Effect of local sintering microatmosphere on mechanical properties of Fe–3Cr–0·5Mo–0·6C steel

Abstract

An improved process is proposed for sintering of Fe–3Cr–0·5Mo–0·6C steel in nitrogen, in a box, additionally containing sources of manganese vapour (ferromanganese lumps) and nascent carbon (naphthalene). The use of a semiclosed container with a labyrinth seal minimises compact interaction with the flowing furnace atmosphere and thus ensures that a dry local ‘microclimate’ exists within and around the sintered specimens. Nascent carbon, from ∼1000°C, is significantly chemically more active than graphite (previously used) and the microclimate thus included, from ∼700°C, manganese vapour. The latter additive ensures that manganese is oxidised in preference to chromium, whereby oxygen uptake to the compact is inhibited and reduction rather than oxidation of chromium occurs. A favourable comparison is made of resultant mechanical properties for the same material sintered also in hydrogen, with published properties of similar Cr–Mo–C steels and with MPIF standard for Cu and/or Ni containing steels.