To provide a metallic material which has a high hardness ultrafine crystal grain layer formed by severe plastic deformation etc., on a surface layer and further, a high hardness layer having a sufficient layer thickness and having higher hardness compared with a base material in the inner layer, and to provide a method for manufacturing the metallic material.
To the metallic material having the ultrafine crystal grain layer at least in a part of the surface layer, hardening by rapid short-time heating is applied, and a hardened structure is formed by leaving the ultrafine crystal grain layer. The ultrafine crystal grain layer can be formed by friction working, etc., using a working tool, and the ultrafine crystal grain layer in which sub-micron crystal grains of 100 nm to 1 μm and nano-crystal grains of <100 nm are present is formed. The hardening by rapid short-time heating can preferably be performed by induction hardening under the conditions of 0.3-1 s heating time and 750-950°C heating temperature. The extreme-surface layer is made to have strength and hardness which are equivalent to those of the induction-hardened product or higher than those of the induction-hardened product, and the base material is hardened too and has high hardness and the fatigue characteristics or the like can be improved.
COPYRIGHT: (C)2011,JPO&INPIT
Yoshitaka Misaka
Kazuhiro Kawasaki
Yoshikazu Todaka
Hironori Nagai
Yu Iguchi
Kaoru Kanna
Umemoto Minoru
Toyohashi University of Technology
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