Japan’s major steelmakers, Nippon Steel Corp. and JFE Steel Corp., said Thursday that they will invest a combined 160 billion yen ($1.1 billion) in a coal mine owned by an Australian mining firm to secure a stable supply of high-quality coal. In a bid to achieve eco-friendly steelmaking, Nippon Steel will pay about 108 billion yen to acquire a 20 percent interest in the Blackwater coal mine in the state of Queensland, while JFE Steel will obtain another 10 percent, valued at around 54 billion yen. The mine, which has an annual output of 10.1 million tons and is held by Whitehaven Coal Ltd., ha…