Aging phenomenon in low molybdenum Fe-21Cr-5Mn-1.5Ni alloy: Microstructure evolution, texture development and corrosion behavior

Abstract

In the present work, the effect of long-term aging at 750°C up to 480 hours on microstructure evolution, texture development and corrosion behavior of a low molybdenum Fe–21Cr-1.5Ni–5Mn alloy has been investigated systematically. An increase in aging time results in increase in proportion of σ-phase. The σ-phase formation took place by the eutectoid decomposition reaction: δ → σ + γ 2 . The σ-phase did not show any specific orientation relationship with neighbouring δ ferrite grains. The initial solution annealed sample showed the presence of strong Brass ({110}<112>), Cube ({100}<001>), Goss ({110}<112>), and minor Cu ({112}<111>) in austenite, and strong γ-fiber (normal direction, ND//<111>) along with minor α-fiber (rolling direction, RD//<110>) in ferrite. After, long-term aging up to 480 hours, austenite showed strong Cu ({112}<111>) and minor Brass ({110}<112>) along with Cube ({100}<001>). Ferrite, on the other hand, showed γ-fiber. The lower amount of Cr/Mo and higher N in Fe-21Cr-1.5Ni-5Mn alloy was not enough to avoid the σ precipitation, however, it delayed its precipitation. The increase in σ-phase with aging time resulted in a decrease in corrosion resistance.