Effect of Niobium on Phase Transformations, Mechanical Properties and Corrosion of Supermartensitic Stainless Steel

The influence of niobium addition in a supermartensitic stainless steel with 13Cr-5Ni-2Mo has been studied. The steel with Nb tempered at 600 A degrees C for 2 h showed improved mechanical resistance properties and lower degree of sensitization, without compromising elongation and pitting corrosion resistance, when compared to the reference steel. In order to understand the Nb effect in such steel, mainly regarding phase transformation, different tempering time intervals have been studied. The better performance of the SM2MoNb is attributed to the hindering effect that Nb has in the kinetics of the phase transformations during tempering, delaying the precipitation start and coarsening stages of the present phases.