Microstructure evolution in Alloy 709 at 550 and 650 °C

Alloy 709, a type of 20Cr-25Ni austenitic stainless steel is studied after thermal aging at 550°C and 650°C. The microstructure is characterized using variety of techniques. The alloy shows excellent thermal stability at its working temperature 550°C, while its microstructure evolves rapidly at 650°C with complex precipitation behaviors. NbX particles are of large amount in as-received material but partially dissolve during thermal aging, showing less stability compared to M23C6 at 650°C. A type of M6C’s variant is found after long-term aging and strongly correlated with M23C6, which could either be the result of a possible transition from M23C6 to M6C, or the dissolution of Nb(C, N). Small amount of Z phase are found to precipitate densely on dislocations and modify the dislocation structure after 3000 hours aging at 650◦C. The results are in good agreement with those of NF709 and further support the idea that the η structure can be stabilized by nitrogen.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Nuclear, Plasma, Radiolgc Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2018

Author dc:creator

• Yan, Huan

Contributors dc:contributor

• Stubbins, James
• Zhang, Yang

• Austenitic Stainless Steel, Thermal Aging, Alloy 709

Statement dc:rights

• Copyright 2018 Huan Yan

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/101081

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/101081