Hydrogen Concentration in Dual‐Phase (DP) and Quenched and Partitioned (Q&amp;P) Advanced High‐Strength Steels (AHSS) under Simulated Service Conditions Compared with Cathodic Charging Conditions

Engineering Failure Analysis

Zhou

Venezuela

et al. 2018

Self Cite

The hydrogen influence was evaluated (A) for laboratory conditions with hydrogen concentrations larger than in service, and (B) at substantial loading rates to simulate a crash. Hydrogen in the studied laboratory conditions caused minimal influence for 980DP and 1200DP, and some influence for 980DP-650YS, 980DP-700YS, 980QP and 950TW. Simulated crash situations caused some influence for 980DP, 980QP and 950TW; their properties quickly reverted after the end of hydrogen charging. Two new mechanisms are proposed: (i) hydrogen enhanced macroscopic plasticity (HEMP) decreasing the yield stress, and (ii) hydrogen assisted micro-fracture (HAM) decreasing ductility at fracture at the ultimate tensile strength.

Section: Tests In Airsupporting

confidence: 93%

Section: Relevance To Dp Qandp and Twip Ahssmentioning

confidence: 99%

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Evaluation of the influence of hydrogen on some commercial DP, Q&P and TWIP advanced high-strength steels during automobile service

Engineering Failure Analysis

Zhou

Venezuela

et al. 2018

Self Cite

“…The theoretical curve for a diffusion transient is given by [4,5,15,[18][19][20]22,123,136,137]: Figure 4. A succession of hydrogen permeation transients were measured with increasing and decreasing hydrogen fugacity, by charging at various potentials in 0.1 M NaOH solution, for pure Fe hydrogen pre-charged at −1.500 V Ag/AgCl in 0.1 M NaOH solution for 48 h to achieve steady state surface conditions on the input side.…”

Section: Permeation Cellmentioning

confidence: 99%

“…Figure 1 illustrates the permeation cell [4,86], which is widely used [19,20,22,23,[117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][132][133][134], and was used in this research project. Hydrogen is produced by the applied cathodic potential on the left hand side of the specimen, by the electrochemical cell on the left hand side of the specimen.…”

Section: Permeation Cellmentioning

confidence: 99%

Influence of Hydrogen on Steel Components for Clean Energy

Atrens

Tapia-Bastidas

et al. 2018

CMD

Self Cite

The influence of hydrogen on the mechanical properties of four, medium-strength, commercial, quenched-and-temped steels has been studied using the linearly increasing stress test (LIST) combined with cathodic hydrogen charging. The relationship was established between the equivalent hydrogen pressure and the hydrogen charging overpotential during cathodic hydrogen charging, though the use of electrochemical permeation experiments and thermal desorption spectroscopy. The cathodic hydrogen charging conditions were equivalent to testing in gaseous hydrogen at hydrogen fugacities of over a thousand bar. Under these hydrogen-charging conditions, there was no effect of hydrogen up to the yield stress. There was an influence of hydrogen on the final fracture, which occurred at the same stress as for the steels tested in air. The influence of hydrogen was on the details of the final fracture. In some cases, brittle fractures initiated by hydrogen, or DHF: Decohesive hydrogen fracture, initiated the final fracture of the specimen, which was largely by ductile micro-void coalescence (MVC), but did include some brittle fisheye fractures. Each fisheye was surrounded by MVC. This corresponds to MF: Mixed fracture, wherein a hydrogen microfracture mechanism (i.e., that producing the fisheyes) competed with the ductile MVC fracture. The fisheyes were associated with alumina oxide inclusion, which indicated that these features would be less for a cleaner steel. There was no subcritical crack growth. There was essentially no influence of hydrogen on ductility for the hydrogen conditions studied. At applied stress amplitudes above the threshold stress, fatigue initiation, for low cycle fatigue, occurred at a lower number of cycles with increasing hydrogen fugacity and increasing stress amplitude. This was caused by a decrease in the fatigue initiation period, and by an increase in the crack growth rate. In the presence of hydrogen, there was flat transgranular fracture with vague striations with some intergranular fracture at lower stresses. Mechanical overload occurred when the fatigue crack reached the critical length. There was no significant influence of hydrogen on the final fracture.

Hydrogen Trapping in Some Automotive Martensitic Advanced High‐Strength Steels

Venezuela

Zhou²,

et al. 2017

Adv Eng Mater

Hydrogen permeation experiments are used to investigate hydrogen trapping in commercial automotive martensitic advanced high‐strength steels. Hydrogen trapping increases with increasing mechanical strength, as indicated by (i) the decrease in the hydrogen diffusion coefficient, and (ii) the increase in reversible hydrogen trap density. The measured trap densities are in the order of ≈1017– ≈ 1018 cm−3. The relationship between trapping characteristics and HE susceptibility of MS‐AHSS is discussed in terms of Hydrogen Enhanced Macroscopic Plasticity (HEMP) and Hydrogen Assisted Micro‐fracture (HAM).