Centrifugally cast composite roll and its production method

A centrifugally cast composite roll comprising an outer layer formed by a centrifugal casting method, and an inner layer made of ductile cast iron and integrally fused to said outer layer;

• said outer layer being made of an Fe-based alloy having a chemical composition comprising by mass at least 0.8-3.0% of Cr, 1.5-6.0% of Mo, and 1.8-5.5% in total of V and Nb, and a metal structure in which the area ratio of graphite is 0.3-10%;
• said inner layer comprising a roll body portion fused to said outer layer, and shaft portions integrally extending from both ends of said roll body portion;
• and
• the total amount of Cr, Mo, V and Nb being 0.15-2.0% by mass in end portions of both shaft portions, and the difference in the total amount of Cr, Mo, V and Nb between one shaft portion and the other shaft portion being 0.2% or more by mass.

A method for producing a centrifugally cast composite roll comprising an outer layer formed by a centrifugal casting method, and an inner layer made of ductile cast iron and integrally fused to said outer layer;

• said outer layer being made of an Fe-based alloy having a chemical composition comprising by mass at least 0.8-3.0% of Cr, 1.5-6.0% of Mo, and 1.8-5.5% of V, and a metal structure in which the area ratio of graphite is 0.3-10%;
• said inner layer comprising a roll body portion fused to said outer layer, and shaft portions integrally extending from both ends of said roll body portion;
• and
• the total amount of Cr, Mo and V being 0.15-2.0% by mass in end portions of both shaft portions, and the difference in the total amount of Cr, Mo and V between one shaft portion and the other shaft portion being 0.2% or more by mass;
• the method comprising the steps of (1) centrifugally casting said outer layer in a rotating, centrifugal-casting, cylindrical mold;
• (2) erecting said cylindrical mold containing said outer layer upright, and attaching upper and lower molds communicating with said outer layer to upper and lower ends of said cylindrical mold to constitute an assembled stationary mold;
• and (3) casting a melt for said inner layer into a cavity defined by said upper mold, said outer layer and said lower mold;
• the elevating speed of a melt surface in said upper mold being 100 mm/second or less, smaller than the elevating speed of a melt surface in said lower mold and said outer layer.