Effect Of Nitrogen Content On The Properties Of Deposited Metal With ER2209MAG Wire

As the generation-II duplex stainless steel, UNS S32205duplex stainless steel (DSS) hasbeen applied more and more widely in the field of petroleum, chemical industry, shipbuilding,paper, salt and sea water desalination at home and abroad for its excellent local corrosionresistance and good mechanical properties. As a result of later research on such material indomestic than abroad, there are not mature matching welding materials with2209series,especially the ER2209gas shielded welding wires，and there is a large gap between theforeign wire and domestic wire., so the problem of domestication of2209have yet to beresolved. Nitrogen is an important element for the second-generation DSS in improving thematerial’s corrosion resistance and guaranteeing the appropriate proportion of ferrite andaustenite. It is also a very important element for supporting welding materials, whichguarantee the phase proportion of welding joint especially HAZ and the corrosion resistance.In order to investigate the effect of nitrogen content on the properties of deposited metal with2209MAG wire, mechanical properties of a series of deposited metal with different nitrogencontent wires was contrasted; In order to investigate the effect of nitrogen on the pittingcorrosion rate and CPT(critical pitting temperature) of2209MAG deposited metal, themethod of chemistry and electrochemistry was used; it was investigated that includedmetallographic structure and fracture appearance and the mechanical properties of depositedmetal was also discussed through adopting analytical method such as OM metallographic test,SEM fracture test and metallographic etc.As research shows: there was an increase trend of the impact value and tensile strengthwith an increase of nitrogen content, whereas the rule cannot be firmly concluded just basedon the increased extent, and there was little change for the percentage reduction of area andpercentage elongation according to current research result; Apparently, there were more slaginclusion over1μm in developed wire deposited metal than imported wire found bysubsequent studies，which were mainly aluminum-silicate semi-plastic slag inclusions. Theexisting of these large semi-plastic slag inclusions reduced the material ductility andtoughness, consequently possibly hided the influencing rule of nitrogen on mechanicalproperties. The effect of nitrogen on mechanical properties still needs further investigation.From the research result about DSS deposited metal pitting corrosion resistance, it was shownthat the pitting corrosion rate reduced with an increase of nitrogen content and then thematerial pitting corrosion resistance enhanced; the etched pits on the corrosion specimenspresented distribution along a straight line as a result of the function of welding thermal cycle. It can be seen from the electrochemistry measure result that the CPT of deposited metal with0.10%nitrogen was37℃in3.5%NaCl solution, the CPT of deposited metal with0.13%nitrogen was45℃,the CPT of deposited metal with0.18%nitrogen was53℃, and it also wasdemonstrated that the pitting corrosion resistance strengthened along with an increase ofnitrogen. It can be known from the CPT result that the CPT calculation formula according toASTM G48cannot precisely characterized the CPT of deposited metal, the pitting corrosionresistance characterization by CPT was much wider and more suitable to engineeringapplication than corrosion current density and breakdown potential. From the viewpoint of theeffect rule of nitrogen on deposited metal mechanical properties and corrosion resistance: thenitrogen content should be controlled between0.14%~0.18%in the2209MAG depositedmetal, the wire nitrogen content should be limited between0.16%~0.20%.