Duplex stainless steel fracture surface analysis using x-ray fractography

A B S T R A C T X-ray (XR) diffraction is a well-known experimental technique used for measuring residual stresses in metallic materials. If we apply the XRD technique to the fracture surface of a broken part, it becomes a fractographical technique, that is to say that it is possible to relate the results of the measurement to the loading condition that lead a component to fail. However, in the past this technique was mainly used to analyse standard specimens and not mechanical components and there are few experimental investigations concerning the possibility of using this technique to investigate the cause of fatigue failures. In this paper, after a brief introduction to the technique, XRD fractography is applied to a diesel engine crankshaft that failed under known fatigue loading. It was possible to determine the load that lead the crankshaft to fail and to evidence some original aspects about the application of this technique to real machine parts. Comparison with finite element results served to confirm that XRD can be used as complementary tool to scanning electron microscope (SEM) observation or as a substitute to SEM observation, in the case of damaged fracture surface. N O M E N C L A T U R Ed = interatomic spacing of a family of crystallographic planes E = elastic modulus FWHM = full width at half maximum of the diffraction peak K max = maximum value of the stress intensity factor R = stress ratio of a fatigue cycle r pc = cyclic plastic zone size r pm = monotonic plastic zone size UTS = ultimate tensile strength α = coefficient of relationship between the plastic zone size and the stress intensity factor K = stress intensity factor range ε = strain ψ = angle between the normal of the sample and the normal of the diffracting plane θ = Braggs' angle of the material σ ys = monotonic yield stress σ ys = cyclic yield stress I N T R O D U C T I O NX-ray (XR) diffraction is an experimental technique used in many scientific and industrial fields to measure different properties of materials. It can be applied to crysCorrespondence: M. Guagliano. talline and poly-crystalline materials and consists of measuring the angle of diffraction of an incident XR beam on a surface. In mechanical engineering, XR diffraction is mostly used to measure residual stresses in materials and machine parts: 1,2 the main advantages of this technique with respect to others is that it is non-destructive if used to obtain residual stresses on the surface and that

show abstract

“…In Ref. [15], fracture surface of a dual phase stainless steel used in chemical plants is investigated. Rajanna et al 16,17 .…”

Section: Introductionmentioning

confidence: 99%

“…In Ref. [15], fracture surface of a dual phase stainless steel used in chemical plants is investigated. Rajanna et al 16,17 performed XR fractographic analyses of C45 steel considering differing temperature of fracture.…”

Section: Introductionmentioning

confidence: 99%

X‐ray fractography of a diesel engine crankshaft

Pariente

Guagliano

2008

Fatigue Fract Eng Mat Struct

View full text Add to dashboard Cite

show abstract

“…Fatigue crack propagation micro‐mechanisms have only scarcely been investigated. More numerous studies deal with FCGB in hot‐ or cold‐rolled duplex stainless steels containing larger amounts of ferrite (45–62%) 14–23 . It has been shown that, in these materials, the fatigue crack growth rate (FCGR) is increasing with thermal ageing and with the amount of ferrite and with the associated embrittlement.…”

Section: Introductionmentioning

confidence: 99%

“…Up to now, the effect of ageing on crack closure in duplex stainless steels is not well established. Moreover, only RICC and TICC mechanisms have been studied 11 , 18–20 , 23 …”

Section: Introductionmentioning

confidence: 99%

“…More numerous studies deal with FCGB in hot-or coldrolled duplex stainless steels containing larger amounts of ferrite (45-62%). [14][15][16][17][18][19][20][21][22][23] It has been shown that, in these materials, the fatigue crack growth rate (FCGR) is increasing with thermal ageing and with the amount of ferrite and with the associated embrittlement. Microstructural effects have also been evidenced but all the authors do not agree on their origin.…”

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

View full text Add to dashboard Cite

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.

show abstract