Which drill bit is stronger Carbide or Cobalt?

Answer 1

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carbide is harder but more brittle... especially if it is just carbide tipped.

Carbide is extreamly hard, handles harder metals with higher rpms but can chip if not used correctly (correct load, rpm, diameter step sizes, etc). This is why you can buy carbide tipped cobalt drills.

Cobalt is a good choice too. It is harder than HSS and tool steel.

There are many choices to find the perfect twist drill you need.

look at the selection and descriptions of the choices at mcmaster.com

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Answer 2

Neither is stronger, but each has it's advantages over the other depending on what application it's intended for.
Carbide could be used to drill something that has already gone through heat treat, or it could be used in an nc mill, it will drill a very accurate diameter that often will not need to be reamed afterward. That is to say if wanted to make 50/ 8mm dowel holes you could use an 8mm carbide drill without having to go back to ream. Careful though carbide is very brittle and easy to break, also once a carbide dill is worn out you might as well toss it, because the cost of a re grind is more than the replacement cost.
Cobalt is ideally used in regular drill press operations, and will hold sharpness much longer than say a high speed steel drill bit.