淬炼

淬炼	cuì liàn	(fig.) to temper; to forge; to toughen (through hardship or repeated trials)
淬	cuì	dip into water / to temper
炼	liàn	to refine; to smelt / to heat or forge (in fire)
炼	liàn	to refine; to temper (variant of 炼) / to polish (wording)