TY - JOUR

T1 - Quantification of hydrogen trapping in multiphase steels

T2 - Part II – Effect of austenite morphology

AU - Turk, A.

AU - Pu, S.D.

AU - Bombač, D.

AU - Rivera-Díaz-del-Castillo, P.E.J.

AU - Galindo-Nava, E.I.

PY - 2020/9/15

Y1 - 2020/9/15

N2 - We tackle the role of austenite in multiphase steels on hydrogen diffusion systematically for the first time, considering a range of factors such as morphology, interface kinetics and the additional effect of point traps using both experiments and modelling. This follows the findings from part I where we showed that austenite cannot be parametrised and modelled as point traps under the assumption of local equilibrium, unlike grain boundaries and dislocations. To solve this, we introduce a 2D hydrogen diffusion model accounting for the difference in diffusivities and solubilities between the phases. We first revisit the as-quenched martensite permeation results from part I and show that the extremely low H diffusivity there can be partly explained with the new description of austenite but is partly likely due to quench vacancies. We then also look at the H absorption and desorption rates in a duplex steel as a case study using a combination of simulations and experiments. The rates are shown to depend heavily on austenite morphology and the kinetics of H transition from ferrite to austenite and that an energy barrier is likely associated to this transition. We show that H diffusion through the ferrite matrix and austenite islands proceeds at similar rates and the assumption of negligible concentration gradients in ferrite occasionally applied in the literature is a poor approximation. This approach is also applicable to other austenite-containing steels as well as other multiphase alloys.

AB - We tackle the role of austenite in multiphase steels on hydrogen diffusion systematically for the first time, considering a range of factors such as morphology, interface kinetics and the additional effect of point traps using both experiments and modelling. This follows the findings from part I where we showed that austenite cannot be parametrised and modelled as point traps under the assumption of local equilibrium, unlike grain boundaries and dislocations. To solve this, we introduce a 2D hydrogen diffusion model accounting for the difference in diffusivities and solubilities between the phases. We first revisit the as-quenched martensite permeation results from part I and show that the extremely low H diffusivity there can be partly explained with the new description of austenite but is partly likely due to quench vacancies. We then also look at the H absorption and desorption rates in a duplex steel as a case study using a combination of simulations and experiments. The rates are shown to depend heavily on austenite morphology and the kinetics of H transition from ferrite to austenite and that an energy barrier is likely associated to this transition. We show that H diffusion through the ferrite matrix and austenite islands proceeds at similar rates and the assumption of negligible concentration gradients in ferrite occasionally applied in the literature is a poor approximation. This approach is also applicable to other austenite-containing steels as well as other multiphase alloys.

KW - Austenite

KW - Duplex stainless steel

KW - Hydrogen desorption

KW - Hydrogen diffusion

KW - Hydrogen permeation

KW - Interface diffusion

KW - Advanced high strength Steel

KW - Diffusion

KW - Ferrite

KW - Grain boundaries

KW - Hydrogen

KW - Morphology

KW - Concentration gradients

KW - Ferrite matrix

KW - H absorption

KW - Hydrogen trapping

KW - Interface kinetics

KW - Local equilibrium

KW - Multi phase alloys

U2 - 10.1016/j.actamat.2020.07.039

DO - 10.1016/j.actamat.2020.07.039

M3 - Journal article

VL - 197

SP - 253

EP - 268

JO - Acta Materialia

JF - Acta Materialia

SN - 1359-6454

ER -