scholarly journals Role of Vanadium Carbide in Hydrogen Embrittlement of Press-Hardened Steels: Strategy From 1500 to 2000 MPa

2021 ◽  
Vol 7 ◽  
Author(s):  
Yi-Ting Lin ◽  
Hong Liang Yi ◽  
Zhi Yuan Chang ◽  
Hsin-Chih Lin ◽  
Hung-Wei Yen
Keyword(s):  
Hydrogen Embrittlement ◽  
Hydrogen Content ◽  
Hydrogen Trapping ◽  
Austenite Grain Size ◽  
Hardened Steels ◽  
Press Hardening ◽  
22Mnb5 Steel ◽  
Vanadium Carbides ◽  
Trapping Sites ◽  
Cathodic Charging

This work investigated hydrogen trapping and hydrogen embrittlement (HE) in two press-hardened steels, 22MnB5 for 1,500 MPa grade and 34MnB5V for 2000 MPa grade, respectively. Superior to the 22MnB5 steel, the newly developed 34MnB5V steel has an ultimate tensile strength of over 2000 MPa without sacrificing ductility due to the formation of vanadium carbides (VCs). Simulated press hardening was applied to two steels, and hydrogen was induced by cathodic charging. Susceptibility to HE was validated by slow strain-rate tensile test. When hydrogen content was high, the 34MnB5V steel fractured in elastic regime. However, when hydrogen content was 0.8–1.0 ppmw, the 34MnB5V steel bore much higher stress than the 22MnB5 steel before fracture. The behavior of hydrogen trapping was investigated by thermal desorption analyses. Although the two steels trapped similar amounts of hydrogen after cathodic charging, their trapping mechanisms and effective trapping sites were different. In summary, a finer prior austenite grain size due to the pinning effect of VCs can also improve the toughness of 34MnB5V steel. Moreover, trapping hydrogen by grain boundary suppresses the occurrence of hydrogen-enhanced local plasticity. Microstructural refinement enhanced by VCs improves the resistance to HE in 34MnB5V steel. Importantly, the correlation between hydrogen trapping by VCs and improvement of HE is not significant. Hence, this work presents the challenge in designing irreversible trapping sites in future press-hardened steels.

scholarly journals The Positive Role of Nanometric Molybdenum–Vanadium Carbides in Mitigating Hydrogen Embrittlement in Structural Steels

Materials ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7269
Author(s):  
Luis Borja Peral ◽  
Inés Fernández-Pariente ◽  
Chiara Colombo ◽  
Cristina Rodríguez ◽  
Javier Belzunce
Keyword(s):  
Diffusion Coefficient ◽  
Hydrogen Embrittlement ◽  
Hydrogen Diffusion ◽  
Hydrogen Permeation ◽  
Fatigue Crack Propagation Rate ◽  
Hydrogen Trapping ◽  
Hydrogen Atoms ◽  
High Hydrogen ◽  
Internal Hydrogen ◽  
Trapping Sites

The influence of hydrogen on the fracture toughness and fatigue crack propagation rate of two structural steel grades, with and without vanadium, was evaluated by means of tests performed on thermally precharged samples in a hydrogen reactor at 195 bar and 450 °C for 21 h. The degradation of the mechanical properties was directly correlated with the interaction between hydrogen atoms and the steel microstructure. A LECO DH603 hydrogen analyzer was used to study the activation energies of the different microstructural trapping sites, and also to study the hydrogen eggresion kinetics at room temperature. The electrochemical hydrogen permeation technique was employed to estimate the apparent hydrogen diffusion coefficient. Under the mentioned hydrogen precharging conditions, a very high hydrogen concentration was introduced within the V-added steel (4.3 ppm). The V-added grade had stronger trapping sites and much lower apparent diffusion coefficient. Hydrogen embrittlement susceptibility increased significantly due to the presence of internal hydrogen in the V-free steel in comparison with tests carried out in the uncharged condition. However, the V-added steel grade (+0.31%V) was less sensitive to hydrogen embrittlement. This fact was ascribed to the positive effect of the precipitated nanometric (Mo,V)C to alleviate hydrogen embrittlement. Mixed nanometric (Mo,V)C might be considered to be nondiffusible hydrogen-trapping sites, in view of their strong hydrogen-trapping capability (~35 kJ/mol). Hence, mechanical behavior of the V-added grade in the presence of internal hydrogen was notably improved.

scholarly journals Numerical Study of Hydrogen Trapping: Application to an API 5L X60 Steel

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Patricia Castaño-Rivera ◽  
Viviana P. Ramunni ◽  
Pablo Bruzzoni
Keyword(s):  
Hydrogen Permeation ◽  
Numerical Study ◽  
Local Equilibrium ◽  
Binding Energies ◽  
Hydrogen Trapping ◽  
Free Energies ◽  
Least Squares Fit ◽  
Permeation Transient ◽  
C 50 ◽  
Trapping Sites

A numerical finite difference method is developed here to solve the diffusion equation for hydrogen in presence of trapping sites. A feature of our software is that an optimization of diffusion and trapping parameters is achieved via a non linear least squares fit. On the other hand, we have demonstrated that usual electrochemical hydrogen permeation tests are enough to assess hydrogen free energies of trapping in the range of −35 kJ/mol to −70 kJ/mol. These conclusions are obtained by assuming the presence of saturable traps in local equilibrium with hydrogen and are validated by means of simulated permeation and degassing transients. In addition, we check our model performing electrochemical hydrogen permeation tests at 30°C, 50°C, and 70°C, on an API 5L X60 as received steel state to study its trapping and diffusion properties considering only one type of trapping site. The binding energies (ΔG) and the trap densities (N) are determined by fitting the theoretical model to the experimental permeation data. The steel presents a high density of weak traps, |ΔG|<35 KJ/mol, namely, N=1.4×10−5 mol cm−3. Strong trapping sites which alter the shape of the permeation transient are also detected; their ΔG values ranged from 57 to 72 KJ/mol.

Effects of Microstructure on the Hydrogen Embrittlement Resistance of Ultra High Strength Martensitic Steel Sheets

2021 ◽  
Vol 1016 ◽  
pp. 1331-1336
Author(s):  
Kosuke Shibata ◽  
Takuya Hiramatsu ◽  
Atsuhiro Shiraki ◽  
Junichiro Kinugasa ◽  
Tatsuya Asai ◽  
...  
Keyword(s):  
Low Temperature ◽  
Hydrogen Embrittlement ◽  
Carbon Content ◽  
Fracture Morphology ◽  
Hydrogen Trapping ◽  
Tempered Martensite ◽  
Interstitial Carbon ◽  
Steel Sheets ◽  
Embrittlement Resistance ◽  
Hydrogen Embrittlement Resistance

In this study, the relationship between hydrogen embrittlement resistance (HER) and the microstructure of low temperature tempered martensite was investigated using steel sheets which were controlled by carbon content and tempering conditions. Focusing on transition carbides and interstitial carbon content which are peculiar microstructures to low temperature tempered martensite, microstructure was evaluated by synchrotron radiation X-ray diffraction (SR-XRD). The HER was evaluated by U-bending and fracture surface was observed after the slow strain rate test (SSRT). As the result, the HER was improved and fracture morphology was changed from intergranular to quasi-cleavage when the high carbon content and high temperature tempering were adopted. In the steels improved the HER, the increase of the volume fraction of transition carbides and the decrease of interstitial carbon content was confirmed. Hydrogen trapping by the transition carbides could explain the change of the HER and fracture morphology. These results suggested that the hydrogen trapping by the transition carbides was effective to improve the HER of the low temperature tempering martensitic steels.

scholarly journals Numerical Evaluation on Analysis Methods of Trapping Site Density in Steels Based on Hydrogen Permeation Curve

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3712
Author(s):  
Bangshu Yang ◽  
Li Li ◽  
Lin Cheng
Keyword(s):  
Hydrogen Permeation ◽  
Effective Diffusivity ◽  
Trapping Site ◽  
Hydrogen Trapping ◽  
Site Density ◽  
Site Characteristics ◽  
Inappropriate Utilization ◽  
Magnitude Difference ◽  
Trapping Sites ◽  
Permeation Test

Hydrogen permeation techniques have been widely utilized to extract hydrogen effective diffusivity, as well as hydrogen trapping site characteristics in steels. Several methods have been proposed to examine reversible and irreversible trapping site characteristics. However, the inappropriate utilization of these simplified models, as well as incorrect value assignment to the key parameters, can result in several orders of magnitude difference in hydrogen trapping site density. Therefore, in order to evaluate these models and verify their application prerequisites, a serial of hydrogen permeation tests were numerically simulated and examined, separately considering reversible and irreversible hydrogen trapping sites. In the meantime, suggestions were given to conduct hydrogen permeation test more effectively, and evaluate hydrogen trapping site characteristics more precisely.

scholarly journals High Temperature Friction and Wear Performance of PVD Coatings under Press Hardening Contact Conditions

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Sergej Mozgovoy ◽  
Jens Hardell ◽  
Braham Prakash
Keyword(s):  
Coefficient Of Friction ◽  
Elevated Temperatures ◽  
Adhesive Wear ◽  
Work Piece ◽  
Pvd Coatings ◽  
Tribological Behaviour ◽  
Press Hardening ◽  
Coated Tools ◽  
22Mnb5 Steel ◽  
Forming Tools

Press hardening is widely employed to produce automotive structural and safety components from advanced high-strength steels. This process depends on friction between the forming tools and the work piece. Wear of the forming tools affects the dimensional accuracy of produced components and reduces their service life. It is therefore desirable to reduce wear of forming tools for press hardening applications. One way to achieve this is by applying hard physical vapour deposited (PVD) coatings on the tool. In this work, the tribological behaviour of PVD coated tool-work piece material pairs has been studied at elevated temperatures in an experimental set-up simulating the tribological conditions in press hardening. Four different PVD coatings deposited on tool steel and uncoated tools as reference were studied during sliding against uncoated and Al-Si coated 22MnB5 steel. Results show that uncoated tools exhibited the lowest coefficient of friction when sliding against uncoated 22MnB5 steel. A CrWN coating initially showed low coefficient of friction but it increased with increasing sliding distance. A TiAlN coating and one of two AlCrN coatings showed similar frictional behaviour when sliding against uncoated 22MnB5 steel. During sliding against uncoated 22MnB5 steel, adhesive wear has been found to be the dominant wear mechanism. Adhesive wear was considerably reduced in the case of hard PVD coated tools in comparison to that of uncoated tools. During sliding against Al-Si coated 22MnB5 steel, no clear advantage in terms of friction behaviour of uncoated or PVD coated tools was observed. However, the transfer of Al-Si coating material from the work piece to the tools was significantly reduced for PVD coated tools. Frictional instabilities in all cases involving Al-Si coated work piece material further confirmed the occurrence of adhesive material transfer.

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