Composite rolling mill roll and rolling method

1. A composite rolling mill roll comprising:

a steel roll shaft; and

an outer layer provided around the roll shaft, wherein

the outer layer includes a sintered body including a base metal which is an iron alloy, a fibrous inclusion which consists of a ceramic and has an average diameter of 1 to 30 μm and an average aspect ratio of 10 to 500, and a particulate inclusion which consists of a ceramic and has an average diameter of 1 to 100 μm,

an amount of the fibrous inclusion is 5 to 40 volume % relative to a volume of the sintered body, and

an amount of the particulate inclusion is 5 to 30 volume % relative to the volume of the sintered body.

2. The composite rolling mill roll according to claim 1 , wherein

a chemical composition of the base metal of the sintered body comprises:

0.8 to 3.5 wt % of C;

1 to 13 wt % of Cr;

0 to 18 wt % of Mo;

0 to 28 wt % of W;

0 to 15 wt % of Ni;

0 to 18 wt % of Co;

2 to 20 wt % of one or more of elements in total, the elements being selected from a group consisting of V, Nb, Ti, Ta, Zr, and Hf; and

a remainder including Fe and an impurity.

3. The composite rolling mill roll according to claim 1 , wherein

the particulate inclusion and the fibrous inclusion are one or more of an oxide, a nitride, and a carbide.

4. The composite rolling mill roll according to claim 3 , wherein

the particulate inclusion is one or more of an alumina, a zirconia, a titania, a boron nitride, a silicon nitride, and a zirconium nitride.

5. The composite rolling mill roll according to claim 3 , wherein

the fibrous inclusion is one or more of the alumina, a mullite, the boron nitride, and the silicon nitride.

6. The composite rolling mill roll according to claim 1 , wherein

a total amount of the particulate inclusion and the fibrous inclusion is 35 to 70 volume % relative to the volume of the sintered body.

7. A composite rolling mill roll comprising:

a steel roll shaft; and

an outer layer provided around the roll shaft, wherein

the outer layer includes a sintered body obtained by sintering a mixture of (a) a powder of an iron alloy, (b) a ceramic fiber which has an average diameter of 1 to 30 μm and an average aspect ratio of 10 to 500, and (c) a ceramic powder which has an average diameter of 1 to 100 μm;

a blending amount of (b) the ceramic fiber before the sintering is 5 to 40 volume % relative to a total amount of (a) the powder of the iron alloy, (b) the ceramic fiber, and (c) the ceramic powder before the sintering;

a blending amount of (c) the ceramic powder before the sintering is 5 to 30 volume % relative to the total amount of (a) the powder of the iron alloy, (b) the ceramic fiber, and (c) the ceramic powder before the sintering; and

(b) the ceramic fiber and (c) the ceramic powder exist independently after the sintering.

8. The composite rolling mill roll according to claim 7 , wherein

a chemical composition of (a) the powder of the iron alloy before the sintering comprises:

0.8 to 3.5 wt % of C;

1 to 13 wt % of Cr;

0 to 18 wt % of Mo;

0 to 28 wt % of W;

0 to 15 wt % of Ni;

0 to 18 wt % of Co;

2 to 20 wt % of one or more of elements in total, the elements being selected from a group consisting of V, Nb, Ti, Ta, Zr, and Hf; and

a remainder including Fe and an impurity.

9. The composite rolling mill roll according to claim 7 , wherein

(c) the ceramic powder is one or more of an oxide, a nitride, and a carbide.

10. The composite rolling mill roll according to claim 9 , wherein

(c) the ceramic powder is one or more of an alumina, a zirconia, a titania, a boron nitride, a silicon nitride, and a zirconium nitride.

11. The composite rolling mill roll according to claim 7 , wherein

(b) the ceramic fiber is one or more of an oxide-type fiber, a carbide-type fiber, and a nitride-type fiber.

12. The composite rolling mill roll according to claim 7 , wherein

a total blending amount of (b) the ceramic fiber and (c) the ceramic powder before the sintering is 35 to 70 volume % relative to the total amount of (a) the powder of the iron alloy, (b) the ceramic fiber, and (c) the ceramic powder before the sintering.

13. A method for rolling comprising:

rolling a metallic material with the composite rolling mill roll according to claim 1 .

14. A method for manufacturing a composite rolling mill roll including an outer layer and a roll shaft, the method comprising:

mixing a powder of an iron alloy, a ceramic powder having an average diameter of 1 to 100 μm, and a ceramic fiber having an average diameter of 1 to 30 μm and an average aspect ratio of 10 to 500 to obtain a raw mixture; and

filling the raw mixture into a tubular capsule installed around the roll shaft, then degassing inside of the capsule, and then sintering the raw mixture by hot isostatic pressing under 70 to 120 MPa of a pressure to obtain the composite rolling mill roll in which the outer layer is joined around the roll shaft; wherein

a blending amount of the ceramic fiber before the sintering is 5 to 40 volume % relative to the total amount of the raw mixture before the sintering; and

a blending amount of the ceramic powder before the sintering is 5 to 30 volume % relative to the total amount of the raw mixture before the sintering.

15. A method for rolling comprising:

rolling a metallic material with the composite rolling mill roll according to claim 7 .

16. The composite rolling mill roll according to claim 1 , wherein

the particulate inclusion is an oxide or a nitride.

17. The composite rolling mill roll according to claim 1 , wherein

the fibrous inclusion is one or more of an oxide excluding an alumina and a mullite, a nitride, and a carbide.

18. The composite rolling mill roll according to claim 7 , wherein

(c) the ceramic powder is an oxide or a nitride.

19. The composite rolling mill roll according to claim 7 , wherein

(b) the ceramic fiber is one or more of an oxide-type fiber excluding an alumina and a mullite, a carbide-type fiber, and a nitride-type fiber.

20. The method for manufacturing a composite rolling mill roll including an outer layer and a roll shaft according to claim 14 , wherein

the ceramic powder is an oxide or a nitride.

21. The method for manufacturing a composite rolling mill roll including an outer layer and a roll shaft according to claim 14 , wherein

the ceramic fiber is one or more of an oxide-type fiber excluding an alumina and a mullite, a carbide-type fiber, and a nitride-type fiber.