You need to know that there is an important difference between standard high speed steel drill bits, cobalt drill bits and titanium nitride coated drill bits.
High Speed Steel is a kind of steel that has a high "red" hardness, meaning that it retains it's hardness better than other steels when it's red hot. That property allowed for faster machining because the tool wouldn't dull as quickly when it got hot, and so this kind of steel is called "high speed" steel. Typically, a high speed steel drill bit will have a Rockwell C hardess in the mid-50's to low 60's.
Cobalt steel drill bits are made from a harder kind of steel. Consequently, cobalt bits will last longer than HSS drill bits. And, when a cobalt bit dulls, you can have it sharpened and you essentially have a new cobalt bit. Cobalt drill bits have a Rockwell C hardness from the mid-to-high 60's.
The "gold" titanium nitride coated drill bits are high speed steel drill bits coated with a VERY hard titanium nitride coating. The titanium nitride coating on a titanium bit has a Rockwell C hardness of about 82, and so it keeps it's sharp edge longer than any other drill bit. However, once the sharp edge on that titanium coating is worn down, then sharpening the bit will grind off the super hard coating, and you're left with an ordinary HSS drill bit. Titanium nitride has a low coefficient of friction, so the coating actually helps the bit clear cuttings as well.
So, I think what happened is that you simply dulled the titanium bit or wore off the coating completely, and the bolt is probably harder than the high speed steel bit, so you're not making much progress. It's going to cost you more than the price of one drill bit to drill a hole in this bolt. I'd either buy some more titanium bits and just go through them on this bolt until you get a deep hole, or buy a cobalt bit and keep having it sharpened. There's no steel in the world that's got a Rockwell C hardness of 80, so titanium bits will eventually put a hole in it. You might want to try one cobalt bit just to sell how long it lasts.
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