EP1013800A2 - Process for pickling stainless steel - Google Patents

Process for pickling stainless steel Download PDF

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Publication number
EP1013800A2
EP1013800A2 EP99123620A EP99123620A EP1013800A2 EP 1013800 A2 EP1013800 A2 EP 1013800A2 EP 99123620 A EP99123620 A EP 99123620A EP 99123620 A EP99123620 A EP 99123620A EP 1013800 A2 EP1013800 A2 EP 1013800A2
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EP
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Prior art keywords
pickling
acidic
electrolyte solution
electrochemical
neutral
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EP99123620A
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German (de)
French (fr)
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EP1013800B1 (en
EP1013800A3 (en
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Jovan Dipl.-Ing. Dr. Starcevic
Dietfried Gamsriegler
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Andritz AG
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Andritz Patentverwaltungs GmbH
Andritz AG
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    • 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
    • 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
    • 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

Definitions

  • Fe 3+ salts sulfate, chloride, nitrate or fluoride salts
  • the aim of the invention is to overcome the disadvantages of both methods, particularly the costly ones Chromate detoxification "to avoid.
  • a favorable further development of the invention is characterized in that that sare and neutral electrochemical pickling stages with each other can be combined, the used electrolyte solution from the neutral electrolyte stage can be metered into the acidic stage.
  • the electrolytic treatment with a charge density of 200 A * sec / dm 2 was carried out in the acidified electrolytic solution, in which the redox potential was set to 440 mV, and then the sample plate in the neutral electrolyte was further treated electrochemically.
  • This combined pickling process has the advantage over a conventional neutral electrolyte treatment that about 20% more pickling loss with a slightly lower gloss could be achieved with the same charge density of, for example, 600 A * sec / dm 2 .
  • a large-scale plant consisting of six electrochemical pickling cells can be optimized so that the first two cells can be operated with acidic electrolyte with a precisely set redox potential and the following four with neutral electrolyte.
  • the resulting advantages are: higher pickling losses in the electrochemical pickling section, ie shorter post-treatment in the subsequent chemical mixed acid (HF + HNO 3 ) pickling section.
  • the end product has the same degree of gloss.
  • the most important advantage, however, is that the entire chromate-containing neutral electrolyte solution can be recycled and the costs for the Cr 6+ reduction are no longer incurred.
  • the sodium sulfate solution (Na 2 SO 4 ) required for pickling in the neutral pH range is obtained by neutralizing the acidic electrolyte solution (H 2 SO 4 , Na 2 SO 4 , Fe 2+ , Fe 3+ , Cr 3+ , Ni 2+ ) with sodium hydroxide (NaOH) or sodium carbonate (Na 2 CO 3 ) and subsequent separation of the metal hydroxides (Fe (OH) 2 , Fe (OH) 3 , Cr (OH) 3 , Ni (OH) 2 ) by filtration, can be recovered.
  • the filtration is advantageously carried out as microfiltration.
  • the experiments are only examples of the process control as defined in the claims.

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  • Chemical & Material Sciences (AREA)
  • Metallurgy (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Electrochemistry (AREA)
  • Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Chemical Treatment Of Metals (AREA)

Abstract

Chemical and/or electrochemical pickling of high grade steel is carried out in an acidic liquid that contains no nitric acid. Consumed electrolyte solution from electrochemical neutral salt pickling lines, preferably sodium sulphate pickling lines, is added.

Description

Die Erfindung betrifft ein Verfahren zum chemischen und/oder elektrochemischen Beizen von Edelstahl in einer salpetersäurefreien und sauren Flüssigkeit.The invention relates to a method for chemical and / or electrochemical pickling of stainless steel in a nitric acid free and acidic liquid.

Beim Beizen von Edelstahlwarmband muß nach dem Warmwalz- und Glühprozeß das Band vom Zunder befreit werden. Dieser Beizvorgang wird in der Regel in Mischsäure (Flußsäure (= HF) und Salpetersäure (= HNO3)) durchgeführt. Hierbei entstehen jedoch nitrose Gase (NOx), so daß in den letzten Jahren zunehmend "salpetersäurefreie Beizverfahren" entwickelt wurden. Das Prinzip aller dieser Beizverfahren besteht darin, daß die Salpetersäure durch eine andere mineralische Säure (Schwefelsäure, Salzsäure) in welcher das Redoxpotential durch den Anteil der Eisenionen verschiedener Wertigkeit (Fe2+/Fe3+) genau eingestellt ist, substituiert wird. Beim Beizen geht Eisen als zweiwertiges Ion in Lösung und das dreiwertige Eisenion wird entweder durch teilweise Oxidation von Fe2+ oder durch Zugabe von Fe3+ - Salzen hergestellt.When pickling stainless steel hot strip, the strip must be freed from the scale after the hot rolling and annealing process. This pickling process is usually carried out in mixed acid (hydrofluoric acid (= HF) and nitric acid (= HNO 3 )). However, this produces nitrous gases (NO x ), so that in the last few years, increasingly "nitric acid-free pickling processes" have been developed. The principle of all these pickling processes is that the nitric acid is substituted by another mineral acid (sulfuric acid, hydrochloric acid) in which the redox potential is precisely set by the proportion of iron ions of different valence (Fe 2+ / Fe 3+ ). When pickling, iron dissolves as a divalent ion and the trivalent iron ion is produced either by partial oxidation of Fe 2+ or by adding Fe 3+ salts.

Es sind Verfahren bekannt, bei denen die Herstellung der dreiwertigen Eisenionen durch Oxidation des Fe2+ mit Wasserstoffperoxid (H2O2) erzeugt werden.Methods are known in which the production of the trivalent iron ions is produced by oxidation of the Fe 2+ with hydrogen peroxide (H 2 O 2 ).

Bei anderen Verfahren werden Fe3+-Salze (Sulfat-, Chlorid-, Nitrat- oder Fluoridsalze) ins Beizbad zugesetzt.In other processes, Fe 3+ salts (sulfate, chloride, nitrate or fluoride salts) are added to the pickling bath.

Nachdem das gebeizte Warmband durch das Walzen zu dünneren Blechstärken reduziert wurde muß es nochmals geglüht werden. Hierbei entsteht eine dünne Zunderschicht, welche auf eine "schonende Art" entfernt werden muß, ohne dabei die Oberflächenqualität (Glanz) zu zerstören. Weltweit hat sich für das Edelstahlkaltband das elektrochemische Beizverfahren in Natriumsulfatlösungen (Neutralelektrolyt) durchgesetzt. Bei diesem neutralen (pH = 7 bis 4) Beizverfahren entsteht das sehr toxische Chromat (Cr6+). Die verbrauchten Beizbäder werden daher in einer separaten Behandlung entgiftet, d.h. Cr6+ wird zu Cr3+ reduziert, bevor sie neutralisiert und die Metallhydroxide abfiltriert werden können. Die Chromat-Entgiftung ist sehr kostenintensiv. Als Reduktionsmittel werden meistens Na2S205 oder ähnliche Schwefelverbindungen eingesetzt.After the pickled hot strip has been reduced to thinner sheet thicknesses by rolling, it must be annealed again. This creates a thin layer of scale, which must be removed in a "gentle way" without destroying the surface quality (gloss). The electrochemical pickling process in sodium sulfate solutions (neutral electrolyte) has established itself worldwide for the stainless steel cold strip. This neutral (pH = 7 to 4) pickling process produces the very toxic chromate (Cr 6+ ). The used pickling baths are therefore detoxified in a separate treatment, ie Cr 6+ is reduced to Cr 3+ before it can be neutralized and the metal hydroxides can be filtered off. Chromate detoxification is very costly. Na 2 S 2 0 5 or similar sulfur compounds are mostly used as reducing agents.

Die Reduktion erfolgt nach folgender Formel: 4 H2CrO4 + 3 Na2S2O5 + 3 H2SO4 => 2 Cr2(SO4)3 + 3 Na2SO4 + 7 H2O The reduction follows the following formula: 4 H 2 CrO 4 + 3 Na 2 S 2 O 5 + 3 H 2 SO 4 => 2 Cr 2 (SO 4 ) 3 + 3 Na 2 SO 4 + 7 H 2 O

Die Reduktion kann auch mit zweiwertigem Eisensulfat FeSO4 durchgeführt werden: 2 H2CrO4 + 6 FeSO4 + 6 H2SO4 => 2 Cr2(SO4)3 + 3 Fe2(SO4)3 + 8 H2O The reduction can also be carried out with divalent iron sulfate FeSO 4 : 2 H 2 CrO 4 + 6 FeSO 4 + 6 H 2 SO 4 => 2 Cr 2 (SO 4 ) 3 + 3 Fe 2 (SO 4 ) 3 + 8 H 2 O

Ziel der Erfindung ist es, die Nachteile beider Verfahren, insbesondere die kostenintensive

Figure 00020001
Chromatentgiftung", zu vermeiden.The aim of the invention is to overcome the disadvantages of both methods, particularly the costly ones
Figure 00020001
Chromate detoxification "to avoid.

Die Erfindung ist daher dadurch gekennzeichnet, daß verbrauchte Elektrolytlösung aus elektrochemischen Neutralsalzbeizlinien, bevorzugt Natriumsulfatbeizlinien, zudosiert wird. Damit kann einerseits das Chromat ohne zusätzliche kostenintensive Reduktionsmittel reduziert ( entgiftet") werden und andererseits eine Oxidation des Eisens von Fe2+ zu Fe3+ erreicht werden.The invention is therefore characterized in that used electrolyte solution from electrochemical neutral salt pickling lines, preferably sodium sulfate pickling lines, is metered in. On the one hand, this means that the chromate can be reduced without additional cost-intensive reducing agents ( are detoxified ") and on the other hand oxidation of iron from Fe 2+ to Fe 3+ can be achieved.

Eine günstige Weiterbildung der Erfindung ist dadurch gekennzeichnet, daß das Redoxpotential in der Beizflüssigkeit durch die Menge an zugegebener Elektrolytlösung auf einen vorgegebenen Wert eingestellt wird, wobei das Reduktions-Oxidationspotential (Redoxpotential) der Beizflüssigkeit gemessen und die Menge der verbrauchten Elektrolytlösung aus elektrochemischen Natriumsulfatbeizlinien entsprechend zudosiert werden kann. Damit kann in vorteilhafter Weise die Beizwirkung für das Edelstahlband in der sauren Beizflüssigkeit eingestellt werden.A favorable further development of the invention is characterized in that that the redox potential in the pickling liquid by the amount of added Electrolyte solution is set to a predetermined value the reduction-oxidation potential (redox potential) of the pickling liquid measured and the amount of electrolyte solution consumed dosed accordingly from electrochemical sodium sulfate pickling lines can be. Thus, the pickling effect for the Stainless steel band can be set in the acidic pickling liquid.

Eine vorteilhafte Ausgestaltung der Erfindung ist dadurch gekennzeichnet, daß bei einem Neuansatz der sauren Beizflüssigkeit ein zweiwertiges und ein dreiwertiges Eisensalz, vorzugsweise Eisensulfate, zugesetzt werden. Damit kann in günstiger Weise ein Start für das Verfahren erreicht werden. Eine vorteilhafte Weiterbildung der Erfindung ist dadurch gekennzeichnet, daß zusätzlich zum verbrauchten Elektrolyten ein anderes Oxidationsmittel, vorzugsweise Wasserstoffperoxid, der Beizflüssigkeit zugeführt wird. Sollte die Menge an anfallender verbrauchter Neutralelektrolytmenge nicht ausreichen, um das gewünschte bzw. notwendige Redoxpotential für den Beizvorgang einzustellen, kann so dieses Redoxpotential in einfacher Weise erzielt werden.An advantageous embodiment of the invention is characterized in that that with a new batch of the acidic pickling liquid a divalent and a trivalent iron salt, preferably iron sulfates, can be added. This enables the process to be started in a favorable manner. An advantageous development of the invention is characterized in that that in addition to the used electrolyte, another oxidizing agent, preferably hydrogen peroxide, fed to the pickling liquid becomes. Should be the amount of neutral electrolyte used not sufficient to achieve the desired or necessary redox potential for Setting the pickling process can make this redox potential easier Way can be achieved.

Eine günstige Ausgestaltung der Erfindung ist dadurch gekennzeichnet, daß Inhibitoren zugesetzt werden. Auf diese Weise kann der Korrosionsangriff auf das Beizgut besser kontrolliert werden.A favorable embodiment of the invention is characterized in that that inhibitors are added. In this way, the corrosion attack be better controlled on the pickling material.

Eine günstige Weiterbildung der Erfindung ist dadurch gekennzeichnet, daß sare und neutrale elektrochemische Beizstufen miteinander kombiniert werden, wobei die gebrauchte Elektrolytlösung aus der Neutralelektrolytstufe in die saure Stufe zudosiert werden kann. Durch diese Kombination läßt sich der Vorteil des Verfahrens in einer Beizlinie erzielen.A favorable further development of the invention is characterized in that that sare and neutral electrochemical pickling stages with each other can be combined, the used electrolyte solution from the neutral electrolyte stage can be metered into the acidic stage. Through this Combination, the advantage of the process can be achieved in a pickling line.

Eine vorteilhafte Ausgestaltung der Erfindung ist dadurch gekennzeichnet, daß die saure Beizflüssigkeit mittels Natronlauge (NaOH) oder Natriumcarbonat (Na2CO3) neutralisiert wird, daß anschließend die entstandenen Metallhydroxide abgetrennt, vorzugsweise abfiltriert werden, beispielsweise mittels einer Mikrofiltration, und daß das entstandene Natriumsulfat (Na2SO4) wieder als Neutralelektrolyt rückgeführt wird. Damit kann neben der Neutralisation und Regeneration der sauren Beizflüssigkeit auch der Neutralelektrolyt regeneriert werden, was zu erheblichen Kosteneinsparungen führt.An advantageous embodiment of the invention is characterized in that the acidic pickling liquid is neutralized by means of sodium hydroxide solution (NaOH) or sodium carbonate (Na 2 CO 3 ), that the metal hydroxides formed are then separated off, preferably filtered off, for example by means of microfiltration, and that the sodium sulfate formed (Na 2 SO 4 ) is returned as a neutral electrolyte. In addition to the neutralization and regeneration of the acidic pickling liquid, the neutral electrolyte can also be regenerated, which leads to considerable cost savings.

Eine günstige Weiterbildung der Erfindung ist dadurch gekennzeichnet, daß die verbrauchte Elektrolytlösung einer oder mehreren Kaltbandbeizlinie(n) entnommen und der salpetersäurefreien und sauren Beizflüssigkeit einer oder mehrerer Warmbandbeizlinie(n) zudosiert wird. Damit kann die für ein Edelstahlwerk günstigste Variante hinsichtlich Investitionskosten und Betriebskosten gewählt werden.A favorable further development of the invention is characterized in that that the used electrolyte solution of one or more cold strip pickling line (s) removed and the nitric acid-free and acidic pickling liquid one or more hot strip pickling line (s) is added. So that for a stainless steel plant cheapest option in terms of investment costs and operating costs can be selected.

Die Erfindung wird nun anhand von Ausführungsbeispielen näher erläutert.The invention will now be explained in more detail on the basis of exemplary embodiments.

Versuch 1:Trial 1:

Am Ende einer langen Testserie über das elektrolytische Beizen von Edelstahlkaltbändern hatte man eine verbrauchte Elektrolytlösung mit Metallgehalten, wie sie auf Großanlagen üblich sind. Die Cr6+ Konzentration betrug 4.8 g/l. ( Das Eisen (Fe3+) und Nickel (Ni2+) liegen in Form von suspendiertem Hydroxidschlamm und das Chrom liegt in Form von Chromat (Cr6+), d.h. chemisch gelöst, vor.)At the end of a long test series on the electrolytic pickling of stainless steel cold strips, a used electrolyte solution with metal contents was found, as is common on large systems. The Cr 6+ concentration was 4.8 g / l. (The iron (Fe 3+ ) and nickel (Ni 2+ ) are in the form of suspended hydroxide sludge and the chromium is in the form of chromate (Cr 6+ ), ie chemically dissolved.)

Es wurde nun eine zweite Lösung bestehend aus einer Mischung von Schwefelsäure, Flußsäure und FeSO4 hergestellt, so daß die nachfolgende chemische Analyse folgende Werte ergab:

  • freie H2SO4 =400g/l
  • freie HF = 50 g/l
  • Fe2+ = 40 g/l
    • A second solution consisting of a mixture of sulfuric acid, hydrofluoric acid and FeSO 4 was now prepared, so that the following chemical analysis gave the following values:
  • free H 2 SO 4 = 400g / l
  • free HF = 50 g / l
  • Fe 2+ = 40 g / l

    • Nun wurden Mischungen aus diesen beiden Lösungen hergestellt, so daß das Redoxpotential der neu hergestellten Mischung bei 400 -500 mV liegt. Die darauf folgenden Beizversuche mit verzundertem Edelstahlwarmband ergaben zwar eine etwas längere Beizzeit als in konventioneller Mischsäure, aber dennoch zufriedenstellende Ergebnisse. Dabei wurden beispielsweise gestrahlte AISI 304-Probebleche in ca. 70 sec zunderfrei gebeizt. Nach mehreren Probebeizungen wurde die Beizflüssigkeit chemisch analysiert und es konnte kein sechswertiges Chrom(Cr6+) nachgewiesen werden. Erwartungsgemäß hat das vorliegende zweiwertige Eisen (Fe2+) es zu dreiwertigen Chrom (Cr3+) reduziert. Es konnte in der durchgeführten Beizserie kein Einfluß von Natriumionen auf das Beizergebnis beobachtet werden und es wurde auch bestätigt, daß ein Zusatz von Inhibitoren von Vorteil ist, um den Korrosionsangriff der Schwefelsäure auf das Grundmaterial zu unterdrücken.Mixtures were now prepared from these two solutions, so that the redox potential of the newly prepared mixture was 400-500 mV. The subsequent pickling tests with scaled stainless steel hot-strip gave a somewhat longer pickling time than in conventional mixed acid, but nevertheless gave satisfactory results. Here, for example, blasted AISI 304 test sheets were pickled in about 70 seconds without scaling. After several sample treatments, the pickling liquid was analyzed chemically and no hexavalent chromium (Cr 6+ ) could be detected. As expected, the present divalent iron (Fe 2+ ) reduced it to trivalent chromium (Cr 3+ ). In the pickling series carried out, no influence of sodium ions on the pickling result was observed and it was also confirmed that the addition of inhibitors is advantageous in order to suppress the corrosion attack of the sulfuric acid on the base material.

    Der Vorteil dieses "nitratfreien Beizverfahrens" bei dem keine nitrosen Gase entstehen ist, daß das dreiwertige Eisenion (Fe3+) durch eine verbrauchte Elektrolytlösung hergestellt wird - d.h. es ergibt sich ein zweifacher Kostenvorteil. Es muß nicht wie bei den bisherigen Verfahren Wasserstoffperoxid (H2O2) als Oxidationsmittel für die Fe3+ Herstellung und kein Reduktionsmittel (Na2S2O5) für die Chromatentgiftung zugekauft werden. Die verbrauchte Elektrolytlösung enthält das dreiwertige Eisen in Form vom suspendiertem Hydroxidschlamm ( Fe(OH)3 ) und sie enthält das sechswertige Chrom (Cr6+), welches unmittelbar mit dem durch den Beizvorgang entstehenden zweiwertigen Eisen (Fe2+) reagiert und dabei Fe3+ und Cr3+ entstehen.The advantage of this "nitrate-free pickling process" in which no nitrous gases are generated is that the trivalent iron ion (Fe 3+ ) is produced by a used electrolyte solution - ie there is a double cost advantage. It is not necessary to purchase hydrogen peroxide (H 2 O 2 ) as an oxidizing agent for Fe 3+ production and no reducing agent (Na 2 S 2 O 5 ) for chromate detoxification as in the previous processes. The used electrolyte solution contains the trivalent iron in the form of the suspended hydroxide sludge (Fe (OH) 3 ) and it contains the hexavalent chromium (Cr 6+ ), which reacts directly with the bivalent iron (Fe 2+ ) resulting from the pickling process and thereby Fe 3+ and Cr 3+ arise.

    Im Verlauf der Beiztests wurde ein Nachlassen der Beizwirkung mit gleichzeitigem Absinken des Redoxpotentials beobachtet. Es ist daher sinnvoll, die verbrauchte Elektrolytlösung in Abhängigkeit vom gemessenen Redoxpotential fortlaufend in das Beizbad nachzudosieren.During the course of the pickling tests, the pickling effect decreased a simultaneous decrease in the redox potential was observed. It is therefore sensible, the used electrolyte solution depending on the measured Continue to add the redox potential to the pickling bath.

    Versuch 2:Trial 2:

    Ein weiterer Versuch wurde mit Edelstahlkaltband durchgeführt. Es wurde der verbrauchten Elektrolytlösung ein zweiwertiges Eisensalz (FeSO4) und 96%-ige Schwefelsäure zugegeben, so daß die Konzentration der freien Schwefelsäure 100g/l und das Redoxpotential 440 mV betrug. Die so gewonnene Flüssigkeit wurde als Elektrolytlösung für elektrochemische Beizversuche eingesetzt. Bei diesen Beizversuchen konnte beobachtet werden, daß, verglichen mit elektrolytischem Beizen in reiner Schwefelsäure, der Korrosionsangriff auf das Grundmaterial geringer ist und der ursprüngliche Glanz der Blechproben nach dem Beizen erhalten bleibt. Gegenüber einer elektrolytischen Behandlung im neutralen Bereich, bei der ein Qualitätsanstieg (=Glanz) mit fortlaufender Behandlung gegeben ist, konnte jedoch ein wesentlich höherer Beizverlust erzielt werden. Another test was carried out with stainless steel cold strip. A divalent iron salt (FeSO 4 ) and 96% sulfuric acid were added to the used electrolyte solution, so that the concentration of free sulfuric acid was 100 g / l and the redox potential was 440 mV. The liquid thus obtained was used as an electrolyte solution for electrochemical pickling tests. In these pickling tests it was observed that, compared to electrolytic pickling in pure sulfuric acid, the corrosion attack on the base material is less and the original gloss of the sheet metal samples is retained after the pickling. Compared to an electrolytic treatment in the neutral range, in which there is an increase in quality (= gloss) with continuous treatment, a significantly higher pickling loss could be achieved.

    Beispielsweise bei einer AISI 304 Edelstahlprobe und einer Behandlung (=Ladungsdichte) von 600 A*sec/dm2 konnte ca. 1.2g/m2 Beizverlust im neutralen und ca. 2.0 g/m2 mit der neu hergestellten sauren Elektrolytlösung ermittelt werden.For example, with an AISI 304 stainless steel sample and a treatment (= charge density) of 600 A * sec / dm 2 , approx. 1.2 g / m 2 pickling loss in the neutral and approx. 2.0 g / m 2 with the newly produced acidic electrolyte solution could be determined.

    Versuch 3:Trial 3:

    Ein weiterer Versuch wurde folgendermaßen durchgeführt:Another experiment was carried out as follows:

    Die elektrolytische Behandlung mit einer Ladungsdichte von 200 A*sec/dm2 wurde in der angesäuerten Elektrolytlösung durchgeführt, in der das Redox-Potential auf 440 mV eingestellt war, und anschließend wurde das Probeblech im neutralen Elektrolyten elektrochemisch weiterbehandelt. Dieses kombinierte Beizverfahren hat den Vorteil gegenüber einer herkömmlichen Neutralelektrolytbehandlung, daß mit der gleichen Ladungsdichte von z.B. 600 A*sec/dm2 ca. 20% mehr Beizverlust bei geringfügig geringerem Glanz erreicht werden konnten. Beispielsweise kann eine Großanlage, welche aus sechs elektrochemischen Beizzellen besteht, so optimiert werden, daß die ersten zwei Zellen mit saurem Elektrolyt bei genau eingestelltem Redoxpotential und die darauffolgenden vier mit Neutralelektrolyt betrieben werden können. Die daraus resultierenden Vorteile sind: höhere Beizverluste im elektrochemischen Beizteil, d.h. kürzere Nachbehandlung im darauf folgenden chemischen Mischsäure-(HF + HNO3) Beizteil. Das Endprodukt hat den gleichen Glanzgrad. Der wesentlichste Vorteil jedoch ist, daß die gesamte chromathaltige Neutralelektrolytlösung verwertet werden kann und somit die Kosten für die Cr6+ - Reduktion nicht mehr anfallen.The electrolytic treatment with a charge density of 200 A * sec / dm 2 was carried out in the acidified electrolytic solution, in which the redox potential was set to 440 mV, and then the sample plate in the neutral electrolyte was further treated electrochemically. This combined pickling process has the advantage over a conventional neutral electrolyte treatment that about 20% more pickling loss with a slightly lower gloss could be achieved with the same charge density of, for example, 600 A * sec / dm 2 . For example, a large-scale plant consisting of six electrochemical pickling cells can be optimized so that the first two cells can be operated with acidic electrolyte with a precisely set redox potential and the following four with neutral electrolyte. The resulting advantages are: higher pickling losses in the electrochemical pickling section, ie shorter post-treatment in the subsequent chemical mixed acid (HF + HNO 3 ) pickling section. The end product has the same degree of gloss. The most important advantage, however, is that the entire chromate-containing neutral electrolyte solution can be recycled and the costs for the Cr 6+ reduction are no longer incurred.

    Ein weiterer Vorteil dieser Optimierung ist, daß die für das Beizen im neutralen pH-Bereich erforderliche Natriumsulfatlösung (Na2SO4) durch Neutralisation der sauren Elektrolytlösung (H2SO4, Na2SO4, Fe2+, Fe3+, Cr3+, Ni2+) mit Natriumhydroxid (NaOH) oder Natriumcarbonat (Na2CO3) und anschließender Abtrennung der Metallhydroxide (Fe(OH)2, Fe(OH)3, Cr(OH)3, Ni(OH)2) durch Filtration, rückgewonnen werden kann. Die Flitration wird hierbei vorteilhafterweise als Mikrofiltration durchgeführt. Die Versuche stellen nur Beispiele der Verfahrensführung dar, wie sie in den Ansprüchen definiert sind.Another advantage of this optimization is that the sodium sulfate solution (Na 2 SO 4 ) required for pickling in the neutral pH range is obtained by neutralizing the acidic electrolyte solution (H 2 SO 4 , Na 2 SO 4 , Fe 2+ , Fe 3+ , Cr 3+ , Ni 2+ ) with sodium hydroxide (NaOH) or sodium carbonate (Na 2 CO 3 ) and subsequent separation of the metal hydroxides (Fe (OH) 2 , Fe (OH) 3 , Cr (OH) 3 , Ni (OH) 2 ) by filtration, can be recovered. The filtration is advantageously carried out as microfiltration. The experiments are only examples of the process control as defined in the claims.

    Claims (10)

    Verfahren zum chemischen und/oder elektrochemischen Beizen von Edelstahl in einer salpetersäurefreien und sauren Flüssigkeit, dadurch gekennzeichnet, daß verbrauchte Elektrolytlösung aus elektrochemischen Neutralsalzbeizlinien, bevorzugt Natriumsulfatbeizlinien, zudosiert wird.Process for chemical and / or electrochemical pickling of Stainless steel in a nitric acid-free and acidic liquid characterized that used electrolyte solution electrochemical neutral salt pickling lines, preferred Sodium sulfate pickling lines is metered in. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Redoxpotential in der Beizflüssigkeit durch die Menge an zugegebener Elektrolytlösung auf einen vorgegebenen Wert eingestellt wird.A method according to claim 1, characterized in that the Redox potential in the pickling liquid through the amount of added Electrolyte solution is set to a predetermined value. Verfahren nach Anspruch 2, dadurch gekennzeichnet, daß das Reduktions-Oxidationspotential (Redoxpotential) der Beizflüssigkeit gemessen und die Menge der verbrauchten Elektrolytlösung aus elektrochemischen Natriumsulfatbeizlinien entsprechend zudosiert wird.A method according to claim 2, characterized in that the Reduction-oxidation potential (redox potential) of the pickling liquid measured and the amount of electrolyte solution used electrochemical sodium sulfate pickling lines metered accordingly becomes. Verfahren nach einem der Ansprüche 1 bis 3, dadurch gekennzeichnet, daß bei einem Neuansatz der Beizflüssigkeit ein zweiwertiges und ein dreiwertiges Eisensalz, bevorzugt Eisensulfate, zugesetzt werden.Method according to one of claims 1 to 3, characterized in that that with a new batch of the pickling liquid a divalent and a trivalent iron salt, preferably iron sulfates, can be added. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß zusätzlich zum verbrauchten Elektrolyten ein anderes Oxidationsmittel, vorzugsweise Wasserstoffperoxid, der Beizflüssigkeit zugeführt wird.Method according to one of claims 1 to 4, characterized in that that in addition to the used electrolyte another Oxidizing agent, preferably hydrogen peroxide, the pickling liquid is fed. Verfahren nach einem der Ansprüche 1 bis 5, dadurch gekennzeichnet, daß Inhibitoren zugesetzt werden.Method according to one of claims 1 to 5, characterized in that that inhibitors are added. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß saure und neutrale elektrochemische Beizstufen miteinander kombiniert werden.Method according to one of claims 1 to 6, characterized in that that acidic and neutral electrochemical pickling stages with each other be combined. Verfahren nach Anspruch 7, dadurch gekennzeichnet, daß die gebrauchte Elektrolytlösung aus der Neutralelektrolytstufe in die saure Stufe zudosiert wird. A method according to claim 7, characterized in that the used Electrolyte solution from the neutral electrolyte stage into the acidic one Level is metered. Verfahren nach Anspruch 7 oder 8, dadurch gekennzeichnet, daß die saure Beizflüssigkeit mittels Natronlauge (NaOH) oder Natriumcarbonat (Na2CO3) neutralisiert wird, daß anschließend die entstandenen Metallhydroxide abgetrennt, vorzugsweise abfiltriert werden, beispielsweise mittels einer Mikrofiltration, und daß das entstandene Natriumsulfat (Na2SO4) wieder als Neutralelektrolyt rückgeführt wird.A method according to claim 7 or 8, characterized in that the acidic pickling liquid is neutralized by means of sodium hydroxide solution (NaOH) or sodium carbonate (Na 2 CO 3 ), that the resulting metal hydroxides are then separated off, preferably filtered off, for example by means of microfiltration, and that the resultant Sodium sulfate (Na 2 SO 4 ) is returned as a neutral electrolyte. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß die verbrauchte Elektrolytlösung einer oder mehreren Kaltbandbeizlinie(n) entnommen und der salpetersäurefreien und sauren Beizflüssigkeit einer oder mehrerer Warmbandbeizlinie(n) zudosiert wird.Method according to one of claims 1 to 6, characterized in that that the used electrolyte solution of one or more cold strip pickling line (s) taken and the nitric acid-free and acidic Pickling liquid metered into one or more hot strip pickling line (s) becomes.
    EP99123620A 1998-12-22 1999-11-27 Process for pickling stainless steel Expired - Lifetime EP1013800B1 (en)

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    KR20000048256A (en) 2000-07-25
    EP1013800A3 (en) 2000-11-15
    ZA997788B (en) 2000-06-30
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