Development and Composition Design of Q235NH Weathering Steel

Q235NH weathering steel is mainly used for bridges, vehicles, towers, railways and other steel structures exposed to the atmosphere for a long time. In order to meet market challenges, Q235NH weathering steel was developed according to the product structure of BBN's medium and thick plates. After several months of production practice, the production process of Q235NH weathering steel has been continuously improved, and the product quality has been significantly improved.

Composition design of Q235NH weathering steel
C is an effective element for strengthening steel. With the increase of C content, the strength and hardness of Q235NH weathering steel are improved, but the plasticity, toughness and weather resistance are decreased. Therefore, the C content is designed to be 0.12%~0.15%.

Cu is the most important and most commonly used alloying element to improve the atmospheric corrosion resistance in Q235NH weathering steel, and the atmospheric corrosion resistance obtained when Cu is used in combination with other elements (such as P and Cr) is better. When the Cu content is 0.25%, the Q235NH weathering steel has good weather resistance. When the Cu content exceeds 0.30%, the corrosion resistance improves slowly, and the effect of continuing to increase the Cu content is not significant.

At the same time, Cu-containing steel has thermal processing sensitivity and is prone to reticular cracks. Therefore, in order to improve the atmospheric corrosion resistance of Q235NH weathering steel and prevent cracks in Q235NH weathering steel, the Cu content is designed to be 0.25%~0.35%.