I would like a more realistic approach, whereby tools get blunted and then have to be sharpened. The lower down the tier the metal, the quicker it blunts, and the longer it takes to do work with it, until eventually it acts like a tier lower and wont work materials its meant to be able to.
Sharpening is a process that takes time and involves making a whetstone (and possibly a grinding device further on in the game.) *however* sharpening could also reduce the life of the tool, eventually leading it to break.