Environmental Engineering Reference
In-Depth Information
Figure 8.5
Static fatigue curves for specimens of different notch sharpness [21].
and spheroidized carbides evenly distributed throughout the matrix possesses
maximum resistance to embrittlement, compared to normalized or bainitic steels
at equivalent strength levels. The resistance also increases with decreasing prior
austenitic grain size. The presence of retained austenite is helpful, possibly be-
cause it either absorbs hydrogen or slows down crack growth. The effects of
individual alloying elements on cracking susceptibility are associated with their
effects on the heat treatment, microstructure, and strength of the steels. In general,
carbon, phosphorus, sulfur, manganese, and chromium increase susceptibility and
titanium decreases the sensitivity to HIC by decreasing the amount of hydrogen
available for cracking.
The behavior of stainless steels in hydrogen environments is dependent on
their strength level. Ferritic stainless steels are extremely resistant to HSC be-
cause of their low hardness. However, in the cold-worked and as-welded condi-
tions they are susceptible. Martensitic and precipitation hardening stainless steels
are most susceptible because of their higher strength. Austenitic stainless steels
are also highly resistant to hydrogen cracking in the annealed or lightly cold-
worked condition. A major factor for this resistance is the fcc structure of the
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