Etude par Sonde Atomique Tomographique de la formation de nano ...

tel-00751814, version 1 - 14 Nov 2012
Chapter 2. Materials, experimental and simulation techniques
Like ODS steel, the MA NDS was studied by both SANS [8] and TEM [11]. Since the
elaboration way to produce NDS steel have never been performed before, a patent was created
by M. Ratti and Y. de Carlan [12].
I.4. Nitrided NDS
One of the advantages of NDS compared to ODS is the possibility to avoid complex step
of mechanical alloying when nitrogen is introduced by simple nitriding process. In this work,
a pre-alloyed Fe-18Cr-1W-0.75Ti powder is plasma nitrided by Bodycote-Nitruvid Company.
The aim of the treatment is to introduce nitrogen in a quantity sufficient to reach the core
of biggest particles. The level of nitrogen is a function of the temperature and duration of the
treatment as well as the chemical activity of nitrogen and hydrogen mixture. The desirable
level of nitrogen ranges between 1000 and 2000 ppm in weight.
Nitriding of 1.4 kg of powder has been performed in rotating drum, shown in Figure 2.1
(a). In order to mix the powder during nitriding, impellers have been implemented in the
drum, Figure 2.1 (b).
(a)
Figure 2.1. Rotary drum (inclined at 45°) where nitriding treatment is conducted [13,14] (a)
full view, (b) impellers with powder.
The nitriding conditions that were used by Bodycote-Nitruvid Company are:
o Atmosphere of N2 (30%)/H2 (70%);
o Nitriding time: 15 hours;
o Temperature: 400°C;
(b)
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