Abstract
The hydrogen diffusion behavior and hydrogen embrittlement susceptibility of dual phase (DP) steels with different martensite content were investigated using the slow strain-rate tensile test and hydrogen permeation measurement. Results showed that a logarithmic relationship was established between the hydrogen embrittlement index (IHE) and the effective hydrogen diffusion coefficient (Deff). When the martensite content is low, ferrite/martensite interface behaves as the main trap that captures the hydrogen atoms. Also, when the Deff decreases, IHE increases with increasing martensite content. However, when the martensite content reaches approximately 68.3%, the martensite grains start to form a continuous network, Deff reaches a plateau and IHE continues to increase. This is mainly related to the reduction of carbon content in martensite and the length of ferrite/martensite interface, which promotes the diffusion of hydrogen atoms in martensite and the aggregation of hydrogen atoms at the ferrite/martensite interface. Finally, a model describing the mechanism of microstructure-driven hydrogen diffusion with different martensite distribution was established.
Highlights
As the automobile industry has developed rapidly, lightweight automobile components have become important means for conserving energy and reducing emissions (Li et al, 2003)
Previous studies have shown that the decrease in hydrogen diffusion coefficient of dual phase (DP) steel is correlated to martensite, which contains a high density of dislocations and other defects to capture hydrogen atoms (Sun et al, 1989; Hadzipasicet al., 2011a; Hadzipasicet al., 2011b; Koyama et al, 2014; Liu et al, 2016a; Liu et al, 2018; Hui et al, 2019)
It is logical to deduce that the hydrogen diffusion coefficients decrease as martensite content increases
Summary
As the automobile industry has developed rapidly, lightweight automobile components have become important means for conserving energy and reducing emissions (Li et al, 2003). When the martensite content increases to 30%, the martensite phase starts to distribute continuously along the grain boundary and hydrogen embrittlement susceptibility reaches a stable value. In this study, we investigated the hydrogen embrittlement behavior of DP steels using slow-strain rate tensile tests. Hydrogen embrittlement susceptibility measurements were carried out on pre-polished tensile samples (26 mm × 6 mm × 1.4 mm) using a slow strain rate tensile test machine (WDML-3) under in situ electrochemical H-charging. The strain rate was selected as 1 × 10−6 s−1 to facilitate keeping the diffusion of hydrogen atoms in step with the dislocation movement, thereby resulting in hydrogen embrittlement (Kumamoto et al, 2019) Both the hydrogen-charged and uncharged specimens were subjected to tensile test, with the former group referred as “H-charged” group, and the latter group referred as “air” group. The microstructure was analyzed to determine the distribution of silver particles on SEM
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