Sigma Phase Formation and Embrittlement of Cast Iron-Chromium-Nickel (Fe-Cr-Ni) Alloys

Babakr, Ali; Al‐Ahmari, Abdulrahman; Al-Jumayiah, K.; Habiby, F.

doi:10.4236/jmmce.2008.72011

Cited by 27 publications

(20 citation statements)

References 18 publications

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“…In addition to the small and rounded carbides inside the austenite grains, coarser and plate or needlelike precipitates of sigma phases are observed within the grains. Similar microstructural features showing plate or needlelike precipitates of sigma phases have been observed by Babakr et al [2] and Łabanowski [7].…”

Section: Microstructural Examinationsupporting

confidence: 71%

“…EDS analysis shows the presence of sigma phases along the grain boundary as well as within the grains. Sigma (r) phase is basically an ironchromium intermetallic compound that develops in austenitic stainless steels under prolonged exposure to high temperature (620-900°C) because of thermal instability [2][3][4]. The presence of sigma phase was confirmed by etching the sample with Groesbeck solution [5,6].…”

Section: Microstructural Examinationmentioning

confidence: 99%

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An Investigation on the Cracking of Air Tubes of Rotary Kilns in a Sponge Iron Plant

Mukhopadhyay

Bhattacharyya

2011

J Fail. Anal. and Preven.

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Cracking of an air tube used for supplying air in rotary kiln of a sponge iron plant is investigated in this paper. The material of the air tube is ASTM A297 HK 40, a member of the heat-resistant cast alloy family (H series) steels widely used for enhanced high-temperature properties. Microstructural degradation occurring at high temperature affects mechanical and corrosion-resistance properties of the component. The failure analysis consists of visual observation, chemical analysis, examination of microstructures using optical and scanning electron microscopes, and characterization with energy-dispersive spectroscopy (EDS). Microstructural characterization reveals (i) intergranular corrosion at the cross section of tube wall, (ii) formation of severe chromium carbide network at the grain boundary, (iii) formation of sigma phases along the grain boundary as well as within the matrix, and (iv) generation of crack at the grain boundary filled with oxides. Analyses of these results suggest that formation of carbide network and sigma phases at the elevated service temperature depletes the alloying elements from the surrounding matrix, enhancing intergranular corrosion, which leads to cracking of the air tube.

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Section: Microstructural Examinationsupporting

confidence: 71%

Section: Microstructural Examinationmentioning

confidence: 99%

An Investigation on the Cracking of Air Tubes of Rotary Kilns in a Sponge Iron Plant

Mukhopadhyay

Bhattacharyya

2011

J Fail. Anal. and Preven.

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“…The role of the coating is pronounced during the transient period of erosion during which it saved the substrate steel from the enhanced E-C loss. The mass loss recorded after the initial transient cycles for both the coatings was meager, which indicates that the coatings could be useful to reduce the It has been reported that sigma (r) phase is hard and fragile, in addition, when forms, it consumes chromium and molybdenum present within the matrix [33], which leads to the depletion in these elements and thereby prevent formation of Cr 2 O 3 . XRD analysis of the exposed coated specimens tested in the given environments indicated that no brittle (sigma) phase was formed in the scales.…”

Section: (A) (B)mentioning

confidence: 97%

Comparative High Temperature Analysis of HVOF-Sprayed and Detonation Gun Sprayed Ni–20Cr Coating in Laboratory and Actual Boiler Environments

Kaushal¹,

Singh

Prakash

2011

Oxid Met

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High-velocity-oxy-fuel (HVOF) spray and detonation-gun (D-gun) spray techniques were used to deposit Ni-20Cr coatings on a commonly used boiler steel ASTM-SAE 213-T22. The specimens, with and without coating, were subjected to molten salt (Na 2 SO 4 -60%V 2 O 5 ) deposition in a laboratory furnace at 900°C to determine hot-corrosion resistance. Specimens were also exposed to the superheater zone of a thermal power plant boiler at an average temperature of 700°C under cyclic conditions to ascertain their erosion-corrosion (E-C) behavior. Mass-change measurements were taken to approximate the kinetics of corrosion and erosion-corrosion. In the case of E-C, the thickness lost data were also taken at the end of the exposure. The exposed specimens were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy/energy dispersive spectroscopy (FE-SEM/EDS). The HVOF-sprayed coating was found to be intact during exposure to both given environments; whereas the D-gun coating showed spallation of its oxide scale during exposure to the molten salt environments. An overall analysis of the results indicated that the HVOF-sprayed Ni-20Cr coating should be a better choice for the given boiler applications.

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“…For the alloys with a Cr content of more than 20%, there is a possibility of forming a σ phase above 550 o C, which also depends on the ageing time and impurity level in the alloy [8]. The formation of the σ phase is detrimental as it makes the material brittle and affects the creep and corrosion properties [9]. The 475 o C embrittlement arises in structural components during service whereas the σ phase embrittlement is produced during heat treatment, welding, or casting.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Embrittlement in Isochronal Aged Fe-Cr Alloys by Magnetic Hysteresis Loop Technique

Mohapatra¹,

Kamada²,

Kikuchi³

et al. 2011

Journal of Magnetics

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Fe-Cr alloys with different Cr contents were prepared by an arc melting technique. The alloys were isochronally aged in the range from 400 o C to 900 o C with 50 o C steps with a holding time of 100 hours. The ageing produced embrittlement in the alloys due to either the formation of a Cr-rich α' phase or a σ phase at high temperatures. Magnetic Hysteresis Loop (MHL) and Micro-Vickers hardness were measured at each step to correlate the magnetic and mechanical properties. Coercivity and hardness of the alloys were increased and remanence decreased up to 500-550 o C due to formation of a Cr-rich α' phase. Beyond 500-550 o C range, the coercivity and hardness decreased and remanence increased due to the coarsening or dissolution of the Cr-rich α' phase. In the Fe-48% Cr alloy, formation of the σ phase at 700 o C reduced the maximum induction of the alloy significantly.

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Sigma Phase Formation and Embrittlement of Cast Iron-Chromium-Nickel (Fe-Cr-Ni) Alloys

Cited by 27 publications

References 18 publications

An Investigation on the Cracking of Air Tubes of Rotary Kilns in a Sponge Iron Plant

An Investigation on the Cracking of Air Tubes of Rotary Kilns in a Sponge Iron Plant

Comparative High Temperature Analysis of HVOF-Sprayed and Detonation Gun Sprayed Ni–20Cr Coating in Laboratory and Actual Boiler Environments

Evaluation of Embrittlement in Isochronal Aged Fe-Cr Alloys by Magnetic Hysteresis Loop Technique

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