FRANKFURT (Reuters) - Thyssenkrupp, Salzgitter and France's Vallourec are reviewing a sale of their steel joint venture HKM after they were approached by a potential buyer, Germany's largest steelmaker said on Friday.

A sale of HKM, in which Thyssenkrupp owns 50%, would be a major step in the group's efforts to restructure its steel business, Germany's largest, ahead of a potential partial sale to Czech billionaire Daniel Kretinsky.

"We confirm that we have been approached by an interested party for the acquisition of HKM," Thyssenkrupp said in a statement.

"A possible sales process is now being carefully examined in close consultation with the shareholders with an open mind and in particular with regard to the responsibility for the workforce."

Detlef Wetzel, labour representative and deputy supervisory board chairman of Thyssenkrupp Steel Europe (TKSE), the German conglomerate's steel division, told regional newspaper WAZ that Hamburg-based investor CE Capital Partners had already presented its plans to parts of TKSE's supervisory board.

(Reporting by Christoph Steitz and Tom Kaeckenhoff; Editing by Miranda Murray)