The Role of Prior Austenite Grains in Fatigue Crack Initiation and Propagation in Low Carbon Martensite

Kunio, Takeshi; Shimizu, Masao; Yamada, Kazuo; Enomoto, M.; Yoshitake, Akihide

doi:10.1111/j.1460-2695.1979.tb01083.x

Cited by 21 publications

(10 citation statements)

References 7 publications

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“…However, with increasing hardness, eventually the bulk grain strength becomes greater than the strength of the interface and cracks nucleate intergranularly. Analogous to this mechanism, intergranular fatigue cracking may occur in low‐carbon martensitic steels where proeutectoid ferrite precipitates at and weakens the prior austenite grain boundaries 21 . Thus, the term ‘processing flaw’ is adopted because the formation of these flaws occurs during the final heat‐treating or manufacturing process.…”

Section: The Hall–petch–murakami Model (Hpm Model)mentioning

confidence: 99%

Competing roles of microstructure and flaw size

Mcgreevy

Socie

1999

Fatigue Fract Eng Mat Struct

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Historically, engineers have relied on macroscopic properties, e.g. hardness and tensile strength to predict fatigue limits as analytical tools to model the process did not exist. Consequently, many empirical modifications to the fatigue limit have been made to account for variables, e.g. surface roughness, state of stress, inclusion content, environmental effects, etc. A mechanistic model is proposed to quantify the effects of these parameters on the fatigue limit of metals, specifically steels. Fatigue resistance, i.e. the threshold condition of a non‐propagating crack, is determined by two parameters: non‐propagating defect or crack size; and the strength of the barrier to crack propagation. The concept of three defect types associated with three different flaw‐dominated fatigue regimes is introduced. Furthermore, application of the model to fatigue mechanisms in high‐strength steels, synergistic effects of surface finish and intergranular cracks, competition between surface and subsurface fatigue nucleation, tempering, and scatter in fatigue behaviour is demonstrated. The model can be implemented in material screening, selection and processing, as well as a guide for future material research and design. Overall, the model is proven as a simple and robust tool for qualifying and statistically quantifying material behaviour.

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Section: The Hall–petch–murakami Model (Hpm Model)mentioning

confidence: 99%

Competing roles of microstructure and flaw size

Mcgreevy

Socie

1999

Fatigue Fract Eng Mat Struct

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“…However, in spite of the fact that the trends of the effects of k t and ρ on fatigue limit are reasonably well indicated, the physical significance of the parameter L 0 is not understood, neither is there a correlation between L 0 and any characteristic microstructural dimension. Tanaka and co‐workers [ 17, 18] have suggested that L 0 usually coincides with the length of the stage I crack, but this coincidence was not clarified. The transition from stage I (mode II) to Stage II (mode I) crack growth depends on notch geometry, stress amplitude and stress state, slip character, grain size, etc.…”

Section: The Notch Size Effect and Stress Gradientsmentioning

confidence: 99%

Fatigue Limit of Blunt‐notched Components

Chapetti

Kitano

Tagawa

et al. 1998

Fatigue Fract Eng Mat Struct

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The position and effective resistance of microstructural barriers and their relation to the fatigue strength of blunt‐notched specimens are analysed and modelled for three low‐carbon steel microstructures. A relationship for the notch size effect on the basis of the experimental evidence that the fatigue limit (both plain and notched) represents the threshold stress for the propagation of the nucleated microstructurally short cracks, was derived. The derived relationship characterizes the fatigue notch sensitivity by means of the parameter ktd defined as the stress concentration introduced by the notch at a distance d from the notch root surface equal to the distance between microstructural barriers, and was experimentally verified for two notch geometries in three microstructures: ferrite, ferrite–bainite and bainite–martensite.

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“…Smaller grainsized specimens, Series A, were also used, together with the series C, D, and E specimens, in order to study the role of prior austenite grain boundary. These series C, D, and E specimens were prepared to make a reduction of the deformation resistance in the narrow band of the prior austenite grain boundaries by the delayed quenching procedure [17].…”

Section: Materials and Experimental Proceduresmentioning

confidence: 99%

“…Figure 8 is a typical example of the crack path independent of the prior austenite grain boundary, which is revealed by the special etching technique [18]. Furthermore, the role of the prior austenite grain boundary was studied by using a smaller grain-sized specimen, series A, and delay-quenched specimens, series C, D, and E, whose resistance for plastic deformation at the grain boundary was intentionally weakened [17].…”

Section: Effect Of Microstructural Parameters On the Initiation And Ementioning

confidence: 99%

The early stage of fatigue crack growth in martensitic steel

et al. 1981

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In low ductility and high strength steels, the early stage fatigue behavior associated with non-metallic inclusions is a highly localized phenomenon near the inclusions. However, the nature of the fatigue crack initiation process is not clear. In this paper, a special emphasis is placed on the possible differences in the mechanism of initiation and the early growth of fatigue cracks between a martensitic steel and ordinary ductile materials.The poor adhesion between matrix and aluminum oxide inclusion leads to the formation of an inclusion pit which serves as a simple stress raiser. The fatigue crack originates at the periphery of this inclusion pit at an angle of 45 degrees to the principal stress direction. Metallurgical and micro-fractographical observations revealed that the initiation and early growth of fatigue cracks from non-metallic inclusion are of the shear rather than the tensile mode. Thus, it is concluded that, though the fatigue process is quite localized in the vicinity of inclusion, the mechanism for an initiation and early growth of fatigue cracks is essentially the same as that for ductile materials. The effects of metallurgical heterogeneities in the martensite, such as the prior austenite grain boundaries, packets, and plates on the initiation and early growth of the cracks, are also discussed from the mechanical-metallurgical viewpoint.

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The Role of Prior Austenite Grains in Fatigue Crack Initiation and Propagation in Low Carbon Martensite

Cited by 21 publications

References 7 publications

Competing roles of microstructure and flaw size

Competing roles of microstructure and flaw size

Fatigue Limit of Blunt‐notched Components

The early stage of fatigue crack growth in martensitic steel

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