Appl Phys A (2010) 99: 489–495
DOI 10.1007/s00339-010-5564-9
Effect of annealing temperature on hardness, thickness
and phase structure of carbonitrided 304 stainless steel
F.M. El-Hossary · N.Z. Negm · S.M. Khalil ·
A.M. Abed El-Rahman · M. Raaif · S. Mändl
Received: 21 August 2009 / Accepted: 11 January 2010 / Published online: 24 February 2010
© Springer-Verlag 2010
Abstract Carbonitriding of AISI 304 austenitic stainless
steel was performed at a plasma-processing power of 450 W
using inductively coupled radio frequency (rf) plasma in
a gas mixture of 50% N
2
and 50% C
2
H
2
. The rate of
carbonitriding, microhardness, phase structure of the com-
pound layer, surface microstructure and cross-section mor-
phology were studied before and after the annealing process.
At the annealing temperature up to 800°C, the microhard-
ness values of the compound zones decrease, while the as-
sociated values of the diffused zones increase. Little change
was found in the thickness of the compound and diffused
zones when the carbonitrided samples were annealed up
to 400°C. However, at a higher annealing temperature, the
thicknesses of both zones increase. The γ -Fe austenite is the
main crystalline phase that can be detected by X-ray diffrac-
tion. As the annealing temperature increases up to 500°C,
X-ray spectra show α-Fe and Fe
5
C
2
phases. Nitrogen dif-
fuses more deeply from the near surface to the interior of
the treated sample as the annealing temperature increases up
to 800°C and this might explain the extent of carbonitrided
thickness and the enhanced microhardness of the diffused
zone.
F.M. El-Hossary · N.Z. Negm · S.M. Khalil ·
A.M. Abed El-Rahman · M. Raaif ( )
Physics Department, Faculty of Science, Sohag University,
Sohag, Egypt
e-mail: mraaif@daad-alumni.de
S. Mändl
Leibniz-Institute für Oberflächenmodifizierung, Permoserstr. 15,
04318 Leipzig, Germany
1 Introduction
Austenitic stainless steels are used in the chemical and food-
processing industries. However, their hardness and wear
resistance are relatively low. Many attempts have there-
fore been made to improve the mechanical properties of
austenitic stainless steels [1–6]. A new inductively coupled
(rf) plasma technique for nitriding [7] and carbonitriding
[8] of stainless steel was used which produces a surface
layer of exceptional hardness (1800 HV) in extremely short
processing time (3 min or longer). The effect of using differ-
ent plasma-processing time, plasma-processing power, and
gases on the properties of 304 stainless steel has been stud-
ied elsewhere [9–11]. While usual nitriding and carboni-
triding conditions, of stainless steels, have faced compre-
hensive investigations in the past, very little is still known
about the various influences of post-annealing at different
temperatures. In this study, experiments were carried out to
investigate the effect of different post-annealing tempera-
tures on the carbonitrided 304 stainless steel samples. The
thicknesses of the compound and diffused zones, the phase
stability and the microhardness values variation are studied.
2 Experimental details
The austenitic stainless steel (AISI) 304 samples consisted
of 1 mm thick rolled sheet, cut into pieces with small dimen-
sions of 1.2 × 2.5 cm
2
. The composition of these samples
was as follows in wt%: 0.08 Si, 1 Mn, (8-11) Ni, (12-20)
Cr, balance Fe and the 304 stainless steel microhardness is
210 HV 0.1. The surface roughness of the used samples was
between 100–120 nm. The samples were carbonitrided us-
ing radio frequency (rf) plasma inductively coupled operated
in continuous mode. The carbonitriding process has been