Experimental Research On Stress Corrosion Cracking Of SAF2205 And S30408 Dissimilar Steel Welded Joints

Duplex stainless steel is widely used in many departments,such as petrochemical industries and offshore engineering due to its attractive mechanical properties and corrosion resistance.In practical applications,welded joint of dissimilar metals is inevitable such as duplex stainless steel and austenitic stainless steel.However,the migration of elements and tissue defects will be produced in the welded joints during welding,and the mechanical properties and corrosion resistance of welded joints will be greatly decreased.At present,the research on the corrosion resistance of the dissimilar metals welded joints of duplex stainless steels,especially the stress corrosion cracking(SCC)resistance,is rarely studied.Moreover,owing to the lack of obvious symptoms,the SCC will cause serious accidents which would be detrimental to the safety of life and property.Three groups of SAF2205 and S30408 dissimilar steels welded joints with different welding heat input were prepared.The organization and structure of these joints were investigated by the surface morphology observation,microhardness measurement,EDS elemental analysis and XRD phase analysis.The stress corrosion sensitivity of these joints in 3.5% sodium chloride solution was tested through slow strain rate test and the fracture morphology was studied by scanning electron microscope(SEM).Results are summarized as follows:(1)There were obvious differences between these joints on metallographic organization.Results indicated that the metallographic structure of the heat affected zone(HAZ)near to SAF2205 was ferrite grain and austenite on the grain boundary of ferrite.The metallographic organization of the heat affected zone(HAZ)near to S30408 was austenite and the metallographic organization of the welding metal(WM)was austenite dendrite.Besides,austenite content increased from 35.3% to 40.8% with the increasing welding current(90A to 150A).(2)The EDS was applied to measure the element distribution on the vicinity of the fusion lines.The content of Ni element had a concentration gradient in the fusion line zone which was near to SAF2205,and the contents of Ni and Mo elements had concentration gradient in the fusion line zone which was near to S30408 while other elements had a uniform distribution without obvious segregation.There was not a carbon migration in the HAZ and WM because of the close carbon content betweent SAF2205 and S30408.(3)The microhardness tester was applied to measure the microhardness of the vicinity of the fusion lines.From the SAF2205 HAZ and the WM to the S30408 HAZ,the microhardness reduced.(4)The XRD was applied to measure the phases of these dissimilar steel welded joints.The phases of these joints were ? phase and ? phase without secondary phases such as nitrides and ? phase.(5)The stress corrosion sensitivity of these joints in 3.5% sodium chloride solution were tested through the slow strain rate test.The results revealed that the stress corrosion sensitivity of dissimilar steel welded joints was higher than the sensitivity of SAF2205 welded joints,lower than the sensitivity of S30408 welded joints.The stress corrosion sensitivity became higher with the increasing welding current(90A to 150A).(6)The fracture morphology was analyzed by scanning electron microscope(SEM).The crack fractures were brittle,with quasi cleavage and ice sugar block pattern.These patterns were the typical characteristics of stress corrosion cracking.