forge, discipline, train
鍛 centers on shaping metal through heat and hammering: forging. The discipline and training senses extend naturally from the idea of repeated, rigorous shaping to strengthen something.
鍛 combines 金 (metal) with 段, which likely contributes the sound and the idea of working or processing. Together they express forging metal.
Metal 金 is heated and hammered on a stepped anvil 段 to forge a strong blade. The repeated hammering also represents the discipline and training needed to shape oneself.
For タン, imagine a blacksmith forging a metal tan-colored sword: tan -> タン, and the metal is shaped with discipline.
forging; tempering
to forge; to temper
blacksmithing; forging; smithery; smithcraft
tempering (metal); annealing; forging
forging
smith; blacksmith
swordsmith
to temper thoroughly
malleability
malleable iron
malleable cast iron
die forging; contour forging; stamp forging
self-discipline; self-improvement
strike while the iron is hot
gunsmith
cast and forged steel
to train thoroughly (one's body, muscles, etc.); to practice (a skill) to perfection
blacksmith's workshop; smithy; forge; foundry
metal worker
cultivation; training