1. General trend
The impact toughness of Q355NH changes regularly with temperature:it is high at room and high temperatures, gradually decreases as temperature drops, and shows a ductile‑to‑brittle transition at low temperatures - typical behavior for structural steel.
2. At room temperature and above
At +20°C and higher temperatures, Q355NH has excellent impact toughness.
The material is in a ductile state, absorbs high energy during impact, and resists fracture.
Long‑term outdoor atmospheric exposure does not significantly reduce this room‑temperature toughness.
3. With decreasing temperature (cooling down)
As temperature falls from room temperature to around 0°C, toughness decreases slowly but remains good.
Between approximately 0°C and –20°C, it enters the ductile‑brittle transition range:impact energy drops noticeably, and the fracture mode gradually changes from fibrous (ductile) to cleavage (brittle).
Below the transition temperature, impact toughness becomes markedly lower, and brittleness increases.
4. Low‑temperature region (below –20°C)
At –20°C and lower, Q355NH shows reduced impact toughness.
It is not a specialized low‑temperature steel (like Q355ND or Q355NE), so its low‑temperature toughness is not designed for extremely cold environments.
In very cold outdoor conditions, brittle fracture risk increases if not properly specified.
5. Comparison with ordinary Q355 carbon steel
The temperature dependence of impact toughness is very similar to Q355B.
Weathering alloy elements (Cu, Cr, Ni, P) do not cause abnormal brittleness or unusual transition behavior.
Q355NH maintains toughness equivalent to conventional structural steel over the full temperature range.
