Larger, more aggressive jet engine and industrial gas turbine designs have increased the demand for large diameter premium superalloy billets for rotating component applications. Forging suppliers are requesting larger diameter billet with structures and properties equivalent to smaller diameter billet. This requires larger diameter ingots since grain size in forging billet is strongly dependent on the amount of work imposed to the starting ingot structure. However, ingot diameter has been limited by segregation tendencies. This paper summarizes the development of larger diameter superalloy ingots for these applications. Much of the work focuses on alloy 718, but advances gained in this alloy system have been applied to alloys 706, 720, and Waspaloy. Extensive process development has been necessary to establish robust practices with defined process windows for each alloy. All steps of the total melt process must be evaluated but special emphasis has been placed on the final melt process where several melt parameters need to be evaluated. Sometimes thermal treatments of electrodes are necessary to prevent melt rate cycles during remelting. Development programs now underway are also presented.

No abstract