Final answer:
To estimate the fatigue strength corresponding to a life of 150 kcycles of stress reversal, we need the SN curve of the material, which is not provided in the question.
Step-by-step explanation:
To estimate the fatigue strength of the steel rotating-beam test specimen corresponding to a life of 150 kcycles of stress reversal, we can use the SN curve of the material. The SN curve relates the stress level (S) to the number of cycles to failure (N). Unfortunately, the question doesn't provide the SN curve for the steel material in question, so we cannot provide an accurate estimate.