Seawater Corrosion Resistance Research Of Ship Driving System Components

In China, the main materials of the component A in the driving system in one model of ship are 40 Cr and 2Cr13, which are connected with each other through thread and interference fit. The main materials of the component B is QAl9-4. In the marine environment, the components A and B are easy to be corroded, leading to the decreasing mechanical property of metal materials and the lose efficacy of their threaded connection. Finally, the function of the ship driving system is lost, which will seriously treaten the navigation safety of ships. In order to ensure that the driving system is stable, reliable, and safe during the operation, it is extremely urgent to carry out the seawater corrosion resistance research and the component materials optimization for the driving system.Corrosion prevention and change/preserve of metal materials are a tedious job. Therefore, it is needed to improve the corrosion resistance of the driving system materials to ensure the navigation safety. So far, the commonly used methods to improve corrosion resistance of the material include: material optimation on the premise of maintained mechanical property, coating protection, and electrochemical protection. Considering the structure and function of driving system, it is not suitable to proceed the coating protection nor electrochemical protection. Therefore, material optimation method is chosen in this project. After sufficient investigation and selection, two of the stainless steel materials 0Cr17Ni4Cu4 Nb, KA145 and HDR with better corrosion resistance are chosen to replace the original materials 40 Cr and 2Cr13 in the component A. Furthermore, to ensure that the component B in the original driving system will not be corroded after the component A is optimized by stainless steels, one copper alloy will be selected from two types of copper alloy QAl10-4-4 and ZCu Al10Fe3-4 to replace QAl9-4 in this work.In order to confirm that the designed proposal is scientific and reasonable, and provide data support for the corrosion resistance of the new driving system, this work mainly focuses on(1) the comparison of the seawater corrosion resistance between the original and the replaced materials in the ship driving system,(2) material optimization of the driving system according to the test results, and(3) providing data and theoretical support for the upgrade and design of new driving system.The obtained conclusions are as follows:(1) For the original and replaced materials of the component A, both of the corrosion rate in artificial seawater full immersion experiment and salt fog/wet/dry alternate circulation experiment for 1000 h follows the order of 40Cr>2Cr13>0Cr17Ni4Cu4Nb>KA145>HDR. The result of the alternating-current impedance test shows that the self anti-corrosion property of the materials in the seawater environment follows the order of HDR>KA145>0Cr17Ni4Cu4Nb>2Cr13>40Cr.(2) The Nyquist plot of 40 Cr in low frequency range is different from that of the other 4 stainless steel materials. It is mainly because that the double electrode layer of 40 Cr has a larger dispersion effect than other materials. The former is denoted by constant phase angle element Qct, and the latter is denoted by capacitance Ct.(3) For the original and replaced materials of the component B, the corrosion rate in artificial seawater full immersion experiment for 1000 h follows the order of QAl9-4>ZCu Al10Fe3>QAl10-4-4, and that in salt fog/wet/dry alternate circulation experiment for 1000 h follows the order of QAl9-4>QAl10-4-4>ZCu Al10Fe3. The results indicate that the anti-corrosion property of QAl10-4-4 in full-immersion seawater is the best, the tidal range anti-corrosion property of ZCu Al10Fe3 is the best, and the anti-corrosion property of QAl9-4 is the worst.(4) The potentials of 0Cr17Ni4Cu4 Nb, KA145, HDR, QAl10-4-4, and ZCu Al10Fe3 increased first and then kept stable with the extension of test time. The potentials of QAl9-4 and 40 Cr decreased first and then kept stable with the extension of test time. The potentials of 2Cr13 increased first and then decreased and finally kept stable with the extension of test time. The corrosion potentials of eight materials in the driving system in the artificial seawater follows the order of HDR>KA145>0Cr17Ni4Cu4Nb>QAl10-4-4>ZCu Al10Fe3>QAl9-4>2Cr13>40Cr.(5) The optimization proposal for ship driving system is as follows: The original materials 40 Cr and 2Cr13 in the component A are replaced by KA145 and HDR. The original material QAl9-4 in the component B is replaced by ZCu Al10Fe3. The results of the above-mentioned actual working condition simulation test indicate that the proposed material optimization proposal for driving system is reasonable and practicable.