Development of Superior Notch Toughness in High-Dilution Weldments of Microalloyed Steel PDF

This report describes the results of a cooperative study having the objective of identifying submerged arc welding consumables suitable for welding base plates containing up to 0.1b percent niobium or higher. Several participants in the study contributed data collected from investigations that used welding conditions representative of pipe production, ship construction and general fabrication utilizing heat inputs up to 195 kJ/in.

The investigations summarized herein considered several experimental and commercial wires, that were combined with a variety of fluxes, and which were used to weld a wide assortment of base plates. Using experimental wires, nickel, boron, molybdenum and titanium additions were studied singly or in combination. No attempt was made to impose a uniform design on the different studies, thus the choice of variables was left entirely to the individual investigators. While this approach allows the opportunity for serendipitous developments, it tends to complicate interpretation of the results collected.

The data collected confirm that fully acicular ferrite microstructures possess the best notch toughness and show the greatest tolerance for high concentrations of microalloys that may be "picked up" from the base plates. The alloying level necessary to achieve the desired microstructure depends on base plate composition and appears to be lowered by increases in base plate niobium content. Wires containing combinations of boron and titanium, both with and without molybdenum, produced welds exhibiting notch toughness values greater than 50 ft. lbs. (68 joules) at -50?¯ F (-46?¯ C) when used in conjunction with basic welding fluxes. The present results combined with earlier findings, provide the foundation for adoption of notch tough 0.15 percent niobium steels in such applications as plate, structural shapes and linepipe, where yield strengths between 55 and 75 ksi (345 to 517 MPa) are needed.