JP2010125494A - Piercing rolling method for billet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piercing rolling method for a billet by which scratches on the inner surface at a distal end part of a material to be rolled hardly occurs in piercing rolling a billet (seamless steel tube base stock) by means of a piercer such as a Mannesmann piercer. <P>SOLUTION: In the piercing rolling method for a billet performing piercing rolling on the billet 10 after heating it, a conical hole piercing work 40 is applied to the center of the distal end face of the distal end part of the billet before performing piercing rolling. The conical hole is formed into a shape in which the depth of the hole is >50 mm and the inlet diameter of the hole is larger than the depth of the hole. The conical hole piercing work 40 is performed by pressing the distal end face of the billet by a projection part of a die by using the die having the projection part after the heating and before the piercing rolling. The seamless steel tube is manufactured by using the above piercing rolling method for the billet. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for piercing and rolling a billet (material for seamless steel pipe), and in particular, when a billet is pierced and rolled by a piercing and rolling machine such as a Mannesmann Piercer, it is difficult to generate internal flaws at the tip of a material to be rolled. The present invention relates to a billet piercing and rolling method.

  As shown in FIG. 1, a piercing and rolling mill, for example, Mannesmann Piercer, has rolls 1 and 2 having a shape in which the roll diameter decreases (drum shape) as it goes from the center to the both ends in the roll axis direction. The plug 3 is arranged such that the plug tip is located near the center of the roll bite and the plug rear end is located downstream in the rolling direction. The material 10 is pierced and rolled inside.

  The principle of piercing and rolling is that the center of the cross section of the billet 10 is embrittled by rotary forging (empty stagnation) in the rolling direction range (empty stagnation part 4) from the roll bite start end position to the plug tip position, and then the plug tip In the rolling direction range from the position to the end position of the roll bite (piercing part 5), the embrittled cross-sectional center part is pressed against the plug 3 and drilled to determine the tube thickness.

  In such piercing and rolling, wrinkles tend to occur intensively at the tip of the inner surface of the pipe (the leading end during rolling). The generation mechanism of this wrinkle is considered as follows. That is, as shown in FIG. 2, billet 10 (square slab → billet rolled material or straight cast billet) is segregated at the center of the cross section 15 (linear segregation in square slab → billet rolled material, and spot shaped in direct cast billet. Segregation). In the segregation 15, the portion located at the tip is oxidized by heating before piercing and rolling. At the time of emptying, this oxidized segregation part is the starting point, and cracks are generated and propagated at the tip part. The cracks on the inner surface of the crack are squeezed down by the plug and fall down, resulting in a flange 50 on the inner surface of the rolling tip of the tube 11.

As a countermeasure for reducing the occurrence of wrinkles as described above, as shown in FIG. 3, a method of shifting the segregation 15 to a position deviated from the central portion of the cross-section of the billet 10 that becomes a drilling site (method of offsetting segregation; patent) Reference 1) and as shown in Fig. 4, using cone type piercers (a piercing and rolling machine with cone-shaped rolls 21 and 22 arranged on the top and bottom) to prevent uneven collapse by suppressing shear deformation during rolling. A method (see Patent Document 2) is known.
JP-A-10-128510 Japanese Patent No. 3021664

  However, in the method of offsetting the above-mentioned segregation, segregation remains inside the tube thickness, resulting in non-uniform quality. Moreover, in the method using the cone type piercer described above, a change in roll shape and a facility for tilting the roll axis with respect to the rolling direction are required, and the investment is enormous. That is, the problem that it is difficult to advantageously prevent the generation of wrinkles on the inner surface of the distal end portion of the seamless steel pipe remains with the conventional technology.

The inventors diligently studied the means for solving the above-mentioned problems and made the present invention described below.
(Claim 1)
In the method for heating and piercing and rolling a billet, the billet piercing and rolling method is characterized in that, prior to the piercing and rolling, the tip of the billet is subjected to cone-like drilling at the center of the tip surface.
(Claim 2)
2. The billet piercing and rolling method according to claim 1, wherein a hole shape of the cone-shaped hole is a hole shape having a hole depth exceeding 50 mm and a hole inlet diameter exceeding the hole depth.
(Claim 3)
The cone-shaped drilling process is performed by pressing a tip end surface of the billet with the protrusions using a mold having a protrusion after the heating and before the piercing and rolling. 3. A method for piercing and rolling a billet according to 2.
(Claim 4)
A seamless steel pipe produced by using the billet piercing and rolling method according to any one of claims 1 to 3.

  ADVANTAGE OF THE INVENTION According to this invention, the generation | occurrence | production of the flaw of a pipe inner surface front-end | tip part can be prevented, without causing the nonuniformity in quality of a seamless steel pipe, and without requiring huge equipment investment.

In the present invention, the billet is heated and pierced and rolled. The heating temperature of the billet may be the heating temperature in normal operation. The piercing and rolling machine used for piercing and rolling may be either the Mannesmann piercer of FIG. 1 or the cone type piercer of FIG. 4, but the Mannesmann piercer is preferable from the viewpoint of equipment cost saving.
In the present invention, before piercing and rolling (before heating or after piercing and rolling after heating), as shown in FIG. The cone-shaped drilling process 40 is applied. Needless to say, the hole shape by the cone-shaped hole drilling process 40 is a divergent shape.

By performing the cone-shaped drilling process 40, the wall thickness reduction by the plug 3 is reduced, and the accompanying shear deformation is reduced. Therefore, the uneven fall of the inner surface of the crack in the perforated portion 5 is reduced.
Due to the above-described action of reducing the collapse of the irregularities on the inner surface of the crack, generation of wrinkles on the inner surface at the tip of the tube is effectively prevented.

In the present invention, no segregation offset is required in the steel making process, and this does not lead to uneven quality of the seamless steel pipe. Moreover, the capital investment for performing cone-shaped drilling at the billet tip is small.
In the present invention, the hole shape of the cone-shaped hole machining 40 is l> 50 mm (more preferably, 100 mm>l> 50 mm), Dh where the hole depth is represented by l and the hole inlet diameter is represented by Dh as shown in FIG. It is preferable to satisfy the condition> l (note that Dh is naturally smaller than the billet diameter). By doing so, the effect of reducing the unevenness collapse becomes greater when a normal plug is used.

  In addition, the cone-shaped drilling process 40 is performed at a stage after heating and before piercing and rolling, for example, as shown in FIG. Other processing methods (such as cold cutting prior to heating, die pressing, etc., or even after hot before piercing and rolling) This method is preferable because it is more advantageous in terms of efficiency, energy saving, equipment cost, etc. than a non-press method.

  Moreover, since the seamless steel pipe of the present invention is manufactured using the billet piercing and rolling method of the present invention, the inner surface of the pipe tip portion does not have wrinkles.

  Billet (circular cross section, with segregation in the center of the cross section) shown in Table 1 is heated to piercing and rolling (rolling with Mannesmann Piercer) under the conditions shown in Table 1, or heated to tip taper and cone A hole (seamless steel pipe) was obtained by punching (rolling with a Mannesmann Piercer) → punching (pressing with a mold as shown in FIG. 6, pressing once) → punching and rolling (rolling with a Mannesmann piercer). Table 1 shows the results obtained by observing the inner surface of the obtained tube from the tip to a position 300 mm in the longitudinal direction of the tube with a fiber scope and examining the presence or absence of wrinkles.

  From Table 1, it can be seen that in the example of the present invention, generation of wrinkles on the inner surface of the tube tip portion was suppressed.

It is explanatory drawing which shows the principle of piercing-rolling. It is explanatory drawing which shows the generation | occurrence | production mechanism of a pipe tip part inner surface flaw. It is explanatory drawing which shows an example of a prior art. It is explanatory drawing which shows an example of a prior art. It is the schematic which shows the front-end | tip part process shape of the billet used for this invention. It is explanatory drawing which shows an example of the suitable tip part processing method of the billet used for this invention.

Explanation of symbols

1 roll (a drum-shaped roll placed on top)
2 rolls (a drum-shaped roll placed below)
3 Plug 4 Empty part 5 Perforated part
10 Billet (material for seamless steel pipe, rolled material)
11 pipe (seamless steel pipe)
15 Segregation
21 roll (cone-shaped roll placed on top)
22 roll (cone-shaped roll placed below)
30 mold
40 Cone drilling
41 Projection
50 疵

Claims (4)

  In the method for heating and piercing and rolling a billet, the billet piercing and rolling method is characterized in that, prior to the piercing and rolling, the tip of the billet is subjected to cone-like drilling at the center of the tip surface.   2. The billet piercing and rolling method according to claim 1, wherein a hole shape of the cone-shaped hole is a hole shape having a hole depth exceeding 50 mm and a hole inlet diameter exceeding the hole depth.   The cone-shaped drilling process is performed by pressing a tip end surface of the billet with the protrusions using a mold having a protrusion after the heating and before the piercing and rolling. 3. A method for piercing and rolling a billet according to 2. A seamless steel pipe produced by using the billet piercing and rolling method according to any one of claims 1 to 3.

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