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Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Quantification of hydrogen trapping in multiphase steels
T2 - Part I – Point traps in martensite
AU - Turk, A.
AU - Joshi, G.R.
AU - Gintalas, M.
AU - Callisti, M.
AU - Rivera-Díaz-del-Castillo, P.E.J.
AU - Galindo-Nava, E.I.
PY - 2020/8/1
Y1 - 2020/8/1
N2 - We quantified systematically the H trap density in martensite resulting from the presence of dislocations, grain boundaries and retained austenite through a combination of detailed microstructural characterisation, H permeation, thermal desorption and diffusion modelling. This thorough analysis allowed for the first time to deconvolve key microstructural constituents affecting H diffusion in multi-trap martensite. Three microstructures were investigated – as-quenched, tempered at 300 °C and tempered at 450 °C. The first two microstructures had identical dislocation densities and grain size, while the as-quenched one also contained 3.5 vol.% of retained austenite. The two tempered microstructures showed a large difference in dislocation density with few other microstructural differences. The as-quenched microstructure exhibited over an order of magnitude lower H diffusivity and increased H trapping due to retained austenite, while the tempered samples exhibited very similar diffusivities, indicating that dislocations have a limited effect on H trapping. Trap density scaling laws were successfully identified and validated through diffusion simulations and experiments. It was also shown that in martensite and heavily deformed ferrite, where the average grain size is small, grain boundaries are more effective trapping sites than dislocations. Our results also show that retained austenite cannot be effectively modelled as a point trap under the local equilibrium assumption, which is frequently used to model its effect on H diffusion, and that bulk trapping must be considered at least in two dimensions, which is addressed in part II of this series. © 2020 Acta Materialia Inc.
AB - We quantified systematically the H trap density in martensite resulting from the presence of dislocations, grain boundaries and retained austenite through a combination of detailed microstructural characterisation, H permeation, thermal desorption and diffusion modelling. This thorough analysis allowed for the first time to deconvolve key microstructural constituents affecting H diffusion in multi-trap martensite. Three microstructures were investigated – as-quenched, tempered at 300 °C and tempered at 450 °C. The first two microstructures had identical dislocation densities and grain size, while the as-quenched one also contained 3.5 vol.% of retained austenite. The two tempered microstructures showed a large difference in dislocation density with few other microstructural differences. The as-quenched microstructure exhibited over an order of magnitude lower H diffusivity and increased H trapping due to retained austenite, while the tempered samples exhibited very similar diffusivities, indicating that dislocations have a limited effect on H trapping. Trap density scaling laws were successfully identified and validated through diffusion simulations and experiments. It was also shown that in martensite and heavily deformed ferrite, where the average grain size is small, grain boundaries are more effective trapping sites than dislocations. Our results also show that retained austenite cannot be effectively modelled as a point trap under the local equilibrium assumption, which is frequently used to model its effect on H diffusion, and that bulk trapping must be considered at least in two dimensions, which is addressed in part II of this series. © 2020 Acta Materialia Inc.
KW - Austenite
KW - Dislocation density
KW - Grain boundaries
KW - Hydrogen diffusion
KW - Thermal desorption analysis (TDA)
KW - Advanced high strength Steel
KW - Diffusion
KW - Grain size and shape
KW - Hydrogen
KW - Microstructure
KW - As-quenched microstructure
KW - Average grain size
KW - Dislocation densities
KW - Hydrogen trapping
KW - Local equilibrium assumption
KW - Microstructural characterisation
KW - Retained austenite
KW - Tempered microstructure
KW - Martensite
U2 - 10.1016/j.actamat.2020.05.007
DO - 10.1016/j.actamat.2020.05.007
M3 - Journal article
VL - 194
SP - 118
EP - 133
JO - Acta Materialia
JF - Acta Materialia
SN - 1359-6454
ER -