The influence of hydrogen on the mechanical and fracture properties of some martensitic advanced high strength steels studied using the linearly increasing stress test, Corrosion Science http://dx. HighlightsHydrogen influence increased with strength, charging potential, and decreasing applied stress rate.The hydrogen influence was manifest by reduced strength, changed fracture and decreased ductility.The decrease in yield stress was attributed to solid solution softening by hydrogen Hydrogen caused a change at the fracture stress when the specimen was mechanically unstable The fracture changed from ductile cup-and-cone fracture to macroscopically brittle shear fracture. ABSTRACTThe influence of hydrogen on the mechanical and fracture properties of four martensitic advanced high strength steels was studied using the linearly increasing stress test and electrochemical hydrogen charging. The hydrogen influence increased with steel strength, decreasing charging potential, and decreasing applied stress rate. Increased hydrogen influence was manifest in (i) the decreased yield stress attributed to solid solution softening by hydrogen and (ii) the reduced macroscopic ductility, and by the change from ductile cupand-cone fracture to macroscopically brittle shear fracture, attributed to a dynamic interaction of hydrogen with the dislocation substructure somewhat similar to the HELP mechanism.Keywords: A. steel; B. SEM; C. hydrogen embrittlement 10].The martensitic AHSS (MS-AHSS) are the strongest, but exhibiting the lowest ductility [11]. Strength and hardness increase with increasing carbon content, whereas the ductility and toughness decrease with increasing carbon content. The lack of ductility also limits formability of these steels, which is important, because auto bodies are mechanically shaped from sheet steel. Nevertheless, MS-AHSS are important because they have the highest strength-to-price ratio among AHSS [8]. MS-AHSS find applications in the parts of the vehicle which require good crash resistance, such as bumper beams and reinforcements, door intrusion beams and reinforcements, windscreen upright reinforcements, and B-pillar reinforcements [1,[12][13][14].Hydrogen embrittlement (HE) has long been the bane of high-strength steels [15][16][17].HE is a failure mode caused by the presence of a relatively small amount of hydrogen. HE may trigger catastrophic failures at relatively-small applied loads, or may cause degradation of ductility and toughness. Recent studies have revealed some HE susceptibility for some AHSS [18][19][20][21][22]. However, past attempts to predict HE resistance based on the microstructure, composition and processing, have not been successful. Hence, a much deeper understanding of how hydrogen interacts with steel is essential to reduce or eliminate HE in AHSS.Several mechanisms have been proposed for HE. For non-hydride forming metals such as steel, the following three mechanisms are the most likely: (i) hydrogen-enhanced decohesion (HEDE), (ii) hydrogen-enhanced local plasticity (HELP)...

Please cite this article in press as: J. Venezuela, et al., Influence of hydrogen on the mechanical and fracture properties of some martensitic advanced high strength steels in simulated service conditions, Corros. Sci. (2016), http://dx. a b s t r a c tThis work investigated the influence of hydrogen on the mechanical and fracture properties of four martensitic advanced high-strength steels in simulated service conditions: (i) immersed in 3.5 wt% NaCl solution, and (ii) at substantial applied stress rates. There was little influence of hydrogen for the four MS-AHSS in 3.5 wt% NaCl. Similarly, there was little influence of hydrogen for hydrogen-precharged MS1300 and MS1500 subjected to tensile tests at substantial stress rates. The diffusivities of hydrogen in MS980, MS1300 and MS1500 were similar. The use of a Pt counter electrode during cathodic hydrogen charging is not recommended.

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The martensitic advanced high-strength steels (MS-AHSS) are used to create fuel-efficient, crashworthy cars. Hydrogen embrittlement (HE) is an issue with high-strength steels; thus, the interaction of hydrogen with MS-AHSS needs to be studied. There are only a few published works on the HE of MS-AHSS. The current literature indicates that the HE susceptibility of MS-AHSS is affected by (i) the strength of the steel, (ii) the applied strain rate, (iii) the concentration of hydrogen, (iv) microstructure, (v) tempering, (vi) residual stress, (vii) fabrication route, (viii) inclusions, (ix) metallic coatings, and (x) specific precipitates. Some of the unresolved issues include (i) the correlation of laboratory results to service performance, (ii) establishing the conditions or factors that lead to a certain HE response, (iii) studying the effect of stress rate on HE, and (iv) a comprehensive understanding of hydrogen trapping in MS-AHSS.

Permeability experiments were used to study hydrogen diffusion and trapping The trapping effect was less significant at a more negative charging potential The lattice diffusion coefficient of hydrogen was measured The densities of reversible hydrogen trap sites was ~ 2 × 10 18 sites cm-2