Thermal Properties of Steel

Thermal Conductivity

• The American Heritage Science Dictionary describes thermal conductivity as a measure of the ability of a material to transfer heat. Given two surfaces on either side of the material with a temperature difference between them, the thermal conductivity is the heat energy transferred per unit time and per unit surface area, divided by the temperature difference. As such, thermal conductivity is usually reported in Watts per Kelvin per meter, or W/(K)(m).

  The thermal properties of steel will vary based on the ratio of alloying elements in the steel. For example, The Engineering Toolbox lists thermal conductivities for steel containing 0.5 percent carbon at 18.23 W/(K)(m), while steel containing 1.5 percent carbon is listed as having a thermal conductivity of 12.35 W/(K)(m). Moreover, the thermal conductivity of stainless steel varies from 12.11 to 45.0 W/(K)(m).

Thermal Resistivity

• Thermal resistivity is the inverse of thermal conductivity. The higher the thermal resistivity, the lower the thermal conductivity. Thus, thermal resistivity also describes the rate at which heat travels through a compound but is most commonly used to describe materials which insulate against heat.

  The thermal resistivity of 0.5 percent carbon is 0.055 (K)(m)/W, while steel containing 1.5 percent carbon is has a thermal resistivity of 0.081 (K)(m)/W, and the thermal resistivity of stainless steel will vary from 0.083 to 0.022 (K)(m)/W.

Thermal transmittance

• Thermal transmittance measurements take into account the thermal conductivity of the steel as well as heat in the surrounding environment. It is commonly reported as the U-value for a particular area of material. The U-value for steel will vary by alloyed elements, area, thickness and the surrounding environment.