Effect of Annealing at High Temperatures on Microstructural Formation of 15Cr-25Ni Austenitic Stainless Steel Cast

Microstructure of 15Cr-25Ni Austenite stainless steel (ASS) cast formed at various high temperatures has been investigated in this study. The steel was synthesized from scrap materials containing Cr and Ni elements, respectively, about 15 and 25 wt.%. This steel designed to have high corrosion resistance or high-temperature oxidation is a steel candidate for evaporator materials in a waste incinerator, and their operating temperature is used for annealing temperatures in this study. The variation of annealing temperatures was carried out at temperatures of 400, 600, 800, 950, and 1078°C for a time of 30 minutes. The ASS as-cast and annealed have a similar microstructure dominated by the dendritic structure of γ-FeNi austenite with the crystal structure of the face-centered cubic interdendritic region of a eutectic structure containing free particle zone and (Fe, Cr) 7 C 3 island compounds. The short dendritic arm spacings for ASS after annealing at temperatures of 400, 600, and 800°C were measured to have about 61.71, 62.11, and 57.85 mm, respectively.  By contrast, the longer dendritic arm spacings were obtained after annealing at temperatures of 950 and 1078°C about 70.29 and 197.04 μm, respectively.  In addition to higher micro-strains, the short dendritic arm spacings formed after annealing at 400-800° C lead in a relatively higher hardness profile, whereas the longer dendritic arm spacings obtained after annealing at 950 and 1078°C result in a low hardness profile in the ASS.