Effect of Application of Short and Long Holds on Fatigue Life of Modified 9Cr-1Mo Steel Weld Joint

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Vol. 45; no. 3; pp. 1390 - 1400
• Main Authors: Shankar, Vani, Mariappan, K., Sandhya, R., Mathew, M. D., Jayakumar, T.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.03.2014; Springer; Springer Nature B.V
• Subjects: Applied sciences; Base metal; Characterization and Evaluation of Materials; Chemistry and Materials Science; Chromium molybdenum steels; Coarsening; Damage; Exact sciences and technology; Fatigue; Heat affected zone; Heat treatment; Joining, thermal cutting: metallurgical aspects; Materials Science; Mechanical properties; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metallic Materials; Metallurgy; Metals. Metallurgy; Microstructure; Nanotechnology; Steel; Steels; Structural Materials; Surfaces and Interfaces; Thin Films; Welded joints; Welding; Fatigue Life; Crack Distribution; Stress Relaxation; Cyclic Stress Response; Tensile Hold; Mechanical properties; Fatigue life; Fatigue; Welding; Welded joint; Application
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-013-2108-x

Modified 9Cr-1Mo steel is a heat-treatable steel and hence the microstructure is temperature sensitive. During welding, the weld joint (WJ) is exposed to various temperatures resulting in a complex heterogeneous microstructure across the weld joint, such as the weld metal, heat-affected zone (HAZ) (consisting of coarse-grained HAZ, fine-grained HAZ, and intercritical HAZ), and the unaffected base metal of varying mechanical properties. The overall creep–fatigue interaction (CFI) response of the WJ is hence due to a complex interplay between various factors such as surface oxides and stress relaxation (SR) occurring in each microstructural zone. It has been demonstrated that SR occurring during application of hold in a CFI cycle is an important parameter that controls fatigue life. Creep–fatigue damage in a cavitation-resistant material such as modified 9Cr-1Mo steel base metal is accommodated in the form of microstructural degradation. However, due to the complex heterogeneous microstructure across the weld joint, SR will be different in different microstructural zones. Hence, the damage is accommodated in the form of preferential coarsening of the substructure, cavity formation around the coarsened carbides, and new surface formation such as cracks in the soft heat-affected zone.