Thermal Conductivity of Type 304 Stainless Steel

The 18 % chromium and 8 % nickel that make 304 corrosion-resistant also make it a poor conductor: 15 W/(m·K) against 50 for carbon steel and 401 for copper. Unusually among metals, stainless conductivity rises with temperature: about 16 W/(m·K) at 100 °C and 21 W/(m·K) at 500 °C.

This is a design driver, not a footnote. Stainless heat-exchanger plates and tubes are made thin (0.4–0.6 mm in plate exchangers) precisely to keep the wall resistance small. It is also why stainless cookware needs an aluminium or copper core to avoid hot spots, why stainless welds distort so readily, heat piles up at the arc instead of spreading, and why a stainless vacuum flask outperforms a steel one. Combine the low conductivity with a thermal expansion coefficient 50 % higher than carbon steel and you get the classic stainless problem: steep local temperature gradients producing large thermal stresses, the root of many cracked pipe attachments and failed dissimilar-metal joints.