The effect of precipitation on microstructure, mechanic properties and corrosion resistance of two UNS S44660 ferritic stainless steels

This study presents research works on the effects of precipitation on microstructure, mechanical properties and corrosion resistance of 27.4Cr–3.8Mo–2.1Ni and 24.7Cr–3.4Mo–1.9Ni ferritic stainless steels after heat treatment. Results show that fine precipitates such as σ phase and χ phase were observed in the 27.4Cr–3.8Mo–2.1Ni ferrite substrate after 0.5 h aging at 950 °C. The orientation relationship between the precipitate and substrate lattice interface was (6 0 0) σ//(0 0 2) α; [0 2 0] σ//[1 1 0]. The σ phase and χ phase precipitates could be dissolved after 0.5-h solution treatment at 1100 °C. Mechanical properties such as RT ductility and macro hardness were significantly affected by aging temperature. The ductile–brittle transition temperature (DBTT) of 27.4Cr–3.8Mo–2.1Ni impact samples with thickness of 2 mm was approximately −50 °C. The order of the pitting potential (Epit) of the specimens in a 6 wt.% NaCl solution of pH 1.0 at 60 °C was: Inconel625 ≈ 9# > 1# > 6# ≫ Incoloy825.

► Precipitates induced the decrease of ductility and increase of hardness.
► Solution temperature of high Cr FSS specimen was higher than low Cr specimen.
► DBTT was obviously affected by specimen thickness.
► Specimen with no precipitates has high pitting potential.
► Corrosion resistance deterioration could be cured by proper solution treatment.