A friend has asked me to sharpen his knife - a double edged dagger, mean looking thing - on the nice bench grinder, but it turns out to really be in need of hardening, since it doesn't keep the edge at all well.
I'm not entirely sure what kind of steel it is - I haven't ground it (to look at the sparks) yet, but I'm wondering if it'd be better to harden and temper it, or to case harden it. I've never case hardened anything in my life, but from the description I read the combination of a very hard outer skin and soft resilient innards sounds great.
But I know nothing about blades, really. I hear that the normal heat hardening process generates long thin crystals which are good for edge-forming. Does that mean that case hardening would be unwise? How about a combination: harden it (to get nice crystals), sharpen it again on a fine stone to get the edge really sharp, then case harden?