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

INTRODUCTION
Work carried out in the last two decades on the sintering of high speed
steel powders has allowed obtaining high density components with near net shapes .
One of these routes is direct sintering, consisting of cold compaction of annealed
water atomized powders and subsequent vacuum sintering to full density . This
technique has been succesfully applied to T1(1), M2(1), T6(2), T42(3,4), T15(5) and
M42(6) .
In many cases to compensate for the loss of carbon due to its reaction
with the oxygen present at the surface of the powders, some elemental carbon is
added to the prealloyed powders before sintering(7-9) . Such addition results also in
an acceleration of the sintering kinetics, explained by some authors by the effect of
carbon reducing the steel solidus temperature (10) . More recently Wright (11) has
proposed that the sintering mechanism in this type of steels is "supersolidus" .
Previous work in CEIT has proposed an alternative route to the
vacuum sintering, reaching theoretical densities by sintering in a flowing atmosphere
of N 2-H 2-CH 4 . Work has been performed on M2(12), T15(13), T42(14), T6(15) and
M42(16) .
In two recent papers, one on T42(17) and the other on T15 and
M2(18), a consistent decrease in the optimum atmosphere sintering temperature
compared with vacuum for T grades has been reported, but the optimum
atmosphere sintering temperature was slightly higher than that found during vacuum
sintering for M2(18) . During atmosphere sintering a finer microstucture is normally
also produced due to the substitution of massive MC carbides by MX fine and
coarsening resistent carbonitrides . It is also reported that for the T grades
oversintering by up to 40K in the gas atmosphere does not significantly modify the
microstucture and continuous films of eutectic are not observed, but a continuous
film of eutectic is observed even for the optimum atmosphere sintering temperature
for M2 .
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