KR20210127238A - Manufacturing method of seamless square steel pipe - Google Patents

Abstract

Provided is a method for manufacturing a seamless prismatic steel pipe capable of obtaining a seamless prismatic steel pipe having a corner S value equivalent to that of the prior art while reducing equipment load. A method for manufacturing a seamless square steel pipe, in which a billet is punched into a cylindrical element pipe, and the cylindrical element tube is hot-rolled into a square tube by a shaping mill having a plurality of corner forming stands, the corner in the shaping mill The number n of the forming stands is 3 or more, the outer diameter shaft diameter ratio Δr1 in the first corner shaping stand, the outer diameter shaft diameter ratio Δr2 in the second corner shaping stand, and the outer diameter shaft diameter ratio R in the whole corner shaping stand, A method for manufacturing a seamless rectangular steel pipe satisfying the following formulas (1) and (2). (Δr1 + Δr2)/R ≥ 0.70 … (1) Δr2 - 0.01 ≤ Δr1 ≤ Δr2 + 0.01 … (2)

Description

Manufacturing method of seamless square steel pipe

The present invention relates to a method for manufacturing a seamless square steel pipe or tube, and in particular, a seamless square steel pipe having a corner S value equivalent to that of the prior art while reducing the equipment load. It relates to a method for manufacturing a rectangular steel pipe.

BACKGROUND ART In recent years, rectangular steel pipes have been used in various applications such as general structures and building materials. Among them, the seamless rectangular steel pipe has the characteristics that it can be thickened compared to the rectangular welded steel pipe, and thus high strength is obtained. Therefore, the seamless square steel pipe is used especially as an object for building materials.

As a method of manufacturing a seamless rectangular steel pipe, a method by hot seamless forming has been proposed. In this method, first, a billet as a starting material is heated in a heating furnace, and then pierced by a pierce to form a cylindrical element pipe. Thereafter, the cylindrical element pipe is treated with an elongator mill (for pipe expansion), a plug mill (for stretching), a reeler mill (for elongation pipe), etc., and then heated in a reheating furnace, followed by shaping ( It is hot rolled with a rolling mill (sizing mill) to obtain a seamless rectangular steel pipe.

1 : is a schematic diagram which shows an example of the rolling stand structure in the shaping|shaping mill 10 used for manufacture of a seamless square steel pipe. The shaping mill 10 is a rolling mill in which a plurality of rolling stands are arranged in tandem, and at the front end (upstream side) of the shaping mill 10, a stand 11 provided with a roll having a circular caliber (ball shape) is a rear end. On the (downstream side), corner forming stands 12 provided with rolls having a rectangular caliber are arranged, respectively. And after rolling so that it may become a circular cross section of a predetermined outer diameter by the stand 11 of a front stage, it shape|molds into a square cross section by the corner forming stand 12 of a rear stage. In addition, the shaping|shaping mill 10 illustrated in FIG. 1 has a 2-roll and 8-stand structure, and the 4 stands of the latter half are corner shaping|molding stands.

In this way, since it is formed from a circular cross section to a square cross section by roll forming, as shown in FIG. 2, the corner portion of the seamless square steel pipe has a round portion to a certain extent. In addition, the S value prescribed|regulated as a "corner dimension" in JIS G 3466 is used as one of the index|index for evaluating the round part of a corner part.

In general, from the viewpoints of designability and performance when used in a method of connecting a beam and a column, a seamless rectangular steel pipe is required to have a sharp corner shape, that is, to have a small S value. Therefore, a study is being conducted on a method for manufacturing a seamless rectangular steel pipe having a small S value.

For example, in Patent Document 1, by controlling the rolling conditions so that the outside diameter reduction in a plurality of corner forming stands of the shaping mill satisfies a predetermined relationship, the curvature of the corner is small and the side is flat. A method for obtaining a seamless prismatic steel pipe has been proposed.

Further, in Patent Document 2, by controlling the rolling conditions so that the perimeter reduction rate, the S value, and the thickness t in the first corner forming stand of the shaping mill satisfy a predetermined relationship, the curvature of the corner portion is A method for obtaining a seamless square steel pipe that is small and has a flat side has been proposed.

Japanese Laid-Open Patent Publication No. 11-104711 Japanese Patent Laid-Open No. 10-258303

According to the technique proposed in Patent Documents 1 and 2, it is possible to obtain a seamless rectangular steel pipe having a small S value. However, in the prior art including Patent Documents 1 and 2, in order to make the S value small, the reduction in diameter in the first (first) corner forming stand in the shaping mill is significantly higher than in other stands. It was imperative to make it bigger.

The solid line in FIG. 3 extracts the experimental result in thickness t=20-30 mm in FIG. 4 of patent document 2. As shown in FIG. Here, the horizontal axis of FIG. 3 is the outer diameter axis-diameter ratio Δr1 in the first corner forming stand, and the vertical axis (left) is the ratio of the S value to the thickness t (S/t). The value of S/t decreases as Δr1 increases. That is, the above experimental results indicate that in order to make the S value small, it is necessary to increase the outer diameter and shaft diameter ratio Δr1 in the first corner forming stand.

On the other hand, the broken line in FIG. 3 shows the load ratio applied to the rolling stand at that time. Here, the load ratio is a relative value of the load applied to the rolling stand, where the load when Δr1 is 0.2 is set to 1. As is also clear from this plot, if ?r1 is made high, S/t can be reduced, but the load applied to the rolling stand is greatly increased accordingly.

In addition, with the expansion of use, additional large-diameter and thickening of seamless rectangular steel pipes are required. As the cross-sectional area (the area of the portion occupied by steel in the cross-section) of the steel pipe increases due to enlargement or thickening, the load required for rolling also increases accordingly.

Therefore, in order to reduce the S value while meeting the demand for the above-described large-hardening and thickening, it is necessary to significantly increase the rolling load. However, since the significant increase in the rolling load results in a significant increase in the load on the manufacturing equipment, the existing manufacturing equipment cannot cope with the additional large-diameter and thickening. In addition, in order to cope with the increase in the load on such manufacturing equipment, a large-scale facility investment is required, such as replacing the main motor of the rolling mill with a larger one, and replacing the housing with a high-strength one in accordance with it.

The present invention has been made in view of the above facts, and even a seamless rectangular steel pipe with a large cross-sectional area can be manufactured without increasing the rolling load, and a method for manufacturing a seamless rectangular steel pipe capable of achieving a sufficiently small S value aims to provide

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, the present inventors conducted detailed examination about the influence which the rolling schedule in a shaping mill has on a rolling load and S value. And as a result, it discovered that the said subject was solvable by controlling rolling conditions based on the way of thinking completely different from the conventional technique of reducing S value by making Δr1 very large. That is, the configuration of the gist of the present invention is as follows.

1. A method for manufacturing a seamless prismatic steel pipe, in which a billet is punched into a cylindrical element pipe, and the cylindrical element tube is hot-rolled into a square tube with a shaping mill having a plurality of corner forming stands, the method comprising:

The number n of corner forming stands in the shaping mill is 3 or more,

The outer diameter shaft diameter ratio Δr1 in the first corner shaping stand, the outer diameter shaft diameter ratio Δr2 in the second corner shaping stand, and the outer diameter shaft diameter ratio R in the entire corner shaping stand are obtained by the following formulas (1) and (2) A satisfactory, seamless square steel pipe manufacturing method.

(Δr1 + Δr2)/R ≥ 0.70 … (One)

Δr2 - 0.01 ≤ Δr1 ≤ Δr2 + 0.01 … (2)

2. The method for manufacturing a seamless square steel pipe according to 1, wherein the temperature of the rolled material is 600 to 1100°C during hot rolling in the corner forming stand.

ADVANTAGE OF THE INVENTION According to this invention, even if it is a seamless square steel pipe with a large cross-sectional area, it can manufacture without increasing a rolling load, and can achieve a sufficiently small S value. Since the increase in rolling load can be suppressed, according to the method of the present invention, it becomes possible to manufacture a seamless square steel pipe having a larger cross-section and having a good corner shape using existing equipment, and the industrial The significance is very great.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows an example of the rolling stand structure in the shaping|shaping mill used for manufacture of a seamless square steel pipe.
2 is a schematic diagram showing the shape of a corner of a seamless rectangular steel pipe and the definition of the S value.
Fig. 3 is a graph showing the relationship between the ratio (S/t) and the load ratio of the S value to the thickness t, and the outer diameter and shaft diameter ratio Δr1 in the first corner forming stand.

Next, the method of carrying out this invention is demonstrated concretely. In addition, the following description shows the preferable embodiment of this invention, and this invention is not limited at all by the following description.

In the present invention, a seamless prismatic steel pipe is manufactured by punching a billet to form a cylindrical element tube, hot rolling the cylindrical element tube with a shaping mill having a plurality of corner forming stands, and forming it into a square tube.

It does not specifically limit about the method of perforating a billet and obtaining a cylindrical element pipe, Arbitrary methods can be used. For example, after the billet is heated in a heating furnace, it can be pierced by a piercer to form a cylindrical element pipe. When heating by the said heating furnace, it is preferable to make into 700-1200 degreeC the temperature at the exit side of a heating furnace.

Prior to hot rolling by the following shaping mill, it is preferable to arbitrarily apply pipe expansion by an elongator mill, extension by a plug mill, or elongation by a reeler mill to the cylindrical element pipe.

Next, using the shaping|molding mill provided with the some corner shaping|molding stand, the cylindrical element pipe is hot-rolled, and it shape|molds into a square cylinder. By the hot rolling, a seamless rectangular steel pipe having final dimensions and cross-sectional shape is obtained.

As said shaping|molding mill, arbitrary things can be used as long as the number n of corner shaping|molding stands is three or more. The upper limit of the number n of corner shaping|molding stands is not specifically limited. However, normally, it is preferable to set n to 3 or 4, and to set it as 4 is more preferable.

The number of rolls per one corner forming stand is not particularly limited, and can be any number. However, in general, it is preferable to set it as 2 or 3, and to set it as 2 is more preferable. In addition, as shown in Fig. 1, the rolls of the corner forming stand are preferably arranged in a direction rotated by 90 degrees in a plane perpendicular to the pass-through direction with respect to the rolls of the adjacent corner forming stands.

The said shaping|molding mill may be equipped with the stand provided with the roll (circular caliber roll) which has a circular caliber (ball die) upstream of a corner shaping|molding stand, for example, as shown in FIG. The number of stands provided with the circular caliber roll is not particularly limited. However, normally, it is preferable to set it as 3 or 4, and it is more preferable to set it as 4.

In the present invention, the outer diameter shaft diameter ratio Δr1 in the first corner shaping stand, the outer diameter shaft diameter ratio Δr2 in the second corner shaping stand, and the outer diameter shaft diameter ratio R in the entire corner shaping stand are the following (1) and ( 2) It is important to control the rolling conditions to satisfy the equation.

(Δr1 + Δr2)/R ≥ 0.70 … (One)

Δr2 - 0.01 ≤ Δr1 ≤ Δr2 + 0.01 … (2)

Here, the outer diameter shaft diameter ratios ?r1, ?r2, and R are defined as follows.

Δr1 = (D0 - D1)/D0

Δr2 = (D1 - D2)/D1

R = (D0 - Dn)/D0

·D0: outer diameter of the pipe before rolling in the first corner forming stand

D1: outer diameter of the pipe after rolling in the first corner forming stand

·D2: outer diameter of the pipe after rolling in the second corner forming stand

·Dn: outer diameter of the pipe after rolling in the final corner forming stand

In addition, the outer diameter of the pipe|tube before rolling in a corner forming stand shall point out the outer diameter of the pipe|tube in the entrance side of the said stand. Similarly, the outer diameter of the tube after rolling in the corner forming stand refers to the outer diameter of the tube on the exit side of the stand. Accordingly, as shown in Fig. 1, D0 is equal to the outer diameter of the cylindrical primary pipe before corner forming is performed. In addition, let Dn be the distance between the outer surfaces of opposing flat parts in the cross section of a rectangular steel pipe. Similarly, D1 and D2 are distances between the outer surfaces of opposing flat portions in the cross section of the steel pipe during forming.

By satisfying the relationship of the formulas (1) and (2), the rolling load can be reduced without increasing the S value. In addition, it is preferable that ((DELTA)r1+(DELTA)r2)/R shall be 0.75 or more. On the other hand, although the upper limit of ((DELTA)r1+(DELTA)r2)/R is not specifically limited, It is preferable to set it as 0.85 or less, and it is more preferable to set it as 0.83 or less.

The present invention is not particularly limited, and can be used for production of seamless rectangular steel pipes of arbitrary outer diameter and thickness. However, as described above, it is when the cross-sectional area is large that the problem of the load on the equipment becomes serious. Accordingly, the present invention can be particularly preferably applied to the production of a seamless rectangular steel pipe having a large cross-sectional area. Specifically, it is preferable that the outer diameter of the manufactured seamless square steel pipe be 250 mm or more. In addition, it is preferable that the thickness of the seamless rectangular steel pipe to be manufactured shall be 25 mm or more. On the other hand, although the upper limit of the outer diameter and thickness of the seamless square steel pipe is not particularly limited, the outer diameter of the seamless square steel pipe is preferably 360 mm or less. Moreover, it is preferable that the thickness of a seamless rectangular steel pipe shall be 40 mm or less.

During the hot rolling in the corner forming stand, the temperature of the material to be rolled is not particularly limited, and may be any temperature. However, when the temperature is 600°C or higher, it is possible to suppress residual deformation due to cold working. Therefore, from the viewpoint of material properties, it is preferable to set the temperature of the steel pipe as the rolled material during hot rolling to 600°C or higher. On the other hand, the upper limit of the temperature is not particularly limited, either, but when the temperature is 1100°C or less, it is possible to suppress the occurrence of scale on the outer surface of the steel pipe. As a result, it is possible to prevent the occurrence of scratches due to the press-fitting of scale during corner forming. Therefore, it is preferable to set the said temperature to 1100 degreeC or less from a viewpoint of an external appearance quality improvement.

In addition, the temperature of a to-be-rolled material shall refer to the surface temperature of a to-be-rolled material (steel pipe) here.

Example

Hereinafter, the present invention will be described in more detail by way of Examples.

A seamless rectangular steel pipe was manufactured in the procedure described below. First, the billet was punched and it was set as the cylindrical tube. After heating the said cylindrical element pipe in a heating furnace, it hot-rolled by the shaping|molding mill provided with the some corner shaping|molding stand, and it shape|molded it into square cylinder, and it was set as the seamless square steel pipe. In the said heating, the furnace exit side temperature was 1000 degreeC.

As said shaping|molding mill, the thing provided with the two-roll type corner shaping|molding stand was used. Among the above two corner forming stands, an upstream one is set as a first stand and a downstream one is set as a second stand.

The molding conditions (outer diameter and shaft diameter ratio) in the corner shaping stand were as shown in Table 1. Then, the rolling load on the first stand and the second stand at that time, and the corner dimension (S value) of the finally obtained seamless square steel pipe were measured. A measurement result is written together in Table 1. In addition, the temperature of the to-be-rolled material during the hot rolling in a corner forming stand was 1000-900 degreeC.

In addition, the dimensions of the said seamless square steel pipe were made into outer diameter (side length): 300 mm, and thickness t: 30 mm. In addition, the outer diameter D0 of the cylindrical element pipe was set to 418 mm.

About the load, it judged based on the following reference|standard, and the result was written together in Table 1.

·Load in the first stand: less than 150 tonf: ○

·Load in the first stand: 150 tonf or more, less than 160 tonf: △

·Load in the first stand: 160 tonf or more: ×

The S value was also determined on the basis of the following criteria, and the results are written together in Table 1.

·S value: less than 30.0 mm: ◎

·S value: 30.0 mm or more, 37.5 mm or less: ○

·S value: over 37.5 mm: ×

Here, 37.5 mm is the allowable range of the S value when the standard S value in a steel pipe of thickness t: 30 mm is set to 0.75 and dimensional tolerance: 0.5t. Also, as shown in Fig. 2, there are two S values for one corner portion of the rectangular steel pipe. Then, for the said determination, the S value in four corners of the obtained seamless square steel pipe, and the arithmetic mean value of a total of eight were used.

Comparative Example No. 1 employs a conventional rolling condition in which S value is reduced by making Δr1 very large. In this No. 1, although the S value was a pass judgment, since the conditions of Formula (2) were not satisfied, the rolling load was very large. That is, when the rolling conditions are selected so that the S value is lowered based on the conventional way of thinking, the rolling load becomes excessive, and a significant load is applied to the production equipment.

Moreover, Comparative Example No. 2 reduced (DELTA)r1 compared with No.1. In this No.2, the S value was a pass judgment similarly to No.1, but since the condition of Formula (2) was not satisfied, the rolling load was also large.

On the other hand, in Invention Example No. 3 which satisfies the conditions of the present invention, compared to Comparative Example No. 1, the load on the first stand was significantly reduced to about 31%. Moreover, despite the fact that the ratio of the outer diameter and shaft diameter in the first stand was significantly reduced, the increase in the S value was sufficiently suppressed against the knowledge in the prior art, and it was a pass level.

Moreover, Comparative Example No. 4 is an example in which Δr1 was further reduced than that of No. 3. No. 4 satisfies the condition of the expression (2), but does not satisfy the condition of the expression (1). As a result, although the load in the 1st stand was low, the S value increased significantly. As can be seen from this result, a good corner shape cannot be realized simply by making ?r1 small and reducing the load. That is, in order to obtain a seamless square steel pipe having a corner S value equivalent to that of the prior art while reducing the equipment load, it is necessary to satisfy both the conditions of the equations (1) and (2).

As described above, according to the technology of the present invention, by overcoming the conventional technical bias and controlling the rolling conditions based on a technical idea completely different from the existing technology, conflicting demands for reduction of S value and suppression of rolling load can be satisfied

1: Cylindrical jurisdiction
2: Seamless square steel pipe
10: Orthopedic rolling mill
11: A stand with a circular caliber
12 : Corner forming stand

Claims (2)

A method for manufacturing a seamless rectangular steel pipe, comprising punching a billet to form a cylindrical element pipe, hot rolling the cylindrical element tube with a shaping mill having a plurality of corner forming stands to form a square tube, the method comprising:
The number n of corner forming stands in the shaping mill is 3 or more,
The outer diameter shaft diameter ratio Δr1 in the first corner shaping stand, the outer diameter shaft diameter ratio Δr2 in the second corner shaping stand, and the outer diameter shaft diameter ratio R in the entire corner shaping stand are obtained by the following formulas (1) and (2) A satisfactory, seamless square steel pipe manufacturing method.
(Δr1 + Δr2)/R ≥ 0.70 … (One)
Δr2 - 0.01 ≤ Δr1 ≤ Δr2 + 0.01 … (2) The method of claim 1,
A method for producing a seamless rectangular steel pipe, wherein the temperature of the rolled material is set to 600 to 1100°C during hot rolling in the corner forming stand.

Images