Cast iron and cast copper
The Chinese idiom Ti ě D ǎ t ó ngzhi ù means made of iron and cast with copper. It's very strong. From Li Zicheng.
The origin of Idioms
Yao xueyin's "Li Zicheng" Volume I Chapter 24: "please rest assured, brother, it's not stupid brother who blows around after drinking, my village is really like cast iron."
Idiom usage
It is often used in writing.
Cast iron and cast copper
rise directly to a high position - fú yáo zhí shàng
throughout the empire all hearts turned to him - tiān xià guī xīn
Strong in heart and weak in strength - xīn cháng lì duǎn
Jumping in the Yellow River - tiào zài huáng hé xǐ bù qīng