Cast iron is not only for pots used for cooking a good old-fashioned stew or soup. Gray cast iron still has numerous uses and advantages in the B2B automotive industry, agriculture, the railroad, and transportation sectors. It is useful in construction and still has value in the world of industrial machinery and for equipment such as elevators and escalators.
After a brief overview, we’re going to take a closer look at the main advantages of gray cast iron and their most common applications.
Gray Cast Iron – Advantages and Types
There are four types of iron cast in foundries. They are:
- Gray cast iron
- White cast iron
- Ductile cast iron
- Malleable cast iron
In summary, it is easy to melt gray iron because of its high carbon content. This makes it easy to weld and machine too. Gray iron’s graphite flakes make it very stable and minimize shrinkage during the casting process. It is resistant to corrosion yet possesses high conductivity.
White cast iron, by contrast, only contains carbon in carbide form, making it abrasions resistant and extremely hard. It is more brittle than gray cast iron. Ductile cast iron is considered the most versatile of the four listed above. It is easy to machine, is strong and tough. The auto industry uses it to make crankshafts, axles for trucks, and engine rods. Today’s cast iron pipes are made from ductile cast iron.
Malleable cast iron undergoes a process to become so. To make it, white cast iron is reheated and then cooled. It has much better machineability than other types and is chiefly used to manufacture transmission gears and connecting rods, as well as heavy-duty valve parts and other applications.
1. Tensile Strength
Gray cast iron is popular because it is versatile and relatively cheap to produce. While its tensile strength and compressive yield strength are no match for most other castings and certainly not for steel, they are still respectable. They are also more than adequate for the many uses to which gray cast iron is put.
ASTM International, formerly the American Society for Testing and Materials develops and publishes voluntary consensus technical standards for a range of materials, including iron and steel materials. Its Standard ASTM A48/A48M gives the standard specifications for gray iron castings.
ASTM A48/A48M categorizes gray iron into classes according to its minimum tensile strength in thousands of pounds per square inch (KSI) as follows.
ASTM Class 20 gray Iron has a minimum tensile strength of 20 ksi (140 MPa). It has a high carbon equivalent and a ferrite matrix.
Class 40 gray irons have a perlite matrix and lower carbon equivalent. If alloyed, it can provide solid solution strengthening, while heat treating can modify the matrix. Because of its desirable combination of mechanical properties, Class 40 gray cast iron is most often chosen for structural applications.
Class 80 is the highest class available in this schema. Its extreme brittleness restricts its scope of application.
Faircast, Inc. foundries can determine the class of gray cast iron by adjusting its composition and the selection of the appropriate casting method. While the tensile strength to Brinell hardness ratio is not constant, the Brinell hardness test is a fair estimate of the tensile strength of the iron once cast.
Added tensile strength is one of the advantages of gray cast iron, having sufficient impact and shock resistance for applications.
2. Compressive Strength
Gray cast iron has a compressive strength (resistance to deformation) roughly 3–4 times that of its tensile strength as is comparable to that of low- and medium-carbon steel.
High compressive strength makes gray cast iron suitable for use in structural parts such as pillars and columns in the construction industry.
Linked primarily to compressive strength, but also to other mechanical properties is gray cast iron’s effectiveness at damping vibrations, making it an excellent material for use in machinery bases and wind turbine housings, and other housing applications. Other structures where operations induce unwanted vibrations, such s crankshafts, also favor the use of gray cast iron.
3. Ease of Machinability
With increased hardness and tensile strength comes reduced machineability. Yet, these properties of ASTM A48 Class 40 make it suitable for the machining of gears, automotive suspension components, disc brake rotors, and hydraulic components.
Gray cast iron’s good machineability means that Faircast, Inc. can cast and machine custom parts for anything within the 1-100 lbs range. Our free Tooling Guide 2020 will give you an idea of our capabilities in this area.
4. Thermal Properties of Gray Cast Iron
Thermal properties deal with the response materials have to changes in their temperature and how they react to the application of heat. Heat capacity, thermal conductivity, and thermal expansion all fall under the umbrella of thermal properties.
The melting point of ASTM A48 Class 40 is around 1260°C. This makes casting straightforward, as casting goes.
At 53 W/(m.K), the thermal conductivity of ASTM A48 Class 40 indicates that as a solid material, it has a good ability to transfer heat by conduction. This means that the material can be used in the manufacture of a range of engine components and automotive parts.
Thermal cycling is the phenomenon of having to undergo successive changes between warmer and cooler temperatures. Gray cast iron withstands such conditions relatively well.
5. Anti-Corrosive Properties
Since gray cast iron is oxidation resistant, it is ideal for all sorts of farm equipment, such as plowshares, and other practical items that need to withstand all-weather conditions, such as manhole covers. Gray cast iron is also extensive used in railroad equipment because of its anti-corrosive properties. At the other end of the scale, it is still popular in the manufacture of cookware for the same reason.
Made in the USA – Advantages of Gray Cast Iron
At Faircast, Inc. we’re proud of the fact that we support local industry and that our foundry casts 100% “made in America” products. In gray cast iron, we have one of the most versatile and useful products around, with clear advantages. If you would like a quote or additional information on what we can do for you, please contact us.
We’ll get back to you just as soon as possible. Our quotations to cast to your specifications are free, too.