The Core Principles of Steel for Ships

　　The core principle behind steel used in shipbuilding lies in the careful design of chemical composition and precise control of heat treatment processes, enabling the steel to achieve mechanical properties, corrosion resistance, and processability that are well-suited for marine service environments. This ensures the safety and durability of ship structures under complex loading conditions and harsh operational environments.

　　Specifically, it can be broken down into the following 3 core logics:

　　1. Principle of Mechanical Property Matching: To ensure a balance between strength and toughness, ships undergoing navigation are subjected to various forces, including hydrostatic pressure, impacts from wind and waves, cargo loads, and hull vibrations. Therefore, steel must simultaneously possess both high strength and high toughness.

　　Composition Control: Adding **manganese (Mn) and silicon (Si)** enhances strength; incorporating **nickel (Ni) and vanadium (V)** refines grain size, improves low-temperature toughness, and helps prevent brittle fracture of ships in extremely cold waters such as polar regions.

　　Process Control: By employing temperature-controlled rolling (TMCP) and normalizing treatment, we achieve a uniform ferrite-pearlite microstructure within the steel, striking a balance between "high strength and high ductility" to meet the varying load-bearing requirements of different vessels—for example, cargo ships prioritize cost-effectiveness, while icebreakers emphasize impact resistance.

　　2. Principle of Resistance to Marine Corrosion: Inhibiting Electrochemical Corrosion—Seawater is a strong electrolyte solution, and prolonged immersion of ship steel in seawater will lead to electrochemical corrosion. Additionally, ships are also susceptible to biofouling corrosion and salt-spray corrosion.

　　Corrosion-resistant alloying: Elements such as chromium (Cr), copper (Cu), and phosphorus (P) are added to form a dense passivation film on the steel surface, which inhibits the penetration of corrosive media. For steels used in chemical vessels, molybdenum (Mo) is also added to enhance resistance to acid and alkali corrosion.

　　Structural and Process Support: By reducing carbon content, the risk of intergranular corrosion is minimized; thick-plate steel designs incorporate Z-directional properties to prevent delamination cracking in welded areas caused by the combined effects of corrosion and stress.

　　3. Principle of Process Performance Adaptation: To meet the requirements of shipbuilding, a ship’s hull is constructed by welding together numerous steel plates. Therefore, the steel must possess excellent weldability and formability to accommodate the complex processing involved in shaping the hull structure.

　　Weldability Assurance: Strictly control the carbon equivalent (CET ≤ 0.40%) to reduce the tendency for cold cracking during welding; add **titanium (Ti) and niobium (Nb)** to fix nitrogen in the steel, thereby preventing embrittlement in the weld heat-affected zone.

　　Formability Assurance: Through a carefully designed composition, the steel exhibits excellent cold and hot bending performance, enabling it to be fabricated into components of various shapes, such as ship hulls, decks, and bulkheads, without cracking or degradation in performance after forming.