JP3295212B2 - Manufacturing method of high strength and toughness forged steel pipe - Google Patents

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 high strength and high toughness forged steel pipe.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 2, a steel strip having a predetermined width is continuously inserted into a heating furnace at a temperature of about 1200.degree.
After heating to ３００1300 ° C., molding is performed with a molding stand, and oxygen blowing is performed immediately before forging to perform forging. After that, it is squeezed with a stretch reducer to a predetermined outer diameter. This method is the most efficient and high-productivity method for producing steel pipes and is widely used in general. However, since it requires a lot of energy to heat it to a high temperature, it is disclosed in Japanese Patent Application No. −
As described in No. 2248, after heating at low temperature,
There is a method in which after high-frequency heating is performed only at the edge end, oxygen blowing is performed immediately before forging to perform forging. Further, in order to improve the quality of the abutting portion, as described in JP-A-60-15082, high-frequency resistance welding is performed at a relatively low temperature, and then bead removal cutting is performed. ° C ~ 110
After heating to 0 ° C, there is a method of squeezing with a stretch reducer.

[0003]

Generally, in a method for manufacturing a forged steel pipe, oxygen blowing is performed immediately before forged welding.
Oxygen blowing has two purposes: to remove the scale attached to the edge and to heat the edge by oxidizing heat. For this reason, the components that can be produced by this method are quite limited. In other words, if there are many added elements such as high-strength and toughness steel pipes, the melting point will decrease and it will be easier to melt, and the scale attached to the edges will be easier to remove, and the former purpose can be achieved. There is a problem that the temperature of the part cannot be raised to a temperature at which forge welding can be performed, and forge welding cannot be performed.

In order to solve this problem, a method of applying high-frequency heating at the time of forging and a method of performing high-frequency resistance welding at a relatively low temperature have been devised. In other words, a bead is generated, and it is necessary to carry out the bead removal cutting after that, and because there is a temperature difference between the forged part and the other parts, uneven thickness occurs when squeezing with a subsequent stretch reducer. I will. So again about 900 ° C ~ 110
After heating to 0 ° C, it must be squeezed with a stretch reducer. These new problems greatly hinder efficiency and productivity.

An object of the present invention is to solve the problems in the conventional method for manufacturing a forged steel pipe, and to provide a method for manufacturing a forged steel pipe having high strength and high toughness.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method for manufacturing a forged pipe in which a steel strip having a predetermined width is heated, hot-formed, and forged. C: 0.1-0.
3% or less, Si: 0.05 to 1.0%, Mn: 2.
0 to 2.5%, P: 0.02% or less, S:
0.02% or less, Al: 0.01 to 0.08
%, Mo: 0.2-0.7%, Cr: 0.2-
0.7%, Ti: 0.01 to 0.07%, B: 1
After heating the forged joint by irradiating a laser from the upstream side of the forged joint at the time of forging, the steel strip having a composition of 0 to 30 PPM as a base and the balance of Fe and inevitable elements is used,
This is a method for producing a high-strength, high-toughness forged steel pipe characterized by forging.

Hereinafter, the present invention will be described in detail. FIG. 1 shows a 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 to 1300 ° C., molding is performed by a molding stand, and oxygen is blown immediately before forging to forge. After that, it is squeezed with a stretch reducer to a predetermined outer diameter. In this way, as mentioned above, the components that can be produced are very limited. In other words, the melting point is reduced when the amount of the added element is large, the melting point is easily reduced, and the scale attached to the edge is easily removed, and the former purpose can be achieved. Cannot perform the forging process.

[0008] In the method of the present invention shown in FIG.
After heating to ℃, it is molded in a molding stand. Thereafter, oxygen forging is performed at the time of forging, and the forged portion is heated by irradiating laser to the forged portion. As a method of laser irradiation, for example, as shown in FIG. 2, a laser beam 2 is irradiated from a laser irradiation device 1 arranged on the upstream side toward an abutting portion. At this time, if it is difficult to hit the entire surface in the thickness direction with one beam due to the capacity of the laser generator, several beams are irradiated. In any case, it is important to uniformly irradiate the laser beam in the thickness direction of the abutting portion and to uniformly heat the laser beam. After laser irradiation and heating, forge welding was performed with the forge welding roll 3 and then squeezed with a stretch reducer.
It has a predetermined outer diameter and thickness. By irradiating the laser, the shortage of the heating by the oxygen blow is compensated, and since the energy density is high, the heating width is also small and no bead is generated.

Although it is necessary to manufacture a high-strength, high-toughness forged steel pipe by the above-described method, the composition of the steel strip is also specified in a specific range. The reasons for limiting the components of the steel strip used in the present invention will be described below. The lower the C content, the better the ductility,
Although the workability was excellent, the required strength was not obtained, so the lower limit was made 0.1%. On the other hand, if it exceeds 0.3%, the formability, cold workability and toughness at the time of pipe formation tend to decrease, and the upper limit is set to 0.3%.

[0010] Si is an effective element for ensuring the strength, but in the case of killed steel, it is difficult to suppress the content to less than 0.05% in terms of steelmaking technology, and if it exceeds 1.0%, the ductility deteriorates. Is difficult to ignore, so the upper limit was made 1.0%.
With respect to Mn, if it is less than 2.0%, the strength becomes insufficient, and if it exceeds 3.0%, the workability deteriorates. Therefore, the lower limit was made 2.0%, and the upper limit was made 3.0%.

P is an element that is inevitably mixed during steelmaking, but if it exceeds 0.02%, cracks in the forged portion are likely to occur particularly during forging of ultra-high-strength steel pipes, so the upper limit was made 0.02%. S is also an element inevitably mixed during steelmaking like P, and if it exceeds 0.02%, a forged joint crack is likely to occur during forging, so the upper limit was made 0.02%. In the case of killed steel, it is difficult to suppress Al to less than 0.01% in terms of steelmaking technology, and if it exceeds 0.08%, it is easy to cause slab cracks and internal defects due to formation of oxide-based giant inclusions. Therefore, the upper limit is set to 0.08%.

Mo is an element that increases the strength of a steel material, and its addition within a range that does not excessively impair ductility is effective in producing a high-strength forged steel pipe. However, if it is too low, the strength will be insufficient. Therefore, Mo has an upper limit of 0.7% and a lower limit of 0.2%.
%. Cr is an element that increases the strength of a steel material like Mo, and its addition in a range that does not excessively impair ductility is effective in producing a high-strength forged steel pipe. However, if it is too low, the strength will be insufficient. Therefore, the upper limit was set to 0.7% and the lower limit was set to 0.2%.

B is an essential element for obtaining a high-strength transformed structure by delaying the ferrite transformation during the cooling process. However, even in the composition of the steel of the present invention, if the composition is less than 10 PPM, the strength becomes insufficient.
Since t is generated and the ductility is significantly reduced, the lower limit is set to 10
PPM, the upper limit was 30 PPM. Ti is an important element for controlling the strength. However, if the content is less than 0.01%, the strength becomes insufficient, and if the content exceeds 0.07%, the effect is not improved. , And the upper limit was made 0.07%. In addition, Nb and V may be added as needed.

[0014]

EXAMPLES Table 1 compares the conventional method and the method according to the present invention with a size of φ42.7 × t4.0. No. In the first conventional method, the quality of the abutting portion was not stable because of the method using oxygen blowing, and a high-strength and high-toughness steel pipe could not be manufactured. N
o. The second conventional method is a method using high-frequency induction heating and oxygen blowing, but it requires bead cutting, and the line is often stopped for adjustment thereof, resulting in a significant decrease in productivity. Compared with these conventional methods, the method of the present invention makes it possible to produce high strength and high toughness forged steel pipes by setting the components to predetermined components and irradiating laser during forging.

[0015]

[Table 1]

[0016]

According to the present invention, if an attempt is made to produce a high-strength, high-toughness forged steel pipe by a conventional production method, the quality of the abutting portion is unstable, and the components that can be produced are considerably limited. In other words, if there are many added elements such as high-strength and toughness steel pipes, the melting point will decrease and it will be easier to melt, and the scale attached to the edges will be easier to remove, and the former purpose can be achieved. There has been a problem that the temperature of the part cannot be raised to a temperature at which forge welding is possible, and forge welding cannot be performed. By applying the method of the present invention, it has become possible to manufacture a high-strength, high-toughness forged steel pipe with a stable joint portion quality.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a laser irradiation method.

FIG. 3 is a diagram showing a conventional manufacturing process.

[Explanation of symbols]

 1 laser irradiation device 2 laser beam 3 forging roll

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ identification code FI // B23K 101: 06 B23K 101: 06 (58) Investigated field (Int.Cl. ⁷ , DB name) B23K 20/00 B21C 37 / 06

Claims (1)

(57) [Claims] 1. A method for manufacturing a forged pipe in which a steel strip having a predetermined width is heated and hot formed, and then forged, wherein: C: 0.1 to 0.3% or less; Si: 0.05 to 1 0.0%, Mn: 2.0 to 2.5%, P: 0.02% or less, S: 0.02% or less, Al: 0.01 to 0.08%, Mo: 0.2 to 0. 7%, Cr: 0.2 to 0.7%, Ti: 0.01 to 0.07%, B: 10 to 30 PPM, and a steel strip having a balance of Fe and unavoidable elements is forged. A method for manufacturing a high-strength, high-toughness forged steel pipe, comprising: forging a welded portion by heating the forged portion by irradiating a laser from an upstream side of the forged portion.