Thermal Conductivity of Carbon Steel

Carbon steel conducts heat about eight times worse than copper because the carbon, manganese and dislocation structure that give it strength also scatter the electrons and phonons that carry heat. Values for mild steel cluster around 45–60 W/(m·K) at room temperature, and the figure falls as temperature rises — near 30 W/(m·K) at 600 °C, opposite to the trend in most non-metals.

In practice this rarely limits a heat exchanger. A 3 mm steel tube wall at 50 W/(m·K) contributes a conduction resistance of 6 × 10⁻⁵ m²·K/W, which is negligible beside a water-side film of about 2 × 10⁻⁴ and an air-side film ten times larger still. Where it does matter is in thermal bridging — a steel stud or a through-bolt short-circuits an insulated assembly and can cut effective wall R-value by a third — and in welding and fire behaviour, where steel's ability to spread heat away from the arc or the flame governs distortion and temperature rise.