Supermartensitic steels are a new class of martensitic stainless steels developed to obtain higher corrosion resistance and better toughness through the reduction of carbon content, and addition of Ni and Mo. They were developed to more critical applications or to improve the performance obtained with conventional grades AISI 410, 420, and 431. In this study, the influences of the tempering parameters on the microstructure, mechanical properties (hardness and toughness), and sensitization of a Ti-alloyed supermartensitc stainless steel were investigated. The material showed temper embrittlement in the 400-600 A degrees C range, as detected by low temperature (-46 A degrees C) impact tests. The degree of sensitization measured by double loop reactivation potentiodynamic tests increased continuously with the increase of tempering temperature above 400 A degrees C. Healing due to Cr diffusion at high tempering temperatures was not observed. Double tempered specimens showed high amounts (> 20%) of reverse austenite but their toughness were similar to specimens single tempered at 625 and 650 A degrees C.