Environmentally Assisted Cracking: Theory and Practice: Hydrogen Embrittlement II
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Bai Cui, University of Nebraska Lincoln; Raul Rebak, GE Global Research; Srujan Rokkam, Advanced Cooling Technologies, Inc.; Jenifer Locke, Ohio State University
Wednesday 8:30 AM
March 22, 2023
Room: Sapphire 410B
Location: Hilton
Session Chair: C. Tasan, Massachusetts Institute of Technology; Tom Depover, Ghent University
8:30 AM Invited
Hydrogen Embrittlement in Alloys with Metastable Phases: C. Tasan1; Menglei Jiang1; Michela Geri1; Hyun Oh1; 1Massachusetts Institute of Technology
In alloys for structural applications, mechanically-induced martensitic transformation can exhibit well-documented beneficial effects, e.g., in delaying plastic instability (through transformation-induced plasticity), or fatigue cracking (through transformation-induced toughening). In presence of hydrogen, however, some of these benefits are lost, and the transformation itself can create preferential cracking sites. Here in this overview talk, phase stability effects in presence of hydrogen will be discussed. The focus will be on Fe-Mn-Co-Cr alloys, and martensitic stainless steels with reverted austenite, showing some light at the end of the tunnel for beneficial metastability effects in presence of hydrogen.
9:00 AM
Hydrogen Effects on Mechanical and Toughness Properties of Pipeline Steels: Xin Pang1; Su Xu1; 1CanmetMATERIALS, Natural Resources Canada
This paper reviews commonly used hydrogen charging methods and effects of hydrogen on Charpy toughness. Preliminary ex-situ Charpy tests of electrolytically pre-charged specimens of three pipe steels were performed at room temperature. The gaseous hydrogen charging method is directly applicable to hydrogen pipelines but the lack of testing capability has limited its utilizations in R&D and qualification. The electrolytic charging method can be convenient and appropriate for investigating the effects of hydrogen especially if correlations between current density or potential and gaseous pressure are established. Preliminary experimental results have shown that the Charpy absorbed energy (CVN) of the electrolytically pre-charged specimens were lower than those of uncharged specimens by 8-20% for the steels investigated. Based on the load-deflection curves, the effects of hydrogen on Charpy toughness were to facilitate fracture initiation from the notch and accelerate fracture propagation after fracture initiation. In-situ Charpy and fracture toughness testing at slow rates would be more suitable for pipeline applications than impact testing.
9:20 AM
Some Antagonist Processes of Hydrogen/Plasticity Interaction in fcc Metal Alloys: The Effect of Ni3Al Precipitate State on Nickel Base Alloys: Siva Prasad Murugan1; Nadjib Iskounen1; Marie Landeiro Dos Reis1; Jamaa Bouhattate1; Abdelali Oudriss1; Feaugas Xavier2; 1LaSIE; 2Lasie Cnrs Umr73
Hydrogen-deformation interactions and their role in plasticity are well accepted as key features in understanding hydrogen embrittlement. To prevent this process, we have studied in nickel base alloys (Waspaloy@) the consequence of Ni3Al precipitation on hydrogen storage and the consequences on the different plasticity mechanisms. Using micro-indentation and TEM characterization three regimes of plasticity (weekly coupled shearing, strongly coupled shearing and Orowan bypassing by looping). The solubility of hydrogen and the misfit of precipitate are correlated, and their evolution coincide with the three regimes previously defined. Using loading and unloading tensile tests and nano-indentation tests, the impact of hydrogen on elementary processes of dislocation shearing and Orowan bypassing by looping is questioned in terme of short- and long-range internal stresses and elasticity properties. Antagonist softening and hardening effects of hydrogen are related and commented on the base of TEM observations and precipitate state.
9:40 AM
Effect of Nickel and Chromium Contents on Hydrogen Embrittlement of High Strength Bolt Steel for Offshore Plants: Byungrok Moon1; Sourav Saha1; Jimin Nam1; Changhoon Lee2; Junho Chung3; Namhyun Kang1; 1Pusan National University; 2Korea Institute of Materials Science; 3Hyundai-Steel
High-strength bolt steel that is directly exposed to low-temperature seawater has to ensure corrosion resistance and low-temperature impact toughness to seawater. And this material is medium carbon steel and is manufactured through rolling, quenching, and tempering heat treatment. The microstructure of this steel is tempered martensite. If this material does not have sufficient resistance to hydrogen embrittlement in low-temperature seawater, stress corrosion cracking caused by hydrogen embrittlement may be accelerated, and this causes a delayed fracture, which occurs suddenly rupture during material use. This study was conducted to investigate the cause of this delayed fracture and to improve the hydrogen embrittlement resistance. To evaluate resistance to hydrogen embrittlement according to elements Nickel and Chromium, an in-situ Slow Strain Rate Test and - 40 ℃ impact test are conducted with electrochemical charging. Finally, diffusivity and trap site concentration of hydrogen are introduced to explain these differences with electrochemical hydrogen permeation.
10:00 AM Break
10:20 AM Invited
Evaluation of the Responsible Hydrogen Embrittlement Mechanism in Martensitic Steels by Advanced Microstructural Characterization: Tom Depover1; Kim Verbeken1; Margot Pinson1; 1Ghent University
This work investigates the susceptibility to hydrogen embrittlement (HE) of martensitic steels. Thermal desorption spectroscopy shows that the main H trapping sites are dislocations and high angle grain boundaries (HAGBs). In-situ bending tests reveal that H causes a transition towards a cleavage fracture, paired with a significant ductility loss explained by hydrogen enhanced decohesion (HEDE), indicating that H at HAGBs play an important role. Next, Al is gradually added as well. For an optimal Al/C ratio, a very thin ferritic film on the PAGBs is formed significantly increasing the ductility in air. When testing in H, the microfilm causes a delay in fracture, since fracture propagation is redirected along the interface resulting in intergranular fracture. The responsible mechanism is an interplay between HEDE and hydrogen enhanced localized plasticity (HELP). Hence, an optimal Al/C ratio in martensitic steels offers the opportunity to increase the HE resistance by inventive grain boundary engineering.
10:50 AM
A Unified Fracture Criterion in Consideration of Hydrogen Effect in Martensitic Steel Sheet: Geonjin Shin1; Hyejin Kim2; Chanyang Kim3; Kijeong Kim2; Seungchae Yoon2; Myoung-Gyu Lee1; 1Seoul National University; 2Hyundai-Steel; 3Korea Institute of Materials Science
In this study, the effect of hydrogen on the mechanical behavior of fully martensitic steel is investigated. The slow strain rate test is conducted for the hydrogen-charged samples. Also, a finite element model is developed to simulate the hydrogen transport in the samples. Then, a new fracture criterion is proposed by considering the effect of hydrogen on the martensitic steel. The experiments show that the plastic hardening of the martensitic steel is lowered, and fracture behavior changes from ductile to brittle as the hydrogen concentration increases. To model the hydrogen effect on mechanical and failure behavior, a sigmoidal softening law is suggested to represent hydrogen-assisted plasticity. Furthermore, a unified fracture model combining the strain-based, and stress-based fracture criteria is proposed as a function of stress triaxiality, lode angle parameter, and hydrogen concentration. The unified fracture criterion can successfully predict the fracture behavior under various stress states and hydrogen conditions.