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Surface hardening of stainless steels

Although impressive surface hardening of stainless steels has been reported in Europe and elsewhere in recent years, using a variety of low temperature carburisation and nitriding technologies, the recognition that the tribological properties of a variety of stainless steels can be significantly improved without serious degradation in other properties has been less widespread in the USA. This symposium was designed to provide a platform for attendees to meet the world’s foremost experts from industry, academia and government, coming together to discuss recent developments in surface hardening processes for stainless steels and the resulting performance and properties. The symposium began with a keynote lecture presented by Dr Hanshan Dong (University of Birmingham, UK), co-authored with Professor Tom Bell, on the surface hardening of stainless steels. Dr Dong gave an overview of the major progress in the surface engineering of stainless steel, with particular focus on S-phase formation, the structure of S-phase, hardening mechanisms and tribochemical properties. He emphasised the importance of these advanced surface hardening technologies by demonstrating applications and highlighted areas of future research. Professor Marcel Somers and T. Christiansen (Technical University of Denmark), presented the science behind low temperature gaseous nitriding/carburising of stainless steel and the development of expanded austenite in their laboratory. Dr Heuer and his colleagues at CWRU, Dr Frank Ernst and Dr G. M. Michael, presented a study on low temperature gas carburising of stainless steels in terms of diffusion kinetics and the thermodynamics of para-equilibrium phenomena. Their work confirms that carburising of austenitic stainless steels at low temperatures leads to a massive increase in surface hardness without carbide formation. This ‘superhardness’ is due to supersaturation by carbon interstitials, leading to residual surface compressive stress which results in a 100-fold improvement in wear resistance and fatigue lifetime. Industrial companies active in this field also demonstrated their surface hardening processes on stainless steels. The commercial processes presented included Bodycote’s Kolsterizing process, Swagelok’s LCTSS process, Nitruvid’s Nivox2, Nivox4 and Nivox LH treatments, and Air Water’s NV Pionite process. A reception and dinner was held at the Crawford Auto-Aviation Museum for the symposium attendees in an unusual environment that was successful in promoting collaboration and informal networking, highlighted by a special banquet speaker, B. Seely of the Michigan Technological University. Just over 100 people from 10 countries attended the symposium and actively participated in two panel discussion sessions. All attendees fully benefited from this symposium and agreed that a similar symposium on the development S-phase technology should be held in the near future.