Abstract:

The testing investigations of underwater friction hydro pillar/taper-pillar welded joints for dissimilar steels are performed by using the X65, Q235C, Q345C and 316L steel pillar combined with X65 base metal, and the varying regularities of microstructures, microhardness and mechanical properties for plug welded joints are discussed. It is found that the dissimilar steel underwater friction hydro pillar/taper-pillar welded joints with free defects can be obtained by using the X65 and Q345C steel pillar under the welding conditions of rotational speed 7 000 r/min, pillar consuming length 14 mm, welding axial forces in 30-50 kN and 20-40 kN ranges respectively. The microstructures of dissimilar steel plug welds are obviously different from that of original materials, the plug welds are composed of bainite or Martensite or their mixture structures; The effectively diffusing metallurgical bonding have been produced by using X65 and Q345C steel pillar and the bonding interfaces are possessed of the features of fine banded ferrite microstructures; but the plug welded joint of 316L steel pillar and X65 plug hole with defect free are hardly obtained. The microhardness values of plug weld zones are generally higher than that of base metal, and these high matching welded joints are beneficial to the increase of tensile strength, however the high hardening tendency around the plug welds should obviously reduce the plasticity of dissimilar steel plug welded joints. The testing results should provide the important testing data to develop the repairing techniques of marine pipeline based on the friction hydro pillar/taper-pillar welding technologies.

Key words: mechanical properties, microstructures, underwater friction hydro pillar/taper-pillar welding, dissimilar steels