Basic oxygen steelmaking

We make steel from hot iron.

First, we pour hot iron into a big pot.

We add some old metal bits to the pot. Then, we blow pure oxygen into the hot metal. This oxygen helps change the iron into steel. It also makes the metal very hot. This way is much faster than old ways.

Now we have strong steel to use! Do you like things made of steel?

How do we make steel? We use a way called basic oxygen steelmaking.

It starts with molten pig iron. This is liquid iron from a blast furnace. It has too much carbon in it to be steel.

First, we put the iron into a large container. This container is called a converter. We also add some old metal scrap to the pot. Next, we use a tool called a lance. The lance has small holes at the tip. It blows pure oxygen into the hot metal at a very high speed.

This oxygen does a few important jobs. It reacts with the carbon in the iron. This reaction makes the metal even hotter. The heat can reach 1700 °C. This heat melts the scrap and turns the iron into steel. We also add fluxes like calcium oxide. These help remove impurities. They also protect the inside of the converter. The whole process is very fast. It can take less than 40 minutes. This is much quicker than old ways of making steel.

Steel is one of the most important materials in our world. To make it, we use a method called basic oxygen steelmaking.

This process turns molten pig iron into strong steel. Pig iron is very hot liquid metal from a blast furnace. However, it has too much carbon inside it to be steel.

By using oxygen, we can lower that carbon level. This change turns the iron into the steel we use for buildings and cars. It is a vital part of how modern industry works.

There is a very specific way this thing happens. First, workers fill a large container called a converter. This container is lined with special material to protect it. They add molten pig iron and some metal scrap to the pot.

Next, a tool called a lance is lowered into the vessel. This lance blows 99% pure oxygen at a very high speed. The oxygen reacts with the carbon in the liquid metal. This reaction creates a lot of heat, reaching about 1700 °C. This heat melts the scrap and cleans the metal. We also add fluxes like calcium oxide to help remove impurities. These fluxes form a layer called slag that floats on top.

This way of making steel has an interesting history. A Swiss engineer named Robert Durrer helped invent the process. He worked on it in the late 1940s. In 1948, his experimental converter produced its first steel. Soon after, two Austrian companies named VÖEST and ÖAMG began using it. They created a version called the LD process. This name comes from the Austrian towns of Linz and Donawitz.

This method was much better than the older Bessemer process. It used pure oxygen instead of just blowing air.

Many numbers show how much this changed the world. Before this, making steel took 10 to 12 hours in an open hearth furnace. Now, a modern furnace can finish the job in less than 40 minutes. It is also much easier for workers. Between 1920 and 2000, the labor needed for steel dropped by a factor of 1,000. In the past, it took more than 3 man-hours per metric ton. Today, it takes only 0.003 man-hours. By the year 2000, these furnaces made 60% of the world's steel.

You can see the results of this science everywhere you look. The steel in your bicycle or the beams in a school comes from these hot converters. The process is like a giant, high-speed cleaning machine for metal. It uses the power of oxygen to burn away what we do not want. It leaves behind the strong, low-carbon steel that we rely on every day. Even though the machines are huge, the science is quite simple. We use oxygen to change the chemistry of the metal.

Basic oxygen steelmaking (BOS) is a vital primary steelmaking method. It converts carbon-rich molten pig iron into high-quality steel. This process is essential for modern industry. It allows manufacturers to produce the strong, low-carbon steel used in buildings and vehicles.

The method is often called the oxygen converter process. It is also known as Linz-Donawitz steelmaking. This name refers to the Austrian towns where the technology was refined. The process is termed "basic" because it uses chemical bases called fluxes. These fluxes help remove impurities and protect the vessel's lining.

The mechanism begins with the charging of the converter. First, molten pig iron is poured into a large, refractory-lined container. This liquid metal is often called hot metal.

Sometimes, workers add steel or iron scrap to the vessel to balance the chemistry. The scrap usually makes up about 25% to 30% of the charge. To clean the metal, workers may add fluxes like calcium oxide or dolomite. These substances form a layer called slag. The slag absorbs unwanted impurities during the reaction.

This layer also prevents the molten metal from damaging the vessel's interior.

Once the ingredients are inside, the blowing stage starts. A water-cooled, copper-tipped lance is lowered into the vessel. This lance has three to seven nozzles. It blows 99% pure oxygen at supersonic speeds onto the surface of the metal. This oxygen reacts with the carbon dissolved in the iron. The reaction is exothermic, meaning it generates its own intense heat. This process raises the temperature to approximately 1700 °C. The heat is so high that it melts the added scrap metal. As the carbon burns, it forms carbon monoxide and carbon dioxide gases. This high-speed oxidation lowers the carbon content to the desired level.

The process can be categorized by its different technological stages and variations. The original LD process involved blowing oxygen over the top of the metal. In the 1960s, engineers developed bottom-blown converters. These use inert gas blowing to stir the metal and remove phosphorus. Another variation is the energy optimization furnace (EOF). This version uses a scrap preheater to capture heat from the off-gas. Modern converters are also highly sophisticated and fully automated. They use advanced control systems to manage automatic blowing patterns. Some modern vessels even feature fixed bottoms with plugs for argon purging.

The history of this technology is a story of rapid innovation. Henry Bessemer patented an early oxygen-blowing process in 1856. However, he used air instead of pure oxygen. For nearly a century, commercial oxygen was too expensive for widespread use. During World War II, several engineers proposed new oxygen-blown methods. Swiss engineer Robert Durrer successfully brought the process to mass production. In 1948, his experimental converter produced its first steel. Shortly after, Austrian companies VÖEST and ÖAMG commercialized the process. They developed the refined LD process by June 1949.

This breakthrough caused a global surge in steelmaking research.

The impact of basic oxygen steelmaking is visible in massive industrial figures. The process is incredibly efficient compared to older methods. An open hearth furnace required 10 to 12 hours to make steel. In contrast, a modern BOS converter takes less than 40 minutes. This speed significantly increased labor productivity across the industry. Between 1920 and 2000, labor requirements dropped by a factor of 1,000. It went from over 3 man-hours per metric ton to just 0.003. By the year 2000, these furnaces accounted for 60% of all global steel output. This efficiency helped lower the capital costs of steel plants worldwide.

Understanding this process requires looking at the broader chemical and industrial systems. The availability of liquid oxygen was a major turning point. In 1939, physicist Pyotr Kapitsa perfected the centrifugal turboexpander. This design allowed for the efficient production of liquid oxygen. This technological link made large-scale oxygen steelmaking possible. Today, most industrial gas liquefaction relies on Kapitsa's design. While electric arc furnaces are now used for scrap steel, the BOS process remains a pillar of steel production. It connects the raw chemistry of molten iron to the massive structural needs of modern civilization.