DE2305996A1 - PROCESS FOR ANTI-CORROSION TREATMENT OF STEEL - Google Patents

Description

PATENT ADVOCATE

DR. HANS ULRICH MAY D 8 MÖNCHEN 2. OTTOSTRASSE la

TELEGRAMS: MAYPATENT MDNCHEN 2305996

TELEPHONE COBIO 0038 82

CP 445/1145 Munich, February 7, 1973 Dr M./rt

B 3613.3 GL

Commissariat ä "1" Energie Atomique in Paris, France

Process for the anti-corrosion treatment of steel,

The invention relates to a method for anti-corrosion treatment of ordinary non-alloyed or low-alloy steels, special; for protection against substances containing fluorine.

More generally, the corrosion protection according to the invention is: - can be used with advantage in all cases where mechanical or other conditions require the use of the specified materials in dry or humid corrosive atmospheres, regardless of whether they are combustion gases, fluorine-containing gases or acidic environments acts.

Various methods for protecting steels against dry or wet corrosion, for example geeen corrosion caused by fluorine-containing agents, are already known. Electrochemical or chemical nickel plating, Ph aiphatie etc. may be mentioned of these processes.

On the other hand, certain protective coatings of this type are sufficient on mild steel, but lose some of their effectiveness or are even completely ineffective, especially against the fluorocarbon

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sion, if the carrier consists of a steel with more than 0.05 % carbon content, e.g. alloyed steels, cast steels or special alloys.

According to the invention, a method for the anti-corrosion treatment of steel with a carbon content above 0.05 % is to be created. The inventive method is characterized in that the steel is heated in a humid mixture of nitrogen and hydrogen at a temperature between 650 and 85q ^O C.

For example, for a nitrogen-hydrogen mixture with 10% Hydrogen content get the optimal water vapor tension by the gas mixture is bubbled through water kept at about room temperature. The duration of treatment ranges from a few minutes up to several hours, depending on the depth of the desired decarburization.

According to a preferred embodiment of the invention, the Superficially decarburized steel is subjected to a protective treatment, which increases its resistance to fluorine corrosion further improved.

In order to carry out this protective treatment, the depth of the decarburization must take into account the subsequent treatment conditions or conditions of use and the type of metal or metals to be treated Alloy to be adjusted. , -

Of course, a greater depth of decarbutation is chosen, if the steel is subject to a later protective treatment

For example, in the case of a common steel, without prior Passivation of exposure to a fluorine-containing environment: should be exposed, as a minimum depth of deearburization 0.1 mm. selected, on the other hand more than 0.1 mm if the steel has been given a protective

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treatment is subject.

According to a modification of this preferred embodiment takes place protective treatment with phosphate baths.

After decarburization over a depth of more than 0.1 mm, the steel can be pickled in a first bath with a mineral acid which contains a corrosion inhibitor, and then put on it _; after a first rinse, bring it into a second bath, which contains iron and / or zinc phosphates, and finally, after a second rinse, treat and dry in a third oxidizing bath.

The steel workpiece to be treated is prior to the decarburization treatment pickled and / or processed, so-leave its surface none Has a trace of tinder. At the end of the decarburization treatment the treated steel must "have a shiny and clean appearance, exactly the same as the appearance of its original surface.

The workpieces treated according to the invention show a remarkable one Resistance to the most aggressive reagents such as elemental fluorine or uranium hexafluoride.

With reference to the accompanying schematic Figures 1 to 3 In the following to explain the invention, various embodiments of the corrosive according to the invention are given only as examples. sion protection procedure described. Of course you can too

¹ TV

equivalent measures are applied.

In the figures, only those are important for understanding the invention Details shown, with corresponding parts in Figures 2 and 3 having corresponding reference numerals.

Fig. 1 shows in the form of curves the influence of temperature on the Kinetics of the decarburization reaction; -

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Figures 2 and 3 show schematically the surfaces (micrographs) of two steel samples that have undergone a decarburization treatment were subjected and of which one (Fig. 3) still a subsequent Has been subjected to treatment.

In Fig. 1, the four curves correspond to the following temperatures :.

1: 685 ° C;

2: 700 ° C; '

3: - 50 ° C; . ·.

4: 8OSJ ⁰ C.

The decarburization depths are dependent on the ordinate in millimeters given by the time in hours (abscissa).

Fig. 2 shows that the structure of the steel in the inner region 1 remains unchanged is, while in the decarburized surface area 2 a recrystallization to coarse basaltic crystals took place.

3 again shows the unchanged internal structure 1 of the steel . Covered with a deearburized layer 2. This in turn will protected by a further phosphate layer 3. ■

Some examples of the corrosion protection of steels are given below.

Example & I 1:.

Steel test bars in accordance with the French standard AFNOR NF 136.205 with a carbon content of 0.18 to 0.25 % were mechanically descaled and degreased and then decarburized to a depth of 0.1 mm using the method described above. The test bars were exposed to corrosion by UFg along with undecarburized test bars of the same steel. . After 500 hours assault at 130 ⁰ C and 150 ° C, the following amounts of UF ₆ had decomposed:

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13O ⁰ C 2305996
1 50 ⁰ C I8g / m ² . 24 g / m ² 240 g / m ² 330 g / m ²

Steel, decarburized to a depth of 0.1 mm
Steel, comparison

Example 2 -

hq Test bars of the same steel that had been subjected to the (equalizing degreasing / - and decarburizing treatment) were tested together with test bars made of steel according to the French standard AFNOR A 30.009, type C10c, which had a carbon content of 0> 04 % and using the same procedure as ¹ corrosion by UF ₆ were indicated above for the steel NF 136 205 mechanically pretreated exposed After 4000 h attack at 130 ⁰ C to give the following values for the decomposition of the UFG:.. steel NF 136 205, on 0.1 mm deep decarburized 38 g / m ² steel (C10c) 30.009 41 g / m ²

The same classifications are obtained in co-operation tests with other fluorine-containing agents, with uncontaminated ambient air at 50 % relative humidity and in an acidic environment also on other steels with a higher initial carbon content.

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Claims (2)

Claims 1. The process for the anti-corrosion treatment of steels with over 0.05 % carbon content, characterized in that the steel is heated to a temperature between 650 and 850 C in a moist mixture of nitrogen and hydrogen. 2. Corrosion protection method according to claim 1, characterized in that that after the heat treatment a protective treatment is carried out by means of a Phosphatxerungsbades. ; 309 8 33 / -1 14 9