Editorial & Advisory Board - Acta Technica Corviniensis

Significant increase in the concentration of carbon at
the beginning of the combined zone can be seen from
Figure 3, where it reaches the level of 0,52% and slightly
decreases at the end of the carbonitrided zone, going to
about 0,48 %. The distribution of the nitrogen in the
carbonitrided zone changes gradually and its
concentration at the end of the combined zone reaches
the level of 7%, while at the beginning of the combined
zone it is about 12,2 %. Under this mode of treatment the
highest level of nitrogen concentration 12.2 % is achieved
in the combined zone and the most gradual change of
the content of nitrogen and carbon in the formed layer
occur in comparison to all the other modes of ion
carbonitriding of 25CrMnSiNiMo steel.
ARMCO‐IRON
After nitriding of Armco‐iron under the 6 th mode of
treatment from Table 2 a layer with micro‐hardness of
415HV 0,1, total thickness of 290 μm and combined zone
thickness of 6μm is obtained. It can be noted from
Figure 4a that the concentration of carbon in the
nitrided layer has not changed at the border between
the basic material and the combined zone. No increase
of the carbon concentration on the surface of the
layer is observed. The nitrogen concentration on the
surface of the combined zone reaches 17,1%. After the
process of ion nitriding the curve of the nitrogen
distribution in the nitride zone does not change
gradually.
Under the modes of nitriding 25CrMnSiNiMo steel is
with higher micro‐hardness but lower total thickness
of the layer and thicker combined zone than Armcoiron.
This is explained by the content of alloying
constituents in the steel, which take part in forming
the nitrides and hardening the surface layer. They
inhibit the diffusion of nitrogen in depth, as a result of
which thinner layers with thicker combined zones are
obtained.
In Armco‐iron carbonitriding under the 4 th mode of
treatment (50%HN 3 + 41% Ar + 9 %CO 2 ) from Table 2 a
layer with surface micro‐hardness of 370HV 0,1 , total
thickness of 210 μm and combined zone thickness of 6
μm is obtained and the distribution of nitrogen and
carbon in depth of the carbonitrided zone is given in
Figure 4b.
From Figure 4b it can be seen that at the end of the
combined zone at 6μm depth slight increase of the
carbon content to 0,24 % is observed, while at the
beginning of the combined zone the carbon content
reaches 1 %. The figure shows that the distribution of
carbon in depth of the combined zone is sharp to 3μm
depth with concentration of 0,20 %. At the end of the
carbonitrided zone the carbon concentration
increases to 0,24 %. The nitrogen distribution change
in the carbonitrided layer goes gradually. At the end of
ACTA TECHNICA CORVINIENSIS – Bulletin of Engineering
the combined zone (6μm) its concentration reaches
3.4 %, while at its beginning the concentration is 8.3%.
C-Concentration [mass %]
C-Concentration [mass %]
C-Concentration [mass %]
C-Concentration [mass %]
1,5
1,0
0,5
N
0,0
0 5 10
0
15
Depth [µm]
а) after nitriding t = 550 0 C, P NH3 = 400 Pa, τ = 4 h
1,5
1,0
0,5
N
C
0,0
0
0 5 10 15
Depth [µm]
b) after carbonitriding t = 550 0 C, P NH3 = 200 Pa,
P 82% Ar + 18% CO2 = 200 Pa, τ = 2
Figure 4. Distribution of carbon (С) and nitrogen (N)
in Armco‐iron
1,5
15
1,0
0,5
0,0
0
0 5 10 15
Depth [µm]
a) after carbonitriding at:
t = 550 0 C, P NH3 = 280 Pa, P 82% Ar + 18% CO2 = 120 Pa, τ = 4 h
1,5
1,0
0,5
N
C
N
C
0,0
0
0 5 10 15
Depth [µm]
b) after carbonitriding at:
t = 550 0 C, P NH3 = 360 Pa, P 82% Ar + 18% CO2 = 40 Pa, τ = 2 h
Figure 5. Distribution of carbon (С) and nitrogen (N) in
Armco‐iron
20
15
10
5
15
10
5
10
5
15
10
5
N-Concentration [mass %]
N-Concentration [mass %]
N-Concentration [mass %]
N-Concentration [mass %]
72
2012. Fascicule 2 [April–June]