Steel is an alloy of iron and carbon, and its ability to transmit energy (conductivity) depends on the specific alloy and the type of energy involved. For steel, the designation of “good conductor” is not a simple yes or no answer. This article explores the properties of steel concerning both electrical current flow and thermal energy transfer.
Electrical Conductivity
Steel is a metal and conducts electricity, but its performance is poor compared to benchmark materials like copper or aluminum. The electrical conductivity of steel typically ranges from only 3% to 15% of that of pure copper, depending on the specific alloy composition.
Steel is approximately 7 to 33 times more resistive to electric current than copper. For instance, a common carbon steel (AISI 1010) has an electrical conductivity of about 6.99 million siemens per meter, while copper’s conductivity is much higher, around 59.6 million siemens per meter. The high electrical resistance of steel makes it impractical for use as wiring or in other applications where minimal energy loss is a priority. Steel is instead valued in construction and structural uses for its mechanical strength and durability.
Thermal Conductivity
Regarding heat transfer, steel is generally considered a moderate thermal conductor, with performance varying widely between alloy types. Carbon steel conducts heat reasonably well, typically falling within the range of 45 to 58 Watts per meter-Kelvin (W/m·K). This moderate conductivity is sufficient for applications like certain tools or structural components where temperature equalization is not a major design constraint.
Stainless steel is a notably poorer conductor of heat compared to carbon steel. The thermal conductivity of stainless steel, such as the common 300-series grades, is significantly lower, often ranging from 15 to 30 W/m·K. This low thermal performance is why stainless steel cookware can heat unevenly. This characteristic is sometimes beneficial, however, such as in applications that require reduced heat transfer or fire resistance.
How Alloying Elements Impact Performance
The substantial differences in conductivity between various types of steel are directly attributable to their specific alloy composition. Metals conduct energy primarily through the movement of free electrons, which carry both electrical current and thermal energy. Steel is an alloy where iron is combined with carbon and other elements like manganese, chromium, and nickel.
The addition of these alloying elements disrupts the highly organized, crystalline lattice structure of the pure iron base. These foreign atoms act as scattering centers, impeding the smooth flow of both the moving free electrons and the lattice vibrations responsible for heat transfer. Elements like chromium and nickel, present in high concentrations in stainless steel, are particularly effective at this disruption, dramatically lowering both electrical and thermal conductivity.
Carbon steel, which has a relatively simple composition, exhibits higher conductivity because its structure is less disrupted. High-alloy stainless steels containing significant amounts of chromium and nickel can have an electrical conductivity as low as 1.3 million siemens per meter. This mechanism explains why alloying steel to gain benefits like strength and corrosion resistance comes at the cost of reduced energy conductivity.