium Substances 0.000 title claims description 83
- 229910052804 chromium Inorganic materials 0.000 title claims description 70
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 title claims description 68
- 239000010960 cold rolled steel Substances 0.000 title claims description 56
- 238000000034 method Methods 0.000 title claims description 49
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 152
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 107
- 239000002253 acid Substances 0.000 claims description 86
- 239000000243 solution Substances 0.000 claims description 71
- 229910001220 stainless steel Inorganic materials 0.000 claims description 58
- 150000003839 salts Chemical class 0.000 claims description 54
- 230000007935 neutral effect Effects 0.000 claims description 53
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims description 46
- 238000000137 annealing Methods 0.000 claims description 34
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 31
- 239000010935 stainless steel Substances 0.000 claims description 24
- 230000033116 oxidation-reduction process Effects 0.000 claims description 20
- 238000007654 immersion Methods 0.000 claims description 19
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims description 14
- 229910052750 molybdenum Inorganic materials 0.000 claims description 14
- 239000011733 molybdenum Substances 0.000 claims description 14
- 229910052710 silicon Inorganic materials 0.000 claims description 14
- 239000010703 silicon Substances 0.000 claims description 14
- 238000005406 washing Methods 0.000 claims description 14
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 13
- 239000008151 electrolyte solution Substances 0.000 claims description 12
- 229910000859 α-Fe Inorganic materials 0.000 claims description 12
- 239000003792 electrolyte Substances 0.000 claims description 9
- 229910052751 metal Inorganic materials 0.000 claims description 8
- 239000002184 metal Substances 0.000 claims description 8
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 6
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims description 6
- 239000010949 copper Substances 0.000 claims description 6
- 229910052742 iron Inorganic materials 0.000 claims description 6
- 229910052938 sodium sulfate Inorganic materials 0.000 claims description 6
- 235000011152 sodium sulphate Nutrition 0.000 claims description 6
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 5
- 229910052802 copper Inorganic materials 0.000 claims description 5
- 238000007598 dipping method Methods 0.000 claims description 5
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 3
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 claims description 3
- 150000002739 metals Chemical class 0.000 claims description 3
- 229910052759 nickel Inorganic materials 0.000 claims description 3
- 239000010936 titanium Substances 0.000 claims description 3
- 229910052719 titanium Inorganic materials 0.000 claims description 3
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 2
- 229910052748 manganese Inorganic materials 0.000 claims description 2
- 239000011572 manganese Substances 0.000 claims description 2
- 229910000831 Steel Inorganic materials 0.000 description 50
- 239000010959 steel Substances 0.000 description 50
- 230000000052 comparative effect Effects 0.000 description 45
- 239000000463 material Substances 0.000 description 13
- 229910052814 silicon oxide Inorganic materials 0.000 description 13
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 12
- 150000004965 peroxy acids Chemical class 0.000 description 11
- 230000003628 erosive effect Effects 0.000 description 10
- 238000005260 corrosion Methods 0.000 description 9
- 230000007797 corrosion Effects 0.000 description 9
- 238000004090 dissolution Methods 0.000 description 9
- 239000002436 steel type Substances 0.000 description 8
- QPJSUIGXIBEQAC-UHFFFAOYSA-N n-(2,4-dichloro-5-propan-2-yloxyphenyl)acetamide Chemical compound CC(C)OC1=CC(NC(C)=O)=C(Cl)C=C1Cl QPJSUIGXIBEQAC-UHFFFAOYSA-N 0.000 description 7
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 6
- 229910017604 nitric acid Inorganic materials 0.000 description 6
- 239000013078 crystal Substances 0.000 description 5
- -1 iron ions Chemical class 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 150000002500 ions Chemical class 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 239000007800 oxidant agent Substances 0.000 description 3
- 238000002791 soaking Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical group Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000007789 gas Substances 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000002351 wastewater Substances 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- JPVYNHNXODAKFH-UHFFFAOYSA-N Cu2+ Chemical compound [Cu+2] JPVYNHNXODAKFH-UHFFFAOYSA-N 0.000 description 1
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 1
- HILYUWSZFGFBNW-UHFFFAOYSA-N S(O)(O)(=O)=O.OO.F Chemical compound S(O)(O)(=O)=O.OO.F HILYUWSZFGFBNW-UHFFFAOYSA-N 0.000 description 1
- MMDJDBSEMBIJBB-UHFFFAOYSA-N [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] Chemical compound [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] MMDJDBSEMBIJBB-UHFFFAOYSA-N 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 229910000963 austenitic stainless steel Inorganic materials 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 238000005282 brightening Methods 0.000 description 1
- 230000001680 brushing effect Effects 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 239000000460 chlorine Substances 0.000 description 1
- 229910052801 chlorine Inorganic materials 0.000 description 1
- 229910000423 chromium oxide Inorganic materials 0.000 description 1
- 239000000599 controlled substance Substances 0.000 description 1
- 229910001431 copper ion Inorganic materials 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000010494 dissociation reaction Methods 0.000 description 1
- 230000005593 dissociations Effects 0.000 description 1
- 238000002848 electrochemical method Methods 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 230000014509 gene expression Effects 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 239000003112 inhibitor Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 150000002505 iron Chemical class 0.000 description 1
- 238000007726 management method Methods 0.000 description 1
- WPBNNNQJVZRUHP-UHFFFAOYSA-L manganese(2+);methyl n-[[2-(methoxycarbonylcarbamothioylamino)phenyl]carbamothioyl]carbamate;n-[2-(sulfidocarbothioylamino)ethyl]carbamodithioate Chemical compound [Mn+2].[S-]C(=S)NCCNC([S-])=S.COC(=O)NC(=S)NC1=CC=CC=C1NC(=S)NC(=O)OC WPBNNNQJVZRUHP-UHFFFAOYSA-L 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000012286 potassium permanganate Substances 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical class [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 239000000080 wetting agent Substances 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
- C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
- C25F1/02—Pickling; Descaling
- C25F1/04—Pickling; Descaling in solution
- C25F1/06—Iron or steel
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/081—Iron or steel solutions containing H2SO4
-
- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/086—Iron or steel solutions containing HF
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Mechanical Engineering (AREA)
- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
Description
本発明は、高クロムフェライト系ステンレス冷延鋼板の酸洗方法に係り、より詳しくは、焼鈍温度及び鋼種成分系によって電解酸洗時、印加電流量を調節し、混酸浸漬時、混酸溶液内の遊離フッ酸の含量と酸化還元電位を調節して酸洗することにより、冷延鋼板に存在する焼鈍スケールを効果的に除去する高クロムフェライト系ステンレス冷延鋼板の酸洗方法に関する。 The present invention relates to a pickling method for high chromium ferritic stainless steel cold-rolled steel sheets, more specifically, by adjusting the amount of applied current during electrolytic pickling according to the annealing temperature and the steel type component system, and during immersion in a mixed acid, in a mixed acid solution. The present invention relates to a pickling method for a high chromium ferritic stainless steel cold rolled steel sheet that effectively removes the annealing scale present in the cold rolled steel sheet by adjusting the content of free hydrofluoric acid and the oxidation-reduction potential.
一般に、フェライト系ステンレス鋼は、クロム含量によって低クロムフェライト系ステンレス鋼と高クロムフェライト系ステンレス鋼に区別される。通常、クロム含量が１１〜１４重量％のものを低クロムフェライト系ステンレス鋼、クロム含量が１７〜２６重量％のものを高クロムフェライト系ステンレス鋼という。
クロム含量によって焼鈍熱処理時に形成されるスケールの特性が変化するため、クロム含量によって酸洗方法を異ならせる必要がある。一般に、低クロムフェライト鋼は、焼鈍熱処理時にスケールが厚く形成され、高クロムフェライト鋼は、焼鈍熱処理時にスケールの厚さが低クロムフェライト鋼に比べて相対的に薄く形成される。
Generally, ferritic stainless steel is classified into low chromium ferritic stainless steel and high chromium ferritic stainless steel depending on the chromium content. Usually, a chromium content of 11 to 14% by weight is called a low chromium ferritic stainless steel, and a chromium content of 17 to 26% by weight is called a high chromium ferritic stainless steel.
Since the characteristics of the scale formed during the annealing heat treatment vary depending on the chromium content, it is necessary to vary the pickling method depending on the chromium content. In general, a low chromium ferritic steel is formed with a thick scale during annealing heat treatment, and a high chromium ferritic steel is formed with a relatively small scale thickness during annealing heat treatment compared to a low chromium ferritic steel.
また、鋼種別特性によって焼鈍時の熱処理温度に差があり、焼鈍温度が高いほど、スケールが厚く形成され、スケール内のクロム成分の含量も高くなる。
一方、このようなスケールは製品の外観品質を低下させるのみならず、酸化スケールから腐食が始まって耐食性を低下させる要因として作用する可能性があるため、酸洗過程を通じて表面に形成されたスケールを除去する必要がある。
通常、ステンレス冷延鋼板を製造するにあたり、鋼板上に形成された酸化スケールを除去して美麗な表面品質を得て、且つ鋼板の耐食性を向上させるために、ブラシ処理やショットボールブラスティングのような物理的デスケーリング、硫酸ナトリウム、硫酸又は硝酸電解質などを用いる電解デスケーリング、塩浴又は混酸などによる化学的デスケーリングなどの多様な方法が行われており、このような過程を包括的に「酸洗工程」という。
In addition, there is a difference in the heat treatment temperature during annealing depending on the characteristics of the steel, and the higher the annealing temperature, the thicker the scale is formed and the higher the chromium content in the scale.
On the other hand, such a scale not only deteriorates the appearance quality of the product, but also acts as a factor that starts corrosion from the oxidized scale and lowers the corrosion resistance. Need to be removed.
Usually, when manufacturing stainless cold-rolled steel sheet, brushing or shot ball blasting is used to remove the oxide scale formed on the steel sheet to obtain beautiful surface quality and improve the corrosion resistance of the steel sheet. There are various methods such as physical descaling, electrolytic descaling using sodium sulfate, sulfuric acid or nitric acid electrolytes, and chemical descaling using salt bath or mixed acid. It is called a pickling process.
このような酸洗工程で電解デスケーリングのような１段階電解酸洗と化学的デスケーリングのような２段階混酸浸漬過程が区別される。
このようにステンレス冷延鋼板を酸洗する工程は、従来から一般に８０〜１８０ｇ／Ｌの硝酸及び２〜４０ｇ／Ｌのフッ酸を含む混酸溶液を用いて行われてきた。しかしながら、混酸溶液内に含まれた硝酸は、酸洗槽内のｐＨを低くしてフッ酸の活動度を高くし、鋼板の表面で溶解された２価鉄イオンを３価に酸化させて酸洗に適正な酸化還元電位を維持させる役割を行うが、大気排出規制物質であるＮＯｘを発生させ、廃酸及び洗浄水に硝酸性窒素（ＮＯ３−Ｎ）が多量に含まれることから問題となっている。
よって、国内外の環境規制強化により排出放流水の総窒素の量を制限し、大気排出施設のＮＯｘの濃度を制限するなどにより、酸洗工程で環境汚染防止施設をさらに設置及び運用することが求められたが、上記のような施設を運用するにあたり費用が多く発生して生産単価が顕著に増加するという問題も発生した。
Such a pickling process distinguishes between a one-step electrolytic pickling such as electrolytic descaling and a two-stage mixed acid soaking process such as chemical descaling.
Thus, the process of pickling a stainless cold-rolled steel sheet has been conventionally performed using a mixed acid solution generally containing 80 to 180 g / L nitric acid and 2 to 40 g / L hydrofluoric acid. However, the nitric acid contained in the mixed acid solution lowers the pH in the pickling tank to increase the activity of hydrofluoric acid, and oxidizes the divalent iron ions dissolved on the surface of the steel plate to trivalent acid. performs the role of maintaining the proper redox potential to washing, the problem since it is generated NO x is atmospheric emission controlled substances, nitrate nitrogen in the waste acid and wash water (NO 3 -N) contains a large amount It has become.
Therefore, it limits the amount of total nitrogen in the exhaust effluent by strengthening national and international environmental regulations, such as by limiting the concentration of the NO x atmospheric discharge facility, further installation and operational environmental pollution prevention facilities in pickling However, there was also a problem that the production unit price was remarkably increased due to the high costs associated with the operation of the above facilities.
したがって、このような問題を解決するために、従来の酸洗工程で用いられていた混酸溶液に含まれる硝酸を塩酸又は硫酸などに代替する方法が提案されたが、その場合には、混酸溶液の酸化性が弱いことからスケールに対する溶解速度が低く、溶解過程で金属の表面に黒変現象が発生する可能性がある。
したがって、酸洗性に最も優れたストリップの表面電位に到達することができるように、過酸化水素、過マンガン酸カリウム、３価鉄イオン及び空気注入によって不足した酸化力を補充する方法が開発されてきており、その中でも特に、分解時にも環境に負担を与えない過酸化水素が酸化剤として通常用いられている。
しかしながら、この場合は、添加される酸化剤の適正投入量を探すことが容易ではないため、場合によっては、未酸洗又は過酸洗の結果をもたらす可能性があり、鋼板の表面に黒変現象が発生するなどの問題に効果的且つ定量的に対応することができないという問題がある。
Therefore, in order to solve such a problem, a method has been proposed in which nitric acid contained in the mixed acid solution used in the conventional pickling process is replaced with hydrochloric acid or sulfuric acid. Since the oxidization property is weak, the dissolution rate with respect to the scale is low, and the blackening phenomenon may occur on the surface of the metal during the dissolution process.
Therefore, a method for replenishing the deficient oxidizing power by hydrogen peroxide, potassium permanganate and iron injection so that the surface potential of the strip with the best pickling performance can be reached has been developed. Among them, hydrogen peroxide that does not give a burden to the environment even during decomposition is usually used as an oxidizing agent.
However, in this case, it is not easy to find an appropriate amount of the oxidant to be added, and in some cases, it may result in unpickling or per-pickling, and the surface of the steel plate may turn black. There is a problem that it is impossible to effectively and quantitatively cope with problems such as the occurrence of a phenomenon.
一方、特許文献１では、硫酸、フッ酸、鉄塩を含有し、過酸化水素を定期的に投入し、湿潤剤、光沢剤、腐食抑制剤などの組成を調節して酸洗し、Ｆｅ（III）及びこれによる酸化還元電位（ｏｘｉｄａｔｉｏｎ−ｒｅｄｕｃｔｉｏｎ ｐｏｔｅｎｔｉａｌ、ＯＲＰ）を自動制御する方式により酸洗溶液を管理する技術が提案された。
また、特許文献１の酸洗溶液は製品ＣＬＥＡＮＯＸ（登録商標）３５２として商用化されて世界中に最も広く用いられており、上記特許の酸洗方法は線材及び熱延製品に実用化されて用いられている。
On the other hand, in Patent Document 1, it contains sulfuric acid, hydrofluoric acid, and iron salt, hydrogen peroxide is periodically added, the composition of the wetting agent, brightening agent, corrosion inhibitor, etc. is adjusted and pickled, and Fe ( III) and a technique for managing the pickling solution by a method of automatically controlling the oxidation-reduction potential (ORP) due to this has been proposed.
The pickling solution of Patent Document 1 is commercialized as the product CLEANOX (registered trademark) 352 and is most widely used all over the world. The pickling method of the above patent is put into practical use for wire rods and hot rolled products. It has been.
しかしながら、上記の特許文献１の酸洗方法による場合、製品の生産単価が既存に比べて２０％以上高く、複雑な溶液組成と管理方法を採択していることから問題となっており、何よりも、酸洗速度が１．５〜３ｇ／ｍ２・ｍｉｎ程度と比較的遅いため、１０〜１００秒内に混酸酸洗が完了しなければならない高速酸洗ラインには適さないという問題が提起されている。
よって、特許文献１に対する改良特許として、特許文献２及び特許文献３では、銅及び塩素イオンを酸洗組成物に追加して酸洗速度を高くする方法が提案されたが、上記方法による場合、フェライト系ステンレス鋼板の表面に形成される表面電位（Ｏｐｅｎ ｃｉｒｃｕｉｔ ｐｏｔｅｎｔｉａｌ、ＯＣＰ）が銅イオンの酸化還元電位である０．１Ｖより低くなると、酸洗過程で鋼板の表面に銅粒子が析出して鋼板を変色させる恐れがあり、酸洗溶液に塩素イオンを一定の濃度以上で含有すると、孔食（ｐｉｔｔｉｎｇ ｃｏｒｒｏｓｉｏｎ）が発生する恐れがある。
However, in the case of the pickling method described in Patent Document 1, the production unit price of the product is 20% or more higher than that of the existing product, which is a problem because a complicated solution composition and management method are adopted. Since the pickling speed is relatively slow, about 1.5 to 3 g / m 2 · min, there is a problem that it is not suitable for a high-speed pickling line where mixed pickling must be completed within 10 to 100 seconds. ing.
Therefore, as an improved patent for Patent Document 1, in Patent Document 2 and Patent Document 3, a method for increasing the pickling speed by adding copper and chloride ions to the pickling composition was proposed. When the surface potential (Open circuit potential, OCP) formed on the surface of the ferritic stainless steel plate is lower than the redox potential of copper ions of 0.1 V, copper particles are deposited on the surface of the steel plate during the pickling process. If the pickling solution contains chlorine ions at a certain concentration or more, there is a risk that pitting corrosion will occur.
本発明の目的は、残留する酸化スケールがなく、表面光沢度に優れたステンレス鋼板を提供することである。
また、本発明の目的は、鋼板を混酸溶液に浸漬するとき、酸化還元電位によって混酸溶液に投入する過酸化水素の適正量を確認することができるようにすることにより、鋼板の表面が未酸洗又は過酸洗されたり黒変現象が発生することを防止することができるようにすることである。
さらに、本発明の目的は、鋼板の酸洗工程時に用いられる混酸溶液として硝酸を用いないため、廃水及び排気ガスに対する処理の負担を減らすことができるようにすることである。
An object of the present invention is to provide a stainless steel plate having no residual oxide scale and excellent surface gloss.
Another object of the present invention is to make it possible to confirm the appropriate amount of hydrogen peroxide to be added to the mixed acid solution by the oxidation-reduction potential when the steel sheet is immersed in the mixed acid solution. That is, it is possible to prevent washing or peracid washing or occurrence of blackening.
Furthermore, an object of the present invention is to not use nitric acid as a mixed acid solution used in the pickling process of the steel sheet, so that the burden of treatment on waste water and exhaust gas can be reduced.
本発明の高クロムフェライト系ステンレス冷延鋼板の酸洗方法の一実施例によれば、１０３０℃以上１０５０℃以下の焼鈍温度で焼鈍された１７〜２６重量％のクロムを含有する高クロムフェライト系ステンレス冷延鋼板を中性塩電解酸洗及び硫酸電解酸洗する電解酸洗段階と、電解酸洗を行った冷延鋼板を硫酸及びフッ酸を含む混酸溶液に浸漬する混酸浸漬段階と、を含み、電解酸洗段階時、中性塩電解酸洗の印加電流量と硫酸電解酸洗の印加電流量の和は１２Ａ／ｄｍ２以上２０Ａ／ｄｍ２以下に調節されることを特徴とする。 According to one embodiment of the pickling method of the high chromium ferrite stainless cold-rolled steel sheet of the present invention, the high chromium ferrite system containing 17 to 26 wt% chromium annealed at an annealing temperature of 1030 ° C. or higher and 1050 ° C. or lower. Electrolytic pickling stage for neutral salt electrolytic pickling and sulfuric acid electrolytic pickling of stainless cold-rolled steel sheet, and mixed acid dipping stage for dipping cold-rolled steel sheet subjected to electrolytic pickling in a mixed acid solution containing sulfuric acid and hydrofluoric acid. In addition, the sum of the applied current amount of the neutral salt electrolytic pickling and the applied current amount of the sulfuric acid electrolytic pickling is adjusted to 12 A / dm 2 or more and 20 A / dm 2 or less during the electrolytic pickling step.
本発明の高クロムフェライト系ステンレス冷延鋼板の酸洗方法の他の実施例によれば、９３０℃以上１０３０℃未満の焼鈍温度で焼鈍された１７〜２６重量％のクロムを含有する高クロムフェライト系ステンレス冷延鋼板を中性塩電解酸洗及び硫酸電解酸洗する電解酸洗段階と、電解酸洗を行った冷延鋼板を硫酸及びフッ酸を含む混酸溶液に浸漬する混酸浸漬段階と、を含み、電解酸洗段階時、中性塩電解酸洗の印加電流量と硫酸電解酸洗の印加電流量の和は３０Ａ／ｄｍ２以上５０Ａ／ｄｍ２以下に調節されることが好ましい。
中性塩電解酸洗の印加電流量は８Ａ／ｄｍ２以上であるか、又は電流の印加なしに浸漬によって行われることが好ましい。
According to another embodiment of the pickling method of the high chromium ferrite stainless cold-rolled steel sheet of the present invention, the high chromium ferrite containing 17 to 26 wt% chromium annealed at an annealing temperature of 930 ° C. or more and less than 1030 ° C. An electrolytic pickling stage for neutral salt electrolytic pickling and sulfuric acid electrolytic pickling of a stainless steel cold-rolled steel sheet; a mixed acid soaking stage for immersing the cold-rolled steel sheet subjected to electrolytic pickling in a mixed acid solution containing sulfuric acid and hydrofluoric acid; In the electrolytic pickling step, the sum of the applied current amount of the neutral salt electrolytic pickling and the applied current amount of the sulfuric acid electrolytic pickling is preferably adjusted to 30 A / dm 2 or more and 50 A / dm 2 or less.
The applied current amount of the neutral salt electrolytic pickling is preferably 8 A / dm 2 or more , or is preferably performed by dipping without applying a current .
冷延鋼板の総重量に対してケイ素（Ｓｉ）含量が０．３重量％以下であるか又はモリブデン（Ｍｏ）含量が０．５重量％以下の場合、混酸浸漬段階時に用いられる混酸溶液は８０〜１５０ｇ／Ｌの硫酸及び５〜１２ｇ／Ｌの遊離フッ酸を含み、酸化還元電位（ＯＲＰ）が５５０ｍＶ以上であることが好ましい。
混酸溶液の酸化還元電位が５５０ｍＶ以上に維持されるように混酸溶液に過酸化水素を追加することができる。
When the silicon (Si) content is 0.3% by weight or less or the molybdenum (Mo) content is 0.5% by weight or less based on the total weight of the cold-rolled steel sheet, the mixed acid solution used during the mixed acid immersion step is 80%. It is preferable that -150g / L sulfuric acid and 5-12g / L free hydrofluoric acid are included, and an oxidation-reduction potential (ORP) is 550 mV or more.
Hydrogen peroxide can be added to the mixed acid solution so that the redox potential of the mixed acid solution is maintained at 550 mV or higher.
冷延鋼板の総重量に対してケイ素（Ｓｉ）含量が０．３重量％を超えるか又はモリブデン（Ｍｏ）含量が０．５重量％を超える場合、混酸浸漬段階時に用いられる混酸溶液は８０〜１５０ｇ／Ｌの硫酸及び２０〜３０ｇ／Ｌの遊離フッ酸を含み、酸化還元電位（ＯＲＰ）が３２０ｍＶ以上であることが好ましい。
混酸溶液の酸化還元電位が３２０ｍＶ以上に維持されるように過酸化水素を追加することができる。
中性塩電解酸洗は、濃度１００〜２５０ｇ／Ｌの硫酸ナトリウムを含む電解液を用いて行われることが好ましい。
When the silicon (Si) content exceeds 0.3% by weight or the molybdenum (Mo) content exceeds 0.5% by weight relative to the total weight of the cold-rolled steel sheet, the mixed acid solution used during the mixed acid immersion step is 80 to It preferably contains 150 g / L sulfuric acid and 20-30 g / L free hydrofluoric acid and has an oxidation-reduction potential (ORP) of 320 mV or higher.
Hydrogen peroxide can be added so that the oxidation-reduction potential of the mixed acid solution is maintained at 320 mV or higher.
The neutral salt electrolytic pickling is preferably performed using an electrolytic solution containing sodium sulfate having a concentration of 100 to 250 g / L.
中性塩電解酸洗時に用いられる電解液の温度は５０〜９０℃であればよい。
中性塩電解酸洗は２４〜１００秒間行われることができる。
硫酸電解酸洗は、５０〜１５０ｇ／Ｌの硫酸又は５０〜１５０ｇ／Ｌの硫酸に鉄、クロム、ニッケル、銅、マンガン及びチタンからなる群から選択された一つ以上の金属が溶解されて形成された金属硫酸塩を含む電解液を用いて行われることが好ましい。
The temperature of the electrolytic solution used at the time of neutral salt electrolytic pickling may be 50 to 90 ° C.
The neutral salt electrolytic pickling can be performed for 24 to 100 seconds.
The sulfuric acid electrolytic pickling is formed by dissolving one or more metals selected from the group consisting of iron, chromium, nickel, copper, manganese and titanium in 50 to 150 g / L sulfuric acid or 50 to 150 g / L sulfuric acid. It is preferable to carry out using an electrolytic solution containing the prepared metal sulfate.
硫酸電解酸洗時に用いられる電解液の温度は３０〜６０℃であることが好ましい。
硫酸電解酸洗は１０〜５０秒間行われることがよい。
混酸浸漬段階は２５〜９０秒間行われることがよい。
混酸浸漬段階時、冷延鋼板の表面電位は−０．２〜０Ｖの範囲に維持されることが好ましい。
The temperature of the electrolytic solution used at the time of sulfuric acid electrolytic pickling is preferably 30 to 60 ° C.
The sulfuric acid electrolytic pickling is preferably performed for 10 to 50 seconds.
The mixed acid immersion step may be performed for 25 to 90 seconds.
During the mixed acid immersion stage, the surface potential of the cold rolled steel sheet is preferably maintained in the range of -0.2 to 0V.
本発明によると、本発明は、残留する酸化スケールがなく、表面光沢度に優れた高クロムフェライト系ステンレス冷延鋼板を提供することができる。
また、本発明は、鋼板を混酸溶液に浸漬するとき、酸化還元電位によって混酸溶液に投入する過酸化水素の適正量を確認することにより、鋼板の表面が未酸洗又は過酸洗されて黒変現象が発生する問題を防止することができる。
また、本発明は、鋼板の酸洗工程時に用いられる混酸溶液として硝酸を用いないため、廃水及び排気ガスに対する処理の負担を減らすことができる。
According to the present invention, the present invention can provide a high chromium ferritic stainless steel cold-rolled steel sheet having no residual oxide scale and excellent surface gloss.
The present invention also provides a method for confirming an appropriate amount of hydrogen peroxide to be added to a mixed acid solution by an oxidation-reduction potential when the steel sheet is immersed in a mixed acid solution, so that the surface of the steel sheet is not pickled or peracid washed and blackened. It is possible to prevent a problem that an abnormal phenomenon occurs.
Moreover, since this invention does not use nitric acid as a mixed acid solution used at the time of the pickling process of the steel sheet, it is possible to reduce the burden of treatment on waste water and exhaust gas.
以下、添付の図面に基づき本発明の好ましい実施形態について説明する。しかし、本発明の実施形態は様々な他の形態に変形されることができ、本発明の範囲は以下で説明する実施の形態に限定されない。
本発明は、冷延鋼板の総重量に対して１７〜２６重量％のクロムを含有する高クロムフェライト系ステンレス冷延鋼板の表面に存在する酸化スケールを除去するために酸洗する方法に関する。
より具体的には、本願発明が提供する高クロムフェライト系ステンレス冷延鋼板の酸洗方法は、高クロムフェライト系ステンレス冷延鋼板を中性塩電解酸洗及び硫酸電解酸洗する電解酸洗段階と、電解酸洗を行った冷延鋼板を硫酸及びフッ酸を含む混酸溶液に浸漬する混酸浸漬段階と、を含み、且つ電解酸洗段階時、焼鈍温度によって印加電流量を調節し、混酸浸漬段階時、鋼種成分によって混酸溶液に含まれた遊離フッ酸（Ｆｒｅｅ ＨＦ）の含量及び酸化還元電位（ＯＲＰ）を調節することを特徴とする。
Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention can be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.
The present invention relates to a pickling method for removing oxide scale present on the surface of a high chromium ferritic stainless steel cold rolled steel sheet containing 17 to 26% by weight of chromium with respect to the total weight of the cold rolled steel sheet.
More specifically, the pickling method of the high chromium ferrite stainless cold-rolled steel sheet provided by the present invention is an electrolytic pickling step in which the high chromium ferrite stainless cold-rolled steel sheet is neutral salt electrolytic pickled and sulfuric acid electrolytic pickled. And a mixed acid immersion step of immersing the cold-rolled steel sheet that has been subjected to electrolytic pickling in a mixed acid solution containing sulfuric acid and hydrofluoric acid, and adjusting the amount of applied current according to the annealing temperature during the electrolytic pickling step, soaking the mixed acid In the step, the content of free hydrofluoric acid (Free HF) and the redox potential (ORP) contained in the mixed acid solution are controlled by the steel type component.
本発明の酸洗方法において、高クロムフェライト系ステンレス冷延鋼板には、電解酸洗過程として中性塩電解酸洗及び硫酸電解酸洗を順次行うことができる。
このとき、中性塩電解酸洗は、濃度１００〜２５０ｇ／Ｌの硫酸ナトリウムを電解質として含む電解液を用いて行われ、具体的には、温度が５０〜９０℃の電解液に冷延鋼板を浸漬した後、鋼板の表面の電位が＋、−、＋の順に少なくとも１回以上帯電されるように密度８〜３０Ａ／ｄｍ２の電流を２４〜１００秒間加えて行われる。
また、硫酸電解酸洗は、５０〜１５０ｇ／Ｌの硫酸、又は上記濃度の硫酸に鉄、クロム、ニッケル、銅、マンガン及びチタンからなる群から選択された一つ以上の金属が電気化学的に溶解されて形成された金属硫酸塩を電解質として含む電解液を用いて行われ、具体的には、温度が３０〜６０℃の電解液に冷延鋼板を浸漬した後、鋼板の表面の電位が＋、−、＋の順に少なくとも１回以上帯電されるように密度０〜３０Ａ／ｄｍ２の電流を１０〜５０秒間加えて行われる。
In the pickling method of the present invention, the high chromium ferrite stainless cold-rolled steel sheet can be sequentially subjected to neutral salt electrolytic pickling and sulfuric acid electrolytic pickling as an electrolytic pickling process.
At this time, the neutral salt electrolytic pickling is performed using an electrolytic solution containing sodium sulfate having a concentration of 100 to 250 g / L as an electrolyte. Specifically, the electrolytic solution having a temperature of 50 to 90 ° C. is cold-rolled steel sheet. Then, a current of 8 to 30 A / dm 2 is applied for 24 to 100 seconds so that the surface potential of the steel sheet is charged at least once in the order of +, −, and +.
In addition, sulfuric acid electrolytic pickling is an electrochemical method in which one or more metals selected from the group consisting of iron, chromium, nickel, copper, manganese, and titanium are added to 50 to 150 g / L sulfuric acid or sulfuric acid having the above concentration. This is performed using an electrolytic solution containing a dissolved metal sulfate as an electrolyte. Specifically, after the cold-rolled steel sheet is immersed in an electrolytic solution having a temperature of 30 to 60 ° C., the surface potential of the steel sheet is increased. It is carried out by applying a current having a density of 0 to 30 A / dm 2 for 10 to 50 seconds so as to be charged at least once in the order of +, − and +.
一方、高クロムフェライト系ステンレス鋼の場合、焼鈍時に生成されるスケールに含まれたクロムの含量が高く、特に、焼鈍温度が高いほど、そのクロム含量がより高くなる。このとき、焼鈍スケールに含まれたクロム含量が高いほど、中性塩電解酸洗時に酸化物の溶解が容易であり、例えば、焼鈍温度が１０３０℃以上の場合は、クロム含量の濃縮が酷くなるため、中性塩及び硫酸電解酸洗時、高い印加電流条件では表面溶解による過酸洗が発生する恐れがある。
よって、本発明の一実施例によれば、１０３０℃以上１０５０℃以下の相対的に高い温度で焼鈍された冷延鋼板を電解酸洗する場合において、中性塩電解酸洗の印加電流量と硫酸電解酸洗の印加電流量の和が１２Ａ／ｄｍ２未満の場合は未酸洗が発生する可能性があり、２０Ａ／ｄｍ２を超える場合は過酸洗による表面侵食が発生する可能性があるため、効果的な酸洗のためには中性塩電解酸洗の印加電流量と硫酸電解酸洗の印加電流量の和が１２Ａ／ｄｍ２以上２０Ａ／ｄｍ２以下となるように調節することが好ましい。
On the other hand, in the case of high chromium ferritic stainless steel, the chromium content contained in the scale generated during annealing is high, and in particular, the higher the annealing temperature, the higher the chromium content. At this time, the higher the chromium content contained in the annealing scale, the easier the dissolution of the oxide during the neutral salt electrolytic pickling. For example, when the annealing temperature is 1030 ° C. or higher, the concentration of the chromium content becomes severe. Therefore, at the time of neutral salt and sulfuric acid electrolytic pickling, there is a risk that per pickling due to surface dissolution may occur under high applied current conditions.
Therefore, according to one embodiment of the present invention, in the case of electrolytic pickling a cold-rolled steel sheet annealed at a relatively high temperature of 1030 ° C. or higher and 1050 ° C. or lower, the applied current amount of neutral salt electrolytic pickling and If the sum of the applied current amounts of sulfuric acid electrolytic pickling is less than 12 A / dm 2, unpickling may occur, and if it exceeds 20 A / dm 2 , surface erosion may occur due to over pickling. Therefore, for effective pickling, the sum of the applied current amount of the neutral salt electrolytic pickling and the applied current amount of the sulfuric acid electrolytic pickling is adjusted to be 12 A / dm 2 or more and 20 A / dm 2 or less. It is preferable.
また、本発明の他の実施例によれば、９３０℃以上１０３０℃未満の相対的に低い温度で焼鈍された冷延鋼板を電解酸洗する場合において、中性塩電解酸洗の印加電流量と硫酸電解酸洗の印加電流量の和が３０Ａ／ｄｍ２未満の場合は未酸洗が発生する可能性があり、５０Ａ／ｄｍ２を超える場合は過酸洗による表面侵食が発生する可能性があるため、効果的な電解酸洗のためには中性塩電解酸洗の印加電流量と硫酸電解酸洗の印加電流量の和が３０Ａ／ｄｍ２以上５０Ａ／ｄｍ２以下となるように調節することが好ましい。
但し、本発明において、電解酸洗時、焼鈍温度とは関係なく、中性塩電解酸洗の印加電流量は８Ａ／ｄｍ２以上であり、硫酸電解酸洗の印加電流量は０又は８Ａ／ｄｍ２以上であることが好ましい。
In addition, according to another embodiment of the present invention, in the case of electrolytic pickling a cold-rolled steel sheet annealed at a relatively low temperature of 930 ° C. or more and less than 1030 ° C., the applied current amount of neutral salt electrolytic pickling If the sum of the applied current amount of sulfuric acid and sulfuric acid electrolytic pickling is less than 30 A / dm 2, unpickling may occur, and if it exceeds 50 A / dm 2 , surface erosion due to over pickling may occur. is therefore, for effective electrolytic pickling, as the sum of the applied current amount of neutral salt electrolytic pickling with applied current amount of sulfuric acid electrolyte pickling is 30A / dm 2 or more 50A / dm 2 or less It is preferable to adjust.
However, in the present invention, at the time of electrolytic pickling, regardless of the annealing temperature, the applied current amount of neutral salt electrolytic pickling is 8 A / dm 2 or more, and the applied current amount of sulfuric acid electrolytic pickling is 0 or 8 A / It is preferably dm 2 or more.
具体的には、中性塩電解酸洗時、印加電流量が８Ａ／ｄｍ２未満の場合は、焼鈍スケールを溶解させることができる表面電位が形成されず、中性塩電解酸洗の効果が不足する可能性があるため、十分なスケールの溶解のためには印加電流量が８Ａ／ｄｍ２以上であることが好ましい。
また、硫酸電解酸洗時、印加電流量が０超８Ａ／ｄｍ２未満の場合は、酸洗後の表面が不均一で粗くなる問題が発生する可能性があるため、鋼板の表面に対する均一な酸洗のためには硫酸電解酸洗の印加電流量が０Ａ／ｄｍ２であるか又は８Ａ／ｄｍ２以上であることが好ましい。
Specifically, when the applied current amount is less than 8 A / dm 2 at the time of neutral salt electrolytic pickling, a surface potential capable of dissolving the annealing scale is not formed, and the effect of neutral salt electrolytic pickling is achieved. Since there is a possibility of shortage, the amount of applied current is preferably 8 A / dm 2 or more for sufficient scale dissolution.
In addition, when the applied current amount is more than 0 and less than 8 A / dm 2 during sulfuric acid electrolytic pickling, there is a possibility that the surface after pickling becomes uneven and rough. For pickling, the applied current amount of sulfuric acid electrolytic pickling is preferably 0 A / dm 2 or 8 A / dm 2 or more.
但し、硫酸電解酸洗の印加電流量が０Ａ／ｄｍ２であるというのは、硫酸電解酸洗の前段階である中性塩電解酸洗において焼鈍スケールの溶解が大きい場合は母材の損傷を防止するために電流の印加なしに浸漬によって行われるということを意味する。
また、本発明において中性塩電解酸洗及び硫酸電解酸洗の印加電流量の上限について、その値は二つの電解酸洗の印加電流量の和によって決まり、特に限定されないが、運転コストなどの経済的な点を考慮すると、例えば、印加電流量の上限は３０Ａ／ｄｍ２以下であることが好ましい。
However, the applied current amount of sulfuric acid electrolytic pickling is 0 A / dm 2 because , if the dissolution of the annealing scale is large in the neutral salt electrolytic pickling, which is the previous stage of sulfuric acid electrolytic pickling, the base material is damaged. It means that it is done by immersion without application of current to prevent.
Further, in the present invention, the upper limit of the applied current amount of the neutral salt electrolytic pickling and sulfuric acid electrolytic pickling, the value is determined by the sum of the applied current amount of the two electrolytic pickling, and is not particularly limited, such as operating cost Considering economical points, for example, the upper limit of the applied current amount is preferably 30 A / dm 2 or less.
図２は、本発明において焼鈍温度によって電解酸洗可能な中性塩電解槽及び硫酸電解槽の印加電流領域を示すものであり、図２の領域Ｉは、１７〜２６重量％のクロム含有フェライト系ステンレス鋼の焼鈍温度が１０３０〜１０５０℃の領域で酸洗可能な中性塩電解槽と硫酸電解槽の印加電流範囲を示すものであり、領域IIは、焼鈍温度が９３０℃以上１０３０℃未満で酸洗可能な中性塩電解槽と硫酸電解槽の印加電流範囲を示すものである。
本発明において電解酸洗を行っている間に高クロムフェライト系冷延鋼板の表面に存在するクロム及び鉄の酸化物層は除去されるが、ケイ素酸化物層は残る可能性がある。よって、本発明の酸洗方法は、上記の電解酸洗段階に引き続き電解酸洗を行った冷延鋼板を硫酸及びフッ酸を含む混酸溶液に浸漬する混酸浸漬段階を行うことにより、鋼板上に残留するケイ素酸化物の層を除去することができる。
FIG. 2 shows an applied current region of a neutral salt electrolytic cell and a sulfuric acid electrolytic cell that can be subjected to electrolytic pickling according to the annealing temperature in the present invention. Region I in FIG. 2 is a 17 to 26% by weight chromium-containing ferrite. Shows the applied current range of a neutral salt electrolytic cell and a sulfuric acid electrolytic cell that can be pickled in a region where the annealing temperature of the stainless steel is 1030 to 1050 ° C., and region II has an annealing temperature of 930 ° C. or more and less than 1030 ° C. It shows the applied current range of the neutral salt electrolytic cell and sulfuric acid electrolytic cell that can be pickled.
In the present invention, the chromium and iron oxide layers present on the surface of the high chromium ferrite cold-rolled steel sheet are removed during the electrolytic pickling, but the silicon oxide layer may remain. Therefore, the pickling method of the present invention performs a mixed acid dipping step in which a cold-rolled steel plate that has been subjected to electrolytic pickling following the electrolytic pickling step described above is immersed in a mixed acid solution containing sulfuric acid and hydrofluoric acid. The remaining silicon oxide layer can be removed.
上記の混酸浸漬段階時に用いられる混酸溶液に含まれたフッ酸（ＨＦ）は、下記式（１）のように溶液内で解離し、下記式（２）のように硫酸が解離して生じた水素イオン（Ｈ＋）の濃度、即ち、酸度（ａｃｉｄｉｔｙ）によって平衡状態が変わる。
したがって、本発明は、混酸浸漬段階時、遊離フッ酸が５〜３０ｇ／Ｌの濃度を有する混酸溶液を用いることが好ましい。遊離フッ酸の濃度が５ｇ／Ｌ未満の場合は、遊離フッ酸として存在する濃度が少なく、ケイ素酸化物層に対する溶解力が不足して鋼板の表面に未酸洗の問題が発生する可能性があり、濃度が３０ｇ／Ｌを超える場合は、母材の侵食速度が速くなって酸洗後に鋼板の表面が粗くなる可能性がある。
上記のように、混酸溶液に含まれたフッ酸は鋼板の表面のケイ素酸化物層を除去することができる酸洗力を提供するが、混酸溶液内では一定の酸度以上に有効遊離フッ酸濃度を維持する必要がある。したがって、本発明は、混酸溶液に含まれたフッ酸が解離しないようにするために、混酸溶液にフッ酸と共に一定濃度以上の硫酸を含むことが好ましい。
このとき、適した硫酸の濃度は８０〜１５０ｇ／Ｌであることが好ましい。硫酸の濃度が８０ｇ／Ｌ未満の場合は、有効遊離フッ酸濃度が維持されないことからフッ酸の解離が発生して酸洗力が低下するため、未酸洗の問題が生じる可能性があり、濃度が１５０ｇ／Ｌを超える場合は、硫酸希釈操業中に発熱が発生して操業が困難となるなどの問題が発生する恐れがある。
Accordingly, in the present invention, it is preferable to use a mixed acid solution having a concentration of 5 to 30 g / L of free hydrofluoric acid during the mixed acid immersion stage. When the concentration of free hydrofluoric acid is less than 5 g / L, the concentration present as free hydrofluoric acid is small, and there is a possibility that the problem of unpickling occurs on the surface of the steel sheet due to insufficient solvency for the silicon oxide layer. In the case where the concentration exceeds 30 g / L, the erosion rate of the base material is increased, and the surface of the steel sheet may become rough after pickling.
As described above, the hydrofluoric acid contained in the mixed acid solution provides a pickling power capable of removing the silicon oxide layer on the surface of the steel sheet, but the effective free hydrofluoric acid concentration exceeds a certain acidity in the mixed acid solution. Need to maintain. Therefore, in the present invention, in order to prevent the hydrofluoric acid contained in the mixed acid solution from dissociating, it is preferable that the mixed acid solution contains sulfuric acid having a certain concentration or more together with the hydrofluoric acid.
At this time, the suitable concentration of sulfuric acid is preferably 80 to 150 g / L. When the concentration of sulfuric acid is less than 80 g / L, the effective free hydrofluoric acid concentration is not maintained, so the dissociation of hydrofluoric acid occurs and the pickling power decreases, which may cause a problem of unpickling. When the concentration exceeds 150 g / L, there is a possibility that problems such as generation of heat during the sulfuric acid dilution operation and difficulty in operation will occur.
一方、フェライト系ステンレス鋼の酸化スケールのうち、ケイ素酸化物は、フェライト系結晶のグレインの表面及びグレインとグレインの間の結晶粒界に全て存在し、結晶粒界のケイ素酸化物は、母材の内部の奥にまで存在する。オーステナイト系ステンレス鋼は、結晶の耐食性が高いことから結晶粒界から優先的に侵食されるのに対し、フェライト系ステンレス鋼は、結晶の耐食性が低いことから結晶の内部と結晶粒の間の侵食速度に差がないため、グレインの表面と結晶粒界が選択性なく完全に溶解される。したがって、ケイ素酸化物を全て除去するためには相当部分の母材が溶解される必要がある。
このとき、母材からＦｅ２＋が溶出され、溶出されたＦｅ２＋は過酸化水素のような酸化剤と反応してＦｅ３＋に酸化し、その後、遊離フッ酸と結合してＦｅＦｘ （３−ｘ）の形の錯化合物が生成されて鋼板の表面から除去される。反応は下記式（３）〜（６）のように表され、このような過程が円滑に行われる場合に酸洗速度を高くすることができる。
On the other hand, among the oxide scales of ferritic stainless steel, silicon oxides are all present on the surface of the grains of ferrite-based crystals and at the grain boundaries between the grains, and the silicon oxide at the grain boundaries is the base material. It exists in the back of the inside. Austenitic stainless steel is preferentially eroded from the grain boundaries because of its high crystal corrosion resistance, whereas ferritic stainless steel is eroded between the inside of the crystal and the crystal grains because of its low crystal corrosion resistance. Since there is no difference in speed, the grain surface and the grain boundary are completely dissolved without selectivity. Accordingly, in order to remove all of the silicon oxide, a considerable part of the base material needs to be dissolved.
At this time, Fe 2+ is eluted from the base material, and the eluted Fe 2+ reacts with an oxidizing agent such as hydrogen peroxide to oxidize to Fe 3+ , and then combines with free hydrofluoric acid to form FeF x (3- A complex compound of the form x) is produced and removed from the surface of the steel sheet. The reaction is represented by the following formulas (3) to (6), and the pickling rate can be increased when such a process is smoothly performed.
一方、上記のように冷延鋼板を混酸溶液に浸漬して酸洗を行う場合、母材を一部溶解し残留するケイ素酸化物層まで除去することができるが、鋼種内のモリブデン（Ｍｏ）の含量が高いほど、耐食性が高く、酸洗時の溶解速度を遅くする可能性があり、ケイ素（Ｓｉ）の含量が高いほど、ケイ素酸化物の層が厚く形成され、混酸溶液が母材を溶解することが困難となる可能性がある。
したがって、本発明の酸洗方法は、上記の混酸浸漬段階時、冷延鋼板に含まれたケイ素（Ｓｉ）及びモリブデン（Ｍｏ）の含量によって混酸溶液に含まれた遊離フッ酸（Ｆｒｅｅ ＨＦ）の含量及び酸化還元電位（ＯＲＰ）を調節して行うことにより酸洗を効果的に行うことができる。
即ち、高クロムフェライト系ステンレス鋼において、ケイ素（Ｓｉ）含量が０．３重量％以下であるか又はモリブデン（Ｍｏ）含量が０．５重量％以下の場合は、焼鈍スケールの大部分が電解酸洗段階で除去され、微量で残留するケイ素酸化物のみを除去すればよいため、遊離フッ酸の濃度を低くして母材の侵食を最小化することが好ましい。
したがって、本発明では、ケイ素含量が０．３重量％以下であるか又はモリブデン含量が０．５重量％以下の場合、混酸溶液は濃度８０〜１５０ｇ／Ｌの硫酸及び濃度５〜１２ｇ／Ｌの遊離フッ酸を含むことが好ましく、黒変現象を防止するために混酸溶液の酸化還元電位（ＯＲＰ）が５５０ｍＶ以上に維持されるように過酸化水素を追加することが好ましい。
On the other hand, when the cold-rolled steel sheet is dipped in a mixed acid solution and pickled as described above, a part of the base material can be dissolved to remove the remaining silicon oxide layer, but molybdenum (Mo) in the steel type The higher the content of, the higher the corrosion resistance and the possibility of slowing the dissolution rate during pickling. The higher the content of silicon (Si), the thicker the silicon oxide layer is formed and the mixed acid solution becomes the base material. It can be difficult to dissolve.
Accordingly, the pickling method of the present invention is based on the content of silicon (Si) and molybdenum (Mo) contained in the cold-rolled steel sheet during the mixed acid immersion step, and free HF (Free HF) contained in the mixed acid solution. Pickling can be effectively performed by adjusting the content and the oxidation-reduction potential (ORP).
That is, in the high chromium ferritic stainless steel, when the silicon (Si) content is 0.3% by weight or less or the molybdenum (Mo) content is 0.5% by weight or less, most of the annealing scale is electrolytic acid. Since only the silicon oxide that is removed in the washing step and remains in a trace amount needs to be removed, it is preferable to reduce the concentration of free hydrofluoric acid to minimize erosion of the base material.
Therefore, in the present invention, when the silicon content is 0.3% by weight or less or the molybdenum content is 0.5% by weight or less, the mixed acid solution has a concentration of 80 to 150 g / L sulfuric acid and a concentration of 5 to 12 g / L. It is preferable to include free hydrofluoric acid, and it is preferable to add hydrogen peroxide so that the redox potential (ORP) of the mixed acid solution is maintained at 550 mV or higher in order to prevent the blackening phenomenon.
これに対し、高クロムフェライト系ステンレス鋼において、ケイ素（Ｓｉ）含量が０．３重量％を超える場合は、電解酸洗後、混酸溶液に浸漬する段階の前に、鋼板の表面にケイ素酸化物が多量に存在する可能性があるため、これを効果的に除去するためには高濃度の遊離フッ酸を用いることが好ましい。
また、高クロムフェライト系ステンレス鋼において、モリブデン（Ｍｏ）の含量が０．５重量％を超える場合は、鋼板に含まれたモリブデンの高い含量に起因して耐食性が高くなるに従って混酸溶液による母材の溶解速度が顕著に低下する可能性があるため、混酸溶液として遊離フッ酸を高濃度で含むものを用いることが好ましい。
したがって、本発明では、ケイ素含量が０．３重量％を超えるか又はモリブデン含量が０．５重量％を超える場合、混酸溶液は濃度８０〜１５０ｇ／Ｌの硫酸及び濃度２０〜３０ｇ／Ｌの遊離フッ酸を含むことが好ましく、黒変現象を防止するために混酸溶液の酸化還元電位（ＯＲＰ）が３２０ｍＶ以上に維持されるように過酸化水素を追加することが好ましい。
但し、本発明の酸洗方法において、上記の混酸溶液の酸化還元電位範囲は、ステンレス鋼に含まれたケイ素及びモリブデン含量にかかわらずその上限が特に限定される必要がないが、一般に高フッ酸操業時に溶液内のメタルの含量が非常に高くなり、このような状況で酸化還元電位を高く維持するためには過酸化水素投入量が過多になって経済的な点で問題となる可能性があるため、例えば、その上限は６００ｍＶ以下に維持されることが好ましい。
On the other hand, in the high chromium ferritic stainless steel, when the silicon (Si) content exceeds 0.3% by weight, after the electrolytic pickling, before the step of immersing in the mixed acid solution, silicon oxide is formed on the surface of the steel plate. In order to remove this effectively, it is preferable to use a high concentration of free hydrofluoric acid.
Further, in the high chromium ferritic stainless steel, when the molybdenum (Mo) content exceeds 0.5% by weight, the base material by the mixed acid solution increases as the corrosion resistance increases due to the high molybdenum content contained in the steel plate. Therefore, it is preferable to use a mixed acid solution containing free hydrofluoric acid at a high concentration.
Therefore, in the present invention, when the silicon content exceeds 0.3% by weight or the molybdenum content exceeds 0.5% by weight, the mixed acid solution has a concentration of 80 to 150 g / L sulfuric acid and a concentration of 20 to 30 g / L free. Hydrofluoric acid is preferably included, and hydrogen peroxide is preferably added so that the redox potential (ORP) of the mixed acid solution is maintained at 320 mV or higher in order to prevent the blackening phenomenon.
However, in the pickling method of the present invention, the upper limit of the oxidation-reduction potential range of the mixed acid solution is not necessarily limited regardless of the silicon and molybdenum contents contained in the stainless steel. During operation, the metal content in the solution becomes very high, and in order to maintain a high oxidation-reduction potential in such a situation, an excessive amount of hydrogen peroxide may become an economical problem. Therefore, for example, the upper limit is preferably maintained at 600 mV or less.
図３は、本発明において冷延鋼板に含まれたケイ素及びモリブデンの含量によって混酸浸漬段階で用いる混酸溶液内に含まれた遊離フッ酸の濃度及び混酸溶液の酸化還元電位領域を示すものである。
具体的には、図３の領域IIIは、高クロムフェライト系ステンレス鋼においてＳｉ含量が０．３重量％以下であるか又はＭｏ含量が０．５重量％以下であるステンレス鋼成分系で電解酸洗した後に混酸溶液に浸漬したとき、酸洗可能な遊離フッ酸の濃度が５〜１２ｇ／Ｌ、溶液の酸化還元電位範囲が５５０ｍＶ以上を示すものである。
また、図３の領域IVは、高クロムフェライト系ステンレス鋼においてＳｉ含量が０．３重量％を超えるか又はＭｏ含量が０．５重量％を超えるステンレス鋼成分系で電解酸洗した後に混酸溶液に浸漬したとき、酸洗可能な遊離フッ酸の濃度が２０〜３０ｇ／Ｌ、溶液の酸化還元電位範囲が３２０ｍＶ以上を示すものである。
FIG. 3 shows the concentration of free hydrofluoric acid contained in the mixed acid solution used in the mixed acid immersion step and the redox potential region of the mixed acid solution depending on the contents of silicon and molybdenum contained in the cold-rolled steel sheet in the present invention. .
Specifically, region III in FIG. 3 is a stainless steel component system in which the Si content is 0.3 wt% or less in the high chromium ferritic stainless steel or the Mo content is 0.5 wt% or less. When immersed in a mixed acid solution after washing, the concentration of free hydrofluoric acid that can be pickled is 5 to 12 g / L, and the redox potential range of the solution is 550 mV or more.
Region IV in FIG. 3 shows a mixed acid solution after electrolytic pickling in a stainless steel component system in which the Si content exceeds 0.3 wt% or the Mo content exceeds 0.5 wt% in the high chromium ferritic stainless steel. When immersed in, the concentration of free hydrofluoric acid that can be pickled is 20 to 30 g / L, and the oxidation-reduction potential range of the solution is 320 mV or more.
また、本発明において、混酸浸漬段階時、冷延鋼板の表面電位は−０．２〜０Ｖの範囲に維持することが好ましい。ステンレス鋼は、表面電位によって、溶解される速度及びパターンが決まる。したがって、表面電位が−０．２Ｖ未満の低い値の場合は、母材が主にＦｅ２＋として溶解されＳＯ４ ２−と反応して表面にＦｅＳＯ４化合物を形成するため、表面に黒変現象が発生する可能性があり、この場合、表面で母材が溶解されるときにグレインの特定方位が溶解されすぎて表面が非常に粗くなり、また、表面電位が高い場合にのみ除去されることができるＦｅ３＋が除去されないため、過酸洗及び未酸洗が混在する可能性がある。
これに対し、表面電位が０Ｖを超える場合は、表面が溶解される前に電位が高くなりすぎ、溶解させて除去しなければならない一部の良くない部分がそのまま残るため、酸洗速度も非常に遅くなり、硫酸−フッ酸−過酸化水素システムで鋼板の表面電位を高く維持するためには過酸化水素消耗量が非常に大きくなるため、経済的にも問題となる可能性がある。
本発明において混酸浸漬段階を行う時間は特に限定されず、操業条件によって変動可能であるが、本発明の酸洗方法による場合は２５〜９０秒の短時間内でも行うことができる。
Moreover, in this invention, it is preferable to maintain the surface potential of a cold-rolled steel plate in the range of -0.2-0V at the time of a mixed acid immersion step. In stainless steel, the melting rate and pattern are determined by the surface potential. Therefore, when the surface potential is a low value of less than −0.2 V, the base material is mainly dissolved as Fe 2+ and reacts with SO 4 2− to form a FeSO 4 compound on the surface, so that the blackening phenomenon occurs on the surface. In this case, when the base material is melted at the surface, the specific orientation of the grains is dissolved too much and the surface becomes very rough, and it is removed only when the surface potential is high Since Fe 3+ that can be removed is not removed, per-acid pickling and non-pickling may be mixed.
On the other hand, when the surface potential exceeds 0 V, the potential becomes too high before the surface is dissolved, and some bad parts that must be dissolved and removed remain as it is, so the pickling speed is also very high. However, in order to keep the surface potential of the steel sheet high with the sulfuric acid-hydrofluoric acid-hydrogen peroxide system, the consumption amount of hydrogen peroxide becomes very large, which may cause a problem economically.
In the present invention, the time for performing the mixed acid immersion step is not particularly limited and can be varied depending on the operating conditions. However, in the case of the pickling method of the present invention, it can be performed within a short time of 25 to 90 seconds.
以下、具体的な実施例を挙げて本発明をより具体的に説明する。しかしながら、下記実施例は、本発明の理解のための例示に過ぎず、本発明の範囲を限定するものではない。
本発明において、以下の実施例では４４１鋼と４３９鋼を用い、４４１鋼と４３９鋼という表現は焼鈍スケール内のＣｒ／Ｆｅ成分の含量比を示すものであり、４４１鋼は１０５０℃、４３９鋼は９７０℃で熱処理したものであり、焼鈍スケール内のＣｒ／Ｆｅ含量の成分比は４４１鋼が８．５、４３９鋼が４．３の水準である。
二つの鋼種ともクロム含量が総重量に対して１７重量％程度の水準であるが、鋼種の特性上、焼鈍温度の差によって焼鈍スケール内のＣｒ／Ｆｅ比に差が発生する。
Hereinafter, the present invention will be described more specifically with reference to specific examples. However, the following examples are merely illustrative for understanding of the present invention and do not limit the scope of the present invention.
In the present invention, in the following examples, 441 steel and 439 steel are used, and the expressions 441 steel and 439 steel indicate the content ratio of Cr / Fe component in the annealing scale. Is heat treated at 970 ° C., and the component ratio of Cr / Fe content in the annealing scale is 8.5 for 441 steel and 4.3 for 439 steel.
Although the two steel types have a chromium content of a level of about 17% by weight with respect to the total weight, due to the characteristics of the steel types, a difference occurs in the Cr / Fe ratio in the annealing scale due to the difference in the annealing temperature.
一方、中性塩電解の場合は、Ｃｒ３＋酸化物であるＣｒ２Ｏ３をＣｒ６＋（Ｃｒ２Ｏ４ ２−）イオンとして酸化溶解させるが、Ｆｅ系の酸化物は溶解することが困難であるという特性があるため、スケール内のクロムの含量が高いほどスケールの除去に有利となる。したがって、４３９鋼と４４１鋼は全て焼鈍スケール内のクロム含量が高いことから中性塩電解酸洗には有利な鋼種であるが、Ｃｒ／Ｆｅ比の高い４４１鋼がより有利であると言える。
また、図１は、４３９鋼及び４４１鋼の焼鈍スケールの深さによるＣｒ／Ｆｅ比をグラフで示すものであり、４３９鋼と４４１鋼は全てスケールの外層から内層に向かってクロム含量が高くなってＣｒ／Ｆｅが増加する傾向を示し、母材側に完全に入ると、母材のＣｒ／Ｆｅ含量比で収斂することが確認できる。
On the other hand, in the case of neutral salt electrolysis, Cr 2 O 3 which is Cr 3+ oxide is oxidized and dissolved as Cr 6+ (Cr 2 O 4 2− ) ions, but it is difficult to dissolve Fe-based oxides. Due to the property of being there, the higher the chromium content in the scale, the more advantageous is the removal of the scale. Therefore, 439 steel and 441 steel are all advantageous for neutral salt electrolytic pickling because of their high chromium content in the annealing scale, but it can be said that 441 steel with a high Cr / Fe ratio is more advantageous.
FIG. 1 is a graph showing the Cr / Fe ratio according to the depth of the annealing scale of 439 steel and 441 steel, and all of 439 steel and 441 steel have higher chromium content from the outer layer to the inner layer of the scale. It can be confirmed that the Cr / Fe content tends to increase, and when it completely enters the base metal side, it converges with the Cr / Fe content ratio of the base material.
［実施例１〜５及び比較例１〜１５］
焼鈍温度が１０５０℃の４４１鋼を、硫酸ナトリウムを電解質として含む中性塩電解槽に下記表１のような電流密度を加え、硫酸を電解質として含む硫酸電解槽に下記表１のような電流密度を加えて電解酸洗し、その後、８０ｇ／Ｌの硫酸及び８ｇ／Ｌの遊離フッ酸を含む４０℃の混酸溶液に３０秒間浸漬した。但し、上記溶液の酸化還元電位が５５０ｍＶ以上に維持されるように残留過酸化水素濃度を３ｇ／Ｌで追加した。
酸洗後の結果を下記表１に共に示し、鋼板の表面にスケールが残留しない場合は○で表示し、スケールが残留する場合は未酸洗と評価して×で表示した。また、過酸洗による表面侵食が発生した場合も×で表示した。
[Examples 1 to 5 and Comparative Examples 1 to 15]
441 steel having an annealing temperature of 1050 ° C., a current density as shown in Table 1 below is added to a neutral salt electrolytic cell containing sodium sulfate as an electrolyte, and a current density as shown in Table 1 below is added to a sulfuric acid electrolytic cell containing sulfuric acid as an electrolyte. Then, the sample was electrolytically pickled, and then immersed in a mixed acid solution at 40 ° C. containing 80 g / L sulfuric acid and 8 g / L free hydrofluoric acid for 30 seconds. However, the residual hydrogen peroxide concentration was added at 3 g / L so that the redox potential of the solution was maintained at 550 mV or higher.
The results after pickling are shown in Table 1 below. When scales do not remain on the surface of the steel sheet, they are indicated by ○, and when scales remain, they are evaluated as non-pickling and indicated by ×. In addition, the case where surface erosion due to peracid washing occurred was indicated by x.
また、比較例１、実施例１、比較例８及び比較例９における酸洗後のステンレス鋼の表面の写真を図４の（ａ）〜（ｄ）に示した。
表１から分かるように、実施例１〜５のように中性塩電解槽の電流が８Ａ／ｄｍ２以上、硫酸電解槽の電流が０又は８Ａ／ｄｍ２以上、二つの電解槽の印加電流量の和が１２Ａ／ｄｍ２以上２０Ａ／ｄｍ２以下の場合は正常な酸洗面が確認できる。
しかしながら、比較例１〜５のように中性塩電解槽の電流が８Ａ／ｄｍ２未満の場合は中性塩電解槽におけるスケール溶解量が不足して未酸洗が発生し、比較例７、９及び１２のように中性塩電解槽の電流が８Ａ／ｄｍ２以上であっても硫酸電解酸洗の電流値が０超８Ａ／ｄｍ２未満の場合は不均一酸洗が発生したことが確認できる。
また、比較例８、１０、１１、１３、１４及び１５のように中性塩電解槽の電流と硫酸電解槽の電流の和が２０Ａ／ｄｍ２を超える場合は過酸洗が発生したことが確認できる。
As can be seen from Table 1, as in Examples 1 to 5, the current of the neutral salt electrolytic cell is 8 A / dm 2 or more, the current of the sulfuric acid electrolytic cell is 0 or 8 A / dm 2 or more, the applied current of the two electrolytic cells When the sum of the amounts is 12 A / dm 2 or more and 20 A / dm 2 or less, a normal pickled surface can be confirmed.
However, as in Comparative Examples 1 to 5, when the current of the neutral salt electrolytic cell is less than 8 A / dm 2, the amount of scale dissolution in the neutral salt electrolytic cell is insufficient, and unpickling occurs. Even if the current of the neutral salt electrolyzer was 8 A / dm 2 or more as in 9 and 12, if the current value of the sulfuric acid electrolytic pickling was more than 0 and less than 8 A / dm 2, non-uniform pickling occurred. I can confirm.
Moreover, when the sum of the current of the neutral salt electrolytic cell and the current of the sulfuric acid electrolytic cell exceeded 20 A / dm 2 as in Comparative Examples 8, 10, 11, 13, 14, and 15, it was found that peracid washing occurred. I can confirm.
図４の（ａ）〜（ｄ）は、それぞれ比較例１、実施例１、比較例８及び比較例９における酸洗後のステンレス鋼の表面を写真で示すものであり、（ａ）からは印加電流量が不足して未酸洗によって残留スケールが存在することが確認でき、（ｂ）からは実施例１による正常な酸洗面が確認できる。また、（ｃ）からは過酸洗によって表面侵食が発生して表面が良くないことが確認でき、（ｄ）からは不均一酸洗によって表面が良くないことが確認できる。
実施例から、スケール成分内のクロム成分比が高い場合は、電解酸洗時、中性塩電解槽と硫酸電解槽の二つの電解槽の印加電流量の和が１２Ａ／ｄｍ２以上２０Ａ／ｄｍ２以下の比較的低い電解槽電流量でも酸洗が可能であることが分かる。
(A)-(d) of FIG. 4 shows the surface of the stainless steel after pickling in Comparative Example 1, Example 1, Comparative Example 8 and Comparative Example 9, respectively. It can be confirmed that there is a residual scale due to unpickling due to a shortage of applied current, and a normal pickled surface according to Example 1 can be confirmed from (b). From (c), it can be confirmed that surface erosion occurs due to peracid washing and the surface is not good, and from (d) it can be confirmed that the surface is not good by non-uniform pickling.
From the examples, when the chromium component ratio in the scale component is high, the sum of the applied current amounts of the two electrolytic baths of the neutral salt electrolytic bath and the sulfuric acid electrolytic bath is 12 A / dm 2 or more and 20 A / dm at the time of electrolytic pickling. It can be seen that pickling is possible even with a relatively low electrolytic cell current amount of 2 or less.
［実施例６〜１２及び比較例１６〜２８］
焼鈍温度が９７０℃の４３９鋼を、硫酸ナトリウムを電解質として含む中性塩電解槽に下記表２のような電流密度を加え、硫酸を電解質として含む硫酸電解槽に下記表１のような電流密度を加えて電解酸洗し、その後、８０ｇ／Ｌの硫酸及び８ｇ／Ｌの遊離フッ酸を含む４０℃の混酸溶液に３０秒間浸漬した。但し、上記溶液の酸化還元電位が５５０ｍＶ以上に維持されるように残留過酸化水素濃度を３ｇ／Ｌで追加した。
酸洗後の結果を下記表２に共に示し、鋼板の表面にスケールが残留しない場合は○で表示し、スケールが残留する場合は未酸洗と評価して×で表示した。また、過酸洗による表面侵食が発生した場合も×で表示した。
[Examples 6 to 12 and Comparative Examples 16 to 28]
439 steel having an annealing temperature of 970 ° C., a current density as shown in Table 2 below is added to a neutral salt electrolytic cell containing sodium sulfate as an electrolyte, and a current density as shown in Table 1 below is added to a sulfuric acid electrolytic cell containing sulfuric acid as an electrolyte. Then, the sample was electrolytically pickled and then immersed in a mixed acid solution at 40 ° C. containing 80 g / L sulfuric acid and 8 g / L free hydrofluoric acid for 30 seconds. However, the residual hydrogen peroxide concentration was added at 3 g / L so that the redox potential of the solution was maintained at 550 mV or higher.
The results after pickling are shown in Table 2 below. When scales do not remain on the surface of the steel sheet, they are indicated by ○, and when scales remain, they are evaluated as non-pickling and indicated by ×. In addition, the case where surface erosion due to peracid washing occurred was indicated by x.
また、比較例１６、実施例６及び比較例２８における酸洗後のステンレス鋼の表面の写真を図５の（ａ）〜（ｃ）に示した。
表２から分かるように、実施例６〜１２のように中性塩電解槽の電流が８Ａ／ｄｍ２以上、中性塩電解槽と硫酸電解槽の二つの電解槽の印加電流量の和が３０Ａ／ｄｍ２以上５０Ａ／ｄｍ２以下の場合は正常な酸洗面が確認できる。
しかしながら、比較例１６〜１９のように中性塩電解槽の電流が８Ａ／ｄｍ２未満の場合は中性塩電解槽におけるスケール溶解量が不足して未酸洗が発生し、比較例２０〜２７のように中性塩電解槽の電流が８Ａ／ｄｍ２以上であっても中性塩電解槽の電流と硫酸電解槽の電流の和が３０Ａ／ｄｍ２未満の場合は未酸洗が発生したことが確認できる。また、比較例２８のように中性塩電解槽と硫酸電解槽の二つの電解槽の印加電流量の和が５０Ａ／ｄｍ２を超える場合は過酸洗が発生することが確認できる。
As can be seen from Table 2, the current of the neutral salt electrolytic cell is 8 A / dm 2 or more as in Examples 6 to 12, and the sum of the applied current amounts of the two electrolytic cells of the neutral salt electrolytic cell and the sulfuric acid electrolytic cell is 30A / dm 2 or more 50A / dm 2 or less when the can confirm normal acid wash.
However, when the current in the neutral salt electrolyzer is less than 8 A / dm 2 as in Comparative Examples 16 to 19, the amount of scale dissolution in the neutral salt electrolyzer is insufficient and unpickling occurs, and Comparative Examples 20 to As shown in Fig. 27, even if the current of the neutral salt electrolytic cell is 8 A / dm 2 or more, if the sum of the current of the neutral salt electrolytic cell and the current of the sulfuric acid electrolytic cell is less than 30 A / dm 2, unpickling occurs. It can be confirmed. Moreover, when the sum of the applied current amounts of the two electrolytic cells of the neutral salt electrolytic cell and the sulfuric acid electrolytic cell exceeds 50 A / dm 2 as in Comparative Example 28, it can be confirmed that the peracid washing occurs.
図５の（ａ）〜（ｃ）は、それぞれ比較例１６、実施例６及び比較例２８における酸洗後のステンレス鋼の表面を写真で示すものであり、（ａ）からは比較例１６における印加電流量が不足して未酸洗によって残留スケールが存在することが確認でき、（ｂ）からは実施例６による正常な酸洗面が確認でき、（ｃ）からは比較例２８における過酸洗によって表面侵食が発生して表面が良くないことが確認できる。
本実施例には示していないが、中性塩電解槽と硫酸電解槽の印加電流の和が正常な酸洗の範囲にあるとしても硫酸電解槽の印加電流が８Ａ／ｄｍ２未満の場合は図４の（ｄ）のように不均一酸洗面を示すため好ましくない。
実施例から、スケール成分内のクロム成分比が相対的に低い場合は、電解酸洗時、中性塩電解槽と硫酸電解槽の二つの電解槽の印加電流量の和が３０Ａ／ｄｍ２以上５０Ａ／ｄｍ２以下の非常に高い印加電流量が必要であることが確認できる。
(A)-(c) of FIG. 5 shows the surface of the stainless steel after pickling in the comparative example 16, Example 6, and the comparative example 28 with a photograph, respectively, and from (a) in the comparative example 16. It can be confirmed that there is a residual scale due to insufficient pickling due to an insufficient amount of applied current. From (b), a normal pickled surface according to Example 6 can be confirmed. From (c), peracid washing in Comparative Example 28 can be confirmed. It can be confirmed that surface erosion occurs and the surface is not good.
Although not shown in the present embodiment, even when the sum of the applied currents of the neutral salt electrolytic cell and the sulfuric acid electrolytic cell is within the normal pickling range, the applied current of the sulfuric acid electrolytic cell is less than 8 A / dm 2. Since a non-uniform pickled surface is shown as shown in FIG.
From the examples, when the ratio of the chromium component in the scale component is relatively low, the sum of the applied current amounts of the two electrolytic baths, the neutral salt electrolytic bath and the sulfuric acid electrolytic bath, is 30 A / dm 2 or more during the electrolytic pickling. It can be confirmed that a very high applied current amount of 50 A / dm 2 or less is necessary.
［実施例１３〜２１及び比較例２９〜３３］
下記表３に記載された鋼種を、焼鈍温度によって図３における領域IIIと領域IVを適用して電解酸洗した後、濃度８０ｇ／Ｌの硫酸及び下記表３に記載された濃度の遊離フッ酸を含む４０℃の混酸溶液に３０秒間浸漬した。但し、混酸溶液に過酸化水素を添加して酸化還元電位（ＯＲＰ）が下記表３に記載された値以上を維持するようにした。
酸洗後の結果を下記表３に共に示し、鋼板の表面にスケールが残留しない場合は○で表示し、スケールが残留する場合は未酸洗と評価して×で表示した。また、過酸洗による表面侵食が発生した場合も×で表示した。
また、比較例２９及び比較例３１における酸洗後のステンレス鋼の表面の写真を図６の（ａ）及び（ｂ）に示し、比較例３２及び実施例１６における酸洗後のステンレス鋼の表面の写真を図７の（ａ）及び（ｂ）に示し、比較例３３及び実施例１９における酸洗後のステンレス鋼の表面の写真を図８の（ａ）及び（ｂ）に示した。
[Examples 13 to 21 and Comparative Examples 29 to 33]
The steel types listed in Table 3 below were subjected to electrolytic pickling by applying the regions III and IV in FIG. 3 according to the annealing temperature, and then sulfuric acid having a concentration of 80 g / L and free hydrofluoric acid having the concentrations described in Table 3 below. Was immersed in a mixed acid solution at 40 ° C. for 30 seconds. However, hydrogen peroxide was added to the mixed acid solution so that the oxidation-reduction potential (ORP) was maintained at or above the value described in Table 3 below.
The results after pickling are shown in Table 3 below. When the scale does not remain on the surface of the steel sheet, it is indicated by ◯, and when the scale remains, it is evaluated as non-pickling and indicated by x. In addition, the case where surface erosion due to peracid washing occurred was indicated by x.
Moreover, the photograph of the surface of the stainless steel after pickling in the comparative example 29 and the comparative example 31 is shown to (a) and (b) of FIG. 6, and the surface of the stainless steel after the pickling in the comparative example 32 and Example 16 (A) and (b) of FIG. 7 are shown, and photographs of the surface of the stainless steel after pickling in Comparative Example 33 and Example 19 are shown in (a) and (b) of FIG.
表３から分かるように、１７重量％のクロムを含む４３９鋼を酸洗する場合（比較例２９〜３１及び実施例１３〜１５）は酸化還元電位が５５０ｍＶ以上、遊離フッ酸（ＨＦ）の濃度が５〜１２ｇ／Ｌの範囲で正常に酸洗されることが分かる。しかしながら、比較例２９のように酸化還元電位が５５０ｍＶ未満の場合は未酸洗が発生し、比較例３１のように遊離フッ酸の濃度が１２ｇ／Ｌを超える場合は過酸洗が発生することが分かる。酸化還元電位が５５０ｍＶ以上とは、酸洗時に残留する過酸化水素の濃度を一定以上に維持しなければならないという意味であり、溶液内に過酸化水素が残留する場合の酸化還元電位は通常５５０〜６００ｍＶで測定される。
一方、クロムを１７重量％で含有する鋼であっても、鋼種成分系においてＳｉ含量が重量比で０．３％を超えるか又はＭｏ含量が重量比で０．５％を超える場合である４３０Ｊ１Ｌ、４３６Ｌ鋼は、遊離フッ酸（ＨＦ）の濃度が２０〜３０ｇ／Ｌの範囲で酸洗が可能であるが、比較例３２及び３３のように低濃度のフッ酸を含む混酸溶液を用いる場合は未酸洗が発生することが確認できる。このとき、酸化還元電位が３２０ｍＶ以上であれば酸洗が可能であり、これは、残留過酸化水素がなくても、溶液内の金属イオンのうちＦｅ３＋イオンとＦｅ２＋イオンの比（Ｆｅ３＋／Ｆｅ２＋）が１以上であれば可能であるが、一般に酸化還元電位を３２０ｍＶ以上に維持し続けるためには過酸化水素を一定量注入し続けなければならない。
As can be seen from Table 3, when pickling 439 steel containing 17 wt% chromium (Comparative Examples 29 to 31 and Examples 13 to 15), the oxidation-reduction potential is 550 mV or more, and the concentration of free hydrofluoric acid (HF). Is found to be pickled normally in the range of 5 to 12 g / L. However, when the redox potential is less than 550 mV as in Comparative Example 29, unpickling occurs, and when the concentration of free hydrofluoric acid exceeds 12 g / L as in Comparative Example 31, over pickling occurs. I understand. The oxidation-reduction potential of 550 mV or more means that the concentration of hydrogen peroxide remaining during pickling must be maintained at a certain level or more, and the oxidation-reduction potential when hydrogen peroxide remains in the solution is usually 550. Measured at ~ 600 mV.
On the other hand, even if the steel contains chromium at 17% by weight, 430J1L is a case where the Si content exceeds 0.3% by weight or the Mo content exceeds 0.5% by weight in the steel type component system. 436L steel can be pickled when the concentration of free hydrofluoric acid (HF) is in the range of 20 to 30 g / L. However, as in Comparative Examples 32 and 33, a mixed acid solution containing a low concentration of hydrofluoric acid is used. It can be confirmed that unpickling occurs. At this time, if the oxidation-reduction potential is 320 mV or higher, pickling is possible. This is the ratio of Fe 3+ ions to Fe 2+ ions (Fe 3+ ions) among metal ions in the solution without residual hydrogen peroxide. / Fe 2+ ) is 1 or more, but in general, in order to keep the oxidation-reduction potential at 320 mV or more, a certain amount of hydrogen peroxide must be continuously injected.
図６の（ａ）及び（ｂ）は、比較例２９及び比較例３１における酸洗後のステンレス鋼の表面を写真で示すものであり、（ａ）からは比較例２９における遊離フッ酸の濃度及び混酸溶液の酸化還元電位が全て低いことから表面に未酸洗が発生したことが確認でき、（ｂ）からは比較例３１における遊離フッ酸の濃度が本発明の範囲を超える場合は過酸洗が発生して表面侵食が発生したことが確認できる。
また、図７の（ａ）及び（ｂ）は比較例３２及び実施例１６における酸洗後のステンレス鋼の表面を写真で示すものであり、（ａ）からは比較例３２における遊離フッ酸の濃度が低いことから表面に未酸洗が発生したことが確認でき、（ｂ）からは実施例１６による正常な酸洗面の形状が確認できる。
また、図８の（ａ）及び（ｂ）は、比較例３３及び実施例１９における酸洗後のステンレス鋼の表面を写真で示すものであり、（ａ）からは比較例３３における遊離フッ酸の濃度が低いことから表面に未酸洗が発生したことが確認でき、（ｂ）からは実施例１９による正常な酸洗面の形状が確認できる。
上記のような実施例から、鋼種に含まれた元素によって酸洗性に差が生じ、これにより、酸洗可能な遊離フッ酸の濃度及び溶液の酸化還元電位にも影響を及ぼすことが分かる。
6 (a) and 6 (b) are photographs showing the surface of the stainless steel after pickling in Comparative Example 29 and Comparative Example 31. From (a), the concentration of free hydrofluoric acid in Comparative Example 29 is shown. Since the redox potentials of the mixed acid solution are all low, it can be confirmed that unpickling has occurred on the surface. From (b), when the concentration of free hydrofluoric acid in Comparative Example 31 exceeds the range of the present invention, peracid It can be confirmed that washing has occurred and surface erosion has occurred.
Moreover, (a) and (b) of FIG. 7 shows the surface of the stainless steel after pickling in Comparative Example 32 and Example 16 with a photograph. From (a), the free hydrofluoric acid in Comparative Example 32 is shown. Since the concentration is low, it can be confirmed that unpickling has occurred on the surface, and from (b), the shape of a normal pickled surface according to Example 16 can be confirmed.
8 (a) and (b) are photographs showing the surface of the stainless steel after pickling in Comparative Example 33 and Example 19. From (a), free hydrofluoric acid in Comparative Example 33 is shown. Since the density | concentration of this is low, it can confirm that the unpickling generate | occur | produced on the surface, and the shape of the normal pickled surface by Example 19 can be confirmed from (b).
From the above examples, it can be seen that the pickling property varies depending on the elements contained in the steel type, and this also affects the concentration of free hydrofluoric acid that can be pickled and the redox potential of the solution.
以上、本発明の実施形態について詳細に説明したが、本発明の権利範囲はこれに限定されず、請求の範囲に記載された本発明の技術的思想から外れない範囲内で多様な修正及び変形が可能であるということは、当技術分野の通常の知識を有する者には明らかである。
The embodiment of the present invention has been described in detail above, but the scope of the present invention is not limited to this, and various modifications and variations can be made without departing from the technical idea of the present invention described in the claims. It will be apparent to those having ordinary knowledge in the art.
Claims (15)
前記電解酸洗を行った冷延鋼板を硫酸及びフッ酸を含む混酸溶液に浸漬する混酸浸漬段階と、を含み、
前記電解酸洗段階時、中性塩電解酸洗の印加電流量と硫酸電解酸洗の印加電流量の和は１２Ａ／ｄｍ２以上２０Ａ／ｄｍ２以下に調節されることを特徴とする高クロムフェライト系ステンレス冷延鋼板の酸洗方法。 An electrolytic pickling step of neutral salt electrolytic pickling and sulfuric acid electrolytic pickling of a high chromium ferritic stainless steel cold rolled steel sheet containing 17 to 26 wt% chromium annealed at an annealing temperature of 1030 ° C or higher and 1050 ° C or lower;
A mixed acid immersion step of immersing the cold-rolled steel sheet subjected to the electrolytic pickling in a mixed acid solution containing sulfuric acid and hydrofluoric acid,
In the electrolytic pickling step, the sum of the applied current amount of the neutral salt electrolytic pickling and the applied current amount of the sulfuric acid electrolytic pickling is adjusted to 12 A / dm 2 or more and 20 A / dm 2 or less. Pickling method for ferritic stainless steel cold rolled steel sheet.
前記電解酸洗を行った冷延鋼板を硫酸及びフッ酸を含む混酸溶液に浸漬する混酸浸漬段階と、を含み、
前記電解酸洗段階時、中性塩電解酸洗の印加電流量と硫酸電解酸洗の印加電流量の和は３０Ａ／ｄｍ２以上５０Ａ／ｄｍ２以下に調節されることを特徴とする高クロムフェライト系ステンレス冷延鋼板の酸洗方法。 An electrolytic pickling step of neutral salt electrolytic pickling and sulfuric acid electrolytic pickling of high chromium ferritic stainless steel cold rolled steel sheet containing 17 to 26 wt% chromium annealed at an annealing temperature of 930 ° C or higher and lower than 1030 ° C;
A mixed acid immersion step of immersing the cold-rolled steel sheet subjected to the electrolytic pickling in a mixed acid solution containing sulfuric acid and hydrofluoric acid,
Wherein during the electrolytic pickling stage, high chromium, wherein the sum of the applied current amount of neutral salt electrolytic pickling with applied current amount of sulfuric acid electrolyte pickling is adjusted to 30A / dm 2 or more 50A / dm 2 or less Pickling method for ferritic stainless steel cold rolled steel sheet.
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| KR10-2013-0091116 | 2013-07-31 | ||
| PCT/KR2014/006812 WO2015016538A1 (en) | 2013-07-31 | 2014-07-25 | Method for pickling high-chrome ferritic stainless steel |
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| KR102020512B1 (en) * | 2017-12-15 | 2019-09-10 | 주식회사 포스코 | High chromium ferritic stainless steel excellent in pickling property and its pickling method |
| KR102264958B1 (en) | 2019-11-15 | 2021-06-16 | 한국생산기술연구원 | Pretreatment Solution for Soot Reduction and Low-Temperature Vacuum Carburizing Method Using the Same |
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