JPH0994610A - Manufacturing method of forged steel pipe and equipment line - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high quality butt-welded steel tube having the excellent surface skin by heating a skelp, forming to tubular form with a forming butt- welding machine, hot cutting after the dimension of the tube is reduced with a hot reducer, cooling to descale and successively reducing the dimension in a prescribed temp. range with a warm reducer. SOLUTION: A skelp 1 continuously supplied is heated in a heating furnace 3 to a prescribed butt-welding temp. and formed to the tubular form with a forming butt welding machine 4, a tubular body 2 is produced by mutually butt-welding the both ends. The tubular body 2 is rolled and reduced to a prescribed dimension with a hot reducer 5. The tubular body 2 is cut to a prescribed size with a rotary hot saw 6, cooled with a cooling head 7 to the cooled warm temp. region. Successively, the tube outside surface is descaled with a descaler 8. The tubular body 2 is further rolled and dimensionally reduced in the tube temp. range of 300-830 deg.C with a warm reducer 9. An outside diameter of the tubular body 2 is set with a sizer 10. In the end, by straightening with a straightener 11, the product is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a forged steel pipe having a good outer surface skin and an equipment line.

[0002]

2. Description of the Related Art Forged steel pipes are usually manufactured by heating a continuously supplied skelp to a high temperature in a heating furnace as shown in FIG. Then, both edges are forged into a complete tube body, and then the diameter is reduced to a predetermined dimension by a hot reducer of several to 20 steps, and then the tube is cut to a fixed length with a rotary hot saw. It is manufactured by determining the outer diameter with a sizer, cooling it with a cooling bed, and finally straightening it with a straightener. Forged welded steel pipe is a highly productive continuous steel pipe manufacturing method, in which several kinds of outer diameter size products can be manufactured from skelps of the same size by adjusting the outer diameter drawing amount of the hot reducer. Forged steel pipes with an outer diameter of 4 inches or less have a
Manufactured at high speeds of 100-400m / min.

By the way, in the forged steel pipe manufactured by the above-described manufacturing process, the skelp must be heated to a temperature at which forging can be performed, so the temperature on the delivery side of the forging machine reaches 1200 to 1300 ° C. After that, during the natural cooling of the pipe body, the diameter is reduced to a predetermined size by the hot reducer, but since the skelp temperature is as high as 1200 ° C or higher and the pipe making speed is very fast, the diameter is reduced by the hot reducer. The temperature is over 1000 ℃.

[0004]

The forged steel pipe manufactured in the above process has a bad surface texture because a large amount of oxide scale (hereinafter simply referred to as scale) is generated on the surface of the pipe body. On the outer surface of the tubular body, during the diameter-reducing rolling with a hot reducer, the peeled scale is caught between the roll and the surface of the tubular body and is stamped on the outer surface of the tubular body, so that the tube has a poor surface texture. Before entering the hot reducer, or even when descaling in the hot reducer, the tube temperature is still in the range of 1000 ° C or higher where scale is easily generated, so the scale is caught between the roll and the tube surface. Is difficult to control, and the effect of improving the surface skin is very small. Also, even if the scale bite is suppressed and the diameter of the hot reducer can be reduced, the scale is generated after passing through the hot reducer because it is still in the high temperature range, and the surface skin problem is not solved. . Specifically, peeling of scale with a sizer and straightener that is placed in the subsequent cooling process to normal temperature
There is a problem of stamping-like rough skin due to biting, and at this time, there is a problem of smallpox-like uneven color caused by partial peeling / falling of scale from the surface of the tubular body. As described above, the forged steel pipe manufactured in the above process becomes a pipe having a poor surface texture, which is an obstacle to high-quality pipe orientation such as a cold-drawing raw pipe.

As a technique for improving the surface skin of a conventional forged steel pipe,
Japanese Patent Application Laid-Open No. 50-99952 discloses a technique for forcibly cooling a pipe body before entering the hot reducer so that the temperature range of the diameter-reduction rolling by the hot reducer becomes a temperature of 750 to 950 ° C. Has been done. However, this technology is mainly aimed at improving the outer surface of the pipe body, but the temperature range of the diameter-reduction rolling is still a temperature range in which secondary scale is easily generated, and descaling is not performed. , It is difficult to dramatically improve the surface skin. Further, since all the diameter-reducing rolling is performed at 900 ° C. or less, there is a drawback that the rolling load of the stand becomes large and the equipment becomes large.

Further, in Japanese Patent Laid-Open Publication No. 54-112768, as a technique for improving the outer surface of the pipe body, the pipe body is forcibly cooled to room temperature on a cooling bed on the outlet side of the sizer and then descaled. Then, a technique for straightening the bend with a straightener is disclosed. Since this technology passes through the straightener after descaling in a temperature range where scale is not generated, it is possible to prevent the occurrence of stamping-like skin roughness due to scale peeling and biting in the straightener, but in the straightener, a reducer, It is not possible to improve even the skin roughness generated in the upstream process such as sizer and to dramatically improve the surface skin.

An object of the present invention is to provide a high quality forged steel pipe having an excellent surface texture.

[0008]

According to a method for manufacturing a forged steel pipe according to a first aspect of the present invention, a skelp continuously supplied is heated in a heating furnace, and the skelp is formed into a tubular shape by a forming / forging machine, and both of them are formed. The edges are welded together to form a tube, the tube is reduced in diameter to a predetermined size by a hot reducer, the tube is hot cut, the tube is cooled and descaled, and then a warm reducer is used. The tube is adapted to be reduced in diameter in the tube temperature range of 300 to 830 ° C.

According to a second aspect of the present invention, in addition to the first aspect of the present invention, the pipe cooling step and the descaling step are simultaneously performed by a high pressure water injection system.

According to a third aspect of the present invention, there is provided a series of forged steel pipe manufacturing equipment, which comprises a heating furnace for heating continuously supplied skelps.
A forming / forging machine for forming the skelp into a tube and forging both edges thereof into a tube, a hot reducer for reducing the diameter of the tube to a predetermined size, and a cutting machine for hot cutting the tube. When,
A cooling device for cooling the pipe, a descaling device for descaling the pipe, and a warm reducer capable of reducing the diameter of the pipe in the pipe temperature range of 300 to 830 ° C. are sequentially arranged. It is a thing.

According to a fourth aspect of the present invention, in addition to the third aspect of the present invention, the cooling device and the descaling device are constituted by a high-pressure water jet cooling device and a descaler. It was done.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a schematic view of the steps of the method of the present invention. In the figure, 1 is a skelp, 2 is a tube, 3 is a heating furnace, 4 is a forming / forging machine, 5 is a hot reducer, 6 is a rotary hot saw, 7 is a cooling bed, 8 is a descaler, 9 is a warm reducer, 10 is a sizer, 11
Is a straightener.

The method of the present invention is performed in the following steps (1) to (7). (1) Forming / forging step The continuously supplied skelp 1 is heated in a heating furnace 3 to a predetermined forging temperature, the skelp 1 is formed into a tubular shape by a forming / forging machine 4, and both edges thereof are forged and joined. The tube body 2 is used.

(2) Hot diameter reducing step The hot reducer 5 reduces the diameter of the tube 2 to a predetermined size.

(3) Cutting process: A rotary hot saw 6 cuts to a fixed length.

(4) Cooling Step The tube 2 is cooled in the warm zone by the cooling bed 7.

(5) Descaling process The outer surface of the pipe is descaled by the descaler 8.

(6) Warm diameter reduction step The tube body 2 is further diameter-reduced by the warm reducer 6 in the tube temperature range of 300 to 830 ° C.

(7) Sizer process The outer diameter of the tube body 2 is determined by the sizer 10. Finally, straightener 11 is used to straighten the product to obtain a product.

The essential points of the present invention will be described below. Descaler 8 and warm reducer 9 Cooling by the cooling bed 7 and descaling by the descaler 8 are carried out at a tube temperature of 830 ° C or lower. This is because the subsequent diameter-reducing rolling with the warm reducer 9 is performed under the condition that the scale is completely removed.
That is, the diameter reduction rolling temperature in the warm reducer 9 is 300 to 83.
Limit to 0 ℃ range. The reason for this is that if the temperature exceeds 830 ° C, scale is likely to be generated, and even if the scale is removed by the descaler 8, the scale is generated again, and the warm reducer 9 causes skin roughness due to biting of the scale. ℃ was made. If the lower limit is less than 300 ° C, the rolling load of the warm reducer 9 will be large, the required power will be large, and large-scale equipment that can withstand this will be required. Also, the material will be work hardened and the elongation properties of the product will deteriorate. The lower limit was set to 300 ° C because the yield ratio increases. The diameter-reducing rolling temperature in the warm reducer 9 is preferably 500 to 700 ° C. in order to stably maintain both the surface texture and the material properties.

The warm reducer 9 is intended to improve the surface texture and plastically deforms the irregularities on the surface of the tubular body by adding an appropriate outer diameter drawing in a temperature range where scale does not form and under conditions where the scale is removed. Can be smoothed,
Roughness caused in the upstream process such as the hot reducer 5 is improved and the surface texture can be improved.

The outer diameter of the warm reducer 9 is 2 to 30%.
Limited to. The reason for this is that if it is less than 2%, it is not possible to sufficiently smooth the uneven surface roughness of the tubular body surface generated in the upstream process such as a hot reducer, and the effect of improving the surface skin is small, so the lower limit is set. It was set to 2%. If it exceeds 30%, the material will be work hardened to deteriorate the elongation property of the product, and a large number of stands will be required with the increase of the outer diameter drawing, so that the equipment will be large and the upper limit was set to 30%. In addition, the warm reducer can improve the surface skin by installing a single stand or a plurality of stands.

The reason for installing the descaler 8 and the warm reducer 9 on the outlet side of the cooling bed 7 is that the cooling time can be easily cooled to the target temperature of 830 ° C. or less by adjusting the holding time of the pipe body in the cooling bed. The bed was on the exit side. If it is installed on the inlet side of the cooling bed, a forced cooling device will be required to cool it to 830 ° C or less, and the equipment will be large.

The descaler 8 may be a known arbitrary device such as a high-pressure water jet system or a wire brushing system other than the shot blast system shown in FIG.

In the present invention, immediately after the hot reduction by the hot reducer 5, the rotary hot saw 6 cuts to a fixed length. Thereby, the conventional general forged steel pipe manufacturing equipment line can be used, and the pipe body is allowed to flow for a long time until the diameter is reduced by the warm reducer 9 or the sizer by the sizer 10, and then the length is cut to a constant length, No need for a long cooling bed or continuous cooling system.

[0026]

EXAMPLE The surface roughness and mechanical properties of the inner and outer surfaces of the forged steel pipe produced by the example apparatus shown in FIG. 1 were investigated. The results are shown in Table 1.

[0027]

[Table 1]

The relationship between the pipe making conditions and the surface skin of the outer surface of the pipe will be described below. Even if descaling is carried out, if the diameter-reducing rolling with a warm reducer is carried out at a temperature exceeding 830 ° C, the surface roughness of the outer surface of the pipe is Rmax 26 to 41 μm and a rough and rough surface texture is obtained (No. 1, 2 ). In addition, when descaling is not performed, the surface roughness of the outer surface of the pipe is Rmax 21-23 μm even if the diameter-reducing rolling with a warm reducer is performed at a temperature of 830 ° C or less.
It is coarse and no significant improvement effect can be obtained (No. 13). Even if descaling is performed and the diameter-reducing rolling with a warm reducer is performed at a temperature of 830 ° C or less, if the outer diameter reduction is less than 2%, the surface roughness of the outer surface of the pipe is improved to Rmax 16 to 18 μm. The effect is small (No.8). Perform descaling,
The surface roughness of the outer surface of the pipe can be significantly reduced to Rmax 4 to 10 μm by performing the diameter-reducing rolling with the warm reducer roll group at a temperature of 830 ° C. or less and an outer diameter reduction of 2% or more. The surface skin has improved dramatically (No.3 ~ 6,
9-11). However, when the shrinking temperature is less than 300 ° C and the outer diameter drawing exceeds 30%, the work hardening of the material is large,
The ratio of the yield strength YS to the tensile strength TS (YS / TS) is 0.9.
And the elongation value El falls below 34%, which is not preferable from the viewpoint of the mechanical properties of the product pipe (No. 7, 12).

As described above, an excellent surface texture can be obtained by producing the pipe under the conditions within the scope of the claims of the present invention. By the way, the surface roughness of the outer surface of the forged steel pipe manufactured by the conventional manufacturing apparatus shown in FIG. 3 is Rmax 48 to 49 μm, which is very rough.
The surface texture is very poor as compared with the method of the present invention.

[0030]

As described above, the method for producing a forged steel pipe according to the present invention greatly surpasses conventional products in terms of surface texture,
It has become possible to deal with high-quality pipe orientation such as cold drawing raw pipes.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example process of the method of the present invention.

FIG. 2 is a schematic diagram showing an example of a descaling method for the surface of a tubular body.

FIG. 3 is a schematic view showing a general forged and welded steel pipe manufacturing process.

[Explanation of symbols]

 1 Skelp 2 Tube 3 Heating furnace 4 Forming and welding machine 5 Hot reducer 6 Rotary hot saw 7 Cooling bed 8 Descaler 9 Warm reducer 10 Sizer 11 Straightener

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C23G 3/04 C23G 3/04 (72) Inventor Osamu Furukun 1-1-1, Kawasaki-cho, Handa-shi, Aichi Prefecture Made by Kawasaki Iron Co., Ltd. Chita Works (72) Inventor Akira Ito 1-1 Kawasaki-cho Handa City, Aichi Prefecture Kawasaki Steel Co., Ltd. Chita Works

Claims (4)

[Claims] 1. A skelp continuously supplied is heated in a heating furnace, the skelp is formed into a tube by a forming / forging machine, and both edges of the skelp are formed into a tube by forging and welding, and the tube is formed by a hot reducer. After reducing the diameter to a predetermined size, the tube is hot-cut, the tube is cooled and descaled, and then the diameter of the tube is reduced by a warm reducer in the temperature range of 300 to 830 ° C. A method for producing a forged steel pipe, which is characterized. 2. The method for manufacturing a forged steel pipe according to claim 1, wherein the cooling step and the descaling step of the pipe are simultaneously performed by a high pressure water injection method. 3. A heating furnace for heating a continuously supplied skelp, a forming / forging machine for forming the skelp into a tube and forging both edges of the skelp to form a tube, and the tube having a predetermined size. A hot reducer that can reduce the diameter, a cutting machine that hot cuts the pipe, a cooling device that cools the pipe, a descaling device that descales the pipe, and a pipe at 300 to 830 ° C. A forged steel pipe manufacturing equipment line characterized by sequentially arranging a warm reducer capable of reducing the diameter within a temperature range. 4. The series of forged steel pipe manufacturing equipment according to claim 3, wherein the cooling device and the descaling device are constituted by a high-pressure water jet cooling device and a descaler.