steel是“钢铁”的意思，钢铁有稳定，坚硬的性质。因此as true as steel既可以指人非常可靠，也可以指一些铁证如山的事实。

【例句】
He is one of my old friends and is as true as steel whatever happens.
他是我的一个老朋友，在任何情况下都是忠实可靠的。

She was proud and could be hard enough but she was as true as steel and would never have deserted a companion, whether she liked him or not.
她是骄傲的，也够厉害的，但她非常可靠，从不抛弃伙伴，不论她是否喜欢他。