Preparation method of bimetal composite seamless tube casting blank

Abstract

The invention discloses a preparation method of a bimetal composite seamless tube casting blank, which is characterized in that an outer-layer hollow material is used as a mold, an inner-layer solid material is solidified in the outer-layer hollow material, and the temperature of stainless steel or nickel-based alloy steel liquid is controlled to be 10-50 DEG C above the melting point of the outer layer. The outer layer is firstly heated to 600-700 DEG C in the solidification process, the temperature of the outer layer is controlled to 900-1050 DEG C in the solidification process, the hollow material wall part of the outer layer is melted and does not flow in the solidification process, and the inner layer and the outer layer are solidified and compounded to prepare the composite pipe blank. In the solidification, accumulation and rising process of the inner-layer solid material, the molten and compounded part at the lower part is subjected to heat preservation so as to be slowly cooled, namely, the stress is eliminated in the compounding process. And the stress is eliminated again after compounding is completed, so that the structure is homogenized, and cracks caused by poor toughness of the high-strength outer layer are overcome.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of bimetallic composite pipe, more particularly, relates to a preparation method of bimetallic composite seamless pipe casting blank. BACKGROUND

[0002] The bimetallic composite pipe is coated with a thin-walled corrosion-resistant alloy on the ordinary petroleum pipe, and meanwhile, the high-strength pipeline steel is used, which has the advantages of high strength and low cost, and the corrosion-resistant alloy layer has the advantage of good corrosion resistance. At present, the bimetallic composite pipe is widely used in oil fields, chemical industry, electric power and other fields, and has obvious economic, environmental and social benefits.

[0003] At present, the mechanical composite pipe is relatively mature internationally, but its bonding strength is weak, and failure accidents are prone to occur. The metallurgical composite pipe can avoid technical risks, and is the development direction at present. At present, the production methods of metallurgical bonding metal composite pipe include hot extrusion method, hot rolling method, centrifugal casting method, centrifugal aluminum thermal method, composite plate welding method, cold working diffusion method, powder metallurgy method, spray forming method and electromagnetic forming method. These methods have advantages but also have limitations, such as high technical requirements and the need for experienced personnel to operate. At the same time, there is also a method of preparing composite pipe by electroslag remelting, that is, the inner layer material is melted in the outer layer hollow material to form a composite pipe blank, but due to the difference in material properties of the two metals after electroslag remelting, the composite pipe produced has internal stress, poor organization consistency and is prone to cracks and other defects. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a preparation method of bimetallic composite seamless pipe casting blank, which can effectively eliminate internal stress and be suitable for seamless steel pipe rolling.

[0005] The technical purpose of the present application is realized by the following technical scheme.

[0006] A preparation method of bimetallic composite seamless pipe casting blank, in the preparation process, a temperature control cover is used, the temperature control cover is arranged on the base and is open in the vertical direction, the whole temperature control cover is a telescopic structure along the vertical direction, an air inlet is arranged at the lower end of the temperature control cover, and an air outlet is arranged at the upper end of the temperature control cover.

[0007] The outer layer steel pipe is placed in the temperature control cover, a casting liquid guide pipe is arranged coaxially in the outer layer steel pipe, a temperature acquisition element is arranged in the temperature control cover, the temperature of the outer layer steel pipe in the temperature control cover is measured, and the temperature signal is transmitted to the outside of the temperature control cover through the air outlet or the air inlet through the wire; according to the temperature signal, the air inlet and outlet and / or temperature are adjusted to control the temperature in the temperature control cover.

[0008] The outer steel pipe is heated from room temperature 20-25 degrees Celsius to 450-500 degrees Celsius at a speed of 10-30 degrees Celsius per hour and kept for 1-10 hours, and then heated for 1-2 hours to reach 600-650 degrees Celsius and kept for 1-6 hours; the inner casting liquid is heated to 1500-1560 degrees Celsius, the protective slag material is added to the steel liquid, and the casting liquid is formed by mixing uniformly; in the process of preparation, the inner casting liquid enters the casting liquid pipe from the casting liquid inlet, enters the outer steel pipe from the lower end of the casting liquid pipe, and cools to form the inner solid material, and as the height of the inner solid material gradually increases, the casting liquid pipe gradually pulls up, and the temperature control cover outside the outer steel pipe also gradually rises to control the temperature of the casting liquid entering the outer steel pipe.

[0009] The pouring speed of the inner casting liquid is 1-20 mm / s, the temperature control area is controlled to 700-800 degrees Celsius through the air inlet and air outlet, and after the inner casting liquid is poured, the temperature in the temperature control cover is kept at 700-800 degrees Celsius, and the holding time is 20-24 hours, then the temperature is lowered to 640-660 degrees Celsius at a speed of 30-50 degrees Celsius per hour and kept for 40-60 hours, then the temperature is lowered to 200 degrees Celsius at a speed of 30-50 degrees Celsius per hour, and finally the furnace is discharged and air cooled.

[0010] In the technical scheme of the present application, the protective slag material is baked before use, and the baking is carried out in an environment of 600 degrees Celsius to 800 degrees Celsius for more than 4 hours.

[0011] In the technical scheme of the present application, the whole temperature control cover is selected as a three-stage telescopic structure, the air inlet is arranged on the first-stage temperature control cover arranged on the base, the second-stage temperature control cover is arranged in the middle, and the third-stage temperature control cover is arranged at the top end, and the air outlet is arranged on the third-stage temperature control cover.

[0012] In the technical scheme of the present application, the area 10-15 cm below the opening of the lower end of the casting liquid pipe is the temperature measuring area.

[0013] In the technical scheme of the present application, the pouring speed of the inner casting liquid is 10-20 mm / s.

[0014] In the technical scheme of the present application, the outer steel pipe is heated from room temperature 20-25 degrees Celsius to 450-500 degrees Celsius at a speed of 20-30 degrees Celsius per hour and kept for 1-6 hours, and then heated for 1-2 hours to reach 600-650 degrees Celsius and kept for 4-6 hours.

[0015] In the technical scheme of the present application, the temperature in the temperature control cover is kept at 750-800 degrees Celsius, the holding time is 20-24 hours, then the temperature is decreased to 650-660 degrees Celsius at a rate of 40-50 degrees Celsius per hour and kept for 50-60 hours, then the temperature is decreased to 200 degrees Celsius at a rate of 40-50 degrees Celsius per hour, and finally the furnace is discharged and air-cooled.

[0016] In the technical scheme of the present application, after the solid pipe with the outer layer steel pipe and the inner layer cast metal is obtained, subsequent processing is performed by using the prior art to obtain the bimetal composite pipe, such as using the skew rolling piercing method.

[0017] The composite material obtained by using the technical scheme of the present application is gradually formed by melting and solidification, the temperature adjusting cover and the melting area continuously rise to achieve the effect of holding and slow cooling, so that defects such as internal transition melting, cracking, grain lines and composite surface damage do not occur. The composite material obtained by using the technical scheme of the present application eliminates stress and avoids cracks caused by poor toughness of high-strength steel, and realizes uniform structure. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a schematic diagram of the preparation method of the present application (1).

[0019] Figure 2 is a schematic diagram of the preparation method of the present application (2).

[0020] Figure 3 is a schematic diagram of the structure of the outer layer steel pipe and the temperature control cover in the present application (1).

[0021] Figure 4 is a schematic diagram of the structure of the outer layer steel pipe and the temperature control cover in the present application (2).

[0022] Wherein 1 is the temperature control cover, 1-1 is a first-stage temperature control cover, 1-2 is a second-stage temperature control cover, 1-3 is a third-stage temperature control cover, 2 is an air inlet, 3 is an air outlet, 4 is an outer layer steel pipe, 5 is a cast liquid guide pipe, 5-1 is a cast liquid inlet, 6 is an inner layer cast liquid, 7 is an inner layer solid material, 8 is a base, and I is a temperature measuring zone.

[0023] Figure 5 is an EBSD test result graph of the composite interface of Example 1 of the present application.

[0024] Figure 6 is a metallographic microstructure photo of the composite interface of Example 1 of the present application.

[0025] Figure 7 is an SEM photo of the composite interface of Example 1 of the present application.

[0026] Figure 8 is a microhardness test graph of the composite interface of Example 1 of the present application.

[0027] Figure 9This is a graph showing the change in microhardness as a function of interface distance in Embodiment 1 of the present invention.

[0028] Figure 10 This is a diagram showing the annular anodic polarization curves of NaCl aqueous solutions of different concentrations in Example 1 of the present invention.

[0029] Figure 11 This is a graph showing the electrochemical impedance spectroscopy test results of Example 1 of the present invention.

[0030] Figure 12 This is an optical microscope image of the composite interface in Embodiment 2 of the present invention.

[0031] Figure 13 This is a graph showing the electrochemical impedance spectroscopy test results of Example 2 of the present invention.

[0032] Figure 14 This is the annular anodic polarization curve of Embodiment 2 of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0034] like Figure 1 As shown in Figure 4, a temperature control cover is used in the preparation method of the present invention. The temperature control cover with a vertical opening is set on the base. The entire temperature control cover is a telescopic structure along the vertical direction. An air inlet is set at the lower end of the temperature control cover, and an air outlet is set at the upper end of the temperature control cover. A three-stage telescopic structure is selected. An air inlet is set on the first-stage temperature control cover set on the base, a second-stage temperature control cover is set in the middle, and a third-stage temperature control cover is set at the top. An air outlet is set on the third-stage temperature control cover.

[0035] An outer steel pipe is placed inside a temperature control enclosure. A casting liquid conduit is coaxially installed inside the outer steel pipe. A temperature acquisition element is installed inside the temperature control enclosure to measure the temperature of the outer steel pipe located inside the enclosure. The temperature signal is transmitted to the outside of the temperature control enclosure via a wire from the air outlet or air inlet. Based on the temperature signal, the airflow and / or temperature are adjusted to control the temperature inside the temperature control enclosure.

[0036] During the preparation process, the inner layer of casting liquid enters the casting liquid conduit through the casting liquid inlet, and then flows into the outer steel pipe from the lower end of the conduit to cool and form a solid inner layer material. As the height of the solid inner layer material gradually increases, the casting liquid conduit is gradually pulled upwards, and simultaneously, the temperature control hood outside the outer steel pipe is also gradually raised to control the temperature of the casting liquid that has entered the outer steel pipe. I is the temperature measurement zone; the temperature of the outer steel pipe within this zone is measured inside the temperature control hood to monitor the internal temperature of the steel pipe. The measurement is performed along the length of the outer steel pipe (i.e.,...). Figure 2The area corresponds to "from the lower end opening of the casting liquid conduit to within 20 cm below the opening", preferably within 10-15 cm, i.e. the area 10-15 cm below the lower end opening of the casting liquid conduit is the temperature measuring area.

[0037] Example 1—Bimetallic composite seamless pipe with outer layer C110 steel pipe + inner layer 316L

[0038] Prepare the outer layer hollow material—C110 steel pipe; prepare the inner layer solid material 316L steel liquid.

[0039] Prepare the protective slag material, and bake the protective slag material before use. The baking is performed at an environment of 600-800 degrees Celsius for more than 4 hours, the purpose is to dry the moisture content in the slag material, to ensure that the H gas in the moisture does not enter the steel. The protective slag material Al2O3, CaO, MgO, SiO2, Fe2O3 and other raw materials are configured, see the reference "Cause and solution of 316L stainless steel pipe ribbon" for details, Wang Shao-bing, Gao Ya-long, Gao Jian-ping, Metal World, CNKI: SUN: JSSJ.0.2020-02-010.

[0040]

[0041] (1) Heat the C110 steel pipe from room temperature 20-25 degrees Celsius to 500 degrees Celsius at a rate of 30 degrees Celsius per hour and keep for 1 hour, then heat for 1 hour to reach 650 degrees Celsius and keep for 1 hour.

[0042] (2) Heat the steel liquid to 1560 degrees Celsius, add the protective slag material to the steel liquid, and mix uniformly to form the casting liquid.

[0043] (3) Place the outer layer steel pipe in the temperature control cover, set the casting liquid conduit coaxially in the outer layer steel pipe, set the temperature collection element in the temperature control cover, pour the inner layer casting liquid 316L steel liquid into the casting liquid conduit from the casting liquid inlet, and into the outer layer steel pipe from the lower end of the casting liquid conduit to cool and form the inner layer solid material. As the height of the inner layer solid material gradually rises, the casting liquid conduit gradually pulls up, and the temperature control cover outside the outer layer steel pipe also gradually rises. Through the air inlet and outlet, the temperature of the casting liquid that has entered the inside of the outer layer steel pipe is controlled, that is, the temperature of the already compounded steel pipe is controlled by air cooling. As the base material solidifies and accumulates upwards, the lower part cools slowly to avoid stress.

[0044] The inner layer of molten 316L steel is gradually poured into the outer hollow material and solidifies gradually. The rising speed of the molten liquid is 10mm / s. The temperature of the molten steel that has entered the outer steel pipe is controlled to 800 degrees Celsius through the air inlet and outlet. After the composite is completed, it is kept at 800 degrees Celsius for 20 hours. Then, it is cooled to 650 degrees Celsius at a rate of 50 degrees Celsius per hour and kept at that temperature for 60 hours. Then, it is cooled to 200 degrees Celsius at a rate of 30 degrees Celsius per hour and air-cooled after being removed from the furnace to obtain a bimetallic composite material of outer C110 steel pipe and inner solid 316L steel pipe.

[0045] (4) The above-obtained "bimetallic composite material of outer C110 steel pipe + inner solid 316L" is rolled to obtain "bimetallic composite seamless pipe of outer C110 steel pipe + inner 316L". The rolling method adopts the skew rolling piercing method. The specific references are as follows: Temperature rise and stress distribution of 825 alloy skew rolling piercing process, Li Xin, Zhao Zhan, Dong Jianxin, Qiu Yunlong, Rare Metal Materials and Engineering, September 2022; Process analysis of Ti80 alloy seamless pipe preparation by skew rolling piercing method, Zhou Dadi, Zeng Weidong, Xu Jianwei, Rare Metal Materials and Engineering, March 2020.

[0046] The technical solution employed in this embodiment involves a gradual melting and solidification composite formation. The temperature-regulating hood and the melting-reintegration zone continuously rise to achieve a heat-preserving and slow-cooling effect, preventing defects such as excessive internal melting, cracking, hairline cracking, and surface tearing. The resulting composite material eliminates stress, avoiding cracking due to the poor toughness of high-strength steel, and achieves a uniform microstructure.

[0047] EBSD metallographic image as follows Figure 5 As shown, a relatively fine grain structure can be observed at the interface, which is due to the lower temperature near the interface during solidification. The interface is also smooth and free of oxide inclusions, pores, and other defects, indicating a good metallurgical bond between the two materials. Observation of the phase composition on both sides of the interface reveals that the 316L side is entirely austenite, while the carbon steel side consists of martensite and ferrite.

[0048] The interfacial microstructure of the original 316L / carbon steel composite pipe sample is as follows: Figure 6 As shown in (a) 200x magnification and (b) 1000x magnification, it can be seen that 316L stainless steel and carbon steel have undergone metallurgical bonding, with a 30-40μm banded bonding region at the interface. The bonding interface is clean and smooth, without cracks or other defects. Due to the significant differences in composition and microstructure between the two metals, and the influence of diffusion of bonding elements, the microstructure at the interface is relatively complex. Figure 6 As can be seen in (a), the material exhibits a partially banded structure due to the effects of rolling. Figure 6In (a), 316L matrix structure appears from top to bottom, i.e. a large number of twinned austenite; width of about 300 μm, with elongated long strip-shaped austenite structure along the interface direction; white band structure not etched out; metallurgical bonding interface; interface transition zone structure with a width of about 40 μm; pure ferrite structure with a width of about 50 μm; banded pearlite structure, 20# carbon steel matrix structure, i.e. ferrite + pearlite structure. To further analyze the microstructure of the material interface, the sample was tested by scanning electron microscope (SEM), and the results are shown in Figure 7 It can be seen that the 316L stainless steel is well combined with the steel, the bonding interface is flat, and there are no defects such as pores, cracks and inclusions, and the interface bonding area is about 5-10 μm. The original sample interface on the stainless steel side is a long strip-shaped austenite, and corrosion gullies appear at the austenite grain boundary, and there is an interface transition zone adjacent to the carbon steel side of the interface bonding area.

[0049] The microhardness test results of the sample composite interface are shown in Figure 8 and Figure 9 It can be found that there is a white structure at the interface of the 316L / carbon steel composite material, and the microhardness is much higher than that of the structures on both sides of the interface. In addition, there is a banded structure on the austenite side of the sample, and the microhardness value is significantly higher than that of the surrounding area. This should be due to the TRIP (Transformation Induced Plasticity) effect of the austenitic stainless steel during rolling. When the austenite is deformed under the action of internal stress, phase transformation occurs, and martensite is formed, thereby improving the strength of the stainless steel side structure of the material. Plotting the microhardness value of the sample and the distance from the interface, it can be found that the microhardness of the sample at the interface appears a peak value, which is significantly higher than that of the structures on both sides of the interface, and the microhardness value of the banded structure on the stainless steel side is also significantly higher than that of the ordinary austenite structure (A). The microhardness of the carbon steel side adjacent to the interface appears a trough, which corresponds to the pure ferrite (F) area. By comparing the microhardness values of the structures on both sides of the interface, it can be found that the hardness of the stainless steel side near the interface is generally greater than that of the carbon steel side. As the distance from the interface increases, the hardness of the stainless steel decreases, while the microhardness of the carbon steel side gradually increases due to the increase of the pearlite (P) content. The interface shear strength of the sample after heat treatment was detected, and it was found that the shear strength of the sample after heat treatment was above 350 MPa, indicating that the bimetallic composite pipe prepared by the improved process has good interface bonding mechanical properties.

[0050] The ring anodic polarization curve test of the sample stainless steel surface in 3.5wt% and 15wt% NaCl aqueous solution was carried out, and the results are shown in Figure 10corresponds to 3.5wt%, b corresponds to 15wt%. In 3.5wt% NaCl solution, the material shows passivation characteristics, but the passivation state is not very stable, and a large number of sawtooth fluctuations occur in the polarization curve of the passivation region. The highest self-corrosion potential is about 30mV, and the sample has a small corrosion tendency. In addition, the breakdown potential of the sample is relatively high, about 0.4V (vs. SCE), indicating that the stability of the passivation film of the sample is good, and the resistance to pitting corrosion is stronger. When the potential is reversed after reaching the breakdown potential, it is found that the sample has no re-passivation phenomenon. In 15wt% NaCl solution, the polarization curve in the passivation region of the sample is relatively smooth, but the breakdown potential decreases to 0.25V, and there is still no re-passivation phenomenon after the potential is reversed.

[0051] The electrochemical impedance spectroscopy (EIS) test was performed on the surface of the sample 316L stainless steel, and the results are shown in Figure 11 , where a corresponds to the Nyquist test analysis of the test results, and b corresponds to the Bode test results. As can be seen from the figure, the sample shows a straight line close to the imaginary part in the test frequency range, and the impedance modulus is relatively large, reaching 10 5 Ω·cm -2 order of magnitude, indicating that the material has good corrosion resistance. In b, the upper curve is the Bode phase angle curve, and the lower curve is the Bode amplitude curve. It can be found that the phase angle shapes of different samples are similar, and there is only one wide peak, indicating that there is only one time constant in the test frequency range, and the phase angle value is relatively high in the medium and low frequency band, indicating that the passivation film has good impedance ability to electrolyte penetration, and a stable passivation film is generated on the surface of the sample. The larger the impedance modulus (|Z|) in the Bode amplitude curve, the more corrosion-resistant the material is. In the low frequency band, the impedance modulus of the sample is large, and the corrosion resistance is good.

[0052] The EIS results were fitted using ZSimpWin software, and the R s (QR t ) equivalent circuit was used to fit the EIS results, where R s is the solution resistance, Q is the constant phase angle element, and R t is the charge transfer resistance. The fitting results are shown in the following table; it can be found that the charge transfer resistance of the sample is large, reaching more than 10 7 Ω·cm 2 , indicating that the material has good corrosion resistance. The n value of the constant phase angle element is close to 1, and the constant phase angle element is close to pure capacitance, indicating that the passivation film has good corrosion resistance.

[0053] EIS fitting results

[0054]

[0055] Example 2 - Double metal composite seamless pipe of outer layer C110 steel pipe + inner layer nickel-based alloy

[0056] Prepare the outer layer hollow material - C110 steel pipe; prepare the inner layer solid material nickel-based alloy steel liquid.

[0057] Prepare the protective slag material, and bake the protective slag material before use. The baking is baked in an environment of 600 to 800 degrees Celsius for more than 4 hours, the purpose is to dry the moisture content in the slag, to ensure that the H gas in the moisture does not enter the steel. The protective slag material Al2O3, CaO, MgO, CaF2 and other raw materials are configured, see the reference for details. Research on the Metallurgical Quality of Large Ingot of Nickel-based Superalloy in Protective Atmosphere Electroslag Remelting, Xing Baofu, Thirteenth China High Temperature Alloy Annual Abstracts, 53wt% CaF2, 22wt% Al2O3, 20wt% CaO, 5wt% MgO, total 100wt%, add appropriate amount of TiO2 powder, such as 3wt%.

[0058] (1) Heat the C110 steel pipe from room temperature 20-25 degrees Celsius to 450 degrees Celsius at a rate of 30 degrees Celsius per hour and keep for 1 hour, then heat for 1 hour to 600 degrees Celsius and keep for 1 hour.

[0059] (2) Heat the steel liquid to 1550 degrees Celsius, add the protective slag material to the steel liquid, mix evenly to form the casting liquid.

[0060] (3) Place the outer layer steel pipe in the temperature control cover, set the casting liquid guide pipe coaxially in the outer layer steel pipe, set the temperature collection element in the temperature control cover, pour the inner layer casting liquid nickel-based alloy steel liquid into the casting liquid guide pipe from the casting liquid inlet, and the inner layer solid material is formed by cooling in the outer layer steel pipe from the lower end of the casting liquid guide pipe. As the height of the inner layer solid material gradually rises, the casting liquid guide pipe gradually pulls up, and the temperature control cover outside the outer layer steel pipe also gradually rises. Through the air inlet and air outlet, the temperature of the casting liquid that has entered the inside of the outer layer steel pipe is controlled, that is, the temperature of the already compounded steel pipe is controlled by air cooling. As the base material solidifies and accumulates upwards, the lower part cools slowly to avoid stress.

[0061] The inner layer casting liquid 316L steel liquid is gradually poured into the outer layer hollow material and gradually solidified, and the pouring liquid rises at a speed of 10mm / s. The temperature of the casting liquid that has entered the inside of the outer layer steel pipe is controlled to 750 degrees Celsius through the air inlet and air outlet. After the compounding is completed, the temperature is kept at 750 degrees Celsius for 20h, then cooled to 650 degrees Celsius at a rate of 50 degrees Celsius per hour and kept for 60h, and then cooled to 200 degrees Celsius at a rate of 30 degrees Celsius per hour. After the furnace is discharged, air cooling is carried out, and the double metal composite material of outer layer C110 steel pipe + inner layer solid nickel-based alloy is obtained.

[0062] (4) The obtained "outer layer C110 steel pipe + inner layer solid nickel-based alloy bimetallic composite material" is rolled to obtain "outer layer C110 steel pipe + inner layer nickel-based alloy bimetallic seamless pipe", and the rolling method adopts the cross-rolling piercing method, and the specific reference is as follows: Temperature rise and stress distribution of cross-rolling piercing process of 825 alloy, Li Xin, Zhao Zhan, Dong Jianxin, Qiu Yunlong, Rare Metal Materials and Engineering, September 2022; Process analysis of Ti80 alloy seamless pipe prepared by cross-rolling piercing method, Zhou Dadi, Zeng Weidong, Xu Jianwei, Rare Metal Materials and Engineering, March 2020.

[0063] The technical scheme of the embodiment is melted and solidified to gradually form a composite, a temperature adjusting cover and a melting area continuously rise to achieve the effect of heat preservation and slow cooling, so that internal defects such as excessive melting, cracking, grain lines and composite surface scratches do not occur. The obtained composite material eliminates stress and avoids cracks caused by poor toughness of high-strength steel, and realizes uniform organization.

[0064] The nickel-based alloy / carbon steel composite material interface is observed using an optical microscope, and the results are shown in Figure 12 , where a corresponds to 200 times, and b corresponds to 1000 times; the upper part of the figure is the nickel-based alloy, and the lower part is the carbon steel. It can be found that the two materials are metallurgically combined, and a white bonding area of 5-10 μm is formed at the interface. Below the bonding area is a ferrite zone, and above the bonding area is an austenite zone. It can be found that the nickel-based alloy austenite grain size difference is large, and the larger grains are extruded and deformed during rolling, showing long strip-shaped grains parallel to the interface.

[0065] The nickel-based alloy surface of the composite material is subjected to electrochemical testing in 3.5wt% NaCl aqueous solution and 15wt% NaCl aqueous solution respectively, and the EIS test results are shown in Figure 13 , where (a) corresponds to the Nyquist test analysis result of the test result, and (b) corresponds to the Bode test result. It can be found from the Nyquist test result that the material impedance spectrum curve is similar in different concentrations of NaCl solution, which is an approximate straight line close to the virtual axis, and the capacitive arc radius is large, indicating that the material forms a dense passivation film, and the material has good corrosion resistance. It can be found from the Bode test result that the material impedance modulus value is large, close to megohm level; from the Bode phase diagram, it can be seen that there is only one wide peak, and the frequency range covered is large, indicating that the material has good corrosion resistance, and the passivation film is stable.

[0066] The material ring anodic polarization curve is shown in Figure 14 , it can be found that the anodic polarization curves of the material in different concentrations of NaCl solution all show passivation characteristics, and re-passivation occurs after the potential reverse scan. The passivation current density in 3.5wt.%NaCl is 10 -7 A·cm -2The breakdown potential is about 0.31V (relative to saturated calomel electrode), and the re-passivation potential is about 0.1V; the passivation current density in 15wt.% NaCl is about 10 -7 A·cm -2 The breakdown potential is about 0.43V, and the re-passivation potential is about 0.15V. It is shown that the passivation film of the material is stable, and the corrosion resistance is good.

[0067] According to the adjustment of the process parameters according to the content of the present application, the preparation of the double-metal composite seamless pipe casting blank can be realized, and the performance tested is basically consistent with the present application. The above has made an exemplary description of the present application, it should be explained that, without departing from the core of the present application, any simple deformation, modification or other equivalent replacement which can not cost the creative labor of the person skilled in the art falls into the protection scope of the present application.

Claims

1. A method of producing a bimetallic composite seamless pipe cast billet, characterized by, In the preparation process, a temperature control cover is used, the temperature control cover is arranged on the base and is open in the vertical direction, the whole temperature control cover is a telescopic structure along the vertical direction, an air inlet is arranged at the lower end of the temperature control cover, and an air outlet is arranged at the upper end of the temperature control cover; The outer steel pipe is placed in the temperature control cover, a casting liquid guide pipe is coaxially arranged in the outer steel pipe, a temperature acquisition element is arranged in the temperature control cover, the temperature of the outer steel pipe in the temperature control cover is measured, and a temperature signal is transmitted to the outside of the temperature control cover through the air outlet or the air inlet; according to the temperature signal, the air inlet and outlet volume and / or temperature are adjusted to control the temperature in the temperature control cover; The outer steel pipe is heated from room temperature 20-25 DEG C to 450-500 DEG C at a speed of 10-30 DEG C per hour and kept for 1-10 hours, and then heated for 1-2 hours to reach 600-650 DEG C and kept for 1-6 hours; the inner casting liquid is heated to 1500-1560 DEG C, the protective slag material is added into the steel liquid, and is uniformly mixed to form the casting liquid; in the preparation process, the inner casting liquid enters the casting liquid guide pipe from the casting liquid inlet, enters the outer steel pipe from the lower end of the casting liquid guide pipe, and cools to form the inner solid material; as the height of the inner solid material gradually increases, the casting liquid guide pipe is gradually pulled up, and the temperature control cover outside the outer steel pipe is also gradually lifted to control the temperature of the casting liquid in the outer steel pipe; from the length direction of the outer steel pipe, the temperature measuring area corresponds to the area within 20 cm below the opening at the lower end of the casting liquid guide pipe; the pouring speed of the inner casting liquid is 1-20 mm / s, the temperature measuring area is controlled to 700-800 DEG C through the air inlet and the air outlet, after the inner casting liquid is poured, the temperature in the temperature control cover is kept at 700-800 DEG C, the holding time is 20-24 hours, then the temperature is lowered to 640-660 DEG C at a speed of 30-50 DEG C per hour and kept for 40-60 hours, then the temperature is lowered to 200 DEG C at a speed of 30-50 DEG C per hour, and finally the furnace is discharged and air cooled.

2. A method of producing a bimetallic composite seamless pipe billet according to claim 1, characterized in that, The protective slag material is baked before use, and the baking is performed in an environment of 600 DEG C to 800 DEG C for more than 4 hours.

3. A method of producing a bimetallic composite seamless pipe billet according to claim 1, characterized in that, The whole temperature control cover is selected to have a three-stage telescopic structure, the air inlet is arranged on the first-stage temperature control cover arranged on the base, the second-stage temperature control cover is arranged in the middle, the third-stage temperature control cover is arranged at the top end, and the air outlet is arranged on the third-stage temperature control cover.

4. A method of producing a bimetallic composite seamless pipe billet according to claim 1, characterized in that, The area 10-15 cm below the opening at the lower end of the casting liquid guide pipe is the temperature measuring area.

5. A method of producing a bimetallic composite seamless pipe billet according to claim 1, characterized in that, The pouring speed of the inner casting liquid is 10-20 mm / s.

6. A method of producing a bimetallic composite seamless pipe billet according to claim 1, characterized in that, The outer steel pipe is heated from room temperature 20-25 DEG C to 450-500 DEG C at a speed of 20-30 DEG C per hour and kept for 1-6 hours, and then heated for 1-2 hours to reach 600-650 DEG C and kept for 4-6 hours.

7. A method of producing a bimetallic composite seamless pipe billet according to claim 1, characterized by, The temperature in the temperature control cover is kept at 750-800 degrees Celsius, the holding time is 20-24 hours, then the temperature is decreased to 650-660 degrees Celsius at a rate of 40-50 degrees Celsius per hour, and the holding time is 50-60 hours, then the temperature is decreased to 200 degrees Celsius at a rate of 40-50 degrees Celsius per hour, and finally the furnace is discharged and the casting is air cooled.

8. A double-metal composite seamless pipe billet prepared by the preparation method according to any one of claims 1-7.

9. Application of the preparation method according to any one of claims 1-7 to the preparation of a double-metal composite seamless pipe.

10. Use according to claim 9, characterized in that, After the double-metal composite seamless pipe billet is prepared, subsequent treatment is performed to obtain a double-metal composite pipe, such as using a cross-rolling piercing method.

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