Yup, use mild steel..  Save that for other projects..   I will be putting out a  "How to" video on figuring out mystery metal and how to use it but it's not going to be ready till mid summer..  Ideally you need to figure out what metal it is before you use it..   without testing it myself and not knowing what temp you forged/bent it at from your description, I'd guess it's an air hardening steel..   Looks like a spring from an old hay rake..