There are very few alloys indeed where it can be said the HAZ in and of itself is responsible for cracking. A reduction in ductility? Yes. A reduction in toughness? Yes. Simply cracking? No.
As posted on another thread the primary culprites for HAZ cracking is the formation of  liquid films, or low melt eutectics, Si, S, P, and such-or, hydrogen induced cracking-neither of which are exclusively HAZ cracking mechanisms,or even predominantly HAZ cracking mechanisms.