Cracks started from the roots of the threads and propagated by SSG. Initial and sulfur inclusions in the microstruc- ture of the alloy promoted HE and propagation of SSC. MnS-type inclusions acted as reversible hydrogen traps, increasing the absorption of hydrogen atoms in the microstructure; this led to HIC and SSC. These inclusions had a significant role in the cracking failure of the stem. From the tests, it is inferred that cleanliness is a significant feature when selecting proper material for a specific use. These inclusions significantly decrease the fatigue resistance of the material, and affect the corrosion resistance of the alloy. The high hardness value of the alloy decreased its resistance to SSC. Therefore, propagation of SSC was accelerated by the deterioration of the microstructure of the alloy over the six years of operation.
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