Evolution of intermetallics in a 26Cr–4Mo–2Ni (Ti + Nb) super ferritic stainless steel aged at 800°C

Abstract

The precipitation of intermetallics in a 26Cr-4Mo-2Ni (Ti + Nb) super ferritic stainless steel during aging at 800°C was investigated. Optical, scanning electron and transmission electron microscopes and X-ray diffractometer were used to characterize the microstructure. Results show that the χ phase formed in 5 min and almost disappeared within 24 h. The σ phase began to form at grain boundaries when aged for 30 min and its amount increased with prolonged aging. After 24 h, the σ phase covered the grain boundaries and grew into the grain interiors. The Laves phase was found to form within 30 min.

Cooling effects on microstructure and mechanical properties of 27Cr–4Mo–2Ni ferritic stainless steel

“…After the solution treatment, the SFSS coils are quickly cooled to room temperature. However, three kinds of precipitates: the sigma (σ ), chi (χ ), and Laves (η) phases are frequently observed in these steels over the preheating temperature range of 600-1100°C [7][8][9][10][11][12][13][14]. The sigma phase shows the tetragonal structure (P42/mmc space group) with lattice parameters a = 0.88-0.92, c = 0.45-0.48, and C = 0.52 nm.…”