Historical
SAE AMS 6409D-2012 (SAE AMS6409D-2012)
Steel, Bars, Forgings, and Tubing 0.80Cr 1.8Ni 0.25Mo (0.38-0.43C) (SAE 4340) Special Aircraft Quality Cleanliness, Normalized and Tempered
This specification covers a low-alloy steel in the form of bars, forgings, mechanical tubing, and forging stock.
These products have been used typically for parts required to meet stringent magnetic particle inspection criteria, having sections 3.5 inches (89 mm) and under in nominal thickness at time of heat treatment, and requiring a through-hardening steel capable of developing a minimum hardness of 40 HRC when properly hardened and tempered and also for parts of greater thickness but requiring proportionately lower hardness, but usage is not limited to such applications.
Certain design and processing procedures may cause these products to become susceptible to stress-corrosion cracking after heat treatment; ARP 1110 recommends practices to minimize such conditions.
These products are not recommended for use in parts heat treated to a hardness greater than 46 HRC (ultimate tensile strength over 220 ksi (1517 MPa)) or where the high transverse properties of remelted steel are required.
Society of Automotive Engineers [sae]