Effect of hydrogen on the fracture toughness of a ferritic/martensitic stainless steel

Effects of hydrogen (H) on the mixed-mode I/III critical J integrals (J{sub MC}) and tearing moduli (T{sub M}) were examined for a ferritic/martensitic stainless steel (F-82H) at ambient temperature. A determination of J{sub MC} was made using modified compact-tension specimens. Different ratios of tension/shear stress were achieved by varying the principal axis of the crack plane between 0 and 55 degrees from the load line. A specimen with 0 degree crack angle is the same as a standard mode I compact tension specimen. Specimens were heat-treated at 1000{degrees}C/20 h/air cooled (AC)-1100{degrees}C/7 min/AC-700{degrees}C/2 h/AC. The specimens were charged with H at a hydrogen gas pressure of 138 MPa at 300{degrees}C for two weeks, which resulted in a H content of 6 ppm(wt), as measured with the {open_quotes}inert gas fusion{close_quotes} technique. J{sub MC} and T{sub M} values were determined with the single specimen technique. Crack lengths were calculated by means of partial unloading compliances. The preliminary results from J integral tests showed that introducing H decreased J{sub MC} and T{sub M} values as compared to those without H. However, the presence of H did not change the dependence of J{sub MC} and T{sub M} values on the crack angles. Both mode Imore » J and T values (J{sub IC} and T{sub I}) exhibited the highest values. Both the minimum J{sub MC} and T{sub M} values occurred at a crack angle between 35 and 55 degrees, corresponding to the load ratio ({sigma}{sub iii}/{sigma}{sub i}) of 0.7 to 1.4.« less