| 摘要 |
PROBLEM TO BE SOLVED: To provide a backup roll unit enabling a shaft to be hard to crack even if a flange part is formed at one side end part of the shaft and also enabling a life to be increased even under such an environment that water and iron powder are easily invaded therein. SOLUTION: This backup roll unit 1 comprises the flange part at one end part of the shaft 3. The shaft 3 is formed of a steel material containing a carbon of 0.15 to 0.3 w.%, and to which a heat treatment including carburization is applied at least starting at the flange part 5 to a shaft side raceway surface 3a. The shaft side raceway surface 3a is formed such that, at a portion 0 to 50μm deeper from the uppermost surface thereof, a carbon content is 1.0 to 1.5 w.%, a residual compressive stress is 150 to 2000 MPa, the maximum diameter of carbide is 3μm or less, and a carbide area ratio is 10 to 25%, and at a portion 50 to a/5μm (a = effective hard layer depth:μm) deeper from the outermost surface, the carbon content is 0.75 to 1.3 w.%, the residual compressive stress is 150 to 1000 MPa, a residual austenite amount is 25 to 45%, the maximum diameter of carbide is 1μm or less, and the carbide area ratio is 15% or less. COPYRIGHT: (C)2006,JPO&NCIPI
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