Process for the production of longitudinally-directed coarse-grained columnar crystals in a workpiece consisting of an oxide-dispersion-hardened nickel-based superalloy

A process for the production of longitudinally oriented coarse-grained columnar crystals in a workpiece consisting of an oxide-dispersion-hardened nickel-based superalloy having a Cr content of 15.5 to 25% by weight of Cr, wherein the workpiece is subjected to the following heat treatment:

• providing the workpiece in a warm-worked fine-grained condition;
• heating the workpiece at a heating rate to a preheating temperature T.sub.pre, which is at least 5.degree. C. below the minimum recrystallization temperature necessary for the material, T.sub.rec min, and is at least at the minimum solution annealing temperature for carbides in the .gamma.-matrix;
• maintaining the workpiece at the preheating temperature T.sub.pre for the purpose of isothermal annealing for at least 5 min;
• immediately heating the workpiece at a heating rate of between 10.degree. C./min and 40.degree. C./min to the recrystallization temperature T.sub.rec without prior cooling;
• and
• cooling the workpiece to room temperature at a cooling rate of between 5.degree. C./min and 200.degree. C./min.