The first number after H represents the basic operation:
H1 – Strain hardening only.
H2 – Strain hardened and partially annealed.
H3 – Strain hardening and stabilizing.
H4 – Strain hardened and sprayed or coated.
The second number after H indicates the degree of strain hardening:
HX2 – Quarter Hardened
HX4 – semi-hardened
HX6 – three-quarter hardened
HX8 – fully hardened
HX9 – Extremely Hard
T Tempering - Subdivisions of Heat Treatment
T1 – Natural aging after cooling from a high temperature forming process such as extrusion.
T2 – Cold working after cooling from the high temperature forming process and then natural aging.
T3 – Solution heat treatment, cold working, natural aging.
T4 – Solution heat treated, natural aging.
T5 – Artificial aging after cooling from the high temperature forming process.
T6 – Solution heat treated, artificially aged.
T7 – Solution heat treated, stable (over-aging).
T8 – Solution heat treatment, cold working, artificial aging.
T9 – Solution heat treatment, artificial aging, cold working.
T10 – Cold working after cooling from the high temperature forming process and then artificial aging.
Extra digits indicate stress relief.
Example:
TX51 or TXX51 – Stress relief by stretching.
TX52 or TXX52 – Stress relief through compression.
