Hydrogen Trapping Behavior in Vanadium-added Steel

Abstract

Hydrogen trapping and de-trapping behavior was investigated for steels with and without V. The de-trapping of hydrogen is very slow while the trapping presumably proceeds rapidly for steels containing VC precipitates. The activation energy for de-trapping is in the range of 33 to 35 kJ/mol. The trapped-hydrogen content and diffusible-hydrogen content in the steady state increase with increasing hydrogen entry rate into the steel. The density of hydrogen trapping sites decides the maximum trapped-hydrogen content; 9 ppm for 1 % V steel tempered at peak secondary hardening temperature. Analysis of hydrogen embrittlement cracking tests in terms of hydrogen contents such as the critical hydrogen content should be performed on the specimens with uniform hydrogen distribution and must consider the nature of hydrogen whether it is trapped or diffusible.

Investigation of the effect of electrolytic hydrogen charging of X70 steel: II. Microstructural and crystallographic analyses of the formation of hydrogen induced cracks and blisters

“…Figure 7 provides representative inverse pole figure (IPF) maps of cracked regions of: the BFP microstructure (Figure 7(a)), the FGB microstructure (Figure 7(b)), and the EFP microstructure (Figure 7(c)). As seen in Figures 7(a-c), the cracks predominantly follow transgranular paths with only a limited incidence of intergranular propagation 1 . Figure 7 (Figure 8(c)).…”

“…As seen in Table 2, 22%, 30% and 10% of the cracks in the BFP, FGB and EFP microstructures occurred by cleavage on {100} planes. However, if the fractions of the 1 It should be noted that intergranular crack propagation along ferrite-pearlite interfaces was also observed in RD-ND sections of the BFP microstructure (see Figures 1 and 2). {110}, {112} and {123} slip planes are combined, fracture along slip planes is the dominant mode of fracture in the three investigated microstructures.…”

“…This detrimental effect is due to the high mobility of hydrogen atoms at ambient temperatures which leads to build-up of hydrogen at stress concentration sites associated with microstructural features such as inclusions and grain/phase boundaries [1].…”

Development of High Concentration References for Measuring Hydrogen Ingress into Steels

“…1) These failures have been generally attributed to the hydrogen-induced damages implying absorption, diffusion, trapping, and interactions of hydrogen atoms in steels. 2,3) Furthermore, complex microstructures due to severe deformation, 4,5) microalloying 6) and local welding 7) imply significant hydrogen trapping sources and also can contain bulk hydrogen concentrations higher than 10 wppm. An amount of the hydrogen penetration is measured by a hot extraction method; by heating a testing sample rapidly, hydrogen atoms located in lattices and trapped in defects are activated and diffuse out from the metallic sample.…”

Stable Charging Conditions for Low Hydrogen Concentrations in Steels

“…Therefore, it is very important to establish a stable hydrogen charging method for low hydrogen concentrations in order to evaluate the hydrogen embrittlement property of high strength steel. 8) In order to establish a hydrogen charging condition by which small amounts of hydrogen stably enter into steel, hydrogen entry behavior was investigated using the hydro-© 2012 ISIJ gen permeation method under the immersion, galvanostaticcharging, and potentiostatic-charging methods in various environments. Table 1 shows the chemical compositions of the tested steel specimens.…”