Process for producing a rotor

A process for producing a rotor, the process comprising the steps of:

• casting an ingot to have at least first and second ingot regions axially aligned within the ingot, the first and second ingot regions being formed of different alloys that intermix during casting to define a transition zone between the first and second ingot regions, the transition zone having a composition that differs from and varies between the first and second ingot regions;
• forging the ingot to produce a rotor forging containing first and second forging regions and a transition zone therebetween corresponding to the first and second ingot regions and the transition zone of the ingot such that the first and second forging regions are formed of the different alloys and the transition zone of the rotor forging has a composition that differs from and varies between the first and second forging regions, the first and second forging regions and the transition zone therebetween being axially aligned along a geometric centerline of the rotor forging, the transition zone of the rotor forging being asymmetrical about the geometric centerline of the rotor forging following the forging step;
• identifying an axial line through the rotor forging that is more centrally located with respect to material properties of the rotor forging than the geometric centerline of the rotor forging;
• and then
• machining the rotor forging to produce a machined rotor containing first and second rotor regions and a transition zone therebetween corresponding to the first and second forging regions and the transition zone of the rotor forging such that the first and second rotor regions are formed of the different alloys and the transition zone of the machined rotor has a composition that differs from and varies between the first and second rotor regions, wherein the machining step is performed so that the axial line of the rotor forging defines an axis of rotation of the machined rotor, the machined rotor exhibiting less deflection when heated to an elevated temperature than would the machined rotor if machined so that the geometric centerline thereof defined the axis of rotation of the machined rotor and the machined rotor were heated to the elevated temperature.