Closed I cannot get to the next stage of iron armour.

For some reason, I cannot unlock the grade 2 iron armour. Anyone know why?

 

I don't quiet understand what you mean, but if you mean the tier 2 armor, that would be the Steel armor.
Go to the Outpost with a wooden crafting table in your inventory. You'll get a quest that will essentially give you an iron crafting table in exchange. With that iron crafting table, you will be able to craft an iron furnace from iron bars. Do it. Now, with the iron furnace, you can make steel bars from 1 iron bar and 1 copper bar. Get a couple of them and craft in the iron crafting table a metalwork station. In the metalwork station you'll be able to craft the steel armour of steel bars.
Good luck.

 

Don't worry, I did not understand the armour system when I made that post. Thank you, though.