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Creep resistance of steels in the field of dislocation creep strongly depends on both thermodynamic and dimensional stability of minor phases. Precipitation of many minor phases in heat resistant steels is now very well documented. But it is not true in the case of some interstitial minor phases in nitrogen-bearing steels. For example, a limited amount of information is available about precipitation of a complex nitride (Nb,V)CrN, so called modified Z-phase, in austenitic steels. This paper deals with the studies on precipitation behaviour of the modified Z-phase in an AISI 316LN steel with vanadium and niobium additions. Thermodynamic equilibrium phases for the steel investigated were calculated using the ThermoCalc software. Furthermore, laboratory annealing of specimens was carried out in the temperature interval from 550 to 1250 °C for times 1, 20 and 50 h. Kinetics of precipitation of the modified Z-phase in the austenitic matrix was fast. Precipitation of this minor phase was observed in the temperature range of 750 – 1050 °C. The solvus temperature corresponded well with the results of thermodynamic calculations. The solvus temperature of the modified Z-phase in the steel investigated was determined to be about 250 °C lower than that calculated for NbCrN type of Z-phase in the AISI 316LN + 0.1Nb austenitic steel.
Keywords: Modified Z-phase, AISI 316LN+V+Nb steel, thermodynamic calculation, solvus temperature© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.