Are Irwin cobalt alloy steel drill bits coated like the titanium ones? If the cobalt bits are rockwell hardness 66 - 67 HRc, what hardness are the titanium bits? Once you sharpen a cobalt bit and the gold coating is gone, is it just a regular bit?

Cobalt bits are not coated, they are cobalt alloy steel through and through. At the end of manufacture, a cobalt bit is baked in an oven to turn the surface color of the steel a dull gold color. This is done primarily for easy identification by color. If the gold wears off or is ground off in sharpening on a cobalt bit, it is still solid cobalt steel. Our cobalt alloy steel drill bits are made of M35 cobalt steel which has a 5 percent cobalt alloy steel content. The Rockwell is approximately 65.5 to 67 Rockwell C. Irwin Titanium Nitride Coated drill bits have a hardness of approximately 64.5 to 65.5 Rockwell C. The Titanium Nitride Coated is much harder at approximately 82 Rockwell C. If you sharpen a cobalt alloy steel bit it is still as good as a new bit, assuming it was sharpened correctly. If you sharpen a titanium Nitride Coated bit its performance will drop because the coating is gone on the tip; however, you still have the benefit of the titanium Nitride Coated in the flute of the bit and on the sides of the bit. It will still perform better than a standard bit.