Both steel and cast iron are popular metals, but they are often used very differently. The key factor distinguishing one from the other is how much carbon each contains, and to a lesser extent, how much silicon. While this may seem like a subtle distinction, it has major implications for the properties and uses of cast iron and steel.
This article explains what makes cast iron and steel unique to help you decide which metal is the right choice for your next casting project.
Cast Iron: Benefits and UsesLike steel, cast iron is an iron-based alloy. However, to be considered cast iron, the metal must have a 2-4% carbon content and 1-3% silicon content by weight. This chemistry imparts cast iron with a number of useful properties:
Cast iron can actually be further subdivided into grey iron, white iron, ductile iron, and malleable iron. Each type focuses on improving certain properties for a specific application, like higher hardness in white cast iron.
The uses for cast iron are wide-reaching, but here are a few notable applications:
Similar to cast iron, steels are iron-based alloys with a few distinct categories. All steels have some carbon content up to a limit of 2% by weight and can be divided into either carbon steel or alloy steel.
They can be further subdivided into low-carbon steels, stainless steels, tool steels, microalloyed steels, and more. While these can offer numerous additional benefits, like high strength and corrosion resistance from stainless steels, this article will focus on cast steel alloys like those defined by ASTM A148.
Since cast steel is more expensive than cast iron, its main advantages over cast iron are:
While forging, rolling, and casting are all possible for steel products, some key applications focused on cast steel are:
This table provides a generalized comparison of cast iron vs steel, keeping in mind that each category represents a range of alloys with different properties.
Material Property Cast Iron Cast Steel Strength Better compressive strength Better tensile strength Toughness Low ductility and limited elongation Much higher ductility and toughness Hardness Good, comparable Good, comparable Melting Temperature Lower, which makes production easier Higher melting temperature Corrosion Resistance Better, frequently limited to surface rust Poor for cast carbon steel, but stainless alloys offer superior rust protection Machinability Easier to machine More time consuming and hard on tooling Weldability Difficult to weld without cracking Better weldability, ranging from poor to very good. Cost Less expensive to melt, pour, and process. More challenging and costly to produceMachining Cast Iron and Steel Products
Cast iron is certainly easier and cheaper to machine than cast steel, but machinability varies widely between different alloys, even in the same group. So if you’re designing a product that will need lengthy machining operations, it may be worthwhile to review available alloys in search of one with better machinability.
But even if you are restricted to using a more difficult-to-machine material, an experienced, world-class machine shop can cut down processing times to save on machining costs. Gensun offers fast, reliable machining services for a wide range of materials and product types.
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