If I have used a folder to field dress a deer, it goes right in the ice chest with the quartered parts. Back at the house, or camp, a stiff brush, dishwashing liquid and water as hot as I can stand, then a good cleaning.
Then letting the hot water run over it as hot as it will get for a few seconds. This heats up the metal and after I dry and blow it out the hot metal will continue to dry it.
A drop of 3n1 oil and working the blade and a good wipe down is all that is needed.
If I have used a folder on something like roofing material or other really dirty items. A good cleaning with WD40 and the air compressor until the gunk is gone. A final blow out of the WD40 with the compressor and then a drop of 3n1 on the blade pivot.
WD40 is a cleaner. Not a lubricant