OUTER LAYER MATERIAL FOR COMPOSITE ROLL FOR ROLLING AND COMPOSITE ROLL FOR ROLLING

Abstract

The present invention provides an outer layer material for a composite roll for rolling, in which the strength of secondary eutectic carbides can be increased by reducing a B amount in the secondary eutectic carbides and surface roughening resistance can be improved, and a composite roll for rolling in which this outer layer material is used in an outer layer. The outer layer material for a composite roll for rolling of the present invention is an outer layer material for a composite roll for rolling containing C in an amount of 1.8 mass % or more and 2.5 mass % or less, Si in an amount of more than 0 mass % and 1.0 mass % or less, Mn in an amount of more than 0 mass % and 1.0 mass % or less, Ni in an amount of more than 0 mass % and 0.5 mass % or less, Cr in an amount of more than 3.0 mass % and 8.0 mass % or less, Mo in an amount of more than 2.0 mass % and 10.0 mass % or less, W in an amount of more than 0 mass % and 10.0 mass % or less, V in an amount of more than 0 mass % and 10.0 mass % or less, and B in an amount of more than 0 mass % and less than 0.01 mass %, and a remaining portion including Fe and inevitable impurities.

Claims

1-6. (canceled)

7. An outer layer material for a composite roll for rolling, comprising: C in an amount of 1.8 mass % or more and 2.5 mass % or less, Si in an amount of more than 0 mass % and 1.0 mass % or less, Mn in an amount of more than 0 mass % and 1.0 mass % or less, Ni in an amount of more than 0 mass % and 0.5 mass % or less, Cr in an amount of more than 3.0 mass % and 8.0 mass % or less, Mo in an amount of 4.0 mass % or more and 10.0 mass % or less, W in an amount of more than 0 mass % and 2.0 mass % or less, V in an amount of more than 0 mass % and 10.0 mass % or less, and B in an amount of more than 0 mass % and less than 0.01 mass %, and a remaining portion including Fe and inevitable impurities.

8. The outer layer material for a composite roll for rolling according to claim 7, wherein Mo in an amount of 4.19 mass % or more and 6.3 mass % or less, Win an amount of 0.43 mass % or more and 1.7 mass % or less.

9. The outer layer material for a composite roll for rolling according to claim 7, further comprising Nb in an amount of 0.01 mass % or more and 2.0 mass % or less, and/or Ti in an amount of 0.01 mass % or more and 1.0 mass % or less.

10. The outer layer material for a composite roll for rolling according to claim 8, further comprising Nb in an amount of 0.01 mass % or more and 2.0 mass % or less, and/or Ti in an amount of 0.01 mass % or more and 1.0 mass % or less.

11. The outer layer material for a composite roll for rolling according to claim 7, wherein when a mass % of a B in a surface of the outer layer material is B(t1) and a mass % of the B in an inner surface of the outer layer material is B(t2), B(t2)−B(t1)>0.002 is satisfied.

12. The outer layer material for a composite roll for rolling according to claim 8, wherein when a mass % of a B in a surface of the outer layer material is B(t1) and a mass % of the B in an inner surface of the outer layer material is B(t2), B(t2)−B(t1)>0.002 is satisfied.

13. The outer layer material for a composite roll for rolling according to claim 9, wherein when a mass % of a B in a surface of the outer layer material is B(t1) and a mass % of the B in an inner surface of the outer layer material is B(t2), B(t2)−B(t1)>0.002 is satisfied.

14. The outer layer material for a composite roll for rolling according to claim 10, wherein when a mass % of a B in a surface of the outer layer material is B(t1) and a mass % of the B in an inner surface of the outer layer material is B(t2), B(t2)−B(t1)>0.002 is satisfied.

15. The outer layer material for a composite roll for rolling according to claim 7, wherein the outer layer material contains a secondary eutectic carbide, and a melting temperature of the secondary eutectic carbide is higher than 1100° C.

16. The outer layer material for a composite roll for rolling according to claim 7, wherein an area percentage of MC carbides of the surface of the outer layer material is 7% to 15%.

17. The outer layer material for a composite roll for rolling according to claim 7, wherein an area percentage of secondary eutectic carbides of the surface of the outer layer material is 1% to 6%.

18. A composite roll for rolling, wherein the outer layer material according to claim 7 is used in an outer layer, and an inner core, or an intermediate layer and an inner core are comprised on an inner side of the outer layer material.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0050] FIG. 1 is a photograph obtained by performing dye penetrant inspection on a test piece of Working Example 3, which is an invention example.

[0051] FIG. 2 is a photograph obtained by performing dye penetrant inspection on a test piece of Comparative Example 2.

[0052] FIG. 3 is a photograph showing an enlarged eroded region in FIG. 2.

DESCRIPTION OF EMBODIMENTS

[0053] A composite roll for rolling of the present invention comprises an outer layer that is used for rolling, an intermediate layer and/or an inner core that are located on the inner side of the outer layer, and a shaft member. Examples of an inner core material for constituting the inner core include high strength materials such as high grade cast iron, ductile cast iron, and graphitic steel, and an example of the intermediate layer material for constituting the intermediate layer is an adamite material.

[0054] The outer layer can be cast by producing a molten alloy of the outer layer material containing the above-described components, and performing centrifugal casting or static casting, for example. Centrifugal casting may be vertical-type (rotation axis is oriented in a vertical direction), inclined-type (rotation axis is oriented in an oblique direction), or horizontal-type (rotation axis is oriented in a horizontal direction).

[0055] When the outer layer material is cast, the solidification speed is set to 8 mm/min or more. Adjustment of the solidification speed can be carried out by air-cooling or water-cooling a mold.

[0056] Defining the solidification speed of the outer layer material in this manner makes it possible to increase the B amount included in the base, and to inhibit B from being mixed into the secondary eutectic carbides.

[0057] A composite roll for rolling is produced by casting an inner core, or an intermediate layer and an inner core into the cast outer layer material, or shrink-fitting, or the like.

[0058] Desirably, quenching treatment is performed on the composite roll for rolling. B can improve the quenching property, and B is not concentrated in the secondary eutectic carbides in the present invention and therefore is included in the base in a large amount, and thus the hardness of the base can be further increased by quenching.

[0059] In the outer layer according to the present invention, a Vickers hardness of the secondary eutectic carbides may be, for example, 1500 HV to 1900 HV due to the above-described components and solidification speed. It is thought that the reason why the hardness increases in this manner is that the B amount in the secondary eutectic carbides decreases.

[0060] Moreover, even if the composite roll for rolling in which the above-described outer layer material is used in the outer layer receives a thermal shock in heat treatment or rolling, suppression of coarsening of the secondary eutectic carbides and an increase in the strength and the melting point make it possible to prevent the secondary eutectic carbides from falling off or eroding.

[0061] When the surface of the produced outer layer was observed, an area percentage of MC carbides was 7% to 15%, an area percentage of secondary eutectic carbides was 1% to 6%, and the remaining portion was the base. Adjustment of the B content and the solidification speed made it possible to suppress the growth of the secondary eutectic carbides. This means that the area percentage of the secondary eutectic carbides was reduced. Also, when the B amount in the outer layer was measured, the B amount in the surface of the outer layer was 0.006%, and the B amount in the inner surface of the outer layer was 0.009%, and when the mass % of the B in the surface of the outer layer material was B(t1) and the mass % of the B in the inner surface of the outer layer material was B(t2), the value B(t2)−B(t1) was 0.002 or more.

[0062] The composite roll for rolling in which the outer layer material of the present invention is used in the outer layer include secondary eutectic carbides with a high strength and has excellent surface roughening resistance. Therefore, it is possible to suppress loss of the surface of the outer layer during rolling, and to reduce the frequency of grinding of the surface of the outer layer and reduce depletion of the outer layer accompanying this.

[0063] In particular, the composite roll for rolling in which the outer layer material of the present invention is used in the outer layer is suitable for application to front and sublevel stands in hot finishing rolling in which operational stability is required.

WORKING EXAMPLES

[0064] A molten alloy containing various components shown in Table 1 was produced and centrifugal casting was performed in a high-frequency induction furnace. The solidification speed of the outer layer material at the time of casting was adjusted to 8 mm/min or more. In Table 1, Working Examples 1 to 5 are invention examples. Note that Comparative Example 1 and Comparative Example 2 are outer layer materials containing B in an amount of more than 0.01%.

TABLE-US-00001 TABLE 1 C Si Mn Ni Cr Mo W V Nb Ti B Work. 2 0.37 0.42 0.46 5.23 6.3 1.63 7.34 0.005 Ex. 1 Work. 2.09 0.63 0.49 0.11 3.93 4.19 0.45 6.05 0.58 0.009 Ex. 2 Work. 2.4 0.59 0.54 0.02 5.38 4.51 0.43 5.74 0.25 0.075 0.003 Ex. 3 Work. 2.3 0.66 0.35 0.36 5.4 5.86 0.46 6.37 0.15 0.041 0.0002 Ex. 4 Work. 1.89 0.61 0.5 0.09 5.38 6.21 1.7 7.27 0.05 0.0008 Ex. 5 Comp. 2.25 0.6 0.45 0.15 5.53 3.98 0.31 6.43 0.2 0.026 0.034 Ex. 1 Comp. 2.09 0.57 0.51 0.22 3.3 4.2 0.45 5.97 0.53 0.05 0.056 Ex. 2 Note that the unit is mass %

[0065] After the outer layer material was cast, the inner core was cast to produce a composite roll for rolling.

[0066] Quenching was performed on the obtained composite roll for rolling. Quenching was performed by performing forced-air cooling with large fans such that a cooling speed on the roll surface from an austenitization temperature to 700° C. was 900° C./h or more.

[0067] With regard to composite rolls for rolling of the working examples and comparative examples on which quenching was performed, machining was performed, a plurality of test pieces were then cut out such that one side of each test piece was 30 mm or more and a thickness of each test piece was about 10 mm, and as shown in Table 2, the test pieces were held at a temperature of 1050° C. to 1125° C. for 30 minutes, and dye penetrant inspection was carried out on the test pieces to observe the states of the surfaces. In Table 2, “−” indicates a test piece in which erosion was not confirmed in dye penetrant inspection, and “+” indicates a test piece in which erosion was confirmed.

TABLE-US-00002 TABLE 2 Work. Work. Work. Work. Work. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 1 Ex. 2 B: 0.005% B: 0.009% B: 0.003% B: 0.0002% B: 0.0008% B: 0.034% B: 0.056% 1050° C., − − − − − − − 30 min 1075° C., − − − − − + + 30 min 1100° C., − − − − − + + 30 min 1125° C., − − − − − + + 30 min

[0068] With reference to Table 2, it is found that in all of Working Example 1 to Working Example 5, which are the invention examples, erosion of the secondary eutectic carbides did not occur even in the case where the test pieces were held at 1050° C. to 1125° C. for 30 minutes. FIG. 1 is a photograph of the test piece of Invention Example 3. With reference to FIG. 1, no indicating mark was observed on the surface of the test piece.

[0069] This means that in the test pieces of the working examples, by setting the solidification speed to 8 mm/min, a large amount of B remained in the base and it was possible to inhibit B from being mixed into the secondary eutectic carbides. That is, it is found that preventing concentrated B from being mixed into the secondary eutectic carbides makes it possible to improve the hardness of the secondary eutectic carbides, and to prevent the secondary eutectic carbides from eroding even if the test pieces were held at high temperatures.

[0070] On the other hand, it is found that in the comparative examples, erosion of the secondary eutectic carbides was not confirmed at 1050° C., but erosion was confirmed at 1100° C. or more. FIG. 2 is a photograph of the test piece of Comparative Example 2. With reference to FIG. 2, indicating marks caused by melted secondary eutectic carbides were observed at a plurality of locations on the surface of the test piece. FIG. 3 is an enlarge photograph of the indicating marks in FIG. 2. As shown in FIG. 3, it is found from the indicating marks that structure loss occurred. This means that as a result of B being concentrated and mixed into the secondary eutectic carbides, the secondary eutectic carbides melted at a high temperature.

[0071] Note that with regard to the working examples, if the test pieces were held in the condition of 1150° C. for 30 minutes, erosion of the secondary eutectic carbides was confirmed.

[0072] The description is for describing the present invention, and should not be interpreted as limiting or restricting the scope of claims of the present invention. Furthermore, it goes without saying that the configurations of the constituent elements of the present invention are not limited to those in the working examples, and that various modifications are possible within the technical scope of the claims

INDUSTRIAL APPLICABILITY

[0073] The present invention is useful for an outer layer material for a composite roll for rolling that is used in hot rolling and a composite roll for rolling in which this outer layer material is used in an outer layer.