Max Stress is ~38 MPa.
Doing some fatigue calculations, the endurance strength will be 94 MPa, therefore we expect no fatigue failure on this part.
Endurance Strength = (Surface Factor) * (Size Factor) * (Loading Factor) * (Tensile Strength) * (0.5)
4140 Tensile Strength is 655 MPa (https://www.azom.com/article.aspx?ArticleID=6769 )
Surface Finish: Machined => Surface Factor = 4.51 * (Tensile Strength) ^ (-0.265) = 0.8089
Size Factor assumed as minimum value since the loading isn’t standard and the size is nearly 10 inches in diameter.
Size Factor = 0.6
Loading Factor assumed again to be the minimum since there is some bending and torsional due to the loading.
Loading Factor = 0.59
Endurance Strength = 93.775 Mpa