JPH04313471A - Manufacture of forge welded steel tube - Google Patents

Abstract

PURPOSE:To stably cut the skelp edge even immediately before forge welding, and to manufacture the forge welded steel tube having a weld zone being sound and having high strength. CONSTITUTION:An edge of a skelp S is subjected to roll forming into a prescribed shape, and thereafter, the skelp concerned S is preheated by a preheating furnace, and subsequently, the edge after roll forming is cut and formed, and thereafter, heated in a non-oxidizing atmosphere, the skelp S is formed to a tubular shape, and thereafter, the edge which is cut and formed is butted and forge welded, and a steel tube is manufactured.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing forge-welded steel pipes,
In particular, the present invention relates to a method for producing a forge-welded steel pipe that can stably cut the scalp edge in a hot state before forge-welding and improve the forge-weld strength of the forge-welded steel pipe.

0002

[Prior Art] Forge welded steel pipes have a skeleton of, for example, 130
It is manufactured by heating it to about 0°C and forming it into a tubular shape, and then pressurizing and welding the butted parts with a forge welding roll.

[0003] Compared to electric resistance welded steel pipes, the forge welded steel pipes undergo a longer heat treatment before welding, so the surface is more likely to be oxidized and scale is generated, and there is no effect of upsetting the generated scale to remove it. As a result, it is easy to get scale involved during welding (forge welding), resulting in large variations in soundness and strength in the welded parts of forge welded steel pipes.

[0004] In order to prevent such variations in the soundness and strength of welded parts, the following various techniques have been proposed.

(1) Forming of Skelp Edges There is a technique for forming the abutting edges of skelps into a predetermined shape using forming rolls.
For example, Special Publication No. 46-40762, Special Publication No. 49-332
59 has been proposed.

[0006] As shown in FIG. 4(A), when the edge of the scalp S is not formed, a V-shaped gap is created at the abutting part of the scalp S, as shown in FIG. 4(B). After forge welding, as shown in Fig. 4(C), a V is formed on the outside of the forge welded pipe P.
There was a drawback that a letter-shaped outer surface notch N was formed, and cracks were likely to occur from the notch N as a starting point. However, according to the edge forming described above, as shown in FIG.
When formed into a tubular shape, the abutting parts can be aligned as shown in Figure 5(B), which eliminates the above disadvantages, and makes it easier to purge scale by cleaning blow before forge welding. Because oxides are easy to diffuse,
This has the advantage of improving welding strength.

(2) Cold cutting of the slit edge Compared to the above-mentioned (1) shaping of the slit edge, this cold cutting of the slit edge removes defective parts on the slit edge surface, making it possible to smooth the edge surface. Moreover, there is an advantage that the edges can be formed into an ideal butt shape for cutting.

(3) Hot cutting of scalp edges This method of hot cutting of scalp edges is described in Japanese Patent Application Laid-Open No. 61-1269.
85, in which both edges are cut with a cutting tool immediately before forge welding is known.

[0009] As shown in FIG. 6, the technique described in the above publication performs edge cutting of the Skelp S immediately before forge welding with a bite B, so that edge defects such as slitting defects, edge damage during transportation, and scale due to heating are avoided. can be removed by cutting. Therefore, there is an advantage that the soundness of the welded part after forge welding can be almost perfected, and that the edge before forge welding can be made into an ideal shape.

(4) Hot ERW This hot ERW (ERW) is a pipe manufacturing method that combines the manufacturing methods of forge welded pipes and ERW pipes, and as shown in FIG.
After heating the Skelp S preheated at 0° C. to a low temperature of 920° C. (usually heated to 1300 to 1450° C.) in the heating chamber 12, edge heating is performed by the induction coil 14 and welding is performed.

[0011] At this time, a large upset is applied to discharge the oxides from the welded portion, and at the same time, the discharge bead formed at that time is cut.

Similar to electric resistance welding pipes, this hot ERW can discharge harmful substances such as oxides to the inner and outer beads by upsetting during welding, so it is less susceptible to the effects of the previous process and can be removed in the final welding process. This has the advantage of ensuring the soundness of welding.

[0013]

[Problems to be Solved by the Invention] Each of the above-mentioned conventional techniques has the following problems.

[0014] The molding of the scalp edge described in (1) above prevents the slit edge surface from having shape defects such as the sagging D shown in FIG. If it is large, the defective part will be pressed in with a forming roll, and there will be little effect on improving the soundness or strength. Further, even if there is no defective portion, since edge forming is generally performed cold, there is no effective countermeasure against edge damage that occurs when the skelp is subsequently transported.

[0015] Furthermore, when roll forming is carried out hot,
The processing amount is small and the conveyance speed is high (for example, 100
m 2 /min or more), it is difficult to control, and the scale that has already occurred is forced into the edge, which may have the opposite effect.

Furthermore, roll forming does not necessarily make it possible to form a shape suitable for forge welding.

[0017] In (2) scalp edge cold cutting, the amount of cutting is minute and the cutting direction must be changed according to the slit edge surface, but it is difficult to follow changes in the width of the scalp, bends, etc. Therefore, cutting control is difficult, and the actual situation is that it is controlled manually.

Furthermore, even if there is a change in the slit edge surface (for example, bar-up or bar-down as shown in FIG. 1(A), which will be described later), in order to keep the cutting shape constant, the amount of cutting must be large. As a result, yield loss is large.

[0019] Furthermore, since the cutting is carried out cold,
There is no effective countermeasure against edge damage that occurs when skelp is transported for heating or the like.

Furthermore, forge-welded steel pipes are manufactured by connecting skelps in the longitudinal direction and feeding them continuously, but since the longitudinal joints of the skelps are subject to large fluctuations in cutting load, it is necessary to protect the cutting tool from the viewpoint of protecting the cutting tool. It is necessary to release the bite at the joint. Therefore, uncut portions remain before and after the joint portion.

[0021] The above (3) hot cutting of the scalp edge is as follows:
As shown in Figure 6, after rounding the skelp, cutting is carried out in a narrow space and in an atmosphere of over 1200°, making it nearly impossible to design the equipment, and even if it were possible, the heat Stable cutting is also difficult due to the
Equipment life is also extremely short.

[0022] In the hot ERW (4), since it is necessary to cut the inner and outer beads, the manufacturing cost becomes high.

Furthermore, even though it is called low temperature heating, since welding is carried out in a situation where there is a large amount of scale compared to a cold electric resistance welded pipe, as shown in FIG. 9, the induction coil 1
The induced current i generated by 4 and flowing preferentially to the edge portion
However, if scale Sc exists, it will cause a short circuit, and there is a high possibility that welding will be defective. Therefore, it can be said that spot welding defects are more likely to occur.

The problems faced by the conventional techniques detailed above can be summarized as follows.

[0025] The best way to form a sound and high-strength weld is to cut the scalp immediately before forge welding as much as possible, but the shape of the edge before cutting is not constant, In addition, stable cutting is difficult because it is performed hot.

The present invention has been made to solve the above-mentioned conventional problems, and makes it possible to stably cut a scalp edge even immediately before forge welding, that is, even during hot welding, and to produce a healthy and strong welded part. An object of the present invention is to provide a method for manufacturing a forge-welded steel pipe that can be formed.

[0027]

[Means for Solving the Problems] The present invention hot-cuts both edges of a skelp and then bends the skelp into a tubular shape.
In the method for manufacturing a forge-welded steel pipe in which edges are forge-welded, the above-mentioned object is achieved by forming both edges of the skeleton into a predetermined shape, and then hot cutting and forge-welding both edges.

[0028] Alternatively, in the method for manufacturing a forge-welded steel pipe, the present invention includes preheating the skelp with both edges formed, hot cutting the skelp, and then heating the skelp in a non-oxidizing atmosphere furnace. By doing so, the above-mentioned problem has been achieved as well.

[0029]

[Operation] In the present invention, both edges of the skelp are formed into a predetermined shape, and then both edges of the skelp are hot-cut, so it is possible to form a predetermined edge shape with a constant amount of cutting. Since it can be cut even just before cutting,
It becomes possible to forge-weld both edges without scale on the edge surfaces, and as a result, it becomes possible to manufacture a forge-welded steel pipe having an extremely sound and high-strength welded part.

[0030] Furthermore, after preheating the skelp on which the edge has been formed, the skelp edge is hot-cut, and then the skelp is heated in a non-oxidizing atmosphere furnace. Since the scalp edges can be forged-welded without producing scale, a sound and high-strength weld can be more reliably formed.

[0031]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory diagram showing an outline of the steps in a method for manufacturing a forge-welded steel pipe according to an embodiment of the present invention, and FIG.
1 is a schematic configuration diagram showing a forge-welded steel pipe manufacturing apparatus applied to this example. In addition, in Figure 1 (D), the Skelp is shown in the same figure (A
) to (C) and are shown in their entirety.

The above manufacturing device includes a forming roll 20 for cold edge forming of the skelp S, a preheating furnace 22 for preheating the skelp S, and a hot cutting of the edge of the skelp after edge forming. A cutting device 24, a non-oxidizing heating furnace 26 that heats the Skelp S after edge cutting, and an edge heater 28 that further heats the edge of the Skelp S after heating.
and a forge welding roll 30 that forms a steel pipe P by forge welding the scalp S after edge heating.

In the non-oxidizing heating furnace 26, the above-mentioned squelp S is heated by the burner 32, but the combustion by the burner 32 at this time is performed in a state in which oxygen is insufficient compared to the fuel, so that a reducing atmosphere is created. The incomplete combustion gas in the heating furnace 26 is supplied to the preheating furnace 22 and
2, complete combustion is achieved.

In this example, the above-mentioned manufacturing apparatus was used to produce the image shown in FIG.
A forge-welded steel pipe is manufactured through the steps shown in (A) to (D).

First, the edge of the transported Skelp S is formed by the forming roll 20 installed at the front stage of the preheating furnace 22. In this edge forming, as shown in FIG. 1(B), the edge surface is directed outward from the normal to the first surface S1 (the surface that becomes the outside after tube formation) by -1 to 7 degrees, preferably 0 to 7 degrees. This is done so that the surface is inclined at 5°.

As a result of the edge formation described above, as shown in FIG. A constant edge shape can always be formed even when the

Next, the edge-formed Skelp S is preheated in a preheating furnace 22, and then cut into edges after forming as shown in FIG. is hot cut to remove the diagonally shaded portion as shown in FIG. 5C to form a cutting edge. In this edge hot cutting, the scalp S heated to, for example, 700° C. is cut so that the cutting edge surface has an inclination of, for example, 7° inward with respect to the normal to the first surface S1. Note that this inclination angle can be changed as appropriate depending on the diameter of the steel pipe P.

[0039] During this hot cutting, since the edge of the Skelp S has a constant shape due to the edge forming, stable cutting is possible even during hot cutting, and the specified shape can be cut with a constant cutting amount. Moreover, an appropriate butt shape can be formed with a minimum amount of cutting.

After the hot edge cutting described above, the Skelp S is heated to, for example, 1200° C. in a non-oxidizing heating furnace 26 and formed into a predetermined tube shape. The edges are heated and then forge welded by a forge welding roll 30 to form the steel pipe P.

Since heating in the non-oxidizing heating furnace 26 is performed in a non-oxidizing (reducing) atmosphere, it is possible to prevent scale from forming on the cut edge surface.

Therefore, according to this embodiment, it is possible to form an abutting part with a clean edge surface and forge welding the abutting part, so that a sound and high-strength welded part can be reliably formed. .

[0043] Furthermore, since the edges of the Skelp S are hot-cut after being rolled, the variation in cutting load is small even when cutting the joints connecting the Skelps in the longitudinal direction. There is no need to release the bite before and after the part to avoid cutting. Therefore, since no uncut portions are produced, forge-welded steel pipes of consistently stable quality can be manufactured.

Furthermore, since the preheating furnace 22 is in an oxidizing atmosphere to completely burn the fuel, the hot cutting is performed in the preheating furnace 22.
It is reasonable to do this at a later stage.

[0045] Here, by applying this embodiment, SGP20
Two types of forge welded steel pipes (the present invention), A and SGP80A, were actually produced, and then the forge welded steel pipes produced by the conventional method (no edge treatment, only edge forming), 90° flatness value and ET (eddy current testing) were produced. ) The defective incidence rate was determined and the results are shown in Tables 1 and 2 below.

[0046]

[Table 1]

[0047]

[Table 2]

Here, the 90° flattening value means, as shown in FIG. 3, when the steel pipe P is pressed vertically with the same load with the weld W placed at the 90° position, the seam cracks. It is expressed as the amount of vertical deformation until . The number of samples of each forge welded steel pipe was 100, and the angle was 90°.
Flat land is the average value. Moreover, σ is the standard deviation.

From Tables 1 and 2 above, it can be seen that according to this example, a welded part with extremely high strength can be formed, and the method of this example is an extremely excellent method for manufacturing forge-welded steel pipes.

Although the present invention has been specifically explained above, the present invention is not limited to what is shown in the above embodiments.
Various changes can be made without departing from the gist of the invention.

For example, the roll forming of the scalp edge is
The cold forming is not limited to the embodiment, but hot forming may also be performed.

Further, the hot cutting of the scalp edge is not limited to the case where it is performed immediately before the non-oxidizing heating furnace, but may be performed, for example, immediately before forge welding. In this case, even when the skelp is heated in an oxidizing atmosphere furnace, high-quality forge-welded steel pipes can be similarly produced.

[0053]

[Effects of the Invention] As explained above, according to the present invention, the scalp edges can be stably hot-cut even immediately before forge welding, so it is possible to manufacture forge welded steel pipes having sound and strong welded parts. Can be done.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an outline of steps in a method for manufacturing a forge-welded steel pipe according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a forge-welded steel pipe manufacturing apparatus applied to this embodiment.

FIG. 3 is a schematic explanatory diagram showing a test method in an example.

FIG. 4 is a schematic explanatory diagram showing conventional problems.

FIG. 5 is a schematic explanatory diagram showing roll forming of a scalp edge.

FIG. 6 is a schematic explanatory diagram showing problems in conventional hot cutting of a scalp edge.

FIG. 7 is a schematic configuration diagram showing a hot ERW manufacturing apparatus.

FIG. 8 is a schematic explanatory diagram showing a defective shape of a scalp edge.

FIG. 9 is a schematic explanatory diagram showing problems with hot ERW.

[Explanation of symbols]

S...Skelp, 20...forming roll, 22... Preheating furnace, 24...Cutting device, 26...Non-oxidation heating furnace, 28...edge heater, 30...Forge welding roll.

Claims (2)

[Claims] 1. A method for manufacturing a forge-welded steel pipe, in which both edges of a skelp are hot-cut, the skelp is bent into a tubular shape, and the edges are forge-welded. A method for manufacturing a forge-welded steel pipe, characterized by hot cutting both edges. 2. The forged welded steel pipe according to claim 1, wherein the skelp with both edges formed is preheated, then both edges are hot cut, and then the skelp is heated in a non-oxidizing atmosphere furnace. manufacturing method.