In metallurgy, stainless steel is a steel alloy with at least 10.5% chromium with or without other alloying elements and a maximum of 1.2% carbon by mass. Stainless steels, also known as inox steels or inox from French inoxydable (inoxidizable), are steel alloys, which are very well known for their corrosion resistance, which increases with increasing chromium content. Corrosion resistance may also be enhanced by nickel and molybdenum additions. The resistance of these metallic alloys to the chemical effects of corrosive agents is based on passivation. For passivation to occur and remain stable, the Fe-Cr alloy must have a minimum chromium content of about 10.5% by weight, above which passivity can occur and below which it is impossible. Chromium can be used as a hardening element and is frequently used with a toughening element such as nickel to produce superior mechanical properties.
Thermal Properties of Stainless Steels
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 Stainless Steels
Melting point of stainless steel – type 304 steel is around 1450°C.
Melting point of ferritic stainless steel – Grade 430 steel is around 1450°C.
Melting point of martensitic stainless steel – Grade 440C steel is around 1450°C.
Melting point of duplex stainless steels – SAF 2205 steel is around 1450°C.
Melting point of precipitation hardening steels – 17-4PH stainless steel steel is around 1450°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 Stainless Steels
The thermal conductivity of stainless steel – type 304 is 20 W/(m.K).
The thermal conductivity of ferritic stainless steel – Grade 430 is 26 W/(m.K).
The thermal conductivity of martensitic stainless steel – Grade 440C is 24 W/(m.K).
The thermal conductivity of duplex stainless steels – SAF 2205 is 19 W/(m.K).
The thermal conductivity of precipitation hardening steels – 17-4PH stainless steel is 18 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:
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.
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