Undoing heat treatment

[Daniel Swanson]

I accidentally hardened a knife before drilling handle holes. This is 3/16” 1080 steel. Hardened in a makeshift charcoal forge and then tempered at 400 for an hour x 2.
I’ve tried drilling holes with almost every available bit... I’ve destroyed through 2 or 3 cobalt bits and 3 concrete bits. I tried using the tip of a spade bit, wrecked that. Tried using the tip of a step bit, destroyed that. I’m using a fairly cheap ~$100 drill press and using oil to cool. I’m about 2/3 of the way through the knife tang but can’t get any further. The only thing I haven’t tried is one of those $25 straight flute bits or a glass/tile bit. But honestly I’m done buying bits just to have them fail.
At this point I’m at a complete loss and I’m ready to just un-harden it if that’s possible somehow, drill the holes, and then re harden. Advice?

 

[Ken H>]

Have you considered annealing the tang?

 

[skillgannon]

I wrap the blade in a wet rag and use a propane torch to give local heat. That should help some. If you are using carbide bits for concrete you need to make sure there is a edge on them and sharpen if needed.

 

[Natlek]

The only thing I haven’t tried is one of those $25 straight flute bits or a glass/tile bit. But honestly I’m done buying bits just to have them fail.

Well , you should try them if you want that hole

https://www.bladeforums.com/threads/sharpening-masonry-drills.1540592/#post-17748361

 

[Daniel Swanson]

I wrap the blade in a wet rag and use a propane torch to give local heat. That should help some. If you are using carbide bits for concrete you need to make sure there is a edge on them and sharpen if needed.

Gotta get it up to annealing temp/cherry red and then cool slowly like in formal annealing process? Or would just heating it and then letting air cool get rid of enough martensite to make it drillable

 

[Michael Black]

As far as I'm concerned, you've got two options in these scenarios: Either anneal the tang (as mentioned above) or cough up a few bucks and buy a full carbide drill. You really only need one and you can save them as your ace up the sleeve for these sort of situations. It will chew through hardened steel like nothing, but they like pretty much as high of speeds of you can get on your drill press, and make sure everything is locked down as tight as it can be. Vibration kills carbide bits pretty quickly.

 

[Natlek]

It will chew through hardened steel like nothing, but they like pretty much as high of speeds of you can get on your drill press, and make sure everything is locked down as tight as it can be. Vibration kills carbide bits pretty quickly.

I have big industrial quality drill press in my service but in home shop I use simple one I make myself to drill hole for pins .Now I start building four wheel 2x42 grinder and for that purpose I borrowed small drill press from friend. On first hole /half inch steel plate / I notice that something is wrong..........I don t like how it drill ............Stand flex on pressure !! No that hole will not be straight because that flex in stand but not drill steel how I used to be when drill on my big drill press . Piece of wood under stand for support make TONS on difference ....NOW that small dril press dril easy ,fast and less heat generated .Then I watch some video on tube ..........on ALL of them stand FLEX ..................

 

[skillgannon]

I just bought some carbide tile bits at home depot today. They went though fully hardened AEB-L without a problem. In fact I will probably use them in the future instead of drilling pre heat treatment. I think they cost around $14 for 4 , from 1/8 to 1/4.