https://iopscience.iop.org/article/10.1088/1468-6996/14/3/033001/pdf

Nitrogen in chromium-manganese stainless steels: a review on the evaluation of stacking fault energy by computational thermodynamics.

Fatigue behavior of three high-Mn TWIP steels with the grain sizes between 4.5 and 55 μm were investigated in reversed plane bending in the high-cycle regime. Crack initiation and propagation stages were examined by optical, scanning electron and atom force microscopy. It was found that the fatigue limit, which is the stress amplitude leading to fatigue life beyond 2 × 10 6  cycles, is quite high, about 400 MPa, for these steels. This value is between 0.42 and 0.48 of the tensile strengths, similarly as for austenitic stainless steels. Refining the grain size still increases the fatigue resistance. Neither martensite is formed nor mechanical twinning takes place in the course of cycling, but intense slip bands are created with extrusions and intrusions. Fatigue cracks tend to nucleate at an early stage of fatigue life, and preferentially on grain and twin boundaries, especially in the intersection sites of slip bands and boundaries, besides slip bands. However, the crack propagation takes place mainly transgranularly creating ductile striations and protrusions on fracture surfaces.

Fatigue behavior of high-Mn TWIP steels

The role of localized deformation in hydrogen-assisted crack propagation in 21Cr–6Ni–9Mn stainless steel

Abnormal effect of nitrogen on hydrogen gas embrittlement of austenitic stainless steels at low temperatures

Mechanical properties of skeletal bone in gene-mutated stöpseldtl28d and wild-type zebrafish (Danio rerio) measured by atomic force microscopy-based nanoindentation

The fracture mode and crack propagation behavior of brittle fracture at 77 and 4 K in an 18Cr-18Mn-0.7N austenitic stainless steel were investigated using optical and scanning electron microscopy. The fracture path was examined by observing the side surface in a partially ruptured specimen. The relationship of the fracture facets to the microstructures was established by observing the fracture surface and the adjacent side surface simultaneously. Three kinds of fracture facets were identified at either temperature. The first is a smoothly curved intergranular fracture facet with characteristic parallel lines on it. The second is a fairly planar facet formed by parting along an annealing twin boundary, a real {111} plane. There are three sets of parallel lines on the facet and the lines in different sets intersect at 60 deg. The third is a lamellar transgranular fracture facet with sets of parallel steps on it. Fracture propagated by the formation of microcracks on a grain boundary, annealing twin boundary, and coalescence of these cracks. The observation suggests that the ease of crack initiation and propagation along the grain boundary and the annealing twin boundary may be the main reason for the low-temperature brittleness of this steel. A mechanism for grain boundary cracking, including annealing twin boundary parting, has been discussed based on the stress concentration induced by impinging planar deformation structures on the grain boundaries.

Y. Hamaguchi

Papers

A study on fractography in the low-temperature brittle fracture of an 18Cr-18Mn-0.7N austenitic steel