百炼成钢（百煉成鋼）　

◎ 百炼成钢 bǎiliàn-chénggāng

[expertise is the result of long and hard practice] 铁经过上百次锤炼才成为钢。比喻将人锻炼成钢铁一般坚强

在战火中百炼成钢