Abstract: There is provided a roll surface layer material including a roll surface layer with excellent fatigue resistance. The roll surface layer material has a composition including, on a mass % basis, C: 2.3% to 2.9%, Si: 0.2% to 0.8%, Mn: 0.2% to 1.0%, Cr: 5.0% to 7.5%, Mo: 4.4% to 6.5%, V: 5.3% to 7.0%, Nb: 0.6% to 1.5%, and Co: 0.1% to 4.0% so as to satisfy 14.0?(Mo+1.7V)?17.0 (where Mo represents a content (mass %) of Mo and V represents a content (mass %) of V) and further including Al: 0.001% to 0.03% and/or REM: 0.001% to 0.03%, wherein a carbide is contained at an area fraction of 13% to 40%. A composite roll obtained by integrally welding a shaft member to the roll surface layer member is treated as a centrifugal cast roll that includes a surface layer with excellent fatigue resistance.

Abstract: A centrifugal cast caliber roll for a hot rolling mill has excellent abrasion resistance, fatigue resistance, and slip resistance. The roll has a chemical composition containing, by mass %, C: 1.8% or more and 3.0% or less, Si: 0.2% or more and 1.0% or less, Mn: 0.2% or more and 1.5% or less, Cr: 5% or more and 9% or less, Mo: 4.0% or more and 7.0% or less, V: 4.0% or more and 7.0% or less, Nb: 0.5% or more and 2.0% or less, and the balance being Fe and inevitable impurities, in which the relationship 0.6?(C?0.24V?0.13Nb)?1.4 (where C, V, and Nb each denote the content (mass %) of the corresponding chemical element) is satisfied, and has a surface hardness of Hs 67 or higher and Hs 76 or lower in terms of shore hardness.

Abstract: A roll outer layer material contains small-size carbides having a circle equivalent diameter of 3 to 30 ?m in a number of 500 to 2500 pieces/mm2 and large-size carbides having a circle equivalent diameter of 50 ?m or more in a number of 20 pieces/mm2 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.

Abstract: A surface layer material of a hot rolling mill roll is provided. The surface layer has a chemical composition containing, by mass %, C: 2.4% or more and 3.5% or less, Si: 1.2% or more and 2.4% or less, Mn: 0.2% or more and 2.0% or less, Cr: 0.8% or more and 2.1% or less, Mo: 0.3% or more and 1.1% or less, Ni: 3.0% or more and 6.0% or less, V: 1.0% or more and 2.2% or less, Nb: 0.1% or more and 0.5% or less, REM: 0.0005%) or more and 0.1% or less, Al: 0.003% or more and 0.05% or less, and the balance being Fe and inevitable impurities. The contents of C, Cr, V, Nb, REM, and Al satisfy the relationships Cr+0.2?C?(0.24×V+0.13×Nb)?3.0 and 0.01?REM/Al?3.2.

Abstract: A roll outer layer material contains small-size carbides having a circle equivalent diameter of 3 to 30 ?m in a number of 500 to 2500 pieces/mm2 and large-size carbides having a circle equivalent diameter of 50 ?m or more in a number of 20 pieces/mm2 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.

Abstract: A tool for a piercing mill, the tool comprising a scale layer in a surface layer of a substrate steel, wherein the scale layer includes a net structure scale layer that is formed on a substrate steel side, has a thickness of 10 to 200 ?m in a depth direction, and is complicatedly intertwined with a metal; and wherein a microstructure on the substrate steel side in a range of at least 300 ?m in the depth direction from an interface between the net structure scale layer and the substrate steel contains a ferrite phase at an area fraction of 50% or more, the ferrite phase containing 400/mm2 or more ferrite grains having a maximum length of 1 to 60 ?m.

Abstract: A surface layer material of a hot rolling mill roll is provided. The surface layer has a chemical composition containing, by mass %, C: 2.4% or more and 3.5% or less, Si: 1.2% or more and 2.4% or less, Mn: 0.2% or more and 2.0% or less, Cr: 0.8% or more and 2.1% or less, Mo: 0.3% or more and 1.1% or less, Ni: 3.0% or more and 6.0% or less, V: 1.0% or more and 2.2% or less, Nb: 0.1% or more and 0.5% or less, REM: 0.0005%) or more and 0.1% or less, Al: 0.003% or more and 0.05% or less, and the balance being Fe and inevitable impurities. The contents of C, Cr, V, Nb, REM, and Al satisfy the relationships Cr+0.2?C?(0.24×V+0.13×Nb)?3.0 and 0.01?REM/A1?3.2.

Abstract: A tool for a piercing mill with excellent wear resistance and a method for producing the tool for a piercing mill are provided. A scale layer is formed in a surface layer of a substrate steel having a composition containing, on a mass % basis, C: 0.05% to 0.5%, Si: 0.1% to 1.5%, Mn: 0.1% to 1.5%, Cr: 0.1% to 1.5%, Mo: 0.6% to 3.5%, W: 0.5% to 3.5%, and Nb: 0.1% to 1.0% and further containing Co: 0.5% to 3.5% and Ni: 0.5% to 4.0% so as to satisfy 1.0<Ni+Co<4.0. The scale layer includes a net structure scale layer that is formed on a substrate steel side, has a thickness of 10 to 200 ?m in a depth direction, and is complicatedly intertwined with a metal. A microstructure on the substrate steel side in a range of at least 300 ?m in the depth direction from an interface between the net structure scale layer and the substrate steel contains a ferrite phase at an area fraction of 50% or more, the ferrite phase containing 400/mm2 or more of ferrite grains having a maximum length of 1 to 60 ?m.

Abstract: There is provided a roll surface layer material including a roll surface layer with excellent fatigue resistance. The roll surface layer material has a composition including, on a mass % basis, C: 2.3% to 2.9%, Si: 0.2% to 0.8%, Mn: 0.2% to 1.0%, Cr: 5.0% to 7.5%, Mo: 4.4% to 6.5%, V: 5.3% to 7.0%, Nb: 0.6% to 1.5%, and Co: 0.1% to 4.0% so as to satisfy 14.0?(Mo+1.7V)?17.0 (where Mo represents a content (mass %) of Mo and V represents a content (mass %) of V) and further including Al: 0.001% to 0.03% and/or REM: 0.001% to 0.03%, wherein a carbide is contained at an area fraction of 13% to 40%. A composite roll obtained by integrally welding a shaft member to the roll surface layer member is treated as a centrifugal cast roll that includes a surface layer with excellent fatigue resistance.

Abstract: High-quality high-speed steel roll which is markedly excellent in abrasion resistance and free of carbide segregation even in the case of production by centrifugal casting of economical benefit; it comprises an outer layer containing, by all weight ratios, C; 2.4-2.9%, Si; not more than 1%, Mn; not more than 1%, Cr; 12-18%, Mo; 3-9%, V; 3-8% and Nb; 0.5-4%, and meeting with the following equations (1) and (2) at one time,0.27.gtoreq.Mo (%)/Cr (%).ltoreq.0.7 (1)C (%)+0.2.multidot.Cr (%).ltoreq.6.2 (2)the outer layer further containing as the balance Fe and unavoidable impurities.

Abstract: A roll outer layer material for hot rolling includes, as analyzed in weight percent, of 2.5-4.0% C, 6.0-20% Cr, 3.0-10.0% V, 0.6-5.0% Nb, 2.0-15% Mo, 3.0% or below Si, 3.0% or below Mn, C, V, Nb and Cr satisfying a following formula (1),10.5(%).ltoreq.6.5.C(%)-1.3.V(%)-0.7.Nb(%).ltoreq.2.Cr(%)-2(%)(1), and the balance being Fe and incidental impurities. A method of manufacturing a roll for hot rolling includes the steps of centrifugally casting an outer layer material having the above composition, centrifugally casting graphite steel containing 0.5% or above of C as an intermediate layer, and casting an axis material which is a spheroidal graphite cast iron, a flake graphite cast iron or a graphite steel. C is present in the intermediate layer in an amount which satisfies a following formula (2),C (intermediate layer).gtoreq.2.0-0.5 (C-0.2 V-0.

Abstract: A centrifugal cast roll shell material composed of a granular MC carbide, graphite and C: 2.5 to 4.7%, Si: 0.8 to 3.2%, Mn: 0.1 to 2.0%, Cr: 0.4 to 1.9%, Mo: 0.6 to 5%, V: 3.0 to 10.0% and Nb: 0.6 to 7.0%, satisfying the following formulae (1), (2), (3) and (4):2.0+0.715 V+0.10 Nb.ltoreq.C (%) (1)1.1.ltoreq.Mo/Cr (2)Nb/V.ltoreq.0.8 (3)0.2.ltoreq.Nb/V (4),the remainder being Fe and inevitable impurities, wherein the pouring temperature is 1,400.degree. C. or higher.

Abstract: A roll outer layer material for hot rolling consists essentially, as analyzed in weight percent, of 2.5-4.0% C, 6.0-20% Cr, 3.0-10.0% V, 0.6-5.0% Nb, 2.0-15% Mo, 3.0% or below Si, 3.0% or below Mn, C, V, Nb and Cr satisfying a formula where 10.5.ltoreq.6.5.C(%)--1.3.V(%)--0.7.Nb(%).ltoreq.2.Cr(%)--2, and the balance being Fe and incidental impurities. A method of manufacturing a roll for hot rolling comprises the steps of centrifugally casting an outer layer material having the above composition, centrifugally casting graphite steel containing 0.5% or above of C as an intermediate layer, and casting an axis material which is a spheroidal graphite cast iron, a flake graphite cast iron or a graphite steel. Carbon is present in the intermediate layer in an amount which satisfies a formula, C (intermediate layer).gtoreq.2.0-0.5?C(%)--0.2.V(%)--0.11.Nb(%)! (outer layer).