An X-ray polychromatic attenuation correction model that explicitly accounts for scatter is proposed for industrial CT defect inspection of aero-engine turbine blades to address the superimposed scatter and beam hardening in cone-beam CT, which cause reduced image contrast, grayscale distortion, and missed detection of micro-defects. The model is constructed as a cascaded cooperative combination of a scatter term and a hardening attenuation term. In the scatter term, a tilted grating plate is used to scan the turbine blade twice, allowing internal and external scatter fields to be separated. Full-angle scatter distributions are reconstructed using bicubic interpolation and angular spline interpolation to obtain effective projections that approximate scatter-free conditions. In the hardening attenuation term, an exponential hardening curve with projection grayscale as the independent variable is employed, and a weighted beam hardening correction method is developed by deriving a compensation expression based on prior penetration-thickness information and introducing a grayscale trade-off factor. Considering that scatter and hardening are mutually coupled in CT imaging, the results of scatter suppression and beam hardening correction are further unified within a mapping framework between penetration thickness and exposure intensity, yielding a cascaded cooperative correction model that simultaneously suppresses scatter artifacts and cupping artifacts. Experimental results on a 450 kV CBCT system demonstrate that the proposed method increases the signal-to-noise ratio, contrast-to-noise ratio, and average gradient of turbine-blade reconstructions by 42.75%, 75.92%, and 181.25%, respectively, outperforming schemes that apply only scatter correction or only beam hardening correction. For an artificial 0.3 mm film-cooling-hole micro-defect, the depth measurement accuracy reaches 0.28±0.008 mm, and the mean absolute error and mean relative error are reduced by 32.5% and 2.2%, respectively, compared with commercial software, confirming the effectiveness of the method in correcting scatter and beam hardening artifacts in real turbine-blade industrial CT imaging.