Effect of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by narrow gap hot wire gas tungsten arc welding process

Hot wire Gas Tungsten Arc Welding (GTAW) process is selected for the fabrication of thick section modified 9Cr 1Mo steel components of Steam Generators (SGs) for 500MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, India. During the welding procedure qualification for fabrication of SGs, the 30 mm and 62 mm thick modified 9Cr 1Mo steel welds were subjected to chemical analysis, visual examination, liquid penetrant examination, radiography examination, micro-hardness tests, longitudinal and transverse tensile tests (at ambient temperature and 525 degrees C), bend tests, drop weight tests and impact tests (at 0 degrees C and +18 degrees C). Literature reveals both positive and negative view on the welding of thick-section steel components. Limited information is available in the open literature on the effect of thickness on material properties of modified 9Cr 1Mo steel welds made by the hot wire GTAW method. In view of the above, authors attempted to systematically investigate the influence of thickness on the mechanical properties of modified 9Cr 1Mo steel welds made by the hot wire GTAW process. In this paper, the chemical compositions, hardness, tensile strength, bending strength and impact properties of 30 mm and 62 mm thick welds produced by narrow gap hot wire GTAW process are characterized and compared. It is found that the mechanical properties of 30 mm and 62 mm thick welds are comparable except the impact properties at 0 degrees C. The impact strength at 0 degrees C for a 62 mm thick weld was found inferior in comparison with a 30 mm thick weld.