DE1771727B2 - Carburization process of steels in cyanide-free molten salts - Google Patents

Description

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The invention relates to a method for carburizing steel for the purpose of hardening in cyanide-free Molten salt with the help of silicon carbide and elemental Carbon combined with metallic silicon as a catalyst.

uie basic condition for hardening steels is the presence of carbon in steel. The process of further hardening of steels consists from charring and hardening. Basically there are possibilities to carburize steels, namely the Liasautkoh ung, the powder carburization and the salt-Daaautkonlung. The last-mentioned type of carburization is predominantly in cyanide content on an industrial scale at the time Salt baths carried out. When carburizing

tion b ^{SPI im Sa! zbad fol} S ^{en (Je Reak} "

^a '

3 Fe \ 2 CO -> Fe ₃ C + CO ₂

The carbon monoxide required for carburization

fEdei ^U £ ikHn ^{ACTION OF Cyanide in the salt bath after the} following reactions:

2 NaCN 4 O ₂ -> 2 NaCNO

4 NaCNO -> Na ₂ CO ₃ } CO-JN ₂ -I 2 NaCN Essential NarhtP.i ,. h · α vn u, ■

hang sSzbadeS s nd "'f H Λ"" ⁸ r V

de Cvänude der hnheL Γ ^^ l " ^G i ^f . ^tlgkeit

tZ.Jil ο Γ ^{S of these products} ' ^d ' e on-

Sn Se Γ ΡηΓΓν T ^ng i ^{k iten the use} e ^ehär lerbiniunJ? J _{d ΪΑ _Η ΓΓ .. ^ΕπΙώΙ " ^Ιί - ^M Co ungslcitune with VorhS '" abatement ^{; do} "g ^der

0 \ y eS "" ή? Der Salzfrirf! F ' ⁿ .T T ^{hr as} υ, ΐ / " b.sen m the molten salt through the reaction FeO + CN - + Fe CNO-

⁵ ° Efforts to remedy these deficiencies led to the development of cyanide-free molten salts based on silicon carbide, boron carbide and other non-cyanide-containing substances. In the work of AN Minkewitsch: Chemical-thermal surface treatment of steel, on pages 128 to 133, charcoal powder, carbon black, calcium carbide and silicon carbide are named as cementation agents. At the same time it is described that the salt baths containing silicon carbide have proven themselves in place of the salt baths containing cyanide and should be distinguished by particular resistance.

It must be noted, however, that the previously known methods for carburizing in cyanide-free Molten salt only allowed a short-term carburization and a large-scale use under economic conditions have not yet taken place.

The purpose of the invention is to carry out the carburization of steels in a salt bath in which the aforementioned deficiencies are largely eliminated _and reduced to a minimum.

The invention is based on the object of developing a method for carburizing steels in cyanide-free molten salts on the basis of a non-carburizing base melt, consisting of chlorides and carbonates of alkali and alkaline earth metals, and in the presence of elemental carbon and silicon carbide. This method must be industrially usable, allowing a long lasting Aufkohlungswirkung and at least ensure the sliding _surfaces Kohlungsparameter as cvanidhaltige salt melts.

According to the invention, the object is achieved in that in non-carburizing molten salts with the addition of elemental carbon in the presence of silicon carbide and elemental silicon or its alloys, the catalytic effect of silicon achieves a carburizing effect that lasts for several hours without further additions. This invention achievable Aufkohlungswirkung can not be achieved by increasing the Siliciumkarbidanteils in the melt, ^as this significantly verschlechten the bath behavior and thus a practical Verwendune impossible ^g

^{The Erfi} " ^du " g ^so "are explained in more detail below using an exemplary embodiment.

To a base melt consisting of 70% sodium carbonate and 30% sodium chloride, 20 percent by weight of ^{the base} melt, consisting of ^silicon, sodium carbonate, silicon carbide and carbon, was added in the course of 45 operating hours.

Similar results are achieved if the non ^- carburizing molten mass consists of chlorides ^and carbonates of the alkaline earth metals in a mixture with ^{chlorides and} carbonates of the alkali metals. In this polluted bath at a temperature between 750 and 1200 C, expedient-

of the cyanide occurs.

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the Act.v, actual control can be seen by means of the C value.

8 hours = 1.75 mm

These results are over
operating hours reproducible.

The process is carried out in the carburizing bath
achieved the same results in all places. at
Increasing the temperature, it is possible to

Significantly reduce several thousand coaling times. It is there of little importance and without any influence which type of crucible is used, so that both in the metal crucible, as well as in the brick-lined crucible can achieve the same effect.

Claims (3)

Patent claims: A) I. Process for the carburization of steels in cyanide-free molten salts from chlorides and Carbonates of the alkali and alkaline earth metals with contents of elemental carbon and silicon carbide characterized in that the melt also elemental silicon or Silicon alloys are added and the process at temperatures between 750 and 1200 C. is operated. 2. The method according to claim I, characterized in that the carburization at temperatures from 900 to 1000 C. 3. The method according to claim I and 2, characterized in that the silicon is elementary or in the form of its alloys in a mixture with silicon carbide carbon and alkali carbonates in powder form or as pellets of the base melt is added.