Hello, fellow HR
As far as I know, the Industrial Relations Manager is more on labor relations issues/concerns such as when there are policies affecting the company's code of conduct or employee discipline and other related areas of concern. While an HR Manager deals with HR on a more general perspective.
As to who is more superior in terms of hierarchical structure, it really depends as to who they report to, an IR Manager can report to the HR Manager or both of them directly reports to the HR Head, whatever may be the position title, e.g. HR Director, VP for HR and etc.
Hope this helps.