Gray Cast Iron and it’s Uses

Please note: there is no difference between the terms Grey Iron Castings and Gray Iron Castings. This is strictly as spelling issue. We will use both spellings throughout the article. Typically, the word is spelled gray in America and grey in the UK. 

Foundries such as Faircast, Inc. have the capabilities of casting many types of materials. Foundries are called upon to work with grey cast iron which is a type of iron with a graphitic microstructure. That is to say that the iron is gray in color due to the presence of graphite in its make-up, yet the primary component is, of course, iron. Gray iron is actually the most common of the cast irons and the most widely used. Housings where the importance of stiffness outweighs the importance of tensile strength is where gray cast iron is usually considered and called for.

Grey Cast Iron will be chosen for these applications based on weight and to some degree heat resistance. Grey iron that is unhardened is considered fragile compared to other cast metals. The graphite flakes can create areas of weakness in the metal allowing for fractures that can split the metal.  This is why grey iron has low tensile and impact strength. However, the positive aspect of the graphite flakes is that they are what create great wear resistance. As friction occurs the graphite in the cast iron acts as a lubricant. 

Grey Cast Iron is the oldest and most commonly produced casting in the world. More pounds of grey iron are is cast throughout the world every single year than any other type of casting.  

Some of the most common uses of gray cast iron include:

  • Cinderblocks – this is the most common use as they are needed for everyday use in construction worldwide
  • Manhole covers – just about everyone in the world is made of grey iron 
  • Internal Combustion Engine Cylinder blocks
  • Electrical Boxes
  • Wind turbine housings.
  • Weights and counterweights
  • Disc Brake Rotors
  • Pump Housings
  • Gears
  • Hydraulic components
  • Automotive suspension components
  • Plow shares
  • Linkages
  • Stove parts
  • Steering knuckles
  • Tractor parts
  • Valves
  • Truck suspension components
  • Machinery bases

Grey cast iron has extremely high thermal conductivity and heat capacity, meaning it moves heat more easily through the metal, so it’s often used to make cast iron cookware. This fact is also a reason why it’s a good choice for the brake rotors. 

If you go to the lawn décor section of a store you may even find outdoor décor items made of gray cast iron. 

What makes the color specifically is the graphite flake structure from the carbon in the component that turns grey during the cooling process. So, it the grey color is in part due to the components and in part due to the heating and cooling process it goes through. The properties of the grey iron can change based on the materials that are used in the melting process. These materials are melted together and poured into the mold of the object being cast. 

You would need a very powerful microscope to be able to see the graphitic microstructure, the little black flakes of graphite, that identifies grey iron. It is those flakes that create the perception of the gray color. 

Grey cast iron components are popular because grey iron is one of the cheapest types of iron castings to produce.  It has offers tensile strength and yield strength while still being impact resistant for most of the applications it is used in and it can often dampen vibrations making it ideal for machinery bases and as well as many housing applications

Another important benefit of grey iron casting is its excellent ability to withstand thermal cycling. When components must goe back and forth between warmer and colder temperatures, this is referred to as thermal cycling. The process of thermal cycling can create stress and premature failure in some types of metal castings. However, grey iron has proven to endure the strain of the thermal cycling process quite well and the grey iron will therefore not stress as easily.

It is true that grey cast iron has less shock resistance and tensile strength than steel or most other castings, it has compressive strength that is comparable to low- and medium-carbon steel. The size and shape of the graphite flakes present in the microstructure are what control the mechanical properties in this type of casting. 

If you are in need of any type of casting and want to work with a reputable and reliable foundry please consider Faircast, Inc. We can manipulate mold designs to cover a large range of industries. Our most common industries served are Agriculture, Auto Mobile Parts, Valves & Piping, Construction, Oil & Gas, and so much more. 


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