Notch tip hydrogen assisted microdamage in fully pearlitic steel: The Tearing Topography Surface (TTS)

Abstract

This paper analyzes the hydrogen assisted microdamage (HAMD) region in high-strength eutectoid pearlitic steel on the basis of slow strain rate tests (SSRT) on axisymmetric round-notched samples under hydrogen embrittlement environmental conditions. The use of very different notched specimens and their associated stress and strain distributions in the vicinity of the notch tip allows a study of local triaxiality effects on hydrogen embrittlement of the round notched samples, as well as the important role of the hydrostatic stress state on hydrogen diffusion and micro-cracking (or micro-damage). The microscopic appearance of the hydrogen-affected region –the so-called tearing topography surface (TTS)– resembles micro-damage, micro-cracking or micro-tearing at a micro- or nano-scale due to hydrogen degradation, thereby affecting the notch tensile strength of the specimens and producing the phenomenon of hydrogen embrittlement/degradation. A micromechanical model is proposed to explain these hydrogen effects on the material on the basis of the lamellar micro- and nano-structure of the pearlitic steel under consideration.