M a x is right, the temperature of boiling water is not nearly high enough to affect the temper.

But I'll add one that I learned from an old-timer that's served me well:

DON'T get in the habit of putting a knife down. Cultivate the habit of always returning it to pocket or sheath. It's the knives that are set down, even for a second, that disappear. The knife you never put down never disappears.