Effect of impurity elements on the creep rupture strength of Gr. 91 steel welded joints at 650 °C

Katsuhiro Sato; Masatoshi Mitsuhara; Kodai Nagata; Keiji Kubushiro; Kyohei Nomura; Takahiro Kimura; Yoshiki Shioda; Kota Sawada; Kazuhiro Kimura; Hideharu Nakashima

doi:10.1016/j.msea.2024.146669

Journal article Effect of impurity elements on the creep rupture strength of Gr. 91 steel welded joints at 650 °C

; ; ; ; ; ; ;

;

Download file (9.31 MB)
Download as zip (9.22 MB)

Collection

Citation

Katsuhiro Sato, Masatoshi Mitsuhara, Kodai Nagata, Keiji Kubushiro, Kyohei Nomura, Takahiro Kimura, Yoshiki Shioda, Kota Sawada, Kazuhiro Kimura, Hideharu Nakashima. Effect of impurity elements on the creep rupture strength of Gr. 91 steel welded joints at 650 °C. Materials Science and Engineering: A. 2024, 903 (), 146669. https://doi.org/10.1016/j.msea.2024.146669

(BibTeX)

Description:

(abstract)

The upper limits for Sb, As, and Sn in Gr. 91 steel are set by the recent standardized
Gr. 91 Type 2 specification. To clarify how the three impurities impact the
microstructures and creep rupture strength of Gr. 91 welded joints, two types of steel
with varying impurity concentrations were prepared. The first contained high impurity
concentrations (Steel 1), while the other had low impurity concentrations (Steel 2). The
results of the creep tests on the welded joints showed that Steel 1 had lower creep
rupture strength compared to Steel 2, indicating premature failure caused by the
impurities. Comparing the microstructures in the as-welded joints, it was observed that
Steel 1 had more M23C6 particles in the fine-grained heat affected zone (FGHAZ) than
Steel 2. This finding indicates that M23C6 dissolution during the welding process was
hindered in Steel 1. It is believed that M23C6 dissolution was reduced due to the
segregation of impurities at the grain boundaries or the interface between the matrix
and M23C6 particles. Consequently, the microstructure in FGHAZ of Steel 1 showed
lower creep resistance because the pinning force by M23C6 was decreased due to the
reduction of re-precipitation on the grain boundaries during post weld heat treatment.
The degradation in the creep rupture strength due to the impurities was attributed to
the earlier progression of recovery process in FGHAZ during creep, leading to
premature creep void formation.