The temperature tolerance of Galvanized steel plate is mainly restricted by the characteristics of the zinc coating and the performance of the substrate. Conventional hot-dip galvanized products can withstand high temperatures of 150-200°C for a long time in a dry environment without significant deterioration. The oxidation rate of the zinc coating at 200°C is approximately 0.5μm/ year. When the temperature rises to 250°C, the diffusion of zinc atoms accelerates, increasing the risk of intergranular corrosion by 50%. According to a 2022 study by NIST, the lifespan of galvanized sheets continuously exposed to this temperature is shortened to 3-5 years, with a reduction rate of over 80% compared to a 20-year lifespan at normal temperature. In automotive exhaust system application cases (as required by Bosch suppliers), a 55% aluminum-zinc alloy coating (Galfan®) needs to be added to raise the tolerance threshold to 315°C and control the oxidation mass loss within less than 15g/m².
In extremely high-temperature environments, there is a critical point for the structural integrity of galvanized sheets. The melting point of zinc at 419°C causes the risk of coating liquefaction and peeling. At this time, the tensile strength of the steel substrate decreases by 30% and the deformation rate increases by 200%. According to the 2019 California Mountain Fire post-building investigation report, the load-bearing capacity of galvanized roof supports exposed to 400°C for 30 minutes decreased by 40%, and the probability of complete coating failure reached 95% when the peak temperature exceeded 480°C. Industrial furnace applications have shown that galvanized sheets with silicon-containing killed steel substrates still maintain a yield strength of 90% under a 350°C thermal cycle (fluctuation of ±50°C), far exceeding the 60% retention rate of conventional SPCC substrates.
Environmental synergy significantly affects temperature tolerance performance. When the humidity is greater than 80%, the environment above 60°C can accelerate the formation of white rust on the coating, and the corrosion rate can reach 0.1mm per year (ISO 9223 standard data). Monitoring of the Singapore Coastal Tunnel project in 2023 shows that the protection life of the galvanized steel support structure under the working conditions of 45°C and 95% humidity has dropped from the designed value of 15 years to 9 years, with a corrosion depth deviation of ±0.3mm. More caution is needed in salt spray environments – ASTM B117 tests show that red rust appears after 300 hours in a 60°C salt (5%NaCl) environment, which is far below the 2000-hour durability threshold of the standard environment.
Technological innovation is breaking through the traditional temperature barriers. The new zinc-magnesium-aluminum coating (such as ArcelorMittal’s Magnelis®) has raised the upper limit of working temperature to 400°C and increased the salt spray tolerance time to 1500 hours (a 300% increase). The SpaceX Starship fuel tank case in 2024 demonstrated that the galvanized sheet treated with nano-ceramic sealing maintained zero structural failure during temperature difference cycles ranging from -180°C to 250°C, and still maintained a zinc layer adhesion of 35MPa within a temperature fluctuation range of 430°C. Thermal reflective coatings (such as PPG’s Tnemec® series) have successfully extended the lifespan of galvanized sheets used in photovoltaic brackets in the Middle East to 25 years and increased the return on investment by 22% by reducing the surface temperature by 15-20°C.
Special scenarios require targeted solutions. In the field of fire protection (refer to NFPA 80 standard), the galvanized fireproof door core board needs to maintain its integrity at 1093°C for 1 hour, and the heat conduction rate is reduced to 0.8W/m·K through the composite vermiculite board. Nuclear power plant applications require galvanized sheets to maintain functionality for 48 hours under LOCA accident conditions (120°C+100% humidity + boric acid environment). Westinghouse Electric’s 2022 test data confirmed that a specific coating formula can reduce corrosion by over 70%. The trend of sustainable development drives the research and development of high-temperature resistant recycled galvanized sheets. Thyssenkrupp’s Bluemint® series achieves a 350°C tolerance while reducing the carbon footprint by 40%, and has obtained UL ECV 2805 certification.