List of Symbols	Definition
HE	hydrogen embrittlement
HIC	hydrogen-induced cracking
physisorption	physical adsorption
chemisorption	chemical adsorption
fcc	face-centered cubic
hcp	hexagonal close-packed
bcc	body-centered cubic
O sites	octahedral sites
T sites	tetrahedral sites
HMT	hydrogen microprint technique
SEM	scanning electron microscopy
TEM	transmission electron microscopy
$AgBr$	silver bromide
$NaN{O}_2$	sodium nitrite
$N{a}_2{S}_2{O}_3$	sodium thiosulfate
$N{H}_{4}SCN$	ammonium thiocyanate
$C{H}_4{N}_{2}S$	thiourea
$C{H}_{3}COOH$	acetic acid
$C{H}_{3}COONa$	sodium acetate
PSU	power supply unit
Pt	platinum
SSRT	slow strain rate tension test
CGHAZ	coarse-grained heat-affected zone
$J$	diffusion flux
$D$	diffusion coefficient
$\mathsf{\partial }c/\mathsf{\partial }x$	concentration gradient
$\mathsf{\partial }c/\mathsf{\partial }t$	the change in concentration over time
${\mathsf{\partial }}^{2}c/\mathsf{\partial }{x}^2$	the second derivative of the concentration with respect to the distance
$c_{0R}$ ($\mathrm{mol}·{\mathrm{m}}^{-3}$)	the hydrogen concentration on the entry side (also referred to as charging side) in the hydrogen permeation test
$i_t$ ($\mathsf{\mu }\mathrm{A})$	transient current in the hydrogen permeation test
$i_{\mathrm{ss}}$ ($\mathsf{\mu }\mathrm{A}$)	the steady-state current in the hydrogen permeation test
$t_{lag}$ ($\mathrm{s}$)	the time elapsed from the beginning of the permeation test until the ratio of transient-to-steady-state current $\left(i_t/i_{\mathrm{ss}}\right)$ reaches 0.63
$t_b$ ($\mathrm{s}$)	the time calculated by extrapolating the linear portion of the rising hydrogen permeation current transient
$D_{eff}$ (${\mathrm{m}}^2·{\mathrm{s}}^{-1}$)	the effective diffusion coefficient in the hydrogen permeation test
$J_{SS}$ ($\mathrm{mol}·{\mathrm{m}}^{-2}{\mathrm{s}}^{-1}$)	permeation flux at steady state in the hydrogen permeation test
$i_0$ ($\mathsf{\mu }\mathrm{A}$)	background current in the hydrogen permeation test
$N_T$ (${\mathrm{m}}^{-3}$)	total density of hydrogen trap
$D_l$ (${\mathrm{m}}^2·{\mathrm{s}}^{-1}\mathrm{A}$)	lattice diffusion coefficient of hydrogen
$E_b$ ($\mathrm{J}·{\mathrm{mol}}^{-1}$)	binding energy
$N_L$ (${\mathrm{m}}^{-3}$)	the density of the interstitial sites in the steel
$N_{ir}$ (${\mathrm{m}}^{-3}$)	the density of irreversible traps in the steel
$N_r$ (${\mathrm{m}}^{-3}$)	the density of reversible traps in the steel
$\Delta H$ ($\mathrm{J}·{\mathrm{mol}}^{-1}$)	dissolution enthalpy of hydrogen into steel
$f_{H_2}$ ($\mathrm{MPa}$)	fugacity of hydrogen
LP	laser peening
HEDE	hydrogen-enhanced decohesion mechanism
CTOD	critical crack tip opening displacement
HELP	hydrogen-enhanced localized plasticity
AIDE	adsorption-induced dislocation emission
HEMP	hydrogen-enhanced macroscopic plasticity
TDA	thermal desorption analysis
CSRT	conventional strain rate test
$I_{\delta }$	elongation loss rate
$I_{\mathsf{\psi }}$	area reduction rate
${\delta }_0$	elongation before charging
${\delta }_H$	elongation after charging
${\mathsf{\psi }}_0$	area reduction before charging
${\mathsf{\psi }}_H$	area reduction after charging
${\mathsf{\sigma }}_{TH}$	threshold stress
LIST	linearly increasing stress testing
SCC	stress corrosion cracking
TWIP	twinning-induced plasticity
DCB	double cantilever beam
SSC	sulfide stress cracking
$K_{ISSC}$	threshold stress intensity factor for SSC
$K_{I0}$	initial stress intensity factor
$K_{IC}$	critical stress intensity factor
a	DCB and fatigue test—specimen crack length
P	DCB test—lift-off load
h	DCB test—specimen height of each arm
B	DCB test—specimen thickness
Bn	DCB test—specimen web thickness
EDM	electro-discharged machine
$H_{2}S{O}_4$	sulfuric acid
D	bent beam test—deflection
S	bent beam test—nominal outer fiber pseudo-stress
l	bent beam test—distance between centerlines of end supports
E	elastic modulus
t	bent beam test—thickness of test specimen
T	bent beam test result
n	bent beam test—total number of specimens tested
DFS	delayed fracture strength
$HCl$	hydrochloric acid
FGCR	fatigue crack growth rate
HAFCGR	hydrogen-affected fatigue crack growth rate
CT	compact tension
N	fatigue test—number of the cycles
ΔK	fatigue test variation in the stress intensity factor