Kinematic Hardening is better for stent simulation than Isotropic Hardening because the operation of a stent is generally that a balloon expands it against the artery wall, and the the stent experiences a reversal of strain when the balloon deflates and the stretched artery pushes back against the stent.
The Yield Strength for Steel can vary over a wide range. You said the Yield Strength for your stent material was 470 MPa. You should use that. Even better if you have the Stress-Strain curve for your material.
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