RESIDUAL STRESS MEASURING METHOD

The present invention is a method for measuring a residual stress in a cast and forged steel product, the method using X-rays, including: irradiating a cast and forged steel product with X-rays; two-dimensionally detecting intensities of diffracted X-rays originating from the X-rays; and calculating a residual stress based on a diffraction ring formed by an intensity distribution of the diffracted X-rays detected in the detecting, wherein, when the residual stress is measured for each of a plurality of measurement positions of the cast and forged steel product, the residual stress for each of the measurement positions is calculated in the calculating based on the diffraction ring for each of the measurement positions and an X-ray elastic constant which varies for each of the measurement positions.