The question of whether steel is heavier than iron is complex because the terms refer to materials with varying compositions. The weight difference between any two materials is determined by their density—the mass contained within a specific volume. Density is a physical property that changes based on the chemical makeup of the material. Therefore, an accurate comparison requires understanding the fundamental difference in their atomic structure and the presence of other elements.
Iron An Element Steel An Alloy
Iron is a naturally occurring metallic element, designated as Fe on the periodic table, and is the base material for all steels and many other ferrous metals. In its pure form, iron is relatively soft and structurally limited for many modern applications. It is the raw material extracted from iron ore through smelting processes.
Steel, by contrast, is not an element but a manufactured alloy. Steel is created primarily by combining iron with a small percentage of carbon, typically less than 2.14% by weight.
Cast iron contains a much higher percentage of carbon, usually between 2% and 4%, which makes it prone to brittleness but easy to cast into complex shapes. The controlled addition of carbon in steel, however, creates a material with superior strength and malleability compared to pure iron.
Comparing Standard Densities
When comparing the density of iron and standard steel, the difference is often marginal. Pure iron has a density of approximately 7.87 grams per cubic centimeter (g/cm³). Standard carbon steel, such as mild steel, has a density that is extremely similar, often cited around 7.85 g/cm³.
This similarity means that for identically sized objects made of pure iron and mild steel, the weight difference would be negligible for most practical purposes. The slight decrease in density for mild steel is due to the small amount of lower-mass carbon atoms displacing some of the denser iron atoms in the crystal structure.
Other common iron alloys show greater variation. Cast iron, which contains a higher carbon content, has a lower density range, often falling between 6.8 and 7.8 g/cm³. The presence of carbon in the form of graphite flakes within cast iron contributes to this lower density. This means that a standard piece of mild steel will actually be slightly denser, and therefore slightly heavier, than an identical piece of common cast iron.
How Alloying Elements Change Steel’s Mass
The density of steel becomes highly variable when specialized alloys are considered, moving beyond simple carbon steel. Modern specialty steels incorporate various elements to achieve specific properties, and these additions directly influence the overall mass and density. The specific alloying elements added, such as nickel, molybdenum, or tungsten, can cause the steel to be significantly heavier or lighter than pure iron. These heavy metals are added to increase hardness and heat resistance.
Specialized steels like stainless steel, which contains a minimum of 10.5% chromium, often have densities slightly higher than mild steel, ranging between 7.7 and 8.0 g/cm³. The addition of high-density metals like tungsten, which has a density of over 19 g/cm³, or molybdenum, can create tool steels that are noticeably heavier than standard iron or carbon steel. Conversely, some alloying elements are lower in density than iron, and their inclusion can reduce the overall mass of the alloy.