Subheading 720310 covers ferrous products obtained directly by reducing iron ore — including DRI and HBI in various forms — regardless of purity level. Subheading 720390 captures other spongy ferrous products that meet the 99.94% or higher iron purity threshold but were not produced by the direct-reduction-of-ore route. In practice, most commercially traded DRI and HBI falls under 720310.

DRI and HBI have very low residual levels of copper, tin, and other tramp elements that accumulate in recycled scrap. EAF mills producing flat-rolled or high-grade long products use DRI/HBI to dilute residuals and meet tight chemistry specifications that scrap alone cannot reliably achieve.