Influence of high temperature aging on microstructure and properties of 2507 super-duplex stainless steel

Aging treatment of 2507 super-duplex stainless steel(SDSS) was performed at 920 ℃ for various holding time.Microstructure evolution and properties of the steel were examined by means of OM,SEM,XRD,EDS analysis,hardness measurement and impact test.The results show that when aging at 920 ℃ a large amount of σ phase precipitate at γ /α or α /α interfaces and grow into the adjacent ferrite grains,and its formation mechanism is a eutectoid reaction of α→γ2 + σ.The amount of σ phase increases with increasing aging time.The high precipitation rate in 2507 SDSS aged within 5 min is observed,and the σ phase increment tends to slow down with further increasing aging time.The σ phase formed in the steel decreases severely impact toughness and causes an obvious increase of hardness.Impact energy and hardness values of the steel are correlated with its σ phase fraction.When aged at 920 ℃ for 30 min,the amount of σ phase reaches about 28%,and the corresponding impact energy and hardness values of the steel are 6 J and 376 HB,respectively.