Temperature-resistant and crack-resistant composite plug with long service life and preparation method of temperature-resistant and crack-resistant composite plug

Abstract

The invention belongs to the field of metal materials, and relates to a long-life temperature-resistant anti-crack composite plug and a preparation method thereof. According to the invention, through elaborate design of components of the metal layer, excellent hardness and wear resistance are provided, the material is suitable for high-temperature and high-wear working conditions, and by adding a proper amount of RE and Ni, the plasticity and toughness are improved while the material strength is improved, the service reliability is remarkably improved, and the service life is remarkably prolonged; an asymmetric thermal field which is fast in internal cooling and slow in external cooling is constructed, high-quality interface bonding and a compact structure are achieved in the composite casting process, a surface pressure stress field beneficial to crack resistance is formed in the service process, thermal stress concentration is effectively relieved, generation and extension of thermal fatigue cracks are restrained, and the service life of the composite casting is prolonged. And the service life, temperature resistance and crack resistance of the composite plug are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and relates to a long-life temperature-resistant and crack-resistant composite plug and a preparation method thereof. BACKGROUND

[0002] The steel tube piercing plug is a key forming tool in the hot rolling production process of seamless steel pipes, and its core function is to pierce a solid pipe blank in a plastic state into a hollow pipe. In the cross piercing mill, the plug is precisely arranged on the pipe blank advancing path. When the high-temperature (about 1100-1250℃) pipe blank rotates and advances under the driving of the roller and contacts the plug, the conical head of the plug acts as an "inner mold" to force the metal to generate a hole cavity in the central area under the action of a large rolling pressure, thereby forming the inner surface of the steel pipe. At the same time, the geometry, size accuracy of the plug and the hole type system composed of the roller and the guide plate jointly determine the inner diameter size and wall thickness uniformity of the pipe, and play a decisive role in the size accuracy and inner surface quality of the steel pipe. In addition, the plug deeply penetrates into the pipe blank during the piercing process, and also plays a supporting and guiding role to prevent defects such as folding and internal cracking caused by metal flow instability.

[0003] However, the plug is in an extremely harsh working environment for a long time, which bears high temperature above 1000℃, severe mechanical friction, periodic impact load and rapid thermal cycle, resulting in significant shortcomings in service life, temperature resistance and crack resistance. First of all, the most important failure mode of the plug is surface wear, especially the nose and working zone, which is quickly worn out due to direct friction with the high-temperature steel blank; at the same time, problems such as thermal fatigue, sticking, plastic deformation (such as "nose collapse" or "thickening") also frequently occur, which limits its service life and requires frequent replacement, directly affecting production efficiency and manufacturing cost.

[0004] Secondly, traditional materials such as H13 hot work die steel are prone to softening, oxidation and microstructure degradation under high temperature for a long time, resulting in strength reduction and surface spalling; even if high-performance molybdenum-based alloys or ceramic materials are used, it is also difficult to completely avoid the problems of performance degradation and insufficient oxidation resistance under high temperature.

[0005] Finally, the plug generates a large thermal stress due to severe thermal cycle, which easily causes thermal fatigue cracks, which are often found in the transition area between the nose and the working zone, and the crack propagation can lead to plug fracture; some materials exhibit intergranular fracture characteristics at high temperature, reflecting the problem of grain boundary weakening; while some high-hardness materials are resistant to wear and heat, but they are brittle and have poor impact and crack resistance.

[0006] It can be seen that although the material and structure design are constantly improved, the modern piercing plug still faces multiple challenges such as insufficient wear resistance, poor high-temperature stability and weak thermal fatigue cracking resistance, which become the key bottleneck restricting the efficient and high-quality production of seamless steel pipes, and it is urgent to continuously improve through comprehensive technical means such as material innovation, structure optimization and surface strengthening. SUMMARY

[0007] The purpose of the present application is to solve the above-mentioned problems existing in the prior art, and a long-life temperature-resistant and crack-resistant composite plug is proposed, which is suitable for high-temperature and high-wear working conditions such as hot rolling piercing machine, the metal layer provides high hardness and wear resistance, and the matrix has high thermal strength and thermal fatigue resistance.

[0008] The purpose of the present application can be realized by the following technical scheme:

[0009] A long-life temperature-resistant and crack-resistant composite plug, the composite plug is composed of a plug blank and a metal layer covering the surface of the plug blank, wherein the composition content of the metal layer is: 0.28-0.38wt% C, 0.7-1.0wt% Si, 0.2-0.3wt% Mn, 4.6-5.2wt% Cr, 1.2-1.6wt% Mo, 0.9-1.0wt% V, 0.2-0.3wt% Ni, 0.001-0.005wt% RE, and the balance is Fe and inevitable impurities.

[0010] The surface metal layer of the composite plug of the present application not only provides excellent hardness and wear resistance, but also significantly improves the overall mechanical properties through reasonable alloy design. The introduction of RE and Ni not only enhances the strength of the material, but also effectively improves the plasticity and toughness of the steel, thereby greatly improving the service reliability and service life of the plug under complex thermal-mechanical coupling conditions. By adding 0.001-0.005wt% RE, the anti-cracking performance of the plug can be improved by more than 30% without increasing brittleness, thereby greatly prolonging the service life of the plug. The addition of 0.2-0.3wt% Ni and Cr, Mo and other elements synergistically enhances the corrosion resistance and oxidation resistance, especially in high-temperature and humid or oxidizing environments. It can be seen that the metal layer of the present application provides excellent wear resistance through high-hardness carbides (such as Cr7C3, VC, Mo2C), and in combination with the micro-alloying effect of Ni and RE, the strength and crack resistance are improved without sacrificing plasticity. This synergistic mechanism of "strengthening and toughening + crack resistance" enables the composite plug to maintain structural integrity under long-term high-temperature, high-wear and high-stress service conditions, effectively avoids early cracking failure, and ultimately significantly prolongs the service life.

[0011] In the long-life temperature-resistant and anti-cracking composite top head, the composition of the top head blank contains 0.40-0.44wt% C, 13.8-14.2wt% Cr, 1.8-2.3wt% Mn, 0.3-0.4wt% Mo, 0.6-0.7wt% W, and the balance of Fe and inevitable impurities.

[0012] The application further provides a preparation method of the long-life temperature-resistant and anti-cracking composite top head.

[0013] S1, preparing raw materials according to the composition of the metal layer;

[0014] S2, melting the raw materials to obtain an alloy liquid;

[0015] S3, placing the top head blank into a mold, then pouring the alloy liquid into the mold, and obtaining a semi-finished top head after cooling;

[0016] S4, finally quenching and tempering the semi-finished top head to obtain the composite top head.

[0017] In the preparation method of the long-life temperature-resistant and anti-cracking composite top head, the melting temperature in step S2 is 1580-1620℃, then refining is performed, and finally the alloy liquid is discharged at a temperature of 1520-1560℃.

[0018] In the preparation method of the long-life temperature-resistant and anti-cracking composite top head, the slag basicity is controlled to be 2.5-3.5 during the refining process, Al is added for deoxidization until the oxygen content is less than or equal to 15ppm, and vacuum degassing treatment is performed at 1550-1580℃.

[0019] In the preparation method of the long-life temperature-resistant and anti-cracking composite top head, the vacuum degree in the vacuum degassing treatment is 30-67Pa, and the time is 10-15min.

[0020] In the preparation method of the long-life temperature-resistant and anti-cracking composite top head, the top head blank is preheated to 200-300℃ before being placed into the mold in step S3, the inner cavity of the top head blank is connected to a circulating cooling water system, the flow rate of the water is controlled to be 1.5-2.5m / s, and the water temperature is 25-40℃.

[0021] The internal cavity connection circulating cooling water system of the plug blank realizes an asymmetric cooling mode of "internal rapid cooling and external slow cooling", which not only optimizes the solidification behavior and interface bonding quality in the casting process, but also endows the plug with excellent heat resistance and thermal crack resistance under subsequent high-temperature service conditions. High-temperature alloy liquid is poured onto the surface of the plug blank which has been preheated and internally provided with a circulating cooling water system. At this time, the circulating cooling water in the internal cavity of the blank continuously takes away heat, so that the blank matrix maintains a relatively low temperature, forming an internal-to-external temperature gradient. Since the inside is forcibly cooled and the outside (alloy liquid side) is slowly cooled, heat is mainly conducted inward through the blank matrix, forming an external-to-internal solidification direction, avoiding shrinkage hole and shrinkage porosity defects caused by external solidification first, allowing bubbles and inclusions to be discharged outward with the liquid phase front, reducing internal defects, and improving the density and uniformity of the metal layer; moreover, when the rapidly cooled matrix surface contacts the high-temperature alloy liquid, a local fusion or semi-fusion layer is formed, promoting atomic diffusion and realizing good metallurgical bonding between the outer alloy and the inner blank, preventing delamination or interface peeling.

[0022] The present application needs to strictly control the flow rate of water, because too low flow rate will cause a sharp drop in heat transfer efficiency, which cannot take away heat in time and is easy to cause thermal cracking; too high flow rate will cause local excessive cooling, causing uneven temperature distribution in the material, and in turn inducing thermal shock cracking. The present application also controls the water temperature to avoid excessive thermal stress or insufficient cooling, and the two work together to effectively improve the high-temperature resistance, thermal crack resistance and service life of the plug.

[0023] In the preparation method of the long-life temperature-resistant and crack-resistant composite plug described above, in step S3, the alloy liquid is poured into the mold at a pouring temperature of 1500-1540℃ and a pouring speed of 0.8-1.2kg / s, and the filling is completed under a pressure of 0.05-0.15MPa.

[0024] In the preparation method of the long-life temperature-resistant and crack-resistant composite plug described above, in step S4, the quenching temperature is 1000-1100℃ and the time is 30-60min.

[0025] In the preparation method of the long-life temperature-resistant and crack-resistant composite plug described above, in step S4, the tempering frequency is 2-3 times, the tempering temperature is 550-600℃, and the time is 90-120min, and each tempering is followed by air cooling to room temperature. Since the composite plug is composed of a high-chromium matrix and a multi-element alloy surface layer, stress concentration is easily generated in the interface area due to thermal expansion difference during heat treatment. The present application gradually releases the stress on both sides of the interface through multiple tempering, avoids delamination or micro-cracks caused by slow stress release during subsequent use due to insufficient one-time tempering, promotes element diffusion and organizational coordination near the interface, and enhances the interface bonding strength.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] 1. This invention constructs an asymmetric thermal field with "fast internal cooling and slow external cooling" by connecting a circulating cooling water system to the inner cavity of the mandrel blank. This not only achieves high-quality interfacial bonding and dense structure during composite casting, but also forms a surface compressive stress field that is conducive to crack resistance during service. This effectively alleviates thermal stress concentration, inhibits the generation and propagation of thermal fatigue cracks, and improves the life, temperature resistance, and crack resistance of the composite mandrel.

[0028] 2. This invention provides excellent hardness and wear resistance through careful design of the metal layer composition, making it suitable for high-temperature and high-wear conditions. By adding appropriate amounts of RE (0.001-0.005wt%) and Ni (0.2-0.3wt%), the material strength is improved while plasticity and toughness are enhanced, significantly improving service reliability and service life.

[0029] 3. The present invention helps to release stress in the interface area of ​​the composite structure through secondary tempering, promotes element diffusion and organizational coordination, enhances the interface bonding strength, and prevents delamination or peeling during use. This allows the composite mandrel to maintain structural integrity under long-term high temperature, high wear, and high stress service conditions, avoids early cracking failure, and increases its service life by more than 2 times compared to traditional mandrels. Detailed Implementation

[0030] The following are specific embodiments of the present invention, which further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0031] To make the objectives, technical solutions, and advantages of this invention patent clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this invention patent and are not intended to limit the scope of this invention patent.

[0032] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a step or method that includes the listed elements is not limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0033] The terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., used in this invention refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms are not necessarily directed at the same embodiment or example. Furthermore, the technical features involved in the various embodiments of the invention can be combined with each other as long as they do not conflict with each other.

[0034] Example 1

[0035] S1. The raw materials are prepared according to the following composition: 0.35wt% C, 0.75wt% Si, 0.28wt% Mn, 4.9wt% Cr, 1.3wt% Mo, 0.93wt% V, 0.22wt% Ni, 0.003wt% RE, with the balance being Fe and unavoidable impurities.

[0036] S2. Add the prepared raw materials to the medium-frequency induction furnace, melt and hold at 1610℃ for 15 minutes, tap the steel to the ladle furnace for refining, control the oxygen content of the molten steel to ≤15ppm, blow argon and stir for 10 minutes, add aluminum granules for final deoxidation, control the oxygen content of the molten steel to ≤15ppm, vacuum at 1560℃ to 45Pa, hold for 15 minutes, so that the temperature of the alloy liquid exiting the furnace is controlled at 1550℃.

[0037] S3. Preheat the mandrel blank to 250℃ and hold for 30 minutes. After preheating, put the blank into the metal mold and connect the internal cavity circulating cooling water system: control the water temperature at 30℃ and adjust the water flow rate to 2.0m / s. The composition of the mandrel blank is: 0.41wt%C, 14.0wt%Cr, 1.9wt%Mn, 0.38wt%Mo, 0.68wt%W, with the balance being Fe and unavoidable impurities.

[0038] S4. The alloy liquid is injected into the mold at 1520℃ and a pouring speed of 1.0 kg / s. A low pressure of 0.10 MPa is applied to assist the filling process to ensure smooth filling without turbulence. After pouring, the mixture is allowed to cool naturally for 60 minutes before demolding to obtain the semi-finished composite mandrel.

[0039] S5. Heat the semi-finished mandrel to 1050℃ at a rate of 100℃ / h, hold for 45 minutes, and after taking it out of the furnace, quickly immerse it in rapid quenching oil to cool to room temperature.

[0040] S6. Reheat the quenched mandrel to 580℃, hold for 100 minutes, and air cool to room temperature. Then reheat the mandrel to 580℃, hold for 100 minutes, and air cool to room temperature to obtain the composite mandrel.

[0041] Example 2:

[0042] S1. The raw materials are prepared according to the following composition: 0.28wt% C, 0.70wt% Si, 0.30wt% Mn, 4.6wt% Cr, 1.2wt% Mo, 1.0wt% V, 0.30wt% Ni, 0.001wt% RE, with the balance being Fe and unavoidable impurities.

[0043] S2. Add the prepared raw materials to the medium-frequency induction furnace, melt and hold at 1610℃ for 15 minutes, tap the steel to the ladle furnace for refining, control the oxygen content of the molten steel to ≤15ppm, blow argon and stir for 10 minutes, add aluminum granules for final deoxidation, control the oxygen content of the molten steel to ≤15ppm, vacuum at 1560℃ to 45Pa, hold for 15 minutes, so that the temperature of the alloy liquid exiting the furnace is controlled at 1550℃.

[0044] S3. Preheat the mandrel blank to 250℃ and hold for 30 minutes. After preheating, put the blank into the metal mold and connect the internal cavity circulating cooling water system: control the water temperature at 30℃ and adjust the water flow rate to 2.0m / s. The composition of the mandrel blank is: 0.41wt%C, 14.0wt%Cr, 1.9wt%Mn, 0.38wt%Mo, 0.68wt%W, with the balance being Fe and unavoidable impurities.

[0045] S4. The alloy liquid is injected into the mold at 1520℃ and a pouring speed of 1.0 kg / s. A low pressure of 0.10 MPa is applied to assist the filling process to ensure smooth filling without turbulence. After pouring, the mixture is allowed to cool naturally for 60 minutes before demolding to obtain the semi-finished composite mandrel.

[0046] S5. Heat the semi-finished mandrel to 1050℃ at a rate of 100℃ / h, hold for 45 minutes, and after taking it out of the furnace, quickly immerse it in rapid quenching oil to cool to room temperature.

[0047] S6. Reheat the quenched mandrel to 580℃, hold for 100 minutes, and air cool to room temperature. Then reheat the mandrel to 580℃, hold for 100 minutes, and air cool to room temperature to obtain the composite mandrel.

[0048] Example 3:

[0049] S1. The raw materials are prepared according to the following composition: 0.38wt% C, 1.0wt% Si, 0.20wt% Mn, 5.2wt% Cr, 1.6wt% Mo, 0.90wt% V, 0.20wt% Ni, 0.005wt% RE, with the balance being Fe and unavoidable impurities.

[0050] S2. Add the prepared raw materials to the medium-frequency induction furnace, melt and hold at 1610℃ for 15 minutes, tap the steel to the ladle furnace for refining, control the oxygen content of the molten steel to ≤15ppm, blow argon and stir for 10 minutes, add aluminum granules for final deoxidation, control the oxygen content of the molten steel to ≤15ppm, vacuum at 1560℃ to 45Pa, hold for 15 minutes, so that the temperature of the alloy liquid exiting the furnace is controlled at 1550℃.

[0051] S3. Preheat the mandrel blank to 250℃ and hold for 30 minutes. After preheating, put the blank into the metal mold and connect the internal cavity circulating cooling water system: control the water temperature at 30℃ and adjust the water flow rate to 2.0m / s. The composition of the mandrel blank is: 0.41wt%C, 14.0wt%Cr, 1.9wt%Mn, 0.38wt%Mo, 0.68wt%W, with the balance being Fe and unavoidable impurities.

[0052] S4. The alloy liquid is injected into the mold at 1520℃ and a pouring speed of 1.0 kg / s. A low pressure of 0.10 MPa is applied to assist the filling process to ensure smooth filling without turbulence. After pouring, the mixture is allowed to cool naturally for 60 minutes before demolding to obtain the semi-finished composite mandrel.

[0053] S5. Heat the semi-finished mandrel to 1050℃ at a rate of 100℃ / h, hold for 45 minutes, and after taking it out of the furnace, quickly immerse it in rapid quenching oil to cool to room temperature.

[0054] S6. Reheat the quenched mandrel to 580℃, hold for 100 minutes, and air cool to room temperature. Then reheat the mandrel to 580℃, hold for 100 minutes, and air cool to room temperature to obtain the composite mandrel.

[0055] Example 4:

[0056] S1. The raw materials are prepared according to the following composition: 0.35wt% C, 0.75wt% Si, 0.28wt% Mn, 4.9wt% Cr, 1.3wt% Mo, 0.93wt% V, 0.22wt% Ni, 0.003wt% RE, with the balance being Fe and unavoidable impurities.

[0057] S2. Add the prepared raw materials to the medium-frequency induction furnace, melt and hold at 1610℃ for 15 minutes, tap the steel to the ladle furnace for refining, control the oxygen content of the molten steel to ≤15ppm, blow argon and stir for 10 minutes, add aluminum granules for final deoxidation, control the oxygen content of the molten steel to ≤15ppm, vacuum at 1560℃ to 45Pa, hold for 15 minutes, so that the temperature of the alloy liquid exiting the furnace is controlled at 1550℃.

[0058] S3. Preheat the mandrel blank to 250℃ and hold for 30 minutes. After preheating, put the blank into the metal mold and connect the internal cavity circulating cooling water system: control the water temperature at 30℃ and adjust the water flow rate to 2.0m / s. The composition of the mandrel blank is: 0.41wt%C, 14.0wt%Cr, 1.9wt%Mn, 0.38wt%Mo, 0.68wt%W, with the balance being Fe and unavoidable impurities.

[0059] S4. The alloy liquid is injected into the mold at 1520℃ and a pouring speed of 1.0 kg / s. A low pressure of 0.10 MPa is applied to assist the filling process to ensure smooth filling without turbulence. After pouring, the mixture is allowed to cool naturally for 60 minutes before demolding to obtain the semi-finished composite mandrel.

[0060] S5. Heat the semi-finished mandrel to 1050℃ at a rate of 100℃ / h, hold for 45 minutes, and after taking it out of the furnace, quickly immerse it in rapid quenching oil to cool to room temperature.

[0061] S6. Reheat the quenched mandrel to 580℃, hold for 100 minutes, and air cool to room temperature.

[0062] Example 5:

[0063] S1. The raw materials are prepared according to the following composition: 0.35wt% C, 0.75wt% Si, 0.28wt% Mn, 4.9wt% Cr, 1.3wt% Mo, 0.93wt% V, 0.22wt% Ni, 0.003wt% RE, with the balance being Fe and unavoidable impurities.

[0064] S2. Add the prepared raw materials to the medium-frequency induction furnace, melt and hold at 1610℃ for 15 minutes, tap the steel to the ladle furnace for refining, control the oxygen content of the molten steel to ≤15ppm, blow argon and stir for 10 minutes, add aluminum granules for final deoxidation, control the oxygen content of the molten steel to ≤15ppm, vacuum at 1560℃ to 45Pa, hold for 15 minutes, so that the temperature of the alloy liquid exiting the furnace is controlled at 1550℃.

[0065] S3. Preheat the mandrel blank to 250℃ and hold for 30 minutes. After preheating, put the blank into the metal mold and connect the internal cavity circulating cooling water system: control the water temperature at 30℃ and adjust the water flow rate to 0.1m / s. The composition of the mandrel blank is: 0.41wt%C, 14.0wt%Cr, 1.9wt%Mn, 0.38wt%Mo, 0.68wt%W, with the balance being Fe and unavoidable impurities.

[0066] S4. The alloy liquid is injected into the mold at 1520℃ and a pouring speed of 1.0 kg / s. A low pressure of 0.10 MPa is applied to assist the filling process to ensure smooth filling without turbulence. After pouring, the mixture is allowed to cool naturally for 60 minutes before demolding to obtain the semi-finished composite mandrel.

[0067] S5. Heat the semi-finished mandrel to 1050℃ at a rate of 100℃ / h, hold for 45 minutes, and after taking it out of the furnace, quickly immerse it in rapid quenching oil to cool to room temperature.

[0068] S6. Reheat the quenched mandrel to 580℃, hold for 100 minutes, and air cool to room temperature. Then reheat the mandrel to 580℃, hold for 100 minutes, and air cool to room temperature to obtain the composite mandrel.

[0069] Example 6:

[0070] S1. The raw materials are prepared according to the following composition: 0.35wt% C, 0.75wt% Si, 0.28wt% Mn, 4.9wt% Cr, 1.3wt% Mo, 0.93wt% V, 0.22wt% Ni, 0.003wt% RE, with the balance being Fe and unavoidable impurities.

[0071] S2. Add the prepared raw materials to the medium-frequency induction furnace, melt and hold at 1610℃ for 15 minutes, tap the steel to the ladle furnace for refining, control the oxygen content of the molten steel to ≤15ppm, blow argon and stir for 10 minutes, add aluminum granules for final deoxidation, control the oxygen content of the molten steel to ≤15ppm, vacuum at 1560℃ to 45Pa, hold for 15 minutes, so that the temperature of the alloy liquid exiting the furnace is controlled at 1550℃.

[0072] S3. Preheat the mandrel blank to 250℃ and hold for 30 minutes. After preheating, put the blank into the metal mold and connect the internal cavity circulating cooling water system: control the water temperature at 30℃ and adjust the water flow rate to 5.0m / s. The composition of the mandrel blank is: 0.41wt%C, 14.0wt%Cr, 1.9wt%Mn, 0.38wt%Mo, 0.68wt%W, with the balance being Fe and unavoidable impurities.

[0073] S4. The alloy liquid is injected into the mold at 1520℃ and a pouring speed of 1.0 kg / s. A low pressure of 0.10 MPa is applied to assist the filling process to ensure smooth filling without turbulence. After pouring, the mixture is allowed to cool naturally for 60 minutes before demolding to obtain the semi-finished composite mandrel.

[0074] S5. Heat the semi-finished mandrel to 1050℃ at a rate of 100℃ / h, hold for 45 minutes, and after taking it out of the furnace, quickly immerse it in rapid quenching oil to cool to room temperature.

[0075] S6. Reheat the quenched mandrel to 580℃, hold for 100 minutes, and air cool to room temperature. Then reheat the mandrel to 580℃, hold for 100 minutes, and air cool to room temperature to obtain the composite mandrel.

[0076] Example 7:

[0077] The only difference from Example 1 is that cooling water is not provided in the inner cavity of the top blank.

[0078] Example 8:

[0079] The only difference from Example 1 is that the water temperature in step S3 is 5°C.

[0080] Example 9:

[0081] The only difference from Example 1 is that the water temperature in step S3 is 100°C.

[0082] Comparative Example 1:

[0083] The only difference from Example 1 is that the metal layer does not contain Ni.

[0084] Comparative Example 2:

[0085] The only difference from Example 1 is that the metal layer does not contain RE.

[0086] Comparative Example 3:

[0087] The only difference from Example 1 is that no metal layer is provided; it is only a top blank.

[0088] Performance testing of the mandrels obtained in Examples 1-9 and Comparative Examples 1-3:

[0089] Using a high-temperature pin-disc wear testing machine (such as HT-1000), the composite mandrel slices and a high-temperature GCr15 steel disc are rubbed against each other at 800-1000℃, with a load of 50-100N and a sliding speed of 0.2-0.5m / s, for 10-20 hours, and the wear rate is calculated.

[0090] Heat the sample to 950℃, hold for 10 minutes, and then quickly cool it to room temperature. Repeat the cycle (similar to GB / T3098.10-2010).

[0091] The composite mandrel of this invention was installed on a hot rolling piercing mill in a seamless steel pipe plant, and the number of Φ159mm steel pipes that could be continuously pierced by a single mandrel was recorded.

[0092] Table 2: Performance test results of the mandrels obtained in Examples 1-9 and Comparative Examples 1-3

[0093]

[0094]

[0095] In summary, this invention, by connecting a circulating cooling water system to the inner cavity of the mandrel blank, constructs an asymmetric thermal field characterized by "rapid internal cooling and slow external cooling (or slow heating)." This not only achieves high-quality interfacial bonding and a dense microstructure during the composite casting process but also creates a surface compressive stress field conducive to crack resistance during service, effectively alleviating thermal stress concentration and suppressing the generation and propagation of thermal fatigue cracks. This design concept of "using cooling to control heating and suppressing cracks" is one of the core technical paths for achieving long service life, temperature resistance, and crack resistance in this composite mandrel, and has significant engineering application value.

[0096] The embodiments described herein cover any points not exhaustively within the scope of the technical claims of this invention, as well as new technical solutions formed by equivalent substitutions of one or more technical features in the embodiments. These are all within the scope of the claims of this invention. Furthermore, in all listed or unlisted embodiments of this invention, each parameter in the same embodiment merely represents an instance (i.e., a feasible solution) of its technical solution, and there is no strict coordination or limitation relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this invention, unless otherwise stated.

[0097] The technical means disclosed in this invention are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

[0098] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A long-life, temperature-resistant, and crack-resistant composite mandrel, characterized in that, The composite mandrel consists of a mandrel blank and a metal layer covering the surface of the mandrel blank. The metal layer comprises: 0.28-0.38 wt% C, 0.7-1.0 wt% Si, 0.2-0.3 wt% Mn, 4.6-5.2 wt% Cr, 1.2-1.6 wt% Mo, 0.9-1.0 wt% V, 0.2-0.3 wt% Ni, 0.001-0.005 wt% RE, with the balance being Fe and unavoidable impurities.

2. The long-life, temperature-resistant, and crack-resistant composite mandrel according to claim 1, characterized in that, The composition of the mandrel blank is: 0.40-0.44wt% C, 13.8-14.2wt% Cr, 1.8-2.3wt% Mn, 0.3-0.4wt% Mo, 0.6-0.7wt% W, with the balance being Fe and unavoidable impurities.

3. A method for preparing a long-life, temperature-resistant, and crack-resistant composite mandrel as described in claim 1, characterized in that, The method includes the following steps: S1. Prepare raw materials according to the composition of the metal layer; S2. Melt the raw materials to obtain a liquid alloy; S3. Place the mandrel blank into the mold, then pour the molten alloy into the mold, and obtain the semi-finished mandrel after cooling. S4. Finally, the semi-finished mandrel is quenched and tempered to obtain the composite mandrel.

4. The method for preparing a long-life, temperature-resistant, and crack-resistant composite mandrel according to claim 3, characterized in that, The melting temperature in step S2 is 1580-1620℃, followed by refining, then adding Al to deoxidize until the oxygen content is ≤15ppm, and then performing vacuum degassing treatment at 1550-1580℃. Finally, the temperature of the alloy liquid exiting the furnace is controlled at 1520-1560℃.

5. The method for preparing a long-life, temperature-resistant, and crack-resistant composite mandrel according to claim 4, characterized in that, During the refining process, the slag basicity is controlled at 2.5-3.

5.

6. The method for preparing a long-life, temperature-resistant, and crack-resistant composite mandrel according to claim 4, characterized in that, The vacuum degassing process involves a vacuum level of 30-67 Pa and a time of 10-15 min.

7. The method for preparing a long-life, temperature-resistant, and crack-resistant composite mandrel according to claim 3, characterized in that, Step S3: Place the mandrel blank into the mold and preheat it to 200-300℃. Connect the inner cavity of the mandrel blank to a circulating cooling water system. The water flow rate is controlled at 1.5-2.5m / s and the water temperature is 25-40℃.

8. The method for preparing a long-life, temperature-resistant, and crack-resistant composite mandrel according to claim 3, characterized in that, In step S3, the molten alloy is injected into the mold at a casting temperature of 1500-1540℃ and a casting speed of 0.8-1.2 kg / s, and the filling is completed under the condition of 0.05-0.15 MPa.

9. The method for preparing a long-life, temperature-resistant, and crack-resistant composite mandrel according to claim 3, characterized in that, The quenching temperature in step S4 is 1000-1100℃, and the time is 30-60min.

10. The method for preparing a long-life, temperature-resistant, and crack-resistant composite mandrel according to claim 3, characterized in that, Step S4 involves 2-3 tempering cycles at a temperature of 550-600℃ for 90-120 minutes, followed by air cooling to room temperature after each tempering cycle.

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