Slag is a byproduct of steel production and is similar in character to volcanic rocks such as basalt and granite. Slag is primarily used in the cement and construction industries, and largely in road construction.
Slags are one of the most natural products of all. They are comparable to fluid magma from the earth’s core. Just like natural rocks, slags contain trace elements, but these are completely bound up within the crystal lattice, and therefore almost impossible to leach out. For instance, a study by the Fraunhofer Institute (german only) showed that wear debris from LD slag used in road construction does not represent a danger to health. In addition, slags have the advantage of a very homogenous structure. That means that their quality and characteristics are consistent within individual charges. As a result of precise analysis and comprehensive process controls in iron and steel production, the detailed composition of every slag is known. And therefore, just as for the entire manufacturing process, slag is permanently subject to process and quality controls.
What are the different types of slag?
Slags are principally divided into blast furnace slag and metallurgical slag. At voestalpine the two types of slag are separately collected, prepared, and processed further into products. As the name suggests, the blast furnace slag is generated in the blast furnace, during the production of liquid pig iron, and is mostly processed further into granulated blast furnace slag which is a valuable additive in the cement industry.
The main type of metallurgical slag is LD slag, the byproduct of the Linz-Donawitz process. It is produced in the LD converter as pig iron is processed into steel.