Form: This specification covers a premium-quality@ low-alloy steel in the form of bars@ forgings@ mechanical tubing@ and forging stock. Application: Primarily for critical parts with section 3.5 in. (89 mm) or less in thickness requiring a through-hardening steel capable of developing a minimum hardness of 53 HRC@ the parts being subject to very rigid magnetic particle inspection standards. Certain design and processing procedures may cause this material to be susceptible to stress-corrosion cracking after heat treatment; ARP 1110 recommends practices to minimize such conditions.