Metallographic diagram of white cast iron

White Cast Iron Microstructure

White cast iron occurs when graphite flakes (and other impurities) are disseminated into the metal matrix. The primary constituents of white cast iron are iron and carbon. White cast iron has a great deal of wear resistance, strength and hardness, which makes it extremely useful for many industrial applications.

White cast iron typically has a gray, white, or grayish-white appearance. It is most commonly used for making heavy-duty components, such as railway tracks, gears, machine tool parts, shafts and rollers. In addition, some elements of white cast iron, such as nickel and chromium, give it some corrosion resistance.

White cast iron contains more graphite than other types of cast iron. This produces a low melting point and makes it relatively easy to cast. In addition, it is generally cheaper than other types of cast iron.

Under a microscope, white cast iron has a very unique microstructure. It is composed of brittle carbide particles suspended in a matrix of soft iron. The carbide particles are typically in the form of lamellar or isometric flake graphite. Because graphite has a layered structure, it makes the microstructure of white cast iron very fragile and prone to breaking if subject to impact or stress.

At the grain boundaries, where the upper and lower layers of the graphite flakes meet, there is a thin layer of cementite, an iron carbide with a composition of two parts carbon and one part iron.

Because of its high levels of wear resistance, white cast iron can be used for many industrial components. These components may be subject to heavy wear and require high strength and hardness. Among its many uses, white cast iron can be used to manufacture gears, shafts, rollers, crushers, and crusher parts.

White cast iron is relatively easy to cast, and because of its high wear resistance, it is often used as a cost-effective alternative to other types of iron. While it is not as ductile or malleable as other cast iron alloys, its wear resistance makes it a popular choice for many industrial components.

When inspecting a sample of white cast iron under a microscope, the graphite flakes and carbide particles should be easily visible, along with the thin cementite layer at the grain boundaries. The presence of these microstructural features confirm the material as white cast iron.

Cast iron is a type of ferrous alloy containing 2% – 4.5% carbon by mass. It can be heat treated to improve its strength, wear resistance, and ductility. Cast iron is widely used in industrial and architecture applications, such as engine blocks and other machine parts, pumps, valves, pipes, and cast iron architectural ornamentation. Its also widely used for casting cookware.

In metals, the microstructure widely affects its physical and mechanical properties. An optical microscope or scanning electron microscope (SEM) is used to inspect its microstructure, including carbide precipitates, retained austenite, or graphite morphology. A metallographic analysis method, gold-plated surface preparation, involves plating the specimen with a thin layer of gold by electrolysis, then observing the pattern of the gold with optical microscopy. It is suitable for the samples with certain thickness and flatness condition.

In the following study, a gold-plated surface preparation method was used to observe the microstructure of grey cast iron. The specimen was first prepared by a grinding and polishing process, then gold plated at 0.3Amp current with a graphite cathode. After a few seconds, it was removed and cleaned with warm water. The specimen was then observed under optical microscopy with a ×40 objective lens.

The microstructure of the specimen appeared as white laths and dots due to the refraction of light on gold-coated surface. The white laths were identified as graphite inclusions, while there were also some cementite particles in the sample. By tracing the microstructure of the specimen, the pearlite and ferrite structures confirmed the presence of white laths, cementite particles, and some nodules of ferrite or pearlite.

Finally, the gold-plated surface preparation proved to be an effective steady for studying the microstructure of a grey cast iron. The method gave an accurate view of the microstructure, which help in evaluating its mechanical properties, such as strength and wear resistance. It is safe, fast, and easy to use.