JPH05169223A - Casting method for rolling roll - Google Patents

Abstract

PURPOSE:To improve the wear resistance of the rolling roll by forming a dense cast structure. CONSTITUTION:The compsn. of the rolling roll consists, by weight% of 1.0 to 4.0 C, 0.1 to 3.0 Si, 0.1 to 3.0 Mn, <=5 Ni, 1 to 15 Cr, <=10 Mo, <=10 W, <=15 V, <=5 Co and further contg. at least one of <=3 Ti and <=3 Zr and consists of the balance Fe. A mold coating material 22 having >=5kcal/mh deg.C thermal conductivity at 1000 to 1400 deg.C is applied at 0.1 to 10mm thickness on the inner peripheral surface of the casting mold 11 and the rolling roll is cast while cooling water is passed through flow passages 17 provided in the casting mold 11 at the time of casting the rolling roll by a centrifugal casting method using the metallic casting mold. The fused metal is cooled at a high solidifying rate. The resulted rolling roll has the dense case structure and has the improved wear resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting hollow or solid rolling rolls by centrifugal casting.

The present invention is used for casting of rolling rolls which are required to have wear resistance, heat resistance or toughness.

[0003]

2. Description of the Related Art For casting concentric products such as hollow cylinders,
Centrifugal casting is widely used because it does not require a core and has high productivity and yield. Especially, since the solidification rate is higher than that of the static casting method and a dense casting structure can be obtained, the centrifugal casting method is adopted for casting of high alloy castings such as rolling rolls that require wear resistance and toughness. ing.

Recently, Cr and M have been used as materials for rolling rolls.
A high speed alloy containing O, W, V, etc. is used.
These Cr, Mo, W and V are high hardness MC, M ₆ C
Since carbides are formed, the wear resistance of the rolling roll is significantly improved. Due to the advantages of centrifugal casting, centrifugal casting is also used in the production of rolling rolls of HSS alloy. (For example, "Material Process" 4-2 (1991), 446-
Also, in the above centrifugal casting, a mold coating material such as SiO ₂ or Al ₂ O ₃ is applied to the inner peripheral surface of the mold.

[0005]

As described above, the centrifugal casting method has a higher solidification rate than the static casting method, but a higher solidification rate is required for the casting of the rolling roll made of the HSS alloy. .. That is, in the case of a high-speed alloy, if the solidification rate is low, carbides are largely precipitated and the cast structure becomes rough. As a result, the hardness decreases and the wear resistance deteriorates.

The present invention provides a casting method capable of obtaining a dense casting structure and improving the wear resistance of a rolling roll.

[0007]

In the method for casting a rolling roll according to the present invention, the composition of the rolling roll is C: 1.0% by weight.
.About.4.0, Si: 0.1 to 3.0, Mn: 0.1 to 3.
0, Ni: ≤ 5, Cr: 1 to 15, Mo: ≤ 10, W:
≦ 10, V: ≦ 15, Co: ≦ 5, and Ti:
At least one of ≦ 3 and Zr: ≦ 3 is contained, and the balance is composed of Fe. When the rolling roll is cast by a centrifugal casting method using a metal mold, the thermal conductivity at 1000 to 1400 ° C. is 5 kcal /
A coating material having a temperature of mh ° C or higher is applied to the inner peripheral surface of the mold in an amount of 0.1 to 10
It is applied with a thickness of mm, and casting is performed while cooling water is allowed to flow through the channel provided inside the mold.

C combines with Cr, V, Mo and W to crystallize high MC type, M ₃ C type and M ₇ C ₃ type carbides to improve wear resistance. When the content of C is less than 1.0%, the amount of carbides is small and sufficient wear resistance cannot be obtained, and when it exceeds 4%, the amount of carbides is too large and the toughness decreases, which is not desirable. The Si content is set to 0.1 to 3.0% in order to obtain good castability. The Mn content is set to 0.1 to 3.0% for deoxidation and desulfurization of the molten metal. Ni improves hardenability. When the Ni content exceeds 5%, the retained austenite increases,
Hardness and rough skin resistance are reduced. Cr easily forms carbides with C, improves wear resistance, and also partially forms a solid solution in the matrix to improve hardenability and improve wear resistance.
When the content of Cr is less than 1%, the effect of improving wear resistance is not obtained, and when it exceeds 15%, carbides are likely to be coarsened and the heat cracking resistance is deteriorated. Mo and W combine with C to form M ₂ C type and M ₆ C type carbides, and at the same time form a solid solution in the matrix to strengthen the matrix, resulting in wear resistance,
Improve high temperature hardness and strength. However, Mo and W
When the amount of carbon is increased, net-like double carbides increase, and not only segregation of net-like carbides as shown in FIG. According to the result of the surface analysis by the X-ray microanalyzer, the net carbide is an M ₆ C type eutectic carbide containing W and Mo as shown in FIG. Segregation of M ₆ C type eutectic carbide can be suppressed by increasing the solidification rate and increasing the viscosity of the molten metal. Further, from the viewpoint of balance of C content with Cr, V, etc., the content of Mo and W is set to 10% or less. V is an element having a large influence on the wear resistance because it forms C and MC type carbides having extremely high hardness and forms as primary crystals. If the V content exceeds 15%, it becomes difficult to uniformly generate VC carbides.

Co forms a solid solution in the matrix to increase the temper softening resistance, and high hardness is obtained by the secondary hardening of high temperature tempering. If the Co content exceeds 5%, the hardenability deteriorates. Furthermore, the inventors have found that when a trace amount of at least one of Ti and Zr is added, the above carbides are finely crystallized around these oxides, and thereby toughness and heat cracking properties are significantly improved. I found it. When the content of Ti and Zr is 3% or less, the above effects are sufficiently exhibited. If Ti and Zr are added at the beginning of melting,
It is rational because it also functions as a deoxidizer.

If the thermal conductivity of the mold coating material is less than 5 kcal / mh ° C., the solidification rate cannot be increased and sufficient abrasion resistance cannot be obtained. As such a coating material, graphite, BN, AlN, SiC or the like powder to which an appropriate binder is added is used. By the way, the thermal conductivity of the conventional coating material is about 0.1 to 0.5 kcal / mh ° C. FIG. 5 shows an example of the relationship between the thickness of the mold coating material and the solidification rate. When the coating thickness of the mold coating material is less than 0.1 mm, the strength of the mold coating material layer is insufficient and the mold coating material easily peels off. On the other hand, if the coating thickness exceeds 10 mm, the thermal resistance of the mold coating material layer increases, the solidification rate decreases, and the wear resistance decreases.

The material of the mold is appropriately selected depending on the material to be cast, but copper is suitable. The channels are formed inside the mold body, and it is desirable to provide a plurality of channels, for example, 4 to 20 channels independent of each other. FIG. 6 shows an example of the relationship between the thermal conductivity of the mold coating material and the solidification rate with respect to the number of channels. In the figure, the thermal conductivity of the high thermal conductivity coating material is 5-10kc.
al / mh ° C., and the thermal conductivity of the normal coating material is 0.1 to 0.
It is 5 kcal / mh ° C. Also, if the number of independent flow paths is increased, the flow path of cooling water from the inlet to the outlet of each flow path can be shortened accordingly, and the temperature rise of the cooling water due to heat transfer from the inner surface of the mold can be suppressed. You can Therefore, the cooling effect of the mold with the cooling water can be enhanced. However, if the number of channels exceeds 20, as shown in FIG. 6, the rate of increase in the solidification rate saturates and the structure of the mold becomes complicated, which is not preferable. Note that FIG. 6 also shows the relationship between the material of the mold and the solidification rate.

[0012]

Function: C, Cr, Mo, W and other specified compositions are
Improves wear resistance, toughness and heat crack resistance of rolling rolls.

During casting of the rolling rolls, cooling water is pressurized by a pump to be supplied to the flow passage inside the mold, and forcedly flows through the flow passage to cool the mold. The molten metal is in contact with the inner peripheral surface of the mold through the mold material layer having a high thermal conductivity. As a result, the molten metal is cooled at a high solidification rate. The thus-obtained rolling roll has a dense casting structure and improved wear resistance. FIG. 7 shows an example of the relationship between the solidification rate and the amount of wear of the rolling rolls.

[0014]

1 is a vertical sectional view of a centrifugal casting apparatus for casting a rolling roll according to the present invention, and FIG. 2 is a sectional view taken along the line AA of FIG.

As shown in these drawings, the mold 11 of the centrifugal casting apparatus has a cylindrical shape as a whole and is supported at an angle of about 30 degrees. The mold 11 is the main body 12 and the upper shaft part mold 1
4 and a lower shaft mold 15 whose bottom is closed. The main body 12 is provided with 16 flow paths 17 at equal intervals in the circumferential direction. Each channel 17 has a U-shape that is open on the lower side and extends toward the upper side. With the bottom plate 18 provided with the cooling water supply port 19 in the center,
The bottom of 2 is closed. Further, a space is provided between the lower shaft portion mold 15 and the bottom plate 18, and the space is formed in the main body 12
The cooling water distribution unit 21 communicates with each of the flow paths 17.
A mold coating material 22 is applied to the inner peripheral surface of the mold 11.

The mold 11 is supported by a cup-shaped support frame 25 and a drive roller 28. That is, the support frame 25 is fixed to the pedestal 23, and supports the bottom plate 18 of the mold 11 via the support rollers 26 provided at the bottom. The drive roller 28 supports the main body 12 via a support ring 13 fixed to the outer periphery of the main body 12 of the mold 11. Both ends of the rotary shaft 29 of the drive roller 28 are supported by bearings 30, and a bevel gear 32 is attached to the central portion. On the other hand, a motor 34 with a reducer is fixed to the pedestal 23, and the motor 3
A large bevel gear 35 that meshes with the small bevel gear 32 is attached to the output shaft of No. 4. When the motor 34 is driven, the drive roller 28 rotates, and the mold 11 rotates due to frictional transmission between the drive roller 28 and the support ring 13.

A rotary joint 36 is attached to the center of the bottom of the support frame 25. The inlet side of the rotary joint 36 is connected to the cooling water supply pump 38 via the pipe 37, and the outlet side of the rotary joint 36 is connected to the mold 1.
The bottom plate 18 is connected to the cooling water supply port 19. A drain port 27 that opens toward the drain tank 40 is provided below the support frame 25.
When the cooling water supply pump 38 is driven, the cooling water passes through the rotary joint 36 and the cooling water distributor 21 and flows through the flow path 17 of the main body 12.
Flow into. Then, the cooling water flows through the flow path 17 while cooling the mold 11, reaches the support frame 18, and flows out to the drain tank 40.

With the centrifugal casting apparatus configured as described above, the body diameter is 890 mm, the shaft diameter is 690 mm, and the length is 1900 mm.
The rolled roll material was cast. Table 1 shows the chemical composition of the roll material
Shown in. Ductile cast iron was used as the core material.

[0019]

[Table 1]

The mold is made of copper, and the outer diameter of the main body is 1350.
mm, the inner diameter is 890 mm. The number of channels is 16 and the diameter is 40 mm. A graphite-based coating material having a thermal conductivity of about 10 kcal / mh ° C was applied to a thickness of 2 mm. The flow rate of cooling water in each flow path was 50 l / min. After casting
The roll material was subjected to destabilizing heat treatment (about 1000 ° C. × 1 h) and tempering (about 500 ° C. × 1 h).

As a result of casting, the solidification rate was 6 mm / min, and the precipitated carbide was refined as shown in FIG. 8 (a). As a conventional example, a similar rolling roll material was cast with a normal coating material without water cooling. As a result, the solidification rate is 2 mm / min
And the precipitated carbides were coarse as shown in FIG. 8 (b). Further, the wear resistance life of the rolling roll cast by the method of the present invention is about 1.5 times longer than that of the conventional one.

[0022]

According to the casting method of the rolling roll of the present invention,
Cooling water is forced to flow through the channel to cool the mold, and since the mold material having high thermal conductivity is used, the molten metal is rapidly cooled and cooled at a high solidification rate. As a result, the rolling roll forms a dense cast structure and wear resistance is improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a centrifugal casting apparatus for casting a rolling roll according to the present invention.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a micrograph of a cross-section in the thickness direction of a centrifugally cast material made of HSS alloy.

FIG. 4 is a photograph showing an area analysis result of a hot rolling roll material made of a high-speed alloy by an X-ray microanalyzer.

FIG. 5 is a diagram showing an example of the relationship between the thickness of a mold coating material and the solidification rate.

FIG. 6 is a graph showing an example of the relationship between the thermal conductivity and the number of channels of the solidification rate.

FIG. 7 is a graph showing an example of the relationship between the solidification rate and the amount of wear of rolling rolls.

FIG. 8 (a) shows a method according to the present invention, and FIG.
(B) is a micrograph showing the structure of a rolling roll cast by a conventional method.

[Explanation of symbols]

11 Mold 26 Support Roller 12 Mold Body 28 Drive Roller 13 Support Ring 30 Bearing 17 Flow Path 32 Bevel Gear 18 Bottom Plate 34 Motor 21 Cooling Water Distributor 35 Bevel Gear 22 Coating Material 36 Rotating Joint 23 Frame 38 Cooling Water Supply Pump 25 Support Frame 40 drainage tank

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location // C22C 37/00 B 7217-4K 37/08 Z 7217-4K (72) Inventor Tsuyoshi Inoue Chiba 20-1 Shintomi, Futtsu-shi, Japan Inside Nippon Steel Co., Ltd. Technology Development Division

Claims (1)

[Claims] 1. A method of casting a rolling roll by a centrifugal casting method using a metal mold, wherein C: 1.0 by weight%.
.About.4.0, Si: 0.1 to 3.0, Mn: 0.1 to 3.
0, Ni: ≤ 5, Cr: 1 to 15, Mo: ≤ 10, W:
≦ 10, V: ≦ 15, Co: ≦ 5, and Ti:
≦ 3 and Zr: ≦ 3, at least one of which is 1000 to 1400
Applying a coating material having a thermal conductivity of 5 kcal / mh ° C or more at ℃ of 0.1 to 10 mm on the inner peripheral surface of the mold, and casting while allowing cooling water to flow through the flow path provided inside the mold. A method for casting a rolling roll, comprising: