Microstructure homogeneity control of GH4706 superalloy turbine disc prepared by integral hot forming

Coarse mixed grains originating from strain-deficient regions during one-step integral hot forming compromise the properties of ultra-large GH4706 superalloy turbine disks. Different from conventional tuning methods centered on temperature and strain rate, this study proposes a homogeneity-oriented control strategy that incorporates an optimized pre-forging step, wherein die geometry is utilized as the primary regulation approach to redistribute the overall strain. This study combines multi-field, multi-scale finite element simulation with Taguchi experimental design and signal-to-noise ratio analysis to realize co-optimization of the overall average grain size (AVG) and its standard deviation (SD). A dual quantification framework integrating analysis of variance (ANOVA) and Sobol sensitivity analysis is adopted, in which the ANOVA contribution rates are validated by first-order Sobol indices calculated via Monte Carlo simulation. The results indicate that pre-forging die geometry is the dominant influencing factor, with a total contribution of 67.0% (concave radius: 36.4%, underfilling height: 21.3%, die angle: 9.3%), followed by strain rate with a contribution of 29.9%. By contrast, deformation temperature only contributes 3.1% within the pre-screened range of 1110 –1140 ℃. Accordingly, it is concluded that the geometric tolerance of pre-forging dies should be strictly controlled, while the deformation temperature window can be appropriately relaxed.