Three-layer bimetallic wear-resistant pipe and its casting method

Abstract

The present application relates to centrifugal casting technical field, specifically disclose a three-layer bimetallic wear-resistant pipe and its casting method. The casting method comprises: the outer layer metal liquid and low melting point protective slag are passed into the pipe mold to carry out centrifugal casting, after pouring, when the temperature of low melting point protective slag is 1400~1500 DEG C, pouring intermediate transition layer metal liquid, pouring temperature is not lower than 1590 DEG C, after pouring, when the temperature of the surface of intermediate transition layer is 1400~1500 DEG C, pouring inner layer metal liquid, pouring temperature is 1420~1500 DEG C, cooling and solidification, obtain three-layer bimetallic wear-resistant pipe. The outer layer and intermediate transition layer of three-layer bimetallic wear-resistant pipe are metallurgical bonding, the inner layer and intermediate transition layer are non-metallurgical seamless bonding, two different bonding modes not only ensure the overall strength of wear-resistant pipe, but also effectively inhibit the crack propagation from the inner layer to the outer layer, compared with the traditional pipeline has higher service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of centrifugal casting, in particular to a three-layer bimetallic wear-resistant pipe and a casting method thereof. BACKGROUND

[0002] The inner layer of the bimetallic centrifugal casting composite pipe is composed of high-chromium cast iron with high wear resistance and corrosion resistance, and the outer layer is composed of alloy steel or low-carbon steel with high toughness. Compared with traditional single-metal pipes, the bimetallic centrifugal casting composite pipe has a longer service life because it has the advantages of high toughness, high wear resistance and high corrosion resistance, and has been widely used in the industry.

[0003] There are currently two main centrifugal casting production processes for bimetallic wear-resistant pipes. One is to use an outer hot-rolled steel pipe and pour high-chromium cast iron liquid into the hot-rolled steel pipe. This process produces a bimetallic wear-resistant pipe without bonding force between the inner and outer layers, and there is a large shrinkage gap between the two layers. The high-chromium cast iron inner layer cannot be protected by the outer steel pipe. The second is to use double-liquid centrifugal casting to produce metallurgical bonding between the two layers. The bimetallic wear-resistant pipe produced by double-liquid centrifugal casting has the following problems: (1) The metallurgical bonding between the inner and outer layers is the result of the mixing of the inner high-chromium cast iron liquid and the outer molten steel. Since the degree of mixing of the inner and outer layers cannot be easily controlled each time, the C and Cr content of the inner layer of different wear-resistant pipes varies greatly. Finally, under the same heat treatment system, the hardness of the high-chromium cast iron varies greatly, resulting in a large difference in wear resistance. (2) While the high-chromium cast iron is being heated for heat treatment, the outer layer is also in a high-temperature austenitizing state. Sometimes, the heating temperature of the high-chromium cast iron needs to reach 1100-1120℃ to achieve the best wear resistance. At this temperature, the outer layer will experience high-temperature overheating, resulting in coarse austenite grains and affecting the mechanical properties of the outer steel layer. 3) When the pipe end is welded with a flange, the welding heat will be transferred to the inner layer, causing thermal stress and cracks in the inner layer. 4) Due to the metallurgical bonding between the inner and outer layers, if the inner hard and brittle high-chromium cast iron produces cracks due to fluid impact, the cracks will extend to the outer layer under the action of fluid impact, thereby causing hidden dangers to the safe use of the wear-resistant pipe. Therefore, there is an urgent need to develop a new centrifugal casting method to improve the quality of bimetallic wear-resistant pipes, increase their service life, and meet the urgent needs of the industry for high-performance and low-cost bimetallic wear-resistant pipes. SUMMARY

[0004] In view of the problems of unstable quality and short service life of existing bimetallic wear-resistant pipes, the present application provides a three-layer bimetallic wear-resistant pipe and a casting method thereof.

[0005] To solve the above technical problems, the technical scheme provided by the embodiments of the present application is:

[0006] In a first aspect, the present application provides a three-layer bimetallic wear-resistant pipe, comprising an outer layer, an intermediate transition layer and an inner layer; wherein the outer layer and the intermediate transition layer are metallurgically combined, and the inner layer and the intermediate transition layer are non-metallurgically and seamlessly combined.

[0007] Compared with the prior art, the three-layer bimetallic wear-resistant pipe provided by the present application uses metallurgical combination between the outer layer and the intermediate transition layer, and the outer layer and the intermediate transition layer form firm chemical bonding through atomic mutual diffusion, which greatly enhances the overall strength of the pipe. During use, when the pipe is subjected to external force impact or internal pressure, the pipe can withstand higher pressure without deformation or rupture. In the alternating working conditions of high temperature heating and rapid cooling, the metallurgical combination can make the outer layer and the intermediate transition layer maintain good coordination during thermal expansion and contraction, and will not cause delamination due to thermal stress, thereby maintaining the stability of the pipe structure and ensuring long-term stable operation of the pipe.

[0008] The inner layer and the intermediate transition layer are non-metallurgically and seamlessly combined, which has certain unique advantages while ensuring the close adhesion of the inner layer and the intermediate layer. The inner layer usually directly contacts the wear medium. During long-term wear process, if the inner layer has local wear or micro cracks, since the non-metallurgical seamless combination is not as tightly connected at the atomic level as the metallurgical combination, the crack will encounter obstacles formed by different combination mechanisms when expanding to the intermediate transition layer. The special combination interface can absorb the energy of crack propagation, change the crack propagation direction, and make it difficult for the crack to quickly penetrate the inner layer and develop deeply into the intermediate transition layer. In addition, when the wear-resistant pipe is welded in subsequent application, the welding heat will be transferred from the outer layer to the inside. Since the intermediate transition layer and the inner layer of high chromium cast iron are seamlessly contacted, the thermal conductivity is much smaller than that of the mixed metallurgical combination. Therefore, the heat generated by the welding of the outer layer can be effectively prevented from being transferred to the inner layer in large quantities, thereby avoiding thermal stress cracks in the inner layer and further ensuring the integrity of the overall structure of the pipe, and greatly improving the service life of the pipe.

[0009] It should be noted that the non-metallurgical seamless combination in the present application refers to an interface without metallurgical combination, which is macroscopically seamless, not microscopically seamless. Metallurgical combination refers to the combination after the mixing of two metal liquids. The three-layer three-metal pipe is still defined as a bimetallic wear-resistant pipe in the present application, mainly because the present application still mainly utilizes the mechanical properties of the outer layer and the wear-resistant properties of the inner layer, and the intermediate layer is only designed to solve the drawbacks of the bimetallic wear-resistant pipe.

[0010] Further, the outer layer is low carbon steel or low alloy steel, the intermediate transition layer is pure iron, and the inner layer is high chromium cast iron.

[0011] The low carbon steel or low alloy steel has good toughness and higher strength, and can effectively bear the pressure applied inside or outside the pipeline as the outer layer component, and can prevent brittle fracture of the pipeline when the pipeline is impacted, vibrated or affected by low temperature environment, and can also make the wear-resistant pipe have good formability, facilitating subsequent processing and use; the intermediate transition layer is made of pure iron, which can form good metallurgical bonding between the intermediate layer and the outer layer, ensure the strength and stability of the bonding interface, and also can better match the inner layer high chromium cast iron, the high chromium cast iron contains a large amount of chromium element, the chromium element has a certain affinity to iron, and the pure iron can provide a suitable bonding basis for the high chromium cast iron, promote the non-metallurgical seamless bonding between the inner layer and the intermediate transition layer, and in addition, the plasticity of the pure iron is good, and even if part of the cracks are combined due to atomic diffusion to make the crack propagation, the pure iron is not sensitive to the crack, and can effectively prevent the crack propagation.

[0012] Further, the thickness of the transition layer is 2mm-3mm.

[0013] The suitable thickness can reasonably disperse the stress during the transmission from the outer layer to the inner layer. If the transition layer is too thin, the stress concentration phenomenon can be intensified, resulting in damage of the pipeline at the weak part; and if the transition layer is too thick, new stress problems can be generated in the transition layer itself.

[0014] In the second aspect, the application further provides a casting method of the three-layer bimetallic wear-resistant pipe, comprising the following steps:

[0015] Step a: melting according to the required components of each layer of the wear-resistant pipe to obtain an outer layer metal liquid, an intermediate transition layer metal liquid and an inner layer metal liquid;

[0016] Step b: introducing the outer layer metal liquid and the low-melting-point protective slag into a pipe mold for centrifugal casting, after the casting is completed, when the temperature of the low-melting-point protective slag is 1400-1500 DEG C, the intermediate transition layer metal liquid is poured, the pouring temperature is not less than 1590 DEG C, after the pouring is completed, when the temperature of the surface of the intermediate transition layer is 1400-1500 DEG C, the inner layer metal liquid is poured, the pouring temperature is 1420-1500 DEG C, and the three-layer bimetallic wear-resistant pipe is obtained after cooling and solidification.

[0017] The casting method of the three-layer bimetallic wear-resistant pipe provided by the application pours the intermediate transition layer metal liquid at a protective slag temperature of 1400-1500 DEG C. The main reason is that the protective slag is in a liquid state at this temperature, and the outer layer molten steel is in a state of just solidifying or not completely solidifying, and the pouring temperature of the intermediate transition layer metal source is relatively high (not less than 1590 DEG C), which can cause the outer layer surface to melt just after solidification, thereby causing metallurgical bonding between the outer layer and the intermediate transition layer. When the surface temperature of the intermediate transition layer is 1400-1500 DEG C, the inner layer metal liquid is poured. At this time, the pure iron of the intermediate transition layer has been solidified, and the pouring temperature of the inner layer metal liquid is not much different from the surface temperature of the intermediate transition layer. Therefore, after the inner layer metal liquid is poured and then enters the mold pipe and is heated by the intermediate transition layer, the unique heat exchange process causes the inner layer metal liquid not to mix with the transition layer, but to form a special non-metallurgical bonding state. The heating of the high-temperature solid-state transition layer to the inner layer metal liquid and the temperature reduction of the inner layer metal liquid to the transition layer interact with each other, thereby optimizing the performance of the bonding interface, ensuring that the inner layer and the transition layer are closely combined, avoiding performance degradation caused by excessive melting, and further improving the wear resistance of the inner layer of the pipe and the reliability of the overall structure.

[0018] Further, the low-melting-point protective slag has a melting point of 1200-1300 DEG C. The low-melting-point protective slag is added in an amount of 0.5-1.5% of the mass of the outer layer metal liquid.

[0019] Specifically, the chemical composition of the low-melting-point protective slag is as follows: CaO: 34.1%, SiO2: 29.8%, Al2O3: 2.51%, CaF2: 7.94%, Na2O: 14.57%, MgO: 2.51%, and BaO: 8.57%.

[0020] It should be noted that, during the pouring process, the temperature of the protective slag and the temperature of the surface of the intermediate transition layer, etc. can be measured by using a chemical outer high-temperature temperature gun.

[0021] In addition, inert gas is introduced into the pipe mold during the entire pouring process to protect the pouring. The inert gas can be nitrogen, argon, etc.

[0022] For example, the inner layer metal liquid and the outer layer metal liquid in the application can be poured by using the existing double ladle for centrifugal pouring, which can be seen from CN204194747U, and the pouring is performed from one end of the pipe mold. The intermediate transition layer is poured by using a single tundish for centrifugal pouring, and the pouring is performed from the other end of the pipe mold.

[0023] Further, before the outer layer metal liquid is discharged into the ladle, an alloy is added to the bottom of the ladle, the alloy is covered with low-melting-point protective slag, a deoxidizer is then added, the outer layer metal liquid is discharged, nitrogen gas is introduced into the bottom of the ladle for stirring after the discharging is completed, and then the pouring is performed.

[0024] When pouring the outer layer, the outer layer metal liquid and the protective slag are mixed and poured, when the outer layer metal liquid and the low-melting protective slag are poured into the pipe mold for centrifugal casting, under the action of centrifugal force, the liquid low-melting protective slag begins to float up, in this process, the protective slag purifies the outer layer molten steel in contact with it, removes impurities therein, and ensures the purity of the outer layer molten steel; with the progress of the centrifugal casting process, the intermediate transition layer pure iron metal liquid and the inner layer high-chromium cast iron metal liquid are poured in turn, in the whole pouring process, the low-melting protective slag remains liquid, and due to the continuous action of centrifugal force, it continuously floats up and penetrates through the transition layer and the inner layer metal liquid, and also purifies the transition layer pure iron metal liquid and the inner layer high-chromium cast iron metal liquid, removes impurities therein, and improves the purity of each layer of metal liquid, thereby laying a solid foundation for finally forming a high-quality three-layer double-metal wear-resistant pipe.

[0025] Further specifically, the alloy is VFe, TiFe and NbFe. Adding V, Ti and Nb to the outer layer metal liquid can form carbonitride to pin austenite crystals, avoiding overheating of the austenite grains. Covering the alloy surface with protective slag can improve the alloy yield, and after the molten steel is tapped, nitrogen gas is introduced into the ladle for stirring, which can increase the nitrogen content in the molten steel and promote the formation of nitrides while purifying the molten steel.

[0026] Further specifically, the deoxidizer is aluminum block.

[0027] Further, when pouring the outer layer metal liquid, aluminum wires are fed into the metal stream and melted with the stream.

[0028] When pouring the outer layer metal liquid, aluminum wires are fed into the stream, which can produce aluminum oxide in the molten steel, pin the grain boundaries after solidification, and avoid overheating of the outer layer steel in the subsequent heat treatment process.

[0029] Further, the pouring superheat of the outer layer metal liquid is not less than 70℃, the rotation speed of the pipe mold is not less than 100G, and the temperature of the pipe mold is 200℃-300℃.

[0030] Further, the pouring speed of the outer layer metal liquid and the intermediate transition layer metal liquid is not less than 15kg / s, and the pouring speed of the inner layer metal liquid is not less than 5kg / s.

[0031] Further, after cooling and solidification, the process further comprises the following steps: after the pipe blank is demolded, it is kept at 1100℃-1150℃ for 1.5h-2h, air-cooled, then heated to 240℃-260℃ and kept for 2h-3h, air-cooled, to obtain a three-layer double-metal wear-resistant pipe.

[0032] The three-layer bimetallic wear-resistant pipe provided by the application has metallurgical combination of the outer layer and the intermediate transition layer and non-metallurgical seamless combination of the inner layer and the intermediate transition layer, which jointly form an organic whole. When the pipe is subjected to complex working conditions, the two combination modes cooperate with each other, the metallurgical combined part guarantees the strength and stability of the whole pipe and resists external large stress, and the non-metallurgical seamless combined part mainly deals with the crack hidden danger caused by the inner layer wear and reduces the crack expansion risk through the unique combination characteristics. The two different combination modes improve the performance of the pipe in all directions through the synergistic effect, so that the three-layer bimetallic wear-resistant pipe can maintain a good working state under various harsh conditions, significantly prolongs the service life, and has higher reliability and economy compared with the traditional pipe. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a schematic diagram of the centrifugal casting device used in the embodiment of the application; wherein 1 is a pure iron melting furnace, 2 is a single tundish, 3 is a pipe mold, and 4 is a double tundish. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the application clearer and more apparent, the application will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0035] In order to better illustrate the application, the following embodiments are further illustrated by examples.

[0036] The chemical composition of the low-melting-point protective slag used in the following embodiments is as follows: CaO: 34.1%, SiO2: 29.8%, Al2O3: 2.51%, CaF2: 7.94%, Na2O: 14.57%, MgO: 2.51%, and BaO: 8.57%.

[0037] The schematic diagram of the centrifugal casting device used in the following embodiments is shown in Figure 1 The outer layer metal liquid and the inner layer metal liquid are poured at one end of the pipe mold, the double tundish 4 is used to guide the metal liquid into the pipe mold 3, the specific structure of the double tundish 4 is described in CN204194747U, and the intermediate transition layer metal liquid is poured at the other end of the pipe mold. Since the amount of the intermediate transition layer metal liquid is small, the pure iron melting furnace 1 is used for melting, and then the molten steel is discharged into the single tundish 2, and then guided into the pipe mold 3 for pouring. Nitrogen is introduced into the pipe mold 3 during the whole pouring process for protective pouring. The pouring ladle nozzle adopts the idea of CN208450598U, the baffle outlet blocks the air, the pipe mold outlet sends nitrogen into the pipe mold to discharge the air.

[0038] Example 1

[0039] The embodiment provides a casting method of a three-layer bimetallic wear-resistant pipe:

[0040] The wear-resistant pipe size is: pipe mold Φ300*3165mm, the outer layer thickness is 12mm, the intermediate transition layer thickness is 2-3mm, the inner layer thickness is 10mm, and the centrifugal wear-resistant pipe size is Φ293*3000mm.

[0041] S1, two intermediate frequency furnaces are used to melt outer layer raw materials and inner layer raw materials respectively, and another intermediate frequency furnace is used to melt industrial pure iron as intermediate transition layer metal liquid; the outer layer raw materials are 20Cr steel, bimetallic wear-resistant pipe waste pipe remelted materials, the inner layer raw materials are high-carbon chromium iron, pig iron, bimetallic wear-resistant pipe remelted materials and scrap steel;

[0042] S2, before tapping of the outer layer metal liquid, VFe, TiFe and NbFe alloys are added to the bottom of the ladle, low-melting-point protective slag is used to cover the alloys, the adding amount of the low-melting-point protective slag is 1.0% of the mass of the outer layer metal liquid, then aluminum block deoxidizers are added, the tapping is completed to the ladle, after the tapping is completed, nitrogen gas is introduced into the bottom of the ladle for stirring, the outer layer metal liquid is poured into the pipe mold through the backflow of the double tundish, aluminum wires are fed for stream melting during pouring, nitrogen gas protection is used in the pipe mold, the pipe mold temperature is 250℃ during pouring, the pipe mold rotating speed is not less than 100G, the outer layer metal liquid superheat degree is not less than 70℃, the pouring speed is not less than 15kg / s, and the outer layer pouring weight is 256kg;

[0043] S3, after the outer layer metal liquid pouring is completed, the pipe mold is withdrawn from the double tundish, the other end is inserted into the single tundish, the temperature is measured by using an infrared high-temperature temperature measuring gun, when the protective slag temperature is 1500℃, the transition layer pure iron metal liquid is poured at the other end of the pipe mold, the pouring temperature is not less than 1590℃, the superheat degree is not less than 70℃, the pipe mold rotating speed is not less than 100G, the pouring speed is not less than 15kg / s, and the pure iron metal liquid pouring weight is 50kg;

[0044] S4, after the transition layer metal liquid pouring is completed, the single tundish is withdrawn, the other tundish of the double tundish is inserted, the temperature is measured by using an infrared high-temperature temperature measuring gun, when the temperature of the transition layer surface is 1460℃, the inner layer metal liquid is poured, the pouring temperature is 1500℃, the pipe mold rotating speed is not less than 100G, the pouring speed is not less than 5kg / s, and the inner layer metal liquid pouring weight is 192kg;

[0045] S5, after the inner layer metal liquid is solidified, the pipe blank is pulled out of the pipe mold, is red-hot into the furnace, is kept at 1150℃ for 1.5h, is taken out of the furnace and air-cooled, then is remelted and heated to 250℃, is kept for 3h, is taken out of the furnace and air-cooled, and the three-layer bimetallic wear-resistant pipe is obtained.

[0046] Embodiment 2

[0047] The embodiment provides a casting method of a three-layer bimetallic wear-resistant pipe:

[0048] The wear-resistant tube size: tube mold Φ300x3165mm, outer layer thickness 12mm, intermediate transition layer thickness 2-3mm, inner layer thickness 10mm, centrifugal wear-resistant tube size Φ293x3000mm.

[0049] S1, melt the outer layer raw material and the inner layer raw material respectively by two intermediate frequency furnaces, melt industrial pure iron as the intermediate transition layer metal liquid by another intermediate frequency furnace; the outer layer raw material is 20Cr steel, double-metal wear-resistant tube waste tube back to the furnace material, the inner layer raw material is high-carbon chromium iron, pig iron, double-metal wear-resistant tube back to the furnace material and scrap steel;

[0050] S2, before tapping the outer layer metal liquid, add VFe, TiFe, NbFe alloy at the bottom of the ladle, cover the alloy with low-melting-point protective slag, the adding amount of low-melting-point protective slag is 0.5% of the mass of the outer layer metal liquid, then add aluminum block deoxidizer, tap into the ladle, after tapping, blow nitrogen gas into the bottom of the ladle to stir, pour the outer layer metal liquid into the tube mold by backflowing through the double tundish, feed aluminum wire during pouring to melt along the flow, use nitrogen gas to protect the tube mold, the tube mold temperature is 300℃ during pouring, the tube mold rotating speed is not less than 100G, the outer layer metal liquid superheat is not less than 70℃, the pouring speed is not less than 15kg / s, the outer layer pouring weight is 256kg;

[0051] S3, after the outer layer metal liquid pouring is completed, the tube mold is withdrawn from the double tundish, the other end is inserted into the single tundish, measure the temperature by infrared high-temperature temperature measuring gun, when the protective slag temperature is 1400℃, pour the transition layer pure iron metal liquid at the other end of the tube mold, the pouring temperature is not less than 1590℃, the superheat is not less than 70℃, the tube mold rotating speed is not less than 100G, the pouring speed is not less than 15kg / s, the pure iron metal liquid pouring weight is 50kg;

[0052] S4, after the transition layer metal liquid pouring is completed, withdraw from the single tundish, insert into the other ladle of the double tundish, measure the temperature by infrared high-temperature temperature measuring gun, when the transition layer surface temperature is 1400℃, pour the inner layer metal liquid, the pouring temperature is 1420℃, the tube mold rotating speed is not less than 100G, the pouring speed is not less than 5kg / s, the inner layer metal liquid pouring weight is 192kg;

[0053] S5, after the inner layer metal liquid solidifies, pull out the tube blank from the tube mold, red-hot into the furnace, keep at 1100℃ for 2h, take out and air cool, then back to the furnace to heat up to 260℃, keep for 2h, take out and air cool, obtain the three-layer double-metal wear-resistant tube.

[0054] Example 3

[0055] The embodiment provides a casting method of a three-layer double-metal wear-resistant tube:

[0056] The wear-resistant pipe size is: pipe mold Φ400*3165mm, outer layer thickness 15mm, transition layer thickness 2-3mm, inner layer thickness 10mm, and centrifugal wear-resistant pipe size is Φ390*3000mm.

[0057] S1, two intermediate frequency furnaces are used to melt outer layer raw materials and inner layer raw materials respectively, and another intermediate frequency furnace is used to melt industrial pure iron as intermediate transition layer metal liquid; the outer layer raw materials are 14Mn steel and scrap steel, and the inner layer raw materials are high-carbon chromium iron, pig iron, double-metal wear-resistant pipe remelted materials and scrap steel;

[0058] S2, before tapping of the outer layer metal liquid, VFe, TiFe and NbFe alloys are added to the bottom of the ladle, low-melting-point protective slag is used to cover the alloys, the adding amount of the low-melting-point protective slag is 1.5% of the mass of the outer layer metal liquid, then aluminum blocks are added as deoxidizers, the tapping is completed, nitrogen gas is introduced into the bottom of the ladle for stirring, the outer layer metal liquid is poured into the pipe mold through the counterflow of the double tundish, aluminum wires are fed for stream melting during pouring, nitrogen gas is used for protection in the pipe mold, the pipe mold temperature is 200℃ during pouring, the pipe mold rotating speed is not less than 100G, the outer layer metal liquid superheat degree is not less than 70℃, the pouring speed is not less than 15kg / s, and the outer layer pouring weight is 256kg;

[0059] S3, after the outer layer metal liquid pouring is completed, the pipe mold is withdrawn from the double tundish, and the other end is inserted into the single tundish, an infrared high-temperature temperature measuring gun is used for temperature measurement, when the protective slag temperature is 1450℃, the transition layer pure iron metal liquid is poured at the other end of the pipe mold, the pouring temperature is not less than 1590℃, the superheat degree is not less than 70℃, the pipe mold rotating speed is not less than 100G, the pouring speed is not less than 15kg / s, and the pure iron metal liquid pouring weight is 50kg;

[0060] S4, after the transition layer metal liquid pouring is completed, the single tundish is withdrawn, and the other tundish of the double tundish is inserted, an infrared high-temperature temperature measuring gun is used for temperature measurement, when the transition layer surface temperature is 1480℃, the inner layer metal liquid is poured, the pouring temperature is 1500℃, the pipe mold rotating speed is not less than 100G, the pouring speed is not less than 5kg / s, and the inner layer metal liquid pouring weight is 192kg;

[0061] S5, after the inner layer metal liquid is solidified, the pipe blank is pulled out of the pipe mold, and is red-hot into the furnace, is kept at 1130℃ for 2h, is taken out and air-cooled, then is reheated to 240℃, is kept for 3h, is taken out and air-cooled, and the three-layer double-metal wear-resistant pipe is obtained.

[0062] The casting method of the three-layer double-metal wear-resistant pipe provided by the embodiment has the following beneficial effects:

[0063] 1) Ensure the stability of the inner layer high chromium cast iron composition: the invention makes full use of the high melting point, plasticity and toughness, and crack insensitivity of the transition layer pure iron. Since the melting point of industrial pure iron is high, the pouring temperature is high, therefore, the transition layer can remelt the outer layer, while the inner layer molten iron cannot remelt the transition layer. In this way, the transition layer and the outer layer are mixed and metallurgically combined to become an integral whole, and the inner layer and the transition layer are combined through shrinkage and high temperature atomic diffusion, which belongs to interface seamless contact, and the binding force is weak, which ensures the stability of the inner layer high chromium cast iron composition, and makes good composition preparation for the consistency of hardness after heat treatment.

[0064] 2) Avoid overheating of the outer steel layer: the outer steel layer uses V, Nb, Ti carbonitride and microparticle alumina to pin the grain boundary, avoid austenite grain growth into coarse grains, and effectively prevent overheating of the outer steel layer.

[0065] 3) Good performance of the wear-resistant pipe: heat treatment not only homogenizes the inner layer high chromium cast iron, but also homogenizes the outer steel layer, improves the as-cast structure, and improves the performance of the wear-resistant pipe.

[0066] 4) Avoid welding thermal stress cracks: if the outer layer uses 16Mn or Q235A, the flange or clamp connection can be connected by welding. When the welding heat is transmitted to the inner layer, the transition layer and the inner layer are in seamless contact, and the thermal conductivity is much smaller than that of the mixed and metallurgically combined heat. When the outer layer is welded, the heat can be transmitted to the inner layer to avoid the generation of thermal stress cracks in the inner layer.

[0067] 5) Prevent the extension of the inner layer cracks to the outer layer: the transition layer and the inner layer belong to interface seamless contact, not mixed and metallurgically combined. The inner layer cracks stop at the interface, even if part of the cracks will expand due to the combination of atomic diffusion, but the transition layer pure iron has excellent plasticity and toughness, and is not sensitive to cracks, which can prevent the expansion of cracks.

[0068] 6) Long service life of the wear-resistant pipe: although the inner layer high chromium cast iron and the transition layer are not metallurgically combined, but the interface seamless contact is formed between them, the high chromium cast iron layer is still supported and protected by the outer layer and the transition layer. Even if cracks occur, they will not break and fall off, and can still work in a wear-resistant state.

[0069] The above only describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement or improvement made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A casting method for a three-layer bimetallic wear-resistant pipe, characterized in that, Includes the following steps: Step a: Melt according to the required composition of each layer of wear-resistant pipe material to obtain outer layer molten metal, intermediate transition layer molten metal and inner layer molten metal; Step b: The outer layer molten metal and low-melting-point protective slag are introduced into the mold for centrifugal casting. After casting, when the temperature of the low-melting-point protective slag is 1400℃~1500℃, the intermediate transition layer molten metal is poured at a temperature not lower than 1590℃. After casting, when the surface temperature of the intermediate transition layer is 1400℃~1500℃, the inner layer molten metal is poured at a temperature of 1420℃~1500℃. After cooling and solidification, a three-layer bimetallic wear-resistant pipe is obtained. The three-layer bimetallic wear-resistant tube includes an outer layer, an intermediate transition layer, and an inner layer; wherein the outer layer and the intermediate transition layer are metallurgically bonded, and the inner layer and the intermediate transition layer are non-metallurgically seamlessly bonded. The outer layer is made of low-carbon steel or low-alloy steel, the intermediate transition layer is made of pure iron, and the inner layer is made of high-chromium cast iron; the thickness of the outer layer is 12mm or 15mm, the thickness of the intermediate transition layer is 2-3mm, and the thickness of the inner layer is 10mm.

2. The casting method of the three-layer bimetallic wear-resistant tube as described in claim 1, characterized in that, Before the outer layer of molten metal is tapped into the ladle, an alloy is added to the bottom of the ladle and covered with a low-melting-point protective slag. Then, a deoxidizer is added, and the steel is tapped. After tapping, nitrogen gas is introduced into the bottom of the ladle for stirring, and then casting is performed.

3. The casting method of the three-layer bimetallic wear-resistant tube as described in claim 1, characterized in that, When the outer layer of molten metal is poured, aluminum wire is fed into the metal stream and melts with the flow.

4. The casting method of the three-layer bimetallic wear-resistant tube as described in claim 1, characterized in that, The superheat of the outer layer molten metal is not less than 70°C, the rotation speed of the mold is not less than 100G, and the temperature of the mold is 200°C to 300°C.

5. The casting method of the three-layer bimetallic wear-resistant tube as described in claim 1, characterized in that, The pouring speed of the outer layer molten metal and the intermediate transition layer molten metal is not less than 15 kg / s, and the pouring speed of the inner layer molten metal is not less than 5 kg / s.

6. The casting method of the three-layer bimetallic wear-resistant tube as described in claim 1, characterized in that, The cooling and solidification process further includes the following steps: after demolding the tube blank, it is kept at 1100℃~1150℃ for 1.5h~2h, then air-cooled, and then heated to 240℃~260℃ and kept at 2h~3h, then air-cooled to obtain a three-layer bimetallic wear-resistant tube.

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