The distinction rests on the alloy element thresholds in the chapter notes to Section XV. Wire is classified as alloy steel when it contains alloying elements — such as chromium, nickel, molybdenum, or boron — at or above the specified minimum percentages. Wire that falls below those thresholds is carbon steel wire under heading 7217, even if it contains small amounts of those elements.

Yes. Silico-manganese wire (722920) is primarily a feedstock for spring wire and certain welding wire applications, and it trades in high volumes as a commodity-grade alloy product. Other alloy wire under 722990 tends to be more specification-driven — tool steel, chromium-vanadium, or boron grades — and is often sourced to tighter chemical and mechanical tolerances for automotive or precision fastener use.