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The Study of Corrosion and Protection of the Mooring Chain Steel Used in the Sea

Author: ZhuCaiJin
Tutor: XieChunSheng
School: Jiangsu University of Science and Technology
Course: Materials Processing Engineering
Keywords: 22MnCrNiMo steel microstructure mechanical property corrosion resistance coating protection
CLC: TG174.4
Type: Master's thesis
Year: 2011
Downloads: 183
Quote: 0
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Abstract


Marine engineering mooring chain is necessary used in exploitation of marine resources and marine transportation. It is used in bad condition which not only for a long time to withstand enormous storm waves shock, but also to withstand erosion of sea water. The life-span of offshore engineering mooring chain is more than 20 years. So the mooring chain need has good integrated mechanical and chemical properties. The research has important engineering significance in forecasting and evaluating the corrosion resistance and protective measures of the 22MnCrNiMo mooring chain. It also has important engineering significance in keep the marine engineering equipment which fixed by the mooring chain safe.According to actual conditions, heat treatment process was chosen as“hold on 910°C ~950°C for 30min rapid heating and water quenching hold on 610°C~670°C for 30min~60min tempering”.Quenching and tempering medium is water. The microstructures and fracture appearance of samples are studied by optical microscopy and scanning electron microscopy. And the mechanical properties are conducted on Rockwell hardness tester, universal testing machine and impact testing machine. At the same time, the effect of heat treatment system on corrosion resistance is studied in this paper.The results show that the microstructure of the rolled steel 22MnCrNiMo includes martensite,bainites, and a small amount of bulk ferrites. After heat treatment, the microstructure of the steel is tempered sorbite. At the same tempering time and tempering temperature, as the quenching temperature rise, the corrosion resistance of the samples decreased. But under quenched at 930°C for 30 minutes, the best comprehensive performance can been obtained. At the same quenching temperature, as the tempering time extended and tempering temperature rise, the strength of the sample decreased, plasticity, impact toughness and corrosion resistance increased. All of the samples which by heat treatment are up to 5 of corrosion resistant metallic materials grade, and belong corrosion resistant materials. Even after quenching in910°C, 930°C and tempering in 630°C, 650°C hold on 45min, the corrosion rate of the samples are up to 4 of corrosion resistant metallic materials grade.The result of the salt spray accelerated corrosion test is the same as the results of polarization curves. Compared with coal tar epoxy paint and chlorinated rubber anticorrosive paint, the coal tar pitch paint has better property of corrosion resistance. The corrosion of samples is serious. The corrosion resistance property of the sample which is by heat treatment is better than the other state. The part of the weld has lower corrosion resistance property than other parts of the mooring chain. The coating can protect the sample. The surface of the sample which has coating is dotted with a number of discrete corrosion pit and groove strip.Comparison of mechanical properties and corrosion resistance, we finally selected heat treatment of double quenching in 930°C for 30 min and tempering in 630°C for 45 min. It provides the theoretical and experimental basis about corrosion protection and heat treatment process for the new 22MnCrNiMo steel which is used in the marine engineering.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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