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

- Needle type : observed only at highly oversintered specimens both for vacuum
and gas sintering .
Figs . 8 a and b show typical SEM micrographs of several eutectic
carbides present in, vacuum oversintered Px30 steel and in gas atmosphere
oversintered Px30S steel . The different eutectic carbides are marked in the
micrograph .
DISCUSSION
Densification Kinetics
The nitrogen analysis results for specimens sintered using the gas
mixture show clearly that this element diffused into the steel . In this case also the
uniformity of microstructures between the specimen periphery and the center would
indicate, as proposed in previous papers for T42(17) and T15 and M2(18) steels,
that nitriding is taking place during the heating up of the specimens or/and at the
beginning of sintering . It is worth emphasizing that the-amount of nitrogen absorved
by steel Px30 (0 .71-0 .76%) is clearly higher than that absorved by steel Px30S (0 .44-
0.45%) ; if in addition to this values those recentely reported : (17) for steel T42 (0.41-
0.48%), (18) for steel M2 (0 .34-0.38%) and for steel T15 (0 .72-0 .78) are taken into
account, it is clear that the amount fo absorved nitrogen is higher the higher the
vanadium concentration in the steel ( 3 .32 %V for Px30, 2 .92%V for Px30S, 4 .7% V
for T15, 1 .86%V for M2 and 2 .91% V for T42) . This effect, which is related with the
formation of vanadium carbonitrides, has also been found in other high speed
steels(24) and is the base of a recent patent (25) .
At first approximation the carbon in MC would be substituted by
nitrogen, giving carbonitrides . The carbon rejected due to the substitution by
8