Using modified Cr-Mo-V steel with small additions of nickel and niobium and reduced silicon, four integral high pressure (HP) and low pressure (LP) combination turbine rotor forgings with 1240-mm maximum barrel diameter were manufactured. To obtain improved toughness in the LP portion and sufficient creep strength in the HP portion, the rotor forgings were differentially heat-treated; HP portions were austenitized at high temperatures and LP portions at low temperatures, followed by forced air cooling in the HP portions and by water spray quenching in the LP portions. Evaluation of the manufactured rotor forgings revealed that the toughness and the creep strength were sufficient in the LP and HP portions, respectively, the residual stress was sufficiently low, and the heat indication testing results were satisfactory in spite of the differential heat treatment.