 ION NITRIDING
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Ion nitriding on Inox - Hardinox®: how to protect stainless properties
On stainless steels, ion process is carried out almost any time to produce items resisting to corrosion (main reason why these steels are used) and to wear, seizing and abrasion. The plasma process, thanks to the presence of active hydrogen on its surface, reduces completely the green rouge allowing immediately the nitrogen diffusion inside the matrix. Its link with chrome forms chrome nitride, Cr2N, extremely hard and efficient against abrasive wear.
Below we sum up the principal characteristics obtained by inox steels after undergoing ion nitriding process:
Tab. 2 : Summary of principal stainless steels and characteristics of ion nitriding process.
The fields in which those materials may be used range from the food to the drug sectors, from the pumps for beverages to thermoplastic mould, from valves in the oil sector to energy etc. The characteristic of all the steels in table 2 is the high hardness obtained thanks to the availability of great quantities of chrome in the steel. It is necessary to pay a great attention to use blends with low nitriding power to avoid cracks and breaking of the hardened layer as showed in the pictures below:
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Steel
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Depth mm
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Temperature °C of ion nitriding
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Time (hours) of maintenance
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Hardness HV
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AISI 410 430 420
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0.05-0.3 mm
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550
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20-50
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900-1200
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AISI 304 -316
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0.05 - 0.25 mm
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550
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20-50
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900-1200
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DUPLEX
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0.05-0.1 mm
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550
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30
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900-1200
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X22CrMoV 12 1
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0.05-0.4 mm
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530-550
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20h (0.1 mm)
50h (0.25-0.3 mm)
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900-1200
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X8CrNiMoVNb113
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0.1-0.15 mm
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580
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5-6 ore
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900-1200
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Fig. 3.: Micrographies of structures on nitrided steels with ion process. The thickness of the layer and its reaction with the chemical reagent underlines the different resistance to corrosion of the hardened layer (above) as compared to the non processed one (below). |
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Fig.4b: an example of energy sector is showed. Those are rotating components in AISI 316 of hydroelectric turbine in Valtellina. Mixed soil with water is usually found inside them, therefore ion nitriding is required to hard the first tenths of mm. and magnetite after oxidizing to retrieve the resistance to corrosion. |
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Fig.4a: Hadinox® treatment on AISI 304 for the food sector, machine cylinders for ice-creams, where the product flows inside and will be scraped with AISI410 blades with 51 HRC induction. Instead of chromium plating, ion nitriding is required for detachment reasons, incompatible with products like food, because the American Food & Drug Administration banned every type of chrome component from food machines. |
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