Heat treatment method of maraging steel solid rocket engine combustion chamber shell

Abstract

The invention discloses a heat treatment method for a maraging steel solid rocket engine combustion chamber shell, and belongs to the technical field of maraging steel heat treatment. The heat treatment method comprises the following steps: firstly, carrying out solution treatment on each part for assembling the combustion chamber shell; then, performing overaging treatment on the parts with lower mechanical property requirements in the parts subjected to solution treatment; and finally, the part subjected to solution treatment and the part subjected to solution treatment and overaging treatment are welded into the combustion chamber shell, and overall aging treatment is conducted. By adjusting the overaging temperature and time, heat treatment of parts with different strength requirements can be met, the hardness is reduced, and by means of an overall aging method after welding, the obdurability of the shell is improved, the milling efficiency is improved, the machining deformation is reduced, and the quality and the qualification rate of the shell are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment of maraging steel, and in particular relates to a heat treatment method for a maraging steel solid rocket engine combustion chamber shell. Background Art

[0002] Maraging steel is a special type of ultra-high strength steel. Different from traditional ultra-high strength steel, it is strengthened by the precipitation of certain intermetallic compounds on an ultra-low carbon iron-nickel martensitic matrix. Therefore, it has excellent strength and toughness combination, high dimensional stability and good weldability. It is widely used in solid rocket engine combustion chamber casings and other aspects.

[0003] The combustion chamber shell of solid rocket motors is usually made of maraging steel such as T250 and C250. The typical structure diagram of the combustion chamber shell is shown in Figure 1 The combustion chamber shell is mainly composed of front connectors, rear connectors, barrels and mounting seats, and is usually welded with the same material, such as T250, C250 and other maraging steel. Before welding, the front connectors, rear connectors, mounting seats and barrels are subjected to solid solution heat treatment, and then the parts are processed and formed. The current mature process flow of the maraging steel combustion chamber shell is: welding of front connectors, rear connectors, mounting seats and barrels → aging → machining of front and rear connectors and mounting seats. Since the barrel and front and rear connectors have to withstand the instantaneous high temperature and high pressure thrust, the mechanical properties are required to be above 1760MPa; and the mechanical properties of the mounting seat and the shell weld are required to be above 1080MPa, so the mechanical properties of the mounting seat are required to be lower. However, since the combustion chamber shell is generally composed of various parts and components of the same material, it is convenient for subsequent welding and heat treatment, which leads to high mechanical properties of all parts and components of the maraging steel T250 and C250 combustion chamber shell after solid solution and aging, with a hardness of up to 52HRC. However, the mounting seat is greatly deformed after welding and heat treatment aging, so a large margin is left before welding and heat treatment, and it needs to be milled and formed after heat treatment. Due to the high hardness of the mounting seat, milling is difficult, and the large cutting force causes large deformation of the combustion chamber shell, and the tool wears quickly. The external hanging parts such as the mounting seat have high processing precision and high assembly requirements, resulting in low processing efficiency of the combustion chamber shell and low product qualification rate.

[0004] Therefore, dissimilar materials are often welded in production to reduce the difficulty of processing. For example, the article "T250 and 30CrMnSiA Dissimilar Materials Welding Technology" published in the 5th issue of Aerospace Manufacturing Technology in 2011 studied the welding process of dissimilar materials T250 and 30CrMnSiA. The weld strength after aging and the dissimilar material 30CrMnSiA both meet the technical requirements of not less than 1080MPa. However, there are certain risks in this technology. Martensitic aging steel T250 is strengthened by the precipitation of intermetallic compounds produced by metal elements such as molybdenum and titanium on the ultra-low carbon iron-nickel martensitic matrix, and the carbon content is required to be no more than 0.03%; while the carbon content in 30CrMnSiA alloy structural steel is between 0.28% and 0.34%, which is more than 10 times the carbon content of T250. Carbon is a harmful element in martensitic aging steel. Carbon and titanium generate titanium carbide non-metallic inclusions, which not only reduce the toughness of steel, but also reduce the strength of T250. This is because titanium is the main strengthening element in maraging steel. After aging, the titanium in the steel almost completely forms a dispersed Ni3Ti intermetallic compound strengthening phase, and the strength of the steel mainly varies with the titanium content. When carbon consumes the titanium element in maraging steel, the dispersed Ni3Ti intermetallic compound strengthening phase in the weld fusion zone is reduced, resulting in a decrease in the strength of the fusion weld with the matrix. At the same time, chain-like titanium carbide brittle non-metallic inclusions are formed along the weld, making the weld brittle and reducing the toughness of the steel. The fracture of maraging steel is usually caused by this inclusion. The above factors will cause the solid rocket engine combustion chamber shell to disintegrate prematurely during operation. Therefore, maraging steel T250 is a pure ultra-low carbon steel with strict metallurgical requirements.

[0005] There are many problems in the design and manufacturing process of the solid rocket engine combustion chamber shell. For example, if the same material is used for maraging steel, the hardness of the mounting seat and other parts after heat treatment is high, the tool wears quickly, the production efficiency is low, and the qualified rate is not high; and if dissimilar materials are used for welding, there are unstable factors such as the matching of welding wire and the two materials, whether the dissimilar materials bring harmful elements to the weld, and the mechanical properties of the weld are reduced, which brings great hidden dangers to the quality of the combustion chamber shell. Therefore, it is imperative to seek a high-efficiency, low-cost, reliable quality, and stable mechanical performance maraging steel combustion chamber shell manufacturing method. Summary of the invention

[0006] Technical issues to be solved:

[0007] In order to avoid the shortcomings of the prior art, the present invention provides a heat treatment method for a combustion chamber shell of a solid rocket engine made of maraging steel, a heat treatment method for different parts of a combustion chamber shell of a solid rocket engine made of the same maraging steel, and a heat treatment method for an overall combustion chamber shell, which avoids the problem of brittle intermetallic compounds generated in the weld joint area caused by welding of dissimilar materials, and reduces the strength of the weld. At the same time, the weld joint strength is improved by welding of the same material. In addition, by adjusting the over-aging temperature and time, the heat treatment of parts with different strength requirements can be met, the hardness is reduced, and the overall aging method after welding is used to improve the toughness of the shell, improve the milling efficiency, reduce processing deformation, and improve the shell quality and qualified rate.

[0008] The technical solution of the present invention is: a heat treatment method for a maraging steel solid rocket engine combustion chamber casing, the specific steps are as follows:

[0009] Step 1: Solution treatment of the parts of the assembled combustion chamber casing;

[0010] Step 2: Perform aging treatment on the parts with relatively low mechanical property requirements after solution treatment;

[0011] Step 3: Weld the parts that have only been solution treated and the parts that have been solution treated and over-aging treated into the combustion chamber shell, and then perform overall aging treatment.

[0012] A further technical solution of the present invention is: the combustion chamber housing comprises a front connecting piece, a cylinder, and a rear connecting piece which are coaxially installed in sequence, a mounting seat is installed on the outer periphery of the cylinder, and adjacent parts are fixedly connected by welding.

[0013] A further technical solution of the present invention is: in step 1, the process parameters of the solution treatment are heating to 820°C±10°C, keeping the temperature for 90min to 120min, and then taking the product out of the furnace and air cooling it to room temperature.

[0014] A further technical solution of the present invention is: in step 2, the process parameters of over-aging are heating to 530° C. to 600° C., keeping warm for 180 min to 360 min, and then taking out of the furnace and air cooling to room temperature after the end of the keeping warm.

[0015] A further technical solution of the present invention is: in step 2, the tensile strength of the parts with lower mechanical property requirements is greater than 1080 MPa and less than 1760 MPa.

[0016] A further technical solution of the present invention is: in step 3, the process parameters of the overall aging treatment are: heating to 480°C to 520°C, keeping warm for 180min to 240min, and air cooling after taking out of the furnace.

[0017] A solid rocket engine combustion chamber casing, characterized in that it includes a front connector, a rear connector, a barrel and a mounting seat made of T250 / C250 material, the front connector and the rear connector are respectively welded to the two ends of the barrel, and the mounting seat is welded to the outer periphery of the barrel; the tensile strength of the front connector, the rear connector and the barrel is greater than 1760MPa, and the hardness is 50-54HRC; the mechanical property requirements of the mounting seat and the weld are greater than 1080MPa, and the hardness is 36-50HRC.

[0018] A further technical solution of the present invention is that the front connecting piece, the rear connecting piece and the cylinder are subjected to a solution treatment before welding, and the combustion chamber shell as a whole is subjected to an aging treatment after welding.

[0019] A further technical solution of the present invention is that: the mounting seat is subjected to a double treatment of solid solution and over-aging before welding, and the combustion chamber shell is subjected to an aging treatment as a whole after welding.

[0020] Beneficial Effects

[0021] The beneficial effects of the present invention are:

[0022] First, the present invention uses T250 or C250 maraging steel of the same material for the mounting seat with lower mechanical property requirements, and successively performs solid solution and over-aging treatment to reduce the hardness before welding the combustion chamber shell. After the shell is welded, the mechanical properties and hardness of the mounting seat will not be changed by re-aging, while other parts are strengthened by aging precipitation, so that they have very excellent strength and toughness combination.

[0023] Second, during the welding process of two maraging steel parts of the same material but in different heat treatment states, there is no need to consider the selection of welding wire when welding dissimilar materials and the harmful inclusions caused by different materials during fusion welding that lead to a significant reduction in the performance of the welded joint. After welding and heat treatment and aging, the weld strength is equivalent to that of the matrix.

[0024] Third, parts with lower strength requirements can be treated by solid solution + over-aging heat treatment method, and the hardness can be adjusted between HRC36 and HRC50 according to design requirements, which not only ensures the high strength requirements of high temperature and high pressure parts, but also meets the low strength and easy processing requirements of non-pressure-bearing parts.

[0025] Fourth, since the strength of the mounting seat is relatively low, the processing efficiency is high, the tool wear is small, and the shell is less deformed during processing, the qualified rate is high, and the overall economic benefits are higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the combustion chamber casing structure.

[0027] Explanation of the reference numerals: 1. front connecting piece, 2. first ring weld, 3. cylinder, 4. mounting seat, 5. second ring weld, 6. rear connecting piece. DETAILED DESCRIPTION

[0028] The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0029] Based on the many problems existing in the design and manufacturing process of the existing solid rocket engine combustion chamber shell, the present invention provides a heat treatment method for the maraging steel solid rocket engine combustion chamber shell, and the specific steps are as follows:

[0030] Step 1: Solution treatment: Solution the parts of the combustion chamber shell, heat to 820℃±10℃, keep warm for 90min~120min, take out of the furnace and air cool to room temperature after the end of the heat preservation;

[0031] Step 2: Overaging: After solution treatment, overaging is performed on parts with lower mechanical property requirements. The parts are heated to 530℃~600℃ and kept at this temperature for 180min~360min. After the end of the heat preservation, they are taken out of the furnace and air-cooled to room temperature.

[0032] Step 3: Aging: Weld the solutionized parts and solutionized + over-aged parts into the combustion chamber shell, and then perform overall aging treatment, heat to 480℃~520℃, keep warm for 180min~240min, and take out of the furnace and air cool after the insulation is completed.

[0033] The heat treatment method of the present invention takes into account the different mechanical properties and hardness requirements of various parts in the solid rocket engine combustion chamber shell, and adopts a distributed heat treatment method; the heat treatment process is simple, which not only solves the problems of high hardness, large shell deformation, low processing efficiency, and fast tool wear, but also improves production efficiency, product quality and qualified rate.

[0034] The above technical solution is further explained below with reference to examples:

[0035] Embodiment 1:

[0036] The heat treatment method of the combustion chamber shell of a martensitic aged steel solid rocket engine described in this embodiment is specifically carried out according to the following steps: solid solution is performed on the blanks such as the front connector, the rear connector, the barrel and the mounting seat of T250 material, and the heat treatment parameters are kept at 820℃ for 90min to 120min, and then air-cooled to room temperature after being taken out of the furnace; then the blank of the mounting seat after solid solution is subjected to over-aging treatment, and the heat treatment parameters are kept at 600℃ for 180min, and then air-cooled to room temperature after being taken out of the furnace. Then the front connector, the rear connector, the barrel and the mounting seat are welded after mechanical processing, and the combustion chamber shell is subjected to aging treatment after welding, and the heat treatment parameters are kept at 500℃ for 180min, and then air-cooled to room temperature after being taken out of the furnace. Then the mounting seat is mechanically processed and formed. The number of tool wear, processing time, deformation before and after processing and qualified rate of a single shell are shown in Table 1.

[0037] In Example 1, after heat treatment, the tensile strength of the cylinder and the front and rear connecting parts is distributed between 1860MPa and 1920MPa, the elongation after fracture is between 6.2% and 6.9%, the tensile strength of the mounting seat weld strength is distributed between 1320MPa and 1350MPa, and the hardness of the mounting seat is between 39.2 and 40.5HRC.

[0038] Comparative experiment 1:

[0039] The blanks of T250 material such as front connector, rear connector, barrel and mounting seat are solid solution treated, and the heat treatment parameters are 820℃ for 90min~120min, and air-cooled to room temperature after being taken out of the furnace; then the front connector, rear connector, barrel and mounting seat are welded after mechanical processing, and the combustion chamber shell is aged after welding, and the heat treatment parameters are 500℃ for 180min, and air-cooled to room temperature after being taken out of the furnace. Then the mounting seat is mechanically processed and formed. The number of tool wear, processing time, deformation before and after processing and qualified rate of single shell are shown in Table 1.

[0040] Comparative Example 1 After heat treatment, the tensile strength of the mounting seat is distributed between 1860MPa and 1910MPa, the elongation after fracture is between 5.9% and 6.9%, the tensile strength of the mounting seat weld strength is distributed between 1820MPa and 1890MPa, and the hardness of the mounting seat is between 51.5 and 52.5HRC.

[0041] Table 1

[0042]

[0043] Analysis of the implementation effect of the present invention:

[0044] Compared with the comparative experiment 1, the tensile strength of the combustion chamber shell formed by mechanical processing after heat treatment in Example 1 is not less than 1760MPa, the elongation after fracture is 5%, and the weld strength of the mounting seat is not less than 1080MPa. The hardness of the mounting seat is between 39.2 and 40.5HRC. The wear of the tool for the single shell is small, the processing time is shorter, the deformation is small, the product qualification rate is high, and the heat treatment process is suitable for the production of mounting seats of different strengths. The mechanical properties of the comparative test all meet the requirements, but the mounting seat has high hardness, is difficult to process, is time-consuming, has low processing efficiency, and the shell qualification rate is not high.

[0045] It can be seen that the maraging steel solid rocket engine combustion chamber casing heat-treated by the method of the present invention has mechanical properties that meet the requirements, moderate hardness, less tool wear on a single casing, shorter processing time, less deformation, and a high product qualification rate. The heat treatment process is suitable for the production of mounting seats of different strengths and can be widely used in the production of maraging steel solid rocket engine combustion chamber casings.

[0046] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A heat treatment method for a maraging steel solid rocket engine combustion chamber casing, characterized in that The specific steps are as follows: Step 1: Solution treatment of the parts of the assembled combustion chamber casing; Step 2: Perform aging treatment on the parts with relatively low mechanical property requirements after solution treatment; Step 3: Weld the parts that have only been solution treated and the parts that have been solution treated and over-aging treated into the combustion chamber shell, and then perform overall aging treatment.

2. The heat treatment method for a maraging steel solid rocket engine combustion chamber casing according to claim 1, characterized in that: The combustion chamber shell comprises a front connecting piece, a cylinder and a rear connecting piece which are coaxially installed in sequence. A mounting seat is installed on the outer periphery of the cylinder, and adjacent parts are fixedly connected by welding.

3. The heat treatment method for a maraging steel solid rocket engine combustion chamber casing according to claim 2, characterized in that: In step 1, the process parameters of the solution treatment are heating to 820°C ± 10°C, keeping the temperature for 90 min to 120 min, and then taking the furnace out of the furnace and air cooling to room temperature.

4. The heat treatment method for a maraging steel solid rocket engine combustion chamber casing according to claim 3, characterized in that: In step 2, the process parameters of over-aging are: heating to 530° C. to 600° C., keeping warm for 180 min to 360 min, and then taking out of the furnace and air cooling to room temperature after the end of the keeping warm.

5. The heat treatment method for a maraging steel solid rocket engine combustion chamber casing according to claim 4, characterized in that: In step 2, the tensile strength of the parts with lower mechanical property requirements is greater than 1080 MPa and less than 1760 MPa.

6. The heat treatment method for a maraging steel solid rocket engine combustion chamber casing according to claim 4, characterized in that: In step 3, the process parameters of the overall aging treatment are heating to 480° C. to 520° C., keeping the temperature for 180 min to 240 min, and air cooling after the temperature is kept.

7. A solid rocket engine combustion chamber casing, characterized in that: It is prepared by the heat treatment method of a maraging steel solid rocket engine combustion chamber shell as described in any one of claims 1 to 6; it includes a front connector, a rear connector, a barrel and a mounting seat made of T250 / C250 material, the front connector and the rear connector are respectively welded to the two ends of the barrel, and the mounting seat is welded to the outer periphery of the barrel; the tensile strength of the front connector, the rear connector and the barrel is greater than 1760MPa, and the hardness is 50-54HRC; the mechanical property requirements of the mounting seat and the weld are greater than 1080MPa, and the hardness is 36-50HRC.

8. The solid rocket engine combustion chamber casing according to claim 1, characterized in that: The front connecting piece, the rear connecting piece and the cylinder are subjected to solution treatment before welding, and the combustion chamber shell as a whole is subjected to aging treatment after welding.

9. A solid rocket motor combustion chamber casing according to claim 1, characterized in that: The mounting seat is subjected to a double treatment of solid solution and over-aging before welding, and the combustion chamber shell is subjected to an aging treatment as a whole after welding.

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