Abstract 
  	The aim of this work is to study and investigate the effect of the heat treatment conditions on the microstructure evolution in the iron base alloy strengthened by carbide precipitation. The Fe - 30.8Ni - 26.6Cr alloy, produced in the form of centrifugally cast tubes, was studied by means of scanning electron microscopy (SEM) after various heat treatment conditions. A complete description of the carbide phase precipitation present in the as cast and aged condition was made as a function of time and temperature. After heat treatment, it was found that the secondary carbide precipitated early near the primary carbides, which are chromium and niobium / titanium carbide networks. The secondary carbide precipitations were also found in the dendrite cores. From the time-temperature-precipitation (TTP) diagram, it showed that the slowest precipitation rate was at 800oC and the fastest precipitation rate was at temperature of 1000oC. The maximum amount of secondary carbide was 0.7 vol. %. The kinetic study after Johnson - Mehl - Avrami equation showed that the secondary carbide precipitated by the two-step reactions. The first step was volume diffusion, which controlled growth of secondary carbide precipitation with the activation energy of 213.2 kJ/mole. In addition, the secondary reaction was grain boundary diffusion controlling the growth of precipitation with the activation energy of 51.7 kJ/mole.  The obtained TTP diagram was established for the aging application and welding of this alloy. It can be summarized also that the heat treatment conditions have a great effect on shape, size, dispersion and the location of the secondary carbides in the microstructures and could result in the different mechanical properties.