JPS601365B2 - Hardening method for metal tubes - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for quenching metal pipes such as steel pipes, and in particular to a so-called axial flow method in which a cooling liquid is flowed along the axial direction on both the inner and outer circumferential sides of the metal pipe to be inserted. This is related to the competition method.

Conventionally, as a method for condensing metal pipes such as steel pipes, a high-pressure cooling liquid such as cooling water is sprayed toward the outer surface of the metal pipe from a number of high-pressure injection nozzles arranged in a ring around the outer circumference of the metal pipe into which moths are to be inserted. A method is known in which the metal tube to be quenched is immersed in a cooling liquid, such as cooling water, in a cooling tank.

However, the former competitive heating method has a problem that the cooling capacity is lower than that of the latter quenching method, and the cooling rate on the inner peripheral surface side of thick-walled pipes is low. In addition to cooling the outer surface by injecting coolant from a high-pressure injection nozzle, a method of inserting a header equipped with an injection nozzle into the metal tube has been put into practical use in order to supplementally cool the inner surface of the metal tube. However, this method is difficult to apply to small diameter pipes, and when processing a large number of metal pipes continuously, the header must be inserted and removed from the metal pipes one by one, which reduces the processing capacity to a certain extent. There were problems such as the fact that it was impossible to increase the amount higher than that. On the other hand, in the latter method of quenching, in which the metal tube is diluted by being thrown into cooling water, simply putting the red-hot metal tube into the cooling water and immersing it will cause the surface of the metal tube to be damaged by the boiling of the cooling water. Since the tube is covered with a vapor film, the cooling rate of the tube becomes slower than the critical cooling rate for martensitic transformation required for normal quenching, and the quenching effect cannot be obtained.

Therefore, in the past, a plurality of injection nozzles were arranged at intervals in the circumferential direction on the outer circumference of the metal tube into which phosphorus was to be charged in the cooling tank, and high-pressure water was injected from the nozzles in the tangential direction of the metal tube. An annular flow is generated along the outer circumference of the metal tube, and in addition to this, an axial water flow is applied to the inner circumference of the metal tube using an appropriate axial jet nozzle. However, in such a quenching method, in order to generate a waste flow on the outer peripheral surface of the metal tube, stationary cooling water that does not directly contribute to cooling the metal tube is also moved, so the energy efficiency is low. Therefore, there is a problem in that the jetting pressure of the cooling water has to be high and the amount of water jetting out has to be increased.Also, in order to uniformly cool the metal pipe in the length direction, it is necessary to set small intervals in the length direction of the metal pipe. Since a large number of injection nozzles must be arranged at the same time, the equipment for carrying out the above method must be complicated and expensive, and furthermore, there is a possibility that one of the injection nozzles may become clogged or There were problems such as the cooling water jetted from each jet nozzle interfering with each other and causing unevenness in the morning. Therefore, the inventors of the present invention have already proposed a so-called "Mari-ryu" type of dawn entry method that can effectively solve the various problems described above.

An outline of the quenching method will be explained with reference to FIG. 1. In FIG. After the red-hot metal tube 4 is inserted into the cylindrical body 1, the outer nozzle is placed close to one end of the cylindrical body 1. The cooling liquid 2 is injected from the outer nozzle 5 to provide a cooling liquid flow 2' along the axial direction between the outer peripheral surface of the metal tube 4 and the inner peripheral surface of the cylindrical body 1, and approximately coaxially with the outer nozzle 5. The cooling liquid is injected from the provided inner nozzle 6 to create a cooling liquid flow 2″ along the axial direction toward the inner peripheral surface of the metal tube 4.
This is a method of giving. In this axial flow type hardening method, if the cooling liquid flows 2' and 2'' are set to a predetermined flow rate or higher,
The cooling liquid that has removed heat from the metal tube 4 quickly flows away toward the rear end of the metal tube 4, and at the same time, the metal tube 4 is not covered by a vapor film, so that the cooling rate exceeds the critical cooling rate required for martensitic transformation. The metal tube 4 can be cooled at a speed of
Furthermore, even without using the header as described above, the metal tube 4
Since the inner peripheral side of the metal tube 4 can be cooled, the metal tube 4 can be hardened continuously and efficiently.

By the way, when the metal tube 4 is quenched by the above-mentioned quenching method, the red-hot metal tube 4 is dropped into the coolant tank 3 from the side and is housed inside the open cylindrical body 1. After that, the cylindrical body 1 will be closed, but when the metal tube 4 is dropped into the cooling liquid tank 3, if the cooling liquid 2 is not flowing, the cooling liquid 2 will flow into both entrance ends of the metal tube 4. A large amount of air and steam generated by evaporation of the coolant 2 are forced into the metal tube 4 at once. The gas remaining in the metal tube 4 in this way is
The cooling liquid flow 2'' injected from the inner nozzle 6 is discharged to the outside from the rear end side of the metal tube 4.
If the metal tube 4 to be hardened is the longest, the gas in the metal tube 4 will be exhausted and the length will be 1 mm, and if there is a large time lag between the insertion of the metal tube 4 and the injection of the coolant, In this case, the gas remains in the metal tube 4 for a long time, and as a result, there are places where the gas is not cooled quickly due to the presence of the gas, so the metal tube 4 as a whole may become uneven, curved, or even have poor roundness. There is a problem that arises. In order to solve this problem, before inserting the metal tube 4 into the cooling liquid tank 3, the cooling water flows 2' and 2 of the flow rate necessary for steady hardening are applied.
'' may be allowed to flow into the cooling liquid tank 3 in advance, but since the flow rate is quite large, high pressure is generated due to the narrowing of the flow path area when the knot-shaped body 1 is closed, and the cylindrical It becomes difficult to close the body 1, and when a large amount of coolant 2 is injected from the nozzles 5 and 6 with the cylindrical body 1 open, the inside of the coolant tank 3 becomes turbulent or turbulent. As a result, there are problems such as the inserted metal tube 4 may not fall to the proper position in the open cylindrical body 1.This invention was made in view of the above circumstances, An object of the present invention is to provide a hardening method that can harden a metal pipe by a rolling type hardening method so that the metal pipe does not suffer from curvature or poor roundness after hardening is completed. In other words, before applying a cooling water flow (so-called bag flow) along the axial direction to the metal tube to be inserted, gas (mainly As mentioned above, if residual air (air) remains, metal pipes are likely to bend, etc. Therefore, in order to prevent the occurrence of distortion, the gas is quickly discharged from the submerged metal pipes placed in the coolant. The inventors of the present invention conducted extensive research and found that in order to quickly discharge gas from inside the metal tube, an axial flow of a predetermined flow rate must be generated in the coolant tank before the metal tube is inserted into the coolant tank. It is advantageous to keep
It was discovered that the required minimum flow rate can be determined based on the cross-sectional area of the flow path on the inner peripheral side of the metal pipe to be inserted and its length.

This invention was made based on the above knowledge, and after a red-hot metal tube is immersed in a cooling liquid, a cooling liquid flow is applied to the inner and outer circumferential sides of the metal tube along the marbling direction, and the metal tube is quenched. To do this, before inserting the metal tube into the coolant and immersing it, the flow rate Q per unit time of the coolant flow generated in advance in the coolant tank is determined by the closed area S on the inner peripheral side of the metal tube. This is characterized by setting the product of Q and length 1 to 30 double notes or more (Q≧30$1).

Hereinafter, an example of an experiment conducted by the inventors of the present invention in order to investigate the correlation between the flow rate of the cooling water that is preliminarily flowed into the cooling liquid tank and the amount of deformation that finally occurs in the metal tube will be shown.

The metal tube used in this experiment was a raw tube with no uneven thickness or bend, and its dimensions were 110 to 34 m in diameter, 6 to 18 m in wall thickness, 9 to 13 m in length, and its composition was C: 0. .18~0.
26%, Si: 0.16-0.26%, Mn: 0.81
~1.39%, and the balance is Fe and impurities.

Moreover, the competition start temperature was set at 89,000 to 94,000. The experimental device has an openable and closable cylindrical body that can accommodate the steel pipe almost horizontally, and cools the inner and outer circumferential sides of the steel pipe housed in the cylindrical body in the direction of the bag line. A cooling tank equipped with an axial flow supply device capable of injecting water was used. Furthermore, the flow rate of the cooling water was determined by using a precise Pitot tube type flow rate measuring device as the product of the measured value and the inner open square area of the steel pipe used in the experiment. The experimental method was to change the flow rate of cooling water that was previously flowed into the cooling tank each time quenching was performed, and measure the flow rate of the cooling water flowing through the steel pipe immediately after the steel pipe was placed in the cooling tank for a unit time. After that, the amount of cooling water on the inner and outer circumferential sides of the steel pipe was increased to the desired flow rate required for quenching, and the amount of deformation of the steel pipe was determined as the maximum amount of bending after quenching was completed. Figure 2 shows the experimental results, and the vertical axis shows the deformation amount 6 (side) and the length 1 (side).
The horizontal axis shows the flow rate Q (d'h) of the cooling water pre-flowed into the cooling tank, the inner exit area S (pillow) and the length 1 (skin) of the steel pipe. It shows the ratio to the product of Q/SI, that is, the water volume ratio Q/SI. As is clear from FIG. 2, it is recognized that when the water ratio becomes about 300 or more, the degree of curvature decreases rapidly. By the way, considering the horizontal transfer of steel pipes, it is considered that the practically acceptable degree of bending of the steel pipe is 6/1≦4×10-3.Therefore, in this invention, the metal pipe into which the moth is to be inserted is The flow rate Q (in/h) of the cooling water that is flowed into the cooling facility before inputting the cooling water should be set to an amount that satisfies the degree of curvature of 6 no 1 ≦ 4 × 10-3, that is, Q/SI ≧ 300 determined from Fig. 2. (Q≧3
0$1). In addition, if the flow rate Q (in/h) of cold water that is flowed into the cooling tank in advance before the metal pipe to be filled with rice bran is immersed in the cooling tank is Q≧30 1 as described above. , deformation of the metal tube can be sufficiently prevented, but if the flow rate Q is increased too much, not only will power be consumed unnecessarily, but the metal tube that has been immersed and diluted will fall to its intended position. In addition, the effect of improving the degree of curvature is saturated, so when carrying out the present invention, it is preferable to set the flow rate Q to 30$1≦Q≦50.

As is clear from the above explanation, according to the dawn insertion method of the present invention, the gas inside the metal tube can be quickly discharged immediately after the metal tube is placed in the cooling liquid tank, so that each part of the metal tube can be discharged immediately. The cooling rate of the steel pipe becomes uniform immediately after it is poured into the cooling liquid tank and concentrated, and as a result, it is possible to reliably prevent the occurrence of curvature or poor roundness of the metal pipe after quenching is completed. A uniform hardness distribution can be obtained in the circumferential direction, thickness direction, and longitudinal direction.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining the axial flow type dawn entry method already proposed by the inventors of the present invention, and FIG. 2 is a diagram showing the results of an experimental example of the present invention. Figure 1 Figure 2

Claims (1)

[Claims] 1. A metal tube to be hardened is immersed almost horizontally in a coolant in a coolant tank, and a coolant flow is applied to the inner and outer circumferential sides of the metal tube in the axial direction. In the quenching method of quenching the metal tube by flowing the metal tube, before inserting and arranging the metal tube into the cylindrical body, the metal tube in the cooling liquid tank should be placed in a flow rate of coolant determined by the following formula. A method for quenching a metal tube, which is characterized by applying water in advance along the axial direction of the metal tube. Q≧300Sl However, Q: Coolant flow rate (m^3/h) S: Channel cross-sectional area on the inner peripheral side of the metal tube to be quenched (m^2
)l: Length (m) of the metal tube to be hardened.