What are the iron idioms?

A heart of stone,

Grinding needle with iron pestle,

Firmly,

Grinding the iron pestle into a needle,

Cycas bloomed,

Danshu iron coupon,

The iron pestle is ground into a needle,

Heart is like stone,

Iron lacquer silver hook,

Hate iron not to produce,

Unscrupulous,

Iron wall,

Iron-bone collision,

Strike while the iron is hot,

Stepped on iron shoes,

Cut iron like mud,

Scrap copper and iron,

Irrefutable evidence,

Nail,

Turn iron into gold,

Selling iron in a pan,

Collision in iron,

Unarmed,

Dan Shu fighters,

Iron bars are ground into needles,

Steel bar,

Wear out the iron inkstone,

Iron plate copper pa,

Things are rare or difficult to achieve.