1. 1) JIS G 4403: 2006, High speed tool steels.
2. 2) JIS G 1220: 1994, Iron and steel—Methods for determination of tungsten content.
3. 3) JIS G 1258-2: 2014, Iron and steel—ICP atomic emission spectrometric method—Part 2: Determination of various elements—Decomposition with phosphoric and sulfuric acids.
4. 4) K. Nakayama and K. Wagatsuma: Anal. Sci., 31 (2015), 851.
5. 5) S. Awaji, K. Nakamura, T. Nozaki and Y. Kato: Resour. Geol., 56 (2006), 471.