Hydrogen embrittlement of a 12 Cr-1 Mo steel

The grain boundary phosphorus and sulfur concentrations of HT-9 were found to depend on heat treatment in a manner consistent with other ferritic steels. After a tempering treatment of 2.5 hrs at 7600C, the grain boundary phosphorus and sulfur concentrations were 0.015 and 0.03 monolayers, respectively while after a heat treatment of 240 hrs at 5400C their grain boundary concentrations were 0.04 and 0.01 monolayers, respectively. Straining electrode tests at cathodic test potentials revealed that HT-9 is sensitive to hydrogen embrittlement with the fracture mode changing from ductile micro-void type fracture in air to a mixed intergranular and quasi-cleavage fracture at cathodic potentials. The reduction of area was 13% at cathodic test potentials and 60% in air. Charpy impact tests revealed a 100C increase in the ductile to brittle transition temperature with heat treatment at 5400C