| 摘要 |
PROBLEM TO BE SOLVED: To provide iron alloy parts improved in surface strength. SOLUTION: Surface hardening treatment (carburizing or carbo-nitriding) is applied to iron alloy parts 1 containing, by weight, 0.1-0.5% C, 0.1-0.5% Si, and 0.3-1.5% Cr as chemical components and also containing iron as a matrix. By this procedure, the structure in the region between the surface and a position at a depth of at least 100μm from the surface is constituted so that it contains martensite 2. Further, martensite grain size is regulated to 7-10 in the case where the grain size is measured by a method identical with the grain size measuring method under a microscope on the objective surface of grain size measurement specified by the method for testing austenite grain size of steel (JIS G0551) and is computed by methods identical with the average grain size number computing method and the grain size computing method based on the results of the microscopic measurement. Moreover, carbides 3 of at least either of Fe and Cr are precipitated in the surface and the average grain size of the carbides 3 is regulated to 0.5-10μm and also the area ratio of the carbides 3 in the structure is regulated to 1-20%, and further, hardness in the region between the surface and a position at a depth of at least 0.5 mm from the surface is regulated to <=Hv700.
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