Microstructural modification during isothermal ageing of a low nickel duplex stainless steel

Calliari, Irene; Brunelli, Katya; Zanellato, Michela; Ramous, E.; Bertelli, Ruggero

doi:10.1007/s10853-009-3505-9

Cited by 16 publications

(9 citation statements)

References 9 publications

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“…In the present work, however, s-phase could not be observed at all, and the volume fraction of dferrite slightly decreased, inconsistent with the thermodynamic calculation results, but in good agreements with the results by Zhang, 14) Toor, 18) and Calliari,19) who confirmed the absence of s-phase precipitation in the steels with similar compositions. The s-phase is enriched with Cr and Mo, and diffusion of Cr and Mo is usually regarded as the main controlling factor for its formation.…”

Section: Discussionsupporting

confidence: 78%

“…Figure 8(c) shows that the nose for the 5 % transformed fraction curve is located around 800°C, in good agreement with the results for a similar composition alloy. 19) The precipitation nose temperature may indicate the maximum amount and the most sensitive embrittlement. In the present work, however, the maximum of volume fraction and the lowest impact energy was found to have occurred after the isothermal ageing at 700°C.…”

Section: Discussionmentioning

confidence: 99%

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Precipitation of Secondary Phases in Lean Duplex Stainless Steel 2101 during Isothermal Ageing

et al. 2010

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The DSS ingot was made by standard vacuum melting and casting, which possessed duplex ferritic-austenitic mi- 286© 2010 ISIJ ISIJ International, Vol. 50 (2010) In the present paper, the precipitation behavior of secondary phases in Lean Duplex Stainless Steel (LDX) 2101 had been studied. The alloy has a typical ferritic-austenitic duplex structure after solution treatment. Isothermal ageing treatments were carried out over the temperature range from 700 to 850°C for the period between 2 min and 1 440 min. Cr 2 N-type nitrides were formed as the main product of precipitates, together with small amount of Cr 23 C 6 -type carbides. Increase of N content and decrease of Cr and Mo contents in the steel had led to the absence of s-phase. Due to the solid solution strengthening by interstitial atoms, the hardness value of austenite was measured to be higher than that of ferrite. With increasing the isothermal ageing time, precipitates were observed to be preferentially nucleated at the d/g interface and grown toward the d phase. The d/g interfce migrated from the precipitate particles into d phase, leaving the precipitates behind along the original interfaces, which could increase the size of the secondary austenite (gЈ) phase and decrease the hardness of both austenite and ferrite. Inside gЈ phase, the hardness was measured to increase from about 3.20 GPa at the original interface to about 3.75 GPa at the newly formed interface of d/gЈ. The isothermal kinetics for the precipitation of secondary phases was measured to obey the JMAK-type law. The TTT (time-temperature-transformation) curve was constructed based on the measurements, which seems to have resulted from the overlap of two different precipitated products. The average impact energy at room temperature for the sample after solid solution treatment was measured to be 105 J. When 2 % secondary phases were precipitated during ageing, the impact energy decreased to about 43 J, reduced by about 59 % as compared with the as-annealed sample, indicating that formation of secondary phases can result in dramatic decrease of steel toughness.

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Section: Discussionsupporting

confidence: 78%

Section: Discussionmentioning

confidence: 99%

Precipitation of Secondary Phases in Lean Duplex Stainless Steel 2101 during Isothermal Ageing

et al. 2010

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“…[4,5] Precipitation behavior has been regarded as one of the most important features of DSS because their mechanical and corrosion properties are profoundly dependent on the formation of second phases. [1][2][3][6][7][8][9][10] Compared with austenitic stainless steels, the precipitation reaction of DSS has been considered to be more complicated in that (1) the nucleation sites of the second phases are diverse: a/c phase boundaries, grain boundaries of both phases and interior of grains, and (2) significant amounts of Cr and Mo, which is the potent elements for the formation of the second phases, are contained for stabilization of a matrix of DSS. [1][2][3] A consensus exists that isothermal aging in conventional UNS S31803 and S32750 induces the decomposition of the supersaturated a matrix and produces various second phases involving secondary austenite (c 2 ), intermetallic sigma (r), chi (v), R phase, and several types of carbide or nitride.…”

Section: Tae-ho Lee Heon-young Ha Byoungchul Hwang and Sung-joon Kimmentioning

confidence: 99%

“…[1][2][3] Despite many investigations on the precipitation behavior of commercial grades of DSS, little information on precipitation reaction of high-nitrogen, nickel-free DSS is available. [2,9,10] Ramirez et al [9] reported that intergranular and intragranular Cr 2 N were observed in aged UNS S32304 and they served as sites for heterogeneous nucleation of intragranular c 2 . Recently, Calliari et al [10] showed that the precipitation of second phases in lean DSS was much more sluggish compared with conventional UNS S31803 and S32750: In UNS 32101, only Cr-rich nitride was detected, whereas no second phase was identified in UNS S32404 even after prolonged aging at 1023 K (750°C) for 750 hours.…”

Section: Tae-ho Lee Heon-young Ha Byoungchul Hwang and Sung-joon Kimmentioning

confidence: 99%

“…[2,9,10] Ramirez et al [9] reported that intergranular and intragranular Cr 2 N were observed in aged UNS S32304 and they served as sites for heterogeneous nucleation of intragranular c 2 . Recently, Calliari et al [10] showed that the precipitation of second phases in lean DSS was much more sluggish compared with conventional UNS S31803 and S32750: In UNS 32101, only Cr-rich nitride was detected, whereas no second phase was identified in UNS S32404 even after prolonged aging at 1023 K (750°C) for 750 hours. Granting that the precipitation reaction shows a strong dependence on chemical composition of the alloys, there have been some inconsistencies regarding the decomposition process of a and related precipitation behavior of second phases.…”

Section: Tae-ho Lee Heon-young Ha Byoungchul Hwang and Sung-joon Kimmentioning

confidence: 99%

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Isothermal Decomposition of Ferrite in a High-Nitrogen, Nickel-Free Duplex Stainless Steel

Lee

Hwang

et al. 2011

Metall Mater Trans A

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The formation and crystallography of second phases during isothermal decomposition of ferrite (a) in a high-nitrogen, nickel-free duplex stainless steel was examined by means of transmission electron microscopy (TEM). At an early stage of aging, the decomposition of a started along the a/c phase boundaries where sigma (r) phase and secondary austenite (c 2 ) precipitated in the form of an alternating lamellar structure. The combined analyses based on the simulation of diffraction patterns and stereographic projection have shown that most of the r phase was related to the c 2 by the following relation: ð111Þ c k ð001Þ r and ½10 " 1 c k ½110 r :The intergranular and intragranular precipitation of Cr 2 N with trigonal structure were identified, and the orientation relationships (ORs) with a and c matrix could be expressed as 110 ð Þ a k 0001 ð Þ Cr 2 N , " 111 Â Ã a k ½ " 1100 Cr 2 N ; ð111Þ c k ð0001Þ Cr 2 N , and " 110 Â Ã c k " 1100 Â Ã Cr 2 N ; respectively. The precipitation of intermetallic v phase was also observed inside the a matrix, and they obeyed the cube-on-cube OR with the a matrix. Prolonged aging changed both the structure of matrix and the distribution of second phases. The c 2 , formed by decomposition of a, became unstable because of the depletion of mainly N accompanied by the formation of Cr 2 N, and it transformed into martensite after subsequent cooling. As a result, the microstructure of the decomposed a region was composed of three kinds of precipitates (intermetallic r,v, and Cr 2 N) embedded in lath martensite.

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Erosion–corrosion behavior of plastic mold steel in solid/aqueous slurry

Wen

2009

J Mater Sci

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Microstructural modification during isothermal ageing of a low nickel duplex stainless steel

Cited by 16 publications

References 9 publications

Precipitation of Secondary Phases in Lean Duplex Stainless Steel 2101 during Isothermal Ageing

Precipitation of Secondary Phases in Lean Duplex Stainless Steel 2101 during Isothermal Ageing

Isothermal Decomposition of Ferrite in a High-Nitrogen, Nickel-Free Duplex Stainless Steel

Erosion–corrosion behavior of plastic mold steel in solid/aqueous slurry

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