Effect of cathodic cage size on plasma nitriding of AISI 304 steel
Introduction
The AISI 304 is one of the family of austenitic stainless steels (ASSs), widely employed in food, chemicals, biomedical and nuclear industries [1], due to their inherent superior corrosion resistance. However, their mechanical properties such as wear resistance and surface hardness are not outstanding [2].
Plasma nitriding is a well know technique to improve the surface properties of various metals including ASSs. In this process, nitrogen atoms are introduced into the surface of the steel specimens at elevated temperatures 400–650 °C [3]. The process transforms the phase composition of a thin layer, at the surface of the specimen. The effectiveness of the process depends on parameters such as gas composition [4], pressure [1], current density [5], cathodic cage (CC) configuration [6] and specimen's temperature [7], geometry [8] and composition [9]. In most studies, metastable nitrogen supersaturated austenite phase has been reported if the specimen temperature is kept below 450 °C [10]. When higher temperature up to 600 °C [11], [12] or longer processing time of 12 h [13] are used, the transforms to iron and chromium nitrides . The formation of nitrides results in much higher surface hardness, but the presence of chromium nitrides significantly deteriorates the corrosion resistance of specimens.
In this work, active screen plasma nitriding is employed at a relatively low temperature of 400 °C for the nitriding of AISI 304 steel, as a function of cathodic cage (CC) diameter.
Section snippets
Experimental details
The mirror polished AISI 304 specimens (square geometry with size ) are processed in a 40 kHz pulsed DC active screen plasma nitriding reactor (similar to the setup used by [9], except dimensional difference; 33.5 cm height and 31.5 cm diameter) under fixed processing conditions. Five CC's (made up of 2 mm thick AISI 304 sheet) of varying diameters from 13 cm to 21 cm are used in this experiment. The diameter of a hole in each CC is 8 mm. The height of CC and CC-specimens vertical separation
Results and discussion
Fig. 1 shows the hardness profile and XRD analysis of base and processed specimens. It shows that the surface hardness increases with the decrease in cathodic cage (CC) diameter. For the specimens processed with the smallest CC diameters, A and B, the surface hardness increases even at higher loads. Such improvement in hardness even at higher loads indicates the in-depth penetration of nitrogen in the steel surface. The change in the surface hardness of specimens can also be assessed by
Conclusion
The influence of cathodic cage size on cathodic cage plasma nitriding of AISI 304 stainless steel is investigated. The results showed that when cathodic cage diameter is decreased; the surface hardness increases even at higher loads and corrosion resistance improves more than two orders of magnitude. These beneficial improvements are caused by phase transformation from conventionally reported -phase to iron nitrides without chromium nitrides. The OES showed that the reduction in
Acknowledgment
This work is partially supported by Higher Education Commission of Pakistan Research Project no. 20-2002 (R&D) and the Quaid-i-Azam University Research Fund for Plasma Physics Laboratory.
References (22)
- et al.
A novel rapid DC plasma nitriding at low gas pressure for 304 austenitic stainless steel
Mater. Lett.
(2013) - et al.
Low temperature anodic nitriding of AISI 304 austenitic stainless steel
Mater. Lett.
(2014) - et al.
Plasma nitriding on welded joints of AISI 304 stainless steel
Surf. Coat. Technol.
(2013) - et al.
Cathodic cage plasma nitriding (CCPN) of austenitic stainless steel (AISI 316): influence of the different ratios of the (N2/H2) on the nitrided layers properties
Vacuum
(2012) - et al.
Increasing the surface properties of a vanadium microalloyed steel by current-controlled plasma nitriding
Int. J. Electrochem. Sci.
(2015) - et al.
The effect of plasma nitriding temperature on the electrochemical and semiconducting properties of thin passive films formed on 316L stainless steel implant material in SBF solution
Surf. Coat. Technol.
(2015) - et al.
Effect of component's geometry on the plasma nitriding behavior of AISI 4340 steel
Mater. Des.
(2012) - et al.
Effect of the distance between screen and sample on active screen plasma nitriding properties
Surf. Coat. Technol.
(2010) - et al.
Decreasing chromium precipitation in AISI 304 stainless steel during the plasma-nitriding process
Surf. Coat. Technol.
(2000) Surface modification of AISI 304 austenitic stainless steel by plasma nitriding
Appl. Surf. Sci.
(2003)
On the formation of expanded austenite during plasma nitriding of an AISI 316L austenitic stainless steel
Surf. Coat. Technol.
Cited by (41)
Influence of screen height and bias voltage on the active screen plasma nitriding of shot-peened Ti-6Al-4V titanium alloy
2024, Surface and Coatings TechnologyDynamic equilibrium of the surface oxide film during plasma oxynitrocarburising and its effect on performances
2022, Journal of Materials Research and TechnologyCitation Excerpt :As has been well known, plasma nitriding (PN) technology is an environmental friendly chemical heat treatment [1,2].
Spectroscopy study of composite coating created by a new method of active screen plasma nitriding on pure aluminum
2020, Surface and Coatings TechnologyCitation Excerpt :In the plasma, free iron atoms react with the available active nitrogen to form FeN, which precipitate on the cathode surface. Since FeN is unstable [15,16], it later turns into Fe2-3N and Fe4N. The nitrogen released from this process then diffuses into the substrate [17].
Effect of Cr/CrN <inf>x</inf> transition layer on mechanical properties of CrN coatings deposited on plasma nitrided austenitic stainless steel
2019, Surface and Coatings TechnologyInvestigation of nanomechanical and adhesion behavior for AlN coating and AlN/Fe<inf>2-3</inf>N composite coatings created by Active Screen Plasma Nitriding on Al 1050
2019, Journal of Alloys and CompoundsCitation Excerpt :As can be seen, the main constituting phase of the uncoated specimen is Al-(f.c.c), the main phase of the CPN-coated specimen is AlN-(f.c.c), and the main phases of the ASPN-coated specimen are AlN-(f.c.c) and ε-Fe2-3N. It should be noted that during the ASPN coating procedure, the creation of plasma on the iron screen leads to detachment of iron particles from the screen surface and their combination with nitrogen to form FeN particles, which then deposit on the surface of the specimen under the screen [19,20]. Since FeN is an unstable phase, it releases a portion of its nitrogen and transforms into the stable ε-Fe2-3N [21,22].