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

17
16
0
FIGURE 4.- Evolution of the volume fraction
of primary particles with sintering temperature
Figure 5 shows particle size distribution histograms for specimens sintered at the
optimum sintering temperature . The MX particle distribution of gas sintered samples is narrower
and more concentrated at finer sizes than that corresponding to vacuum sintering . On the other
hand, M6C particle distribution is similar for both sintering techniques .
60
>a
w
b
N
0
0 10 20 30
OVERSINTERING ('C)
Volurne Fraction (%)
0-1 1-2 9-3 0- • •- 5 !-6 6-7
M6C
7-6 6-9
Particle Size (microns)
Figure 4 shows the evolution of the
volume fraction of primary particles with
sintering temperature . It is apparent that
although the volume fraction for gas sintered
samples remains approximately constant, for
vacuum sintered samples the total amount of
primary carbides decreases with oversintering,
due to dissolution and a subsequent formation
of eutectic carbides during cooling . The volume
fraction of each particle type in gas sintered
samples, with and without carbon addition, was
approximately constant in the evaluated
temperature range, from the optimum up to
30 °C above it : the mean values were 3 .7% for
MX and 8.5% for M6C for T42 steel . Particle
distribution analysis has shown that MX
carbonitrides were very resistant to coarsening
resulting in a mean particle size of 1 µm at the
optimum temperature and 1 .3 µm at 30°C
above it; no particles larger than 3 .5 µm were
found .
Particle Size (m icrons)
FIGURE 5.- Particle size histograms for specimens sintered at the optimun sintering temperature
Table II summarizes the quantitative values of microstructural features such as : austenite
grain size, volume fraction of retained austenite and % volume fraction and size for MX particles
and M6C carbides at the optimum sintering temperature .