Cast iron is easily hardened. It is loaded with carbon. There are high end shops doing new high pressure guns. Read an article in a machining magazine. Did not sound affordable.
A Japanese 6.5 or 7.7 action should not be case hardened. The material is very close to if not chrome molly. I don't know what kind of material a 99 Savage is, but suspect it is also chrome molly. I never had a receiver bad enough to waste it testing. I got into arguments with people that own 99's that are color cased and told them to ask their "Smith" what kind of material it was. The answer is usually "steel". Anybody that heat treats a material and does not know what it is should leave his hands off the firewrench. It is possible to boost chrome molly to 70 RC by quenching it in water. You would not want to drop it on cement.