Absorption of hydrogen in a high-strength nickel-chromium-molybdenum steel during tensile deformation in 0.5 MPa gaseous hydrogen was examined using a thermal desorption analysis method. The tensile strength of the specimen was varied in the range from 1 214 to 947 MPa by heat treatment. The dislocation density of the specimens was measured by X-ray diffractometry after tensile testing in a hydrogen atmosphere. The hydrogen content absorbed during tensile deformation increased with increasing tensile strain in proportional elastic range until just before yielding. The yield stress was defined as 0.2 % proof stress in this work. At the same tensile strains, the hydrogen content of lower-strength specimens was larger than that of higher-strength specimens. The dislocation density gradually decreased until just before yielding, corresponding to the proportional increase of hydrogen content to the tensile strain. This implies that the hydrogen absorption behavior during tensile deformation in gaseous hydrogen is related to the motion of mobile dislocations initially contained in the specimens. The activation energy for desorption of hydrogen absorbed during tensile deformation did not depend on the strength of the steel. This indicates that the trap sites of hydrogen atoms created through the tensile deformation were the same regardless of the strength levels.
The effect of grain size on the susceptibility of high-strength low alloy steels to hydrogen environment embrittlement in a 45 MPa gaseous hydrogen atmosphere was examined in term of the hydrogen content penetrating the specimen during the deformation. Notch tensile tests were performed in a 45 MPa hydrogen environment using specimens with different prior austenite grain size numbers varying from 2.5 to 5.4. The hydrogen content was measured by thermal desorption analysis with a quadrupole mass spectrometer before and after the tensile test. The fracture stress of the notch tensile test increased with increasing grain size number; this showed that grain refinement was effective in reducing the susceptibility of the specimens to hydrogen environment embrittlement in a high-pressure hydrogen atmosphere. The addition of nickel did not affect the fracture stress. A remarkable increase in the content of diffusive hydrogen was observed after the notch tensile test. Assuming that part of the diffusive hydrogen desorbed from grain boundaries, it can be inferred that grain refinement can reduce the mass of hydrogen in the unit grain boundary area, and the susceptibility to high-pressure hydrogen environment embrittlement.
Synopsis :Absorption of hydrogen in a high-strength nickel-chromium-molybdenum steel during tensile deformation in 0.5 MPa gaseous hydrogen was examined using a thermal desorption analysis method. The tensile strength of the specimen was varied in the range from 1214 to 947 MPa by heat treatment. The dislocation density of the specimens was measured by X-ray diffractometry after tensile testing in a hydrogen atmosphere. The hydrogen content absorbed during tensile deformation increased with increasing tensile strain in proportional elastic range until just before yielding. The yield stress was defined as 0.2% proof stress in this work. At the same tensile strains, the hydrogen content of lower-strength specimens was larger than that of higher-strength specimens. The dislocation density gradually decreased until just before yielding, corresponding to the proportional increase of hydrogen content to the tensile strain. This implies that the hydrogen absorption behavior during tensile deformation in gaseous hydrogen is related to the motion of mobile dislocations initially contained in the specimens. The activation energy for desorption of hydrogen absorbed during tensile deformation did not depend on the strength of the steel. This indicates that the trap sites of hydrogen atoms created through the tensile deformation were the same regardless of the strength levels.
Internal pressure fatigue properties of Cr-Mo steel (JIS G 4052, SCM435H) in high-pressure hydrogen or nitrogen atmosphere were investigated by the internal pressure fatigue test using a specially designed apparatus. Internal pressure was varied in the range from 0 to 40.5MPa, and test temperature was 20°C. The cycle length of internal pressure was varied up to 1000 seconds. We obtained the following results. 1. The number of fracture cycles in 45MPa hydrogen atmosphere was much less than those of in the 45MPa nitrogen atmosphere. 2. The number of fracture cycles was not depended on the cycle length. 3. In the fracture surface region where quasi-cleavage and intergranular surfaces are coexisting, the crack growth behavior is different from that of in the quasi-cleavage region.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.