Sinterizazio-atmosferaren eragina M graduko (ASP 30 ... - Euskara

gas atmosphere (see Table IV for quantitative values) . A small amount of eutectic is
observed for all the specimens sintered at the optimum temperature .
The microstructures for Px30S and Px30S + 0 .2%C vacuum and gas
atmosphere sintered are very similar to the equivalent for Px30, the only diffence
between the two materials being the presence of big manganese sulfide inclusions
(10 um) for Px30S, as shown in Fig .4. The manganese sulfide chemical
composition, obtained by EDS, resulted in 35%S, 2%V, 10%Cr, 50%Mn and 3%Fe .
Table IV summarizes the values of the microstructural features such
as: austenite grain size and the volume fraction of MX particles and M 6C carbides at
the optimum sintering temperature. For both materials the big round and grey MC
carbides, rich in V, observed at the vacuum sintered specimens, are substituted by
the small black and square MX carbonitrides, even richer in V than the MC . In all the
four micrographs the bright M 6C carbides, rich in W or/and Mo, present similar
geometric forms . In Fig . 4 the manganese sulfide particles are also clearly apparent .
Table V summarizes the mean chemical composition of primary particles type MX
and M 6C.
The variation of austenite grain size with the deviation of temperature
from the optimum sintering temperature is observed in Figs . 5 a and b for both steels
with and without the addition of free carbon . It is clearly apparent that for vacuum
sintering the grain growth results very fast at temperatures higher than the optimum
(positive deviation), but the grain size increases only very slowly above the optimum
sintering temperature for gas sintered steels . Grain growth is very similar for both
steels when sintered under the same conditions .
Chemical analysis of dispersed particles has shown that only the use
of the gas mixture during sintering instead of vacuum, in both steels and in samples
with and without carbon addition, produces differences in chemical composition of
MX type particles . Table V also shows that MX particles found in Px30 steel are
richer in V than those found in Px30S steel, being the M 6C type particles of similar
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