How to Tell the Difference Between Cast Iron and Steel

As a scrapper, identifying the type of metal you’re dealing with is crucial for effectively sorting and maximizing your profits. Two of the most common metals you’ll encounter are cast iron and steel. While they may seem similar (or are even graded the same) at first glance, several key differences can help you distinguish between them.

What Are Cast Iron and Steel?

Cast iron is an iron-carbon alloy with 2-4% carbon and 1-3% silicon making it hard but incredibly wear and heat-resistant. Steel has less carbon (less than 2%) and often contains other alloying elements like manganese and chromium. While both are strong, Steel is much more versatile, and as such, both metals are used for vastly different real-world applications.

Common Forms of Cast Iron Scrap

  • Radiators: Older heating systems commonly contain cast iron radiators.
  • Cookware: Items like skillets and pans are widespread. Make sure any contaminants are removed from these items before scrapping.
  • Rotors or Auto Cast: Includes cleaned brake rotors or steel rims. Ensure the brake pads are not attached, as they can lower you to a dirty price if you don’t.

Common Forms of Steel Scrap

Because Steel is an umbrella term for many types of metal, there are too many to list, but here are a few grades and some common examples:

  • Light Iron (Shred, Tin, or Sheet Iron): This is among the most common for scrapping. It includes items like folding chairs or thin metal sheets.
  • Unprepared Heavy Iron: This consists of much heavier and thicker items, typically used for supporting substantial loads. Examples include Beams, channels, steel girders, and structural steel.
  • Automobiles/Car Scrap: While they have tons of parts that aren’t steel, a good chunk of it is also. Items like exhaust pipes, radiators, car frames, and wheel rims

Visually Identifying Cast Iron vs. Steel

Due to how it is constructed, cast iron typically has a rougher, more porous surface. Look for signs of casting, such as seams, lines, sand pitting, or anything that shows it was once in a mold. On the other hand, steel has a smoother surface, which indicates its use in commercial applications. Generally, cast iron will also be the heavier of the two, so if you find similar-sized items and one of the two seems lighter, chances are that’s the steel one.

Other Ways To Identify Cast Iron vs. Steel

You can also differentiate between these two metals in a few other ways that involve a little more testing than purely picking it up and eyeballing it:

  • Sound Test: When struck with a hammer or another piece of metal, it produces a dull thud. On the other hand, steel makes a clear, ringing sound when struck, indicating its ductility and toughness.
  • Spark Test: When ground, cast iron produces short, reddish sparks that are less bright and numerous. Steel produces longer, more colorful, and more numerous sparks. The spark pattern can vary with different steel types, but steel sparks are generally more pronounced than cast iron ones.
  • Drop It On The Ground: You heard that right! Cast Iron tends to break or shatter rather than bend. If you apply significant force, it will snap with a grainy fracture. On the other hand, steel is more malleable and bends rather than breaks. If it does break, the fracture surface is typically smoother than that of cast iron.