International Symposium: “HYDROGENIUS, I2CNER and HydroMate Joint Research Symposium on
HydrogenMaterials Interactions 2021”, Invited talk, January 28th and 29th, 2021, Kyushu University, JapanThe synergistic action of HELP and HEDE mechanismsof hydrogen embrittlement in steels
Oral presenter: Milos B. Djukic 1
1Associate Professor,
University of Belgrade, Faculty of Mechanical Engineering,
Department of Engineering Materials and Welding & Welding and WeldedStructures Module, Kraljice Marije 16, 11200 Belgrade, SerbiaAuthors: Milos B. Djukic 1, Gordana M. Bakic 1, Vera Sijacki Zeravcic 1, Bratislav Rajicic 1,Aleksandar Sedmak 1, Muhammad Wasim 2,3 and Jovana Perisic 1
12

University of Belgrade, Faculty of Mechanical Engineering, Kraljice Marije 16, 11120 Belgrade, Serbia
School of Engineering, Infrastructure Engineering Department, The University of Melbourne, 3010 Melbourne,VIC, Australia
3
School of Engineering, Civil Engineering Department, RMIT University, 3000 Melbourne, VIC, Australia

Abstract
Hydrogen effects and provoked degradation of mechanical properties are expressed in diverse
and often in opposite ways depending on three main factors: material, mechanic, andenvironmental. The deleterious and often multifaceted effects of hydrogen on the mechanicalproperties of different metallic structural materials, including different grades of steel has
been confirmed in numerous studies. Simultaneous action in a cooperative manner of thehydrogen-enhanced localized plasticity (HELP) and hydrogen-enhanced decohesion (HEDE)
mechanisms (HELP+HEDE model) of hydrogen embrittlement (HE) were detected and fully
confirmed experimentally to be active, depending on the local concentration of hydrogen insteel [1-3], and not only through simulation and modeling. However, critical evaluation andquantification of the synergy between the HELP and HEDE mechanisms, and their combined
effects on various macromechanical properties, still does not exist. The recently proposed
HELP+HEDE model of HE is based on the correlation of mechanical properties to SEM
microscopy fractography analysis of fracture surfaces in the presence of simultaneous action
in a cooperative manner of the HELP and HEDE mechanisms of HE depending on the local
concentration of hydrogen [3]. Particular emphasis is given to the proposal of the novel andunified HELP + HEDE model based on the specific microstructural mapping of the dominant
HE mechanisms with implications on the fracture process and resulting hydrogen-assisted
fracture modes [3]. This presentation provides recent results and the current state of the art inunderstanding in overview-form of critical discussion about the synergistic action andinterplay of HE mechanisms in steels and iron, experiments, and models. Also, the effect ofhydrogen on the material mechanical properties and ductile to brittle fracture transition
resulting from the concurrent and synergistic (HELP+HEDE) or due to the competing actionof HELP and HEDE mechanisms is discussed. The proposed model should enable enhanced
predictive maintenance of industrial component systems.
[1] M.B. Djukic, V. Sijacki Zeravcic, G.M. Bakic, A. Sedmak, B. Rajicic, Hydrogen damage ofsteels: A case study and hydrogen embrittlement model, Engineering Failure Analysis, 58 (2015), pp.
485-498.
[2] M.B. Djukic, G.M. Bakic, V. Sijacki Zeravcic, A. Sedmak, B. Rajicic, Hydrogen embrittlement ofindustrial components: prediction, prevention, and models, Corrosion, 72 (2016), pp. 943-961.
[3] M.B. Djukic, V. Sijacki Zeravcic, G.M. Bakic, A. Sedmak, B. Rajicic, The synergistic action andinterplay of hydrogen embrittlement mechanisms in steels and iron: Localized plasticity anddecohesion, Engineering Fracture Mechanics 216 (2019), p. 106528.