The Difference Between Steel and Cast Iron

Table of Contents

• Introduction
• Carbon Content: The Main Difference Between Steel and Cast Iron
• Comparison of Steel and Cast Iron
  • Castability
  • Machinability
  • Cost

Introduction

Casting offers a unique ability to design intricate details, often eliminating the need for additional construction and assembly. Many materials, including various metals and synthetic substances, can be cast. However, iron and steel have particularly excellent mechanical properties for a wide range of applications.

Although steel and cast iron may look similar on the surface, each has distinct advantages and disadvantages, from production to application. Understanding these benefits and limitations allows for selecting the appropriate material based on the desired function.

Carbon Content: The Main Difference Between Steel and Cast Iron

Both cast iron and steel are ferrous metals primarily made of iron atoms. However, the production process is more complex. Various alloys are used in production. For better understanding, it’s important to differentiate between the iron used in everyday products and the chemical element iron (Fe). Elemental iron is typically found in nature as an oxide, which is extracted through a smelting process.

Pure iron is too soft to be practical for most applications. When combined with carbon, it becomes a harder alloy, enhancing its usefulness. The main distinction between cast iron and steel is the amount of carbon. Cast iron usually contains more than 2% carbon, while steel typically contains between 0.1% and 0.5%.

Comparison of Steel and Cast Iron

The following compares the characteristics of steel and cast iron.

Castability

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

Cast iron is easier to cast than steel because it flows well and shrinks less. This means it fills empty spaces in molds more easily, requiring less molten material. This fluidity makes cast iron ideal for structural or decorative ironworks, such as fences and benches.

In contrast, casting steel is more challenging because it is less fluid than molten cast iron and more reactive with mold materials. It also shrinks more when it cools, requiring more molten material in the mold (usually in an additional container called a riser).

Machinability

Depending on the final application, cast parts may need machining to achieve specific tolerances or desired finishes. Some materials are more difficult to machine than others. Generally, while the mechanical performance of metals improves with alloying, their machinability decreases.

Cost

Cast iron is often cheaper than steel, requiring less cost for materials, energy, and labor to produce the final product. Raw steel is more expensive and requires more time, energy, and attention for casting. However, when designing cast products, considering long-term usage and replacement costs is valuable. Notably, in many cases, more expensive parts to produce can have lower costs in the long run.

Steel is available in various prefabricated forms, such as sheets, rods, pipes, and beams, and can often be machined or assembled for a specific application. Depending on the product and quantity required, fabricating available steel products may be a cost-effective option.