Effect of Kolsterising treatment on surface properties of a duplex stainless steel

Abstract

In recent years, attempts of engineering the surface of duplex stainless steels were made in order to enhance
their hardness and tribological properties, without affecting their corrosion resistance. A possibility of
improving these properties is provided by a family of processes developed by Prof. B.H. Kolster in the
Netherlands in the late 1980’s. These processes (usually referred to as Kolsterising® treatments) consist in a low
temperature surface carburizing, which involves the diffusion of large quantities of carbon atoms (up to 6-7
wt.%) into the steel at a diffusion temperature below 450 °C. In the present paper a characterization of the
surface layer of Kolsterised duplex SAF 2205 stainless steel was carried out to study the effects of this treatment
on surface properties. The characterization includes optical metallographic examination, microhardness tests
and SEM-EDS investigation on the Kolsterised steel in the as treated condition and after annealing treatments at
200, 250, 300, 350 and 400°C for 10 hours, to evaluate the stability of Kolsterised layer’s properties with a
moderate increase in temperature. Moreover, complying with ASTM G48-03 Method E Standard, in order to
evaluate the effect of the Kolsterising® treatment on steel pitting resistance, the critical pitting temperature was
obtained for Kolsterised duplex SAF 2205 stainless steel compared with the base metal.