TWA 9
Weld Characteristics
The advent of steels with very low contents of sulphur to improve fracture toughness led to difficulties due to lack of penetration during automatic welding using the tungsten inert gas (TIG) technique. The observed behaviour could be explained on the basis of surface-tension driven flow within the weld pool. The presence of small amounts of surface-active constituents such as sulphur could have had a controlling influence. The aim of this TWA was to produce a compositional standard to improve the consistency of weld penetration in the TIG welding of steels. The work was coupled with a project to examine the fracture toughness of welded joints in steel.
A measurement program was agreed for the study of the influence of trace elements on variable weld penetration in steels. The aim was to provide a data base for the definition of specification limits for surface active elements. A round robin intercomparison was designed to test the consistency of various current methods of TIG welding in terms of weld penetration in well-characterised steels.
The results suggested that control of surface active elements, particularly sulphur, could have a marked effect on weld profile. Elements such as calcium and zirconium which had a strong affinity for sulphur had to be controlled if appropriate fluid flow conditions were to be achieved in the weld pool.
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