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In modern aerospace industry, material selection directly impacts aircraft performance, safety, and service life. Faced with extreme temperature variations, high stress loads, and harsh corrosive environments, engineers impose extremely high requirements on structural materials. Among numerous stainless steel grades, 321 stainless steel plates have become a “favorite” in the aerospace sector due to their unique compositional design and excellent comprehensive properties. What exactly makes 321 stainless steel plates highly favored in this high-end application field? This article will conduct an in-depth analysis from multiple dimensions including its chemical composition, thermal stability, corrosion resistance, welding performance, and practical application scenarios. I. Basic Properties of 321 Stainless Steel 321 stainless steel is a titanium (Ti)-stabilized austenitic stainless steel with a standard composition: approximately 17–19% chromium (Cr), 9–12% nickel (Ni), and a titanium content not less than 5 times the carbon (C) content (typically Ti ≥ 5×C%). The addition of titanium is the key distinction between 321 and ordinary austenitic stainless steels such as 304. Titanium combines with carbon in the steel to form stable titanium carbide (TiC), effectively preventing “intergranular corrosion” caused by the formation of chromium carbide (Cr₂₃C₆) from carbon and chromium reactions in the temperature range of 450–850℃. This property enables 321 stainless steel to maintain good corrosion resistance and mechanical properties after exposure to high temperatures or welding, making it particularly suitable for components requiring long-term service in high-temperature environments. II. Excellent High-Temperature Stability Aerospace vehicles experience severe temperature fluctuations during flight. For instance, components such as jet engine exhaust systems, combustion chamber surrounding structures, and rocket thruster casings often operate at temperatures exceeding 600℃, even reaching over 800℃. Under such high-temperature conditions, ordinary stainless steel tends to suffer reduced strength, accelerated oxidation, and even structural failure. Thanks to its titanium stabilization mechanism, 321 stainless steel maintains excellent oxidation resistance and structural stability at temperatures up to 900℃. The American ASTM standard clearly specifies that the maximum continuous service temperature of 321 stainless steel can reach approximately 870℃, significantly higher than that of 304 stainless steel (around 650℃). Therefore, 321 has become the preferred material for aviation components requiring resistance to sustained high temperatures or frequent thermal cycles. III. Superior Intergranular Corrosion Resistance Intergranular corrosion is a common failure mode of austenitic stainless steel during welding or high-temperature service. When the material remains in the sensitization temperature range (approximately 450–850℃), carbon combines with chromium to precipitate chromium carbide, leading to chromium depletion near grain boundaries and loss of corrosion resistance. This issue is particularly dangerous in aerospace structures, as tiny corrosion cracks can rapidly propagate under high stress, causing catastrophic consequences. By adding titanium, 321 stainless steel preferentially combines with carbon to form stable TiC, avoiding chromium consumption and fundamentally inhibiting the occurrence of intergranular corrosion. Even after multiple welding processes or long-term high-temperature exposure, its corrosion resistance remains reliable. This property makes it widely used in critical components such as engine ducts, heat exchangers, and exhaust manifolds. IV. Good Welding and Processing Performance Despite containing titanium, 321 stainless steel retains the typical excellent ductility and toughness of austenitic stainless steels. It is easy to cold-form at room temperature into thin plates, pipes, or special-shaped parts of complex shapes. Meanwhile, it exhibits good welding performance, enabling high-quality joints without post-weld heat treatment, which greatly simplifies the manufacturing process. In aerospace manufacturing, components often require precision welding without defects. 321 stainless steel not only has low welding crack sensitivity but also avoids sensitization in the weld zone, ensuring the consistency and reliability of the overall structure. V. Practical Application Cases In commercial and military aircraft, 321 stainless steel plates are widely used in manufacturing: – Engine exhaust systems (e.g., nozzles, heat shields) – High-temperature pipelines for fuel and hydraulic systems – Rocket engine casings and combustion chamber components – Thermal protection structures for high-altitude reconnaissance aircraft and spacecraft For example, some Boeing and Airbus models use 321 stainless steel in the exhaust pipes of auxiliary power units (APUs); NASA also utilized this material in thermal control systems for early space missions. These successful applications fully validate its reliability under extreme operating conditions. VI. Comparative Advantages Over Other Materials Compared with 304 stainless steel, 321 offers better high-temperature stability; compared with 316 stainless steel, although 316 contains molybdenum (Mo) to enhance pitting corrosion resistance, it is still inferior to 321 in terms of high-temperature oxidation resistance and anti-sensitization. When compared with nickel-based superalloys, 321 has lower costs and easier processability, delivering higher cost-effectiveness in the medium-high temperature range (600–800℃). In summary, 321 stainless steel plates are highly favored in the aerospace field due to their unique titanium-stabilized design, which provides excellent high-temperature stability, intergranular corrosion resistance, superior weldability, and reliable mechanical properties. In modern aviation engineering pursuing lightweight, high reliability, and long service life, 321 stainless steel, with its “combination of rigidity and flexibility,” serves as an important material bridge connecting safety and efficiency. With the development of new material technologies, although composite materials and advanced alloys continue to emerge, 321 stainless steel will still occupy an irreplaceable position in specific high-temperature application scenarios for a long time.