Duplex Stainless Steels

Duplex stainless steels are accurately termed Duplex austenitic-ferritic stainless steels. This terminology is derived from the approximately equal amounts of ferrites and austenite’s in the metallurgical structure. These steels have high chromium contents (18% to 28%) with low amounts of nickel (4.5% to 8%) and most grades contain molybdenum in the range of 2.5% to 4%.

Duplex steels are commonly referred to as lean duplex, duplex or super duplex in type. Lean duplex is achieved with the substitution of manganese where nickel may have been used and super duplex have chromium levels of 25% or more.

Characteristics of Duplex steels:

• Good weldability and formability.
• Higher tensile and yield strengths compared to standard austenitic and ferritic grades.
• Increased resistance to stress corrosion cracking but do not match that of ferritic grades.
• Small nitrogen addition enhances both strength and pitting resistance.
• Increased level of passivity.

Grade and typical applications:

S31803 – (2205) – Superior corrosion resistance to 316L used in heat exchangers, gas scrubbers, fans, chemical tanks, marine and refinery applications.

S32304 – (2304) – Similar corrosion resistance to 316L with higher yield strength used in marine, mining, construction, food and power industries.

S32750 – (2507) – Extremely high corrosion resistance in severe marine, chloride and acid environments.