JP3305540B2 - Manufacturing method of composite roll of cemented carbide and cast iron - Google Patents

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, a bar, or the like, a composite roll in which a carbide ring formed of a carbide metal in an annular shape is fitted to a roll body is known. The composite roll includes a mechanically assembled carbide ring on a roll body and a molded-in carbide ring.
In the former case, the number of parts is increased, the assembling is troublesome, and the cost is increased. In the latter case, the cost can be reduced as much as the necessity of assembling is eliminated, but there is a problem that the roll is liable to crack due to the production method. In the latter roll manufacturing method, first, as shown in FIG. 4, the outer periphery of a carbide ring (2) is embedded in the inner periphery of a mold (1) formed of a sand mold (step 1). template
Pour the molten metal as the cast-in metal (30) into (1) (step 2). The molten metal is naturally cooled and solidified in the mold (1), and the solidified portion is formed into a 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 dimensions (Step 5).

[0003]

The temperature of the molten metal poured into the mold (1) in step 2 is to melt 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 about high temperature. Therefore, the boundary between the cast-in metal (30) and the carbide ring (2) is in a fused state. However, the difference in thermal expansion between the cemented carbide ring (2) and the cast metal (30) is large.
When it is in the welded state in (2), the degree of freedom of deformation is suppressed. For this reason, residual stress is generated in the roll. There is a risk that the roll will crack due to the residual stress, and even if cracks are not seen at the cooling stage, cracks may occur if post-processing is performed with residual stress remaining. . As a material for the cast-in metal (30), if high-Ni cast iron or the like close to the difference in thermal expansion of the cemented carbide ring (2) is used, the occurrence of roll cracking can be suppressed. high. An object of the present invention is to clarify a method of manufacturing a composite roll made of a cemented carbide and cast iron, which prevents the roll from cracking at the manufacturing stage.

[0004]

According to the present invention, there is provided a method for manufacturing a composite roll, comprising: a step of fixing a cemented carbide ring (2) formed of a cemented carbide, ceramics, cermet or other such cemented carbide material to a mold (1); In a method of manufacturing a composite roll of a 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) An inclined surface (21) is formed on the side end surface so as to gradually become narrower, and the narrow outer peripheral portion of the carbide ring (2) is bitten into the inner surface of the mold (1), and is disposed. ), A molten metal having a temperature lower than the temperature at which the surface of the carbide ring (2) is melted is poured, and the carbide ring (2) is cast and solidified to form a solidified portion as a roll body (3).

[0005]

[Function and effect] The temperature of the molten metal is lower than the temperature at which the surface of the carbide ring (2) is melted, and the cast-in metal (30) and the carbide ring (2) are merely in contact with each other and are not welded. Therefore, the degree of freedom of thermal deformation of the as-cast metal is increased. For this reason, the residual stress of the roll can be kept low, and the crack of the roll caused by the residual stress can be prevented. Also, the outer peripheral side of the carbide ring (2) is gradually narrowed, and when the heat shrinkage of the as-cast metal is performed, a force acts inward by tightening the side surface of the carbide ring (2). Even if the cemented carbide ring (2) and the cast-in metal (30) are not fused as in the past, the two are tightly joined together, and the cemented carbide is applied to the roll body (3) in the past machine or at the time of use. There is no problem that the ring (2) runs idle.

It is also possible to adjust the residual stress by applying the following heat treatment step to the as-cast product taken out of the mold (1). The heat treatment is a heat treatment in which part of the cast-in metal (30) undergoes pearlite transformation, and the remainder undergoes bainite transformation. The pearlite transformation generates residual stress in the as-cast metal (30), and the bainite transformation accompanied by expansion causes
The residual stress due to the difference in thermal expansion between (2) and the cast-in metal (30) is reduced. In the case of the bainite transformation alone, the cast-in metal (30) becomes brittle and the carbide ring (2) may become a residual tensile stress.

[0007] Even if a special component such as high Ni cast iron is not used as the cast-in metal (30), cracks and the like do not occur in the roll during the roll manufacturing process. Relatively inexpensive materials such as ductile cast iron can be used, and the cost can be kept low.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 made of a cemented carbide and cast iron according to the present invention includes a step of disposing a cemented carbide ring (2) in a mold (1) (step 1); A step of pouring the molten metal at a temperature higher than the temperature at which the surface melts (step 2); and a step of naturally cooling and solidifying the molten metal (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 dimensions
(Step 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 configured such that the upper and lower parts are reduced in diameter and the lower part is closed. The enlarged diameter portion of the mold (1) has an inner diameter of φ375 mm. The carbide ring (2)
The outer peripheral side is sloped (21) (2
1) is formed. The inclined surface (21) may be formed on only one of the two end surfaces of the ring (2).

[Carbide ring] Ingredients: 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 90mm (thickness 55m
m), Perimeter width (75mm) Height of inclined surface 35mm Thermal expansion coefficient: 7 × 10 ^-6 (1 / ° C)

The molten metal solidifies to form the roll body (3), and is a ductile cast iron having the following components. [Molten] Ingredient (unit: wt%) CSiMnPSMgFe 3.3 2.3 0.4 0.010 0.009 0.05 Residual coefficient of thermal expansion: 12 × 10 ^-6 (1 / ° C)

[Manufacturing Method] [Step 1 (Fixing and Heating of Carbide Ring)] Carbide Ring (2)
The center of the mold (1) coincides with the axis of the mold (1), and the outer periphery of the ring (2) is cut into the inner surface of the mold (1) to a uniform depth.
(2) is fixed inside the mold (1). 10 carbide rings (2)
Preheat to 0-500 ° C. At this time, if the preheating of the carbide ring (2) is set to approximately 100 ° C. or less, due to the thermal shock at the time of casting the molten metal,
The carbide ring (2) may be broken. When preheating to 500 ° C or more, the surface of the carbide ring (2) is oxidized,
It is necessary to perform a surface treatment such as Ni plating, which is troublesome. In the example, the heating temperature of the carbide ring (2) was 250 ° C.

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

[Step 3 (Cooling)] After the molten metal is poured into the mold (1), the molten metal solidifies and is left to cool to room temperature to be naturally cooled slowly. The temperature of the molten metal is lower than the temperature at which the surface of the carbide ring (2) is melted, and the cast-in metal (30) and the carbide ring (2)
Are merely in contact with each other and are not welded, so that the degree of freedom of thermal deformation of the cast-in metal is increased. For this reason, the residual stress of the roll can be kept low, and the crack of the roll caused by the residual stress can be prevented. Also, the outer peripheral side of the carbide ring (2) is gradually narrowed, and when the heat shrinkage of the as-cast metal is performed, a force acts inward by tightening the side surface of the carbide ring (2). Carbide ring (2) and cast-in metal (30)
However, even if they are not fused as in the prior art, they are tightly connected to each other, and there is no problem in use such as the carbide ring (2) running idle with respect to 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 carbide ring (2). Due to this pearlite transformation, an unstable stress state occurs in the entire roll, and if machining is performed in this state, the roll may be broken. Even if the roll is not broken by machining, it is considered that the product is broken by rolling the product using the roll. Therefore, step 4 described later
The roll body is heat-treated to transform the roll body (3) from an unstable state of only pearlite transformation to a partial pearlite transformation and a remainder bainite transformation.

[Step 4 (heat treatment)] In the above step, the mold (1)
An antioxidant is applied to the exposed portion of the ultra-hard ring (2) of the as-cast product taken out of the product, and heat treatment is performed. In the heat treatment, an appropriate compressive residual stress is generated in the carbide ring (2) by appropriate quenching and tempering heat treatment in accordance with the components of the cast-in metal (30). Here, the appropriate quenching and tempering heat treatment means that in the cooling process after heating, part of the cast-in metal (30) undergoes pearlite transformation, and the rest at low temperature (about 300 ° C to about 450 ° C). This 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 reduced. In the case of only pearlite transformation, the residual stress generated in the carbide ring (2) is too high, and in the case of only bainite transformation,
The cast-in metal (30) becomes brittle, and the cemented carbide ring (2) becomes tensile residual stress, which is not preferable for rolling use.

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

[Step 5 (machining)] The heat-treated product prepared in the above-mentioned step is machined to finish it 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. Further, the configuration of each part of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made within the technical scope described in the claims. For example, the cemented carbide ring (2) is made of a cemented carbide metal containing WC as a main component, but the components and shapes are not limited to those in the above-described embodiment, and cermets, ceramics, and the like can also be used. Similarly, a high chromium cast iron that undergoes bainite and pearlite transformation during heat treatment can be used as the as-cast metal (30).

[Brief description of the drawings]

FIG. 1 is a 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-in metal.

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI C21D 9/38 C21D 9/38 A (72) Inventor Tatsuo Kawanaka 64 Nishimujimajima-cho, Amagasaki City, Hyogo Prefecture Inside Kubota Amagasaki Plant (56 References JP-A-4-319059 (JP, A) JP-A-61-199567 (JP, A) JP-A-4-344808 (JP, A) JP-A-59-24564 (JP, A) 58-138551 (JP, A) JP-A-47-14019 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 19/16 B21B 27/00 B21B 27/02

Claims (2)

(57) [Claims] 1. A cemented carbide ring (2) formed of an annular cemented carbide such as cemented carbide, ceramics, cermet, etc., is fixed to a mold (1), and molten metal is poured into the mold (1) for solidification and solidification. In a method of manufacturing a composite roll of a cemented carbide and a cast iron having a roll body (3) as a part, a cemented carbide ring (2) has an inclined surface ( 21) is formed, the narrow outer peripheral portion of the carbide ring (2) is bitten into the inner surface of the mold (1), and the temperature is set so that the mold (1) melts the surface of the carbide ring (2). A method for producing a composite roll of cemented carbide and cast iron in which a molten metal having the following temperature is poured, a cemented carbide ring (2) is cast and solidified 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 after the roll body (3) is partially transformed into pearlite, a heat treatment for transforming the remainder into bainite is performed.