1989 Volume 7 Issue 3 Pages 385-390
The weld deposits of 17.5Cr-16.5Ni-6.5Mn-2.3Mo system was previously investigated using SMA welding process for the welding construction of superconducting coil container which was used at cryogenic temperature. The combination of yield strength and fracture toughness was not sufficiently attained by the SMA weld deposits. The fracture toughness was about 150MPa√m when the yield strength was controlled to be 1000 MPa for the weld deposits at 4.2K. It is very desirable to increase the fracture toughness of the weld deposits without decrease of the yield strength for the application to the container.
The fracture surface of the JIC test specimen of the weld deposit entirely consisted of dimples. So, the crack extension of the weld deposits is thought to be dominated by the nucleation and growth of the void in the vicinity of'the crack tip. In order to increase the fracture toughness, it should be effective to decrease the distribution density of inclusions in the weld deposits. Then, TIG and MIG Welding processes were applied to vary the distribution of inclusions in the weld deposits which have the same chemical composition as above mensioned and have the yield strength of about 1000 MPa.
The relationship between the fracture toughness and inclusion spacing in the weld deposits was investigated. The results of the investigations are summerised as follows: (1)Fracture toughness increases with the increase in the inclusion spacing in the weld deposits, (2)The inclusion spacing in the weld deposits was longest for the TIG process, medium for the MIG process and shortest for the SMA process.