铁石心肠: heart of stone [steel]; a rocky [stony] heart; be dead to all feelings; be iron-hearted [hardhearted]; marble-hearted; steel one's heart against pity; unmoved by feelings
冷酷无情: unfeeling; cold-blooded; as hard as nails; as cold as charity; merciless; with cruel coldness; have a heart of stone; stony-hearted; unrelenting