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.

Keywords:

• PM chromium structural steels
• Mechanical properties
• Sintering atmospheres
• Semiclosed container

This work was sponsored by the Polish Ministry of Science and Higher Education under contract no. 11.11.110.158. Appreciation is also expressed to Professor A. S. Wronski for his comments on the manuscript.