DE1191653B - Process for the galvanic deposition of iron-chromium-nickel alloy coatings on metal surfaces - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. α .:

C23b

German class: 48 a - 5/32

Number: 1191653

File number: A 37516 VI b / 48 a

Filing date: May 24, 1961

Opening day: April 22, 1965

The invention relates to a method for the electrodeposition of iron-chromium-nickel alloy coatings on base metals such as iron, zinc, nickel, copper or their alloys. The alloy coatings can in particular have the approximate composition of stainless steels.

It is known that the corrosion resistance of certain metal surfaces is increased by the deposition of chromium or nickel or alloys of iron and chromium or iron and nickel can. When producing a coating that contains chromium and nickel and possibly also iron, is z. B. rolled a sheet of stainless steel in the heat on the surface of the metal to be protected or molten stainless steel is sprayed onto the surface with the aid of compressed air. This However, spraying is difficult and also expensive. Rolling on is only possible on flat surfaces. In addition, the rolling process has the disadvantage that when cutting such sheets, the cut surfaces and edges are unprotected and therefore the base metal is exposed to corrosion at these points is exposed.

It has been proposed to make stainless steel coatings on iron objects in such a way that that one separately deposited chromium and nickel coatings by a temperature treatment diffuses into the iron. However, such a treatment does not lead to the desired result Success.

It has now been found that it is possible to electrolytically deposit iron, chromium and nickel simultaneously on base metals in order to apply an alloy of these three metals to them. According to the invention, the bath for producing iron-chromium-nickel alloy coatings contains at least 0.1 mol per liter of the individual alloy components, calculated as metal ions, and 1 to 4 mol per liter of urea and / or 0.2 to 0.6 mol per liter of boric acid . It is at temperatures between 30 and 8O ⁰ C, in particular 30 and 55 ⁰ C, at pH values between 1.5 and 3.5, in particular 2.1 and 2.3, and at a current density from 3.3 to 33 , 3 A / dm ² , in particular 10 and 33 A / dm ² , worked.

The alloy components are preferably added as sulfates and / or chlorides.

The type of chlorides and sulfates used is not critical, but it is in the interests of economy it is preferable to use the hydrated salts of the metals concerned.

Usual insoluble anodes such as. B. used from platinum or graphite. Processes for the electrodeposition of
Iron-chromium-nickel alloy coatings
on metal surfaces

Applicant:

Amchem S. Α., Zug (Switzerland)
ίο representative:

Dr.-Ing. A. van der Werth, patent attorney,
Hamburg-Harburg 1, Wilstorfer Str. 32

Named as inventor:

Dipl.-Ing. Dr. techn. habil. Willibald Machu,

Vienna;

Dr. Mohamed Fathi El-Ghandour, Cairo

Claimed priority:

Egypt of May 24, 1960 (243)

Soluble stainless steel anodes can also be used, preferably stainless steel anodes, the under the Designation SAE steel 304 and 305 is known. When using such anodes made of stainless steel the electrolyte solution should contain chlorine ions to facilitate the dissolution of these anodes.

Discharge and other losses can be caused by the addition of salts or bath components be balanced.

If less than 1.0 mol per liter of urea is used, the chromium deposition is adversely affected, so that only very small amounts of this metal are deposited in the overall coating can. On the other hand, if more than 4.0 moles per liter of urea is used, chromium will precipitate Cost of nickel with increased rate of deposition in the alloy, so that the coating only more contains very small amounts of nickel.

Boric acid, like urea, prevents the formation of oxides and reduces cracks in them Coats or completely eliminates them, provided that the concentration, current density, the pH and the temperature are kept at appropriate values.

The dissolution of the metal salts can result in the addition of acid in the form of hydrochloric acid or sulfuric acid.

509 540/314

1

demand. These acids are used to bring the pH of the electrolyte to the corresponding value between 1.5 and 3.5. If the pH of the bath drops to a value below 1.5 during preparation or use , small amounts of ammonium hydroxide can be added to set the desired pH. A pH value below 1.5 is undesirable because it not only leads to reduced chromium deposition in the coating, but also to a reduction in the overall weight of the deposition and an increase in pitting in the coatings. At a pH value above 3.5 , there is a tendency towards a reduction in the current yield for iron and chromium as well as a greater increase in the nickel content in the coating.

It is also possible to add brighteners to the baths according to the invention.

As is known per se in the case of the electrodeposition of alloys or metals, it is also possible, for certain purposes, to subject the object being drawn to a subsequent heat treatment to remove hydrogen which has been absorbed by the coating or the base metal during the deposition. It is also possible to work with stirring of the electrolyte and / or movement of the cathodes, to filter the bath solution or to clean it from unwanted foreign metals from time to time.

To show the influence of changes in the pH value in the electrolyte, reference is made to the following examples. A number of tests were carried out for which the bath contained the following components:

Cr ₁ (SOJ ₃ · 15 H ₄ O 0.4 mol

FeSO ₄ · 7 H ₂ O 0.2 mole

NiSO ₄ · 7 HjO 0.4 mol

Urea 3.0 moles

H ₃ BO ₃ 0.4 mol

The baths of this composition were operated with copper cathodes at 50 ° C. and a current density of 26.6 A / dm ^a for 5 minutes. The following table I shows the test results obtained for various pH values.

Gram % Tabel 82.0 lin I. % Current efficiency Cr Fe for Legie
tion Metal 76.8 ■ ung
Ni Legie
tion 1.95 4.75 Ni pH 0.0202 the Legiei
Cr I Fe 74.1 18.0 5.73 3.71 11.1 0.98 1.1 0.0504 0 72.4 14.6 15.11 3.71 13.0 2.00 1.5 0.0610 8.4 70.6 12.8 18.86 5.01 14.7 2.13 1.7 0.0704 13.1 71.3 12.2 22.04 5.75 14.8 2.35 2.1 0.0726 15.3 75.5 12.3 22.97 4.64 14.1 2.44 2.3 0.0684 17.1 14.0 21.33 1.85 13.5 2.63 3.0 0.0622 14.7 18.0 18.45 3.07 3.5 6.4

From this Table I it can be seen that under the specified conditions at a pH between 2.1 and 2.3, alloy coatings of stainless steels which approximately correspond to the types SAE steel 305, 316 and 347 are obtained.

As mentioned above, the iron- chromium-nickel alloys are deposited at current densities of about 3.3 to 33.3 A / dm ² . In the example of the 653

Table I was, as indicated, a current density of 26.6 A / dm ² is used. If current densities of more than about 33 A / dm ^{2 are used} , the coating of the deposited alloy tends to form cracks and fissures, and sometimes burned spots also occur in the base metal. On the other hand, however, at current densities of around 3 A / dm ^2, the chromium content of the coatings tends to drop to values that are too low, and the overall current yield also decreases.

To show the influence of changes in current density, another series of experiments was carried out carried out, the results of which are given in Table II below. The solution used was the same as given in Table I, as were the working conditions, with the pH value in all Trials was kept constant at about 2.1. The cathode used was also made of copper.

Table II

current Gram 0 /
/ 0 Metal in Ni ° / ₀ current efficiency for Cr Fe Ni density Legie the alloy 19.9 Legie 1.67 10.1 2.63 A / dm * tion Cr Fe 18.5 tion 2.60 12.5 3.07 6.6 0.0121 7.6 72.4 15.2 14.4 3.96 14.5 2.90 13.3 0.0302 9.4 72.0 12.3 18.2 5.10 15.0 2.41 20.0 0.0521 12.4 72.3 13.1 21.3 6.90 17.8 3.15 26.6 0.0720 15.3 72.4 12.7 22.5 6.24 15.8 2.72 33.3 0.1101 16.9 70.0 27.8 36.6 0.1074 17.3 70.0 24.7

From this table it can be seen that under the bath conditions where current densities of about 26.6 up to about 33.3 A / dm ² are used, one gets closer to the 305, 136 and 347 stainless steel types.

In order to demonstrate the effect of changes in the bath temperature, another series of experiments was carried out, the results of which appear in Table III below. In these experiments the bath was the same as given for Tables I and II, and copper cathodes were again used. The pH of the electrolyte solution was kept at about 2.1, and the current density used was 26.6 A / dm ² .

Table III

Tempe Gram ° / o Metal in "ung
Ni ° / o current efficiency Cr Fe for rature
⁰ C Legie
tion the
Cr Legiei
Fe 3.7 Legie
tion 8.4 13.3 Ni 30th 0.0667 27.1 69.1 7.9 22.3 6.3 13.9 0.66 40 0.0675 20.1 71.8 12.3 21.7 5.1 14.8 1.48 50 0.0710 15.3 72.4 18.1 22.2 2.8 16.6 2.38 60 0.0786 7.9 73.9 24.4 23.3 1.9 17.3 3.89 70 0.0850 4.8 70.8 29.3 24.9 0.4 19.4 5.67 80 0.0966 0.9 69.7 27.5 7.75

The table shows that lower temperatures favor chromium deposition at the expense of nickel. This can be seen both in the total weight of the deposited metal and in that on the individual Metal-related, percentage current yield. It also shows that the iron related Current efficiency increases gradually with increasing temperatures. The total deposited alloy increases with increasing temperature, whereby one

Coatings with an approximate composition of the stainless steel types 305, 316 and 347 obtained under these test conditions in the temperature range from about 40 to 50 ^° C.

With regard to the treatment time, it has been found that the duration of the electrodeposition has essentially no appreciable influence on the composition of the alloy, apart from the fact that the prolonged electrolysis under otherwise constant conditions tends to reduce the current yield and also to dull surfaces Coatings can lead. In order to demonstrate this behavior, a number of experiments are given in Table IV below, using the same solutions as for Tables I to III. The cathode consisted as in the previous experiments of copper, the temperature was about 5O ⁰ C and the pH 2.1.

Table IV

Current density Time Gram % Metal in the alloy 11.8 ⁰ I. alloy ο current efficiency for Fe Ni A / dm ³ Minutes alloy Cr I Fe j Ni 12.3 22.2 Cr 14.8 2.4 26.6 2 0.0284 15.1 73.3 12.2 22.2 5.0 14.8 2.4 26.6 5 0.0710 15.3 72.4 12.2 22.2 5.1 14.8 2.4 26.6 10 0.1430 15.3 [ 72.5 12.3 21.9 5.1 14.6 2.4 26.6 15th 0.2100 15.3 72.7 18.6 5.0 12.4 2.0 26.6 20th 0.2370 15.3 ι 72.7 4.2

With regard to the base metal which is suitable for the coating, the method according to the invention can be used for the coating of metals from the group consisting predominantly of copper, iron, nickel, zinc and their alloys, these metals being the predominant constituent. In order to show the influence of the composition of the cathode material made of these metals on the deposited coating, Table V lists a number of tests. Here, too, the solution was the same as in Tables I to IV, the pH was 2.1, the current density 26.6 A / dm ² , the temperature 50 ° C. and the treatment time 5 minutes.

Table V

Base metal

Gram
alloy

% Metal in the alloy Cr I Fe Ni

° / o current efficiency for

alloy

Cr

Fe I Ni

copper
Brass
Nickel.
Zinc...
Iron ..

0.0712
0.0660
0.0780
0.0870
0.0880

15.33
15.30
15.27
15.28
15.34

72.4 72.4 72.3 71.7 72.3 12.26
12.27
12.30
12.28
12.28

22.28
20.66
24.42
27.24
27.52

5.05 14.85 4.68 13.76 5.52 16.26 6.17 18.13 6.26 18.24

2.38
2.21
2.63
2.93
3.00

From the results of Table V it can be seen that slight changes in the layer weight on the different cathodes occur, but the composition of the alloy is practically constant remain. The greatest current yields were when using zinc and iron as cathodes, the least preserved on brass cathodes.

Claims (2)

Patent claims: 1. A method for the galvanic deposition of iron-chromium-nickel alloy coatings on base metals such as iron, zinc, nickel, copper or their alloys, characterized in that an aqueous solution with a content of at least 0.2 mol per liter of the individual alloy components, calculated as metal ions and 1 to 4 mol per liter of urea and / or 0.2 to 0.6 mol per liter of boric acid and used at a pH between 1.5 and 3.5, in particular 2.1 to 2.3, at a current density from 3.3 to 33.3 a / dm ^2, in particular 10 to 33 a / dm ² and a bath temperature between 30 and 8O ⁰ C, in particular 30 and 55 ⁰ C, is carried out. 2. The method according to claim 1, characterized in that the alloy components as Sulphates and / or chlorides are added. Considered publications:
German patent specification No. 942 429. 509 540/31 * 4.65 © Bundesdruckerei Berlin