| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a gas-quenching method with which a quenched product having high hardness on the surface and excellent toughness in the inner part (core part) can be obtained. <P>SOLUTION: The gas-quenching method is provided with a first cooling step, in which the core part of a work (quenching product) is gas-cooled at a first cooling speed from the quenched temperature to a first temperature zone of the higher temperature than Ms point of the core part in the work, and thereafter, a second cooling step, in which the work is gas-cooled with a second cooling speed of smaller speed than the first cooling speed, in the lower temperature zone than the first temperature zone. Then, the first cooling speed and the second cooling speed are controlled so that the surface of the work after quenching may become a martensitic structure, and the effective hardened layer depth in the work may be larger than the depth in the case of gas-cooling the work with the second cooling speed from the quenched temperature to the room temperature, and may become the same or smaller in the case of cooling the work with the first cooling speed from the quenched temperature to the room temperature and further, the hardness of the core part in the work may become the same grade as in the case of gas-cooling the work with the second cooling speed from the quenched temperature to the room temperature. <P>COPYRIGHT: (C)2013,JPO&INPIT |
