JPH08276213A - Manufacture of butt-welded steel tube prevented outside score and rolling-in of admixture in butt-weld zone - Google Patents

Abstract

PURPOSE: To prevent outside score and rolling-in of admixture in the butt-weld zone by providing a rotary cutting device between forming rolls and butt-welding rolls and removing by cutting the edge part of a tubular skelp. CONSTITUTION: Besides an oxigen blow from the nozzle 7 of a welding horn 5 just before butt-welding, the rotary cutting device 8 is provided between the forming rolls 4 and the butt-welding rolls 6 and rotary cutting tools 9 are attached. In this way, the shape of butt-welding surface in the edge parts of the tubular skelp is made into flat and scale which is stuck to the butt-welding surface in both edge parts of the tubular skelp in a heating furnace and during hot forming is removed. Thus, uniform press-contacting force acts on the whole butt-welding surface and the generation of outside score and inside bead is eliminated.

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 which prevents the outer surface stripes of the forged portion of the forged steel pipe and the inclusion of foreign matters.

[0002]

2. Description of the Related Art A conventional method of manufacturing a forged steel pipe is shown in FIG.
The forged steel pipe is made by continuously heating the steel strip 1 used as the material in the heating furnace 2.
It is heated to 200 ° C. to 1300 ° C., molded by the molding rolls 3 and 4, and oxygen is blown from the nozzle 7 of the welding horn 5 just before forging to the edge portion for forge welding. After that, it is successively drawn by a drawing roll and rolled to continuously produce a forged steel pipe having a predetermined outer diameter and thickness. At this time, the oxygen blowing direction is the same as the traveling direction of the tubular skelp, and the position where oxygen is blown from the oxygen nozzle to the edge portion is immediately before forging welding,
There is a problem in that the scale near the edge portion that has not been removed and the scale that has been blown away and that has entered the vicinity of the forged contact bite into the forged surface and become foreign matter that reduces the strength of the forged portion. In order to prevent foreign matter from being caught in the forged portion of the forged steel pipe and streaks on the outer surface during the production of the forged steel pipe, JP-A-03-2 is used.
As in 48715, there is a method of cutting and removing the outer surface of the forge-welded portion between the forge-welded roll and the drawing roll to prevent the outer surface of the forged-welded portion.

[0003]

As shown in FIG. 3, in the conventional manufacturing process, the position where oxygen is blown is from the nozzle 7 of the welding horn 5 immediately before forging, and the tubular skelp 1 advances in the direction of oxygen blow. In the same direction as the method. For this reason, there is a problem in that the scale near the edge of the tubular skelp 1 that has not been removed and the scale that has been blown off and that has entered the vicinity of the forge welding become caught in the forged surface and become foreign matter, which reduces the strength of the forged portion. As shown in FIG. 2, there are two types of skelp edge shapes when cut into a predetermined width of steel strip with a slitter, bar up (a) and bar down (b). When the edges with a shape like a bar down are butted against each other, the inner surface side has a larger pressure contact force than the outer surface side and an inner bead occurs, and the outer surface side has an outer surface line due to insufficient pressure contact force. There is a problem of deterioration. Further, the oxygen blowing from the welding horn just before the forging welding according to the conventional method must simultaneously satisfy the two effects that the scale is blown out of the forging surface and the temperature of the forging surface is instantly raised by FeO formation heat. JP-A-53-
As in 90148, there is a method in which the direction of oxygen blow is made opposite to the method of advancing the tubular skelp to prevent scale entrapment at the forging welded surface. Since the temperature decreases, a sufficient forge welding temperature cannot be maintained, and there are problems of poor forge welding and scale entrapment. By applying the method of the present invention, the outer surface line of the forged portion and the biting of the scale are completely eliminated, and a forged steel pipe of high strength and high quality can be manufactured.

[0004]

According to the present invention, a steel strip which is a material is heated in a heating furnace, and the heated steel strip is hot-formed into a tubular shape. In the process of manufacturing a forged steel pipe in which oxygen is blown from the nozzle of the Ding horn and forged, the shape of the forged surface of the edge part of the tubular skelp is adjusted to be flat and the butting is improved.
Also, in order to completely remove the scale generated on the forged surface of the edge of the tubular skelp during the heating furnace and hot forming, in addition to oxygen blow just before forging, a rotary cutting installed between the forming roll and the forging roll. A method for producing a high-strength forged welded steel pipe having a high strength at a forged portion, which is characterized in that an edge portion of a tubular skelp is cut and removed by an apparatus.

The present invention will be described in detail with reference to FIGS. 1 (a) and 1 (b).

As shown in FIGS. 1 (a) and 1 (b), in addition to oxygen blowing from the nozzle 7 of the welding horn 5 immediately before forging, a rotary cutting device 8 is installed between the forming roll 4 and the forging roll 6. Then, a rotary cutting tool 9 is attached to the rotary cutting device 8. The cutting tool can move freely up and down, left and right, and the mounting angle θ so that it can cut all pipe sizes. Table 1 shows the shape of the cutting tool of the rotary cutting device. The cutting tool cuts at a high temperature exceeding 1000 ° C, but it is sufficient to use commercially available high temperature super steel or fine ceramics and water cooling.

[0007]

[Table 1]

As shown in FIGS. 1 (a) and 1 (b), the forming roll 4 installed for stabilizing the hot forming significantly reduces the quality defects due to the edge buckling and the twist forming. It may not be done. When not installed, the rotary cutting device 8 is installed at an intermediate position between the forming roll 3 and the forging roll 6. The forging surface of the edge portion of the tubular skelp is adjusted to a flat shape by the rotation prescripting device 8, and the scale adhered to the forging surface of both edge portions of the tubular skelp is removed during the heating furnace and hot forming. By making the forged surface flat, a uniform pressure contact force acts on the entire forged surface, and the generation of inner surface bead is completely eliminated. By installing a rotary cutting device between the forming roll and the forging roll, the oxygen probe from the welding horn just before forging can be used only for the purpose of raising the sound of the forging surface just before forging. Oxygen blow condition can be easily set. As a result, a sufficient forge welding temperature can be maintained, and a high-strength forged welded steel pipe with high strength can be easily manufactured. From the above, by applying the present invention, the outer surface streaks and scales of the forged portion are completely eliminated and the forged portion has high strength,
High quality forged steel pipe can be manufactured.

[0009]

EXAMPLES Table 2 shows the practical test results by the manufacturing process of the embodiment of the method of the present invention shown in FIG. 1, and Table 3 shows the practical test results by the conventional manufacturing process. The methods of calculating the flatness ratio and the expansion ratio shown in Tables 2 and 3 are shown in the following equations.

Flatness == (1-H / D) × 100 (%)
D: Outer diameter of raw pipe H: Flat height Expansion ratio = D '/ D D: Outer diameter of raw pipe
D ′: Outer diameter after pipe expansion The forged steel pipe manufactured by the manufacturing method of the present invention completely eliminates the outer surface streaks of the forged welded portion and the inclusion of foreign matter, and has a higher strength and higher quality than the forged steel pipe manufactured by the conventional manufacturing process. It was possible to manufacture the forged steel pipe of.

[0011]

[Table 2]

[0012]

[Table 3]

[0013]

EFFECTS OF THE INVENTION According to the manufacturing process of the conventional method, oxygen is blown immediately before forging, and since the scale is in the same direction as the traveling direction of the tubular skelp, the scale cannot be completely removed from the vicinity of the edge of the tubular skelp and is blown off. Moreover, there is a problem that the scale penetrates into the vicinity of the forged contact and the scale is caught in the forged contact surface to deteriorate the strength and quality of the forged contact portion. By applying the method of the present invention, the outer surface streaks and scale biting of the forged portion can be completely eliminated, and the forged portion high strength and high quality forged steel pipe can be manufactured.

[Brief description of drawings]

1A is a plan view showing a method for manufacturing a forged steel pipe according to the method of the present invention, and FIG. 1B is a cross-sectional view near a rotary cutting device according to the method of the present invention.

FIGS. 2A and 2B are diagrams showing skelp edge shapes when cut by a slitter.

FIG. 3 is a plan view showing a manufacturing process of a conventional forged steel pipe.

[Explanation of symbols]

 1 ... Steel strip 2 ... Heating furnace 3 ... Forming roll 4 ... Forming roll 5 ... Welding horn 6 ... Forging roll 7 ... Nozzle 8 ... Rotating cutting device 9 ... Rotary bite

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinori Ogata 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu Steel Works

Claims (1)

[Claims] 1. A steel strip as a material is heated in a heating furnace, and the heated steel strip is hot-formed into a tubular shape, and oxygen is blown from a nozzle of a welding horn immediately before forging on the forged surface of the edge portion of the tubular skelp. In the manufacturing process of forged steel pipes that are forged and welded, the shape of the forging surface of the edge part of the tubular skelp was adjusted to be flat and the butt was improved, and it was generated on the forging surface of the edge part of the tubular skelp during the heating furnace and hot forming. In order to completely remove the scale, in addition to oxygen blow immediately before forging, the outer surface of the forging part is characterized by cutting and removing the edge part of the tubular skelp by a rotary cutting device installed between the forming roll and the forging roll. , A method for manufacturing a forged steel pipe for preventing inclusion of foreign matters.