Doubleriflejack gave you a well thought out reply on the history of hardening steel. I can think of no good reason to not harden your action after you have spent so much time, effort, and money on it. Hardening it will substantially increase both the tensile and yield strength. I would not consider not hardening it. I would advise, however, if you are going to have it engraved do your engraver a favor and let him or her do the engraving before you send it to the furnace! I will make one other caution, as Doublerifejack said there are many alloys so be sure you choose one suitable for your project as all are not created equal.----Bill