The Development and Application of High-Performance Ultra-High Strength Stainless Steel Subject to Marine Environment

An alloy chemical composition of a new ultra-high strength stainless has been successfully designed through strengthening mechanisms of carbide and intermetallic compounds. The forging round bar with diameter of 200 mm has been manufactured by means of ultra-high purity smelting and the whole process technologies of micro-unit refinement and phase change control. It was revealed that the developed steel assumes tensile strength of 1960MPa, elongation of 13.5%, fracture toughness KIC greater than 90MPa·m1/2, and KISCC greater 60MPa·m1/2. Based on the microstructural observation and phase identification, it was found that the M2C and the Laves phase were precipitated in the martensitic laths and a small amount of austenite phase was retained in between the Martensitic lath interfaces, which were related to the improved strength and toughness of the developed steel. Furthermore, it was indicated that the steel also presents high fatigue properties and good high-temperature mechanical properties. The corrosion resistance of the steel is equivalent to that of 15-5PH stainless steel but much better than that of the Aermet100 steel under the condition of the marine atmosphere and sea water immersion. This developed steel can be applied in marine corrosive environment without the surface protection and thus can save the expensive maintenance costs and avoid environmental pollution. Based on the promising properties, it was concluded that the developed steel has wide application prospects in the fields of aviation, aerospace, ships, advanced machinery, and advanced machinery manufacturing and other high-tech.