The Nickel element also promotes its austenite structure. The acidic conditions are also appropriately resisted. Molybdenum (4%) restricts localized corrosion and helps increase its mechanical properties. This chemical composition of the grade along with other alloying elements, like nitrogen provide exceptional resistance to chloride pitting, chloride stress corrosion cracking, better mechanical and thermal properties. The grade has low coefficient to thermal expansion resulting in a stable weld at the heat affected zone, the base metal thus provides better weldability.
High impact and tensile strength are provided along with high thermal conductivity. The grade can be suitably used for structural and dynamic applications. However, it is not recommended to use the grade at elevated temperatures. Using the grade above 320°C is avoided since it might lose its strength, toughness and corrosion resistance on prolonged exposure. The UTS (ultimate tensile strength) at 20°C is 116 KSI and at elevated temperature of 215°C, the UTS becomes 94 KSI. The impact strength of the alloy is somewhat retained at lower temperatures but it is not recommended for lower cryogenic temperatures.
At room temperature, the impact strength is 162 ft. lbs and at -40°C, the impact strength is 140 ft. lbs. While at very low temperatures like -100°C, the impact strength becomes 30 ft. lbs. The grade has low carbon content (0.03%max), due to which carbide precipitation at the heat affected zone is neglected. Hence, inter-granular corrosion due to carbide precipitation at grain boundaries is strongly avoided. Due to the higher strength of the grade, lighter sections of the grade having the same strength and design are often used in replacement of nickel grade alloys to achieve lighter weight products.
Hence, cost of fabrication and machining is also reduced. Duplex SS 2507 is almost 10% lighter than grade 316 and also has a greater life cycle. The grade can be suitably hot worked and cold worked. Hot working can be done around 1020-1230°C, followed by careful solution annealing at 1050°C. Since the grade has very high strength, large forces are required to cold deform the grade, spring back allowances could be required to complete the process. Intermediate solution anneals would be required when 10% cold deformation takes place.
