On the role of the stacking fault energy in the beneficial effect of aluminium on the hydrogen embrittlement sensitivity of twinning-induced plasticity (TWIP) steel

Abstract

The hydrogen embrittlement sensitivity of three twinning-induced plasticity steels is investigated. A reference TWIP steel (18Mn-0.6C) is compared to an aluminium added TWIP steel (18Mn-0.6C-1.5Al) and a TWIP steel with an increased manganese content (24.5Mn-0.6C), exhibiting an identical stacking fault energy as the aluminium added material. As such, the importance of the stacking fault energy in the reduction of the hydrogen embrittlement sensitivity with aluminium addition is evaluated, which is considered as one of the possible underlying mechanisms. Through thermal desorption spectroscopy analysis, it is shown that both aluminium and manganese addition increase the hydrogen solubility while the hydrogen diffusivity is increased by manganese addition and decreased by aluminium addition. These effects can be considered as the bulk effects of both alloying additions on the hydrogen properties. With respect to the mechanical properties, aluminium addition leads to the expected increased resistance to hydrogen while manganese addition reduces the hydrogen resistance, despite the equal stacking fault energy. The aluminium added TWIP steel shows increased resistance to hydrogen-assisted crack initiation and propagation suppressing intergranular fracture in the presence of hydrogen. On the contrary, the increased manganese content increases the tendency for intergranular cracking in the presence of hydrogen. The critical hydrogen concentration might therefore be higher with the addition of aluminium.