Precipitation behavior of σ phase in 23Cr-14Ni high-nitrogen austenitic stainless steel

Abstract

Precipitation behavior of σ phase in 23Cr-14Ni high-nitrogen austenitic stainless steel was investigated by empirical formulas, thermodynamic calculations, Gleeble thermo-mechanical simulation, optical microscope, scanning electron microscopy and transmission electron microscopy analysis. Results show that the σ phase in 23Cr-14Ni high nitrogen austenitic stainless steel can be precipitated at 960-1030℃ and dissolved above 1050℃. The σ phase shows unusually rapid precipitation kinetic behavior, which can directly precipitate from austenite grain boundary after solution-treated at 1030℃ for 1 min and precipitate prior to carbonitride. The kinetics and the σ phase precipitation sequence comparing to carbonitride are significantly different from that of traditional austenitic stainless steels. The increase of σ phase equilibrium precipitating temperature due to the high contents of Cr, Mn and Mo elements as well as the segregation of Mo on grain boundary, is the main reason for the acceleration of σ phase precipitation.

Keywords

• 23cr-14ni
• σphase
• rapid precipitation
• precipitation sequence
• austenitic stainless steel