The Difference Between Steel and Cast Iron

Casting offers a unique ability to design detailed structures, often eliminating the need for additional assembly or fabrication. Many materials, including various metals and synthetic substances, can be cast, but iron and steel, in particular, possess excellent mechanical properties for a wide range of applications.

Carbon Content: The Main Difference Between Steel and Cast Iron:

Both cast iron and steel are considered ferrous metals, primarily composed of iron atoms. However, the production of these materials is not straightforward, as various alloys are used in the process. To understand them better, it’s essential to distinguish between the iron used in everyday products and the scientific element iron (Fe). Iron, as an element, is usually found in nature in an oxidized form, which is extracted through smelting.

Pure iron is too soft to be practical in most applications. When combined with carbon, it becomes a harder alloy, enhancing its usefulness. In essence, the carbon content is the main distinguishing factor between cast iron and steel. Cast iron typically contains over 2% carbon, whereas steel generally has between 0.1% and 0.5% carbon.

Comparing Steel and Cast Iron:

Below, we compare and examine the characteristics of steel and cast iron.

Casting Ability:

Iron melts at around 1260°C (2300°F), while steel melts at around 1426°C (2600°F). Both materials are cast at even higher temperatures. Those working with molten iron and steel quickly notice significant differences in their fluidity and shrinkage.

Cast iron is easier to cast than steel, as it flows more readily and does not shrink as much as steel. This means it easily fills mold cavities, requiring less molten material. This flowability makes cast iron ideal for structural or decorative ironwork, such as fences and benches.

In contrast, casting steel is more challenging due to its lower fluidity compared to molten cast iron and its greater reactivity with mold materials. Additionally, steel shrinks more upon cooling, meaning more molten material needs to be poured into the mold (usually in an additional reservoir called a riser).

Machinability:

Depending on the final application, cast components may require machining to achieve specific tolerances or finishes. Some materials are more difficult to machine than others. As a general rule, while mechanical properties improve with alloying, machinability tends to decrease.

Cost:

Cast iron is often cheaper than steel. The production of the final product requires less material, energy, and labor. Raw steel, however, is more expensive and requires more time, energy, and care in casting. Nonetheless, when designing cast products, it is worthwhile to consider the long-term usage and replacement costs. Notably, in most cases, parts with higher production costs may have lower costs in the long run.

Steel is available in many pre-fabricated forms, such as sheets, rods, pipes, and beams, and can often be machined or assembled for a specific purpose. Depending on the product and required quantity, manufacturing with readily available steel products may be a cost-effective option.