Abstract
The as-atomized steel powders containing Mn and Cr were coated with phenol resin. Then, the powders were compacted and sintered in N2 atmosphere. Oxides in the surface layer of the atomized powders were actively reduced and the required carbon contents were obtained with residual carbon after decomposition of resin. The results were summarized as follows:
(1) In the low alloy steel powders of Mn, Cr series which are more difficult to be reduced than that of Ni, Mo series, the amount of residual oxygen could be decreased from 7200 p.p.m. to 200 p.p.m. through the reduction sintering at 1200°C for 120 min.
(2) The as-atomized steel powders were coated with thermosetting phenol resins. The phenol resin has many effects such as lubricating and binding between the powders at compacting, and reducing the oxygen and adding the carbon at sintering.
(3) In the as-atomized steel powders, it is desirable that the contents of Al and Si being difficult to be reduced and the amount of oxides to be mixed in the melting process must be decreased. The oxygen content desired is less than 10000 p.p.m. and the carbon content is less than 0.1 %.
(4) The optimum amount of phenol resin is from 2.0% to 3.5% to maintain the strength of green compaction and prevent cracking at the sintering.
