JPS58157581A - Manufacture of forge welded tube - Google Patents

Abstract

PURPOSE:To reduce streaky defects generated in forge welding zone in a method that manufactures a forge welded tube by butting both edge parts and forge welding, by butting and forge welding while applying axial stress on both side edge parts. CONSTITUTION:A skelp is passed through a heating furnace, and both side edge parts are heated to forge welding temperature. It arrives at a forming roll 2 from a roller 15 in a state that distance of moving differs between the central part of the skelp and edge parts on both sides, and stronger axial tension is applied to the both edge parts than the central part. Further, axial stress is controlled by adjusting the height of the roll 15. Accordingly, in moving to the forming roll through the roll 15, the skelp arrives at a forge welding roll while being given circumferential stress and axial stress to the both side edge parts, and both edge parts are butted and forge welded.

Description

Detailed Description of the Invention This hole F3A relates to a method for manufacturing forge-welded pipes that makes it possible to eliminate or reduce minute defects occurring in forge-welded parts.Generally, forge-welded pipes are made by passing the raw material skelp through a heating furnace. After heating the edges of both sides of the skelp to a temperature suitable for forge welding (simply referred to as lead welding), it is passed through a forming roll to form a cylindrical shape with the edges facing each other, and then passed through a forge welding roll. However, the forge welded pipes produced through this process are prone to various defects such as weld cracks, roll marks, and pit flaws. One of the surface defects of such forge-welded pipes is a streak defect that appears in the form of a minute groove with a depth of about 0.3 mm in the forge-welded part. Conventionally, this streak defect has rarely been considered a problem. However, in recent years, as the use of forge-welded pipes as blank pipes for cold drawing has increased, the pipes are expanded further after drawing.

If secondary processing such as flattening is applied, the forge-welded pipe may break due to the notch effect caused by the strip defects, and when used as a member that is subjected to alternating loads, stress will concentrate on the strip defect area, causing fatigue limits to be reached. This has led to problems such as a significant drop in performance.

The inventors of the present invention have conducted experiments and research to eliminate or reduce the above-mentioned strip defects, and have discovered the following fact. In general, the main control items in the forge welded pipe manufacturing process are the forge welding temperature and the amount of upset expressed by the following formula, where the amount of upset = α (wo + πto) - πDmα: expansion rate W. : Skelp width t. :Skelp thickness Dm: Average diameter of forge-welded roll Absent amount is ultimately summarized in lateral pressure to be applied to the skelp, in other words, local stress to be generated in the skelp. Therefore, it can be said that most of the control items in the forge welded pipe manufacturing process are the forge welding temperature and the opening direction stress, but this stress in the circumferential direction at the forge welding temperature is also related to the strip defect, and in fact, the forge welding temperature It has been confirmed that increasing the local rotation stress also reduces strip defects. However, if the stress in the circumferential direction at the forge welding temperature is increased too much, the forge weld part swells up and a bead is formed, which is an inconvenience.Therefore, methods other than these are desired to eliminate the strip defects.

Since increasing the stress in the two local directions at the forge welding temperature as described above by the present inventors means increasing the plastic deformability of the skelp itself, it is not considered that the stress in the axial direction contributes to increasing the plastic deformability of the skelp. As a result of conducting experiments on the relationship between total force and row defects, it was concluded that controlling stress in the axial length direction is extremely effective in eliminating or reducing row defects. However, in the past, there was of course no concept of controlling the stress in the axial direction for the purpose of eliminating row defects or mitigating the structure, but the stress in the axial direction itself was not zero, and the example for squelp is heating. Stress in the axial direction is exerted over the entire width of the skelp due to resistance from the return drum before entering the furnace, frictional resistance with the supporting lambda skid in the heating furnace, or cutting resistance when performing edge shaping. It is thought that the sag is approximately 40 inches relative to the deformation resistance value of the skelp itself.

However, this tension shows a constant value depending on the equipment, and 1i
Of course, it is not targeted for 11 ml.

The present invention has been developed based on this knowledge, and its purpose is to manage the stress in the longitudinal direction of the axis, especially the stress acting on both edge portions, in addition to the stress in the circumferential direction at the forge welding temperature, and to An object of the present invention is to provide a method for manufacturing a forge-welded pipe that enables a significant reduction in defects.

Method for manufacturing a forge-welded pipe according to the present invention A lamp-heated skelp is
In the method of manufacturing a forge-welded pipe by curving the edges on both sides to face each other and forge-welding the edges on both sides, longitudinal stress is applied to the edges in the axial direction in order to reduce the streak defects that occur in the forge-weld. It is characterized by butt forge welding while being applied.

The present invention will be specifically explained below based on drawings showing embodiments thereof. Fig. 481 shows a partially cut away spoon a' for carrying out the method for manufacturing a forge-welded pipe according to the present invention (hereinafter referred to as the method of the present invention). A schematic side view, and FIG. 2 is an enlarged view showing the control mode of axial longitudinal stress on the squelp, and in the figure, the sit squelp,
lij heating furnace, 2 forming rolls, 3Fi welding rolls, 4
a, 4b...-4n#-i Squeezing roll, 5 indicates the real saw. Skelp S is pulled out from an uncoiler or the like, transferred in the direction of the white arrow, h1, and first passed through the heating furnace IK. The configuration of the heating furnace IH itself is well known, with a preheating zone 11 for preheating the Skelp S in the upper part, and a heating zone 12 in the lower part (8I) of the Skelp S.
First, introduce it into the preheating zone 11 from one end side of the heating furnace 1.
The hook is turned around a return drum 13 placed near the other end, folded back into a U-shape, pulled back outward from one end, and then reshaped into a U-shape along a turnaround 14 placed at one end S of the heating furnace l. The heating zone h1 is folded back and introduced into the heating zone 12. During the process of moving in the heating zone 12, the scale S is heated at least at its edges on both sides to around 1300° C., which is the forge welding temperature. It crosses over to the forming roll 2 side. In the process from the roll 15 to the forming roll 2, as shown by the imaginary line in Figure #-i$2, the pass line at the center of the squelp S usually leaves the heating furnace 1 and moves horizontally until it reaches the forming roll 2. However, the pass line of the edge portions on both sides of the squelp S is gradually curved downward by the shadow of the forming roll 2 immediately after passing the roll 15, and as a result, the path line of the edge portions on both sides of the squelp S draws a gentle curve and forms It is moved downward by a dimension approximately equal to the diameter and reaches the forming roll 2. Therefore, the moving distance is different between the central part and both edge parts of the squelp S from the roll 15 to the forming roll 2,
In other words, a difference in trajectory occurs, and the sheet reaches the forming roll 2 in a state in which no stronger longitudinal tension is applied to the edge portions on both sides than in the center portion. At this time, the stress acting in the longitudinal direction of both edge portions due to the tension, that is, the stress before the axial length, is approximately E<, 0.4 K t (Kf: deformation resistance force of the material) as described above. In the method of the present invention, in addition to this, the roll 15 is also used to adjust the stress before the axial length to a desired Fi.
o, controlled to be about 5Kf to 0.9Kf. A specific means for the control is, for example, by adjusting the height of the roll 15 by one shift as shown by the solid line in FIG.

Now, in FIG. 2, if the roll 15 is moved upward by a distance d from the conventional general position shown by the imaginary line, the pass line of the squelp S changes as shown by the solid line. Therefore, when the trajectory difference 1 between the edge portions on both sides of the squelp S is determined when the roll 15 is at the position shown by the imaginary line and when it is at the position shown by the solid line, the following is obtained.

In order to simplify the explanation, in each case, the edge portions on both sides approach each other from the positions X, , X2 where the edge portions contact the roll 15, and the central portion of the squelp S and the edge portions on both sides form a substantially parallel movement pair. The moving path 11t, f passing through WItY to the vertical plane intersecting the direction of movement of the squelp S is assumed to be a straight line. First, when the roll 15 is in the position shown by the imaginary line, an arc a? with Xl as the center and distance R1 from X to the intersection Z of the vertical plane and the center of the squelp S is formed. If the intersection of this circular arc a and the edge portion is Ml, it can be seen that the edge portion of the scalp S is more elongated than the center portion by M and Y. Next, if you look at roll 15 or the position shown by the solid line, it will be Xz? If we draw an arc b' (i-) whose radius is the distance R2 from Xl to Z with the center as the center, and let M2 be the intersection point of this arc with the edge part, then the edge part of the Skelp S will be wider than the center part by M and Y. Therefore, M, Y
Comparing M and Y, the latter is more MI M than the former.
, , that is, it can be seen that the edge portion is stretched more by Δl, in other words, it is under stronger tension.

Since the Δl difference changes in relation to the moving dimension d of the roll 15, by calculating the bond f of both in advance, the axial length pre-stress dzfo to be applied to the edge portion can be calculated from 5Kf to 0.
．． This means that the setting can be controlled as appropriate between 9 Kf.

Although the axial force L in the longitudinal direction is set to 0.5 Kf or more, if it is less than this, the effect of reducing strip defects will hardly be noticeable.

Furthermore, if the temperature is set to 0.9 K f or less, there is a risk that the Skelp S will break.

In the process of passing through the Skelp sVi roll 15 and reaching the forming roll 2, it reaches the forge welding roll 3 while applying an inward stress and an axial length pre-stress equivalent to 0.5 Kf to 0.9 Kf to the edge portions on both sides. , the edge portions on both sides are brought into contact with each other by equal forging.

The circumferential stress acting on the Skelp S in the circumferential direction due to the squeezing effect of the forge welding roll 3 is the same as the conventional one, and ranges from -3Kf to -1.
, 7K f.

The graph in FIG. 3 shows the forge welding conditions as described above in comparison with the conventional method. In the graph of FIG. 3, the horizontal axis indicates circumferential stress (usually shown as a negative value).

The axial stress It is plotted on the vertical axis, and the shaded region in the graph is the range where Skelp SK plastic deformation can occur, and the forge welding condition region v, according to the method of the present invention is shown in outline. . The area indicated by dots corresponds to the conventional method.The line g represents the 7resca yield formula in which the simple yield stress is the difference between the maximum principal stress and the minimum principal stress. Yielding, that is, no plastic change occurs within the region of force surrounded by the coordinate axes of .

Next, the results of a comparative test between the method of the present invention and the conventional method will be explained. The test was conducted using carbon steel (C: 0.08 cm, Mn: 0.
50%) was made into a pipe using a forge-welded roll with a diameter of 60.14 mm, and then reduced and rolled with a final reducer with an exit diameter of 28.19 mm, and further [with a 3-stand sizer to form a pipe with a diameter of 27.89 mm]. In the process of finishing a forge welded pipe, the forge welding temperature, IN
We applied a method of setting and controlling the axial longitudinal stress together with the directional stress within a predetermined range, a conventional method, and a method of controlling only the local directional stress at contact temperature.

Test conditions - Forge welding temperature: 1300°C - Circumferential stress and axial stress are also as indicated by A, B, C, and D in the 3rd and 1st graphs.

In the graph of Figure 3, the horizontal axis shows the localized cracking resistance and the vertical axis shows the axial stress. There is.

The results are shown in Table IK.

As is clear from Table 1, the welding pead height itself tends to be higher when the method of the present invention is used compared to the conventional method, but the depth of the row defect is also higher when the method of the present invention is used. It can be seen that the amount has been significantly reduced to almost half compared to the case using the conventional method. In addition, in the above-mentioned embodiment, a configuration is shown in which the existing roll 15 provided for removing scale and supporting the surface of the Skelp S is used as a means for applying stress in the axial direction to the edge portion of the Skelp S. Of course, the present invention is not limited to this, and a roll or the like for applying tension may be separately provided.

As described above, in the method of the present invention, tension is applied to both edge portions of the heated skelp while the edge pieces on both sides are butt-welded to each other, so that the streak defects formed in the forge-welded holes are significant [2]. As a result of reducing the notch effect caused by row defects, it is possible to expand the use of bone fitting as raw pipe for various processing, as well as the quality of forge welding.
The present invention has excellent effects.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the implementation state S of the method of the present invention, and Fig. 2 is a schematic diagram showing the main part of the method S! Figures A and 3 are graphs showing the relationship between the circumferential force applied to the squelp and the axial stress. 1... Heating furnace 2... Forming roll 3... Forge welding rolls 4a, 4b*e-drawing roll 5... Hot saw 11... Pre-preparation zone 12... Heating zone 13
... Return drum 14 ... Turn Arachundo 1
5...Roll S...Skelp Patent Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Noboru Kono Dog Procedural Amendment (Spontaneous) 571 da P28, Commissioner of the Japan Patent Office /, Indication of Case Showa 57 Metropolitan Patent - No. 39931 No. 2
Title of the invention Method for manufacturing forge-welded pipes J Person making the amendment Patent applicant/agent j Exclusion of "detailed description of the invention" and "drawings" of the specification to be amended g Contents of the amendment 6-1 Details of the invention Explanation: On page 9, line 11 of the specification, it says, ``It becomes a thing.-
Toa 2, 1 copy of the catalog correction drawing of attached documents

Claims (1)

[Scope of Claims] 1. In a method of manufacturing a forge-welded pipe by bending a heated skelp so that its edge portions on both sides face each other and forge-welding the edge portions on both sides, A method for manufacturing a forge-welded pipe, characterized by performing butt forge welding while applying stress in the axial direction to both edge portions in order to reduce defects. 2. The axial longitudinal stress applied to both edge portions is 50 to 90 times greater than the deformation resistance force of the skelp.Claim 1
2. Method for manufacturing forge-welded pipes as described in Section 1.