Fatigue Properties of Ultra-Fine Grain Austenitic Stainless Steel and the Effect of Hydrogen

Kubota, Masanobu; Macadre, Arnaud; Mori, Kōichi; Mori, Ryusaburo

doi:10.1051/matecconf/201816503007

Cited by 1 publication

(1 citation statement)

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“…Masanobu et al compared the fatigue properties of austenite stainless steels with ultra-fine grain size and coarse grain size. They found grain refinement significantly reduces the crack tip opening displacement (CTOD), which is proportional to the crack growth rate [26]. This may be because nanosized grains impede crack propagation by crack deflection along grain boundaries, increasing the fracture toughness through increased fractality of the crack surface.…”

Section: Factors Impacting Scc Resistancementioning

confidence: 99%

Stress–Corrosion Cracking of AISI 316L Stainless Steel in Seawater Environments: Effect of Surface Machining

Ren

Ernst

2020

Metals

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To understand the effect of surface machining on the resistance of to SCC (stress–corrosion cracking) in marine environments, we tested nuts surface-machined by different methods in a seawater-spraying chamber. Two forms of cracks were observed: on the machined surface and underneath it. On the surface, cracks connected with the pitting sites were observed to propagate perpendicular to the hoop-stress direction, identifying them as stress–corrosion cracks. Under the surface, catastrophic transgranular cracks developed, likely driven by hydrogen embrittlement caused by the chloride-concentrating level of humidity in the testing environment. Under constant testing conditions, significantly different SCC resistance was observed depending on how the nuts had been machined. Statistical evaluation of the nut surface-crack density indicates that machining by a “form” tool yields a crack density one order of magnitude lower than machining by a “single-point” tool. Microstructural analysis of form-tool-machined nuts revealed a homogeneous deformed subsurface zone with nanosized grains, leading to enhanced surface hardness. Apparently, the reduced grain size and/or the associated mechanical hardening improve resistance to SCC. The nanograin subsurface zone was not observed on nuts machined by a single-point tool. Surface roughness measurements indicate that single-point-tool-machined nuts have a rougher surface than form-tool machined nuts. Apparently, surface roughness reduces SCC resistance by increasing the susceptibility to etch attack in Cl--rich solutions. The results of X-ray diffractometry and transmission electron microscopy diffractometry indicate that machining with either tool generates a small volume fraction (< 0.01) of strain-induced martensite. However, considering the small volume fraction and absence of martensite in regions of cracking, martensite is not primarily responsible for SCC in marine environments.

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Section: Factors Impacting Scc Resistancementioning

confidence: 99%