JPH04311526A - Production of high strength electric resistance welded steel tube excellent in haz softening resistance - Google Patents

Abstract

PURPOSE:To improve the roll formability and weldability at the time of tube- manufacturing by specifying the compsn. of a steel for a tube, its coiling temp. at the time of hot sheet thickness rolling and its heat treating temp. after the tube-manufacturing. CONSTITUTION:The components of a steel are formed of, by weight, 0.10 to 0.65% C, 0.05 to 0.60% Si, 0.25 to 2.0% Mn, 0.020 to 0.150% Ti, 0.01 to 0.5% Mo, 0.01 to 0.1% Nb, 0.01 to 0.1% V and the balance Fe with inevitable elements. This steel for a tube is coiled at 400 to 600 deg.C or 700 to 750 deg.C at the time of hot sheet thickness rolling. The steel is manufactured into an electric resistance welded steel tube, and after that, this steel is subjected to heat treatment at 600 to 700 deg.C to precipitate Ti. At the time of additionally executing cold sheet thickness rolling or tube manufacturing on-line cold sheet thickness rolling after the coiling at the time of the hot sheet thickness rolling, work hardening is executed, by which the steel tube having high strength can be manufactured.

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 high-strength electric resistance welded steel pipes.

0002

[Prior Art] We are considering reducing the weight of mechanical structural steel pipes used as structural members such as automobile pipes and drive transmission members in order to improve fuel efficiency, and one of the measures is to increase their strength. It is being said. Conventionally, there are two types of manufacturing methods for high-strength ERW steel pipes.
There is a manufacturing method in which the steel plate itself is made to have a high tensile strength using the method described in the above publication, and then it is made into an ERW pipe.The other method is to heat the steel plate, that is, to heat it, after making the ERW pipe. Alternatively, it is a method of manufacturing by quenching and tempering.

0003

There are two types of methods described in the prior art as described above. Figure 3 shows a typical manufacturing process for electric resistance welded steel pipes. In general, it is either molded, welded, or shaped as it is, or it is then heat treated. The purpose of this heat treatment is to homogenize or ensure ductility of the electric resistance welded part. However, in order to manufacture high-strength steel pipes in this process, the steel plate itself must be made high-strength and then manufactured by ERW pipe-making. Roll forming is difficult, resulting in a poor shape during electric resistance welding, resulting in defective electric resistance welding. In the second manufacturing method, which involves heat refining, that is, quenching or quenching and tempering after forming the ERW pipe, the refining cost is extremely high;
It is not common unless it is unavoidable.

[0004] A common problem with both methods is softening of the heat affected zone (HAZ) during pipe joint welding or accessory welding. The object of the present invention is to solve the problems in the manufacturing method of such high-strength electric resistance welded steel pipes.

[0005]

[Means for Solving the Problems] The gist of the present invention is as follows. (1) Component composition is C: 0.10-0.65% by weight
, Si: 0.05-0.60%, Mn: 0.25-2.
0%, Ti: 0.020-0.150%, Mo: 0.0
1-0.5%, Nb: 0.01-0.1%, V: 0.0
1% to 0.1%, with the balance being Fe and other unavoidable elements, the method includes coiling and forming pipes at 400 to 600°C or 700 to 750°C during hot plate thickness rolling of pipe steel materials. A method for producing a high-strength electric resistance welded steel pipe with excellent HAZ softening resistance, characterized by carrying out heat treatment at 600 to 700°C.

(2) Component composition is C: 0.10 by weight
~0.65%, Si:0.05~0.60%, Mn:0
．． 25-2.0%, Ti: 0.020-0.150%,
Mo: 0.01-0.5%, Nb: 0.01-0.1%
, V: 0.01 to 0.1%, and the balance is Fe and unavoidable elements.
High strength with excellent HAZ softening resistance characterized by coiling at 0°C, followed by cold plate thickness rolling or pipe forming online cold plate rolling, and heat treatment at 600 to 700°C after pipe forming. Manufacturing method of ERW steel pipe.

The present invention will be explained in detail below. FIG. 1 shows the manufacturing process according to claim 1. In the conventional process, as mentioned above, in order to manufacture high-strength steel pipes, the steel plate itself is made high-strength, and then the electric resistance welding pipe is formed. It is difficult to perform roll forming during sewing pipe manufacturing, resulting in a poor shape during electric resistance welding, resulting in defective electric resistance welding.

In contrast, the present invention aims to manufacture high-strength steel pipes by making the steel plate itself a soft material that can be formed, and by controlling the heat treatment temperature after pipe forming. First, the components of the steel plate used in the present invention will be explained. The lower the C content, the better the ductility and workability, but since the required strength cannot be obtained, the lower limit is set to 0.
．． It was set at 10%. Moreover, if it exceeds 0.65%, cold workability such as formability during pipe manufacturing and toughness tend to decrease, and the heat affected zone hardens during pipe manufacturing welding of ERW steel pipes, resulting in poor workability. Therefore, the upper limit was set at 0.65%.

[0009] In the case of killed steel, it is difficult to suppress Si to less than 0.05% in terms of steel manufacturing technology, and on the other hand, if it exceeds 0.60%, it has a negative effect on ductility and deteriorates surface quality due to scale formation. , the upper limit was 0.60%. Regarding Mn, in terms of strength, if it is less than 0.25%, the strength will be insufficient, and if it exceeds 2.0%, cracks may occur due to lack of ductility during processing such as forming during pipe manufacturing, so the lower limit is set. was set at 0.25%, and the upper limit was set at 2.0%.

[0010] Ti is an important element for increasing strength, but if it is less than 0.020%, the strength will be insufficient;
Since there is no improvement in the effect even if the amount is added in excess of 0.0%, the lower limit was set to 0.020% and the upper limit was set to 0.150%. Mo is an important element for preventing softening during welding of joints between pipes, but if it is less than 0.01%, it has no effect on softening resistance;
Since there is no need to add more than 5%, the lower limit is set at 0.
01%, with an upper limit of 0.5%.

[0011] Nb is also an important element for preventing softening during welding, but if it is less than 0.01% it has no effect on softening resistance, and there is no need to add more than 0.1%, so the lower limit is was set at 0.01%, and the upper limit was set at 0.1%. V is also an important element for preventing softening during welding, but if it is less than 0.01% it has no effect on softening resistance and there is no need to add more than 0.1%, so the lower limit is set to 0. 01%, upper limit 0.1%
And so.

Next, the steel having the above components was hot rolled to a thickness of 40
Wind up at 0-600°C or 700-750°C. This is to prevent the precipitation effect of Ti and make the material as soft as possible. If the temperature is lower than 400°C, the effect of Ti precipitation is small, but the cooling rate becomes faster, so the strength increases and the toughness decreases. Above 600°C and below 700°C, the precipitation effect of Ti is most present. Temperatures exceeding 750°C are impossible for manufacturing purposes. Therefore, by winding steel having the above-mentioned components at 400 to 600°C or 700 to 750°C during hot plate thickness rolling, a relatively soft material with little Ti precipitation effect can be obtained.

[0013] After this, the pipe is formed, but since the material is relatively soft, there are no problems in forming and welding which were conventional problems, and high quality electric resistance welded steel pipes can be formed. Next is the heat treatment after pipe forming, which produces the effect of Ti precipitation. That is, heat treatment is performed at 600 to 700°C. 600
If the temperature is less than 700° C., Ti will overage, and if it exceeds 700° C., Ti will not be sufficiently analyzed, and neither effect will be obtained.

Although claim 1 has been described above, a method according to claim 2 may also be used. FIG. 2 shows the process according to claim 2. After the hot plate thickness rolling in the process according to claim 1, cold plate thickness rolling or online cold plate thickness rolling for pipe production is added. In this way, by adding cold plate thickness rolling or pipe-making online cold plate thickness rolling after hot plate thickness rolling, it is possible to work harden the steel pipe and produce a steel pipe with even higher strength.

[0015]

[Example] Tables 1 to 4 show that the size φ
An example of manufacturing a high-strength electric resistance welded steel pipe of 101.6 × t4.4 is shown.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

[0019]

[Table 4]

[0020]

Effects of the invention: If high-strength steel pipes were to be manufactured using the conventional process, the steel plate itself would have to be made high-strength, and then the ERW pipe would be manufactured. Roll forming during pipe manufacturing was difficult, resulting in a defective shape during ERW welding, resulting in defective ERW welding, but by applying the method of the present invention, there were no problems with forming or welding. , and it becomes possible to economically manufacture HAZ high-strength electric resistance welded steel pipes.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a manufacturing process according to claim 1.

FIG. 2 is a diagram showing a manufacturing process according to claim 2.

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

Claims (2)

[Claims] Claim 1: The component composition is C: 0.10 to 0.0 by weight.
65%, Si: 0.05-0.60%, Mn: 0.25
~2.0%, Ti:0.020~0.150%, Mo:
0.01-0.5%, Nb: 0.01-0.1%, V:
In a method for producing an electric resistance welded steel pipe containing 0.01 to 0.1% and the balance being Fe and unavoidable elements, the method includes: coiling at 400 to 600°C or 700 to 750°C during hot plate thickness rolling of pipe steel material; A method for producing a high-strength electric resistance welded steel pipe with excellent HAZ softening resistance, which comprises performing heat treatment at 600 to 700°C after pipe forming. 2. The component composition is C: 0.10 to 0.0 by weight.
65%, Si: 0.05-0.60%, Mn: 0.25
~2.0%, Ti:0.020~0.150%, Mo:
0.01-0.5%, Nb: 0.01-0.1%, V:
In a method for producing an electric resistance welded steel pipe containing 0.01 to 0.1% and the balance being Fe and unavoidable elements, the method includes: coiling at 400 to 600°C or 700 to 750°C during hot plate thickness rolling of pipe steel material; A method for producing a high-strength electric resistance welded steel pipe with excellent HAZ softening resistance, which is then subjected to cold plate thickness rolling or pipe-making online cold plate rolling, and then heat-treated at 600 to 700°C after pipe-making.