JP2019098371A - Die for continuous casting and method of manufacturing the same - Google Patents

Abstract

To prolong the service life of a die for continuous casting by coating an alloy known to be excellent in heat resistance, corrosion resistance, and abrasion resistance, with little change in its composition, and with good adhesion to a surface of a copper or copper alloy substrate.SOLUTION: A nickel-base alloy layer of 0.1-3 mm in thickness is formed by laser irradiation to melt and solidify heat resistant nickel-base alloy powders on a surface of a copper or copper alloy substrate while supplying the powders. By multilayering the nickel-base alloy, a die for continuous casting with a build-up coating layer having a thickness of 0.2-10 mm is prepared. The coating layer includes a first layer in which a part of copper or the copper alloy is dissolved in a build-up layer so that the content of copper is 10 wt.% or less, and a laser build-up multilayer formed on the first layer. In the laser build-up multilayer, an amount of the copper solid solution in the build-up layer is gradually reduced from the inside to the surface.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a continuous casting mold provided with a coating layer excellent in heat resistance and abrasion resistance on the surface, and a method of manufacturing the same.

  In general, copper and copper alloys are often used as a material for a continuous casting mold generally used in a steel making process from the viewpoint of thermal conductivity so that cooling in a forming process from molten steel can be effectively performed. However, copper and copper alloys are inferior in heat resistance and corrosion resistance to nickel-based alloys etc. and have low hardness and low abrasion resistance, so they form corrosion and heat-resistant layers or wear-resistant layers on copper or copper alloy substrate surfaces. It is known to extend the life of the mold.

  As a method of forming a corrosion-resistant, heat-resistant or wear-resistant coating layer on the surface of a copper or copper alloy substrate of a continuous casting mold, an electroplating method of Ni, Co, Cr and alloys thereof or a self-fluxing alloy Thermal spraying methods using are known and are in fact used in the steelmaking process.

  For example, in Patent Document 1, a plated layer made of an alloy containing Fe, Mn, or Co in Ni or Ni is formed on the surface of a copper or copper alloy substrate of a continuous casting mold, and in Patent Document 2, Ni, Fe is used. It has been proposed to form a Co-based alloy plating layer to be contained to improve the wear resistance.

  Further, in Patent Document 3, Cr, B, Si, C, Fe, Co, Mo, and Cu are contained on the surface of a copper or copper alloy substrate of a continuous casting mold, and furthermore, a fine powder of wear-resistant hard ceramics 5 It has been proposed to improve heat resistance and wear resistance by thermal spraying a nickel base self-fluxing alloy containing 50 wt%.

JP-A-54-46131 JP-A-8-191973 JP 2002-86248 A

  The coating layer by the conventional plating method, for example, it is difficult to coat an alloy containing many kinds of metals such as hastelloy developed by a metallurgical method as a heat resistant alloy with an optimum composition. On the other hand, in the thermal spraying method, it is necessary to activate the particle surface in order to form a dense alloy layer from the thermal spray powder by plasma heat, and a self-soluble alloy containing an activator such as B or Si must be used. Do not get. Further, in the thermal spraying method, there is also a problem in the adhesion with the copper or copper alloy substrate.

  The present invention is an alloy which is known to be excellent in heat resistance, corrosion resistance and wear resistance in order to achieve longer life of a continuous casting mold, with little change in the composition, and The object is to coat the surface of a copper or copper alloy substrate with good adhesion.

  According to the first aspect of the present invention, the surface of the copper or copper alloy substrate is irradiated with a laser while supplying a nickel-based heat-resistant alloy powder, and the powder is melted and solidified to form a nickel-based alloy layer having a thickness of 0.1 to 3 mm. , A continuous casting mold having a multilayer buildup covering layer with a thickness of 0.2 to 10 mm.

  According to the invention of claim 2, in the mold for continuous casting according to claim 1, a part of copper or copper alloy is dissolved in the buildup layer such that the content of copper is 10 wt% or less in the covering layer. A multi-layered laser build-up layer having a first layer and a multi-layered laser build-up layer formed on the first layer, wherein the solid solution amount of copper in the build-up layer decreases from the inside to the surface It is characterized by

  According to a third aspect of the invention, in the mold for continuous casting of the first or second aspect, the nickel-based heat-resistant alloy powder comprises Hastelloy C (53Ni19Mo17Cr), Inconel (80Ni13Cr), Monel (65Ni31Cu4 (Fe + Mn)), NiCoCrAlY (47. 9Ni23Co20Cr8.5Al0.6Y), NiCr (50Ni50Cr), and Waspaloy (58Ni19Cr14Co4.5Mo3Ti).

  The invention according to claim 4 is the method for manufacturing a continuous casting mold according to any one of claims 1 to 3, wherein copper is irradiated when the laser is irradiated while supplying the nickel base heat-resistant alloy powder to the substrate surface. Alternatively, laser cladding is performed while heating the copper alloy substrate to 100 to 400 ° C.

  The continuous casting mold according to the present invention is a nickel-based nickel base having a thickness of 0.1 to 3 mm formed by melting and solidifying a powder by irradiating a laser while supplying a nickel-based heat-resistant alloy powder to the surface of a copper or copper alloy substrate. Since the alloy layer is provided with a coating layer in which the thickness is 0.2 to 10 mm, the nickel-based alloy layer can exhibit the original characteristics of the alloy. Moreover, compared with the case where a surface protection film is formed by the thermal spraying method, there is an advantage that the surface protection film can be formed with good adhesion.

  According to the second aspect of the present invention, the first layer can be joined to the surface of the base with good adhesion as strongly as a part of copper or copper alloy of the base becomes solid solution in the nickel base alloy layer of the first layer. In addition, a multilayer laser build-up layer is formed on the first layer, and a multilayer laser build-up layer is formed in which the solid solution amount of copper in the build-up layer is gradually decreased from the inside to the surface. The nickel base alloy layer has an effect that it is hardly influenced by the copper or copper alloy of the substrate.

  According to the invention of claim 3, an alloy which is known to be excellent in heat resistance, corrosion resistance and wear resistance can be attached on the surface of a copper or copper alloy substrate with almost no change in its composition and good adhesion. Since it can be coated, superior heat resistance, corrosion resistance and wear resistance can be exhibited as compared to a continuous casting mold in which a surface protective film is formed by an alloy plating method or a thermal spraying method.

  According to the invention of claim 4, when irradiating the laser while supplying the nickel base heat-resistant alloy powder to the surface of the substrate, the laser cladding is performed while heating the high thermal conductivity copper or copper alloy substrate to 100 to 400 ° C. Therefore, it is possible to prevent the laser energy from being dissipated except for the purpose of melting the alloy powder.

FIG. 6 is an explanatory view showing a cross-sectional structure of the first embodiment of the present invention in contrast to the cross-sectional structures of comparative examples 1 and 2; It is a figure which shows the thickness of the buildup layer of Example 2 of this invention, and the relationship of Cu content in a film, and film hardness.

  In a continuous casting mold, while pouring molten steel into a mold, steel is continuously cast and formed by removing heat and solidifying molten steel on the surface of the mold whose back surface is cooled with cooling water. High heat resistance and corrosion resistance are required in the vicinity of the meniscus portion at the top of the mold. At the same time, it receives the strongest thermal stress due to the temperature difference with the cooling water, and a thermal crack is likely to occur. In the lower part of the mold where the molten steel is cooled and solidified, the mold is worn away by the wear of the vitreous ceramic powder contained in the mold powder and the weight increase of the steel itself after the molten steel solidifies and shrinks in volume. It can also lead to life from mold wear due to strong rubbing of the surface. Further, it is also necessary to take measures against chemical corrosion due to sulfur components in the molten steel and corrosion and wear of the lower part of the mold due to steam of the cooling water for cooling the steel after passing through the mold.

  Thus, there is a need for a mold that exhibits excellent resistance to thermal shock, abrasion and chemical corrosion due to thermal load, which is a life factor of continuous casting molds. For mold substrates, copper or copper alloy with excellent thermal conductivity and high cooling effect is used, but a substrate protective layer having heat resistance, corrosion resistance, wear resistance and strength is indispensable, and copper or copper alloy substrate surface It is thought that the problem can be solved by forming a known nickel base alloy layer such as Hastelloy or Inconel, which is developed by metallurgical methods and is excellent in corrosion resistance and wear resistance at high temperature, and the laser deposition method of this research Realized by

  In order for the built-up nickel-based alloy layer to exhibit the original characteristics of the alloy, it is necessary that there is no defect such as a void in the alloy layer and the density of the alloy has reached its original density. In order to obtain a void-free true density of the alloy layer, it is required that the alloy portion contributing to the buildup be completely melted once. Energy is supplied from the outside for complete melting of the alloy part, but it escapes by heat conduction from a copper or copper alloy substrate with good thermal conductivity, so the amount of energy supplied to obtain a good alloy layer It is important to be able to control all of the heat of fusion and the amount of thermal diffusion of the metal powder.

  In the present invention, in order to use laser energy efficiently for melting of the supplied alloy powder, the size and temperature of the molten pool which the alloy powder melts and forms are controlled, and the laser energy is controlled. That is, the surface of a copper or copper alloy substrate is irradiated with a laser while supplying a nickel-based heat-resistant alloy powder to form a molten pool of the powder, which is solidified to form a 0.1-3 mm thick nickel-based alloy. After coating the laser buildup layer, a multilayer buildup coating layer is formed to a thickness of 0.2 to 10 mm by the same laser buildup method. This makes it possible to produce a continuous casting mold having a coating layer having an alloy composition having excellent heat resistance, corrosion resistance, and wear resistance.

  The metal buildup method includes a method of using a welding rod and a method of melting an alloy sheet. However, these methods are compared to the method of using a powder, and escape from the welding rod or unmelted alloy sheet by heat conduction. Not only does it become difficult to control the amount of heat due to the large amount of thermal energy, it is also necessary to supply excessive energy from the outside. For this reason, it has a great influence on the copper or copper alloy substrate, and at the same time, causes a large thermal strain to occur.

  On the other hand, in the present invention, while supplying the alloy powder to be used together with the laser beam from the laser irradiation nozzle, the nozzle is scanned on the substrate surface and the laser is piled up, so the laser energy is to be supplied. It can only be used and is the most efficient.

  It is further important that the alloy build-up layer be in intimate contact with the copper or copper alloy substrate and have sufficient adhesion strength under severe thermal shock environments in which a continuous casting mold is used. In the present invention, it is possible to control the laser energy while mainly using the laser energy to melt the supplied alloy powder while at the same time managing the size and temperature of the molten pool formed by the melting of the powder.

  According to the present invention, by controlling the supply amount of the nickel-based heat-resistant alloy and the irradiation laser energy, the outermost surface of the surface is dissolved in the molten pool without excessively dissolving the copper or copper alloy substrate. As a result, it has become possible to form a strong buildup layer which has no defects at the interface and is excellent in adhesion to the base substrate. In addition, the amount of solid solution from the lower substrate can be suppressed to a low level, and the composition change by the solid solution component of the base of the alloy buildup layer can be as low as 10 wt% or less.

  The method of performing laser deposition while heating the copper or copper alloy substrate to 100 to 400 ° C. facilitates energy control and reduces energy dissipation due to heat conduction from the substrate during laser deposition. This is effective because the solid solution component to the base layer can be reduced, the adhesion is excellent, and the characteristics of the heat-resistant alloy can be exhibited. When the substrate heating temperature is higher than 400 ° C., the strength of the copper or copper alloy substrate of the mold is reduced, and the function as a continuous casting mold may be greatly reduced and it may become unusable. On the other hand, even at 100 ° C. or less, the effect of preventing energy dissipation is observed, but the ease of energy control did not improve so much.

  At present, the wavelength of a laser that can be used in the laser deposition method is 900 to 1200 nm, and a nickel-based alloy can efficiently absorb light and can make laser deposition relatively easy. On the other hand, with copper or copper alloys, laser light can not be used to heat a copper or copper substrate because it does not absorb light of this wavelength. Blue semiconductor lasers and harmonic lasers that can absorb copper or copper alloys have been developed, but at present, they can not release energy that can be used for mass production. In the near future where high power will be possible in the future, the need for substrate heating will diminish and it is expected that energy control will be easier.

  The melting point of copper, which is the main component of the mold base, is 300 ° C. or more lower than the melting point of the heat-resistant nickel-based alloy, and melts at a lower temperature than the nickel-based alloy. As a result, the heat resistance of the nickel base alloy in which copper is solid-solved is lost. When laminating the build-up layer in multiple layers, it is necessary to dissolve the surface portion of the lower layer and dissolve it in the upper layer to maintain the adhesion strength of the upper and lower layers at a high level. In this case, although the copper component in solid solution in the lower layer is also in solid solution in the upper layer, the copper composition becomes 1/10 or less of that of the lower layer. When the laser cladding of the present invention is repeated three or more layers, the solid solution amount of copper decreases stepwise and gradually, and on the surface of the third or more layer, the copper content may be substantially brought close to zero. It was possible to form a buildup layer of the same composition as the used nickel base alloy powder. As a result, it has been possible to obtain known nickel base alloy buildup layers such as Hastelloy and Inconel, which are developed by metallurgical methods and are excellent in corrosion resistance and wear resistance at high temperatures.

  A laser is irradiated while supplying the nickel base heat-resistant alloy powder of the present invention to form a molten pool of the powder, and solidifying it to form a built-up layer is performed in an inert gas atmosphere. Specifically, the alloy powder is supplied to the buildup point together with Ar gas. In the case where a defect occurs in the buildup layer, after-seal with Ar gas is performed to suppress the oxidation of the buildup layer and improve the wettability. The alloy powder particle size affects the laser energy and the buildup thickness that form the molten pool, and the particle size is preferably 20 to 150 μm. When the particle size is larger than 150 μm, a large amount of energy is required to melt the powder, the control accuracy of the size and temperature of the melt pool is deteriorated, and the thickness of the overlaying layer is also increased. If the particle size is small, it is suitable for precision overlaying because the overlay accuracy is improved, but if it is 20 μm or less, the powder is too light and scattering of the powder becomes excessive, and the conversion efficiency to the overlaying layer decreases. Not only does the deterioration of the working environment by dust progress. From this point of view, it is not preferable to use too fine powder.

  The thickness of the laser overlay is preferably 0.1 to 3 mm. When the thickness is less than 0.1 mm, it is necessary to reduce the particle size of the powder, and the use of the fine powder is not preferable in terms of the working environment and the yield. In order to make the buildup layer thicker than 3 mm, the size of the alloy melt pool also increases, and a large laser energy is required. When the energy becomes excessive, it becomes more difficult to control the solid solution amount of the substrate or the base layer, the solid solution amount of the substrate or the base layer becomes large, and the buildup layer composition largely deviates from the original heat resistant alloy composition. On the other hand, due to the difficulty of energy control, when energy is insufficient, a defect may occur in the interface or film, resulting in a weak or brittle overlaying layer.

  In the laser build-up method, in order to form a dense build-up layer with good adhesion, 10 wt% or less of solid solution is required from the base body or the base layer, and a deviation occurs from the original alloy composition of the supplied powder. However, by stacking the laser build-up layers in multiple layers, the amount of copper solid solution from the substrate is reduced, and a build-up layer having the composition inherent to the alloy can be obtained. The thickness of one layer is preferably 0.1 to 3 mm, and a total thickness of 0.3 to 10 mm is required to form three or more layers. Although the total thickness may be 10 mm or more, it was determined that the thickness of 10 mm or more is not necessary in consideration of the lifetime of the entire mold caused by causes other than the covering layer. In addition to the lower part of the inner surface of the mold, the piled-up layer may be formed in the vicinity of the meniscus portion at the upper part of the inner surface of the mold.

  The nickel base alloy buildup layer was prepared by a method of selecting an alloy composition having excellent heat resistance and corrosion resistance, and supplying a laser beam of these alloys. Hastelloy C (53Ni19Mo17Cr), Inconel (80Ni13Cr), Monel (65Ni31Cu4 (Fe + Mn)), NiCoCrAlY (47.9Ni23Co20Cr8.5Al0.6Y), NiCr (50Ni50Cr), Waspaloy (58Ni19Cr14Co4. 4) as nickel base alloys excellent in heat resistance and corrosion resistance. One type of 5Mo3Ti) was selected, and all commercially available alloy powders were used. In addition, the alloy powder which can be used is not limited to these, Ni: 30% or more and 93% or less, Co: 1% or more, Cr: 8% or more, Mo: 1% or more, W: 0.5% or more, Al: 0.2% or more, Ti: 0.4 to 6%, Nb: 0.4 to 6%, Ta: 0.1 to 4%, Y: 0.1% or more As mentioned above, the remainder, the thing which consists of unavoidable impurities, etc. can be used.

The thicker the overlay, the worse the surface roughness of the overlay. For this reason, after the formation of the laser build-up layer, the surface is polished and the surface roughness is flattened to Ry 10 μm or less, whereby the occurrence of abnormal wear of the build-up layer can be suppressed.
Hereinafter, the present invention will be described in detail based on the test results of the present invention.

  On the surface of the mold short side (size 230 mm x 900 mm x 50 mm), a nickel-based alloy powder with a particle size of 45 to 125 μm is irradiated with a semiconductor laser with a powder feed rate of 8 g / min, a nozzle scan rate of 600 mm / min, and a wavelength of 950 to 1070 nm. , And a nickel base alloy buildup layer of 0.5 mm was formed. Table 1 shows the results of analysis of the Cu content dissolved in the buildup layer by EPMA. Due to the difference in laser energy, as shown in Table 1, the amount of dissolved Cu in the buildup layer changes. If the laser energy is too large, as in Comparative Example 1, the amount of solid solution of Cu exceeds 10 wt%, and the heat resistance of the overlaying layer is lowered. On the other hand, when the laser energy was small, as in Comparative Example 2, defects and abnormal tissue were observed in the interface and in the overlaying layer. Therefore, the inventive example in which the solid solution amount of Cu is 10 wt% or less is excellent. The laser deposition conditions differ depending on the type of substrate metal and the die size and shape, and the thermal diffusion rate due to thermal conduction differs, so the optimum deposition conditions also differ, but the amount of dissolved Cu becomes 10 wt% or less The conditions should be selected as follows.

  FIG. 1 is an explanatory view showing a cross-sectional structure of an example of the present invention in contrast to the cross-sectional structures of Comparative Examples 1 and 2. FIG. In the figure, 1 is a copper base, 2 is a buildup layer, 3 is a crack, and 4 is a pore. The figure (a) is a cross-section of the example of the present invention, and a small waved state is seen at the interface with the substrate, and a melting reaction at the interface is seen. There are no defects found inside the film. The figure (b) is a cross-sectional structure of the comparative example 1, and the interface with a raw material is greatly wavy, and the heat affected zone in a base interface is also seen large also in a base part. In addition, a crack is generated inside the film in the vicinity of the interface. The figure (c) is a cross-section of comparative example 2, an interface with a substrate is linear, and melt reaction of an interface is not seen. A large number of pore-like defects occur in the film near the interface.

  The first laser build-up layer is performed under the conditions of Example 1, and the second and subsequent laser build-up layers are carried out except that the powder supply rate is 24 g / min, the nozzle scan rate is 1000 mm / min, and the laser energy is 2800 W Under the conditions of Example 1, four laser build-up layers were produced with a total of 5 mm of 1.25 mm × 4 layers. The amount of Cu solid solution in each layer was measured by EPMA, and the results are shown in Table 2 and FIG. As the buildup layers are stacked, the Cu content decreases, the Cu content is about 0.5 wt% in the third layer, and the Cu content is less than 0.1 wt% in the fourth layer, so the original alloy A composition layer could be obtained.

  FIG. 2 is a view showing the relationship between the thickness (mm) of the build-up layer of Example 2 of the present invention, the Cu content (wt%) in the film, and the film hardness (HV). In the figure, ◆ indicates the Cu content (wt%) in the film, and ■ indicates the film hardness (HV). From the transition of the Cu content in the figure, it can be seen that the amount of dissolved Cu in the buildup layer decreases gradually from the inside to the surface. In addition, it can be seen from the transition of the coating hardness that the nickel-based alloy layer on the surface is hardly affected by Cu from the base, and exhibits the characteristics (abrasion resistance and the like) inherent to the alloy.

  While the Cu mold substrate (size: 200 mm × 200 mm × 40 mm) was heated to 350 ° C. by a high frequency heating method, laser cladding was carried out under the conditions of Example 1 except that the laser energy was 2000 W. By heating the substrate, no defects were found even if the laser energy was reduced, and it was possible to form a dense laser build-up layer in which a small amount of Cu of 2.2 wt% was solid-solved.

  The mold for continuous casting according to the present invention has excellent heat resistance, corrosion resistance, and wear resistance as a mold for steel making from molten steel, but the long life and high accuracy maintenance at high temperature of the mold are maintained. Properties can also be used in high-quality molded article manufacturing applications in high temperature and corrosive environments.

Claims (4)

The surface of a copper or copper alloy substrate is irradiated with a laser while supplying a nickel base heat resistant alloy powder, and the powder is melted and solidified to form a nickel base alloy layer having a thickness of 0.1 to 3 mm, a thickness of 0.2 to 10 mm Continuous casting mold with multi-layered cladding layer. The coating layer is a multi-layered laser beam formed on the first layer in which the copper or copper alloy is partially dissolved in the buildup layer so that the copper content is 10 wt% or less The continuous casting mold according to claim 1, characterized in that it is a multi-layered laser build-up layer provided with a build-up layer, and the amount of solid solution of copper in the build-up layer gradually decreases from the inside to the surface. Nickel-based heat-resistant alloy powder is selected from Hastelloy C (53Ni19Mo17Cr), Inconel (80Ni13Cr), Monel (65Ni31Cu4 (Fe + Mn)), NiCoCrAlY (47.9Ni23Co20Cr8.5Al0.6Y), NiCr (50Ni50Cr), Waspaloy (58Ni19Cr14Co4.5Mo3Ti) The continuous casting mold according to claim 1 or 2, characterized in that: The laser cladding is performed while heating the copper or copper alloy substrate to 100 to 400 ° C. when irradiating the laser while supplying the nickel base heat-resistant alloy powder to the substrate surface. The manufacturing method of the continuous casting mold as described in 4.