Environmental Engineering Reference
In-Depth Information
Figure 8.6
Static fatigue curves of a 4340 steel specimen showing the gradual recovery
of ductility on baking at 570°C with increasing length of time [21].
alloy, which is relatively impermeable to diffusion of atomic hydrogen. In the
heavily cold-worked condition, however, the austenitic stainless steels are prone
to hydrogen cracking, which is attributed to the deformation-induced formation
of martensite or the formation of a metastable iron-chromium-nickel hydride.
Nickel and nickel alloys also are prone to HSC to a much lesser degree than
steels because of their fcc structure. Cold working and aging treatment of alloys
increase susceptibility to cracking. Cold working increases the strength of the
materials, and aging leads to the segregation of sulfur and phosphorus to grain
boundaries.
The mode of fracture in hydrogen embrittlement can be both intergranular and
transgranular. Intergranular cracking along the prior austenitic grain boundaries
is generally observed in steels (Fig. 8.8), but the crack path depends to a large
extent on the nature and degree of segregation or partitioning of alloying elements
in the matrix and at the grain boundaries. For example, the integranular cracking
