In order to investigate the fracture toughness of 9% nickel steel at low temperature, the specimen’s taken from Q+T pressure vessel plate of ASTM A553 Type I. Compact tension test was conducted on the test piece at subzero temperature -196°C. The fracture toughness value K_Ic is determined by using J-integral method:

K_Ic (at -196°C [-320°F]) = 184 MPa*m^1/2 or 167 ksi*in^1/2.