I encourage you to please refer the Knowledge article I shared in my last post as that will help you around with most of the elemental problem you may encounter while setting up a plasticity model.
Unlike structural steel, cast iron is not known to undergo plastic deformation. Hence, the default cast iron material in AIM library does not have Bilinear Isotropic Hardening definition added to it. However, if for some reason you want to incorporate it, you can manually add the same and provide required material inputs.
Attached below is the properties of default structural steel and "Bilinear Isotropic Hardening" can be seen here, but if we go to cast iron, this property is not available by default:
Thanks & Regards,