A method for manufacturing a cylindrical housing and use of a cylindrical housing

Abstract

The application relates to a preparation method of a cylindrical shell and application of the cylindrical shell, and the preparation method of the cylindrical shell comprises the following steps: (1) blank preparation: containing 0.0010-0.0035 wt% B; (2) blank heating: the blank is heated to 1180-1220 DEG C through staged temperature rising; (3) inclined rolling piercing: the diameter of a top head is 120-125 mm, the top head protrudes by 55-65 mm, the diameter reduction rate is 10-12%, and the rolling roller rotating speed is 20-30 r / min; (4) rough pipe sawing: cutting into several pipe sections; (5) heat treatment; and (6) mechanical processing. Through the staged gradient temperature rising mode, the internal temperature distribution of the blank is more uniform, and the structure is fully austenitized; meanwhile, through control of the top head diameter, the top head protruding amount, the diameter reduction rate and the rolling roller rotating speed parameters, the blank forms a stable and continuous metal flowing state in the piercing process.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, specifically to a method for preparing a cylindrical shell and the application of the cylindrical shell. Background Technology

[0002] The warhead casing is a load-bearing component that maintains structural integrity during projectile launch, flight, and penetration. When the warhead impacts a target, the casing disintegrates under internal explosive loads, forming high-speed, dispersed fragments that constitute the primary damage element. To achieve higher damage effectiveness, projectile steel is being developed towards higher strength and higher fragmentation rates. Research shows that adding trace amounts of boron can effectively improve the hardenability and fragmentation properties of projectile steel. For example, Chinese invention patent application CN201210543746.8 (publication number CN103866195A) discloses a medium-carbon low-alloy boron-containing structural steel and its heat treatment method, with a chemical composition of C 0.37–0.44 wt%, Si 1.2–1.6 wt%, Mn 0.50–0.80 wt%, Cr 0.6–1.1 wt%, B 0.0005–0.0035 wt%, and the balance being Fe. The chemical composition of this steel is similar to that of 40Cr steel, but its comprehensive mechanical properties are superior to those of 40Cr after quenching and tempering, especially its hardenability is significantly improved.

[0003] Another example is the Chinese invention patent application with patent application number CN202511528075.1 (publication number CN121451043A), which discloses a medium-carbon, boron-containing weathering shard killed steel and its production process. Based on boron-containing steel, it takes into account the sharding performance requirements and provides a manufacturing process from electric furnace smelting to continuous casting and rolling of bars, which can obtain bars with uniform composition and structure.

[0004] The two existing patents mentioned above provide a material basis for warhead shells from the perspectives of alloy composition design and bar preparation. However, neither patent addresses how to process the material so that the final formed component can meet the performance requirements of the warhead shell.

[0005] The warhead casing is primarily a cylindrical structure, and currently, it is mainly manufactured using two processes: one is direct machining from bar stock. While this method is simple, it results in low material utilization, generates a large amount of expensive alloy steel chips, and has long machining times and high tool consumption, leading to high production costs. The other method involves using forging processes such as hot drawing to obtain a casing blank of approximately the desired shape, followed by machining and heat treatment. Although this method improves material utilization, it requires expensive specialized forging dies and is suitable for mass production. For multi-variety, small-to-medium batch casing products, the amortization cost of the dies is high, resulting in poor economic efficiency.

[0006] Due to its high yield and high production efficiency, skew rolling piercing technology has become a core solution for producing high-strength and high-toughness seamless pipes. However, currently, this technology is mainly used in the production of standard pipes made of traditional high-strength steel, and there is no technical solution for manufacturing boron-containing alloy steel pipe blanks using skew rolling piercing process, because the high resistance to high-temperature deformation of boron-containing steel makes piercing and forming difficult.

[0007] For example, Chinese invention patent application number CN202310003974.4 (publication number CN116000574B) discloses a manufacturing method and application of a thin-walled cylindrical blank. This method involves forging a high-purity steel ingot with a large deformation ratio, followed by processes such as piercing, precision rolling, and sizing to produce the thin-walled cylindrical blank, which can be used for engine housings. However, the steel used in this patent does not contain boron, and its process design focuses on the high strength and high toughness requirements of the thin-walled engine housing, without addressing the specific requirements of projectile housings for high fragmentation and excellent fragmentation rate.

[0008] In summary, although existing technologies have provided high-performance medium-carbon boron-containing projectile steel materials and their bars, there is a lack of a process for manufacturing projectile shells from such boron-containing projectile steel bars through skew rolling and piercing. Existing shell piercing manufacturing methods are designed for boron-free steel grades, and their processes and heat treatment regimes cannot meet the damage performance requirements of warhead shells for high fragmentation and excellent fragmentation rate. Summary of the Invention

[0009] The first technical problem to be solved by the present invention is to provide a method for preparing a cylindrical shell of boron-containing steel based on the skew rolling piercing technology, in light of the current state of the prior art.

[0010] The second technical problem to be solved by the present invention is to provide an application of the above-mentioned cylindrical shell in view of the current state of the prior art.

[0011] The technical solution adopted by the present invention to solve the first technical problem mentioned above is as follows: A method for preparing a cylindrical shell includes the following steps:

[0012] (1) Billet preparation: The billet is a cylindrical bar containing 0.0010 to 0.0035 wt% B;

[0013] (2) Billet heating: The billet is heated in stages to 1180-1220°C to achieve a microstructure suitable for skew rolling piercing;

[0014] (3) Inclined rolling piercing: The heated billet is fed into the inclined rolling piercing unit for piercing processing to obtain hollow tubes; the piercing process parameters are: mandrel diameter 120~125mm, mandrel extension 55~65mm, diameter reduction rate 10~12%, and roll speed 20~30r / min.

[0015] (4) Capillary sawing: After the perforated capillary is air-cooled to room temperature, the surface quality and size are inspected. For qualified capillary, it is cut into several sections according to the shell size requirements.

[0016] (5) Heat treatment: The pipe section is heat treated to meet the specified mechanical performance requirements;

[0017] (6) Machining: The heat-treated pipe section is machined to prepare the shell.

[0018] Preferably, in step (1), the billet contains the following components and their mass fractions: C 0.35~0.45wt%, Si 1.2~1.6wt%, Mn 0.60~1.0wt%, Cr 0.6~1.0wt%, S≤0.005wt%, P≤0.015wt%, B 0.0010~0.0035wt%, with the balance being Fe.

[0019] Preferably, in step (1), the outer diameter of the blank is 183-187 mm and the length is 1500-2000 mm.

[0020] Preferably, in step (2), the heating process specifically involves: first preheating the billet to 880–920°C and holding it for 1–1.5 hours; then heating it to 1090–1110°C and holding it for 1.5–2 hours; and finally heating it to 1180–1220°C and holding it for 1–1.5 hours. Through multi-stage gradient heating, the forging bar gradually and uniformly austenitizes, obtaining a plastic deformation structure suitable for skew rolling piercing, thus avoiding excessive internal thermal stress in the boron-containing steel due to excessively rapid heating, which could lead to cracks or delamination.

[0021] Preferably, in step (3), the skew rolling piercing is performed using a two-roll skew rolling piercing mill. The parameters are optimized and matched to the deformation characteristics of medium carbon boron steel to avoid defects such as cracks or folds caused by excessive deformation resistance, and to ensure that the tube is successfully pierced and formed.

[0022] Preferably, in step (5), the heat treatment process is as follows: the normalizing temperature is 870-880℃, held for 20-40 minutes, and then air-cooled to room temperature; the quenching temperature is 890-900℃, held for 20-40 minutes, and then water-cooled to room temperature; the tempering temperature is 500-550℃, held for 120-150 minutes, and then water-cooled to room temperature. Normalizing can refine the grains and homogenize the structure, providing a good pre-structure for subsequent quenching; quenching, combined with the significant improvement of hardenability by boron, enables the shell to obtain a martensitic structure, thereby increasing its strength; tempering, by controlling the tempering temperature and holding time, regulates the strength and toughness of the shell.

[0023] Preferably, in step (6), the shell has a tensile strength of 1100-1500 MPa and an elongation of 13-15%.

[0024] The technical solution adopted by the present invention to solve the second technical problem mentioned above is: an application of a cylindrical shell, which is obtained by the above preparation method, and is used as a warhead shell.

[0025] Compared with the prior art, the advantages of the present invention are:

[0026] (1) This invention realizes the combination of boron-containing steel and skew rolling piercing technology: In view of the characteristics of steel containing B element having high deformation resistance and certain crack sensitivity at high temperature, by adopting a staged gradient heating method, the internal temperature distribution of the billet is made more uniform and the structure is fully austenitized, thereby reducing the deformation resistance during piercing and improving the plastic deformation capacity of the billet during skew rolling piercing; at the same time, by controlling the parameters of mandrel diameter, mandrel extension, diameter reduction rate and roll speed, the billet forms a stable and continuous metal flow state during piercing, avoiding excessive local deformation or uneven deformation, reducing the risk of defects such as piercing cracks and internal folds, and improving the stability of skew rolling piercing forming of boron-containing steel and the quality of the tube.

[0027] (2) The present invention uses skew rolling piercing to directly obtain hollow tubes from forged bars. The material utilization rate is significantly higher than that of integral bar cutting, which shortens the machining time and significantly improves production efficiency.

[0028] (3) Only a few tooling tools such as the top of the skew rolling piercing mill need to be replaced to adapt to the production of shells with different inner diameter specifications. The mold amortization cost is low, which makes the preparation method of the present invention highly adaptable to the process and suitable for multi-variety, small and medium batch production. Attached Figure Description

[0029] Figure 1 The process flow of the preparation method of the present invention is as follows;

[0030] Figure 2 The capillary tube prepared in Example 2;

[0031] Figure 3 The metallographic structure of the capillary prepared in Example 2;

[0032] Figure 4 The metallographic structure of the pipe section after heat treatment in Example 2 is shown. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. Those skilled in the art should understand that the embodiments described are only for the purpose of helping to understand this invention and should not be considered as specific limitations on this invention.

[0034] Example 1

[0035] The method for preparing the cylindrical shell in this embodiment includes the following steps:

[0036] (1) Billet preparation: The billet is a cylindrical bar with dimensions of φ183×1500mm. The billet contains the following components and their mass fractions: C 0.42wt%, Si 1.41wt%, Mn 0.68wt%, Cr 0.83wt%, S 0.002wt%, P 0.005wt%, B 0.0022wt%, with the balance being Fe;

[0037] (2) Billet heating: The prepared billet is loaded into the inclined bottom tube billet heating furnace and heated in the following three-stage heating process: First, the billet is preheated to 880℃ and held for 1 hour; then the temperature is raised to 1090℃ and held for 1.5 hours; finally, the temperature is raised to 1180℃ and held for 1 hour to obtain good plastic deformation ability and make the billet reach a microstructure suitable for inclined rolling piercing.

[0038] (3) Skew rolling piercing: The bar stock heated to 1180℃ is quickly fed into the φ150mm two-roll skew rolling piercing mill. The process parameters are: mandrel diameter 120mm, mandrel extension 55mm, diameter reduction rate 10%, and roll speed 20r / min. Under the above parameters, hot piercing is performed. The bar stock is deformed under the combined action of the rolls and the mandrel, and finally pierced into a continuous hollow tube.

[0039] (4) Capillary sawing: The perforated capillary is immediately lowered into the pit and air-cooled to room temperature. Then, the surface quality and dimensions are inspected. The inner and outer surfaces of the tube are free of defects such as folds and cracks. The outer diameter and wall thickness meet the requirements of subsequent machining. If the requirements are met, the head and tail of the capillary are removed according to the design length of 400mm of the shell part, and the capillary is cut into 6 sections. If the surface quality and dimensions of the capillary do not meet the requirements, the capillary is discarded.

[0040] (5) Heat treatment: The pipe section is heat treated in a box-type resistance furnace. The specific heat treatment process is as follows: the normalizing temperature is 870℃, and after holding for 20 minutes, it is air-cooled to room temperature; the quenching temperature is 890℃, and after holding for 20 minutes, it is water-cooled to room temperature; the tempering temperature is 500℃, and after holding for 120 minutes, it is water-cooled to room temperature, so that the pipe section meets the specified mechanical performance requirements.

[0041] (6) Machining: The heat-treated pipe section is clamped in a CNC turning center and machined according to the dimensions set on the drawing to obtain the shell part.

[0042] Example 2

[0043] The method for preparing the cylindrical shell in this embodiment includes the following steps:

[0044] (1) Billet preparation: The billet is a cylindrical rod with dimensions of φ185×1500mm. The billet contains the following components and their mass fractions: C 0.42wt%, Si 1.41wt%, Mn 0.68wt%, Cr 0.83wt%, S 0.002wt%, P 0.005wt%, B 0.0022wt%, with the balance being Fe;

[0045] (2) Billet heating: The prepared billet is loaded into the inclined bottom tube billet heating furnace and heated in the following three-stage heating process: First, the billet is preheated to 900℃ and held for 1 hour; then the temperature is raised to 1100℃ and held for 2 hours; finally, the temperature is raised to 1200℃ and held for 1 hour to obtain good plastic deformation ability and make the billet reach a microstructure suitable for inclined rolling piercing.

[0046] (3) Skew rolling piercing: The bar stock heated to 1200℃ is rapidly fed into a φ150mm two-roll skew rolling piercing mill. The process parameters are: mandrel diameter 120mm, mandrel extension 60mm, diameter reduction rate 11%, and roll speed 25r / min. Under the above parameters, hot piercing is performed. The bar stock deforms under the combined action of the rolls and the mandrel, and is finally pierced into a continuous hollow tube, such as... Figure 2 , 3 As shown;

[0047] (4) Capillary sawing: The perforated capillary is immediately hoisted into the pit and air-cooled to room temperature. Then, the surface quality and dimensions are inspected. There are no defects such as folds or cracks on the inner and outer surfaces of the pipe. The outer diameter and wall thickness meet the requirements of subsequent machining. If the requirements are met, the head and tail of the capillary are cut off according to the design length of 400mm of the shell parts, and the capillary is cut into 6 pipe sections. If the surface quality and dimensions of the capillary do not meet the requirements, the capillary is discarded.

[0048] (5) Heat treatment: The pipe section is heat-treated in a box-type resistance furnace. The specific heat treatment process is as follows: normalizing temperature is 880℃, held for 30 minutes and then air-cooled to room temperature; quenching temperature is 890℃, held for 30 minutes and then water-cooled to room temperature; tempering temperature is 520℃, held for 120 minutes and then water-cooled to room temperature, so that the pipe section meets the specified mechanical property requirements, such as... Figure 4 As shown;

[0049] (6) Machining: The heat-treated pipe section is clamped in a CNC turning center and machined according to the dimensions set on the drawing to obtain the shell part.

[0050] Example 3

[0051] The method for preparing the cylindrical shell in this embodiment includes the following steps:

[0052] (1) Billet preparation: The billet is a cylindrical rod with dimensions of φ183×1500mm. The billet contains the following components and their mass fractions: C 0.42wt%, Si 1.41wt%, Mn 0.68wt%, Cr 0.83wt%, S 0.002wt%, P 0.005wt%, B 0.0022wt%, with the balance being Fe;

[0053] (2) Billet heating: The prepared billet is loaded into the inclined bottom tube billet heating furnace and heated in the following three-stage heating process: first, the billet is preheated to 920℃ and held for 1.5h; then, it is heated to 1100℃ and held for 2h; finally, it is heated to 1220℃ and held for 1.5h to obtain good plastic deformation ability and make the billet reach a microstructure suitable for inclined rolling piercing.

[0054] (3) Inclined rolling piercing: The bar stock heated to 1200℃ is quickly fed into the φ150mm two-roll skewed rolling piercing mill. The process parameters are: mandrel diameter 120mm, mandrel extension 65mm, diameter reduction rate 12%, and roll speed 30r / min. Under the above parameters, hot piercing is carried out. The bar stock is deformed under the combined action of the roll and the mandrel, and finally pierced into a continuous hollow tube.

[0055] (4) Capillary sawing: The perforated capillary is immediately lowered into the pit and air-cooled to room temperature. Then, the surface quality and dimensions are inspected. The inner and outer surfaces of the tube are free of defects such as folds and cracks. The outer diameter and wall thickness meet the requirements of subsequent machining. If they do not meet the requirements, the head and tail of the capillary are cut off according to the design length of 400mm of the shell part, and the capillary is cut into 6 sections. If the surface quality and dimensions of the capillary do not meet the requirements, the capillary is discarded.

[0056] (5) Heat treatment: The pipe section is heat treated in a box-type resistance furnace. The specific heat treatment process is as follows: the normalizing temperature is 880℃, and after holding for 40 minutes, it is air-cooled to room temperature; the quenching temperature is 900℃, and after holding for 40 minutes, it is water-cooled to room temperature; the tempering temperature is 550℃, and after holding for 150 minutes, it is water-cooled to room temperature, so that the pipe section meets the specified mechanical performance requirements.

[0057] (6) Machining: The heat-treated pipe section is clamped in a CNC turning center and machined according to the dimensions set on the drawing to obtain the shell part.

[0058] In step (1) of the above embodiments, the billet is prepared using the method disclosed in CN121451043A; molten steel with qualified composition is obtained through electric furnace smelting, ladle refining and vacuum degassing, and then bar stock with uniform composition and structure is obtained through continuous casting and rolling. Of course, the billet can also be purchased.

[0059] Figure 1 The preparation method of the present invention is as follows: Figure 2 , Figure 3 , Figure 4 The capillary tube, the capillary tube metallographic structure, and the metallographic structure of the tube section after heat treatment prepared in Example 2 show that the capillary tube prepared by skew rolling and piercing has good surface quality and no defects such as cracks or folds. The microstructure is mainly composed of network ferrite and lamellar pearlite. After heat treatment, the microstructure of the tube section is mainly composed of tempered sorbite composed of dispersed fine carbides.

[0060] The shells prepared in Examples 1, 2, and 3 above were sampled and subjected to room temperature tensile property tests according to GB / T 228.1 standard. The results are shown in Table 1. These examples fully demonstrate that the manufacturing method provided by this invention can not only efficiently manufacture medium-carbon boron alloy steel shells, but also achieve comprehensive control of strength and toughness by adjusting the heat treatment process, meeting the needs of multi-variety, small-batch projectile manufacturing.

[0061]

Claims

1. A method for preparing a cylindrical shell, characterized in that, Includes the following steps: (1) Billet preparation: The billet is a cylindrical bar containing 0.0010 to 0.0035 wt% B; (2) Billet heating: The billet is heated in stages to 1180-1220°C to achieve a microstructure suitable for skew rolling piercing; (3) Inclined rolling piercing: The heated billet is fed into the inclined rolling piercing unit for piercing processing to obtain hollow tubes; the piercing process parameters are: mandrel diameter 120~125mm, mandrel extension 55~65mm, diameter reduction rate 10~12%, and roll speed 20~30r / min. (4) Capillary sawing: After the perforated capillary is air-cooled to room temperature, the surface quality and size are inspected. For qualified capillary, it is cut into several sections according to the shell size requirements. (5) Heat treatment: The pipe section is heat treated to meet the specified mechanical performance requirements; (6) Machining: The heat-treated pipe section is machined to prepare the shell.

2. The preparation method according to claim 1, characterized in that: In step (1), the billet contains the following components and their mass fractions: C 0.35-0.45wt%, Si 1.2-1.6wt%, Mn 0.60-1.0wt%, Cr 0.6-1.0wt%, S≤0.005wt%, P≤0.015wt%, B 0.0010-0.0035wt%, with the balance being Fe.

3. The preparation method according to claim 1, characterized in that: In step (1), the outer diameter of the blank is 183-187 mm and the length is 1500-2000 mm.

4. The preparation method according to claim 1, characterized in that: In step (2), the heating process is as follows: first, the billet is preheated to 880-920℃ and kept at that temperature for 1-1.5h; then, the temperature is raised to 1090-1110℃ and kept at that temperature for 1.5-2h; finally, the temperature is raised to 1180-1220℃ and kept at that temperature for 1-1.5h.

5. The preparation method according to claim 1, characterized in that: In step (3), the skew rolling piercing is performed using a two-roll skew rolling piercing mill.

6. The preparation method according to claim 1, characterized in that: In step (5), the heat treatment process is as follows: the normalizing temperature is 870-880℃, and after holding for 20-40 minutes, it is air-cooled to room temperature; the quenching temperature is 890-900℃, and after holding for 20-40 minutes, it is water-cooled to room temperature; the tempering temperature is 500-550℃, and after holding for 120-150 minutes, it is water-cooled to room temperature.

7. The preparation method according to claim 1, characterized in that: In step (6), the shell obtained has a tensile strength of 1100-1500 MPa and an elongation of 13-15%.

8. An application of a cylindrical shell, characterized in that, The cylindrical shell is obtained by the preparation method described in any one of claims 1 to 7, and the cylindrical shell is used as a warhead shell.

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