Super duplex grades introduction
Duplex Stainless Steel (DSS) refers to stainless steel with 50% of ferrite and 50% of austenite, and generally requires a minimum content of 30% less one. In the case of lower C, Cr content of 18% to 28%, Ni content of 3% to 10%. Some steel also contains Mo, Cu, Nb, Ti, N and other alloying elements.
Duplex stainless steel has the following performance characteristics
1. Molybdenum duplex stainless steel has good resistance to chloride stress corrosion under low stress. Generally 18-8 austenitic stainless steel is susceptible to stress corrosion cracking in neutral chloride solutions above 60 ° C and equipment such as heat exchangers and evaporators made from this type of stainless steel in trace chlorides and hydrogen sulfide industrial media There is a tendency to produce stress corrosion cracking, while duplex stainless steel has good resistance.
2. Molybdenum duplex stainless steel has good corrosion resistance. The same PIT (PRE = Cr% + 3.3Mo% + 16N%), the duplex stainless steel and austenitic stainless steel have similar critical pitting potential. Durability stainless steel have equal corrosion resistance with austenitic stainless steel and AISI 316L. corrosion resistance propertiy of nitrogen-containing high chromium duplex stainless steel exceeds AISI 316L
3. Has good corrosion resistance and wear and tear corrosion. In some corrosive media conditions, suitable for the pumps, valves and other power equipment.
4. Good mechanical properties. High strength and fatigue strength, yield strength is 2 times of 18-8 type austenitic stainless steel. Elongation rate of solid solution reached 25%, toughness AK (V-notch) is more than 100J
5. Good solderability, small hot cracking tendency, usually don’t need preheating before welding, and don’t need heat treatment after welding, can weld with 18-8 type austenitic stainless steel or carbon steel.
6. Duplex stainless steels with low Cr (18% Cr) hot working temperature range are wider than 18-8 austenitic stainless steels and have low resistance. They can be directly rolled to produce billets without forging. Duplex stainless steels with high chromium (25% Cr) are slightly more difficult to hot-work than austenitic stainless steels and can produce boards, tubes and wires.
7. hardening effect during cold working will be bigger then 18-8 type austenitic stainless steel, in the early deformation of the tube or board, need to exert greater stress to make deformation
8. Compared with austenitic stainless steel, the thermal conductivity is large, the coefficient of linear expansion is small, suitable for lining the equipment and the production of composite board. Also suitable for the production of heat exchanger die, heat transfer efficiency is higher than austenitic stainless steel
9. There are still a variety of brittle tendencies of high chromium ferritic stainless steels and should not be used at working conditions above 300 ° C. the lower chromium content of Duplex stainless steel, the smaller harm of σ and other brittle phase.