low-carbon steel vs mild steel

low-carbon steel and mild steel both are nouns.

Word	Noun	Adjective	Verb	Adverb
low-carbon steel	Yes	No	No	No
mild steel	Yes	No	No	No

As nouns, low-carbon steel and mild steel are synonyms defined as:

Other synonyms of low-carbon steel include soft-cast steel.

low-carbon steel (noun)	mild steel (noun)
steel with less than 0.15% carbon	steel with less than 0.15% carbon