Details

Autor(en) / Beteiligte

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

Titel

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

Ist Teil von

• Materials science & engineering. A, Structural materials : properties, microstructure and processing, 2024-06, Vol.903, p.146669, Article 146669

Ort / Verlag

Elsevier B.V

Erscheinungsjahr

2024

Quelle

Elsevier ScienceDirect Journals

Beschreibungen/Notizen

• 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. [Display omitted] •The creep rupture strength of the high-impurity-containing steel was inferior to that of the low-impurity-containing steel. “Impurity” refers to the three elements: Sb, As, and Sn.•In the as-welded joint, higher amount of M23C6 carbide remained as undissolved particles at fine-grained heat affected zone (FGHAZ) in the high-impurity-containing steel.•It was suggested that M23C6 dissolution at FGHAZ during welding was likely suppressed by impurities.•The higher the amount of remaining undissolved M23C6, the lesser the pinning force due to the reduction of M23C6 re-precipitation on the grain boundaries during post-weld-heat-treatment.•The degradation in the creep rupture strength by impurities was attributed to the accelerated progression of recovery process at FGHAZ during creep and subsequent creep void formation.