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Q345B is a widely utilized low-alloy high-strength structural steel in China, specified in the national standard GB/T 1591. The "Q" denotes "yield strength" in Chinese pinyin, "345" indicates that the minimum yield strength of this steel grade is 345 MPa, and "B" represents that it is required to undergo an impact test at room temperature (20℃), ensuring its toughness under normal working conditions.

This steel grade stands out with its remarkable features. It offers significantly higher strength compared to common carbon steels, enabling it to bear heavier loads while reducing material consumption. Despite its enhanced strength, Q345B maintains good plasticity and weldability, allowing for convenient processing and assembly in manufacturing. Additionally, it has better corrosion resistance than ordinary carbon steels, extending the service life of components in various environments.

Regarding its chemical composition, Q345B is based on iron and contains alloying elements like manganese, silicon, and vanadium. Manganese (content around 1.0 - 1.6%) improves the strength and hardenability of the steel, while silicon (≤ 0.55%) helps with deoxidation and contributes to strength enhancement. Vanadium, niobium, or titanium may be added in trace amounts to refine the grain structure, further optimizing its mechanical properties. The carbon content is usually controlled within 0.20%, balancing strength and toughness. Strict limits are also imposed on impurities such as phosphorus (≤ 0.040%) and sulfur (≤ 0.040%) to ensure reliable performance.

Q345B finds extensive application across multiple industries. In construction, it is used for large-scale buildings, bridges, and high-rise structures, providing the necessary strength and stability. In the machinery manufacturing sector, it is suitable for making heavy-duty mechanical parts and equipment frames. It is also employed in the petrochemical industry for constructing pressure vessels and pipelines due to its high strength and corrosion resistance. Overall, Q345B's excellent comprehensive performance makes it a preferred choice for a wide range of demanding industrial applications.

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