Carbon is an essential part of making steel. To get pure carbon, the process starts by converting coking coal to coke by driving off the impurities leaving behind pure carbon.

The process involves heating coking coal to around 1100⁰C in the absence of oxygen. This eliminates all the volatile compounds resulting in a hard but porous material known as coke.

The oven used to produce the coke is called a coke battery. It features many coke ovens stacked in rows where the coal is loaded. The process of producing the coke takes 12-36 hours. Once ready, the coke is pushed out and quenched with water or air to cool. It is then stored or transferred to the blast furnace to assist in making iron. 

The second stage of making steel begins with making iron. Iron occurs as an oxide in the earth’s crust that can be mined in around 30 countries around the world.

Once the iron ore is mined, it’s fed into a blast furnace along with coke and other minerals like limestones used to collect impurities.

Using nozzles in the lower section of the furnace, air pre-heated to about 1200⁰C is blown into the furnace. As a result, the coke in the furnace burns to produce carbon monoxide, which reacts with the iron ore causing it to melt.

Once all the iron ore is melted, a tap at the bottom of the furnace is opened for the molten iron and impurities to drain off.

The Blast Furnace (Basic Oxygen Furnace) is the most common way of making steel. The iron is melted inside the furnace and combined with varying amounts of steel scrap (usually less than 30%) and some amounts of flux ( to remove impurities).

A lance that blows 99% pure oxygen into the furnace is introduced, causing the temperature to rise to 1700⁰C. The scrap melts, the impurities are oxidized, and the carbon content inside the furnace is reduced by up to 90%.

The other method of making steel is using an electric arc furnace or a mini-mill. This process doesn't involve iron-making. Instead, it re-uses existing steel, which foregoes the need for the processing of raw materials.

In this process, the furnace is charged with steel scrap. For chemical balance, some direct reduced iron or pig iron can also be added.

The oven relies on an electrical charge between two electrodes that provides heat. These raise the temperature to 1600⁰C melting the scrap. Adding fluxes into the oven removes impurities, and the slag is then drained through the tap hole. 

There are other methods used in the making of iron, which include Pulverised Coal Injection (PCI) technology that injects the coal directly into the blast furnace. There's also recycling because steel is 100% recyclable.

After the initial processes, the steel can now start taking different forms depending on the grade of steel and the tasks at hand. The grades of steel are determined by the amount of elements in the metal, which include carbon dioxide.

For structural steel, more carbon is left inside to give the steel more tensile strength. The methods used to control the level of impurities left differ depending on the grade desired. Such methods include:

·         Stirring

·         Raising or lowering the temperature

·         Ladle injection

·         Removing the gases

After the right grade is achieved, the molten steel is cast into cooling molds. The steel is drawn out of the molds after solidifying, but while it's still hot. Guided rollers pull out the steel and cut it to length in different forms, including beams, billets, or slabs. Once the parts cool entirely, they are ready for the next step.

The roughcast items in the previous stage are formed into shapes through hot rolling in this stage. Forging helps to remove defects in the shape, creating the desired quality of steel. This process is used to make seamless tubing and long, flat steel products for various applications.

Secondary forming adds the finish and final shape of the steel. During this step, multiple procedures can be carried out on the steel, depending on the requirements. Some of these secondary techniques include:

·         Coating

·         Riveting

·         Machining

·         Joining

·         Thermal treating

Once the steel is complete, the metal can then be used to make a wide variety of steel alloys that include stainless steel and galvanized steel, all of which are available at thyssenkrupp.