JPS5923820A - Heat treatment of steel pipe - Google Patents

Abstract

PURPOSE:To adjust the cooling rate for a heated steel pipe of the A3 point or above over a wide range and heat treat said pipe while making the material quality in the circumferential and axial directions uniform by rotating the steel pipe and oscillating axially the same during cooling the steel pipe with a cooling fluid. CONSTITUTION:The above-described heated steel plate 1 is cooled at a prescribed cooling rate by the cooling water injected 25A from main cooling headers 25 while the pipe is kept revolved by revolving rolls 21 in a cooler 20 and is kept moved back and forth axially by oscillators 24. The cooling water is injected from the cooling nozzles 26A of auxiliary cooling headers 26 as well if the pipe 1 is upset and the wall thickness in the end part thereof is thicker than the wall thickness in the intermediate part. The cooling rate in the upset part of the pipe 1 is thus increased and the steel pipe is cooled in the state of making the cooling rate in the upset part and the cooling rate in the intermediate part equal. The pipe 1 is preferably revolved at >=60 revolutions/min. rotating speed in order to make the cooling rate in the circumferential direction of the pipe 1 equal.

Description

[Detailed description of the invention] The present invention relates to a steel pipe heat treatment method.

In the manufacture of steel pipes, heat treatments such as quenching and tempering, normalizing, or direct quenching and tempering are usually performed in order to impart high strength and toughness to the steel pipes. by the way,
Instead of using the above-mentioned normal heat treatment method, so-called controlled cooling, which cools the steel pipe while controlling the cooling rate of the steel pipe after hot forming or austenitizing heating, can relatively easily improve the balance between strength and toughness. It becomes possible to manufacture steel pipes that have been removed.

As a method of implementing the heat treatment by controlled cooling described above, (
A) W! A ring quench device that injects cooling water from the inner surface of a ring-shaped cooling water pipe through which the pipe can be inserted is used to achieve a predetermined cooling rate by adjusting the water pressure, water volume, etc. of the cooling water, or (B) Alternatively, an aqueous solution having an appropriate composition or the like is used to cool the material while being conveyed while being rotated for cooling which is slower than the cooling rate by ordinary water quenching. However, since the rollers are used for both rotation and conveyance, it is difficult to apply high-speed rotation to the steel pipe, and the rotation speed is usually low, about 20 rotations per minute or less. Under rotating conditions, the uniformity of the cooling rate in the circumferential direction of the steel pipe is insufficient, and the occurrence of bending due to cooling strain cannot be avoided. Also, like a steel pipe with an upset finish on the end,
When controlling a steel pipe that has portions with different wall thicknesses by this method (4), the cooling rate in the upset part is slower than that in the middle part of the pipe, and the material in the axial direction of the steel pipe may also be non-uniform. There is.

In method (B), the cooling rate is made uniform because the steel pipe is immersed in the cooling liquid, but the range of achievable cooling rates is narrow. For example, it is difficult to obtain a cooling rate that is slightly faster than air cooling. However, the cooling rate of the upset part is slower than that of the middle part of the pipe, as in the case of method (4).

The present invention makes it possible to adjust the cooling rate over a wide range, and to make the material uniform in the circumferential direction and the axial direction.
It is an object of the present invention to provide a steel pipe heat treatment method that can suppress the occurrence of bending due to cooling strain.

In order to achieve the above object, the present invention provides a steel pipe heat treatment method in which a steel pipe heated to a point A3 or higher is cooled and heat-treated by a cooling fluid injected from a cooling nozzle, in which a steel pipe is cooled by the cooling fluid. It rotates and swings in its axial direction.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a front view showing an example of a device used for carrying out the present invention, and FIG. 2 of the coffin is a 7α cross-sectional view taken along line II-II in FIG.

The steel pipe 1 to be heat treated is heated to A3 in the heating furnace 10.
The heated copper tube 1 is heated to an austenitizing temperature above a temperature of The cooling device 200 is transferred onto rotating rollers 21. Note that the steel pipe 1 may be heated to the A3 point or higher by sensible heat after hot forming, not by the heating furnace 10.

The rotating roller 21 of the cooling device 20 is +11112
driven by a drive morph 23 connected to 2;
The steel pipe 1 can be rotated by -L-C. A rocking device 24 for reciprocating the steel pipe 1 in the axial direction at a predetermined cycle and stroke is provided at a portion corresponding to the tip Diid)τb and the rear end of the steel pipe 1 on the rotating roller 21. .

Furthermore, the cooling device 20 is provided with main cooling headers 25 extending in the axial direction of the steel pipe 1 at a plurality of positions (third position fi) around the steel pipe 1 on the rotating roller 21 . The main cooling header 25 is capable of injecting cooling fluid such as mist or cooling water over the entire length of the steel pipe 1 from cooling nozzles 25A arranged in large numbers in its longitudinal direction. Also, steel pipe 1
Auxiliary cooling headers 26 having cooling nozzles 26A capable of injecting cooling fluid only to the ends of the steel pipe 1 are provided at multiple positions It, (3 positions M,) around both ends of the steel pipe 1.

Next, the operation of the above embodiment will be explained. A3 or higher
The steel pipe 1 heated to the second temperature state is cooled by a cooling device 20.
, while being rotated by the rotating roller 21 and given reciprocating movement in the axial direction by the rocking device 24, it is cooled at a predetermined cooling rate by the cooling water injected from the cooling nozzle 25A of the main cooling header 25. Ru.

When the steel pipe 1 is subjected to an upset process and the wall thickness at the end portion is thicker than the wall thickness at the middle portion, cooling water is also injected from the cooling nozzle 26A of the auxiliary cooling header 26,
The cooling rate of the upset part of the steel pipe is increased, and the cooling rate of the upset part and the intermediate part are made equal.

The rotational speed given to the steel pipe 1 by the rotary lawn 21 of the cooling device 20 is preferably higher in order to equalize the cooling rate in the circumferential direction of the steel pipe 1, and is preferably 60 rotations or more. . In addition, the rocking device 24
In order to equalize the cooling rate in the axial direction of the steel pipe 1, the moving distance in the axial direction given to the steel pipe 1 can be set to be at least 1 (amplitude) of the distance between the cooling nozzles installed in the cooling header). It is necessary, but under normal conditions it is desirable to make it equal to the nozzle installation distance. The period of reciprocating movement by the rocking device 24 is related to the cooling rate, for example,
When obtaining a cooling rate of approximately 0/sec, approximately 10
By rocking at a period of seconds, it is possible to equalize the cooling rate in the axial direction of the copper tube 1. The period of reciprocating movement by this rocking device R24 needs to be shortened as the cooling rate increases.

Next, experimental results of the present invention will be explained. In this experiment, material C=0.25%, 5i=0.3%, Mn=1
．． Carbon steel pipes having a diameter of 3 mm, an outer diameter of 127.0 mm, and a wall thickness of 9.19 mm were heat-treated under the cooling conditions of Examples 1 to 6 shown in Table 1.

The present invention allows self-tempering to occur by cooling to 500°C at a cooling rate and air cooling in the lower temperature range, thereby achieving high strength without the need for two-time heat treatment as in normal quenching and tempering. This is an example of a method. The second example is an example of the method of the present invention in which the strength is increased by cooling at a much faster cooling rate than usual normalizing.

The fourth example is a method for comparison with the first example in which the steel pipe is not shaken, the fifth example is a normalizing method to be compared with the second example, and the sixth example is controlled cooling using a quench ring. It depends on the method.

Table 2 shows the heat treatment results of Examples 1 to 6 shown in Table 1.

That is, in the case of each method of the first example and the third example, the variation in the hardness in the axial direction of the steel pipe and the bending are both smaller than the heat treatment results of the first, fourth and sixth examples. It is now possible to obtain superior steel pipes with uniform material quality. In the case of the method of the second example, since the cooling rate is faster than that of ordinary normalizing as in the fifth example, it is possible to achieve high strength. In addition, in the case of the second example, although variations in hardness and bending are slightly inferior to those in the case of ordinary normalizing, these do not pose a problem in terms of quality.

As described above, the present invention provides a steel pipe heat treatment method in which a steel pipe heated to a point A3 or above is cooled and heat-treated by a cooling fluid injected from a cooling nozzle, in which the steel pipe is rotated while being cooled by the cooling fluid. , and is swung in the axial direction, making it possible to adjust the cooling rate over a wide range, making the material uniform in the circumferential and axial directions, and suppressing the occurrence of bending due to cooling distortion. It has the effect of being able to

[Brief explanation of drawings]

FIG. 1 is a front view showing an example of an apparatus used for carrying out the present invention, and FIG. 2 is a sectional view taken along line II-II in FIG. DESCRIPTION OF SYMBOLS 1... Steel pipe, 10... Heating furnace, 20... Cooling device, 21... Rotating roller, 24... Rocking device, 25
...Main cooling header, 25A...Cooling nozzle, 26.
...Auxiliary cooling header, 26 people...Cooling nozzle. Agent Patent Attorney Osamu Shiokawa

Claims (1)

[Claims] (1) In a steel pipe heat treatment method in which a steel pipe heated to a point A3 or above is cooled and heat treated by a cooling fluid injected from a cooling nozzle, the C steel pipe is rotated while being cooled by the cooling fluid, and its axis is A steel pipe heat treatment method characterized by shaking in the direction.