I started a sword and board on master, but I don't want to reach the armor cap - but I would like to get close to it.

Will steel plate smithed to legendary reach the cap? Steel? Iron?

What about unimproved dragonplate?

thanks.

All heavy armors and most light armors can reach the damage cap with smithing.

Solution is to either not smith or stop at a reasonable point.

I wonder what would be more challenging - master with smithing steel or steel plate, or expert without improving armor and weapons at all?

Would unimproved dargonplate reach the cap?

I agree ...

Why would you not want to hit the armor cap?

I find the game gets way too easy, even on master.

I limit my current character on master, 500 armor rating with a shield, around 430 without.

For the extra challenge.

Reading these comments has me confused.

I'm currently wearing the same leather set I crafted at level 1, with only two changes since crafting: upgrade to "Superior" and adding enchantments, which don't affect rating.

I can easily see the armor has gained experience as well.

I've applied 90% of my level upgrades to health and, when it's open, add the light armor perk bonus (the next one will be 80%).

I'm at level 30, but I'm finding the game's getting a bit easy now (to be honest, this is more at fault of my 80+ bow with tons of perks, but those dragon lords are a pita).

Is there a limited life span to leather armor I'm not aware of, and if so, what level will this happen?

I was hoping to keep it throughout the game given how cool it looks comparitively.

No.
But there is a armor cap that is set somewhere around 570 (if i recall correctly). So even if your super duper armor adds up to 1000 armor rating, the game only uses 570 of that.
There really is no use pushing your AR beyond 570.

And at a high enough level, you can reach the 570 cap with pretty much any type of armor in the game.

Excellent news.

I can now sell the glass armor I've been finding.

Just look at armor ratings on the wiki and do the math...

If Leather and Fur Armor could hit the Armor Rating cap, I'd use those over my Dragon.

The maths is : maximum damage mitigation is 80%, you always take 20% of damage.
Armour rating shown for a piece is not the whole story, the game adds 25 per piece, 100 for a full set, 75 for no helmet but chest, feet, arms, etc.
Mitigation is (total of displayed armour ratings + 25 per piece) x 0.12.

This can give some surprising results. For example, the Lord Stones bonus of 50 armour sounds like a lot, but only translates to 6% less damage, and even if wearing a full set of rubbish furs, the +25 bonuses give you 12% mitigation on their own.

Cap with four pieces is 567. (567+ 4x25) x 0.12 = 80% armour [well it 80.04, but whatever]
Cap with no helm needs a higher rating, 592 from the three pieces in total.

I'm going to lean towards master if you play very defensively, and expert if you play very offensively; smithing your weapon allows you such an incredible offensive burst that if you're aggressive, it almost doesn't matter what you wear if it's not pajamas on your head.