Duplex steel grades S31803 (also known as 2205) and S32205 are highly versatile and widely used types of duplex stainless steel sheets and plates. They belong to the family of stainless steels that have a mixed microstructure of austenite and ferrite, typically in a roughly 50/50 ratio. This combination provides them with enhanced properties compared to standard austenitic or ferritic stainless steels.

Key Characteristics and Properties:
Composition:
S31803 (2205): Typically contains around 22% Chromium (Cr), 5-6% Nickel (Ni), 3% Molybdenum (Mo), and 0.14-0.20% Nitrogen (N).
S32205: This is an enhanced version of S31803 with a slightly higher Chromium content (22-23%), similar Nickel (4.5-6.5%) and Molybdenum (2.5-3.5%) content, and a similar Nitrogen range (0.08-0.20% or 0.14-0.20% depending on the specific standard). The higher Cr and often Mo and N contribute to slightly improved corrosion resistance.
Strength: Duplex steels, including S31803 and S32205, exhibit significantly higher yield and tensile strength compared to common austenitic stainless steels like 304 or 316L. This can allow for thinner gauges in design, leading to weight savings.
Corrosion Resistance: They offer excellent resistance to various forms of corrosion, including:
Pitting and Crevice Corrosion: The presence of chromium, molybdenum, and nitrogen enhances resistance, particularly in chloride-containing environments. Their Pitting Resistance Equivalent Number (PREN = Cr + 3.3Mo + 16N) is generally higher than that of 316L.
Stress Corrosion Cracking (SCC): Duplex steels have superior resistance to chloride-induced SCC compared to austenitic stainless steels.
General Corrosion: They offer good resistance to a wide range of corrosive media.
Weldability: While not as easily weldable as some austenitic grades, S31803 and S32205 can be welded using standard welding processes with appropriate filler metals and procedures to maintain the desired phase balance in the weld and heat-affected zones.
Ductility and Toughness: They offer good ductility and toughness, better than ferritic stainless steels but generally slightly lower than austenitic grades. However, they typically have excellent notch ductility, even at sub-zero temperatures.
Thermal Properties: Duplex steels have lower thermal expansion and higher thermal conductivity compared to austenitic stainless steels.
Magnetic Properties: Unlike austenitic stainless steels, duplex steels like S31803 and S32205 are magnetic due to their ferritic phase. This can be a useful property for material identification.