JP2012030270A - Method for manufacturing metal tube with uneven thickness - Google Patents

Abstract

When manufacturing a differential thickness metal tube having a different thickness in the circumferential direction of the tube, variations in the structure and mechanical properties in the circumferential direction are reduced.
In manufacturing a differential metal pipe having a non-uniform circumferential thickness from a metal pipe having a uniform circumferential thickness, the metal pipe is warmed over the entire circumferential direction. After heating to a hot temperature region and then further partially heating a specific position in the circumferential direction to give a temperature distribution in the circumferential direction of the metal tube, reduction rolling is performed.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a differential thickness metal tube having a different thickness in the circumferential direction of the tube.

In recent years, as a part of environmental measures, weight reduction of a vehicle body for the purpose of improving the fuel efficiency of an automobile has been promoted. There are many automobile parts that have a solid structure such as a stabilizer or a drive shaft that is manufactured from a metal bar. In these parts, since the material can be reduced in weight by replacing the metal rod material with the metal tube material, the usage rate of the metal tube material as the material of these parts is increasing.
In addition, parts manufactured by pressing and welding metal plates (for example, lower arms, rear axle beams, bumper beams, etc.) are being replaced with metal pipes.

When manufacturing a metal tube part, the thickness of the metal tube is determined from the viewpoint of securing strength. However, even when using a metal tube, the portion that requires strength does not necessarily extend over the entire circumference of the metal tube, so if a differential thickness metal tube in which only a portion necessary for strength is thick can be used, Further weight reduction of parts can be realized.
For this reason, the need for a differential thickness metal tube having a different thickness in the circumferential direction of the tube is increasing.

  For example, Patent Document 1 discloses a method of manufacturing an uneven tube by generating an uneven thickness increase in the circumferential direction with respect to a metal tube base tube formed with a uniform thickness in the circumferential direction. . This method is characterized in that after the cross section of the metal tube base pipe is constituted by a low-strength region and a high-strength region in the circumferential direction, plastic working is performed to reduce the outer diameter. Here, as means for configuring the low-strength region and the high-strength region, softening heat treatment is performed on a part of the circumferential direction of the work-cured metal tube material, or a temperature distribution is formed in the circumferential direction of the metal tube material. Is listed.

JP 2004-276040 A

By the technique of the above-mentioned Patent Document 1, it is possible to manufacture differential thickness pipes having different wall thicknesses in the circumferential direction of the pipe.
However, it has been found that the metal tube manufactured by this method has the following problems.

That is, as in Patent Document 1, when the diameter distribution processing is performed by providing a temperature distribution by partially heating only the target portion in the circumferential direction of the metal tube material, the circumference of the formed uneven tube is There is a difference in metallographic structure in the direction, and as a result 1) there is a difference in strength in the circumferential direction of the pipe, which deforms unevenly in the secondary processing.
2) The thinner the part, the softer it will be, so it will not fit as a fatigue resistant member.
3) It has been found that problems such as the occurrence of characteristic differences such as corrosion resistance due to structural differences occur.
Further, in the method described in Patent Document 1, when the ratio between the wall thickness t and the outer diameter D is small (t / D <0.05), there is still a problem where buckling is likely to occur.

  If the mechanical properties of the material differ depending on the circumferential position of the tube, there is a problem that the required durability strength cannot be obtained partially after commercialization, and it can be applied to the parts such as the lower arm, rear axle beam, and bumper beam described above. It becomes difficult.

  The present invention advantageously solves the above problems, and even if the thickness of the metal pipe is different in thickness in the circumferential direction of the pipe, the mechanical properties and corrosion resistance are uniform in the circumferential direction of the pipe. The object is to propose an advantageous method of manufacturing tubes.

Now, the inventors have intensively studied to solve the above problems.
As a result, the metal tube element tube is first heated to a warm region or a hot region, and then subjected to partial heating that gives a temperature difference in the circumferential direction of the metal tube element tube, and then subjected to reduction rolling, It has been found that the high temperature part is thicker than the other low temperature parts, and in this case, the mechanical properties do not vary much in the circumferential direction of the tube.
Further, the reduced diameter rolling is divided into rough reduced diameter rolling and finish reduced diameter rolling, and rough reduced diameter rolling is performed by giving a temperature difference in the circumferential direction. It was found that by rolling after eliminating the temperature difference, there was almost no variation in mechanical properties in the circumferential direction of the tube.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
(1) When manufacturing a differential thickness metal pipe having a non-uniform circumferential thickness from a metal pipe having a uniform circumferential thickness, the metal pipe is heated or heated over the entire circumferential direction. The differential thickness metal tube is heated to an intermediate temperature range, and then partially heated at a specific position in the circumferential direction to give a temperature distribution in the circumferential direction of the metal tube, and then subjected to diameter reduction rolling (1st invention).

(2) When manufacturing a differential metal pipe having a non-uniform circumferential thickness from a metal pipe blank having a uniform circumferential thickness, the metal pipe is heated or heated throughout the entire circumferential direction. After heating to an intermediate temperature range, and then partially heating a specific position in the circumferential direction to give a temperature distribution in the circumferential direction of the metal tube base tube, then performing coarse diameter reduction rolling, and then by heat treatment in the circumferential direction A method for producing a differential thickness metal tube (second invention), characterized in that after the temperature distribution is made uniform, finish diameter reduction rolling is performed.

(3) The method for producing a differential thickness metal tube according to (1) or (2), wherein the partial heating is performed by high-frequency heating.

(4) The temperature difference between the high temperature portion and the low temperature portion in the temperature distribution applied in the circumferential direction of the metal tube base tube is 25 ° C. or more and 100 ° C. or less, wherein (1) to (3) The manufacturing method of the difference thickness metal tube in any one.

(5) The diameter reduction rolling is performed by using a diameter reduction rolling mill equipped with one or more diameter reduction rolling mills provided with a plurality of perforated rolls (1), (3), (4 The manufacturing method of the difference thickness metal pipe in any one of.

(6) The rough reduction rolling and the final reduction rolling are reduced by providing two or more reduction rolling mills provided with a plurality of perforated rolls and a high-frequency heating device provided between the reduction rolling mills. The method for manufacturing a differential metal pipe according to any one of (2) to (4), wherein the method is performed using a diameter rolling facility.

According to the first aspect of the present invention, it is possible to manufacture a differential thickness metal pipe having substantially uniform mechanical characteristics in the circumferential direction of the pipe, although it is a differential thickness pipe having a different thickness in the circumferential direction of the pipe.
Further, according to the second invention, the mechanical properties of the material can be made more uniform in the circumferential direction of the pipe for the differential thickness pipes having different thicknesses in the circumferential direction of the pipe.

It is a schematic diagram of the production line of a suitable difference thickness steel pipe used for implementation of the present invention. It is sectional drawing of a differential thickness steel pipe. It is a schematic diagram of a production line of a differential thickness steel pipe suitable for carrying out two-stage reduced diameter rolling according to the present invention.

Hereinafter, the present invention will be specifically described. In the following description, a case where a differential thickness steel pipe is manufactured as the differential thickness metal pipe will be described.
FIG. 1 schematically shows a production line for a differential thickness steel pipe suitable for use in the practice of the present invention.
In the figure, the upper part shows the process of manufacturing a steel pipe (electrically welded steel pipe) from a steel strip. Number 1 is an uncoiler that pays out a steel strip S that is a material for steel pipe production, and 2 is a payout. A forming machine group for forming the formed steel strip S to be an open pipe, 3 is a welding machine that heats the edge part of the open pipe and then abuts and joins the edge part, and 4 cuts a bead of a seam part on the inner and outer surfaces of the raw pipe A cutting tool, and 5 is a cutting machine for cutting the raw pipe P from which the bead has been removed to a required dimension.

Further, the lower part of FIG. 1 shows a process of manufacturing a differential thickness steel pipe according to the present invention, wherein 6 is a heating device for heating the raw pipe P having a required dimension over the entire circumference of the pipe, and 7 is a heating device. A partial heating device that locally heats only a specific portion in the circumferential direction of the raw pipe P that has come out of 6, and a diameter reduction rolling mill that 8 reduces the diameter of the raw tube P heated by the heating device 6 and the partial heating device 7. 9 is a hot saw that further cuts the base tube after diameter reduction rolling into a required length.
Here, the partial heating device 7 is composed of, for example, an induction heating device, and the induction heating coil is disposed so as to face only a portion in the circumferential direction of the raw tube, and only a portion (in the example of FIG. 1, the side surface on the near side). Only) to form a high temperature portion T. Further, as the reduced diameter rolling mill 8, for example, a reduced diameter rolling mill group in which a four-roll rolling mill in which four rolls are arranged along the outer periphery of the raw pipe P is connected in a plurality of stages (four stages in the example of FIG. 1) is advantageous. Fits.

In the present invention, prior to the diameter reduction rolling, the heating device 6 is first heated to the warm or hot temperature range over the entire circumferential direction of the steel base pipe P.
Here, the warm temperature range means about 600 to 850 ° C., and the hot temperature range means about 850 to 1100 ° C.

After the heating to the warm or hot temperature range, the partial heating device 7 further partially heats only a part of the raw tube in the circumferential direction to give a temperature distribution in the peripheral direction of the raw tube. That is, the high temperature part T whose temperature is higher than other parts is formed.
Here, the temperature difference between the high temperature portion and the low temperature portion in the temperature distribution applied in the circumferential direction is preferably 25 ° C. or more and 100 ° C. or less. This is because if this temperature difference is less than 25 ° C., the desired thick part cannot be formed, while if it exceeds 100 ° C., the high temperature part tends to be locally buckled in reduced diameter rolling after heating. is there.

  Thereafter, the diameter reduction rolling is performed by the diameter reduction mill 8. At this time, since the temperature distribution is given to the raw pipe P, the high temperature portion T is rolled to be thicker than other portions, and finally Specifically, as shown in FIG. 2, when viewed in the cross section of the pipe, the steel pipe has a thick portion A that is partially thick in the circumferential direction.

  In the case of the method described in Patent Document 1, a large difference remains in the residual strain and the metal structure between the portion processed in the cold region and the portion processed in the warm region. Later, the rolling is finished in the hot to hot range without a temperature difference of several to several tens of degrees Celsius, so the mechanical properties of the steel pipe finally obtained are almost uniform in the circumferential direction of the pipe. .

  Further, in the present invention, the above-mentioned reduced diameter rolling is divided into rough reduced diameter rolling and finish reduced diameter rolling, and the coarse reduced diameter rolling is performed under the condition that a temperature difference is given in the circumferential direction as described above, and continues. The finish diameter reduction rolling is performed in a state in which the temperature difference in the circumferential direction is eliminated and the temperature distribution in the circumferential direction is made uniform, thereby further reducing the variation in mechanical characteristics in the circumferential direction of the pipe.

FIG. 3 schematically shows a production line for a differential thickness steel pipe suitable for carrying out the above-described two-stage reduced diameter rolling. Since the main part of the production line is the same as that shown in FIG. 1 described above, the same reference numerals are given, the reference numeral 10 is a coarse reduction mill, 11 is a finish reduction mill, and 12 is the reduction diameter. An intermediate heating device disposed between the rolling mills 10 and 11. In the figure, 13 is an inlet side thermometer, 14 is an outlet side thermometer, 15 is an outlet side thickness gauge, and 16 is a motor.
In this intermediate heating device 12, heat treatment is performed so as to eliminate the temperature difference in the circumferential direction of the pipe remaining after the coarse diameter reduction rolling, and then the rough rolled pipe having a uniform circumferential temperature distribution is finished. Reduced diameter rolling is performed.

In this way, when forming a thick portion that is partially thick in the circumferential direction, first, a temperature difference is given in the circumferential direction to perform coarse diameter reduction rolling, and subsequent finish diameter reduction rolling is performed in the circumferential direction. By performing the temperature distribution in a uniform state, not only the structure can be made uniform, but also the mechanical characteristics can be made more uniform.
According to this method, even when the ratio of the wall thickness t to the outer diameter D is small (t / D <0.05), the diameter reduction rolling can be performed effectively without occurrence of buckling.

Example 1
Using the production line shown in FIG. 1, a differential thickness steel pipe was produced.
First, an ERW steel pipe having an outer diameter of 90 mm was manufactured using SAE15B37H having a plate thickness of 8 mm. This was heated as a raw tube to various warm temperature ranges or hot temperature ranges shown in Table 1, and then a part of the circumferential direction (circumferential width: 45 mm) was partially heated to various temperatures. Subsequently, a differential thickness steel pipe having an outer diameter shown in Table 1 was manufactured by reduction rolling.
Table 1 shows the results of examining the uniformity of the structure and the uniformity of the mechanical properties in the circumferential direction of the differential thickness steel pipe thus obtained.
The uniformity of the tissue over the circumferential direction was investigated as follows.
After the cross section of the tube was polished, it was etched with a nital solution, and the structure of the partially heated portion and the portion facing this (180 ° facing portion) was observed at a magnification of 100 using an optical microscope with three fields of view. And it was confirmed whether the same structure | tissue was obtained by comparing a partial heating part and a 180 degree opposing part.

Example 2
Next, the differential thickness steel pipe was manufactured using the manufacturing line shown in FIG.
The same production line as in Example 1 was used until the production of the base pipe (electrically welded steel pipe). The outer diameter of the tube is 90mm and the wall thickness is 2.5mm.
After this element tube was heated to various warm temperature ranges or hot temperature ranges shown in Table 1, a part in the circumferential direction (circumferential width: 30 mm) was partially heated to various temperatures. Next, a differential thickness steel pipe semi-finished product having various outer diameters shown in Table 1 was obtained by rough diameter reduction rolling. Next, after making the temperature distribution in the circumferential direction of the pipe uniform (temperature difference in the circumferential direction ≦ 30 ° C.) using the intermediate heating device 12, differential thickness steel pipe products with various outer diameters are obtained by finish reduction rolling. Manufactured.
Table 1 shows the results of examining the uniformity of the structure and the uniformity of the mechanical characteristics of the differential thickness steel pipe thus obtained in the circumferential direction.

As shown in Table 1, the invention example (first invention) obtained according to Example 1 had no structural difference in the circumferential direction, and the variation in mechanical characteristics was small.
In addition, in the invention example (second invention) obtained in accordance with Example 2, it is obvious that there is no difference in structure in the circumferential direction, but the variation in mechanical properties is remarkably reduced. In addition, in this case, even when the ratio t / D between the wall thickness t and the outer diameter D is less than 0.05, the diameter reduction rolling can be performed without occurrence of buckling.

DESCRIPTION OF SYMBOLS 1 Uncoiler 2 Forming machine group 3 Welding machine 4 Cutting tool 5 Cutting machine 6 Heating device 7 Partial heating device 8 Reduction rolling mill 9 Hot saw
10 Rough rolling mill
11 Finishing reduction mill
12 Intermediate heating device
13 Inlet thermometer
14 Outlet thermometer
15 Outlet thickness gauge
16 motor

Claims (6)

  When manufacturing a differential thickness metal pipe with a non-uniform thickness in the circumferential direction from a metal pipe base tube with a uniform thickness in the circumferential direction, the metal pipe is divided into a warm or hot temperature region over the entire circumferential direction. And then, after the specific position in the circumferential direction is partially heated to give a temperature distribution in the circumferential direction of the metal tube base pipe, the diameter-reduced rolling is performed. .   When manufacturing a differential thickness metal pipe with a non-uniform thickness in the circumferential direction from a metal pipe base tube with a uniform thickness in the circumferential direction, the metal pipe is divided into a warm or hot temperature region over the entire circumferential direction. After that, a specific position in the circumferential direction is further partially heated to give a temperature distribution in the circumferential direction of the metal tube, and then subjected to rough diameter reduction rolling, and then the temperature distribution in the circumferential direction is determined by heat treatment. A method for producing a differential thickness metal tube, characterized in that after finishing it uniform, finish diameter reduction rolling is performed.   The method of manufacturing a differential thickness metal tube according to claim 1 or 2, wherein the partial heating is performed by high-frequency heating.   4. The difference according to claim 1, wherein the temperature difference between the high temperature portion and the low temperature portion in the temperature distribution applied in the circumferential direction of the metal tube is 25 ° C. or more and 100 ° C. or less. Manufacturing method of thick metal pipe.   5. The difference according to claim 1, wherein the diameter reduction rolling is performed using a diameter reduction rolling mill equipped with at least one diameter reduction rolling mill provided with a plurality of perforated rolls. Manufacturing method of thick metal pipe.   Reduced diameter rolling equipment having two or more reduced diameter rolling mills provided with a plurality of perforated rolls and a high-frequency heating device disposed between the reduced diameter rolling mills for the rough reduced diameter rolling and the final reduced diameter rolling. The method for producing a differential metal pipe according to any one of claims 2 to 4, wherein

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