纯铁的冷却曲线 T 1538 394 8-Fe, bcc 912 y-Fe, fcc 铁磁 a-Fe, bcc Cooling curve纯铁的冷却曲线 T t 1538 1394 912 }-Fe，bcc }-Fe，bcc }-Fe，fcc Cooling curve 770 铁磁性