Note the verb pattern: rust 'grows on' or 'forms on' something — 生铁锈 / 长铁锈 (lit. 'grow rust'). The English 'iron has rusted' is most naturally 铁生锈了.
culture
By extension, 铁锈带 is the Chinese term for the American 'Rust Belt' — the deindustrialized Midwest. It surfaces often in news commentary on US politics.
