I am interested in establishing fatigue endurance levels for a 3mm thick hardened and tempered alloy 75Cr1 spring steel with a hardness reading of HRC 48 - 50.
As an estimate, you can start with UTS/2 for the fatigue strength at 106 cycles. For 48 HRC, the UTS is ~ 1575, so maximum allowable stress under fatigue loading would be ~ 780 MPa. In order to further refine this estimate, you need to understand the loading conditions (tension-tension? one-way or reversed bending? tension-compression?), the geometry (notches, holes, etc.), surface (roughness, residual stresses, defects), and microstructure (inclusions, decarburization, grain boundary embrittlement, etc.).
The actual part is 3 x 110 x 525mm which will be water jet cut from cold rolled bright feed sheet and then shot penned on the cut edges. It is held rigid on one short end by two bolts and the action is one way. The amount of flex is at the tip is about 100mm. It's purpose is to hold a hardened and tempered tool steel blade against graphite anodes to remove a thin layer prior to reuse.
