Effect of Atmosphere Composition on Physical Properties in High Temperature Ferrous Sintering

Endothermic gas is not an effective protective atmosphere for ferrous sintering at 2350°F. But, strong parts of medium to high carbon content are produced by sintering in a nitrogen-based atmosphere at 2350°F. This nitrogen-based atmosphere must contain a small amount of hydrogen and carbon monoxide. A low level of hydrogen will minimize decarburization of the parts and promote a higher degree of sintering. The carbon monoxide promotes a uniform carbon structure. The use of methane to control carbon potential is difficult due to the high carburizing rate of methane at 2350°F which causes recar-burization of the parts. Small amounts of Cu or Ni can be added to ferrous powder to further improve the strength of the sintered parts. These elements also tend to stabilize the carbon in the parts and allow small amounts of methane to be added to the atmosphere to further improve the strength of the material without producing recarb.