Plasma and Fusion Research

Volume 11, 2405039 (2016)

Regular Articles

Effect of HIP Temperature and Cooling Rate on Microstructure and Hardness of Joints for ODS-RAFM Steels and JLF-1 Steel
Haiying FU, Takuya NAGASAKA, Takeo MUROGA, Akihiko KIMURA1) and Shigeharu UKAI2)
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan
1)
Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan
2)
Graduate School of Engineering, Hokkaido University, N13, W18, Kita-ku, Sapporo 060-8628, Japan
(Received 30 November 2015 / Accepted 24 February 2016 / Published 15 April 2016)

Abstract

Dissimilar-metal joints between ODS-RAFM (oxide-dispersion-strengthened reduced activation ferritic/ martensitic) steels and JLF-1 steel were fabricated by hot isostatic pressing (HIP) at 1000 - 1100 °C with a cooling rate of 5 °C/min. After the HIP, it was always quenched martensite for JLF-1 steel. However, coarse precipitates were found in 9Cr-ODS. Additional annealing experiments to simulate HIP conditions were conducted for 9Cr-ODS with cooling rate ranged from 0.5 to 36 °C/min at 800 - 1100 °C. The results showed that, to form quenched martensite for 9Cr-ODS, the HIP temperature should be above 1000 °C with cooling rate no less than 25 °C/min. When the cooling rate is increased to 36 °C/min, the microstructure of 9Cr-ODS is quenched martensite with precipitate size similar as that before HIP. If the limitation of precipitate size in 9Cr-ODS is 0.2 μm, HIP temperature above 1050 °C with cooling rate no less than 30 °C/min is needed. In this case, post-weld heat treatment (PWHT) with only tempering is necessary to recover the microstructure of 9Cr-ODS to tempered martensite. For 12Cr-ODS, the HIP temperature and cooling rate has no effect on hardness and precipitate size. PWHT is not necessary for the single-metal joint of 12Cr-ODS from the view point of precipitation control. However, for the dissimilar-metal joints between ODS-RAFM steels and JLF-1 steel, the PWHT condition should be comprehensively determined by considering microstructural evolution of each part in the joints after HIP.

Keywords

ODS-RAFM, hot isostatic pressing, coarse precipitate, cooling rate, post-weld heat treatment

DOI: 10.1585/pfr.11.2405039

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