Very likely the pins you refer to are made from steel of low carbon content (easy to machine) and will not through harden as will higher carbon content steel. Since they will work for some time, it is easy to see that a small increase in steel strength, such as produced by case hardening, will give you a satisfactory part. This also leads to the conclusion that unhardened O-1 and grade 8 bolt steel will be entirely satisfactory. Also, that properly hardened O-1 will be almost overkill.