Super duplex stainless steel refers to the duplex stainless steel with PREN > 40, 25% Cr and high molybdenum (> 3.5%) and high nitrogen (0.22% ～ 0.30%).
Super duplex stainless steel(SDSS) refers to the duplex stainless steel with prEN > 40, 25% Cr and high molybdenum (> 3.5%) and high nitrogen (0.22% ～ 0.30%). The main brands are UNS S32550 (ur52n +), S32750 (SAF 2507) and S32760 (zeron 100).
They were developed by cli in France, Sandvik in Sweden and mater + Platt in England.
The composition of these three steels is similar.
SAF 2507 super stainless steel
SAF 2507 (UNS S32750) duplex stainless steel has strong strength and corrosion resistance, which is mainly used in chemical processing, petrochemical, and subsea equipment.
2507 duplex steel has strong chloride corrosion resistance, high thermal conductivity, and low coefficient of thermal expansion. It has high resistance to pitting corrosion, crack corrosion, and general corrosion.
Its impact strength is also very high. SAF 2507 alloy is not suitable to be used at temperatures higher than 570 ℃. In such an environment for a long time, its toughness will be reduced.
Super duplex stainless steel has the same corrosion resistance as s31254 and 254SMO. The PREN of 2507 stainless steel is 43, which has very high corrosion resistance.
Compared with 300 series stainless steel, super duplex stainless steel is also more cost-effective. Its yield strength is twice that of 300 series stainless steel. Under the condition of bearing the same weight, thinner steel can be used.
Super duplex stainless steel can reduce the cost of raw materials and reduce the cost
Because of the high nitrogen content, the super duplex stainless steel has twice the yield strength and tensile strength than the ordinary stainless steel, so the wear resistance of the material is significantly higher than that of the ordinary material. In some pipelines or equipment with corrosion performance, super duplex stainless steel has a longer service life.
In the development of duplex stainless steel and super duplex stainless steel, some physical and metallurgical problems have attracted people’s attention.
① The content of Cr% + Mo% in steel should be more than or equal to 21%. It is used to prevent the property degradation of steel caused by martensitic transformation caused by cold working. The effect of cold deformation on martensite formation and corrosion resistance of modified 18-5 duplex stainless steel has been studied in China. The results show that the stress corrosion resistance and pitting corrosion resistance of the steel decrease with the increase of martensite content.
② In order to increase the corrosion resistance of duplex stainless steel, it is necessary to take measures to prevent the deterioration of plasticity, toughness, hot workability, and welding and corrosion resistance of duplex stainless steel caused by CR% + Mo% ≥ 35%.
③Nitrogen is a very useful and important element. But, the addition of a large amount of nitrogen will cause the formation of chromium nitride and precipitate along the grain boundary, which will cause corrosion damage such as intergranular corrosion and the decrease of toughness. It caused a large amount of waste products will be caused due to the escape of nitrogen during steel solidification.
④ If a large amount of manganese is added to improve the solid solubility of nitrogen in steel, the harm of manganese sulfide formation should also be evaluated.