Heavy melting steel (HMS) or heavy melting scrap, is a designation for recyclable steel and wrought iron. It is broken up into two major categories: HMS 1 and HMS 2. The difference between the two is HMS 1 does not contain galvanized and blackened steel, whereas HMS 2 does.
Both HMS 1 & 2 comprise obsolete scrap only. That is iron and steel recovered from items demolished or dismantled at the end of their life. This density, sizing and preparation makes for efficient furnace operation by minimizing the time to charge enough scrap for a full melt. In contrast, thin mixed scrap greatly increases charging time, cutting furnace productivity. HMS is usually traded as a blend of 1 & 2, (80:20).