Impact of hydrogen and crosshead displacement rate on the martensitic transformations and mechanical properties of 304L stainless steel

Abstract

In-situ tensile testing of electrochemically hydrogen charged 304L stainless steel at different crosshead displacement rates results in a largely different elongation at fracture compared to the corresponding test in air. At slow engineering strain rates (below 1E-2 s−1), large ductility losses are observed and the alloy suffers from clear hydrogen embrittlement (HE). The HE increases with decreasing strain rate due to the increased time that is given for hydrogen to diffuse and accumulate. However, at higher engineering strain rates (above 1E-2 s−1), the ductility increases with hydrogen charging. Due to intense martensitic transformations triggered by a combined temperature and hydrogen effect, the strain hardening of the alloy improves and necking is postponed. The temperature effect is restricted by reference testing in solution showing that HE still prevails. The enhanced martensitic transformations with hydrogen open opportunities for the creation of hydrogen resistant materials where the balance between HE and enhanced martensitic transformations can be optimized for the required application. Furthermore, tensile pre-straining results in an increased HE susceptibility due to the presence of stress concentrations and α’-martensite.