Metal Hardness Identification

in Aircraft Materials Processes and Hardware

Where used, the temper designation follows the alloy designation and is separated from it by a dash: i.e., 7075-T6, 2024-T4, and so forth. The temper designation consists of a letter indicating the basic temper which may be more specifically defined by the addition of one or more digits. These designations are as follows:

  • F — as fabricated
  • O — annealed, recrystallized (wrought products only)
  • H — strain hardened
  • H1 (plus one or more digits) — strain hardened only
  • H2 (plus one or more digits) — strain hardened and partially annealed
  • H3 (plus one or more digits) — strain hardened and stabilized

The digit following the designations H1, H2, and H3 indicates the degree of strain hardening, number 8 representing the ultimate tensile strength equal to that achieved by a cold reduction of approximately 75 percent following a full anneal, 0 representing the annealed state.