Abstract  
	This work has an aim to study and investigate the relationship between heat treatment conditions on microstructural evolution and mechanical properties in the iron-based alloy, Fe-30.8 Ni -26.6 Cr alloy, strengthened by carbide precipitation. Various aging temperatures (800, 900, 1000 and 1100?C) with various aging times are systematically introduced to the as-received alloy. After aging, it was found that the secondary carbides 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. The amounts of needle-like carbides and secondary carbide films increased with time and temperature of aging. However, by EDS analysis, the composition of secondary carbides was almost the same as that of primary carbides. It can be summarized that the heat treatment conditions have greatly effect on shape, size, dispersion and the location of secondary carbides in microstructure and result in the different mechanical properties such as hardness, yield strength and tensile strength. Aging at 800 and 900?C, the very fine precipitates of secondary carbide particles locate and concentrate in the area close to primary carbide. Aging at 1000 and 1100?C, the coarser secondary carbides disperse to the cores of dendrites. The needle-like and film carbides were found in heat-treated specimens at 900, 1000 and 1100?C. The precipitated secondary carbides precipitated after various heat treatment conditions are chromium carbide, which its chemical composition is similar to primary chromium carbide. It could be concluded that the uniform precipitation and dispersion of fine secondary carbides result in the higher ultimate tensile and yield strengths as well as hardness. However, the obtained result of some mechanical tests did not show any significant effect of aging conditions, especially in ductility and modulus of toughness. The most proper heat treatment condition to maximize tensile strength is aging at 1100?C for 10 hours.