Method for producing metal ingot

A method for producing a metal ingot by using an electron-beam melting furnace having an electron gun capable of controlling a radiation position of an electron beam and a hearth that accumulates a molten metal of a metal raw material, said hearth having four side walls, the metal ingot containing 50% by mass or more in total of at least one of titanium, tantalum, niobium, vanadium, molybdenum and zirconium, said method comprising:

• supplying the metal raw material into the molten metal, which is inside the hearth, at positions along supply lines adjacent to side walls on long sides of the hearth, along inside faces of said side walls on long sides of the hearth, wherein said side walls on long sides of the hearth are side walls that face each other in an X direction of the hearth and are parallel to the longitudinal direction Y of the hearth;
• and
• radiating a first electron beam in a concentrated manner along a first irradiation line, wherein said first irradiation line is adjacent to a corresponding supply line on the surface of the molten metal, wherein said first irradiation line is in a linear shape extended along said corresponding supply line, disposed along said corresponding supply line, and closer to a central part of the hearth than said corresponding supply line;
• wherein:
• among the four side walls of the hearth, which accumulate the molten metal of the metal raw material, one side wall is provided with a lip portion for causing the molten metal in the hearth to flow out into a mold and is identified as a primary side wall, and remaining side walls other than the primary side wall are identified as secondary side walls;
• the radiation of the first electron beam along the first irradiation line increases a surface temperature (T2) of the molten metal at the first irradiation line above an average surface temperature (T0) of the entire surface of the molten metal in the hearth, and forms, in an outer layer of the molten metal, a first molten metal flow from the first irradiation line toward the corresponding supply line;
• the supply lines are set in a straight-line shape that is substantially parallel to inside faces of the side walls on the long side of the hearth,
• the first irradiation line is set in a straight-line shape that is substantially parallel to the corresponding supply line,
• a distance between an inside face of each of the side walls on the long side of the hearth and the corresponding supply line is constant, and
• a distance between each irradiation line and the corresponding supply line is constant.