Future Trends of Low Temperature Surface Hardening of Stainless Steel
Future Trends of Low Temperature Surface Hardening of Stainless Steel
Thursday, April 21, 2016: 8:30 AM
Ballroom C (Hyatt Regency Savannah)
While the excellent corrosion resistance of austenitic stainless steels has resulted in wide commercial application of these materials, poor tribological behavior, especially low abrasive / adhesive wear resistance and a tendency to fretting, has prevented the use of these materials in applications where both corrosion and wear resistance are required. For more than 20 years, low temperature carburizing or nitriding has offered a solution to enhance mechanical properties without altering the corrosion resistance. These thermo-chemical diffusion processes form carbon or nitrogen S-phase while avoiding carbide or nitride precipitation that causes sensitization.
This paper shows current applications and limitations of such processes starting from the automotive, ending up in the medical industry. Beside improved wear, fatigue, galling, fretting and cavitation resistance the use of these processes stands and falls with the corrosion resistance. Due to the fact that the supersaturated microstructure is in para-equilibrium, the precipitation of carbides or nitrides can be promoted by an inadequate surface condition. Also the occurance of non desired phases or non-metallic inclusions in stainless steels influence the corrosion properties after surface hardening even more than for non hardened surfaces.
This is why dedicated alloys for low temperature surface hardening of stainless steels are in focus currently. Compared to nitriding steels the main task is to safely avoid non-desired precipitations in the diffusion zone also for inadequate surface conditions.
Further, major future applications will arise from engineering dedicated for heat treatment. This means, as for classical hardening processes, the engineer takes the properties and characteristics of the surface hardened stainless steel into account when designing a component. Uncomplex slide bearings in corrosive environments have great potential for functional integration. The unique ductility and cavitation resistance also in smallest bores opens new applications for high pressure injection. The wear resistance can be significantly influenced and the corrosion resistance of stainless steel can even be enhanced by using low temperature surface hardening.
This paper shows current applications and limitations of such processes starting from the automotive, ending up in the medical industry. Beside improved wear, fatigue, galling, fretting and cavitation resistance the use of these processes stands and falls with the corrosion resistance. Due to the fact that the supersaturated microstructure is in para-equilibrium, the precipitation of carbides or nitrides can be promoted by an inadequate surface condition. Also the occurance of non desired phases or non-metallic inclusions in stainless steels influence the corrosion properties after surface hardening even more than for non hardened surfaces.
This is why dedicated alloys for low temperature surface hardening of stainless steels are in focus currently. Compared to nitriding steels the main task is to safely avoid non-desired precipitations in the diffusion zone also for inadequate surface conditions.
Further, major future applications will arise from engineering dedicated for heat treatment. This means, as for classical hardening processes, the engineer takes the properties and characteristics of the surface hardened stainless steel into account when designing a component. Uncomplex slide bearings in corrosive environments have great potential for functional integration. The unique ductility and cavitation resistance also in smallest bores opens new applications for high pressure injection. The wear resistance can be significantly influenced and the corrosion resistance of stainless steel can even be enhanced by using low temperature surface hardening.