Grain Refinement Alters Deformation Mechanisms to Mitigate Hydrogen Embrittlement in an Interstitial Nitrogen-Alloyed Austenitic Stainless Steel

Abstract

This study investigates the effects of grain size on deformation behavior and hydrogen embrittlement (HE) in an interstitial nitrogen-alloyed austenitic stainless steel (QN1906). Using slow strain rate testing (SSRT), thermal desorption spectroscopy (TDS), and electron microscopy, the work reveals that grain refinement from 56 to 4 μm significantly enhances yield strength (369.8 to 523.6 MPa) via the Hall-Petch effect while reducing HE susceptibility (elongation loss decreases from 33.3% to 24.2%). Coarse-grained samples exhibit pronounced twinning-induced plasticity (TWIP), whereas fine grains suppress twinning, shifting deformation mechanism to dislocation slip. Hydrogen accelerates both dislocation activity and twinning, decreasing twin spacing, attributed to the hydrogen-enhanced localized plasticity (HELP) mechanism. Hydrogen-induced cracks (HICs) nucleate at twin intersections and propagate along grain/twin boundaries due to strain concentration and hydrogen segregation. Grain refinement mitigates HE by reducing hydrogen content (1.22 to 0.19 wppm), effective diffusion coefficient (135.0×10−10 to 5.2×10−10 cm2/s), and local strain concentration at twin intersections. These findings highlight the critical role of grain size in balancing strength and HE resistance through tailored deformation mechanisms and hydrogen transport control.

Keywords: Nitrogen-alloyed austenitic stainless steels, Twinning, hydrogen embrittlement, HELP