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

Using the above equivalence for the substitution of carbon by nitrogen,
in Fig . 15 the optimum sintering temperature variation with the combined action of
carbon and nitrogen, is shown for the three steels . For T42 the actual results fall in a
line close parallel to and above the solidus line reported by Grinder et al (21) . For
T15 also the experimental points fall in a line, on which an experimental solidus point
(22) is also included . The experimental values for the optimum sintering temperature
for steel Px30 together with the solidus line for M2 is also represented in the figure
and it is clearly apparent that the optimum sintering temperatures are above the
solidus line, which could indicate that the densification in the present material takes
place also by a supersolidus mechanism, as admitted by other authors (23,12) for
the densification of high speed steels . In the present case perhaps the shift between
the M2 solidus line and the optimum sintering temperature is too big, but this could
be due to the presence of Co in these M grade steel, which has an effect of
increasing the optimum sintering temperature when added to steel M3/2, as have
been observed recently (24) .
It is worth emphasizing that also in these materials in the case of
atmosphere sintering, where an important increase in nitrogen is observed a model
based on supersolidus sintering, assuming a certain equivalence between nitrogen
and carbon in atomic percentage, would explain the experimental results .
On the other hand, the influence of carbon and nitrogen on the
minimum temperature for the appearance of the continuous film of eutectic carbide
in all cases M6C carbide) at the grain boundaries, is shown also in Fig . 15 . It is
clearly apparent that the slope of the line for the appearance of the eutectic carbide
presents a slope smaller than the corresponding - - to - the optimum sintering-
temperature . This figure explains clearly why increasing the amount of carbon or/and
nitrogen, this last by sintering in the gas atmosphere broadens the sintering range or
the sintering gate .
Precipitates : Effect on Austenite Grain Growth .
As pointed out before, sintering in nitrogen rich atmosphere produces
the transformation of MC carbides present in vacuum sintering to MX carbonitrides .
This transformation has been confirmed using WDS micronalysis, as described
elsewhere (12) and also using X-Ray diffraction techniques (18) . It is worth
emphasizing that the MX carbonitrides in gas sintered specimens present a mean