Method for producing a boron alloy powder mixture, boron alloy powder mixture, method for producing a combined powder structure, combined powder structure, method for producing a steel pipe and steel pipe

Abstract

A method for producing a boron alloy powder mixture, the method comprising: Preparing a mixed powder containing a boron-iron alloy powder and a target powder; and heat-treating the mixed powder to form a boronized region in the target powder by boronizing at least a portion of the target powder and to form a deborized region in the boron-iron alloy powder by deborizing at least a portion of the boron-iron alloy powder, thereby lowering the melting point of the boron-iron alloy powder.

Description

[0001] Method for producing a boron alloy powder mixture, boron alloy powder mixture, method for producing a combined powder structure, combined powder structure, method for producing a steel pipe and steel pipe Technical area

[0002] The present invention relates to a method for producing a boron alloy powder mixture, the method comprising: preparing a mixed powder containing a boron-iron alloy powder and a target powder; and heat-treating the mixed powder to form a boronized region in the target powder by boronizing at least a portion of the target powder and to form a deborized region in the boron-iron alloy powder by deborizing at least a portion of the boron-iron alloy powder, thereby lowering the melting point of the boron-iron alloy powder.The present invention relates to a boron alloy powder mixture comprising: a boron-iron alloy powder; and a target powder having at least a part in which a boron-containing region is formed, wherein the boron-iron alloy powder has at least a part in which a deborated region is formed by deboriding the boron-iron alloy powder, wherein the deborated region has a lowered melting point caused by reducing a boron content due to deboriding.

[0003] The present invention relates to a combined powder structure comprising: a target powder having at least a part in which a boron-containing region is formed, and a boron-iron alloy powder having at least a part in which a deborated region is formed, wherein the boron-containing region and the deborated region combine with each other by melting and solidifying at least a part of at least one of the boron-containing region and the deborated region, or by sintering the boron-containing region and the deborated region, and a method for producing a combined powder structure, the method comprising: heating a mixed powder containing a deborated boron-iron alloy powder and a boron-containing target powder to a predetermined temperature to combine the deborated boron-iron alloy powder with the boron-containing target powder.

[0004] The present invention relates to a steel pipe comprising a coating layer on an inner surface of the steel pipe, the coating layer having a solidified structure formed by melting and solidifying a boron-iron alloy powder and a target powder, the boron-iron alloy powder acting as a matrix metal or a binder and having at least a partial region in which a deborated region is formed, the target powder having at least a partial region in which a boron-containing region is formed, and a method for manufacturing a steel pipe, the method comprising: loading a powder mixture into a steel pipe, the powder mixture containing a boron-iron alloy powder having at least a partial region in which a deborated region is formed and a target powder having at least a partial region in which a boron-containing region is formed;and melting the powder mixture loaded into the steel pipe by heating and then solidifying the powder mixture to form a coating layer on an inner surface of the steel pipe; Technical background

[0005] Generally, a wear-resistant composition is formed by dispersing ceramic powder with high hardness and high wear resistance as a hardening phase in a metal matrix. Various high-hardness powders, such as tungsten carbide (WC), titanium carbide (TiC), or titanium boride (TiB2), are used as such ceramic powders. However, these powders are expensive, and they are difficult to disperse evenly in a metal matrix when used to form a composition using gravity casting or centrifugal casting due to a large difference in specific gravity with respect to the metal matrix. Furthermore, the binding force of these powders with respect to the metal matrix is ​​insufficient due to their low adhesive strength.

[0006] To produce metal parts or metal-ceramic composite parts with high wear resistance or high corrosion resistance using casting or sintering, different powders can be combined to form a combined powder structure. To obtain excellent properties of the combined powder structure, the powders must have a high cohesive strength to bond to each other. To maintain the high cohesive strength, the contact surface between the powders is partially melted; this combines the powders. In the case of high-hardness ceramic composite material, low-melting-point metal powder can be used as a binder to combine high-hardness ceramic powder.

[0007] A binary iron-boron compound can be used for a high-hardness ceramic powder used as a reinforcing agent or used to form a combined powder structure.

[0008] A binary iron-boron compound can be used as a reinforcing agent or as a high-hardness ceramic powder for forming a combined powder structure. The binary iron-boron compound can be FeB or Fe2B depending on the boron content. More specifically, when the boron content is 8.83 wt%, the Fe2B compound with a melting point of 1389°C can be formed, while when the boron content is 16.23 wt%, the FeB compound with a melting point higher than 1650°C can be formed. In addition, when the boron content is 3.8 wt%, the binary iron-boron compound has a lower melting point of 1177°C. Among them, Fe2B has a specific gravity of 7.3 g / cm 3and a hardness value of HK 1800 to 2000, and the FeB has a specific weight of 7.0 g / cm 3 and a hardness value of HK 1900 to 2100. In other words, Fe2B and FeB both exhibit very high hardness, excellent self-melting properties, and adhesive properties. Furthermore, iron-boron compounds are particularly suitable, as their specific gravity is approximately 7.5 g / cm 3 which is similar to that of iron-based metal, very suitable for producing a metal composition containing an iron-based metal matrix material using gravity die casting or centrifugal casting.

[0009] US 4 235 630 A relates to a wear-resistant and abrasion-resistant boron alloy and a process for its production.

[0010] DE 36 18 887 A1 relates to a process for producing metallic materials for components of nuclear reactors that are exposed to neutron irradiation.

[0011] JP 2007-14 966 A relates to a method for applying an internal coating to self-melting alloys. Detailed description of the inventionTechnical task

[0012] The present invention provides a method for producing iron-boron compound powder with high hardness and excellent self-fusing and adhesive properties.

[0013] The present invention provides a powder mixture and a method for producing the powder mixture. The powder mixture is prepared by mixing and heat-treating a boron-iron alloy powder and a target powder so that at least a portion of the target powder is boronized and at least a portion of the boron-iron alloy powder is deboridated, thereby lowering the melting point. This method differs from a conventional method in which separately prepared high-hardness boride powder is mixed with a low-melting-point metal powder that acts as a binder.

[0014] The present invention provides a combined powder structure and a method for producing the combined powder structure. The combined powder structure is produced by heating a mixed powder containing a deborated boron-iron alloy powder and a borated target powder to a predetermined temperature to combine the deborated boron-iron alloy powder with the borated target powder. This method differs from a conventional method in which separately prepared high-hardness boride powder is mixed with a low-melting-point metal powder that acts as a binder.

[0015] The present invention provides a steel pipe and a method for manufacturing the steel pipe. The steel pipe has an inner surface coated with a coating layer, the coating layer having a solidified structure formed by melting and solidifying a boron-iron alloy powder and a target powder, the boron-iron alloy powder acting as a matrix metal or a binder and having at least a portion in which a deborated region is formed, the target powder having at least a portion in which a borated region is formed. The coating layer has excellent wear resistance, oxidation resistance, and corrosion resistance properties and is manufactured at low cost using the combined powder structure. Technical solution

[0016] According to one aspect of the present invention, there is provided a manufacturing method for a boron alloy powder mixture, the method including: preparing a mixed powder containing a boron-iron alloy powder and a target powder; and heat-treating the mixed powder to form a boronized region in the target powder by boronizing at least a portion of the target powder and to form a deborized region in the boron-iron alloy powder by deborizing at least a portion of the boron-iron alloy powder, thereby lowering the melting point of the boron-iron alloy powder.

[0017] Embodiment of the present invention, wherein a boron content in the boron-iron alloy powder before deboring may be 17 atomic% or more.

[0018] Embodiment of the present invention, wherein a boron content in the boron-iron alloy powder after deboring can be in a range of 5 atomic % to 35 atomic %.

[0019] Embodiment of the present invention, wherein a boron content in the boron-iron alloy powder after deboring can be in a range of 10 atomic % to 25 atomic %.

[0020] Embodiment of the present invention, wherein the deboriding can be performed until the target powder is completely boronized or the boron-iron alloy powder is completely deboridated.

[0021] Embodiment of the present invention, wherein the target powder may contain a metal that forms a solid solution with boron or that combines with boron to form a boron compound.

[0022] Embodiment of the present invention, wherein the metal may be at least one selected from iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si) and tungsten (W).

[0023] Embodiment of the present invention, wherein a melting point of the boronized region in the target powder may be lower than a melting point of the target powder before boronizing.

[0024] Embodiment of the present invention, wherein an amount of the boron-iron alloy powder in the mixed powder may be in a range of 5 wt% to 95 wt%.

[0025] Embodiment of the present invention, wherein the mixed powder contains an active agent in the amount of 0.5 wt% to 20 wt%.

[0026] Embodiment of the present invention, wherein the active agent may contain at least one of Na3AlF6, KBF4, AlF3, NaCl, NaF, CaF2 and NH4Cl.

[0027] Embodiment of the present invention, wherein the deboriding can be carried out under an antioxidant atmosphere.

[0028] Embodiment of the present invention, wherein the antioxidant atmosphere may be at least one of a nitrogen atmosphere, an argon atmosphere, a hydrogen atmosphere, and a vacuum atmosphere.

[0029] According to one aspect of the present invention, there is provided a boron alloy powder mixture comprising: a boron-iron alloy powder; and a target powder having at least a portion in which a boron-containing region is formed, wherein the boron-iron alloy powder has at least a portion in which a deborated region is formed by deboriding the boron-iron alloy powder, wherein the deborated region has a lowered melting point caused by reducing a boron content due to deboriding.

[0030] Embodiment of the present invention, wherein the target powder may be fully boronized or the boron-iron alloy powder may be fully deborized.

[0031] Embodiment of the present invention, wherein the deborated region may be located on the surface of the boron-iron alloy powder.

[0032] Embodiment of the present invention, wherein the boron-iron alloy powder may further contain at least one of Si and C.

[0033] Embodiment of the present invention, wherein the borated region may be either a solid metal-boron solution or a boron compound of metal and boron.

[0034] Embodiment of the present invention, wherein the metal may be at least one selected from iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si) and tungsten (W).

[0035] Embodiment of the present invention, wherein a melting point of the boronized region may be lower than a melting point of the metal.

[0036] Embodiment of the present invention, wherein the boronized region may be located on the surface of the target powder.

[0037] According to one aspect of the present invention, there is provided a manufacturing method for a combined powder structure, the method including: heating a mixed powder containing a deborated boron-iron alloy powder and a borated target powder to a predetermined temperature to combine the deborated boron-iron alloy powder with the borated target powder.

[0038] Embodiment of the present invention, wherein the method may further include: preparing a mixed powder containing a boron-iron alloy powder and a target powder, and heat-treating the mixed powder to boronize at least a portion of the target powder and deboronize at least a portion of the boron-iron alloy powder, thereby lowering a melting point of the boron-iron alloy powder.

[0039] Embodiment of the present invention, wherein the method may further include: adding other powder to the deborated boron-iron alloy powder and the boron-containing target powder to combine the other powder with at least one of the deborated boron-iron alloy powder and the boron-containing target powder.

[0040] Embodiment of the present invention, wherein the other powder may include a pure metal powder, an alloy powder, or a ceramic powder.

[0041] Embodiment of the present invention, wherein the alloy powder may contain a self-fusing alloy powder.

[0042] Embodiment of the present invention, wherein the ceramic powder may contain at least one of a metal oxide, a metal carbide, a metal nitride and a metal boride.

[0043] Embodiment of the present invention, wherein the mixed powder may further contain a borax such as Na2B4O7 10H2O.

[0044] Embodiment of the present invention, wherein a boron content of the boron-iron alloy powder before deboring may be 17 atomic% or more.

[0045] Embodiment of the present invention, wherein a boron content in the boron-iron alloy powder in the mixed powder after deboring may be in a range of 5 atomic % to 35 atomic %.

[0046] Embodiment of the present invention, wherein a boron content of the boron-iron alloy powder in the mixed powder after deboring may be in a range of 10 atomic % to 25 atomic %.

[0047] Embodiment of the present invention, wherein the boron-iron alloy powder may further contain at least one of Si and C.

[0048] Embodiment of the present invention, wherein the target powder may contain a metal that forms a solid solution with boron or that combines with boron to form a boron compound.

[0049] Embodiment of the present invention, wherein the target powder may be at least one selected from iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si) and tungsten (W).

[0050] Embodiment of the present invention, wherein a content of the boron-iron alloy powder in the mixed powder may be in a range of 5 wt% to 95 wt%.

[0051] Embodiment of the present invention, wherein the mixed powder contains an active agent in the amount of 0.5 wt% to 20 wt%.

[0052] Embodiment of the present invention, wherein the active agent may contain at least one of Na3AlF6, KBF4, AlF3, NaCl, NaF, CaF2 and NH4Cl.

[0053] Embodiment of the present invention, wherein the deboriding can be carried out in an antioxidant atmosphere.

[0054] Embodiment of the present invention, wherein the antioxidant atmosphere may be at least one of a nitrogen atmosphere, an argon atmosphere, a hydrogen atmosphere, and a vacuum atmosphere.

[0055] According to one aspect of the present invention, there is provided a combined powder structure including: a target powder having at least a portion in which a boron-containing region is formed, and a boron-iron alloy powder having at least a portion in which a deborated region is formed, wherein the boron-containing region and the deborated region combine with each other by melting and solidifying at least a portion of at least one of the boron-containing region and the deborated region, or by sintering the boron-containing region and the deborated region.

[0056] Embodiment of the present invention, wherein the deborated region may be located on the surface of the boron-iron alloy powder.

[0057] Embodiment of the present invention, wherein the boron-iron alloy powder may further contain at least one of Si and C.

[0058] Embodiment of the present invention, wherein the borated region may be either a solid metal-boron solution or a boron compound of metal and boron.

[0059] Embodiment of the present invention, wherein the metal may be at least one selected from iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si) and tungsten (W).

[0060] According to one aspect of the present invention, there is provided a manufacturing method for a steel pipe, the method including: loading a mixed powder into a steel pipe, the mixed powder containing a boron-iron alloy powder having at least a portion in which a deborated region is formed and a target powder having at least a portion in which a boron-containing region is formed; and melting the mixed powder loaded into the steel pipe by heating and then solidifying the mixed powder to form a coating layer on an inner surface of the steel pipe.

[0061] Embodiment of the present invention, wherein the melting and then solidification of the powder mixture can be carried out such that the steel pipe with the powder mixture loaded therein is heated and cooled while rotating.

[0062] An embodiment of the present invention, wherein loading the powder mixture into the steel pipe may include: mixing a boron-iron alloy powder and a target powder; and heat-treating the mixture of the boron-iron alloy powder and the target powder to boronize at least a portion of the target powder to form the boronized region, and simultaneously deborizing at least a portion of the boron-iron alloy powder to form the deborized region.

[0063] Embodiment of the present invention, wherein the boron-iron alloy powder may further contain at least one of silicon and carbon.

[0064] Embodiment of the present invention, wherein the target powder may contain at least one of iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si) and tungsten (W).

[0065] Embodiment of the present invention, wherein a content of the boron-iron alloy powder in the powder mixture may be in a range of 5 wt% to 95 wt%.

[0066] Embodiment of the present invention, wherein average particle sizes of the boron-iron alloy powder and the target powder can be in a range of 200 mesh (75 µm) to 20 mesh (850 µm) according to ASTM standard sieves.

[0067] Embodiment of the present invention, wherein the mixed powder in the steel pipe may further contain at least one of a chromium-iron alloy powder and a flux.

[0068] Embodiment of the present invention, wherein the chromium-iron alloy powder may contain 2 wt% or more of carbon and 50 wt% or more of chromium.

[0069] Embodiment of the present invention, wherein an amount of the chromium-iron alloy powder in the powder mixture can be in a range of 5 wt% to 95 wt%.

[0070] Embodiment of the present invention, wherein the chromium-iron alloy powder may further contain at least one of iron, chromium, silicon and carbon.

[0071] Embodiment of the present invention, wherein an average particle size of the chromium-iron alloy powder may be in a range of 200 mesh (75 µm) to 4 mesh (4800 µm) according to ASTM standard sieves.

[0072] Embodiment of the present invention, wherein a rotational speed of the steel pipe can be in a range of 5 G to 120 G, where G is given by the following equation: G = centrifugal force / gravity force = 5.6 × 10 -7 × Inner diameter of the steel pipe (mm) × (Speed ​​(min -1 )) 2 .

[0073] Embodiment of the present invention, wherein the heating can be performed by any one of fuel gas heating, electric resistance heating and high frequency induction heating.

[0074] Embodiment of the present invention, wherein the heating can be carried out at a heating temperature of 1000 °C to 1500 °C.

[0075] According to one aspect of the present invention, there is provided a steel pipe, the steel pipe including: a coating layer on an inner surface of the steel pipe, the coating layer having a solidified structure formed by melting and solidifying a boron-iron alloy powder and a target powder, the boron-iron alloy powder acting as a matrix metal or a binder and having at least a part in which a deborated region is formed, the target powder having at least a part in which a boronized region is formed.

[0076] Embodiment of the present invention, wherein the coating layer may further contain a chromium-iron alloy as a reinforcing agent.

[0077] Embodiment of the present invention, wherein the reinforcing agent may contain iron, 10 wt% to 80 wt% chromium, 2 wt% to 10 wt% carbon, and 2.5 wt% or less silicon.

[0078] Embodiment of the present invention, wherein the binder may contain iron and boron, wherein the reinforcing agent contains at least one of iron, chromium, silicon and carbon.

[0079] Embodiment of the present invention, wherein the binder may have a boron content in a range of 5 atomic% to 35 atomic%.

[0080] Embodiment of the present invention, wherein the coating layer may contain at least one of iron, chromium, silicon, carbon and boron.

[0081] Embodiment of the present invention, wherein a boron content of the coating layer may be in a range of more than 0 wt% to 10 wt% or less.

[0082] Embodiment of the present invention, wherein a carbon content of the coating layer may be in a range of more than 0 wt% to 10 wt% or less.

[0083] Embodiment of the present invention, wherein a chromium content of the coating layer may be in a range of more than 0 wt% to 60 wt% or less.

[0084] Embodiment of the present invention, wherein a silicon content of the coating layer may be in a range of more than 0 wt% to 2.5 wt% or less. Beneficial effects

[0085] When a method for producing iron-boron compound powder according to an embodiment of the present invention is used, iron-boron compound powder having high hardness and excellent self-fusing and adhesive properties can be obtained.

[0086] A boron alloy powder mixture produced according to an embodiment of the present invention contains a boron alloy powder mixture with a lower boron content; due to deboriding and reducing the boron content, the boron alloy powder may have a lower melting point. Furthermore, in some cases, a target powder in the powder mixture may have increased hardness and a lowered melting point due to boroniding and increasing the boron content. Accordingly, in the case of the boron alloy powder mixture according to an embodiment of the present invention, the deboridated boron-iron alloy powder and the boronized target powder are not separated, and these powders can be used directly, or other higher-hardness compound powder is added thereto, and then the resultant is heated at a relatively low temperature for use in preparing a high-hardness combined powder structure.

[0087] A combined powder structure produced according to an embodiment of the present invention includes a powder mixture including a boron-iron alloy powder having a lower boron content due to deboriding and a target powder having a higher boron content due to boriding, and the boron-iron alloy powder may have a lower melting point due to the reduction in boron content, and the target powder may have a higher hardness and a lower melting point due to the increase in boron content caused by boriding.Accordingly, in the case of the boron alloy powder mixture according to an embodiment of the present invention, the deborated boron-iron alloy powder and the boron-containing target powder are not separated, and these powders can be used directly, or other higher hardness compound powder is added thereto, and then the resultant is heated at a relatively low temperature for use in preparing a high-hardness combined powder structure.

[0088] According to another embodiment of the present invention, a steel pipe with excellent wear resistance, oxidation resistance, and corrosion resistance properties and a method for producing the steel pipe can be realized at low cost. Furthermore, due to its high hardenability, very high hardness and strength can be achieved without separate heat treatment.

[0089] The effects described above are provided as examples only for some embodiments and do not limit the scope of the present invention. Description of the drawing Fig. 1 to 3 are schematic views of an apparatus for producing a compound powder. Fig. 4 is a sectional view of the iron-boron compound powder particle produced using the compound powder production method. Fig. 5 is a sectional view of the iron-boron compound powder prepared according to the experimental example. Fig. Figure 6 shows X-ray diffraction (XRD) analysis results of the iron-boron compound powder prepared according to the experimental example. Fig. 7 and Fig.8 are views for explaining deboriding of the boron-iron alloy powder and boronizing of the target powder occurring in the powder mixture according to an embodiment of the present invention. Fig. 9 is an exemplary view of a structure formed by boronizing the target powder, according to an embodiment of the present invention. Fig. 10 is a phase diagram of iron and boron according to one embodiment of the present invention. Fig. 11 shows X-ray diffraction results of the boron-iron alloy powder and the chromium (Cr) powder in the powder mixture before deboriding, according to an embodiment of the present invention. Fig. 12 shows X-ray diffraction results of the boron-iron alloy powder and the chromium (Cr) powder in the powder mixture after deboriding, according to an embodiment of the present invention. Fig. 13 and Fig.14 are sectional views of the boron-iron alloy powder and the chromium (Cr) powder in the mixed powder after deboriding and show ESMA analysis results of the boron-iron alloy powder and the chromium powder in the mixed powder after deboriding, according to an embodiment of the present invention, respectively. Fig. 15 shows the microstructure of the combined powder structure prepared according to the experimental example, according to an embodiment of the present invention. Fig. 16 shows the microstructure of the combined powder structure prepared according to an experimental example, according to an embodiment of the present invention. Fig. 17 to 20 are schematic views of the steel pipe according to an embodiment of the present invention. Fig. 21 is a schematic view illustrating a method of manufacturing a steel pipe according to an embodiment of the present invention. Fig. 22 is a sectional view of a part of the steel pipe according to an embodiment of the present invention. Fig. 23 to 25 are curves of the hardness of a section through the formed coating layer according to an embodiment of the present invention. Fig. 26 to 28 show the microstructure of the formed coating layer according to an embodiment of the present invention. Best execution

[0090] The present invention will now be described in more detail with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and concise, and will fully convey the concepts of the invention to those skilled in the art. Furthermore, for ease of description, the sizes of elements in the drawings may be exaggerated for clarity.

[0091] In the following embodiments, the x-axis, y-axis, and z-axis are not limited to the three axes in a rectangular coordinate system and can be understood to encompass a broader meaning, including the description provided above. For example, the x-axis, y-axis, and z-axis can be perpendicular to each other, or they can also indicate three other directions that are not perpendicular to each other.

[0092] The term "iron-boron alloy" as used herein may contain about 10 wt% or more boron and is a compound containing iron and boron having a melting point of about 1450°C or more and may be called ferroboron, an iron-boron alloy, or the like.

[0093] In addition, the term “target powder” used here means powder to be borated due to boron supplied by a boron-iron alloy powder and to be mixed with the boron-iron alloy powder to form a mixed powder.

[0094] In embodiments of the present invention, a boron-iron alloy powder is a boron source material that provides boron for boronizing a target powder and is deborated to reduce the boron content during boronizing of the target powder. Furthermore, the target powder can be used as a low-melting-point binder after boronizing. The boronizing of the target powder performed by a boron-iron alloy powder and the deboration of the boron-iron alloy powder can be performed by mixing the target powder and the boron-iron alloy powder, and then heat-treating the mixture. Accordingly, the heat treatment may also be referred to as a deboration step or deboration process with respect to the boron-iron alloy powder.

[0095] The boron-iron alloy powder having at least a portion in which a deborated region is formed referred to herein refers to the boron-iron alloy powder having a lower melting point than a boron-iron alloy powder in which the deborated region is not formed. With reference to the iron-boron phase diagram of Fig. 10, the melting point of iron is 1538 °C, and the melting point of boron is 2092 °C. When 64 atom% boron is added to iron, a peritectic transformation can occur at a temperature of 1500 °C, and when 17 atom% boron is added, the peritectic transformation can occur at a relatively low temperature of 1174 °C. Accordingly, when the boron content in the boron-iron alloy is reduced from 50 atom% to 17 atom%, the melting point of ferroboron can decrease from 1650 °C to 1174 °C.

[0096] For example, if the initial boron content of the boron-iron alloy powder is 50 at%, and a deborated region with the boron content of 17 at% is formed on the surface of the boron-iron alloy powder during deboration, the formation of the deborated region can lead to a reduction in the melting point of the surface of the boron-iron alloy powder from 1650°C to 1174°C, thereby lowering the melting temperature by approximately 480°C. Accordingly, the boron-iron alloy powder having at least a portion in which the deborated region is formed refers to a boron-iron alloy powder having a lower boron content than its initial boron content.

[0097] In addition, the boron-iron alloy powder may further contain at least one of silicon (Si) or carbon (C), and in this case, due to deboriding, the melting point of the boron-iron alloy powder may be further lowered to below 1174 °C. A silicon content may be 5 wt% or less, and a carbon content may be 2 wt% or less.

[0098] Similarly, forming a boronized region in at least a portion of the target powder means that the target powder has a portion whose melting point is lower than that of the non-borated target powder. For example, with reference to Fig.10 If the target powder is pure iron powder, the target powder is boronized by the boron-iron alloy powder, thus increasing its boron content from 0 to 17 atomic%. The melting point of the target powder drops from 1538 °C to a process temperature of 1174 °C, which is a eutectic temperature. Furthermore, even if Fe2B is formed as a boron compound in the boronized region, the melting point of the target powder drops to 1389 °C, which is lower than the melting point of pure iron of 1538 °C.

[0099] The target powder is a metal with an affinity for boron, and such a metal need not be restricted as long as the metal combines with boron to form a boron compound. For example, the target powder can contain at least one of iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si), and tungsten (W).

[0100] Embodiments of the present invention will be described in detail.

[0101] Fig. 1 is a sectional view of an apparatus 100 for producing a compound powder, which is perpendicular to an x-direction. With reference to Fig. 1, the device 100 includes a retort 10 and a furnace structure 20 for heating the retort 10.

[0102] The retort 10 may have a shape of a hollow cylindrical tube extending in a y-axis direction. The retort 10 has an interior into which a mixed powder 40 of two or more types of powder for producing compound powder is loaded, and the mixed powder 40 is protected from oxidation and sintering. The retort 10 mixes the loaded powders to form the mixed powder 40. The retort 10 may rotate with respect to a center line extending in the y-axis direction, as shown in FIG. Fig.1. The retort 10 has an end region with a door 30 for loading the powder.

[0103] The furnace assembly 20 includes a frame 21 enclosing the retort 10 and a heating unit 22 arranged to heat the retort 10 within the frame 21. The heating unit 22 may be any of various heating sources for generating heat to be supplied to an outer peripheral surface of the retort 10. An example of the heating unit may be an electric resistance heater, a high-frequency induction heater, or a halogen lamp.

[0104] The furnace structure 20 may comprise a plurality of partial furnace structures that are separable from one another and movable with respect to one another. Fig. 2 is a sectional view of the apparatus 100, which includes a plurality of partial furnace assemblies perpendicular to the extension direction of the retort 10 (i.e., the y-direction of Fig. 1) contains.

[0105] For example, as in Fig. 2, the furnace assembly 20 includes two sub-furnace assemblies, such as a first sub-furnace assembly 20a and a second sub-furnace assembly 20b. The first sub-furnace assembly 20a includes a first sub-frame 21a arranged to enclose a portion of the outer peripheral surface of the retort 10, and a first heating unit 22a arranged within the first sub-frame 21a. The second sub-furnace assembly 20b includes a second sub-frame 21b arranged to enclose the remaining outer peripheral surface of the retort 10, and a second heating unit 22b arranged within the second sub-frame 21b.

[0106] As in Fig.2, the first partial furnace assembly 20a may be disposed above the retort 10, and the second partial furnace assembly 20b may be disposed below the retort 10. For example, the first partial furnace assembly and the second partial furnace assembly may be disposed on the left and right sides of the retort 10, respectively.

[0107] As described above, the first and second partial furnace assemblies 20a and 20b of the furnace assembly 20 are coupled to the outer peripheral surface of the retort 10 to heat the retort 10. On the other hand, the first and second partial furnace assemblies 20a and 20b can be separated from each other and removed from the outer peripheral surface of the retort 10 to cool the retort 10. Fig. 3 is a view of the retort 10 with the furnace assembly 20 removed.

[0108] Furthermore, an element 50 is provided within the retort 10. The element 50 allows the mixed powder 40 to rotate along an inner surface of the retort 10 when the retort 10 rotates.

[0109] When the apparatus 100 is used, the mixed powder 40 charged into the retort 10 is heated to cause a reaction between materials of the mixed powder 40 to obtain a desired compound powder.

[0110] For example, iron-boron compound powder can be produced using apparatus 100. If the mixed powder 40 contains iron powder and a boron source material, the iron powder and the boron source material react with each other in the retort 10, thereby borating the iron powder to convert the iron powder into an iron-boron compound powder. The iron-boron compound can be FeB, Fe2B, or a mixture thereof.

[0111] The boron source material may be a material for supplying boron that reacts with iron powder, and may be provided as a powder. Accordingly, the iron powder and the boron source material powder are mixed together, and then the mixed powder is loaded into the retort 10 of the device 100. The iron powder and the boron source material powder may be loaded into the retort 10 separately, without mixing.

[0112] The iron powder can be iron with relatively low levels of other alloying elements, including carbon, i.e., pure iron. When iron contains other alloying elements, the diffusion rate of boron is low, thus suppressing the formation of an iron-boron bond, making it difficult to form a bond uniformly from the surface to the center of the powder particles. The iron powder can be prepared by decarburizing shot peening waste after use as carbon steel.

[0113] The boron source material may, for example, contain at least one of a boron powder, a boron compound powder, and a ferroboron powder. The boron compound may, for example, contain boron carbide (B4C) or boron oxide (B2O3).

[0114] The average diameter of the boron source material powder particles can be smaller than the average diameter of the iron powder particles. This makes it easier to separate the iron-boron compound powder formed during boron etching from the remaining boron source material powder after boron etching. For example, the diameter of boron source material powder particles can range from 5 µm to 950 µm, and the diameter of iron powder particles can range from 10 µm to 1000 µm.

[0115] When the diameter of iron powder particles exceeds 1000 µm, it is difficult to form a uniform bond from the surface to the center of the iron powder. When the diameter of iron powder particles is less than 10 µm, it is difficult to separate the iron-boron bond powder formed during boronization from the remaining boron source material powder.

[0116] Furthermore, an active agent may be added to the mixed powder 40 containing the iron powder and the boron source material in the retort 10 to allow the iron powder to react with the boron source material. The active agent may lower the reaction temperature of the iron powder and the boron source material to further activate the reaction between iron and boron. The active agent may contain at least one of Na3AlF6, KBF4, AlF3, NaCl, NaF, CaF2, and NH4Cl.

[0117] When the iron powder, the boron source material in powder form and the active agent are mixed to form a mixture, an amount of the boron source material may be in a range of 5 to 50 wt% in the mixture, and an amount of the active agent may be in a range of 0.5 to 10 wt% in the mixture.

[0118] Then, the retort 10 is rotated and heated using the heating unit 22 of the furnace assembly 20.

[0119] When the furnace assembly 20 is not coupled to the outer peripheral surface of the retort 10, the furnace assembly 20 is moved and then coupled to the outer peripheral surface of the retort 10, and then the first and second heating units 20a and 20b of the furnace assembly 20 are controlled to heat the retort 10.

[0120] When the furnace assembly 20 includes the first partial furnace assembly 20a and the second partial furnace assembly 20b, which are arranged above and below the retort 10, respectively, as shown in Fig.2, the first partial furnace assembly and the second partial furnace assembly 20a and 20b are moved so as to be coupled to the outer peripheral surface of the retort 10.

[0121] Since the retort 10 rotates during heating, as in Fig. 1, the powder particles in the mixed powder 40 are evenly mixed, and the heat introduced by the heating unit 22 is evenly supplied to the mixed powder 40.

[0122] As described above, the retort 10 is heated, and the iron powder reacts with the boron source material powder in the mixed powder 40 loaded into the retort 10, thereby borating the iron powder. The boron supplied from the boron source material can diffuse from the surface into the interior of the iron powder according to the second law of diffusion.

[0123] When the concentration of boron diffused into iron powder is low, a diffusion layer containing boron moves into the iron, forming a solid iron-boron solution. However, when the boron concentration increases, an iron-boron compound, such as FeB or Fe2B, can be formed due to the reaction between iron and boron.

[0124] Accordingly, during boronizing, the iron powder may have different regions in a direction from its surface inwards, depending on the concentration of boron, as in Fig. 4. For example, the iron powder has three regions containing a FeB layer 41, a Fe2B layer 42 and a layer 43 of a solid iron-boron solution, as in Fig. 4A. For example, the iron powder has two regions containing an Fe2B layer 42 and a boron solid solution layer 43, as shown in Fig.4B. For example, the iron powder has a region containing a FeB or Fe2B compound 44, as shown in Fig. 4C.

[0125] A thickness x of the compound layer can depend on a treatment temperature and time according to the following second diffusion law (Equation 1). Here, "x" indicates the thickness of the compound layer, "t" indicates a processing time, and "D" indicates a diffusion coefficient. x=(Dt)1 / 2

[0126] As described above, when iron contains other alloying elements, the diffusion rate of boron decreases, the formation of FeB or Fe2B is suppressed, and it is difficult to form a compound uniformly from the surface to the center of the powder. If the diameter of the iron powder particles is too large, it is difficult to evenly convert all the iron powder into the compound. Accordingly, from this perspective, the iron powder particles can be pure iron powder with a diameter of 1000 μm or less.

[0127] The treatment temperature can be kept at least 850 °C for boronizing iron. The treatment temperature can be kept lower than the lowest melting point of the iron-boron alloy, i.e., 1177 °C, to prevent the formation of a layer of liquid iron-boron compound during boronizing. The treatment temperature can be, for example, 1050 °C or lower.

[0128] The treatment time can range from 30 minutes to 600 minutes. If the treatment time is shorter than 30 minutes, the iron powder may not be sufficiently boronized. If the treatment time is longer than 600 minutes, the boronization may reach its saturation point, and thus further boronization may be unnecessary.

[0129] When the boronization of the iron powder in the retort 10 is completed, the furnace assembly 20 is separated and removed from the outer peripheral surface of the retort 10. Due to the removal of the furnace assembly 20, the heating unit 22 used to heat the retort 10 is removed, and accordingly, the retort 10 can begin to cool naturally. Since the retort 10 continues to rotate, the powder in the retort 10 can be cooled evenly.

[0130] After the retort 10 has cooled sufficiently, the powder mixture containing the iron-boron compound powder is discharged from the retort 10.

[0131] The powder mixture may contain iron-boron compound powder formed by reacting the iron powder and the boron source material powder, the remaining source powder, and the active agent powder. Accordingly, a separation process may be performed to separate the powder mixture into iron-boron compound powder and the other powders. The separation process may be performed using, for example, a sieve to separate the iron-boron compound powder and the other powders from the powder mixture.

[0132] As another alternative for producing the iron-boron compound powder, boron feed gas can be used as the boron source material instead of a solid-phase powder. The boron feed gas is the gas used to supply boron for reacting with the iron powder and can include boron gas or boron compound gas.

[0133] The boron compound gas may include any of B2H6, BF3, BCl3, BI3, BBr3, (CH3)3B and (C2H5)3B.

[0134] Iron powder is loaded into the retort 10 as source material 40. Then, the retort 10 is heated to a predetermined temperature using the furnace assembly 20. While maintaining the temperature within a predetermined temperature range, for example, 850°C to 1050°C, boron feed gas is introduced into the retort 10. The retort 10 can be rotated to allow the iron powder and the boron feed gas to react evenly with each other.

[0135] The boron feed gas can be supplied to the retort 10 through a gas pipe (not shown) extending from a gas reservoir (not shown) into the interior of the retort 10. The boron feed gas can be supplied in the form of a mixed gas prepared by mixing it with a carrier gas. The amount of the boron feed gas can range from 2 vol% to 40 vol%, based on the mixed gas.

[0136] When the reaction between the iron powder and the boron feed gas in the retort 10 is completed, the supply of boron feed gas is stopped, and then the furnace assembly 20 is separated from the retort 10 to cool the retort 10. To achieve uniform cooling, the retort 10 may rotate.

[0137] After cooling is complete, the iron-boron compound powder produced by the reaction with iron powder is discharged from the retort 10. The boron source material is supplied in the form of gas; the separation process for separating the iron-boron compound powder from other remaining powder does not need to be further performed. [Experiment Example 1]

[0138] Iron powder with an average particle size of 80 mesh to 100 mesh (180 to 150 µm) was mixed with boron carbide powder (B4C) with an average particle size of 120 mesh (125 µm) or less, which served as a boron source material, and Na3AlF6 powder, which served as an active agent, to produce a mixed powder. The amount of boron carbide powder was 10 wt%, and the amount of Na3AlF6 powder was 1 wt% in the mixed powder.

[0139] The mixed powder was introduced into the retort 10 of the device 100 of Fig.1, and then the retort 100 was heated to a temperature of 950 °C for 3 hours to boronize iron powder. During heating, the retort 10 rotated at 50 min -1 .

[0140] When the boronizing was completed, the furnace structure 20 was separated from the outer peripheral surface of the retort 10, and then the retort 10 was cooled while rotating, as shown in Fig. 3. After cooling was completed, the powder mixture was discharged from the retort 10 and then sieved to separate the powder mixture into the iron-boron compound powder obtained from boronizing and the remaining boron carbide powder.

[0141] Fig. Figure 5 shows a sectional view of the iron-boron compound powder prepared according to the present experimental example. Referring to Fig. 5 it is confirmed that the powder is formed from an iron-boron compound. Fig. Figure 6 shows X-ray diffraction results of the powder, and with reference to Fig. 6 it is confirmed that the powder is formed from Fe2B as an iron-boron compound.

[0142] The hardness of the powder was measured using a Vickers hardness tester (weight 20 g). The achieved hardness value is up to HV 1650.

[0143] The following is in connection with Fig. 7 and Fig. 8 Deboration according to an embodiment of the present invention is described.

[0144] Fig. 7 is a schematic diagram showing a boron-iron alloy powder 400 and a target powder 410 in contact with each other in the mixed powder before deboring.

[0145] The target powder 410 may be any of various metallic elements that have affinity for boron and are combined with boron to form a boron compound. Such a metallic element may, for example, be at least one selected from the group consisting of iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si), and tungsten (W).

[0146] With reference to Fig.7, when the mixed powder in which the boron-iron alloy powder 400 is in contact with the target powder 410 is heated to a predetermined temperature, the boron from the boron-iron alloy powder 400 can diffuse into the target powder 410, thereby borating the target powder 410 due to a chemical reaction. Accordingly, the boron-iron alloy powder 400 is deborated to reduce the boron content therein, but the boron content in the target powder 410 can increase due to the addition of boron.

[0147] The deboronization of the boron-iron alloy powder 400 may start from the surface of the boron-iron alloy powder 400, and the increase in the boron content of the target powder 410 may also start from the surface of the target powder 410. Fig.8 illustrates, by way of example, a deborated region 420 of the boron-iron alloy powder 400 and a boron-containing region 430 of the target powder 410 formed during deboriding. The deboridated region 420 is a region of the boron-iron alloy powder 400 in which the boron content is reduced due to deboriding, and the boron-containing region 430 is a region of the target powder 410 in which the boron content is increased due to the addition of boron.

[0148] During deboriding, the deboridated region 420 formed on the surface of the boron-iron alloy powder 400 due to deboriding may have a lower melting point than before reducing the boron content. This is explained with reference to the iron (Fe)-boron (B) phase diagram of Fig. 10 explained.

[0149] With reference to the iron-boron phase diagram of Fig.10, the melting point of iron is 1538 °C, and the melting point of boron is 2092 °C. When 64 atom% boron is added to iron, the peritectic transformation can occur at a temperature of 1500 °C. When 17 atom% boron is added, the eutectic transformation can occur at a relatively low temperature of 1174 °C. Accordingly, when the boron content in the boron-iron alloy is reduced from 50 atom% to 17 atom%, the melting point of the boron-iron alloy can decrease from 1650 °C to 1174 °C.

[0150] For example, if the initial boron content of the boron-iron alloy powder 400 is 50 atomic%, and then the deborated region 420 with the boron content of 17 atomic% is formed on the surface of the boron-iron alloy powder 400 due to deboridation, the formation of the deborated region 420 can lead to a reduction in the melting point of the surface of the boron-iron alloy powder 400 from 1650°C to 1174°C. That is, the melting point temperature decreases by approximately 480°C.

[0151] As described above, the boron-iron alloy powder 400 is a boron source material for boronizing the target powder 410, and its melting point is also significantly lowered due to the deboriding caused by the release of boron.

[0152] The boron content of the boron-iron alloy powder in the powder mixture before deboriding may be 17 atomic% or more, and may, for example, range from 17 atomic% to 80 atomic%. Furthermore, after deboriding, the boron content of the boron-iron alloy powder in the powder mixture may range from 5 to 35 atomic%, and further range from 10 atomic% to 25 atomic%.

[0153] In addition, the boron-iron alloy powder 400 may further contain at least one of silicon (Si) or carbon (C), and in this case, due to the deboriding, the melting point of the boron-iron alloy powder 400 may be further lowered to below 1174°C. The Si content may be 5 wt% or less, and a C content may be 2 wt% or less.

[0154] In addition, the boronized region 430 formed on the surface of the target powder 410 may be either a region where the metal in the target powder 410 forms a solid solution with boron, or a boron compound layer formed by the reaction between boron and the metal in the target powder 410. For example, before deboriding, the target powder 410 in the mixed powder may be iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si), and tungsten (W), and boron compounds thereof may be FeB, TiB2, CrB2, ZrB2, HfB2, VB2, AlB 12 , SiB6, NiB, CoB, TaB2, Mo2B5, or W2B5. These boron compounds can have a high hardness value of HK 2000 or more.

[0155] For example, in the case where the target powder 410 is an iron powder (Fe), when the concentration of boron diffusing into the iron powder is low, a diffusion layer may be formed in which the iron forms a solid solution with boron in the borated region 430, and when the concentration of boron increases, FeB or Fe2B may be formed as an iron-boron compound due to the reaction between iron and boron.

[0156] For example, the iron powder, as in Fig. 9, during boronization from its surface inwards depending on the concentration of boron to layers of solid solution 430c, 430b and 430a ( Fig. 9A) of FeB-Fe2B-boron or to solid solution layers 430b and 430a ( Fig. 9B) of Fe2B-boron or to a compound layer 430d ( Fig. 9C).

[0157] A thickness x of the compound layer can depend on a treatment temperature and time according to the following second diffusion law (Equation 2). Here, "x" indicates the thickness of the compound layer, "t" indicates a processing time, and "D" indicates a diffusion coefficient. x=(Dt)1 / 2

[0158] For example, in the case where the target powder is iron powder, if the iron powder contains other alloying elements, the diffusion rate of boron decreases, the formation of FeB or Fe2B is suppressed, and it is difficult to form a compound uniformly from the surface to the center of the powder. If the diameter of the iron powder particles is too large, it is difficult to evenly convert all of the iron powder into the compound. Accordingly, from this aspect, the iron powder particles can be pure iron powder with a diameter of at most 1000 μm. Target powders other than iron powder described above may have a diameter of at most 1000 μm for the same reason and can be used in a pure state thereof. However, the present invention is not limited to this, and alloy powder to which other elements are added may be used as the target powder in consideration of purpose, cost, and other effects.

[0159] In addition, the melting point of the boronized region 430 of the target powder 410 may be lower than before boronization. For example, with reference to Fig. 10. When the target powder is pure iron powder, the target powder is boronized by the boron-iron alloy powder; its boron content increases from 0 to 17 atomic%, and thus the melting point of the target powder drops from 1538°C to a process temperature of 1174°C, the eutectic temperature. In addition, when the boronized region contains Fe2B as a boron compound, the melting point of the target powder is 1389°C, which is lower than the melting point of pure iron, which is 1538°C.

[0160] Accordingly, in this case, both the boron-iron alloy powder contained as a boron source material and the target powder subjected to boronizing, which are contained in the powder mixture before deboriding, have a lower melting point than before deboriding.

[0161] Accordingly, in the powder mixture subjected to deboriding, at least a portion of the boron-iron alloy powder has a deboridated region with a relatively low boron content due to the deboridation, and at least a portion of the target powder has a boronized region. Thus, the powder mixture subjected to deboridation is called a boron alloy powder mixture.

[0162] The deborated region with a relatively lower boron content has a relatively low melting point compared to a region that is not deborated and thus has a relatively high boron content.

[0163] The degree of deboration of the boron-iron alloy powder or the degree of boronization of the target powder may depend on the deboration conditions or the size of the boron-iron alloy powder and the target powder. That is, if deboration is carried out at high temperature for a sufficiently long time or the size of the boron-iron alloy powder and the target powder is small, the boron-iron alloy powder can be completely deborated, or the target powder can be completely boronized.

[0164] For example, if FeB as a boron-iron alloy powder is mixed with Cr powder and then deboridation is performed, a portion of the boron-iron alloy powder may be deboridated to Fe2B, or the boron-iron alloy powder may be completely deboridated to Fe2B due to deboridation. Similarly, the Cr powder may be partially or completely boronized to CrB due to boriding.

[0165] The deborated boron-iron alloy powder in the powder mixture can be directly used as a binder for binding the boron-iron target powder 410. That is, since the boron-iron alloy powder is mixed with the boron-iron alloy powder having a lower melting point due to deboration in the powder mixture, the powder mixture can be directly used to prepare a combined powder structure without separating the boron-iron target powder.

[0166] For example, when the powder mixture subjected to deboriding is heated to a temperature higher than the melting point of the boron-iron alloy powder, which is lowered due to the reduction in the boron content, at least a portion of the boron-iron alloy powder may melt to form a liquid phase, and the liquid phase may surround the boron-iron target powder particles, thereby combining them. In this case, the liquid phase formed by melting at least a portion of the boron-iron alloy powder surrounds the boron-iron target powder particles, thereby combining them.

[0167] As described above, due to the reduction in the boron content of the boron-iron alloy powder during deboriding, the melting point of the boron-iron alloy powder can be lowered to 1174°C, and then the heating temperature can be much lower than for the part of the boron-iron alloy powder that is not deboridated. When the liquid phase of the molten boron-iron alloy powder comes into contact with and envelops the target powder, the liquid phase solidifies; a combined powder structure is formed in which the target powder and the boron-iron alloy powder are combined.

[0168] The boron-containing region of the target powder can also be melted due to its lower melting point. In this case, the deborated region of the boron-iron alloy powder and the boron-containing region of the target powder are melted and fused together, thereby increasing the bonding force between the powders.

[0169] In some embodiments, while the deborated region of the boron-iron alloy powder is in contact with the boron-containing region of the target powder, the deborated region and the boron-containing region are combined together by sintering.

[0170] Accordingly, in the combined powder structure prepared as described above, at least a part of the boron-iron alloy powder having a deboridated region or at least a part of the target powder having a boron-containing region melts and solidifies to combine the deboridated region with the boron-containing region, or the deboridated region and the boron-containing region may be sintered to form a combined structure.

[0171] The deborated region of the boron-iron alloy powder forming the combined powder structure may be located on the surface of the boron-iron alloy powder. The boron-iron alloy powder may further contain at least one of Si and C, and in this case, the melting point of the boron-iron alloy powder may be further lowered when forming the combined powder structure.

[0172] In addition, the boron-containing region 430 formed on the surface of the target powder 410, which forms the combined powder structure, may be either a boron solid solution, which is a region of the target powder 410 where the metal in the target powder 410 forms a solid solution with boron, or a boron compound layer formed by the reaction between boron and the metal in the target powder 410. For example, before deboring, the target powder 410 in the mixed powder may contain at least one of iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si), and tungsten (W), and boron compounds thereof may be FeB, TiB2, CrB2, ZrB2, HfB2, VB2, AlB 12 , SiB6, NiB, CoB, TaB2, Mo2B5, or W2B5. These boron compounds can have a hardness value of up to HK 2000 or more.

[0173] According to another embodiment of the present invention, other powder may be added to the powder mixture subjected to deboriding to combine the other powder with at least one of the deboridated boron-iron alloy powder and the boron-containing target powder, thereby forming a combined powder structure.

[0174] The other powder may include pure metal powder, alloy powder, or ceramic powder. For example, the pure metal powder may be at least one selected from iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si), and tungsten (W).

[0175] The alloy powder of the other powder may contain a self-fusing alloy powder. The self-fusing alloy may be an alloy that is self-deoxidized or forms slag during melting, and representative examples of these may be a boron-containing nickel-based, silicon-containing nickel-based, cobalt-based, or iron-based alloy. When the self-fusing alloy powder is added, the wear resistance, oxidation resistance, and corrosion resistance properties can be improved.

[0176] Furthermore, the ceramic powder may contain at least one of a metal oxide, a metal carbide, a metal nitride, or a metal boride from the other powder. For example, the ceramic powder may be a nitride, carbide, boride, or oxide of iron (Fe), titanium (Ti), chromium (Cr), zirconium (Zr), hafnium (Hf), vanadium (V), tantalum (Ta), molybdenum (Mo), nickel (Ni), cobalt (Co), aluminum (Al), silicon (Si), and tungsten (W). When the combined powder structure is prepared by adding high-hardness ceramic powder, the mechanical properties, such as hardness or strength, of the combined powder structure can be further enhanced.

[0177] The target powder of the mixed powder can act as a high-hardness boride powder, as described above. The target powder of the mixed powder can be melted with the boron-iron alloy powder to allow the other powder to combine with the boron-iron alloy powder or the target powder. Accordingly, the other powder can also be combined with at least one of the deborated boron-iron alloy powder and the boron-iron target powder.

[0178] In some embodiments, a flux may be further added to the powder mixture to create a combined powder structure. An example of the flux is borax (Na2B4O7·10H2O).

[0179] The deboration of the powder mixture can be carried out with reference to Fig. 1 to 3 can be understood.

[0180] Below is the deboration of the powder mixture in connection with Fig. 1 to 3.

[0181] With reference to Fig.1 to 3, when using the reactor and apparatus 100 described above, the mixed powder 40 loaded into the retort 10 is heated to perform deboration of the boron-iron alloy powder of the mixed powder 40 and boronization of the target powder of the mixed powder 40. Furthermore, an active powder other than the boron-iron alloy powder and the target powder of the mixed powder 40 may be additionally loaded into the retort 10. The active agent may lower a reaction temperature of the boron-iron alloy powder and the target powder to promote thermochemical precipitation. The active agent may be provided in the form of powder and may contain at least one of Na3AlF6, KBF4, AlF3, NaCl, NaF, CaF2, and NH4Cl. The active agent may be contained in an amount of 0.5 to 20 wt% based on the mixed powder.

[0182] Furthermore, the active agent may be supplied in the form of a gas and may include at least one of HCl gas and CCl4 gas. The active agent gas may be introduced into the retort 10 through a gas tube (not shown) extending from an active agent gas reservoir (not shown) into the interior of the retort 10.

[0183] With reference to Fig.1, the mixed powder 40 of the boron-iron alloy powder and the target powder is first loaded into the retort 10. The boron-iron alloy powder and the target powder may be loaded separately and then mixed, or the boron-iron alloy powder and the target powder may be pre-mixed to form a mixed powder, and then the mixed powder is loaded into the retort 10. The amount of the boron-iron alloy powder may range from 5 wt% to 95 wt%, for example, 10 to 90 wt%, based on the mixed powder 40. In addition, the active agent powder as described above may be added to the mixed powder 40.

[0184] Then, the retort 10 is rotated and heated using the heating unit 22 of the furnace assembly 20. When the furnace assembly 20 is not coupled to the outer peripheral surface of the retort 10, the furnace assembly 20 is moved and then coupled to the outer peripheral surface of the retort 10, and then the first and second heating units 20a and 20b of the furnace assembly 20 are controlled to heat the retort 10.

[0185] When the furnace assembly 20 includes the first partial furnace assembly 20a and the second partial furnace assembly 20b, which are arranged above and below the retort 10, respectively, as shown in Fig. 3, the first partial furnace assembly and the second partial furnace assembly 20a and 20b are moved so as to be coupled to the outer peripheral surface of the retort 10.

[0186] Since the retort 10 rotates during heating, as in Fig.As shown in Figure 1, the powder particles in the mixed powder 40 are uniformly mixed, and the heat introduced by the heating unit 22 is evenly supplied to the mixed powder 40. When the retort 10 is heated, the target powder is boronized using the boron-iron alloy powder loaded into the retort 10.

[0187] The deboriding can be carried out in an antioxidant atmosphere. For this purpose, an inert gas, such as nitrogen or argon, can be introduced into the retort 10, or a reducing gas, such as hydrogen, can be introduced to form an antioxidant atmosphere. According to another embodiment of the present invention, a vacuum pump is used to evacuate the interior of the retort 10 to form the antioxidant atmosphere.

[0188] To prevent the formation of the liquid phase during deboriding, the deboriding temperature can be kept at a lower temperature than the melting point of the boron-iron alloy powder or the target powder. For example, if the target powder is iron powder, considering the lowering of the melting point of the boron-iron alloy powder due to deboriding during deboriding, the deboriding temperature can be kept below 1177°C, which is the lowest melting point of an iron-boron alloy. For example, the deboriding temperature can be 1050°C or lower.

[0189] The treatment time can range from 30 to 600 minutes. If the treatment time is shorter than 30 minutes, the target powder may not be sufficiently boronized. If the treatment time is longer than 600 minutes, boronization may reach its saturation point, and thus further boronization may be unnecessary.

[0190] Then, the furnace assembly 20 is removed from the outer peripheral surface of the retort 10. Due to the removal of the furnace assembly 20, the heating unit 22 used to heat the retort 10 is removed, and accordingly, the retort 10 can begin to cool naturally.

[0191] Since the retort 10 continues to rotate, the mixed powder 40 in the retort 10 can be cooled evenly. To achieve uniform cooling, the retort 10 can rotate during cooling. After the retort 10 has sufficiently cooled, the mixed powder 40, which is fully boronized or deborized, is discharged from the retort 10. Once the deborization is complete, a boron alloy powder mixture in which ferroboron containing the deborized region is mixed with the target powder containing the boronized region is formed from the mixed powder 40.

[0192] The boron alloy powder mixture is used as the source material for preparing the combined powder structure. That is, the mixed powder 40 exhibits very high hardness and excellent high-temperature oxidation and corrosion resistance properties, and can be used in forming coating layers of various mechanical parts that require such properties. Furthermore, due to the relative lowering of the melting point due to deboriding and boronizing, the heating temperature for producing the combined powder structure can be lowered, or the fusion property of the powders can be improved to produce a combined powder structure with stronger bonding force.

[0193] For example, the boron alloy powder mixture can be sintered or melted / solidified to produce a combined powder structure suitable for use in mechanical parts. Before heating, the powder mixture is placed in a mold with a predetermined shape and then heated to produce the combined powder structure. In some embodiments, the powder mixture placed in a mold can be further pressed using a press to produce a molded product. The molded product is heated to produce a combined powder structure with a predetermined shape. [Experiment Example 2]

[0194] 78 wt% of boron-iron alloy powder particles with a size of 30 mesh (600 µm) to 100 mesh (150 µm), 20 wt% of Cr powder with a size of 10 mesh (2000 µm), and 1 wt% each of KBF4 and AlF3 serving as the active agent were charged into a retort, and then the mixture was heated under rotation and then kept at a temperature of 950 °C for 3 hours to perform deboronization of the boron-iron alloy powder and boronization of Cr powder, followed by cooling.

[0195] Fig. 11 and Fig. 12 show X-ray diffraction results before and after deboriding and boronizing the powder mixture. With reference to Fig. 11 and Fig. 12, the powder mixture before deboriding and boronizing contains FeB and Cr, and after deboriding and boronizing, FeB powder is deboridated, and Cr powder is boronized, producing Fe2B and CrB, each having a relatively low melting point.

[0196] Fig. Figure 13 shows the sectional view of the deborated boron-iron alloy powder and ESMA analysis results of its composition. With reference to Fig. 13, it was confirmed that a deborated area (i.e., the deboration layer of Fig. 13) with a reduced boron content due to deboriding was formed on the surface of the boron-iron alloy powder.

[0197] Fig. Figure 14 shows the sectional view of borated Cr powder and ESMA results thereof, and with reference to this figure, it was confirmed that a borated region (i.e., the borated layer of Fig. 14) with an increased boron content was formed on the surface of the Cr powder due to boronization. [Experiment Example 3]

[0198] 90 wt% carbon steel shot peening waste and 10 wt% boron-iron alloy powder were mixed, and then the mixture was heated to deboride the ferroboron and boronize the shot peening waste, producing a mixed powder. 10 wt% borax (Na2B4O7·10H2O) as a flux was added to 90 wt% of the mixed powder, and then the resultant was loaded into a mold made of a carbonaceous material, followed by heating at a temperature of 1250°C for 10 minutes to produce a combined powder structure. Fig. Figure 15 shows the microstructure of the combined powder structure. With reference to Fig. 15, the microstructure contains an iron-boron compound (the white area of Fig. 15) and a structure that has solidified in the process (the black area of Fig.15). The combined powder structure was measured using the Rockwell hardness tester, and the result was a hardness value of HRA 78. [Experiment Example 4]

[0199] A 10 wt% boron-iron alloy powder was added to 90 wt% iron powder and then heated to produce a powder mixture containing boron-iron powder and deborated boron-iron alloy powder. 45 wt% of the powder mixture, 45 wt% self-fusing alloy powder (B26, manufactured by Polema), and 10 wt% borax flux (Na2B4O7·10H2O) were mixed. The mixture was then loaded into a mold, followed by heating to a temperature of 1250 °C for 10 minutes to produce a combined powder structure. Fig. Figure 16 shows the microstructure of the combined powder structure. With reference to Fig. 16, the microstructure contains an iron-boron compound (the white area of Fig.16) and a martensite structure (the black area of Fig. 16). The combined powder structure was measured using the Rockwell hardness tester, and a hardness value of it was HRA 82.

[0200] As described above, according to the present invention, a combination having a very high hardness can be achieved by using a relatively inexpensive alloying element, and thus parts to which it is applied can be used for a long period of time, and also the consumption of costly natural resources can be reduced.

[0201] As another example, the powder mixture may be loaded into a pipe (or a steel pipe), and then the pipe is heated under rotation to form a high-hardness coating layer formed from the combined powder structure on an inner surface of the pipe.

[0202] Fig.17 to 20 are sectional views of a steel pipe 500 according to an embodiment of the present invention. More specifically, Fig. 17 a sectional view of the steel tube 500 perpendicular to the x-direction. Fig. 18 to 20 are sectional views of the steel tube 500 perpendicular to the y-direction.

[0203] The following is based on Fig. 17 to 20, a method of manufacturing the steel pipe 500 according to an embodiment of the present invention is described, according to an embodiment of the present invention.

[0204] Fig.17 is a schematic view of the steel pipe 500 for manufacturing a steel pipe on which a coating layer is formed according to an embodiment of the present invention. The steel pipe 500 may be rotated and heated using a heating unit (not shown) before the mixed powder is loaded thereinto. According to another embodiment of the present invention, a mixed powder 600 may be pre-injected into the steel pipe 500 before heating, and the mixed powder 600 may include a boron-iron alloy powder having at least a portion containing a deborated region and a target powder having at least a portion containing a boronized region.

[0205] In some embodiments, the boron-iron alloy powder may not contain the deborated region, and the target powder may not contain the boron-containing region. In some embodiments, only at least one of the boron-iron alloy powder and the target powder may not contain the deborated region or the boron-containing region. In this case, deboration of the boron-iron alloy powder and / or boron-containing the target powder may be performed in the steel tube.

[0206] For example, if the target powder does not contain the boron-containing region, when the target powder and the boron-iron alloy powder are heated while the target powder is in contact with the boron-iron alloy powder, boron (B) may diffuse from the boron-iron alloy powder into the target powder due to a chemical reaction to form a boron-containing region in the target powder. While the target powder is boron-containing to form a boron-containing region, the boron-iron alloy powder is deborated to form a deborated region. The formation of the boron-containing region and the deborated region leads to a lowering of the melting points of the boron-iron alloy powder and the target powder. The powder mixture 600 containing the boron-iron alloy powder with the deborated region and the target powder with the boron-containing region can be used directly without separating the boron-containing target powder.

[0207] The steel pipe 500 may have a hollow cylindrical pipe shape, and when heated under rotation using the heating unit (not shown), the powder mixture 600 may be partially or completely melted to form a molten layer 603 in a liquid phase, and the molten layer 603 may be applied to the inner surface of the steel pipe 500 due to a centrifugal force of the rotating steel pipe 500, as shown in Fig. 19, and then the molten layer 603 solidifies upon cooling to form a coating layer 605 in the steel pipe 500. Based on the powder mixture 600, an amount of the boron-iron alloy powder may range from 5 wt% to 95 wt%, for example, 10 wt% to 90 wt%. Average particle sizes of the boron-iron alloy powder and the target powder may range from 200 mesh (75 µm) to 20 mesh (850 µm) by ASTM standard sieves.

[0208] The powder mixture in the steel tube 500 may further contain, in addition to the boron-iron alloy powder and the target powder, chromium-iron alloy powder and / or a flux. The flux can prevent oxidation of the powder mixture upon exposure to the atmosphere and can also improve the flowability of the powder mixture. The flux may contain at least one of Na2B4O7, NaSiO3, NaHCO3, H3BO3, B2O3, CaSi, CaO, 3NaF, and AlF3. The chromium-iron alloy powder may contain 2 wt% or more of carbon and 50 wt% or more of chromium. The chromium-iron alloy powder consists of chromium, which is a main component, along with iron and carbon, is inexpensive, and has a specific gravity similar to that of the low-melting-point boron-iron alloy powder. Accordingly, the chromium-iron alloy powder can be uniformly dispersed during casting, such as sintering or centrifugal casting.

[0209] In addition, the low-melting point boron-iron alloy powder can be produced by deborizing boron-iron alloy powder, and the low-melting point target powder can contain iron powder, which is inexpensive. Furthermore, the low-melting point target powder can be replaced with a structure made by boronizing shot peening waste and chips. A layer or coating layer formed as above can form a passive layer due to the high concentration of chromium, achieving a hardness of up to HV 1200. The resulting steel pipe can also exhibit wear resistance, corrosion resistance, and excellent high-temperature oxidation resistance. Furthermore, since a waste material is used as the source material, conservation of natural resources and prevention of environmental pollution can be achieved.

[0210] In the powder mixture containing the chromium-iron alloy powder, the amount of the chromium-iron alloy powder can range from 5 wt% to 95 wt%, and the chromium-iron alloy powder can contain at least one of iron, chromium, silicon, and carbon. The average particle size of the chromium-iron alloy powder particles can range from 200 mesh (75 µm) to 4 mesh (850 µm), as evaluated based on ASTM standard sieves.

[0211] After the powder mixture 600 is provided in the steel tube 500, the ends of the steel tube 500 are covered using a cover member (not shown), and then the steel tube 500 is rotated and heated. The rotational speed of the steel tube 500 can be determined according to Equation 3 below. Speed=[G×107 / 5.6×inner diameter of the steel pipe(mm)]1 / 2 where G can be obtained using the following equation 4: G=Centrifugal force / Gravity=5.6×10−7×Inner diameter of the steel pipe (mm)×(Speed)(min−1))2

[0212] The rotational speed applied when forming a coating layer according to an embodiment of the present invention can vary within 5 G to 120 G, depending on the composition ratio of the powder mixture. If the centrifugal force is 5 times or less of the acceleration due to gravity, the centrifugal force is insufficient to perform proper centrifugal casting, and if the centrifugal force is 120 times or more of the acceleration due to gravity, excessive force is unnecessarily applied.

[0213] Then, the powder mixture 600 in the steel pipe 500 may be heated to a temperature higher than the melting point of the powder mixture 600 to form the coating layer 605 with high hardness. To form the coating layer 605, the powder mixture 600 may be melted and then solidified. First, to melt the powder mixture 600, a heating element such as a fuel gas heater, an electric resistance heater, or a high-frequency induction heater may be used. The heating element may be any of various heating elements that generate heat for the outer peripheral surface of the steel pipe 500. The heating temperature may be lower than the melting point of the steel pipe 500, for example, in a range of 1000°C to 1500°C.

[0214] When the steel pipe 500 is rotated and heated, the powders of the powder mixture 600 can be evenly mixed, and the heat supplied by using the heating element can also be evenly supplied to the powder mixture 600. When the powder mixture 600 is heated above its melting point, the powder mixture 600 can be partially or completely melted, and thus the molten layer 603 is formed on the inner surface of the steel pipe 500. The liquid phase formed by melting at least one of the boron-iron alloy powder can surround the boron-containing target powder to allow the target powder particles to combine with each other. In some embodiments, at least one of the target powder can be melted to increase a bonding force between the target powder and the boron-iron alloy powder.

[0215] Fig.21 is a schematic view illustrating a method of forming the steel pipe according to an embodiment of the present invention.

[0216] With reference to Fig. 21, a high-frequency induction heater may be used as a heating element for forming the coating layer 605 in the steel pipe 500. A high-frequency induction heater 700 may be surrounded by coils, and at least one high-frequency induction heater 700 may enclose at least a portion of the outer peripheral surface of the steel pipe.

[0217] For example, one high-frequency induction heater is arranged on one side of the steel pipe 500 in the +z direction, and the other high-frequency induction heater is arranged on the opposite side, that is, the -z direction, so that the high-frequency induction heaters face each other. According to another embodiment of the present invention, the high-frequency induction heater 700 may be integrally arranged along the entire outer peripheral surface of the steel pipe 500 in its circumferential direction. According to another embodiment of the present invention, a plurality of high-frequency induction heaters 700 may be arranged spaced apart from each other along the outer peripheral surface of the steel pipe 500 in its circumferential direction. The high-frequency induction heaters 700 may supply heat locally and may be connected to a movable unit (not shown) and movable in the ±y directions, which is a longitudinal direction of the steel pipe 500.

[0218] In such a method, in which the high-frequency induction heater 700 is used as a heating unit to form the coating layer 605 in the steel pipe 500, a mixed powder 600 containing a boron-iron alloy powder, a target powder, and at least one of a chromium-iron alloy powder and a flux is first loaded into the steel pipe 500. The mixed powder 600 can be uniformly loaded in the ±y directions of the steel pipe 500.

[0219] The steel tube 500 may be rotatable and may be rotated before or after feeding the powder mixture 600. If the powder mixture 600 is evenly mixed while the steel tube 500 rotates, the steel tube 500 may be locally heated while the high-frequency induction heaters 700 are moved from one side of the steel tube 500 (+y direction) to the other side (-y direction). In this case, the high-frequency induction heaters 700 may have a frequency of 300 Hz to 5 kHz and may apply electrical energy to coils to heat the powder mixture 600 to a melting point, i.e., from 1000°C to 1500°C.

[0220] A view of a section along a line I - I of Fig. 21 is in Fig. 18, and a view of a section along a line II - II of Fig. 21 is in Fig. 19 shown.

[0221] As shown in the drawing, due to the rotation of the steel pipe 500, the powders of the powder mixture 600 can be uniformly mixed in the steel pipe 500 and thereby settle. When high-frequency induction heating is performed thereon, at least a portion of the powder mixture 600 in the steel pipe 500, corresponding to at least a portion of the steel pipe 500 near the heating unit, can be locally heated and melted to form the molten layer 603, at least a portion of which has a liquid phase on the steel pipe 500. The molten layer 603 can be applied to the inner surface of the steel pipe 500 when the steel pipe 500 rotates, and a portion of the molten layer 603 that has passed through the high-frequency induction heaters 700 can solidify to form the coating layer 605.

[0222] Unlike the local heating for forming the coating layer 605 described above, the steel pipe 500 may be fully heated to melt the powder mixture 600. Then, when the powders are partially or completely melted to combine with each other, the heating of the steel pipe 500 may be stopped, or a heating element may be removed, and thus the steel pipe 500 is naturally cooled. If the cooling is performed while the steel pipe 500 is rotating, a portion of the powder mixture 600 that is in direct contact with the steel pipe 500 may begin to solidify, and a portion of the powder mixture 600 that is farthest from the steel pipe 500 may finally solidify, thereby forming the coating layer 605 with high hardness. A separate cooling device (not shown) may be used to rapidly solidify metal.

[0223] In addition, in order to improve wear, lubrication and oxidation properties, the powder mixture 600 may be partially or completely melted when forming the coating layer 605, and the molten metal is provided in the steel pipe 500 and melted by heating and then cooled under rotation.

[0224] The coating layer 605 formed from the iron-boron alloy prepared as described above can exhibit a low melting point and high wettability. Furthermore, there is no need to further add various elements to achieve such properties. Examples of such added elements are tungsten carbide (WC), vanadium (V), cobalt (Co), molybdenum (Mo), nickel (Ni), boron (B), silicon (Si), and carbon (C). Accordingly, no additional cost is incurred, and at the same time, high hardenability can be achieved, and thus very high hardness and strength can be achieved without separate heat treatment.In addition, since the melting point of the mixed powder 600 is relatively lowered due to deboriding and boronizing, the coating layer 605 can be formed at a lower temperature, and due to the increase in the fusion property between powders, a formed combined powder structure can have a stronger bonding force.

[0225] Fig. 20 is a sectional view of the steel pipe 500 according to an embodiment of the present invention, which is perpendicular to a y-direction. The steel pipe 500 according to the present embodiment of the present invention is used in conjunction with Fig. 20 described in detail.

[0226] On the steel pipe 500, as described above, a boron-iron alloy powder having at least a portion containing a deborated region and a target powder having at least a portion containing a boron-containing region are melted and solidified to form the coating layer 605. The coating layer 605 may be formed such that the boron-iron alloy powder acting as a matrix metal or binder and having at least a portion containing a deborated region and the target powder having at least a portion containing a boron-containing region are melted by heating and then cooled to solidify. At least a portion of the boron-iron alloy powder is melted to come into direct contact with and envelop the target powder.

[0227] The coating layer 605 disposed on the inner surface of the steel pipe 500 may further contain pelletized chromium-iron alloy as a reinforcing agent. Due to the inclusion of chromium-iron alloy, high hardness can be achieved, and because chromium has excellent wear-resistant properties and a high concentration, a passive layer can be achieved. Since chromium has a specific gravity similar to that of boron-iron alloy powder, chromium can be evenly dispersed in the coating layer; excellent corrosion resistance and high-temperature oxidation properties can be achieved, effectively preventing wear caused, for example, by gravel and sand from liquid concrete transported under high pressure in the steel pipe.

[0228] The reinforcing agent may contain 10 wt% to 80 wt% chromium, 2 wt% to 10 wt% carbon, and 2.5 wt% or less silicon and iron (as a supplementary balance), and the binder may contain 5 atomic% to 35 atomic% boron. The binder may contain iron and boron, and the reinforcing agent may contain at least one of iron, chromium, silicon, and carbon.

[0229] As described above, a material for forming a coating layer with wear-resistant properties applied to the inner surface of a steel pipe may be at least one of iron, chromium, silicon, carbon, and boron. For example, the coating layer may contain 10 wt% or less of boron, 60 wt% or less of chromium, 10 wt% or less of carbon, and 2.5% or less of silicon.

[0230] In addition, the boron content of the coating layer may be 10 wt% or less (more than 0). Due to the inclusion of boron, the melting point of the binder may be lowered and its hardness may be increased. However, if the boron content exceeds 10 wt%, bubbles may form in a coating layer during melting and solidification, and a boron compound may be formed, thus increasing the brittleness of the coating layer.

[0231] Due to the inclusion of boron in the coating layer, high hardness, wear resistance, corrosion resistance, and excellent high-temperature oxidation properties can be achieved. However, if the amount of chromium exceeds 60 wt%, the composition ratio of the binder decreases, resulting in a reduction in molten bond strength. In addition, if a large amount of chromium is added, brittleness may be generated, and at the same time, the increase in hardness may be reduced. Accordingly, chromium can be used in an amount of 60 wt% or less.

[0232] Carbon can be added to the coating layer to lower the melting point of the coating layer and form a chromium carbide to achieve high hardness, that is, excellent wear resistance properties.

[0233] If the amount of carbon exceeds 10 wt%, its effects are negligible. Accordingly, carbon can be added in an amount of 10 wt% or less (more than 0). Furthermore, the amount of silicon added to the coating layer can be 2.5 wt% or less (more than 0). When silicon has such an amount, the melting point can be lowered, and deoxidation effects can be achieved without reducing mechanical properties.

[0234] Experimental examples are provided below to aid in understanding the present invention. However, the experimental examples are provided here for illustrative purposes only, and the present invention is not limited thereto. [Experiment Example 5]

[0235] Table 1 shows chemical components and hardness of a coating layer according to a mixing ratio of powders used for manufacturing a steel pipe according to an embodiment of the present invention. [Table 1] coating layer Powder mixture (wt%) Chemical components of the coating layer Hardness (HV) Boron (B) surface n-alloy shot peening waste Boron (B) surface alloyed pure iron powder Fe-Cr Cr Si B C Fe Sample 1 100 - - 0,25 1,85 0,42 rest 950 Sample 2 75 25 14,5 0, 74 1,45 2,45 rest 1000 Sample 3 50 50 28,5 1,45 0, 94 4,55 rest 1200 Sample 4 25 75 39,5 2,25 0,55 5,52 rest 1200 Sample 5 - 100 - 0,2 1,75 0, 18 rest 875 Sample 6 - 75 25 13,5 0,55 1,25 2,25 rest 985 Sample 7 - 50 50 29,5 0,35 0,85 4,25 rest 1150 Sample 8 - 25 75 40,5 2,15 0,65 4,95 rest 1100

[0236] Referring to Table 1, samples 1 to 4, which are boron (B) surface-alloyed shot peening waste, were prepared by mixing 10 wt% of a boron-iron alloy powder and 90 wt% of shot peening waste, followed by boronizing and deboriding at a temperature of 950 °C for 3 hours, and samples 5 to 8, which are boron surface-alloyed pure iron powder, were prepared by mixing 10 wt% of the boron-iron alloy powder and 90 wt% of pure iron powder, followed by boronizing and deboriding at a temperature of 950 °C for 3 hours.

[0237] Sample 1 is a coating layer formed using the boron (B) surface-alloyed shot peening waste, and Samples 2 to 4 are coating layers formed at mixing ratios of the boron (B) surface-alloyed shot peening waste and the chromium-iron alloy powder of 3:1, 1:1, and 1:3, respectively, as shown in Table 1. Sample 5 is a coating layer formed using boron (B) surface-alloyed pure iron powder, and similarly, Samples 6 to 8 are coating layers formed at mixing ratios of the boron (B) surface-alloyed pure iron powder and chromium-iron alloy powder of 3:1, 1:1, and 1:3, respectively, as shown in Table 1. Samples 1 to 4 and samples 5 to 8 were all prepared by melt heating using an induction heater while rotating at 30 G at a temperature of 1250 °C, followed by solidification.

[0238] Fig.22 shows a picture of a section through a steel pipe with a coating layer formed therein, and as in Fig. 25, it was confirmed that a coating layer (dark gray) was formed in a steel pipe (gray).

[0239] Referring to Table 1, the hardness of samples 1 to 8 was always very high at HV 800 to HV 1200, and due to the inclusion of chromium-iron alloy powder, the hardness was further increased.

[0240] Fig. 23 to 25 are curves of the hardness of a cut through a coating layer formed in a steel pipe depending on an amount of the chromium-iron alloy powder, and Fig. 23 is a curve of sample 2, Fig. 24 is a curve of sample 3, and Fig. 25 is a curve of sample 4.

[0241] As shown in Table 1 and Fig.As shown in Figures 23 to 25, when 25 wt% chromium-iron alloy powder was added, the hardness was HV 1000, which is approximately 50% higher than when no chromium-iron alloy powder was added. When chromium-iron alloy powder was added at 50 wt%, the hardness was up to HV 1200, and even at 75 wt%, such a high hardness was achieved.

[0242] Fig. 26 to 28 show a microstructure of a coating layer formed in a steel pipe depending on an amount of chromium-iron alloy powder, and Fig. 26 shows the microstructure of sample 2, and Fig. Figure 27 shows the microstructure of sample 3. From these images, it was confirmed that chromium-iron alloy microparticles (light gray) were formed on a matrix. In addition, Fig.28 shows a microstructure of Sample 4. When chromium-iron alloy powder was added therein at an amount of 75 wt%, there were large chromium-iron alloy powder particles that were not dissolved. That is, due to the inclusion of chromium-iron alloy powder, the resulting structure has smaller particles, and due to the presence of molten chromium-iron alloy of high hardness, the hardness was increased.

[0243] The present invention is defined by the following claims.

Claims

[1] A method for producing a boron alloy powder mixture, the method comprising: Preparing a mixed powder containing a boron-iron alloy powder and a target powder; and heat-treating the mixed powder to form a boronized region in the target powder by boronizing at least a portion of the target powder and to form a deborized region in the boron-iron alloy powder by deborizing at least a portion of the boron-iron alloy powder, thereby lowering the melting point of the boron-iron alloy powder. [2] The method according to claim 1, wherein a boron content in the boron-iron alloy powder before deboring is 17 atomic% or more. [3] The method according to claim 1, wherein a boron content in the boron-iron alloy powder after deboring is in a range of 5 atomic% to 35 atomic%. [4] The method according to claim 3, wherein a boron content in the boron-iron alloy powder in the mixed powder after deboring is in a range of 10 atomic% to 25 atomic%. [5] The method of claim 1, wherein the target powder contains a metal that forms a solid solution with boron or that combines with boron to form a boron compound. [6] The method according to claim 5, wherein the metal is at least one selected from iron, titanium, chromium, zirconium, hafnium, vanadium, tantalum, molybdenum, nickel, cobalt, aluminum, silicon and tungsten. [7] The method according to claim 1, wherein a melting point of the boronized region in the target powder is lower than a melting point of the target powder before boronizing. [8] The method according to claim 1, wherein an amount of the boron-iron alloy powder in the mixed powder is in a range of 5 wt% to 95 wt%. [9] Boron alloy powder mixture comprising: a boron-iron alloy powder; and a target powder having at least one part in which a boronized region is formed, wherein the boron-iron alloy powder has at least a part in which a deborated region is formed by deborating the boron-iron alloy powder, wherein the deborated region has a lowered melting point caused by reducing a boron content due to the deboration. [10] The boron alloy powder mixture according to claim 9, wherein the boron-iron alloy powder further contains at least one selected from Si and C. [11] A boron alloy powder mixture according to claim 9, wherein the borated region is either a metal-boron solid solution or a boron compound of metal and boron. [12] The boron alloy powder mixture according to claim 11, wherein the metal is at least one selected from iron, titanium, chromium, zirconium, hafnium, vanadium, tantalum, molybdenum, nickel, cobalt, aluminum, silicon and tungsten. [13] The boron alloy powder mixture according to claim 11, wherein a melting point of the boronized region is lower than a melting point of the metal. [14] A method for producing a combined powder structure, the method comprising: Heating a mixed powder containing a deborated boron-iron alloy powder and a boron-containing target powder to a predetermined temperature to combine the deborated boron-iron alloy powder with the boron-containing target powder. [15] The method of claim 14, further comprising: Preparing a mixed powder containing a boron-iron alloy powder and a target powder, and Heat treating the mixed powder to boronize at least a portion of the target powder and deboronize at least a portion of the boron-iron alloy powder, thereby lowering a melting point of the boron-iron alloy powder. [16] The method of claim 14, further comprising: Adding other powder to the deborated boron-iron alloy powder and the boron-containing target powder to combine the other powder with at least one of the deborated boron-iron alloy powder and the boron-containing target powder. [17] The method according to claim 15, wherein a boron content of the boron-iron alloy powder before deboring is 17 atomic% or more. [18] The method according to claim 15, wherein a boron content in the boron-iron alloy powder in the mixed powder after deboring is in a range of 5 atomic% to 35 atomic%. [19] The method according to claim 18, wherein a boron content of the boron-iron alloy powder in the mixed powder after deboring is in a range of 10 atomic% to 25 atomic%. [20] The method of claim 14, wherein the target powder contains a metal that forms a solid solution with boron or that combines with boron to form a boron compound. [21] Combined powder structure comprising: a target powder having at least one part in which a boronized region is formed, and a boron-iron alloy powder having at least one part in which a deborated region is formed, wherein the boronized region and the deborated region combine with each other by melting and solidifying at least a part of at least one of the boronized region and the deborated region, or by sintering the boronized region and the deborated region. [22] The combined powder structure of claim 21, wherein the borated region is either a metal-boron solid solution or a boron compound of metal and boron, and wherein the metal is at least one selected from iron, titanium, chromium, zirconium, hafnium, vanadium, tantalum, molybdenum, nickel, cobalt, aluminum, silicon, and tungsten. [23] A method of manufacturing a steel pipe, the method comprising: Loading a powder mixture into a steel pipe, the powder mixture containing a boron-iron alloy powder having at least one portion in which a deborated region is formed, and a target powder having at least one portion in which a borated region is formed; and Melting the powder mixture loaded into the steel pipe by heating and then solidifying the powder mixture to form a coating layer on an inner surface of the steel pipe. [24] A method according to claim 23, wherein the melting and solidification of the powder mixture are carried out in such a way that the steel pipe with the powder mixture loaded therein is heated and cooled while rotating. [25] The method of claim 23, wherein loading the powder mixture into the steel tube comprises: Mixing a boron-iron alloy powder and a target powder; and Heat treating the mixture of the boron-iron alloy powder and the target powder to boronize at least a portion of the target powder to form the boronized region and simultaneously deborizing at least a portion of the boron-iron alloy powder to form the deborized region. [26] The method of claim 23, wherein the target powder contains at least one of iron, titanium, chromium, zirconium, hafnium, vanadium, tantalum, molybdenum, nickel, cobalt, aluminum, silicon and tungsten. [27] The method according to claim 23, wherein the mixed powder in the steel pipe further contains at least one of a chromium-iron alloy powder and a flux. [28] The method according to claim 27, wherein the chromium-iron alloy powder contains 2 wt% or more of carbon and 50 wt% or more of chromium. [29] The method according to claim 27, wherein an amount of the chromium-iron alloy powder in the powder mixture is in a range of 5 wt% to 95 wt%. [30] Steel pipe, comprising a coating layer on an inner surface of the steel pipe, wherein the coating layer has a solidified structure formed by melting and solidifying a boron-iron alloy powder and a target powder, wherein the boron-iron alloy powder acts as a matrix metal or as a binder and has at least one partial region in which a deborated region is formed, wherein the target powder has at least one partial region in which a boronized region is formed. [31] A steel pipe according to claim 30, wherein the coating layer further contains a chromium-iron alloy as a reinforcing agent. [32] A steel pipe according to claim 31, wherein the reinforcing agent contains iron, 10 wt% to 80 wt% chromium, 2 wt% to 10 wt% carbon and 2.5 wt% or less silicon. [33] A steel pipe according to claim 30, wherein the coating layer contains at least one selected from iron, chromium, silicon, carbon and boron. [34] A steel pipe according to claim 33, wherein a boron content of the coating layer is in a range of more than 0 wt% to 10 wt% or less. [35] A steel pipe according to claim 34, wherein a carbon content of the coating layer is in a range of more than 0 wt% to 10 wt% or less. [36] A steel pipe according to claim 33, wherein a chromium content of the coating layer is in a range of more than 0 wt% to 60 wt% or less.

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