Stainless Material Selection for Fastener

[Designer99]

Dear Forum:

I am working on a fastener design, and I am trying to select the proper grade of S/S. Here are some of the restraints:
1.) The fastener is to be machined(screw machine or CNC lathe) from 5/16 dia. bar stock
2.) The required tensile after machining needs to be b/w 145-175 ksi
3.) I'd like to avoid heat treating if possible (mainly to cater to the cosmetic requirements i.e. the fastener needs to blend in color with mating 303 S/S parts) Heat treating is an option if there is a way to prevent discoloration.

I've tried 303, and 304 in the annealed condition and the tensile is not quite enough. If someone offered 303 bar stock in the 1/4 or 1/2 hard condition, this would most likely solve the problem. Any guidance would be much apreciated.

Jason

 

[TVP]

In order to guarantee tensile strength of 145-175 ksi, your options are Type 416 or XM-6 in the H condition (hardened) according to ASTM A 582 (free-machining stainless steel bars); Type XM-21 in the B condition (cold-finished) according to ASTM B 276; or one of the age hardening grades like Type 630 or Type 631 according to ASTM A 564. The age hardening grades can be provided in the solution annealed condition or in the hardened condition. Annealed strength is only ~ 125 ksi maximum, whereas hardened condition ranges from 125-190 ksi, depending on aging temperature.