Have you ever looked at a steel I-beam on new building construction and thought, "How do they do that?" It might surprise you to learn all of the processes that iron and other metals go through to become steel, and then from steel to this series of I-beams in front of you in what will become a massive structure. Here are the basic processes that go into industrial structural steel fabrication.
Massive crucibles fired to thousands of degrees are filled with so many bars of iron and so many bars of other metals. The whole collection of bars melts into one metal "soup" within the crucible. This is the smelting process, but steel is not really steel just yet at this point.
As you can imagine, you cannot simply dip a large spoon into an industrial crucible of molten metal and stir. Instead, the molten metal is either spun slowly or poured from one pot to the next to get the metals to meld into one. It is a very slow process since no one wants to accidentally spill molten metal on anybody or anything.
Next, the molten metal is poured into molds or injected into hot chambers that will not melt when they touch the molten metal. The molds or chambers are designed to shape the steel as it cools. Pour after pour, this is repeated to get several duplicate steel products.
The products are removed from the injection chambers or molds and moved into the forging process. Here, they are heated and hammered, banged and shaped, shaved and shaped some more. The forge is where all steel products are cured of physical imperfections that could cause problems when the steel products are used in construction or manufacturing.
Annealing is only used if there are areas on a steel product where it is desirable to weaken the steel. For example, some I-beams may have thinner plates through which it is easier to stud weld bolts. Annealing would be used to weaken the steel just enough to make the stud welding possible. Otherwise, annealing would only be used to make weaker steel products.
Tempering is the process of making steel even stronger and more resilient. This is a desirable trait in industrial structural steel fabrication since products like I-beams have to withstand several tons of pressure of finished building on and around the beams. Tempering is often one of the last processes applied before the product is allowed to cool completely and be stacked for shipping.