JPS62247061A - Manufacture of alloying-galvanized resistance welded tube - Google Patents

Abstract

PURPOSE:To improve the adhesive strength and corrosion resistance of a repair plating layer, by carrying out the adhesion of zinc as well as the machining of weld bead zone of a resistance welded tube prepared by forming an alloying- galvanized steel strip into tubular state under a nonoxidizing atmosphere at a limited molten-zinc temp. CONSTITUTION:The alloying-galvanized steel strip is formed into tubular state with being horizontally moved, whose abutting zone is welded. Then, the resulting weld bead zone is machined under a nonoxidizing atmosphere and, simultaneously, molten zinc of 520-850 deg.C is allowed to adhere to the above weld bead zone while the temp. of this zone is high.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention involves cutting the weld bead under specific conditions in the process of continuously manufacturing ERW steel pipes using single-alloyed galvanized steel strip as a raw material. The present invention also relates to a method for manufacturing an alloyed galvanized electric resistance welded steel pipe which can be hot dip galvanized to form a good plating layer substantially homogeneous with the plating layer of the raw material.

[Conventional technology and problems]

Alloyed galvanized steel pipe has good weldability and coating adhesion.

6-alloyed galvanized ERW steel pipe, which is widely used in construction materials, automobile parts, electrical machine base materials, etc. due to its excellent corrosion resistance, is an alloyed galvanized steel pipe that is pre-plated with zinc and further alloyed. It is manufactured by using a steel strip as a material, bending it in the width direction with rolls, abutting both side edges to form a tubular shape, and welding and stitching the abutted portions. Since this method destroys the plating layer near the weld bead, the original properties such as corrosion resistance are lost in that area, and the weld bead, which forms part of the surface of the ERW steel pipe, is No plating layer originally has such characteristics.

Conventionally, one method for imparting properties such as corrosion resistance to the weld bead and its vicinity (collectively referred to as the weld bead), which did not have such properties, was to reduce the thickness of the weld bead after welding. A method of forming a plating layer by cutting away the bulge and spraying zinc, which is the same metal as the material plating layer, on that part (referred to as the weld bead cut part) is carried out. However, the repair plating layer formed in this way is not essentially a layer that has reacted metallurgically homogeneously with the base material, but has a structure different from that of the material plating layer formed on the material before weld bead formation. I have to. In other words, this thermal sprayed repair plating layer has poor adhesion because it adheres to the cut part of the weld bead due to the anchoring effect, and since the zinc spraying is carried out in an oxidizing atmosphere, the repair plating layer itself is susceptible to oxides. It becomes a porous thing that is rolled up,
Performance such as corrosion resistance will be significantly inferior to that of the raw plating layer. Furthermore, when the electrical resistance welded steel pipe obtained by thermal spraying as described above is coated, blistering of the coating film, which is thought to be caused by moisture entering the repair mating layer during the pre-painting treatment process, is less likely to occur. There wasn't. To solve these problems, it is possible to improve the thermal spraying technology to strengthen and homogenize the bond between the repair mating layer and the base material, or to repair it by applying metal powder mixed with flux to the weld bead and heating it. Attempts have been made to form a plating layer, but the repair plating layer formed in this way cannot be constructed like the good material plating layer that the material before pipe making has. The problem is not resolved.

[Means for solving problems]

The present inventors have solved the above-mentioned conventional problems, and have found that the repair plating layer formed on the cut part of the weld bead has good adhesion, weldability, and paint film adhesion, similar to the alloyed galvanized layer of the raw material. sex,
The purpose of this research was to provide a method for manufacturing an alloyed galvanized electric resistance welded steel pipe that has excellent performance such as corrosion resistance and almost no blistering of the coating film. As a result, by cutting the weld bead and applying molten zinc to the cut part of the weld bead in a non-oxidizing atmosphere while the temperature is still high after ERW, it is possible to improve the adhesion and corrosion resistance of the galvanized layer. While very good results were obtained, there remain problems, namely, the pre-painting process and the coating film between the alloyed galvanized layer of the raw copper strip and the repair plating layer formed on the cut part of the weld bead. The problem of not being able to prevent the occurrence of blistering in the paint film due to the difference in adhesion is that the weld bead is cut and the molten zinc is deposited under the above-mentioned non-oxidizing atmosphere. The present invention was completed by determining that the object could be achieved by adding a condition of using molten zinc at a temperature much higher than that used in hot-dip galvanizing.

In other words, the present invention involves cutting the weld bead in a non-oxidizing atmosphere during the process of continuously manufacturing ERW steel pipes by moving the alloyed galvanized steel strip horizontally, and cutting the weld bead immediately after that while moving the alloyed galvanized steel strip horizontally. The present invention relates to a method for manufacturing an alloyed galvanized electric resistance welded steel pipe, which comprises depositing molten zinc at a temperature of 520 to 850°C on the cut portion.

[Explanation of configuration]

The method of the present invention will be described in detail below.

The basic process of continuously manufacturing ERW steel pipes using alloyed galvanized steel strip as a raw material steel strip can be done by following the conventional process as follows.In other words, while moving the raw material steel strip horizontally, The machine's forming rolls are used to curve the edges in the width direction, and the edges on both sides are butted together to form a tubular shape.The abutted parts are welded using a squeeze roll to form a weld bead, and the weld bead is cut with a cutting tool to create the electric resistance weld. It is made into a steel pipe and is fed horizontally through straightening rolls while being supported by support rolls.

By the way, in the method of the present invention, in the above-mentioned manufacturing process, the weld bead portion is cut, and immediately after that, while the weld bead portion exposed there is still at a high temperature, the temperature is reduced to 520 to 85
Molten zinc at 0° C. is deposited, and the cutting of the weld bead and the attachment of the molten zinc to the cut portion of the weld bead are performed in a non-oxidizing atmosphere.

The molten zinc may be applied by thermal spraying or other known methods. However, in order to apply molten zinc to the weld bead cut portion with a uniform thickness, the following method is preferred:
In other words, the weld bead cutting section is positioned at the top or the bottom of the pipe and moved horizontally, and in the former case, the nozzle that opens downward is connected to the weld bead cutting section, and in the latter case, the nozzle that opens upward is moved horizontally. The nozzle is connected to the molten zinc tank, in which the molten zinc is maintained at a constant level and temperature higher than the nozzle surface, with a rib or a siphon. Molten zinc at a predetermined temperature is supplied to the nozzle according to the difference, and is deposited on the weld bead cut portion while flowing out from the nozzle, and the amount of deposit (plating thickness) is controlled by adjusting the head difference and pipe forming speed.

In addition, in order to form a non-oxidizing atmosphere, a seal box containing a part for cutting the weld bead and adhering molten zinc to the cut part of the weld bead is provided, and the seal box contains the N2 gas gA
It is sufficient to fill the seal box with a non-oxidizing gas such as R gas, and it is preferable to make the seal box as small as possible in order to save the amount of non-oxidizing gas used. It is preferable to use a pipe making machine equipped with a repair gluing device consisting mainly of a device for depositing molten zinc and a device for forming a non-oxidizing atmosphere (Japanese Patent Application No. 59-246240, No. 60-151222, No. 60-250476) reference)
.

The reason why the temperature of molten zinc is set in the range of 520 to 850°C is as follows. If the temperature of the molten zinc is less than 520°C, the alloying reaction will not proceed in the short time allotted for the Fe-Zn alloying reaction due to the equipment layout in the process, and the interface between the repair plating layer and the raw steel strip will not proceed. This is because only a Fe-Zn alloy phase is formed and the entire repair plating layer does not become an Fe-Zn alloy.Furthermore, if the temperature of the molten zinc exceeds 850°C, the Fe-Zn alloying reaction progresses too much. This is because the resulting repair plating layer has a high Fe concentration, resulting in poor adhesion, corrosion resistance, etc., and also increases evaporation and oxidation of zinc, making it unfavorable for work.

In addition, in the method of the present invention, the alloying reaction between the base material of the weld bead cut part and the molten zinc deposited thereon utilizes the heat of the molten zinc and the residual heat during electric resistance welding. It is preferable that the temperature at which molten zinc is applied to the cut part of the weld bead is approximately the same as that of molten zinc, and the timing of molten zinc adhesion, that is, the pipe forming speed and the position of molten zinc adhesion, should be adjusted to achieve such a temperature relationship. For example, it is preferable to adjust the relationship with the nozzle position in the above example.

〔effect〕

As described above, according to the method of the present invention, cutting of the weld bead and adhesion of molten zinc to the cut portion of the weld bead are performed in a non-oxidizing atmosphere during the manufacturing process of ERW steel pipes made from alloyed galvanized steel sheets. and by controlling the temperature of the molten zinc to a high temperature within a specific range.

Not only does it improve the performance of the repair plating layer, such as its adhesion and corrosion resistance, but it also makes it possible to make the degree of alloying of the repair plating layer almost homogeneous with the alloyed galvanized layer of the raw steel strip, which makes it easier to bake the paint. This can prevent the subsequent occurrence of blistering of the paint film and improve the adhesion of the paint film.

〔Example〕

Hereinafter, the method of the present invention will be explained in more detail with reference to Examples.

Alloyed galvanized steel sheet with plate thickness of 1.6 mm [Plating coverage: 6
0g/rrr (single side) 1 Fe concentration near the surface of the alloy layer 6
．． 5%] was passed through a tube-making machine equipped with the repair plating device described above to form a tube, and the butt portions were welded.

An electric resistance welded steel pipe with an outer diameter of 25.4 cm was manufactured by cutting the weld bead in an Ar gas atmosphere and immediately adhering molten zinc to the cut part of the weld bead while it was still hot. At this time, the temperature of molten zinc was set to 680°C.

As a result, the weld bead cut part had a thickness of approximately 15 μm.
A Zn alloy layer was formed. Fe near the surface of this alloy layer
When the concentration was measured with an X-ray microanalyzer, it was 6%.
It was almost the same as that of the material plating layer.

The adhesion and corrosion resistance of the plated layer of the obtained electric resistance welded steel pipe were far superior to those of electric resistance welded steel pipes obtained by conventional methods.

Separately, this ERW steel pipe was degreased, washed with water, and treated with phosphate, and then powder coated with polyester paint (film thickness 60 μm).
) and baked at 200°C for 20 minutes. The thus obtained coated ERW steel pipes were exposed outdoors for a long period of time, but the repair plating layer did not show the same coating film as was seen on the repair plating layer of the ERW steel pipes obtained by the conventional method. No blistering was observed, and the adhesion of the coating film was also good as determined by the cross-cut test.

Claims (1)

[Claims] 1. In the process of continuously manufacturing ERW steel pipes while horizontally moving an alloyed galvanized steel strip, the weld bead is cut in a non-oxidizing atmosphere, and immediately after that, the still hot cut part is A method for manufacturing an alloyed galvanized electric resistance welded steel pipe, which comprises depositing molten zinc at ~850°C.