I'm 100 smithing, with all of the heavy armour perks + arcane blacksmith.. I go to a forge and I can't smith steel plate? But I can smith Daedric? Doesn't sound right...

Am I missing something? Is there a way to unlock the ability to forge steel plate armour??

It's under the Advanced armors perk which is on the light armor side.

Its on the light path for "Advanced Armors" perk. If you want to waste two perks for elven and then that go for it.

It's in advanced armors on the light side of the tree for some reason.

Ahhhhh crap... so is steel plate armour not actually heavy armour then?

yes it has exactly the same defence as orcish armour also to smith it you look under the steel section

i mean yes as in it is heavy armour

It's placement on light armor side of the smithing tree isn't a big deal. After all if you are after that stuff you won't be breaking out in a rash your Skyforge Steel sword is about 8% less damage than a dadric sword. Now if you are a collector then just beat it out of a bandit war chief after level 25.

I am miffed there is no shields in the advanced armors.