Differences between duplex steel grades

I came into contact with it last year – the double-phase steel 2205, 00Cr22Ni5Mo3N. After developing the 3RE60 double-phase stainless steel, Sweden went on to develop the SAF2205 steel for use in pipelines in the oil and gas industry; this steel is covered by standards such as ASTM A789, A790, A240, and A276. Its equivalent American grade is UNS S31803； After the 1980s, various countries successively developed similar steel grades and incorporated them into standards. In Germany, it is W-Nr.1.4462 and DIN X2Gr-NiMoN2253; in France, it is Z2CND-22-05-03; in Sweden, it is SS2377; and in the UK, it is BS318S13, among others. SAF2205 steel has been used in oil and gas pipelines since the late 1970s; it was the first duplex stainless steel to be employed in this application. To improve phase balance and prevent the formation of harmful phases, UNS S32205 was developed from UNS S31803 in recent years. The latter has a narrower range of allowable compositions. ASTM has established testing standards (ASTM A923-98) for detecting harmful intermetallic phases in these two types of steel. In the 1980s, China also began developing the 00Cr22Ni5Mo3N duplex stainless steel, which is similar to SAF2205 steel. Its resistance to stress corrosion in neutral chloride solutions and H2S is superior to that of 304L and 316L austenitic stainless steels as well as 18-5Mo-type duplex stainless steels. It can be processed and shaped through cold and hot methods, and it has good weldability. This steel is suitable as a structural material, and it is currently the most widely used grade among duplex stainless steels worldwide.

Duplex stainless steel possesses high mechanical strength and thermal conductivity, as well as a low coefficient of thermal expansion. Its corrosion resistance is also superior to that of austenitic stainless steels, and it is widely used in the petrochemical industry for manufacturing, storage, and transportation equipment, as well as in rotating equipment that requires corrosion and fatigue resistance. Experimental results show that increasing the strain rate raises the tensile strength and yield strength of duplex steel, while decreasing its elongation. In terms of fatigue testing, duplex steel initially shows rapid hardening followed by a stable cycle of softening; its fatigue life is better than that of SAF 2507. The fatigue strength of both materials decreases after welding. The average stress variation is more pronounced at low strain amplitudes. In the welded joint, the main crack originates in the base metal area, and the crack propagation follows a path that passes through the pearlitic phase. In terms of corrosion resistance, SAF 2507 performs best as the material, followed by SAF 2205 ； Regarding welded joints, SAF 2205 welded joints are more sensitive in an environment of strong acid HCl, while SAF 2507 welded joints have weaker resistance to chloride ions in seawater, resulting in the formation of corrosion pits; these pit corruptions start by rapidly spreading through the ferrite phase before eventually penetrating the austenite phase.

What is the difference between 2207 and 2205?

Description: UNS No., Maximum or Typical values: Cr 1, Ni 1, Mo 1, N 1 & Others. PREN value: 3; TS KSI value: 4; 4YS KSI value: 4. Materials: 2205, S31803; 0.321–234.5–6.5; 2.5–3.5; 0.08–0.2% N; 34.39% for 9065. Material: 2507; S32750: 0.0325, 74.3% N; 4311680. PREN value: The theoretically calculated pitting resistance index = %Cr + 3.3%Mo + 16%N. Yield/tensile strength unit: 1 KSI = 6.9 MPa = 6.9 N/mm2. In general, 2507 has better corrosion resistance and mechanical properties than 2205, and its price is also higher. 2205 is more widely used; there are not many companies in China that have experience in using 2507 to manufacture equipment. Special attention should be paid to the qualifications and experience of welders.

In simple terms, S32750 is a super duplex stainless steel, and its corrosion resistance is better than that of the ordinary duplex stainless steel S31803.