Nucleation and Growth of Bubbles in Hydrogen Attack of 2.25Cr-1Mo Steel Determined by Hydrogen Permeation and Steel Density Measurements at Lower Temperatures

Abstract

The quations to estimate the density and the radius of bubbles formed in the incubation period for hydrogen attack of 2.25 Cr-1 Mo steel were proposed. By relating the hydrogen diffusivity and the change in density of steel with the bubble density ρ_s and the bubble radius γ, it is derived that
ρ_s=L_AK³/72πΔγ³(-Δρ/ρ)² γ=3Δγ(-Δρ/ρ)/K
where Δρ/ρ is the change in density caused by bubbles, Δγ is the thickness of shell around each bubble which acts as trapping site of hydrogen atoms, K is the total volume of the shells and L_A is the mean intercept length of prior austenite grains.
The hydrogen diffusivity and the change in density were measured on the quenched and tempered steel which had been exposed to high temperature and high pressure hydrogen atmosphere. ρ_s and γ obtained by substituting these values into the above equations agreed well with the microscopical observation.