Structure and properties of carbon steel to duplex stainless steel submerged arc welds

Submerged arc welding (SAW) of stainless steel to carbon steel plate can produce a number of quality problems. Lack of control of the consumable wire position within the weld preparation can lead to uneven dilution from the parent plates. In addition a relatively heavy but equal dilution from both parent plates will also create problems. In the situation of SAW of duplex stainless steel to carbon steel with a Y weld preparation, which had a 4 mm nose on it, an undesirable situation was created, in which hard zones in the weld metal were observed. In addition, it was found that a bias of the electrode wire to the carbon steel side of the weld preparation created a situation where excessively high hardness measurements occurred (> 600 HV10). Those specific regions were found to contain martensite, which was positively identified using selected area electron diffraction in a TEM investigation on thin foils taken from the high hardness region. A V weld preparation with central positioning of the consumable resulted in acceptable hardness levels in the root region combined with a skeletal ferrite microstructure. This allowed the dilution in the root area to be reduced, whilst achieving a balanced parent plate dilution in the remainder of the weld from the SAW process.