JP2542293B2 - Manufacturing method of ERW steel pipe with less hardening of ERW welded part - 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 an electric resistance welded steel pipe in which the electric resistance welded portion is hardened.

[0002]

2. Description of the Related Art Steel pipes for mechanical structures used as structural members such as automobile pipes and drive transmission members are widely manufactured by the electric resistance welded steel pipe method in view of their quality characteristics. However, if an attempt is made to increase the tensile strength, the contained elements will inevitably increase, and the electric resistance welded portion will be hardened and hardened. As a result, the ductility of the electric resistance welded portion is reduced and the workability is deteriorated.

One of means for solving this is a method of annealing or normalizing the electric resistance welded portion or the entire pipe after electric resistance welding. This makes it possible to homogenize the electric resistance welded portion and the base material portion. Another means is disclosed in JP-A-52-114.
In the method described in Japanese Patent No. 519, etc., the steel sheet itself is made to have a high tension by optimizing the components and hot rolling conditions, and then electric resistance welding is performed. Even if the sewn welded portion is hardened, the hardness of the base material is high, and therefore the difference in hardness is small.

[0004]

As described above, there are two types of conventional ERW pipe manufacturing technology. FIG. 1 is a diagram showing a manufacturing process of a general electric resistance welded steel pipe. Generally, a steel pipe is formed, welded, and shaped into a steel pipe, but if an attempt is made to increase the tensile strength, the electric resistance welded portion is hardened. However, the first method is to heat-treat after pipe making to homogenize and secure ductility of the electric resistance welded portion. However, this method requires heat treatment, and thus high cost is inevitable. Further, as in the second method described above, by optimizing the components and hot rolling conditions, the steel plate itself is made to have a high tension, and then electric resistance welding is used.
It is difficult to homogenize the width direction and the length direction of the plate, and it is necessary to cut off some unstable portions.

An object of the present invention is to solve the problems in such a method for manufacturing an electric resistance welded steel pipe.

[0006]

The gist of the present invention is that C: 0.02 to 0.15% by weight and Si: 0.0
5 to 0.60%, Mn: 0.25 to 2.0%, Ti:
In manufacturing an electric resistance welded steel pipe having 0.020 to 0.150% as a basic component and the balance being Fe and inevitable elements, 400 to 600 ° C. or 700 to 700 ° C. at the time of hot plate thickness rolling of pipe steel
A method for producing an electric resistance welded steel pipe having less hardening of an electric resistance welded portion, which comprises winding at 750 ° C., hot rolling and then online reduction cold rolling of 5% to 30% of rolling reduction is added. It is in.

The present invention will be described in detail below. FIG. 2 shows the manufacturing process of the present invention. In the conventional process, if an electric resistance welded steel pipe with less hardening of the electric resistance welded portion is to be produced, as described above, heat treatment is performed after the pipe is made, or the steel plate itself is made to have a high tension by quenching, and then electric resistance welding is performed. However, in both cases, the cost becomes high and the manufacturing becomes unstable.

Therefore, in the present invention, the steel plate itself is made of a material that is hard to be softened by the influence of welding heat, and a pipe forming online cold plate thickness rolling is added before the pipe forming to work-harden the whole plate and then electric resistance welding. Therefore, even if the electric resistance welded portion is hardened, it is intended to manufacture an electric resistance welded steel pipe in which the electric resistance welded portion hardly hardens by making the base material portion which is work hardened to be substantially homogeneous. Therefore, the components of the steel sheet used in the present invention will be described first.

If the amount of C is small, the ductility is good, the workability is excellent, and the hardening of the electric resistance welded portion is small, but the required strength cannot be obtained, so the lower limit was made 0.02%.
Further, if it exceeds 0.15%, the method of the present invention also
The heat-affected zone is hardened during pipe-making welding of the electric resistance welded steel pipe and the workability is deteriorated, so the upper limit was made 0.15%. In the case of killed steel, it is difficult to control Si to less than 0.05% from the viewpoint of steelmaking technology, and if it exceeds 0.60%, the ductility and toughness are adversely affected, and the surface properties are deteriorated due to scale formation. The upper limit was set to 60%.

Regarding Mn, from the viewpoint of strength, if it is less than 0.25%, the strength becomes insufficient, and if it exceeds 20,0%, cracks may occur due to insufficient ductility at the time of processing such as forming during pipe forming. Therefore, the lower limit is 0.25% and the upper limit is 2.0.
%. Ti is a heavy element for increasing strength,
Although it has an effect on HAZ softening resistance, if it is less than 0.020%, the strength becomes insufficient, and if it is added in excess of 0.150%, the effect is not improved. Therefore, the lower limit is 0.020% and the upper limit is 0. It was set to 150%.

Next, the steel having the above-mentioned components is heated to 40% during hot plate rolling.
Wind at 0-600 ° C or 700-750 ° C. This is to prevent the precipitation effect of Ti by hot rolling, to precipitate Ti under the influence of heat at the time of electric resistance welding, and to prevent softening due to the effect of heat.
On the contrary, the cooling speed is fast, the strength increases, and the toughness also decreases. 60
When it is more than 0 and less than 700 ° C., the Ti precipitation effect is most present. Above 750 ° C is impossible in manufacturing. Therefore, the steel of the above components is 400 to 600 ° C. during hot plate thickness rolling.
Alternatively, by winding at 700 to 750 ° C., a material having a small precipitation effect of Ti is obtained, and the material is precipitated by the heat effect of the subsequent electric resistance welding, and softening due to the heat effect is prevented.

Next, tube-making on-line cold plate thickness rolling, whose purpose is for work hardening. Work hardening is performed on a rolling machine before pipe making on the pipe making line. In this case, if the rolling reduction is less than 5%, almost no work hardening occurs and 3
If it exceeds 0%, the ductility is remarkably reduced, so the rolling reduction is set to 5 to 30%. The work-hardened plate is formed and subjected to electric resistance welding, but in general, the electric resistance welded portion is hardened at the time of electric resistance welding. However, the hardness at this time is almost determined by the components such as C. Therefore, if the plate, that is, the base material portion is work hardened, the hardness difference between the electric resistance welded portion and the base material portion will be reduced. On the other hand, the heat-affected zone softens due to the heat effect during electric resistance welding, but this can be prevented by adding Ti as described above, and the hardness distribution becomes almost uniform.

By the above method, it is possible to manufacture an electric resistance welded steel pipe in which the electric resistance welded portion is hardened.

[0014]

EXAMPLES Table 1 and Table 2 (continued from Table 1) with a size of φ50.8 × t5.0 show a comparison between the conventional method and the method of the present invention.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

EFFECTS OF THE INVENTION In order to manufacture an electric resistance welded steel pipe in which the electric resistance welded portion is hardened in the conventional process, heat treatment is performed after the pipe is made, or the steel plate itself is strengthened by quenching or the like, and then electric resistance welding is performed. It is either manufactured by welding, but both become expensive or unstable in manufacturing, but by applying the method of the present invention, there is no manufacturing problem, and It has become possible to economically manufacture electric resistance welded steel pipes with less hardening of the electric resistance weld.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional manufacturing process.

FIG. 2 is a diagram showing a method of the present invention.

Claims (1)

(57) [Claims] 1. The component composition by weight is C: 0.02 to 0.1.
5%, Si: 0.05-0.60%, Mn: 0.25-
When manufacturing an electric resistance welded steel pipe consisting of 2.0% and Ti: 0.020 to 0.150% as a basic component and the balance Fe and unavoidable elements, 400 to 60 at the time of hot plate thickness rolling of the steel for pipes.
Rolling at 0 ° C. or 700 to 750 ° C., hot-rolled plate thickness rolling followed by pipe reduction 5-30% rolling reduction online cold-rolled plate thickness rolling. Manufacturing method of sewn steel pipe.