JP2007092180A - Method for restraining buildup on roller for carrying high temperature material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for restraining the buildup on a roller for carrying a high temperature material, excellent in an effective buildup resistance, even in the case of use under high temperature atmosphere, such as in the heat treatment furnace. <P>SOLUTION: When the high temperature material is carried with the rollers for carrying the high temperature material constituted of the uppermost surface with metal-carbide composite film, composed of 20-70 vol% carbide and the balance metal on the basic material surface disposed in the heat treatment furnace; the buildup formed on a scale is restrained by detaching metallic oxide existent in the scale generated on the metal-carbide combined film to detach the scale. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for suppressing buildup of a conveying roller suitable for conveying a high-temperature material, particularly a metal material.

  In the hot working of metal materials such as the production of seamless steel pipes in the hot state, a roller conveyor or the like is used to transport processing materials and products (hereinafter collectively referred to as high temperature materials) heated to a high temperature in a heat treatment furnace. In many cases, it is conveyed using a roller. The same applies to a high temperature environment such as the inside of a heat treatment furnace.

  When a slip or the like occurs between the high temperature material and the conveyance roller during conveyance by the high temperature material roller, seizure occurs between the high temperature material and the conveyance roller. The oxide adheres locally to both surfaces. Due to these deposits (hereinafter simply referred to as build-up), there is a problem that indentation flaws are generated on the surface of the high-temperature material being conveyed, and the surface quality and yield of the product are lowered.

  In order to suppress such a defect, a method of making the material of the conveying roller excellent in seizure resistance such as Cr, Ni alloy steel has been conventionally performed. A sufficient effect is not obtained.

  Patent Document 1 discloses a hot conveying roller excellent in wear resistance and seizure resistance, in which no adhesion occurs between two surfaces of the hot material and the roller when conveying the hot material, which is one type of high temperature material. The manufacturing method of this is proposed. This is because the surface of the roller base material is weld-welded with a heat-resistant material containing 30-50% by volume of NbC in a 3Cr-1Ni-Fe-based alloy, and then heat-treated in an oxidizing atmosphere containing CO gas. , A strong oxide scale film is imparted to the surface.

Patent Document 2 discloses a two-layer structure comprising a metal-carbide composite film containing 20 to 70% niobium carbide particles by volume on the surface of a base material and an oxide film formed on the outermost surface of the film. A technique for preventing seizure of a hot tool characterized by having a film is disclosed.
Japanese Patent No. 2511596 JP-A-6-315704

  The technique proposed in Patent Document 1 intends to prevent seizure by performing build-up welding on the roller surface and further providing a strong oxide scale on the surface. However, the roller surface is constantly impacted by the material being conveyed. When the oxide scale on the roller surface falls off due to repeated impacts or the like, seizure occurs at that portion. For this reason, there exists a problem that it may become difficult to perform good conveyance without build-up for a long time. In addition, the above-described conventional invention does not include a description regarding the build-up resistance of a roller used in a high-temperature atmosphere that normally reaches 800 to 1100 ° C., and in some cases, around 1200 ° C. as in a heat treatment furnace.

  The technique described in Patent Document 2 relates to a hot rolling tool used under a high surface pressure, which is different from a conveying roller. In the initial stage of use of the tool, after the oxide film is peeled off by rolling, the seizure is prevented by the carbide of the build-up base material. Patent Document 2 is only intended not to burn.

  The object of the present invention is to improve the build-up resistance of a roller for conveying a high-temperature material and to prevent build-up of a high-temperature material conveyance roller that can prevent indentation of the high-temperature material to be conveyed. Is to provide.

  Furthermore, a specific problem of the present invention is to improve build-up resistance even when used in a high-temperature atmosphere such as in a heat treatment furnace and to prevent build-up of a high-temperature material conveying roller effective in preventing indentation flaws. Is to provide.

  As a result of various researches on build-up prevention methods that are effective even when transported by rollers in a high-temperature atmosphere that sometimes reaches about 1200 ° C., such as in a heat treatment furnace, the present inventors have obtained the following knowledge.

  a. Conventional buildup prevention methods have focused on preventing seizure and adhesion between the high temperature material and the conveying roller. For this reason, it has been aimed at utilizing and improving the hot lubrication action by the oxide scale on the surface of the conveying roller, but this prevention method has a limit in suppressing the occurrence of indentation flaws due to build-up. In other words, in the past, emphasis has been placed on, for example, strengthening the oxide scale that has a hot lubrication effect and making it difficult to peel off. However, the oxide scale becomes thinner or peels off due to impact after a long period of use. The build-up could not be suppressed.

  b. Therefore, in order to change the idea and effectively suppress the occurrence of indentation flaws on the surface of the high-temperature material being conveyed, the inventors focused on reducing the adhesion of the scale on the roller surface and improving the peelability. Even if the scale of the high-temperature material is welded to the roller, such a scale is now easily peeled off from the roller surface together with the roller scale, thereby preventing build-up and pushing the high-temperature material to be conveyed. It is possible to effectively suppress the occurrence of surface flaws.

  c. Here, in order to improve the peelability of the scale on the roller surface, a metal-carbide composite film (hereinafter simply referred to as a low-oxidation-resistant carbide that reduces scale adhesion) is dispersed on the base material surface of the transport roller. It has been found that it is effective to provide a "composite film".

  As the carbide constituting the composite film, a carbide having low oxidation resistance, particularly niobium carbide, tungsten carbide, titanium carbide, vanadium carbide, chromium carbide and the like are suitable.

  d. These carbides dispersed in the form of particles on the surface of the composite film on the roller surface layer are easily peeled off from the surface. Therefore, even if the scale of the high-temperature material is welded to the surface of the composite film, such a welded material is easily peeled off from the roller surface due to the peeling action of the carbide from the surface of the composite film. In addition, the presence of a large number of carbide particles on the roller surface reduces the area of the matrix metal where the scale is easily welded.

  For these reasons, in a roller provided with a composite coating containing an appropriate amount of the above-mentioned carbide, the scale does not weld firmly as in the prior art, and a high-temperature material conveying roller based on a different idea from the prior art can be realized. .

  e. Although various alloy steels can be used as the matrix metal, the use of a metal having low reactivity with the scale is more effective for improving the build-up resistance. For example, an oxide scale generated in a Ni-based alloy such as Hastelloy has a low reactivity with an Fe-based scale. Therefore, if a Ni-based alloy is used as the matrix metal, the scale adhesion on the roller surface can be made weaker.

  By providing a composite film having such properties on the surface of the base material of the transport roller, even if a scale of a high-temperature material such as a seamless steel pipe material is welded to the surface of the transport roller and build-up occurs, Since it peels off before it grows, the build-up does not grow greatly. Thereby, a high temperature material can be conveyed over a long period of time without generating surface flaws.

Below, the experiment content that the present inventors have obtained these findings will be described.
FIG. 1 is a schematic cross-sectional view showing the configuration of a rotary friction pressure bonding tester that simulates the occurrence of build-up on a transfer roller when a high temperature material is transferred by a roller conveyor or the like in a heat treatment furnace. In FIG. 1, reference numerals 1 and 1b are cylindrical or prismatic test materials, reference numerals 2 and 2b are composite coatings on the end face of the test material 1, reference numeral 3 is a carbon steel round bar, reference numeral 4 is a heating chamber, reference numeral 5 is A coil for high-frequency heating, reference numeral 6 is an atmospheric gas supply port, reference numeral 7 is an atmospheric gas discharge port, and reference numeral 8 is a microscope. The test material 1 simulates a conveying roller, and the round bar 3 simulates a high-temperature material that is a material to be conveyed.

  As shown in FIG. 1, the test material 1 is arranged at a position A in the heating chamber 4. Initially, the round bar 3 is in a standby position above the test material 1 as shown in FIG. The round bar 3 is movable above and below the test material 1 and is held so as to be able to rotate about its axis as a rotation axis.

First, the high frequency heating coil 5 is energized to heat the test material 1 and the round bar 3 to the test temperature. Next, a constant load P is applied while rotating the round bar 3, its end face is pressed against the surface of the composite coating 2 of the test material 1, and after rotating for a certain time, the round bar 3 is moved to the upper standby position. . This is one pressing operation. After such pressure welding operation is performed 300 times, the test material 1 is moved to the microscope observation position (indicated by symbol B in FIG. 1), and the surface of the composite coating 2b is observed with the microscope 8 to generate buildup and wear. Investigate the situation. The atmosphere in the heating chamber 4 supplies a gas having the same composition as the heat treatment furnace of the actual production line (composition: 6% CO ₂ -20% H ₂ S—N ₂ remainder).

The base material of the test material 1 was JIS-G5122 SCH22. The dimensions were 20 mm in diameter and 50 mm in length. In the composite film 2, as a matrix metal, Hastelloy C276 (mainly Mo: 16% by mass, Cr: 15% by mass, W: 4% by mass, balance is Ni), Stellite 21 (mainly Cr: 27% by mass, Mo: 5% by mass) %, Ni: 3% by mass, the balance being Co), JIS-G3214 SUS410 (mainly Cr: 13% by mass, the balance being Fe) and the like. NbC, Cr ₃ C ₂ or the like was used as the carbide.

  These powders, in which various components are mixed in various proportions, are fed into the plasma generated between the electrode and the base material to perform a so-called plasma powder overlaying method. The composite film was provided on the end face of the test material 1. The thickness of the composite film was 3 mm.

  In addition, as a conventional example, a test material made of SCH22 (mainly Cr: 25% by mass, Ni: 20% by mass, the balance being Fe), which is a heat-resistant cast steel material defined in JIS-G5122, is prepared, and its performance is also evaluated. did. This SCH22 test material did not have a composite film.

The material of the round bar (diameter: 20 mm, length: 50 mm) 3 was JIS-G4051 S20C (C: 0.20%) carbon steel.
The test temperature was 1050 ° C., the test load P applied to the round bar 3 was 0.98 kN (pressure welding stress was 3.1 MPa), the rotation speed was 5 rpm, and the pressure welding time in one pressure welding operation was 6 seconds.

  That is, hold at the test temperature for 1 h → rotational load load at the test load P (6 sec, 5 rpm) → no load (99 sec) → (the above rotary load load → no load is repeated 100 times) → replacement of the round bar 3, Each cycle was repeated for a total of 3 sets (load → no load total 300 times).

Table 1 shows the observation results of the end face of the test material after the rotary frictional pressure bonding test.
In the evaluation results of Table 1, the ◎ mark in the build-up column in the visual evaluation shows no build-up at all, particularly good, ○ indicates a fine build-up is fine, △ indicates a build-up, but passes less than before, x indicates It means that it is unsuccessful in the build-up more than before.

  In the wear column, ◎ indicates that wear is particularly good with minimum wear, ○ indicates that the wear is small and good, Δ indicates that the wear is acceptable, and X indicates that the wear is large and is not acceptable. A mark of 特 に means particularly good, a mark of ○ means good, a mark of Δ means pass, and a mark of x means fail.

  As shown in Table 1, in the conventional SCH22 having no composite film, build-up occurrence on the pressure contact test surface was remarkable. In the test material with the composite film, the occurrence of build-up was greatly improved. In particular, when a composite film having carbides of NbC and a matrix metal of Hastelloy was provided (A3), particularly excellent build-up resistance was exhibited.

  Next, the influence of the amount of carbide contained in the composite film was investigated. A test material having composite coatings of various compositions was prepared by plasma powder overlaying method, with the matrix metal being Hastelloy C276 and the carbide being NbC, with various contents of NbC being varied. The thickness of the composite film, the pressure contact test conditions, and the evaluation method of the test results were the same as in the above experiment.

  Table 2 shows the observation results of the end face of the test material after the rotary frictional pressure bonding test. The meanings of symbols in the evaluation result column in Table 2 are the same as those in Table 1.

  As shown in Table 2, when the composite film did not contain NbC (test number B1), build-up occurred remarkably, and the test was stopped when the number of rotational friction welding reached 200 times. Further, when the NbC content of the composite film was less than 20% by volume, the buildup prevention effect was insufficient. When the NbC content is 20% by volume or more, there is a build-up prevention effect, and when it is 30% by volume or more, the effect is remarkable. Further, when the content of NbC is excessively increased, wear becomes remarkable. Therefore, it is understood that an upper limit needs to be provided for the NbC content. A similar trend was observed for the effects of other carbides.

The present invention has been completed on the basis of these findings, and the gist thereof is a method for suppressing build-up of a high-temperature material conveying roller described in (1) to (4) below.
(1) A metal-carbide composite coating containing 20 to 70% by volume of carbides on the surface of a base material disposed in a heat treatment furnace, the balance being made of metal, is the metal-carbide composite coating. When high temperature material is conveyed by the high temperature material conveyance roller constituting the surface, the build-up formed on this scale is suppressed by peeling off the scale generated on the metal-carbide composite film. A method for suppressing buildup of a roller for conveying a high-temperature material, which is characterized.

(2) The method for suppressing build-up of the high-temperature material conveying roller according to (1), wherein the scale is peeled off when a metal oxide existing on the scale is peeled off.
(3) The above (1) or (1), wherein the carbide is made of one or more carbides selected from the group consisting of niobium carbide, tungsten carbide, titanium carbide, vanadium carbide and chromium carbide. The buildup suppression method of the high temperature material conveyance roller as described in 2).

  (4) For transporting a high-temperature material according to any one of (1) to (3) above, wherein the metal is any one of a Ni-based alloy, a Co-based alloy, and stainless steel. Roller build-up suppression method.

  According to the build-up suppressing method for a high-temperature material conveyance roller according to the present invention, build-up does not occur over a long period of time even when a high-temperature material is conveyed in a high-temperature environment such as in a furnace of a heat treatment furnace. No indentation occurs. Also, the durability of the roller is excellent. Therefore, in addition to improving the quality and yield of hot-worked products, it greatly contributes to reducing the manufacturing cost by extending the life of the conveying roller, and the effect is remarkable.

Hereinafter, embodiments of the present invention will be described in detail.
The roller for conveying a high-temperature material used in the present invention has a metal-carbide composite film containing 20 to 70% of carbide in a volume ratio in a matrix metal on the surface of the roller base steel.

  As the matrix metal, a metal having both high-temperature strength and toughness is desirable, and it is desirable to use an Fe-based alloy, Ni-based alloy, Co-based alloy or the like having such characteristics. When used in a high temperature environment that sometimes reaches as high as 1200 ° C. as in a furnace of a heat treatment furnace, those that are particularly excellent in wear resistance, oxidation resistance, and seizure resistance are desirable. In this sense, it is desirable to use a Ni-based alloy or a Co-based alloy when the usage environment is severe.

  For example, martensitic stainless steel or austenitic stainless steel is suitable for an Fe-based alloy. Hastelloy is preferred as the Ni-based alloy, and stellite as the Co-based alloy.

  The oxide scale generated from the Ni-based alloy has low reactivity with the scale generated from the Fe-based alloy. For this reason, by using a Ni-based alloy as the matrix metal, it is possible to obtain a high-temperature material conveying roller that is more difficult to be scale-welded and has excellent build-up resistance.

  As the carbide constituting the composite film, an oxide having low oxidation resistance is desirable. In this sense, the carbide is preferably composed of one or more particles in the group consisting of niobium carbide, tungsten carbide, titanium carbide, vanadium carbide and chromium carbide.

  The carbide content is set to 20% or more by volume ratio with respect to the composite film in order to improve the scale peelability on the surface of the conveying roller. Desirably, it is 30 volume% or more. On the other hand, if the carbide content exceeds 70% by volume, the build-up resistance improving effect is saturated, the ratio of the matrix metal is lowered, the carbide holding power is lowered, and the formation of the composite film becomes difficult. In order to avoid this, the carbide content in the composite film is 70% by volume or less.

  The size of the carbide is not particularly limited, but it is effective to uniformly disperse in the matrix. Therefore, it is desirable that the average diameter of the carbide particles is in the range of 70 μm to 150 μm.

The thickness of the composite film is not particularly limited, but preferably has a thickness of 0.5 mm or more in order to ensure sufficient surface strength in the range from room temperature to high temperature.
As the base material of the high-temperature material conveying roller used in the present invention, known steel that has been conventionally used as a conveying roller can be used. In particular, when used in a high-temperature furnace (in a high-temperature atmosphere), it is necessary that deformation due to repeated thermal stress and cracking due to the progress of cracks do not occur. These may be selected as appropriate.

  In general, stainless steel, carbon steel, alloy steel such as SKD, or the like may be used as the base material. Carbon steel, low alloy steel, etc. may be used as long as the load conditions applied to the conveying roller are not particularly severe.

  The composite film is formed by a method in which a mixed powder of metal and carbide is encapsulated between a base material and a capsule and hot isostatic pressing is performed (HIP method), and a laser is applied after the mixed powder is applied to the surface of the base material. A method of melting and solidifying partially by irradiation (laser cladding method), a method of feeding the mixed powder into a plasma generated between an electrode and a base material and depositing on the surface of the base material (plasma) A known method such as a powder overlaying method may be used. According to the plasma powder overlaying method, it is possible to form a film more easily and it is advantageous in terms of production cost.

  After forming the composite film on the surface of the base material, it can be used as a product as it is. Moreover, you may give stress relief annealing, the cutting process of an outer surface, etc. suitably. It is not necessary to perform heat treatment for imparting scale to the surface.

An actual machine application test was conducted under the following conditions.
Implementation method: The high temperature material conveying roller according to the present invention was applied to a part of the in-furnace extraction conveyor roller of the walking beam type heat treatment furnace (furnace temperature: 800 ° C. to 1100 ° C.), and the buildup occurrence state was investigated.

  Specification of roller used for test: A composite film having a thickness of 6 mm was provided on the surface of a base material roll (material: JIS-G5122 SCH22) by plasma powder overlaying. The composition of the composite film was as follows.

(i) Hastelloy C276 (50% by volume) + NbC (50% by volume)
For comparison, a roller made of heat-resistant steel SCH22 was also used as a conventional material.
These rollers were arranged as conveyor rollers, and after passing through 30,000 pipes, the surface of each roll was inspected to investigate the occurrence of build-up. As a result, build-up did not occur in the roller provided with the composite film described in the number (i) according to the present invention. A small buildup occurred in the SCH22 roller. Although the wear resistance is slightly lower than that of SCH22, it was found that it can be used by replacing every several years. From these facts, it was confirmed that if the high temperature transfer roller according to the present invention is used, it is possible to prevent indentation into the material over a long period of time, and it is possible to stably manufacture a product with good quality.

It is a cross-sectional schematic diagram which shows the structure of a rotary friction crimping tester.

Explanation of symbols

1 and 1b: Test materials 2 and 2b: Metal-carbide composite coating 3: Carbon steel round bar 4: Heating chamber 5: High-frequency heating coil 6: Atmospheric gas supply port 7: Atmospheric gas outlet 8: Microscope

Claims (4)

  A metal-carbide composite coating comprising 20-70% by volume of carbides on the surface of the base material disposed in the heat treatment furnace and having the balance made of metal, and the metal-carbide composite coating constitutes the outermost surface. When the high temperature material is conveyed by the high temperature material conveyance roller, the build-up formed on the scale is suppressed by peeling off the scale formed on the metal-carbide composite film. To suppress build-up of high-temperature material transport rollers.   2. The method for suppressing buildup of a high-temperature material conveying roller according to claim 1, wherein the scale is peeled off by peeling off a metal oxide present in the scale.   3. The high temperature according to claim 1, wherein the carbide is one or more of the group consisting of niobium carbide, tungsten carbide, titanium carbide, vanadium carbide, and chromium carbide. Material buildup roller buildup suppression method.   The build-up of a high-temperature material conveying roller according to any one of claims 1 to 3, wherein the metal is any one of a Ni-based alloy, a Co-based alloy, and stainless steel. Suppression method.

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