To avoid the Japanese, you start off with a higher class of iron than pig iron.
The repeated folding reduces the carbon content which is why Japanese smiths started with “pig iron”. What you end up with is still fairly good steel.
As a practical matter, an underground steelmaker will have to take a piece of rebar and make a steel sword out of it, using very crude tools. A forge and bellows, an anvil, hammer and tongs, safety goggles, heavy gloves and apron. Hardest thing to acquire would be coal.
Home Depot had replica William Wallace (Mel Gibson Braveheart) swords for $49.95, but I’m pretty sure they’re sold out.