Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 28 WEDNESDAY AFTERNOON
JS1-WeA-P.6 DC-PULSED PLASMA NITRIDING (DCPPN) OF STANLESS STEEL:
MICROSTRUCTURE, CORROSION A WEAR BEHAVIOUR. P. Corengia 1 , E. De Las
Heras 2 , M. Brizuela 1 , D. González 1 , A. García-Luis 1 , G. Ybarra 2 , C. Moina 2 . 1 Fundación INASMET-
Tecnalia, Paseo de Mikeletegi 2, 20009 San Sebastián, Spain. 2 Instituto Nacional de Tecnología Industrial,
Av. Gral. Paz 5445, C.C. 157, (B1650 WAB) San Martín, Argentina.
Stainless steels are usually employed as engineering materials due to high corrosion resistance.
However, low wear resistance and poor tribological behaviour limit their use in some industrial applications.
Therefore, there is an increasing interest in improving surface properties through plasma
assisted treatments, notably ion nitriding. Although stainless steels can be nitrided with the consequential
increase in surface hardness, which improves their tribological performance, this is accompanied
by a loss of corrosion resistance of the nitrided case. Nitriding of stainless steels leads to a
depletion of chromium content in the matrix, thus reducing the corrosion resistance of the nitrided
layer.
In the present work, industrial-scale DC-pulsed plasma nitriding for 20 h at 673K was used to improve
the surface properties of both martensitic (AISI 410) and austenitic (AISI 316L) stainless
steels. The effect of nitriding on structural and mechanical properties of the nitrided layer was investigated
by optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and
microhardness.
The tribological behaviour was studied and compared to the behaviour of the same steel in asreceived
condition. The wear resistance was investigated using an Amsler-disc-machine, employing
a dry combined contact of rolling–sliding with three different applied loads. The wear mechanisms
involved during the test of unnitrided and plasma nitrided steels were investigated by microscopic
observation of the surfaces, the corresponding cross-sections and the produced wear debris. In addition
microhardness profiles were done in order to evaluate the work hardening effect during the wear
process. Electrochemical experiments in 3% NaCl solution were carried out to characterize the corrosion
behaviour of unnitrided and nitrided stainless steels.
Analysis and discussion of the tribological results show that plasma nitriding improves the wear resistance
of the surface on stainless steels and the main wear mechanism appears to be delamination.
Consequences on the load bearing capacity are discussed.
The modified layers of the nitrided AISI 316L steel were composed of “expanded austenite”, while
the nitrided AISI 410 samples were characterized by the presence of “expanded ferrite”, CrN and
Fe 4 N.
The DCPPN samples of both AISI 316L and AISI 410 revealed a surface hardness above 1000 HV
and a sharp interface between the case (nitrided layer) and the core (matrix).
Results of electrochemical measurements of unnitrided and DCPPN specimens were analysed and
related to the microstructural characteristics of the nitrided case.
Corresponding author: Tel: +34 943 003700; fax: +34 943 003800, e-mail:
pablo.corengia@inasmet.es
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