Can you harden stainless steel?
It's always said that austenitic steel cannot be hardened. Only by diffusion processes (e.g. nitriding) a wear-resistant surface can be achieved. But all so far used procedures limit corrosion resistance significantly. So the positive properies of austenitic materials are changed to the loss.
RaDurplus procedure
This procedure allows to haarden stainless, austenistic steel. The surface treatmen is no „martensitic “ hardening as known from unalloed steel but results in a similar effect: enrichment of the peripheral shell with carbon accumulates a 20 to 35 μm coating of high haardness (HV about 1000). Abrasion is decreased remarably, die Fressneigung beseitigt. Above all the corrosion properties persist completely, sometimes even improved.
The obtained combination of properties is important to many industries, particularly in food processing, der process engineering, chemical apparatus construction, medical technology, pharmaceutical and cosmetical industry (certificate about innocuousness of the RaDurplus procedure in food processing is available).
Details:
1. Corrosion properties
The excellent corrosion properties of austenitic steel are not influenced by the RaDurplus processing. Consistancy against pitting and stress corrosion cracking, especially in chloride containing material, is improved considerably.
2. Wear properties
The work experience is confirmed by laboratory measuring (model abrasion). Mainly this applies to adhasive abrasion (metal-metal-contact). Friction forces are much reduced, no more fretting. This is valid when two RaDurplus processed specimen abrade against each other as well as a RaDurplus processed specimen abrading against another steel probe.
In practice an increasement of durybility at a factor > 10 is determined.
Notably clear is the minimising of abrasion at heterodyning with corrosion exposure. Untreated austenitic steel is known to be sensitive to halogen ions.
3. Coat properties
Dependant on material and application a case of 20 to 35 μm can be achieved (case is defined as the edge distance, with an abrasiveness 100 HV over core hardness). The gainable hardness is 700-1100 HV 0,02 dependent on the used material. As it is a diffusion coating it cannot peel off.
The coating is highly even defined, not showing any edge effects such as bulging etc.. Even on awkward geometries the hardening operates quite well. For example: at through borings with a diameter up to 3 mm the entire coating thickness is achieved, at blind holes with the same diameter the coating thickness in 10 mm depth is still about 70% of the surface value. Still to mention is an optical interference of the surface. After the RaDurplus treatment the surface is shimmering slightly yellow. Anyway, this changing of surface has no influence on the corrosion properties at all.
4. Materials
Always every austenitic steel and duplex steel is appropriate to the treatment (look at restrictions in chapter 7). Notably good results are achieved with molybdenum alloyd steel such as 1.4401, 1.4404, 1.4429 and 1.4439.
5. Size alteration, look of surface
The treatment does not effect any size alteration. The surface finish persists, no surface wrinkling and no levelling. The look of the surface widely remains constant, at the most a slightly dark colouration can be monitored.
6. Mechanical properties of basic material
Naturally an influence of RaDurplus processing can only be expected on those mechanical properties, where the peripheral shell plays a decisive role. Accordingly properties such as wie tensile strength, compression strength, elastic limit, notched flexural impact strength etc. are effected only on thin walled material with a high coating thickness over residual section ratio. At this material resistance properties, tensile strength as well as breaking elongation, dependant on the ratio - enhance as expected.
7. Limitations of use
RaDurplus treated components may not be adopted at temperatures over 400°C, not even short-time. It is assumption for a successful treatment that the steel containes as few δ-Ferrite as possible.
8. Applications
The RaDurplus process can be applied successfully when austenitic steel is required due to its corrosion properties but abrasion properties are insufficient.
In many cases zu alternative solutions are used, for example hard-facing or non-ferrous metal. Frequently short durability of the component is accepted with ease of exchangeability.
In such cases RaDurplus offers better and more economical solutions.
Due to the low corrosion affection of RaDurplus treated components it is frequently possible to avoid elaborate gaskets and lubricating systems.
What can we do for you?
We advise on material selection and on design when indicated. We arrange test treatments of unique specimen or small batches reconsider the results with you. We will talk with you about our options and facilities (capacities, size of furnaces) and about the costs.
We would be pleased to receive your requests and orders!
