22nd November, 2017

Processes - Inert Hardening

Control of furnace atmospheres during the austenitizing cycle is critical in obtaining precise metallugical specifications. The prevention of oxidation or surface decarburisation when components are held at high temperatures can be achieved by the generation of several chemically neutral furnace atmospheres.

At Metaltech the most commonly prepared atmospheres are endothermic-based which are employed during the austenitizing cycle of the engineering steels such as: 080M40 (EN8), 080M50 (EN43A), 070M55 (EN9), 708M40 (EN19) and 817M40 (EN24).

Using oxy-probes to control the carbon potential in the furnace usually in the range of 0.4% - 0.45% C, oxidation and de-carbrisation of the surface layers is prevented. A slight discolouration of the components results from the oil quenching operation although the discolouration is readily removed by a light shotblast operation.

In addition we offer nitrogen based protective atmospheres through a combination of liquid nitrogen/prism generated nitrogen and methanol. These atmospheres can be used for hardening operations and also for bright annealing operations.

Vacuum furnace applications which are dealt with a preceeding section employ inert nitrogen atmospheres of contaminant levels less than 0.01% are used in the purging and quenching stages of vacuum heat treatment cycle to prevent de-alloying of volatile elements and protect against oxidation of key alloying elements specially in tool-steel hardening.

Next Page: Carburising
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