阅读说明：本技术 穿轧机顶头 (Piercing mill plug ) 是由 日高康善 东田泰斗 白泽尚也 于 2019-01-18 设计创作，主要内容包括：本发明提供一种耐磨耗性得以进一步提高的穿轧机顶头。穿轧机顶头(10)具备顶头主体(11)和在顶头主体(11)的表面形成的喷镀覆膜(12)。喷镀覆膜(12)包含铁基合金及其氧化物。利用荧光X射线分析对喷镀覆膜(12)进行分析而得到的铬浓度为3～20质量％。(The invention provides a piercing-rolling mill plug with further improved wear resistance. A piercing plug (10) is provided with a plug body (11) and a sprayed coating (12) formed on the surface of the plug body (11). The sprayed coating (12) contains an iron-based alloy and an oxide thereof. The sprayed coating (12) is analyzed by fluorescent X-ray analysis, and the chromium concentration is 3-20 mass%.)

1. A piercing-rolling mill plug is provided with:

a plug body; and

a sprayed coating formed on the surface of the plug body,

the sprayed coating contains an iron-based alloy and an oxide of the iron-based alloy,

the concentration of chromium obtained by analyzing the sprayed coating by fluorescent X-ray analysis is 3 to 20 mass%.

Technical Field

The invention relates to a piercing-rolling machine plug.

Background

Conventionally, a piercing plug used for piercing-rolling of a seamless steel pipe is used to form an oxide film on the surface thereof in order to ensure heat insulation, lubricity, and heat-resistant adhesion of the surface.

The scale coating gradually wears away with each piercing-rolling. When the oxide scale coating is completely worn and the base material (plug body) is exposed, the base material is melted and stuck to the target material. In the piercing of a difficult-to-work material such as stainless steel, the wear of the scale film is significant, and the scale film may be worn away several times. In this case, a heat treatment for forming a scale coating again is required, but the heat treatment requires several hours to several tens of hours, and therefore, the efficiency is poor.

International publication No. 2009/057471 proposes a technique for forming a sprayed coating containing iron and an oxide on the surface of a base material of a piercing-rolling plug. International publication No. 2014/034376 discloses a piercing-rolling mill plug comprising, in addition to iron and iron oxides, C: 0.015 to 0.6%, Si: 0.05-0.5%, Mn: 0.1 to 1.0%, Cu: 0 to 0.3% of a sprayed coating.

Disclosure of Invention

The sprayed coating is excellent in adhesion to the base material and wear resistance as compared with the oxide scale coating, and can be formed in several minutes to several tens of minutes. Therefore, the sprayed 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 improve the efficiency of manufacturing seamless steel pipes, it is preferable to further extend the life of the piercing mill plug. For this reason, it is preferable to further increase the abrasion resistance of the coating film.

The invention aims to provide a piercing-rolling mill plug with further improved wear resistance.

A piercing-rolling plug according to an embodiment of the present invention includes a plug main body and a sprayed coating formed on a surface of the plug main body. The sprayed coating contains 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 mass%.

According to the present invention, a piercing-rolling mill plug with further improved wear resistance can be obtained.

Drawings

Fig. 1 is a longitudinal sectional view of a piercing mill plug according to an embodiment of the present invention.

Fig. 2 is a diagram showing an example of an apparatus for forming a sprayed coating.

Fig. 3 is a cross-sectional view of the cored wire.

Fig. 4 is a longitudinal sectional view of a piercing mill plug according to another embodiment of the present invention.

Fig. 5 is a longitudinal sectional view of a piercing mill plug according to another embodiment of the present invention.

FIG. 6 is a photomicrograph showing a cross-sectional view of a sprayed coating containing no Cr.

FIG. 7 is a photomicrograph of a cross-section of a sprayed coating containing Cr.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and description thereof will not be repeated. The dimensional ratio between the structural members shown in the drawings does not necessarily represent an actual dimensional ratio.

[ Structure of piercing-rolling mill plug ]

Fig. 1 is a longitudinal sectional view of a piercing mill plug 10 according to an embodiment of the present invention. The piercing plug 10 includes a plug body 11 and a sprayed coating 12.

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

The sprayed coating 12 is formed on the surface of the plug body 11. The sprayed coating 12 covers the entire surface of the plug body 11 except for the rear end surface 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 at the distal end portion 11a than at the cylindrical portion 11b of the plug body 11.

The sprayed coating 12 contains at least an iron-based alloy and an oxide thereof. The sprayed coating 12 may contain compounds other than them.

The iron-based alloy in the sprayed coating 12 contains iron (Fe) as a main component, and contains carbon (C), silicon (Si), manganese (Mn), chromium (Cr), and the like. The iron-based alloy in the sprayed 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 sprayed coating 12 may be microscopically different. For example, a portion containing almost no Cr and a portion containing a high Cr content may be mixed microscopically.

The oxide in the sprayed coating 12 is an oxide formed by oxidizing the iron-based alloy. The oxide in the sprayed coating 12 is specifically iron oxide, a composite oxide of iron and chromium, or the like. Iron oxides such as FeO, Fe₃O₄And the like. The complex oxide of iron and chromium is, for example, (Fe, Cr)₃O₄And the like. The oxide in the sprayed coating 12 may contain a metal oxide other than the above.

In the sprayed coating 12, the higher the ratio of the metal component (iron-based alloy), the more the adhesion to the plug body 11 is improved. On the other hand, the higher the ratio of the oxide, the more the heat insulating property is improved. The content of the oxide in the sprayed coating 12 is not limited to this, but is preferably 25 to 80 vol%, and more preferably 35 to 65 vol%. Further, the vicinity of the plug main body 11 is preferably: the ratio of the metal component is high, and the ratio of the oxide is higher toward the surface. With this configuration, the adhesion to the plug main body 11 can be further improved. The volume fraction of the oxide can be calculated by observing the cross section of the sprayed coating 12.

In the piercing-rolling mill plug 10 according to the present embodiment, the chromium concentration (hereinafter referred to as "XRF — Cr concentration") obtained by analyzing the sprayed coating 12 by fluorescent X-ray analysis is 3 to 20 mass%.

If the XRF — Cr concentration is 3 mass% or more, excellent wear resistance can be obtained as compared with the case of less than 3 mass%. This is considered to be 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 mass%, the lubricity of the sprayed coating 12 is reduced, and the piercing efficiency is reduced. The lower limit of the XRF — Cr concentration is preferably 5 mass%, and more preferably 8 mass%. The upper limit of the XRF — Cr concentration is preferably 18 mass%, and more preferably 16 mass%.

The XRF-Cr concentration was measured as follows. X-rays are incident from the surface of the sprayed coating 12, and fluorescence X-rays are detected by a detector. Incident X-ray application target: rh, output Power: 40kV x 100 muA, 3mm phi facula collimator. The detector is set as a silicon drift detector (Si drift detector). The Cr concentration in mass% was determined using all the elements detected as denominators. The molecules at XRF-Cr concentrations include both Cr in iron-based alloys and Cr in oxides.

In the piercing-rolling mill plug 10 according to the present embodiment, the iron concentration obtained by analyzing the sprayed coating 12 by fluorescent X-ray analysis is preferably 50 mass% or more. The iron concentration analyzed by fluorescent X-ray analysis was measured in the same manner as the XRF-Cr concentration.

[ method for producing piercing-rolling mill plug ]

An example of a method of manufacturing the piercing-rolling mill plug 10 will be described below. The method described below is merely an example, and the method for manufacturing the piercing plug 10 is not limited thereto.

The plug body 11 is prepared. The plug body 11 may be a known one.

A sprayed coating 12 is formed on the plug body 11. The sprayed coating 12 can be formed using an arc spraying apparatus 20 shown in fig. 2.

The arc spraying apparatus 20 includes a spraying gun 21 and a spin base 24. The spray gun 21 generates an arc at the tip of the continuously fed anode wire 22 and cathode wire 23, and sprays the molten metal with compressed air.

The chemical composition and XRF-Cr concentration of the sputtered film 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 of the same chemical composition or wires of different chemical compositions. When wires of 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 thereto, and are, for example, carbon steel or stainless steel. Further, as the anode wire 22 and the cathode wire 23, a cored wire 30 shown in fig. 3 may be used. 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 spray gun 21 to the surface of the plug body 11 (hereinafter referred to as "spray distance"), the higher the ratio of the oxide in the spray coating 12. This is because: oxidation of the metal sprayed from the front end of the spray gun 21 is accelerated depending on the spraying distance. The spraying distance is not limited to this, and is, for example, 100 to 1400 mm. Further, by performing thermal spraying while gradually increasing the thermal 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 as the surface is approached.

As mentioned above, the XRF-Cr concentration molecules include both Cr in the iron-based alloy and Cr in the oxide. Therefore, even if the ratio of the oxide in the sprayed coating 12 is changed, the XRF — Cr concentration does not change significantly. Therefore, the XRF-Cr concentration does not change significantly even if the spray distance is changed.

The thermal spray coating 12 is thermally sprayed until the thermal spray coating has a predetermined thickness while the plug body 11 is rotated about the axis by the rotating base 24. The thickness of the sprayed coating 12 is not limited to this, and is, for example, 200 to 3000 μm.

After the sprayed coating 12 is formed, a heat treatment for diffusion is preferably performed. This enables the plug body 11 and the sprayed coating 12 to further adhere to each other. The heat treatment for diffusion is preferably performed at 600 to 1250 ℃ for 10 minutes or longer, for example. The heat treatment temperature is more preferably 600 to 1100 ℃.

The piercing plug 10 according to the embodiment of the present invention is described above. In the present embodiment, the XRF-Cr concentration of the thermal spray coating 12 is set to 3 to 20 mass%. This can further improve the wear resistance of the piercing plug 10.

In the above embodiment, the case where the plug body 11 has a shell shape has been described. However, the plug body 11 may have any shape. The piercing plug may have a sprayed coating 12 formed on a plug body 13 having a tip-protruding shape shown in fig. 3, or may have a sprayed coating 12 formed on a plug body 14 having a divided shape shown in fig. 4, for example.

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