Hydrogen trapping phenomena in AISI 5160 Spring steel was investigated by the thermal analysis experiment. The dominant nonmetallic inclusions in the spring steel specimen was found to be $Al_2O_3, SiO_2$ and Fe-oxides by SEM and EDAX analysis. The hydrogen evolution peaks of the thermal analysis were observed at 160℃,330℃,430℃,530℃,630℃ and 750℃ at the constant heating rate of 3.3℃/min. By the analysis the evolution peak at 160℃ was due to the hydrogen trapping effect of cementite-ferrite interface, the evolution peak at 330℃ was due to the microvoid, the evolution peaks at 430℃ and 530℃ were due to the Fe-oxides, the evolution peaks at 630℃ and 750℃ were due to $SiO_2$ and $Al_2O_3$.
A new mathematical relationship was derived, which enabled to calculate the trap activation energy of the new trapping site from the peak temperatures and the known activation energy without experiments. The trap activation energy was 4.3 Kcal/mole for the 160℃ peak, 8.8 Kcal/mole for the 330℃ peak, 12.1 Kcal/mole for the 430℃ peak, 16.6 Kcal/mole for the 530℃ peak, 20.6 Kcal/mole for 630℃ peak, and 26.8 Kcal/mole for the 750℃ peak respectively.
The oxide inclusion interface was found to be a very strong trap with respect to the cementite-ferrite interface or microvoid in AISI 5160 Spring Steel.
