JP2001259711A - Method of manufacturing seamless steel tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the inexpensive and simple manufacturing method of a seamless steel tube by which the damage in the body part of a plug is prevented when performing skew piercing of a billet of high alloy steel or the like. SOLUTION: In a Mannesmann skew piercing process, a material to be pierced has a through hole in the center part of a cross section and, furthermore, a lubricant is blown into the inside of the through hole from the rear end of the material to be pierced on the inlet side of a skew piercing machine before piercing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a seamless steel pipe using an inclined drilling machine, and more particularly to a method for improving the durability of a drilling plug used in a drilling machine.

[0002]

2. Description of the Related Art In order to manufacture a seamless steel pipe by inclined drilling such as the Mannesmann method, a round steel (hereinafter, referred to as a billet) having a cross section of about 100 to 400 φ is usually charged into a heating furnace, and about 1100 mm. ℃ ~ 1350 ℃,
The hollow shell is pierced by a piercer using a cored bar (hereinafter referred to as a perforated plug). Next, the hollow shell is stretched by a rolling mill such as an elongator, a plug mill or a mandrel mill, and finally the outer diameter and the wall thickness are determined by a sizer or a stretch reducer.

[0003] In rolling mills such as piercers, elongators, plug mills, and mandrel mills, tools are generally arranged on the inner surface of a raw tube to perform rolling. The tools disposed on these inner surfaces are subjected to severe processing by contacting a high-temperature billet or hollow shell, and are heated to a high temperature because they receive strong radiation from the entire circumference. Although it is cooled each time it is used, it may be deformed as the number of uses increases, or in extreme cases, may be damaged by erosion. Above all, the damage is remarkable in the piercing plug used in the piercer.

Further, when drilling a billet containing a large amount of an alloy component such as Cr, Mo or Ni,
The service life of the perforated plug is extremely small, about several passes. Incidentally, the durability of carbon steel is several hundred passes, and erosion-like deformation and seizure mainly occur at the tip (hereinafter referred to as the head). If used continuously with damage, it may cause flaws on the inner surface of the hollow shell, so it is necessary to replace the plug frequently, which not only reduces the efficiency but also reduces the tool unit consumption. There is a problem that the cost of the final product decreases.

In addition, if the damage is severe, there is a problem that the Mannesmann perforation becomes impossible, and an abnormal situation of producing a final product by another production method is caused.

Therefore, many technical developments have been made in order to improve the durability of the pierced plug, and in particular, to solve the deterioration of the durability of the pierced plug when drilling a billet made of a high alloy steel or a high alloy. Broadly speaking, the high-temperature strength of the perforated plug is increased (Prior Art 1), the surface is made to have abrasion resistance (Prior Art 2), and a direct contact with the perforated material is made by using a lubricant, an oxide scale or the like. To prevent image sticking and prevent image sticking (prior arts 3 to 5) have been proposed.

For example, the technique described in Japanese Patent Publication No. 2-133106 uses molybdenum Mo, which has a much higher high-temperature strength than a material billet, for a perforated plug to prevent plug damage due to deformation. Although Mo itself is highly effective in preventing seizures, Mo oxides can be expected to improve seizure resistance.
It is very brittle in a temperature range lower than about 400 ° C., and cracks due to thermal stress and the like are apt to occur. (Prior art 1)

The technique described in Japanese Patent Application Laid-Open No. 63-192504 is intended to prevent seizure and wear by attaching a hard material or the like to the plug surface by various surface treatments. Although it is possible to suppress surface damage, it is said that the technology used in actual equipment has been established in that the wear layer is a hard material, which easily breaks due to repeated thermal stress, and the surface treatment layer peels off. hard. (Prior art 2)

The technique described in Japanese Patent Publication No. 63-54066 uses a low alloy steel as a plug base material, and applies an oxidized scale to the surface in advance to suppress the deterioration of durability.
That is, a plug made of a low-alloy steel, for example, 3% Cr-1% Ni is heat-treated before drilling, and the surface scale generated therefrom is used as a lubricant or a heat insulating film. . Furthermore, the technology described in Japanese Patent Application Laid-Open No. 8-193241 discloses that a plug can be improved to a material having a large amount of oxide scale, and that a high alloy steel can be drilled up to about 20 passes. Nevertheless, it does not reach the level of durability when drilling ordinary steel at all, and there is a demand for a significant improvement in tool unit consumption and an improvement in rolling efficiency. (Prior art 3)

Further, in the technique described in Japanese Patent Application Laid-Open No. 1-180712, a method is proposed in which a lubricant is applied from the perforated plug itself to the interface between the plug and the material to be perforated during perforation. However, problems such as reduction in strength and breakage due to processing of the plug itself and clogging of the coating hole remain, and the plug has not been put to practical use. (Prior art 4)

Further, the technique described in Japanese Patent Application Laid-Open No. 8-117815 discloses that a steel plate is joined to a tip end surface of a billet on a piercing side to apply an oxide scale to a plug every time a hole is drilled, thereby reducing consumption of the oxide scale. Preventing. Therefore, the seizure suppression effect of the oxide scale achieves a plug durability of five times or more as compared with the conventional case in drilling high alloy steel. In addition, it is not necessary to replace the plug every time the hole is drilled, and the hole can be continuously drilled, thereby improving the productivity. However, according to the present technology, although the seizure of the plug head, which is the main cause of damage to the plug, could be suppressed, conventionally inconspicuous damage such as seizure of the plug body and deformation of the aggressive shape has become frequent. Was.
(Prior art 5)

[0012]

As described above, in view of the above, in the prior art 1, the plug itself is expensive (problem 1).
It is necessary to preheat to 400 ° C. or higher prior to use, and the preparation work is complicated (problem 2), and cracks due to thermal stress and the like, particularly damage to the plug body are likely to occur (problem 3). And there was a problem.

Further, in the prior art 2, the surface treatment layer is easily cracked due to repetition of thermal stress (problem 3) or the surface treatment layer peels off (problem 4), particularly in the plug body.
There was such a problem.

Further, the prior art 3 has a problem that it cannot be used for drilling high alloy steel due to insufficient durability (problem 3).

Further, the prior art 4 has a problem that the plug is easily broken (problem 3), and the lubricant application hole is clogged (problem 5).

Furthermore, in the prior art 5, a preparation work for joining a steel plate to the end face of the billet occurs (problem 2), and damages such as seizure of the plug body and deformation such as aggression cannot be prevented (problem 3). ) And had a problem.

In particular, most of the prior arts regarding the plug durability (problem 3) mainly focus on suppression of deterioration of the head of a pierced plug made of an alloy steel component, and a central portion in the longitudinal direction of the pierced plug. There is almost no technique for improving the durability by preventing damage to the rear part (hereinafter referred to as the trunk).

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is inexpensive, does not require any special preparation work, and does not require any damage to the plug body when obliquely drilling a billet of high alloy steel or the like. It is an object of the present invention to provide a method for manufacturing a seamless steel pipe, which can prevent such a problem, does not have a special treatment layer on the plug surface, and does not have a lubricant coating hole on the plug itself.

[0019]

According to the present invention, there is provided a method for manufacturing a seamless steel pipe, comprising: a roll inclined with respect to a pass line of a material to be pierced; and a plug for piercing the material to be pierced on the pass line. The method for manufacturing a seamless steel pipe in an inclined drilling machine, wherein the drilled material has a through hole in the center of the cross section, and further, before the drilling, after the drilled material on the entry side of the inclined drilling machine. The lubricant is injected into the through hole from the end.

Further, in the method for obliquely drilling a seamless steel pipe, a lubricant is supplied mainly to the rear end side inside the through hole of the material to be drilled.

Further, the inner diameter of the through hole of the material to be pierced is 10% or more of the outer diameter of the material to be pierced.

Further, the material to be pierced contains at least one of Cr, Mo or Ni in an amount of 5% or more.

[0023]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, a punching roll 1 is installed on a punching machine (not shown) with its rotation axis inclined with respect to a pass line. The piercing plug 2 is rotatably installed at the tip of a mandrel (not shown), and moves back and forth on a pass line on the rear surface of the piercing machine. Perforating roll 1 for perforation
Is advanced to a gap substantially at the center of the hole and stopped, and the inner surface is machined while being rotated by the material 4 to be drilled during drilling. The pusher 3 is installed in front of the drilling machine, and moves forward and backward on the pass line. In addition, a lubricant jetting device 31 and a billet pressing device 32 that rotates freely when the material to be pierced 4 starts rotating are installed at the tip portion (the end portion on the drilling machine side) of the pusher 3. .

The material to be perforated (hereinafter referred to as a billet) 4 is
After being transferred onto the pass line in front of the drilling machine, it is pushed out toward the drilling machine by the pusher 3 and is bitten by the punching roll 1. Thereafter, the billet 4 advances while rotating, and is perforated so as to be sandwiched between the perforation roll 1 and the perforation plug 2 to form a hollow shell. After the drilling, the hollow shell is transferred to the rear surface of the drilling machine and transferred to the next step.

Further, a through hole 4 is provided at the center of the billet 4.
1 is provided, and a lubricant is ejected from the lubricant ejection device 31 into the through hole 41 prior to the start of drilling.

The timing of ejection is as follows: (1) Billet 4
Is a predetermined length of time until the biting roll 1 bites,
(2) Short time immediately before biting, (3) Short time immediately before biting, immediately after biting, (4) Time of a predetermined length from just before biting to after biting, (5) predetermined time after biting Length of time.

Further, the jetting strength is such that the lubricating material
1 or may be supplied to a part of the ejection side. Further, the ejection strength may be changed over time.

The operation of the present invention will be described below. 2 and 3 show the surface temperature distribution of a perforated plug (made of 3% Cr-1% Ni) when carbon steel and 13% Cr steel are perforated, respectively. In each case, the surface temperature increases as perforation is repeated (it is considered that cooling after completion of perforation is insufficient).

Also, comparing FIG. 2 with FIG. 3, in the case of carbon steel, the tip side of the pierced plug has a gentle curve of high temperature, and even if the number of piercings is repeated, a peak occurs at the center of the plug. No, the average temperature did not exceed 800 ℃. On the other hand, in the case of alloy steel, a temperature peak (hereinafter, referred to as a peak temperature) also occurs at the center of the drilled plug, and the peak temperature increases as the number of drillings increases. High alloy steel has higher deformation resistance, and the contact state is different due to the higher surface pressure applied to the surface of the drilled plug. This is due to a phenomenon peculiar to perforation. Further, since the processing heat (calorific value) during drilling is higher in the high alloy steel, the generation of the peak temperature is also promoted by this.

FIG. 4 shows the relationship between the peak temperature and the number of drilling times. The SKT3 steel has a higher durability than the 3% Cr-1% Ni steel drilling plug, but reaches 800 ° C. Then it is abandoned.

As described above, in order to suppress the damage to the body of the perforated plug, the peak temperature should not be generated, or if it does, the temperature should not be raised to 800 ° C. or more.
That is, it has been found that it is important to keep the surface pressure of the piercing plug low and to shorten the piercing time.
Therefore, as a method of preventing direct contact and shortening the perforation time, a method of providing a through hole in the billet and injecting a lubricant into the through hole from the rear end of the billet before drilling was invented.

FIG. 5 shows the effect of the through hole and the lubricant on the forward efficiency during drilling. In FIG.
SUS304 steel billet without through holes (hereinafter referred to as solid material), billet provided with through holes of 10% of the billet outer diameter (hereinafter referred to as hollow material), and lubricant on the inner surface of the hollow material (Hereinafter, referred to as lubricating hollow material)
Were compared for the forward efficiency. The advance efficiency is defined as a ratio of a billet traveling speed to a pass line direction component of a roll peripheral speed. Therefore, when the forward efficiency is 0.5, the billet travel speed is 、 and the perforation time is twice as long as when the forward efficiency is 1.0.

From FIG. 5, it can be seen that the traveling speed is improved by 20% for the hollow material and 70% for the lubricated hollow material, and the drilling time is reduced by about 17% for the hollow material and about 41% for the lubricated hollow material as compared with the solid material. Therefore, it is recognized that the present invention is excellent.

FIG. 6 shows that in FIG.
It is a comparison of the number of perforations reaching 0 ° C. In FIG. 6, the hollow material is extended by about 40% and the lubricated hollow material is extended by 130% as compared with the solid material, which indicates that the present invention is excellent. In the lubricated hollow material, wear of the perforated plug is suppressed. This is because the number of contacts (sliding distance) between the piercing plug and the inner surface of the billet is improved by improving the forward efficiency.
It is considered that the number has decreased. Further, by providing the through-hole, deformation of the tip of the piercing plug was reduced, and damage to the tip of the piercing plug was almost eliminated.

FIG. 7 is a correlation diagram showing the relationship between the ratio of the number of times of discarding and the inner diameter of the through hole provided in the billet. In FIG. 6, when the inner diameter of the through hole exceeds about 10% of the outer diameter of the billet, the ratio of the number of times of the discarded holes rapidly increases, and the ratio increases to 20%.
On the side, the rate of rise stably becomes higher and lower.

The effect of the inner diameter of the through hole is considered as follows. Usually, barrel-type rolls are used in Mannesmann perforation. That is, once drilling is started, the outer diameter is once reduced, and then expanded while being rolled by a drilling plug and a drilling roll. At this time, if there is not enough diameter of the through hole, the through hole is closed at the stage of diameter reduction, and only the lubricant that has been sprayed from the rear end side of the billet adheres to the initial stage. Does not contribute to Therefore, a through hole having a certain size is required. Further, if the lubricant is to be directly adhered to the plug during drilling, a through hole having a larger diameter is required. However, if the hole diameter is too large, the temperature of the billet drops significantly before reaching the drilling machine, and as a result, abrasion occurs due to an increase in the surface pressure applied to the drilling plug. Therefore, about 50% or less is desirable.

Therefore, it is considered that the through-hole which has a sufficient effect for improving the durability is 10% or more and 50% or less of the material diameter.

When the lubricant is blown from the front end of the billet (drilling machine side), extra time is required for the lubricant blowing device to retreat outside the line, so that the lubricant may be deteriorated. There is a disadvantage that the operating efficiency of the drilling machine is reduced.

Example 1 Table 1 shows the effects of the present invention confirmed by a drilling test using a model drilling machine. 3% Cr-1% N commonly used for drilling plugs such as carbon steel drilling
After making a perforated billet heated to 1250 ° C. with a model perforator, the durability was evaluated. The steel was made of i-steel and hot tool steel (JIS-SKT3 equivalent material). At the same time, the surface temperature of the plug was measured with a radiation thermometer, and the effect was tested.

The perforated billet was made of 13% Cr steel, and the perforated plug was heat-treated in advance to adjust the surface oxide scale thickness to approximately 350 μm, which is almost the same as that of the actual machine. The perforated billet was a solid material and a hollow material provided with a through hole having an outer diameter of 30%. The lubricant was ejected onto the inner surface of the raw material during transportation from the tip of the pusher (rear end of the billet), that is, immediately before the billet was bitten by the punch.

As a result, when a perforated plug made of 3% Cr-1% Ni steel was used, the temperature of the perforated plug surface after one pass reached 715 ° C. in the comparative example, but the hollow billet was used. The temperature was controlled to 530 ° C, and the perforation time was shortened by about 45%.

In Table 1, the durability of the perforated foam is represented by the ratio of the number of perforations until the discard of the hollow billet to the number of perforations until the discard of the solid billet.

Further, in Table 1, the degree of increase in the peak temperature of the perforated flux is shown by the surface temperature ratio at the time of disposal. The surface temperature ratio at the time of disposal is such that the hollow billet is compared with the number of perforations when the peak temperature of the solid billet reaches 800 ° C. (surface temperature at the time of disposal) (hereinafter referred to as the reference number of perforations). It is the ratio of the peak temperature of the perforated fiber when perforated the number of times. When a 3Cr-1Ni steel perforated plug is used, the standard number of times of discarding is 3 passes, the peak temperature of the hollow billet during the same 3 passes is 690 ° C, and it reaches 800 ° C in 9 passes. The hourly surface temperature ratio is 690/800 = 0.87, and the ratio of the number of perforated holes is 9/3 = 3. In Table 1, when any of the perforated plugs is used, the ratio of the number of times of discarding perforations and the surface temperature ratio at the time of discarding are improved, and according to the present invention, the temperature rise of the perforated plugs is suppressed, and the durability is also improved. You can see that.

[0044]

[Table 1]

[Example 2] Table 2 shows that hot tool steel (JIS-SK
Uses a perforated plug made of T3 equivalent material), the billet has a through hole diameter of 20% of the outer diameter, and the material is 1% Cr steel, 5% Cr steel, 9% Cr
The results of performing the same tests as in Example 1 for three types of steel are shown. Table 1 compares the measurement results of the lubricating hollow material with the measurement results of the solid material as 1.0 (reference) for each billet material. In any of the materials, the ratio of the number of times of discarding perforation and the surface temperature ratio at the time of discarding are both improved, and the improvement effect of the present invention is recognized.

It should be noted that the present invention is not limited to the Mannesmann drilling machine (first drilling machine), but can be applied to an inclined drilling machine using three rolls and a so-called second drilling machine (elongator). is there.

Further, the lubricant is not limited to graphite powder, but may be glass powder. In addition, nitrogen gas, the atmosphere, or the like can be properly used for jetting.

[0048]

[Table 2]

[0049]

The method for manufacturing a seamless steel pipe according to the present invention comprises:
Using a hollow billet, lubricant is injected into the through hole from the rear end of the hollow billet before drilling, so the surface pressure acting on the body of the plug during drilling is suppressed, and the rise in the peak temperature of the body is suppressed. As a result, the plug body is hardly damaged, and the durability of the plug can be greatly improved. In particular, since the lubricant can be reliably supplied to the rear half of the hollow billet, the above effect is remarkable in a long hollow billet.

Further, especially in a high alloy containing 5% or more of an alloy component such as Cr, Ni, and Mo, the life of a drilled plug is improved while using the same steel pipe manufacturing method as in the past, and even after drilling, there is no difference. Since the product can be finished in a process without any trouble, the improvement of the production efficiency can be achieved, thereby enabling the supply of inexpensive products.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a perforation situation showing an embodiment of the present invention.

FIG. 2 shows the surface temperature distribution of a perforated plug when a carbon steel billet is perforated in the prior art.

FIG. 3 shows a surface temperature distribution of a perforated plug when a 13% Cr steel billet according to the related art is perforated.

FIG. 4 shows the relationship between the peak temperature and the number of perforations in the prior art.

FIG. 5 shows the effect of the through hole and the lubricant on the forward efficiency in the present invention.

FIG. 6 is a comparison of the number of perforations at which the peak temperature in FIG. 5 reaches 800 ° C.

FIG. 7 is a correlation diagram showing the relationship between the ratio of the number of times of discarding perforation and the inner diameter of a through hole provided in a billet.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 punch roll 2 punch plug 3 pusher 4 billet 31 lubricant jetting device 32 billet pressing device

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Takashi Ariizumi, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Tatsuharu Oda 1-2-1, Marunouchi, Chiyoda-ku, Tokyo No. Nippon Kokan Co., Ltd. (72) Inventor Motoharu Yamazaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (4)

[Claims] 1. A method for manufacturing a seamless steel pipe in an inclined drilling machine which arranges a roll inclined with respect to a pass line of a material to be pierced and a plug for piercing the material to be drilled on the pass line. The material to be pierced has a through hole in the center of the cross section, and a lubricant is injected into the through hole from the rear end of the material to be pierced from the rear end of the material to be pierced on the entry side of the inclined drilling machine prior to piercing. Manufacturing method of seamless steel pipe. 2. The method for producing a seamless steel pipe according to claim 1, wherein the lubricant is supplied mainly to the rear end side inside the through hole of the material to be pierced. 3. The method for producing a seamless pipe according to claim 1, wherein the inner diameter of the through hole of the material to be pierced is 10% or more of the outer diameter of the material to be pierced. 4. The material to be pierced is Cr, Mo, or Ni.
The method for producing a seamless steel pipe according to claim 1, wherein at least one of the steels is contained in an amount of 5% or more.