Rene 65 is a nickel-based superalloy used in aerospace components such as turbine blades and disks. The microstructure in the as-received condition of the superalloy consists of about 40% volume fraction of gamma prime precipitates, which is so strong that thermomechanical processing is problematic. The aim of this work is to find a heat treatment to reduce hardness for manufacturing purposes without changing grain size in the final application. For the design of the heat treatments, Taguchi’s L8 matrix is used and the factors that are examined include cooling rate, hold temperature, hold time, and cooling method to room temperature.

For over two decades, heat treat modeling has progressed from an academic concept to a mature production tool. This presentation will discuss many barriers that have been mitigated with a wide range of developments. Early limitations included solver speed and robustness, material data, specialized heating and the requirement to include microstructure development models over a series of dissimilar operations and processes. Solver improvements ranging from parallel processing to specialized iteration methods allow models with millions of elements to run on a personal computer. Additional degrees of freedom have greatly improved solution accuracy. Meshing techniques allow users to identify critical regions for a finer mesh, such as the surface of gear teeth that will be carburized. Rotational (and other) symmetry is frequently used to further refine many models. Driven by the demand for modeling data, sources for quality material properties have increased over the years. Additionally, tools to approximate required data based on chemistry are available and maturing. Radiant, convective, electrical resistance and induction heating effects are incorporated into heat treat simulation systems. Integrated simulation systems also include large deformation behavior to capture the effects of forging, coining or other mechanical processes on the microstructure. A vision of the future will include the use of Design of Experiments (DOE) and optimization in heat treat simulation. How companies will model the entire process chain to build a more accurate fatigue model for the part in service will be discussed. In terms of TRL (technology readiness level), heat treat simulation was in the 2 – 3 range in the 1990’s. Today it is in the 7 – 8 range and moving quickly.

Larsen Miller is a formula used to calculate broad equivalent Thermal Effect (TE) stress relieving and tempering recipes. However, results are not precise. The purpose of this work is to determine a more exact procedure. ANOVA design of experiment was used and three supplemental variables were identified as a source of thermal effect variances added to temperature and time: ramp rate, soak time and correlation between Temperature and Soak time. It was then possible to predict the most effective process temperature and soak time necessary to produce the desired stress relief as defined by the angle position of a torsion spring. The results apply to one spring type and one configuration. More work is necessary to expand the methodology to families of parts, i.e. compression springs.