Grain refining method for 36Cr2Ni5Mo2V1 steel hollow part

Abstract

The application relates to a high-alloy Cr-Ni-Mo-V type steel hollow piece grain refining method, which comprises a blank, hollow forging, quenching + primary tempering + secondary tempering, direct quenching + tempering after adopting the hollow forging, the forging heating temperature is controlled in the range of 900-980 DEG C, the grain size is prevented from being coarsened during forging heating; the forging deformation variable is controlled in the range of 45%-65%, the structure and carbide form are small, and the distribution is uniform; after the hollow forging is finished and stress is eliminated, the full power is used to heat to the quenching temperature 930 DEG C-1000 DEG C and is kept, the quenching is discharged and cooled, the cooling mode is water cooling, the water cooling-air cooling-water cooling-air cooling-full water cooling mode is adopted, the keeping of the coarse martensite or bainite needle-shaped organization genetic is avoided, the uniform and small tempered martensite structure and the small carbide precipitated phase are obtained, the grains are small and uniform, the high strength and high toughness matching is achieved, and the fatigue life is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high alloy Cr-Ni-Mo-V steel hollow piece production, and particularly relates to a 36Cr2Ni5Mo2V1 steel hollow piece grain refinement method capable of homogenizing and refining the structure of a hollow piece with mixed crystal and coarse crystal high alloy Cr-Ni-Mo-V steel characteristics. BACKGROUND

[0002] The high alloy Cr-Ni-Mo-V steel hollow piece is a main pressure-bearing component of high-temperature and high-pressure equipment, and in the use process, bears high instantaneous high temperature, high pressure, mechanical friction and ablation, and the working condition is relatively complex, so the selected material needs to have high comprehensive performance, especially small and uniform structure, so as to improve the strength and toughness and meet the fatigue life requirement.

[0003] At present, the traditional process route of the high alloy Cr-Ni-Mo-V steel hollow piece for pressure bearing is blanking, forging, complete annealing or normalizing + spheroidizing annealing and hydrogen expansion after forging, rough machining, double normalizing and quenching and tempering. The complete annealing after forging + double normalizing + quenching and tempering is used to realize the refinement of the structure, but there are problems. The high alloy Cr-Ni-Mo-V is a hypereutectoid steel, complete annealing is performed after forging, and the net-like secondary cementite is precipitated, so that the hardness of the steel is increased, the brittleness is increased, the strength, plasticity and impact toughness are significantly reduced, and the cutting performance is deteriorated. The net-like structure is as shown in FIG. 1. If normalizing + spheroidizing annealing and hydrogen expansion are performed after forging, due to the high alloy content of the material, the surface is easy to form quenched martensite, and the inside is easy to form bainite structure. Even if the spheroidizing time is particularly long, the granular pearlite structure cannot be obtained, and the coarse martensite or bainite needle cannot be eliminated, so that the structure is genetically strong, the subsequent performance heat treatment cannot refine the structure, the coarse crystal and mixed crystal phenomenon is serious, and the structure morphology is as shown in FIG. 2. The above two methods cannot realize the uniform and refined structure, and the purpose of improving the strength and toughness, so as to affect the fatigue life, and even endanger the life safety of the operating personnel. Figure 1 Figure 2 The high alloy Cr-Ni-Mo-V steel involved in the application is a main high-temperature and high-pressure component of weapons and equipment and high-pressure and super-high-pressure vessels, and the working condition is relatively complex. The material needs to have high comprehensive mechanical properties to ensure the fatigue life and safety, and needs to be designed through a suitable production process to meet the design and use requirements of the equipment.

[0004] The high alloy Cr-Ni-Mo-V steel involved in the application is a main high-temperature and high-pressure component of weapons and equipment and high-pressure and super-high-pressure vessels, and the working condition is relatively complex. The material needs to have high comprehensive mechanical properties to ensure the fatigue life and safety, and needs to be designed through a suitable production process to meet the design and use requirements of the equipment. SUMMARY

[0005] ​The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for grain refinement of 36Cr2Ni5Mo2V1 steel hollow parts for the production of weapon equipment and high-temperature and ultra-high-pressure vessel main pressure-bearing components that can meet the use requirements. The product specifications involved in the present invention are hollow forgings with an outer diameter of φ400 to φ200 mm and an inner hole of φ80 to φ130 mm, which can withstand high instantaneous high temperature, high pressure, mechanical friction, and ablation.

[0006] The object of the present invention is achieved as follows: A method for grain refinement of 36Cr2Ni5Mo2V1 steel hollow parts, comprising the following technical routes and steps: Technical route: billet → hollow forging → quenching + primary tempering + secondary tempering, the specific steps are as follows:

[0007] Step 1) Hollow forging the blank: To refine the structure, strictly control the forging heating temperature, the heating temperature is 50-150℃ above Ac3, heat it to 900-980℃ at full power and keep it warm for 2-4h / 100mm, then forge it out of the furnace to ensure that the forging temperature is 30-80℃ above Ac3; hollow forging is performed on a SXP-65 1400t precision forging machine using a φ80-φ130 mandrel, and the process is completed in one pass without returning to the furnace; the deformation is 45%-65%;

[0008] Step 2) Post-forging quenching: The hollow forgings after step 1) are heated to a quenching temperature of 930-1000°C. After the heat preservation is completed, the hollow forgings are taken out of the furnace and quenched. The quenching medium is water.

[0009] Step 3) Primary tempering: Place the hollow forgings obtained in step 2) into a tempering furnace at 570°C to 620°C for the first tempering, keep warm, then air cool and perform heat calibration;

[0010] Step 4) Secondary tempering: Place the hollow forgings after step 3) into a tempering furnace at 530°C to 580°C for secondary tempering, keep warm, then air cool and heat calibrate.

[0011] In step 2), to ensure that the workpiece will not crack during quenching due to the existence of forging stress and structural stress, the hollow forgings need to be directly placed in the furnace after forging and heated at 600-650℃ for uniform temperature and insulation to relieve stress. The uniform temperature should be visually observed and the insulation time should be 2-4h / 100mm. Then, the temperature is raised to 930-1000℃ at full power for quenching heating, uniform temperature and insulation. The uniform temperature and insulation time is 1.5h / 100mm. After the insulation is completed, it can be taken out of the furnace for quenching.

[0012] In step 2), in order to refine the microstructure and obtain high-strength and high-toughness mechanical properties, water cooling is used as the cooling method after quenching. At the same time, in order to avoid cracking of the workpiece due to thermal stress and microstructure stress during quenching, the early stage of quenching adopts water cooling-air cooling-water cooling-air cooling-full water cooling. The specific quenching cooling method includes the following steps: a. Air cooling: 1.5-2.5 min / 100 mm; b. Water cooling: 2-2.5 min / 100 mm, where the initial water temperature is ≤25°C; c. Air cooling 0.5-1 min; d. Filling the water tank with water, water cooling: 3-5 min / 100 mm; d. Draining the water tank, air cooling 0.5-1 min; e. Filling the water tank with water, water cooling: 10-20 min / 100 mm.

[0013] The beneficial effects of the present invention are as follows: The present invention provides a manufacturing technology for hollow parts made of 36Cr2Ni5Mo2V1 steel, comprising the following technical route: billet → hollow forging → quenching + primary tempering + secondary tempering, as well as the hollow forging and heat treatment processes provided by the present invention. While ensuring that the hollow parts do not crack, a uniform and fine structure and high-strength and high-toughness mechanical properties are achieved, meeting the design and use requirements of the main pressure-bearing components of high-temperature and high-pressure pressure-bearing equipment. The hollow forging + quenching + primary tempering + secondary tempering technical route, hollow forging, and heat treatment processes of the present invention meet the comprehensive performance requirements of harsh working conditions such as high temperature and high pressure, internal wall mechanical friction, and ablation, while significantly shortening the production cycle and reducing production costs.

[0014] The technical route of the present invention is designed as follows: billet→hollow forging→quenching+primary tempering+secondary tempering; the implementation of the technical solution mainly lies in controlling the hollow forging and direct quenching process after forging.

[0015] Hollow forging design: Because the 36Cr2Ni5Mo2V1 steel involved in the present invention has a stubborn structure and contains many carbide-forming elements, a hollow forging design is adopted to control the forging temperature. The forging heating temperature is required to be between 900 and 980°C to prevent the grain size from coarsening during forging heating. The forging deformation is controlled between 45% and 65% to make the structure and carbide morphology fine and evenly distributed.

[0016] Design of post-forging quenching process: Since the 36Cr2Ni5Mo2V1 steel involved in the present invention has high carbon and alloy contents and is a hypereutectoid steel, in order to reduce the microstructure inheritance and precipitation of network cementite that affect the strength, toughness and processability, after the hollow forging is completed and the stress is relieved, the temperature is raised to the quenching temperature of 930°C to 1000°C at full power and kept warm, and then the steel is taken out of the furnace for quenching and cooling. The cooling method is water cooling, and the method adopts water cooling-air cooling-water cooling-air cooling-full water cooling.

[0017] Traditional process route 1 is billet → forging → full annealing + spheroidizing annealing and hydrogen expansion after forging → rough machining → double normalizing + tempering; full annealing is cooled with the furnace, the cooling is slow, and double normalizing pretreatment is required after rough machining and before tempering, which results in large energy loss and a long production cycle. After the final tempering of the workpiece, the network cementite cannot be completely eliminated, the mechanical properties of tensile strength are between 1450 and 1550 MPa, the impact energy at -40°C is between 15 and 22 J, and the grain size is 6-5; traditional process route 2 is billet → forging → normalizing + spheroidizing annealing and hydrogen expansion → rough machining → double normalizing + tempering. After the final treatment of the workpiece, the mechanical properties of tensile strength are ≥1500 MPa, the impact energy at -40°C is between 18 and 25 J, the grain size is 7-3, the mixed crystal is serious, and the grains are coarse.

[0018] The 36Cr2Ni5Mo2V1 steel produced by the production technology of the present invention reduces the workload of rough processing after hollow forging, eliminates the double normalizing pretreatment before quenching, greatly shortens the production cycle, reduces energy loss and production costs, and the tensile strength of the workpiece after final heat treatment is greater than 1600MPa, the impact energy at -40℃ is greater than 22J, and the grain size of the workpiece reaches level 9. The heat treatment curve after forging and the microstructure refinement morphology are shown in the figure. Figure 3 、 4 shown. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a morphology diagram of the fully annealed network cementite structure of the steel before the implementation of the present invention.

[0020] Figure 2 This is a morphology diagram of the mixed crystal and coarse crystal structure of the steel before the implementation of the present invention.

[0021] Figure 3 This is a process curve diagram of post-forging heat treatment according to the present invention.

[0022] Figure 4 This is a diagram of the uniform and fine structure after the final heat treatment of the present invention. DETAILED DESCRIPTION

[0023] Example 1: A method for grain refinement of a 36Cr2Ni5Mo2V1 steel hollow part, using a high-alloy Cr-Ni-Mo-V steel, 36Cr2Ni5Mo2V1. The blank has an outer diameter of φ350 mm and an inner diameter of φ150 mm, and the finished product has an outer diameter of φ250 mm and an inner diameter of φ110 mm.

[0024] The technical route and steps are as follows: billet → hollow forging → quenching + primary tempering + secondary tempering.

[0025] The specific steps are as follows:

[0026] Step 1) Hollow forging the blank: To refine the structure, strictly control the forging heating temperature, the heating temperature is 50-150℃ above AC3, and the temperature is raised to 900-980℃ at full power and kept warm for 5 hours. The blank is forged after being taken out of the furnace and the air cooling time is ≤8min to ensure that the forging temperature is around Ac3. The blank is hollow forged in an SXP-65 1400t precision forging machine with a φ110 mandrel. The blank is completed in one pass and the furnace return is not allowed. The deformation is 45%-65% and the drawing speed is 1-2m / min.

[0027] Step 2) Post-forging quenching: The hollow forgings after step 1) are heated to a quenching temperature of 930°C to 1000°C. After the heat preservation is completed, the hollow forgings are taken out of the furnace and quenched. The quenching medium is water.

[0028] In step 2), to ensure that the workpiece does not crack during quenching due to the presence of forging stress and structural stress, the hollow forgings need to be directly placed in a furnace after forging and heated at 600-650°C for 3 hours and then held for 4 hours; then the temperature is raised to 930-1000°C at full power for quenching heating, heating and holding, with a heating and holding time of 1.5 hours. After the holding time is completed, the workpiece is taken out of the furnace for quenching;

[0029] In step 2), in order to refine the structure and obtain high-strength and high-toughness mechanical properties, water cooling is used for cooling after quenching. At the same time, in order to avoid cracking of the workpiece due to thermal stress and structural stress during quenching, water cooling-air cooling-water cooling-air cooling-full water cooling is adopted in the early stage of quenching; the specific quenching cooling method includes the following steps: a. Air cooling: 1.5-2.5 min / 100 mm; b. Water cooling: 2-2.5 min / 100 mm, where the initial water temperature is ≤25°C; c. Air cooling 0.5-1 min; d. Water cooling: 3-5 min / 100 mm; d. Water-air cooling 0.5-1 min; e. Water cooling: 10-20 min / 100 mm.

[0030] Step 3) Primary tempering: Place the hollow forgings obtained in step 2) into a tempering furnace at 570°C to 620°C for the first tempering, keep warm, then water cool and heat calibrate;

[0031] Step 4) Secondary tempering: Place the hollow forgings after step 3) into a tempering furnace at 530°C to 580°C for secondary tempering, keep warm, then air cool and heat calibrate.

[0032] After hollow part forging + direct quenching + tempering, the inheritance of coarse martensite or bainite positional needle-like structure is avoided, and uniform and fine tempered martensite structure and fine carbide precipitation phase are obtained. The grains are fine and uniform, achieving a match of high strength and high toughness. The grain size of the workpiece reaches level 9, the tensile strength is ≥1600MPa, and the impact energy at -40℃ is greater than 22J. The fatigue life is greatly improved, meeting the fatigue life and safety requirements of the design and use of the main pressure-bearing components of high-temperature and high-pressure pressure-bearing equipment.

Claims

1. A method for grain refinement of 36Cr2Ni5Mo2V1 steel hollow parts, characterized in that: The process is carried out according to the following technical route: billet → hollow forging → quenching + primary tempering + secondary tempering. The specific steps are as follows: Step 1) Hollow forging the blank: To refine the structure, strictly control the forging heating temperature, which is 50-150℃ above AC3. Heat it to 900-980℃ at full power and keep it warm for 2-4h / 100mm. Forge it out of the furnace to ensure that the forging temperature is 30-80℃ above Ac3. Use φ80-φ130 mandrel for hollow forging on SXP-65 1400t precision forging machine. Complete the process in one pass without returning to the furnace. The deformation is 45%-65%. Step 2), quenching after forging: the hollow forgings after step 1) are heated to the quenching temperature, the quenching heating temperature is 930℃~1000℃, and after the holding is completed, they are taken out of the furnace for quenching, and the quenching medium is water; to ensure that the workpiece does not cause quenching cracking due to the existence of forging stress and structural stress, the hollow forgings need to be directly placed in the furnace after forging and heated at 600~650℃ for uniform temperature and insulation to relieve stress, and the uniform temperature is visually observed, and the insulation time is 2~4h / 100mm; then the temperature is raised to 930℃~1000℃ at full power for quenching heating, uniform temperature and insulation, and the uniform temperature insulation time is 1.5h / 100mm. After the insulation is completed, they are taken out of the furnace for quenching; In step 2), in order to refine the microstructure and obtain high-strength and high-toughness mechanical properties, water cooling is used for cooling after quenching. At the same time, in order to avoid cracking of the workpiece due to thermal stress and microstructure stress during quenching, water cooling-air cooling-water cooling-air cooling-full water cooling is used in the early stage of quenching. The specific quenching cooling method includes the following steps: a. Air cooling: 1.5-2.5 min / 100 mm; b. Water cooling with water in the water tank: 2-2.5 min / 100 mm, where the initial water temperature is ≤25°C; c. Drain the water tank and air cool for 0.5-1 min; d. Drain the water tank and water cool for 3-5 min / 100 mm; d. Drain the water tank and air cool for 0.5-1 min; e. Drain the water tank and water cool for 10-20 min / 100 mm. Step 3) Primary tempering: Place the hollow forgings obtained in step 2) into a tempering furnace at 570°C to 620°C for the first tempering, keep warm, then air cool and perform heat calibration; Step 4) Secondary tempering: Place the hollow forgings after step 3) into a tempering furnace at 530°C to 580°C for secondary tempering, keep warm, then air cool and heat calibrate.

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