Relationship between evolution of mechanical properties of various cast duplex stainless steels and metallurgical and aging parameters: outline of current EDF programmes

Bonnet, Stéphanie; Bourgoin, J.; Champredonde, J.; Guttmann, D.; Guttmann, M.

doi:10.1179/mst.1990.6.3.221

Cited by 67 publications

(9 citation statements)

References 3 publications

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“…The chemical composition of the two investigated steels is given in Table 1, together with the ferrite volume fraction measured by a magnetic method. The two steels contain almost the same ferrite volume fraction; the values agree well with those calculated using the formula given by Bonnet et al 5 Room temperature tensile, microhardness and impact toughness properties are summarised in Table 2. In aged conditions, the impact toughness of the two steels is The solidification microstructure is columnar near the surface and equiaxed in the bulk of the component, as shown in Fig.…”

Section: Methodssupporting

confidence: 83%

“…The main transformations are the demixtion of α into α and α , a chromium-rich phase, and the precipitation of a G phase (Ni 16 Ti 6 Si 7 ). [2][3][4][5][6][7] As a consequence, the ferrite phase becomes hard and brittle, which induces a significant decrease in toughness and tensile strain to failure. 5 Moreover, foundry flaws cannot be avoided in large cast components.…”

Section: Introductionmentioning

confidence: 99%

“…[2][3][4][5][6][7] As a consequence, the ferrite phase becomes hard and brittle, which induces a significant decrease in toughness and tensile strain to failure. 5 Moreover, foundry flaws cannot be avoided in large cast components. Cracks could initiate from them under fatigue loading induced, for example, by power variations of the nuclear plant or incidental conditions.…”

Section: Introductionmentioning

confidence: 99%

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Fatigue crack propagation in cast duplex stainless steels: thermal ageing and microstructural effects

Calonne

Gourgues

Pineau

2004

Fatigue Fract Eng Mat Struct

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A B S T R A C TThe ferrite phase of cast duplex stainless steels becomes embrittled after thermal ageing, leading to a significant decrease in fracture properties. In the present paper, the influence of ageing and solidification structure on the fatigue crack growth rates (FCGRs) and on the fatigue crack growth mechanisms in a cast duplex stainless steel is studied. FCGRs measured at room temperature increase slightly after ageing at 400 • C, due to ferrite cleavage and to the resulting irregular shape of the crack front. The crack propagates without any preferential path by successive ruptures of ferrite and austenite phases. The macroscopic crack propagation plane depends on the crystallographic orientation of the ferrite grain. Secondary cracks can appear due to the complex solidification structure. This in turn influences the FCGR. The fatigue crack closure level decreases with increasing ageing. This can be explained by a decrease in the kinematic cyclic hardening of these materials.Keywords cast duplex stainless steels; crack closure effect; crack propagation; EBSD; fatigue. N O M E N C L A T U R Ea = crack length B = specimen thickness K = K max -K min K eff = K max -K op K max = stress intensity factor at maximum load K min = stress intensity factor at minimum load K op = stress intensity factor at opening load P = applied load P max = maximum applied load P min = minimum applied load P op = crack opening load R = isotropic part of hardening W = specimen width X = kinematic part of hardening α = ferrite γ = austenite ε = total strain ε p = plastic strain σ = stress I N T R O D U C T I O NDuplex stainless steels containing up to 30% ferrite (α) in an austenite (γ ) matrix are used for the fabrication of pipes in nuclear power plants. These materials combine the qualities of each phase: the ferrite resistance to corrosion and to hot cracking and the austenite toughness. 1 However, it has been established that microstructural transformations occur in ferrite after long time exposures at the service temperature, i.e., about 300 • C.

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Section: Methodssupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Fatigue crack propagation in cast duplex stainless steels: thermal ageing and microstructural effects

Calonne

Gourgues

Pineau

2004

Fatigue Fract Eng Mat Struct

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“…With increasing ferrite spacing at constant ferrite content, the size of the ferrite island increases and the probability of a continuous path of ferrite through the thickness of the cast component increases. Bonnet et al [55] selectively dissolved the austenite phase from samples of CF8M and found that the ferrite phase remains continuous at ferrite volume fractions as low as 5% Therefore, the thermal ageing of Grade CF8M with such a ferrite distribution needs to be evaluated.…”

Section: The 475 • C Embrittlementmentioning

confidence: 99%

“…The volume fraction, distribution in the matrix, grain size and grain shape of the ferritic phase are observed to affect the nature of precipitation and the degree of embrittlement [54]. The bcc-fcc structural difference gives rise to factors such as load sharing between the two phases due to a difference in elastic and plastic response [55,56], difference in the ability to resist crack propagation. The majority of work, on the effect of 475 • C embrittlement on mechanical properties is reported from nuclear power industries.…”

Section: Introductionmentioning

confidence: 99%