Development of Numerical Model to Predict Cleavage Fracture Toughness of Ferrite Steel

Shibanuma, Kazuki; Aihara, Shuji; Matsubara, M.; Shirahata, Hiroyuki; Handa, Tsunehisa

doi:10.2355/tetsutohagane.99.40

Cited by 7 publications

(9 citation statements)

References 9 publications

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“…14) We employed the same steels in the present study. The steels have two types of chemical compositions as shown in Table 1.…”

Section: Preparation Of the Test Steelsmentioning

confidence: 99%

“…In addition, the maximum thicknesses of cementite particle, the average and the maximum sizes of ferrite grains obtained by the EBSD measurement, 16) and yield stresses at room temperature obtained by tensile tests are shown in Table 5. 14) In order to quantify the influencing factors on cementite cracking, tensile tests using circumferential notched round bar specimens were conducted. These tests are the same as those in the author's previous study.…”

Section: Measurements Of Cementite Particle Thicknessmentioning

confidence: 99%

“…6,14) On the other hand, in a microscopic aspect, the cementite cracking is expected to be generated when an internal stress of cementite particle reaches a critical value, i.e., fracture stress. In this section, a finite element analysis was first shown to clarify the microscopic behavior related to cementite cracking.…”

Section: Estimation Of Internal Stress Of Cementitementioning

confidence: 99%

“…14) This model requires only the stress-strain curve, distributions of ferrite grain size and cementite particle thickness, but not any fitting parameters. It was developed considering three stages on the microscopic process of cleavage fracture initiation: (I) a formation of fracture nucleation by cementite cracking; (II) a propagation of the cementite crack into a ferrite matrix and formation of a cleavage crack; and (III) a propagation of the cleavage crack across ferrite grain boundary.…”

Section: Introductionmentioning

confidence: 99%

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Observation and Quantification of Crack Nucleation in Ferrite-Cementite Steel

2014

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It is known that a cracking of brittle phase such as cementite works as a trigger of cleavage fracture initiation. This study shows a microscopic observation of cracked cementite and its quantitation of the cracking nucleation in ferrite-cementite steels. Seven steels with various sizes of microstructures are produced by laboratory scale vacuum melting and rolling. The cementite particle thickness was measured by a SEM observation and an image analysis. Tensile tests using circumferential notched round bar specimens were conducted. A trace analysis of cleavage surface of cementite using the EBSD analysis indicated a possibility that the cleavage surface coincides with (010) plane. Distributions of cementite particle crack lengths were measured for various strain and stress conditions. In order to understand a microscopic internal stress of cementite particle, a finite element analysis was carried out. An estimation formula of internal stress of the cementite particle from macroscopic stress and strain was developed based on the numerical results. A nucleation of cementite cracking should be quantitated based on a stochastic framework because of its uncertainties such as distribution, shape, orientation and so on. The measured distributions of cementite particle thickness and crack length were approximated by introducing a distribution function considering upper limit. Probability of nucleation of cementite cracking was formulated as a function of cementite particle thickness and macroscopic stress and strain, based on the approximated distribution function and the estimation formula of internal stress of the cementite particle.

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“…14) We employed the same steels in the present study. The steels have two types of chemical compositions as shown in Table 1.…”

Section: Preparation Of the Test Steelsmentioning

confidence: 99%

Section: Measurements Of Cementite Particle Thicknessmentioning

confidence: 99%

Section: Estimation Of Internal Stress Of Cementitementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Observation and Quantification of Crack Nucleation in Ferrite-Cementite Steel

2014

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“…[12][13][14][15] This model requires only two kinds of material information: distributions of ferrite grain and cementite particle sizes and a true stress-strain curve, without any adjustable parameters. The model is composed of two parts, i.e.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Micro-crack Initiation as a Trigger of Cleavage Fracture in Ferrite-pearlite Steels

et al. 2017

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This study presents investigations of the micro-crack formation in pearlite microstructure as a trigger of unstable cleavage crack propagation in ferrite-pearlite steel. In order to clarify the micro-crack formation mechanism, a trace analysis was conducted to compare the direction of crack surface with those of cleavage and slip planes of ferrite in pearlite. It is found that any directions of crack surface were not coincident with those of {100} planes. On the other hand, all of the directions of crack surfaces showed good agreement with those of {110} planes. The result showed a probability that the micro-cracks in pearlite are formed by the shear fracture on slip planes in ferrite. The condition of unstable propagation from a microcrack in pearlite into a neighbor ferrite grain was investigated. Effective surface energy was estimated by the crack length obtained by SEM observation and the local stress calculated by finite element analysis. The result showed the estimated effective surface energy of a propagation from micro-crack in pearlite into ferrite matrix is larger than that of cleavage crack propagation across boundary between ferrite grains. A probability of the micro-crack formation in pearlite was quantified by the measurement of micro-cracks in steels having various ferrite-pearlite microstructures and finite element analysis. As a result, the probability of micro-crack formation could be effectively estimated as a function of only the equivalent plastic strain, independently from temperature, volume fraction of pearlite and loading condition.

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