Ernie:
I hate to throw things away if they may be useful in the future. My son borrowed a good set of jobber-length cobalt steel bits and burned a few of them. No idea what he was drilling, but when next I opened the index –long after he had gone back to college, the ends were very colorful — ranging from black to spring steel blue, with straw down an inch or so.
Three questions:
A) Can these bits be re-tempered by an amateur, and if so, if the process the same as you described for tool steel
B) Would a pro sharpening shop be able to rehabilitate them?
C) Is the steel useful for anything else we could make with a small coal forge?
Joe
Replies
The name "cobalt steel" connotes very high grades of High Speed Steel, generally between 14 and 20% tungsten with 5 to 12% tungsten. Being HSS you (or your even your son) can draw the temper in these drills. They can be resharpened to like new condition. Sharpening by eye (with skilled hands) will make them work quite well but a jig is necessary to get them to drill perfectly. Most sharpening service could handle the problem nicely and there are a number of good and inexpensive jigs.
You cannot forge HSS, for its workability in a forge is very poor. What is more you have barely enough temperature to reach critical temperature (2200 degrees F) and could not cool it slowly enough to anneal it.
Resharpen and use some more.
With best regards,
Ernie Conover
Excellent. Thanks very much for the advice.
Joe
Your welcome.Regards,
Ernie Conover
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