Graphitization Behaviors of Creep-ruptured 0.3% Carbon Steel at 673 to 773 K

• Published in: ISIJ International 2021/03/15, Vol.61(3), pp.993-1001
• Main Authors: Hatakeyama, Tomotaka, Sawada, Kota, Sekido, Kaoru, Hara, Toru, Kimura, Kazuhiro
• Format: Article
• Language: English
• Subjects: carbon steel; long-term creep; microscopy; phase transformation
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.ISIJINT-2020-575

Graphitization in carbon steels must be prevented because it reduces the amount of carbon in the matrix, which degrades the material performance due to loss in strength. In addition, when graphite particles are aligned, they can cause fracture by their linkage. The safety management standards for carbon steels in high-temperature applications state that graphitization should be considered at 698 K and above. The number of reported cases on graphitization in steels below 698 K is limited, and the mechanism has not yet been well investigated. This paper reports the finding of unprecedented graphitization at 673 K in creep-ruptured carbon steel and an elongated form of graphite that appears after a much shorter time at 673–773 K than other previously reported times. Furthermore, the formation mechanism of this elongated graphite is discussed. Dislocations and inclusions in the vicinity of grain boundaries may facilitate graphitization kinetics at these temperatures.