The ultralow temperature impact tests for S31608 stainless steel(/%:0.065C

16.50Cr

11.80Ni

2.2Mo) Φ168 mm×13 mm extruded seamless pipe (solid-solution-treated at 1060- 1020 ℃ with grain size 50.2- 17.6 μm)at 20 ℃ and-40--269 ℃ are carried out

and the impact fracture is analyzed by scanning electron microscope. The results show that the S31608 steel has high impact energy i.e.290-360Jat-269-20 ℃

and only the grain size of steel has obvious effect on impact energy at -80℃ and- 120 ℃

the impact energy of steel with grain size 25.3-50.2 μm (solid-solution-treated at 1060- 1040℃)at-80℃ and- 120℃ is330-360J

but that of steel with grain size 17.6 μm(solid-solution-treated at1020℃)at-80℃ and- 120℃ is 320-360J.