Vacuum heat treatment process method for T250 martensite aging steel thin-wall cylinder

Abstract

The present application relates to a kind of T250 martensite age steel thin-walled cylinder vacuum heat treatment process method, cylinder blank solid solution is heated in box-type air furnace, after heating, water cooling mode is selected to cool quickly.The cylinder after spinning is carried out double vacuum solid solution treatment, control solid solution heating rate, select nitrogen filling gas cooling mode.Cylinder blank solid solution adopts water cooling, because cooling speed is fast and uniform, the second phase is inhibited to precipitate, ensure that the structure is uniform after solid solution, hardness is uniform.Vacuum solid solution is used, avoid the surface oxidation generated in air heating, improve surface quality, heat treatment deformation is small.Double solid solution process method is used, because there is the first solid solution organization preparation, after repeated solid solution, the structure is more uniform, cylinder diameter shrinkage consistency is better.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metal material heat treatment, and relates to a vacuum heat treatment process method for a T250 maraging steel thin-wall cylinder. BACKGROUND

[0002] The maraging steel has the advantages of super-high strength, high toughness, excellent cutting performance, simple heat treatment process and the like, and is widely applied to the fields of aerospace and cutting-edge weapons. In the 1990s of the 20th century, China began to develop the T250 maraging steel, and the T250 maraging steel was first applied to a certain type of solid rocket engine. With the deepening of the application of the T250 maraging steel to the rocket engine, more and more engineering application problems are exposed. In the manufacturing process of the engine shell, the diameter of the cylinder will shrink. Among them, the heat treatment before and after spinning has a great influence on the diameter size precision of the cylinder, and the improper heat treatment process method and parameter control leads to that the final size precision of the cylinder does not meet the design requirements, which is one of the most prominent problems.

[0003] QJ 20574-2016 "T250 maraging steel heat treatment process requirement" lists the typical workpiece process flow of the engine. Among them, the machining flow of the integral spinning cylinder is: 1 blanking-2 cylinder blank solution-3 machining-4 spinning-5 cylinder solution-6 cylinder aging-7 machining. According to the relevant process requirements, the cylinder blank and cylinder solution process method is: after the furnace temperature rises to 820℃-860℃, the workpiece is hung in the pit furnace by the lifting appliance, and is kept at 820℃-860℃ for 90min-120min, and then is taken out of the furnace and air cooled after the heat preservation is finished.

[0004] According to the above process method, after the cylinder blank solution treatment, due to the non-uniform air cooling, the hardness of the two ends of the cylinder blank is inconsistent, the hardness difference is greater than 2HRC, the diameter of the high-hardness end of the cylinder is obviously expanded during spinning, the diameters of the two ends are inconsistent, and the difference is large, and the maximum difference is 4mm. After the cylinder solution treatment, the heat treatment deformation is large, and the ovality reaches 2mm-4mm. The diameter of the cylinder along the length direction is consistent in the manufacturing process of the engine shell, and the problem of poor diameter consistency and difficult size precision control of the cylinder is solved

[0005] Therefore, in actual production, this heat treatment process method still has certain limitations, is affected by the structure and hoisting mode of the lifting appliance, the heating equipment can only select the pit furnace, the loading capacity is limited, the air cooling is not conducive to the uniform and rapid cooling of the cylinder blank, the production efficiency is low, and the heat treatment process method cannot adapt to mass production. SUMMARY

[0006] Technical problems to be solved

[0007] In order to avoid the deficiencies of the prior art, the application provides a vacuum heat treatment process method for a T250 martensite aging steel thin-wall cylinder, so that the diameter of the cylinder is uniformly contracted along the length direction during the manufacturing process of the engine shell, and the problems of poor diameter consistency and difficult size precision control of the cylinder are solved.

[0008] Technical scheme

[0009] A vacuum heat treatment method for a T250 martensite aging steel thin-wall cylinder, characterized in that the first step is as follows:

[0010] Step 1: solid solution is performed on the cylinder blank, and the cooling mode is water cooling, so that the cylinder blank is uniformly cooled, a supersaturated solid solution structure is obtained, the hardness of the blank is 27HRC-32HRC, and the hardness difference of the two ends is not more than 2HRC;

[0011] Then the solid-solutioned cylinder blank is processed into a thin-wall cylinder, and then two vacuum solid solution treatments are performed:

[0012] Step 2: the first vacuum solid solution is performed to eliminate the stress in the metal matrix inside after spinning processing, eliminate the banded texture structure after spinning, and obtain equiaxed grains after recovery and recrystallization;

[0013] Step 3: the second vacuum solid solution is performed to further eliminate the texture structure after spinning and refine the equiaxed grains after the first solid solution, and the diameter of the cylinder is stably contracted;

[0014] Step 4: the last aging treatment is performed; the two vacuum solid solution treatments adopt a nitrogen cooling mode to ensure uniform cooling of the cylinder.

[0015] The heating and holding parameters for the solid solution of the cylinder blank in step 1 are as follows: heating to 820-860 DEG C, holding for 120-150 min; after the heating and holding is completed, water cooling is adopted to cool to room temperature.

[0016] The cylinder blank is solid-solutioned in a box-type air furnace in step 1.

[0017] The heating and holding parameters for the first vacuum solid solution are as follows: heating from room temperature to 800-820 DEG C, holding for 15-30 min; after the heating and holding is completed, nitrogen cooling is adopted to cool to 200-300 DEG C.

[0018] The heating and holding parameters for the second vacuum solid solution are as follows: heating to 550-650 DEG C, holding for 15-30 min; then heating to 800-820 DEG C, holding for 90-120 min.

[0019] The heating and holding parameters of the aging treatment of the solid solution cylinder are as follows: loading into an air furnace at 500 DEG C to 530 DEG C, holding for 180 min to 240 min after being heated at 500 DEG C to 530 DEG C, and air cooling after being discharged from the furnace.

[0020] When the nitrogen gas is used for cooling during the two vacuum solid solution treatments, the pressure of the filled nitrogen gas is 2 bar to 5 bar.

[0021] The temperature rising time of each stage is 15 DEG C to 20 DEG C / min.

[0022] The cylinder blank is a T250 martensite aging steel pipe material, and the cylinder blank with a designed length of the cylinder is obtained by spinning.

[0023] The thin-walled cylinder is processed by machining and spinning forming.

[0024] Beneficial effects

[0025] The T250 martensite aging steel thin-walled cylinder vacuum heat treatment process method provided by the application is characterized in that the cylinder blank is heated in a box-type air furnace during solid solution, and is rapidly cooled by using a water cooling mode after being heated.

[0026] The solid cooling mode of the cylinder blank is water cooling, which can ensure uniform cooling of the cylinder blank, obtain a supersaturated solid solution structure, and make the blank hardness be 27HRC to 32HRC and the hardness difference of both ends be not more than 2HRC, thereby preparing the structure for the subsequent spinning process and eliminating the phenomenon of inconsistent diameter expansion after spinning caused by large hardness difference of the cylinder blank.

[0027] The vacuum solid solution of the cylinder can reduce heat treatment deformation and is beneficial to the processing and deformation control of the subsequent process of the cylinder.

[0028] During the whole process, the solid solution mode of each step has certain effects on the thin-walled cylinder.

[0029] (1) the existing solid solution process method, the cylinder blank solid solution adopts air cooling, because of uneven cooling, the hardness of the cylinder blank two ends is inconsistent, the hardness difference causes the spinning cylinder diameter expansion phenomenon, the diameters of the cylinder two ends are inconsistent. The cylinder blank solid solution of the present application adopts water cooling, because of fast and uniform cooling speed, the second phase precipitation is inhibited, the uniformity of the solid solution organization and the hardness are ensured.

[0030] (2) the existing solid solution process method, the cylinder solid solution is carried out in an air furnace, the cylinder surface is oxidized in high temperature air, the heat treatment distortion is large. The present application adopts vacuum solid solution method, avoids the surface oxidation generated by heating in air, improves the surface quality, and the heat treatment deformation is small.

[0031] (3) the existing solid solution process method, the heat treatment parameters have a great influence on the cylinder diameter shrinkage, the present application adopts the double solid solution process method, because of the first solid solution organization preparation, after repeated solid solution, the organization is more uniform, and the cylinder diameter shrinkage consistency is better. DETAILED DESCRIPTION

[0032] The content of the present application will be further illustrated in combination with specific examples, but the content of the present application is not limited to the following examples only.

[0033] Example 1

[0034] A certain type of rocket engine cylinder, the design diameter is Φ200mm, the wall thickness is 1.5mm. The spinning blank selects Φ219mm*Φ185mm*305mm. The blank is uniformly and spaced vertically placed in the effective heating zone of the box furnace, the furnace loading capacity is 30 pieces, after loading, the temperature is raised to 860℃, and the temperature is kept for 120min. After the end of the temperature keeping, the furnace is taken out and cooled in the water tank. Randomly select 3 pieces, detect the hardness of the two ends, the detection result is 29HRC~30.5HRC. After the blank is machined and spun, 100% of the cylinder diameter is detected, 3 cross-sectional diameters of each cylinder along the length direction are measured, and the measurement result is Φ200.6mm~200.7mm. The cylinder is subjected to the first vacuum solid solution, the temperature is raised to 820℃ from room temperature at a rate of 20℃ / min, the temperature is kept for 30min, 2bar nitrogen gas is filled, and the temperature is cooled to 200℃. The second solid solution is carried out at a rate of 20℃ / min to 600℃, the temperature is kept for 15min. The temperature is raised to 820℃ at a rate of 20℃ / min, the temperature is kept for 90min. 2bar nitrogen gas is filled, and the temperature is cooled to below 50℃ and taken out of the furnace. 100% of the cylinder diameter is detected, 3 cross-sectional diameters of each cylinder along the length direction are measured, and the measurement result is Φ200.1mm~200.2mm, which meets the design requirements.

[0035] Example 2

[0036] A certain type of rocket engine cylinder, design diameter Φ299mm, wall thickness 2mm. Spinning blank selected Φ330mm x Φ284mm x 320mm. Blank in the box furnace effective heating zone uniform interval vertical single layer placed, 18 pieces of loading, after loading, heating to 860℃, 150min. After the end of the heat preservation, out of the furnace into the water tank cooling. Randomly selected 3, detection of both ends of the hardness, the test results for 29HRC ~ 31HRC. After machining, spinning blank, 100% detection cylinder diameter, each cylinder along the length direction of 5 cross-sectional diameter, measurement results for Φ299.6mm ~ 299.8mm. Cylinder for the first time vacuum solid solution, from room temperature to 820℃ at 20℃ / min, 30min, 3bar nitrogen cooling to 200℃. Again solid solution, at 20℃ / min to 600℃, 15min. Again at 20℃ / min to 820℃, 90min. 2bar nitrogen cooling to 50℃ below the furnace. 100% detection cylinder diameter, each cylinder along the length direction of 3 cross-sectional diameter, measurement results for Φ299.0mm ~ 299.2mm, meet the design requirements.

[0037] Example 3

[0038] A certain type of rocket engine cylinder, design diameter Φ399.5mm, wall thickness 2.75mm. Spinning blank selected Φ426mm x Φ378mm x 430mm. Blank in the box furnace effective heating zone uniform interval vertical single layer placed, 10 pieces of loading, after loading, heating to 840℃, 150min. After the end of the heat preservation, out of the furnace into the water tank cooling. Randomly selected 3, detection of both ends of the hardness, the test results for 30HRC ~ 32HRC. After machining, spinning blank, 100% detection cylinder diameter, each cylinder along the length direction of 8 cross-sectional diameter, measurement results for Φ400.5mm ~ 400.8mm. Cylinder for the first time vacuum solid solution, from room temperature to 820℃ at 20℃ / min, 30min, 3bar nitrogen cooling to 200℃. Again solid solution, at 20℃ / min to 600℃, 30min. Again at 20℃ / min to 820℃, 120min. 3bar nitrogen cooling to 50℃ below the furnace. 100% detection cylinder diameter, each cylinder along the length direction of 3 cross-sectional diameter, measurement results for Φ399.4mm ~ 399.8mm, meet the design requirements.

Claims

1. A vacuum heat treatment method for thin-walled cylindrical bodies of T250 martensitic aging steel, characterized in that... The first step is as follows: Step 1: The cylindrical blank is solution-treated and cooled by water to ensure uniform cooling and obtain a supersaturated solid solution structure. The hardness of the blank is between 27 HRC and 32 HRC, and the hardness difference between the two ends does not exceed 2 HRC. The solution-treated cylindrical blank is then machined into a thin-walled cylindrical body, followed by two vacuum solution treatments: Step 2: First vacuum solution treatment to eliminate the stress inside the metal matrix after spinning and to eliminate the banded texture structure after spinning, so as to obtain equiaxed grains after recrystallization. Step 3: Second vacuum solution treatment further eliminates the texture structure after spinning and refines the equiaxed grains after the first solution treatment, resulting in a stable shrinkage of the cylinder diameter; Step 4: Finally, perform an aging treatment; the two vacuum solution treatments are performed using nitrogen cooling to ensure uniform cooling of the cylinder. The heating and holding parameters for the second vacuum solution treatment are as follows: heat up to 550℃~650℃ and hold for 15min~30min; then heat up to 800℃~820℃ and hold for 90min~120min. During the two vacuum solution treatments, when nitrogen cooling is used, the pressure of nitrogen introduced is 2 bar to 5 bar. The heating time for each stage is 15℃~20℃ / min.

2. The vacuum heat treatment method for T250 martensitic aging steel thin-walled cylindrical body according to claim 1, characterized in that: The heating and heat preservation parameters for the solution treatment of the cylinder blank in step 1 are: heating to 820℃~860℃ and holding for 120min~150min. After the heating and heat preservation process is completed, the material is cooled to room temperature using water cooling.

3. The vacuum heat treatment method for T250 martensitic aging steel thin-walled cylindrical bodies according to claim 1 or 2, characterized in that: In step 1, the cylindrical blank is heat-treated in a box-type air furnace during solution treatment.

4. The vacuum heat treatment method for T250 martensitic aging steel thin-walled cylindrical body according to claim 1, characterized in that: The heating and holding parameters for the first vacuum solution treatment are as follows: heating from room temperature to 800℃~820℃ and holding for 15min~30min; after heating and holding, cooling to 200℃~300℃ using nitrogen.

5. The vacuum heat treatment method for T250 martensitic aging steel thin-walled cylindrical body according to claim 1, characterized in that: The heating and heat preservation parameters for the aging treatment of the solution-treated cylinder are as follows: it is loaded into an air furnace at 500℃~530℃, and then kept at 500℃~530℃ for 180min~240min before being removed from the furnace and air-cooled.

6. The vacuum heat treatment method for T250 martensitic aging steel thin-walled cylindrical body according to claim 1, characterized in that: The cylindrical blank is a cylindrical blank of the designed length obtained by spinning T250 martensitic aging steel pipe material.

7. The vacuum heat treatment method for T250 martensitic aging steel thin-walled cylindrical body according to claim 1, characterized in that: The thin-walled cylinder is processed by machining and spinning. The thin-walled cylinder ultimately meets the requirements of consistent diameter expansion after spinning and stable diameter shrinkage after solution treatment, thus satisfying the dimensional accuracy requirements.