LOW-TEMPERATURE STAINLESS STEEL & TITANIUM SURFACE HARDENING

Anti-wear, anti-galling and scratch resistance are well known properties associated with low-temperature interstitial hardening processes, however corrosion resistance is not always unaffected, although claimed so. A somewhat underestimated negative influence on corrosion performance is the presence of delta ferrite and deformation martensite in the outmost surface, resulting from machining a component. Both ‘defects‘ act as nucleation sites for unwanted Cr-nitrides and/or Cr-carbides during low-temperature surface hardening. Therefore, despite lowering process temperatures, Cr depletion occurs and compromises the stainless properties. A series of advanced processes for low temperature surface hardening of stainless steel and Titanium have been developed by Expanite. The gaseous processes allow precise control for accurate tailoring of materials’ properties including corrosion resistance. This is illustrated in the present contribution, in which an overview of some of the fundamental scientific aspects of low temperature thermochemical treatment of stainless steel and a unique insight into the applicability and the industrialization of these processes are given. It’s furthermore shown, how some major challenges like surface activation and mitigation of surface defects are overcome. Finally, selected technological examples of thermochemical treatment of stainless steel and Titanium are presented.