Influence of heat treatments on the micro-abrasion wear resistance of a superduplex stainless steel

Duplex and superduplex stainless steels are corrosion resistant materials with increasing applications on chemical, petrochemical, power generation and storage and transport industrial sectors. This work investigates abrasive wear resistance of a superduplex stainless steel UNS S32750 carried in a micro-abrasion test. The microstructure of the steel was changed by heat treatments at 475 °C, 850 °C and 950 °C. These treatments induced a hardening effect on steel due to the precipitation of tertiary phases (α′, χ and σ). Micro-abrasion tests were conducted in a fixed-ball apparatus. Topographical analysis showed that the wear scar reproduced the counter-body shape. The cap diameter was measured using an image acquisition system attached to the equipment, which captures an amplified image of the wear scar. The abrasion was evaluated after 14 min of testing, regarding a well described steady state criterion. Results showed that the abrasion wear resistance increased 50% in comparison to the non-treated material, due to the presence of phase precipitation. The heat treatments leaded to an interesting increase of mechanical strength and wear resistance. Results showed a clear tendency of the decrease of abrasive wear coefficient with the increase of hardness. The effects on toughness and corrosion resistance were also analyzed and discussed. The sample heat treated at 475 °C and 8 h (presence of α′ precipitate) resulted in the same toughness and corrosion resistance of the non-treated sample. Analysis carried out using scanning electron microscopy (SEM), showed different wear mechanisms when comparing precipitation phases and the austenite phase.