Database Development for Thermodynamic Simulation of Ta-based Z-Phase Formation in Martensitic Z-Steels

Riedlsperger, F. K. (Speaker), Bernadette Gsellmann (Contributor), Erwin Povoden-Karadeniz (Contributor), Sonderegger, B. (Contributor)

Activity: Talk or presentationPoster presentationScience to science


To raise efficiency of thermal power plants and to reduce CO2 emissions, creep-resistant materials suitable for higher operation temperatures and pressures are needed. One materials group fulfilling the demands of reaching at least 600°C and 300 bar (without being too expensive for the energy sector) are 9-12% martensitic Cr-steels. Z-steels represent a new promising generation of 12% Cr steels which contain Tantalum. High Cr content and Ta addition cause a very fast transformation of carbo-nitride precursor phases MX and M2X into long-term stable and finely distributed Z-phase CrTaN. This CrTaN Z-phase (in contrast to its harmful relative CrVN) provides significant precipitation strengthening during creep conditions.
To simulate thermodynamic equilibrium and precipitation kinetics of Z-steels in MatCalc, further development of an existing CALPHAD steel database was required, incorporating Ta and its interactions with matrix as well as particles. Tests of the database were conducted with 2 sample alloys, proving the successful Ta implementation. Mean size and chemical composition of simulated Z-phases are compared to measurement data from APT and TEM, showing satisfactory agreement.
Period26 Sep 2019
Event titleAdvanced Materials Day 2019
Event typeOther
LocationGraz, Austria


  • Thermodynamics
  • Precipitation Kinetics
  • Modeling
  • Steel
  • Creep