Effect of Annealing Process on Microstructure of 29Cr-4Mo Super Ferritic Stainless Steel

Abstract:

The effect of different annealing processes on microstructure of 29Cr-4Mo super ferritic stainless steel seamless tube after cold rolling was investigated. The results show that the main inclusions in 29Cr-4Mo super ferritic stainless steel are Cr2O3·MnO·Al2O3. After annealing at 900 ℃for 30 min, the grain boundaries especially on triple junctions and near the inclusions firstly formed a small amount of σ phase. The average area fraction of σ phase increases with time prolonging while decrease with the temperature raising. There is no σ phase precipitating after holding for 50 min at 1000 ℃ and not founding χ phase during 900 ℃ to 1050 ℃. The empirical formula of ferrite recrystallization grain growth under classical Sellars model is established. The formula can accurately predict the average grain size in the whole annealing process by comparing the calculated value and the experimental value.