You'll find the tip will blacken from the flux in the solder itself - wipe it down when finished and melt more solder all over the tip before cooling.
I followed that tip (to tin the tip really well - after - each use) and am getting much better life and heat transfer now! (also be careful with modern steel tips, not to clean them too abrasively, as if you break or crack the coating, the tip will erode very quickly!)