An austenitic stainless steel suited for ultra supercritical boilers, which consists
of C: 0.03-0.12%, Si: 0.1-1%, Mn: 0.1-2%, Cr: not less than 20% but less than 28%,
Ni: more than 35% but not more than 50%, W: 4-10%, Ti: 0.01-0.3%, Nb: 0.01-1%,
sol. Al: 0.0005-0.04%, B: 0.0005-0.01%, and the balance Fe and impurities; and
also characterized by the impurities whose contents are restricted to P: not more
than 0.04%, S: not more than 0.010%, Mo: less than 0.5%, N: less than 0.02%, and
O (oxygen): not more than 0.005%. Heat resistant pressurized parts excellent in
thermal fatigue properties and structural stability at high temperatures, which
have a coarse grain whose grain size number is 6 or less, and whose mixed grain
ratio is 10% or less.
