Characteristics of premature creep failure in over-tempered base metal of grade 91 steel weldment. (August 2021)

• Record Type: Journal Article
• Authors: Wang, Yiyu; Zhang, Wei; Wang, Yanli; Feng, Zhili
• Is Part Of: International journal of pressure vessels and piping. Volume 192(2021)
• Publication Date: 2021-08
• Subjects: Grade 91 steel -- Creep strength -- Heat affected zone -- Over-tempered base metal -- Microstructure -- Digital image correlation -- Type IV Cracking; Pressure vessels -- Periodicals; Pipe -- Periodicals; Récipients sous pression -- Périodiques; Tuyaux -- Périodiques; Pipe; Pressure vessels; Periodicals; 681.76041
• DOI: 10.1016/j.ijpvp.2021.104396
• Languages: English
• ISSNs: 0308-0161

Abstract

Abstract: In this work, characteristics of premature creep failure in the over-tempered base metal (OT-BM) of a Grade 91 steel weldment are investigated with specially designed creep experiments and advanced microstructure characterization. In situ digital image correlation (DIC) strain measurements reveal that local creep strain as high as 100% accumulated in the OT-BM, compared with only 10% nominal strain over the gauge length. The creep strain rate in the OT-BM is identical to that in the intercritical heat-affected zone and fine-grained heat-affected zone at the secondary creep stage and early tertiary stage, but faster at the late tertiary stage. Microstructural analysis shows that highly recovered microstructure in the OT-BM leads to the lowest hardness, the largest grain size, the lowest fraction of coincidence site lattice boundaries, and the lowest localized strain energy. Dislocation creep and transgranular creep fracture are the dominant deformation and fracture mechanisms in the OT-BM under the current creep testing condition of a low temperature (550 °C) and a high stress (215 MPa). Highlights: Nonuniform creep deformation across heterogeneous 9Cr steel weldments was quantified with digital image correlation. Over-tempered base metal deformed fastest with the highest creep strain rate across the weldment. Dislocation creep and transgranular creep fracture are the dominant deformation and fracture mechanisms in the OT-BM.