Blue steel?

Geo-TH,In · Nov 7, 2019

I realize steel turns blue when heated in presence of oxygen.

So is a drill bit junk if tip turns blue?

Janicholson · Nov 7, 2019

Yes and No. If it is sharpened (below the blue (keeping it cool to prevent chasing the blue) yes. if you don't know how to sharpen a drill, no. The blue color change is a surface indication of reaching its lower critical temperature, and loss of carbon. Jim

unc · Nov 7, 2019

So is a drill bit junk if tip turns blue?[/quote]

If a bit is very old (say 75 years) or very cheap, it may be made of ordinary high carbon steel. If the cutting edges have turned blue, you are on the edge of reducing it's hardness.
Most bits today are made of high speed steel. This steel contains alloying elements that allow it to keep it's hardness at low red heat. You're probably okay. unc

4wdtom · Nov 8, 2019

Try it and find out. If it dulls then this your chance to learn to sharpen it by grinding it back to past the blue area. Get a drill point gauge and look at how you would hold a good bit at the grinder or belt sander to get the right angle.

BarnyardEngineering · Nov 8, 2019

Blue means the steel has been heated to 540-600F and has lost a significant amount of hardness. Not good for a drill bit. It's now probably softer than the steel you're trying to drill with it.

Andy Martin · Nov 8, 2019

(quoted from post at 16:37:26 11/07/19) I realize steel turns blue when heated in presence of oxygen.

So is a drill bit junk if tip turns blue?

It is not junk if you know how to sharpen it.

Sharpen it first, then head it red with a propane torch to the point a magnet will not stick to it then quickly dunk it in used or new motor oil, swishing it vigorously until it is cool. Don't mind a little flame off the oil. It will go out.

If you don't know how to sharpen it, then it is junk to you because the cutting edge has already been dulled.

I routinely heat treat damaged drill bits although I usually quench in water then reheat to a straw color. Oil works fine with no tempering. After a garage fire I salvaged about 100 drill bits this way.

You can learn how to sharpen drill bits by hand. I have a Drill Doctor but it is faster and easier freehand. Lots of videos on sharpening drill bits on YouTube including mine.

Blue steel?

Geo-TH,In

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Janicholson

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unc

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4wdtom

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BarnyardEngineering

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Andy Martin

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