JP2002102921A - Method for manufacturing hollow steel or hollow round bar - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a flattening and small bored hollow steel capable of manufacturing a long sized steel of 2000 mm or more with a hole diameter 5 mm or less by resolving inconveniences given by the use of a lubricant in the groove rolling. SOLUTION: By heating a steel stock bored in advance and forming a scale layer inside the bored hole, filling a core material with a larger thermal expansion coefficient than the steel stock while leaving the scale layer as it is, heating the steel stock and the core material in the heating furnace, and reducing the cross section into a prescribed square shape from a rhombus for successively rolling with the rolling mill, and after cooling, removing the core material from the steel stock, and then, annealing the steel stock, and the profile is formed into a prescribed shape dimension by pulling the die.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow steel or a round steel having a hollow hole at the center of a rod-shaped or linear steel and a method for producing the same.

[0002]

2. Description of the Related Art A thick and long hollow round steel (for example, having an outer diameter of about 6 mm).
mm ~ 50mm, inner diameter is about 5 ~ 30% of outer diameter)
It is used for shafts of various machine parts, hydraulic equipment parts, ejector sleeves and punches for mold parts, cutting tools, etc. In a method of manufacturing a hollow round steel used for these applications, a short product is often drilled by machining such as a drill or a small-diameter material is drilled by electric discharge machining. For long products having a length of 2000 mm or more, see Special Steel Guide, Vol. 1, pp. 115-126 (published by the Special Steel Club, September 1975).
As described in FIG. 3 of No. 314206, a method of manufacturing by groove rolling (a grooved roll row) is disclosed.

As shown in FIG. 2, in a conventional round steel bar formed by groove forming, a step (a) of drilling a steel piece having a square or circular cross section by a drill or the like, and a step (b) of filling a core material into the drilled hole. (C) heating a work piece, which is a steel slab filled with a core material so that the work piece can be easily rolled, and rolling the work piece into a predetermined shape by groove-type rolling in which the work piece is sequentially passed between rolls having an angular cross-sectional shape. (D), and a core removing step (e) of drawing a core material filled in the perforations of the material to be processed after rolling into a hollow steel bar. Further, in order to easily pull out the core material in the core removing step, a lubricant in which powdered talc is melted with a binder or the like is interposed between the inner surface of the hole and the core material when the core material is filled in the hole. After the coring step, annealing, straightening, external grinding, cutting, surface treatment and the like are appropriately performed according to required specifications.

[0004] In the rolling step, the hollow material is gradually formed into a predetermined shape by passing between hollow rolls (hole type) opposed to each other. For example, as shown in FIG. 2, the cross section of the hollow material is often rolled from a round shape to a diamond shape, a diamond shape gradually decreasing in cross-sectional area, a square shape, an ellipse, and a circular shape.
When the cross section is a pentagon or a hexagon having a rectangular shape or more, the shape is adjusted after the diamond shape or the square shape.

[0005]

However, when a lubricant is used, there is a problem that pretreatment such as production and application of the lubricant, collection of the lubricant, post-treatment such as cleaning, and the accompanying management are required. Was. Also, with the conventional method described above, it was difficult to produce hollow steel having a hole diameter of less than 5 mm when the length was 2000 mm or more. Furthermore, the round hole has a problem that the hollow hole is easily flattened as compared with the square to octagonal shapes. An object of the present invention is to eliminate the inconvenience of using a lubricant in groove rolling in view of the above problems. In addition, the hole diameter is 5 mm or more with a length of 2,000 mm or more using a grooved roll.
It is an object of the present invention to provide a method for producing a hollow steel which can be processed below or even a thick wall. Another object is to reduce the flatness of the round hollow hole.

[0006]

In order to solve the above-mentioned problems, according to the first aspect of the present invention, a steel material pre-perforated is heated to form a scale layer on the inner surface of the perforation. Is filled with a core material having a larger coefficient of thermal expansion than the steel material, and the steel material and the core material are heated in a heating furnace. The above problem was solved by providing a method for producing hollow steel, characterized in that a hollow wire or a rod was formed by removing the core material from the steel material after rolling in order, and then cooling the steel material.

That is, in contrast to the conventional method in which the core material is filled and then heated, the perforated steel material is heated before filling the core material to form a scale layer on the inner surface of the perforated hole and leave the scale layer. The core material is filled as it is, and the scale layer is interposed between the perforations and the core material instead of the conventional lubricant. Without a lubricant, the surface of the hole machined by a drill etc. is smooth and the surface of the core material is also smooth, so the steel material and the core material are in close contact with each other in the subsequent heating process and hole forming rolling process, and the mutual alloy It is presumed that as a result of the progress of the element diffusion phenomenon, a component change occurs in the core material, the elongation decreases, and the core removal property decreases in the core removal step. On the other hand, the scale layer on the inner surface of the perforation prevents diffusion and movement of components between the steel material and the core material, thereby preventing deterioration of the core material and improving core removal. In order to form the scale layer, it is necessary to select a heating temperature and a heating time in an appropriate oxidizing atmosphere depending on the material of the steel material. In other words,
The steel is heated in an atmosphere in which oxides of steel are stably present, and an oxidized oxide coating layer (scale layer) is intentionally formed on the surface of the steel to substitute for a lubricant. In addition, the thickness of the scale layer is set to a value that does not leave harmful surface defects such as decarburization on the inner surface of the steel material.
It is preferably set to 01 mm.

The reason for using a core material having a larger coefficient of thermal expansion than that of steel is that a gap is easily formed by utilizing the difference in the cross-sectional shrinkage between the steel material and the core material of the work material cooled after the die rolling. It is effective for enhancing the core removal. The core material is one that can be subjected to plastic working at the same time and has a property of elongation higher than that of steel material when cored. Further, for the heating after filling the core material of the material to be processed, a required heating condition which has high deformability during rolling and has no surface defects is selected depending on the material of the steel material. Further, the heating furnace may be associated with a usual rolling facility. Further, only the lubricant application step is replaced with a heating step, and a conventional heating furnace may be used under different conditions, and there is no need to increase the number of facilities and the like. Although it is easy to use a rolling mill having a grooved roll row for rolling the material to be processed, a plurality of rolling mills or the like may be used. The core removal after rolling and cooling is performed before annealing in order to improve the core removal property between the steel material and the core material. If the coring process is performed after annealing, the steel material during annealing will undergo a shrinkage phenomenon in the process of transforming from austenite to ferrite, increasing the coring resistance, or if a material such as austenitic stainless steel is used for the core material, This is because during the annealing, the embrittlement is caused by the precipitation of the σ phase and the elongation of the core material is deteriorated. Although the scale layer is left on the inner surface of the perforation in place of the conventional lubricant, it goes without saying that a lubricant may be used in addition to the scale layer.

[0009] Even when the lubricant is replaced with a scale layer, the flatness is almost the same as the conventional one, and the round shape is preferably further improved. Therefore, in the present invention according to claim 2, the core material having a larger thermal expansion coefficient than the steel material is filled into the perforations of the pre-drilled steel material via a lubricant,
The steel material and the core material are heated in a heating furnace, and are sequentially rolled to a predetermined angular shape while reducing the cross section from a rhombus shape by a rolling mill. After cooling, the core material is removed from the steel material and the core material is removed from the steel material. After that, the steel material was further annealed, and the flatness was reduced by forming the outer shape into a predetermined shape by die drawing.

That is, rolling by a rolling mill such as a grooved row is stopped at a square shape of about square to octagonal, and after removing the core material from the steel material, it is further drawn out with a die, and then a polygonal shape to a hexagonal shape to a hexagonal shape. Into a predetermined shape. For example, in the process of rolling into a diamond shape ... diamond shape-square shape (square to hexagonal), the cross-sectional shape is relatively similar, the deformation amount is constant, and the flatness of the hollow hole is small. Further, the core material can be easily pulled out. However, in the rolling process from the square shape to the oval (elliptical) shape to the round shape, since the cross-sectional shape changes greatly and the deformation amount is large, the flatness of the core hole becomes large. On the other hand, by holding the die in the square hole shape before the oval hole shape and performing die drawing, uniform plastic deformation from the outer shape can be obtained, and a hollow round steel with the desired hole accuracy can be manufactured.

Further, a scale layer according to claim 1 may be provided instead of the lubricant. Therefore, in the present invention according to claim 2, a steel material that has been drilled in advance is heated,
Forming a scale layer on the inner surface of the perforation, filling the perforation with a core material having a larger coefficient of thermal expansion than the steel material while leaving the scale layer, heating the steel material and the core material in a heating furnace, and rolling. After rolling, the core material is removed from the steel material after cooling, and then the steel material is further annealed, and the outer shape is formed into a predetermined shape and size by die drawing. It was decided to. The operation and the like are the same as those described above, and a description thereof will be omitted. In the case where the outer diameter of the product is square to octagonal, the drawing step may not be provided (claim 1). Die pulling is suitable for those having a round or circular outer diameter (claim 4). Further, a hollow steel (Claim 5) and a hollow round steel (Claim 6) are provided by the manufacturing method. The scale layer of the hollow hole having a thickness of 0.05 mm at the time of molding in a heating furnace is about 0.01 mm after the processing, which is a degree that does not hinder practical use. In the post-processing, the scale layer of the hollow hole may be deleted.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a process diagram of a method for manufacturing a hollow round bar by slot rolling, which is an example of an embodiment of the present invention. In FIG. 1, a step (a) of drilling a steel slab having a square or circular cross section by a drill or the like, a step (b) of oxidizing the surface of the drilled steel slab in a heating furnace to form a scale layer, and filling a core material into the drilled hole (C), a step of heating a work piece, which is a steel slab filled with a core material so that it can be easily rolled, (d), and a hole rolling method in which the work piece is sequentially passed between rolls having a square cross section. Rolling step of rolling round or square steel slab into diamond shape, diamond shape or square shape by (e), core drawing process of drawing out core material filled in perforations of material to be processed after rolling into hollow steel bar ( f), an annealing step (g) for removing work hardening distortion and the like by rolling again into a heating furnace, and a die pulling step of die-drawing into a final round shape with a die. In addition, die removal is 1
Up to two times may be sufficient. After the die is drawn, annealing, straightening, contour grinding, cutting, surface treatment and the like are appropriately performed according to required specifications.

[0013]

An embodiment according to the manufacturing method of the present invention will be described with reference to the steps. Pre-drilled steel material: JIS SKH51, diameter 90mm, length 1500m
Two types of steel materials having a perforation of 9 mm and 18 mm were prepared. The perforations were made from both sides of the steel using a gun drill. In order to form a scale layer on the inner surface of the perforation of this steel material, the steel material was charged into a single furnace in an air atmosphere, uniformly heated to 860 ° C., and gradually cooled. After that, JIS which becomes the core material to this steel material
An SUS304 wire was inserted into the workpiece before rolling.
Insert the workpiece into the heating furnace and heat it uniformly at 1110 ° C.
It is passed through a triple rolling mill having a coarse row and an intermediate row (gradual rolling in a diamond shape and a square shape in the final pass (pass)).
× 17mm, rectangular cross section of length 32m and 25 × 25m
m, an intermediate material having a rectangular cross section with a length of 15 m, further cut into a length of 2000 mm and air-cooled. A cut groove was formed in the outer periphery of one end of the intermediate material, and the core material was pulled out using a draw bench. The obtained rectangular hollow material was subjected to a complete annealing treatment using an atmosphere annealing furnace, and then was drawn twice using a draw bench having a round die so that the outer diameter × inner diameter × length was 16 × 1.6 × 2000 mm. And 24 × 4.8 × 20
Two types of hollow round steel having a hollow hole with a small flatness of 5 mm or less of 00 mm were manufactured.

The shape of the hole (flatness) and the removability of the core were evaluated for each of the two types of products obtained in the present invention. As the evaluation method, the hole shape was determined by measuring the major axis length and the minor axis length of the cross section of the hollow hole and determining the major axis / minor axis ratio. In addition, the coring property was evaluated by the number of products obtained when coring was performed on 10 fixed lengths of 2000 mm in the coring process, that is, the yield rate at the time of coring. Here, as a comparative material, a hollow round steel having the same dimensions as the present invention obtained by a manufacturing method having different steps shown in Table 1 is shown. Table 2 shows the results.

[0015]

[Table 1]

[0016]

[Table 2]

As is clear from Table 2, the hole shapes of the two types of products obtained by the present invention were as follows: the ratio of the major axis to the minor axis was 1.5 or less, and the comparative method of rolling to a round steel by hole rolling was used. B-1.
A significant improvement over 7 to 2.1 is observed. Also, as for the core removal property, the core removal cannot be performed because the scale layer is not formed in the comparative method A, and the yield rate in the core removal method of the comparative method B in which the scale layer is formed is as poor as half or less. On the contrary,
Despite a product having a small hollow hole diameter that cannot be obtained by the conventional manufacturing method, the manufacturing method of the present invention is 2000 mm.
With a 100% yield. In the present invention, even when the rolling process is completed after the rolling process is performed while leaving the scale layer in a square shape, the yield rate of core removal is 10%.
It was as good as 0%.

According to the production method of the present invention, the following hollow round steel can be obtained. The outer diameter is determined by the dimensions of the polygonal material after rolling. The polygon material size is determined from the minimum polygon size according to conditions such as the rolling mill's equipment capacity, a pass schedule that does not cause surface marks or dimensional defects due to a temperature drop, and the like. In experiments conducted by the present inventor, processing up to an outer diameter of 13 mm was possible. The inside diameter of the hollow hole can be reduced to the extent that core removal is possible. If the speed of pulling out the core material is not slowed down in the centering step, the pulling force increases and the core material is disconnected, and if the centering speed is lowered, the processing time increases and productivity is impaired. In the experiment, the inside diameter of the hollow hole was 5-1 of the outside diameter.
It could be reduced to about 0%. Although it is possible to increase the diameter of the hollow hole, it is considered that it is suitable for processing up to about 30% of the outer diameter from the viewpoint of the hole shape accuracy and the economical advantage as compared with a method using machining such as a drill. In addition, the eccentricity of the hollow hole was equivalent to the conventional and the present invention.

[0019]

As described above, in the present invention,
Since the scale layer can be interposed between the perforated hole and the core material instead of the conventional lubricant, the need for a lubricant can be eliminated, providing a stable quality hollow steel without the inconvenience of using a lubricant. Was.

Further, since the rolling by a rolling mill such as a grooved row is stopped to a square shape, the core material is removed from the steel material, and then formed into a predetermined shape by die drawing. Therefore, the flatness of the hollow hole is small, and Since it is easy to pull out, a hollow steel having a small diameter and a small flatness and a hollow round steel have been provided.
In particular, the present invention provides hollow steel and hollow round steel which can be machined with a length of 2000 mm or more and a hole diameter of 5 mm or less or a thick wall.

Accordingly, a hollow round bar having a large thickness, a long length and a high hole diameter accuracy can be mass-produced at low cost. Since it is not limited to the type of steel material, it can be applied to a wide range of fields such as machine parts, molds and tools. Further, since it is a long material, a relatively short processed product can be cut and used as it is or can be used for a pilot hole, which can lead to a reduction in setup time and a drill processing time. In addition, it is possible to obtain effects such as being able to be applied to long parts which have been impossible to process.

[Brief description of the drawings]

FIG. 1 is a process chart of a method for producing a hollow round bar by slot rolling, which is an example of an embodiment of the present invention.

FIG. 2 is a process chart of a conventional method for producing a hollow round steel by groove rolling.

FIG. 3 is a diagram simulating a cross-sectional shape of a grooved roll row of grooved rolling.

Claims (6)

[Claims] A steel material which has been drilled in advance is heated, a scale layer is formed on the inner surface of the drill hole, and a core material having a larger thermal expansion coefficient than the steel material is filled in the drill hole while the scale layer remains, The steel material and the core material are heated in a heating furnace, and are sequentially rolled to a predetermined shape while reducing the cross section from a rhombus shape by a rolling mill, and after cooling, the hollow material is removed by removing the core material from the steel material. A method for producing hollow steel, characterized by using a bar. 2. A core material having a coefficient of thermal expansion larger than that of the steel material is filled into the perforated inner surface of the previously drilled steel material via a lubricant, the steel material and the core material are heated in a heating furnace, and Rolled sequentially to a predetermined angular shape while reducing the cross section from the rhombus shape, after cooling, after removing the core material from the steel material and the core material from the steel material, further annealing the steel material,
A method for producing hollow steel, wherein an outer shape is formed into a predetermined shape and size by die drawing. 3. A pre-perforated steel material is heated to form a scale layer on the inner surface of the perforation, and the perforation is filled with a core material having a larger thermal expansion coefficient than the steel material while the scale layer remains, The steel material and the core material are heated in a heating furnace, and are sequentially rolled to a predetermined angular shape while reducing the cross section from a rhombus shape by a rolling mill. After cooling, the core material is removed from the steel material, and then the steel material is further removed. Characterized in that the outer shape is formed into a predetermined shape and size by drawing a die. 4. The method for producing a hollow round steel according to claim 2, wherein the predetermined shape of the outer shape according to claim 2 or 3 is circular. 5. A hollow steel manufactured by the manufacturing method according to claim 1. 6. A hollow round steel manufactured by the manufacturing method according to claim 4. Description: