Hydrogen permeability of annealed and deformed carbon steels with a granular cementite structure

Hydrogen permeability of St.40, U8, and U12 steels with granular cementite structures was studied. It was established that polytherms of the rate of hydrogen permeation obtained for annealed specimens of these steels have deflection points at t_cr=400°C. The permeability parameters (E, p₀) of these steels for t < t_cr increase to a lesser extent than in the case of specimens consisting of lamellar pearlite. After plastic deformation followed by annealing at various temperatures, substantial changes in the permeability are also observed but only for t < t_cr; the effect is smaller, however, than that observed for the same steels with a lamellar pearlite structure. The results obtained were attributed to the influence of ferritecarbide phase boundaries whose adsorption power is changed as a result of plastic deformation and subsequent annealing.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 5, No. 5, pp. 588–591, September–October, 1969.     

Hydrogen permeability of annealed and deformed carbon steels with a lamellar pearlite structure

Tests were carried out on specimens of carbonyl iron and St. 20, St. 40, U8, and U12 carbon steels with a lamellar pearlite structure. It was established that the structure sensitivity of hydrogen permeability of steel is relatively low at elevated temperatures (t>t_cr) and extremely high at low temperatures (tcr). As a result, curves representing the temperature dependence of annealed iron and steel specimens have deflection points at t_cr=400° C.Plastic deformation and subsequent annealing also produce substantial changes in hydrogen permeability only at tcr. Substantial differences in the laws of recovery of the rate of hydrogen permeation through iron and steel were observed; they were attributed mainly to the two-phase structure of steel and, especially, to the presence of interphase boundaries between ferrite and cementite.     

Effect of modification of the surface on the hydrogen permeability of reactor steels and their welded joints

We study the characteristics of hydrogen permeability of 10Kh9VFA and 12Kh18N10T reactor steels in the intact state and in the presence of welds and analyze the influence of oxidation and irradiation with protons on these characteristics. It is shown that the proton irradiation increases the thermal stability and the degree of protection against the penetration of hydrogen into the oxidized specimens. To determine the contribution of the welds to the solubility of hydrogen, we apply, for the first time, a combined approach, namely, the diffusion coefficient of hydrogen in the weld is found according to the changes in the electric resistance in the process of hydrogenation and the hydrogen permeability of the welded joint is determined from the ratio of the areas of the base metal and the weld. It is shown that the oxide films with structures of chromium spinel formed on the surface of steels decrease their hydrogen permeability by 1.5–2 orders of magnitude.     

Hydrogen embrittlement in power plant steels

In power plants, several major components such as steam generator tubes, boilers, steam/water pipe lines, water box of condensers and the other auxiliary components like bolts, nuts, screws fasteners and supporting assemblies are commonly fabricated from plain carbon steels, as well as low and high alloy steels. These components often fail catastrophically due to hydrogen embrittlement. A brief overview of our current understanding of the phenomenon of such hydrogen damage in steels is presented in this paper. Case histories of failures of steel components due to hydrogen embrittlement, which are reported in literature, are briefly discussed. A phenomenological assessment of overall process of hydrogen embrittlement and classification of the various damage modes are summarized. Influence of several physical and metallurgical variables on the susceptibility of steels to hydrogen embrittlement, mechanisms of hydrogen embrittlement and current approaches to combat this problem are also presented.     

Hydrogen pickup in ion nitrided steels

Abstract

Using the energy recoil detection analysis technique, hydrogen close to the surface of ion nitrided AISI steel M2 was studied. A surface hydrogen peak was observed in all samples, with or without exposure to the glow discharge. Some bulk hydrogen was also measured in all cases; its distribution was dependent on the history of the sample. The effect of the glow discharge is to drive part of the surface hydrogen into the bulk, depending on the treatment time. No obvious correlation with previously measured nitrogen profiles or microhardness profiles was found.

MST/1750     

Hydrogen assisted intergranular cracking in steels

McMahon suggested that interface decohesion at grain-boundary carbides and precipitates is the mechanism of hydrogen assisted intergranular cracking, HAIC, in high strength steels. In general, cleavage of grain-boundary carbides, adhesion failure or interface decohesion at grain-boundary carbides and precipitates, and crack-tip shear slip along the grain boundary could be the mechanisms of HAIC. Hydrogen reduces cleavage strength, adhesion strength and the resistance to shear slip; therefore, hydrogen assists intergranular cracking. A method of identifying such mechanisms is suggested. A generalized theory of hydrogen assisted cracking is deduced. Brittle crystals cleave on their cleavage planes. Cleavage cracking of such crystals is anisotropic. When the crack-tip stress intensity factor, K, is low, the tortuous cracking process from the anisotropy results in rapidly increasing Stage-I crack growth rate with respect to K. The mechanism of the crack growth threshold, K_TH, is also discussed.     

Hydrogen permeability of nonsymmetric metallic membranes

Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 27, No. 6, pp. 76–79, November–December, 1991.     

Effect of vacuum remelting on hydrogen permeability of steels

The results are reported of a study of the effect of vacuum remelting on hydrogen permeability of steels at 200°–700° C. It was shown that vacuum-arc remelting reduces the degree of contamination of steel and, as a result, produces a reduction in its hydrogen permeability, the chemical composition of steel being a decisive factor.     

Hydrogen permeability of multiphase V-Ti-Ni metallic membranes

Development of advanced hydrogen separation membranes in support of hydrogen production processes such as coal gasification and as front end gas purifiers for fuel cell based system is paramount to the successful implementation of a national hydrogen economy. Current generation metallic hydrogen separation membranes are based on Pd-alloys. Although the technology has proven to be successful, at issue is the high cost of palladium. Evaluation of non-noble metal based dense metallic separation membranes is currently receiving national and international attention. The focal point of the reported work was to evaluate a Group 5A-Ta, Nb, V-based alloy with respect to microstructural features and hydrogen permeability. Electrochemical hydrogen permeation testing of the V-Ti-Ni alloy is reported herein and compared to pure Pd measurements recorded as part of this same study. The V-Ti-Ni was demonstrated to have a steady-state hydrogen permeation rate an order of magnitude higher than the pure Pd material in testing conducted at 22 °C.