JP2019025508A - Rolling method of seamless steel pipe and manufacturing method of seamless steel pipe - Google Patents

Abstract

To provide a rolling method of a seamless steel pipe and a manufacturing method of seamless steel pipe capable of preventing defective circularity of difficult-to-work material which contains Cr of 5.0 mass% or more, in manufacture of the seamless steel pipe using a barrel type roller.SOLUTION: In relation to a rolling method of a seamless steel pipe which contains Cr of 5.0 mass% or more, the rolling method of the seamless steel pipe is characterized in that, when a steel casting piece which contains Cr of 5.0 mass% or more is heated in a heating furnace, thereafter, is pierced by a piercing mill, subsequently, is expanded and rolled by an elongator which has a barrel type roller shape, an expansion rate on the elongator is E (therein, E>1.0), diagonal length in a roller bite upon expansion rolling on the elongator is Xand inlet side element pipe outer diameter is OD, the steel casting piece is expanded and rolled by the elongator so as to satisfy the following relation (1): 0.87×E+0.44≤(X/OD)≤0.91×E+0.46 (1).SELECTED DRAWING: Figure 3

Description

  The present invention relates to a rolling method of a seamless steel pipe containing 5.0 mass% or more of Cr and a manufacturing method of the seamless steel pipe.

  Seamless steel pipes frequently used for oil well pipes and the like are manufactured using a steel slab called a billet (round or square cross section) as a raw material. For example, as shown in FIG. 1, a steel slab (for example, a round billet) that is a material 1 is heated in a heating furnace 2, and then a plug 4 is pushed onto the material 1 by a piercer mill (gradient rolling mill) 3. The base tube 5 is formed by perforating. Then, from the elongator 6, the plug mill 7, the reeler 8 or the mandrel mill (not shown) that inserts the plug 4 into the hole of the raw tube 5 in the same manner as described above, and expands, stretches, and polishes the tube. Is formed and rolled into a tubular shape by a rolling mill. Further, the tube body 9 is made into a product by passing through a reheating furnace 10 and narrowing the outer diameter and thickness to predetermined dimensions by a multi-stage drawing mill called a sizing mill 11.

  In a tilting rolling mill with a barrel-type roll like a conventional elongator or reeler, when trying to expand and roll a hollow shell with an elongator, it may cause a bite failure of the core tube, a butt-out failure, or flaring. It is known that the hollow will break. In general, in the piercing and rolling in which barrel type rolls are arranged at a predetermined inclination angle, the roll diameter gradually decreases on the exit side from the gorge portion, and the circumferential speed becomes slow. This is because the material to be rolled increases in speed, and as a result, the material to be rolled is twisted and additional shear strain is generated in the cross section. In particular, in the case of a material containing 5.0 mass% or more of Cr (difficult-to-process material), since the hot workability of the raw pipe is poor, the expansion of the raw pipe at the time of pipe expansion does not return, and the perfect circle on the rear end side Defects are likely to occur.

  In patent document 1, in order to improve such a problem peculiar to a barrel type roll, the technique using a cone type roll is disclosed.

Japanese Patent Application Laid-Open No. 02-24912

  In the technique of Patent Document 1, a cone-type roll is used, and in the production of a seamless steel pipe using a barrel-type roll, the problem of poor roundness still remains.

  This invention is made | formed in view of the said situation, In manufacture of the seamless steel pipe using a barrel type roll, roundness failure of the difficult-to-work material containing 5.0 mass% or more of Cr is prevented. It is an object of the present invention to provide a seamless steel pipe rolling method and a seamless steel pipe manufacturing method.

The gist of the present invention is as follows.
[1] A rolling method for seamless steel pipes containing 5.0 mass% or more of Cr, in which a steel slab containing 5.0 mass% or more of Cr is heated in a heating furnace and then pierced by a piercer mill. Then, when expanding and rolling with an elongator having a barrel-shaped roll shape,
The tube expansion rate at the elongator is E (where E> 1.0), the diagonal length in the roll bite at the time of tube expansion rolling at the elongator is X _dia , and the outer diameter of the inlet side raw tube is OD,
A rolling method of a seamless steel pipe, characterized by performing pipe expansion rolling with an elongator so as to satisfy the following formula (1).
0.87 × E + 0.44 ≦ (X _dia /OD)≦0.91×E+0.46 (1)
[2] A method for producing a seamless steel pipe containing 5.0 mass% or more of Cr, in which a steel slab containing 5.0 mass% or more of Cr is heated in a heating furnace and then drilled with a piercer mill. Then, when expanding and rolling with an elongator having a barrel-shaped roll shape,
The tube expansion rate at the elongator is E (where E> 1.0), the diagonal length in the roll bite at the time of tube expansion rolling at the elongator is X _dia , and the outer diameter of the inlet side raw tube is OD,
A method of manufacturing a seamless steel pipe, characterized by performing pipe expansion rolling with an elongator so as to satisfy the following formula (1).
0.87 × E + 0.44 ≦ (X _dia /OD)≦0.91×E+0.46 (1)

  ADVANTAGE OF THE INVENTION According to this invention, in manufacture of the seamless steel pipe using a barrel-type roll, the roundness defect of the difficult-to-work material containing 5.0 mass% or more of Cr can be prevented. Therefore, it is possible to stably manufacture a seamless steel pipe that is a difficult-to-work material.

Drawing 1 is a mimetic diagram showing the manufacturing process of the seamless steel pipe using a barrel type roll. FIG. 2 is a diagram for explaining the elongator rolling, (a) is a schematic diagram showing the positional relationship between the rolling roll, the hollow shell and the plug during the elongator rolling, and (b) is an arrow view of (a). It is XX sectional drawing, and is a schematic sectional drawing in the roll bite at the time of elongator rolling. FIG. 3 shows the results of examining the relationship between the diagonal length in the roll bite / the outer diameter of the inlet tube (X _dia / OD) and the rear end shape after elongator rolling for each tube expansion rate.

  In tube rolling using an elongator (elongator rolling), as shown in FIG. 2 (a), the hollow shell 5 that is a material to be rolled is made up of upper and lower barrel-type rolling rolls (61 is an upper roll, and 62 is a lower roll). ) And a plug (a plug for constraining the tube inner surface) 63 between the rolling rolls, while being thinned and expanded, the outer diameter is determined by being constrained by left and right guide shoes (not shown).

  FIG.2 (b) is XX sectional drawing of Fig.2 (a), and is a schematic sectional drawing in a roll bite. The hollow shell during the elongator rolling spreads in the diagonal direction of the roll bite surrounded by the upper and lower rolling rolls 61 and 62 and the left and right guide shoes 64 and 65. A guide plate 66 is disposed to prevent the tube peripheral portion from protruding outward due to the expansion in the diagonal direction.

  In the rolling of difficult-to-process materials containing a large amount of Cr, rolling ends without the hollow shell expanded diagonally in the roll bite at the end of rolling without returning to a perfect circle. Therefore, the roundness is poor at the rear end, leading to a trouble that the next process rolling becomes impossible.

  As shown in FIG. 2B, when the distance between the upper and lower rolling rolls 61 and 62 is defined as e and the distance between the left and right guide shoes 64 and 65 is defined as h, the ratio between the rolling roll and the shoe spacing is If a certain h / e is increased, the tube curvature as indicated by the dotted line in FIG.

  When finishing to the target dimensions, the outer diameter of the tube is roughly determined by the guide shoe interval h. The wall thickness is roughly determined by the gap between the rolling roll / plug. Here, the guide shoe interval h is uniquely determined by the target outer diameter. On the other hand, regarding the wall thickness, a plurality of equipment arrangements for obtaining the same wall thickness are conceivable.

Therefore, the present inventors examined the correlation between various parameters on the premise that the same thickness is obtained. As a result, the aspect ratio in the roll bite of each pipe expansion ratio (diagonal length in the roll bite, X _dia in FIG. 2 _(b)) found that there is a correlation between the rear end shape of the elongator after rolling It was. The contents of the experiment that found the correlation will be described below.

A round billet (Cr: containing 9.0 mass%) heated to 1230 ° C. or higher in a rotary heating furnace was punched with a piercer mill to obtain a hollow shell having an outer diameter of 220 to 378 mm. The hollow raw pipe to pipe expansion rolled in expansion ratio such that the outer diameter 243~419mm in elongator, within the roll bite of each expansion ratio diagonal length / inlet side element outer diameter _(X dia / OD), elongator rolling The relationship with the rear end shape was examined. In the examination, _Xdia was calculated by (e ² + h ² ) ^(1/2) for convenience.

  The rear end shape after the elongator rolling was evaluated based on whether or not the next process could be rolled.

The results are shown in FIG. From the result of FIG. 3, it was found that the roundness failure at the rear end can be suppressed under the condition satisfying the following formula (1).
0.87 × E + 0.44 ≦ (X _dia /OD)≦0.91×E+0.46 (1)
In the above formula (1),
E: Tube expansion rate at Elongator (however, E> 1.0)
X _dia : Diagonal length OD in the roll bite at the time of pipe expansion rolling with an elongator OD: outer diameter of the inlet side raw pipe.

When X _dia / OD is less than 0.87 × E + 0.44, the roll bite is close to a square or the outer diameter of the inlet side pipe becomes larger. Interference between the guide shoe and the base pipe disposed in the tube becomes a problem, and rolling failure may occur. When X _dia / OD exceeds 0.91 × E + 0.46, since the diagonal length in the roll bite is large, the tube curvature becomes large, and roundness failure tends to occur.

  Moreover, it does not specifically limit about manufacturing conditions other than elongator rolling.

  In the present invention, the above formula (1) can be applied to the production of a seamless steel pipe which is a difficult-to-process material containing 5.0 mass% or more of Cr. In addition, although it does not specifically limit about components other than Cr, C: 0.080-0.110mass%, Si: 0.10-0.50mass%, Mn: 0.32-0.60mass%, P: 0. 022 mass% or less, S: 0.40 mass% or less, Cu: 0.10 mass% or less, Ni: 0.10-0.30 mass%, Mo: 0.350-1.030 mass%, V: 0.160-0. The component composition which contains 240 mass% and Nb: 0.043-0.095 mass%, and consists of remainder Fe and an unavoidable impurity is preferable.

A round billet heated to 1230 ° C. or higher in a rotary heating furnace was punched with a Piercer mill to obtain a hollow shell having an outer diameter of 242 mm (Cr: containing 9.0 mass%). This hollow shell was expanded and rolled with an elongator so that the outer diameter was 279 mm and the expansion ratio was 1.152. At this time, the length of the diagonal line inside the roll bite / the outer diameter of the inlet tube (X _dia / OD) was changed in the range of 1.42 to 1.52. Note that the outer diameter of the entry-side element pipe is 242 mm. Further, the diagonal length _Xdia in the roll bite was controlled by the balance between the roll interval e and the advanced amount of the plug 63 from the roll center. For example, if the roll interval e is increased to reduce _Xdia , the outer diameter of the outlet side pipe changes and the wall thickness increases, so that the outlet side pipe can be adjusted by appropriately adjusting the advanced amount of the plug 63. The outer diameter was made constant.

  Each material was evaluated as to whether or not the next process can be rolled. The case where the next process rolling became possible was evaluated as “◯”, and the case where the next process rolling became impossible was evaluated as “x”.

  The results are shown in Table 1.

  From the results in Table 1, no. In No. 1, rolling failure occurred due to contact with the guide shoe during rolling. No. In No. 6, rear end roundness failure occurred during rolling. On the other hand, no. 2-5 satisfy | filled Formula (1), and there was no generation | occurrence | production of a rear end roundness defect at the time of rolling, and it became a favorable rolling result.

  In addition, the number of non-rollable materials generated due to poor roundness has decreased from the previous 4.6 cases / period to 0 / period.

1 Material (steel slab)
2 Heating furnace 3 Piercer mill (tilt rolling mill)
4 plug 5 element tube (hollow element tube)
6 Elongator 7 Plug mill 8 Reeler 9 Tube 10 Reheating furnace 11 Sizing mill 61 Upper roll 62 Lower roll 63 (For pipe inner surface restraint) Plug 64 (Left) Guide shoe 65 (Right) Guide shoe 66 Guide plate e Roll plug advanced amount from the diagonal length AA roll center in the interval h shoe interval OD inlet side element outer diameter X _dia roll bytes

Claims (2)

A rolling method of a seamless steel pipe containing 5.0 mass% or more of Cr, and a steel slab containing 5.0 mass% or more of Cr, after being heated in a heating furnace, pierced with a piercer mill, and subsequently, When expanding and rolling with an elongator having a barrel-shaped roll shape,
The tube expansion rate at the elongator is E (where E> 1.0), the diagonal length in the roll bite at the time of tube expansion rolling at the elongator is X _dia , and the outer diameter of the inlet side raw tube is OD,
A rolling method of a seamless steel pipe, characterized by performing pipe expansion rolling with an elongator so as to satisfy the following formula (1).
0.87 × E + 0.44 ≦ (X _dia /OD)≦0.91×E+0.46 (1) A method for producing a seamless steel pipe containing 5.0 mass% or more of Cr, wherein a steel slab containing 5.0 mass% or more of Cr is heated in a heating furnace, then drilled with a piercer mill, and subsequently, When expanding and rolling with an elongator having a barrel-shaped roll shape,
The tube expansion rate at the elongator is E (where E> 1.0), the diagonal length in the roll bite at the time of tube expansion rolling at the elongator is X _dia , and the outer diameter of the inlet side raw tube is OD,
A method of manufacturing a seamless steel pipe, characterized by performing pipe expansion rolling with an elongator so as to satisfy the following formula (1).
0.87 × E + 0.44 ≦ (X _dia /OD)≦0.91×E+0.46 (1)