There is no alloy identified as 18-8 stainless steel.
18-8 is a group of 300 series stainless steel alloys with 18% chromium and 8% nickel. These alloys cannot be heat treated like 400 series stainless steel.
If anyone tries to sell you parts made from “Heat Treated 18-8 stainless”, ask them what specific alloy the parts are made from, the rockwell hardness and what heat treating recipe was used.
18-8 stainless is acceptable for screws. It is not acceptable for pivots or folder stop pins because it is too soft.