JPS6410571B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for cooling steel pipes in the manufacturing process of steel pipe products, and more particularly to a controlled cooling method for steel pipes that controls the cooling stop temperature and cooling rate.

BACKGROUND TECHNOLOGY In the manufacturing process of steel pipes, it is often necessary to forcefully cool the steel pipes by water cooling mainly during the heat treatment process, and a typical example of this is a quenching process in which the heated steel pipes are rapidly cooled to around room temperature. Similarly, as an example of water cooling a steel pipe during heat treatment, a so-called controlled cooling process is known in which a heated steel pipe is forcibly cooled by water cooling to a specific temperature range, and then allowed to cool naturally or subjected to the next processing process. ing. However, the above-mentioned controlled cooling process is still only an idea in the field of steel pipes, and has been difficult to implement in reality.

For example, in Japanese Patent Publication No. 54-31459, it is stated that in the manufacturing process of seamless steel pipes, after passing through a reeler,
A steel pipe with a temperature of 700℃, just below the A1 transformation point.
A technique has been disclosed in which the material is rapidly cooled to a certain degree to form a fine grain structure, and then squeezed to a predetermined outer diameter using a sizer to form a product. Also, JP-A-58-
Publication No. 52426 discloses a quenching method in which the tube is rotated while flowing cooling water from above the tube in a laminar flow over almost the entire length of the tube. It is stated that this includes Interrupted Quench.

However, none of these proposals discloses what specific means to use to control the cooling rate or cooling stop temperature, and in particular, it is not necessary to actually measure and monitor the steel pipe temperature during cooling to control it. Since nothing is disclosed about what will happen, if you actually try to implement these methods, you will have to rely on empirical rules or data obtained through experiments in advance to calculate the cooling temperature based on the measured pipe temperature before starting cooling. There is no other choice but to apply means such as estimating and controlling the tube temperature inside, and it is difficult to accurately control the cooling rate and cooling stop temperature with such means. For example, in the case of the method of No. 54-31459 mentioned above, the temperature of the tube immediately after the reeler varies considerably depending on the tube size (particularly the wall thickness), and even among tubes of the same size, there are variations from tube to tube, and the tube temperature is cooled to a constant temperature. In order to achieve this, it is necessary to vary the cooling duration for each tube size or for each tube, but such control is extremely difficult using only the conventional estimation method described above. Control that continuously measures and monitors the tube temperature and immediately stops cooling when a predetermined temperature is reached is essential. In addition, the above-mentioned Japanese Patent Application Laid-open No. 58-52426 also mentions Interrupted Quench, which stops cooling at a low temperature during quenching, but even if you try to stop cooling at a constant temperature using this method, it will not work online. Since no means for actually measuring the tube temperature during cooling is specified, such control is also difficult to implement.

In the case of normal hardening treatment, it is common to perform further tempering treatment after quenching and then adjust the material to the required material and produce the product, but in the case of controlled cooling, usually no tempering treatment is performed. Use the product as it is cooled. In other words, controlled cooling is based on the idea of realizing a wide range of pipe materials even from materials with the same composition by controlling the cooling stop temperature and cooling rate. In such controlled cooling, properties such as strength and toughness greatly depend on the cooling stop temperature and cooling rate, so it is impossible to stably manufacture steel pipes with the desired material without accurately controlling these factors. It is not possible.

In the field of ordinary steel plates, controlled cooling treatment often refers to an operation in which a certain temperature range is cooled at a predetermined, relatively slow specific cooling rate, but even in the case of quenching, which has a fast cooling rate,
By controlling the cooling stop temperature, subsequent tempering is not necessary, and it is possible to obtain a product with the desired material quality while cooling. This kind of quenching-cooling stop type heat treatment differs from the aforementioned controlled cooling treatment in fields such as steel plates in that it uses rapid cooling as the starting point; They are the same in the sense that they eliminate the need for return, and therefore, the two are not distinguished in this specification, and "controlled cooling" refers to cooling that controls the cooling rate and cooling that controls the cooling stop temperature. It shall include both of them, and also include a cooling method that combines both of them.

Problems to be Solved by the Invention In order to realize the above-mentioned controlled cooling process, it is essential to continuously measure and monitor the temperature of the steel pipe during cooling. Publication No. 54-31459 and Japanese Unexamined Patent Publication No. 58-52426 do not disclose any means for this purpose. In the conventional general steel pipe cooling method, it is extremely difficult to actually measure the temperature of the steel pipe during cooling. This point will be explained in more detail below.

First, the main conventional cooling methods for steel pipes are the continuous partial cooling method, which cools a portion of the steel pipe locally and advances the steel pipe continuously, ultimately cooling the entire length of the steel pipe. It is broadly divided into full-length simultaneous cooling method, which cools the entire length of the steel pipe almost simultaneously.Furthermore, the former continuous partial cooling method includes the following (1) and (2), and the latter full-length simultaneous cooling method. The following methods (3) to (6) are available.

Continuous partial cooling method: (1) A method in which a part of the steel pipe that gradually comes out of the heating furnace or induction heating coil is surrounded by a quenching ring, and only the outer surface of the steel pipe is continuously cooled as the pipe progresses. .

(2) In addition to the quenching ring described in (1) above, a header for internal cooling is inserted into the tube, and the tube is quenched from both the inside and outside.

Full-length simultaneous cooling method: (3) A method in which water is injected at high speed into the steel pipe extracted from the heating furnace, and the entire length of the pipe is cooled almost simultaneously from the inner surface only.

(4) At the same time, water is injected at high speed into the steel pipe extracted from the heating furnace, and at the same time, a layered or film-like water flow (flat laminar flow) flows down the outer surface of the pipe along the longitudinal direction of the pipe. Rotate it,
A method that cools the tube almost simultaneously from both the inside and outside over its entire length.

(5) A method in which the steel pipes extracted from the heating furnace are placed in a water tank and water is injected into the pipes at high speed to cool both the inside and outside of the pipes almost simultaneously over the entire length of the pipes.

(6) A method in which the rotation of the tube is added to the method (5) above.

In conventional general steel pipe cooling methods as shown in (1) to (6) above, even when measuring the outer surface temperature of the steel pipe before the start of cooling in order to understand the heat treatment conditions, There is no precedent for actually measuring the tube temperature during cooling, and it was virtually difficult to actually measure it.

That is, the temperature of steel pipes in the production line must be measured using a non-contact type thermometer, and usually a light radiation thermometer or a two-color thermometer is used. It is impossible to measure the inner surface temperature of the pipe during cooling using these devices in the case of cooling methods in which water is passed into the pipe, such as methods (3) to (6) above. Also method
In methods (1) and (2), the tube is advancing, so in order to determine the cooling rate of the inner surface, it is necessary to move the temperature measurement position in accordance with the advancing speed of the tube, and in method (1), When the rear end of the tube passes through the quenching ring, a large amount of water flows into the tube, and in method (2), it is also cooled from the inner surface, making it difficult to measure the inner surface temperature.

On the other hand, it is difficult to measure the outer surface temperature of the tube during cooling when methods (1), (2), and (4) involve external cooling; In the first place, it is impossible to put it into an aquarium. However, it is possible to measure the outer surface temperature only in the case of (2), a cooling method that simply passes water into the pipe.
However, the problem in this case is that even if the temperature of the tube during cooling can be measured, it is difficult to stop the cooling at a predetermined temperature. That is, it is difficult to instantaneously stop the injection of water into the pipe, and even if it is stopped, water remains unevenly in the pipe, which tends to cause material variations. In addition, in the case of the water flow system, the cooling rate of the tube differs between the inlet and outlet sides of the cooling water, and the difference increases as the tube gets longer, so there is also the problem that it is difficult to stop cooling the entire length at the same temperature. Another option is to immerse only the bottom of the tube in water and measure the temperature from the top while rotating the tube, but in this case too, it is difficult to stop the cooling, and a large amount of water vapor is generated, so a radiation thermometer or two There is a drawback that measurements using a color thermometer are unreliable.

The present invention was made against the background of the above circumstances, and makes it possible to actually measure the temperature of a steel pipe while it is being cooled, which was previously considered impossible or difficult, and thereby to control the cooling rate and/or cooling stop temperature. ensure that it can be performed accurately in actual operation,
Furthermore, it is an object of the present invention to provide an epoch-making method for heat treatment of steel pipes, which makes it possible in actual operation to omit tempering after quenching.

Means for Solving the Problems In the controlled cooling method for steel pipes of the present invention, when cooling the steel pipes, at least the temperature detection end of a non-contact temperature measuring device is inserted into the inside of the steel pipes. The steel pipe being cooled is cooled by water only from its outer surface while being rotated, and air is injected inside the steel pipe to seal at least the vicinity of the temperature detection end against intrusion of cooling water into the inside of the steel pipe. It is characterized in that the temperature of the inner surface is actually measured in a non-contact manner by the temperature measuring device to control the cooling stop and/or the cooling rate.

Effect: In the cooling control method of the present invention, by cooling the steel pipe with water only from the outer surface, it is possible to actually measure the temperature of the pipe during cooling from the inner surface.
Here, in order to cool the steel pipe at a uniform cooling rate over the entire length of the steel pipe, or to stop cooling at a uniform temperature over the entire length of the steel pipe, the outer surface of the steel pipe is It goes without saying that approximately the same amount of water should be applied to the material in its longitudinal direction. Further, rotating the steel pipe is necessary to make cooling conditions uniform in the circumferential direction of the steel pipe.

The temperature of the inner surface of the tube is measured by inserting at least the temperature detection end of a non-contact temperature measuring device using an optical fiber or the like into the tube end. In some cases, a small amount of water may enter the pipe from the end of the pipe and generate water vapor, which may impede accurate temperature detection. At least the vicinity of the temperature detection end inside the pipe is sealed against cooling water. Note that sealing the entire inside of the tube to prevent cooling water from entering the tube is also effective in avoiding variations in the material of the tube after cooling.

As described above, the temperature of the inner surface of the pipe is actually measured during cooling, and based on the measured value, the cooling stop temperature and/or
Alternatively, by controlling the cooling rate, it becomes possible to accurately control the cooling stop temperature and cooling rate.

Embodiment FIGS. 1 and 2 show an example of a situation in which the method of the present invention is implemented, particularly in the vicinity of the end of a steel pipe. The outer surface of the steel pipe may be cooled using a spray nozzle or spray, but
If the main purpose is rapid cooling, along the longitudinal direction of the pipe,
It is desirable to apply a method in which a layered or film-like laminar flow is caused to flow down on the top line of the tube, and this example also shows a case in which a method using a laminar flow is adopted.

In FIGS. 1 and 2, a steel pipe 1 to be cooled is placed and supported on a rotating roll 2, and rotated about its axis by the rotation of this rotating roll 2. Above the steel pipe 1 is a water tank 3 containing cooling water.
A slit nozzle 4 is formed at the bottom of the water tank 3. This slit nozzle 4 is constructed so as to cause the cooling water to flow down as a laminar or film-like flat laminar flow along the longitudinal direction of the rotating steel pipe 1 and onto the top line of the pipe.

A metal tube 5 for temperature measurement is inserted into the steel tube 1 from its tube end, and inside the tip of the metal tube 5 is a reflecting mirror or prism 6 for receiving the radiant light i from the inner surface of the steel tube 1. An optical fiber (not shown) for transmitting the radiant light received by the reflecting mirror or prism 6 is built in the metal tube 5, and this optical fiber is connected to the rear end of the metal tube 5. It is continuous or connected to an external fiber optic cable 7 at. Furthermore, cooling water is introduced into the metal cylinder 5 from a cooling water supply port 8 at the rear end, circulates therein, and is discharged from a cooling water discharge port 9. Moreover, the outside of the metal cylinder 5 except for its tip part has an air flow path 10.
A nozzle 12 is formed at the tip of the outer cylinder 11 to communicate with the air flow path 10, and a nozzle 12 is formed in the shape of an umbrella. At the rear end of 11 is an air introduction pipe 13.
is connected. The metal tube 5 and the outer tube 11
is held by an annular holding part 15 on the outside of the steel pipe 1, and this annular holding part 15 is connected to the support arm 1.
6 to a forward/backward drive device such as an air cylinder 17
A mask plate 19 is connected to the supporting arm 16 to prevent cooling water from directly flowing down near the end of the steel pipe 1.

The external fiber optic cable 7 is connected to a converter 20 using PbS, Ge, or the like for converting light into an electrical signal (for example, a voltage proportional to temperature). It is desirable to use a converter 20 that is effective within a temperature range of at least 300 to 900°C. The output of the converter 20 is led to a recorder or monitor 21 and, at the same time, to a control circuit (or control computer) 22. This control circuit 22
It is for controlling the cooling stop flap 23 shown in the figure, and is configured to, for example, control the operation of a drive device with a servo mechanism for operating the flap via a PID controller. As shown in FIG. 2, the cooling stop flap 23 is disposed below the slit nozzle 4 of the water tank 3, and is not shown in FIG. 1 to simplify the drawing. Axis 2
By rotating about 4, the cooling water flowing down from the slit nozzle 4 can be switched between two states: a state where the cooling water is applied to the steel pipe 1 and a state where it is not applied.

In the apparatus shown in FIGS. 1 and 2 above,
By moving the advancing/retracting rod 18 forward and backward as indicated by the symbol k, the tip portion of the temperature measuring metal cylinder 5 (that is, the temperature sensing end) and the umbrella-shaped nozzle 12 of the outer cylinder 11 are
can be inserted into and removed from the pipe end of the steel pipe 1. By blowing air into the air introduction pipe 13 with these parts inserted into the steel pipe 1, air is ejected from the inside of the steel pipe toward the end of the pipe as shown by arrow g from the umbrella-shaped nozzle 12. By doing so, it is possible to prevent cooling water from entering from the tube end. Further, when the advancing/retracting rod 18 is advanced and the temperature detection end is inserted into the steel pipe 1, the mask plate 19 is located above the end of the steel pipe. Therefore, this mask plate 19 prevents the flat laminar flow from being applied directly to the tube ends, which is also effective in preventing cooling water from entering from the tube ends.
On the other hand, the temperature of the inner surface of the steel pipe 1 can be determined by the radiated light passing through a reflecting mirror or prism 6 to the temperature measuring metal tube 5.
transducer 20 by means of its internal optical fiber and external optical fiber cable 7.
The electric signal obtained is guided to a recorder or monitor 21, and the inner surface temperature of the steel pipe is indicated or recorded. The electrical signal is also sent to the control circuit 22, which controls the cooling to be stopped by operating the flap 23, for example, when the detected temperature reaches a predetermined temperature.

Further, the overall operating procedure of the above-mentioned apparatus will be described below, taking as an example a case where the cooling is controlled to be stopped when a certain temperature is reached after the start of rapid cooling.

First, until the steel pipe 1 is set at a predetermined position on the rotating roll 2 and rotation is started, the flap 23 in FIG.
As shown in the figure, the cooling water is released to prevent the cooling water from splashing onto the steel pipe 1. Also, of course, the advancing/retracting rod 18 is also moving backwards. Next, when the advancing/retracting rod 18 moves forward and the temperature detection end (the tip of the metal cylinder 5 for temperature measurement) and the umbrella-shaped nozzle 12 are inserted into the steel pipe 1, and the rotation of the steel pipe 1 is started, the flap is immediately removed. 23 is lowered to the position Q, and cooling water is applied to the outer surface of the steel pipe 1 as shown by the arrow d using a flat laminar flow. The inner surface temperature of the tube is measured while preventing the cooling water from entering from the tube end by the air jet from the umbrella-shaped nozzle 12 and the mask plate 19, and the flap 23 is immediately returned to the original position P when a predetermined temperature is reached. and stop cooling.

The above procedure describes the case where cooling is stopped at a predetermined temperature, but if you want to perform relatively slow cooling, the flap 23 can be operated repeatedly between PQ and steel pipe 1 intermittently. All you have to do is multiply. In this case, since the tube temperature during cooling is actually measured, the cooling rate can be controlled over a wide range by comparing the temperature curve assumed in advance with the actually measured temperature and controlling the operation of the flap 23. Also in this case, it is of course possible to stop cooling at a predetermined temperature.

Although the embodiment shown in FIG. 1 includes a mask plate 19 for a tube end mask, this may not necessarily be necessary. In other words, when cooling a steel pipe whose ends have already been trimmed, as in normal reheating and quenching, the end surface is perpendicular to the pipe axis, so water cannot flow in from the pipe end without using the mask plate 19. few. Therefore, simply by injecting air from the umbrella-shaped nozzle 12 in the direction of arrow g, it is possible to sufficiently prevent water from entering the pipe. However, in cases such as direct quenching or controlled cooling of seamless steel pipes immediately after rolling, the steel pipes have fins at their ends, and if a flat laminar flow is allowed to flow down, a large amount of water will flow in from the ends. Therefore, in this case, it is desirable to mask the end of the tube with a mask plate 19 as shown in the figure to allow water to escape as indicated by arrow a. This slows down the cooling rate near the tube ends, but this does not pose any problem because the portions near the tube ends with fins are eventually cut off.

Although FIG. 1 only shows the situation near one tube end, the temperature measurement may be performed from only one tube end or from both tube ends. If the measurement is performed from both tube ends, it is also possible to take the average value of the temperatures at both positions and use this for control.

Furthermore, even when temperature is measured from only one tube end, it is necessary to prevent water from flowing in from the opposite tube end. The reason for this is that when air is injected at one end of the tube as shown by arrow g, an air current is generated within the tube, which increases the amount of water flowing in at the opposite end of the tube, and the generated water vapor is carried away and the temperature is measured. This is because there is a possibility that it may be inaccurate. To prevent this,
Either an umbrella-shaped nozzle 12 similar to that described above is inserted into the opposite end of the tube to eject air to prevent water from flowing in, or, as shown in FIG. It is desirable to spray. That is, in the example shown in FIG. 3, a part of the air introduced into the air flow path 10 is ejected from the flap-like opening 25 at the tip as shown by arrow h, flows toward the front end of the tube, and prevents water from entering. To prevent.

FIG. 4 shows an example of an actual measurement record of the tube inner surface actual temperature by controlled cooling of the present invention applied when cooling is stopped at a predetermined temperature. The measurement was carried out using a two-color thermometer using an optical fiber as described above. Here, the flow rate of laminar flow is per 1 m of steel pipe length.
0.3m ³ /min, steel pipe size: outer diameter 139.7mm, wall thickness
13.0mm, steel pipe heating temperature is 920℃. Also, the steel pipe rotation speed is 60 rpm.

In the example shown in Fig. 4, the temperature curve in the figure is A
Water cooling by laminar flow starts from about 850℃ at the point,
Water cooling was stopped at about 650°C, which is the C point. Although a low peak appears along the way near point B due to transformation heat generation, it can be seen that almost linear cooling of about 9° C./sec is achieved on average. Also, after stopping water cooling at point C,
The inner surface temperature of the steel pipe continues to fall to point D and converges at approximately 580°C, but this is because there is a temperature gradient within the pipe wall when cooling is stopped, and the temperature is lower on the outer surface and higher on the inner surface. This corresponds to the process in which this temperature difference gradually decreases and the temperature averages out after water cooling is stopped. Therefore, when setting a convergence temperature such as point D as a target, it is necessary to anticipate the temperature drop as described above in advance and stop water cooling at a temperature that is higher by that amount. However, the ultimate goal is to obtain the pipe material itself after cooling, and to obtain a predetermined pipe material with small variations, so if the relationship between the water cooling stop temperature and the pipe material is known in advance, it is possible to It is also possible to directly set a water cooling stop temperature as a target.

In any case, such control is only possible by actually measuring the temperature of the steel pipe during cooling as in this example, and it is clear from this example that it is actually possible.

In the case of controlled cooling such as the method of this invention, the controlled cooled steel pipe is made into a product as it is cooled, and tempering after cooling is usually not required. Of course, it may also be applied to a tempering process.

For example, when quenching steel pipes that are prone to quench cracking, such as high-carbon steel or high-alloy steel, the pipes are rapidly cooled to near the Ms point and then slowly cooled, or cooling is stopped immediately above the Ms point. Although it is preferable to start cooling again after slow cooling for a while in order to prevent quench cracking, such a cooling method becomes possible by actually measuring the tube temperature during cooling.
In addition, in general, rapid cooling during quenching treatment is
It is sufficient to cool the tube to around the point, but since the temperature of the tube during cooling is unknown, it is usually cooled to around room temperature to allow some margin. However, if the tube temperature is actually measured using the method of this invention, cooling will be stopped near the Ms point.
Cycle time can be shortened. Reducing the cooling time is important to avoid a drop in productivity, especially in the case of online heat treatment such as direct quenching of seamless steel pipes. All of these can be regarded as a type of controlled cooling treatment in that they involve a cooling stop, but in order to adjust the tube strength, a tempering treatment is required after cooling.

Furthermore, the controlled cooling method of the present invention can also be applied to the following treatments.

That is, in a seamless steel pipe rolling line, there may be a reheating furnace located after the reeler and before the sizer (or stretch reducer) for restoring the steel pipe temperature that has decreased during rolling. In the case of normal rolling, the tube is inserted into the reheating furnace even after reeling before the temperature drops below the _{transformation} point. When inserted into a heating furnace, austenite crystal grains can be significantly refined during reheating. So when it happened like this
If the tube is air-cooled after being cooled to Ar ₁ point or less and passed through a sizer after reheating, the tube will have been normalized online during the rolling process, and if it is directly quenched after being sized, the tube will be has undergone normal reheating and quenching online.

If such cooling is to be carried out before the reheating furnace, it is important to cool the entire tube as uniformly as possible and to avoid cooling it more than necessary. This is because the lower the cooling stop temperature, the longer the time required for the next reheating, which impedes the production efficiency of the entire line. The controlled cooling method of the present invention is extremely effective in such cases as well, making it possible to uniformly cool the entire tube and stop cooling just below the Ar ₁ transformation point.

Furthermore, the controlled cooling method of the present invention can also be applied to cooling steel pipes after tempering. In other words, the collapse strength (the crushing strength due to external pressure) of oil well steel pipes depends on the residual stress, and especially when the residual stress in the circumferential direction exists in the form of tension on the outer surface and compression on the inner surface, the collapse strength decreases significantly. On the other hand, when a moderate amount of tensile residual stress exists on the inner surface side, the collapse strength improves. In order to introduce tensile residual stress on the inner surface to improve collapse strength, it is sufficient to forcibly cool the tube after tempering from the outer surface. It is necessary to accurately control the speed and cooling stop temperature. The method of the present invention is also effective as a cooling method in such cases. Also in this case,
With the side effect of reducing the cooling time required after tempering, the tube is cooled while rotating to avoid bending, eliminating the need for subsequent cold straightening and reducing residual stresses in the form that are detrimental to collapse strength. This can also have the effect of avoiding the reintroduction of

Effects of the Invention As is clear from the above explanation, the method of the present invention makes it possible to actually measure the temperature of a steel pipe during cooling of the steel pipe, which was previously considered impossible or difficult. Therefore, it is possible to control the cooling stop temperature or the cooling rate, or both, and therefore, a remarkable effect can be obtained in that the cooling stop temperature and cooling rate of the steel pipe can be accurately controlled in actual operation. By applying it to various steel pipe manufacturing processes including heat treatment of steel pipes, it can contribute to stabilizing the material quality and improving the properties of steel pipes.In particular, it can be used to improve the cooling stop temperature and cooling rate in the heat treatment process of steel pipes. Accurate control makes it possible in actual operation to omit tempering after quenching while accurately controlling quality to obtain steel pipes of the required quality, which significantly reduces steel pipe manufacturing costs. became possible.

[Brief explanation of drawings]

FIG. 1 is a schematic front view showing an example of a situation in which the method of the present invention is being carried out, particularly around the tube end, and FIG. 2 is a schematic diagram showing an example of a situation in which the method of the present invention is being carried out. 3 is a schematic front view showing another example of a situation in which the method of the present invention is implemented, and FIG. 4 is a schematic side view of a steel pipe when the method of the present invention is applied to cooling stop temperature control. FIG. 3 is a diagram showing an example of actual measurement of inner surface temperature.

Claims (1)

[Claims] 1. When cooling a steel pipe, insert at least the temperature detection end of a non-contact temperature measuring device into the inside of the steel pipe, cool the steel pipe with water only from its outer surface while rotating, and cool the inside of the steel pipe while it is being cooled. while sealing at least the vicinity of the temperature detection end against intrusion of cooling water into the inside of the steel pipe by injecting air at
The temperature of the inner surface of the steel pipe during cooling is actually measured non-contact by the temperature measuring device, and the cooling stop temperature and/or
Or a controlled cooling method for steel pipes, characterized by controlling the cooling rate.