Open circuit potential of nodular cast iron plunger pump block

As a hydraulic component, plunger pump has the characteristics of precision, high cost and sensitivity to oil level pollution. When the piston pump is working, the hydraulic oil has a certain corrosion effect on the piston pump cylinder body. Therefore, this paper compares the electrochemical test results of three parts of lzqt600-3 ductile iron profile, and studies the open circuit curve, impedance diagram and potentiodynamic polarization curve of different parts to obtain the conclusion that the best corrosion resistance part can be obtained.

As shown in the figure, the corrosion potential and time curve of lzqt600-3 ductile iron profile obtained after immersion in 3.5% NaCl solution for 3600 s, that is, the relationship between natural corrosion potential and time, and the steady-state potential of the sample can be obtained. The open circuit potential shows a changing process, that is, the electrode is from unstable state to stable state. It reflects the process of forming protective film on the sample surface and its stability. It can be seen from the figure that the potential of different parts of lzqt600-3 ductile iron profile is in a state of decline at the beginning of the test, and the rate is almost the same, and then the rate decreases slowly, and the three parts basically reach a stable value around 600 s. From the edge to the heart, the steady-state potential decreased gradually, which were -0.66, – 0.67 and -0.68 V, respectively.

Compared with the open circuit potential of lzqt600-3 ductile iron profile, it can be inferred that the corrosion resistance tendency of different parts is: edge > 1 / 2R > center. The reason is that the microstructure in the center is relatively coarse and the diameter of graphite ball is the largest. The number of pearlite and the distance between pearlite lamellae are higher than those in other parts. Therefore, the corrosion liquid is easy to enter into the matrix and have corrosion behavior, so the corrosion resistance is poor.