If you’ve ever wondered how iron ore is turned into steel, look no further.
This handy infographic from Bank of America Merrill Lynch (BAML) has the answer, be it using a blast or electric arc furnace. It even shows you the different type of steel products that are produced using real world examples.
In this instance, we’re going to focus on steel production using a blast furnace, shown in the top left of the infographic, given its main ingredient is iron ore.
And we already know the question you’re asking — what the heck is a blast furnace?
Don’t worry, BAML has that covered, too.
Here’s how it works:
The two main raw material inputs into the blast furnace production process are iron ore and coking coal. Iron ore, coking coal, and limestone are added into the top of the blast furnace while heated air is blown into the bottom of the furnace to drive the combustion process. The combustion of iron ore with other materials in the blast furnace produces molten pig iron, which is then converted to steel. Limestone is added to the blast furnace to capture impurities and create a waste slag.
Think of pig iron as an intermediate product. It’s not iron ore but it’s not steel either.
Once the pig iron ore has been produced it is sent to an basic oxygen furnace, or BOF, to turn it into steel.
Molten iron from a blast furnace is “charged” (poured from a ladle) into the BOF, and a water-cooled lance is lowered into the vessel. As liquid iron and additional scrap steel (~20%) are charged into the basic oxygen furnace, oxygen is blown through the lance at high pressure reacting chemically with carbon to burn off impurities. Oxygen reacts with the high levels of carbon in the pig iron and scrap to form CO and CO2.
Blowing oxygen forces impurities (oxides, silicates, phosphates, etc.) to react with flux to form slag or escape through the top of the furnace as fumes. Flux (limestone) acts as the chemical cleaning agent, absorbing the iron impurities and leaving behind molten steel. The result is separate levels of slag and molten steel, which is now ready to be poured into a ladle for casting. Before casting, a variety of different alloys can be combined with the steel to modify the strength, formability, or durability.
According to BAML, around 1.5 tonnes of iron ore is required to produce one tonne of steel.
In comparison to a blast furnace, an electric arc furnace predominantly uses scrap steel product, rather than iron ore, as the main ingredient.
Electric Arc Furnace (EAF) mills use steel scrap rather than iron ore as the main raw material input, and require a smaller initial investment versus the more capital-intensive blast furnace process. In general, EAF’s tend to produce lower quality steel in terms of finish which are more often used in construction/infrastructure end markets.