SAE AS 9207A Document Information:
Title
(R) SCREW, MACHINE - STEEL, DIFFUSED NICKEL-CADMIUM PLATED, DOUBLE HEXAGON EXTENDED WASHER HEAD, UNS K14675, 195 KSI MIN, .1640-36 UNJF-3A
There are two grades - A and B - for this material.
I am looking in the Metals and Alloys UNS, 8th edition:
K14675: Alloy Steel (17-22A), it is contained in AMS 6304 and 6305 as well as MIL SPEC MIL-S-24502.
There is a complete listing of the chemistry which I will post if you need it.
Charles