forge, temper, anneal
釟 centers on working metal with heat and force: forging, tempering, and annealing to shape or strengthen it.
釟 combines 金 (metal) with 八, which likely acts as a phonetic component. The exact historical development is uncertain, but the character is associated with metalworking processes.
Metal 金 is shaped by the number eight 八, like a blacksmith hammering metal into an eight-shaped form to forge and temper it.
For ハチ, imagine a forge where a metalworker uses a hatch to control the heat: hatch -> ハチ, and the metal is tempered inside.