Failure Analysis of Stainless Steel Pitting Corrosion
The corrosion resistance of stainless steel depends on the passivation film formed on its surface. Once the passivation film is destroyed and lacks self-passivation conditions and capabilities, corrosion will occur. Pitting corrosion is the concentration of corrosion at certain specific points to form corrosion. Small holes. Pitting corrosion of stainless steel usually occurs in a specific medium. When halogen ions and dissolved oxygen are present in the medium, especially in aqueous solutions containing chloride ions, pitting corrosion is prone to occur, and pitting pits are formed on the surface.
Judging the failure of pitting corrosion can be analyzed from a macroscopic perspective. Corrosion pores are distributed on the surface, and these pores develop deep, while most of the surface remains blunt. Observed by the metallographic section, the shape of pitting pits can be observed in the polished state.
Explanation: The pitting corrosion pit profile morphology of 0Cr18Ni9 stainless steel after being soaked in 0.5%K3Fe(CN)6 and 4%NaCl solution for 1h at room temperature is butterfly-shaped. The depth of the pitting pit is 0.11mm.
Description: The profile morphology of the pitting corrosion pit of 0Cr18Ni9 stainless steel after being soaked in 10%FeCl3·6H2O solution for 6h at room temperature. The diameter of the pitting hole is about 0.5mm.
Explanation: After 1Cr17Mn9Ni4Mo3Cu2N duplex stainless steel is immersed in 10%FeCl3·6H2O solution for 47h at room temperature, the profile morphology of closed pitting pits produced, the corrosion pits extend in the depth direction, about 2.8mm deep.
Explanation: In Figure 4, the sample in the same field of view was etched with the composite reagent to corrode the pit and the microstructure near the pit. It can be seen that the front end of the pitting pit is preferentially corroded along with the band structure. The microstructure is ferrite distributed on the austenite matrix in a fibrous form in the rolling direction.
Explanation: The pitting pit morphology of 1Cr13 stainless steel after being soaked in 10%FeCl2·6H2O solution for 4h at room temperature is in a closed-form. The diameter of the black corrosion pit is 1mm.
Explanation: The profile morphology of the pitting corrosion pits of 1Cr17Mn9Ni4Mo3Cu2N duplex stainless steel after being immersed in a 10%FeCl2·6H2O solution for 4h at room temperature. The diameter of the large black corrosion pits is about 1 mm.
Description: The steam turbine blades of a geothermal power station made of 2Cr13 stainless steel will cause pitting corrosion pits due to the corrosion of the surrounding environment after using them for a period of time. The figure shows the cross-sectional morphology of the pitting pit. The diameter of the black hole is about 0.5mm.