FILE PHOTO: The logos of Nippon Steel Corp. are displayed at the company headquarters in Tokyo, Japan March 18, 2019. Picture taken March 18, 2019. REUTERS/Yuka Obayashi TOKYO : Nippon Steel Corp could buy more stakes in coking coal and iron ore mines even after its recent decision to invest in a Canadian mine, as it sees a risk of commodity prices staying high, an executive at the world's No.4 steelmaker said.