Effect of cooling temperature on the microstructure and corrosion behavior of X80 pipeline steel

• Published in: International journal of minerals, metallurgy and materials metallurgy and materials, 2020-03, Vol.27 (3), p.347-353
• Main Authors: Ma, Jing, Feng, Fan, Yu, Bai-qing, Chen, Hai-feng, Fan, Li-feng
• Format: Article
• Language: English
• Subjects: Bainite; Ceramics; Characterization and Evaluation of Materials; Composites; Cooling; Cooling effects; Corrosion; Corrosion and Coatings; Corrosion cell; Corrosion effects; Corrosion resistance; Corrosion resistant steels; Dual phase steels; Ductility; Ferrite; Glass; Grain boundaries; Grain size; High strength low alloy steels; Martensite; Materials Science; Mechanical properties; Metallic Materials; Microstructure; Natural Materials; Seawater; Steel; Structural steels; Surfaces and Interfaces; Temperature; Thin Films; Tribology
• ISSN: 1674-4799; 1869-103X
• DOI: 10.1007/s12613-019-1882-x

Dual-phase accelerated cooling (DPAC) was applied to X80 pipeline steel to obtain its microstructure with different amounts of bainite and ferrite. The microstructure, hardness, and polarization behaviors of the steel, cooled to different temperatures, were investigated. Results showed that, with decreasing cooling temperature, the amount of polygon ferrite (PF) increased while that of acicular ferrite (AF) decreased. The amount of bainite correspondingly decreased, except when cooled to 760°C. Moreover, the grain size of ferrite increased. The corrosion behaviors of different phases were distinct. Martensite/austenite (M/A) islands presented at the grain boundary of the PF phase caused small pits. Numerous micro-corrosion cells were formed in the AF and bainite phases, where micropores were prone to form. X80 pipeline steel cooled to 700°C had the best corrosion resistance in the simulated seawater. The decreased amount of the PF phase reduced the area of cathode, resulting in slight corrosion. About 40vol% of the bainite phase provided strength while the PF phase provided adequate ductility to the X80 steel. It was concluded that the appropriate cooling temperature was 700°C for ideal corrosion resistance and mechanical properties.