Effects of H-2 Atmospheres on Sintering of Low Alloy Steels Containing Oxygen-Sensitive Masteralloys

摘要

Processing of novel sintered steels with compositions including oxygen-sensitive elements requires deep understanding of the chemistry of sintering. The use of H-2 atmospheres alleviates the oxygen transference from the base powder to the oxygen-sensitive particles. However, in H-2, methane formation at 700-1200A degrees C causes dramatic homogeneous decarburization of the part that affects both mechanical behavior and dimensional stability. The intensity and the critical temperatures of this effect depend strongly on the alloying elements, being significantly enhanced in presence of Si. When combining the alloying elements as Fe-Mn-Si masteralloys, methane formation is enhanced around 760A degrees C due to the high Mn content (40 wt.%) in the masteralloys. Nevertheless, the benefits of H-2 towards oxide reduction can still be advantageously used if diluting it in the form of N-2-H-2 atmospheres, or if limiting the use of H-2 to temperatures below 500A degrees C. Thus, decarburization due to methane formation can be successfully controlled.