Steel, an alloy of iron and carbon, is a manufactured material, not a natural resource. It does not exist in a naturally occurring state on Earth, instead requiring extensive human labor and energy to produce. This distinction is crucial for understanding the environmental and economic context of steel, which is one of the world’s most widely used engineering materials. The process of creating steel from raw components clearly classifies it as a product of manufacturing.
Distinguishing Natural Resources from Manufactured Materials
A natural resource is a material or substance found in the environment that humans utilize with minimal modification, such as crude oil, timber, or iron ore. These resources exist independently of human creation, forming the base of all industrial activity. They can be renewable, like wind and solar energy, or non-renewable, such as mineral deposits.
A manufactured material, conversely, is a product created by combining or treating raw materials through human intervention, energy, and specialized processes. These materials are designed to have specific properties that the original natural resources do not possess. Steel, plastic, and concrete are examples of manufactured materials, as their final form and characteristics are engineered by people.
The Natural Components Required to Make Steel
The production of steel is fundamentally dependent on several natural resources that must be extracted from the earth. The most significant is iron ore, which is a naturally occurring mineral compound rich in iron and oxygen, such as hematite or magnetite. Iron ore makes up about 5% of the Earth’s crust, making it an abundant raw material.
The other main natural input is a carbon source, traditionally metallurgical coal, which is processed into coke. This coke acts as both a fuel and a reducing agent during the initial stage of steelmaking. Additionally, limestone is used as a flux to help remove impurities from the molten iron. Other naturally occurring elements, like manganese, nickel, or chromium, are also mined and later added to create specific steel alloys.
The Manufacturing Process: Why Steel is an Alloy
Steel’s classification as a manufactured material is confirmed by the complex process required to transform its natural components into a functional metal. Steel is defined as an alloy, which is a mixture of metals and non-metals, primarily iron and carbon. The first step involves intense heat, often in a blast furnace, to smelt the iron ore, coke, and limestone. This process reduces the iron oxide into liquid iron, which is known as pig iron, but it contains an excessive carbon content (often around 4%), making it brittle.
The defining step of steelmaking is refining this pig iron by reducing its carbon content and removing impurities like sulfur and phosphorus. This is typically done in a Basic Oxygen Furnace (BOF) or an Electric Arc Furnace (EAF), where pure oxygen is blown through the molten metal to burn off the excess carbon. The final product must have a carbon content of less than 2.1% by weight to be classified as steel. This precise, human-controlled adjustment of chemical composition is what creates the superior strength and ductility of steel.
Steel’s Status in the Recycling Economy
Despite being a manufactured material, steel holds a unique position in the modern economy due to its high recyclability. Steel is considered a permanent material and is 100% recyclable, meaning it can be melted down and reformed into new products of the same quality repeatedly without degradation. This closed-loop capability allows steel to function as a “secondary resource” in the circular economy.
The magnetic properties of steel make it easy and affordable to recover from waste streams, which is why it is the most recycled material globally. Utilizing one ton of recycled steel scrap in an Electric Arc Furnace conserves significant amounts of primary natural resources, including iron ore, coal, and limestone. This practice reduces the demand for newly mined raw materials, establishing steel as a model for resource efficiency and sustainability.