CA1119080A - Method for controlling pickling solution of stainless steel - Google Patents
Method for controlling pickling solution of stainless steelInfo
- Publication number
- CA1119080A CA1119080A CA000304951A CA304951A CA1119080A CA 1119080 A CA1119080 A CA 1119080A CA 000304951 A CA000304951 A CA 000304951A CA 304951 A CA304951 A CA 304951A CA 1119080 A CA1119080 A CA 1119080A
- Authority
- CA
- Canada
- Prior art keywords
- bath
- pickling
- oxidation
- reduction potential
- ferrous sulfate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000005554 pickling Methods 0.000 title claims abstract description 67
- 238000000034 method Methods 0.000 title claims abstract description 29
- 229910001220 stainless steel Inorganic materials 0.000 title claims abstract description 14
- 239000010935 stainless steel Substances 0.000 title claims abstract description 14
- 230000033116 oxidation-reduction process Effects 0.000 claims abstract description 34
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 32
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims abstract description 26
- 239000000203 mixture Substances 0.000 claims abstract description 8
- DGCPSAFMAXHHDM-UHFFFAOYSA-N sulfuric acid;hydrofluoride Chemical compound F.OS(O)(=O)=O DGCPSAFMAXHHDM-UHFFFAOYSA-N 0.000 claims abstract description 7
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 claims description 26
- 229910000359 iron(II) sulfate Inorganic materials 0.000 claims description 24
- 235000003891 ferrous sulphate Nutrition 0.000 claims description 22
- 239000011790 ferrous sulphate Substances 0.000 claims description 22
- 239000000463 material Substances 0.000 claims description 5
- 238000005259 measurement Methods 0.000 claims description 5
- 239000013078 crystal Substances 0.000 claims description 3
- 150000003467 sulfuric acid derivatives Chemical class 0.000 claims description 3
- 238000009825 accumulation Methods 0.000 claims description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims 1
- 230000000694 effects Effects 0.000 claims 1
- -1 ferrous sulfate Chemical class 0.000 claims 1
- 230000002311 subsequent effect Effects 0.000 claims 1
- 239000000243 solution Substances 0.000 abstract description 45
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 35
- 229960002050 hydrofluoric acid Drugs 0.000 description 19
- RUTXIHLAWFEWGM-UHFFFAOYSA-H iron(3+) sulfate Chemical compound [Fe+3].[Fe+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O RUTXIHLAWFEWGM-UHFFFAOYSA-H 0.000 description 18
- 229910000360 iron(III) sulfate Inorganic materials 0.000 description 18
- 229960001781 ferrous sulfate Drugs 0.000 description 15
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 10
- 229960002163 hydrogen peroxide Drugs 0.000 description 10
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 229910052759 nickel Inorganic materials 0.000 description 5
- 238000011069 regeneration method Methods 0.000 description 5
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 4
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 4
- 229910052804 chromium Inorganic materials 0.000 description 4
- 239000011651 chromium Substances 0.000 description 4
- 230000001276 controlling effect Effects 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 3
- 238000000137 annealing Methods 0.000 description 3
- ZPMKVQYPTODMMF-UHFFFAOYSA-L chromium(3+) nickel(2+) sulfate Chemical compound S(=O)(=O)([O-])[O-].[Cr+3].[Ni+2] ZPMKVQYPTODMMF-UHFFFAOYSA-L 0.000 description 3
- GRWVQDDAKZFPFI-UHFFFAOYSA-H chromium(III) sulfate Chemical compound [Cr+3].[Cr+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O GRWVQDDAKZFPFI-UHFFFAOYSA-H 0.000 description 3
- 230000008929 regeneration Effects 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- 239000002253 acid Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- ZOMNIUBKTOKEHS-UHFFFAOYSA-L dimercury dichloride Chemical class Cl[Hg][Hg]Cl ZOMNIUBKTOKEHS-UHFFFAOYSA-L 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 150000007522 mineralic acids Chemical class 0.000 description 2
- 229910017604 nitric acid Inorganic materials 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 101100165177 Caenorhabditis elegans bath-15 gene Proteins 0.000 description 1
- XWROUVVQGRRRMF-UHFFFAOYSA-N F.O[N+]([O-])=O Chemical compound F.O[N+]([O-])=O XWROUVVQGRRRMF-UHFFFAOYSA-N 0.000 description 1
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910021607 Silver chloride Inorganic materials 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 230000000875 corresponding effect Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 150000002431 hydrogen Chemical class 0.000 description 1
- GPRLSGONYQIRFK-UHFFFAOYSA-N hydron Chemical compound [H+] GPRLSGONYQIRFK-UHFFFAOYSA-N 0.000 description 1
- 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 1
- LGQLOGILCSXPEA-UHFFFAOYSA-L nickel sulfate Chemical compound [Ni+2].[O-]S([O-])(=O)=O LGQLOGILCSXPEA-UHFFFAOYSA-L 0.000 description 1
- 229940053662 nickel sulfate Drugs 0.000 description 1
- 229910000363 nickel(II) sulfate Inorganic materials 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000010948 rhodium Substances 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
-
- 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)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Mechanical Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
Abstract
ABSTRACT
According to the present invention, there is provided a method for controlling the composition of a pickling solu-tion characterized in that in the pickling for stainless steel using a ferric sulfate-hydrofluoric acid bath, the oxidation-reduction potential of the pickling solution is held in a predetermined range by adding hydrogen peroxide and sulfuric acid into the pickling solution.
According to the present invention, there is provided a method for controlling the composition of a pickling solu-tion characterized in that in the pickling for stainless steel using a ferric sulfate-hydrofluoric acid bath, the oxidation-reduction potential of the pickling solution is held in a predetermined range by adding hydrogen peroxide and sulfuric acid into the pickling solution.
Description
9~
METHOD FOR CONTROLLING PICKLING SOLUTION OF STAINLESS STE~L
This invention relates to a method for controlling the composition of a pickling solution of stainless steel.
More particularly, in the pickling for stainless steel using a ferric sulfate-hydrofluoric acid bath, this in-vention is concerned with a method of controlling the com-position of the pickling solution through adjustment of the oxidation-reduction potential of the same solution.
In the conventional descaling pickling method for stainless steel, two to four inorganic acids are selected 10 from such inorganic acids as sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid and phosphoric acid according to the kind of the material to be pickled, the degree of adhesion of annealing scale, and the purpose of pickling.
Above all, a pickling solution consisting of a mixed nitric-hydrofluoric acid is generally used widely. This pickling solution has a sufficient pickling ability, but its repeated use tends to lower the pickling ability com-paratively in an early stage. To prevent this, it is re-20 quired to replenish nitric acid and hydrofluoric acid intermediate in pickling, or to newly make the same bath.
Thus, it is very troublesome to control the pickling solu-tion.
- 1 - ~;~
f~
~, - . . . - ~ ..
~9~ 30 In the case of such conventional pickling solution, moreover, an environmental pollutlon due to the generation of NOx (nitrogen oxide gases) gas now causes a serious social problem. Various methods of treating NOx gas have been pro-posed, but at present there is no method that is technicallyfree of drawback and economical. Therefore, such a pickling solution as does not generate ~70X gas is requested and many proposals have been made, among which a pickling method using a ferric sulfate-hydrofluoric acid bath is known.
However, such pickling solution ages in a short period, so that many operations are needed, Eor example, replenishing chemicals or making a new bath. It is more troublesome in the control of pickling solution and less economical than the mixed nitric-hydrofluoric acid bath 15 which is now generally used widely. Therefore, such con-ventional pickling solution is not practical.
Moreover, as the method of preparing a ferric sulfate solution, it is publicly known to obtain ferric sulfate by oxidizing a ferrous sulfate solution with hydrogen per-20 oxide and sulfuric acid. From this, it is inevitably con-ceivable and publicly known that in a ferric sulfate-hydrofluoric acid bath, the ferrous sulfate which is pri-marily produced in the pickling solution for stainless steel when pickled is oxidized using hydrogen peroxide 25 and sulfuric acid to regenerate ferric sulfate, and the latter is used repeatedly in the pickling. Even in this method, however, it is very difficult to control the con-centration of ferric sulfate when aged after pickling and the concentration thereof after regeneration by the oxi-30 dation with hydrogen peroxide and sulfuric acid. Thisdifficulty causes a problem, and so this method is not actually adopted.
The foregoing problems associated with the conven-tional pickling methods, are solved according to the 35 present invention characterized in that in the pickling of stainless steel using a ferric sulfate-hydrofluoric 30~0 acid bath, the oxidation-reduction potential of the pickling solution is held in a predetermined range by adding hydrogen peroxide and sulfuric acid into the pickling solution. The addition of the hydrogen peroxide and sulfuric acid can be done continuously while pickling stainless steel.
An excellent feature of the present invention resides in that by only a simple operation of adding hydrogen per-oxide and sulfuric acid so as to maintain the oxidation-reduction potential in a ;onstant range, ferric sulfate can 10 be held in a constant range of concentration without the need for a chemical analysis of the composition with the result that uniform surface finish and pickling time can be achieved.
Furthermore, according to the method of the present 15 invention, it becomes possible to make a complete auto-mation, continuation and solution closing, with ~Ox gas not generated and the amount of waste liquor to be treated largely decreased. Thus, the method of the present invention is an epoch-making method which has 20 remedied the drawbacks encountered in the prior art pick-ling methods. Besides, as compared with the conventional ferric sulfate-hydrofluoric acid bath, the pickling cost can be reduced to a large extent; and even in comparison with the nitric acid-hydrofluoric acid bath presently in 25 use, a low cost comparable thereto can be attained.
Figure 1 shows the results of measurement of the oxi-dation-reduction potential in the form of a graph which results serve as basic data for working the method of controlling a pickling solution of the present invention 30 in which measurement the concentration of ferrous sulfate in the pickling solution was 30 grams per litre and the concen-tration of ferric sulfate and that of hydrofluoric acid (HF) were varied, and the oxidation-reduction potential of each was measured at the solution temperature of 50C.
In working the present invention, the concentration range of ferric sulfate and that of hydrofluoric acid are predetermined according to the kind of material to be pickled, the degree of annealing scale and the purpose of pickling, and further the range of oxidation-reduction po-tential in balance therewith is decided. And hydrogen per-oxide and sulfuric acid are added and pickling is carriedout within such range of oxidation-reduction potential.
It is desired that the molar ratio of hydrogen per-oxide and sulfuric acid to be added be about 1:1. The con-centration of hydrogen peroxide and that of sulfuric acid l0 to be used are not specially restricted.
If the pickling for stainless steel is carried out in a ferric sulfate-hydrofluoric acid bath, the ferric sulfate is consumed for the dissolving of stainless steel and there are produced ferrous sulfate, chromium sulfate and nickle 15 sulfate according to the composition of the material to be pickled. On the other hand, the hydrofluoric acid is partially consumed as hydrogen ion in the dissolving of stainless steel, but fluoride ion is not consumed and exists in the pickling solution. The consumed hydrogen 20 ion can be replenished by slightly increasing the amount of sulfuric acid to be added in the oxidation-regeneration operation. If pickling is continued, there accumulate in the solution ferrous sulfate in an amount exceeding the necessary amount for the regeneration of ferric sulfate, 25 and also unoxidized chromium sulfate and nickel sulfate.
It is mainly the concentration of ferric sulfate and that of hydrofluoric acid that affect the oxidation-reduction potential of the pickling solution. Ferrous sulfate somewhat affects the same potential. Chromium sulfate and nickel sul-30 fate have no influence. It has become clear that in case ameasurement of oxidation-reduction potential is made by changing the concentration bf ferric sulfate and that of hy-drofluoric acid, there is nearly a straight-line relationship between the concentration of ferric sulfate and the oxidation-35 reduction potential, and that the straight line shifts in a ~Ll9~
parallel manner by the change in hydrofluoric acid concen-tration. As previously noted, fluoride ion in the solution is not consumed and exists, so that if the concentration of hydrofluoric acid in the pickling solution is maintained constant, the oxidation-reduction potential becomes cor-responding to the change in ferric sulfate concentration.
The concentration of ferrous sulfate affects the oxidation-reduction potential in such a manner that in case the con-centration of ferric sulfate and that of hydrofluoric acid 10 are made constant, the oxidation-reduction potential tends to decrease as the concentration of ferrous sulfate becomes higher. In this case, however, the decreasing degree of the oxidation-reduction potential is not so large.
Therefore, with these facts taken into account in ad-15 vance, it is necessary to be aware of the minimum concen-tration of ferric sulfate required for pickling, regard the oxidation-reduction potential at that time as the minimum potential and maintain the potential always above the minimum value during pickling and regeneration, whereby even 20 if the oxidation-reduction potential somewhat decreases due to the presence of ferrous sulfate which gradually ac-cumulates in the solution, it has no influence upon process control, and uniform pickling finish and pickling time can be achieved. It has become clear that the change in concen-25 tration of ferrous sulfate due to its accumulation does notgreatly affect the oxidation-reduction potential up to its concentration of about 200 g/l. At a concentration of fer-rous sulfate above 200 g/l, it is deposited as crystals tmainlY FeSO4 . 7H2O) on standing at room temperature.
30 Therefore, through combination with this method it is also possible to keep the concentration of ferrous sulfate below 200 g/l. The amount of ferrous-, chromium- and nickel-sulfate which accumulate in the pickling solution differs according to the amount of solution brought out of the 35 system in an adhered state of steel after pickling. The larger the amount of solution brought out of the system, 0~0 the smaller becomes the amount of sulfates which accumulate.
At the same time, however, fluoride ion is also brought out of the system, so it is necessary to replenish hydrofluoric acid on the basis of a calculated amount, or alternatively measure the concentration of fluoride ion using an ion meter or the like and replenish hydrofluoric acid.
Conversely, in case the amount of solution brought out of the system is small and the amount of sulfates which ac-cumulate becomes large, the amount of solution to be drawn 10 out is determined so as to qive a concentration not affecting the oxidation-reduction potential. In this case, there is adopted a method in which the solution is drawn out con-tinuously or intermittently, or a method in which the bath is cooled for removal as crystals outside the system.
These operations can be made regular once pickling is experienced. The oxidation-reduction potential of the pickling solution is affected by temperature, so when measuring such potential it is necessary to pay attention so that the temperature is the same.
With respect to the electrodes used in the measurement of the oxidation-reduction potential, as a reference elec-trode there may be used those which are normally in use, for example, a saturated calomel electrode and a silver chloride electrode, and as a measuring electrode there 25 may be used any electrodes if only they are inert to the pickling solution, for example, noble metal electrodes such as platinum, gold and rhodium.
The following examples are given to further illustrate the present invention:
Example 1 h~ith the concentration of ferrous sulfate of 30 g/l, the concentration of ferric sulfate and that of hydro-fluoric acid were varied and the oxidation-reduction po-tential of each was measured at the solution temperature 35 of 50-C, the results of which are shown in Figure 1 hereto attached.
In the above measurement of the oxidation-reduction potential, a saturated calomel electrode was used as a reference electrode and a platinum electrode as a measuring electrode.
Example 2 Into pickling solutions containing ferric sulfate and hydrofluoric acid in amounts set out in Table 1 below were added ferrous sulfate in concentrations of 30 g/l, 100 g/l and 200 g/l and chromium- and nickel-sulfate in concentra-lO tions of 20 g/l and 40 g/l as chromium plus nickel (whose ration was 1:1j. Using the same electrodes as in Example 1, the oxidation-reduction potential of each pickling solution at 50DC was measured, the results of which are shown in Table 1.
Example 3 A pickling solution containing 150 g/l of ferric sulfate, 5% of hydrofluoric acid and 30 g/l of ferrous sulfate was pre-pared. With the pickling solution thus prepared, annealing scales respectively of pipe, bar wire and plane sheet of SUS
20 304, 308 and 316 were pickled continuously. Using the same electrodes as in Example 1 and with the pickling temperature held at 50 C, the minimum value of the oxidation-reduction potential was set to +300mV and hydrogen peroxide (35~) and sulfuric acid t98%) were added at times in the molar ratio 25 of 1:1 so that the oxidation-reduction potential was kept above +300mV at all times during pickling. The amount of the pickling solution was adjusted-according to the amount of hydrogen peroxide and sulfuric acid used for the oxi-dation-regeneration and the amount of solution brought out 30 of the system in an adhered state to the samples after descaling. And a small amount of hydrofluoric acid was replenished at times.
As the pickling proceeded in a continuous manner, ferrous-, chromium- and nickel-sulfate accumulated grad-35 ually and reached the respective concentrations of 180g/l, 14 g/l as chromium and 16 g/l as nickel. Even at this moment, a constant pickling time just the same as that in the initial bath and a good finish were achieved.
Table 1 Experiment No. 1 2 3 4 Concentration of ferric 150 g/l 150 g/l 150 g/l 150 g/l sulfate Concentration of errous 30 g/l 100 g/l 200 g/l 30 g/l sulfate Concentration of chromium - - - 20 g/l + nickel Concentration of hydro-5% 5% 5~ 5%
fluoric acid Oxidation-reduction+415mV +395mV+370mV +410mV
potential Experiment No. 5 6 7 8 Concentration of ferric 150 g/l 150 g/l 100 g/l 100 g/l sulfate Concentration of ferrous 30 g/l 200 g/l 30 g/l 200 g/l sulfate Concentration of chromium 40 g/l 40 g/1 + nickel Concentration of hydro-5% 5% 5% 5%
fluoric acid Oxidation-reduction +410mV+370mV+335mV+295mV
potential -
METHOD FOR CONTROLLING PICKLING SOLUTION OF STAINLESS STE~L
This invention relates to a method for controlling the composition of a pickling solution of stainless steel.
More particularly, in the pickling for stainless steel using a ferric sulfate-hydrofluoric acid bath, this in-vention is concerned with a method of controlling the com-position of the pickling solution through adjustment of the oxidation-reduction potential of the same solution.
In the conventional descaling pickling method for stainless steel, two to four inorganic acids are selected 10 from such inorganic acids as sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid and phosphoric acid according to the kind of the material to be pickled, the degree of adhesion of annealing scale, and the purpose of pickling.
Above all, a pickling solution consisting of a mixed nitric-hydrofluoric acid is generally used widely. This pickling solution has a sufficient pickling ability, but its repeated use tends to lower the pickling ability com-paratively in an early stage. To prevent this, it is re-20 quired to replenish nitric acid and hydrofluoric acid intermediate in pickling, or to newly make the same bath.
Thus, it is very troublesome to control the pickling solu-tion.
- 1 - ~;~
f~
~, - . . . - ~ ..
~9~ 30 In the case of such conventional pickling solution, moreover, an environmental pollutlon due to the generation of NOx (nitrogen oxide gases) gas now causes a serious social problem. Various methods of treating NOx gas have been pro-posed, but at present there is no method that is technicallyfree of drawback and economical. Therefore, such a pickling solution as does not generate ~70X gas is requested and many proposals have been made, among which a pickling method using a ferric sulfate-hydrofluoric acid bath is known.
However, such pickling solution ages in a short period, so that many operations are needed, Eor example, replenishing chemicals or making a new bath. It is more troublesome in the control of pickling solution and less economical than the mixed nitric-hydrofluoric acid bath 15 which is now generally used widely. Therefore, such con-ventional pickling solution is not practical.
Moreover, as the method of preparing a ferric sulfate solution, it is publicly known to obtain ferric sulfate by oxidizing a ferrous sulfate solution with hydrogen per-20 oxide and sulfuric acid. From this, it is inevitably con-ceivable and publicly known that in a ferric sulfate-hydrofluoric acid bath, the ferrous sulfate which is pri-marily produced in the pickling solution for stainless steel when pickled is oxidized using hydrogen peroxide 25 and sulfuric acid to regenerate ferric sulfate, and the latter is used repeatedly in the pickling. Even in this method, however, it is very difficult to control the con-centration of ferric sulfate when aged after pickling and the concentration thereof after regeneration by the oxi-30 dation with hydrogen peroxide and sulfuric acid. Thisdifficulty causes a problem, and so this method is not actually adopted.
The foregoing problems associated with the conven-tional pickling methods, are solved according to the 35 present invention characterized in that in the pickling of stainless steel using a ferric sulfate-hydrofluoric 30~0 acid bath, the oxidation-reduction potential of the pickling solution is held in a predetermined range by adding hydrogen peroxide and sulfuric acid into the pickling solution. The addition of the hydrogen peroxide and sulfuric acid can be done continuously while pickling stainless steel.
An excellent feature of the present invention resides in that by only a simple operation of adding hydrogen per-oxide and sulfuric acid so as to maintain the oxidation-reduction potential in a ;onstant range, ferric sulfate can 10 be held in a constant range of concentration without the need for a chemical analysis of the composition with the result that uniform surface finish and pickling time can be achieved.
Furthermore, according to the method of the present 15 invention, it becomes possible to make a complete auto-mation, continuation and solution closing, with ~Ox gas not generated and the amount of waste liquor to be treated largely decreased. Thus, the method of the present invention is an epoch-making method which has 20 remedied the drawbacks encountered in the prior art pick-ling methods. Besides, as compared with the conventional ferric sulfate-hydrofluoric acid bath, the pickling cost can be reduced to a large extent; and even in comparison with the nitric acid-hydrofluoric acid bath presently in 25 use, a low cost comparable thereto can be attained.
Figure 1 shows the results of measurement of the oxi-dation-reduction potential in the form of a graph which results serve as basic data for working the method of controlling a pickling solution of the present invention 30 in which measurement the concentration of ferrous sulfate in the pickling solution was 30 grams per litre and the concen-tration of ferric sulfate and that of hydrofluoric acid (HF) were varied, and the oxidation-reduction potential of each was measured at the solution temperature of 50C.
In working the present invention, the concentration range of ferric sulfate and that of hydrofluoric acid are predetermined according to the kind of material to be pickled, the degree of annealing scale and the purpose of pickling, and further the range of oxidation-reduction po-tential in balance therewith is decided. And hydrogen per-oxide and sulfuric acid are added and pickling is carriedout within such range of oxidation-reduction potential.
It is desired that the molar ratio of hydrogen per-oxide and sulfuric acid to be added be about 1:1. The con-centration of hydrogen peroxide and that of sulfuric acid l0 to be used are not specially restricted.
If the pickling for stainless steel is carried out in a ferric sulfate-hydrofluoric acid bath, the ferric sulfate is consumed for the dissolving of stainless steel and there are produced ferrous sulfate, chromium sulfate and nickle 15 sulfate according to the composition of the material to be pickled. On the other hand, the hydrofluoric acid is partially consumed as hydrogen ion in the dissolving of stainless steel, but fluoride ion is not consumed and exists in the pickling solution. The consumed hydrogen 20 ion can be replenished by slightly increasing the amount of sulfuric acid to be added in the oxidation-regeneration operation. If pickling is continued, there accumulate in the solution ferrous sulfate in an amount exceeding the necessary amount for the regeneration of ferric sulfate, 25 and also unoxidized chromium sulfate and nickel sulfate.
It is mainly the concentration of ferric sulfate and that of hydrofluoric acid that affect the oxidation-reduction potential of the pickling solution. Ferrous sulfate somewhat affects the same potential. Chromium sulfate and nickel sul-30 fate have no influence. It has become clear that in case ameasurement of oxidation-reduction potential is made by changing the concentration bf ferric sulfate and that of hy-drofluoric acid, there is nearly a straight-line relationship between the concentration of ferric sulfate and the oxidation-35 reduction potential, and that the straight line shifts in a ~Ll9~
parallel manner by the change in hydrofluoric acid concen-tration. As previously noted, fluoride ion in the solution is not consumed and exists, so that if the concentration of hydrofluoric acid in the pickling solution is maintained constant, the oxidation-reduction potential becomes cor-responding to the change in ferric sulfate concentration.
The concentration of ferrous sulfate affects the oxidation-reduction potential in such a manner that in case the con-centration of ferric sulfate and that of hydrofluoric acid 10 are made constant, the oxidation-reduction potential tends to decrease as the concentration of ferrous sulfate becomes higher. In this case, however, the decreasing degree of the oxidation-reduction potential is not so large.
Therefore, with these facts taken into account in ad-15 vance, it is necessary to be aware of the minimum concen-tration of ferric sulfate required for pickling, regard the oxidation-reduction potential at that time as the minimum potential and maintain the potential always above the minimum value during pickling and regeneration, whereby even 20 if the oxidation-reduction potential somewhat decreases due to the presence of ferrous sulfate which gradually ac-cumulates in the solution, it has no influence upon process control, and uniform pickling finish and pickling time can be achieved. It has become clear that the change in concen-25 tration of ferrous sulfate due to its accumulation does notgreatly affect the oxidation-reduction potential up to its concentration of about 200 g/l. At a concentration of fer-rous sulfate above 200 g/l, it is deposited as crystals tmainlY FeSO4 . 7H2O) on standing at room temperature.
30 Therefore, through combination with this method it is also possible to keep the concentration of ferrous sulfate below 200 g/l. The amount of ferrous-, chromium- and nickel-sulfate which accumulate in the pickling solution differs according to the amount of solution brought out of the 35 system in an adhered state of steel after pickling. The larger the amount of solution brought out of the system, 0~0 the smaller becomes the amount of sulfates which accumulate.
At the same time, however, fluoride ion is also brought out of the system, so it is necessary to replenish hydrofluoric acid on the basis of a calculated amount, or alternatively measure the concentration of fluoride ion using an ion meter or the like and replenish hydrofluoric acid.
Conversely, in case the amount of solution brought out of the system is small and the amount of sulfates which ac-cumulate becomes large, the amount of solution to be drawn 10 out is determined so as to qive a concentration not affecting the oxidation-reduction potential. In this case, there is adopted a method in which the solution is drawn out con-tinuously or intermittently, or a method in which the bath is cooled for removal as crystals outside the system.
These operations can be made regular once pickling is experienced. The oxidation-reduction potential of the pickling solution is affected by temperature, so when measuring such potential it is necessary to pay attention so that the temperature is the same.
With respect to the electrodes used in the measurement of the oxidation-reduction potential, as a reference elec-trode there may be used those which are normally in use, for example, a saturated calomel electrode and a silver chloride electrode, and as a measuring electrode there 25 may be used any electrodes if only they are inert to the pickling solution, for example, noble metal electrodes such as platinum, gold and rhodium.
The following examples are given to further illustrate the present invention:
Example 1 h~ith the concentration of ferrous sulfate of 30 g/l, the concentration of ferric sulfate and that of hydro-fluoric acid were varied and the oxidation-reduction po-tential of each was measured at the solution temperature 35 of 50-C, the results of which are shown in Figure 1 hereto attached.
In the above measurement of the oxidation-reduction potential, a saturated calomel electrode was used as a reference electrode and a platinum electrode as a measuring electrode.
Example 2 Into pickling solutions containing ferric sulfate and hydrofluoric acid in amounts set out in Table 1 below were added ferrous sulfate in concentrations of 30 g/l, 100 g/l and 200 g/l and chromium- and nickel-sulfate in concentra-lO tions of 20 g/l and 40 g/l as chromium plus nickel (whose ration was 1:1j. Using the same electrodes as in Example 1, the oxidation-reduction potential of each pickling solution at 50DC was measured, the results of which are shown in Table 1.
Example 3 A pickling solution containing 150 g/l of ferric sulfate, 5% of hydrofluoric acid and 30 g/l of ferrous sulfate was pre-pared. With the pickling solution thus prepared, annealing scales respectively of pipe, bar wire and plane sheet of SUS
20 304, 308 and 316 were pickled continuously. Using the same electrodes as in Example 1 and with the pickling temperature held at 50 C, the minimum value of the oxidation-reduction potential was set to +300mV and hydrogen peroxide (35~) and sulfuric acid t98%) were added at times in the molar ratio 25 of 1:1 so that the oxidation-reduction potential was kept above +300mV at all times during pickling. The amount of the pickling solution was adjusted-according to the amount of hydrogen peroxide and sulfuric acid used for the oxi-dation-regeneration and the amount of solution brought out 30 of the system in an adhered state to the samples after descaling. And a small amount of hydrofluoric acid was replenished at times.
As the pickling proceeded in a continuous manner, ferrous-, chromium- and nickel-sulfate accumulated grad-35 ually and reached the respective concentrations of 180g/l, 14 g/l as chromium and 16 g/l as nickel. Even at this moment, a constant pickling time just the same as that in the initial bath and a good finish were achieved.
Table 1 Experiment No. 1 2 3 4 Concentration of ferric 150 g/l 150 g/l 150 g/l 150 g/l sulfate Concentration of errous 30 g/l 100 g/l 200 g/l 30 g/l sulfate Concentration of chromium - - - 20 g/l + nickel Concentration of hydro-5% 5% 5~ 5%
fluoric acid Oxidation-reduction+415mV +395mV+370mV +410mV
potential Experiment No. 5 6 7 8 Concentration of ferric 150 g/l 150 g/l 100 g/l 100 g/l sulfate Concentration of ferrous 30 g/l 200 g/l 30 g/l 200 g/l sulfate Concentration of chromium 40 g/l 40 g/1 + nickel Concentration of hydro-5% 5% 5% 5%
fluoric acid Oxidation-reduction +410mV+370mV+335mV+295mV
potential -
Claims (5)
1. Method for controlling the composition of a ferric sulfate-hydrofluoric acid bath during the pickling of stain-less steel therewith, said bath having an initial composi-tion, said method comprising the steps of:
determining upper and lower limits of the range of the oxidation-reduction potential of the said bath suitable for a pickling operation, with a bath of said initial com-position, on a particular stainless steel material to be pickled and the kind of pickling operation to be performed;
after starting a pickling operation on said material in said bath, measuring the oxidation-reduction potential of the bath from time to time;
before the oxidation-reduction potential of the bath falls substantially below the value of said determined lower limit, adding to the bath hydrogen peroxide and sulfuric acid in predetermined molar ratio to each other and; in an amount that raises the oxidation-reduction potential to a value which does not substantially exceed said determined upper limit, and repeating this adding step after a subse-quent measurement shows the oxidation-reduction potential is again approaching the value of said determined lower limit; and maintaining the concentration of ferrous sulfate be-low 200 g/l;
all oxidation-reduction potentials being measured at a predetermined fixed temperature.
determining upper and lower limits of the range of the oxidation-reduction potential of the said bath suitable for a pickling operation, with a bath of said initial com-position, on a particular stainless steel material to be pickled and the kind of pickling operation to be performed;
after starting a pickling operation on said material in said bath, measuring the oxidation-reduction potential of the bath from time to time;
before the oxidation-reduction potential of the bath falls substantially below the value of said determined lower limit, adding to the bath hydrogen peroxide and sulfuric acid in predetermined molar ratio to each other and; in an amount that raises the oxidation-reduction potential to a value which does not substantially exceed said determined upper limit, and repeating this adding step after a subse-quent measurement shows the oxidation-reduction potential is again approaching the value of said determined lower limit; and maintaining the concentration of ferrous sulfate be-low 200 g/l;
all oxidation-reduction potentials being measured at a predetermined fixed temperature.
2. Method according to claim 1 wherein said predeter-mined molar ratio of the added hydrogen peroxide and sulfuric acid is a molar ratio of about 1:1.
3. Method according to claim 1 wherein said determined lower limit is set so as to maintain the concentration of ferrous sulfate in the pickling solution at a value below 200 g/l, whereby gradual accumulation of ferrous sulfate in solution during the pickling of stainless steel with said bath is not permitted to continue indefinitely and a neglig-ible effect of ferrous sulfate concentration on oxidation-reduction potential is assured.
4. Method according to claim 3 wherein the bath is from time to time allowed to stand at room temperature and after each such standing ferrous sulfate deposited as FeSO4?7(H2O) crystals is then separated therefrom in order to maintain a concentration of ferrous sulfate which is below 200 g/l.
5. Method according to claim 3 in which method a portion of said bath is drawn out therefrom during at least part of the performance of the method in order to reduce the amount of sulfates, including ferrous sulfate, which have accumulated therein.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP7439877A JPS549120A (en) | 1977-06-24 | 1977-06-24 | Method of controlling acid cleaning liquid for stainless steel |
| JP74398/1977 | 1977-06-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1119080A true CA1119080A (en) | 1982-03-02 |
Family
ID=13546033
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000304951A Expired CA1119080A (en) | 1977-06-24 | 1978-06-07 | Method for controlling pickling solution of stainless steel |
Country Status (16)
| Country | Link |
|---|---|
| JP (1) | JPS549120A (en) |
| AT (1) | AT355390B (en) |
| AU (1) | AU3733978A (en) |
| BE (1) | BE868219A (en) |
| BR (1) | BR7804006A (en) |
| CA (1) | CA1119080A (en) |
| DE (1) | DE2827697A1 (en) |
| ES (1) | ES471061A1 (en) |
| FR (1) | FR2395331A1 (en) |
| GB (1) | GB2000196A (en) |
| IN (1) | IN147685B (en) |
| IT (1) | IT1096676B (en) |
| LU (1) | LU79861A1 (en) |
| NL (1) | NL7806638A (en) |
| SE (1) | SE7807184L (en) |
| ZA (1) | ZA783397B (en) |
Families Citing this family (24)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3222532A1 (en) * | 1982-06-16 | 1983-12-22 | Arno 5042 Erftstadt Kuhlmann | Process and means for the acidic etching of austenitic stainless steels |
| ATE121804T1 (en) | 1985-01-22 | 1995-05-15 | Ugine Sa | METHOD FOR ACID PICKLING STEEL, PARTICULARLY STAINLESS STEEL. |
| US5154774A (en) * | 1985-09-19 | 1992-10-13 | Ugine Aciers De Chatillon Et Gueugnon | Process for acid pickling of stainless steel products |
| FR2587369B1 (en) * | 1985-09-19 | 1993-01-29 | Ugine Gueugnon Sa | PROCESS OF ACID STRIPPING OF STAINLESS STEEL PRODUCTS |
| EP0259533A1 (en) * | 1986-09-11 | 1988-03-16 | Eka Nobel Aktiebolag | Method of reducing the emission of nitrogen oxides from a liquid containing nitric acid |
| GB2220005A (en) * | 1988-06-28 | 1989-12-28 | Borsodi Vegyi Komb | Process for removing oxide layer and scale from metals and metal alloys |
| FR2650303B1 (en) * | 1989-07-26 | 1993-12-10 | Ugine Aciers Chatillon Gueugnon | PROCESS FOR ACIDIC STRIPPING OF METAL PRODUCTS CONTAINING TITANIUM OR AT LEAST ONE CHEMICAL ELEMENT OF THE TITANIUM FAMILY |
| US5338367A (en) * | 1989-07-26 | 1994-08-16 | Ugine, Aciers De Chatillon Et Gueugnon | Pickling process in an acid bath of metallic products containing titanium or at least one chemical element of the titanium family |
| SE9000166L (en) * | 1990-01-17 | 1991-07-18 | Eka Nobel Ab | redox |
| FR2657888B1 (en) * | 1990-02-08 | 1994-04-15 | Ugine Aciers | STRIPPING METHODS FOR STAINLESS STEEL MATERIALS. |
| FR2673200A1 (en) * | 1991-02-25 | 1992-08-28 | Ugine Aciers | METHOD FOR OVERDRAWING STEEL MATERIALS SUCH AS STAINLESS STEELS AND ALLIED STEELS. |
| US5354383A (en) * | 1991-03-29 | 1994-10-11 | Itb, S.R.L. | Process for pickling and passivating stainless steel without using nitric acid |
| IT1245594B (en) * | 1991-03-29 | 1994-09-29 | Itb Srl | PICKLING AND PASSIVATION PROCESS OF STAINLESS STEEL WITHOUT NITRIC ACID |
| IT1255655B (en) * | 1992-08-06 | 1995-11-09 | STAINLESS STEEL PICKLING AND PASSIVATION PROCESS WITHOUT THE USE OF NITRIC ACID | |
| DE4417284C2 (en) * | 1993-05-24 | 1999-03-25 | Alfred Schmitz | Process for pickling workpieces from high-alloy materials |
| IT1276955B1 (en) * | 1995-10-18 | 1997-11-03 | Novamax Itb S R L | PICKLING AND PASSIVATION PROCESS OF STAINLESS STEEL WITHOUT THE USE OF NITRIC ACID |
| IT1276954B1 (en) * | 1995-10-18 | 1997-11-03 | Novamax Itb S R L | PICKLING AND PASSIVATION PROCESS OF STAINLESS STEEL WITHOUT THE USE OF NITRIC ACID |
| SE510298C2 (en) | 1995-11-28 | 1999-05-10 | Eka Chemicals Ab | Procedure when picking steel |
| FR2745301B1 (en) * | 1996-02-27 | 1998-04-03 | Usinor Sacilor | PROCESS FOR STRIPPING A STEEL PART AND PARTICULARLY A STAINLESS STEEL SHEET STRIP |
| GB9807286D0 (en) | 1998-04-06 | 1998-06-03 | Solvay Interox Ltd | Pickling process |
| DE19850524C2 (en) * | 1998-11-03 | 2002-04-04 | Eilenburger Elektrolyse & Umwelttechnik Gmbh | Nitrate-free recycling pickling process for stainless steels |
| IT1303814B1 (en) * | 1998-12-02 | 2001-02-23 | Henkel Kgaa | APPARATUS AND METHOD TO CONTROL PERACCIAIO PICKLING PROCESSES. |
| IT1312556B1 (en) | 1999-05-03 | 2002-04-22 | Henkel Kgaa | STAINLESS STEEL PICKLING PROCESS IN THE ABSENCE OF ACIDONITRICO AND IN THE PRESENCE OF CHLORIDE IONS |
| CN103882455A (en) * | 2014-03-18 | 2014-06-25 | 浙江大学 | Nitric-acid-free stainless steel acid washing solution and preparation method thereof |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2748037A (en) * | 1951-03-23 | 1956-05-29 | Rohr Aircraft Corp | Method of treating articles requiring annealing |
| DE1303190C2 (en) * | 1963-08-05 | 1976-02-19 | Jung Arn Lokomotivfabrik Gmbh | PROCESS FOR CONTINUOUS PREPARATION OF SALT-ACID IRON PICKLING |
| NL155315B (en) * | 1964-06-09 | 1977-12-15 | Ver Kunstmestfabriekn Mekog Al | PROCEDURE FOR CLEANING IRONS OR STEEL, INTERNAL SURFACES OF INDUSTRIAL EQUIPMENT |
| GB1115445A (en) * | 1965-06-18 | 1968-05-29 | Forestal Ind U K Ltd | Descaling solution |
| JPS50133125A (en) * | 1974-04-10 | 1975-10-22 | ||
| US3962005A (en) * | 1975-06-30 | 1976-06-08 | Zenith Radio Corporation | Method for etching shadow mask and regenerating etchant |
-
1977
- 1977-06-24 JP JP7439877A patent/JPS549120A/en active Granted
-
1978
- 1978-06-06 IN IN418/DEL/78A patent/IN147685B/en unknown
- 1978-06-07 CA CA000304951A patent/CA1119080A/en not_active Expired
- 1978-06-13 ZA ZA00783397A patent/ZA783397B/en unknown
- 1978-06-14 IT IT24576/78A patent/IT1096676B/en active
- 1978-06-16 BE BE188655A patent/BE868219A/en unknown
- 1978-06-16 AT AT439378A patent/AT355390B/en not_active IP Right Cessation
- 1978-06-20 NL NL7806638A patent/NL7806638A/en not_active Application Discontinuation
- 1978-06-21 AU AU37339/78A patent/AU3733978A/en active Pending
- 1978-06-21 GB GB7827449A patent/GB2000196A/en not_active Withdrawn
- 1978-06-22 FR FR7818767A patent/FR2395331A1/en not_active Withdrawn
- 1978-06-22 SE SE7807184A patent/SE7807184L/en unknown
- 1978-06-22 LU LU79861A patent/LU79861A1/en unknown
- 1978-06-23 ES ES471061A patent/ES471061A1/en not_active Expired
- 1978-06-23 DE DE19782827697 patent/DE2827697A1/en not_active Withdrawn
- 1978-06-23 BR BR787804006A patent/BR7804006A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BR7804006A (en) | 1979-01-16 |
| BE868219A (en) | 1978-12-18 |
| IT7824576A0 (en) | 1978-06-14 |
| JPS568109B2 (en) | 1981-02-21 |
| FR2395331A1 (en) | 1979-01-19 |
| ZA783397B (en) | 1979-06-27 |
| NL7806638A (en) | 1978-12-28 |
| JPS549120A (en) | 1979-01-23 |
| AU3733978A (en) | 1980-01-03 |
| GB2000196A (en) | 1979-01-04 |
| SE7807184L (en) | 1978-12-25 |
| LU79861A1 (en) | 1979-02-02 |
| IT1096676B (en) | 1985-08-26 |
| ES471061A1 (en) | 1979-01-01 |
| AT355390B (en) | 1980-02-25 |
| ATA439378A (en) | 1979-07-15 |
| IN147685B (en) | 1980-05-14 |
| DE2827697A1 (en) | 1979-01-11 |
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