The Analysis and Research of Secondary Phases Generated during Isothermal Aging of Duplex Stainless Steels

2012 ◽  
Vol 193-194 ◽  
pp. 411-417 ◽  
Author(s):  
Kai Lin ◽  
Hong Qi Shi ◽  
Li Qun Ma ◽  
Yi Ding
Keyword(s):  
Stainless Steels ◽  
Isothermal Aging ◽  
Heat Treating ◽  
Duplex Stainless Steels ◽  
Secondary Phases ◽  
Factors Affecting ◽  
Σ Phase ◽  
Α Phase ◽  
The Right ◽  
Χ Phase

The properties and precipitation rules of secondary phases generated during isothermal aging of duplex stainless steels and factors affecting the precipitates were reviewed in this article. These secondary phases include carbides(M23C6,M7C3), nitrides(Cr2N,CrN) and intermetallic phases(σ-phase, χ-phase, Fe3Cr3Mo2Si2, R-phase, π-phase, α′-phase). With the right understanding about the phases, the aim is the suitable heat-treating processes would be chose to avoid the unfavorable influences of secondary phases.

scholarly journals Quantitative Description of the Microstructure of Duplex Stainless Steels Using Selective Etching

2021 ◽  
Vol 3 (1) ◽  
pp. 4
Author(s):  
Aleksandr Fedorov ◽  
Andrey Zhitenev ◽  
Darya Strekalovskaya ◽  
Aleksandr Kur
Keyword(s):  
Stainless Steels ◽  
Quantitative Description ◽  
Distribution Patterns ◽  
Selective Etching ◽  
Duplex Stainless Steels ◽  
Quantitative Phase Analysis ◽  
Solution Annealing ◽  
Secondary Phases ◽  
Σ Phase ◽  
Metallographic Technique

: The properties of duplex stainless steels (DSSs) depend on the ferrite–austenite ratio and on the contents of secondary phases. Therefore, it is necessary to control the volume fractions, morphologies, and distribution patterns of all phases. The phases in the samples were identified using thermodynamic modeling and scanning electron microscopy. Investigated specimens were obtained after different heat treatments, such as solution annealing and quenching from 1050 to 1250 °C to obtain different amounts of ferrite and annealing at 850 °C to precipitate the σ-phase. Therefore, a metallographic technique for assessing the phases in DSSs based on selective etching and subsequent analysis according to ASTM E 1245 was developed. It was shown that the developed method of quantitative analysis based on selective etching and metallographic assessment according to ASTM E 1245 allows obtaining much more accurate results compared to the proposed ASTM E 562 method, which correlates well with the XRD quantitative phase analysis.

Thermal Ageing Embrittlement of Casting Duplex Stainless Steels for Nuclear Power Plant

2010 ◽  
Author(s):  
Yuhong Yao ◽  
Jianfeng Wei ◽  
Jiangnan Liu ◽  
Zhengpin Wang ◽  
Yu Wang
Keyword(s):  
Stainless Steels ◽  
Thermal Aging ◽  
Nuclear Power ◽  
Power Plants ◽  
Ageing Time ◽  
Thermal Ageing ◽  
Duplex Stainless Steels ◽  
Impact Properties ◽  
Α Phase ◽  
The Impact

Cast duplex stainless steels (CSS) used for PWR pipes are degraded due to thermal ageing embrittlement during long-term service at 288 °C to 327 °C. Z3CN20-09M Cast duplex Stainless Steels (CSS) made in France for domestic nuclear power plants were thermally aged at 400 °C for 100 h, 300 h, 1000 h, 3000 h and 10000 h. The tensile properties and the impact properties at different thermal aging duration were measured and the effects of the thermal aging time on the microscopic structures and substructures of Z3CN20-09M were respectively investigated by optical microscopy and transmission electron microscopy. The results showed that the tensile strengths of Z3CN20-09M CSS increased gradually with the increment of the thermal ageing time, whereas the impact properties decreased with the prolonging of the thermal ageing time. After long thermal ageing time the dislocation configurations were greatly changed in austenite, and there were precipitates along the austenite-ferrite interface. Moreover, the iron-rich α phase and the chromium-rich α phase precipitated in ferrite aged for 10000h by nucleation and growth rather than the spinodal decomposition. All of above revealed that Z3CN20-09M CSS became brittle during thermal ageing.

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

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).

Measuring secondary phases in duplex stainless steels

JOM ◽  
2009 ◽  
Vol 61 (1) ◽  
pp. 80-83 ◽  
Author(s):  
I. Calliari ◽  
K. Brunelli ◽  
M. Dabalà ◽  
E. Ramous
Keyword(s):  
Stainless Steels ◽  
Duplex Stainless Steels ◽  
Secondary Phases

Effects of W substitution on the precipitation of secondary phases and the associated pitting corrosion in hyper duplex stainless steels

2012 ◽  
Vol 544 ◽  
pp. 166-172 ◽  
Author(s):  
Soon-Hyeok Jeon ◽  
Soon-Tae Kim ◽  
In-Sung Lee ◽  
Ji-Soo Kim ◽  
Kwang-Tae Kim ◽  
...  
Keyword(s):  
Pitting Corrosion ◽  
Stainless Steels ◽  
Duplex Stainless Steels ◽  
Secondary Phases

Sigma phase precipitation on welded SAF 2205 Duplex Stainless Steels after isothermal heat treatment

2014 ◽  
Vol 1611 ◽  
pp. 177-182
Author(s):  
A. F. Miranda Pérez ◽  
R. Sandström ◽  
I. Calliari ◽  
F. A. Reyes Valdés
Keyword(s):  
Corrosion Resistance ◽  
Stainless Steels ◽  
Duplex Stainless Steels ◽  
Austenitic Steels ◽  
Isothermal Treatment ◽  
Ferromagnetic Behavior ◽  
Isothermal Heat Treatment ◽  
Σ Phase ◽  
Δ Ferrite ◽  
Saf 2205

ABSTRACTDuplex stainless steels are commonly used for various applications owing to their superior corrosion resistance and/or strength. They have ferromagnetic behavior together with a good thermal conductivity and a lower thermal expansion as a result of higher ferrite content than austenitic steels. Their ferrite matrix suffers a decomposition process during aging in the temperature range 650-950° C producing precipitation of austenite, σ and χ, carbides and nitrides. These intermetallic phases are known to be deleterious for corrosion resistance and mechanical properties.In this work the effect of aging time during isothermal treatment at 850°C and 900°C on the microstructure of SAF 2205 Duplex Stainless Steels welded plates has been investigated. The aim of this work is to determine the morphology of σ phase, and perform a quantitative analysis of the precipitation process.Submerged Arc Welding is used for processing. It produces a high content of δ ferrite in the heat affected zone and low content of austenite in the weld. Microstructural examination shows that the σ phase precipitates at δ ferrite/γ interphases. Longer aging treatments give rise to an increase of volume fraction together with a coarser morphology.

Crystallographic relations during decomposition of the ferritic phase by isothermal ageing of duplex stainless steel

2012 ◽  
Vol 46 (1) ◽  
pp. 135-141 ◽  
Author(s):  
Tibor Berecz ◽  
Peter J. Szabo
Keyword(s):  
Stainless Steels ◽  
Electron Backscatter Diffraction ◽  
Parent Phase ◽  
Duplex Stainless Steels ◽  
Σ Phase ◽  
Orientation Relations ◽  
Mathematical Expressions ◽  
Duplex Steel ◽  
Isothermal Ageing ◽  
Backscatter Diffraction

In highly alloyed and duplex stainless steels the range of alloying elements leads to many different phases precipitating at higher temperatures. Duplex stainless steels consist of almost equal ratios of austenite and ferrite, and between 923 and 1273 K the ferrite begins decomposing into secondary austenite (γ2) and the σ phase. Several orientation relations between the austenitic, ferritic and σ phases have been determined by other researchers. The calculation and testing of mathematical expressions for these orientations are important for a close understanding of changes in duplex steel hardness, ductility, and other qualitative measures imposed by annealing or heat ageing. The method described in this article also offers an approach for determining parent phase orientations from inherited orientations in other metallic microstructures. When the orientation relations of adjacent grains calculated from mathematical equations and those measured by electron backscatter diffraction were compared, naturally it was found that the average orientation differs less between grains that inherit matrix structure from common parents. However, it was also found that the degree of difference depended on the variants involved in the orientations. This phenomenon can be explained by features of the microstructure and decomposition of the ferritic phase: initially the microstructure contains only primary austenite (γ1) and ferrite, then after a while it contains [beside primary (γ1) austenite] increasing amounts of secondary (γ2) austenite and the σ phase, and decreasing amounts of ferrite. The presence of two variants of austenite makes it difficult to verify parent relations for secondary (γ2) austenites.

Effect of Secondary Phases Precipitation on Corrosion Resistance of Duplex Stainless Steels

2016 ◽  
Vol 879 ◽  
pp. 1495-1500 ◽  
Author(s):  
Luca Pezzato ◽  
Mattia Lago ◽  
Katya Brunelli ◽  
Marco Breda ◽  
Enrico Piva ◽  
...  
Keyword(s):  
Corrosion Resistance ◽  
Stainless Steels ◽  
Room Temperature ◽  
Volume Fraction ◽  
Secondary Phase ◽  
Duplex Stainless Steels ◽  
Secondary Phases ◽  
Critical Range ◽  
Pitting Corrosion Resistance ◽  
Equivalent Number

Duplex Stainless steels (DSS) are biphasic austeno-ferritic steels in which the best combination of mechanical and corrosion resistance properties is achieved for almost equal volume fraction of the phases. These steels are classified according to their pitting corrosion resistance, assessed by the PREN index (Pitting Resistance Equivalent Number) which, although qualitatively, is widely employed as comparison. The present work is aimed to study the pitting resistance of four DSS grades (SAF 2101, 2304, 2205 and 2507) in the as-received condition and after isothermal aging in the critical range 750°C-900°C, to highlight the effect of secondary phases precipitation on the corrosion behavior. The materials were potentiodynamically tested in artificial seawater (pH7) at room temperature and the corresponding Critical Pitting Temperatures (CPT) were determined according to ASTM G150. Secondary phase precipitation mainly affected the lean duplex grades whereas the high-alloyed DSS were more stable even if large precipitation occurred.

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