Composite roll for rolling and its production method
A composite roll for rolling having a structure comprising centrifugally cast outer and intermediate layers of an Fe-based alloy integrally fused to an inner layer of ductile cast iron; the outer layer having a composition comprising by mass 1-3% of C, 0.3-3% of Si, 0.1-3% of Mn, 0.5-5% of Ni, 1-7% of Cr, 2.2-8% of Mo, 4-7% of V, 0.005-0.15% of N, and 0.05-0.2% of B, the balance being Fe and inevitable impurities; the intermediate layer containing 0.025-0.15% by mass of B; the B content in the intermediate layer being 40-80% of that in the outer layer; and the total amount of Cr, Mo, V, Nb and W in the intermediate layer being 40-90% of that in the outer layer.
1. A composite roll for rolling having a structure comprising centrifugally cast outer and intermediate layers both made of an Fe-based alloy, and an inner layer of ductile cast iron, said layers being integrally fused to each other;
said outer layer having a composition comprising by mass 1-3% of C, 0.3-3% of Si, 0.1-3% of Mn, 0.5-5% of Ni, 1-7% of Cr, 2.2-8% of Mo, 4-7% of V, 0.005-0.15% of N, and 0.05-0.2% of B, the balance being Fe and inevitable impurities;
said intermediate layer containing 0.025-0.15% by mass of B;
the B content in said intermediate layer being 40-80% of the B content in said outer layer; and
the total amount of carbide-forming elements in said intermediate layer being 45-90% of the total amount of carbide-forming elements in said outer layer.
2. The composite roll for rolling according to claim 1 , wherein said outer layer further contains 0.1-3% by mass of Nb and/or 0.1-5% by mass of W.
3. The composite roll for rolling according to claim 1 , wherein said outer layer further contains at least one selected from the group consisting of 0.1-10% of Co, 0.01-0.5% of Zr, 0.005-0.5% of Ti, and 0.001-0.5% of Al by mass.
4. A method for producing the composite roll for rolling recited in claim 1 , comprising
(1) centrifugally casting said outer layer in a rotating cylindrical centrifugal-casting mold;
(2) while the inner surface temperature of said outer layer is equal to or higher than the solidification completion temperature of the outer layer melt, pouring a melt for the intermediate layer at a temperature equal to or higher than the solidification start temperature of the intermediate layer+110° C. into a cavity of said outer layer, to centrifugally cast said intermediate layer; and
(3) after the solidification of said intermediate layer, casting a ductile cast iron melt for said inner layer into a cavity of said intermediate layer to form said inner layer.