Interstitial defects in 316L austenitic stainless steel containing “colossal” carbon concentrations: An internal friction study

Carburization of 316L austenitic stainless steel under paraequilibrium conditions results in extremely hard (∼1100 HV) single-phase cases containing surface carbon concentrations of ∼15 mol.% and very high residual compressive stresses (⩾2 GPa). Carburization produced an anelastic relaxation peak at 543 K (1.0 Hz), due to a carbon-containing defect with a highly anisotropic strain field. Interstitial solid-solution strengthening theories can explain the approximate three-fold increase in hardness, using reasonable parameters for the strain ellipsoids of these defects.