Neither SAE 8620 nor SAE 3115 (no longer a standard grade) are equivalent steel grades to DIN 16MnCr5. Stahlschluessel lists SAE 5115 as the equivalent. 8620 is a Cr-Mo-Ni steel, and 3115 is a Cr-Ni steel. The chemical compositions for 8620 and 5115 are listed in SAE J404, whereas 3115 is listed in SAE J1249 (Former SAE Standard and Former SAE Ex-Grades):
8620 3115 5115
C 0.18/0.23 0.13/0.18 0.13/0.18
Mn 0.70/0.90 0.40/0.60 0.70/0.90
Si 0.15/0.35 0.20/0.35 0.15/0.35
P 0.030 max 0.040 max 0.030 max
S 0.040 max 0.040 max 0.040 max
Cr 0.40/0.60 0.55/0.75 0.70/0.90
Ni 0.40/0.70 1.10/1.40 0.70/0.90
Mo 0.15/0.25 - -