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Why Is Stainless Steel Not Rusty?
Jun 14, 2018

The corrosion resistance of stainless steel is generally increased with the increase of chromium content. When the chromium content in the steel is Cr more than 12%, a very thin layer of steel will be formed on the surface of the steel, but the very dense oxide film (commonly known as passivation film) will not be oxidized or corroded. Therefore, the stainless steel has excellent corrosion resistance.

1. Molybdenum containing duplex stainless steel has good chloride stress corrosion resistance under low stress. Normal 18-8 type austenitic stainless steel is prone to stress corrosion cracking in the neutral chloride solution above 60 C. In the micro chloride and hydrogen sulfide industrial medium, the heat exchanger, evaporator and other equipment made of this kind of stainless steel have the tendency to produce stress corrosion fracture, but the dual phase stainless steel has good resistance. Power。

2. Molybdenum containing duplex stainless steel has good pitting resistance. The critical pitting potential of duplex stainless steel and austenitic stainless steel is similar to that of austenitic stainless steel when the same hole resistance equivalent value (PRE=Cr%+3.3Mo%+16N%) is obtained. The pitting corrosion resistance of duplex stainless steel and austenitic stainless steel is similar to that of AISI 316L. The corrosion resistance and crevice corrosion properties of 25%Cr containing, especially nitrogen containing high chromium duplex stainless steel, exceed AISI 316L.

3. It has good corrosion fatigue and wear corrosion resistance. Under certain corrosive medium conditions, it is suitable for making power equipment such as pumps and valves.

4. The comprehensive mechanical properties are good. It has higher strength and fatigue strength and yield strength is 2 times of that of type 18-8 austenitic stainless steel. The elongation of solid solution reaches 25%, and the toughness value AK (V notch) is above 100J.

5, good weldability, small hot cracking tendency, no preheating before general welding, no heat treatment after welding, and welding with type 18-8 austenitic stainless steel or carbon steel.

6. The hot working temperature of the dual phase stainless steel with low chromium (18%Cr) is wider than that of type 18-8 austenitic stainless steel, and the resistance is small, and the steel plate can be produced by direct rolling without forging. Duplex stainless steel containing high chromium (25%Cr) is slightly more difficult to heat processing than austenitic stainless steel, and can produce products such as plates, pipes and wires.

7, cold working has greater work hardening effect than that of type 18-8 austenitic stainless steel. In the initial stage of deformation, the tube and plate need to exert greater stress to deform.


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