MX2014012498A

MX2014012498A - Manufacturing method for piercing plug.

Info

Publication number: MX2014012498A
Application number: MX2014012498A
Authority: MX
Inventors: Yasuto Higashida; Yasuyoshi Hidaka; Kenichi Saitou
Original assignee: Nippon Steel & Sumitomo Metal Corp
Priority date: 2012-06-05
Filing date: 2013-04-19
Publication date: 2015-01-15
Also published as: CA2866802C; EP2857545A4; US20150184276A1; EP2857545A1; RU2014153911A; EP2857545B1; CN104364413A; RU2598414C2; AR091250A1; CA2866802A1; CN104364413B; WO2013183213A1

Abstract

This manufacturing method for a piercing plug used in a piercing mill for manufacturing a seamless steel pipe includes a shot blasting step wherein shot blasting is applied to the plug surface and an arc spraying step wherein a thermal spraying wire is arc-sprayed onto the surface of base material of the shot-blasted plug in order to form a coating thereon. In the arc spraying step, the arc spraying is carried out by using a cored wire (1), which is produced by filling an iron tube (2) with iron particles (4) and at least low-thermal-conductivity material particles (3) that are selected from among low-thermal-conductivity material particles (3) having lower thermal conductivity characteristics than that of iron oxide(for example, ZrO2 particles), in order to form a coating comprising iron oxide, Fe, and the low-thermal-conductivity material. Because a coating with high heat-insulating performance can be formed, a plug that allows the plug life to be improved for the piercing process can be manufactured.

Description

METHOD TO PRODUCE PUNCH FOR DRILLING THROUGH TECHNICAL FIELD LAMINATION The present invention relates to a method for producing a punch for perforation by rolling (hereinafter also referred to simply as "punch") to be used in a mill for perforation by rolling (hereinafter, also referred to simply as "perforator") for producing pipes. and seamless steel pipes, in particular to a method for producing a punch for rolling perforation having a film formed by arc-spraying a spray wire containing mainly iron, on a metal base punch.

BACKGROUND Seamless steel tubes and pipes are produced by the Mannesmann production process. The Mannesmann procedure for the manufacture of tubes includes the following steps: 1. perforation by lamination of an initial material (round billet) heated to a predetermined temperature to form a hollow block using a perforator; 2. lamination-stretching of the hollow block by means of a rolling-drawing mill (for example, a mill of mandril); Y 3. lamination to regulate the diameter in the hollow block that has been stretched by rolling to obtain a predetermined outside diameter and a certain wall thickness using a diameter regulating mill (e.g., a stretch-reducer).

In the process of perforation by rolling using the perforator, a punch is used as a drilling tool. This punch is mounted to the front end of a mandrel in order to drill a billet heated to high temperature, at approximately 1200 ° C; in this way, the punch is exposed to a hostile environment with a very high surface temperature and high temperature. In general, the punch consists of a base metal made of steel for hot work, and an oxide scale forming a film on the surface of the base metal by a hot process carried out in advance in order to protect said base metal, after which is used the punch in the process of perforation by lamination. During this process, the scale or film on the surface of the punch blocks the transfer of heat from the billet to the base metal of the punch, and thereby prevents seizing between the billet and the punch.

The repetitive perforation carried out by the The punch in whose surface the husk is formed causes the gradual abrasion of said scale. The abrasion of the scale deteriorates the thermal insulation effect of the film and as a result increases the temperature of the punch during drilling, so that metal losses due to casting and deformation by the heat of the metal are likely to occur. punch base metal. If the scale is worn and the base metal of the punch makes direct contact with the billet, seizure occurs and this generates defects in the inner surface of the pipe or spout. Consequently, the punch is rendered useless the moment the film is worn, thus ending the useful life of the punch.

In particular, in the production of seamless tubes / pipes made of high alloy steel, such as steel with high Cr content, of around 9% or more, alloy based on Ni and stainless steel, there is a manifest abrasion of the scale of the punch surface during drilling, so that the life of the punch is significantly reduced. For example, when stainless steel is drilled, the scale that is on the surface of the punch is worn in two or three passes (ie, the number of times of continuous drilling), and the service life of this punch ends. This requires a frequent replacement of the punch, which deteriorates the efficiency of the production considerably. In the production of seamless pipes / pipes of high alloy steel, it is necessary to improve the service life of the punch during the process of drilling by rolling, which improves the efficiency of the production of pipes and pipes steel.

To satisfy this requirement, as an example of the film that forms on the surface of the base metal of a punch, Patent Literature 1 describes a punch with an oxide-containing film and Fe formed on the base metal surface of a punch. by means of the arc spraying of iron wires, instead of using the scale made by thermal treatment. Since the punch that has the film formed on its surface, and said film made by arc-spraying contains oxide and Fe, it is excellent in thermal insulation and to prevent seizing, it being possible to achieve an improvement in the duration of life useful of the punch.

However, even in the punch with the film produced by arc-spraying which is described in this Patent Literature, wrinkles are generated in said film as a result of the repetitive heat supply when the punch is subjected to repeated perforations by rolling, which produces the end of the useful life of said punch. A longer time in the perforation by rolling increases the load of the punch, which produces the detachment of the film or wrinkles of said film, which in turn produces the termination of the duration of its useful life. Such a situation often occurs when using a larger long billet to be drilled, or a billet with greater resistance to high temperatures. To reduce the occurrence of wrinkles in the film produced by arc spraying, it is effective to increase the thickness of the film in order to improve the thermal insulation performance of the film. However, increasing the thickness of the film deteriorates the adhesiveness between the base metal of the punch and the film, which in turn causes the film to detach early. Therefore, there is still room to improve a stable improvement of the durability of the punch life and therefore it is strongly desired to produce a punch for perforation by rolling which can improve said points.

QUOTES PATENT LITERATURE Patent Literature 1: Japanese Patent No. 4279350 COMPENDIUM OF THE INVENTION TECHNICAL PROBLEM An object of the present invention, which has been realized to solve the problems of the prior art, is to provide a method for producing a punch for perforation by rolling with a film formed on a surface of the base metal of the punch by performing sprayed by arc of a spray wire containing iron; the method that has the following characteristic: guarantee stable improvement of the useful life of the punch.

SOLUTION TO THE PROBLEM The following is the compendium of the present invention: The present invention provides a method for producing a punch to be used in a drill mill by rolling for the production of seamless steel pipes and tubes, and The method for producing the punch for perforation by rolling comprises the steps of: peening a punch surface; and spraying a spray wire to form a film on a surface of a base metal of the punch that is shot peened.

In the arc-spraying step, arc-spraying is performed using, as a spray wire, a wire with hard core whose tube-sheath is loaded with at least specific particles that contribute to the improvement of the useful life of the punch between the iron particles and the specific particles, so as to form a film containing iron oxide, Fe and the specific particles.

In this production method, the specific particles are preferably particles of low thermal conduction with a thermal conductivity lower than that of the iron oxide. In this case, the low thermal conductivity particles are preferably Zr02 particles, and the proportion of the Zr02 particles in the hard core wire is preferably 2.5 to 30.0 volume%.

In this production method, the specific particles are preferably solid lubricant particles. In this case the solid lubricant particles are preferably BN particles, and the proportion of BN particles in the hard core wire is preferably 5.0 to 20.0% by volume.

ADVANTAGEAL EFFECTS OF THE INVENTION The method for producing a punch for perforation by lamination according to the present invention achieves the following important effect: ensures stable improvement of punch life.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional drawing illustrating a spray wire for use in arc spraying in the method for producing a punch for rolling perforation according to the first embodiment of the present invention.

FIG. 2 is a cross-sectional drawing showing a spray wire for use in arc spraying in the method for producing a punch for rolling perforation according to the second embodiment of the present invention.

FIG. 3 shows a relationship between the proportion of ZrC particles > 2 on the hard core wire and the deformation of the base metal of the punch, as a result of the test illustrated in Example 1.

FIG. 4 shows a relationship between the proportion of BN particles in the hard core wire and a life expectancy of a punch as a result of the test illustrated in Example 2.

DESCRIPTION OF THE REALIZATION MODE In order to achieve the aforementioned objects, these inventors conducted several tests and intensive studies on the method for forming a film on a surface of a base metal of a punch by spraying an arc of a spray wire especially with iron content, These inventors obtained the following results.

The spray arc generates arcs between the front ends of two lines of wire spray serving as electrodes to melt the wires spray while a jet of compressed air or a stream of nitrogen gas between the above extremes is provided of the spray wires so that the molten material is ejected and thus the molten material is sprayed onto the object in which it is desired to form a film, for example. In the arc spray described in Patent Literature 1, an iron wire is used as a spray wire, and thus the film formed on the base metal surface of the punch contains Fe and Fe oxide. The content in the film is generated by casting the iron wire during the arc spray, and the molten iron is oxidized in the air before the molten iron reaches the surface of the base metal of the punch. The Fe contained in the film is obtained from the cast iron that has reached the surface of the base metal of the punch without oxidizing in the air. 1. Simultaneously, the film containing Fe (iron oxide) oxide, Fe and material of low thermal conductivity can be formed on the surface of the base metal of the punch by performing the arc spraying of a hard core wire like spray wire; and the hard core wire comprises a tube with an outer sheath of iron which is the same as that of the iron wire, and is charged with particles of low thermal conductivity which have lower thermal conductivity than iron oxide, and also with particles of iron. iron in some cases. The oxide of Fe contained in this film is generated in such a way that the tube that forms an iron sheath included in the hard core wire as well as the iron particles are melted during the arc spraying and the molten iron is oxidized in the air before reaching the surface of the base metal of the punch. The Fe contained in the film is generated in such a way that the molten iron reaches the surface of the base metal of the punch without oxidizing in the air. The material of low thermal conductivity in the film is generated in such a way that the particles of low thermal conductivity found in the hard core wire reach the surface of the base metal of the punch.

In this way, the film formed by the arc-spraying using a hard core wire consists of material of low thermal conductivity with thermal conductivity lower than that of Fe Oxide, which is due to the low thermal conductivity particles included. in the hard core wire; in this way the performance of the thermal insulation improves without increasing the thickness of the film. Therefore, the punch with the film formed by arc-spraying has an excellent performance of the thermal insulation of said film during the perforation by repetitive lamination, which stably improves the useful life of the punch. Specifically, the particles of low thermal conductivity are specific particles that contribute to improving the useful life of the punch. 2. The film containing the Fe (iron oxide) oxide, the Fe and the solid lubricant can be formed on the surface of the base metal of the punch using the hard core wire consisting of a tube forming an outer iron sheath which is equal to that of the iron wire and that is loaded with particles of solid lubricant, and also with iron particles in the tube that forms an iron sheath in some cases and the arc sprinkling is performed using said hard core wire. The oxide of Fe contained in this film is generated in such a way that the tube that forms an iron sheath and the iron particles found in the hard core wire melt during the arc spray, and the molten iron oxidizes in the air before reaching the punch base metal surface. The Fe contained in the film is generated in such a way that the molten iron reaches the surface of the base metal of the punch without oxidizing in the air. The solid lubricant in the film is generated in such a way that the particles of the solid lubricant found in the hard core wire reach the surface of the base metal of the punch.

As described above, the film formed by arc spraying using a hard core wire with solid lubricant content was obtained as a result of the solid lubricant particles present in the hard core wire; therefore, it improves lubricity during drilling by rolling. Therefore, the punch having said film produced by arc-spraying has excellent lubricity of the film during perforation by repetitive lamination, which in turn improves stably the useful life of the punch. Specifically, the solid lubricant particles are specific particles that contribute to the improvement of the useful life of the punch.

The present invention has been made based on the checks described in points (1) and (2) above. Hereinafter, a description will be given of the embodiment of the method for producing the punch according to the present invention. < First embodiment > In the method for producing the punch according to the first embodiment of the present invention, before the arc-spraying, peening is performed on the surface of the punch. If the punch is used for its reproduction after its useful life has ended due to the perforation by repetitive lamination, the film is removed in its condition of having made the perforation by rolling as it is on the surface of the punch by blasting in order to expose the surface of the base metal of the punch, and to leave the surface of the base metal of the punch duly rough. If a new punch is being produced, the surface of the base metal of the punch is left moderately rough by blasting. The reason for the shot blasting treatment is that the base metal of the punch can acquire a moderately rough surface free of traces of film to improve the adhesiveness between the base metal of the punch and the film at the time of the arc spraying.

In the method for producing the punch according to the first embodiment, following the previous step, the hard core wire mainly containing iron, used as a spray wire, is sprayed by arc on the surface of the base metal of the punch to which HE applied the shot blasting, and therefore a film is formed.

FIG. 1 is a cross-sectional view showing a spray wire for use in arc spraying in the method for producing a punch for perforation by lamination according to the first embodiment of the present invention. As illustrated in this drawing, in the first embodiment, a hard core wire 1 is used as a spray wire. Said hard core wire 1 has a tube that forms an outer sleeve 2 of iron.

The tube that forms an iron sheath 2 is loaded with particles of low thermal conductivity 3. The particles of low thermal conductivity 3 are characterized by having lower thermal conductivity than iron oxide, and are consumed with difficulty and disappear during the sprayed by arch. Examples of the low thermal conductivity particles 3 may include metal particles and ceramic particles. In particular, zirconia particles (Zr02) having a very low thermal conductivity are preferred. The particles of low thermal conductivity 3 are not simply limited to being in the form of a particle and may include powders or chopped fibers. In this case, iron oxide contains iron (II) oxide (FeO), iron (III) oxide (Fe2Ü3), and iron oxide (II, III) (Fe304).

The tube that forms an iron sheath 2 can also be charged with iron particles 4 in addition to the particles of low thermal conductivity 3. The iron particles 4 are not limited simply to a particle shape and can include powders or chopped fibers.

Arc spray using the hard core wire (spray wire) 1 having the configuration described above allows the film containing Fe (iron oxide) oxide, Fe and the material of low thermal conductivity to form on the surface of the base metal of the punch. Since the punch that has the film produced by arc spraying in this way contains in its film material of low thermal conductivity whose thermal conductivity is lower than that of the Fe oxide, the performance of the thermal insulation during the perforation by repetitive lamination improves without increasing the thickness of the film, and therefore stably improving the service life of the punch.

In the case of applying the particles of Zr02 as particles of low thermal conductivity 3, the proportion of the particles of Zr02 in the whole of the hard core wire 1 including the tube that forms an iron sheath 2, the particles of low thermal conductivity 3, and the iron particles 4 is preferably from 2.5 to 30.0% by volume. As was found in Example 1 that described below, if the proportion of the particles of Zr02 is less than 2.5% volume, the performance of the thermal insulation during the perforation by rolling can not be improved enough because an insufficient amount of Zr02 contained in the punch film, so that the deformation of the base metal of the punch will be significant, which makes it unsuitable for being used again and prevents the stable improvement of the useful life of the punch. On the contrary, if the proportion of Zr02 particles is greater than 30.0% volume, the adhesiveness between the base metal of the punch and the film deteriorates, the film detachment occurs early due to an excessive amount of Zr02 contained. in the punch film, and the base metal of the punch melts, which does not allow it to be used again. This ratio is more preferably from 5.0 to 30.0% by volume. < Second embodiment > In the method of producing the punch according to the second embodiment of the present invention, before performing the arc spraying, shot peening is applied to the surface of the punch, in a manner similar to the first embodiment. Then, the surface of the base metal of the punch to which the blasting was applied is subjected to the arc spray using the core wire hard that contains mainly iron as spraying wires, in order to form the film on said surface. The hard core wire used in the second embodiment is different from the hard core wire of the first embodiment in the following characteristics.

FIG. 2 is a cross-sectional view illustrating a spray wire for use in arc spraying in the method for producing a punch for rolling perforation according to the second embodiment of the present invention. As illustrated in this drawing, in the second embodiment, a hard core wire 1 is attached as a spray wire. This hard core wire 1 includes an outer shell formed by a tube in the form of an iron sheath 2.

The tube forming an iron sheath 2 is loaded with particles of solid lubricant 5. The particles of solid lubricant 5 have a function as a solid lubricant during perforation by rolling, and burn with difficulty and disappear during arc-spraying. Examples of solid lubricant particles 5 may include metal particles and ceramic particles. In particular, boron nitride (BN) particles, which are extremely excellent in solid lubricity, are preferred. The particles of lubricant solid \ 5 are not limited to the particle form but can include powders and short fibers.

The tube that forms an iron sheath 2 can be loaded with 4 iron particles in addition to the particles of solid lubricant 5. The iron particles 4 are not limited simply to the particle form but may include powders and chopped fibers.

Through arc-spraying using the hard-core wire (the spray wire) 1 with the configuration described above, the film with Fe (iron oxide), Fe content can be formed on the surface of the base metal of the punch. , and solid lubricant. The punch with the film produced by arc spraying in this manner includes the solid lubricant in said film, so that the lubricity during perforation by repetitive lamination improves and also improves the useful life of the punch.

In the case of applying the BN particles as particles of solid lubricant 5, the proportion of the BN particles throughout the hard core wire 1, including the iron sheath tube 2, the solid lubricant particles 5, and the iron particles 4 is preferably from 5.0 to 20.0% by volume.

As checked in Example 2, which is described below, if the proportion of BN particles is less than 5.0% by volume, lubricity during lamination drilling will not be sufficiently better due to an insufficient amount of BN in the punch film, which will impede a satisfactory improvement in drilling efficiency and punch life it will not be able to improve steadily. On the contrary, if the proportion of the BN particles is higher than 20.0% by volume, the adhesiveness between the base metal of the punch and the film deteriorates and the release of the film occurs early, due to an excessive amount of BN in the film. the punch film, and the base metal of the punch is fused, which makes it unsuitable for reuse and impairs the stable improvement of punch life. This ratio is preferably from 7.5 to 20.0% by volume.

The efficiency of drilling in the present means the following: the speed at which the billet is transferred in an axial direction during drilling by rolling (hereinafter referred to as "feed rate") is defined by the number of rotations of the roll and the actual feed rate is delayed relative to the theoretical feed rate calculated based on the number of rotations of the drill string assembly, due to the influence of friction resistance and the like between the punch and the billet that are in contact with each other. Generally, the speed coefficient (= (actual feed speed) / (theoretical feed rate) x 100 [%]) is called "drilling efficiency". Drilling efficiency is an index of lubricity. Greater lubricity not only improves the production efficiency of the drill mill by rolling but also reduces the time the punch is in contact with the billet, and therefore prolongs the useful life of the punch.

In the method for producing the punch according to the present invention, arc spraying can be performed while the spraying equipment is gradually moved away from the base metal surface of the punch, in order to increase the spraying distance gradually during forming of the film by means of the arc spray. Thus, said film is formed in the base metal of the punch which gradually increases in its ratio of the region containing Fe oxide (hereinafter called "oxide coefficient") to the surface. The film with said oxide coefficient which is lower in a part adjacent to the base metal of the punch, and larger in its surface is useful to ensure performance in the thermal insulation and in the prevention of seizure on the surface of the film, as well as also ensure the adhesiveness between film and the adjacent part of the base metal of the punch. [E emplos] For the purpose of checking the effects of the present invention, a perforation test was carried out by rolling so that punches were produced for perforation by rolling and each of them was mounted on a perforator to perform the perforation by rolling. The condition of the test was as follows. < Example 1 > [Test Method] (1) Production of the punch A number of bullet-shaped punches were prepared, each with a maximum diameter of 147 mm using a hot production tool specified in the JIS standard as the base metal. Punches were produced with films produced by arc spraying so that after the peening applied to the surface of each punch, arc spraying was performed using wires of hard cores, as illustrated in FIG. 1, in order to form a film on the surface of the base metal of each punch. In the formation of the arc-spray film, the arc-spraying was performed by setting the spray distance from the spray gun to the surface of the base metal of the punch initially at 200 mm, and the Arc spray was performed while the rolling gun gradually moved away from the base metal surface of the punch to a final distance of 1000 mm.

At that time, Zr02 particles were used as low thermal conductivity particles in the hard core wire, and in the hard core wires used the proportion of Zr02 particles was loaded as illustrated in Table 1 below. The iron sheath of each hard core wire was loaded with iron particles, as well as the Zr02 particles, according to the proportion of Zr02 particles.

Table 1 (Note) The symbol "-" means the detachment of the film and the loss of metal by casting in the base metal of the punch. (2) Drilling by rolling The following hollow blocks were produced by repetitive perforation by rolling, heating the pieces (materials) to about 1200 ° C.

- Measurement of the piece: billet of diameter of 191 mm and length of 2200 mm - Material of work: Cr 13% Steel - Hollow tube: 196 mm outside diameter, 16.82 mm wall thickness, 6520 mm long [Evaluation] The perforation was carried out by rolling successively for 10 times with each punch, and then an inspection was made of the appearance of each punch in order to examine the condition of the surface, that is, to verify if there had been loss by smelting of the metal. punch base due to the detachment of the film. Likewise, shot blasting was carried out on the punch surface in order to remove remains of the punch film and then the height of the base metal of the punch (the length in axial direction) was measured in order to evaluate the deformation after use. of the punch, that is, the difference in height of the base metal of the punch before and after the use of the punch. In this case, the deformation of the base metal of the punch was adjusted by 2.0 mm or less in a real operation. If the deformation of the base metal of the punch reaches more than 2.0 mm, this punch is no longer suitable for being used again. Therefore, for the test, the case in which the deformation of the base metal of the punch was 2.0 mm or less was taken as "preferable", without the loss of base metal having occurred.

[Test Result] The result of the test is illustrated in Table 1 and FIG. 3. FIG. 3 shows a relationship between the proportion of ZrO2 particles in the hard core wire and the deformation of the base metal of the punch, as a result of the test of Example 1. Said result suggests the following conclusions.

Zr02 particles were used as particles of low thermal conductivity in the hard core wire, and the film produced by arc spraying was formed using said hard core wires. In this case, as illustrated in Exhibits Nos. 2 a. 6, the proportion of the Zr02 particles in the hard core wire was set at 2.5% by volume or higher, so that the deformation of the base metal of the punch was reduced to 2.0 mm or less. The reason for this is the appropriate amount of particles of Zr02 found in the punch film, which improves the performance of thermal insulation. Therefore, it was verified that the punch with the film produced by arc spraying using the hard core wire with a Zr02 particle content of 2.5% by volume or more, stably improves the useful life of the punch, and can return to use.

As illustrated in Tests Nos. 7 and 8, in the punch with the film produced by arc-spraying formed using the hard core wire with Zr02 particles content in greater than 30.0% by volume, the punch film was separated at an early stage and the base metal of the punch was melted. The reason for them is that the punch film contained an excessive amount of Zr02 / and the adhesiveness between the base metal of the punch and the film deteriorated, although it improved the performance of the thermal insulation. Therefore, it was verified that the punch with the film produced by arc spraying using hard core wires with Zr02 particle content in more than 30.0% by volume can not stably improve the useful life of the punch.

On the other hand, as illustrated in Test No. 1, on the punch with the film produced by arc-spraying using hard core wires with Zr02 particle content of 0% by volume (equivalent to the case of the formation of the film by arc-spraying using iron wires according to Patent Literature 1), the deformation of the base metal of the punch was greater than 2.0 mm.

The reason for this is that since the punch film did not contain Zr02 with low thermal conductivity and therefore the performance of the thermal insulation did not improve. Accordingly, it was found that the punch with the film produced by arc spraying using hard core wires with Zr02 particle content in proportion better than 2.5% by volume can not stably improve the useful life of the punch. < Example 2 > [Test Method] (1) Production of the punch A number of bullet-shaped punches were prepared, each with a maximum diameter of 147 mm using a hot production tool specified in the JIS standard as the base metal. Punches were produced with films produced by arc spraying so that after the peening applied to the surface of each punch, arc spraying was performed using wires of hard cores, as illustrated in FIG. 2, so as to form a film on the surface of the base metal of each punch. In the formation of the film sprayed by arc, the arc spray was made by setting the spray distance from the spray gun to the base metal surface of the punch initially at 200 mm, and the arc spray was performed while the gun was gradually moving away from the metal surface punch base up to a final distance of 1000 mm.

At this time, BN particles were used as solid lubricant particles in the hard core wires, and said wires were used in which the proportion of BN particles was loaded according to the values illustrated in Table 2, below. The iron sheath of each hard core wire was loaded with iron particles, as well as BN particles according to the proportion of BN particles.

Table 2 Note) The symbol "-" shows the detachment of the film and the loss occurred due to casting of the base metal of the punch. (2) Drilling by rolling The following hollow blocks were produced by repetitive perforation by rolling, heating the pieces (materials) to about 1200 ° C.

• Measurement of the piece: billet of diameter of 191 mm and length of 2200 mm • Working material: Cr 13% steel • Hollow tube: 196 mm outside diameter, 16.82 mm wall thickness, 6520 mm long [Evaluation] The drilling efficiency was evaluated during the drilling by rolling with respect to each punch. The Drilling efficiency in a real operation is set as a target at 70% or higher, and said efficiency is rated as "preferable". Likewise, an inspection was made after completing each perforation to verify the appearance of each punch. The number of perforations made by each punch was controlled until it became unusable due to the release of the film, or otherwise, when the punch exhibited loss of metal due to smelting or deformation at the front end of the punch; in other words, the number of billets that passed successfully through drilling by rolling (the number of times of drilling by continuous rolling) was counted. Said number of times of perforation by continuous rolling was taken as the useful life of the punch. As described in Patent Literature 1, the useful life of the punch was evaluated with respect to each of the punches based on the useful life coefficient (hereinafter referred to as the "useful life coefficient"), in which the useful life of the punch equivalent to a punch with film produced by arc-spraying using the iron wire, that is, the punch with the film produced by arc-spraying using the hard core wire free of BN particles (0% by volume) as illustrated in Exhibit No. 11 of Table 2 above defined with reference "1.00".

[Test Result] The result of the test is shown in Table 2 and FIG. 4. FIG. 4 shows a relationship between the proportion of BN particles in the hard core wire and a punch life coefficient, as a result of the test in Example 2. The result of this test suggests the following.

The BN particles were used as solid lubricant particles in the hard core wire, and the produced film was formed by arc spraying using hard core wires. In this case, as illustrated in Tests Nos. 13 to 17, it was found that the proportion of BN particles in the hard core wire was set at 5.0% by volume or higher, so that the drilling efficiency was assured. at 70% or higher and the life expectancy of the punch improved. The reason for this is that the punch film contained an appropriate amount of BN, which improved the lubricity. Therefore, it was found that the punch with the film produced by arc-spraying using the hard-core wire with a content of BN particles of 5.0% by volume or higher stably improves the useful life of the punch.

As illustrated in Tests Nos. 18 to 20, in the punch with the film produced by arc-spraying using hard core wires containing BN particles or more than 20.0% by volume, the punch film peeled off early and the base metal of the punch melted. This was due to an excessive amount of BN in the punch film, so the adhesiveness between the base metal of the punch and the film deteriorated, although the lubricity improved. It was therefore found that in the punch with the film produced by arc spraying using hard core wires with BN particle content of more than 20.0% by volume, the useful life of the punch can not be stably improved.

On the other hand, as illustrated in Tests Nos. 11 and 12, in the punch with the film produced by arc-spraying using hard core wires with BN particle content of less than 5.0% by volume (including 0% by weight). volume), the drilling efficiency was less than 70%, and a small improvement in the useful life of the punch was observed. This was because there was no BN functioning as a solid lubricant or there was an insufficient amount of BN in the punch film, and therefore the lubricity was not improved enough. Therefore, it was found that the punch with the film produced by arc-spraying using hard core wires with a BN particle content of less than 5.0% by volume can not improve either. stably the service life of the punch; INDUSTRIAL APPLICABILITY The present invention can be used effectively in the production of seamless steel tubes and pipes of high alloy steel.

REFERENCE SIGNS 1: Hard core wire (wire produced by spraying), 2: Iron sheath, 3: low thermal conductivity particles, 4: Iron particles, 5: Solid lubricant particles

Claims

i CLAIMS

1. A method for producing a punch to be used in a mill for punching by rolling for the manufacture of seamless steel tubes and trunks, characterized in that the method for producing the punch for punching by rolling comprises the steps of: blasting a surface of the punch; and arc-spraying a spray wire to form a film on a surface of a metal base of the punch that has been shot peened, wherein in the arc-spray step, the arc spray is performed using as the spray wire a hard core wire whose iron sheath is loaded with at least specific particles that contribute to improving the useful life of the punch between iron particles and the specific particles, in order to form a film with iron oxide content , Fe and the specific particles.

2. The method for producing a punch for perforation by lamination according to claim 1, characterized in that the specific particles are particles of low thermal conductivity with thermal conductivity lower than that of iron oxide.

3. The method for producing a punch for perforation by rolling according to the claim 2, characterized in that the particles of low thermal conductivity are particles of Zr02-

4. The method for producing a punch for perforation by rolling according to claim 3, characterized in that the proportion of the particles of Zr02 in the hard core wire it is from 2.5 to 30.0% by volume.

5. The method for producing a punch for punching by lamination according to claim 1, characterized in that the specific particles are particles of solid lubricant.

6. The method for producing a punch for perforation by lamination according to claim 5, characterized in that the solid lubricant particles are BN particles.

7. The method for producing a punch for perforation by lamination according to claim 6, characterized in that the proportion of BN particles in the hard core wire is 5.0 to 20.0% by volume.