Steam oxidation of ferrous sintered parts: Contribution to study

Abstract

Steam oxidation is a process widely used in sintered material treatments to increase superficial hardness and to provide protection from external agents. Despite its extensive use, phenomena connected with the process often are not well known. It is supposed that oxidation must grow with time depending on temperature, porosity and the powder used to prepare the specimens. Often, in industrial practice, an anomalous phenomenon happens and it can reduce the productivity of the steam oxidation process: for longer treatment times instead of an increase of oxide layer thickness there is a reduction of the total oxide mass of the oxidised parts. This phenomenon causes the mass v. time curves to show a maximum for intermediate times.

The effect has a greater probability in industrial production because large quantities of parts are put in the furnace and they need a certain period of time to reach the desired treatment temperature. The phenomena, dealing with formation and increase of the various types of obtainable oxides, are studied in relation to process optimisation. In particular, on the basis of some thermodynamic considerations, the authors try to suggest some criterion to increase process productivity.