JPH04258303A - Roll for hot rolling wire rod - Google Patents

Abstract

PURPOSE:To offer a roll for hot rolling a wire rod with which good finish can be ensured for a long time. CONSTITUTION:A roll of sintered body containing a hard phase of preferably 30-90wt.% which essentially consists of one kind or more kinds of double borate of Ni, Mo, double borate of Ni, W, double borate of Ni, Mo, W and the balance of binder phase comprising primarily Ni, Mo is excellent in impact resistance, and oxidation resistance and deformation resistance at a high temp. When this roll is used for hot rolling wire rod, the excellent finish state of wire rod can be ensured for a long time.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll for hot rolling wire rods, that is, a rolling roll used for hot rolling metal wire rods such as iron.

0002

2. Description of the Related Art Conventionally, metal wire rods, particularly steel wire rods, have been produced by a multi-stage rolling method in which wires are passed through several stages of rolling rolls. In the past, rolls made of adamite were often used in the first stage of finishing, and rolls made of alloy grain cast iron were used in the second stage, but the hardness of the rolls in the latter stage in particular has a large effect on the finished surface of the wire, so it is necessary to use harder rolls. The use of rolls has become increasingly popular, and high Cr cast iron and even cemented carbide rolls have come into use.

0003

[Problems to be Solved by the Invention] Cemented carbide is mainly used as a hot rolling roll for steel wire rods in the latter stages of finishing, but even in such processes, wire rod temperatures of 900 to
Since high-temperature and high-speed processing is performed at 1100° C. and a wire speed of 5 to 100 m/s, the surface of the carbide roll often becomes rough and cracked due to wear even after a short period of use. Rough skin or cracks on the rolls in the latter stages of finishing have a great effect on the finished surface of the wire rod, so the rolls must be replaced, and the continuous rolling line must be stopped during this time. As described above, in the production of wire rods, roll defects are the biggest cause of rolling line stoppages.

[0004] Possible causes of the above defects in cemented carbide rolls are as follows. Cemented carbide is a material with excellent strength and hardness at room temperature, but has poor oxidation resistance at high temperatures. Therefore, on the surface against which the high-temperature wire rod is pressed during rolling, oxides that easily fall off are generated, and wear progresses rapidly. Furthermore, the strength and hardness of cemented carbide decrease significantly at high temperatures, so in order to ensure deformation resistance and a good finished state of the wire, the ratio of the metallic phase of the cemented carbide used in the roll is limited. be done. For this reason, the thermal shock resistance of the alloy is limited, and cracks occur when the wire rod and surrounding equipment are constantly exposed to cooling water.

[0005] In addition, in recent years, rolling rolls made of ceramic sintered bodies (JP-A-59-1045, JP-A-59-1
No. 97307, etc.), but since the impact resistance is not sufficient, there are cases where the tip of the wire rod rolled at high speed in the previous stage is chipped when the tip hits it. Furthermore, due to poor thermal shock resistance, workability is poor as it takes a long time to preheat at the start of rolling, and there is a large difference in thermal expansion between the metal shaft and the metal shaft that fits into the center, and the fitting part may chip during operation. Many problems have been pointed out, such as the occurrence of problems, and it has not been put into practical use. Further, ceramic-coated metal rolls have been considered, but cannot be used because they do not essentially improve deformation resistance at high temperatures and the adhesion of the coating layer is insufficient.

[0006]

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and includes Ni, Mo complex boride,
It is characterized by being composed of a sintered body consisting of a hard phase mainly composed of Ni, W complex boride and one or more of Ni, Mo, and W complex boride, and a binder phase mainly composed of Ni and Mo. The present invention provides a hot wire rod rolling roll. The compound boride sintered body which is the material of the hot rolling roll of the present invention is known as boride cermet, but WC
Since it is a ceramic-metal composite material similar to -Co, a significant increase in service life was not expected.

The rolling roll of the present invention can be obtained by the method described below. For example, MoB, WB, and Ni powders are ground and mixed in an organic solvent such as ethanol using a rotary pot mill, a vibration mill, or the like. After drying this powder, it is pressure-molded using a metal press or a rubber press, and then
, H2 in an inert or reducing atmosphere such as 11
A sintered body is obtained by heating to about 00 to 1500°C for a certain period of time or more. The sintered body thus obtained is processed into a predetermined shape and size using a diamond grindstone or the like to obtain a rolling roll.

[0008] The raw material powder used to obtain the sintered body does not necessarily have to be a combination of the above-mentioned MoB, WB, and Ni powders, but may be a combination of Ni-B alloy powder, Mo powder, W powder, or Ni,
A combination of individual metal powders such as Mo and W and B powder may also be used. In addition to these main raw materials, TaB
It is also possible to add borides such as 2.2 and NbB2, metal carbides such as WC and TiC, and metal nitrides such as TiN and TaN.

The structure of the material constituting the rolling roll of the present invention will be explained as follows. It is desirable that the binder phase is distributed so as to surround the hard phase, and that the hard phases are not continuous but independent. Further, the hard phase has a polygonal shape with a not very large aspect ratio and an average particle size of 5 μm or less. The maximum width of the binder phase is about 5 μm, and it is almost uniformly distributed.

[0010] Regarding the specific microstructure of the sintered body, no matter which combination of raw materials is used, a hard phase mainly consisting of Mo2 NiB2 or W2 NiB2 or (Mo, W)2 NiB2 and a mainly Ni −
It consists of a binder phase that is a Mo alloy, and the weight percent of this hard phase is preferably 30 to 90%. The reason why it is preferable to set the ratio of the hard phase to 30 to 90% by weight is that the ratio of the hard phase is 30% to 90% by weight.
If it is less than 90% by weight, the hardness and deformation resistance at high temperatures of the rolling roll surface will not be sufficiently improved, and if it exceeds 90% by weight, cracks are likely to occur due to thermal shock during wire rolling. Note that a particularly preferable ratio of the hard phase is 40 to 80%.

[0011] In contrast to the hard phase, the binder phase is mainly composed of Ni and Mo, and it is preferable that most of the binder phase, for example, 85% or more, be composed of one or two of these or an alloy phase. This is because the binder phase of Ni and Mo has a wide solid solution range at high temperature with the hard phase of the above-mentioned complex boride, and Ni is optimal for ensuring mutual interface strength. . On the other hand, Mo dissolves in the Ni phase, is effective in improving strength and hardness, and does not react with the hard phase to produce lower-grade borides. The amount of Mo in Ni is suitably 5 to 20% by weight, more preferably 10 to 18% by weight. It is preferable that the surface of the rolling roll of the present invention is as smooth as possible. On the other hand, surface treatments such as plating, thermal spraying, and overlaying may be applied to the surface, and the service life may be further extended in some cases.

0012

[Operation] Compound boride, which is the main component of the sintered body constituting the rolling roll according to the present invention, essentially exhibits less decrease in hardness and strength at high temperatures than tool steel, and is composite with Ni-Mo metal. Even so, its characteristics are clearly demonstrated. Furthermore, the interface between the hard phase and the binder phase of this sintered body is very strongly connected, and the strength and hardness of the sintered body are inevitably high even at high temperatures. Therefore, as the rolling roll material, it is possible to use a material with significantly more metal phase than cemented carbide. As a result, the thermal shock resistance of the mill roll is improved, the occurrence of cracks on the surface is suppressed, and the life of the mill roll is significantly extended.

[0013] As described above, if the metal phase is increased, there is a concern that the rolling roll and the wire will seize, but the hard phase existing on the rolling roll surface not only improves the seizure resistance but also improves the B content contained in the hard phase. After a portion of it is liberated and oxidized, it forms an extremely thin glass-like layer along with scale, which functions as a lubricant. Therefore, the seizure property of the rolling roll according to the present invention with the wire rod is significantly improved compared to the conventional rolling roll.

[0014]

[Example] (Example 1) MoB: 43%, WB: 7%,
Using each powder of Ni: 45% and Mo: 5% as raw materials, N
A sintered body containing i-Mo, Ni-W, and Ni-Mo-W complex borides in a weight percentage of 68% was prepared, and a rolling roll was manufactured. When this roll was used as a post-finishing roll for carbon steel wire, it could be used for 40 hours until scratches appeared on the surface of the wire, which were thought to be caused by cracks in the roll. In addition, when the hardness of this roll was measured, Hv = 830 kg/mm2 at room temperature and 480 kg at 800°C.
/mm2.

(Examples 2 to 6 and Comparative Examples 1 to 2) After producing a sintered body and manufacturing a rolling roll in the same manner as in Example 1,
Table 1 shows the results of an actual machine test conducted in the same manner as in Example 1. (Comparative Example 3) As shown in Table 1, the conventional material WC-Co
An alloy rolling roll was prepared and tested in the same manner as in Example 1.

[0016]

[Table 1]

[0017]

[Effects of the Invention] As described above, the rolling roll according to the present invention has significantly improved hardness at high temperatures, deformation resistance, and seizure resistance with workpiece materials compared to rolling rolls using conventional WC-Co alloys. Therefore, long life can be achieved. As a result, the number of rolling roll changes during hot processing of steel wire rods is significantly reduced, improving manufacturing efficiency and stabilizing product quality.

Claims (2)

[Claims] [Claim 1] A hard phase mainly composed of one or more of Ni, Mo complex boride, Ni, W complex boride, and Ni, Mo, W complex boride, and a binder phase mainly composed of Ni and Mo. A hot wire rod rolling roll, characterized in that it is composed of a sintered body made of. 2. The hot wire rod rolling roll according to claim 1, wherein the weight percent of the hard phase of the sintered body constituting the rolling roll is 30 to 90%.