JPH08243636A - Manufacture of butt-welded steel tube excellent in quality of butt part - Google Patents

Abstract

PURPOSE: To provide a manufacturing method for butt-welded steel tube excellent in the quality of a butt part. CONSTITUTION: In a manufacturing method of a butt-welded tube which is butt-welded after the steel strip of the prescribed width is heated and hot rolled, the scale suppressing agent is applied to each edge in the width direction of the steel strip, and heated to achieve the hot rolling, and the edges are blown with the air of >=500 deg.C to <=1400 deg.C, and the butt welding is achieved by omitting the subsequent oxygen blow to manufacture the butt-welded steel tube excellent in the quality of the butt part.

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 forged steel pipe having excellent forged abutting portion quality.

[0002]

2. Description of the Related Art Generally, a forged welded tube is manufactured by inserting a steel strip having a predetermined width into a heating furnace continuously as shown in FIG.
After heating to ˜1350 ° C., it is molded by a molding stand, and oxygen blow is performed just before forging to perform forge welding. After that, squeeze with a stretch reducer to make the outer diameter wall thickness. This method is the most efficient and highly productive method for producing steel pipes and is widely used, but it requires a lot of energy to heat it to a high temperature and the edge of the steel strip. Scale is generated in the, and if it is left as it is, the generated scale is caught in the forged abutting portion and causes a defect.

Therefore, as described in Japanese Patent Application Laid-Open No. 58-122188, there is a method in which after low temperature heating, only the edge ends are subjected to high frequency heating, and then oxygen blow is carried out immediately before forging welding. Further, in order to improve the quality of the abutting portion, as described in JP-A-60-15082,
There is a method in which high-frequency resistance welding is performed at a relatively low temperature, bead removal cutting is performed thereafter, the temperature is again heated to about 900 ° C to 1100 ° C, and then squeezed with a stretch reducer.

[0004]

Generally, in a method for manufacturing a forged steel pipe, oxygen blow is carried out immediately before forging.
The oxygen blow has two purposes of removing the scale attached to the edge, heating the edge with oxygen heat, and removing the scale generated at that time.
However, the former adhered scale is a scale that is generated when the steel strip is heated and a scale that is adhered from others at that time, but it is very difficult to remove the adhered scale from the edge. Therefore, a problem arises in that the scale is caught in the forged butting portion during forging.

In order to solve this problem, a method has been devised in which the steel strip is heated to a relatively low temperature to suppress the generation of scale, and high frequency induction heating is added near the forged abutting portion after heating. , Since this method uses frequency resistance welding, the heating width is wide, and swelling occurs during forging, that is, a bead is generated, and then it is necessary to perform cutting to remove the bead, and at the forged portion and other parts. Due to the temperature difference, uneven thickness will occur when squeezing with a stretch reducer thereafter. So again about 900 ℃ -11
It must be squeezed with a stretch reducer after heating to 00 ° C. Due to these new problems, efficiency and productivity are greatly impaired.

The present invention solves the problems in the method for manufacturing a forged steel pipe as described above, and proposes a forged steel pipe having excellent abutting portion quality.

[0007]

Means for Solving the Problems The present invention for achieving the above-mentioned object is to provide a forged welded tube manufacturing method in which a steel strip having a predetermined width is heated and hot-formed and then forged. After applying the scale inhibitor to both edges in the width direction, heating is performed to perform hot forming and the edges are 500 ° C. or more, 1400
It is a method for producing a forged steel pipe with excellent quality at the abutting portion, which comprises blowing with air at a temperature of ℃ or less and then omitting oxygen blowing.

The present invention will be described in detail below. FIG. 1 shows the manufacturing process of the present invention. In the conventional process, a steel strip having a predetermined width is continuously inserted into a heating furnace as shown in FIG.
After heating at ℃ to 1350 ℃, it is molded by a molding stand, oxygen blow is performed just before forging, and forging is performed. After that, squeeze with a stretch reducer to make the outer diameter wall thickness. The method of the present invention, as shown in FIG. 1, applies a scale inhibitor to the edge of a steel strip before continuously inserting the steel strip of a predetermined width into a heating furnace. The application place may be before the continuous insertion of the heating furnace or in the state of the slitting coil.

After that, the sample is continuously heated in a heating furnace, but due to the scale suppressing effect, the scale generation amount is smaller in the edge coated with the scale suppressing agent than in other portions. However, as usual, in this state, about 1200 ° C to 135 ° C
When heated to 0 ° C, molded with a molding stand, and oxygen blown just before forging welding, the biggest problem is that the scale inhibitor applied to the edge is not completely removed by oxygen blowing just before forging welding. That is, the forged quality is deteriorated by being bitten in the abutting part.

Generally, a scale inhibitor forms a heat-resistant film by mixing an inorganic substance and an organic substance, or reacts with an iron substrate to form an iron-based heat-resistant film, thereby blocking oxygen from the iron substrate and suppressing scale. . Therefore, the organic matter is burned down by heating, but the inorganic matter (or its oxide) remains.

Therefore, air is blown from the heating furnace until the oxygen is blown, and these inorganic substances (or their oxides) are blown off. At this time, if the temperature of the air is room temperature, the temperature of the heated edge is lowered, so the temperature is set to 5000 ° C. or higher. If the temperature exceeds 1400 ° C., the edge will melt, so the temperature should be below this value.

Further, if the edge is completely removed by air blow, it is not necessary to blow oxygen as in the conventional case.
That is, the purpose of oxygen blowing is to remove the scale attached to the edge and heat the edge with the heat of oxidation,
Moreover, it has two purposes of removing the scale generated at that time. The former purpose can be replaced by applying scale inhibitor + air blow. In the latter case, if the edge has no scale and the temperature of the edge is 1200 ° C. or higher, forging can be performed without raising the temperature by oxygen blow. At the same time, it is possible to prevent the scale from remaining due to oxygen blowing.

By thus combining the scale inhibitor and the air blow and omitting the oxygen blow, it is possible to manufacture a forged steel pipe having an excellent abutting portion quality.

[0014]

EXAMPLES Table 1 shows a method of manufacturing a forged steel pipe having a size of φ42.7 × t4.0 (mm) according to the conventional method and the method of the present invention.
It showed in comparison with. In the conventional method, oxygen is blown at the time of forging, but either when the scale inhibitor is not used, when the air blow is not applied even if it is used, or when the temperature of the air blow is not appropriate even when the scale inhibitor is applied + air blow. Even in this case, the scale is caught in the forged butting portion, and the flatness is reduced. In the method of the present invention, by applying the scale inhibitor coating + air blow to make the temperature of the air blow proper and omitting the oxygen blow, it becomes possible to secure excellent abutting part quality.

[0015]

[Table 1]

[0016]

INDUSTRIAL APPLICABILITY Generally, in a method for manufacturing a forged steel pipe,
The adhesion scale before forging is the scale that occurs when heating the steel strip and the scale that adheres from others at that time.
In both cases, it is very difficult to remove the material attached to the edge. For this reason, there arises a problem that the scale is caught in the forging abutting portion during the forging welding. This problem cannot be solved by the conventional method, which causes the deterioration of the quality of the forged butting portion. The present invention can solve the problems in such a method for manufacturing a forged steel pipe and obtain a forged steel pipe with excellent abutting portion quality.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process of a method of the present invention.

FIG. 2 is a diagram showing a manufacturing process of a conventional method.

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[Procedure amendment]

[Submission date] July 3, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

Therefore, air is blown from the heating furnace until the oxygen is blown, and these inorganic substances (or their oxides) are blown off. At this time, if the temperature of the air is room temperature, the temperature of the heated edge is lowered, so the temperature is set to 500 ° C. or higher. If the temperature exceeds 1400 ° C., the edge will melt, so the temperature should be below this value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinya Sakamoto 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corp. Kimitsu Works Ltd.

Claims (1)

[Claims] 1. A method for producing a forged tube in which a steel strip having a predetermined width is heated to perform hot forming and then forged, and a scale inhibitor is applied to both edges of the steel strip in the width direction and then heated. Performs hot forming and the edge is 500 ° C or higher, 1400
A method for producing a forged steel pipe having excellent forged abutting part quality, which comprises performing blow forging with air at a temperature of ℃ or less and then omitting oxygen blowing.