Gray cast iron is a commonly used alloy due to its low cost and workability. It contains 2.5% to 4% carbon and 1% to 3% silicon, which allows for the formation of graphite and a graphitic microstructure. The presence of graphite makes it easily workable and aids in wear and tear resistance. There are several grades of gray iron, each with different tensile and compressive strengths. Higher grade alloys have less carbon and higher compressive strength but are more brittle.
Gray cast iron is the most commonly used cast iron alloy. When gray iron is broken, it can reveal the gray color from which it gets its name. This color is the result of the presence of graphite in the alloy. The presence of graphite is the result of particular ratios of carbon and silicon in the alloy, which helps facilitate the formation of what is known as a graphitic microstructure. Gray cast iron is a relatively inexpensive alloy used extensively in the casting of everything from engine blocks to cookware.
To create gray iron, the alloy must contain 2.5% to 4% carbon and 1% to 3% silicon. The presence of carbon and silicon in these ratios allows the alloy to form the graphitic microstructure for which it is known. Graphite is a hexagonal crystallized carbon allotrope, therefore the presence of carbon is necessary for the formation of graphite. However, the silicon in the alloy is required to act as a stabilizing agent for the graphite. An alloy with a lower silicon content can allow iron carbides to form rather than graphite, especially if the alloy is cooled rapidly, instead resulting in what is known as white iron.
Gray cast iron has lower tensile strength than steel, although its compressive strength is similar. It is less expensive to produce than steel, making it useful in applications where tensile strength is not of paramount importance. This has led to the fact that gray cast iron is the most commonly used cast iron alloy.
The presence of graphite in the alloy helps to make it easily workable. This is due to the lubricating nature of the graphite flakes present in the alloy. Graphite can also aid in wear and tear resistance, while the presence of silicon can aid in corrosion resistance.
There are several grades of gray iron, each of which has a different tensile and compressive strength. In the US, these grades are defined by numbers that correspond to the amount of tensile strength of the material. Therefore, grade 20 gray iron should have a minimum tensile strength of 20 kilo pounds per square inch (KSI) or 20,000 pounds per square inch (PSI) (about 6.894 kilopascals). Compressive strength increases along with tensile strength, so a higher grade alloy will also have higher compressive strength than a lower grade alloy. Higher grade alloys contain less carbon than lower grade alloys and also tend to be more brittle.
Protect your devices with Threat Protection by NordVPN
