JP2007290020A - Manufacturing method of medium diameter seamless steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a medium diameter seamless pipe by which eccentric uneven thickness of the rolled stock succeeding to a detected rolled stock is reduced by detecting the generation of the eccentric uneven thickness on the spot during the piercer rolling of the same pipe-making lot. <P>SOLUTION: In the method of manufacturing the medium diameter seamless steel pipe including the piercer rolling by which the inclined rotation piercing rolling is performed with upper and lower rolls 31, 32 and a plug 11 between the rolls while guiding the rolled stock 9 with right and left shoes 33, 34, by monitoring shoe load during the piercer rolling, the shoe position on the side where a monitored value is below the prescribed lowest limit is changed to a position near the pass center line. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a method for producing a medium diameter (product outer diameter: 177.8 to 426.0 mm) seamless steel pipe, and more particularly, to a method for producing a medium diameter seamless steel pipe capable of reducing eccentric thickness deviation caused by inclined rotary piercing rolling. .

  The medium-diameter seamless steel pipe is manufactured by a series of hot rolling as shown in FIG. 3, for example. In this example, the round billet 1 is heated to about 1200 ° C. or more in the heating furnace 2, tilted and pierced and rolled by the piercer 3 to form a hollow 10, this is rotated and rolled by the elongator 4, and then the axial hole by the plug mill 5. A manufacturing process was shown in which die rolling was performed, then the tube was polished with a reeler 6, reheated to about 800 to 900 ° C. in a reheating furnace 7, and then formed into an outer diameter with a sizer 8.

In such a manufacturing process, an eccentric thickness deviation (Non-Patent Document 1) is known as a shape defect that tends to occur in piercer rolling (tilted rotary piercing rolling). As shown in FIG. 4, the eccentric thickness deviation means that the inner circle center O ₂ is deviated with respect to the outer circle center O ₁ of the tube 20, and this deviation is in the same direction and in the same cycle as the twist of the material by piercing rolling. It is generated and extends spirally in the longitudinal direction of the tube. There are two types of eccentric thickness deviations, one due to heat deviation and the other due to equipment.

  Eccentricity deviation due to heat deviation is due to the fact that the material is fixed to the rotary hearth and radiantly heated, so that the top side near the center heats up faster than the bottom side, and finally the relatively high temperature part (deformation resistance) Is generated when a piercer plug is guided to a relatively high temperature portion, and the spiral period is relatively long. As a measure to prevent the occurrence of uneven heat, a furnace temperature setting pattern that lowers the furnace temperature slightly (20-30 ° C) after reaching the maximum temperature on the material surface to promote heat conduction in the cross section and soak or heat A method of changing the furnace to a walking beam type is known.

Eccentricity deviation due to equipment is caused by piercer plug bar bending, plug processing accuracy failure, piercer body swing block clamp failure, or bar swinging due to insufficient bar stay media hold, etc. The spiral period is relatively short. The common belief is that there is no other way but to strengthen equipment management.
Edited by Japan Iron and Steel Institute: Third Edition Steel Handbook III (2) Common Steel, Steel Pipe and Rolling Equipment (November 20, 1980; issued by Maruzen), p. 938-939

However, it is difficult to completely prevent uneven heat by only taking measures to equalize the temperature by changing the furnace temperature setting pattern. In addition, the countermeasure to change the heating furnace to the walking beam type has a great effect of reducing the heat deviation, but requires a large-scale facility modification.
In addition to the implementation of the above-mentioned heat equalization measures or the adoption of a walking beam type heating furnace, even if the facility management is sufficiently strengthened, the allowable limit is suddenly exceeded from the rolling order of the same pipe lot. Eccentric thickness deviation (eccentricity deviation thickness failure) occurs, and the final rolling (sizer rolling) products after the rolling order may all be out of order. The presence or absence of such eccentric eccentric thickness defects can only be determined by measuring the cross-sectional dimensions in the finishing line after sizer rolling, and it is unclear whether there are eccentric eccentric thickness defects in the rolled material during piercer rolling. .

  That is, in the conventional technology, it is impossible to detect the occurrence of eccentric eccentric thickness failure during pierce rolling on the spot, and even if it can be detected, effective eccentric thickness reduction means that can be taken on the spot are not available. It was unknown. Therefore, in the same pipe making lot, when an eccentric eccentric thickness defect occurs in a rolled material that is being rolled sequentially, in many cases, an eccentric eccentric thickness defect also occurs in the subsequent rolled material. This was a major impediment to yield improvement.

  Therefore, the present invention detects the occurrence of eccentric eccentric thickness failure on the spot during piercer rolling of the same pipe-making lot, and reduces the eccentric eccentric thickness of the rolled material subsequent to the rolled material subjected to the detection. It aims at providing the manufacturing method of a medium diameter seamless steel pipe.

The inventors have intensively studied to achieve the above object, and as a result, found that there is a significant correlation between the degree of eccentric thickness deviation after piercing and the shoe load during piercing. The present invention was made based on this finding.
That is, the present invention is as follows.
1. In a method for producing a medium-diameter seamless steel pipe including piercer rolling, in which a rolled material is guided by a left and right shoe while tilting rotary piercing rolling with upper and lower rolls and a plug between the rolls, the shoe load during the piercing rolling is monitored, A method for producing a medium-diameter seamless steel pipe, characterized in that the position of the shoe on the side where the monitored value falls below a predetermined lower limit is changed to a position approaching the path center line.

2. The method for manufacturing a medium-diameter seamless steel pipe according to item 1, wherein the roll interval between the upper and lower rolls is changed together with the change of the shoe position.
3. The method for producing a medium-diameter seamless steel pipe according to item 1 or 2, wherein the arrangement position of the plug between the rolls in the pass line direction is changed together with the change of the shoe position.
4). The execution time of the change of the shoe position, the change of the roll interval, and the change of the arrangement position of the plug is followed by the next rolling of the rolled material after the piercer rolling of the rolled material whose shoe load monitoring value is below the lower limit. 4. The method for producing a medium-diameter seamless steel pipe according to any one of items 1 to 3, wherein the material is before pierce rolling.

  According to the present invention, during the pierce rolling of the same pipe-making lot, the occurrence of eccentric eccentric thickness failure is detected on the spot, and the eccentric thickness deviation of the rolled material following the rolled material subjected to the detection is reduced. It becomes possible.

  In the piercer rolling, for example, as shown in FIG. 2, the rolled material 9 is inclined and pierced and rolled by upper and lower rolls 31 and 32 and plugs (piercer plugs) 11 arranged between these rolls. In order to adjust the outer diameter of the piercer exit side hollow to the target, shoes 33 and 34 are arranged on the left and right sides to guide the rolled material 9. By the way, when the rolled material 9 comes into contact with the shoes 33, 34, a pressing force acts on the shoes 33, 34. The pressing force is measured by a measuring means such as a load cell (not shown) attached to the shoes 33 and 34, which is a shoe load.

According to the above findings of the inventors, the relationship between the shoe load, the wall thickness ratio, and the outer diameter (piercer outlet side hollow outer diameter) in piercer rolling of a medium-diameter seamless steel pipe is as shown in a schematic graph in FIG. Here, the thickness deviation rate is the average thickness t _ave (i) obtained from the thickness data in the circumferential direction at n positions i (i = 1,..., N) in the longitudinal direction of the piercer exit side hollow. Using the maximum wall thickness t _max (i) and the minimum wall thickness t _min (i), the following equation is used.

Unevenness ratio = Max [(t _max (i) −t _min (i)) / t _ave (i)] (× 100%)
The thickness measuring means in the circumferential direction is not particularly limited, but an automatic ultrasonic thickness meter (USADT; manufactured by JFE Advantech) was used here. The means for measuring the outer diameter is not particularly limited, but an outer diameter path is used here.
As shown in FIG. 1, the thickness deviation rate is high and stable in a range where the shoe load is smaller than a certain value, for example, F1, but significantly decreases as the shoe load increases when the shoe load exceeds F1. On the other hand, the outer diameter is almost constant when the shoe load is larger than F1, for example, F2, and below, and this constant value is targeted. However, when the shoe load exceeds F2, the outer diameter decreases significantly as the shoe load increases. To do. Therefore, the left and right shoe loads are monitored during piercer rolling, and the monitored value falls below a predetermined lower limit appropriately selected within the range of F1 to F2, for example, the shoe load corresponding to the allowable upper limit of the thickness deviation rate. In this case, it can be determined that a relatively large eccentric thickness deviation has occurred in the rolled material subjected to the piercer rolling. In this way, by monitoring the shoe load, it is possible to detect the occurrence of the eccentric thickness defect of the rolled material on the spot during the piercer rolling of the same pipe making lot.

  Then, when the rolled material following the rolled material subjected to this detection (the shoe load on either the left or right or both falls below a predetermined lower limit) under the same conditions is pierced, the eccentric eccentric thickness defect is similarly generated. Very likely. Therefore, a measure is taken so that the shoe load on the side where the shoe load falls below the predetermined lower limit (either one of the left or right side or both) is returned to the range above the predetermined lower limit.

As shown in the schematic graph of FIG. 1A, for example, this measure appropriately determines a shoe position change amount, for example, α based on the relationship between the shoe position and the shoe load, and passes the shoe position by α from the current position. It is executed by changing to a position shifted to the center line side.
The relationship as shown in FIG. 1 and FIG. 1A can be determined in advance by experiment. These specific numerical relationships differ depending on the steel type of the material, and also differ depending on the roll interval between the upper and lower rolls (piercer roll interval) and the arrangement position of the plug between the rolls in the pass line direction (piercer plug position). It is preferable to determine the specific numerical relationship for each of a plurality of levels appropriately determined for each of the roll interval and the piercer plug position.

However, even if α is made as small as possible by changing the shoe position described above, the shoe load may exceed F2 and the outer diameter may fall below the target range. In such a case, troubles such as a biting failure are likely to occur in the elongator rolling in the next process, and the effect of reducing uneven thickness in the subsequent rolling process is reduced.
Therefore, in such a case, based on the specific numerical relationship determined for each of the plurality of levels, the level of the piercer roll interval and / or the piercer plug position where the outer diameter can be within the target range (for example, the shoe for α) It is preferable to select a level at which the amount of change in load is smaller) and change the current level to the selected level. At this time, the piercer roll interval should be changed to the enlarged side (the direction in which the outer diameter of the piercer outlet side hollow increases), and the piercer plug position to the upstream side (the direction in which the gap between the plug and the upper and lower rolls decreases). preferable. These change amounts can be appropriately determined based on the specific numerical relationship.

  The shoe position change, or the piercer roll interval change and / or the piercer plug position change added thereto may be executed from any order of the rolled material subsequent to the rolled material subjected to the detection. Of course, from the viewpoint of minimizing the number of occurrences, the execution timing of each of the change measures is the time before the start of piercing rolling of the rolled material to be rolled immediately after the end of piercing rolling of the rolled material affected by the detection. Time is preferred.

  Note that suitable steel types of the present invention include those shown in Table 1.

  The round billet (diameter 260mm) of material standard TCM14 (equivalent to JIS G7220) is used as the raw material, and in the manufacturing process shown in FIG. A medium-diameter seamless steel pipe having a finishing dimension = outer diameter of 355.6 mm × thickness of 35.7 mm was manufactured. Process No. 1 corresponds to a conventional example, and Process Nos. 2 to 4 correspond to examples of the present invention. The target range of the outer diameter of the piercer exit side hollow was set such that the lower limit = 290 mm and the upper limit = 300 mm. The furnace temperature of the heating furnace was set to 1230 ° C, and the furnace temperature of the reheating furnace was set to 980 ° C.

[Condition 1] During the piercer rolling of N lots of 1 lot (all N pieces; the value of N is shown in Table 3) one by one, roll interval: fixed, piercer plug position: fixed, shoe interval: fixed, Shoe load: Not monitored.
[Condition 2] Roll piercing and piercing plug position: Same as Condition 1 while shoe piercing: Table during the piercing of N lots of 1 lot (all N pieces; the value of N is shown in Table 3) one by one. Change at any time in procedure A in 2 (however, the values of F _min and α are shown in Table 3), shoe load: monitor.

[Condition 3] During the pierce rolling of N lots of 1 lot (all N pieces; however, the value of N is shown in Table 3) one by one, roll interval: change at any time in the procedure B in Table 2 (however, β The values are shown in Table 3), the piercer plug position: the same as condition 2, and the shoe spacing and shoe load: the same as condition 2.
[Condition 4] Roller interval, shoe interval and shoe load: Same as condition 3, during piercer rolling of N lots of 1 lot (N in total; the value of N is shown in Table 3) one by one. Position: Changed as necessary in the procedure C of Table 2 (however, the value of γ is shown in Table 3).

  About the conventional example and the example of this invention, the failure rate (failure number rate) resulting from eccentricity unevenness in the product after sizer rolling was investigated. Here, those with an uneven thickness ratio of 10% or less were accepted, and those with an uneven thickness percentage were rejected. The survey results are shown in Table 3. From Table 3, it can be seen that according to the present invention, it is possible to effectively suppress the occurrence of eccentricity wall thickness in piercer rolling.

  The round billet (diameter 350 mm) of the material standard TK24H (equivalent to JIS G3456) is used as the material, and in the manufacturing process shown in FIG. A medium-diameter seamless steel pipe having a finishing dimension = outer diameter of 406.4 mm × thickness of 44 mm was manufactured. Process No. 5 corresponds to a conventional example, and Process Nos. 6 to 8 correspond to examples of the present invention. The target range of the outer diameter of the piercer exit side hollow was set such that the lower limit = 378 mm and the upper limit = 381 mm. The furnace temperature of the heating furnace was set to 1260 ° C, and the furnace temperature of the reheating furnace was set to 980 ° C.

  About the conventional example and the example of this invention, the failure rate (failure number rate) resulting from eccentricity unevenness in the product after sizer rolling was investigated. Here, those with an uneven thickness ratio of 10% or less were accepted, and those with an uneven thickness percentage were rejected. The survey results are shown in Table 3. From Table 3, it can be seen that according to the present invention, it is possible to effectively suppress the occurrence of eccentricity wall thickness in piercer rolling.

It is a schematic graph which shows the relationship between a shoe load, a thickness deviation rate, and an outer diameter (piercer exit side hollow outer diameter). It is a schematic graph which shows the relationship between a shoe position and shoe load. It is a schematic diagram which shows the mode of piercer rolling. It is a schematic diagram which shows an example of the manufacturing process of a medium diameter seamless steel pipe. It is a schematic diagram which shows the aspect of eccentricity thickness deviation.

Explanation of symbols

1 round billet (material)
2 Heating furnace (rotary hearth type heating furnace)
3 Piercer (vertical 2-roll inclined rotary piercing and rolling mill)
4 Elongator (vertical 2-roll inclined rotary rolling mill)
5 Plug mill (plug mill type axial hole rolling mill)
6 Leela (Horizontal 2-roll rotating inner and outer surface polishing pipe machine)
7 Reheating furnace (walking beam type reheating furnace)
8 Sizer (8-stand 2-roll caliber type outer diameter molding machine)
9 Rolled material
10 Hollow (hollow material)
11 Plug (Piercer plug)
12 Plug (Elongator plug)
13 Plug (plug mill plug)
14 Plug (Reeler plug)
20 tubes
31 roll (upper roll)
32 rolls (lower roll)
33 shoe (left shoe)
34 shoe (right shoe)

Claims (4)

  In a method for producing a medium-diameter seamless steel pipe including piercer rolling, in which a rolled material is guided by a left and right shoe while tilting rotary piercing rolling with upper and lower rolls and a plug between the rolls, the shoe load during the piercing rolling is monitored, A method for producing a medium-diameter seamless steel pipe, characterized in that the position of the shoe on the side where the monitored value falls below a predetermined lower limit is changed to a position approaching the path center line.   The method for producing a medium-diameter seamless steel pipe according to claim 1, wherein a roll interval between the upper and lower rolls is changed together with the change of the shoe position.   The method for producing a medium-diameter seamless steel pipe according to claim 1 or 2, wherein the arrangement position of the plug between the rolls in the pass line direction is changed together with the change of the shoe position.   The execution time of the change of the shoe position, the change of the roll interval, and the change of the arrangement position of the plug is followed by the next rolling of the rolled material after the piercer rolling of the rolled material whose shoe load monitoring value is below the lower limit. The method for producing a medium-diameter seamless steel pipe according to any one of claims 1 to 3, wherein the material is before pierce rolling.

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