JPH0938762A - Production of complex roll of cemented carbide and cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the crack of a roll on a producing process, in the production of the complex roll composed of a cemented carbide and a cast iron. SOLUTION: In the producing method of the complex roll composed of the cemented carbide alloy and the cast iron by fixing cemented carbide rings 2 forming the cemented carbide alloy to a mold 1 as annular state and pouring molten metal into the mold 1 and solidifying to form the solidified part as the roll body 3, the cemented carbide rings 2 are formed to inclined surfaces 21 at the side end parts so that the outer peripheral sides gradually become narrow width and the narrow width outer peripheral parts of the cemented carbide rings 2 are arranged so as to bite into the inner surface of the mold 1. The molten iron having a temp. at lower than the melting temp. of the surface of the cemented carbide ring 2 is poured into the mold 1 and the cemented carbide rings 2 are inserted as cast-in and the poured molten iron is solidified and the solidified part is made to the roll body 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a roll used for rolling steel wires, bars and the like.

[0002]

2. Description of the Related Art As a roll used for rolling a wire rod, a rod or the like, there is known a composite roll in which a cemented carbide ring formed of a cemented carbide metal is fitted in a roll body. The composite roll includes a mechanically assembled carbide ring on a roll body and a molded-in carbide ring.
The former causes an increase in the number of parts, a laborious assembling process, and a high cost. The latter can reduce the cost due to the fact that assembly is unnecessary, but there is a problem that the roll is likely to crack due to the manufacturing method. In the latter roll manufacturing method, first, as shown in FIG. 4, the outer circumference of the cemented carbide ring (2) is embedded in the inner peripheral surface of the mold (1) composed of a sand mold (step 1). template
A molten metal which is a cast metal (30) is poured into (1) (step 2). The molten metal is naturally cooled and solidified in the mold (1), and the solidified portion becomes the roll body (3) (step 3). The as-cast product taken out of the mold (1) is heat-treated (step 4). The as-cast product is machined into a desired shape and size (step 5).

[0003]

The temperature of the molten metal poured into the mold (1) in step 2 melts the surface of the carbide ring (2) in order to increase the bonding force between the carbide ring (2) and the roll body. It is a high temperature. Therefore, the boundary between the cast metal (30) and the cemented carbide ring (2) is in a fused state. However, since the difference in thermal expansion between the carbide ring (2) and the cast metal (30) is large, when the cast metal is thermally deformed, the carbide ring
The welded state in (2) suppresses the degree of freedom of deformation. Therefore, residual stress occurs in the roll. This residual stress may cause cracks in the rolls, and even if cracking does not occur in the cooling stage, cracking may occur if the post-process is performed with residual stress remaining. . As a material for the cast metal (30), if high Ni cast iron or the like having a thermal expansion difference close to that of the cemented carbide ring (2) is implemented, it is possible to suppress the occurrence of roll cracking, but high Ni cast iron or the like is costly. high. An object of the present invention is to clarify a method of manufacturing a composite roll composed of a cemented carbide and cast iron that prevents the roll from cracking during the manufacturing stage.

[0004]

[Means for Solving the Problems] The method for producing a composite roll according to the present invention comprises fixing a cemented carbide ring (2) formed by annularly forming a cemented carbide material such as cemented carbide, ceramics or cermet to a mold (1). In a method for producing a composite roll of cemented carbide and cast iron, in which a molten metal is poured into the mold (1) and solidified to form a solidified portion as a roll body (3), the cemented carbide ring (2) is An inclined surface (21) is formed on the side end surface so that the width gradually becomes narrower, and the narrow outer peripheral portion of the cemented carbide ring (2) is set so as to bite into the inner surface of the mold (1). ) Is poured with a molten metal having a temperature equal to or lower than the temperature for melting the surface of the super hard ring (2), and the super hard ring (2) is cast and solidified to form a solidified portion as a roll body (3).

[0005]

[Operation and effect] The temperature of the molten metal is below the temperature at which the surface of the carbide ring (2) is melted, and the cast metal (30) and the carbide ring (2) are simply in contact with each other and are not welded. Therefore, the degree of freedom of thermal deformation of the cast metal is increased. Therefore, the residual stress of the roll can be suppressed to be low, and the cracking of the roll due to the residual stress can be prevented. Also, the outer peripheral side of the carbide ring (2) is gradually narrowed, and when the cast metal is heat-shrinked, the side surface of the carbide ring (2) is tightened and a force acts inwardly. Even if the carbide ring (2) and the cast metal (30) are not fused as in the conventional case, they are tightly coupled and the cemented carbide against the roll body (3) is used in the past machine or in the later process. The problem that the ring (2) spins does not occur.

It is also possible to adjust the residual stress by subjecting the as-cast product taken out from the mold (1) to the following heat treatment process. The heat treatment is a heat treatment in which a part of the cast metal (30) undergoes pearlite transformation and the rest undergoes bainite transformation. Due to the pearlite transformation, residual stress is generated in the cast metal (30), and the bainite transformation accompanied by expansion causes the carbide ring.
Residual stress due to the difference in thermal expansion between (2) and the cast metal (30) is relaxed. In the case of only bainite transformation, the cast metal (30) becomes brittle and the cemented carbide ring (2) may have residual tensile stress, which is not preferable for rolling.

Even if a special component such as high Ni cast iron is not used as the cast metal (30), cracks do not occur in the roll during the roll manufacturing process. It is possible to use a relatively inexpensive material such as ductile cast iron, which has a certain amount, and to keep the cost low.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below.
This will be described in detail with reference to the drawings. The method for producing a roll composed of a cemented carbide and cast iron according to the present invention comprises a step of arranging the cemented ring (2) in the mold (1) (step 1), and a step of forming the cemented carbide ring (2) in the mold (1). The step of pouring a melt having a temperature equal to or higher than the surface melting temperature (step 2) and the step of naturally cooling the melt to solidify it (step 3). A step of heat treating the as-cast product taken out of the mold (1) (step 4), a step of machining the heat-treated as-cast product into a desired shape and size.
(Process 5)

First, the mold (1), the carbide ring (2), the fixing jig (4) and the molten metal will be described. FIG. 1 is a sectional view of the mold (1). The mold (1) is a sand mold formed around an iron frame (not shown), and has an inner surface shape such that the upper part and the lower part are reduced in diameter and the lower part is closed. The expanded diameter portion of the mold (1) has an inner diameter of φ375 mm. Carbide ring (2)
Inclined surfaces (21) (2
1) has been formed. The inclined surface (21) may be formed on only one of the two end surfaces of the ring (2).

[Cemented Carbide Ring] Component: WC 75% by weight + binder metal 25% by weight Binder metal composition: Co 12% by weight, Ni 12% by weight, C
r 1% by weight Dimensions: outer diameter φ450mm, inner diameter φ290mm, inner circumference width 90mm (thickness 55m
m), peripheral width (75 mm) Height of inclined surface 35 mm Thermal expansion coefficient: 7 × 10 ^-6 (1 / ° C)

The molten metal, which solidifies to form the roll body (3), is ductile cast iron composed of the following components. [Melted metal] Ingredient (unit: wt%) C Si Mn P S Mg Fe 3.3 3.3 0.4 0.010 0.009 0.05 Balance thermal expansion coefficient: 12 × 10 ^-6 (1 / ° C)

[Manufacturing Method] [Step 1 (Fixation and heating of carbide ring)] Carbide ring (2)
The center of the ring is aligned with the axis of the mold (1), and the outer peripheral portion of the ring (2) is bitten into the inner surface of the mold (1) to a uniform depth to form a ring.
(2) is fixed inside the mold (1). Carbide ring (2) 10
Preheat to 0-500 ℃. At this time, if the preheating of the carbide ring (2) is set to about 100 ° C or less, due to thermal shock during casting of the molten metal,
The carbide ring (2) may be cracked. When preheated to 500 ℃ or more, the surface of the carbide ring (2) is oxidized,
This requires a surface treatment such as Ni plating, which is troublesome. In the examples, the heating temperature of the carbide ring (2) was 250 ° C.

[Step 2 (Pouring of molten metal)] Carbide ring
After heating (2), it is heated below the temperature at which the surface of the carbide ring (2) melts. In the example, a molten metal heated to 1250 ° C. is poured.

[Step 3 (Cooling)] After pouring the molten metal into the mold (1), the molten metal is allowed to solidify and is allowed to stand at room temperature, followed by natural gradual cooling. The temperature of the molten metal is below the temperature at which the surface of the carbide ring (2) is melted, and the cast metal (30) and the carbide ring (2)
Are merely in contact with each other and are not welded, and thus the degree of freedom of thermal deformation of the cast metal is increased. Therefore, the residual stress of the roll can be suppressed to be low, and the cracking of the roll due to the residual stress can be prevented. Also, the outer peripheral side of the carbide ring (2) is gradually narrowed, and when the cast metal is heat-shrinked, the side surface of the carbide ring (2) is tightened and a force acts inwardly. Carbide ring (2) and cast metal (30)
However, even if they are not fused as in the conventional case, they do not cause any problems in use, such as the two being tightly coupled and the carbide ring (2) spinning around the roll body (3).

The molten metal expands by causing only pearlite transformation by slow cooling, and applies thermal stress and thermal compressive force to the cemented carbide ring (2). Due to this pearlite transformation, an unstable stress state occurs in the entire roll, and if mechanical processing is performed in this state, the roll may crack. Even if the roll is not cracked by machining, it may be cracked when the product is rolled using the roll. Therefore, step 4 described later
The heat treatment is performed on the roll to transform the roll body (3) from the unstable pearlite transformation only state to the partial pearlite transformation and the remaining bainite transformation.

[Step 4 (heat treatment)] In the above step, the mold (1)
An antioxidant is applied to the exposed portion of the as-cast carbide ring (2) taken out from the product, and heat treatment is performed. The heat treatment is performed by appropriate quenching and tempering heat treatment depending on the composition of the cast metal (30) so that an appropriate compressive residual stress is generated in the carbide ring (2). Here, appropriate quenching and tempering heat treatment means that in the cooling process after heating, part of the cast metal (30) undergoes pearlite transformation, and the rest is at low temperature (approximately 300 ° C to approximately 450 ° C). It is a heat treatment for bainite transformation accompanied by expansion. By combining these transformations, the residual stress due to the difference in thermal expansion between the carbide ring (2) and the cast metal (30) is relaxed. In the case of only pearlite transformation, the residual stress generated in the carbide ring (2) becomes too high, and in the case of only bainite transformation,
The cast metal (30) becomes brittle and the cemented carbide ring (2) becomes a tensile residual stress, which is not preferable for rolling use.

In the present embodiment, the quenching temperature was 900 ° C., air cooling was performed, and the tempering temperature was 550 ° C. The difference in thermal expansion between the carbide ring (2) and the cast metal (30) during quenching and tempering heat treatment is as shown in FIG. 3, and the cast metal (30) has a pearlite transformation (see FIG. 3). By causing section A) and bainite transformation (section B in Fig. 3), cast metal (30) and carbide ring (2)
The difference in thermal expansion between and can be approximated.

[Step 5 (Machining)] The heat-treated product produced in the above step is machined to a desired size.

The description of the above embodiments is for the purpose of illustrating the present invention and should not be construed as limiting the invention described in the appended claims or reducing the scope thereof. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims. For example, as the cemented carbide ring (2), a cemented carbide metal containing WC as a main component is used, but the component and shape are not limited to those in the above-mentioned examples, and cermet, ceramics, or the like may be used. Similarly, as the cast metal (30), high chromium cast iron that undergoes bainite and pearlite transformation during heat treatment can be used.

[Brief description of drawings]

1 is a cross-sectional view of a mold of the present invention.

FIG. 2 is a perspective view of a carbide ring and a fixing jig.

FIG. 3 is a graph showing a difference in thermal expansion between a carbide ring and a cast metal.

FIG. 4 is a cross-sectional view of a conventional mold and a carbide ring.

[Explanation of symbols]

 (1) Mold (2) Carbide ring (21) Inclined surface (3) Cast metal

Front page continued (72) Inventor Tsunao Kawanaka 64 Nishimukojima-cho, Amagasaki City, Hyogo Prefecture Kubota Amagasaki Plant

Claims (2)

[Claims] 1. A cemented carbide ring (2) formed by annularly cementing cemented carbide, ceramics, cermet or the like is fixed to a mold (1) and poured into the mold (1) to solidify and solidify. In a method for producing a composite roll of cemented carbide and cast iron, the portion of which is the roll body (3), the cemented carbide ring (2) has a slanted surface ( 21) is formed, the narrow outer peripheral portion of the cemented carbide ring (2) is arranged so as to bite into the inner surface of the mold (1), and the temperature at which the surface of the cemented carbide ring (2) is melted in the mold (1) A method for producing a composite roll of cemented carbide and cast iron, which comprises pouring a molten metal having the following temperature and solidifying it by casting around a cemented carbide ring (2) to form a solidified portion as a roll body (3). 2. The method for producing a cemented carbide composite roll according to claim 1, wherein the roll body (3) is partially pearlite-transformed and then the rest is subjected to bainite transformation.