Process for hardening workpieces in a pulsed plasma discharge

Details Process for hardening workpieces in a pulsed plasma discharge Process for hardening workpieces in a pulsed plasma discharge

1993-04-29

1995-01-24

Dean, Richard O.

Metal treatment

Process of modifying or maintaining internal physical...

Carburizing or nitriding using externally supplied carbon or...

148235, 204164, 21912158, 21912159, C23C 822

Patent

active

053839803

ABSTRACT:
Workpieces of steel are hardened by carburizing the surface and then quenching. The carburizing is performed by means of a plasma discharge in a vacuum, in the presence of gaseous hydrocarbons at voltages between 200 and 2000 volts, preferably between 300 and 1000 volts, and preferably with the admixture of argon. The plasma is produced by means of electrodes operated in a vacuum, the cathode of which serves as workpiece holder and is operated by pulsed operation. In order to achieve a uniform hardness distribution and to reduce the mass flow of carbon, even in the case of irregularly shaped workpieces, the carburization is performed at a total pressure between 14 and 30 mbar, the pulse duration is selected between 110 and 10,000 .mu.sec, and the pause duration is selected between 30 and 10,000 .mu.sec. After the start-up phase has ended, the average power fed to the plasma discharge is reduced either continuously or step-wise by shortening the pulse duration and/or by prolonging the pulse duration, such that, without interruption of the pulsed operation, the carbon content at the surface of the workpiece will at no time exceed the carbon saturation limit of the steel in the austenite region.

REFERENCES:
patent: 4762756 (1988-08-01), Bergmann et al.
patent: 4853046 (1989-08-01), Verhoff et al.
Grube, W. L. and Gay, J. G., High-Rate Carburizing in a Glow-Discharge Methane Plasma, Metallurgical Transactions A vol. 9A, Oct. 1978, 1421-1429.

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