Hello, fellow HR,
As far as I know, the Industrial Relations Manager is more focused on labor relations issues and concerns, such as policies affecting the company's code of conduct, employee discipline, and other related areas. An HR Manager, on the other hand, deals with HR from a more general perspective.
Regarding hierarchical superiority, it depends on who they report to. An IR Manager may report to the HR Manager, or both may report directly to the HR Head, regardless of their position title (e.g., HR Director, VP for HR, etc.).
I hope this information helps.