Method and facility for carbonitriding one or more steel parts under low pressure and at a high temperature

Abstract

The invention relates to a carbonitriding facility (IC) which includes: a heating chamber (CC), for heating at least one steel part (PA) to a first temperature, in the presence of a neutral gas and under a selected pressure; a first enriching chamber (CE1) for enriching the heated part with nitrogen, by nitriding same in [alpha]-phase at a second temperature no higher than the first temperature; a second enriching chamber (CE2) for enriching the nitrogen-enriched part with carbon, by carburising same at a third temperature higher than the second temperature; a quench chamber (CT) for quenching the nitrogen- and carbon-enriched part under pressure; a transfer airlock (ST) communicating with the chambers and suitable for temporarily receiving the part in a controlled atmosphere; and transfer means (MT) for transferring the part from one chamber to another chamber via the transfer airlock (ST).

Description

technical field [0001] The present invention relates to certain thermochemical treatments for strengthening steel parts, and more precisely to the carbonitriding of such steel parts. Background technique [0002] In some fields, for example in the field of vehicles (optionally motor vehicles), it is necessary to enhance the durability of some steel parts, and more precisely at least the fatigue resistance of these steel parts, so that these steel parts can withstand higher large stresses and / or in order to increase the service life of these steel parts. This strengthening can be obtained by carbonitriding. [0003] Note that carbonitriding is a thermochemical diffusion treatment that involves enriching the surface of the steel with carbon and nitrogen prior to the quenching step in order to obtain a martensitic structure and strengthening. Enrichment with nitrogen (here carried out into the austenitic phase) is called nitriding to alpha phase, and enrichment with carbon is...

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Problems solved by technology

[0005] As known to those skilled in the art, known carbonitriding treatments take longer and are compromised to provide a non-optimal metallurgical effect

In fact, said carbonitriding treatment uses relatively low treatment temperatures (typically around 850° C.) in order to optimize the nitrogen-enriched operation (and more precisely to avoid nitriding in alpha phase ammonia (NH3) Most crack before touching the part), but this detracts from the carbon enrichment operation (which requires higher temperatures) and detracts from the processing time (which is due to Relatively low processing temperature needs to be increased)

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