Super duplex stainless steel refers to duplex steel with PREN>40, containing 25% Cr and high molybdenum (>3.5%), high nitrogen (0.22%~0.30%), the main grades are UNS S32550 (UR52N+), S32750 (SAF 2507) And S32760 (Zeron 100) were developed by companies such as French CLI, Swedish SANDVIK and British MATER+PLATT.

Their deformed materials came out around 1990 and 1991, and entered the market in recent years. The composition of these three steels is similar, the difference is the content of tungsten and copper.

Since the beginning of 2000, the development of modern duplex stainless steel has shown two major trends:

First, while paying attention to the thermal stability of the structure of the steel, further increase the content of chromium, molybdenum, and nitrogen in the steel to obtain higher strength and better corrosion resistance, to meet the needs of modern industrial development and facilitate The competition between austenitic stainless steels and the emergence of super-duplex stainless steels with PRE values ​​close to 50, such as SAF 2707 HD and SAF 3207 HD.

The second is to turn to the development of economical duplex stainless steel with low nickel content and no precious element molybdenum or only a small amount of molybdenum to reduce the production cost and selling price of duplex stainless steel and improve the hot workability and weldability of duplex stainless steel. This will increase the competitiveness of duplex stainless steel and other types of general-purpose stainless steel, especially 304 and 316 chrome-nickel austenitic stainless steels.

There are already earlier SAF 2304 and AL 2003, LDX2101, Armo Nitronic 19D, ATI 2102, 2201, 2202, LDX2404 and other brands that have only been available since 2000. The mass production and application of economic duplex stainless steel has brought a tremendous impact on the survival and development of the first generation 18Cr type (containing about 3% molybdenum) duplex stainless steel 3RE60.

Which grade is most commonly used?

At present, the main grades of super duplex stainless steel in China are 2507 (S32750) and 2507 (UNS S32750) duplex stainless steel, which has strong strength and corrosion resistance, and is mainly used in chemical processing, petrochemical industry and subsea equipment.

They have strong resistance to chloride corrosion, higher thermal conductivity and lower coefficient of thermal expansion. With higher chromium, molybdenum and nitrogen content, it has high resistance to pitting corrosion, crevice corrosion and general corrosion.

The impact strength is also very high, 2507 alloy is not suitable for use in a temperature environment higher than 570 ℃, long-term exposure to such an environment, its toughness will be reduced.

Applications

Commonly used in special chemical environments such as offshore oil platforms (heat exchanger tubes, water treatment and water supply systems, fire protection systems, sprinkler systems, water stabilization systems), desalination (desalination) equipment (high pressure pipes in Ro equipment, seawater pipes), etc. In the device. Name S32750, SAF2507, F53, national standard 00Cr25Ni7Mo4N.

Application areas: oil and gas industry equipment; offshore platforms, heat exchangers, underwater equipment, fire fighting equipment; chemical processing industry, utensils and pipeline industry; desalination plants, submarine pipelines; mechanical components (high-strength, corrosion-resistant components), Energy industry FGD system, industrial scrubbing system, absorption tower, etc.