Effect of Diffusible Hydrogen on Mechanical Properties of Underwater Welded Joints

Study on Impoving the Mechanical Properties of Underwater Welded Joints

Abstract

The effect of diffusible hydrogen on mechanical properties of underwater wet welded joints by gravity welding process is investigated. The 4 and 6 mm dia. coated electrodes of five types and SM41 steel base metals of 6 and 9 mm in thickness are used.
Main results obtained are summarized as follows;
(1) The volume of diffusible hydrogen in underwater weld is much more than that in air weld. H_D of underwater weld.increases with increasing of weld heat input and welding current and with an decreasing of thickness of base metal. However, H_W shows roughly a constant value regardless of welding current and thickness of base metal.
(2) The mechanical properties of the underwater weld, that is, tensile strength, elongation, bending ductility and notch toughness, can be improved remarkably by post weld heat treatment.
(3) The evolution process of hydrogen from bead and butt weld and the recovery process of the mechanical properties of welds are able to be analysed by using the one-dimensional weld model. Consequently it becomes clear that the time factor r=Dt/l₀², by which the great part of diffusible hydrogen diffuses out of weld, should be selected as the condition of post weld heat treatment.