Fatigue Crack Growth under High Pressure of Gaseous Hydrogen in a 15-5PH Martensitic Stainless Steel: Influence of Press
- PDF / 1,085,203 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 68 Downloads / 236 Views
INTRODUCTION
THE predicted shortage of conventional energy sources as well as the environmental concerns motivates the development of hydrogen-based energy infrastructure. Commonly, steels are considered for components of storage, transportation, and distribution systems such as piping, valves, etc. However in service these components, directly exposed to high-pressure hydrogen gas, might be subjected additionally to fluctuating cyclic loading. Hence, special attention has to be paid to the fatigue resistance of the materials in the presence of gaseous hydrogen. It is well established that a degradation of mechanical properties induced by hydrogen (commonly designated as ‘‘hydrogen embrittlement’’) occurs in many steels, especially in high-strength steels.[1] Indeed, a high strength allows a higher stress to be sustained by these materials and, as a consequence, a higher hydrogen concentration to be collected in regions of increased stress before failure.[2] More particularly, in a gaseous hydrogen environment, these steels exhibit a decrease in ductility under monotonic loading[3] and enhanced fatigue crack growth under cyclic loading.[4–6] Numerous mechanisms have been proposed in the literature to account for this hydrogen embrittlement. However, three main theories have received a larger attention during the last years. The first two theories, Z. SUN, Doctor, C. MORICONI, Ph.D. Student, G. BENOIT, Engineer, and D. HALM and G. HENAFF, Professors, are with the Prime Institute, UPR 3346 CNRS - ENSMA - Universite´ de Poitiers, ENSMA, F-86961 Futuroscope Chasseneuil, France. Contact e-mail: gilbert.henaff@isae-ensma.fr Manuscript submitted September 13, 2011. Article published online April 3, 2012 1320—VOLUME 44A, MARCH 2013
which were designated as the hydrogen enhanced decohesion (HEDE)[7–9] and the hydrogen enhanced localized plasticity (HELP),[10–14] are based on the concept that the hydrogen atoms that might have penetrated into the process zone at the crack tip would subsequently modify the deformation and/or damage mechanisms at the crack tip. The HEDE theory is based on the hypothesis that the cohesive strength of the metals is weakened by interstitial hydrogen or the hydrogen atoms segregated at grain boundaries or at any other microstructural interface. This implies that the hydrogen decreases the energy barrier for either grain boundary or cleavage plane decohesion. The HELP mechanism is characterized by an enhanced plastic activity in the preferred crystallographic planes. This mechanism can be described as a local softening and a deformation localization, which both led to a decrease in the macroscopic ductility of the materials.[12] It is noteworthy that the combinations of HEDE and HELP mechanisms are likely to occur in many cases. Finally, the adsorption-induced dislocation emission (AIDE) mechanism[15] does not consider any possible effect of hydrogen atoms that might have entered in the lattice within the process zone, but it considers only the effect of hydrogen present on the surface at the crack tip.
Data Loading...
