A Computational Approach to Examine Effect of Nb/Ti Doping on the Precipitation Behavior of Cast Super Duplex Stainless Steel

Duplex Stainless steel with tailored nanoscale carbides and precipitates in the duplex microstructure, which forms during heat treatment, makes the steel resistant toward wear and erosion, which it encounters in the pipelines used in oil and gas/petroleum industries. Owing to more no of alloying elements, precipitation takes place, and as a result, multiple metastable phases transform into more stable carbides/nitrides. This work illustrates the impact of Nb/Ti on modifying the precipitates in super duplex steel. 25Cr-8Ni-4Mo-Mn-N cast super duplex stainless steel, and its variants with Niobium (Nb) and Titanium (Ti) supplement were solution treated and then aged for favoring the precipitations. The heat treatment temperatures were decided based on thermodynamic calculations. The work researches the complex thermodynamics and kinetics of such precipitations in the steel as well as guides to an optimum alloying strategy to meet the best of desired properties. Nb/Ti additions were found to lower the driving force for nucleation of detrimental phases and thus improves material properties. The results were in good correlation with the experimental results obtained by microscopy and x-ray diffractometry.