Effect of Cooling Rate from Solution Heat Treatment on Waspaloy Microstructure and Properties

Achievement of critical dimensions after wholesale removal of stock from large, ring rolled Waspaloy forgings and fabrications has been complicated by residual stresses induced via rapid quench from the solution heat treat cycle. Part movement during machining can be reduced significantly by substituting air cool for the oil quench commonly specified to achieve high mechanical strengths. However, excessive time in the sub-)/ solvus temperature range during slow cooling results in undesirable precipitate coarsening with an attendant degradation in strengths. Therefore, cooling rates must be achieved which strike a balance between manufacturing ease and Propew controlling microstructural features. This report provides microstructural and mechanical property data for flash welded, shaped Waspaloy bar stock subjected to various cooling rates from a 1018’C/4 hour solution cycle followed by a stabilize and age heat treat. Average cooling rates evaluated in this investigation ranged from 5.5 to 145”C/minute through the f precipitation temperature range of 982 through 760°C. Oil quench data from production hardware are also provided for reference. A significant improvement iu 538 and 760°C yield strengths, 760°C tensile strengths, and 704°C creep resistance were significantly improved by increasing cooling rates. Ductility simultaneously decreased at 760°C but did not exhibit dependence at 538’C. Minimum cooling rates of approximately 4OYYminute were necessary to approach the properties and microstructural features typical of oil-quenhed Waspaloy.