Patent ID: 9708695
Date: 2017-07-18
CPC Classifications: B21B,B32B,C21D,C22C

Claim:
1. A roll outer layer material, which is a cast-iron roll outer layer material for an outer layer of a composite roll for hot rolling, the 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, wherein the roller outer layer has 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, wherein contents of Cr, Mo, and V satisfy expression below: where Cr, Mo, and V respectively represent the contents (mass %) of the corresponding chemical elements.