Hydrogen traps, repellers, and obstacles in steel; Consequences on hydrogen diffusion, solubility, and embrittlement
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Sample No. No. No. No. No.
1 2 3 4 5
CH4 Emission (Arb. Unit)
HE Emission (Arb. Unit)
Percentage of Brittle Fracture
110 130 180 20 8
7 12 35 17 8
70 70 75 0 5
H20 emission were not observed, while the CH4 emission was always significant. The H2 emission was less pronounced than the CH4 emission. Typical results for the embrittled regions are shown in Figure I. The partial pressures vs time curves for CH4 and H2 are presented in Figure 1. Both curves are normalized to the pressure before fracture. The fracture occurred at time zero. The results for a sample taken from the region that was not embrittled are presented in Figure 2. If the fracture time is much less than the decay of the gas emission signal (less than 0.1 second), the area under the peaks can be used as a relative measure of the gas emission during fracture. Table II summarizes some typical results of the gas emission and SEM measurements. Sample numbers 1 to 3 were cut from the embrittled part of the tube while sample numbers 4 and 5 were taken from the part of the tube which was not embrittled. The methane emission for sample numbers 4 and 5 and the hydrogen emission for all samples (except number 3) are given to characterize the noise level of the system. It is clear from Table II that the samples studied can be divided into two groups: ductile samples (percentage of brittle fracture less than 15 pct) and brittle samples (percentage of brittle fracture is in the range of 70 to 80 pet). Thus, a function connection, reflecting the correlation, between the brittleness and methane emission could not be established. Table II, however, demonstrates clearly that only the brittle fracture is associated with methane emission; thus, we conclude that the formation of methane filled bubbles, cracks, etc. may be primarily responsible for the brittleness of these evaporator tubes. In summarizing, we conclude that this simple measurement technique is suitable to identify the gas content of the cracks, bubbles, etc. revealed by the fracture.
Hydrogen Traps, Repellers, and Obstacles in Steel; Consequences on Hydrogen Diffusion, Solubility, and Embrittlement G.M. PRESSOUYRE It is now a well-established fact that hydrogen may be more or less reversibly trapped at particular defect sites in steel; direct evidence such as that obtained by autoradiography techniques, ~ or indirect evidence as in permeation experiments, 2 are numerous. These results even have allowed the drawing of various classifications of possible traps in steel, e.g., References 1, 3, 4, 5, 6. The aim of this communication is to propose an additional classification of defects that have the opposite effect of trapping, i.e., that repel hydrogen. As will be shown, such "hydrogen repellers" are numerous in steel; furthermore, some of their effects may be mistaken for those of trapping. Hence, we will also indicate how to distinguish between "traps" and "repellers".
Identification of hydrogen traps, repellers, and obstacles in steels. In a recent classification, 3 several reasons were given to e
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