DIE FOR EXTRUSION FORMING OF METAL MATERIAL AND CRYSTAL FINING METHOD OF METAL MATERIAL USING THE DI

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PROBLEM TO BE SOLVED : To provide a die for extrusion forming of metal material which permits fining of a crystal by efficiently applying a shear strain to metal material and can improve strength of the material without injuring tenacity even when addition of rare metal or the like is not performed. SOLUTION : An extrusion forming course 11 for performing extrusion forming of a columnar metal material includes : a material charging part 12 which arrives at an outlet of the extrusion forming course 11 and assumes a columnar shape; a material cross-section deformation part 13 which is provided successively on the material charging part 12 and deforms the metal material from a circular cross-section to an elliptical shape; a non-linear torsion part 14 causing the metal material deformed to the elliptical shape on the material cross-section deformation part 13 to assume a torsion shape which gradually increases a torsion rate while retaining the elliptical shape; and a cross-section shape recovery part 15 for recovering a shape of the metal material which gets to the elliptical shape while retaining such a state that rotation of the outlet of the non-linear torsion part 14 is not hindered to the columnar shape. SELECTED DRAWING : Figure 1 COPYRIGHT : (C)2018, JPO&INPIT