Temperature Dependence of σ Phase Formation in Surface Melted Duplex Stainless Steel

Specimens of 2507 super-duplex stainless steel aging at 850°C for 5 min, 15 min and 60 min were investigated to evaluate the pitting corrosion resistance in 3.5% NaCl solution at 30°C and 50°C. The results are correlated with the microstructures obtained with different aging time. The precipitation of σ phase remarkably decreases the pitting corrosion resistance of the steel and the specimen aged for 60 min presents the lowest pitting potential at both 30°C and 50°C. With increasing the ambient temperature from 30°C to 50°C, the pitting potential exhibits a reduction tendency, while this tendency is less obviously in enhancing the ambient temperature than in extending the isothermal aging duration from 5 to 60 min. SEM analysis shows that the surrounding regions of σ phase are the preferable sites for the formation of corrosion pits which grew up subsequently. This may be attributed to the lower content of corrosion resistance elements in these regions formatted with σ phase precipitation.

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Examination of the Orientation Relationships between the Main Phases of Duplex Stainless Steel by EBSD

Materials Science Forum ◽

10.4028/www.scientific.net/msf.537-538.297 ◽

2007 ◽

Vol 537-538 ◽

pp. 297-302

Author(s):

Tibor Berecz ◽

Péter János Szabó

Keyword(s):

Stainless Steel ◽

Duplex Stainless Steel ◽

Stainless Steels ◽

Electron Backscatter Diffraction ◽

Duplex Stainless Steels ◽

Alloying Elements ◽

Orientation Relationships ◽

Σ Phase ◽

Electron Backscatter ◽

Backscatter Diffraction

Duplex stainless steels are a famous group of the stainless steels. Duplex stainless steels consist of mainly austenitic and ferritic phases, which is resulted by high content of different alloying elements and low content of carbon. These alloying elements can effect a number of precipitations at high temperatures. The most important phase of these precipitation is the σ-phase, what cause rigidity and reduced resistance aganist the corrosion. Several orientation relationships have been determined between the austenitic, ferritic and σ-phase in duplex stainless steels. In this paper we tried to verify them by EBSD (electron backscatter diffraction).

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Thermal cycling induced stress–assisted sigma phase formation in super duplex stainless steel

Materials & Design ◽

10.1016/j.matdes.2019.108003 ◽

2019 ◽

Vol 182 ◽

pp. 108003 ◽

Cited By ~ 1

Author(s):

Jian-Sin Li ◽

Guan-Ju Cheng ◽

Hung-Wei Yen ◽

Liberty T. Wu ◽

Yo-Lun Yang ◽

...

Keyword(s):

Stainless Steel ◽

Thermal Cycling ◽

Duplex Stainless Steel ◽

Phase Formation ◽

Sigma Phase ◽

Super Duplex Stainless Steel ◽

Induced Stress

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Effect of Thermal Cycle on Microstructure and Corrosion Behavior of Duplex Stainless Steel SAF 2205 Electron Beam Welded Joint

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.786.119 ◽

2018 ◽

Vol 786 ◽

pp. 119-127

Author(s):

Sameh M. Khafagy ◽

Morsy Amin Morsy ◽

H.M. El Sherbini ◽

Y.F. Barakat

Keyword(s):

Stainless Steel ◽

Corrosion Resistance ◽

Duplex Stainless Steel ◽

Thermal Cycle ◽

Welded Joint ◽

Volume Fraction ◽

Holding Time ◽

Σ Phase ◽

Phase Volume Fraction ◽

Saf 2205

It is known that heat treatment (HT) highly affects the properties of base metal (BM) and fusion zones (FZ) of duplex stainless steel (DSS). In fact, it may give unwanted structure changes. Duplex stainless steels SAF 2205 welded joint was subjected to thermal cycle at temperature of 850◦C at holding times 1, 3, 5 and 7 hours. The influence of heating cycles and concentration of corrosive medium on the corrosion properties and microstructure of 2205 alloy was the objective of this work. It was found that process led to noticeable decrease in the corrosion resistance of BM and FZ specimens; moreover the decrease was large in BM than FZ. It was also found that sigma phase (σ) precipitated in the different zones of the structure. σ phase volume fraction was found to increase with increasing the holding time of HT, and its increase is larger in BM. Corrosion resistance was found to be oppositely related to σ phase formation. Secondary austenite phase (γ2) was also precipitated and its volume fraction in FZ was found to increase with increasing the holding time of HT and decreased in BM.

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The Study on Welding HAZ Microstructure of SAF 2507 Duplex Stainless Steel by Simulation Tests

Materials Science Forum ◽

10.4028/www.scientific.net/msf.804.277 ◽

2014 ◽

Vol 804 ◽

pp. 277-280 ◽

Cited By ~ 2

Author(s):

Ren Long Tao ◽

Jie Liu ◽

Guang Wei Fan ◽

Xu Chang

Keyword(s):

Stainless Steel ◽

Duplex Stainless Steel ◽

Cooling Rate ◽

Significant Influence ◽

Thermal Simulation ◽

Cooling Time ◽

Phase Precipitation ◽

Σ Phase

Thermal simulation by GLEEBLE3800 is adopted to obtain the simulated welding HAZ microstructures in SAF 2507 duplex stainless steel with the GLEEBLE3800 thermal simulation machine. The simulation peak temperatures are 800oC, 900oC, 950oC, 1000oC, 1050oC and 1100oC, The cooling velocities are t12/8=3.6s, 7s, 20s and 40s (t12/8 is cooling time of 1200oC to 800oC which is used to describe the cooling rate). The results indicate that the peak temperatures have significant influence on the microstructures of austenite and ferrite. At 900oC, the content of σ phase precipitation reaches the maximum, which is distributed mainly in α or at α/γ junction. When the temperature is set above 1050oC, the σ phase disappears. A faster cooling rate passing through 800~1050oC is required to avoid brittle σ phase precipitation.

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