GTAW & SMAW Butt Welds Investigation Of 2205 Duplex Stainless Steel Thin Plate

Duplex stainless steel(DSS)2205 has good yield strength & corrosion resistance.It is widely used in marine and offshore industry.Rapidly heated and cooled welding is one ciritical manufacture process.And 30–70vol% of austenite volume content is requried in the exposed weld meatal & heat affected zone(HAZ).Weld heat input,with weld speed as one of its essential factors.affects heating & cooling cycle,and then causes microstructure phase changing.Therefore it is neccessary to design and evaluate weld speed & heat input range to ensure weld has acceptable NDE quality,mechanical properies and pitting corrosion resistance.Gas tungsten arc welding(GTAW)and shielded metal arc welding(SMAW)are popular and economic welding methods.Based on original approval WPSs,GTAW and SMAW of 4-mm-thick 2205 plate under different heat inputs are made,being adjusted solely by changing weld speed.Nine welds,under different heat inputs,have been tested by NDE,transverse tensile test,bend test,hardness test,v-notch test,macro/micro test,ferrite volume content measurement,alloy measurement,checmical corrosistion test and polarization curves experiment.Relationships between those results and heat inputs & weld speeds are tried to be established.As per testing results,the best welding heat inputs are setted for SMAW and GTAW separately.For both sides multi-run GTAW,the best root weld speed and heat input range is2.1-2.6mm/s and 386-361J/mm,and the best filling & coverage weld speed and heat input range is 1.0-1.2mm/s and 1021-899J/mm;for both sides two-run SMAW,the best weld speed and heat input range is 2.76-4.09mm/s and 1136-750J/mm.It reavels that,within recommended ranges as above,HAZ austenite volume content and impact v-notch toughness are increased and then slightly decreased with heat input increasing.The reason is investigated.HAZ austnite content is controlled by cooling rate,which is affected by ratio of heat input to penetration depth.With weld speed decreasing,weld heat inpu is increased,and penetration depth is kept steady and then distinctly increased,then ratio of heat input to penetration depth is increased and then slightly decreased,which causes austenite content changing.For v-notch toughness has linear relationship with anustenite content,toughness is increased and then slightly decreased with weld heat input increasing.Compared with mechanical properies and pitting corrosion resistance,HAZ is the weakest area of GTAW for coarsed miscrostructrue,and welding metal is the weakest area of SMAW for a large quantity of micro inclusions within it.SEM investigation on impact v-notch process shows that,micro inclusions in SMAW dimple root reduce fracture loading area and then worsen v-notch toghness of SMAW than GTAW.Pitting corrosion process investigation reveals that,PREN elements Cr/Mo content differences between Ferrite/Austenite phases,lower Cr content in Austenite phase than base metal and GTAW ausntentie phase,and Cr depletion micro inclusions make SMAW easier to get pitting corrosion than GTAW,for micro electrochemical potentials differences and pitting corrosion resistance is mainly controled by weakest phase or area.The best weld heat input range is estimated by theory formulas.And being affected by energy transmission factors,tested ranges of GTAW and SMAW are 7%,18% bigger than estimated ones repectively.For SMAW and GTAW,weld speed adjusting can change heat input to adjust cooling rate to get balanced dual phases to achieve proper mechanical properies and pitting corrosion resistance.Therefore,on weld heat input design and proper propery ensuring method,this article could be helpful for duplex stainless steel welding in marine and offshore industry.