JP6540441B2 - Plug manufacturing method - Google Patents

Description

  The present disclosure relates to plugs, and more particularly, to a method of manufacturing a plug used for billet drilling.

  The Mannesmann tube method is widely adopted as a method for producing seamless tubes. In the Mannesman tube method, a billet heated to a predetermined temperature is pierced and rolled by a piercing machine. The drilling machine comprises a pair of inclined rolls and a plug. The plug is disposed on the pass line between the pair of inclined rolls. The drilling machine presses the billet into the plug while rotating the billet in the circumferential direction by the inclined roll and pierces and rolls the billet into a hollow shell.

  In conventional plugs, an oxide scale film is formed on the surface of a base material in advance during piercing and rolling of a billet. The oxide scale film is formed by subjecting the plug to heat treatment. Thereby, the heat shielding property, the lubricity and the seizure resistance of the surface of the plug can be secured.

  Oxide scale coatings are progressively worn away by repeated piercing and rolling. The film is worn each time piercing rolling is performed (every pass). When the coating is completely worn out and lost, the plug base material is exposed. In this case, melting loss at the exposed portion of the base material, seizing of the plug and the billet which is the opposite material, and the like occur, and the plug reaches its life.

  In particular, when drilling a billet made of stainless steel, the wear of the oxide scale film is remarkable, so the life of the plug is very short. When drilling a billet made of stainless steel, the coating usually wears in several passes. Each time the coating wears, a heat treatment is required to produce an oxide scale on the surface of the plug matrix. The heat treatment generally takes several hours to several tens of hours. Therefore, the formation efficiency of the oxide scale film is low.

  On the other hand, in patent documents 1 and 2, the art which forms the tunic which consists of iron and an oxide on the surface of the base material of a plug by arc spraying is proposed. In the case of arc spraying, the raw material of the film is only an iron wire rod, and the time required to form the film is as short as several minutes to several tens of minutes. Therefore, a film can be formed on the surface of the base material at low cost and with high efficiency. In addition, the thermal spray coating has higher adhesion to the base material and wear resistance as compared with the oxide scale coating. Therefore, the life of the plug can be extended.

  The thermal spray coating is excellent in adhesion to the plug base material and wear resistance. However, for example, when drilling a high strength billet made of a high alloy, or when the drilling length of the billet is very long, the thermal spray coating may peel off the surface of the base material during the drilling. When the base material is exposed by the peeling of the thermal spray coating, melting of the plug and seizing of the billet to the plug occur from the exposed portion.

  Patent Document 3 discloses that the plug body on which the thermal spray coating is formed is subjected to heat treatment in order to make the thermal spray coating difficult to peel off. Patent Document 3 describes that by setting the heat treatment temperature to 400 to 550 ° C., the iron ratio and the magnetite ratio in the sprayed coating increase, and the adhesion of the sprayed coating to the plug body increases.

  Patent Document 4 discloses that a Ni-Cr layer is formed as an adhesive layer between a plug body and a thermal spray coating to enhance the adhesion of the thermal spray coating to the plug body. In patent document 3, the adhesiveness of the thermal-sprayed coating with respect to a plug main body is further improved by heat-processing to the plug main body in which the Ni-Cr layer and the thermal spray coating were formed.

  Patent Documents 5 to 7 disclose techniques for improving the adhesion of a film to a substrate by heat treatment, which is not applied to a plug for drilling a billet.

Patent 4279350 gazette Patent No. 5169982 JP, 2013-248619, A International Publication No. 2014/013963 JP-A-64-11956 JP-A-3-277764 International Publication No. 2011/151929

  As described above, when the film peels off from the plug body, erosion of the plug and burning of the billet to the plug occur. In order to prevent such a situation, the adhesion of the film to the plug body is preferably as high as possible.

  An object of the present disclosure is to provide a method of manufacturing a plug that can improve the adhesion of the film to the plug body.

  The present disclosure relates to a method of manufacturing a plug used for drilling a billet. The method of manufacturing the plug comprises the steps of preparing a plug body having a film containing iron and iron oxide formed on the surface, and maintaining the plug body having the film formed thereon at 700 to 1250 ° C. for 10 minutes or more, Causing interdiffusion between the coating and the plug body.

  According to the plug manufacturing method of the present disclosure, the adhesion of the film to the plug body can be improved.

FIG. 1 is a partial cross-sectional view of a plug according to an embodiment. FIG. 2 is a diagram for explaining a process of the plug manufacturing method according to the embodiment. FIG. 3A is a diagram for explaining the effects of the embodiment. FIG. 3B is a diagram for explaining the effect of the embodiment. FIG. 4 is a partial cross-sectional view of a plug according to a modification of the embodiment. FIG. 5 is a partial cross-sectional view of a plug according to another modification of the embodiment. FIG. 6 is a micro observation image of the cross section of the film portion of each test piece according to Example 1 and Comparative Example 1. FIG. 7 is a graph showing the shear adhesion between the film and the substrate for each of the test pieces according to Example 1 and Comparative Example 1.

  The method for manufacturing a plug according to the embodiment comprises the steps of preparing a plug body having a film containing iron and iron oxide formed on the surface, and the plug body having the film formed thereon at 700 to 1250 ° C. for 10 minutes or more And holding to cause interdiffusion between the coating and the plug body (first configuration).

  According to the first configuration, the plug main body on which the film is formed is subjected to a heat treatment of holding at 700 to 1250 ° C. for 10 minutes or more. This causes interdiffusion of atoms contained in the film and atoms contained in the plug body at the interface between the film and the plug body. Therefore, the adhesion of the film to the plug body can be improved.

  The portion of the coating disposed on the tip of the plug body may have a thickness of 1300 μm or more (second configuration).

  At the tip of the plug body, the coating is preferably thick because the load at the time of drilling is large. However, in general, when the thickness of the film is increased, the film easily peels off the plug body. According to the second configuration, although the thickness of the film on the tip portion of the plug body is as large as 1300 μm or more, the adhesion of the film to the plug body is enhanced by the interdiffusion between the plug body and the film. For this reason, it is possible to suppress peeling of the film from the plug body while effectively protecting the tip portion of the plug body by the film.

  The step of preparing may include a step of forming a film on the surface of the plug body by performing arc spraying using an iron wire material (third configuration).

  According to the third configuration, a film excellent in adhesion and wear resistance can be easily formed on the surface of the plug body.

  Hereinafter, embodiments will be described with reference to the drawings. The same or corresponding components in the drawings have the same reference characters allotted, and the same description will not be repeated. For convenience of explanation, in each drawing, the configuration may be simplified or schematically illustrated, or a part of the configuration may be omitted.

[Plug structure]
First, the structure of the plug will be described. FIG. 1 is a longitudinal sectional view of a plug 10 according to an embodiment. As shown in FIG. 1, the plug 10 includes a plug body 11 and a film 12.

  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. In short, the shape of the plug body 11 is substantially shell-shaped. The plug body 11 is made of, for example, an iron-based alloy.

  The coating 12 is formed on the surface of the plug body 11. The film 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 film 12 may not be constant throughout. In the film 12 according to the present embodiment, the thickness of the portion disposed on the tip end portion 11 a of the plug main body 11 is larger than the thickness of the portion disposed on the body portion 11 b of the plug main body 11.

  The thickness T of the film 12 on the tip 11a is preferably 1300 μm or more. The thickness T is preferably 3000 μm or less. The thickness T is evaluated by the film thickness at the tip of the tip 11a.

  The film 12 contains iron and iron oxide. The film 12 is mainly composed of iron and iron oxides, but may contain a small amount of elements and / or compounds other than iron and iron oxides. In the film 12, it is preferable that the iron content is low and the iron oxide content is high as going from the plug main body 11 side to the surface side.

  Although not shown, a diffusion layer is formed at the interface between the plug body 11 and the film 12. The diffusion layer is a layer formed by mutual movement of atoms between the plug body 11 and the film 12 by diffusion heat treatment to be described later.

[Method of manufacturing plug]
Next, a method of manufacturing the plug 10 will be described.

  First, the plug main body 11 in which the film 12 is formed on the surface is prepared. The coating 12 can be formed on the surface of the plug body 11 by arc spraying. However, the coating 12 may be formed on the surface of the plug body 11 by a method other than arc spraying.

  Arc spraying can be performed, for example, using the arc spraying apparatus 4 shown in FIG. The arc spraying apparatus 4 includes a spraying gun 41 and a rotating table 42. The thermal spray gun 41 melts a wire for thermal spraying by an arc and sprays it from the nozzle by compressed air. In the present embodiment, an iron wire is used as a wire for thermal spraying. The iron wire rod is a wire rod of carbon steel (normal steel) mainly composed of iron (Fe). Typically, it is a so-called ordinary steel mainly composed of Fe and composed of carbon (C), silicon (Si), manganese (Mn) and impurities, but it also contains an element such as tungsten (W) Good.

  When forming the coating 12, the plug body 11 is placed on the rotating table 42 of the arc spraying apparatus 4. Then, while the plug body 11 is rotated about the axis by the rotation table 42, arc spraying of the iron wire material is performed on the plug body 11. Thereby, the film 12 containing iron and iron oxide is formed on the surface of the plug body 11. Formation of the coating 12 ends when a desired thickness of material is deposited on the surface of the plug body 11. Preferably, a material having a thickness of 1300 μm or more is deposited on the tip end portion 11 a of the plug body 11. The thickness of the material deposited on the tip 11a is preferably 3000 μm or less.

  The coating 12 is preferably formed while gradually increasing the spraying distance. The thermal spraying distance refers to the shortest distance from the tip of the nozzle of the thermal spray gun 41 to the surface of the thermal spray target. The coating 12 can be formed by arranging the thermal spray gun 41 at a predetermined distance from the plug body 11 to start arc spraying and continuing the arc spraying while gradually separating the thermal spray gun 41 from the plug body 11.

  The longer the spraying distance, the higher the oxide content of the thermal spray material in the coating 12. Therefore, if the coating 12 is formed while gradually increasing the thermal spraying distance, in the coating 12, the content of iron decreases and the content of iron oxide increases as going from the plug main body 11 side to the surface side. Thereby, while the adhesion between the plug body 11 and the film 12 is improved, the thermal conductivity on the surface layer side of the film 12 is lowered to improve the heat shielding property, and the seizing of the billet to the plug 10 is suppressed. However, during the formation of the coating 12, the spraying distance can also be kept constant.

  Next, diffusion heat treatment is performed on the plug body 11 on which the film 12 is formed. The diffusion heat treatment can be carried out using a known heat treatment furnace. Specifically, the plug body 11 on which the film 12 is formed is placed in a heat treatment furnace, and held at 700 to 1250 ° C. for 10 minutes or more. In the diffusion heat treatment, a more preferable holding temperature (processing temperature) is 1000 to 1200 ° C., and a more preferable holding time (processing time) is 1 to 6 hours.

  The diffusion heat treatment may be performed in an atmosphere in which the oxidation of the film 12 is difficult to progress. For example, the diffusion heat treatment can also be performed in an inert gas atmosphere such as argon gas or nitrogen gas.

  The diffusion heat treatment may be performed in the air (in the air). When the diffusion heat treatment is performed in the air, the treatment time is preferably 20 minutes or less.

  By holding the plug body 11 on which the film 12 is formed at 700 to 1250 ° C. for 10 minutes or more, a diffusion layer is formed at the interface between the film 12 and the plug body 11. Thereby, the plug 10 according to the embodiment is completed.

[effect]
In the present embodiment, diffusion heat treatment is performed on the plug body 11 on which the film 12 is formed. As a result, mutual diffusion occurs between the film 12 and the plug body 11, and the adhesion of the film 12 to the plug body 11 can be improved. This effect will be described in more detail with reference to FIGS. 3A and 3B.

  FIG. 3A is a view schematically showing a cross section in the vicinity of the surface of the plug body 11 before the diffusion heat treatment is performed. A film 12 is formed on the surface of the plug body 11.

  By subjecting the plug body 11 on which the film 12 is formed to diffusion heat treatment at 700 to 1250 ° C. for 10 minutes or more, as shown in FIG. 3B, atoms mutually form between the plug body 11 and the film 12 Diffusion occurs, and a diffusion layer is formed at the interface between the plug body 11 and the film 12. Thus, the adhesion between the plug body 11 and the film 12 is enhanced, and the peeling of the film 12 from the plug body 11 can be suppressed.

  In the present embodiment, the thickness T of the film 12 on the distal end portion 11 a of the plug body 11 is preferably 1300 μm or more. In the conventional plug, when the thickness of the film at the tip end is increased to 1300 μm or more, there is a problem that the film is easily peeled off. However, in the present embodiment, since the adhesion of the film 12 to the plug body 11 is improved by mutual diffusion, even when the thickness T of the film 12 on the tip portion 11a is 1300 μm or more, the film 12 from the plug body 11 Peeling hardly occurs. That is, it is possible to effectively protect the tip end portion 11a while suppressing the peeling of the film 12 from the plug main body 11.

  The thickness T of the film 12 on the tip portion 11a is 3000 μm or less from the viewpoint of suppressing the occurrence of a crack caused by the accumulation of residual stress inside the film 12 during thermal spraying, the occurrence of peeling of the film 12, etc. Is preferred.

  In the present embodiment, the diffusion heat treatment may be performed in the air. In this case, since it is not necessary to control the atmosphere of the diffusion heat treatment, equipment for performing the diffusion heat treatment can be simplified. When the diffusion heat treatment is performed in the air, the treatment time is preferably 20 minutes or less. Thereby, oxidation of the film 12 can be suppressed during the diffusion heat treatment.

  In the present embodiment, the coating 12 is preferably formed on the surface of the plug body 11 by performing arc spraying using an iron wire material. In the arc spraying, only the iron wire material is used as a raw material, and the coating 12 can be formed in a short time. Thus, the plug 10 can be manufactured at low cost and with high efficiency. In addition, by forming the coating 12 by arc spraying, the adhesion and wear resistance of the coating 12 can be enhanced.

  As mentioned above, although embodiment was described, this indication is not limited to the said embodiment, A various change is possible unless it deviates from the meaning.

  For example, although the substantially shell-shaped plug main body 11 is used in the above embodiment, a plug main body having another shape can also be used.

  The plug 20 shown in FIG. 4 includes a plug body 21 having a tip projecting shape. In the plug main body 21, the tip end portion 21a is continuous with the body portion 21b as in the plug main body 11 shown in FIG. However, in the plug body 11, the tip end portion 11a and the body portion 11b are smoothly continued, while in the plug body 21, there is a relatively clear boundary between the tip end portion 21a and the body portion 21b. The distal end portion 21 a of the plug main body 21 having a tip projecting shape has a shape closer to a cylinder than the distal end portion 11 a of the substantially shell-like plug main body 11.

  The side surface of the body 21 b of the plug body 21 is covered by the film 12. The film 12 is also disposed on the distal end portion 21 a of the plug body 21. More specifically, the film 12 is formed on the tip surface of the tip 21a, and not formed on the side surface of the tip 21a. Such a coating 12 can be formed by performing arc spraying while masking the side surface of the tip portion 21a.

  The plug 30 shown in FIG. 5 includes a plug body 31 having a divided shape. In the plug main body 31, the tip end portion 31a is configured to be attachable to and detachable from the body portion 31b.

  The tip portion 31 a is covered with the coating 12 on the entire surface except for the rear end surface. The body 31 b is also covered with the coating 12 on the entire surface except for the rear end face. The diffusion heat treatment may be applied to the entire plug body 31 or may be applied to a part of the plug body 31. For example, the diffusion heat treatment can be performed only on the tip 31a having a large load during drilling. That is, the tip 31a on which the film 12 is formed can be removed from the body 31b, and only the tip 31b can be held at 700 to 1250 ° C. for 10 minutes or more.

Hereinafter, the present disclosure will be described in more detail by way of examples. However, the present disclosure is not limited to the following examples.
<1. Evaluation of adhesion between substrate and film>
Two test pieces (base materials) of plate-like steel materials were prepared, and arc spraying using an iron wire was performed under the conditions shown in Table 1 to form a film on each test piece. A diffusion heat treatment was performed on one of the test pieces as an aftertreatment of film formation, an argon (Ar) atmosphere and atmospheric pressure, a treatment temperature: 1180 ° C., and a treatment time: 3 hours (Example 1). No post-treatment for film formation was performed on the other test piece (Comparative Example 1).

  For each of the test pieces according to Example 1 and Comparative Example 1, a micro observation image of the cross section of the film portion was obtained. Each micro observation image is shown in FIG. It can be seen from FIG. 6 that in the test piece of Example 1, interdiffusion occurs at the interface between the substrate and the film.

  FIG. 7 is a graph showing the shear adhesion between the substrate and the film in Example 1 and Comparative Example 1. The shear adhesion is a stress when a film formed on a substrate is loaded in the shear direction and peeled from the substrate. From FIG. 7, it can be seen that in Example 1 in which the diffusion heat treatment was performed after the formation of the film, the shear adhesion was significantly higher than in Comparative Example 1 in which no treatment was performed after the formation of the film.

  Therefore, it could be confirmed that the shear adhesion between the film and the substrate was significantly improved if the diffusion heat treatment was performed after the film was formed on the substrate.

<2. Plug performance evaluation (1)>
For each of Example 2, Comparative Example 2-1, Comparative Example 2-2, and Comparative Example 2-3, a plug main body (21) with a tip projecting shape shown in FIG. 4 was prepared. The maximum diameter of each plug body (21) is 56.4 mm, the total length is 129.2 mm, and the material is steel containing C: 0.15% by mass, W: 3.5% by mass.

  In Example 2, a coating (12) was formed on the surface of the plug body (21) by arc spraying using an iron wire material. In Example 2, after forming the film (12), the plug body (21) was subjected to a diffusion heat treatment under an argon (Ar) atmosphere and atmospheric pressure, at a treatment temperature of 1180 ° C., and for a treatment time of 3 hours. In Example 2, the thickness (T) of the film (12) on the tip portion (21a) was 1500 μm.

  Also in Comparative Examples 2-1 to 2-3, the coating (12) was formed on the surface of the plug body (21) by arc spraying using an iron wire material. In Comparative Examples 2-1 and 2-3, the plug main body (21) was not particularly treated after the formation of the film (12). In Comparative Example 2-2, after forming the film (12), heat treatment was performed on the plug body (21) under an argon (Ar) atmosphere and atmospheric pressure, at a treatment temperature of 500 ° C., and for a treatment time of 3 hours. In Comparative Examples 2-1 and 2-2, the thickness (T) of the film (12) on the tip end portion (21a) is 1200 μm, but in Comparative Example 2-3, the thickness (T) is the same as in Example 2. Is set to 1500 μm.

  Using each of the plugs according to Example 2 and Comparative Examples 2-1 to 2-3, piercing and rolling of a billet made of SUS304 and having a diameter of 70 mm and a length of 400 mm heated to 1230 ° C. was repeatedly performed. About each of Example 2 and Comparative Examples 2-1 to 2-3, the number of times of drilling (the number of life passes) until the plug was damaged and the peeling condition of the film were confirmed. The results are shown in Table 2.

  In the plug according to Comparative Example 2-1, the film (12) was largely peeled off at the body portion (21b) after the two passes. Also in the plug according to Comparative Example 2-2, peeling of the film (12) occurred in the body portion (21b) after the three passes. In the plug according to Comparative Example 2-3, peeling of the film (12) occurred at the tip end (21a) after completion of one pass. On the other hand, in the plug according to Example 2, peeling of the film (12) did not occur even after 5 passes. Therefore, it is understood that the adhesion of the film (12) to the plug body (21) is improved by the diffusion heat treatment, and the peeling of the film (12) is suppressed.

  In Comparative Examples 2-1 and 2-2 in which the thickness (T) of the film (12) at the tip portion (21a) is less than 1300 μm, peeling of the film (12) at the tip portion (21a) did not occur. In Comparative Example 2-3 in which (T) was 1300 μm or more, peeling of the film (12) at the tip portion (21a) occurred. In Comparative Example 2-3, deformation of the tip end portion (21a) also occurred. It is considered that this deformation occurs because the heat shielding property is lost as a result of peeling of the film (12) at the tip portion (21a), and the tip portion (21a) is damaged by heat and melted away. As described above, it is difficult to set the thickness (T) to 1300 μm or more in the conventional plug which has not been subjected to the diffusion heat treatment.

  On the other hand, in Example 2, although the thickness (T) was 1300 μm or more, peeling of the film (12) at the tip portion (21a) did not occur. Therefore, if the diffusion heat treatment is performed after the formation of the film (12), the thickness (T) of the film (12) at the tip portion (21a) can be 1300 μm or more, and the film (12) at the tip portion (21a) Can be suppressed.

<3. Plug performance evaluation (2)>
For each of Example 3 and Comparative Example 3, a plug body (31) of a divided shape shown in FIG. 5 was prepared. The maximum diameter of each plug body (31) is 76.9 mm and the total length is 229.4 mm. The material of each plug body (31) is a steel in which the tip portion (31a) contains a Ni-based alloy, the body (31b) contains C: 0.15% by mass, and W: 3.5% by mass.

  In each of Example 3 and Comparative Example 3, the coating (12) was formed on the surface of the plug body (31) by arc spraying using an iron wire material. In each of Example 3 and Comparative Example 3, the thickness (T) of the film (12) at the tip portion (31a) is 1500 μm. In Example 3, after forming the film (12), the plug body (31) was subjected to diffusion heat treatment under an argon (Ar) atmosphere and atmospheric pressure, at a treatment temperature of 1180 ° C., and for a treatment time of 3 hours. In Comparative Example 3, after the formation of the film (12), no particular treatment was performed on the plug body (31).

  Perforating a billet heated to 1200 ° C. using each of the plugs according to Example 3 and Comparative Example 3 and having a diameter of 65 mm, a length of 600 mm and containing 25% by mass of Cr and 35% by mass of Ni The rolling was repeated. For each of Example 3 and Comparative Example 3, the number of perforations (number of life passes) until the plug was damaged and the peeling state of the film were confirmed. The results are shown in Table 3.

  In the plug according to Comparative Example 3, after completion of one pass, peeling occurred in a portion near the tip portion (31a) on the body portion (31b), that is, in a discontinuous portion of the film (12). On the other hand, in the plug according to the third embodiment, since the tip end (31a) was deformed after completion of the second pass, it was determined that the third pass continuous drilling was not possible, but in both the tip end (31a) and the body (31b) There was no peeling of the film (12). Also from this result, it is understood that the adhesion of the film (12) to the plug body (31) is improved by the diffusion heat treatment, and the peeling of the film (12) can be suppressed.

10, 20, 30: Plugs 11, 21, 31: Plug bodies 11a, 21a, 31a: tip 12: film

Claims (3)

A method of manufacturing a plug used for drilling a billet, comprising:
Preparing a plug body containing iron and iron oxide and having a film formed on a surface of the plug formed on the surface;
Holding the plug body on which the film is formed at 700 to 1250 ° C. for 10 minutes or more to cause mutual diffusion between the film and the plug body;
A method of manufacturing a plug. A method of manufacturing a plug according to claim 1, wherein
The method for manufacturing a plug, wherein a portion of the coating disposed on the tip of the plug body has a thickness of 1300 μm or more. A method of manufacturing a plug according to claim 1 or 2, wherein
The method for manufacturing a plug, the step of preparing includes the step of performing arc spraying using an iron wire material to form the coating on the surface of the plug body.