The Influence of Strain on Hydrogen Entry and Transport in a High Strength Steel in Sodium Chloride Solution

Abstract

The influences of mechanical strain on hydrogen entry and transport are reported for a high strength steel alloy (AISI 4340) under cathodic polarization in aqueous sodium chloride solution. The overall rate of hydrogen permeation and the quantity of hydrogen absorbed are shown to be particularly low in alkaline chloride at low cathodic current densities if the charging surface has been contaminated by slight corrosion. Evidence is presented that illustrates the role of mechanical strain in promoting enhanced hydrogen absorption as a result of film rupture. In addition to the conventional Devanathan-Stachurski method, results from plastic straining of a cylindrical annular Devanathan-Stachurski sample confirm the film rupture concept. Film removal is shown to enhance the overall rate of hydrogen entry by increasing the hydrogen surface coverage and possibly the adsorption-absorption rate constant on the bare surfaces formed. This increases the mobile hydrogen concentration in the metal lattice. The presence of the intact metastable film modifies the kinetics of the hydrogen evolution reaction, lowering the cathodic hydrogen overpotential at a given cathodic current density. This, consequently, is shown to lower hydrogen absorption for a given cathodic current density. The net effect of film rupture is to promote an increase in the hydrogen permeation rate independent of changes in the diffusion coefficient. Additional information indicates that long range enhanced diffusion of hydrogen by dislocation transport is not observed. Further evidence suggests that for sharp cracks, the rate of hydrogen accumulation at a position a distance from the crack tip where the crack initiates is an absorption controlled transport process. These findings provide additional insight on the rate limiting steps controlling the "time dependent" hydrogen assisted failure process of high strength steels in sodium chloride solution.Classical treatments describing the stress corrosion cracking behavior of metals in aqueous media typically incorporate surface film rupture as a necessary stage in the *Electrochemical Society Active Member. **Electrochemical Society Student Member. 1Present address: Sandia National Laboratories, Mechanical Metallurgy Division, Albuquerque, New Mexico 87185. overall process. For example, criteria for stress corrosion cracking susceptibility in metals usually place emphasis on the amount of corrosion occurring after film rupture before repassivation occurs (1-5). Less generally acknowledged is the role of surface film rupture in the environmental hydrogen assisted cracking of high strength steels in aqueous environments where atomic hydrogen is clearly ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 134.117.10.200 Downloaded on 2015-06-24 to IP Experimentol ProceduresMaterials and specimen preparation.--Specirnens were produced from a single heat of AISI 4340 steel (UNS no~ G43400), which had been heat-treated to form tempered marten...

Measurement and Modeling of Hydrogen Environment-Assisted Cracking in Monel K-500

“…[14] For alloys in aqueous environments, the damaging effect of slow-rising K may be ascribed to the effect of crack tip strain and strain rate on crack surface film stability and reactivity leading to increased H uptake. [75,91] Slow-rising K similarly lowered the threshold for hydrogen embrittlement of steel, either stressed in pure H 2 , [49] or precharged with H then stressed in air. [13] For these cases, the different behavior of a stationary crack under rising K vs a propagating crack under fixed or falling K is related to interaction of FPZ stress, plastic strain, and trapped H leading to ''plasticity-related hydrogen induced cracking'' (PRHIC).…”

Evaluation of Hydrogen Absorption into Iron by Alternating Current Responses in an Electrochemical Hydrogen Permeation Cell

“…[11][12][13][14] This technique has been applied to the measurement of hydrogen absorption into metallic materials and confirmed to be quite useful for in-situ evaluation of the amount of hydrogen absorption into metals and alloys. [15][16][17] Normally, in the Devanathan-Stachurski permeation technique, two identical vessels in each of which electrochemical measurements can be performed with a conventional threeelectrode-system are prepared, and then a thin metallic film, "membrane", is placed between the vessels and tightened up with them. In this study, two identical glass vessels were used; one of the glass vessels used for the hydrogen-entry side is referred to "H-entry-side" cell, and the other is for the hydrogen-withdrawal side to "H-withdrawal-side" cell, as shown in Fig.…”

Strain Gradient Plasticity-Based Modeling of Damage and Fracture

“…This behavior differs from the σ H insensitivity of the HEAC predictions for Monel K-500 (Figure 8.3), and is due to the wider range of E APP examined for the steels, as well as the absolute values of C Hσ , which can be very high for ultra-high strength steel. For this high σ H regime, the bounded definition of crack tip hydrogen solubility in (8.6) and (8.7) is affirmed, as is particularly evident by comparison of the solid line predictions of da/dt II versus E APP above -0.800 V SCE in Figures 8.7 and 8.8 (speculatively, crack growth rates for E APP below -0.850 V SCE are lower than the hydrogen-diffusion model prediction due to surface reaction rate limitation [185]). The K T H versus E APP predictions are mixed.…”

“…The variability of measured K T H for -0.800 V SCE < E APP < -0.625 V SCE is due in part to this limitation. Finally, surface reaction may interact with hydrogen diffusion for E APP below about -0.750 V SCE [185]. da/dt II from the hydrogen diffusion model in (8.2) is an upper bound when surface reaction rate is slow.…”