substandard vs inferior

substandard is not a noun while inferior is a noun.

Word	Noun	Adjective	Verb	Adverb
substandard	No	Yes	No	No
inferior	Yes	Yes	No	No

As adjectives, substandard and inferior are synonyms defined as:

Other synonyms of substandard include deficient.

substandard (noun)	inferior (noun)
	a character or symbol set or printed or written beneath or slightly below and to the side of another character
	one of lesser rank or station or quality

substandard (adjective)	inferior (adjective)
falling short of some prescribed norm	written or printed below and to one side of another character
	of or characteristic of low rank or importance
	of low or inferior quality
	having an orbit between the sun and the Earth's orbit
	lower than a given reference point
	falling short of some prescribed norm