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Thursday, June 5, 2008 - 10:05 AM

Buried Gas Tungsten Arc Welding of High Strength 10% Ni Steel

R. J. Wong, J. J. DeLoach, Naval Surface Warfare Center Carderock Division, West Bethesda, MD

A study was conducted to evaluate the feasibility of using the Buried Gas Tungsten Arc Welding (BGTAW) process to join thick section 10% Nickel steel without filler material. The 10% Ni steel is an experimental high strength ferritic steel with a nominal ultimate tensile strength of 1000 MPa (150 ksi) and an adjustable yield strength of 828-900 MPa (120-130 ksi).

Full penetration weldments were made in 1‑1/2‑in. thick 10% Ni steel plate in two passes (one from each side) using the BGTAW process with a 1500A welding current. The calculated heat input for the welds investigated in this study was as high as 15.8 MJ/m (400-kJ/in). 

Initial mechanical property results were encouraging. The yield strength of fusion zone was 923‑985 MPa (134‑143 ksi), which was similar to the base plate properties. Charpy V-notch (CVN) tests of the fusion zone indicated that the impact energy of the first side welded was somewhat lower than that measured from the second side.  The second side welded exhibited an average CVN toughness of over 81 J at ‑51oC (60 ft-lbs at ‑60oF). 

Metallographic characterization and microhardness mapping were performed to determine the nature of the toughness variation in the fusion zone. The lower toughness is believed to be due in part to overheating of the first pass, caused by the high heat input of the second pass.  Metallurgical investigation indicated the fusion zone microstructure exhibited a dendritic structure with a fine lath structure within the grain boundaries.  This was the predominant microstructure of both the first and second side fusion zones.  Microhardness mapping was used to identify differences in hardness of the fusion zone.  The fusion zone was found to vary in hardness from 360-440 Vickers hardness.


Summary: A study was conducted to evaluate the feasibility of using the Buried Gas Tungsten Arc Welding (BGTAW) process to join thick section 10% Nickel steel without filler material. Full penetration weldments were made in 1 1/2 in. thick 10% Ni steel plate in two passes (one from each side) using the BGTAW process with a 1500A welding current. The calculated heat input for the welds investigated in this study was as high as 15.8 MJ/m (400-kJ/in). Initial mechanical property results were encouraging. The details of this study on the evaluation of the feasibility of using BGTAW to join thick section 10% Ni steel are presented.