Duplex stainless steel in the development of three generations, has: 1 generation represented by the mid – 1960-3 re60 steel, the steel has problems of welding heat affected zone; After 2 to the 1970 s, the development has the characteristics of ultra-low carbon and nitrogen, on behalf of the brand in 2205, pitting equivalent index PRE 32-39; 3 on behalf of the late 1980 s the development of ultra low carbon, high molybdenum, high nitrogen content of super duplex stainless steel, on behalf of the grades 2507, 32750, etc., the PRE value is greater than 40.
In recent years as people constantly improve the requirements and the development of the duplex stainless steel, higher strength, better corrosion resistance performance of a new generation of duplex stainless steel material, super duplex stainless steel arises at the historic moment, represented by 32707, 33207, 2707, hd.
Its performance characteristics are
1, chemical composition design and organizational characteristics
High alloying is super duplex stainless steel design train of thought, in further improving chromium, molybdenum and nitrogen content in steel to increase strength and corrosion resistance at the same time, adjust the reasonable ratio of other elements, close to 50 of the super duplex stainless steel PRE values.
2) phase ratio control
Super duplex stainless steel in low temperature solid solution, have a certain amount of harmful phase in the sigma phase, the phase at above 1100 ℃ can be basic solution, the ferrite and austenite phase about each half, the other is preferred in order to prevent the weaker phase corrosion, steel each of the two phase austenite and ferrite of pitting corrosion resistance index (PRE) design, in 32707, for example, two phase PRE value flat, on average, less than 1.
2, corrosion resistance
32707 and 33207, pitting the theory of equivalent to about 50, both critical pitting temperature higher than 90 ℃, and 32750 is about 80 ℃. Austenitic stainless steel corrosion in the standard fast environment, the use of special super duplex stainless steel and even can replace high alloy austenitic stainless steel and nickel base alloy.
3, the mechanical properties of
Super duplex stainless steel yield strength is with its pitting corrosion resistance of austenitic stainless steel 2 times. Heat exchanger pipe 32707 material yield strength of 800 mpa, general tensile strength of 1000 mpa, quenching heat treatment condition of elongation is more than 25%. And 33207 has higher tensile strength, the quenching heat treatment state, the tensile strength is higher than the super dual phase steel 32750 20%. In addition, the 32707 has the very good impact toughness, its brittle transition temperature is below – 50 ℃.