Chapter 72 covers the material: pig iron, ferro-alloys, flat and long products, up to semi-finished forms. There it stops. Anything that is a recognisable article belongs to Chapter 73.
This chapter is governed by its notes more than by its wording. Note 1 defines in law what alloy steel, stainless steel and a flat-rolled product are: these are numeric composition thresholds, and an analysis that crosses one changes the heading, whatever the product is called commercially.
Every number opens on the lines beneath it, down to the eight-digit statistical code.