JP2005248302A - Method for producing long, large diameter, and thin-walled seamless steel pipe having little bending - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a long, large diameter, and thin-walled seamless steel pipe having little bending in a longitudinal direction. <P>SOLUTION: In a heat-treatment for annealing the seamless steel pipe 2 produced with a Mannesman method, while rotating the seamless steel pipe 6 at ≥5 rpm around the center axis, the outer surface is cooled from the upper and the lower directions with a cooling device 5 by shifting at ≤0.5 m/min speed in the axial direction of the seamless steel pipe 2. The above seamless steel pipe 2 is the long, large diameter, and thin-walled seamless steel pipe having ≥3 m length (L), ≥70 mm outer diameter (D) and ≥10 the ratio (D/t) of the outer diameter (D)/the thickness (t). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a long, large-diameter, thin-walled seamless steel pipe with little bending in the longitudinal direction.

  There is a Mannesmann method as a method for producing a seamless steel pipe. The seamless steel pipe manufactured by this manufacturing method is manufactured by the following processes: hot working (Assel rolling) → cold working (cold billger rolling) → heat treatment (strain relief annealing) → correction → end face processing → inspection.

  In addition to the manufacturing process of the seamless steel pipe, heat treatment such as quenching and tempering is performed. In the heat treatment, cooling by water cooling is performed after heating.

  Furthermore, in order to adjust hardness and remove residual strain, heat treatment is performed to heat and cool the seamless steel pipe at a predetermined temperature after hot working. As a line for such a heat treatment process, a steel pipe is continuously rotated in the longitudinal direction while rotating about its axis using a rotating roll, and continuously passes through a heating device and a cooling device for heat treatment. Conventionally, a heat treatment line in which heating and cooling are continuously performed has been widely used.

  In the heat treatment line as described above, in order to heat treat a steel pipe supplied in a large amount at a time, a furnace having a length and a width corresponding to the length of the steel pipe is required. To increase the size of the furnace There was a problem that the capital investment of the company became enormous.

  In particular, in the case of a cooling device having a short overall length compared to the total length of the heating furnace, air cooling is not sufficient for cooling, and it is necessary to perform rapid cooling by water cooling at the heating furnace outlet.

  Also, when performing rapid cooling with cooling water, if the cooling is uneven in the circumferential direction of the seamless steel pipe, the seamless steel pipe is deformed, and in the case of a seamless steel pipe with a large ratio of outer diameter to wall thickness, the seamless steel pipe There was a problem that the bend of became large.

  Furthermore, when a seamless steel pipe having a large bend is supplied to a subsequent straightening process, the straightening process causes a residual stress due to straightening to be inherent in the steel pipe of the product.

  For this reason, in water cooling in the quenching of seamless steel pipes, etc., correction is performed by using a cooling device that sprays cooling water on the outer and inner surfaces of the seamless steel pipe and by using a method of performing uniform cooling in the circumferential direction or using restraining rolls. However, the bending at the time of cooling is suppressed by a method of performing a heat treatment or the like.

  As a conventional heat treatment method for a steel pipe, an apparatus (Patent Document 1) that uniformly cools the surface on the circumference of a steel pipe with a movable annular cooling medium spray nozzle is disclosed.

  Moreover, the method (patent document 2) which correct | amends the deformation | transformation of a steel pipe in the inside of a heating furnace at the time of cooling with a restraint roll is disclosed.

  Furthermore, a heat treatment line (Patent Document 3) is disclosed in which a steel pipe bending straightening device including a heating device and a cooling device is disposed by rotating the steel pipe in the length direction before the heat treatment. .

  However, in these apparatuses and methods, the seamless steel pipes supplied in large quantities at a time cannot be heat-treated, resulting in a problem that the cost is increased economically.

  Conventional hot working (Assel rolling) → cold working (cold Birger rolling) → heat treatment (strain relief annealing) → straightening → end face processing → inspection, straightening the bow and forward bend of the seamless steel pipe after heat treatment In order to do so, a strong correction is required.

However, in such a strong straightening, the residual stress due to the straightening is inherent in the seamless steel pipe, in particular, the length is 3 m or more, the outer diameter is 70 mm or more, and the ratio between the outer diameter and the wall thickness, that is, For long, large-diameter, thin-walled seamless steel pipes having an outer diameter / thickness of 10 or more, straightness failure occurs due to the strain caused by this residual stress during correction.
Japanese Patent Laid-Open No. 51-103011 JP 52-0777812 A JP 62-161918 A

  As described above, the conventional methods for dealing with the uneven cooling in the circumferential direction at the time of heat treatment for a seamless steel pipe having a bend are both large in heat treatment equipment, leading to high equipment costs, There were problems such as requiring troublesome maintenance.

  On the other hand, it is possible to keep straightness within the required standard by re-correcting the seamless steel pipe whose straightness has decreased, but re-correction in the cold is considerable. The fact is that it is inevitable that it takes time and effort. Further, the residual stress is further accumulated due to re-correction, and there is a possibility that the adverse effect (roundness defect) of the residual stress may increase in the secondary processing (cutting / cutting).

  The present invention has been made against the background of the above circumstances, and is a cooling device that sprays cooling water from above and below by rotating in a longitudinal direction while rotating a long large-diameter thin-walled seamless steel pipe by a rotating roller. This is a manufacturing method that realizes uniform cooling in the circumferential direction of a long large-diameter thin-walled seamless steel pipe with little bending.

  The manufacturing process of the present invention consists of hot working (Assel rolling) → cold working (cold billger rolling) → heat treatment (strain relief annealing) → correction → end face processing → inspection process. The purpose is to reduce the bending of the thin-walled seamless steel pipe.

  That is, the means of the present invention for solving the above-mentioned problem is that in the first configuration of the manufacturing method of the long large-diameter thin-walled seamless steel pipe with less bending according to the present invention, the seamless steel pipe manufactured by the Mannesmann method is used. In the annealing heat treatment, the seamless steel pipe is moved at a speed of 0.5 m / min or less in the axial direction of the seamless steel pipe while rotating it at 5 rpm or more around the central axis, and the outer surface is cooled in the vertical direction by a cooling device. It is characterized by making it.

  According to a second configuration of the present invention, in the first configuration, the seamless steel pipe has a length (L) of 3 m or more, an outer diameter (D) of 70 mm or more, an outer diameter (D), and a wall thickness (t). It is a long large-diameter thin-walled seamless steel pipe having a ratio (D / t) of 10 or more.

  The production method of the present invention is a method for producing a long large-diameter thin-walled seamless steel pipe by using a cooling device that advances in the longitudinal direction and sprays cooling water from above and below while rotating the long large-diameter thin-walled seamless steel pipe by a rotating roller. Bending can be prevented.

  According to the present invention, even for a long thin seamless steel pipe whose bending is increased by the conventional heat treatment method, the bending can be significantly reduced by rapid cooling with cooling water after heating, and a seamless steel pipe having excellent dimensional accuracy is manufactured. be able to.

  In addition, this heat treatment method can heat long, large-diameter, thin-walled seamless steel pipes that are supplied in large quantities at a time, and does not increase the equipment cost. Further, there is no need for a process associated with bending, that is, a correction process. Therefore, the manufacturing cost can be greatly reduced.

  In the production method of the present invention, the formed long large-diameter thin-walled seamless steel pipe is heated to a high temperature, and then injected by cooling water from a plurality of cooling nozzles provided at approximately equal intervals in the vertical direction, respectively. The cooling nozzles are uniformly cooled in the vertical direction at the same position where the cooling nozzles are arranged, so there is no temperature difference in the circumferential direction of the seamless steel pipe due to cooling, and deformation and bending are prevented, resulting in significantly improved work efficiency. High quality seamless steel pipe can be manufactured.

  Details of the present invention will be described below with reference to FIGS. 1, 2, and 3 showing an example of implementation. FIG. 1 is a side view of the heat treatment step. FIG. 2 is a side view of the state where the seamless steel pipe is rotated, and FIG. 3 is a side view of the state where the seamless steel pipe is cooled by the cooling nozzle. 1, 2, and 3, 1 is a transport roll for moving a seamless steel pipe in the longitudinal direction, 2 is a seamless steel pipe, 3 is a transport table, 4 is a heating furnace, 5 is a cooling device, and 6 is a seamless A rotating support roll for the steel pipe 2, 7 is a cooling nozzle.

  The long large-diameter thin-walled seamless steel pipe of the present invention is hot-worked and formed by the Mannesmann method. Then, it finishes to a predetermined dimension (diameter, thickness) by cold rolling (cold billger rolling). As shown in FIG. 1, a plurality of seamless steel pipes 2 are arranged in parallel on a transfer table 3 in parallel with the full length direction of a heat treatment furnace having a total length of 50 m and a width of 2 m. To heat to a predetermined temperature. At that time, as shown in FIG. 2, by heating the plurality of seamless steel pipes 2 arranged on the transport table 3 while being rotated by the rotating roll 6 of the transport table 3, there is no uneven heat due to heating, and the heating furnace The bending within 4 can be reduced, and deformation due to its own weight can also be prevented. The seamless steel pipe 2 is transported at a constant speed of 0.5 m / min or less in the axial direction of the seamless steel pipe 2 to the cooling device 5 on the left side of the figure while rotating at a rotational speed of 5 rpm by a rotating roll 6. By setting the transfer speed to 0.5 m / min or less, the temperature of the seamless steel pipe 2 after passing through the cooling device 5 is lowered to room temperature.

  If the transfer speed exceeds 0.5 m / min, the cooling with the cooling water is insufficient and the seamless steel pipe 2 is not cooled. By setting the rotation speed to 5 rpm or more, it is possible to reduce the uneven heat due to cooling in the circumferential direction of the seamless steel pipe. When the rotational speed is 5 rpm or less, the heat deviation due to cooling in the circumferential direction of the seamless steel pipe increases, and the bending of the seamless steel pipe 2 increases.

  After passing through the heating furnace 4, the seamless steel pipe 2 transferred at a constant speed while being rotated by a rotating roll 6 as shown in FIG. 3 was arranged in a metal cylindrical pipe having a diameter of 30 mm at intervals of 30 mm. In the cooling device 5 provided with the cooling nozzle 7 having a diameter of 5 mm above and below, the cooling water of the cooling nozzle 7 is immediately injected from the vertical direction of the seamless steel pipe 2 and cooled to a predetermined temperature. Cooling in the circumferential direction becomes uniform, and straightness deterioration during cooling can be prevented.

  A seamless steel pipe made of SUJ2, which is a bearing steel with an outer diameter (D) of 96.2 mm, a wall thickness (t) of 4.8 mm (D / t = 20.0), and a length (L) of 4.2 m, is used as a heating furnace. While being heated at 720 ° C. for 0.8 h and rotating at a rotation speed of 5 rpm, it was moved in the axial direction of the seamless steel pipe at a speed of 0.5 m / min, and cooled with cooling water from the vertical direction of the cooling device.

(Conventional method 1)
Also, as a conventional method, seamless steel pipes of the same material and the same dimensions as in Example 1 were used to heat the 720 ° C., 0.8 h seamless steel pipes without any gaps in a heating furnace, and the seamless steel pipes were rotated without giving rotation. It was moved in the axial direction at a speed of 0.6 m / min and cooled with cooling water from above the cooling device.

  A seamless steel pipe made of SCr420, which is a structural steel having an outer diameter (D) of 70.2 mm, a wall thickness (t) of 6.8 mm (D / t = 10.3), and a length (L) of 4.3 m. While being heated at 680 ° C. for 1.2 hours and rotating at a rotational speed of 5 rpm, it was moved in the axial direction of the seamless steel pipe at a speed of 0.5 m / min and cooled with cooling water from the vertical direction of the cooling device.

(Conventional method 2)
In addition, as a conventional method, the seamless steel pipes are arranged without gaps, moved in the axial direction of the seamless steel pipes at a speed of 0.6 m / min without giving rotation, and cooled with cooling water from above the cooling device. Comparison was made using seamless steel pipes of the same material and dimensions.

  A seamless steel pipe made of SUJ2, a structural steel having an outer diameter (D) of 75.5 mm, a wall thickness (t) of 11.6 mm (D / t = 6.5), and a length (L) of 4.1 m, is used as a heating furnace. While being heated at 680 ° C. for 1.2 hours and rotating at a rotational speed of 5 rpm, it was moved in the axial direction of the seamless steel pipe at a speed of 0.5 m / min and cooled with cooling water from the vertical direction of the cooling device.

(Conventional method 3)
Also, as a conventional method, the seamless steel pipes are arranged without gaps, moved in the axial direction of the seamless steel pipes at a speed of 0.6 m / min without giving rotation, and cooled with cooling water from above, and the same material as in Example 4 Comparison was made using seamless steel pipes of the same dimensions.

(Comparative Example 1)
A seamless steel pipe made of SUJ2, which is a bearing steel with an outer diameter (D) of 96.2 mm, a wall thickness (t) of 4.8 mm (D / t = 20.0), and a length (L) of 4.2 m, is used as a heating furnace. While being heated at 720 ° C. for 0.8 h and rotating at a rotation speed of 6 rpm, it was moved in the axial direction of the seamless steel pipe at a speed of 1.5 m / min, and cooled with cooling water from the vertical direction of the cooling device.

(Comparative Example 2)
A seamless steel pipe made of SUJ2, which is a bearing steel with an outer diameter (D) of 96.2 mm, a wall thickness (t) of 4.8 mm (D / t = 20.0), and a length (L) of 4.2 m, is used as a heating furnace. While being heated at 720 ° C. for 0.8 h and rotating at a rotation speed of 3 rpm, it was moved in the axial direction of the seamless steel pipe at a speed of 0.8 m / min and cooled with cooling water from the vertical direction of the cooling device.

  Table 1 shows the straightness of the seamless steel pipe according to the process of the present invention, the straightness of the seamless steel pipe by cooling from above without rotating the conventional seamless steel pipe, and the transfer speed as a comparative example. The straightness of the seamless steel pipe was shown. The straightness is represented by an average bending amount (mm / m) per 1 m of the steel pipe length.

  The straightness of the long, large-diameter, thin-walled seamless steel pipe that is the object of the present invention is 2 mm / m when the ratio (D / t) of the outer diameter (D) to the wall thickness (t) is 10-15. Below, when the ratio (D / t) of the outer diameter (D) and the wall thickness (t) is 15 to 20, the aim was to suppress the straightness to 3 mm / m or less.

  In Table 1, while rotating the seamless steel pipe of the present invention at a rotation speed of 5 rpm, the ratio of the outer diameter (D) and the wall thickness (t) is transferred at a speed of 0.5 m / min and cooled from the vertical direction ( The straightness of Example 1 with D / t) of 20 was 2.1 mm / m, which was higher than the target of 3 mm / m.

  Further, Example 2 in which the ratio (D / t) of the outer diameter (D) to the wall thickness (t) was 10.3 was 1.7 mm / m, which was higher than the target of 2 mm / m.

  Further, Example 3 in which the ratio (D / t) of the outer diameter (D) to the wall thickness (t) was 6.5 was 1.2 mm / m, which was higher than the target of 2 mm / m.

  Any of these examples exceeded the target straightness, and had a significant effect on bending in the longitudinal direction.

  The ratio (D / t) of the outer diameter (D) and the wall thickness (t), in which the seamless steel pipe, which is a conventional method, is transferred at a speed of 0.6 m / min without being rotated and cooled with the cooling water from above. The straightness according to the conventional method 1, which is 20, was 4.2 mm / m, which was significantly bent from the target of 2 mm / m.

  Further, the conventional method 2 in which the ratio (D / t) of the outer diameter (D) to the wall thickness (t) is 10.3 is 4.2 mm / m, which is bent from the target of 3 mm / m.

  Further, the conventional method 3 in which the ratio (D / t) of the outer diameter (D) to the wall thickness (t) is 6.5 was slightly bent from the target 2 mm / m at 2.2 mm / m. For this reason, the method of cooling with cooling water from above without rotating it was ineffective for bending in the longitudinal direction.

  While rotating the seamless steel pipe as a comparative example at a rotational speed of 6 rpm, it is transferred at a speed of 1.5 m / min and cooled with cooling water from above and below, and the ratio of the outer diameter (D) and the wall thickness (t) ( The straightness according to Comparative Example 1 in which D / t was 20 was 3.4 mm / m, which was slightly bent from the target of 3 mm / m.

  In addition, while rotating the seamless steel pipe at a rotational speed of 6 rpm, it is transferred at a speed of 0.8 m / min and cooled with cooling water from above and below, and the ratio of the outer diameter (D) and the wall thickness (t) (D / Comparative Example 2 in which t) was 20 was significantly bent from the target 3 mm / m at 4.3 mm / m.

  Therefore, in the comparative example, when the transfer speed was transferred exceeding 0.5 m / min, there was no effect on the bending in the longitudinal direction as in the case of the rotation speed.

It is a side view of a heat treatment process. It is a side view of the state which rotates a seamless steel pipe. It is a side view of the state which cools a seamless steel pipe with cooling water.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ......... Conveyance roll 2 ......... Seamless steel pipe 3 ......... Conveyance table 4 ......... Heating furnace 5 ......... Cooling device 6 ......... Rotating roll 7 ......... Cooling nozzle

Claims (2)

  In a heat treatment for annealing a seamless steel pipe manufactured by the Mannesmann method, the seamless steel pipe is moved at a speed of 0.5 m / min or less in the axial direction of the seamless steel pipe while being rotated at a speed of 5 rpm or more around the central axis, and cooled. A method for producing a long, large-diameter, thin-walled seamless steel pipe with less bending, characterized in that the outer surface is cooled in the vertical direction by an apparatus. The seamless steel pipe has a long large diameter thin wall having a length (L) of 3 m or more, an outer diameter (D) of 70 mm or more, and a ratio (D / t) of the outer diameter (D) and the thickness (t) of 10 or more. 2. The method for producing a long large-diameter thin-walled seamless steel pipe with little bending according to claim 1, wherein the pipe is a seamless steel pipe.

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