On the Microstructural Basis of Cleavage Fracture Initiation in Ferritic and Bainitic Steels

Abstract

The microstructural basis of the critical tensile stress criterion of cleavage fracture is discussed. It is shown that cleavage can be carbide induced in bainitic steels as well as in ferritic steels. The plastic work expended in brittle crack propagation is shown to be somewhat smaller for bainitic steels than for ferritic steels. This is proposed to be caused by the much higher dislocation density of the bainitic microstructure. The statistical nature of the cleavage fracture initiation process is shown to result in a test piece geometry dependent cleavage fracture stress.

Cleavage fracture and irradiation embrittlement of fusion reactor alloys: mechanisms, multiscale models, toughness measurements and implications to structural integrity assessment

“…This seems reasonable for V à , since it depends directly on the coarse-scale trigger particle microstructure. Measurements based on blunt notch tests, where cleavage is controlled by a broadly peaked r n , also support the assumption that r à is approximately independent of temperature [31,[33][34][35][40][41][42][43][44]. A corollary is that the inherent matrix K l is also temperature-independent.…”

“…However, in at least two cases, r à was approximately constant up to temperatures of %100°C [31,42]. Interpretation of these results is complicated by the fact that the r à , or corresponding statistical model Weibull strength parameters, are different for blunt notches compared to the A à -V à cleavage criterion for cracks [39,40,66]. Cracks have higher, but more spatially localized, distributions of r n compared to the notches with lower but more broadly distributed stress fields.…”

Fracture of brittle particles in a ductile matrix

“…A relatively simple expression capable of describing the particle size distribution is [10][11][12] By combining (2) and (3) it is then easy to calculate the total fracture probability P(f) of the particle distribution at any given stress…”

Micromechanisms and toughness for cleavage fracture of steel

“…The difference between sharp and blunted cracks may be due to a decrease in the crack tip stress field combined with an increase in the highly deformed region associated with the loss of constraint due to decreasing notch acuity. Both factors need to be combined into a Weibull weakest-link analysis to describe the effect of crack-tip blunting on cleavage [20]. There are also differences in plastic zone size associated with stationary and slowly growing cracks [21), which may be related to the differences in K 1 between reinitiation of a sharp cleavage crack and cleavage initiation from the fip of a sharp ductile crack.…”