JP2000140910A - Manufacture of seamless pipe and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel pipe having high strength and high resistance to corrision, that is, the steel pipe of a heavy-load bearing material, after obtaining a hollow pipe stock by piercing a material to be rolled whose hot ductility is lowered at a temp. not less than a specified temp. at a temp. less than the hot ductility lowering temp., by assistantly heating this pipe stock before a mandrel bar is inserted and rolling this hollow pipe stock which is assistantly heated with a mandrel mill. SOLUTION: A round billet which is heated with a heating furnace 1 so that the temp. of the material to be rolled after piercing is less than the temp. (>=1000 deg.C) where the hot ductility is rapidly lowered is pierced with a piercer 2 at the temp. less than the hot ductility lowering temp. and the hollow pipe stock is conveyed to a shape straightening machine 3 and, moreover, heated before inserting a mandrel bar with a solenoid type induction heating device 4 for assistantly heating. By inserting the mandrel bar into the hollow pipe stock which is heated to a degree that the rolling capacity of the mandrel mill 5 is satisfied, the pipe stock is rolled to a prescribed thickness with the mandrel mill 5, the mandrel bar is pulled out and the pipe stock is conveyed to the reheating furnace in the next stage.

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 pipe, and more particularly to a method for producing a seamless pipe of a high-alloy steel (having a high rolling load and high power), which is a high-load material, and a facility therefor.

[0002]

2. Description of the Related Art One of the methods for producing a seamless steel pipe is by mandrel mill rolling. In mandrel mill rolling, a round steel slab heated by a rotary hearth heating furnace is pierced by a piercing machine to form a hollow shell. Thereafter, a mandrel bar is inserted into the hollow shell, fed to a tandem-arranged mandrel mill, and rolled. The tube that has been rolled by the mandrel mill (with the mandrel bar inside) is sent to the mandrel mill stripper table, and the mandrel bar is pulled out of the tube.

[0003] On the other hand, as a trend of seamless pipe users in recent years, steel pipes having higher strength and higher corrosion resistance have been desired with the severer use environment. In order to satisfy such requirements, it is inevitable to use a high alloy steel containing a large amount of alloying elements such as stainless steel. However, such high-alloy steels have a higher deformation resistance than ordinary steel, so that the rolling load and power are large, and there is a problem that production cannot be carried out with existing small-load-resistant mills designed for ordinary steel.

[0004] In addition to installing a new rolling mill with a large load capacity,
As a method for reducing the rolling load, there is a method that utilizes a decrease in deformation resistance at a high temperature. Examples of the method include (A) a method of extracting a round steel piece by heating at a high temperature, and (B) a method of reheating in the middle of a rolling line.

[0005]

The above method (A) cannot be adopted because not only the scale amount is increased due to heating, but also an internal surface defect occurs at the time of drilling due to a decrease in hot ductility value depending on the type of steel. On the other hand, as the method (B), a method in which a material to be rolled is heated and rolled before a mandrel mill is proposed in JP-A-61-154704. This method describes that the material is induction-heated while the mandrel bar is in the hollow shell. Although this method is certainly effective in reducing the rolling load, it has the following problems. (1) Since the amount of heat transfer (between the rolled material and the mandbar) from charging to pulling out the mandrel bar is large, the temperature of the mandrel bar increases, and the bar thermally expands to form a kind of "shrink fit". It is difficult to pull out the pipe (if the pipe is forcibly pulled out, a flaw on the inner surface of the pipe will occur).

(2) In order to heat only the material to be rolled,
Complex equipment and control to change the frequency of the induction heating device according to the wall thickness of the hollow shell after drilling is required,
This is a large investment.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is an object of the present invention to provide a method for producing a seamless steel pipe of a high load material on a rolling line using a mandrel mill, and to provide a facility therefor. Aim.

[0008]

In order to solve the above problems and achieve the object, the present invention uses the following means.

(1) The production method of the present invention comprises the steps of perforating a rolled material having a reduced hot ductility at a temperature of 1000 ° C. or higher at a temperature lower than the hot ductility lowering temperature to obtain a hollow shell. A method for manufacturing a seamless tube comprising a step of auxiliary heating a hollow shell before inserting a mandrel bar, and a step of mandrel mill rolling the auxiliary heated hollow shell.

(2) The equipment of the present invention comprises: a punching machine for punching a material to be rolled having a reduced hot ductility at a temperature of 1000 ° C. or higher at a temperature lower than the temperature at which the hot ductility is reduced; Production of a seamless tube comprising a solenoid coil type induction heating device for auxiliary heating before inserting the mandrel bar, and a mandrel mill for inserting the mandrel bar into the auxiliary heated hollow shell and rolling. Equipment.

(3) The equipment according to the above (2), characterized in that the equipment of the present invention further comprises a straightening device for correcting a longitudinal bending of the hollow shell on the inlet side of the induction heating device. It is a seamless pipe manufacturing facility as described.

The above-mentioned supplementary heating does not mean that heating is actively performed in-line. It is clear that excessively relying on in-line heating using high-frequency heating increases the cost of electricity and deteriorates the fuel consumption rate. In addition, since the capacity of the heating device increases, the equipment becomes large-scale. Therefore, the expression of auxiliary heating is used here.

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have obtained the following findings.

First, with respect to the inner surface defect at the time of high-temperature heat extraction, which is the first problem, the temperature of the material to be rolled after perforation becomes lower than the temperature at which the hot ductility rapidly decreases (hereinafter, referred to as T0). The problem can be solved by adjusting the heating furnace extraction temperature as described above. This inevitably results in a lower furnace extraction temperature and an increased rolling load on the downstream mandrel mill. However, this problem can be solved by reducing the deformation resistance of the material to be rolled by supplementarily heating the material to be rolled (hollow shell) before inserting the mandrel bar.

The details will be described below. Figure 1 shows SUS30
4 shows the change in hot ductility of Steel 4. When the temperature is lower than 1280 ° C., good ductility is exhibited, but at temperatures higher than 1280 ° C., the ductility sharply decreases (T0 = 1280 ° C.). If the temperature after drilling is in the temperature range of T0 or more, the workability is poor and an internal flaw is induced, so the drilling temperature must be lower than T0. Since T0 varies depending on the type of steel, it is necessary to perform a material test in advance and adjust the temperature of the heating furnace and the temperature at the side of the punch.

This temperature restriction, that is, the temperature drop of the material to be rolled (hollow shell) after perforation and the temperature drop of the material to be rolled at the entrance side of the mandrel mill are set between the drilling machine and the mandrel mill. The problem can be solved by heating the material to be rolled using an auxiliary heating device. The heating device only needs to have a heating capacity enough to cover the above-mentioned temperature constraint, and therefore does not lead to a significant increase in energy cost.

As the heating method, gas heating, electric heating, and induction heating can be considered.
Considering the ability to raise the temperature in a short time, etc., induction heating is desirable. As the induction heating method, a solenoid type with high heating efficiency is used. In the present invention, since the material to be rolled (hollow shell) is heated before inserting the mandrel, the heat transfer to the mandrel during the mandrel mill rolling is minimized and the stripping property of the bar after the mandrel mill rolling is deteriorated. Absent. Further, the frequency used for induction heating may be set at one level based on the maximum wall thickness after perforation of the material to be rolled and the skin effect, so that large-scale capital investment is not achieved. The heating capacity of the heating equipment may be calculated from the dimensions of the material to be heated, the conveying speed in the heating zone, the rolling capacity of the mandrel mill, and the like.

From the viewpoint of improving the heating efficiency, the distance between the heating coil and the material to be rolled must be as small as possible.

However, since the material to be heated after drilling has some "bends" in the longitudinal direction, there is a risk that the material to be heated collides with the heating coil. Therefore, in a mill having a problem in the longitudinal shape of the material to be rolled (hollow shell) after perforation, a shape correcting facility is required on the inlet side of the heating device.

Based on the above findings, the present inventors have proposed 10
A step of obtaining a hollow shell by piercing a rolled material having a reduced hot ductility at a temperature lower than the hot ductility reduction temperature at a temperature lower than the hot ductility reduction temperature at a temperature of 00 ° C. or higher, and inserting the hollow shell into a mandrel bar before insertion A step of auxiliary heating with a solenoid coil type induction heating device, and a step of mandrel mill rolling the auxiliary heated hollow shell, and furthermore, if necessary, an induction heating device before the mandrel mill. To provide a straightening device for correcting the longitudinal bending of the hollow shell on the entry side, in a rolling line using a mandrel mill, to find a method and equipment for manufacturing a seamless steel pipe of high load material,
The present invention has been completed.

Hereinafter, embodiments of the present invention will be described.

FIG. 2 shows an arrangement diagram of a seamless pipe rolling facility according to one embodiment of the present invention. In FIG. 2, 1 is a heating furnace, 2 is a drilling machine, 3 is a shape straightening machine, 4 is an induction heating device, and 5 is a mandrel mill.

The round steel slab heated so that the temperature of the material to be rolled on the exit side of the piercing machine is less than T0 is pierced to a predetermined thickness by the piercing machine 2, and then conveyed to the shape straightening machine 3 where the mandrel is provided. The mandrel bar is inserted while being heated to the extent that the rolling capacity of the mill 5 is satisfied. Immediately thereafter, it is rolled to a predetermined thickness by a mandrel mill, the mandrel bar is pulled out, and is conveyed to a reheating furnace (not shown) in the next step. By such a manufacturing process, it is possible to manufacture a seamless pipe that satisfies the temperature restriction during drilling and the rolling restriction of the mandrel mill. In addition to the present embodiment, various transport paths for the material to be rolled (hollow shell) can be considered, but it is important to reduce the temperature drop of the material to be rolled during transport as much as possible. It is desirable that the structure has a heat retaining cover.

[0023]

As described above, according to the present invention,
By specifying the manufacturing conditions and equipment configuration,
It is possible to provide a method and equipment for manufacturing a seamless pipe having high corrosion resistance at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in hot ductility of SUS304 steel.

FIG. 2 is a layout view of a seamless pipe according to an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating furnace, 2 ... Punching machine, 3 ... Shape straightening machine, 4 ... Induction heating apparatus, 5 ... Mandrel mill.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tatsuro Katsumura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Tatsuharu O1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (72) Inventor Yoshihide Okamoto 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Japan Inside Nippon Kokan Co., Ltd. (72) Inventor Tsutomu Sugiyama 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun Honko Tube Co., Ltd.

Claims (3)

[Claims] 1. A step of obtaining a hollow shell by piercing a material to be rolled whose hot ductility decreases at a temperature of 1000 ° C. or higher at a temperature lower than the hot ductility lowering temperature, and inserting a mandrel bar into the hollow shell. A method for manufacturing a seamless tube, comprising: a step of auxiliary heating before; and a step of mandrel mill rolling the auxiliary heated hollow shell. 2. A drilling machine for drilling a material to be rolled whose hot ductility decreases at a temperature of 1000 ° C. or more at a temperature lower than the hot ductility lowering temperature, and a drilled hollow shell before inserting a mandrel bar. And a mandrel mill for rolling a mandrel bar by inserting a mandrel bar into an auxiliary heated hollow shell. 3. The seamless pipe manufacturing equipment according to claim 2, further comprising a straightening device for correcting a longitudinal bending of the hollow shell at an inlet side of the induction heating device. .