Indian Welding Journal

Chittaranjan Das ¹, Arun Kumar Bhaduri ², V. Thomas Paul ², S. K. Albert ², M. Vijayalakshmi ², Krishnam Raju ³, B. Ravisankar ⁴

Affiliations
1 Indira Gandhi Centre for Atomic Research, Kalpakkam 60310, IN
2 Indira Gandhi Centre for Atomic Research, IN
3 National Institute of Technology, Tiruchirapalli 62001, IN
4 Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, IN

Abstract

Modified 9Cr-1Mo steel is extensively used for high temperature applications due to its good thermo-physical, weldability, fabricability and high temperature properties. While Type IV cracking is of concern during service of weld joints, toughness of its weldmetal is an important consideration during qualification of weld joints, especially for those made by SMAW process. The weldmetal toughness is significantly influenced by deposition process and sequence, and temperature and duration of PWHT. For a special-purpose mod.9Cr-1Mo steel weldmetal, containing intentional addition of 2.4wt% of nickel and manganese, the A and A transformation temperatures, calculated using ThermoCalc software, was found as 945 and 1065K, respectively. To understand its tempering behavior, the weldmetal was subjected to PWHT at 1013, 1033 and 1053K for different durations. The weldmetal hardness decreased significantly on PWHT at 1013K compared to that at 1033 and 1053K. The weldmetal toughness increased monotonically with PWHT temperature; from 27J for 923K PWHT to 32J and 132J for 973K and 1023K PWHTs, respectively, and then decreased marginally to 113J on PWHT at 1153K. These results suggested formation of fresh martensite during PWHT at 1053K. Bright-field transmission electron microscopic examination revealed formation of lath martensite in the weldmetal, with the lath sizes being finer than those reported in other mod. 9Cr-1Mo steel weldmetal prepared using similar process. Hence, detailed microstructural analyses was carried out to investigate this anomalous variation in mechanical properties, as also to study the effect of temperature and duration of PWHT on the microstructure and toughness of this modified 9Cr-1Mo steel weldmetal.

Full Text

     

C. Sudha ¹, T. N. Prasanthi ¹, S. Saroja ¹, M. Vijayalakshmi ¹

Affiliations
1 Physical Metallurgy Division, Metallurgy and Materials Group, Indira Gandhi Center for Atomic Research, Kalpakkam-603 102, Tamilnadu, IN

Abstract

Explosive welding process was used for joining Ti-5Ta-1.8Nb alloy to 304L austenitic stainless steel to avoid the formation of intermetallic phases at the interface which otherwise form in fusion welding processes. Both X-ray diffraction and electron microprobe based analysis showed the absence of intermetallic phases at the weld interface within their detection limits. Strain induced phase transformation due to the deformation induced by explosive welding was observed in both the base materials. The 'as received' explosive joints were further heat treated at 873 and 1073 K for durations in the range of 1 to 20 h to select appropriate temperature for further processing subsequent to welding. Detailed analysis using electron microprobe showed considerable microstructural and micro chemical modification at the weld interface due to inter-diffusion of Fe, Ti, Cr and Ni. The width and number of reaction zones varied as a function of heat treatment temperature and time. From the experiments, it was inferred that even the lowest temperature-time combination, i.e. 873 K-1h, is not suitable for heat treatment of explosive joints of Ti-5Ta-1.8Nb/SS 304L, and further lowering of the process temperature is required.

Keywords

Explosive Welding, Ti-5Ta-1.8Nb, 304L Stainless Steel, Heat Treatment, Intermetallic Phases.

Full Text