[ Super Duplex ]
[ Super Duplex ]
Table 2 : Comparison of interphase distance with previous findings
No Material Condition % Sec . Phases at 850 ° C for 10 min * Average Interphase distance ( μm )
1 UNS S32760 ( ASTM A890 ) Cast 0.5-1 45
2 Zeron 100 SDSS Wrought 5-6 33
* Average distance of γ / δ interfaces , Calculate with Interceptions Method
ferritic grains . At 60 min , a maximum of chi phase is converted to sigma phase and some nitrides are present inside the chi phase . At 90 min , no chi phase is detected , which indicates that chi phase keeps good stability until 900 ° C temperature , which is in agreement with our observation . A maximum of 13 % of sigma phase formed at 90 min . For wrought SDSS , at 950 ° C the first precipitates of χ appear after 3 min , generally decorating the grain boundaries and a few inside the ferrite grains , while ϭ appears after 5 min . The fraction of ϭ phase increases with time , while that of the χ phase decreases after 30 min . At 60 min , no chi phase and a maximum 14 % of sigma phase appear at this time .
Comparison of interphase distance Grain size or interphase distance significantly impacts the percentage of secondary phases that precipitate ( 7 ) , as described previously . The interphase distance of our findings was compared with previous findings that concluded that with larger interphase distance , less secondary phases formed , while with less distance more precipitations are observed . In our finding , double interphase distance was found to have significantly less sigma and chi phases .
Conclusions
• During the ageing treatments , the χ phase is the first intermetallic phase that precipitates , always at the α / γ boundaries and at the triple points ; it is followed by the σ phase that gradually becomes embedded and eventually replaces the former .
• Cast SSDSS showed less precipitation as compared to wrought SDSS . Wrought SDSS has less interphase distance compared to cast SDSS .
References
1 . Kim YJ , Chumbley LS , Gleeson B . Continuous Cooling Transformation in Cast Duplex Stainless Steels CD3MN and CD3MWCuN . J Mater Eng Perform . 2008 Apr ; 17 ( 2 ): 234 – 9 .
2 . Michalska J , Sozańska M . Qualitative and quantitative analysis of σ and χ phases in 2205 duplex stainless steel . Mater Charact . 2006 Jun ; 56 ( 4 – 5 ): 355 – 62 .
3 . Calliari I , Breda M , Ramous E , Brunelli K , Pizzo M , Menapace C . Impact Toughness of an Isothermally Treated Zeron ® 100 SDSS . J Mater Eng Perform . 2012 Oct ; 21 ( 10 ): 2117 – 23 .
4 . Acuna A , Riffel KC , Ramirez A . Sigma phase kinetics in DSS filler metals : A comparison of sigma phase formation in the as-welded microstructure of super duplex stainless steel and hyper duplex stainless steel . Mater Charact . 2024 Jan ; 207:113433 .
5 . Angelini E , De Benedetti B , Rosalbino F . Microstructural evolution and localized corrosion resistance of an aged superduplex stainless steel . Corros Sci . 2004 Jun ; 46 ( 6 ): 1351 – 67 . Other references can be provided on demand .
Fig 4 : % Volume Fraction at 950 ° C for cast and wrought SDSS
About the author
Saira Sehar is a PhD Student in Material Engineering Department of University of Padua , Italy . Her main focus is on phase transformations in SDSS through isothermal heat treatment in cast and wrought SDSS and their effects on Mechanical and Electrochemical properties of SDSS . She will start working on Additively Manufactured SDSS to compare it with cast and wrought SDSS . Email : Saira . sehar @ studenti . unipd . it
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