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What are Thermal Properties of White Cast Iron – Definition

Thermal Properties of White Cast Iron – Ni-Cr-HC Martensitic White Cast Iron. Heat capacity, thermal expansion, and thermal conductivity are properties that are often critical in the practical use of solids.

As was written, cast irons are one of the most complex alloys used in industry. Because of the higher carbon content, the structure of cast iron, as opposed to that of steel, exhibits a carbon-rich phase. Depending primarily on composition, cooling rate, and melt treatment, the carbon-rich phase can solidify with formation of either a stable (austenite-graphite) or a metastable (austenite-Fe3C) eutectic.

With a lower silicon content (containing less than 1.0 wt% Si – graphitizing agent) and faster cooling rate, the carbon in cast iron precipitates out of the melt as the metastable phase cementite, Fe3C, rather than graphite. The product of this solidification is known as white cast iron (also known as chilled irons). White cast irons are hard, brittle, and unmachinable, while gray irons with softer graphite are reasonably strong and machinable. A fracture surface of this alloy has a white appearance, and thus it is termed white cast iron. It is difficult to cool thick castings fast enough to solidify the melt as white cast iron all the way through. However, rapid cooling can be used to solidify a shell of white cast iron, after which the remainder cools more slowly to form a core of gray cast iron. This type of casting, sometimes referred to as a “chilled casting” has a harder outer surface and a tougher inner core.

Thermal Properties of White Cast Iron – Ni-Cr-HC Martensitic White Cast Iron

Thermal properties of materials refer to the response of materials to changes in their temperature and to the application of heat. As a solid absorbs energy in the form of heat, its temperature rises and its dimensions increase. But different materials react to the application of heat differently.

Heat capacity, thermal expansion, and thermal conductivity are properties that are often critical in the practical use of solids.

Melting Point of White Cast Iron – Ni-Cr-HC Martensitic White Cast Iron

Melting point of martensitic white cast iron (ASTM A532 Class 1 Type A) steel is around 1260°C.

In general, melting is a phase change of a substance from the solid to the liquid phase. The melting point of a substance is the temperature at which this phase change occurs. The melting point also defines a condition in which the solid and liquid can exist in equilibrium.

Thermal Conductivity of White Cast Iron – Ni-Cr-HC Martensitic White Cast Iron

The thermal conductivity of martensitic white cast iron (ASTM A532 Class 1 Type A) is 15 – 30 W/(m.K).

The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.

The thermal conductivity of most liquids and solids varies with temperature. For vapors, it also depends upon pressure. In general:

thermal conductivity - definition

Most materials are very nearly homogeneous, therefore we can usually write k = k (T). Similar definitions are associated with thermal conductivities in the y- and z-directions (ky, kz), but for an isotropic material the thermal conductivity is independent of the direction of transfer, kx = ky = kz = k.

References:
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White Cast Iron

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