Is A Particular Type of Corrosion a Proper Noun?

There is a particular type of corrosion called 'stress corrosion cracking'.

Is this a proper or common noun?

You have a noun phrase built up of a base (cracking) and an attributive noun phrase (stress corrosion). Stress corrosion itself is a combination of the base corrosion and the attributive noun stress). Attributive nouns describe the nouns they're paired with, so stress corrosion describes the cause of the cracking (ThoughtCo).

It is not a proper noun, defined as

a noun belonging to the class of words used as names for specific or unique individuals, events, or places, and may include real or fictional characters and settings (ThoughtCo),

because stress corrosion cracking does not refer to a specific event by name (ex. The Battle of the Bulge) but rather to a general physical phenomenon (ex. a pitched battle). Even if you decide to make an acronym out of it, like SCC (which the Wikipedia article uses a lot), it's still a common noun phrase. (Ex. ATM, or automated teller machine, is a common noun phrase referring to the kind of machine, not the trademarked name of a specific design like a Nixdorf ATM.)