Steel (ugh) cases
The steelies CAN be reloaded. For the life of me I can't see why anyone would bother--requires extra effort on the press, may be bad for yr dies, etc, etc. Also less elastic than brass, therefore poorer at sealing the gun's chamber against gas leakage.
Steel cases were designed to be cheap military ammo, used once and discarded to rust on the battlefield. They were most certainly NOT designed with maximum accuracy, nor reloading, in mind.
Brass cases for all the cartridges which can be had in steel cases, are easily available, and not THAT gosh-dern expensive. (If you can afford to buy guns, drive to the range, shoot, buy supplies, and reload, you certainly can afford brass cases.)
Nickel-plated cases are brass underneath. They reload--and behave when fired--like pure brass cases, except the plating makes the cases a bit brittle, therefore prone to neck-splitting a little more easily. How to tell 'em from steel cases? Nickel-plate cases are shiny. Steel cases are "matte-finished" and dull. And of course there's the magnetic difference.
Steel cases can be recycled like any other steel items. Throw 'em in with the "tin" cans and take 'em to the recycler.
Some people (see above post) do reload steel cases. I suspect it's out of stubbornness. But hey, each to his own, and whatever makes you happy.