What Is Slag

Steel Plant Training Course
Section II: What is Slag? Basic Steelmaking for Electric Arc Furnaces
Page 1 of 25 Introduction: A variety of lime products and blended lime products are used in the production of steel. In the electric arc furnace practice it is common to see high calcium pebble lime, dolomitic pebble lime and iron coated dolomitic pebble lime being charged over the roof in a bucketor through some type of feed system. New technologies are being developed to provide “co-jet” type injection of lime directly into the slag/metal interface for optimization of foamy slag characteristics.

Pebble lime

Iron coated pebble lime

Lime being charged into a scrap bucket before loading scrap into the furnace.

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Steel Plant Training CourseSection II: What is Slag? Basic Steelmaking for Electric Arc Furnaces
Page 2 of 25

Lime injection through sidewalls of Electric Arc Furnace

Lime is critical to steelmaking. The science of how lime products interact with the various components formed during melting and during ladle refining has become the basis for understanding the old phrase “ Make the slag and the steel will make itself.” Steelproduction involves an oxidation process usually in the furnace and a reduction process usually in the ladle that depends on lime to refine impurities from the liquid metal through formation of a liquid slag that reacts with the liquid metal. Remember, oxidation is simply the addition of oxygen into the furnace causing metals and non-metallics to form oxides that are lighter than the liquid steelthat float to the surface of the bath. Some metallic oxides are acid products which can react with the basic refractories of the furnace or ladle unless we make a basic slag using lime and dolomitic lime that will perform this function instead. The oxygen can also react with carbon to create a gas that provides bubbles for foaming the liquid slag and for chemical energy used in melting. Examplesof different methods of getting oxygen into the metal and slag are shown below:

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Steel Plant Training Course
Section II: What is Slag? Basic Steelmaking for Electric Arc Furnaces
Page 3 of 25

Badische Stahlwerks – Kehl, Germany

Oxygen blowing through slag door with pipe style manipulator – Oxidation Process

Gallatin Steel – Ghent, Kentuckky

Oxygenblowing through slag door using supersonic lance – Oxidation Process

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Steel Plant Training Course
Section II: What is Slag? Basic Steelmaking for Electric Arc Furnaces
Page 4 of 25 When you are blowing oxygen into the scrap metal and other metallics that have been charged into the furnace, the oxygen reacts with a portion of the metals to form a new compoundwith oxygen called oxides. These new compounds usually are acid compounds that react with the basic bricks in the furnace or ladles. An example of the oxidation equations can be shown for oxidation: Aluminum 2(Al) Silicon (Si) Iron (Fe) + + + Oxygen 3(O) reacts to give Oxygen 2(O) reacts to give Oxygen (O) reacts to give
(bubbles)

Aluminum oxide (Al2O3)
(acid oxide) (acid oxide)

Silica(SiO2) Iron oxide (FeO)

Carbon (C) + Oxygen (O) reacts to give

CO + (O) reacts

CO2
(energy)

It can be seen that there are differences in some of the properties of metals and then when they combine with oxygen to form new compounds called “oxides”. Metals and their oxides have tremendous differences as can be seen in the Table I below:

Table I.
Metal Iron

Metals versus their OxidesOxide Metal Melting Color Temperature Black Red 2799 oF Black White 1220 oF White 2570 oF Oxide Melting Temperature 2840 oF 2800 oF 3,630 oF 3137 oF 5072 oF 4,658 oF Found in or as

Aluminum Silicon

Symbol Oxide Oxide Name Fe FeO Wustite Fe2O3 Hematite Fe3O4 Magnetite Al Al2O3 Alumina Si SiO2 MgO CaO Silica

rust, iron ore bauxite, bricks sand, ash in coal, dirt gunning material,bricks...