The influence of welding heat input on submerged arc welded duplex steel joints imperfections

The influence of the heat input submerged arc welding (SAW) of duplex steel UNS S31803 on kind and quantity of welded butt joints defects has been determined. Defects were identified by a radiographic method. For the defectiveness rate in the ratio of quantity negative test results RN to complete radiographic test RC were taken. Radiograms have been classified on the base of Polish and European Standards. The mechanical properties of the joints and value of ferrite share test have been done. Analysis of welding heat input influence on mechanical properties of test joints using heat input from 2.5 to 4.0 kJ/mm. For analysis of welding heat input influence on creation of welding imperfections, there were executed welding of sheet of thickness 10-32 mm using two ranges of the welding heat input: up to 2.5 and up to 3 kJ/mm. It was shown that submerged arc welding of duplex steel with the heat input from 2.5 up to 4.0 kJ/mm has no negative influence on mechanical properties of the joints. Experiment showed, that welding with heat input up to 3.0 kJ/mm reduces welding defects of joints, e.g. slags, lack of a joint penetration for plates of thickness of 10-23 mm, as well as sticks, cracks, and the thoroughly decrease of other defects existence. Usage of larger welding heat input provides the best joints quality, what decreases the joints control and repair costs.