WO2019176279A1 - Piercer plug - Google Patents

Abstract

Provided is a piercer plug having further improved wear resistance. The piercer plug (10) is equipped with a plug body (11) and a sprayed coating film (12) formed on the surface of the plug body (11). The sprayed coating film (12) includes an iron-based alloy and an oxide thereof. The chromium concentration obtained by analyzing the sprayed coating film (12) by fluorescent x-ray analysis is 3-20% by mass.

Description

Piercer plug

The present invention relates to a piercer plug.

Conventionally, piercer plugs used for piercing and rolling of seamless steel pipes are used by forming a scale film on the surface in order to ensure surface thermal insulation, lubricity, and seizure resistance.

The scale film gradually wears with each piercing and rolling. When the scale film is completely worn and the base material (plug body) is exposed, the base material is melted and seized with the counterpart material. In the drilling of difficult-to-process materials such as stainless steel, the wear of the scale film is noticeable and may be worn in several passes. Each time, heat treatment for re-forming the scale film is required, but this heat treatment requires several hours to several tens of hours, and thus there is a problem that efficiency is poor.

International Publication No. 2009/057471 proposes a technique for forming a sprayed coating made of iron and oxide on the surface of a base material of a piercer plug. In WO2014 / 034376, in addition to iron and iron oxide, in mass%, C: 0.015 to 0.6%, Si: 0.05 to 0.5%, Mn: 0.1 A piercer plug with a thermal spray coating containing ˜1.0% and Cu: 0˜0.3% is disclosed.

The thermal spray coating has better adhesion to the base material and wear resistance than the scale coating, and can be formed in several minutes to several tens of minutes. Therefore, the thermal spray coating has a longer life than the scale coating and can be regenerated in a short time even when worn. On the other hand, in order to increase the production efficiency of the seamless steel pipe, it is preferable to further increase the life of the piercer plug. For this purpose, it is preferable to further increase the wear resistance of the coating.

An object of the present invention is to provide a piercer plug with further improved wear resistance.

A piercer plug according to an embodiment of the present invention includes a plug body and a thermal spray coating formed on the surface of the plug body. The thermal spray coating includes an iron-based alloy and an oxide of the iron-based alloy. The chromium concentration obtained by analyzing the sprayed coating by fluorescent X-ray analysis is 3 to 20% by mass.

According to the present invention, a piercer plug with further improved wear resistance can be obtained.

FIG. 1 is a longitudinal sectional view of a piercer plug according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of an apparatus used for forming a thermal spray coating. FIG. 3 is a cross-sectional view of a cored wire. FIG. 4 is a longitudinal sectional view of a piercer plug according to another embodiment of the present invention. FIG. 5 is a longitudinal sectional view of a piercer plug according to still another embodiment of the present invention. FIG. 6 is a cross-sectional photomicrograph of a thermal spray coating not containing Cr. FIG. 7 is a cross-sectional micrograph of a sprayed coating containing Cr.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated. The dimensional ratio between the constituent members shown in each drawing does not necessarily indicate the actual dimensional ratio.

[Piercer plug structure]
FIG. 1 is a longitudinal sectional view of a piercer plug 10 according to an embodiment of the present invention. The piercer plug 10 includes a plug body 11 and a thermal spray coating 12.

The plug body 11 has a shell shape. Specifically, the plug main body 11 has a circular cross-sectional shape and an outer diameter that increases from the front end of the plug main body 11 toward the rear end. The plug body 11 is made of, for example, an iron-based alloy.

The thermal spray coating 12 is formed on the surface of the plug body 11. The thermal spray coating 12 covers the entire surface of the plug body 11 except for the rear end face of the plug body 11. The thickness of the sprayed coating 12 may not be constant. The thermal spray coating 12 is preferably formed thicker on the distal end portion 11 a than on the body portion 11 b of the plug body 11.

The sprayed coating 12 contains at least an iron-based alloy and its oxide. The sprayed coating 12 may contain a compound other than these.

The iron-based alloy in the thermal spray coating 12 is mainly composed of iron (Fe) and contains carbon (C), silicon (Si), manganese (Mn), chromium (Cr), and the like. The iron-based alloy in the thermal spray coating 12 may contain only a part of C, Si, Mn, and Cr, or may contain elements other than C, Si, Mn, and Cr. The chemical composition of the iron-based alloy in the thermal spray coating 12 may not be microscopically uniform. For example, microscopically, a portion that hardly contains Cr and a portion that has a high Cr content may be mixed.

The oxide in the thermal spray coating 12 is an oxide formed by oxidizing the iron-based alloy. Specific examples of the oxide in the thermal spray coating 12 include iron oxide and a composite oxide of iron and chromium. Examples of the iron oxide include FeO and Fe ₃ O ₄ . The composite oxide of iron and chromium is, for example, (Fe, Cr) ₃ O ₄ . The oxide in the sprayed coating 12 may contain a metal oxide other than the above.

The higher the ratio of the metal component (iron-based alloy) in the sprayed coating 12, the better the adhesion with the plug body 11. On the other hand, the higher the oxide ratio, the better the heat shielding properties. The ratio of the oxide in the thermal spray coating 12 is not limited to this, but is preferably 25 to 80% by volume, more preferably 35 to 65% by volume. Moreover, it is preferable that the ratio of a metal component is high in the vicinity of the plug main body 11, and the ratio of an oxide becomes high as it goes to the surface. According to this configuration, the adhesiveness with the plug body 11 can be further increased. The volume ratio of the oxide can be calculated from cross-sectional observation of the sprayed coating 12.

The piercer plug 10 according to the present embodiment has a chromium concentration (hereinafter referred to as “XRF-Cr concentration”) obtained by analyzing the sprayed coating 12 by fluorescent X-ray analysis of 3 to 20 mass%.

When the XRF-Cr concentration is 3% by mass or more, excellent wear resistance is obtained as compared with the case of less than 3% by mass. This is presumably because the hardness of the thermal spray coating 12 is increased by the composite oxide of iron and chromium. On the other hand, if the XRF-Cr concentration exceeds 20% by mass, the lubricity of the thermal spray coating 12 decreases and the perforation efficiency decreases. The lower limit of the XRF-Cr concentration is preferably 5% by mass, more preferably 8% by mass. The upper limit of the XRF-Cr concentration is preferably 18% by mass, and more preferably 16% by mass.

XRF-Cr concentration is measured as follows. X-rays are incident from the surface of the thermal spray coating 12, and the fluorescent X-rays are detected by a detector. For incident X-rays, target: Rh, output: 40 kV × 100 μA, 3 mmΦ spot collimator is applied. The detector is a Si drift detector. Using all the detected elements as the denominator, the Cr concentration is determined by mass%. The XRF-Cr concentration molecules include both Cr in the iron-base alloy and Cr in the oxide.

The piercer plug 10 according to the present embodiment preferably has an iron concentration obtained by analyzing the sprayed coating 12 by fluorescent X-ray analysis of 50% by mass or more. The iron concentration obtained by analysis by fluorescent X-ray analysis is measured in the same manner as the XRF-Cr concentration.

[Piercer plug manufacturing method]
Hereinafter, an example of the manufacturing method of the piercer plug 10 will be described. The method described below is merely an example, and the manufacturing method of the piercer plug 10 is not limited to this.

Prepare the plug body 11. A known plug body 11 can be used.

The thermal spray coating 12 is formed on the plug body 11. The sprayed coating 12 can be formed using the arc spraying apparatus 20 shown in FIG.

The arc spray device 20 includes a spray gun 21 and a turntable 24. The spray gun 21 generates an arc at the tips of the anode wire 22 and the cathode wire 23 that are continuously supplied, and injects molten metal with compressed air.

The chemical composition and XRF-Cr concentration of the thermal spray coating 12 can be adjusted by the chemical composition of the anode wire 22 and the cathode wire 23. The anode wire 22 and the cathode wire 23 may be wires having the same chemical composition or may be wires having different chemical compositions. When wires having different chemical compositions are used, the metal of the anode wire 22 and the metal of the cathode wire 23 are mixed to form a pseudo alloy.

The anode wire 22 and the cathode wire 23 are not limited to this, but are, for example, carbon steel or stainless steel. Further, the cored wire 30 shown in FIG. 3 may be used as the anode wire 22 and the cathode wire 23. The cored wire 30 includes a carbon steel outer shell 31 and a filler 32 filled in the outer shell 31. By changing the type of the filler 32, the chemical composition of the metal sprayed from the spray gun 21 can be arbitrarily changed.

The longer the distance from the tip of the thermal spray gun 21 to the surface of the plug body 11 (hereinafter referred to as “thermal spray distance”), the higher the ratio of oxide in the thermal spray coating 12. This is because the oxidation of the metal sprayed from the tip of the spray gun 21 proceeds according to the spray distance. The spraying distance is not limited to this, but is, for example, 100 to 1400 mm. Further, by spraying while gradually increasing the spraying distance, the ratio of the metal component in the vicinity of the plug body 11 can be increased, and the ratio of the oxide can be increased toward the surface.

As described above, the molecule having the XRF-Cr concentration includes both Cr in the iron-based alloy and Cr in the oxide. Therefore, the XRF-Cr concentration does not change greatly even if the ratio of the oxide in the thermal spray coating 12 changes. Therefore, the XRF-Cr concentration does not change greatly even if the spraying distance is changed.

While the plug body 11 is rotated around the axis by the turntable 24, spraying is performed until the sprayed coating 12 reaches a predetermined thickness. The thickness of the sprayed coating 12 is not limited to this, but is, for example, 200 to 3000 μm.

After forming the thermal spray coating 12, it is preferable to perform a heat treatment for diffusion. Thereby, the plug main body 11 and the thermal spray coating 12 can be more closely attached. For example, the heat treatment for diffusion is preferably held at 600 to 1250 ° C. for 10 minutes or more. The heat treatment temperature is more preferably 600 to 1100 ° C.

The piercer plug 10 according to the embodiment of the present invention has been described above. In this embodiment, the XRF-Cr concentration of the thermal spray coating 12 is 3 to 20% by mass. Thereby, the wear resistance of the piercer plug 10 can be further improved.

In the above embodiment, the case where the plug body 11 has a bullet shape has been described. However, the shape of the plug body 11 is arbitrary. For example, the piercer plug may be one in which the spray coating 12 is formed on the plug body 13 having a protruding tip shape shown in FIG. 3, or the spray coating 12 is formed on the plug body 14 having a split shape shown in FIG. It may be a thing.

In the above embodiment, the case where the sprayed coating 12 is formed by arc spraying has been described. However, the method of forming the sprayed coating 12 is not limited to this. The thermal spray coating 12 can be formed by, for example, plasma spraying, flame spraying, high-speed flame spraying, or the like.

Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.

The main component is 0.15C-0.5Si-1.0Ni-0.5Mn-1.5Mo-3.0W-Bal. A thermal spray coating was formed on the Fe model plug. As the anode wire and the cathode wire, low carbon steel, SUS410 and SUS430 wires, and a cored wire with a changed Cr concentration were combined to adjust the components of the thermal spray coating.

The XRF-Cr concentration of the thermal spray coating was analyzed by the method described in the embodiment. The fluorescent X-ray analyzer was analyzed using JEOL's DP2000 DELTA Premium, using JEOL's ALLOY PLUS alloy analysis software.

The Vickers hardness of the sprayed coating of each plug was measured. The Vickers hardness was measured at three points for each plug, and the average was obtained.

Table 1 shows the relationship between the XRF-Cr concentration and the average hardness. In Table 1, “-” in the column of XRF-Cr concentration indicates that the XRF-Cr concentration was less than the lower limit of analysis.

As shown in Table 1, the higher the XRF-Cr concentration, the higher the average Vickers hardness.

FIG. 6 is a cross-sectional micrograph of the thermal spray coating of mark A in Table 1. FIG. 7 is a cross-sectional photomicrograph of the thermal spray coating of mark C in Table 1. As shown in FIG. 7, the thermal spray coating containing Cr was composed of a metal component and an oxide, like the thermal spray coating not containing Cr (FIG. 6). In the figure, a relatively bright portion is a portion made of a metal component, and a dark gray portion is a portion made of an oxide. The ratio of the metal component to the oxide was almost the same in all the sprayed coatings prepared this time, and the ratio of the oxide was about 45 to 55% by volume.

Subsequently, using these plugs, a drilling test was conducted using SUS304 as a counterpart material, and the amount of film abrasion was measured. Table 2 shows the relationship between the XRF-Cr concentration and the amount of wear. In the column of “Conventional specific wear amount” in Table 2, the wear amount of the thermal spray coating of the plug of the mark A is set to 1, and the wear amount of the thermal spray coating of each plug is described as a relative value.

As shown in Table 2, the higher the XRF-Cr concentration, the lower the wear amount. In particular, by setting the XRF-Cr concentration to 3% by mass or more, the amount of wear could be reduced to about 70% in the case of the mark A. On the other hand, when the XRF-Cr concentration exceeded 20% by mass, the drilling efficiency was lowered and rolling became difficult.

These results confirmed that the wear resistance of the piercer plug can be further improved by setting the XRF-Cr concentration to 3 to 20% by mass.

As mentioned above, although embodiment of this invention was described, embodiment mentioned above is only the illustration for implementing this invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

Claims (1)

A plug body;
A thermal spray coating formed on the surface of the plug body,
The thermal spray coating includes an iron-based alloy and an oxide of the iron-based alloy,
A piercer plug having a chromium concentration of 3 to 20% by mass obtained by analyzing the thermal spray coating by fluorescent X-ray analysis.

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