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

The presence of these MX carbonitrides, which do not dissolve at high temperature (see
figure 3), can explain why grain growth is only marginal for oversintering in the gas atmosphere .
Using the expression proposed by Zener for the relation between the limiting grain size (D) and the
size (d) and volume fraction (f) of second phase dispersion :
D = 4d/3f
and taking the data of Table II referring to volume fraction and mean size of carbonitrides and
working out a weighted mean value :
d = (dmx .fmx + dM6c .fM6c)/(fMX + fM6C)
the limiting grain sizes shown in Table II were calculated . If the confidence limits of the
experimental results of volume fracction and particle size are taken into account, confidence limits
around ±20% are obtained . It is worth emphasizing that the grain size values calculated from the
Zener equation for the different steels at the optimum sintering temperature both in the gas
atmosphere and the vacuum agree very well with the grain sizes observed experimentally .
TABLE II.- Quantitative values of the microstructural features of sintered samples .
Grain MX MX M6C M6C Limiting
Steel Atmosphere Size Volume Size Volume Size grain
(/IM) fraction (µm) fraction (µm) size
(µm)
T42
T42
Vacuum
N2-H2-CHa
16 .8
14 .3
5 .4
3 .8
1 .6
0 .96
6 .3
7 .7
1 .39
1 .35
17 .0
14 .0
T42+0,2%C Vacuum 17 .6 6 .5 1 .6 4 .4 1 .39 18 .5
T42+0,2%C N2-H2-CHa 13 .4 3 .8 0 .96 8 .3 1 .35 13 .5
T15 Vacuum 13 .2 6 .6 2 .8 6 .2 1 .9 24 .6
T15 N2-H2-CHa 13 .3 7 .4 1 .4 10 .9 1 .6 11 .1
T15+0,2%C Vacuum 26 .9 8 .5 3 .1 6 .0 2 .0 24 .3
T15+0,2%C N2-H2-CHa 10 .4 8 .5 1 .4 13 .2 1 .8 10 .1
PX30S Vacuum 40 2 .3 3 .4 7 .9 1 .65 26 .7
PX30S N2-H2-CHa 15 .4 2 .6 1 .05 6 .0 1 .7 22.7
PX30S+0,2%C Vacuum 38 5 .4 1 .7 6 .0 1 .66 19 .6
PX30S+0,2%C N2-H2-CHa 12 .9 4.8 0 .83 11 .0 1 .48 10 .8
PX30 Vacuum 21 7 .1 3 .1 8 .5 1 .34 18 .5
PX30 N2-H2-CHa 11 .3 5 .0 1 .1 10 .0 1 .33 11 .2
PX30+0,2%C Vacuum 19 .5 6 .7 3 .6 6 .74 1 .47 25 .2
PX30+0,2%C N2-H2-CHa 10 .5 5 .3 0 .84 10 .3 1 .12 8 .8
M 3/2+1%Co Vacuum 37 .2 - - 11 .0 2 .3 27 .8
M 3/2+1%Co N2-H2-CHa 17 .6 5 .0 1 .1 8 .1 1 .6 14 .3
M 3/2+2%Co N2-H2-CHa 19 .2 4 .5 1 .0 5 .2 1 .8 19 .6
M 35+0,2%C Vacuum 18 - - 10 .0 1 .3 17 .3
M 35+1%Co Vacuum 45 - - 7 .2 1 .9 35 .2
M 35 N2-H2-CHa 18 4 .7 0 .9 10 .0 1 .5 11 .9
M 35+0,2%C N2-H2-CHa 15 6 .3 0 .8 11 .0 1 .5 9 .6
M 35+1 %Co N2-H2-CH4 17 .3 3 .1 1 .0 8 .5 1 .4 14 .9