There is metal textures for planks and beams. Download pnb plugin. It’s a really helpful plugin if you didn’t know!
And so far as adding steel planks and beams as items in the game..I doubt Red51 will do this, since you can change the texture to a metal texture...perhaps he will add more textures, including metal ones?
And if he did add metal beams, I am sure they’d be under workbench tier 2