Carburization of austenitic and ferritic alloys in carbon-saturated sodium at 916 K

Gwyther, John R.; Hobdell, M.R.; Hooper, Alan

doi:10.1179/030716974803288220

Cited by 6 publications

(3 citation statements)

References 2 publications

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“…The M 7 C 3 (MϭCr, Fe) carbides can only be found in austenitic stainless steels for very high carbon:chromium ratios, 17,51) for example, during carburizing. During surface carburization of type AISI 316 stainless steel, 52) the near surface region of the steel comprised predominantly M 7 C 3 where the local carbon content was about 4 wt%. The ratio to M 23 C 6 to M 7 C 3 phases increased as the carbon content decreased from the surface to the center.…”

Section: Cmentioning

confidence: 99%

Decomposition of Austenite in Austenitic Stainless Steels

2002

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Austenitic stainless steels are probably the most important class of corrosion resistant metallic materials. In order to attain their good corrosion properties they rely essentially on two factors: a high chromium content that is responsible for the protective oxide film layer and a high nickel content that is responsible for the steel to remain austenitic. Thus the base composition is normally a Fe-Cr-Ni alloy. In practice the situation is much more complex with several other elements being present, such as, Mo, Mn, C, N among others. In such a complex situation one almost never has a single austenite phase but other phases invariably form. Those phases are, with few exceptions, undesirable and they can be detrimental to the corrosion and mechanical properties. It is therefore of considerable importance to study the formation of such phases. In this work the decomposition of austenite in austenitic stainless steels is reviewed in detail. First the binary equilibrium diagrams relevant to the system Fe-Cr-Ni are briefly presented as well as other diagrams, such as the Schaeffler diagram, that traditionally have been used to predict the phases present in these steels as a function of composition. Secondly the precipitation of carbides and intermetallic phases is presented in detail including nucleation sites and orientation relationships and the influence of several factors such as composition, previous deformation and solution annealing temperature. Next, the occurrence of other constituents such as nitrides, sulfides and borides is discussed. TTT diagrams are also briefly presented. Finally the formation of martensite in these steels is discussed.KEY WORDS: austenitic stainless steel; precipitation behaviour; carbides; intermetallic compounds; TTT diagram; strain induced martensite. Phase DiagramsPhase diagrams are important to predict the phases present in the austenitic stainless steels. Nevertheless they have limitations due to the complexity of multicomponent thermodynamic calculations and also due to the transformation kinetics that may prevent the attainment of the equilibrium phases. Regarding the first limitation, the number of relevant components is often more than five and published diagrams are rarely found to contain more than four components. As to the second limitation, the diffusion of alloying elements in austenite can be very slow and the precipitation of certain intermetallic compounds can take thousands of hours. Equilibrium DiagramsIn this section the most relevant features of the binary diagrams 3,4) Fe-Cr, Fe-Ni, Cr-Ni, Fe-Mo, Fe-Ti, Ni-Ti, FeNb, Fe-Mn and Fe-Si are considered. Next the Fe-Cr-Ni and Fe-Cr-Mo ternary diagrams and the quaternary FeCr-Ni-Mo diagram are discussed. The individual characteristics of each phase will be presented later in this review.The two main features of the Fe-Cr diagram, shown in Fig. 1, which are relevant to austenitic stainless steels, are the ferrite stabilizing character of Cr and the presence of sigma (s) phase.The Fe-Ni diagram clearly shows the strong ...

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Section: Cmentioning

confidence: 99%

Decomposition of Austenite in Austenitic Stainless Steels

2002

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“…The nature and kinetics of caburization of steels in liquid sodium at 450-650°C, where the activity of carbon in sodium is close to unity, were studied in the past. These studies led to the development of simplified carburization models predicting the evolution of the carburization kinetics of stainless steels in sodium [2][3][4][5][6][7]. In these approaches, apparent diffusion coefficients of carbon D app were calculated by fitting the carbon concentration profiles with the usual solution of the Fick's second law [8].…”

Section: Introductionmentioning

confidence: 99%

“…In these approaches, apparent diffusion coefficients of carbon D app were calculated by fitting the carbon concentration profiles with the usual solution of the Fick's second law [8]. In most of the studies, this parameter was neither clearly related to the diffusion of carbon in the matrix (ferrite or austenite) nor related to an effective grain boundary coefficient [2][3][4][5][6]. Only Dickson et al [7] proposed a prediction of the carbon concentration profiles using two different apparent diffusion coefficients, D app , one for the apparent diffusion of carbon in the grains and another one for the apparent grain boundary diffusion of carbon.…”

Section: Introductionmentioning

confidence: 99%

Carburization of austenitic and ferritic stainless steels in liquid sodium: Comparison between experimental observations and simulations

et al. 2019

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Three steels were exposed in carburizing sodium at 600 and 650°C. The kinetics and extent of carburization were characterized. Numerical simulations using the coupled thermodynamic-kinetic modeling software DICTRA were performed. It was proposed that the observed carbon diffusion profiles were induced by the combined diffusion of carbon in the grains and at grain boundaries coupled with the slow formation of carbides. The blocking effect of carbides on the carbon diffusion was observed to evolve as a function of time and microstructure. Acceptable agreement between experimental and simulated intragranular carbon profiles was achieved by optimizing the labyrinth factor and phases.

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The initiation of breakaway oxidation of Fe-9Cr-1Mo in a high pressure CO2 atmosphere

Newcomb

Stobbs

1986

Oxid Met

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Carburization of austenitic and ferritic alloys in carbon-saturated sodium at 916 K

Cited by 6 publications

References 2 publications

Decomposition of Austenite in Austenitic Stainless Steels

Decomposition of Austenite in Austenitic Stainless Steels

Carburization of austenitic and ferritic stainless steels in liquid sodium: Comparison between experimental observations and simulations

The initiation of breakaway oxidation of Fe-9Cr-1Mo in a high pressure CO2 atmosphere

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