SEM and EBSD techniques are used to evaluate hydrogen induced cracking susceptibility in
API X70 pipeline steels produced by thermo-mechanical controlled process (TMCP) in
laboratory scale. Based on the observations, there is no dominant texture in the specimens
and the grains are randomly distributed. Different TMCP parameters and rolling processes
generates different grain size, and grains are often elongated along the rolling direction.
The results also show that cooling rate is another factor affecting the grain size. A high
cooling rate does not allow the grains to grow. The reason for the transgranular type of
cracking might be the strong grain boundaries in ambient temperatures which prevents
the intergranular cracking. Based on experiments, the hydrogen environment does not
have permanent effects on the mechanical properties of the investigated specimens. The electrochemical hydrogen charging experiment shows that the grain refinement improves
the resistance to hydrogen embrittlement.