Crystal structure, transformation and thermal stability of nanostructured 316LSS alloyed with 2 and 6 wt.% aluminum

Phase transformation, crystal structure and thermal stability of 316LSS, 316LSS-2 wt.% Al and 316LSS-6 wt.% Al were studied during cryomilling and annealing at various temperatures. Cryomilling of the three alloys resulted in complete phase transformation from FCC to BCC and the evolution of a nanocrystalline grain structure. Aluminum was found to enhance the thermal recovery of FCC from the BCC phase induced during milling. Complete recovery of the FCC was achieved between 565 and 594 °C for 316LSS-6 wt.% Al and in the range of 605–618 °C for 316LSS-2 wt.% Al depending on the heating rate. However, heat treatment of 316LSS at temperatures up to 1000 °C yielded incomplete reversion of the induced BCC phase. Annealing the alloys at different temperatures and studying the accompanied grain growth indicated that FCC phase recovery and grain growth are independent phenomena. The activation energy of phase recovery and grain growth for 316LSS-6 wt.% Al was calculated.