In this research, stress-oriented hydrogen induced cracking (SOHIC) test was carried out
on a 50 mm thickness of a commercial API 5L X70 steel plate. The evolution of microscopic features
such as phase, boundary, interface, grain, and crystallographic data was analyzed before and after
SOHIC, in order to comprehend the effect of crystallographic orientation on SOHIC propagation.
Chemical composition and previous thermomechanical processing even finish rolling temperature
and cooling rate determine the ferrite matrix microstructure. A recrystallized ultrafine ferrite grain
with about 3−5% degenerated pearlite dispersed in the microstructure was characterized, called asreceived
specimen. The average lattice strain and dislocation density was calculated first using multiple
Gaussian peak-fitting method from XRD pattern. Electrochemically charged combination
mixed H2S-CO2 solution, constant hydrogen injection, and external loading were applied to tensile
specimen, in order to simulate the H2S and CO2 environment. The results show that local misorientation
and Taylor factor analyses predicted the possibility of hydrogen crack nucleation especially
at boundaries and interfaces. Moreover, SOHIC crack propagation occurred along the mid-thickness
of the cross section of steel plate along the ferritic boundaries, pearlitic colonies, and ferritecementite
interfaces. Moreover, the crack propagated along distorted {110} and {001} grains, indicating
a strong strain gradient towards the boundaries. The analysis of XRD patterns of SOHIC
tested specimen by multiple Gaussian peak-fitting method estimated about 68% increment in microdeformation
and approximately 170% increase in dislocation density.