| 摘要 |
Provided is a roll outer layer material for hot rolling and a composite roll for hot rolling which have a surface layers excellent in terms of fatigue resistance and with which fatigue damages and chipping are less likely to occur. A roll outer layer material containing small-size carbides having a circle equivalent diameter of 3 to 30 µm in a number of 500 to 2500 pieces/mm 2 and large-size carbides having a circle equivalent diameter of 50 µm or more in a number of 20 pieces/mm 2 or less, preferably having a chemical composition containing, by mass%, C: 2.4% or more and 2.9% or less, Si: 0.2% or more and 1.0% or less, Mn: 0.2% or more and 1.0% or less, Cr: 4.0% or more and 7.5% or less, Mo: 4.0% or more and 6.5% or less, V: 5.3% or more and 7.0% or less, Nb: 0.5% or more and 3.0% or less, and the balance being Fe and inevitable impurities, in which the contents of Cr, Mo, and V satisfy the relationship 1.5 ‰¤ (Cr+Mo)/V ‰¤ 2.4, where Cr, Mo, and V respectively represent the contents (mass%) of the corresponding chemical elements, or more preferably having the chemical composition further containing, one or more of Al: 0.001% or more and 0.05% or less and REM: 0.001% or more and 0.03% or less. In addition, a composite roll for hot rolling having an outer layer made of the outer layer material. |
