JP5360046B2 - Manufacturing method of hot extruded tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a hot extrusion tube that can reduce uneven thickness caused to the obtained extrusion tube without causing problems of decrease in productivity and deterioration of a tool unit requirement. <P>SOLUTION: The method of manufacturing a hot extrusion tube is a method to manufacture the hot extrusion tube that is a seamless tube by a hot extrusion pipe making method using a hollow billet, and is characterized as follows. The hollow billet is heated so that an outer periphery temperature is made 1,050-1,300&deg;C, and an inside and outside temperature gradient &Delta;T is made to fill formula (1): &Delta;T=Tx-Ty&ge;150, and the hollow billet is inserted in a container to be processed by a hot extrusion, wherein the inside and outside temperature gradient is &Delta;T(&deg;C), the outer periphery temperature is Tx(&deg;C), and an inner periphery temperature is Ty(&deg;C). In the invention, as the hollow billet, it is desirable to use the hollow billet whose material is a duplex stainless steel. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a method for producing a hot extruded tube, which is a seamless tube, by a hot extrusion tube forming method represented by the Eugene Sejurune method. More specifically, the present invention relates to a method for manufacturing a hot extruded tube capable of reducing uneven thickness generated in the obtained hot extruded tube.

  The hot extrusion pipe making method represented by the Eugene Sejurune method is a method of producing a seamless pipe using a hollow billet, and the hot extrusion pipe making method adds a relatively high degree of processing to the hollow billet. Because of its excellent pipe forming properties, it is frequently used in the production of seamless pipes made of difficult-to-process materials such as high alloys.

  FIG. 1 is a schematic view showing hot extrusion processing by a hot extrusion pipe making method using a hollow billet. In the figure, a container 1, a die 2 detachably mounted using a die holder 3 and a die backer 4, a mandrel 5, a stem 6, a dummy block 7, a glass disk 8, a die backing ring 9, A hollow billet B and an extruded tube P are shown.

  In the hot extrusion pipe manufacturing method, after the hollow billet B heated to a predetermined temperature is accommodated in the container 1, the mandrel 5 is inserted into the axis of the hollow billet B. In this state, when the stem 6 is moved (moving in the direction of the white arrow in the figure) along with the driving of the ram (not shown), the bottom side end surface of the hollow billet B is pressed through the dummy block 7 to be a material. The hollow billet deforms and comes into close contact with the container 1, the mandrel 5 and the glass disk 8. At this time, the glass disk 8 used as a lubricant is pressed against the pressed hollow billet B and deformed, and is in close contact with the die holder 3 and the die. By pressing the bottom side end face of the hollow billet B in this way, the material is filled (filled up) in the container 1.

  When the bottom side end surface of the hollow billet B is further pressed with the material filled up in the container 1, the extruded tube P, which is a seamless tube, is extruded from the gap formed by the die 2 and the mandrel 5. can get. When extruding a material from the gap formed by the die 2 and the mandrel 5, if the position of the core of the mandrel 5 is displaced with respect to the core of the die 2, the thickness of the resulting extruded tube becomes uneven and biased.

  FIG. 2 is a cross-sectional view schematically showing uneven thickness generated in a hot extruded tube. When the mandrel core is displaced with respect to the die core when the material is extruded, the center of the inner surface Py and the center of the outer surface Px of the obtained extruded tube P are displaced as shown in FIG. Thickness is uneven. When such uneven thickness occurs, as shown in the figure, the angle A formed by the thinnest portion and the thickest portion is usually 180 °. If the uneven thickness generated in the extruded tube exceeds the standard, the extruded tube will be discarded as defective, or the portion where the uneven thickness exceeds the standard will be discarded, resulting in a large material loss and a deteriorated production yield of the extruded tube. There was a problem.

  Various proposals have heretofore been made with respect to a method for reducing the uneven thickness generated in the extruded tube obtained by the hot extrusion tube forming method. For example, there are Patent Documents 1 and 2. In the method of manufacturing a hot extruded tube proposed in Patent Document 1, an extrusion die and a centering die are prepared, and the mandrel is first held in a hole provided in the centering die. After centering, the hollow billet is pressed by a predetermined amount to bring the hollow billet into close contact with the outer surface of the mandrel. Next, in place of the centering die, an extrusion die is mounted, and then a hollow billet is further pressed to obtain an extruded tube.

  In the method for manufacturing a hot-extruded tube proposed in Patent Document 1, such a replacement work is required in which the centering die is removed and the extrusion die is attached during the extrusion process, and this replacement work takes time. Therefore, productivity is significantly reduced. Furthermore, when the hollow billet is pressed by a predetermined amount, it is necessary to perform a replacement work, and there is a problem that it becomes difficult to control the pressing to the hollow billet.

  In the method for manufacturing a hot-extruded tube proposed in Patent Document 2, a die holder is provided with a tool portion that restrains the tip portion of the hollow billet, and the outer diameter Db (mm) of the hollow billet and the inner diameter Dh (mm) of the tool portion of the die holder. ), And after satisfying 0.5 mm ≦ Dh−Db ≦ 0.025 × Dc and Dc−Dh> 0, a hollow billet is extruded to obtain an extruded tube. Here, Dc is the inner diameter (mm) of the container.

  In Patent Document 2, the hollow billet is centered well and the uneven thickness can be reduced by inserting the tip of the hollow billet into the tool portion of the die holder having a smaller diameter than the container. However, the method for manufacturing a hot-extruded tube proposed in Patent Document 2 requires that the inner diameter Dh and the container inner diameter Dc of the tool portion of the die holder be managed with high accuracy. There is a problem that deterioration occurs.

Japanese Patent Publication No.59-4206 Japanese Patent Laid-Open No. 7-1306710

  As described above, in the production of a hot extruded tube by the hot extrusion tube making method using a hollow billet, there is a problem that the production yield is deteriorated due to uneven thickness generated in the obtained extruded tube. The conventional method of manufacturing a hot-extruded tube can improve the uneven thickness. However, it is necessary to replace the die in the middle of processing with a centering die, or to replace the die for extruding. Since it is necessary to manage the inner diameter of the portion and the inner diameter of the container with high accuracy, there is a problem in that productivity is lowered and tool basic unit is deteriorated.

  This invention is made | formed in view of such a condition, and can reduce the uneven thickness which arises in the obtained extruded pipe, without generating the problem of a fall of productivity and the deterioration of a tool basic unit. It aims at providing the manufacturing method of a hot extrusion pipe | tube.

  In order to solve the above problems, the present inventors conducted various tests and made extensive studies. As a result, when heating the hollow billet, the inner peripheral portion of the hollow billet was set to a lower temperature than the outer peripheral portion, and the hollow Finding that by inserting a billet into a container and performing hot extrusion, it is possible to reduce the uneven thickness that occurs in the resulting extruded tube without causing problems of reduced productivity and tool unit deterioration. did.

  The present invention has been completed on the basis of the above findings, and the gist thereof is the following (1) and (2) hot-extruded tube manufacturing methods.

(1) A method for producing a hot-extruded pipe that is a seamless pipe by a hot-extrusion pipe-making method using a hollow billet,
The hollow billet is heated so that the outer peripheral temperature is 1050 to 1300 ° C. and the internal / external temperature difference ΔT is a temperature satisfying the formula (1), and the hollow billet is inserted into a container and hot extruded. A method for manufacturing a hot-extruded tube.
ΔT = Tx−Ty ≧ 150 (1)
Here, the internal / external temperature difference ΔT (° C.), the outer peripheral temperature Tx (° C.), and the inner peripheral temperature Ty (° C.).

(2) The method for producing a hot-extruded tube according to (1), wherein the material of the hollow billet is duplex stainless steel.

In the method for producing a hot-extruded tube of the present invention, the inner peripheral temperature and the outer peripheral temperature of the hollow billet are measured by the following procedure.
(1) The end face temperature of the hollow billet is measured to obtain a temperature distribution in the radial direction.
(2) In the obtained radial temperature distribution, the temperature at the inner surface position is defined as the inner peripheral temperature, and the maximum temperature within a predetermined width from the outer surface position is defined as the outer peripheral temperature.

  FIG. 3 is a schematic view showing a temperature distribution in the radial direction on the end face of the heated hollow billet. The temperature distribution in the radial direction of the hollow billet shown in the figure is obtained from the result of measuring the end face of the hollow billet with an infrared radiation thermometer immediately before the induction heated hollow billet is inserted into the container. It is what was done. As shown in the drawing, the temperature distribution in the radial direction at the end face of the hollow billet tends to decrease in temperature in the vicinity of the outer surface, and this tendency is generated when the atmosphere extracts heat from the outer surface of the hollow billet.

  In the present invention, in order to evaluate the temperature distribution by eliminating the influence of the temperature drop in the vicinity of the outer surface, the maximum temperature in the range of a predetermined width from the outer surface position is set as the outer peripheral temperature. Therefore, the predetermined width when obtaining the outer peripheral temperature is set wider than the width of the temperature lowering portion in the vicinity of the outer surface. What is necessary is just to set the predetermined width | variety at the time of calculating | requiring outer periphery temperature according to the material and atmospheric temperature of a hollow billet.

The method for producing a hot extruded tube of the present invention has the following remarkable effects.
(1) The hollow billet is heated so that the inner peripheral temperature is lower than the outer peripheral temperature, and the internal / external temperature difference is 150 ° C. or more. By subjecting the hollow billet to hot extrusion, uneven thickness generated in the extruded tube can be reduced.
(2) For this reason, the uneven thickness which arises in an extrusion pipe can be reduced, without generating the problem of the fall of productivity and the deterioration of a tool basic unit.

It is a schematic diagram which shows the hot extrusion process by the hot extrusion pipe manufacturing method using a hollow billet. It is sectional drawing which shows typically the thickness deviation which arises in a hot extrusion pipe | tube. It is a schematic diagram which shows the temperature distribution of the radial direction in the end surface of the heated hollow billet. It is a figure which shows the relationship between the internal / external temperature difference of a hollow billet, and the thickness deviation rate of an extruded tube.

As described above, the method for manufacturing a hot-extruded tube of the present invention is a method for manufacturing a hot-extruded tube that is a seamless tube by a hot-extrusion pipe manufacturing method using a hollow billet, and heating the hollow billet. The outer peripheral portion temperature is 1050 to 1300 ° C., and the inner / outer temperature difference ΔT is set to a temperature satisfying the expression (1), and the hollow billet is inserted into a container and subjected to hot extrusion.
ΔT (° C.) = Tx−Ty ≧ 150 (1)
Here, the internal / external temperature difference ΔT (° C.), the outer peripheral temperature Tx (° C.), and the inner peripheral temperature Ty (° C.). Below, the reason and preferable range which prescribed | regulated the manufacturing method of the hot extrusion pipe | tube of this invention as mentioned above are demonstrated.

  In the method for producing a hot-extruded tube of the present invention, the hollow billet is heated, and, as defined by the above formula (1), the internal / external temperature difference which is the difference between the outer peripheral temperature and the inner peripheral temperature is 150 ° C. or more. That is, the inner peripheral temperature is made lower than the outer peripheral temperature.

  In the conventional method for producing a hot-extruded tube, the hollow billet is heated so that the temperatures of the outer peripheral portion and the inner peripheral portion are uniform, and the hollow billet is inserted into a container for hot extrusion. In this case, after the bottom side end surface of the hollow billet is pressed to fill up the material, the bottom side end surface is further pressed to allow the material to pass through the gap between the die and the mandrel while being extruded (initial stage of extrusion). The mandrel core was displaced from the die core, resulting in uneven thickness of the resulting extruded tube.

  In the method for producing a hot-extruded tube of the present invention, the bottom end surface is further formed after the material is filled up in the container by heating the hollow billet and lowering the inner peripheral temperature compared to the outer peripheral temperature. When the material is pushed and passed through the gap between the die and the mandrel (initial stage of extrusion), the surface pressure applied from the material to the mandrel directly under the die increases. This increased contact pressure promotes self-centering to guide the mandrel core to the position of the die core. Therefore, in the top portion of the resulting extruded tube (the portion that passed through the die at the beginning of extrusion processing) Can be reduced.

  Thus, by promoting self-centering in the initial stage of extrusion, the method for producing a hot-extruded tube of the present invention can reduce uneven thickness over the entire length of the obtained extruded tube. This is presumably due to the promotion of self-centering at the beginning of the extrusion process, which promotes self-centering of the mandrel core even when the temperature of the hollow billet subsequently changes.

  As described above, the method for producing a hot-extruded tube of the present invention reduces the uneven thickness generated in the extruded tube by setting the inner peripheral temperature to a lower temperature than the outer peripheral temperature and setting the temperature difference to 150 ° C. or more. Can be reduced. For this reason, the manufacturing method of the hot-extruded tube of the present invention does not require a replacement operation of replacing the die with the centering die during the processing and mounting the extrusion die, and the inner diameter of the tool portion and the container inner diameter of the die holder are not required. There is no need to manage with high accuracy. Therefore, in the method for manufacturing a hot-extruded tube of the present invention, the uneven thickness generated in the extruded tube can be reduced without causing the problems of productivity reduction and tool unit deterioration.

  In the method for producing a hot-extruded tube of the present invention, the temperature difference between the inner and outer surfaces of the hollow billet is preferably 300 ° C. or less. If the temperature difference between the inside and outside of the hollow billet exceeds 300 ° C., the inner peripheral temperature of the hollow billet is excessively lowered, the deformation resistance of the hollow billet is increased, and the heat required for extruding the material by pressing the bottom side end face The pushing force of the intermediate extrusion device increases. If the pushing force required for extruding the material exceeds the equipment capacity of the hot extrusion device, the extrusion process stops and the tool used may be significantly damaged. If the extrusion force required to extrude the material exceeds the equipment capacity of the hot extrusion equipment, it is possible to perform extrusion without stopping by increasing the equipment capacity of the hot extrusion equipment. Rises.

  When the temperature of the outer peripheral portion of the hollow billet exceeds 1300 ° C., the hot workability is remarkably lowered, and cracks and covering wrinkles are likely to occur on the surface after hot tube extrusion. In addition, if the temperature of the inner peripheral portion of the hollow billet is less than 900 ° C., the deformation resistance of the material increases, so that the pushing force required when extruding the material increases, which may exceed the equipment capacity of the hot extrusion device. There is. For this reason, when the outer peripheral temperature of the hollow billet is less than 1050 ° C., it becomes difficult to set the internal / external temperature difference to 150 ° C. or more. From these, the manufacturing method of the hot extrusion pipe | tube of this invention heats a hollow billet, and makes peripheral part temperature 1050-1300 degreeC. Preferably, it is 1150-1280 degreeC.

  Since the lower limit of the outer peripheral temperature of the hollow billet varies depending on the equipment capacity of the hot extrusion device, in actual operation, the lower limit of the outer peripheral temperature of the hollow billet is set to 1050 to 1300 according to the pushing force of the hot extrusion device. What is necessary is just to set from the range of ° C.

  In the method for producing a hot-extruded tube of the present invention, the hollow billet having the above-described temperature condition is inserted into a container and hot-extruded. In other words, the above temperature condition means a temperature condition “immediately before inserting the hollow billet into the container”. This is because it is difficult to measure the temperature distribution of the hollow billet inserted into the container.

  Further, “immediately before being inserted into the container” means that the hollow billet having the above-described temperature condition is immediately inserted into the container and subjected to hot extrusion without further processing. This is to keep the temperature change over time to a minimum and to hot extrude the hollow billet as close to the above temperature conditions as possible. For this reason, it is preferable that the time required for inserting the hollow billet into the container and starting the hot extrusion process is as short as possible.

  The internal / external temperature difference, the outer peripheral temperature and the inner peripheral temperature can be set to desired temperatures by changing the heating conditions. For example, when heating a hollow billet with an induction heating device, the internal / external temperature difference, the outer peripheral temperature, and the inner peripheral temperature are set to desired temperatures by changing heating conditions such as input power amount, heating time, and frequency. Can do.

  In the method for producing a hot extruded tube of the present invention, the material of the hollow billet is preferably a duplex stainless steel. When the material of the hollow billet is a duplex stainless steel, the duplex stainless steel is more dependent on the deformation resistance (sensitivity) with respect to temperature than the austenitic stainless steel. For this reason, if the material of the hollow billet is duplex stainless steel, the manufacturing yield of the extruded tube can be remarkably improved by reducing the uneven thickness of the extruded tube by the manufacturing method of the hot extruded tube of the present invention.

  The method for producing a hot-extruded tube of the present invention is, as a duplex stainless steel, in mass%, C: 0.03% or less, Si: 1% or less, Mn: 0.1-4%, Cr: 20-35. %, Ni: 3 to 10%, Mo: 0 to 6%, W: 0 to 6%, Cu: 0 to 3%, N: 0.15 to 0.60%, the balance being Fe and impurities It is preferable to use a duplex stainless steel having the following chemical composition. In addition to the above elements, one or more of Ca, Mg, and rare earth elements (REM) may be contained.

  The reason why it is preferable to make the chemical composition of the duplex stainless steel as described above in the method for producing a hot extruded tube of the present invention will be described below. In the following description, “%” display of the content of each element means “mass%”.

C: 0.03% or less C is an element having the effect of stabilizing the austenite phase and improving the strength, and the effect of precipitating carbides at the time of temperature increase in heat treatment to obtain a fine structure. However, if its content exceeds 0.03%, carbide precipitation becomes excessive due to heat effects such as heat treatment and welding, and the corrosion resistance and workability of the steel deteriorate. For this reason, it is preferable to make the upper limit into 0.03%.

Si: 1% or less Si is an element that is effective as a deoxidizer, and is also an element that has the effect of precipitating intermetallic compounds at the time of temperature increase in heat treatment to obtain a fine structure. be able to. However, if its content exceeds 1%, the precipitation of intermetallic compounds becomes excessive due to the heat effect during heat treatment and welding, and the corrosion resistance and workability of the steel deteriorate, so the Si content should be 1% or less. preferable.

Mn: 0.1 to 4%
Mn is an element that is effective as a deoxidizer, as is the case with the above-mentioned Si, and fixes S inevitably contained in steel as a sulfide to improve hot workability. The effect is obtained with a content of 0.1% or more. However, if the content exceeds 4%, not only the hot workability is lowered, but also the corrosion resistance is adversely affected. For this reason, the Mn content is preferably 0.1 to 4%.

Cr: 20 to 35%
Cr is a basic component effective for maintaining corrosion resistance and improving strength. These effects can be obtained by setting the Cr content to 20% or more. However, if the Cr content exceeds 35%, the σ phase is likely to precipitate, and both corrosion resistance and toughness deteriorate. Therefore, the Cr content is preferably 20 to 35%.

Ni: 3 to 10%
Ni is an element contained for stabilizing the austenite phase and obtaining a two-phase structure. When the content is less than 3%, a ferrite phase is the main component and a two-phase structure cannot be obtained. On the other hand, if it exceeds 10%, the austenite is the main component and a two-phase structure cannot be obtained, and since Ni is an expensive element, the economy is also impaired, so the Ni content is 3 to 10%. Is preferred.

Mo: 0 to 6% (including no additive)
Mo is an element that improves the pitting corrosion resistance and crevice corrosion resistance and improves the strength by solid solution strengthening, and can be contained as necessary. On the other hand, if it is contained excessively, the σ phase is liable to precipitate and the toughness deteriorates. For this reason, it is preferable to make Mo content into 0 to 6%.

W: 0 to 6% (including no additive)
W, like Mo, is an element that improves the pitting corrosion resistance and crevice corrosion resistance and improves the strength by solid solution strengthening, and thus can be contained if necessary. On the other hand, if it is contained excessively, the σ phase is liable to precipitate and the toughness deteriorates. For this reason, the W content is preferably 0 to 6%.

Cu: 0 to 3% (including no additive)
Cu is an element that improves the corrosion resistance and intergranular corrosion resistance, and can be contained as necessary. On the other hand, when the content exceeds 3%, the effect is saturated, and conversely, hot workability and toughness are lowered. Therefore, the Cu content is preferably 0 to 3%.

N: 0.15-0.60%
N is an element that enhances the stability of austenite and enhances the pitting corrosion resistance and crevice corrosion resistance of the duplex stainless steel. Moreover, it is an element which stabilizes an austenite phase and improves strength in the same way as C. If the content is less than 0.15%, a sufficient effect cannot be obtained. On the other hand, if it exceeds 0.60%, the toughness and hot workability deteriorate, so the content is preferably 0.15 to 0.60%.

  In the method for producing a hot-extruded tube of the present invention, the duplex stainless steel may further contain one or more of Ca, Mg and rare earth elements (REM) in addition to the above elements. . The reason why these elements may be contained and the contents at that time are as follows.

One or two or more of Ca: 0.01% or less, Mg: 0.01% or less, and rare earth element (REM): 0.2% or less. These components may be contained as necessary. If any of them is contained, S that inhibits hot workability is fixed as a sulfide, and there is an effect of improving hot workability. However, if both Ca and Mg exceed 0.01%, and if REM exceeds 0.2%, a coarse oxide is formed, which leads to a decrease in hot workability. Therefore, when these are contained, the upper limit of each is preferably 0.01% for Ca and Mg and 0.2% for REM.

  Here, REM is a general term for 17 elements in which Y and Sc are combined with 15 lanthanoid elements, and one or more of these elements can be contained. Further, the content of REM means the total content of these elements.

  The “impurities” in “Fe and impurities” refers to those mixed due to various factors in the manufacturing process, including raw materials such as ore or scrap, when the alloy is manufactured industrially.

As for duplex stainless steel, what consists of said chemical composition can be manufactured with the manufacturing equipment and manufacturing method which are normally used for commercial production. For example, for melting of duplex stainless steel, an electric furnace, an Ar—O ₂ mixed gas bottom blowing decarburization furnace (AOD furnace), a vacuum decarburization furnace (VOD furnace), or the like can be used. The molten metal may be cast into an ingot, or may be cast into a rod-shaped billet by a continuous casting method. These billets are perforated into hollow billets, and the obtained hollow billets are used for hot extrusion by the method for producing hot extruded tubes of the present invention to obtain hot extruded tubes made of duplex stainless steel. Can be manufactured.

  In order to verify the effect of the method for manufacturing a hot-extruded tube of the present invention, a hollow billet is hot-extruded by a hot-extrusion method using the hot-extruding tube manufacturing method described with reference to FIG. A test was conducted to obtain an extruded tube.

[Test method]
In this test, a hollow billet made of duplex stainless steel was induction-heated, and the hollow billet was inserted into a container and subjected to hot extrusion to obtain a seamless tube. The hollow billet was made of a duplex stainless steel corresponding to A312-S39274 whose material is defined by ASTM. Table 1 shows the typical composition of the hollow billet made of the duplex stainless steel used in this test.

  The conditions for induction heating of the hollow billet are: the frequency is 60 Hz, the input power is adjusted to 525 to 600 kW, the heating time is adjusted to 60 to 120 seconds, and the outer peripheral temperature and the inner temperature of the heated hollow billet are adjusted. The peripheral temperature was set to a desired temperature.

  Immediately before the heated hollow billet is transported and inserted into the container, the temperature distribution of the end surface on the top side of the hollow billet (the end surface on the side pressed against the die with the glass disk interposed) is measured with an infrared radiation thermometer (NEC Avio). It was measured by Infrared Technology Co., Ltd., Thermo Viewer. The temperature distribution in the radial direction as shown in FIG. 3 is obtained from the measured temperature distribution of the end face. In the obtained temperature distribution, the temperature at the inner surface position is defined as the inner peripheral temperature, and the maximum in the range of 10 mm from the outer surface position. The temperature was the outer peripheral temperature.

  In this test, the hollow billet whose temperature distribution was measured by an infrared radiation thermometer was immediately inserted into a container and subjected to hot extrusion without further processing. The time required from the measurement of the temperature distribution of the hollow billet by the infrared radiation thermometer to the insertion into the container to start the hot extrusion process was about 15 seconds.

In this test, test no. 1-6 and test no. Using hollow billets having different sizes from 7 to 12, extruded pipes having different sizes were finished by hot extrusion. Test No. The test conditions in 1-6 are as follows.
Hollow billet: outer diameter 177.0mm, inner diameter 29.0mm, length 417mm
Tool dimensions: Die inner diameter 34.7 mm, mandrel outer diameter 26.0 mm,
Container inner diameter 182.0mm
Extruded tube: Outer diameter 34.0 mm, wall thickness (average) 4.0 mm, length 24738 mm

In addition, Test No. The test conditions in 7-12 are as follows.
Hollow billet: outer diameter 177.0mm, inner diameter 31.0mm, length 466mm
Tool dimensions: Die inner diameter 40.7 mm, mandrel outer diameter 28.0 mm,
Container inner diameter 182.0mm
Extruded tube: Outer diameter 40.0 mm, wall thickness (average) 6.0 mm, length 16299 mm

  Table 2 shows the test category, test number, extrusion tube size, hollow billet temperature, and test results. In Table 2, as the temperature of the hollow billet, the outer periphery temperature, the inner periphery temperature, and the inner / outer temperature difference obtained from the obtained radial temperature distribution are shown. The uneven thickness evaluation is shown.

[Evaluation criteria]
Observing the uneven thickness of the obtained extruded tube by visual observation, measuring the thickness (t1) of the thinnest part as shown in FIG. 2 and the thickness (t2) of the thickest part, The thickness (t3 and t4) was measured at ± 90 ° position from the thickest part. Thickness is measured by cutting the extruded tube at a position of 200 mm in the longitudinal direction from the end surface on the top side (the end surface that is initially processed by hot extrusion), and the thickness at the cut surface is measured by a digital hand. The measurement was performed with a caliper (manufactured by Furusato Seiki Seisakusho Co., Ltd.)

From the measured thickness (t1, unit mm) of the thinnest part and the thickness (t2, unit mm) of the thickest part, the uneven thickness value h1 (mm) is calculated by the following equation (2). did.
h1 = t2-t1 (2)
Further, the thickness deviation rate h2 (%) was calculated from the measured thicknesses (t1 to t4, unit mm) by the following equation (3).
h2 = (t2-t1) / ta (3)
However, the average thickness ta (mm) is the average of the measured four thicknesses (t1 to t4).

The meanings of the symbols in the “Evaluation of uneven thickness” column shown in Table 2 are as follows:
(Circle): It shows that the calculated thickness deviation rate is 20% or less.
X: Indicates that the calculated thickness deviation ratio exceeded 20%.

[Test results]
FIG. 4 is a diagram showing the relationship between the internal / external temperature difference of the hollow billet and the thickness deviation rate of the extruded tube. From the figure, it was confirmed that the difference in temperature between the inside and outside of the hollow billet and the wall thickness ratio of the extruded tube had a correlation, and that the wall thickness ratio decreased when the inside and outside temperature difference was increased.

  From FIG. 4 and Table 2, test no. 1 to 3 and test no. 7 to 12, the internal / external temperature difference Δt (° C.) of the hollow billet is 150 ° C. or more satisfying the above-mentioned expression (1), the thickness deviation rate of the extruded tube is 20% or less, and the thickness deviation evaluation is all “good”. It was. On the other hand, test No. which is a comparative example. 4 to 6, the internal / external temperature difference Δt (° C.) of the hollow billet is less than 150 ° C. that does not satisfy the formula (1), the thickness deviation rate of the extruded tube exceeds 20%, and the thickness deviation evaluation is x. became.

  From these, the method for producing a hot-extruded tube of the present invention is such that a hot billet is heated to extrude a hollow billet having an internal-external temperature difference Δt (° C.) of 150 ° C. or higher that satisfies the above equation (1). It became clear that uneven thickness generated in the tube can be reduced.

The method for producing a hot extruded tube of the present invention has the following remarkable effects.
(1) The hollow billet is heated so that the inner peripheral temperature is lower than the outer peripheral temperature, and the internal / external temperature difference is 150 ° C. or more. By subjecting the hollow billet to hot extrusion, uneven thickness generated in the extruded tube can be reduced.
(2) For this reason, the uneven thickness which arises in an extrusion pipe can be reduced, without generating the problem of the fall of productivity and the deterioration of a tool basic unit.

  Therefore, by applying the method for producing a hot-extruded pipe of the present invention to the production of a steel pipe that is a seamless pipe, it is possible to produce a high-quality steel pipe with reduced unevenness and to improve the production yield. Can do.

1: container, 2: die, 3: die holder, 4: die backer,
5: Mandrel, 6: Stem, 7: Dummy block, 8: Glass disc,
9: die backing ring, B: hollow billet, P: hot extruded tube, Px: outer surface,
Py: inner surface, t1: wall thickness of the thinnest part, t2: wall thickness of the thickest part,
A: Angle formed by the thinnest part and the thickest part

Claims (2)

A method of producing a hot extruded tube that is a seamless tube by a hot extrusion tube making method using a hollow billet,
The hollow billet is heated so that the outer peripheral temperature is 1050 to 1300 ° C. and the internal / external temperature difference ΔT is a temperature satisfying the formula (1), and the hollow billet is inserted into a container and hot extruded. A method for manufacturing a hot-extruded tube.
ΔT = Tx−Ty ≧ 150 (1)
Here, the internal / external temperature difference ΔT (° C.), the outer peripheral temperature Tx (° C.), and the inner peripheral temperature Ty (° C.).   The method for producing a hot-extruded tube according to claim 1, wherein the material of the hollow billet is duplex stainless steel.

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