Crystallographic details of precipitates in Fe-22Cr-21Ni-6Mo-(N) superaustenitic stainless steels aged at 900 °C

Lee, Tae‐Ho; Kim, Sung-Joon; Jung, Yun-Chul

doi:10.1007/s11661-998-0332-6

Cited by 118 publications

(89 citation statements)

References 35 publications

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“…It is well known that formation of second phases can cause a decrease in the mechanical properties and corrosion resistance of highly alloyed steels ( Ref 1,2,4,5). For this reason, ASTM A923 Methods A, B, and C have been developed as a means of detecting the presence of intermetallics that may be detrimental to the mechanical properties and corrosion performance of cast duplex alloys .…”

Section: Introductionmentioning

confidence: 99%

Fracture Toughness of Heat-Treated Superaustenitic Stainless Steels

Müller

Chumbley

2009

J. of Materi Eng and Perform

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Cast duplex and superaustenitic stainless steels are attractive alloys for applications that desire high strength and high corrosion resistance. Due to the large amounts of alloying additions present in these systems, a proper solution heat-treatment schedule is critical in ensuring that the alloys are able to meet the desired specifications. While studies to determine the phase transformation behavior of duplex and superaustenitic alloys have shown that the precipitation kinetics are comparatively slow when considering large amounts of precipitation, studies involving Charpy impact specimens have noted significant decreases in impact strength in materials improperly heat treated for times as short as 10 min, well before any significant amount of precipitation (<1>vol.%) has occurred. The goal of this study was to investigate a particular superaustenitic alloy, CN3MN, in an effort to determine the reason for this large drop in impact strength. Charpy impact specimens were tested from polycrystalline and single crystal samples in the solution heat-treated condition and after heat treatment at 872 °C for times ranging from 5 to 60 min to embrittle the material. Fracture surfaces were characterized using optical and scanning electron microscopy (SEM), Auger spectroscopy, and energy dispersive x-ray spectroscopy. The fracture surfaces showed ductile and brittle characteristics for the standard and improperly treated samples, respectively. Close observation using SEM reveals precipitation takes place initially on grain boundaries, which may account for the observed embrittling effect. While difficult to see at very short times, measurements of linear coverage of precipitation along grain boundaries of polished samples show a definite relationship between drop in fracture toughness and grain boundary precipitation. The results of the Charpy tests and SEM observations, along with chemical analysis studies of the grain boundaries using x-rays and auger electrons, will be presented. Cast duplex and superaustenitic stainless steels are attractive alloys for applications that desire high strength and high corrosion resistance. Due to the large amounts of alloying additions present in these systems, a proper solution heat-treatment schedule is critical in ensuring that the alloys are able to meet the desired specifications. While studies to determine the phase transformation behavior of duplex and superaustenitic alloys have shown that the precipitation kinetics are comparatively slow when considering large amounts of precipitation, studies involving Charpy impact specimens have noted significant decreases in impact strength in materials improperly heat treated for times as short as 10 min, well before any significant amount of precipitation (<1 vol.%) has occurred. The goal of this study was to investigate a particular superaustenitic alloy, CN3MN, in an effort to determine the reason for this large drop in impact strength. Charpy impact specimens were tested from polycrystalline and single crystal samples in the s...

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Section: Introductionmentioning

confidence: 99%

Fracture Toughness of Heat-Treated Superaustenitic Stainless Steels

Müller

Chumbley

2009

J. of Materi Eng and Perform

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“…Superaustenitic stainless steels are Fe-based systems highly alloyed with Cr, Ni, Mo, and N to produce excellent pitting and crevice corrosion-resistant properties at high temperatures and in seawater (Ref [1][2][3][4][5]. When exposed to elevated temperatures for long periods of time, large amounts of precipitates, including carbides, nitrides, and intermetallic phases, can form in these steels (Ref [1][2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%

“…When exposed to elevated temperatures for long periods of time, large amounts of precipitates, including carbides, nitrides, and intermetallic phases, can form in these steels (Ref [1][2][3][4][5]. The most commonly observed secondary phases include M 23 C 6 carbide, and intermetallic r, v, and Laves phases (Ref [1][2][3][4][5]. Other less common secondary phases include M 6 C, p, R, and Cr 2 N (Ref [1][2][3][4][5].…”

Section: Introductionmentioning

confidence: 99%

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Phase Transformations in Cast Superaustenitic Stainless Steels

Steven

Chumbley

Gleeson

2009

J. of Materi Eng and Perform

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The goal of this investigation was to study phase transformations in cast superaustenitic stainless steels. Experiments were performed to determine the phase transformation behavior for alloys CN3MN and CK3MCuN. Samples were taken from keel bars that were heat treated between 1160 and 1230 °C and then isothermally held for times ranging from 1 min to 2040 h at temperatures in the range of 700-900 °C. The resulting microstructures were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy and wavelength dispersive spectroscopy. The microstructures, composed primarily of sigma-and Laves-phases within a purely austenitic matrix, showed relatively slow transformation kinetics, with transformation not completed even after the longest anneals. SEM and TEM analysis of superaustenitic samples reveal that precipitation takes place initially on grain boundaries and proceeds intragranularly. The results of these SEM and TEM investigations, along with volume fractions and number densities as a function of time and temperature, will be presented and discussed. The goal of this investigation was to study phase transformations in cast superaustenitic stainless steels. Experiments were performed to determine the phase transformation behavior for alloys CN3MN and CK3MCuN. Samples were taken from keel bars that were heat treated between 1160 and 1230°C and then isothermally held for times ranging from 1 min to 2040 h at temperatures in the range of 700-900°C. The resulting microstructures were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy and wavelength dispersive spectroscopy. The microstructures, composed primarily of sigma-and Laves-phases within a purely austenitic matrix, showed relatively slow transformation kinetics, with transformation not completed even after the longest anneals. SEM and TEM analysis of superaustenitic samples reveal that precipitation takes place initially on grain boundaries and proceeds intragranularly. The results of these SEM and TEM investigations, along with volume fractions and number densities as a function of time and temperature, will be presented and discussed.

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“…Heat treatment at temperatures below 600°C also results in nitride precipitation in the duplex stainless steel of high ferrite content. 9) In almost all the investigations on duplex stainless steels as well as austenitic stainless steels of high nitrogen content, [10][11][12] only hexagonal type nitride Cr 2 N was observed. However, Hertzman reported that cubic CrN might exist in welds of duplex stainless steels.…”

Section: Introductionmentioning

confidence: 99%

Nitride Precipitation in Weld HAZs of a Duplex Stainless Steel.

Liao¹

2001

ISIJ International

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Crystallographic details of precipitates in Fe-22Cr-21Ni-6Mo-(N) superaustenitic stainless steels aged at 900 °C

Cited by 118 publications

References 35 publications

Fracture Toughness of Heat-Treated Superaustenitic Stainless Steels

Fracture Toughness of Heat-Treated Superaustenitic Stainless Steels

Phase Transformations in Cast Superaustenitic Stainless Steels

Nitride Precipitation in Weld HAZs of a Duplex Stainless Steel.

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