Many grades of tool steel. You didnt specify. Might be possible to reheat it and anneal it to soften, then drill, then reheat, and quench. Depending on grade steel, you could quench in oil. After quench you will need to reheat into temper range to avoid brittle condition. There are some online resources the for knife making guys , and thet might help you. If strength is not critical, just anneal to soften, and no follow-on heat treating need.