JPH04325628A - Production of resistance welded tube minimal in hardening in resistance welded zone - Google Patents

Abstract

PURPOSE:To economically produce a resistance welded tube minimal in hardening in a resistance welded zone by performing coiling at specific temp. and then carrying out specific cold sheet thickness rolling at the time of subjecting a steel tube stock having a specific composition consisting of C, Si, Mn, Ti, and Fe to hot plate thickness rolling. CONSTITUTION:A resistance welded tube is produced by using a steel tube stock which has a composition containing, by weight, 0.02-0.15% C, 0.05-0.60% Si, 0.25-2.0% Mn, and 0.020-0.150% Ti as essential components and having the balance Fe with inevitable elements. At this time, at the time of subjecting the above steel tube stock to hot plate thickness rolling, coiling is done at 400-600 deg.C or 700-750 deg.C. By the above procedure, the maximum region of Ti precipitating effect, that is, the region between >600 and <700 deg.C can be avoided. Then, tube making on-line cold sheet thickness rolling at 5-30% rolling reduction is applied. By this method, at the time of resistance welding, Ti can be effectively precipitated in a heat affected zone to prevent softening and also the work-hardened base material zone and the hardened resistance welded zone can be made practically homogeneous.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an electric resistance welded steel pipe in which hardening of the electric resistance welded portion is minimized.

0002

2. Description of the Related Art Mechanical structural steel pipes 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 tension, the content of elements will inevitably increase, and the electric resistance welded part will become hardened and hardened. As a result, the ductility of the electric resistance welded part decreases, resulting in poor workability.

One of the means to solve this problem is to anneal or normalize the electric resistance welded portion or the entire pipe after electric resistance welding. Thereby, it is possible to make the electric resistance welding part and the base metal part homogeneous. Another method is JP-A-52-114
This is a method of increasing the tensile strength of the steel plate itself by optimizing the composition and hot rolling conditions using the method described in Publication No. 519, etc., and then performing electric resistance welding. Even if the seam weld hardens, there is little difference in hardness because the strength of the base material is high.

0004

[Problems to be Solved by the Invention] There are two types of conventional electric resistance welded steel pipe manufacturing techniques as described above. FIG. 1 is a diagram showing the manufacturing process of a general electric resistance welded steel pipe. In general, steel pipes are formed, welded, and shaped into steel pipes, but if you try to make them high-strength, the electric resistance welds will harden. However, the first method above is
This method attempts to homogenize and ensure ductility of the electric resistance welded joint by performing heat treatment after pipe formation, but this method requires heat treatment, which inevitably increases costs. In addition, as in the second method above, the steel plate itself is made to have a high tensile strength by optimizing the composition and hot rolling conditions, and then electric resistance welding is performed, which makes the plate homogeneous in both the width and length directions. This is difficult and requires cutting off some unstable parts.

[0005] The object of the present invention is to solve these problems in the method of manufacturing electric resistance welded steel pipes.

[0006]

[Means for Solving the Problems] The gist of the present invention is that C: 0.02 to 0.15%, Si: 0.0% by weight.
5-0.60%, Mn: 0.25-2.0%, Ti: 0
．． 0.020 to 0.150% as a basic component, with the remainder being Fe and other unavoidable elements.When manufacturing electric resistance welded steel pipes, the temperature is 400 to 600°C or 700 to 700°C during hot plate thickness rolling of pipe steel materials.
A method for manufacturing an ERW steel pipe with less hardening of the ERW welded part, characterized by coiling at 50°C and adding on-line cold thickness rolling with a rolling reduction of 5 to 30% after hot thickness rolling. It is in.

The present invention will be explained in detail below. FIG. 2 shows the manufacturing process of the present invention. In the conventional process, as mentioned above, if you want to manufacture ERW steel pipes with less hardening at the ERW welding part, you need to heat treat the tube after making the pipe, or increase the tension of the steel plate itself by hardening, etc., and then ERW welding. However, either method results in high costs or manufacturing instability.

Therefore, in the present invention, the steel plate itself is made of a material that is difficult to soften due to the effects of welding heat, and before pipe forming, on-line cold plate thickness rolling is added to work harden the entire plate, and the subsequent electric resistance welding is performed. Even if the ERW welded part hardens during the process, it is intended to manufacture an ERW steel pipe in which the ERW welded part hardens less by making the ERW welded part almost homogeneous with the work-hardened base material. First, the components of the steel plate used in the present invention will be explained.

[0009] The lower the C content, the better the ductility, the better the workability, and the less hardening of the electric resistance welded part, but since the required strength cannot be obtained, the lower limit is set at 0.02%. Moreover, if it exceeds 0.15%, even by the method of the present invention,
The upper limit was set at 0.15% because the heat-affected zone hardens during pipe manufacturing and welding of ERW steel pipes, reducing workability. In the case of killed steel, it is difficult to suppress Si to less than 0.05% due to steel manufacturing technology, and if it exceeds 0.60%, it has a negative effect on ductility and the surface quality deteriorates due to scale formation. The upper limit was set at .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 insufficient ductility during processing such as forming during pipe manufacturing. Therefore, the lower limit is 0.25% and the upper limit is 2.0%.
%. Ti is a heavy element for increasing strength,
Although it is effective for HAZ softening resistance, if it is less than 0.020%, it will lack strength, and if it is added more than 0.150%, the effect will not improve, so the lower limit is set to 0.020% and the upper limit is set to 0.
．． It was set to 150%.

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 during hot rolling, precipitate Ti due to the heat effect during electric resistance welding, and prevent softening due to the heat effect.
On the contrary, the cooling rate is faster, the strength increases, and the toughness decreases. 60
Above 0°C and below 700°C is where the precipitation effect of Ti is most present. Temperatures exceeding 750°C are impossible for manufacturing reasons. Therefore, by winding steel with the above components at 400 to 600 °C or 700 to 750 °C during hot plate thickness rolling, it becomes a material with less precipitation effect of Ti, which precipitates due to the thermal influence of subsequent electric resistance welding. This will prevent softening due to heat effects.

[0012] Next, there is online cold plate thickness rolling for pipe making, and the purpose of this is to work harden the pipe. It is work-hardened in a rolling mill on the pipe-making line before pipe-making. In this case, when the rolling reduction is less than 5%, almost no work hardening occurs, and 30%
%, the ductility will drop significantly, so the rolling reduction was set at 5 to 30%. The plate thus work-hardened is shaped and subjected to electric resistance welding, and generally during electric resistance welding, the electric resistance welded portion becomes hardened and hardened. However, the hardness at this time is almost determined by components such as C. Therefore, if the plate, that is, the base material part, is work hardened, the difference in hardness between the electric resistance welded part and the base material part 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, resulting in a substantially uniform hardness distribution.

[0013] By the above method, it is possible to manufacture an electric resistance welded steel pipe with less hardening of the electric resistance welded portion.

[0014]

[Example] Tables 1 and 2 (continued from Table 1) show a comparison between the conventional method and the method of the present invention using the size φ50.8×t5.0.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

Effects of the Invention: If an attempt is made to manufacture an ERW steel pipe with less hardening of the ERW welded part using the conventional process, it is possible to heat-treat the pipe after making the pipe, or increase the tension of the steel plate itself by hardening, etc., and then However, by applying the method of the present invention, it can be manufactured by welding without any manufacturing problems. It has become possible to economically manufacture ERW steel pipes with less hardening of ERW welded parts.

[Brief explanation of drawings]

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

Claims (1)

[Claims] Claim 1: The component composition is C: 0.02 to 0.02 by weight.
15%, Si: 0.05-0.60%, Mn: 0.25
~2.0%, Ti: 0.020~0.150% as a basic component, and the balance is Fe and unavoidable elements.
The electric resistance welding part is coiled at 00°C or 700 to 750°C, and after hot plate thickness rolling, on-line cold plate thickness rolling with a rolling reduction of 5 to 30% is added. Manufacturing method of sewn steel pipe.