Abstract: In a Ni-base alloy, an area-equivalent diameter D is calculated. D is defined by D=A1/2 from an area A of a largest nitride in a field of view when an observation area S0 is observed. This process is repeated in n fields of view for measurement, where n is the number of the fields of view for measurement, so as to acquire n pieces of data on D, and the pieces are arranged in ascending order D1, D2, . . . , Dn to obtain a reduced variate yj. The obtained values are plotted on X-Y axis coordinates, where an X axis corresponds to D and a Y axis corresponds to yj. In a regression line yj=a×D+b, yj is obtained when a target cross-sectional area S is set to 100 mm2. When the obtained yj is substituted into the regression line, the estimated nitride maximum size is ?25 ?m in diameter.

Abstract: A Ni-based alloy having excellent hot forgeability and corrosion resistance includes, by mass %, Cr: more than 18% to less than 21%, Mo: more than 18% to less than 21%, Ta: 1.1% to 2.5%, Mg: 0.001% to 0.05%, N: 0.001% to 0.04%, Mn: 0.001% to 0.5%, Si: 0.001% to 0.05%, Fe: 0.01% to 1%, Co: 0.01% or more and less than 1%, Al: 0.01% to 0.5%, Ti: 0.01% or more and less than 0.1%, V: 0.005% or more and less than 0.1%, Nb: 0.001% or more and less than 0.1%, B: 0.0001% to 0.01%, Zr: 0.001% to 0.05%, and a balance consisting of Ni and unavoidable impurities.

Abstract: In a Ni-base alloy, an area-equivalent diameter D is calculated. D is defined by D=A1/2 from an area A of a largest nitride in a field of view when an observation area S0 is observed. This process is repeated in n fields of view for measurement, where n is the number of the fields of view for measurement, so as to acquire n pieces of data on D, and the pieces are arranged in ascending order D1, D2, . . . , Dn to obtain a reduced variate yj. The obtained values are plotted on X-Y axis coordinates, where an X axis corresponds to D and a Y axis corresponds to yj. In a regression line yj=a×D+b, yj is obtained when a target cross-sectional area S is set to 100 mm2. When the obtained yj is substituted into the regression line, the estimated nitride maximum size is ?25 ?m in diameter.