Study on microstructure–mechanical integrity of the dissimilar gas tungsten arc weld joint of sDSS 2507/X-70 steels for marine applications

• Published in: Journal of materials science Vol. 58; no. 27; pp. 11392 - 11423
• Main Authors: Maurya, Anup Kumar, Kumar, Naveen, Chhibber, Rahul, Pandey, Chandan
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-07-2023; Springer; Springer Nature B.V
• Subjects: Austenite; Base metal; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crystallography and Scattering Methods; Dissimilar materials; Duplex stainless steels; Elongation; Evolution; Fillers; Gas pipelines; Gas tungsten arc welding; Hardness; Heat affected zone; Heat treating; Impact strength; Integrity; Iron compounds; Materials Science; Mechanical properties; Metals & Corrosion; Microhardness; Microstructure; Natural gas; Optical microscopes; Petroleum pipelines; Polymer Sciences; Residual stress; Risers; Solid Mechanics; Structural steels; Tensile strength; Toughness; Tungsten; Welded joints; Welding; Weldments
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-023-08723-w

The present research focuses on investigating the changes in microstructure–mechanical integrity of the dissimilar joint between X-70 pipeline steel and super duplex stainless steel (sDSS 2507). Gas tungsten arc welding with ER 309L austenitic filler at 0.73 and 1.4 kJ/mm heat inputs was employed. The microstructure was characterized using a scanning electron microscope with energy-dispersive spectroscopy and an optical microscope. The weld joint’s mechanical characteristics and overall integrity were evaluated through microhardness, cross-weld tensile, and impact toughness tests. Oil and gas pipelines and hydrocarbon drilling risers use this type of dissimilar joint. The filler material ER309L solidifies into a ferrite–austenite microstructure with skeletal and lathy ferrites and interdendritic austenite. The study revealed that the weld zone and heat-affected zone (HAZ) microstructure displayed Type II boundaries and macro-segregation for lower heat input (LHI) and higher heat input (HHI) welding conditions. Additionally, three distinct types of HAZs were identified in the X-70 base metal, each associated with a different thermal peak temperature during welding: coarse grain, fine grain, and inter-critical. The hardness values ranged from 190 to 290 Hv
0.5
, with an average of 205 ± 6 Hv
0.5
for LHI and 225 ± 4 Hv
0.5
for HHI weldment. The tensile strength and elongation of the LHI samples were found to be 609.4 MPa and 25.3%, while the HHI samples were 601.7 MPa and 30.8%. The impact toughness was 195 ± 5 J and 185 ± 2 J for the cap and root sections of the LHI weldment, compared to 180 ± 4 J and 200 ± 3 J for the HHI weldment. As a result, the investigation sheds insight into the evolution of welding processes and microstructural evolution in the weld zone and HAZ, variations in mechanical characteristics, and changes in residual stresses for the sDSS 2507/X-70 DWJ.