I'd always assumed that these types of steel were made from wrought iron by repeatedly heating in a "rich" fire (one with more carbon than oxygen) then folding and hot-hammering thin.

But AFAIK real wrought iron could not have contained impurities of vanadium or chromium because those metals would have been removed by substitution by iron oxides in the flux/slag.

I wonder if perhaps they hot-hammered together layers of wrought iron with crucible steel from eastern sources, which contained the impurities, with enough foldings to reduce the original layer thickness to atomic scales (30-40 folds?).