JPH0533300B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rolling casting roll having a composite structure consisting of metal and tungsten carbide particles.

A metal-carbide particle composite material with a composite structure consisting of a metal base and tungsten carbide particles uniformly and densely dispersed in the base has high wear resistance due to the tungsten carbide particles and strength due to the metal base that binds the particles together.・Has both toughness and toughness. The manufacturing method for this composite material uses a casting method, in which a solid-liquid mixture of molten metal and carbide particles is cast into a mold, and due to the difference in specific gravity between the molten metal and carbide particles, carbide particles P are formed as shown in Figure 6. The molten metal is allowed to settle and coagulate within the molten metal M, and after the molten metal has solidified, the cast body is placed in the mold 1.
If the upper metal phase portion B, in which carbide particles have been separated by specific gravity, is cut and removed, the lower portion A can be obtained as a composite casting consisting of metal M and carbide particles.

When this composite casting is used as a rolling roll, there are two properties that should be provided: wear resistance and surface roughness resistance. In other words, wear resistance is a property directly related to roll life, etc. If the wear resistance is poor, the continuous service life will be short, and it will be necessary to rework (recut) the worn surface, replace the rolls, and operate the rolling line. Interruptions become more frequent and the total lifespan of the roll becomes shorter. Further, wear on the roll surface also causes a decrease in the dimensional accuracy of the rolled product. On the other hand, roughening resistance is also a property that greatly influences the quality of rolled products and roll life. If roughness occurs on the roll surface, the unevenness will be transferred to the surface of the rolled material as roll marks, significantly impairing the quality of the rolled material.To prevent this, the roll surface must be frequently modified. As a result, it is inevitable to replace the rolls and interrupt the line for reshaping, increase the cost of reshaping, and shorten the total life of the rolls.

In view of the above, the present invention provides a composite cast roll having excellent wear resistance and surface roughness resistance, and having the optimum material for a rolling roll.The present invention is characterized by a metal base of cast iron or alloy cast iron. More than 80% of the carbide particles in the composite structure consisting of and tungsten carbide particles are 53 to 88μ
m, and the volume ratio of carbide particles in the composite structure is in the range of 50 to 75%.

The present invention will be explained in detail below.

The particle size of the tungsten carbide particles constituting the composite structure and the volume ratio occupied in the structure are related to wear resistance and the soundness of the cast structure (particularly the presence or absence of microporosity, which is a casting defect). To give a specific example, Fig. 1 compares the wear resistance according to particle size in terms of specific wear amount, and the average particle size of test material A is 63 μm, and that of test material B is 44 μm. The base metal is nickel grain cast iron, and the carbide is
_W2C . The volume ratio of carbide particles is 60%). The specific wear amount is the value obtained from the Okoshi type rapid wear test (however, mating material: SUJ-2, no lubrication, wear distance: 200
mm, speed: 3.4m/s, final load: 18.6Kgf). From the figure, the specific wear amount of specimen B (average particle size 44 μm) containing fine carbide particles is 8.0×10 ^-8 mm ² /Kgf, while that of specimen B containing coarse carbide particles A
(63 μm) has a specific wear amount of 3.7×10 ⁻⁸ mm ² /Kgf, which is less than half of the former, and it can be seen that the larger the particle size, the better the wear resistance.

FIG. 2 shows the influence of the grain size of carbide particles on the size and number of microporosities generated in the matrix of the composite structure. The figure shows the composite structure of the sample material A (average grain size of 63 μm);
Composite structure containing 200μm coarse carbide (sample material C)
, and large pinholes H are generated in sample material C containing coarse carbide particles. A simple measurement and graph of the size and number of individual microporosities in sample materials A and C is shown in Figure 3.
There are no coarse pinholes larger than 50 μm like in sample material C (200 μm), and the total amount of microporosity (total size of microporosity) is only about 1/3 that of sample material C. It can be seen that the organization has excellent soundness.

Figure 4 shows the influence of the volume ratio of carbide particles in the composite structure (particle filling rate) in relation to the wear resistance (specific wear amount; the measurement method is the same as above). The particle volume ratio of material D is approximately 60%, and that of sample material E is approximately 20% (in both cases, the base metal is Ni grain cast iron, and the carbide is W ₂ C with an average grain size of 63 μm).
particle). The specific wear amount of specimen E, in which the volume ratio of carbide particles is low at 20%, is approximately 9.0×10 ^-8 mm ² /Kgf, whereas that of specimen D, in which the volume ratio of carbide particles is relatively high at 60%. The amount of wear was about 3.7×10 ^-8 mm ² /Kgf, which is more than twice the wear resistance of the former.

As mentioned above, for wear resistance, coarse carbide particles are desirable, and if the carbide particles are too fine, the effect of imparting wear resistance will be weak. In order to obtain sufficient wear resistance as a rolling roll, it is necessary that 80% or more of the total number of carbide particles in the composite structure have a particle size of 53 μm or more. The larger the particle size, the higher the wear resistance, but on the other hand, microporosity (pinholes) are more likely to occur in the metal base between the particles as casting defects due to solidification shrinkage, as shown in FIG. 2. Large microporosity directly affects the roughness of the roll surface, causing problems similar to rough skin. Although fine microporosity does not immediately have the same negative effect as rough skin, it can develop into rough skin during the rolling process, or cause cracks to occur and surface cracks can occur due to thermal fatigue, etc. It induces loss of skin and causes rough skin. Therefore, it is desirable that microporosities be as small as possible, and even if complete prevention is difficult, the occurrence of coarse microporosities must be reliably avoided. For this reason, the particle size of carbide particles in the structure is
It is required that 80% or more of the total number of particles be within a range not exceeding 88 μm.

On the other hand, the volume ratio of carbide particles in the composite structure is related to wear resistance and strength/toughness, and if there are few carbide particles, the composite effect of carbide particles will be weak and wear resistance will be insufficient. The more carbide particles there are, the better the wear resistance will be, but if there are too many carbide particles, the metal matrix will become brittle due to a relative decrease in volume. In order to meet the desired wear resistance for rolling rolls and sufficient strength and toughness to withstand high loads and stress during use, the volume ratio of carbide particles in the composite structure should be in the range of 50 to 75%. It is necessary that there be.

The base metal constituting the casting roll of the present invention is various cast irons, such as ductile cast iron, or various low-alloy/high-alloy cast irons, such as nickel grain cast iron, and is appropriately selected depending on the usage conditions and required performance of the roll. . In general, iron-based metals have good wettability with tungsten carbide particles, so they are easy to mix with each other and are advantageous in forming a strong bond at the metal-particle interface. In addition, cast iron has a low solidification temperature, so it is possible to increase the degree of superheating to compensate for the temperature drop due to heat absorption by the particles when they are mixed with carbide particles. It is also advantageous in that it is easy to maintain fluidity. Furthermore, cast iron is a material that has a sufficient track record and reliability as a rolling roll material.

On the other hand, tungsten carbide is WC (specific gravity 15.7),
W ₂ C (17.2) or tungsten titanium double carbide. These carbides are extremely hard and have excellent anti-wear effects. In addition,
The specific gravity of tungsten titanium double carbide varies depending on the type.
Although it is different from 4.9 to 17.2, it goes without saying that a material with a higher specific gravity than the molten metal should be selected in order to cause sedimentation and agglomeration in the molten metal during casting, and in order to promote sedimentation, a specific gravity of 10 or more is required. It is preferable.

The roll of the present invention can also be cast as a solid cylindrical body, but since the wear resistance required for rolls is a matter of the outer surface, instead of a solid cylindrical body, cast as shown in FIG. It may be cast as a hollow cylindrical casting, and the hollow hole may be filled with an inexpensive metal material as a core by casting or the like. This not only reduces the consumption of expensive tungsten carbide particles, but also has the advantage of increasing strength and toughness due to the metal material of the core.

In casting the roll of the present invention, it goes without saying that appropriate molten metal temperature and fluidity should be provided in order to form a healthy composite structure through sedimentation and agglomeration of carbide particles. In addition to adjusting the casting temperature and preheating the carbide particles, effective methods include adjusting the casting speed of the molten metal and carbide particles (the amount supplied into the mold per unit time) and the ratio of the casting speeds of the two. .

To show a specific example of the method of casting the roll of the present invention, in FIG. 5, 1 is a mold, 2 is a casting hopper placed directly above the mold, and the molten metal M and carbide particles P are placed in a ladle 3 and a carbide powder dispenser, respectively. It is supplied from the jig 4 to the casting pot 2 and cast into the mold 1 as a solid-liquid mixture. The mold 1 has a cylindrical core 12 at the center of the bottom of a cylindrical outer wall 11, and allows the solid-liquid mixture to flow down the center of the hemisphere at the top of the core.
By dispersing the solid-liquid mixture radially from the center of the top of the core, the solid-liquid mixture is uniformly poured into each part of the mold in the circumferential direction. In order to further improve the uniformity of dispersion, it is also effective to place the mold 1 on a horizontal rotary table 5 and perform casting while rotating it at an appropriate rotation speed. A required amount of molten metal and carbide particles are poured into the mold, and the carbide particles settle and coagulate to form a composite structure in the cylindrical space defined by the core 12 and the outer wall 11 at the inner bottom of the mold, and then solidify. After completion, the upper metallic phase portion is cut and removed, and the lower composite structure portion can be obtained as a hollow cylindrical composite casting as shown in FIG.

To explain an embodiment of the present invention, W ₂ C particles (average particle size 63 μm) 13
kg and 45 kg of molten Ni grain cast iron were cast into a mold to produce a cylindrical composite casting. However, mold 1 was a ceramic mold, which was set in frame 8 with back sand 7 and preheated to 850°C before use. The molten metal casting temperature was 1550°C, and the W ₂ C particles were preheated to 350°C and administered into the molten metal. As a comparative example, a cylindrical composite casting was obtained under the same casting conditions as above except that coarse W ₂ C particles with a particle size of 200 μm were used. The volume ratio of W ₂ C particles in the composite structure of the casting of the invention example is 66%, and that of the comparative example is 63%.

After dismantling each of the obtained castings and polishing the cross section, we performed a color check and found that coarse W ₂ C particles (200μ
In the comparative example using m), a large number of microporosity appeared and it could not be used as a rolling roll, whereas the inventive example had no coarse microporosity and had a dense and healthy structure. It was observed that

As described above, the cast roll of the present invention has high wear resistance, has a dense structure with little microporosity, has excellent surface roughening resistance, and has excellent properties such as strength and toughness, making it suitable as a rolling roll. It has the following. Therefore, compared to conventional rolls, it has a superior continuous service life and total life, and has various effects such as a reduction in the frequency of roll surface modification, a corresponding reduction in the frequency of rolling line interruptions, and a significant reduction in modification costs.

[Brief explanation of the drawing]

Figures 1 and 4 are graphs showing specific wear amount;
Fig. 2 is a micrograph for drawing (42x magnification) showing the composite structure of the casting, Fig. 3 is a graph showing the distribution of microporosity, Fig. 5 is a longitudinal cross-sectional view showing an example of a casting method, 6 is a plan view of the mold portion, FIG. 6 is a vertical cross-sectional view schematically showing how carbide particles settle and agglomerate within the mold, and FIG. 7 is a perspective view illustrating the shape of the composite casting. 1: Mold, 2: Casting hopper, M: Metal,
P: Tungsten carbide particles.

Claims (1)

[Claims] 1 It has a composite structure consisting of a cast iron or cast alloy cast iron base and tungsten carbide particles uniformly mixed in the base, and the grain size of the carbide particles in the composite structure is in the range of 53 to 88 μm in which 80% or more of the total number of particles A rolling casting roll having excellent wear resistance and surface roughening resistance, characterized in that the volume ratio of carbide particles to the total volume is in the range of 50 to 75%.