Papers by Keyword: Hydrogen Embrittlement

Abstract: Effect of hydrogen-charging was investigated with respect to the tensile properties of three types of cast irons: JIS FCD400, FCD450 and FCD700. In this study, hydrogen charging led to a marked ductility loss in all the cast irons. The thermal desorption spectroscopy and the hydrogen microprint technique revealed that, in the hydrogen-charged specimens, most of solute hydrogen was diffusive and mainly segregated at graphite, graphite/matrix interface zone and pearlite. In the fracture process of non-charged specimen, neighboring graphites were interconnected with each other mainly by ductile dimple fracture. On the other hand, in the fracture process of hydrogen-charged specimen, the graphites were interconnected by cracks. The difference in the fracture morphology between the non-charged and the hydrogen-charged specimens is attributed to the presence of diffusive hydrogen in graphite and graphite/matrix interface. During early stage of fracture process in hydrogen-charged specimen, the interspace between graphite and matrix is filled with hydrogen gas, which leads to the ductility loss of matrix in the vicinity of graphite. Even after the initiation of crack from graphite, hydrogen is continuously outgassed from graphite and supplied to the crack tip. Therefore, concerning the hydrogen effect on the strength of cast irons, a role of subsurface graphite as a “local hydrogen supplier” should be taken into consideration.

Abstract: In order to investigate the susceptibility of HSLA steels to hydrogen embrittlement (HE) when cathodic protection system was applied, a new electrochemical hydrogen permeation test method was performed to measure the hydrogen permeation current behavior through X65 steel and X80 steel in artificial seawater with different polarized potentials. Besides, slow strain rate test (SSRT) was introduced to study the effect of penetrated hydrogen atoms on the HE susceptibility of the steels. Results showed that with the decrease of the polarized potential, the sub-surface hydrogen concentration in the steels became higher and higher, and the corresponding HE susceptibility increased as well. What’s more, the X80 steel was more vulnerable to HE, and that owns to the minor grain size and M-A microstructure, which may trap more hydrogen atoms, and thus led to the HE susceptibility difference between the two steels. All these findings would be used as guidance when cathodic protection were carried out for offshore HSLA steel structures.

Abstract: The hydrogen diffuses and accumulates at the stress concentration area like a crack tip and it causes hydrogen embrittlement. To clarify the mechanism of hydrogen embrittlement, it is important to obtain the hydrogen concentration behavior. However, experimental detection is not feasible due to the high diffusivity of hydrogen and numerical analyses have been preceded. In this paper, by using a finite element and finite difference coupled method at which the diffusion analysis is performed by FDM coupled with the stress analysis by FEM, the analyses of hydrogen diffusion were conducted under cyclic loading conditions.

Abstract: Bolt connection is a usual connection in power transmission and power transformation steel structures, and preservative treatments such as rust removal and galvanization are adopted to protect the bolts. In order to investigate the influence of hot-dip galvanizing on the tensile strength of bolt, common strength bolts and high strength bolt produced in four factories were tested to gain tensile strength. The results indicate that hot-dip galvanizing may reduce the tensile strength of bolts, and galvanizing technics of different factory have difference influence on the tensile strength of bolts.

Abstract: Thermal desorption spectroscopy (TDS) is a very important tool in hydrogen embrittlement (HE) related research and has been applied on many different materials over the last decades in order to improve knowledge on the HE phenomenon. TDS provides the opportunity to distinguish between different types of hydrogen traps based on the analysis of a spectrum with different peak temperatures each corresponding to hydrogen desorption from a specific trap. These peak temperatures, and consequently the different traps in a material, arise from the various microstructural characteristics of the material. However, TDS results are also influenced by many other parameters, such as the sample surface preparation, the electrolytes used for hydrogen charging, sample geometry, charging time, current density, charging temperature. Even though the use of thermal desorption to evaluate hydrogen-metal interactions has increased over the past years, a careful evaluation of the effect of these other parameters was not yet performed. In this work, the impact of some of the above mentioned parameters was studied. It was demonstrated that the sample geometry, the surface roughness, and the initial total pressure of the TDS chamber influenced significantly the obtained TDS spectrum.

Abstract: Thermal desorption spectroscopy (TDS) is a very important tool in hydrogen related research. It allows to distinguish between the different types of microstructural hydrogen traps based on the analysis of the different temperatures at which hydrogen desorbs from the material during heating. These peak temperatures depend on the metallurgical and microstructural characteristics of the steel under investigation and provide important information on the possible mechanisms for hydrogen embrittlement (HE). In the present work, multiple TDS experiments and an in-depth study of the microstructure were performed on a TRIP steel (TRIP700) that was previously cold deformed in order to make a correlation between the microstructural features of this material, e.g. grain boundaries, dislocations, martensite formation and the peaks that became visible during TDS. The results obtained for the TRIP grade were compared with those obtained for electrolytic pure iron, which only contained a limited amount of possible trap sites such as grain boundaries and an increasing amount of dislocations due to previous application of cold deformation. Significant differences between both materials and a significant impact of the degree of cold deformation for TRIP steels were observed.

Abstract: In this experiment two kinds of 410L stainless steel, i.e., the first one is prepared by the I/M process and the second one is prepared by MIM process were used, and their corrosion behavior under stress in deionized water and the aqueous solution of 0.01kmol·m^-3HCl+1.72mol·m^-3MgCl₂ (pH=2.33) has been investigated by Electrochemical Impedance Spectroscopy (hereafter shortened as EIS) under Slow Strain Rate Tensile (hereafter shortened as SSRT) test. The charge transfer resistance (R_ct) of the I/M specimen is larger than that of the MIM specimen irrespective of under stress or non-stress, which means that the I/M specimen has the better corrosion resistance than the MIM specimen in the 0.01kmol·m^-3HCl+1.72mol·m^-3MgCl₂ (pH=2.33) solution. It was also confirmed from the fracture surface observation that hydrogen embrittlement occurred on the MIM specimen in the aqueous solution of 0.01kmol·m^-3HCl+1.72mol·m^-3MgCl₂ (pH=2.33). This result would be confirmed to be due to the existing impurities and defects in the MIM specimen.

Abstract: The role of microstructure in susceptibility to hydrogen uptake and property degradation is being evaluated using a number of high strength pipeline steels. To do so, a cellular automaton (CA) model has been used to examine the effect of grain size, as a first step in assessing the influence of microstructure. The simulation results of hydrogen diffusion into microstructures with different grain sizes are presented.

Abstract: The aim of this work is to study the effects of hydrogen absorption on mechanical properties of pipe API 5L X70 steel. This study is conducted in special soil solution NS4 with pH 6.7 It show that the tensile properties like yield stress, ultimate strength and elongation at failure reduced under hydrogen embrittlement. Several fatigue tests (three (03) points bending tests) on roman tile specimens with notch are performed. Fatigue initiation is detected by acoustic emission. A comparison between specimens electrolytically charged with hydrogen and specimens without hydrogen absorption is made and it has been noted that fatigue initiation time is reduced when hydrogen embrittlement occurs. The field of elastoplastic stresses near the notch is computed by the finite-element method with the Abaqus software package. Effective distance and stress are calculated with the volumetric approach and the Notch intensity Factor of the roman tile specimen is determined for each loading value used in our tests.

Abstract: Investigation on the behavior of hydrogen is needed to spread the use of hydrogen fuel cell vehicles. Hydrogen microprint technique (HMPT) has been known as an effective method to investigate the hydrogen behavior by visualizing the microscopic location of hydrogen in relation to the microstructure. In the present study, the behavior of electrolitically charged hydrogen in 6061 and 7075 aluminum alloys with T6-temper has been investigated by means of HMPT. Both in the two alloys, hydrogen was detected on constituent particles and in the matrix. Total amount of detected hydrogen was markedly larger in 7075 than in 6061, although the distribution in depth direction far narrower and the fraction of hydrogen detected in the matrix with respect to that on the constituent was larger. These fact was presumed to be caused by the difference in the fine precipitates between the two alloy formed during final aging treatment.