Gray Iron Properties and Grades Explained

Posted on Aug 17, 2020

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Gray Iron Properties and Grades Explained

Gray iron is basically re-molten pig iron (crude iron) and an alloy of carbon and iron. It also contains a small amount of silicon, phosphorus, manganese, and sulfur. The reason for its popularity is the ability to manufacture complex structures and low cost. Furthermore, the excellent properties of gray iron make it one of the most commonly used alloys. In gray iron, graphite is spread in the form of flakes in the ferrite or pearlite matrix. The fracture surface has a gray color and is named after gray iron.

Under tensile load, graphite flakes serve as stress concentrators, making them fragile and brittle in tensile strength but high in compression and nodularity. It is also an inexpensive material and is relatively easy to cast with minimal risk of shrinkage. This is why gray iron is usually used for pump parts with medium strength requirements. Because gray iron has a high vibration damping capacity, it is also commonly used to manufacture motor blocks. In this blog post, we will focus on the characteristics of gray iron and analyze the main differences between gray iron and nodular iron.

 

Grades and Applications Of Gray Iron

EN-GJL-300 gray iron (GG30) is alloyed to achieve the properties, giving excellent wear resistance, strength & heat-treatment response compared to EN-GJL-200/250. At the same time, it still has reasonable machinability and excellent surface finish. This level of noise and vibration damping is excellent. This type of gray iron is used to manufacture heavy-duty machine tools, bed bodies, presses, high-pressure hydraulic parts, frames, gears, bushings, piston rings, cams, crankshafts, cylinder blocks, cylinder heads, etc.

EN-GJL-200 and class 250 gray iron (GG20 and GG25) offers exceptional machinability and is extremely resistant to heat and corrosion. EN-GJL-250 (GG25) is the most commonly used gray cast iron alloy. It provides a good combination of strength and wear resistance, but is still easy to process and can be finished to high standards. It is layered cast iron with mainly pearlite structure. This material is also easy to complete and very effective in attenuating sound and vibration. The strength and wear resistance of this material is limited, and heat treatment is not recommended to increase the hardness. EN-GJL-200 and 250 gray iron are suitable for all types of mechanical parts that are not subject to high mechanical stress. Therefore, it is very suitable for stove bars of old steam locomotives and g-bars and bridges for steam-powered ships and railings. Lampposts are also used for ingot molds in the gold and banking industries. It can also be used for the manufacture of cylinders, bases, machine beds, flywheels, cylinder liners, cylinder blocks, pistons, brake wheels, gearboxes, pressure valves, coupling plates, and others.

EN-GJL-100 and 150 (GG10 and GG15) are considered the lowest, most basic gray cast iron material grades. These types of gray iron are suitable for more simple parts with lower overall requirements such as covers, protective covers, frames, handwheels, hammers, handles, boxes, pulleys, workbenches, pump bodies, pipes, valves and similar products that have lower rigidity and heat resistance capabilities.

:: Read more : The Many Advantages of Gray Cast Iron

 

The Most Important Gray Iron Properties

• Compressive Strength

The strength is defined by the durability of any metal or alloy to withstand its compressive force. Gray cast iron has a high compressive strength, which is why it is widely used in building pillars and columns. Also, their compressive strength can be as high as some mild steel.

• Tensile Strength

There are different varieties of gray iron, and its tensile strength changes accordingly. Some varieties have a tensile strength of 5 tons per square inch, and some have a tensile strength of 19, but the average strength is 7 tons per square inch. However, adding vanadium can increase the strength of gray cast iron.

• Deformation Resistance

Gray iron is ideal for strong frames as it has a very high deformation resistance. and provides a strong frame. However, if there are some construction-related problems, even structures made of gray cast iron will collapse.

• Low Melting Point

Gray Iron has a low melting point of – 1140 ºC to 1200 ºC.

• Oxidation Resistance

Gray iron has a high anti-rust capability, which is formed by the reaction of oxygen and iron. This is the ideal solution to avoid corrosion problems.

 

How are Gray Iron and Nodular Iron different?

Maybe you would like to understand the differences between gray iron and nodular iron, also referred to as nodular iron? Let us talk a bit about the differences in microstructure, physical properties, and chemical composition.

• Microstructure

The main advantage of gray iron is that it contains flakes of graphite created during the calibration. This graphite flakes give a special gray color to the cast iron when broken, and also contribute to many physical properties of this iron alloy. The nodular iron microstructure is a discrete type of balls made of graphite. Nodular cast iron is produced through an alloying process that transforms the graphite flakes of gray cast iron into nodular cast iron that increases the probability of cracks. Through this microstructure transformation, the metal obtains excellent ductility and elongation properties.

• Physical Properties

Nodular iron has an absolute strength advantage as compared to gray iron. The nodular iron's maximum tensile strength is 90000 psi, and gray iron's maximum tensile strength is just 35000 psi. In yield strength, nodular cast iron is usually superior to gray iron. Nodular iron 's maximum yield strength is 40000 psi; gray iron's hardness or hardness is not very strong, and fracturing is simple. Nodular cast iron has greater strength and elasticity than other cast iron. Nodular iron has higher strength, higher elongation, and greater impact resistance than gray iron. The nodular cast iron series provides design engineers with a unique combination of strength, wear resistance, fatigue resistance, and toughness, as well as excellent ductility. In all its classes, nodular iron has mechanical properties that make it the perfect material for mechanical and automobile components. Gray iron is indeed the most durable of all the foundry metals and is the most widely used metal for construction purposes, with the exception of wrought steel. Gray iron is an extremely cheap metallic product and is readily available in nearly any foundry in large quantities.

:: Read more : How to choose the right grade of Ductile Cast Iron

 

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