你心已变铁
[nĭ xīn yĭ biàn tiĕ]
The phrase "你心已变铁" (Nǐ xīn yǐ biàn tiě) translates to "Your heart has turned into iron." It implies that the owner's feelings for someone have turned cold or unyielding, often expressing disappointment or sorrow over a lost relationship, or someone's change of heart toward the worse.